Table of Content

20 November 2015, Volume 24 Issue 11

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Net primary production and forage quality of desert steppe plant communities under different grazing systems and growing seasons

YANG Xia, WANG Zhen, YUN Xiang-Jun, WEI Zhi-Jun

2015, 24(11):  1-9.  DOI: 10.11686/cyxb2015081

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Forage value and productivity are important grassland traits. Plant community ANPP, crude protein, crude fiber, crude ash, ether extract, calcium, phosphorus and nitrogen-free extract were measured and analyzed under different grazing systems during two hydrologically contrasting growing seasons in a desert steppe. The results showed that grazing significantly decreased community ANPP in 2011 which was dry. ANPP was the highest after 60 days without grazing in 2012, a wet year. In 2011 plant community ANPP, crude protein, crude fiber, crude ash, ether extract, calcium, phosphorus was 2.67, 1.08, 1.27, 1.26 and 3.75 times that in 2012. The highest crude protein and phosphorus content was detected after 60 days without grazing. With continuous grazing, crude protein, ether extract, crude ash, calcium and phosphorus content initially increased and then decreased; peak values occurred in July or August and the lowest values were found at the end of the growing season (October). However, crude fiber and nitrogen-free extract was lowest in July and highest in October. Precipitation has a major influence on community ANPP and the seasonal dynamic of community forage quality; grazing and yearly rainfall variation co-limited the change of community forage nutrient content.

Net ecosystem carbon exchange and its main driving factors in meadow grassland ecosystems in the Horqin Sand Lands

WANG Jing, LIU Ting-Xi, LEI Hui-Min, ZHANG Sheng-Wei, DUAN Li-Min

2015, 24(11):  10-19.  DOI: 10.11686/cyxb2014530

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The objectives of this study were to investigate the main drivers of ecosystem carbon dynamics in meadow grasslands in the Horqin Sand Lands, and to understand the relationship between net ecosystem CO₂ exchange (NEE) and key meteorological factors in this region. We continuously measured (NEE) and environmental factors in meadow grasslands in the Horqin Sand Lands from October 2013 to September 2014 using the eddy covariance method. The results showed that the diurnal variation in NEE differed significantly among seasons, especially among vegetation growing seasons. The highest seasonal diurnal absorption rate of CO₂ was in July, followed by August, September, June, and then May. The NEE was controlled by photosynthetically active radiation (PAR) and the leaf area index (LAI) during vegetation growing seasons. The relationship between NEE and PAR was expressed by a rectangular hyperbolic function. The simulated apparent initial average light-use efficiency was 0.0015 μmol CO₂/μmol PAR, and the maximum photosynthetic rate (P_max) was 0.65 μmol CO₂/(m²·s). The NEE was influenced by LAI, which was expressed by piecewise functions. When the LAI was greater than 3.08, NEE-PAR showed a gradual saturation-type relationship. The higher the LAI, the stronger the response of net carbon exchange to the amount of PAR. A light saturation response occurred when 1.5<VPD<2 kPa, and NEE was significantly inhibited under high VPD. The day-time net CO₂ exchange was inhibited by heavy rainfall (cumulative rainfall>40 mm/day), while sustained low-intensity rainfall (rainfall length>15 h) stimulated soil respiration at night. The night-time respiration rate of the ecosystem (R_eco) increased exponentially as the soil temperature (T_s) increased, and the temperature-sensitive coefficient Q₁₀ was 2.63.

Vegetation characteristics, abundance of soil microbes, and soil physico-chemical properties in desertified alpine meadows of Maqu

JIN Hong-Xi, HE Fang-Lan, LI Chang-Long, HAN Sheng-Hui, WANG Qiang-Qiang

2015, 24(11):  20-28.  DOI: 10.11686/cyxb2015134

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In recent years, desertification has been a serious threat to the alpine meadow ecosystem in the Maqu County of Gansu Province. To evaluate the effects of desertification on alpine meadow soil and vegetation, four types of plots with different grades of desertification were established in 2012. The vegetation characteristics, soil physico-chemical properties, and abundance of soil microbes were measured and analyzed in August 2013. At the same time, the relationship between the vegetation characteristics and soil microorganisms was analyzed. The results showed that the plant diversity index, soil moisture content, soil organic matter, total nitrogen (N), and available phosphorus (P) decreased as the degree of desertification intensified, and the plant dominance index and pH value increased conversely. The deep-soil organic matter, total N, and available P showed the highest values in the lightly desertified plots. Bacteria were the most abundant soil microorganisms in all plots, followed by actinomycetes, fungi, and then nitrogen-fixing bacteria. The lightly desertified plots had the largest number of microbes. A partial correlation analysis showed that the total quantities of soil microorganisms and bacteria were negatively related to above-ground plant richness index, plant biomass, and below-ground plant biomass, but positively related to the above-ground/below-ground biomass ratio. There were significant correlations between the abundance of nitrogen-fixing bacteria and aboveground plant biomass, and between the abundance of fungi and below-ground plant biomass. The quantity of soil microorganisms was positively related to the above-ground/below-ground biomass ratio, but negatively related to all of the other measured vegetation characteristics.

Artemisinin and flavonoids in wild Artemisia annua and surrounding soil and the influence on soil microbes

LI Qian, YUAN Ling, LUO Shi-Qiong, HUANG Jian-Guo

2015, 24(11):  29-37.  DOI: 10.11686/cyxb2014510

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Artemisia annua releases various kinds of allelochemicals into soils via rain leaching, root exudation and dead tissue decomposition during the growing season, with resulting inhibition of the growth and development of adjacent plants and succeeding crops. The present experiments were thus conducted to detect artemisinin derivatives, flavonoids and effects on soil microbes in wild A. annua and surrounding soil. The allelochemical concentrations ranked: bud break period>early flowering period>full bloom period>vegetative growth period (artemisinin in leaves and root zone soil) and stem>leaf>root>flower (flavonoids in plants). In sampled soils, the mean concentration of deoxyartemisinin was highest, followed by artemisic acid and artemisinin in soil and the sum of these artemisinin derivatives was 516.93 μg/kg dry soil. Concentrations of all three compounds tested were highest in root surface soil and much higher in the root surface soil and rhizosphere soil than in non-rhizosphere soil. Soil flavonoid concentrations increased steadily during the growing season of A. annua and reached their highest levels at full-bloom stage (434.77 μg/kg dry soil). Hence it is concluded that flavonoids are released into soils through root exudation. The numbers of bacteria and actinomycetes showed significant negative correlations with artemisinin concentration (r=-0.508^* and -0.478^*, n=24). There was also a negative correlation between deoxyartemsinin contents and actinomycete numbers (r=-0.528^**, n=24). In summary, artemisinin and its derivatives released from A. annua appear to inhibit microbial growth and reproduction, and are therefore likely to influence biochemical reactions in soils.

Optimization of fermentation conditions of swine manure and screening for efficient microbial deodorant strains

ZHANG Sheng-Wei, YAO Tuo, HUANG Wang-Zhou, YANG Qiao-Li, GUN Shuang-Bao

2015, 24(11):  38-47.  DOI: 10.11686/cyxb2014513

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By combining NH₃ and H₂S selective media for a first qualitative screening, and the boric acid absorption and zinc amine complex salt absorption colorimetric methods for a second quantitative screening, 5 strains which could efficiently reduce NH₃ release, and 3 strains reducing H₂S release were identified, of which a strain designated BX3 achieved emission reduction rates of NH₃ and H₂S, respectively, compared with control treatments, of 80.07%, 76.92%. An L₈(2⁷) orthogonal optimum design was employed to identify combinations of different strains with high deodorizing efficiency, and AF2+DZ1+BX3+DZ3+BZ1+EZ3+AX4 was found to be the optimal strain combination. With this combination, the emission rates of NH₃ and H₂S were significantly lower than that of other combinations. Compared with a blank control group, the emission reductions of NH₃ and H₂S, respectively, were 82.14%, 80.84% on the fifth day of the experiment. The optimal microbial combination for deodorizing activity was studied under differing fermentation conditions and the quantities of NH₃ and H₂S released were smallest with additive combinations of 10% inoculation, 30% moisture content and 10% bran addition, and 15% inoculation, 40% moisture content and 10% bran addition, respectively. The microbial strains isolated in this study have potentially broad application prospects in the fields of odor prevention and control of environmental pollution caused by livestock and poultry manure.

Isolation of MsWRKY33 transcription factor and its genetic transformation in Medicago sativa

FENG Guang-Yan, WANG Xue-Min, FU Yuan-Yuan, FANG Zhi-Hong, GAO Hong-Wen, ZHANG Xin-Quan

2015, 24(11):  48-57.  DOI: 10.11686/cyxb2015131

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Plant-specific WRKY transcription factors (TFs) are widely involved in various stress responses. However, their roles in abiotic stresses are still not well known in alfalfa (Medicago sativa). In this study, a WRKY gene, containing 1536 bp CDS length encoding a putative protein of amino acid 512, designated as MsWRKY33, was isolated from alfalfa. The alignment results revealed that the MsWRKY33 protein contains two conserved DNA-binding domains (WRKY domain) of 60 amino acids and a C2H2 zinc finger region (C-X4-C-X23-H-X-H), falling into group I of the WRKY protein. Protein localization prediction analysis indicated that MsWRKY33 is a nuclear-targeting protein. The expression of MsWRKY33 gene was up-regulated by salinity (NaCl), drought (PEG) and cold temperature (4℃), indicating that MsWRKY33 gene may be involved in the regulation of environmental stress responses in alfalfa. The fragment encoding 10-239AA was inserted into pET-30α (+) to construct the expression vectors, and SDS-PAGE analysis revealed that the MsWRKY33 protein could be expressed in prokaryotic cells. The full length cDNA of MsWRKY33 was amplified from alfalfa RNA and the plant expression vector pBI121-MsWRKY33 was constructed based on the pBI121 vector. Transgenic plants were obtained through somatic embryogenesis by Agrobacterium tumefaciens-mediated transformation. The npt Ⅱ gene and vector sequence were tested by PCR in the genome of transgenic plants and indicated that the target gene had been transferred. The qRT-PCR testing showed that the MsWRKY33 gene was over expressed in transgenic plants. This study will lay a foundation for further study of the function of the WRKY transcription factor in stress-tolerance regulation in alfalfa.

Analysis of drought tolerance and herbicide resistance in transgenic potato plants over-expressing DREB1A/Bar

JIA Xiao-Xia, QI En-Fang, MA Sheng, HU Xin-Yuan, WANG Yi-Hang, WEN Guo-Hong, GONG Cheng-Wen, LI Jian-Wu

2015, 24(11):  58-64.  DOI: 10.11686/cyxb2014533

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In order to compare drought resistance of DREB1A/Bar transgenic potato plants, with a control cultivar (non-transgenic Longshu 10), 5-7 cm seedlings of DREB1A transgenic lines were grown in pots using vermiculite and regularly watered. Watering continued to the 15-16 leaf stage after which plants were not watered for 18 days to impose for drought stress. During the drought stress, plant phenotypic features were recorded using visual observation and digital camera images. After 10 days of drought stress, stress-related physiological and biochemical parameters were determined. During the normal watering phase both the non-transgenic control and the transgenic potato lines grew well, the MDA content, relative electrical conductivity and superoxide dismutase (SOD) activity were not significantly different (P>0.05). After 10 days of drought stress the control plants began to wilt, but the transgenic lines remained in good condition. MDA content and relative electrical conductivity in the transgenic line was significantly lower than those of the non-transgenic plants (P<0.05), while the SOD activity was significantly higher than that of non-transgenic plants (P<0.05). After for 18 days of drought stress 74.33% of the control plants were dead whereas fewer transgenic plants had died; the mortality of DR2 and DR5 was 20.43% and 5.65% respectively. The resistance of DREB1A/Bar transgenic potatoes to glufosinate, a systemic non-selective herbicide, compared with non-transgenic lines was determined by treating plants with a 0.3% glufosinate spray. Ten days after treatment all non-transgenic plants had died, while the transgenic plants were affected slightly. The study indicated that introduction of DREB1A and Bar genes significantly enhanced drought tolerance and herbicide resistance in transgenic potato plants.

Effects of the Epichloё gansuensis endophyte on the disease resistance of drunken horse grass to powdery mildew

LIU Li, GUO Chang-Hui, LV Hui, GU Li-Jun, LI Chun-Jie

2015, 24(11):  65-71.  DOI: 10.11686/cyxb2014471

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Previous studies have shown that endophytes can increase the resistance of drunken horse grass (Achnatherum inebrians) to many stresses, such as insects, diseases, waterlogging, drought, salt, and heavy metals. The aim of this study was to compare the resistance of endophyte-infected (E⁺) and endophyte-free (E^-) drunken horse grass to powdery mildew (Blumeria graminis). Forty pots of drunken horse grass (20 E⁺ plants and 20 E^- plants) were grown in a greenhouse. After 2 months, the natural infection rates, the percentage of diseased leaves, and the disease indexes of powdery mildew in both E⁺ and E^- plants were estimated and recorded. At the same time, the E⁺ and E^- drunken horse grass plants were scored as healthy, slightly diseased, or severely diseased based on a disease index. Then, four replicates of E⁺ and E^- plants were randomly selected to measure several physiological indexes; chlorophyll content, activities of superoxide dismutase (SOD) and peroxidase (POD), and the contents of malondialdehyde (MDA) and proline (Pro). Chlorophyll content was measured by acetone extraction, SOD and POD activities were evaluated using nitroblue tetrazolium and guaiacol assays, respectively, and MDA and Pro contents were determined using the sulfosalicylic acid and glucosinolate barbituric acid methods, respectively. The disease infection rate, the percentage of diseased leaves, and disease indexes of E^- plants were 97%, 86%, and 82.49, respectively, significantly higher (P<0.05) than their respective values in E⁺ plants (48%, 60%, and 50.76). The chlorophyll and proline contents and SOD and POD activities were higher in E⁺ plants than in E^- plants, regardless of whether the plants were slightly or severely infected. The MDA content was significantly (P<0.05) lower in E⁺ plants than in E^- plants. These results provide evidence that endophyte infection can increase the resistance of drunken horse grass to powdery mildew disease.

Pathogenicity of Rhizoctonia solani to alfalfa seedlings and disease resistance of alfalfa varieties

GUO Yu-Xia, ZHANG Ming, GUAN Yong-Zhuo, LIU-Fang, GUO Zhi-Peng, ZHANG Hong-Rui, YAN Xue-Bing, WANG Cheng-Zhang

2015, 24(11):  72-81.  DOI: 10.11686/cyxb2015197

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The aim of this study was to evaluate the pathogenicity of Rhizoctonia solani isolates to various alfalfa (Medicago sativa) varieties. We used 14 varieties of alfalfa and six pathogen isolates that were isolated from roots of six different alfalfa varieties from three locations. We estimated the disease index, relative germination rate, relative root length, and relative seedling length at 14 days after inoculation with the various isolates. There were significant differences among the 14 alfalfa varieties inoculated with the six pathogen isolates (P<0.05). The isolate from ‘Goldenqueen’ showed significantly stronger pathogenicity (P<0.05) than the other isolates. The isolate from ‘Powerplant’ showed the weakest pathogenicity. All the fungi used in this study resulted in lower germination rates and shorter roots of alfalfa seedlings, and the isolate from ‘Goldenqueen’ showed the strongest effects. Based on the comprehensive evaluation of all traits, R. solani isolated from ‘Goldenqueen’, ‘8920MF’, and ‘Affinity’ showed the strongest pathogenicity to alfalfa seedlings. Among the 14 alfalfa varieties, ‘Vernal’, ‘Algonguin’, and ‘Alfaking’ were more resistant to R. solani, while ‘Powerplant’ and ‘Amerileaf 721’ were the most sensitive.

Involvement of the ascorbate-glutathione cycle in resistance of creeping bentgrass to Rhizoctonia solani induced by 2, 3-butanediol and 2R, 3R-butanediol

FANG Yuan-Yuan, MA Hui-Ling

2015, 24(11):  82-90.  DOI: 10.11686/cyxb2014519

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The compounds 2, 3-butanediol (BD) and 2R, 3R-BD can cause creeping bentgrass to show increased resistance against Rhizoctonia solani. To evaluate the mechanisms of this induced resistance, we determined the activities of antioxidant enzymes in the ascorbate-glutathione cycle and the redox states of various antioxidant compounds in leaves of creeping bentgrass that were injected with 250 μmol/L 2, 3-BD and 100 μmol/L 2R, 3R-BD before inoculation with R. solani. The 2, 3-BD and 2R, 3R-BD treatments significantly decreased the disease incidence in creeping bentgrass plants inoculated with R. solani and increased the activities of glutathione reductase (GR) and ascorbate peroxidase (APX). However, the increase in APX activity was smaller than that in the control (no BD). In the plants treated with 2, 3-BD and 2R, 3R-BD, the ascorbic acid (AsA) content decreased at an early stage and increased at a later stage after inoculation, while the content of dehydroascorbic acid (DHA) peaked at 1 and 9 d after inoculation at levels significantly higher than those in the control. The AsA/DHA ratios of plants treated with 2, 3-BD and 2R, 3R-BD reached a maximum at 5 days after inoculation (5.0 and 3.4 times the AsA/DHA ratio in the no-BD control at 5 d after inoculation, respectively). In plants treated with 2, 3-BD and 2R, 3R-BD, the glutathione (GSH) content significantly increased and the GSH/GSSG ratios peaked at 9 days after inoculation at 2.34 and 1.66 times that in the no-BD control, respectively. These results suggest that in creeping bentgrass, the resistance against R. solani induced by 2, 3-BD and 2R, 3R-BD involves the ascorbate-glutathione cycle, which maintains efficient metabolism and participates in the plant disease resistance response.

Population parameters of two pea aphid (Acyrthosiphon pisum) color morphs at different temperatures

DU Jun-Li, WU De-Gong, LV Ning, LIU Chang-Zhong

2015, 24(11):  91-99.  DOI: 10.11686/cyxb2014289

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In order to clarify the effects of temperature on the population dynamics of the red and green color morphs of pea aphid (Acyrthosiphon pisum), the development, reproduction, and life cycle of these two pea aphid color morphs were studied at six constant temperatures ranging from 12 to 32℃. Neither of the two pea aphid color morphs could develop to adulthood at 32℃. The net reproduction rate (R₀), and intrinsic rate of increase (r_m) of the two color morphs of pea aphid increased with increase in temperature over a range from 12 to 20℃, and the R₀ of the red color morph was numerically higher than that of the green color morph over this range, and significantly higher at 16 and 20℃ (P<0.05). At 24℃, the R₀ of the red color morph was significantly lower than for the same color morph at 16 and 20℃ (P<0.05), and the R₀ of green color morph was significantly higher than for the same color morph at 12-20℃ (P<0.05), and significantly higher than the R₀ of red color morph at 24℃ (P<0.05). At 28℃, the R₀ values of the two color morphs were both significantly lower than for the same color morph at 12-24℃ (P<0.05). The r_m of two color morphs increased with increasing temperature over the range 12 to 24℃, and there were no differences in r_m between red and green colour morphs over this range of temperatures (P>0.05). At 28℃, the r_m of the red color morph was significantly lower than the green color morph (P<0.05). Hence the red color morph was found to be better adapted to lower temperature, and the green color morph better adapted to higher temperature.

Preliminary research on Cd-tolerance of Panicum virgatum and Panicum maximum

LIU Chang-Hao, LOU Lai-Qing, GUO Tao, LUO Tian-Peng, CAI Qing-Sheng

2015, 24(11):  100-117.  DOI: 10.11686/cyxb2014495

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It is important to evaluate the capability of heavy metal tolerance of high biomass grasses for developing bioenergy plants suited to heavily polluted environments, particularly metal pollutants, reducing the problem of bioenergy crops competing with staple food crops. Both switchgrass (Panicum virgatum) and guinea grass (P. maximum) are important bioenergy plants because of their high yield potential. These grasses were used to examine the effects of cadmium (Cd) on seedling growth under 0, 0.5, 5, 10, 20, 50, 100 μmol/L Cd for switchgrass, 0, 2, 5, 7.5, 10 μmol/L Cd for guinea grass grown using hydroponic techniques. Root and shoot fresh weights of both grasses were recorded and root morphological data of switchgrass were obtained using an EPSON scanner and WinRHIZO software. ICP-AES was used to examine Cd accumulation in switchgrass. The results showed that the biomass and root elongation of switchgrass and guinea grass were significantly affected by Cd. The root biomass of switchgrass decreased greatly under 50 μmol/L Cd conditions, but root biomass, shoot biomass, total biomass and root elongation in guinea grass were decreased by 86.1%, 83.5%, 84.1% and 96.3% respectively by the 2 μmol/L Cd treatment; root elongation in switchgrass was reduced by 55% in 5 μmol/L Cd solution. The Cd concentration in shoots of switchgrass was 40 mg/kg and the biomass was reduced by 45% in the 20 μmol/L Cd treatment. In addition, the root length and root tip numbers in switchgrass were significantly decreased in Cd treatments in comparison with the control. However, mean root diameter increased in Cd solutions. There was a significant negative correlation between root length, root surface area and root volume, and Cd accumulation and a strong positive correlation between root length, root surface area and root volume and TFs in the 0-1 mm mean root diameter class suggesting that fine roots may play an important role in Cd accumulation.

Responses of three Zoysia grass species to salt stress

ZHAO Ying, LI Jing-Yuan, DUAN Yan-Xin, DONG Xiao-Ying

2015, 24(11):  109-117.  DOI: 10.11686/cyxb2015161

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The effects of salt (NaCl) on the antioxidant system and soluble protein content during growth of Zoysia macrostachys, Z. matrella and Z. japonica was investigated. The biomass and the soluble protein contents of all three grasses reduced gradually with increasing salt concentration and duration of exposure, while leaf relative conductance and malondialdehyde (MDA) content increased. Under lower salt concentration (0.2%-0.4%), leaf relative conductance and MDA increased slightly, but both peaked at 0.8% salt. The proline content peaked 10 days after treatment application but subsequently declined. Under lower salt concentrations the activities of catalase and superoxide dismutase in all three grasses reduced gradually, while under 0.6%-0.8% salt, they initially increased, declined and then increased again. Z. macrostachys had the lowest leaf relative conductance and the lowest MDA, but the highest protective enzyme activity and soluble protein content. Consequently Z. macrostachys demonstrated greater salt resistance than Z. matrella and Z. japonica.

Correlation analysis of photosynthetic rate and biomass of different leaf positions with seed yield of Elymus sibiricus

LIU Jin-Ping, YOU Ming-Hong, ZENG Xiao-Lin, CAI Jian, ZHANG Xiao-Jing

2015, 24(11):  118-127.  DOI: 10.11686/cyxb2014518

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In the present study, photosynthetic parameters (photosynthetic rate, photosynthetic contribution rate) and biomass parameters (leaf biomass, inflorescence biomass, 1000-seed weight, seed yield) of leaves at different positions were measured during seed development of Elymus sibiricus. The aim of this study was to investigate changes in photosynthetic parameters and biomass parameters with the advance of seed development, and to determine the relationship between seed yield and photosynthetic performance of leaves at different positions during seed development. There were significant differences in photosynthetic rate and photosynthetic contribution rate of leaves at different positions at different stages of seed development, and among leaves of different positions at the same stage. Leaf biomass and leaf water content of different leaf positions changed significantly with seed development. At the flowering stage, seed yield was positively correlated with photosynthetic rate, leaf biomass and total leaf biomass in leaves at positions 1 to 5. At the seed filling stage photosynthetic rate of the first and third leaves and leaf biomass of the first two leaves were correlated with seed yield. At the milk stage, seed yield had a negative correlation with photosynthetic rate and leaf biomass from the fourth to fifth leaf. At the dough and ripe stages, seed yield had a positive correlation with photosynthetic rate of the first leaf and with leaf biomass of the first two leaves, but a significant negative correlation with photosynthetic rate from the third to fifth leaf and with leaf biomass from the third to fifth leaf. Seed yield was negatively correlated with total leaf biomass after the filling stage and with inflorescence biomass at the filling and milk stages, but a positive correlation with inflorescence biomass at the dough and ripening stages. It was concluded that crop management should promote growth and nutrient accumulation of leaves at different positions during vegetative growth to promote seed production. After the filling stage, it is very important to protect the integrity and health of the first three leaves to increase seed yield and seed quality.

Influences of precipitation regimes and elevated CO₂ on photosynthesis and biomass accumulation in Leymus chinensis

LIU Yu-Ying, LI Zhuo-Lin, HAN Jia-Yu, MU Chun-Sheng

2015, 24(11):  128-136.  DOI: 10.11686/cyxb2014474

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Leymus chinensis is a dominant, rhizomatous perennial C₃ species found in the grasslands of Songnen Plain, Northern China, where its productivity has decreased year by year due to environmental changes. As a dominant species growing in arid and semiarid regions, precipitation is a key factor limiting plant productivity. To determine how this species&#x02019; productivity responds to different precipitation regimes and increased CO₂ levels, we conducted an experiment that measured photosynthetic parameters, along with the accumulation and partitioning of biomass. Plants were subjected to combinations of three precipitation gradients (normal precipitation, normal&#x000b1;40%) and two CO₂ levels (380&#x000b1;20 and 760&#x000b1;20 &#x003bc;mol/mol) in environment-controlled chambers. The interaction between increased CO₂ and precipitation had significant effects on photosynthetic parameters, belowground biomass and root&#x02236;shoot ratio, but no effect on aboveground biomass. Net photosynthetic rate, stomatal conductance, transpiration rate, aboveground and total biomass rose with increases in precipitation and CO₂ concentration, but no significant change was observed when precipitation increased from normal to high under CO₂ enrichment. There was no significant difference in the ratio of root to shoot among precipitation regimes at the low CO₂ condition, but it changed significantly with CO₂ enrichment and low precipitation. Water use efficiency and intercellular CO₂ concentration increased significantly when precipitation was low, but decreased when precipitation was high under CO₂ enrichment. The effect of elevated CO₂ on photosynthesis and biomass accumulation was more obvious at low precipitation than at normal or high precipitation. The results suggest that at ambient CO₂ levels, net photosynthetic rate and biomass of L. chinensis increase with precipitation, but that these measures are not further affected by additional precipitation when CO₂ is elevated. Furthermore, CO₂ may partly compensate for the negative effect of low precipitation on the growth and development of L. chinensis.

Effect of water and nitrogen coupling on leaf senescence and yield of Zhengmai 9023 wheat during the grain-filling stage

XU Guo-Wei, WANG He-Zheng, NI Jiao-Jiao, CHEN Ming-Can, LI You-Jun

2015, 24(11):  137-145.  DOI: 10.11686/cyxb2015070

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Soil moisture and nitrogen nutrients are the principal factors affecting crop production. Elucidation of their influences and coupling effects would have great significance for optimizing yield and input efficiencies. Domestic and foreign scholars have conducted extensive research on interactions between water and fertilizers but most research to date has focused on soils rather than plant effects and the conclusions are not consistent. The purposes of this study were to investigate leaf senescence and yield differences in crops grown under conditions of nitrogen and water coupling. Three nitrogen levels of no nitrogen (N₁), 200 kg N/ha (N₂), 300 kg N/ha (N₃) and two irrigation regimes of irrigation control (W₁), water stress conditions (W₂) were trialed in the field during the grain-filling stage of Zhengmai 9023, a winter wheat cultivar. Chlorophyll content, photosynthetic rate, malondialdehyde (MDA) content and relative conductivity in flag leaves, along with soluble sugar and starch in stems and grain yield, were measured at 7 and 21 days after the flowering stage. The results showed that leaf chlorophyll contents and photosynthetic rates increased with nitrogen augments. However, MDA content and relative conductivity decreased in flag leaves 7 days after anthesis under the same levels of water treatment. Non-structural carbohydrate content first increased and then decreased with increases in nitrogen application. Soluble sugar and starch content in stem and sheath decreased by 10.6% and 10.1% under the condition of 300 kg N/ha (N₃) compared with 200 kg N/ha (N₂). Chlorophyll content, photosynthetic rate, soluble sugar and starch content reduced under water stress conditions (W₂) with the same nitrogen level as the irrigation control (W₁), while the opposite result was observed with MDA content and relative conductivity in flag leaves, especially in the N₃ treatment. These trends applied to both 7 and 21 days after anthesis. Wheat yield was higher for the N₂ treatments when crops were grown under the same water conditions. Compared with N₁, N₂ increased yields by 72.1% and N₃ by 61.4%. The N₃ treatment returned 6.6% less yield than N₂. With the same levels of nitrogen fertilizer, water stress improved wheat production compared to the control. These results suggest that mild water stress and appropriate nitrogen applications can produce interaction effects that promote nitrate assimilation and increase yield by improving seed-setting rates and grain weight.

Effects of α-amylase on fermentation of rice (Oryza sativa) straw

XU Neng-Xiang, DONG Chen-Fei, GU Hong-Ru, CHENG Yun-Hui, ZHANG Wen-Jie, DING Cheng-Long

2015, 24(11):  146-154.  DOI: 10.11686/cyxb2014499

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Rice (Oryza sativa) straw harvested at the appropriate time to achieve good nonstructural carbohydrate content (NSC) was utilized in this study; the main NSC was starch. Starch in rice straw should be initially hydrolyzed into water soluble carbohydrates (WSC) which are able to be utilized by lactic acid bacteria during the ensiling process. Two rice varieties (hybrid indica rice, variety Liangyoupeijiu and common japonica rice, variety Wuxiangjing 14) containing different NSC in the straw were treated with four different concentrations of α-amylase (0.5, 1.0 and 1.5 g/kg) to investigate the effects of α-amylase on rice straw silage quality. The results revealed that the NSC and starch content in the straw of Liangyoupeijiu was 6.89% and 3.68% respectively, significantly lower than Wuxiangjing 14 (P<0.05), 16.51% and 10.63% respectively. The forage quality and fermentation quality of rice straw resulting from different α-amylase treatments also differed significantly (P<0.05). 1.5 g/kg of α-amylase was optimum for Liangyoupeijiu whereas 1.0 g/kg α-amylase was optimum for Wuxiangjing 14. After α-amylase application (2-3 days), the NSC, WSC and starch content in the straw of Liangyoupeijiu, and the NSC and starch in the straw of Wuxiangjing 14 decreased, while the WSC in Wuxiangjing 14 increased and was significantly higher than the control. However during the 5th to 14th days of ensiling the WSC content decreased sharply and differences between α-amylase treatments were minimal.

Reproductive biology in the distylous species of Polygonum orientale

WEN Hui-Hui, CHEN Ming-Lin, ZHANG Zi-Sheng

2015, 24(11):  155-162.  DOI: 10.11686/cyxb2014515

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Our research has clearly confirmed distyly in Polygonum orientale. Long-styled and short-styled morph exhibited a precise reciprocal herkogamy which was significantly correlated with corolla length. Research showed that anther heights, tepals, stigma and pollen size and number were dimorphic (P<0.01). Compared with the pins, the thrums had larger tepals and the stigma had more but shorter papillae. The anther produced significantly bigger but fewer pollen grains. There was no significant difference between long-styled and short-styled in terms of tepal length (P>0.01). In terms of micro-morphological characteristics, pollen grains were spherical or sub-orbicular, with irregular margins and scattered holes. Thrips, ants and flower flies were the main visitors to the flowers. Artificial pollination revealed that pollen tube shape was normal in both morphs, with the tubes reaching the ovary 0.5 h after pollination. Not all pollen tubes growing down the stylar canal and ovary wall were able to reach the ovary, indicating the existence of chalazogamy in P. orientale.Long-styled and short-styled intramorph fruit sets were 14.00% and 13.33% respectively. Self-pollination fruit sets were 4.62% and 2.86% and intermorph fruit sets were 43.33% and 44.61% respectively. Self-pollination showed some affinity, but the fruit sets were low and the flowers were still predominantly intermorph.

Tissue culture in vitro and plant regeneration of Viola prionantha

LI Jun-Qiang, LIN Li-Hua, ZHANG Fan, WAN Xue-Qin, LIU Min, ZHAO Jing-Long

2015, 24(11):  163-173.  DOI: 10.11686/cyxb2015160

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The effects of various hormone ratios on adventitious buds, callus inductions and differentiation were investigated using the cotyledon node, leaf blade and petiole of Viola prionantha as explants. Finally, a plant regeneration system via tissue culture was established. The results showed that the optimal medium for adventitious bud induction from the cotyledon node and petiole was MS+2.0 mg/L 6-BA+0.1 mg/L NAA,but the leaf blade was not suitable as an explant. Three kinds of explants could induce callus formation. The optimal medium for callus induction from the cotyledon node and petiole was MS+1.0 mg/L 6-BA+0.5 mg/L 2,4-D with the highest callus induction rate being 98.3% and 96.7%, respectively. The optimal medium for callus induction from the leaf blade was MS+1.0 mg/L 6-BA+0.5 mg/L 2,4-D+0.05 mg/L NAA with the highest callus induction rate being 88.3%. The best medium for callus differentiation was MS+1.5 mg/L 6-BA+0.1 mg/L NAA with the highest callus differentiation rate being 100%. The optimal medium for the proliferation of adventitious buds was MS+1.5 mg/L 6-BA+0.075 mg/L NAA,the highest proliferation times being 4.68. The rooting rate of regenerated plants was up to 92.3% on half strength MS medium supplemented with 1.0 mg/L 6-BA. Rooted plantlets were grown on mixture with perlite: sand: humus (1:2:2); survival rate was up to 100% with good growth.

Correlation analysis of the main agronomic traits and performance of 21 alfalfa varieties

FU Bing-Zhe, GAO Xue-Qin, GAO Yong-Fa, LI Dong-Ning, ZHANG Long, ZHANG Rong

2015, 24(11):  174-182.  DOI: 10.11686/cyxb2014541

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Relationships between the major agronomic traits and production performance of 21 alfalfa varieties have been studied using correlation and grey correlation degree analysis. The results showed that alfalfa hay yields were significantly correlated with growth rate, plant height and the fresh-dry ratio (P<0.01). The correlation coefficients were 0.87, 0.86 and 0.55 respectively. The grey correlation coefficients were 0.8360, 0.8330 and 0.7716 respectively. Hay yields were not significantly correlated with either plant number or branch number (P>0.05). The grey correlation coefficient was 0.5921, 0.6267 and 0.7406 respectively. The production performances of the 21 alfalfa varieties were evaluated using the method of optimal correlation degree. The production performance of Gannong No.5, Golden Queen, WL363HQ, WL319HQ and Sandeli were superior to the other varieties. The Aohan, Caoyuan No.3 and Gannong No.2 varieties were the poorest performers in the Ningxia irrigation area.

Response of soil carbon cycling to climate warming: challenges and perspectives

CHEN Long-Fei, HE Zhi-Bin, DU Jun, YANG Jun-Jun, ZHU Xi

2015, 24(11):  183-194.  DOI: 10.11686/cyxb2014521

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Climate warming can directly or indirectly affect soil carbon cycling in a variety of ways. The response of soil carbon cycling to climate warming has been identified as one of the major sources of uncertainty in model projections of future climate change. In this paper, we discuss the responses and adaptation mechanisms of soil respiration to climate warming, and review recent advances on the responses of soil microorganisms (reactors of soil respiration) and soil organic carbon (substrate for soil respiration) to climate warming. We also explore the effects of the synergy between climate warming and other climate change factors, and the effects of the synergy between above- and below-ground components on soil carbon cycling. The main conclusions are summarized as follows: 1) autotrophic and heterotrophic components of soil respiration respond differently to climate warming. Autotrophic components, especially root respiration, are more sensitive to climate warming because of their dependence on photosynthesis; 2) soil respiration initially increases in response to warming and then declines. The decline can be attributed to thermal adaptation, substrate depletion, and nitrogen or soil moisture constraints; 3) the responses to climate warming vary among different kinds of microorganisms. Climate warming can induce changes in microbial physiology and even community structure, leading to the adaptation of soil respiration to climate warming; 4) soil organic matter decomposition is sensitive to climate warming. The temperature sensitivity of this decomposition is determined by chemical conformation (quality), environmental constraints (physico-chemical protection, drought, flooding, and freezing, which affect accessibility), and microbial physiology and enzyme production (efficiency). Finally, we discuss future developments in this research field: 1) soil microbial processes should be included in climate change models; 2) new molecular biological techniques such as stable-isotope probing and ‘meta-omic’ methods should be used for in-depth studies on soil microorganisms; 3) long-term experiments and field studies should investigate the combined effects of multiple climate change factors on soil carbon cycling; 4) there should be further systematic research on the interaction between above-ground and below-ground ecological processes.

Progress in understanding relationships between the physiological mechanisms of endogenous abscisic acid and drought resistance of alfalfa

LI Yue, WAN Li-Qiang, LI Xiang-Lin

2015, 24(11):  195-205.  DOI: 10.11686/cyxb2014489

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The shortage of water resources and related ecological crises due to climate change make the drought resistance of crops an important research topic. As a plant stress hormone, abscisic acid (ABA) plays an important role in drought stress response. Abscisic acid is synthesized from the 2-C-methyl-D-erythritol-4-phosphate (MEP) pathway. Through binding with its receptor, ABA controls stomatal closure by a series of signal transductions and/or regulates stress-related gene expression through other pathways. Alfalfa (Medicago sativa) is a high-performing legume that is widely cultivated for forage. Under conditions of drought stress, ABA accumulates in alfalfa and is closely related to vegetative protein storage in the tap root, gene expression and a range of osmolyte responses. Research on the relationship between ABA and drought resistance in alfalfa is under development. This research will assist understanding drought resistance mechanisms in alfalfa and will have profound influences on the breeding of alfalfa cultivars.

Progress on sex differentiation in unisexual flower plants

GAO Ming, CHEN Yi-Cun, YANG Su-Su, LIU Ying-Guan, ZHU Hui-Ping, WANG Yang-Dong

2015, 24(11):  206-217.  DOI: 10.11686/cyxb2015046

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Sexual reproduction is a universal phenomenon in the world of eukaryotes, and sex differentiation and determination are major events in the evolutionary history of angiosperms. The production of unisexual flowers has evolved numerous times from hermaphroditic ancestors, resulting in dioecious (5%) and monoecious (7%) plant taxa. Through developmental process, two broad categories of unisexual flowers have been recognized; the former results from flowers that are bisexual at initiation and become unisexual by termination of the development of the androecium (or the male reproductive organs) or gynoecium (or the female reproductive organs) and the latter results from sex differentiation occurring before initiation of stamens and carpels. Attempts have been made to understand regulatory mechanisms for plant sex determination by investigating unisexual flowers. The determinants of sexual phenotype in plants are diverse and complicated, including sex-determining genes in monoecious plants, Zea mays (corn) and Cucumis sp. (cucumber and its relatives); sex chromosomes in Silene latifolia and Carica papaya, which ensure the stable segregation of sexual phenotypes by preventing the recombination of sex determining genes; epigenetic regulatory mechanism, which alter gene expression, and hormonal regulation in Z. mays and Cucumis sativus. Sex determination is generally regulated by interactions between hormones, genetics and epigenetic modification. However, many important questions remain to be answered on the regulatory mechanisms of sex determination and sex differentiation, for example why few sex determination genes have been cloned, why the proportion of species with sex chromosomes is low, the relatively small portion of the dioecious species that have sex chromosomes, and the major epigenetic maintainers in genotypic sex determination (GSD). The recent research aimed at understanding the regulatory mechanisms of sex determination and sex differentiation in unisexual flowers, including phenotype traits, genetic base, epigenetics and physiological mechanisms were reviewed in this paper. Challenges and strategies are proposed to provide an effective contribution to elucidate the regulatory mechanisms of sex determination and sex differentiation in plants.

Biological characteristics of the exotic weed Sorghum halepense and measures to control its spread

LIAO Fei-Yong, XIA Qing-Fang, CAI Si-Qi, JIANG Hui, HUANG Chen-Fei

2015, 24(11):  218-226.  DOI: 10.11686/cyxb2015130

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Sorghum halepense is a noxious exotic weed in China that has become widely spread, and it affects the growth of several crops. In this article, we review research on S. halepense and measures to control its spread. First, we summarize the main differences between S. halepense and other plants belonging to the same genus. The stalk diameter of S. halepense is 0.5 cm, the ligule length is 1.0-1.5 cm, and the outer glume top has three slits. The presence of S. halepense in soil inhibits the germination and growth of other plants. For example, in soil containing S. halepense, the seed germination rates of cotton, lettuce, and wheat were inhibited by more than 40%, and the growth of above-ground parts of wheat, corn, and cotton was inhibited by more than 9.8%. There are several effective methods to control S. halepense. White radish and some insects can inhibit the growth of S. halepense. Among the chemical control methods, 10% urea and 15% ammonium bicarbonate can kill seeds of S. halepense. Other chemicals used to control S. halepense include imazethapyr, imazamox, glufosinate, and clethodim and glufosinate, which can kill up to 94% of S. halepense plants. Propaquizafop and quizalofop can reduce the growth of S. halepense plants by 97%. S. halepense can be used as feed for Oxya chinensis and as a raw material for paper manufacturing. Further studies on this weed should include in-depth physiological ecology studies, research on enhancing herbicide efficacy and screening of specific herbicides, the use of biological controls, landscape utilization, and comprehensive use of the plant material.

Nutrient variation and forage evaluation of Vicia unijuga in alpine grasslands

MAO Zhu-Xin, FU Hua, NIU De-Cao, NIE Bin, CHEN Hao

2015, 24(11):  227-233.  DOI: 10.11686/cyxb2015123

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Breeding and cultivating high-quality legumes is an important way to develop livestock agriculture on alpine grasslands. Vicia unijuga is a perennial legume with high feeding value. Research on its hay yield and nutrient dynamics is needed to inform its production and utilization as forage. A field trial has been conducted on Gannan alpine grasslands with the aim of investigating the feeding value of V. unijuga at different growth stages. Samples were taken at branching, squaring, 20% bloom and 80% bloom stages. Measurements were made to determine forage yield, crude protein (CP) and water soluble carbohydrate (WSC) contents, as well as the levels of ash and various other mineral elements. Results showed that hay yield increased with growth stage but that CP levels were higher at the early growth stage. While CP decreased at the late growth stage (80% bloom), WSC contents reached their highest level at this point. Ash levels showed a single-peak curve variation across the different growth stages. However, mineral element contents varied less consistently. P, Zn, Ca and Mn varied in half-peak or peak type curves, Na and Mg in linear type, K and Cu in wave type. In conclusion, CP contents reached the levels of first-class forage grasses in America. Hay yield and WSC levels were highest at the 80% bloom stage, at which point the levels of P, K, Na, Mg, Mn and Zn are sufficient to satisfy the basic needs of livestock. Grey relational analysis and weight assignment methods were used to evaluate the above results. This analysis showed that the evaluation index was highest at the 80% bloom stage, which is thus the optimal cutting point of V. unijuga for alpine grassland agriculture.

Effects of polyethylene glycol priming on the vigor of aged oat seeds

XIA Fang-Shan, YAN Hui-Fang, MAO Pei-Sheng, WANG Ming-Ya, ZHENG Hui-Min, CHEN Quan-Zhu

2015, 24(11):  234-239.  DOI: 10.11686/cyxb2014520

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A study has been undertaken to explore the effects of polyethylene glycol (PEG) priming on the vigor of aged oat seeds (Avena sativa). The research also aimed to determine the optimal PEG concentration and priming time. Seeds with ultra-dry moisture content (4%) were deteriorated for 48 d at 45℃. They were then primed for 0 (control), 3, 6 and 12 h with different concentrations of PEG-6000 (0, -0.3, -0.6, -0.9 and -1.2 MPa). The germination percentage, germination index, mean time to germination and seedling vigor index were then analyzed. The results showed that the germination percentage, germination index and seedling vigor index of aged oat seeds decreased after priming with low concentrations of PEG (0--0.6 MPa) in relation to the control, but that mean time to germination increased. However, the opposite trend was observed after priming with high PEG concentrations (-0.9 and -1.2 MPa). These results indicate that PEG priming not only prevents the imbibition damage for oat seeds with ultra-dry moisture content but also repairs damage from seed ageing. The effect of PEG priming was closely related to its concentration, priming time and their interaction. This study determined that the appropriate concentration and priming time was -1.2 MPa and 12 h for aged oat seeds. However, further research is needed to confirm whether these levels can be practically applied in agricultural production.

Study of resistance to dehydration in Haloxylon ammodendron and Suaeda physophora seedlings

DING Xiao-Dong, ZHANG Shi-Rong, LIU Yang-Chao, FENG Gu

2015, 24(11):  240-246.  DOI: 10.11686/cyxb2014542

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The previous research has been concentrated on the dehydration resistance of the seedlings in the two halophytes: Haloxylon ammodendron and Suaeda physophora. Comparing with the psammophyte Haloxylon persicum, both the seedling survival rate and the root damage after the desiccation were investigated, the results showed that: No significant difference was found in the survival rates of H. persicum among the 7, 14, 21 and 28 days desiccation treatments, however, the survival rates of H. ammodendron and S. physophora has been significantly decreased with the desiccated duration, in which the seedlings of S. physophora were all died in the 28 days desiccation treatment. The seedling root of H. persicum was rarely damaged by the 28 days desiccation treatments, which was better than that in H. ammodendron, in the 300 mmol/L NaCl treatment, the root tip of the H. ammodendron seedlings were all bended and died. It was showed that H. persicum, H. ammodendron and S. physophora were all “homoiochlorophyllous” resurrection plants, they would not degrade their chlorophyll during the desiccation time, and could survive fast when the water supplied again, which was an important adapt strategy to the extremely drought environment.

Preliminary assessment of fall dormancy in 45 alfalfa cultivars

FANG Shan-Shan, SUN Qi-Zhong, YAN Ya-Fei, LIU Zhi-Ying, TAO Ya, LI Feng

2015, 24(11):  247-255.  DOI: 10.11686/cyxb2014511

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Following the methods of Teuber and using 11 different American fall dormancy standard alfalfa cultivars as contrasts, we assessed the fall dormancy class of 45 alfalfa cultivars from the drought area of western Inner Mongolia in 2013 and 2014. We conducted a regression analysis of the relationship between fall dormancy class and natural plant height after final clipping and compared results with the 11 American cultivars. Results showed that natural plant height at 21 days after autumn clipping and fall dormancy class had a linear relationship with R² of 0.9643 and 0.9867 respectively. Analysis showed that the correlation coefficient between actual fall dormancy class and the 11 comparator varieties is 0.994. The correlation coefficient for 13 known fall dormancy introduced varieties is 0.969. Cluster analysis showed that 90% of 21 domestic alfalfa cultivars are either dormant or highly dormant types. The actual fall dormancy classes of Yumu No.1, Gannong No.5 and Liangmu No.1 were 6.8, 7.4 and 8.5, indicating that they belong to the non-dormant type.