Table of Content

20 May 2023, Volume 32 Issue 5

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Spatio-temporal analysis of the alpine grassland carrying capacity in Qinghai Province considering a supply-consumption relationship

Jie GAO, Xin-quan ZHAO, Wen-ting LIU, Xiao-xia YANG, Chun-ping ZHANG, Yang YU, Quan CAO, Yu-zhen LIU, Xue ZHANG, Quan-min DONG

2023, 32(5):  1-12.  DOI: 10.11686/cyxb2022192

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Qinghai Province is an important part of the Qinghai-Tibet Plateau. To achieve the sustainable use of grassland resources in this region， it is important to explore the local grass-livestock balance and determine the spatial and temporal trends in the carrying capacity of its grassland ecosystem. In this study， we focused on animal husbandry in Qinghai Province， and combined remote sensing image data with livestock statistics to analyze the carrying state of grassland ecosystems in this province. It was found that： 1） According to the statistical yearbook provided by the Qinghai Provincial Bureau of Statistics， the number of grazing livestock in Qinghai Province increased by 25.35% between 2005 and 2020. In terms of livestock structure， Yushu Tibetan Autonomous Prefecture and Guoluo Tibetan Autonomous Prefecture are dominated by yak breeding， while Haibei Tibetan Autonomous Prefecture， Hainan Tibetan Autonomous Prefecture and Haidong City are dominated by sheep breeding. 2） The consumption of grassland resources in Qinghai Province increased by 13.21% over 16 years， showing an overall increasing trend with differences among administrative regions. 3） The number of prefectures with severe overloading of livestock in Qinghai Province dropped to fewer than three in 2010 for the first time， and the best overall grass-livestock balance was in 2013. In general， the animal-grazing pressure has decreased over time. Sorted by region， Hainan Tibetan Autonomous Prefecture showed the most obvious increase in carrying pressure， and Guoluo Tibetan Autonomous Prefecture showed the most obvious decrease in animal-grazing pressure. The results showed that the number of grazing livestock in Qinghai Province has increased between 2005 and 2020， but there has been a tendency for the grazing pressure to ease， with each administrative region showing some variability in livestock structure and changes in grazing pressure. This highlights the importance of adapting measures to local conditions. These results provide a scientific basis for the ecological management of alpine grasslands and the development of the livestock industry in Qinghai Province.

Ecosystem service value evaluation and temporal-spatial evolution characteristics in an agro-pastoral ecotone of Gansu Province based on LUCC

Yun-liang LIANG, Jie LI, Yan-hua LU, Guang LI

2023, 32(5):  13-26.  DOI: 10.11686/cyxb2022232

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This study aimed to clarify the impact of land-use changes on ecosystem service values， based on land use/cover change （LUCC） for the agro-pastoral ecotone of Gansu Province in 2000， 2010， and 2020. We used an equivalence factor to quantitatively assess the ecosystem service value of the agro-pastoral ecotone of Gansu Province， then used a spatial autocorrelation analysis method to study the temporal-spatial changes in ecological service values in each township unit. It was found that： 1） From 2000 to 2020， the main land-use types in the agro-pastoral ecotone of Gansu Province were grassland， cultivated land， and woodland. During the period from 2000 to 2020， the areas of grassland， woodland， and construction land increased， while the areas of cultivated land and wetlands decreased. 2） From 2000 to 2020， the total value of ecosystem services in the agro-pastoral ecotone of Gansu Province increased by 11.2358×10⁸ yuan， and regulatory services dominated in all periods. Regulation of water flows and climate had large ecological service values. Grassland and woodland played significant roles in maintaining the value of hydrological and climatic regulation services， and were the key land-use types to maintain the total ecosystem service value （ESV） in the agro-pastoral ecotone of Gansu Province. 3） The ESV showed a strong positive spatial correlation， with an overall significant spatial pattern of agglomeration， and the spatial evolution of high- and low-value agglomerations remained stable. These results provide a scientific basis for formulating appropriate ecological protection policies， and for establishing a long-term strategy for ecological protection and restoration in the agro-pastoral ecotone of Gansu Province.

Characteristics of plant diversity and aboveground productivity and their relationship driven by subshrub expansion

Mei-hui LI, Yu-hua LI, Xin-hui YAN, Hang-hang TUO, Meng-ru YANG, Zi-lin WANG, Wei LI

2023, 32(5):  27-39.  DOI: 10.11686/cyxb2022367

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Shrub/subshrub expansion can significantly change the original vegetation landscape and its ecological processes. However， there is still a lack of systematic research on the characteristics of grassland plant diversity， aboveground productivity， and their relationship driven by subshrub expansion. In this study， the typical grassland of Yunwu Mountain in Ningxia on the Loess Plateau was selected as the study site. Grasslands with subshrub expansion at three levels of intensity （light， moderate， and heavy） were selected， and natural grassland without subshrub expansion served as the control. We analyzed species diversity， community level plant functional traits， functional diversity， and aboveground productivity and their intrinsic relationships. The results showed that： 1） The composition and structure of the grassland community changed significantly under the driver of subshrub expansion. The subshrub species Artemisia sacrorum replaced the original herb as the new dominant grassland species， which resulted in a significant decrease in species diversity. 2） Compared with the control， sites with subshrub expansion showed significantly decreased community-level leaf dry matter content， but increased community-level specific leaf area， and leaf carbon， nitrogen， and phosphorus contents. There was no significant difference in functional richness， while functional dispersion and functional evenness had significant differences under different expansion intensities. 3） Subshrub expansion significantly increased the aboveground biomass and litter biomass of the community， which was manifested as a significant increase in the biomass of weeds and a significant decrease in the biomass of legumes. However， grass biomass increased significantly under severe subshrub expansion. 4） The aboveground productivity of the grassland community was negatively correlated with species diversity， community-level leaf dry matter content， and functional dispersion， while positively correlated with leaf carbon， leaf nitrogen and leaf phosphorus contents at community level. The results of a random forest model and ANOVA further showed that community-level functional traits explained 68.28% of the variation in aboveground productivity， and that the community-level leaf nitrogen content and leaf dry matter content were the most important explanatory factors. The species diversity index was able to explain 64.38% of variation， while the interpretability of the functional diversity index was 11.16%. Our results showed that， with increasing subshrub expansion， species shifted to a strategy of rapid growth and resource acquisition， and the degree of species niche differentiation increased. Compared with functional diversity， plant functional traits and species diversity explained higher proportions of variation in the above-ground productivity of the community. The results of this study provide a foundation for further studies on the regime shift theory of natural grasslands on the Loess Plateau. These findings will also be useful for designing adaptability and sustainable management strategies for grasslands under shrub/subshrub expansion.

Retrieval of grassland aboveground biomass based on airborne LiDAR and SuperView-1 data

Kai-hong XU, Zhao SHI, Lei-chao MA, Ping WANG, Ang CHEN, Xing WANG, Ming CHENG, Yue-xin XIAO, Rong-tan WANG

2023, 32(5):  40-49.  DOI: 10.11686/cyxb2022199

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Grassland aboveground biomass （AGB） is an important indicator in grassland monitoring. It is an important index when designing strategies for the ecological protection and rational utilization of grassland resources. In addition， it is of great significance for the sustainable development and scientific management of grassland. In this study， shrub grassland in Xing’an County， Guangxi was the subject of the research， and data were obtained from airborne LiDAR data and high-resolution multispectral satellite images. The retrieval of grassland AGB was investigated using data collected from 89 field quadrats in 2021 and five basic regression models. The accuracy of different indicators and models was evaluated by root mean square error （RMSE）， mean absolute error （MAE）， and R-square values. It was found that grass height metrics were very important information for grassland AGB retrieval. We calculated correlation coefficients between pairs of indexes. In terms of vegetation indexes， the highest correlation coefficient was between the enhanced vegetation index （EVI） and AGB （0.666）. In terms of vegetation height indexes， the highest correlation coefficient was between average grass height （CHM_mean） and AGB （0.686）. In terms of combined indexes， the highest correlation coefficient was between the ratio vegetation index （RVI）×CHM_mean and AGB （0.735）. The accuracy and verification results showed that the minimum RMSE of the EVI models was 292.047 g·m^-2， the minimum RMSE of CHM_mean models was 245.084 g·m^-2， and the minimum RMSE of RVI×CHM_mean models was 225.872 g·m^-2. Our results show that grass height information can be effectively extracted from airborne LiDAR data， and although there is an obvious underestimation， it still has great application potential in research on grassland AGB.

Effects of enclosure and long-term mowing on vegetative reproduction characteristics of Leymus chinensis and Arundinella hirta populations in the Songnen Grassland， China

Ji FENG, Zhi-kuo LIU, Hai-yan LI, Yun-fei YANG, Jian GUO

2023, 32(5):  50-60.  DOI: 10.11686/cyxb2022203

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Vegetative reproduction is one of the main ways in which clonal grasses regenerate their populations. It is useful to determine the potential population that can be regenerated to predict the spatial structure and dynamics of the population. Enclosure and long-term mowing can directly or indirectly affect plant growth and reproductive strategies. In this study， we compared and analyzed the composition， size， and vegetative propagation capacity of potential populations generated by tillers and rhizomes of the common dominant species Leymus chinensis and the accompanying species Arundinella hirta under enclosure and long-term mowing treatments in the Songnen Grassland. It was found that the potential populations of the two grasses under enclosure and long-term mowing were composed of buds and juvenile tillers derived from tillers and rhizomes. The potential populations of L. chinensis and A. hirta were composed of three and two age classes， respectively. The first age class accounted for the highest proportion of the potential population. Compared with enclosure， long-term mowing significantly promoted the output of buds from tillers and rhizomes of both grasses， and this promotion effect was stronger for L. chinensis than for A. hirta. The number of juvenile tillers produced by tillers and rhizomes of L. chinensis was significantly higher than in A. hirta under both enclosure and long-term mowing. Long-term mowing significantly promoted the potential population increase of L. chinensis， but was not conducive to the formation of an A. hirta potential population. Long-term mowing promoted the vegetative propagation capacity， but not to a significant level. The vegetative reproduction strategy of L. chinensis under enclosure was to produce a large number of buds and some juvenile tillers to enhance the potential population. Its vegetative reproductive strategy under long-term mowing was to produce a large number of juvenile tillers to grow into tillers after successfully overwintering. The vegetative reproduction strategy of A. hirta under enclosure was to produce buds only， while that under long-term mowing was to produce a similar proportion of buds and juvenile tillers. Overall， L. chinensis and A. hirta populations had the same adaptive characteristics， in that young age-class tillers and rhizomes had a high vegetative propagation capacity under enclosure and long-term mowing， and the formation of juvenile tillers was promoted under long-term mowing. At the same time， differences in the vegetative propagation strategies of L. chinensis and A. hirta appear to explain why L. chinensis is the dominant species and A. hirta is the accompanying species in this study area.

Quantitative and nutrient characteristics of dominant species in different age classes on the Loess Plateau of Eastern Gansu

Cheng-xia ZHANG, Le-ta WA, Xiao-ming MOU, Sheng-hua CHANG

2023, 32(5):  61-70.  DOI: 10.11686/cyxb2022212

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The aim of this study was to determine the quantitative characteristics of a plant population， including different age classes， to explore how it adapts to interference by environmental factors and livestock grazing. Previous studies on the quantitative characteristics of plant population in grassland lack age-level data. In this study， we determined the quantitative characters and nutrient characteristics of a three species plant clusters （Stipa bungeana， Lespedeza davurica， and Artemisia capillaris） in the typical steppe of the Loess Plateau， and separated the plant population into different age classes. It was found that： 1） The quantitative characters of the three plants were weakly influenced in the 6^th and 11^th years by rotational grazing； 2） The three plant species were ranked， from weakest to strongest influence of grazing on the plant cluster characteristics at each age class， as follows： A. capillaris<S. bungeana and L. davurica. The plant cluster characteristics of the three plant species increased with age class in two grazing years. The crown width and base diameter of L. davurica and the crown width， base diameter， and tiller number of S. bungeana were lower in the juvenile age class than in the other age classes. 3） The phosphorus content in S. bungeana was lower in the juvenile age class than in the reproductive and presenile+senile age classes， but higher in the juvenile age class than in the older age classes of L. davurica and A. capillaris. In the three plant species， the crude protein content was lower in the presenile+senile age class than in the juvenile and reproductive age classes， while the acid detergent fiber and neutral detergent fiber contents were lower in the juvenile and reproductive age classes than in the presenile+senile age class. The contents of phosphorus， calcium， potassium， and magnesium in each age class were lower in S. bungeana than in L. davurica and A. capillaris. These results show that age classes can be effectively determined by the characteristics of tillers or branches and the “hollowing” （bald spots in the clusters） of species. The quantitative characters of these plants remained relatively stable under rotational grazing on the Loess Plateau， and the effect of livestock grazing on plant quantitative characteristics depended mainly on the age class.

Monitoring of rodent damage areas in grassland using unmanned aerial vehicle remote sensing technology

Rui HUA, Daerhan BAO, Rui DONG, Zhuang-sheng TANG, Bin CHU, Yuan-yuan HAO, Li-min HUA

2023, 32(5):  71-82.  DOI: 10.11686/cyxb2022234

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Rodent pests are the greatest and most widespread biological problem affecting pastoral land in China and their impact can reach ‘disaster’ level. Obtaining accurate data for rodent-damaged areas in grassland is a priority for evaluating the degree of pest damage and for devising pest management strategies. At present， survey grid and mapping methods are the main methods used to identify rodent-damaged areas in grassland. However， both of those methods have problems in terms of low efficiency and poor accuracy， so they do not meet the requirements for precise management of grassland pests. According to the principles of ecology and statistics， we used unmanned aerial vehicle （UAV） remote sensing technology and a stratified sampling method to detect damage areas from plateau pika， a dominant rodent pest on the Qinghai-Tibetan Plateau. These trials were conducted at four townships in Maqu County in Gansu Province. First， we selected the primary investigation area according to its suitability for rodents. Then， the first survey area was divided according to different habitat types into secondary survey plots， and each plot was divided into a grid. A certain number of quadrats in the secondary sample plots was randomly sampled， each as a three-level sample with a UAV survey. According to the average area of rodent pest damage across multiple quadrats， the damaged area in each secondary plot was calculated. The areas of damage in all the secondary plots were added to obtain the total pest-damaged area in the primary investigation area. The total area of grassland in the test area was 4.6×10⁵ ha， the area suitable for plateau pika was 2.5×10⁵ ha， and the area of plateau pika damage in the test area was 1.05×10⁴ ha. There were 50 sampling sites in total， and each site had an area of 1 ha. Taking one site as a sample， it takes one person 20 min to complete the work in terms of UAV flying and image interpretation. Compared with the grid survey method and mapping method， this new method can detect areas of rodent damage in grassland on a larger scale because it is more efficient， accurate， and cost-effective.

Effects of litter decomposition with different qualities on soil organic carbon content and its stability in grassland on the Loess Plateau

Xin GUO, Huan LUO, Xue-mei XU, Ai-xia MA, Zhen-yan SHANG, Tian-hu HAN, De-cao NIU, Hai-yan WEN, Xu-dong LI

2023, 32(5):  83-93.  DOI: 10.11686/cyxb2022349

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Plant litter is the most important source of soil organic carbon （SOC）， and the quality of litter may affect the amount and stability of newly formed SOC. In this study， we evaluated the effects of decomposition of litters of different quality （AS： Artemisia sacrorum stem， SR： Stipa bungeana root， SL： S. bungeana leaf， SAL： Sophora alopecuroides leaf）， which were selected from the typical grassland of the Loess Plateau in the middle of Gansu Province， on SOC and its stability. According to their chemical composition， litters were divided into high-quality litters （higher soluble components content and lower lignin content） and low-quality litters （lower soluble components content and higher lignin content）. The litters were co-incubated with soil to study the decomposition process and determine how it affected SOC content and stability. Compared with low-quality litters （AS and SR）， high-quality litters （SAL and SL） had a relatively higher decomposition rate due to their higher content of labile components and lower carbon/nitrogen （C/N）. After decomposition for 2 years， the SOC content had increased in each treatment. The increases in SOC and the formation efficiency of new carbon （C） were significantly higher in the high-quality litter treatments than in the low-quality litter treatments. These results indicated that， compared with low-quality litters， high-quality litters made a greater contribution to SOC sequestration after decomposition. The amounts of all soil aggregate components did not vary significantly among treatments. After decomposition for 2 years， the SOC content in <0.053 mm soil aggregates was significantly increased in all the treatments. The SOC content and efficiency of new C formation in <0.053 mm soil aggregates were significantly higher in the high-quality litter treatments than in the low-quality litter treatments. Overall， these results show that， compared with low-quality litter， high-quality litter more readily forms stable mineral-associated organic matter after decomposition.

Spatial differences in， and factors influencing， the shear strength of typical herb root-soil complexes in the Loess Plateau of China

Yu-ying CAO, Xue-meng SU, Zheng-chao ZHOU, Qun-wei ZHENG, Jia-hui YUE

2023, 32(5):  94-105.  DOI: 10.11686/cyxb2022228

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The aim of this study was to explore the spatial differences in the shear resistance of root-soil complexes of herbaceous plants on the Loess Plateau of China. Soils with three different textures were selected from three sites： From north to south， Liudaogou （sandy loam in Shenmu）， Fangta （silty loam in Ansai）， Yongshouliang （clay loam in Yongshouliang）. Lolium perenne （with a fibrous root system） and Medicago sativa （with a tap root system） were planted in pots containing these soils. The soils without plants served as controls. After 4 months， the soil physicochemical properties， root characteristics， and shear strength （cohesion and internal friction angle） of root-soil complexes in the 0-10 cm， 10-20 cm， and 20-30 cm layers were measured. It was found that： 1） Soil organic matter （SOM）， mean weight diameter （MWD）， and cohesion （c） increased after planting L. perenne and M. sativa as compared to soils without plants， but the internal friction angle （φ） was basically unchanged. The influence of plants on the soil physiochemical and shear strength decreased with depth within the soil profile， and L. perenne had stronger effects than M. sativa on the soils’ physical and physicochemical properties and shear strength. 2） From sandy loam， to silty loam， to clay loam soils， c showed an increasing trend， andthe values of root parameters and bulk density （BD） decreased. The soils were ranked， from highest to lowest SOM and MWD， as follows： clay loam>sandy loam>silty loam. The highest values ofSOM， MWD， and c were in the clay loam soil. 3） A principal component analysis showed that root characteristics contributed significantly to the shear strength of root-soil complexes in sandy loam soil， while the soil characteristics contributed significantly to the shear strength of the root-soil complexes in silty loam and clay loam soils. This multivariate evaluation of the shear strength of root-soil complexes of herbaceous plants provides basic data and a theoretical reference for further studies of soil and water conservation on the Loess Plateau of China.

Impact of the different duration years of grazing prohibition on the mechanical strength characteristics of Elymus nutans roots and its composite systems in the Yellow River source region

Wei-peng HE, Xia-song HU, Chang-yi LIU, Xuan LI, Xi-lai LI, Jiang-tao FU, Hai-jing LU, Fu-cheng YANG, Guo-rong LI

2023, 32(5):  106-117.  DOI: 10.11686/cyxb2022351

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The aim of this research was to investigate how the duration years of grazing prohibition affects the mechanical properties of Elymus nutans roots and its root-soil composite systems. The study sites were the grassland with no grazing prohibition （CK） and the grasslands with 1， 4， or 10 years of grazing prohibition in Henan County， which is located in the Yellow River source region. The researchers conducted a set of laboratory-based tests on the tensile properties of roots of E. nutans and direct shear tests on the root-soil composite systemsto quantify the effect of the duration years of grazing prohibition on the mechanical properties of soil. The results showed that a shorter period of grazing prohibition positively affected the growth of E. nutans with the increased growth index， but a longer period had the negative effect with the decreased growth index. With prolonged grazing prohibition， the tensile resistance of the roots initially increased and then decreased， with root tensile resistance increased by 15.9% after 1 year and 14.8% after 4 years of grazing prohibition. Meanwhile， the tensile strength of single roots and the cohesion of root-soil composite systems decreased gradually with prolonged grazing inhibition. The tensile strength and cohesion decreased by 57.3% and 63.5%， respectively， after 10 years of grazing prohibition compared with CK. The cohesion of root-soil composite systems was positively correlated with root diameter and soil natural density and negatively correlated with the soil moisture content. The relationship between cohesion and root content initially became stronger and then weakened with prolonged prohibition of grazing. These results provide theoretical support and practical guidance for the effective prevention and control of grassland degradation， soil erosion， and other forms of environment damage in alpine regions.

Relationship between plasticity and invasiveness in the anatomical structure of the fine roots of the invasive species Xanthium strumarium

Mei-shan CHEN, Xian CHEN, Xiao-zhen MAN, Chuang LIU, Jia-lin TONG, Bo QU

2023, 32(5):  118-126.  DOI: 10.11686/cyxb2022240

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Fine roots affect plant growth because they are an important organ for the absorption of groundwater and nitrogen. Plant growth can be supported by adjustments in the morphology and anatomy of fine roots under different environmental conditions. The great majority of invasive plants are dominant species in the community. The aim of this study was to explore whether the root anatomical structure of an invasive plant allows it to acquire more resources compared with a native species. Therefore， we compared the effects of different water and nitrogen treatments on anatomical structure between the invasive species， Xanthium strumarium， and a native species， Xanthium sibiricum. Paraffin sections were used to study various functional traits such as root diameter， cortical thickness， stele diameter， and the aerenchyma area of fine roots formed in different growth environments. The results showed that the aerenchyma area was wider in X. strumarium than in X. sibiricum. Under high-resource conditions， the root diameter of X. strumarium was smaller than that of X. sibiricum. Under sufficient nitrogen conditions， the cortex was thinner and the endodermis and xylem were smaller in X. strumarium than in X. sibiricum under excess water conditions， but under sufficient water conditions， the total xylem area was smaller in X.strumarium than in X. sibiricum. The above results indicate that the plasticity of the aerenchyma and cortical structures is a major factor affecting the anatomical structure of X.strumarium， and the plasticity of the anatomical structure of the root is relatively stable in response to a heterogeneous environment. The anatomical structural plasticity of X.strumarium confers growth advantages in various environments. Compared with X. sibiricum， X.strumarium has fine roots with more highly evolved anatomical structure and plasticity. This is an important factor in its efficient invasion strategy of high underground resource use with a low consumption cost.

Effect of planting ratio on the stability of forage yield and population density in two alfalfa-grass mixtures

Ting YE, Xiao-juan WU, Yi-xiao LU, Sheng-juan LIU, Zhuo-hui JIANG, Hui-min YANG

2023, 32(5):  127-137.  DOI: 10.11686/cyxb2022205

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The planting ratio is one of the main factors affecting the suitability and stability of mixed forage crop plantings， and it differs among different regions and areas because of differences in climate and soil conditions. In the rainfed area of the Longdong Loess Plateau of China， it is urgent to generate mixed alfalfa （Medicago sativa） forage crop plantings with an optimized combination and mixing ratio. In this study， to reveal the stability of mixed grasslands under different combinations and mixing ratios， we analyzed the dynamics of forage yield and population density in two different mixtures； alfalfa-smooth bromegrass （Bromus inermis） （MB） and alfalfa-timothy grass （Phleum pratense） （MP）. Three alfalfa∶grass planting ratios were established： 7∶3， 5∶5 and 3∶7. The controls were alfalfa only and grass only. The planting ratio significantly affected the stability of forage yield and the population density of MP and MB， and the stability of community structure decreased with grassland age. The yield of alfalfa and grass and total yield were significantly higher for MB than for MP at all ages except 2 years and 5 years. As the proportion of alfalfa increased in the two mixtures， the total forage yield initially increased and then decreased at the 2-， 4- and 5-year ages， but only increased at the 3-year age. With the increase in the proportion of alfalfa in the two types of mixture， the relative yield dissimilarity coefficient of alfalfa decreased and then increased （except for 3-year MB）， while there were inconsistent changes for the grasses. In MP， the relative population density dissimilarity coefficient of alfalfa and grass initially decreased and then increased with increasing proportions of alfalfa， and the stability of community structure was the weakest in the 5∶5 MP treatment. In MB， the relative population density dissimilarity coefficient of alfalfa and grass increased with increasing proportions of alfalfa only in the 5-year grasslands. In conclusion， compared with MP， MB can significantly increase forage yield and better maintain community stability. In the rainfed Loess Plateau area， it is recommended to establish an alfalfa-smooth bromegrass mixture with a planting ratio of 7∶3， and to replant or supply fertilizer in the fifth year.

Effect of microplastics on the growth and physiological characteristics of alfalfa （Medicago sativa）

Chao-nan LI, Lei WANG, Ji-qiang ZHOU, Chang-xing ZHAO, Xiao-rong XIE, Jin-rong LIU

2023, 32(5):  138-146.  DOI: 10.11686/cyxb2022237

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A pot experiment was conducted under controlled conditions to comprehensively understand the toxic effects and ecological risks of microplastics on the grassland agro-ecosystem. Two types of microplastics， low density polyethylene （mLDPE） and polylactic acid （mPLA）， were added to soil at five different doses （0.1%， 0.5%， 1%， 5%， 10%， w/w， dry soil weight）. The growth and physiological characteristics of alfalfa （Medicago sativa） plants growing in these treatments were evaluated and compared with those of plants in the control （no microplastics）. The results showed that a high concentration （10%） mPLA reduced the biomass， total chlorophyll content， and net photosynthetic rate of alfalfa plants， while mLDPE significantly decreased the aboveground biomass and net photosynthetic rate of alfalfa plants. The malondialdehyde （MDA） content and the activities of superoxide dismutase （SOD）， peroxidase （POD）， and catalase （CAT） increased as the dose of MPs increased. Compared with the control， the 10% mPLA treatment group showed a 67.30% higher MDA content and 56.68% and 85.63% higher activities of SOD and CAT， respectively. Among the mLDPE treatments， only the 10% dose significantly affected SOD and POD activities. The results of this study show that the toxic effect of microplastics on alfalfa is related to both the type and concentration of the microplastics. High concentrations of mPLA strongly affected alfalfa plants by damaging the photosynthetic system， decreasing plant photosynthesis， and causing oxidative damage， resulting in growth inhibition， which had a stronger influence than mLDPE.

Screening of internal reference genes of Lactobacillus strain OL77 and determination of CspP expression patterns under low-temperature and low-pH stress

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

2023, 32(5):  147-158.  DOI: 10.11686/cyxb2022183

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The aim of this study was to explore aspects of gene expression under low temperature and low pH in the cold-tolerant bacterium Pediococcus pentosaceus OL77， which was selected during low-temperature ensiling. To investigate the cold tolerance mechanism of P. pentosaceus OL77， we obtained its CspP gene by homologous cloning. GeNorm， NormFinder， BestKeeper， and RefFinder procedures were used to select internal reference genes with stable expression in OL77 under low-temperature and low-pH stress as detected using SYBR-Green real-time fluorescence quantitative PCR （RT-qPCR）. The selected internal reference genes were then used to analyze the transcriptional profile of CspP under low temperature. It was found that the relatively stably expressed internal reference genes of OL77 under low-temperature and low-pH stress were Ldh， tufa， and 6PGDH， while GAPDH and GyrA were not stably expressed. A gene fragment of CspP was obtained by homologous cloning， and its relative transcript levels in OL77 at 0， 1， 3， 6， 12 and 24 h of treatment at 25， 15 and 5 ℃ were analyzed using Ldh and 6PGDH as internal reference genes. The transient expression of CspP increased sharply under low temperature. Its transcript level was increased by 86 times at 5 ℃ compared with that at 25 ℃， suggesting that it plays roles in the cold tolerance of OL77. The cold tolerance of OL77 may result from increased expression of a cold shock protein at low temperature. Our findings suggest that CspP could be used as a cold tolerance indicator gene for OL77.

Effects of starter feed in different physical forms on the rumen transcriptome of lambs

Rui-xin YANG, Yong LI, Xiao-fang CAI, Cheng-xing HAN, Yan-li GUO

2023, 32(5):  159-170.  DOI: 10.11686/cyxb2022217

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The physical form of the starter feed can affect the rumen development of ruminants. In this study， we investigated the effects of different physical forms of starter feed on the rumen transcriptome of pre- and post-weaning lambs. The overall aim was to explore the molecular mechanism by which starter feed in different physical forms affects the rumen development of lambs. Twenty-four 8-day-old male Hu lambs with similar birth weight ［average， （5.04±0.75） kg body weight］ were randomly assigned to two groups with 12 lambs per group. Each lamb was considered to be one replicate. The two groups were assigned to one of two dietary treatments （pelleted starter， PS； and textured starter， TS）. Lambs were fed from their dams until 7 days of age and were separated from them at 8 days of age. From 8 to 35 days of age （pre-weaning）， the lambs were bottle fed with milk replacer （MR） with ad libitum access to their respective starter feed. Feeding with MR was stopped at day 35. Six lambs per treatment were euthanized pre- （21 d） or post-weaning （42 d） for sampling. The abdominal sac tissue was collected from the rumen. RNA-Seq was used for transcriptome sequencing. A total of 4478 genes were differentially expressed between the two groups. Compared with the PS group， the TS group showed 194 up-regulated genes and 293 down-regulated genes pre-weaning， and 1763 up-regulated genes and 2228 down-regulated genes post-weaning. Gene ontology （GO） annotation and Kyoto Encyclopedia of Genes and Genomes （KEGG） pathway enrichment analyses showed that the differentially expressed genes were mainly enriched in key metabolic pathways such as peptide and amino acid biosynthesis， peptide metabolism， carbohydrate metabolism， lipid metabolism， butyric acid metabolism， pyruvate metabolism， and apoptosis. According to the enrichment results， 15 differentially expressed genes were selected for verification of their expression patterns by qRT-PCR. The results obtained from the qRT-PCR analyses were consistent with those obtained from transcriptome sequencing. In conclusion， the up-regulation of genes related to fatty acid metabolism， cyclins and kinases， and growth， and down-regulation of genes related to apoptosis of the rumen epithelium of the TS group may be the important factors in promoting the rumen development of lambs.

Effects of oat hay and oat cubes on feeding behavior and production performance of Pengbo semi-fine wool sheep

Zi-fan WANG, Xiao-qing ZHANG, Zhi-ming ZHONG, Xin QUAN

2023, 32(5):  171-179.  DOI: 10.11686/cyxb2022200

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This study explored the effects feeding oat （Avena sativa） hay and oat cubes on the feeding behavior and production performance of Pengbo semi-fine wool sheep. Twelve Pengbo semi-fine wool sheep that were about 1 year old and had a similar body weight were randomly divided into two groups of six sheep （three male， three female）. One group was fed with unprocessed oat hay （OH， control）， and the other group was fed with oat cubes （OC）. Animals in the two groups were fed with a commercial concentrate at a rate of 0.10 kg·head^-1 per day in October， increasing to 0.26 kg·head^-1 per day in November. The experiment duration was 60 days， and consisted of a 10-day feed adaptation period and a 50-day formal experiment period. During the experiment， the feeding behavior， feed intake， and body weight of the two groups of sheep were measured. At the end of the experiment， all sheep were slaughtered to measure various performance indexes. The results showed that： 1） There was no significant difference in concentrate intake time between the two groups （P>0.05）， but the roughage and total feed intake time was significantly shorter in the OC group than in the OH group （P<0.001）. The feeding rate was significantly higher in the OC group （84.04%） than in the OH group （79.65%， P<0.001）. The feeding rate was significantly higher in October （85.29%） than in November （78.79%， P<0.001）. The rest time did not differ significantly between the two groups （P>0.05）， but the rumination time was longer in the OC group （581.25 min·d^-1） than in the OH group （506.67 min·d^-1； P<0.001）. The chewing rate， number of rumination boli， and rumination cycle did not differ significantly between the two groups （P>0.05）， but the number of rumination boli was significantly higher in October （558.50 No·d^-1） than in November （445.67 No·d^-1； P=0.009）. 2） Compared with the OH group， the OC group had higher intake of total dry matter， crude protein， and neutral and acid detergent fiber （P=0.001）. Season had a significant effect on the dry matter intake of the sheep （P<0.001）； for each 1 ℃ drop in air temperature， the dry matter intake of the sheep increased by 0.01 kg·d^-1 （R²=0.432， P=0.001）. 3） In terms of production performance， there was no significant difference between the two groups in the final weight， feed to weight ratio， and slaughter and carcass weights of sheep （P>0.05）， but the average daily weight gain was significantly higher in the OC group （117.50 g·d^-1） than in the OH group （98.77 g·d^-1； P=0.048）. These results showed that， compared with oat hay， oat cubes led to significantly prolonged rumination time， improved feeding efficiency， dry matter intake， and daily weight gain of Pengbo semi-fine wool sheep， although feeding with oat cubes did not significantly increase meat production. Overall， the feeding effect of oat cubes was superior to that of oat hay for these sheep.

Effects of additives on the fermentation quality and α-tocopherol and β-carotene contents in Italian ryegrass silage

Meng-qi LIANG, Qi-feng WU, Tao SHAO, Ai-li WU, Qin-hua LIU

2023, 32(5):  180-189.  DOI: 10.11686/cyxb2022354

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The objective of this study was to improve the fermentation quality of Italian ryegrass silage and inhibit the loss of α-tocopherol and β-carotene during ensilage. Italian ryegrass was ensiled without additives （CK）， or with 0.4% propionic acid （PA）， Lactobacillus plantarum B11 （LP）， Bacillus circulans 12（BC）， or the combination of LP and BC （LP+BC）. At days 3， 7， 35， and 70 after ensiling， the Italian ryegrass silage fermentation quality， nutritional quality， α-tocopherol content， and β-carotene content were evaluated. It was found that additives significantly affected the silage fermentation quality （P<0.05）. The silage fermentation quality was the highest in the LP+BC treatment， followed by the LP treatment. In the later period of ensilage， compared with CK， all treatment groups showed lower pH values， all of which were below 4.0. Compared with CK， silages fermented with LP， BC， and LP+BC showed significantly increased lactic acid content and lactic acid/acetic acid ratio （P<0.05）. The addition of PA inhibited lactic acid fermentation in the early stage of ensilage and improved the fermentation quality in the later stage， but the effect of PA was weaker than those of the other three additives. During ensiling， the α-tocopherol content was significantly higher in silages fermented with PA than in those fermented with other additives or in CK （P<0.05）. After ensiling for 35 and 70 days， except for silages fermented with PA， those fermented with LP had the highest α-tocopherol contents （P<0.05）. After ensiling for 7 days， the β-carotene contents were higher in all the treatment groups than in CK （P<0.05）， and silage fermented with LP had the highest β-carotene content at days 7 and 35 after ensiling （P<0.05）. In conclusion， the addition of LP to Italian ryegrass silage resulted in good fermentation quality， reduced α-tocopherol losses， and increased the β-carotene content.

Function of high-affinity potassium transporters in maintaining ion homeostasis and other plant responses to abiotic stresses

Xiao-han YANG, Guo-qiang WU, Ming WEI, Bei-chen WANG

2023, 32(5):  190-202.  DOI: 10.11686/cyxb2022207

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Potassium ions （K⁺）^{play an important role in plant growth and development as well as in resistance to various abiotic stresses. High-affinity K+ transporters （HKT） are one of the most important cation transporter families， and the members of this family are extensively involved in the absorption and transport of K+ and sodium ions （Na+） in plants. Many studies have shown that the expression of HKT family genes is regulated by several factors， such as calcium ions （Ca2+）， humic acid， and cytosine methylation. The HKT proteins mediate long-distance Na+ transport， maintain homeostasis of K+ and magnesium ions （Mg2+）， and play a key role in abiotic stress tolerance in plants. In this review， we summarize the results of research on the discovery of HKT family members， their structure and classification， biological function， gene expression patterns， regulatory mechanisms， and their roles in responses to abiotic stresses. We also propose directions for further research. The information in this review provides a theoretical basis and identifies genetic resources for the genetic improvement of crops to produce new， stress-resistant varieties.}

Seasonal variation in vegetation during restoration of sandy grassland at the southern edge of the Tengger desert

Jing MA, Fang-jun GUO, Zhi-hui ZOU, Lin SUN, Fang CHEN

2023, 32(5):  203-210.  DOI: 10.11686/cyxb2022210

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The dynamic changes in vegetation during the growing season reflect the most sensitive and intuitive responses of the terrestrial ecosystem to climate change. In this study， we investigated the restoration sequence of sandy grassland in shifting， semi-fixed， and fixed sandy lands at the southern edge of the Tengger desert， and compared the desert vegetation with the zonal vegetation in the adjacent desert steppe as the control. The dynamic characteristics of vegetation coverage and species diversity at different stages of the restoration process during the growing season were analyzed. The overall aims were to determine the appropriate period and quantitative indexes for the investigation and monitoring of sandy grassland， and to provide a basis for sample plot investigation， remote sensing monitoring， and the restoration and utilization of sandy grassland. It was found that the vegetation coverage and species diversity significantly differed among sandy grasslands at different stages of restoration. The average vegetation coverage of the desert steppe was close to that of fixed sandy land， and was 27.6-times and 2.3-times that of shifting and semi-fixed sandy land， respectively. The Shannon’s diversity index of vegetation on the desert steppe was 2.7-times， 1.5-times， and 1.7-times that of shifting， semi-fixed， and fixed sandy lands， respectively. The seasonal variation in sandy grassland differed in terms of magnitude and specific trends depending on the stage of restoration. The vegetation coverage， herb coverage， and species richness showed a gradually increasing trend， and the plant diversity initially decreased and then increased from shifting， to semi-fixed， to fixed sandy land sites. The best time to evaluate sandy grassland is from September to October. Shifting sandy land showed the largest seasonal variation coefficients of vegetation coverage and herb coverage， and the lowest variation coefficients of Gleason’s richness index and diversity index. The desert steppe showed the lowest seasonal variation coefficients of vegetation coverage and herb coverage， reflecting the poor stability of sandy grassland in the early stage of restoration. In conclusion， the establishment of artificial fixed-sand vegetation accelerated the restoration and succession of sandy grassland， changed its seasonal variation patterns， and enhanced its community stability. However， enclosure is also necessary to promote the restoration and succession of fixed sandy grassland to zonal desert steppe vegetation.