Table of Content

20 April 2021, Volume 30 Issue 4

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Hyperspectral remote sensing inversion of meadow aboveground biomass based on an XGBoost algorithm

Yi-ran ZHANG, Ting-xi LIU, Xin TONG, Li-min DUAN, Yu-chen WU

2021, 30(4):  1-12.  DOI: 10.11686/cyxb2020190

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It is of great significance to agricultural production and animal husbandry， the management of grassland resources， and the sustainable utilization of forage to have efficient access to accurate information on aboveground biomass. This paper uses field data on the spectral reflectance of the grass canopy together with data on the aboveground biomass obtained in the same period， to analyze the correlation between spectral differences and meadow aboveground biomass， using a mutual information method. The correlation between the optimized vegetation index and the aboveground biomass of the meadow is then analyzed. In this paper， an extreme gradient boosting （XGBoost） algorithm and a simulation model estimating the aboveground biomass of different vegetation spectral index data sets are constructed. This model is compared with a model established by multiple linear regression （MLR） and random forest （RF） methodology. It was found that the first-order and second-order differentiation of spectral reflectance curves and the conjoint application of spectral vegetation index transformation from both spectral differentiation orders is helpful to improve the correlation between canopy spectra and aboveground biomass. Of the three approaches tested using the original spectral vegetation index to predict aboveground biomass， the XGBoost algorithm simulation model performed best， followed by the RF model. The MLR model displayed poor accuracy. The root mean square error of the XGBoost model was 140.26 g·m^-2； the mean absolute error was 97.20 g·m^-2； the Nash-Sutcliffe efficiency coefficient was 0.81， and the index of agreement was 0.94. It is concluded that the XGBoost algorithm can be used to create models for the estimation of steppe meadow aboveground biomass. The technology developed in this study provides a method for the rapid and accurate hyperspectral remote sensing monitoring of forage biomass， and lays a foundation for high-precision estimation of regional grassland herbage accumulation on a regional scale.

Characteristics of community patches under three grazing modes in Sunite Desert-steppe

Zhong-ju MENG, Yan-jie CHEN, Si-qin BAO

2021, 30(4):  13-23.  DOI: 10.11686/cyxb2020194

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This research investigated the characteristics of vegetation micro-patches in the desert steppe and their relationship with environmental conditions. The landscape index， fractal model， stability index and univariate point pattern methods were used to explore the characteristics， shape fractal， stability and distribution pattern of plant community micropatches under different grazing modes （rested from grazing： It refers to the short-term prohibition of grazing； free grazing： It is a kind of grazing way to drive the herd to swim and feed in a large range； and rotational grazing： It is a kind of grazing way of reincarnation or circular grazing according to season grassland and grazing plot） in Sunite Desert-steppe， Inner Mongolia. It was found that： 1） The patch characteristics of the three grazing methods varied significantly. The area of Achnatherum splendens patches in the area rested from grazing accounted for 91.15% of the overall landscape area. For this community the contat degree index was 77.92， indicating good connectivity and the fractal dimension was 1.43， indicating poor stability. The spatial distribution of Convolvulus ammannii patches was the densest under free grazing. The number of Caragana rosea patches in the rotational grazing area was the largest. For these patches the SPLIT index was 46.99， indicating a high degree of fragmentation. The highest fractal dimension was 1.88， indicating the most irregular shape. 2） Under all three grazing methods， the patch types were mainly distributed in clusters in the scale range of the sampling plots， with random and uniform distributions appearing occasionally. The aggregation scale of each patch type was large in the free grazing state， indicating that the resource distribution was uneven.

Effect of seasonal timing of drought on carbon exchange in the alpine meadow ecosystem of the Qinghai-Tibetan Plateau

Zi-xin WANG, Guo-zheng HU, Hong-wei SHUI, Yi-qing GE, Ling HAN, Qing-zhu GAO, Ganjurjav HASBAGAN, Luo-bu DANJIU

2021, 30(4):  24-33.  DOI: 10.11686/cyxb2020276

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Extreme drought events can significantly change soil hydrothermal conditions and plant community characteristics， and then affect the ecosystem carbon exchange. In this study， we used rain shelters to artificially produce early season growing drough （ED， greening up stage， May-June） and middle growing season drought （MD， rapid growing stage， July-August）， to study the responses of plant community responses and ecosystem carbon exchange. It was found that vegetation height， cover and aboveground biomass were significantly lower in ED than in control （P<0.05） during the middle of the growing season. ED and MD depressed the total ecosystem productivity （GEP） and ecosystem respiration （ER） significantly （P<0.05） in the middle of the growing season. Moreover， net ecosystem carbon exchange significantly decreased （P<0.05） under the MD treatment. Regression analysis showed that there was a significant positive correlation between the soil moisture and ER （P<0.05） under ED in the middle of growing season. Also， ER was significantly positively correlated with soil moisture and community biomass （P<0.05） in the MD treatment during the early growing season. The mechanisms of drought impact differed with different seasonal timing of imposed drought. The ED mainly affected carbon exchange by inhibiting plant growth processes， while the MD primarily affected carbon exchange by inhibiting plant physiological activity. This study expands knowledge of how this alpine meadow ecosystem responds to drought at different times within the growing season， and provides data supporting climate change projection research.

Changes in soil particle size distribution and fractal characteristics across an anthropogenic transition from desert steppe grassland to shrubland in eastern Ningxia

Zhong-chao SUN, Tian-dou GUO, Lu YU, Yan-ping MA, Ya-nan ZHAO, Xue-ying LI, Hong-mei WANG

2021, 30(4):  34-45.  DOI: 10.11686/cyxb2020175

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This research aimed to characterize changes in soil particle size and fractal dimensions across a grassland-shrubland vegetation transition boundary in the desert steppe of Eastern Ningxia. Following ecological boundary theory and standard methodology， sites located in desert grassland， at the grassland edge， at the shrubland edge， and in shrubland were selected as representative of the main states found in a typical anthropogenic grassland-shrubland transition in vegetation mosaics in the region. Samples were collected for 0-10 cm， 10-20 cm and thereafter 20 cm soil depth increments to 100 cm. It was found that the percentage of soil volume by particle size in the transition zone studied was sand>silt>clay. The proportion of sand increased gradually across the anthropogenic transition from approximately 70% in grassland to 95.54%-98.97% in the shrubland， depending on soil depth. Conversely， soil fractal dimension decreased with increasing sand content from 2.10-2.42 in desert grassland to 1.02-1.78 in shrubland. Soil fractal dimension did not differ significantly between desert grassland， grassland edge and shrubland edge （P>0.05）， but the soil fractal dimension at all three of these site categories was significantly higher， by 36.79%-41.48%， than in shrubland （P<0.05）. The change of soil fractal dimension across the vegetation transition zone was significantly positively correlated with clay content （<2 μm） and silt particle content （2-50 μm）， but significantly negatively correlated with sand content （50-2000 μm）. The soil fractal dimension also showed a very significant positive correlation with soil moisture content， capillary porosity， organic carbon content， and soil total phosphorus （P<0.01， P<0.05）， and a significant negative correlation with soil bulk density （P<0.01）. A principal component analysis indicated that soil silt and sand content， soil capillary porosity， soil bulk density， and soil organic carbon and total phosphorus contents were the parameters most closely associated （P<0.05） with the change in soil fractal dimension across the studied anthropogenic vegetation community transition.

Responses of soil microbes across an anthropogenic transition from desert steppe grassland to shrubland in eastern Ningxia

Ji-xiong GU, Tian-dou GUO, Hong-mei WANG, Xue-ying LI, Dan-ni LIANG, Qing-lian YANG, Jin-yue GAO

2021, 30(4):  46-57.  DOI: 10.11686/cyxb2020195

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This research investigated the impacts on soil microbes and their enzyme activities， of the anthropogenic transition process from desert steppe to shrubland vegetation. Four site categories： desert grassland （DG）， grassland edge （GE）， shrubland edge （SE） and shrubland （SL） in grassland-shrubland mosaic were selected to represent the transition process， and soil properties， microbial population counts， microbial biomass and enzyme activity in the 0-20 cm soil layer under vegetation patches （VP） and bare interspaces （BI） at each site were measured. It was found that soil moisture， soil organic carbon， total carbon， total nitrogen and total phosphorus decreased from 6.84%， 8.54 g·kg^-1， 22.67 g·kg^-1， 0.85 g·kg^-1， 0.32 g·kg^-1 in DG to 1.78%， 5.85 g·kg^-1， 6.63 g·kg^-1， 0.16 g·kg^-1， 0.23 g·kg^-1 in SL， respectively （P<0.05）， while pH was not significantly changed. Across the transition， bacteria numbers were lowest at GE and SE sites， and slightly lower in SL than DG. Fungi showed a “decrease-rise-decrease” trend， with slightly higher population numbers in SL than in DG. Actinomycete population numbers decreased significantly in SL， compared to DG. The amount of microbial biomass carbon and nitrogen decreased from 87.66 and 5.94 mg·kg^-1 in DG， to 9.94 and 1.85 mg·kg^-1 in SL， respectively （P<0.05）. The activities of catalase， alkaline phosphatase and sucrase showed a significant “decrease-rise-decrease” decline trend in the transition from DG to SL， and urease activity was significantly lower in DG than in SL （P<0.05）. The soil microbe characteristics and enzyme activities were significantly higher under VP than in BI （P<0.05）. Across the vegetation transition， soil moisture， total carbon and total nitrogen were positively correlated with soil microbe-related parameters （actinomycete numbers， soil microbial biomass carbon and nitrogen， and catalase， urease， alkaline phosphatase activities） （P<0.01）， and soil organic carbon and total phosphorus were significantly correlated with soil microbial biomass carbon and urease activity （P<0.05）， while pH was not significantly correlated with soil microbe-related parameters （P>0.05）. Actinomycete numbers， and the enzymatic activities of catalase， alkaline phosphatase and urease were positively correlated with microbial biomass carbon and nitrogen （P<0.01）. However， the numbers of bacteria and fungi and sucrase activities were not significantly correlated with microbial biomass carbon and nitrogen. Across the DG-SL ecological boundary transition （established nearly 30 years）， the indexes observed differed between DG and SL， with SL being significantly lower than DG in most cases， showing that the soil microbial activity of DG is significantly decreased after 30 years as shrubland.

Effects of mulching with caragana （Caragana intermedia） branches on soil moisture content and temperature and reseeded forage biomass in desertified grassland in Ningxia Province， China

Ru ZHANG, Jian-ping LI, Wen-dong PENG, Fang WANG, Zhi-gang LI

2021, 30(4):  58-67.  DOI: 10.11686/cyxb2020172

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As well as being the main natural factor affecting grassland degradation in the eastern desertification area of Ningxia， drought is also the primary limiting factor influencing natural grassland reseeding. Caragana （Caragana intermedia）， which is extensively planted in grasslands in this area， is an abundant source of herbage for mulching for soil water retention. However， little research has been conducted to date on the use of caragana herbage for mulching. In this study， caragana branches were cut and collected from local grasslands， and were then transported and applied as a mulch for water retention on nearby grassland not planted with caragana. Four treatments were applied： control （no mulching， TSM₀）， and caragana mulch applied on the soil surface of degraded grassland to a thickness of 1 cm （TSM₁）， 2 cm （TSM₂）， and 3 cm （TSM₃）. During the experimental period， the soil moisture content and temperature of the 0-40 cm soil layer were monitored， together with the above-ground biomass of reseeded forages. It was found that the mean soil water content was significantly increased by mulched caragana branches， and the thicker the mulch layer， the greater the soil moisture water. However， the soil water contents of the 0-20 cm soil layer did not differ significantly from TSM₀ （P>0.05） in either of two seasons for which data were collected， 2018 and 2019. In contrast， the three mulching treatments increased soil water content in the 20-40 cm soil layer compared with TSM₀， and exhibited a gradation TSM₃>TSM₂>TSM₁>TSM₀. Moreover， mulching with caragana branches decreased soil temperature of the 0-10 cm soil layer during the growing season. The soil temperatures at 8：00， 14：00 and 18：00 were all decreased by mulching， and this effect increased with increasing thickness of caragana branch mulch. In addition， the coefficients of variation for soil temperature in 2019 were 4.6%， 2.3%， 1.7% for treatments TSM₁， TSM₂ and TSM₃， respectively， suggesting that the mulching treatments had a buffering effect on soil temperature fluctuation. We also found that the biomass of reseeded grasses increased as the thickness of caragana-branch mulch increased. Lastly， the biomasses of reseeding grass species Agropyron mongolicum and Astragalus adsurgens， as well as the total biomass of reseeding grasses were positively correlated with the soil water content of the 20-40 cm soil layer （P<0.05）. In conclusion， the application of mulched caragana branches improved soil water content and reduced soil temperature in degraded grassland， and also created a beneficial environment for reseeded forage growth. Therefore， use of mulched caragana branches has the potential to provide a method for enhancement of reseeding and restoration of degraded grassland in this region and other similar environments.

Evaluation of soil quality in Leymus chinensis-Achnatherumsplendens grassland and in Stipa sareptana grassland

Li-xing ZHANG, Chun-xing HAI, Yao-wen CHANG, Xiao-mei GAO, Wen-bang GAO, Yun-hu XIE

2021, 30(4):  68-79.  DOI: 10.11686/cyxb2020371

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This research investigated soil quality of the vegetation communities in typical grassland in Inner Mongolia. Two sites （approximately 1340 m altitude）， one dominated by Leymus chinensis and Achnatherum splendens （Lc-As） mixed grassland （tolerant of soil salinity） andthe other by Stipa sareptana （Ss） grassland （intolerant of soil salinity） were selected for study. Soil quality data were evaluated for six soil horizons in Lc-As （A₁， A₂， AB， B_k， B_b， C>130 cm） and five horizons in Ss （A₁， A₂， AB， B_k， C>90 cm） using multivariate nonlinear methods. Initially， 10 soil physicochemical parameters were measured and a principal component （PC） analysis performed on these. From these 10 parameters a ‘minimum data set’ （MDS） was selected based on a ‘Norm’ score which assessed the influence of each parameter based on size of PC coefficients （≥0.5） and uniqueness of information （low Pearson correlation with other parameters）. In this way three parameters were selected for inclusion in the MDS： soil organic matter （OM， indicative of nutrient status）， electrical conductivity （EC， indicative of salinity） and bulk density （BD， lower bulk density indicating better soil aeration）. It was found that： 1） Soil water content and electrical conductivity of Lc-As grassland in the A₂ to B_k horizons was significantly higher than that of Ss grassland （P<0.05）， and pH of Lc-As grassland in the A₂ and AB horizons was higher than in Ss grassland （P<0.05）. The average nutrient content of Lc-As grassland was higher than that of Ss grassland in the A horizon （P<0.05）， but the opposite was true in the B_k to C horizons. 2） A soil quality index （SQI） was calculated from the MDS with OM， EC and BD weighted 0.39， 0.16 and 0.45， respectively. 3） The SQI of Lc-As grassland was higher than that of Ss in the A₁ horizon， while in the A₂ to C horizons， the SQI of Lc-As grassland was significantly lower than in Ss grassland （P<0.05）. These research results provide scientific parameters useful for the development of sustainable grassland management practices.

Plant community diversity and soil factor interpretation of adaptive region of Deschampsia caespitosa in the source region of the Yellow River

Qiao-yu LUO, Yan-long WANG, Lei DU, Nian LIU, Li LI, Yu-shou MA

2021, 30(4):  80-89.  DOI: 10.11686/cyxb2020350

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Theoretically speaking， the ecological characteristics of plant communities are the result of long-term adaptation and co-evolution of plants， climate， soil， terrain and other ecological environment complexes. This research studied plant community diversity characteristics and environmental factors influencing plant community composition in the adaptive region of Deschampsia caespitosa in the source region of the Yellow River. Five plant community types commonly found in Maqin county were studied： I， D. caespitosa （Poaceae） dominant； Ⅱ， Blysmus sinocompressus （Cyperaceae） dominant； Ⅲ， B. sinocompressus and D. caespitosa mixed community； Ⅳ， Kobresia schoenoides （Cyperaceae） dominant； V， K. schoenoides and D. Caespitosa mixed community. Plant species present were surveyed in mid-August 2018， and soil samples collected at the same time to establish key parameters of the plant environment. Correlation analysis and redundancy analysis （RDA） were used to analyze the association between plant species and environment factors and various ecological diversity indexes were calculated. Across the study sites 83 species were recorded belonging to 17 families and 49 genera. Notably， the widely distributed species were members of the Asteraceae， Poaceae， Cyperaceae， Ranunculaceae， Gentianaceae and Scrophulariaceae families. The community species diversity indexes varied greatly between the communities. For community I， the species richness and Shannon-Weiner indexes were lower， and the Alatalo and Pielou Jsw evenness indexes， together with the % cover， height， biomass and importance value of D. caespitosa were significantly higher than in the other communities. There were also significant differences in soil nitrogen （N）， phosphorus （P）， carbon （C）， organic matter （SOM）， soil water content （W） and pH between the different plant communities across the 5 study sites in the adaptive region of D. caespitosa. The multivariate analysis of community species diversity indexes， population characteristics and environmental factors showed that the % cover， height， biomass and importance value of D. caespitosa were negatively associated with species richness， Simpson dominance index， Shannon-Wiener index， soil P， soil moisture water， and positively associated with the Alatalo evenness index and soil pH. RDA analysis showed that pH was the main environmental factors affecting community species diversity. D. caespitosa was more suited to a moist to mesophytic soil environment with low P， while the importance value of D. caespitosa decreased significantly with increasing species richness in the community， indicating that D. caespitosa has some characteristics of a pioneer species characteristics and a potential use in restoration and management of degraded grassland.

Study on soil physical and chemical properties and carbon and nitrogen sequestration of grassland under different utilization modes

Chao ZHANG, Rui-rui YAN, Qing-wei LIANG, Ri-su NA, Tong LI, Xiu-fang YANG, Yu-hai BAO, Xiao-ping XIN

2021, 30(4):  90-98.  DOI: 10.11686/cyxb2020278

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This research investigated the effects of natural grassland and artificial grassland degradation on soil physical and chemical properties， in particular the change in carbon and nitrogen contents and carbon sequestration. Representative areas of natural grassland， grazed artificial grassland and mown artificial grassland in Ar Horqin Banner， Inner Mongolia， were selected for study. Parameters measured in the study area were soil moisture content， soil bulk density， soil microbial content and soil nutrient levels. Growth status of the study sites was also evaluated using the NDVI value and in general the ranking for growth status under the different utilization modes was： mown artificial grassland>grazed artificial grassland>natural grassland. Soil water content in the 0-20 cm depth ranked： grazed artificial grassland>mown artificial grassland>natural grassland， and the differences were significant （P<0.05）. The total carbon and total nitrogen contents in the grazed artificial grassland were the highest. The total carbon contents in the grazed artificial grassland and natural grassland for the 10-30 cm soil depth were significantly higher than that of the mown artificial grassland （P<0.05）. The total soil nitrogen content of the grazed artificial grassland for the 0-10 cm soil depth was （0.88±0.11） g·kg^-1， which was significantly higher than those of the natural grassland and the mown artificial grassland （P<0.05）. The soil microorganism carbon and nitrogen content in the three grassland types ranked： grazed artificial grassland>mown artificial grassland>natural grassland. The soil microorganism nitrogen content of the grazed artificial grassland for the 0-10 cm depth was （28.45±8.30） mg·kg^-1， which was significantly higher than values in the natural grassland and mown artificial grassland （P<0.05）. Soil carbon and nitrogen storage for the three categories of grassland ranked： natural grassland>grazed artificial grassland>mown artificial grassland， and soil carbon and nitrogen storage of natural grassland and grazed artificial grassland for the 10-30 cm depth were significantly higher than that of mown artificial grassland （P<0.05）. The performance characteristic of grazed artificial grassland was soil carbon and nitrogen accumulation， while that of mown artificial grassland was carbon and nitrogen loss. In addition， with increase in soil depth， the carbon and nitrogen storage of natural grassland and mown artificial grassland show a decreasing trend. Thus it can be seen that the establishment of artificial grassland and human intervention such as seeding and irrigation will effectively improve soil quality and grassland growth status， but to a certain extent there may be a negative effect on soil carbon and nitrogen sequestration potential.

Herbage production and forage quality responses to cutting height and fertilization of legume-grass mixtures in the Hexi region

Xin-you WANG, Wen-xia CAO, Xiao-jun WANG, Yu-zhen LIU, Rui GAO, Shi-lin WANG, Hai-tao AN, Xiu-xia DENG, Wen-hu WANG

2021, 30(4):  99-110.  DOI: 10.11686/cyxb2020467

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Mowing and fertilization are extremely important field management decisions in the cultivation of legume-grass mixtures. Appropriate stubble height at mowing and optimal application rates of nitrogen and phosphorus fertilizers can enhance the productivity of mixed grassland. This research was conducted in the Hexi Corridor area and explored the effects of different stubble heights and fertilizer application rates on the yield and quality of a three-year-old perennial legume-grass mixture comprising Medicago sativa， Bromus inermis and Elytrigia elongata at a planting ratio of 1∶1∶1. The experiment used a split-plot design with three stubble heights as main plots： 5 cm （A₁）， 8 cm （A₂） and 11 cm （A₃）. Six fertilizer treatments were included as sub-plots： no fertilization （CK， B₁）， single phosphorus （150 kg P₂O₅·ha^-1， B₂）， low nitrogen and high phosphorus （75 kg N·ha^-1+225 kg P₂O₅·ha^-1， B₃）， equal nitrogen and phosphorus （150 kg N·ha^-1+150 kg P₂O₅·ha^-1， B₄）， single nitrogen application （150 kg N·ha^-1， B₅）， high nitrogen and low phosphorus application （225 kg N·ha^-1+75 kg P₂O₅·ha^-1， B₆）. The leguminous forages in the mixed grassland were mowed at the early-flowering stage， and fertilized after the first mowing. It was found that： the A₃B₃ treatment combination had the highest annual yield （19626 kg·ha^-1）； and the A₂B₂ treatment combination had the lowest annual yield （14342 kg·ha^-1）. Increasing the stubble height reduced the crude protein content of alfalfa to some extent， and adding nitrogen enhanced the crude protein levels of poaceous forages. The relative forage value （RFV） of herbage was increased by increasing nitrogen and decreasing phosphorus， and the forage RFV was also decreased when the fertilizer application rate was too high. The optimal combination of nitrogen and phosphorus fertilizer was 150 kg N·ha^-1+150 kg P₂O₅·ha^-1. Based on the combined results for yield and quality， the appropriate application rate of phosphate fertilizer application significantly improved the nutritional quality of forage grass. Using the TOPSIS comprehensive evaluation model to evaluate the yield of mixed grassland and the nutritional quality of each mixed forage， the 8 cm stubble height and 150 kg N·ha^-1+150 kg P₂O₅·ha^-1 is the optimal combination of stubble height and fertilizer application for the mixed forage cropping of M. sativa+B. inermis+E. elongata in the Hexi Corridor.

Breeding of Lanjian No. 3 common vetch and evaluation of its characteristics

Zhi-biao NAN, Yan-rong WANG, Bin NIE, Chun-jie LI, Wei-guo ZHANG, Chao XIA

2021, 30(4):  111-120.  DOI: 10.11686/cyxb2020344

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A common vetch （Vicia sativa） breeding program was started in 1999 using germplasm materials introduced from the International Centre for Agricultural Research in Dry Areas （ICARDA）. The objective was to develop cultivars adapted to the alpine grassland conditions to improve the degree to which nutritional requirements of livestock production at Qinghai-Tibetan Plateau could be met. After 12 years of continuous effort， a new cultivar named Lanjian No.3 was developed through a combination of single plant selection and bulk selection. The most prominent characteristics of the new cultivar are early maturity and higher seed yield. The mean number of days required from seedling emergence to seed maturation was only 100 days with a range of 92 to 106 days， and the mean seed yield was 2023 kg·ha^-1， when it was grown in Xiahe county of Gansu province， China， a typical alpine grassland where the elevation is 3000 meters above sea level. Compared with a reference cultivar 333/A， the mean growing days to maturity was 13 days shorter and seed yield was 174.9% higher. The mean herbage dry matter yield of Lanjian No.3 is 2769 kg·ha^-1， which is similar to the reference cultivar. Its herbage dry matter yield was 3214 kg·ha^-1 （14.3% higher than 333/A） when grown in summer as a cover crop on the Loess Plateau. Therefore， it is concluded that Lanjian No. 3 is a productive new cultivar for the Qinghai-Tibetan Plateau. It also could be used as a short-term rotation crop or green manure crop in traditional crop production regions.

Selection for reproductive traits and their adaptation in Stellera chamaejasme in degraded alpine grassland

Wang-long LUO, Jian-qiang XIA, Jia-xin LI, Shu-fan SUN, Rui WANG, Bo ZHANG

2021, 30(4):  121-129.  DOI: 10.11686/cyxb2020182

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The reproductive traits of angiosperms are widely believed to have evolved largely through pollinator-mediated natural selection. The present study focused on Stellera chamaejasme, a dominant poisonous species in degraded alpine meadow in Tianzhu County of Gansu Province in China. S. chamaejasme was chosen as a model species to explore adaptation of floral traits and possible selective mechanisms by detecting their selection differentials and selection gradients. It was found that flower number per inflorescence and corolla tube length had both significant selection differentials and selection gradients (P<0.05), indicating positive directional selection for both traits. Also, significant nonlinear selection gradients (P<0.05) were detected for these two traits, possibly indicating stable selection occurring for them. Negative directional selection was detected for inflorescence length, with a significant linear selection gradient of -0.102±0.039 (P=0.008). No significant selection was detected for the other traits measured, such as corolla entrance size and inflorescence number per plant. In conclusion, the data indicate that some reproductive traits in S. chamaejasme exhibited a trend of adaptive evolution under natural selection, and individuals, which have relatively shorter inflorescence length, longer corolla tubes and more flowers per inflorescence, tend to be selected for due to their advantage in achieving reproductive fitness.

A study of the correlation between seed shattering and agronomic traits of Elymus sibiricus on the Qinghai-Tibetan Plateau

Rui WU, Wen-hui LIU, Yong-chao ZHANG, Yan QIN, Xiao-xing WEI, Min-jie LIU

2021, 30(4):  130-139.  DOI: 10.11686/cyxb2020170

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This research screened Elymus sibiricus germplasm in the Qinghai-Tibetan Plateau for anti-shattering traits and investigated the relationship between the degree of shattering and agronomic traits. Fifteen E. sibiricus germplasm lines collected in different regions of Qinghai were studied. Analysis of variance， correlation， principal component， regression and cluster analyses were carried out to evaluate the association between agronomic traits and the degree of shattering of E. sibiricus. The results showed that： 1） There were significant differences in natural shattering rate between the 15 E. sibiricus germplasm lines. A line numbered 17-124 had the most severe shattering， with an average rate of 56.92%. Lines numbered 17-064 and 17-050 had the strongest shattering resistance， with rates of 17.54% and 18.63%， respectively， and there was a large genetic difference between the germplasm lines. 2） Repeated measurements over time indicate that the shattering in each germplasm line indicates that the shattering rate continues to increase from the third day to the fifteenth day after the ‘milk’ stage of grain ripening， and there were extremely significant differences in shattering between maturity stages （P<0.01）. 3） There was a significant positive correlation （coefficient 0.437， P<0.01） between the number of spikelets and the shattering rate. There were also significant positive correlations between the fringe number， length of inflorescence， spikelet width and lemma length and shattering （P<0.05）， an extremely significant negative correlation between inflorescence width （P<0.01）， and a significant negative correlation between awn length and shattering （P<0.05）. Combining the results of principal component analysis and regression analysis， number of spikelets， awn length and inflorescence width were the main factors that affected the shattering rate. 4） The 15 germplasm lines were clustered into 4 groups by agronomic traits and shattering rate： Group Ⅰ included the genotypes which exhibited a high shattering rate averaging 41.24%， together with a high number of spikelets and seeds per inflorescence； Group Ⅱ and Group Ⅳ included genotypes with low shattering rates averaging only 18.63% and 17.54%， respectively. These can be used as candidate materials for screening of low-shattering germplasm； Group Ⅲ included genotypes with a high shattering rate averaging 42.41%， and with a high number of spikelets per spike， but with the least spikelets per inflorescence.

Analysis of the floristic diversity of vascular plants in Duoer National Nature Reserve， Gansu

Sheng-jing SHI, Jun GAO, Chun-xia WANG, Zhen JIANG, Xue-lin CHEN

2021, 30(4):  140-149.  DOI: 10.11686/cyxb2020192

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This paper reports an analysis of the species composition and distribution types of vascular plants in Duoer National Nature Reserve， based on field investigation， plant collection specimens and literature research. We found that there were 1323 species of vascular plants present in the study area. These belong to 469 genera and 115 families， among which 61 species belonging to 25 genera and 14 families were pteridophytes， 25 species belonging to eight genera and four families were gymnosperms， and 1237 species belonging to 436 genera and 97 families were angiosperms. The floristic diversity of the dominant vascular plant species in Duoer Reserve was obvious， in that 879 species （66.44% of those present） were found to belong to a dominant family with 20 or more species represented. There was a relatively high ratio of monotypic genera or oligotypic genera and these accounted for 95.31% of the total genera and 75.51% of the total species present in the basin. At the family level， tropical families （30.43%） were slightly more numerous than families of temperate origin （26.96%）. At the genus level， the temperate families （72.49%） were significantly more numerous than the tropical families （13.01%）. At the species level， there were 545 endemic species， of which 538 species were also found in surrounding provinces， reflecting the obvious transition between and convergence of different floral assemblages in this region. The geographical composition of vascular flora in this reserve was complex and diverse， and there were 15 geographic distribution types and five variants among the genera present. Species of temperate geographic distribution type were dominant， especially those of north temperate distribution. There were many rare and endangered wild plants present in this area， and 37 species were listed as protected. Some ancient relict plants had a good primitive distribution in the reserve. The study has improved knowledge of the floristic characteristics of vascular plants in Duoer National Nature Reserve and provided strong foundation for building understanding of plant species biodiversity in the reserve in the future.

Mitigative effect of exogenous ascorbic acid on the growth of copper-stressed chicory （Cichorium intybus） seedlings

Long WANG, Jie FAN, Chang WEI, Ge-zi LI, Jing-jing ZHANG, Qiu-juan JIAO, Guo CHEN, Luan-zi SUN, Hai-tao LIU

2021, 30(4):  150-159.  DOI: 10.11686/cyxb2020411

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This research explored the mitigative effect of exogenously applied ascorbic acid （AsA） on the growth， Cu accumulation and physiological characteristics of chicory （Cichorium intybus） seedlings under copper stress （Cu-stress）. Cu-stress was achieved by growing seedlings in hydproponic culture with 50 μmol·L^-1 Cu²⁺ added to the culture solution. It was found that Cu-stress at 50 μmol·L^-1 severely suppressed the chlorophyll content， and photosynthesis and biomass accumulation of the chicory seedlings. Cu-stress also increased the degree of cell membrane lipid peroxidation， and reduced soluble protein contents and the antioxidant activities of superoxide dismutase， peroxidase， catalase and ascorbate peroxidase. In contrast， exogenous AsA decreased the absorption and transport of Cu by the root system and ameliorated the damage of Cu-stress to chicory seedlings. Specifically， exogenous AsA increased the root system， shoot and total dry matter biomass， decreased the degradation of photosynthetic pigments （chlorophyll a， chlorophyll b， total chlorophyll， and carotenoid） and enhanced the photosynthetic parameters， reduced the damage of lipid peroxidation to the cell membrane， and enhanced the antioxidant activities， soluble protein levels and endogenous AsA concentration. These results provide reference data for the application of exogenous AsA in mitigating Cu toxicity to plants and enhancement of the Cu tolerance mechanism of chicory.

Endogenous hormone responses to nitric oxide in alfalfa seedlings under PEG stress

Xiao-fang ZHANG, Xiao-hong WEI, Fang LIU, Xue-mei ZHU

2021, 30(4):  160-169.  DOI: 10.11686/cyxb2020173

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This research studied the endogenous hormone responses to nitric oxide （NO） in leaves and roots of 50-day old alfalfa seedlings under PEG stress. Polyethylene glycol （PEG-6000） was used as the osmotic regulator to simulate drought stress. Exogenous spraying of NO releasing agent sodium nitroprusside （SNP） and NO scavenger carboxy-PTIO （cPTIO）， and liquid chromatography/mass spectrometry methods were used to study the response of four endogenous hormones （abscisic acid， ABA； indole-3-acetic acid， IAA； salicylic acid， SA； gibberellin， GA₃） to NO in the leaf and root systems of alfalfa seedlings under PEG stress. Treatments included in the experiment were： T₁， distilled water （CK）， T₂， PEG added； T₃， SNP+PEG added； and T₄， cPTIO+PEG added. It was found that： 1） The application of exogenous NO under PEG stress （T₃） can promote the NO content in the leaf and root of alfalfa， and the NO scavenger cPTIO （T₄） significantly reduced the NO content in leaves of alfalfa. 2） With increasing duration of PEG stress， the levels of ABA and SA in leaves and roots increased gradually， but the ABA and SA levels in the root system increased later than those in the leaves. On the 8th day of stress， the leaf ABA content in plants of T₃ was 6.68 times higher than the SA content， while the ABA content in plants of T₄ was 77.22% higher than the SA content， and the leaf ABA content in leaves of T₃ plants was significantly higher than that in roots. 3） NO rapidly induces an increase in the IAA and GA₃ concentrations in leaves and roots. On the 4th day of stress， the IAA levels in leaves under exogenous NO treatment were 1.65 times higher than in the cPTIO scavenger treatment. Meanwhile the IAA concentration in roots was 8.70% higher in T₄ than T₃， and the GA₃ content in leaves and roots of T₃ was 54. 49% and 84. 65% higher， respectively， than in T₄. GA₃ content reached its maximum on the second day of treatment and decreased thereafter. In summary， NO is here shown to regulate the growth and stress resistance of alfalfa plants by raising or lowering the metabolic levels of IAA， ABA， GA₃ and SA， the regulation of ABA and SA in alfalfa is particularly prominent.

Effect of overexpression of the alfalfa MsHB7 gene on drought tolerance of Arabidopsis

Yi-yao HOU, Xiao LI, Rui-cai LONG, Qing-chuan YANG, Jun-mei KANG, Chang-hong GUO

2021, 30(4):  170-179.  DOI: 10.11686/cyxb2020181

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The homeodomain-leucine zipper （HD-Zip） protein subfamily I plays an important role in the regulation of plant abiotic stress. There are few reports of HD-Zip I genes in alfalfa， although they have been cloned and identified in many species. The purpose of this study was to investigate the role of MsHB7， a HD-Zip I gene from alfalfa， in the regulation of Arabidopsis thaliana drought resistance. The MsHB7 gene with an open reading frame of 738 bp and encoding 245 amino acids was obtained by cloning. Multiple sequence alignment and phylogenetic tree analysis showed that MsHB7 belonged to the HD-Zip I subfamily and was closely related to ATHB7 and ATHB12 in A. thaliana. Real-time fluorescence quantitative analysis showed that the MsHB7 gene was induced by drought. The MsHB7 gene was transformed into A. thaliana and positive plants were obtained. After drought treatment， the transgenic A. thaliana wilted more obviously. The relative water content of transgenic plants was significantly lower than that of wild-type A. thaliana， and the proline and malondialdehyde levels accumulated in transgenic plants were more than wild-type. qRT-PCR results showed that the expression levels of stress response genes ATCAT1， ATDREB2A and ATRD29A in the transgenic A. thaliana were significantly increased， while the expression levels of ATLEA3 were significantly decreased after stress. The above results indicate that the overexpression of MsHB7 gene can reduce the drought tolerance of transgenic A. thaliana， which provides theoretical information as a basis for the further development and utilization of this gene.

Effects of feeding level on the gastrointestinal development， rumen fermentation and rumen microbiota in Altay sheep

Hong LI, Shu-zhen SONG, Liang-shuang GAO, Xia LANG, Li-shan LIU, Xu-yin GONG, Yu-bing WEI, Jian-ping WU

2021, 30(4):  180-190.  DOI: 10.11686/cyxb2020184

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The purpose of this experiment was to study the effects of relative feeding level on rate of bodyweight gain， carcass dressing out performance， meat quality and organ development in Altay sheep. Thirty 3.0 to 3.5 month old Altay female lambs with a similar body weight of （19.16±10.54） kg and uniform tail size were randomly divided into 3 groups with 10 lambs per group. After 60 daysof adlibitumfeeding， three differential feeding levels were imposed for a further 30 days. The differential feeding levels were calculated based on feeding standards published by the National Research Council， USA， in 2007， defining maintenance energy （Em） requirements and lambs in each group were fed diets supplying 1.5× （1.5Em）， 1.0× （1.0Em） or 0.5× （0.5Em） the calculated Em （0.75， 0.50 and 0.25 MJ metabolizable energy per kg^0.75 body weight， respectively）. It was found that： 1） The weights of the whole stomach， rumen， and small intestine and a rumen size index decreased with decrease in feeding level， and the weights of the whole stomach， rumen and small intestine fed at 1.5Em were significantly higher （P<0.05） than in groups fed 1.0Em and 0.5Em， while the length of small intestine and a small intestine size index in groups fed 1.5Em and 1.0Em were significantly increased （P<0.05） compared with the group fed 0.5Em. And there was no significant difference between the 1.5Em and the 1.0Em groups （P>0.05）. 2） The pH of rumen fluid was highest in the 1.0Em group and rumen pH for the group fed 1.5Em was significantly lower （P<0.05） than both the 1.0Em and 0.5Em groups. NH₃-N content decreased gradually with decrease feeding level， but the differences between the three groups was not statistically significant （P>0.05）. Total volatile fatty acids （TVFA）， acetic acid， propionic acid， butyric acid， valeric acid， isobutyric acid and isovaleric acid concentrations in rumen fluid of lambs fed 1.0Em were the lowest， and rumen TVFA， acetic acid and propionic acid levels of lambs fed 1.0Em were significantly lower （P<0.05） than in lambs fed 1.5Em and 0.5Em. The length of the small intestine and the small intestine size index of lambs fed 1.5Em and 1.0Em were increased significantly （P<0.05） compared to lambs fed 0.5Em. Rumen butyric acid and valproic acid concentrations and acetic∶propionic acid in groups fed 1.0Em and 0.5Em groups were significantly lower （P<0.05） than in the group fed 1.5Em. 3） The activities of digestive enzymes in rumen fluid decreased with the decrease of feeding level； the activities of lipase and protease in the group fed 1.5Em were significantly higher （P<0.05） than in the groups fed 1.0Em and 0.5Em， and there was no significant difference （P>0.05） between the groups fed 1.0Em and 0.5Em. Alpha-amylase activity differed significantly （P<0.05） among three groups. 4） The relative abundance of fungi and protozoa in rumen fluid of lambs fed 1.5Em was significantly higher （P<0.05） than in lambs fed 1.0Em and 0.5Em， and the differences between 1.0Em and 0.5Em groups were not significant （P>0.05）. Counts of Fibrobacter succinogenes and Ruminococcus albus were the lowest in lambs fed 1.0Em， and were significantly lower （P<0.05） than counts in the 1.5Em and 0.5Em groups. Ruminococcus flavefaciens counts did not differ significantly among the three groups （P>0.05）. These results show that feeding level has a significant effect on the gastrointestinal development， rumen fermentation parameters， activities of digestive enzymes and rumen microbiota in Altay sheep.

Progress in research on detection， risk assessment and control of mycotoxins in forage products

Yu-yu LI, Yu-shan JIA, Gen-tu GE, Zhi-jun WANG, Shuai DU, Lin SUN, Xiao-wei JIANG, Hong-xin WU, Mei-ling HOU, Xi-mei CHEN

2021, 30(4):  191-204.  DOI: 10.11686/cyxb2020193

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During harvesting， processing， storage and transportation， forage and plant products may be exposed to rain， or subject to deterioration arising from incomplete drying or physical crushing during handling when being loaded or unloaded. Such factors can cause leaf abscission and fungal invasion， resulting in quality deterioration， which not only incurs direct economic losses， but also raises the possibility that some mycotoxins may pose a safety hazard to livestock and human health. Mycotoxins are another key risk factor affecting the quality and safety of forage products along with pesticide residues， diseases and insect pests and inorganic pollutants. It is important to build a body of knowledge on their sources and occurrence， detection methods， standards for tolerance limits and risk Assessment related to mycotoxins in plant-derived products. Such information will generally enhance the quality and safety of forage and plant products. This review summarizes the main mycotoxins in plant and forage products： aflatoxins， ochratoxin， zearalenone， deoxynivalenol， T-2 mycotoxin and fumonisin. Levels of pollution and toxicity， analyzed and summarized of its detection methods， standards for tolerance limits and risk assessment are discussed. Mycotoxins in forage products can be controlled， degraded and controlled by chemical， physical and biological methods， but not can be completely removed. Safety with respect to mycotoxins in plant and forage products needs focus on “prevention” rather than “removal”. The present work should form a basis from which to identify the future research directions for research on mycotoxins in forage products， and provide a reference for researchers in this field.

Factors inducing plant apomixis and its potential application in Kentucky bluegrass breeding

Jin-qing ZHANG, Kui-ju NIU, Yu-zhu LI, Hui-ling MA

2021, 30(4):  205-217.  DOI: 10.11686/cyxb2020176

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The main factors affecting the development of apomictic embryogenesis in plants are summarized from five perspectives： genetic control， environmental impact， ploidy implications， hormone levels and mineral regulation， and the timing and location of the aposporous initiation cell. The purpose of this review is to develop a systematic understanding of the mechanism of apomixis in plants. In particular， research on apomixis in Poa pratensis is reviewed， factors limiting its occurrence are identified， theoretical advantages of its application are evaluated， and prospects for the use of apomixis in P. pratensis breeding and new germplasm creation are explored. This study provides a theoretical basis for the breeding and development of new varieties of P. pratensis.