Table of Content

20 June 2018, Volume 27 Issue 6

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The rate of soil nitrogen transformation decreased by the degradation of alpine grasslands in the Qinghai Tibet Plateau

WANG Xue-xia, DONG Shi-kui, GAO Qing-zhu, ZHANG Yong, HU Guo-zheng, LUO Wen-rong

2018, 27(6):  1-9.  DOI: 10.11686/cyxb2017291

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Alpine meadow and alpine steppe were studied to explore the mechanisms of degradation in soil nitrogen transformation and the key factors that affect soil N transformation in grasslands of the Qinghai Tibet Plateau. The net nitrification rate and net ammonification rate, as well as the microbial aspects of nitrogen transformation, plant and soil factors, were investigated using the method of in situ incubation. The results showed that: 1) The net nitrification and ammonification rates were significantly reduced by degradation in alpine grassland ecosystems; 2) The number of nitrifiers and ammonifiers in the soil, soil urease and protease activities decreased in the degraded meadows and steppe. 3) NH₄-N and NO₃-N contents were significantly reduced and microbial biomass nitrogen (MBN) also decreased. Soil nitrification and ammonification rates were closely related to the number of ammonifiers and nitrifiers, microbial biomass, and the extent of protease and urease in soils. Plant biomass, soil water, organic carbon and total nitrogen content were the main factors affecting soil N transformation by influencing the number of microbes, microbial biomass and enzyme activities. In conclusion, soil N transformation rates and the supply of available nitrogen in soils declined in degraded alpine grassland due to reductions in nitrogen transformation microbes and soil enzyme activities.

Soil erosion changes and driving factors in the Three-River Headwaters region

CAO Wei, LIU Lu-lu, WU Dan

2018, 27(6):  10-22.  DOI: 10.11686/cyxb2017359

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In this study, the annual soil erosion modulus and amount of soil loss during 1997 to 2012 in the Three-River Headwaters region were calculated using the revised universal soil loss equation (RUSLE), and the spatial and temporal dynamics of soil erosion after the first stage of ecological conservation and restoration project were compared and analyzed. The impacts of rainfall erosivity and fractional vegetation coverage on soil erosion were analyzed using the spatial overlay tool in ArcGIS, and contribution rates of ecological projects and climate change were measured using the model variable control method. The results showed that: 1) The conservation and restoration projects did not curb the trend of increased soil erosion. During 1997 to 2012, total soil erosion increased by 6.5%, although soil erosion decreased in nearly 45% of the total area. 2) Among the three main watersheds, the Yangtze River watershed showed the smallest change in soil erosion. Soil erosion increased by 45% in the Yellow River watershed, and decreased by 9.8% in the Lancang River watershed. 3) The continuous increase in precipitation was the main reason for the increase in soil erosion (contribution rate, 180%), while the increase in fractional vegetation coverage reduced soil erosion by 80%. Persistent efforts are required to curb the trend of increasing soil erosion in the Three-River Headwaters Region.

Study of microorganism abundance and communities in response to soil factors in Binggou Valley, the upper reaches of Heihe

GAO Hai-ning, LI Cai-xia, SUN Xiao-mei, CHEN Nian-lai, ZHANG Yong

2018, 27(6):  23-33.  DOI: 10.11686/cyxb2018106

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In order to study changes in bacteria abundance and communities in response to soil factors in Binggou Valley, the upper reaches of Heihe, we collected 10 surface soil samples at different altitudes and analyzed the culturable microorganisms’ abundance and the soils’ physico-chemical properties. The results showed that soil nutrients vary markedly by altitude. High concentrations of soil organic carbon (SOC), total N and P, nitrate N, ammonium N and available P were found at high altitudes, while the concentrations of total K and available K were high at low altitudes. The abundance and diversity of culturable microorganisms vary markedly according to vegetation types and degree of cover. The abundance of phosphorus bacteria and fungi are significantly positively related to total N and P (P<0.05). Bacillus is significantly positively related to pH (P<0.05). The comprehensive evaluation of soil composition at different altitudes showed that the most fertile soil is located at 3479 m altitude, the second most fertile at 3204 m, followed by 2911 and 3172 m. Analysis of surface soil composition showed that phosphorus bacteria, potassium bacteria and silicate bacterium are the dominant strains. Analysis of the main components of microorganisms showed the most significant diversity in samples taken at 3205 m altitude. These results indicate that soil nutrients and microorganism abundance in the Binggou valley are mainly influenced by altitude, vegetation types and degree of cover.

Growth dynamics and optimum harvest period of the forage grass Yucao No.5

LI Hua-xiong, JIANG Wei-ming, WU Zi-zhou, LI Ying-zheng, CHENG Ming-jun, YANG Shi-peng, SUN Ru-long, YAN Xu, ZHANG Hong-fen, YANG Min, RONG Ting-zhao, ZHOU Shu-feng, WU Yuan-qi, CAO Mo-ju, TANG Qi-lin

2018, 27(6):  34-42.  DOI: 10.11686/cyxb2017269

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Yucao No.5 (Tripsazea creammaize) is a new type of perennial forage grass that combines the desirable characteristics of maize, Zea perennis and Tripsacum dactyloides, such as luxuriant growth, a well-developed root system, numerous tillers, and good plant regeneration. To understand the growth dynamics of Yucao No.5 and determine the best harvest time, we investigated the growth rate, the fresh and dry matter accumulation and distribution at different stages, and the nutrient values in a field experiment. The results showed that some growth dynamics [plant height, tiller number, fresh (dry) matter yield, stem:leaf ratio] of Yucao No.5 fitted a logistic model. From the tillering to initial tasseling stages, the yield and stem:leaf ratio gradually increased, while the moisture content and nutrient value gradually decreased. At this stage, the fresh and hay yields of Yucao No.5 were 96.607 and 14.768 t·ha^-1, respectively, while crude protein (CP), ether extract (EE), crude ash (CA), neutral detergent fiber (NDF), acid detergent fiber (ADF), and relative feeding value (RFV) were 11.37%, 2.87%, 7.95%, 52.01%, 31.53%, and 115.90%, respectively. At the silking stage, the yields of hay and CP remained high and the moisture content was relatively low. To obtain greater biomass, nutritive value, and regeneration capacity, Yucao No.5 should be harvested as a green feed at the initial tasseling stage, and harvested to produce silage at the tasseling stage. Yucao No.5 production was evaluated at three sites in Sichuan, Southwest China. The fresh yields with one cutting in the first year ranged from 77.758 and 89.207 t·ha^-1, and the total fresh yield of three cuttings at Daan village was 109.411 t·ha^-1 in the second year. The results of these field trials show that the new perennial forage grass Yucao No.5 has high yields and good quality, and is suitable for cultivation in the southwest and in the “forage-livestock” region in southern China. This forage grass has great potential for production and broad application prospects.

Effects of salt stress on growth and physiology of Isatis indigotica seedlings

MI Yong-wei, WANG Guo-xiang, GONG Cheng-wen, CAI Zi-ping, WU Wei-guo

2018, 27(6):  43-51.  DOI: 10.11686/cyxb2017282

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The effects of different concentrations of NaCl solution (0, 30, 60, 90, 120 and 150 mmol·L^-1) on the growth, biomass, leaf relative water content, root activity, root membrane permeability, osmotic adjustment and protective enzyme activity of Isatis indigotica seedlings (cv. Dinglan No.1) were assessed to determine the response of growth and physiological traits associated with resistance to salt stress after 14 days of exposure. Plant height, root length, root dry weight and leaf dry weight of I. indigotica seedlings under NaCl treatment were significantly reduced compared with the control (no salt). Reductions were greater under higher salt concentrations. As NaCl concentration increased leaf relative water content and root activity declined while root membrane permeability and leaf proline content increased. Superoxide dismutase (SOD) and peroxidase (POD) activity, malondialdehyde (MDA) content and rates of tissue autoxidation (RAD) all initially increased at lower salt levels and then declined. However seedling growth was not significantly inhibited under salt stress and root activity showed no obviously decrease. Malondialdehyde and proline content, SOD and POD activity were not affected by NaCl concentration <90 mmol·L^-1. This study showed that I. indigotica seedlings had some tolerance to low salt stress.

Effects of enclosure on the soil seed bank of two plant communities on the desert steppe

LI Guo-qi, SHAO Wen-shan, ZHAO Pan-pan, JIN Chang-qing

2018, 27(6):  52-61.  DOI: 10.11686/cyxb2017274

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The soil seed bank (SSB), as a potential source of vegetation, has significance for vegetation restoration and community succession on the desert steppe. In this study, we analyzed the SSB of two plant communities (Sophora alopecuroides and Achnatherum splendens communities), fenced and unfenced, on the desert steppe in Yanchi County, Ningxia Province. Four relatively even and flat quadrats (25 m×30 m each) of S. alopecuroides and A. splendens communities, fenced and unfenced, were selected for these analyses. The soil samples from the four quadrats were separated into three layers (0-2 cm, 2-5 cm, and 5-10 cm) and sieved, and then the species of the seeds in the SSB were identified by direct observations and then by germination tests. We compared the characteristics of two communities (SSB species composition, seed density, diversity, and similarity) between fenced (enclosed) and unfenced conditions. The results showed that: 1) Enclosure increased the number of species in the SSB in both communities, but its effects on seed density in the SSB differed between the two communities. The seed density of the S. alopecuroides community SSB was slightly different between the fenced and unfenced areas, while that of the A. splendens community SSB was markedly higher inside the fenced area. 2) The number of species in the SSB and the seed density tended to decrease with increasing soil depth in both communities, inside and outside the fence. Although the number of species in different soil layers was greater in the fenced area for both communities, the effect of enclosure on the vertical distribution of seed density in the SSB differed between the two communities. 3) The diversity, evenness, and abundance of the SSB were greater inside the fenced area than outside the fenced area for both communities, but the effects of enclosure on SSB diversity differed between the two communities. The S. alopecuroides community was more stable than the A. splendens community on the desert steppe. 4) The SSBs of the two communities showed relatively high similarity, and there was a trend towards succession of the S. alopecuroides community to the A. splendens community after enclosure.

Interspecific relationships in Savanna grassland in Yuanmou, a dry-hot valley upstream of the Yangtze River

HE Guang-xiong, YAN Bang-guo, JI Zhong-hua, SHI Liang-tao, FAN Bo, FAN Jian-cheng, ZHANG Meng-yin

2018, 27(6):  62-71.  DOI: 10.11686/cyxb2017300

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Understanding the interspecific relationships in harsh environments can reveal how plant species adapt and assemble into communities under disadvantageous conditions. In this study, we used variance tests to detect species’ associations, and used chi-squared tests, the Jaccard index, and Spearman’s rank correlation analyses to analyze interspecies associations and correlations for 18 dominant species from Savanna communities in Yuanmou, a dry-hot valley of the Jinsha River, upstream of the Yangtze River in southwest China. The results showed that: 1) There were significant negative correlations among Savanna grassland plants in Yuanmou. These negative correlations were indicative of strong resource competition or difficult ecological relationships among dominant species; 2) The 18 dominant species were weakly inter-associated, and had a low frequency of common occurrence in plots. Spearman’s rank correlation analyses of the 18 dominant species revealed positive interspecific correlations, with 31 significant or very significant species pairs and 18 very significant species pairs (20.3% and 11.8%, respectively, of a total of 153 species pairs); 3) The 18 dominant species were divided into four specific ecological groups. Among these species, Cymbopogon goeringii, Eulaliopsis binata, Bothriochloa pertusa and widespread species Heteropogon contortus were key band species bundled with other species to form communities in the dry-hot ecosystem in Yuanmou valley. These results suggested that Savanna grassland plants have strong resource competition and/or difficult ecological relationships. The main species showed insolated distribution patterns and the communities were easily disturbed. In practice, species like H. contortus should be prioritized as key species for vegetation restoration, and functional communities should be protected to preserve groups of species that are adapted to the harsh conditions of the hot-dry ecosystem.

Effect of different mutagenesis methods on microstructure and ultrastructure of alfalfa

FENG Peng, SUN Li, SHEN Xiao-hui, LI Ru-lai, LI Zeng-jie, LI Zhi-min, ZHENG Hai-yan, JIANG Cheng, YNAG He, LIU Jun-gang, GUO Wei, ZHANG Ying-jun

2018, 27(6):  72-80.  DOI: 10.11686/cyxb2017285

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The overall aim of this research was to identify the optimal mutation method(s) for breeding new alfalfa varieties to cultivate in alpine regions. In this study, we investigated the effects several mutagenesis treatments [⁶⁰COγ-ray irradiation, ultraviolet radiation, ethyl methyl sulfonate (EMS), and magnetic field-free space] on the microstructure and ultrastructure of the leaves of four alfalfa cultivars; Gongnong 1, Wega7F, WL319HQ, and Aohan. The mutagenesis treatments were as follows: ⁶⁰COγ-ray irradiation (150, 300, 450 Gy), ultraviolet radiation (30, 60, 90 min), ethyl methyl sulfonate [0.1%, 0.2%, 0.4% (v/v)], and magnetic field-free space (180 d). The microstructure and ultrastructure of the leaf were analyzed after these treatments. All of the mutagenesis treatments increased leaf thickness. The greatest increase was in Gongnong 1 under the 0.4% EMS (v/v) treatment, where the final leaf thickness was increased by 25.86 μm to 446.16 μm. The degree of leaf vein protuberance was decreased by the mutagenesis treatments. The degree of cell tightness in Gongnong 1 increased after ⁶⁰COγ-ray irradiation and ultraviolet radiation treatments. The cells in the leaves of wega7F were closer together after all the mutagenic treatments. The ultramicrostructure of the chloroplasts in the alfalfa leaves was also observed under different mutagenic treatments. Under lower doses or concentrations of mutagenic treatments [150 Gy ⁶⁰Co-γ, 30 min ultraviolet radiation, 0.1% (v/v) EMS], the chloroplasts were distorted with disrupted membranes, loose grana lamellae, disintegrated thylakoids, and increased numbers of lipid droplets. Under the highest doses or concentrations of mutagenic treatments [450 Gy ⁶⁰Co-γ, 90 min ultraviolet radiation, 0.4% (v/v) EMS, and 180 d magnetic field-free space] the chloroplasts became swollen, distorted, and severely damaged with fractured grana lamellae and disintegrated membrane systems. The numbers of plastids and starch grains in cells were increased under these treatments. Compared with the other treatments, the ⁶⁰COγ-ray irradiation and EMS treatments showed higher mutagenic efficiency, produced more mutant materials, and were simpler to operate. Therefore, we concluded that these were the best mutation methods. The 150 Gy ⁶⁰COγ-ray irradiation, 60 min ultraviolet radiation, and 0.4% EMS treatments were the mutagenic treatments that were most conducive to screening mutants.

The expression of the salt tolerance gene AtSOS in Medicago

MA Dong-mei, QIN Chu

2018, 27(6):  81-91.  DOI: 10.11686/cyxb2017281

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In this study, alfalfa was genetically engineered to improve its salt tolerance. The SOS1-SOS2-SOS3 genes from Arabidopsis thaliana were incorporated into Algonquin using tumefaciens-mediate transformation technology. Transgenic plants were identified by PCR, herbicide resistance screening and RT-PCR. The salt resistance of the transgenic plants was evaluated by exposing them to different concentration (100, 200 and 300 mmol·L^-1) of NaCl for 6 days and comparing them to unmodified plants. Physiological and biochemical indexes, plant height, Na⁺ and K⁺ content, cell membrane permeability and chlorophyll content were measured. The results showed that under different salt treatments, the height of all plants increased but transgenic plant height was significantly higher than that of unmodified plants at 100 and 200 mmol·L^-1 NaCl. After salt exposure the chlorophyll content of all plants initially increased before declining but the chlorophyll content of unmodified plants was lower than that of transgenic plants. Under 100 and 200 mmol·L^-1 NaCl treatments, membrane permeability, superoxide dismutase activity and proline content of transgenic plants were lower than that of unmodified plants. However, peroxidase activity, catalase activity and soluble sugar were higher than that of unmodified plants. Malondialdehyde content declined in all plants but the decline was greater in unmodified plants. The accumulation of Na⁺ in roots of transgenic plants was less than in unmodified plants, while K⁺ content was more than that of unmodified plants. Transgenic plants displayed increased Na⁺ efflux, reducing cellular ion toxicity, alleviating the damage from salt stress.

Heterologous expression of WZY2-1 affects drought resistance of Arabidopsis plants

QIANG Zhi-quan, YANG Wen-bo, ZHANG Shuai, YU Zheng-yang, SHI Xue-ying, WANG Xin, ZHU Wei-ning, ZHANG Lin-sheng

2018, 27(6):  92-99.  DOI: 10.11686/cyxb2017293

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Dehydrins (DHNs) belong to a protein family whose expression may be induced or enhanced by environmental stresses that lead to cell dehydration. All DHNs contain at least one motif, or K-fragment, which can form an amphipathic helix. This structure play an important role in DHN function. The wheat gene WZY2-1, a K9-type DHN gene, can be activated by low temperature, drought and salt stress. In this work, the WZY2-1 recombinant protein was purified. In vitro lactate dehydrogenase (LDH) assays revealed that WZY2-1 had a potent protective effect during freezing-thawing temperature stresses. Subcellular localization showed that WZY2-1 was localized in the nucleus and cell membrane. To further elucidate the function of WZY2-1 in plants, transgenic Arabidopsis plants that overexpress WZY2-1 were tested. The transgenic Arabidopsis lines showed a better tolerance to drought stress than unmodified. This suggests that the WZY2-1 gene may also play an important role in drought tolerance in wheat.

Physio-ecological responses to drought and subsequent re-watering in sorghum seedlings

LIU Ting-ting, CHEN Dao-qian, WANG Shi-wen, YIN Li-na, DENG Xi-ping

2018, 27(6):  100-110.  DOI: 10.11686/cyxb2017410

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Adaption to drought in plants includes drought resistance during the drought period and post drought recovery. The aim of this study was to investigate the relationships between drought resistance and drought recovery and to determine the physiological parameters which could be used to indicate drought adaptability. Eight sorghum cultivars grown in pots were exposed to drought and re-watering treatments during the seedling stage. Biomass, relative water content, water potential, osmotic potential, and photosynthetic parameters were measured. The results showed that “LZ21”“ had the highest drought resistance; biomass production under drought stress was not different to the control (well watered), while “GZZ”“ and “Gadambalia”“ had poor drought resistance producing 38% and 34% less biomass under drought stress. Relative water content, water potential, osmotic potential, chlorophyll content and photosynthetic parameters decreased after imposition of drought but all parameters recovered fully after re-watering. Correlation analysis showed that drought adaption is more closely related to drought recovery (r=0.85) than drought resistance (r=0.46). Maintaining higher photosynthetic and lower transpiration rate contributed to drought resistance while maintaining high relative water content improves drought recovery. These results demonstrated that drought recovery ability is more important for drought adaption than drought resistance. The physiological basis of drought resistance and drought recovery are clearly different. Relative water content and photosynthetic rate could be used to select drought adapted cultivars in sorghum.

Soil water utilization characteristics of slope land in hedgerow and grain crop intercropping systems on the Loess Plateau

LIU Jia-he, NIU Yi-ning, LUO Zhu-zhu, CAI Li-qun, ZHANG Ren-zhi, XIE Jun-hong

2018, 27(6):  111-119.  DOI: 10.11686/cyxb2017298

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This study investigated soil water utilization characteristics in hedgerow intercropping systems by analyzing the grain yield and water consumption characteristic in hedgerow and grain crop intercropping systems on the Loess Plateau of central Gansu. Five treatments were compared: fallow (F), wheat monoculture (W), wheat and Licorice inter-cropping (W/L), wheat and Radix isatidis intercropping (W/I) and wheat and alfalfa intercropping (W/A). The results showed that the soil moisture along 0-200 cm soil profile of croplands with different treatments was obviously lower, being equal to crop lower limit. Soil water content at 0-30 cm was greatly improved under hedgerows and grain crop intercropping systems with highest soil water content in the W/A treatment. The highest water consumption (251.0 mm) occurred in the W/L treatment, while the lowest (197.3 mm) occurred in the W treatment. The ratio of soil evaporation and water consumption was higher than 80% in the F treatment, indicating that water loss was mainly through evaporation in the F treatment but mainly through transpiration in hedgerows-crop intercropping systems. Hedgerows and grain crop intercropping systems were able to decrease E/ET to some extent and increase crop transpiration. There were treatment differences for water consumption, but grain yields in intercrop systems were 60.0% to 83.6% higher than wheat monoculture. As a result, water use efficiency improved from 49.7% to 76.1% under hedgerows and grain crop intercropping systems compared to wheat monoculture.

Physiological response and ecological adaptability of different Jerusalem artichoke genotypes to salt stress

ZHU Ju-hua, SUN Xing, XU Bing, LIANG Ting, LIU Ming, MIAO Jian, ZHAO Geng-mao

2018, 27(6):  120-127.  DOI: 10.11686/cyxb2017304

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The physiological and ecological adaptability of different genotypes of Jerusalem artichoke were analyzed to measure the responses of their morphology, antioxidant enzymes and endogenous hormones to salt stress. This study provides a theoretical basis for both varieties selection and ecological planting. Using the eurytopic varieties of Southern Jerusalem artichoke No.1 (N1) and Puyang Henan (M1) as experimental materials, two salt-stressed treatments of 100 mmol·L^-1 NaCl (low salt level) and 200 mmol·L^-1 NaCl (high salt level) were laid out in a randomized complete block design with 3 replications in each case. The results showed that: 1) Salt stress significantly inhibited seedling growth in Jerusalem artichoke, resulting in plant dwarfing, stunted root growth and a dry matter decrease of M1 and N1. 2) Salt stress did not affect the synthesis of chlorophyll-a, chlorophyll-b and total chlorophyll in M1 (except for chlorophyll-a under 200 mmol·L^-1 NaCl stress), but it blocked photosynthetic pigment synthesis in N1. 3) Low salt stress significantly increased superoxide dismutase (SOD), peroxidase (POD) and catalase (CAT) activities in M1 and N1, while high salt stress markedly decreased enzyme activities in N1 and had no effect on enzyme activities in M1 (except for CAT). 4) Low salt stress promoted the synthesis of GA₃ (gibberellin) and ABA (abscisic acid) in N1, but IAA (indoleacetic acid) content was relatively stable and endogenous hormone content in M1 was not obviously changed. High salt stress decreased the content of IAA and GA₃ in N1, but there was no obvious change in ABA. The content of GA₃ in M1 increased, while IAA and ABA were relatively stable. The differences in salt tolerance between the Jerusalem artichoke genotypes were significant (M1>N1), and the internal adaptation of antioxidant enzymes and endogenous hormones could improve the plant’s ecological adaptability to salt stress.

Effects of exogenous citric, malic and oxalic acids on the tolerance and enrichment efficiency of Elymus dahuricus under cadmium-stress

XUE Bo-han, LI Na, SONG Gui-long, LI Shi-gang, PUYANG Xue-hua, LI Jin-bo

2018, 27(6):  128-136.  DOI: 10.11686/cyxb2017457

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A study has been undertaken to investigate the effects on Elymus dahuricus of different concentrations (1,2,4 mmol·L^-1) of exogenous citric, malic and oxalic acids on the biomass, Cd content in above-ground plant and root, and changes in morphological parameters and plant growth. Pot culture tests were carried out under Cd stress to reveal how organic acids affect the absorption, transport and accumulation of Cd. The main results are as follows. When treated with Cd₅₀, plant height, root length and biomass significantly reduced (P<0.05). The three exogenous organic acids could increase the content of Cd and biomass in the roots and shoots of E. dahuricus. In terms of cadmium accumulation, oxalic acid had the strongest effects; under Cd₅₀+OA₂ treatment conditions, the E. dahuricus translocation coefficient was 1.38 and Cd concentration in shoots reached the maximum value of 268.511 μg·plant^-1. On the other hand, from the point of view of improving plant growth, the citric acid treatment performed best; under Cd₅₀+CA₄ treatment conditions, the root and shoot biomass were 1.82 and 1.53 times higher than that of Cd₅₀. Comprehensive analysis shows that the three exogenous organic acids can strengthen Cd-contaminated E. dahuricus. The use of these acids is likely to be an effective way to improve the phytoremediation efficiency of soils contaminated by heavy metals.

Chemical profiles of cuticular waxes in arid steppe plant species and their response to continuous grazing

LI Xiao-ting, ZHAO Xiao, WANG Deng-ke, HUANG Lei, YAO Lu-hua, WANG Dang-jun, HE Yu-ji, GUO Yan-jun

2018, 27(6):  137-147.  DOI: 10.11686/cyxb2017435

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Cuticular wax plays an important role in protecting plants from harsh environments. Understanding the responses of cuticular wax to grazing may provide information that can be used to improve grassland management regimes. Leaves from Stipa krylovii, Leymus chinensis and Cleistogenes squarrosa were taken from ungrazed and continuously grazed typical and meadow steppes in Inner Mongolia, China. We analyzed the characteristics of cuticular waxes among plant species and steppe types. The results indicated that the total wax coverage differed greatly among plant species, with the highest in L. chinensis, followed by S. krylovii with the lowest in C. squarrosa. Seven wax compounds were identified in L. chinensis, including fatty acids, alkanes, secondary alcohols, primary alcohols, β-sitsterols, β-diketones and alkylresorcinols. Five wax compounds were identified in S. krylovii including fatty acids, alkanes, primary alcohols, α-amyrin and β-sitsterols and six in C. squarrosa including fatty acids, alkanes, aldehydes, primary alcohols, alkyl esters and β-amyrin. The relative content of secondary alcohols was the highest in L. chinensis while primary alcohols were highest in C. squarrosa, whereas alkanes were highest in S. krylovii. Steppe types significantly influenced total wax coverage and the relative abundance of alkyl esters in C. squarrosa, total wax coverage in S. krylovii, and the relative abundance of secondary alcohols and β-diketones in L. chinensis. Grazing significantly influenced the relative abundance of fatty acids in C. squarrosa, total wax coverage and the relative abundance of α-amyrin and β-sitsterols in S. krylovii, and total wax coverage and the relative abundance of secondary alcohols in L. chinensis. The distribution of different chain length alkanes were relative stable, whereas those of primary alcohols, fatty acids and aldehydes varied greatly between steppe types and grazing management. It is suggested that different steppe plant species developed their own specific cuticular wax adaptive mechanisms during their evolution. Steppe plants may be able to adapt to changing environments through altering wax biosynthesis and deposition.

Effects and residual dynamics of 2, 4-D butyl ester on the safety and yield of covered oat under field conditions

ZHAO Gui-qin, JU Ze-liang, CHAI Ji-kuan

2018, 27(6):  148-157.  DOI: 10.11686/cyxb2017296

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The aim of this study was to evaluate the weed-control effects and the persistence of the herbicide 2, 4-D butyl ester in field crops of covered oat. Covered oat (cultivar Longyan No.3) at the 3-4 leaf stage was treated with 2, 4-D butyl ester at three application rates (450, 750, and 1050 mL·ha^-1). The dissipation and residue dynamics of 2, 4-D butyl ester and its decomposition products in covered oat plants were evaluated at 1, 7, 14, 21, and 28 days after application, and at the flowering, grain filling, and maturity stages. The effects of this herbicide on weeds and on the safety, yield, and plant height of oat were investigated. The results showed that 2, 4-D butyl ester significantly affected the safety and yield of oat, but was effective in controlling weeds in oat fields. High dosages caused damage to the oat crop, such as top sagging, leaf redness, and medicine spots. The efficacy of weed control improved with increasing concentrations of 2, 4-D butyl ester. The 1050 mL·ha^-1 treatment had the strongest control effect, with up to 90% weed control at 45 days after treatment. The application of 2, 4-D butyl ester decreased oat plant height by 10.49% at the 1050 mL·ha^-1 dosage. The 450 mL·ha^-1 concentration of 2, 4-D butyl ester reduced oat hay yield, but it did not differ significantly (P>0.05) from that of the control, and improved oat grain yield by 22.64%. The 750 mL·ha^-1 concentration of 2, 4-D butyl ester improved oat yield by 40.57%. The 1050 mL·ha^-1 dosage of 2, 4-D butyl ester significantly (P<0.05) reduced oat hay yield by 8.85%. The degradation dynamics of 2, 4-D butyl ester and 2, 4-D in covered oat were positively related to the dosage of 2, 4-D butyl ester. The largest amounts of 2, 4-D butyl ester and 2, 4-D residues (0.168 and 0.011 mg·kg^-1, respectively) were in covered oats at 28 days after application of 2, 4-D butyl ester at the highest dosage (1050 mL·ha^-1), and were significantly higher than the amounts of residues at 28 days after applying lower dosages. On the basis of these experimental results, we concluded that application of 2, 4-D butyl ester at 750 mL·ha^-1 is the best treatment to control weeds in covered oat fields.

Effect of cellulase addition on the quality of dried corn straw and cabbage residue mix silage

REN Hai-wei, LIU Fei-fei, WANG Li, LI Zhi-zhong, WANG Yu, SUN An-qi, SHEN Jia-li, SUN Wen-bin, YU Qian-qian

2018, 27(6):  158-167.  DOI: 10.11686/cyxb2017286

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Dry corn straw (DCS) and cabbage waste (CW) were mixed and ensiled trans-seasonally; the effect of cellulase addition on silage quality and microbial community diversity were assessed. Three treatments were compared; a control (ME) (no cellulase), 0.1% cellulase (CA) and 0.3% cellulase (CB). All silages were ensiled for 60 days in airtight containers. Chemical composition and fermentation quality were measured over a 30 day period. Microbial community diversity was analyzed using Miseq high-throughput sequencing technologies. The results showed that neutral detergent fiber (NDF), acid detergent fiber (ADF) and cellulose (CL) in groups CA and CB were significantly lower than ME after 30 days (P<0.05); pH and ammonia nitrogen to total nitrogen ratio (AN/TN) were also significantly lower than ME after 30 days (P<0.05). Lactic acid (LA) and water soluble carbohydrates (WSC) were significantly higher than the ME treatment (P<0.05). Lactic acid to acetic acid ratio’s (LA/AA) were greater than 3 and LA to total organic acid ratio’s (LA/TOA) were greater than 0.6 for all treatments after 60 days, but fermentation intensity was highest in the CB treatment. The microbial community diversity results showed that Firmicutes and Proteobacteria were dominant at the phylum level, the dominant microflora at the genus level were Paralactobacillus, Lactobacillus and Enterobacter. Over time, the abundance of Enterobacter gradually decreased and the abundance of Paralactobacillus and Lactobacillus increased, which indicated that the addition of cellulase improved the abundance of lactic acid bacteria and reduced the abundance of spoilage bacteria. It was concluded that low cellulase (0.1%) was the most appropriate application rate; it was conducive to the preservation of hemicellulose (HC), CL and WSC and improved fermentation quality.

Modification of GsDREB2 from Glycine soja increases plant tolerance to salt and osmotic stress

CAI Hua, SUN Na, SONG Ting-ting

2018, 27(6):  168-176.  DOI: 10.11686/cyxb2017283

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The DREB transcription factor is a dehydration responsive element (DRE)-binding protein that specifically interacts with the DRE/CRT (C-repeat) cis-acting element in the promoter region of stress-inducible genes. This interaction controls the expression of many stress-inducible genes in plants and can increase plants’ tolerance to drought, low temperature, high salt, and heat. Many studies have reported on the complexity of DREB signal transduction, action, and expression. To explore the role of the DREB2 gene in Glycine soja (GsDREB2), the nucleotides encoding the negative regulatory domain (NRD, amino acid residues 140-204) were deleted from GsDREB2. The transcriptional activation and DRE element-binding capacity were compared between proteins encoded by the full-length gene (FLDREB2) and the truncated gene GsDREB2-mNRD in yeast. The nuclear localization capacity of GsDREB2-mNRD was also evaluated. FLDREB2 and GsDREB2-mNRD were each transferred into Arabidopsis. After screening and testing, the phenotype of the transgenic Arabidopsis lines was evaluated, and their stress tolerance level was determined by measuring their germination rate and fresh weight under salt and osmotic treatments. The results indicated that the amino acid region 140-204 negatively controls the transcriptional activation ability and DNA-binding capacity of DREB2. Both GsDREB2-mNRD and FLDREB2 were located in the nucleus. Transgenic Arabidopsis overexpressing GsDREB2-mNRD showed increased tolerance to salt and osmotic stress. The transgenic plants overexpressing GsDREB2-mNRD showed a higher germination rate and fresh weight than those of plants expressing FLGsDREB. These results demonstrate that GsDREB2-mNRD, which encodes a mutated DREB2, can enhance plant tolerance to salt and osmotic stress.

Research on the current situation of carbon trading markets and the potential of grassland carbon sinks

WANG Sui-zi, LIU Shuai, FAN Jiang-wen, ZHANG Ya-xian

2018, 27(6):  177-187.  DOI: 10.11686/cyxb2017276

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Carbon trading is a market mechanism and key instrument in the mitigation of climate change. This paper summarizes the transaction agencies, types, trading mode and the condition of global carbon trading markets, along with the sequestration projects underway in each continent. We also analyze the potential of grassland carbon sinks. Although there is no unified international carbon trading market, the major developed countries have their own emissions trading systems. The European Union scheme covers a large proportion of global carbon trading volume. Projects located in North America, South America, Asia, Africa and Oceania, maintain total carbon sequestration schemes to reduce CO₂ emissions through reforestation, reducing deforestation, conserving biodiversity, improving energy efficiency and sustainable management. China is responsible for a large proportion of the world’s registered and issued projects for the Clean Development Mechanism (CDM). These CDM projects are mainly distributed in the Sichuan, Yunan and Neimenggu provinces. The major type of emission reduction is the promotion of alternative and renewable energy. Chinese certified emission reduction (CCER) is up to 1028.98 Mt CO₂e, ranking first in the world. In China, the carbon trading market of Hubei has the highest turnover in quota projects, while the Shanghai market has the highest volume. China has enormous potential to both lower emission reduction costs and increase the size of the CDM market. China also has abundant meadow resources. Although the grassland carbon sinks are not in the CDM project, they will play an important role in future trading markets.

Effects of the proportion of pomelo peel and alfalfa in different concentrate-roughage ratios on the associative effects of diets in vitro

YUAN Jiu, TANG De-fu, WAN Xin-jie, ZHU Bao-zhen, HE Tian-le, YU Hai-shan, WANG Jun-jun

2018, 27(6):  188-196.  DOI: 10.11686/cyxb2017301

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An experiment was conducted to investigate the effects of the proportions of pomelo peel and alfalfa in different concentrate-roughage ratios (C:R) on the associative effects (AE) of diets in vitro. Pomelo peel:alfalfa proportions were 80:0, 70:10, 60:20, 50:30, 40:40, 30:50, 20:60, 10:70,0:80 when C:R was 20:80. Pomelo peel:alfalfa proportions were 70:0, 60:10, 50:20, 40:30, 30:40, 20:50, 10:60, 0:70 when C:R was 30:70. Pomelo peel:alfalfa proportions were 60:0, 50:10, 40:20, 30:30, 20:40, 10:50, 0:60 when C:R was 40:60. Gas production (GP) was recorded at 0, 2, 4, 6, 9, 12, 24, 36, 48, 72, 96 h. AE was defined as the difference between the observed in vitro GP_{24 h} and the predicted value from individual feed fermented alone. The results showed that the NDF content of pomelo peel was lower and its gas parameters were higher than either concentrate or alfalfa. The AE of all groups were negative and the AE of the group of pomelo peel:alfalfa at 80:0 was significantly greater than the 0:80 group (P<0.05) when C:R was 20:80. The AE of all groups were not significantly different when C:R was 30:70 (P>0.05). The AE of the groups 30:40 and 10:60 were 14.74% and 3.61% respectively and the AE of the 30:40 group was higher; the other groups were negative when C:R was 30:70. The AE of the 0:60 group was significantly greater than the 60:0 group (P<0.01) and significantly greater than the 30:30 group (P<0.05) when C:R was 40:60, and the AE of the 10:50 group tended to be greater than the 60:0 group (P=0.079). The AE of the 0:60, 10:50, 20:40 groups were greatest when C:R was 40:60. In conclusion, AE is the greatest when high levels of concentrate (C:R, 40:60) and low proportions of pomelo peel (0,10,20) are combined, when middle levels of concentrate (C:R, 30:70) and pomelo peel (30) are combined, and when low levels of concentrate (C:R, 20:80) and a high proportion of pomelo peel (80) are combined.