Table of Content

20 October 2019, Volume 28 Issue 10

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Effects of grazing on carbon exchange in a Leymus secalinus grassland ecosystem in the agro-pastoral ecotone of Northern Shanxi

XING Peng-fei, LI Gang, CHEN Xiao-peng, LI De-ying, WANG Chang-hui, DONG Kuan-hu, ZHAO Xiang

2019, 28(10):  1-11.  DOI: 10.11686/cyxb2018724

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Ecosystem net carbon exchange (NEE) is an important index to evaluate the carbon cycle, and is calculated from total primary productivity (GEP) and ecosystem respiration (ER). The aim of this study was to explore the effects of grazing on carbon exchange in the Leymus secalinus grassland ecosystem in the agro-pastoral ecotone of Northern Shanxi. Using the static chamber technique (LI-840a), we measured the daily and seasonal dynamics of NEE, ER, and GEP in the L. secalinus grassland under grazing during 2015 and 2016, and analyzed the correlation between these indexes and atmospheric temperature, soil temperature, soil moisture content, and aboveground and belowground biomass. The NEE, ER, and GEP showed clear daily and seasonal variations, which were the unimodal type. The values of NEE were lower in May, June, and September, but higher in July and August. The daily dynamics of NEE were mainly controlled by air temperature, while the seasonal changes were mainly controlled by soil temperature. Correlations between aboveground biomass as well as belowground biomass and NEE, ER, and GEP were extremely significant. Compared with fencing, grazing significantly decreased the NEE rate of the ecosystem in this grassland, but it did not affect the daily and seasonal trends in NEE. These results showed that, compared with enclosure, grazing can decrease the carbon exchange capacity and weaken the carbon sink function of a grassland ecosystem by reducing the proportion of photosynthetic matter in grassland vegetation.

Effects of short-term nitrogen and phosphorus addition on soil labile organic carbon in desert grassland

ZHANG Ya-rou, AN Hui, LIU Bing-ru, WEN Zhi-lin, WU Xiu-zhi, LI Qiao-ling, DU Zhong-yu

2019, 28(10):  12-24.  DOI: 10.11686/cyxb2019234

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In this study, nitrogen (N) and phosphorus (P) were added to desert grasslands in arid and semiarid regions. We determined the concentration and efficiency of dissolved organic carbon (DOC), microbial biomass carbon (MBC), and easily oxidized organic carbon (EOC), and we calculated carbon management indicator (CMI) and sensitivity index (SI) values. The results showed that nutrient addition (N, P, and N+P) significantly increased the soil DOC concentration in the 0-20 cm layer, but did not affect the soil MBC concentration in the 0-20 cm layer. The soil EOC concentration in the 0-10 cm layer was significantly increased by the addition of N+P. In the 0-30 cm layer, all sensitivity indexes of soil DOC were higher than those of soil EOC, indicating that soil DOC was more sensitive than soil EOC to short-term N and P addition. Therefore, soil DOC could be used as an indicator of the changes in SOC after short-term N and P additions to desert grassland. The CMI and soil organic matter content were increased by short-term N and P addition. These results indicate that short-term N and P addition can promote the restoration of soils in desert grassland.

Driving force analysis of changes in grassland coverage on the Qinghai-Tibet Plateau based on NDVI in 2000-2016

LI Chong-yang, FAN Wen-tao, LI Guo-mei, GAO Jing, TANG Zeng, SONG Ren-de

2019, 28(10):  25-32.  DOI: 10.11686/cyxb2018701

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In this study, we analyzed the driving forces underlying changes in grassland coverage on the Qinghai-Tibet Plateau. For these analyses, we used statistical data collected from 2000 to 2016 from 573 herdsmen’s pastures scattered across five provinces on the Qinghai-Tibet Plateau. These data comprised remote sensing, meteorological, socio-economic, and other data. We used an empirical model to calculate the vegetation coverage of herdsmen’s pastures to analyze the degree of grassland degradation, the trends in various factors, and the key drivers of grassland change on the Qinghai-Tibet Plateau since the beginning of the 21st century. The results indicate that mild degeneration is dominant in the study area, with the area of degraded pasture accounting for 69% of the total area. The analyses indicated that the changes in grassland vegetation coverage are the result of interactions between natural and socio-economic factors: increased temperature and rainfall from climate change have positively affected the growth of grassland vegetation; whereas increases in economic development and population density have led, and will continue to lead, to decreases in grassland vegetation coverage. Furthermore, grassland vegetation coverage is continuing to decrease as the distance between neighboring cities decreases. In terms of the mechanisms of change, there is a significant negative correlation between the livestock carrying capacity of grassland and vegetation coverage, and overgrazing is still the key driver of grassland change on the Qinghai-Tibet Plateau.

Activation of insoluble phosphorus and its absorption by Sorghum dochna, Sorghum hybrid Sudan grass, and Dolichos lablab

WANG Ya-qi, YUAN Ling

2019, 28(10):  33-43.  DOI: 10.11686/cyxb2018652

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Phosphorus fertilizer is readily absorbed and fixed by soil particles after it is applied to soil, resulting in low bioavailability. Therefore, it is an important goal to improve the bioavailability of phosphorus fertilizer by modifying crop cultivation systems. The aim of this experiment was to compare the ability of different forages to activate and absorb insoluble phosphorus. The forage growth and phosphorus absorption characteristics of Sorghum dochna, Sorghum hybrid Sudan grass, and Dolichos lablab were evaluated under four treatments in hydroponic culture. The four treatments were water-soluble phosphorus (SP, 1/4SP, 1/8SP) and insoluble phosphorus (IP) supplied in the hydroponic growth medium. The responses of forage to insoluble phosphorus and low phosphorus varied among forage species and phosphorus levels. In the IP, 1/4SP, and 1/8SP treatments, the plant roots showed restricted growth, and forage growth was inhibited. The maximum inhibition of root length, stem length, and biomass were 2.25%-55.92%, 3.10%-63.35%, and 4.06%-57.72%, respectively, in the low phosphorus and IP treatments compared with the SP treatment. The nutrient contents and nutrient accumulation in forage were also significantly lower in the IP, 1/4SP, and 1/8SP treatments than in the SP treatment. In contrast, compared with the SP treatment, the IP, 1/4SP, and 1/8SP treatments showed increased root to crown ratios and increased organic acid secretion (maximum increases of 162.9%-337.1%, 84.4%-428.9%, and 354.6%-1027.3% in IP, 1/4SP, and 1/8SP, respectively). The H₂PO4- contents in the nutrient solutions of S. dochna and Sorghum hybrid Sudan grass were significantly higher under IP treatment than under the 1/4SP and 1/8SP treatments, but did not differ significantly among the treatments with D. lablab. These results indicated that the roots of the three forage plants can secrete organic acids to dissolve insoluble phosphorus in the nutrient solution and turn it into available phosphorus for crop absorption and utilization. The three species could be ranked, from highest phosphate solubilizing ability under low phosphorus stress to lowest, as follows: S. dochna>Sorghum hybrid Sudan grass>D. lablab. Therefore, adding a forage grass that can efficiently activate and utilize insoluble phosphorus as a green manure in a rotation system can reduce the application of phosphorus fertilizer and promote the soil nutrient cycle.

Root characteristics and accumulation of nitrogen, phosphorus, and potassium in rice plants cultivated under three different systems

WAN Qi-hui, MA Li-hua, JIANG Xian-jun

2019, 28(10):  44-52.  DOI: 10.11686/cyxb2018743

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The aim of this study was to determine the effects of different cultivation methods on the root characteristics of rice (Oryza sativa), the accumulation of nitrogen (N), phosphorus (P) and potassium (K) in rice plants at different growth stages, and rice yield. The rice variety Y Liangyou 6 was grown in soil containing sufficient amounts of N, P, and K. The design was based on a long-term field experiment (initiated in 1990), with three treatments: flooded paddy field (FPF), conventional paddy-upland rotation tillage (CT), and combined ridge and no-tillage (RNT). The actual yield of the RNT system was 8750.8 kg·ha^-1, significantly higher than the yields from the CT and FPF systems (P<0.05). The rice root length density, root surface area, and specific root length were higher significantly in RNT than in CT at the elongation stage (P<0.05). Compared with the root surface area in the FPF and CT systems, that in RNT was increased by 3.37% and 6.71%, respectively, at the heading stage (1.74 cm²·cm^-3). The RNT system increased rice stem N, P, and K contents by 49.26%, 33.20%, and 59.70% compared with their respective contents in CT at the heading stage. There was no significant difference in the P content of stems and leaves of rice among the three tillage methods, but NPK accumulation was significantly higher in rice plants in the RNT treatment than in those in the CT treatment (P<0.05) at the heading stage. The accumulation rate of NPK in rice plants was significantly higher (P<0.05) in the RNT treatment than in the other treatments at the heading stage, indicating that the accumulation of N, P, and K was significantly increased under RNT. Compared with the N content in mature rice grains in FPF and CT, that in RNT was increased by 24.80% and 14.30%, respectively (P<0.05). The lowest N:K and highest K:P were in the RNT treatment from the tillering to the heading stage, which meant that the absorption, utilization, and distribution of K in rice was significantly improved by the combined ridge cultivation no-tillage system. In conclusion, rice plants cultivated under the RNT system formed strong and active root systems, and were more efficient at accumulating NPK and taking up K from soil. The rice plants cultivated under the RNT system showed the most efficient internal K utilization mechanisms throughout the lifecycle. These results provide a scientific basis for achieving high yields in rice production.

Effects of mowing frequency on competitiveness and quality of Zoysia tenuifolia lawn invaded by Imperata koenigii

WANG Zhi-yu, LI Ying, LIU Jin-ping, YANG Xiao-qin, HE Lin-jiang

2019, 28(10):  53-65.  DOI: 10.11686/cyxb2018735

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Warm-season lawns are vulnerable to Imperata koenigii invasion in summer in subtropical regions. The purpose of this study was to determine the effects of mowing frequency on the competitiveness, plant growth, and quality of a Zoysia tenuifolia lawn invaded by I. koenigii to varying degrees. We established an experiment in which Z. tenuifolia lawn was artificially planted with I. koenigii at five different proportions (10%, 20%, 30%, 40%, 50%) and mowed at four different frequencies (0-3 times per month) to a stubble height of 7 cm for 3 consecutive months. Competitive parameters such as relative yield, total relative yield, attack power, and competitive balance index were determined for both plants. Growth parameters including plant height, number of tillers, number of leaves, biomass, and root-shoot ratio were also analyzed. The quality of the lawn was evaluated comprehensively by calculating indexes of density, texture, leaf color, and uniformity, and by determining grass height and biomass. The results showed that: 1) The mowing frequency significantly affected the aboveground and underground competition parameters of Z. tenuifolia and I. koenigii (P<0.05). Mowing increased the antagonistic effect of the aboveground parts between the two plants, while the antagonistic effect of the underground parts between the two plants was reduced by mowing 2-3 times per month. 2) Mowing frequency and the proportion of I. koenigii had stronger effects on the aboveground parts of Z. tenuifolia than on its underground parts. Mowing once per month improved the aboveground competitiveness of Z. tenuifolia, while mowing twice per month improved its underground competitiveness. The synergistic effect of mowing frequency and increased proportions of I. koenigii increased its attacking power against the Z. tenuifolia root system. 3) The mowing frequency and proportion of invasion significantly affected the growth of I. koenigii and Z. tenuifolia. Mowing 1-2 times per month increased the tiller number and leaf number of both plants. Mowing twice per month increased the tiller number and leaf number of Z. tenuifolia increased by about 40%. The biomass of Z. tenuifolia decreased when the proportion of I. koenigii was 10% or more, and the tiller number of Z. tenuifolia decreased when the proportion of I. koenigii was 20% or more. When the proportion of I. koenigii was 30% or more, the plant height of Z. tenuifolia increased but its leaf number decreased. Mowing frequency was the main factor affecting the plant height, tiller number, leaf number, and root-shoot ratio of Z. tenuifolia. The proportion of I. koenigii mainly affected the biomass of single Z. tenuifolia plants. 4) Mowing frequency mainly affected the density, height, and biomass of the lawn, but the proportion of I. koenigii mainly affected the texture, leaf color, and uniformity of the lawn (P<0.05). The best combination in terms of the comprehensive quality of the lawn was 10% or less I. koenigii and mowing twice per month. The lawn quality was mainly affected by the mowing frequency, followed by the proportion of I. koenigii. 5) Mowing 1-2 times·month^-1 significantly increased the aboveground and underground competitiveness of Z. tenuifolia against invading I. koenigii, and promoted tiller formation in Z. tenuifolia, reduced lawn height, and improved the density and texture of the lawn. However, mowing could not change the fact that the aboveground and underground competitiveness of Z. tenuifolia lower than that of I. koenigii. Therefore, the basic requirements for maintaining the quality of a Z. tenuifolia lawn in summer are to control the proportion of I. koenigii at 10% or less and mow twice per month.

Effects of Epichloё endophytic fungi infection in wild barley (Hordeum brevisubulatum) on soil chemical properties and the soil microbial community

JIN Yuan-yuan, BOWATTE Saman, JIA Qian-min, HOU Fu-jiang, LI Chun-jie

2019, 28(10):  66-77.  DOI: 10.11686/cyxb2018677

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An 8-month greenhouse study was conducted to investigate the belowground effects of infection of wild barley by the foliar endophyte Epichloё bromicola. The effects of endophyte infection status (E+: endophyte infected; E-: endophyte free) on soil chemical and microbiological properties were tested in three soils collected from Maqu, Yuzhong, and Linze in Gansu province, China. We measured the dry matter production of plants at 3, 6, and 8 months after establishment. The soil carbon, nitrogen, and phosphorous contents, pH, and the abundance of bacteria, fungi, and key bacteria involved in the soil nitrogen cycle were determined at 6 and 8 months after plant establishment. The dry matter production of wild barley was significantly higher in E+ plants than in E- plants in all three soils. Irrespective of endophyte status, the dry matter production was highest in Linze soils and lowest in Maqu soils. The presence of the endophyte significantly increased soil total nitrogen content and the abundance of ammonia-oxidizing bacteria. The effects of endophyte status on total soil carbon, microbial biomass carbon, pH, abundance of bacteria, fungi, denitrifying bacteria, and nitrous oxide-reducing bacteria varied with soil type and plant age. The total phosphorus content in soil varied significantly with soil type and plant age but not with endophyte status. These results confirmed that E. bromicola infection of wild barley influences the chemical and microbiological properties of soil in a soil type- and plant age-dependent manner. We suggest that long-term field studies in the future would be beneficial for understanding the mechanisms driving these observed changes in soil properties.

Growth adaptation characteristics of three Salsola species with different photosynthetic systems

ZHOU Wen-fei, LIU Fu-rong, YAO Zhen-ye, GONG Chun-mei

2019, 28(10):  78-90.  DOI: 10.11686/cyxb2018204

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Drought is one of the external forces that has promoted the evolution of the C₄ photosynthetic pathway. It is great of significance to explore the photosynthetic evolution of the C₄ pathway under drought stress for the protection and restoration of vegetation in areas threatened by desertification. Because the Salsola genus contains different photosynthetic types, it is an ideal material to study C₄ evolution driven by drought. Most previous studies on the photosynthetic evolution of plants have focused on changes at the anatomical level, rather than on the characteristics of growth adaptation. On the basis of the phylogenetic relationships of various species in the Salsola genus, we chose Salsola abrotanoides (C₃), Salsola laricifolia (C₃-C₄) and Salsola orientalis (C₄) as the experimental materials. We analyzed growth adaptation characteristics such as leaf morphology and anatomy, seed morphology, resistance physiological indicators, and ecological chemometric indexes. The results showed that the C₃-photosynthetic type in the Salsola genus is the original ancestor, and that the C₃-C₄ photosynthetic type and the C₄ photosynthetic type have evolved from the C₃ photosynthetic type. Compared with the C₃ species S. abrotanoides, the C₃-C₄ species S. laricifolia and the C₄ species S. orientalis have gradually adapted to drought by changing their external morphology and anatomical structure, and by adjusting their seed propagation strategies by forming differently sized seeds. The high photosynthetic capacity of C₄ plants provides materials (soluble sugars) involved in regulation, and with the evolution to C₄ photosynthesis, the drought resistance capacity of the Salsola genus has been enhanced. To increase the amount of carbon fixed by photosynthesis, S. laricifolia has increased its nitrogen and phosphorus use efficiencies, while S. orientalis has increased its nitrogen and phosphorus contents. Compared with S. abrotanoides, S. laricifolia and S. orientalis are more adapted to barren environments. These experimental data provide evidence of the physio-ecological adaptations that have improved C₄ photosynthesis, consistent with evolutionary theory.

Fine root turnover and distribution characteristics in different soil layers of three alfalfa varieties under drip irrigation

SUN Yan-mei, MIAO Xiao-rong, LIU Jun-ying, ZHANG Qian-bing, YU Lei, MA Chun-hui

2019, 28(10):  91-100.  DOI: 10.11686/cyxb2018728

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In this study, we monitored fine root turnover and root distribution characteristics of three alfalfa varieties (WL343HQ, WL363HQ, and WL366HQ) to determine the relationship between these characteristics and hay yield. The three alfalfa varieties were from the Oasis Region of Northern Xinjiang. Fine root production and mortality of the three alfalfa species were monitored using minirhizotrons to clarify the dynamic characteristics of fine root turnover and characteristics in different soil layers. The total fine root standing crop of the three alfalfa species reached their maximum values on July 21 (0.294, 0.861, and 0.568 cm·cm^-3 in WL343HQ, WL363HQ, and WL366HQ, respectively). In WL343HQ, WL363HQ, and WL366HQ, fine root production had two, three, and two peaks, and fine root mortality had two, two and three peaks, respectively. The maximum fine root crop of alfalfa occurred during the period July 6 to July 21. The cultivars were ranked, from largest fine root crop to smallest, as follows: WL363HQ (0.455 cm·cm^-3)>WL366HQ (0.260 cm·cm^-3)>WL343HQ (0.116 cm·cm^-3). The maximum mortality of alfalfa fine roots occurred at different times in the three cultivars. Fine root growth and death occurred at different stages, and the size of the fine root standing crop was lower during the cutting period than during the unprocessed period. This result indicates that cutting can reduce the growth of alfalfa fine roots and reduce the fine root standing crop. The soil layers were ranked, from most fine roots of the three alfalfa species to least, as follows: 0-20 cm>20-40 cm>40-60 cm. The fine root turnover rates of WL343HQ, WL363HQ, and WL366HQ were 1.566, 1.973, and 1.859 yr^-1, respectively, and there was no significant difference among them (P>0.05). In correlation analyses, the total hay yield of alfalfa was significantly positively correlated with annual fine root mortality (P<0.01), and the maximum annual standing crop of fine roots was significantly positively correlated with annual fine root production. The results indicated that fine root mortality in alfalfa affects the growth and development of above-ground parts and the hay yield. The fine root standing crop, production quantity, and hay yield were higher in WL363HQ than in WL343HQ and WL366HQ, indicating that WL363HQ performs better in local areas and is more suitable for local cultivation.

Potential allelopathic effect of Aster subulatus on Triticum aestivum and Brassica chinensis

HE Ping, DENG Yu-jun, HU Xiao-yin, PAN Hui-min, DENG Hong-ping

2019, 28(10):  101-109.  DOI: 10.11686/cyxb2019284

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Aster subulatus is a common weed of wheat (Triticum aestivum) and Chinese cabbage (Brassica chinensis) in farmland. To explore its invasion mechanism, a Petri dish method was used to evaluate the potential allelopathic effect of aqueous extracts from the stem and leaf of A. subulatus on T. aestivum and B. chinensis. In general, the germination rates and germination indexes of T. aestivum and B. chinensis decreased with increasing concentrations of the A. subulatus aqueous extracts. T. aestivum was not sensitive to lower concentrations of the aqueous extracts but was more strongly inhibited than B. chinensis by higher concentrations (20, 40 g·L^-1) of the aqueous extracts. The fresh weight, shoot length, and root length of T. aestivum and B. chinensis were more strongly inhibited as the concentration of the aqueous extracts increased. The aqueous extracts at higher concentrations (20, 40 g·L^-1) had significant negative effects on the fresh weight and shoot length of B. chinensis, and significant negative effects on those of T. aestivum at lower concentrations (5, 10 g·L^-1). In all treatments, higher concentrations of the aqueous extracts had stronger negative effects than lower concentrations. The aqueous extracts at the lowest concentration (5 g·L^-1) negatively affected the root length of T. aestivum, but not that of B. chinensis. As the concentration of the aqueous extracts increased, the activities of protective enzymes (catalase, peroxidase, superoxide dismutase) gradually decreased, except that the catalase activity fluctuated in B. chinensis. During treatment with the aqueous extracts, the malondialdehyde content and membrane permeability gradually increased in B. chinensis, while the malondialdehyde content of T. aestivum decreased first and then increased, and its root activity and chlorophyll content showed downward trends. Overall, the aqueous extracts had stronger negative effects on the physiological indexes of B. chinensis than on those of T. aestivum. The results of this study showed that aqueous extracts of A. subulatus inhibited the germination and growth of two crop plants by reducing protective enzyme activities, disrupting the membrane system, and affecting respiration and photosynthesis. For all measured indexes, the standard error values were higher for B. chinensis than for T. aestivum, indicating that B. chinensis was more sensitive than T. aestivum to the aqueous extracts of A. subulatus.

Effects of grassland cultivation on ecosystem water use efficiency in a grazed temperate grassland area

LI Yu-zhe, SHAO Quan-qin, FAN Jiang-wen, CHEN Yi, CHEN Zhi, GUAN Hui-lin, ZHANG Xin-yuan

2019, 28(10):  110-121.  DOI: 10.11686/cyxb2019259

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Water use efficiency (WUE) is an indicator of coupling between ecosystem carbon and water cycles, so it is an important reference for the measurement of regional resource transformation efficiency. The purpose of this study was to determine the effects of cultivation on the WUE of a grazed grassland ecosystem. On the basis of the vorticity-related system monitoring data in adjacent grazed and cultivated areas and combined community investigations and sampling measurements, this study analyzed the dynamic difference and effects of two different management patterns on the WUE of the ecosystem (gross primary productivity; GPP) (WUE_GPP). The results indicated that: 1) WUE_GPP reached its peak each year in summer; in June, the daily average WUE_GPP of the cultivated sites (3.61 g C·kg^-1 H₂O) was 58% higher than that of the grazed sites, and the annual WUE_GPP of the former (3.07 g C·kg^-1 H₂O) was 50% higher than that of the latter. 2) The higher WUE_GPP of the cultivated sites was due to the higher GPP during the growing season and lower evapotranspiration (ET) during the non-growing season. 3) The ET explained the change in the WUE_GPP of the grazed sites (26%, P<0.001), while GPP explained the change in WUE_GPP of the cultivated sites (45%, P<0.001) better than did ET. 4) Among the environmental factors, soil moisture had the strongest effect on the change in WUE_GPP and the negative correlation between them was extremely significant both for the cultivated and grazed sites (P<0.001). These results show that different land management practices and utilization types can significantly affect ecosystem WUE on the temperate steppe. Among the various environmental factors, soil water content explained the changes in WUE_GPP at both the grazed and cultivated sites, and so soil water supply may be the most important factor regulating WUE in regional ecosystems. These results provide a useful reference for scientific planning of regional land use and for the reinforcement of more efficient use of key resources in arid areas.

Effects of time after rejuvenation pruning and stand age on leaf functional traits of Ammopiptanthus mongolicus and stoichiometric characteristics of rhizosphere soil

DONG Xue, HAO Yu-guang, XIN Zhi-ming, LI Xin-le, DUAN Rui-bing, LIU Fang, ZHAO Ying-ming, HUANG Ya-ru

2019, 28(10):  122-133.  DOI: 10.11686/cyxb2018741

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Carbon (C), nitrogen (N), and phosphorus (P) stoichiometry are critical indicators of biogeochemical coupling in terrestrial ecosystems. Therefore, nutrient stoichiometry has been used as an indicator of community succession and vegetation restoration in recent years. The aim of this study was to clarify the effects of time elapsed after pruning and shrub age on leaf functional traits and on the chemical characteristics of C, N, and P in leaves of Ammopiptanthus mongolicus. Variance and correlation analyses were used to detect the adaptive strategies of shrubs during restoration and growth after a pruning treatment. This information is helpful to solve technical conservation problems and for the development of germplasm resources in theory and in practice. The results provide basic data for the prediction and evaluation of the natural population of A. mongolicus in this ecosystem. The results showed that: 1) The leaf area of A. mongolicus increased significantly after a rejuvenation pruning treatment (P<0.05). Specific leaf area, leaf N content, and leaf P content were significantly increased by 1 year after rejuvenation pruning (P<0.05). They declined during subsequent years after pruning and with shrub age. Leaf dry matter content showed the opposite trend to that of specific leaf area. The C content of leaves did not differ significantly (P>0.05) with age or among different years after the pruning treatment. The leaf N content was significantly positively correlated with leaf P content and specific leaf area. Leaf dry matter content was significantly negatively correlated with specific leaf area, and significantly negatively correlated with leaf P content and specific leaf area. 2) The responses of C, N, and P contents and stoichiometric ratio to shrub age and the number of years after the pruning treatment were not exactly the same between leaves and soil. The number of years after the pruning treatment and shrub age significantly affected soil C content under the shrubs (P<0.05), but not the P content in soil (P>0.05). Only shrub age significantly affected the N content in soil. With prolonged time after the pruning treatment and increasing shrub age, the soil C and N contents increased, but the soil P content showed a downward trend. 3) For the leaf C, N, and P and stoichiometric ratio, P and C:P were most sensitive to the number of years after the pruning treatment and the age of A. mongolicus, implying that these indices can reflect the regeneration, growth, and the dynamic changes in this population. The average N:P of the leaves at 1, 3, and 8 years after the pruning treatment were 14.79, 15.77, and 17.81, respectively. The average N:P ratios of the leaves of the young, middle-aged, and mature shrubs were 15.32, 18.23, and 21.76, respectively. These results suggest that with increasing time after the pruning treatment and with increasing plant age, the growth of A. mongolicus gradually shifted from being restricted by N and P to being more restricted by P.

Effects of positive plant interactions on seedling regeneration in the hill-gully region of the Loess Plateau

GE Fang-hong, LIU Hong-yan, ZHAO Fu-wang, WANG Ning, ZHOU Zheng-chao

2019, 28(10):  134-143.  DOI: 10.11686/cyxb2018719

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The seedling stage is the most fragile and critical stage of the plant life cycle. The aim of this study was to determine whether existing dominant species could serve as nurse species to play a positive role in improving seedling establishment and survival on a loess slope where soil erosion is a serious problem. Three typical plant communities (Bothriochloa ischaemum, Sophora viciifolia, and Artemisia gmelinii) in the hill-gully region of the Loess Plateau were selected for in-depth analyses. For each community, the species composition, seedling densities, species diversity, and their relationship with the standing vegetation in two microhabitats (plant patches and bare land patches) were surveyed and analyzed. The results showed that: 1) the seedlings represented 52 species belonging to 22 families. Most seedlings in the B. ischaemum, S. viciifolia, and A. gmelinii communities belonged to the Poaceae, Leguminosae, and Poaceae family, respectively. Perennial herbs made up the largest proportion of seedlings. 2) Seedling density, seedling species diversity, and similarity indexes showed similar trends in seedling and standing vegetation. The values of these indexes were higher in vegetated patches than in bare land patches. In vegetated patches, the highest seedling density and species diversity index were in the A. gmelinii community; the lowest seedling density was in the B. ischaemum community; and the lowest species diversity index was in the S. viciifolia community. In the bare land patches, the communities could be ranked, from highest seedling density and species diversity index to lowest, as follows: A. gmelinii community>S. viciifolia community>B. ischaemum community. The similarity index between seedling and standing vegetation was less than 0.5 in both microhabitats of the three plant communities, indicating that the seedling and standing vegetation of each community were extremely dissimilar or moderately dissimilar. 3) These results show that adult plants of the three dominant species can play a positive role in the regeneration of seedlings in the surrounding area, and the strength of this positive interaction differs among species. The results indicate that all three plant species can serve as nurse plants to improve seedling survival, but that the positive interaction may weaken and turn into a competitive relationship as the seedlings grow, so that there is little similarity between seedlings and standing plants.

Effects of exogenous selenium on grass yield and nutritive value of forage ramie

ZHU Juan-juan, YU Chun-ming, CHEN Ji-kang, WANG Yan-zhou, CHEN Ping, XIONG He-ping

2019, 28(10):  144-155.  DOI: 10.11686/cyxb2018575

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The aim of this study was to improve the nutritional value of forage ramie by providing optimal selenium (Se) nutrition. The effects of different Se doses on the grass yield and nutritive values of forage ramie were determined using the forage ramie cultivar “Zhongsizhu No1” as the experimental material. The experiments consisted of a pot experiment (1 year) and a field experiment (2 years) with a randomized block design. The doses of applied selenium were 0, 0.25, 0.50, 0.75, and 1.00 kg Se·ha^-1, applied as sodium selenite. We determined nutritive values including crude protein (CP), crude fat (CF), ash, neutral detergent fiber (NDF), acid detergent fiber (ADF), and relative feeding value (RFV), and the contents of Se, phosphorus (P), potassium (K), and calcium (Ca). The results showed that exogenous Se had no significant effect on the grass production of forage ramie. Exogenous Se had some effects on nutritional values, but these effects varied depending on the Se dose, cutting time, and year. In the 2-year field experiment with Se doses of 0.25, 0.50, 0.75, and 1.00 kg Se·ha^-1, on average, crude protein content was increased by 1.52%, 0.96%, -0.10%, and -4.29%, respectively; crude fat content was decreased by 0.25%, 3.93%, 1.54%, and 9.34%, respectively; ADF content was increased by 1.92%, 2.15%, 2.32%, and 3.22%, respectively; crude ash content was increased by 1.37%, 1.23%, 2.29%, and 0.85%, respectively; the change in NDF content was -2.97%, -0.97%, 2.01%, and 2.63% respectively; the change in RFV content was 1.74%, -0.103%, -3.14%, and -4.30% respectively; the change in Ca content was 0.07%, -2.01%, 1.27%, and -0.59%, respectively; the change in P content was 7.26%, 7.68%, 4.63%, and 4.54%, respectively; and the change in K content was 4.59%, 12.31%, -2.04%, and 2.83%, respectively, compared with the control (0 kg Se·ha^-1). The Se content in forage ramie increased with increasing doses of applied Se, reaching a maximum of 2.07 mg·kg^-1. A comprehensive evaluation by principal component analysis combined with the membership function method showed that the range of 0.25-0.50 kg Se·ha^-1 was optimal for Se application in this region to improve the nutritional value of forage ramie.

Effect of straw incorporation and nitrogen fertilizer reduction on spring maize yield and eco-physiological traits in an arid farming area

ZHANG Jian-jun, DANG Yi, ZHAO Gang, FAN Ting-lu, WANG Lei, CHENG Wan-li, LI Shang-zhong, WANG Shu-ying, LEI Kang-ning, ZHANG Chao-wei

2019, 28(10):  156-165.  DOI: 10.11686/cyxb2018749

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A 3-year field experiment was conducted in a dryland area on the Loess Plateau, eastern Gansu Province, China, to study the effects of straw incorporation and nitrogen fertilizer reduction on the yield, water use efficiency (WUE), and physiological traits of spring maize (Zea mays). The six treatments included normal fertilization with nitrogen fertilizer at 225 kg N·ha^-1 (F), total straw incorporation of 9000 kg dry matter·ha^-1 (TS), F+TS, 80% F+TS, 60% F+TS, and no fertilization or straw incorporation (control, CK). Compared with the F+TS treatment, both the 80% F+TS and 60% F+TS treatments increased the yield and WUE of spring maize. However, the differences in the grain yield and WUE were not significant among the F+TS, 80% F+TS, and 60% F+TS treatments. The treatments could be ranked, from highest 3-year average yield and WUE to lowest, as follows: 80% F+TS>60% F+TS>F+TS>F>TS>CK. Compared with the F+TS treatment, the 80% F+TS treatment increased yield by 9.9% and the WUE by 8.2%. Compared with CK, the 80% F+TS treatment increased yield by 46.9% and increased the WUE by 52.4%. Compared with the F+TS treatment, the 60% F+TS treatment increased yield by 2.6% and increased the WUE by 37.2%. Compared with CK, the 60% F+TS treatment increased yield by 3.7% and increased the WUE by 46.1%. Compared with all other treatments, the 80% F+TS and 60% F+TS treatments increased soil and plant analyzer development (SPAD) values and dry matter accumulation during the whole growth period of spring maize. The results of this study suggest that 60%-80% F+TS treatments are the optimal fertilization methods for spring maize crops cultivated in dryland areas on the Loess Plateau in eastern Gansu Province, China.

Dynamics of feed quality-related traits in different maize stalk parts after fresh ear harvest and guidelines for harvesting as forage

DONG Chen-fei, XU Neng-xiang, DING Cheng-long, GU Hong-ru, ZHANG Wen-jie

2019, 28(10):  166-177.  DOI: 10.11686/cyxb2018630

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Fresh maize (Zea mays) is widely cultivated throughout China. The stalk is a good forage resource, but few studies have focused on the yield and feed quality dynamics of the stalk after harvesting the fresh ears. In this study, the experimental material was the fresh corn variety Sukenuo No. 5, cultivated in Jiangsu. The yield of the stalk, leaf, stem, and sheath at different nodes, and the feed quality-related traits were determined at 1 week, 2 weeks, and 3 weeks after harvesting fresh corn ears, both for the plants that retained fresh ears and harvested fresh ears. The results indicated that for the plants that harvested the fresh ears, the dry matter yield of the stalk and the content of nonstructural carbohydrates (NSC) in the stalk increased after ear harvest, and both those parameters peaked at 2 weeks after ear harvest. The NSC content was 39.56%, and was mainly concentrated in the top 6th node and its surrounding nodes. The main component of NSC was water soluble carbohydrates. The contents of neutral detergent fiber (NDF) and acid detergent fiber increased over time, and both were concentrated in basal nodes. The crude protein content decreased over time, and it was concentrated in the upper and middle leaves and sheath. In plants that retained the fresh ears, the dry matter yield of the stalk decreased over time, and the dry matter yield, NSC content, and in vitro dry matter digestibility were significantly lower than those of plants in the harvested-ear treatments (P<0.01). The NDF content was significantly higher in the plants that retained the fresh ears than in those in the harvested-ear treatments (P<0.01). In conclusion, our results show that picking fresh ears promotes dry matter and NSC accumulation in maize stalks, that the suitable harvest and utilization period of fresh maize stalks as forage is 2 weeks after harvesting fresh maize ears, and that the cutting height should be above the 10th node.

Effects of environmental factors on population genetic diversity of Tamarix chinensis

SUN Li-kun, LIU Guang-xiu, ZHANG Bao-gui, ZHANG Gao-sen

2019, 28(10):  178-186.  DOI: 10.11686/cyxb2018691

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In this study, we examined the relationships between environmental factors and the genetic diversity of 20 Tamarix chinensis. populations throughout its native range. Genetic diversity was evaluated by comparing the sequences of nuclear ribosomal internal transcribed spacer regions (ITS) and two chloroplast DNA (cpDNA) regions (trnL-trnF and rps16). Eleven haplotypes were identified on the basis of 10 variable sites within the 616 bp sequenced ITS region, and the total nucleotide diversity and haplotype diversity indexes were 2.170 and 0.814, respectively. Sixteen haplotypes were identified on the basis of 14 variable sites within the two chloroplast regions (1542 bp), and the total nucleotide diversity and haplotype diversity indexes were 0.500 and 0.586, respectively. The results showed that the genetic diversity based on the ITS region is influenced mainly by altitude, temperature, and longitude. Populations with rich genetic diversity exist at lower altitudes, in warmer habitats, and in eastern regions nearer to the sea. We detected no significant relationships between the genetic diversity of cpDNA and environmental variables. Using the Mantel test, a significant relationship was detected between matrices of ITS genetic differentiation and matrices of geographical distance, but this relationship was not detected from the cpDNA data. This result further proved that seed flow is an important factor contributing to the low genetic differentiation of T. chinensis populations.

Overexpression of Medicago sativa Multi protein Bridging Factor 1c (MsMBF1c) enhances thermotolerance of Arabidopsis

LI Xiao-dong, SHANG Yi-shun, WU Yu-di, WANG Xue-min, XIONG Xian-qin, CHEN Guang-ji, SUN Fang, ZHANG Wen, CAI Yi-ming

2019, 28(10):  187-198.  DOI: 10.11686/cyxb2018739

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High temperature negatively affects plant growth and development, and is one of the major abiotic stress factors limiting the growth of alfalfa (Medicago sativa) in southern China. The full-length coding sequence of the gene encoding Multi protein Bridging Factor 1c (MsMBF1c) was isolated from the alfalfa variety “Zhongmu 1”. The MsMBF1c protein in alfalfa was found to be homologous to AtMBF1c in Arabidopsis thaliana, with 72% similarity at the amino acid sequence level. The transcript levels of AtMBF1c were measured in the root, stem, leaf, flowers, and fruit; and changes in transcript levels were monitored under high temperature, drought, and the combination of these stress conditions. The highest transcript level of MsMBF1c was detected in the flowers, followed by the root, leaf, stem, and fruit. MsMBF1c was induced by high temperature, drought, and their combination (up-regulated by 4.21, 2.15, and 4.59 fold, respectively). The pBI121-35S:MsMBF1c overexpression vector was constructed and transformed into wild-type (WT) Arabidopsis seedlings. Overexpression (OE) lines without the separation of kanamycin resistance were obtained in the T3 generation. The OE lines were then crossed with the mbf1c mutant (MUT) to generate complementary lines (COM). The presence of the transgene in the plant materials was confirmed by PCR, and the transcript levels of AtMBF1c and MsMBF1c were determined by qRT-PCR. To evaluate the heat resistance conferred by MsMBF1c, the seed germination rates and seedling survival rates were determined for the OE, COM, MUT, and WT Arabidopsis lines. The seed germination rates differed slightly among the OE, COM, MUT, and WT lines (97.6%-100.0%) under normal conditions (P>0.05). After a heat stress treatment, the germination rate of WT decreased to 71.7%; that of the MUT line decreased to 66.0%, significantly lower than that of WT (P<0.05); and those of three individual OE lines and the COM line decreased to 79.3%-87.0%, significantly higher than that of WT (P<0.05). The seedling survival rate did not differ significantly among the OE, COM, MUT, and WT lines under normal conditions. However, after a heat stress treatment, the survival rate of WT decreased to 16.7%; that of MUT decreased to 10.0%, significantly lower than that of WT (P<0.05); and those of three individual OE lines and the COM line decreased to 40.0%-76.7%, which were significantly higher than that of WT (P<0.05). The expression levels of genes encoding key regulators, including HSFA1a, HSFA2, HSFA3, HSFB1, WRKY25, WRKY18 and DREB2a were analyzed in the OE, MUT, and WT lines by real-time PCR. Under normal conditions, the transcript levels of HSFA2, WRKY18, and DREB2a were low in the MUT line (0.33-0.47 of that in WT); while the transcript levels of HSFA2, HSFA3, HSFB1, WRKY25, WRKY18 and DREB2a in the OE lines were 1.74 to 3.80 fold their respective levels in WT. After heat stress, compared with WT, the MUT line showed significantly decreased transcript levels of HSFA2, HSFA3, HSFB1, WRKY18, and DREB2a, and the OE lines showed increased transcript levels of WRKY18 but none of the other tested genes. In conclusion, MsMBF1c is a functional conserved gene in the heat regulation pathway. Overexpression of MsMBF1c can complement the thermotolerance deficiency of the mbf1c mutant, and also enhance the thermotolerance of Arabidopsis at the seed germination and young seedling stages. The function of MsMBF1c may be similar to that of AtMBF1c, which regulates plant thermotolerance with other key heat resistance genes.

Transcriptome analyses provide insights into differences in nutritional quality among different alfalfa varieties

CHENG Qi-ming, GE Gen-tu, SA Duo-wen, WANG Zhi-jun, FAN Wen-qiang, BU Zhen-kun, SI Qiang, LI Jun-feng, LU Juan, JIA Yu-shan

2019, 28(10):  199-208.  DOI: 10.11686/cyxb2018721

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To enrich alfalfa (Medicago sativa) transcriptome data and clarify which genes and pathways are related to differences in nutritional quality among cultivars, two alfalfa varieties (Zhungeer and WL319HQ) were selected for de novo sequencing using the Illumina HiSeq 4000 platform. We obtained about 39 Gb total nucleotides and more than 200 million reads, and assembled 66734 unigenes with an average length of 869 bp. Then, 44888 (67.26%), 29190 (43.74%), 24844 (37.23%), and 15647 (23.45%) unigenes were annotated on the basis of information from the NCBI nonredundant protein (Nr), Swissprot (a manually annotated and reviewed protein sequence database), clusters of euKaryotic Orthologous Groups (COG), and Kyoto Encyclopedia of Genes and Genomes (KEGG) databases, respectively. We identified 1098 unigenes as differentially expressed genes (DEGs) in leaves between the two varieties of alfalfa (706 unigenes up-regulated and 392 unigenes down-regulated in Zhungeer vs. WL319HQ). The DEGs were subjected to Gene Ontology (GO) functional analysis and KEGG pathway enrichment analysis, the results of which preliminarily identified the intrinsic reasons for differences in nutritional quality between the two varieties. The data obtained in this study dramatically enrich the transcriptome data available for alfalfa. In addition, these data provide theoretical guidance for transcriptome sequencing of alfalfa in the future, as well as a reference for production practices.

Progress in fluorescent protein labeling

YANG Xiao-mei, YAO Tuo, SHI Shang-li

2019, 28(10):  209-216.  DOI: 10.11686/cyxb2019020

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Fluorescent protein labeling is an important method for research in the fields of medicine, genetic breeding, and grassland vegetation resistance. The selection of, and methods for using, fluorescent protein molecular markers are related to their specific DNA-binding properties. Gene structure affects fluorescent protein labeling, gene communication, and gene expression. Fluorescent protein labeling technology involves two types of transformation; heat shock and electric shock transformation. In both methods, Escherichia coli is used as a carrier of the gene construct encoding the fluorescent protein label. Monitoring of fluorescent protein labels is the main method used for macromolecular tracer detection and for observing colonization. Studies involving fluorescent protein labeling have been used for monitoring the colonization of pathogens and rhizosphere bacteria and for optimizing the use of excellent strains. However, it is difficult to study fluorescent protein labeling because the interactions occur at the molecular level. In this paper, we review fluorescent protein labeling in terms of its principles, the applicability of various markers, and different methods of using markers based on published literature. Various fluorescent protein labeling methods are also discussed. This review provides a reference for further studies on fluorescent protein labeling in China.