Table of Content

20 May 2022, Volume 31 Issue 5

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Variations in carbon flux and factors influencing it on the northern slopes of the Tianshan Mountains

Wen-zhang GUO, Chang-qing JING, Xiao-jin DENG, Chen CHEN, Wei-kang ZHAO, Zhi-xiong HOU, Gong-xin WANG

2022, 31(5):  1-12.  DOI: 10.11686/cyxb2021137

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The desert steppe is a widely distributed grassland type on the northern slopes of the Tianshan Mountains， and it plays an important role in regulating the carbon balance of the grassland ecosystem in this area. The aim of this study was to elucidate the characteristics of carbon flux in desert steppe ecosystems on the northern slopes of the Tianshan Mountains and to determine the main environmental factors that influence carbon flux. A micro-meteorological observation system and a LI-840 CO₂/H₂O infrared analyzer were used to obtain continuous observation data. The data were quantitatively analyzed to detect variations in carbon flux in the desert steppe and the factors that influence it. During the growing season， the net ecosystem carbon exchange of desert steppe vegetation on the northern slopes of the Tianshan Mountains showed an inverted “U” curve on a daily scale. On a seasonal scale， the vegetation was a carbon sink in June， July， and August； and a carbon source in September and October. The total carbon assimilation in the desert steppe from June to October was 15.50 g C·m^-2， and the highest carbon assimilation was 23.03 g C·m^-2 in August. The trend in the ecosystem respiration rate showed a “single-peak” curve on a daily scale. On a seasonal scale， carbon emissions showed a trend of increasing and then decreasing， with the highest carbon emissions of 128.42 g C·m^-2 in July. The daily variation in carbon flux in the desert steppe ecosystem was not significant in October. Photosynthetically active radiation was the main factor influencing the daily net ecosystem carbon exchange， and the relationship between these two factors fitted a rectangular hyperbola model. The daily net ecosystem carbon exchange decreased with increasing photosynthetically active radiation. The relationship between ecosystem respiration and the 5 cm soil temperature fitted the Van’t Hoff model， with a temperature sensitivity coefficient Q₁₀ of 1.69 and an optimum soil water content of 0.16 m³·m^-3. Excessively high or low soil water contents inhibited ecosystem respiration in this area.

Sensitivity analysis of WOFOST model crop parameters in different grassland types

Ge-xia QIN, Jing WU, Chun-bin LI, Shuai-jie SHEN, Huai-hai LI, Dao-han YANG, Mei-rong JIAO, Qi QI

2022, 31(5):  13-25.  DOI: 10.11686/cyxb2021391

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World Food Studies （WOFOST） is a simulation model for the quantitative analysis of the growth and production of crops. It is based on the physiological and ecological processes of crops， and can be used to predict the effects of CO₂， soil， climate， and other factors on yield. The aim of this study was to conduct a parameter sensitivity analysis for different types of grasslands （i.e.， those under different management measures and climatic conditions）. Four sites were selected in different grassland zones in Tianzhu Zangzu Autonomous County. The extended Fourier amplitude sensitivity test （EFAST） method was used to analyze the sensitivity of different parameters of grasslands in the WOFOST model under potentially productive and water-restricted conditions based on meteorological data， field sampling data， and soil data. The accuracy of the WOFOST simulations for grasslands with different degrees of coverage were evaluated by comparisons with measured data. The sensitive parameters for estimating grassland above-ground biomass （AGB） under potentially productive conditions were specific leaf area （SLATB）， light-use efficiency of a single leaf （EFFTB）， maximum leaf CO₂ assimilation rate at daily temperatures of 0 and 40 ℃ （AMAXTB）， relative maintenance respiration rate of roots （RMR）， and fraction of root and leaf system out of total dry matter （FRTB and FLTB）； and the sensitive parameters under restricted water conditions were SLATB， AMAXTB， RMR， and FLTB. The sensitive parameters for estimating leaf area index （LAI） were the same under both production levels. From emergence to 60 d after emergence， the LAI was mainly affected by SLATB， FLTB， and FRTB. From 60 to 200 d after emergence， the sensitive parameters were FLTB， FRTB， SLATB， and extinction coefficient for diffuse visible light （KDIFTB）. After the LAI began to decline， it was enhanced by KDIFTB. Compared with measured values， the simulated values of AGB were most accurate for slope meadow （R²=0.94， RMSE=11.71 g·m^-2） and least accurate for alpine meadow （R²=0.83， RMSE=32.68 g·m^-2）； and the simulated values of LAI were most accurate for temperate desert steppe （R²=0.96， RMSE=0.02） and least accurate for warm steppe （R²=0.66， RMSE=0.38）. Thus， the application of the sensitivity analysis method in the WOFOST model reduces the influence of human subjectivity and greatly shortens the parameter adjustment time.

Impacts of desertification and artificial revegetation on soil bacterial communities in alpine grassland

Ya-ni WANG, Yi-gang HU, Zeng-ru WANG, Yi-kang LI, Zhen-hua ZHANG, Hua-kun ZHOU

2022, 31(5):  26-39.  DOI: 10.11686/cyxb2021120

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Characteristics of the soil microbial communities indicate the health of grasslands and quality of the environment. To elucidate the effects of desertification and artificial revegetation on the respective soil bacterial communities， four alpine grassland types including natural grassland （NG）， desertified grassland （DG）， grass-based artificial grassland （AG） and shrub-basedartificial grassland （AS） in a small watershed of Guinan County， Qinghai Province were selected and qPCR and Illumina MiSeq high-throughput amplicon sequencing technologies were used to study the variation between the communities in bacterial biomass， diversity and structure. We also analyzed the key factors shaping soil bacterial community structure and their contributions based on variations in vegetation and soil properties. It was found that grassland desertification significantly reduced bacterial community biomass and α diversity （P<0.05）， but that bacterial community biomass could be almost restored to the level of undegraded grassland after 22 years of artificial revegetation. Desertification significantly increased the relative abundance of Gemmatimonadota， while abundance of Proteobacteriaand Planctomycetota significantly decreased （P<0.05）. Artificial revegetation promoted the succession of dominant bacteria towards the community structure found in NG， and after 22 years of artificial revegetation， most of the bacterial relative abundances paralleled those of the undegraded status. Dissimilarity in bacterial community structure was noted between NG and DG， AG and AS， community structure in AG and AS were very similar. Soil bacterial community structure significantly positively correlated with the majority of vegetation and soil physiochemical properties （P<0.05）. However， compared to soil physical （6.3%） and chemical （1.9%） properties， vegetation properties explained more variation （10.0%） in bacterial community structure. In total， the measured vegetation and soil indices explained 72.0% of variation in soil bacterial community structure， implying that vegetation and soil determine the shifts of soil bacterial community structure. Accordingly， it is essential and meaningful to strengthen vegetation and soil protection， and implement artificial revegetation in desertified grassland for protection and restoration of soil bacterial communities in Tibetan alpine grassland. However， the choice between shrub and grass planting during revegetation made little difference to the superficial soil bacterial community structure in artificial revegetation.

Effect of cutting time during the growing season on the soil bacterial community under an artificial Caragana intermedia plantation

Ying TIAN, Zhe XU, Li-zhen ZHU, Jun WANG, Xue-fei WEN

2022, 31(5):  40-50.  DOI: 10.11686/cyxb2021129

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Caragana intermedia is a shrub that plays an important role in ecological restoration in Northwest China， and cutting is an effective measure to promote its regeneration. In this study， we determined the effect of the cutting time of an artificial C. intermedia plantation on the desert steppe of Ningxia on the soil bacterial community. The artificial C. intermedia plantation was cut at seven different times： April （Y4）， May （Y5）， June （Y6）， July （Y7）， August （Y8）， September （Y9）， and October （Y10）. Soil samples were collected， and DNA extracted from the soil samples was sequenced using the Illumina Hiseq sequencing platform. The sequence data were analyzed to determine differences in soil bacterial community structure， species composition， and diversity characteristics among the treatments. The dominant phyla in soil samples were Proteobacteria， Actinobacteria， Acidobacteria， Chloroflexi. The abundance of Proteobacteria， Actinobacteria， Gemmatimonadetes， Rokubacteria， and Nitrospirae differed among the seven sampling times. The different cutting time were ranked， from highest abundance of the dominant bacterial phylum Proteobacteria to lowest， as follows： Y9>Y8>Y4>Y5>Y7>Y6>Y10. The proportion of Proteobacteria was highest in Y9 （29.74%）， and significantly higher than that in Y10 （P<0.05）， but not significantly different among the other treatments （P>0.05）. The highest relative abundance of Actinobacteria was in Y5， and was significantly higher than that in Y4， Y6， Y7， Y8， and Y9 （P<0.05）. The lowest abundance of Acidobacteria was in Y9. The treatments were ranked， from highest bacterial community abundance index to lowest， as follows： Y8>Y7>Y4>Y5>Y6>Y9>Y10. The diversity index of soil bacteria differed among treatments. Bacterial diversity was highest in Y4 and Y5， and was significantly lower in Y9 than in the other treatments （P<0.05）. Redundancy analyses showed that the main soil environmental factors affecting the distribution of the soil bacteria in different treatments were soil total phosphorus， available nitrogen， and soil organic matter. Presence of Actinobacteria and Acidimicrobiia was positively related to soil pH； presence of Alphaproteobacteria was positively related to soil organic matter； presence of Deltaproteobacteria was significantly positively correlated with soil water content and total potassium； and Gammaproteobacteria and Gemmatimonadetes were positively correlated with soil organic matter， available nitrogen， and total phosphorus. Thus， the cutting time significantly affected the soil bacterial community structure. The dominant bacterial community in the soil was richly distributed and the nutrient content in soils was higher when C. intermedia was cut in April-August， the vigorous growth period， than when it was cut in September-October. These results have practical significance for maintaining ecological benefits and developing Caragana forage.

Effects of silicon on biomass allocation and uptake and utilization of nitrogen， phosphorus， and potassium in two tall fescue （Festuca arundinacea） cultivars under different salinity conditions

Wen-rui CHEN, Zhao JIANG, Qi-xin ZHOU, Yun-qin WANG, column:LI Chun-ming, Peng-hui GUO, Hui-xia LIU

2022, 31(5):  51-60.  DOI: 10.11686/cyxb2021121

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In many areas where tall fescue is cultivated， soils are salinized or may become salinized because of frequent irrigation. The application of silicon （Si） can improve the salt tolerance of plants by reducing the absorption of sodium and increasing the absorption of nitrogen， phosphorus， and potassium， although the extent to which Si improves salt tolerance varies among plant species and varieties. In this study， pot experiments were conducted to investigate the effects of Si application on the biomass of two tall fescue （Festuca arundinacea） cultivars （K31 and XD） under salt stress and on the N， P， K⁺， and Na⁺ concentrations in their shoots and roots. The two cultivars differed in their salt tolerance； K31 was salt-sensitive while XD was highly salt-resistant. The two cultivars were grown in a mixture of vermiculite and perlite with a range of salinities. As the salinity increased， the shoot and root biomass decreased， the N， P， and K⁺ concentrations in the shoots and roots of the two cultivars decreased， and the Na⁺ concentrations increased. These negative effects of salinity were ameliorated by Si， and to a greater extent in the salt-tolerant cultivar than in the salt-sensitive cultivar. The application of Si increased shoot and root biomass， the root∶shoot， N， P， K⁺ concentrations， and the K⁺∶Na⁺， and decreased Na⁺ concentrations in the shoots and roots of both tall fescue cultivars in medium- and low-salinity treatments. However， Si application did not affect these parameters in the high-salinity treatments because the salinity level exceeded the degree of salt tolerance and Si was not able to regulate plant responses. The application of Si had a similar effect on shoot and root biomass and on Na⁺ and P concentrations in the two cultivars， but different effects on K⁺ and N concentrations. The beneficial effects of Si on K⁺ and N concentrations in shoots of salt-stressed plants were stronger in the salt-tolerant cultivar XD than in the salt-sensitive cultivar K31. These results indicate that Si can promote the growth of tall fescue under low and medium salinities， and is especially effective for salt-tolerant tall fescue cultivars.

The effect of mixed sowing and sowing rate of different alfalfa varieties on the yield and quality of forage

Man-you LI, Dong-ning LI, Bin WANG, Xiao-yun LI, Xiao-tian SHEN, Li-juan CAO, Wang NI, Teng-fei WANG, Jian LAN

2022, 31(5):  61-75.  DOI: 10.11686/cyxb2021109

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This research investigated the effect of planting pattern and sowing rate on the yield and quality of alfalfa （Medicago sativa） from 2017-2019 under drip irrigation conditions in arid areas. Alfalfa varieties ‘Magna Graze Ⅶ’ （also known as ‘Magnum Ⅶ’） and ‘Sanditi’ were sown as pure stands， mixed within rows or mixed in alternate rows and there were three sowing rates （13.5， 18.0， 22.5 kg·ha^-1） making up a two-factor randomized complete block design. Data were subjected to multivariate evaluation by principal component analysis （PCA）， in order to identify the optimum planting pattern and sowing rate for alfalfa. It was found that the planting pattern and sowing rate had significant （P<0.05） effects on the average plant height， number of primary branches， hay yield， crude ash， neutral detergent fiber content and relative feeding value of alfalfa over the 2017 to 2019 investigation period. There were no significant effects on herbage dry matter percentage， leaf∶stem ratio， acid detergent fiber content and crude protein content. Among the treatments， Magnum Ⅶ and Sanditi mixed within rows and sown at 18.0 kg·ha^-1 had an alfalfa hay yield （16.79 t·ha^-1） significantly higher than other treatments. The lowest hay yield （14.25 t·ha^-1） was obtained with Magnum Ⅶ and Sanditi were sown in alternate rows at 22.5 kg·ha^-1. The relative feeding value of alfalfa when Magnum Ⅶ and Sanditi were mixed within rows at a sowing rate of 18.0 kg·ha^-1 was 156.87， and was second only to mixed sowing of the two varieties within rows at a rate of 13.5 kg·ha^-1. Analysis by PCA indicated the planting of Magnum Ⅶ and Sanditi mixed within rows at a sowing rate of 18.0 kg·ha^-1 as having the best overall performance. This planting pattern and rate can be recommended for adoption by growers in the Ningxia Yellow River irrigation district.

Effects of foliar spray with various bioactive compounds on seed number and seed weight of Chinese milk vetch （Astragalus sinicus）

Chun-zeng LIU, Chun-feng ZHENG, Liang-peng NIE, Lin ZHANG, Ji-shi ZHANG, Yu-hu LV, Ben-yin LI, Wei-dong CAO

2022, 31(5):  76-83.  DOI: 10.11686/cyxb2021099

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The effects of various foliar sprays on Chinese milk vetch （Astragalus sinicus cv. Xinzi-1） seed number and seed weight at the squaring stage were studied in order to provide reference information for improving yield through use of chemical regulators. Foliar spraying of paclobutrazol （PP₃₃₃）， 6-benzylaminopurine （6-BA）， brassinolide （BR）， alginate oligosaccharides （AOS） and compound nutrition preparation （NCD） were performed at the squaring stage， while spraying water as the control. At the flowering and harvest stages， the seed setting was investigated for inflorescences at the basal， central， and apical inflorescence positions on the main stem. It was found that， compared with the water control， the various spray treatments improved the pod and seed setting rates in the examined inflorescence positions at flowering， and improved the seed number and seed weight in those inflorescence positions at harvest. NCD was the best treatment； the seed number at the basal， central and apical inflorescence positions was increased by 27.79%， 29.35% and 71.25%， respectively， and the seed weight at the same positions was increased by 27.18%， 28.65% and 71.05%， respectively， compared with the control. The seed yields under NCD， PP₃₃₃， BR， 6-BA and AOS treatments were significantly higher than those of the control， with increases of 29.73%， 22.02%， 19.02%， 10.52% and 10.01%， respectively. The seed yield under NCD treatment was the highest， and was 601.37 kg·ha^-1. Among the treatments， PP₃₃₃ and 6-BA treatments induced significant increases in seed number， but no obvious effect on seed weight， while the BR and AOS treatments induced significant increases in seed weight， but not seed number. The NCD treatment induced significant effects both on seed number and seed weight. In summary， foliar spray of plant regulators at squaring stage significantly promoted increased seed yield and the NCD treatment has the greatest effect， followed by PP₃₃₃， BR， 6-BA and AOS.

Reproductive success and phenotypic selection on floral traits of Salvia digitaloides under different pollination conditions

Bo ZHANG, Shu-fan SUN

2022, 31(5):  84-91.  DOI: 10.11686/cyxb2021404

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The reproduction of plants is generally pollen-limited in natural populations. The theory of phenotypic selection suggests that pollinator-mediated selection occurs when the degree of pollen limitation varies among individuals within a plant population. In this study， we explored aspects of floral adaptation and selection mechanisms in Salvia digitaloides by comparing the differences in reproductive success and selection of floral traits under different pollination conditions. The main results were as follows： 1） The reproductive efficiency of plants （i.e.， fruit set and number of seeds set per flower） was significantly negatively correlated with the height of the stigma in flowers under open pollination （P<0.05）， but significantly negatively correlated with flower production under supplementary hand pollination. The number of seeds set per flower was negatively correlated with style exsertion under supplementary hand pollination （P=0.031）. 2） The extent of the decrease in the number of seeds set per flower due to pollen limitation under open pollination was negatively correlated with both flower production and style exsertion （P=0.006， 0.041）. 3） Under both open and supplementary hand pollination， flower production was subject to significant directional selection， but the selection intensity was much lower under supplementary hand pollination than under open pollination. There was significant negative directional selection for stigma height under open pollination， and for style exsertion under supplementary hand pollination. There was positive correlational selection for the combination of corolla entrance size and style exsertion. Together， the results show that the floral traits of S. digitaloides are subject to significant pollinator-mediated selection， with the floral structural traits showing a trend of functional integration for the improvement of pollination efficiency.

A preliminary study on substances that inhibit germination in the seeds of Agropyron mongolicum

Jin-tian YU, Jing WANG, Bing-zhe FU, Xue-qin GAO

2022, 31(5):  92-102.  DOI: 10.11686/cyxb2021141

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Agropyron mongolicum， commonly known as Mongolian wheatgrass， is one of the main plants in desert steppe and typical steppe vegetation in sandy land. It has excellent characteristics of resistance to drought， cold， disease， salt， and alkali. However， the seeds of A. mongolicum retain some wild characteristics such as a low germination rate and a long duration of germination. This affects the artificial seed reproduction， production， and utilization of A. mongolicum. To explore the dormancy mechanism of A. mongolicum seeds， the seed husks were extracted with five different solvents （petroleum ether， ether， ethyl acetate， methanol， acetone， and pure water） and the inhibitory effects of the extracts on seed germination of Brassica pekinensis （cabbage） were evaluated. In addition， gas chromatography-mass spectrometry （GC-MS） analyses were conducted to determine the types of compounds in the extracts. The five extracts from the husks of A. mongolicum seeds inhibited the germination rate， root length， and seedling height of cabbage to different degrees. Among the five types of extracts， the water extract had the strongest inhibitory effect， followed by the ethyl acetate extract and then the methanol extract. In the GC-MS analyses， 32 kinds of organic substances in nine classes （alkanes， alcohols， esters， ketones， benzenes， amides， acetals， acids， and phenols） were detected in the extracts of A. mongolicum. Most of those substances were water soluble， and the most abundant substances were alcohols， ketones and alkanes. Therefore， one of the main reasons for the dormancy of A. mongolicum seeds is the presence of inhibitors such as alcohols， ketones， and alkanes in the husks. The results of this study will be useful for developing methods to break the dormancy of A. mongolicum seeds.

Screening and identification of low temperature tolerant lactic acid bacterial epiphytes from oats on the Qinghai-Tibetan Plateau

Dou-dou LIN, Ze-liang JU, Ji-kuan CHAI, Gui-qin ZHAO

2022, 31(5):  103-114.  DOI: 10.11686/cyxb2021358

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This research aimed to identify potential lactic acid bacteria （LAB） strains that provide improved fermentation quality of oat （Avena sativa） silage under low temperature. Epiphytic LAB were collected from oat plants at different altitudes on the Qinghai-Tibetan Plateau. Cold tolerant strains were screened by restricted culture， and their acid and salinity tolerance， acid production and growth rate were compared. These strains were identified by means of 16S rDNA sequence analysis. In the initial isolation 232 strains of lactic acid bacteria were isolated， and 56 of these were retained for further screening after Gram’s stain testing， microscopy and a catalase test. Low temperature screening revealed 18 low-temperature tolerant strains. These could grow at temperatures of 5-20 ℃， 3.0% and 6.0% NaCl， and pH 3.0-5.0. Among these 18 strains， 14 were homofermentative and 4 strains were heterofermentative. For the 14 homofermentative LAB strains， strains designated OCPP₃， OL₃， OL₈， OL₂₅， OL₃₆， OL₅₄， OL₇₇ and OL₁₂₂ had higher acid production and growth rate than others. OCPP₃， OL₃₆ and OL₇₇ were identified as Pediococcus pentosaceus， OL₃ and OL₅₄ as Lactobacillus pentosus， and OL₈， OL₂₅ and OL₁₂₂ as Lactobacillus plantarum. After culturing for 25 h， the optical density （OD） value of strain OL₇₇ （2.52） was the highest among all cultured strains， followed by OL₅₄ （2.50）. Considering the observed low temperature tolerance， acid production and growth rate， and their diversity， these three LAB strains show promise as potential additives for oat silage fermentation at low temperature on the Qinghai-Tibetan Plateau.

Effects of mycorrhiza on nutrient release during fine root decomposition in degraded sandy grassland

Jie-ping DING, Yong-qing LUO, Wei-chun LIU, Fei WEN, Li-long WANG, Xu-yang WANG, Yu-long DUAN, Jie LIAN

2022, 31(5):  115-123.  DOI: 10.11686/cyxb2021375

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The release of nutrients during the decomposition of fine roots is the key process in the circulation of materials in soils in low-vegetation areas， but the role of mycorrhiza in this process is unclear. In this study， we explored the dynamics of nutrient （nitrogen， phosphorus， potassium） release during the fine root decomposition of Artemisia halodendron， a pioneer shrub during vegetation restoration in degraded sandy grassland. The in-growth core method was used to collect samples from two treatments （living fine roots+mycorrhiza， and mycorrhiza only） and a root-free control. We found that mycorrhiza affected the nutrient contents of A. halodendron fine root litter during decomposition， with the strongest effect at the later stage of the decomposition period （after 1 year）. When the decomposition period was longer than 1 year， mycorrhiza significantly reduced the N content of fine root litter， and this was not affected by presence of living fine roots. The N content of litter in the mycorrhiza+living fine roots and mycorrhiza treatments was 15.3% and 9.5% lower， respectively， than that of litter in the control. The P and K contents in fine root litter were significantly lower in the mycorrhiza treatment than in the control after 1 year of decomposition （P<0.05）， but this effect was weakened by the presence of living fine roots. The P and K contents did not differ significantly between the living fine roots+mycorrhiza treatment and the control （P>0.05）. Analyses of the dynamics of nutrients remaining in the litter showed that the mycorrhiza significantly promoted N release during decomposition （P<0.05）， and this promoting effect mainly occurred in the middle stage of decomposition. For the release of P and K， the promoting effect of mycorrhiza was mainly at the late stage of decomposition， and the effect was weakened by the presence of living fine roots. These results indicate that mycorrhiza affect nutrient release during fine root decomposition， and should be paid more attention in research on root decomposition and its relationship with the turnover of materials in soil.

Expression pattern and biological functions of an annexin encoding gene MtANN2 in Medicago truncatula under salt stress

Ya-nan LIU, Ren-jie YU, Yan-li GAO, Jun-mei KANG, Qing-chuan YANG, Zhi-hai WU, Zhen WANG

2022, 31(5):  124-134.  DOI: 10.11686/cyxb2021087

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Annexins are a conserved， multi-member protein family. They are present in eukaryotes and participate in diverse stress-related biological processes by binding membrane phospholipids in a Ca²⁺-dependent way. Most studies of annexins have focused on vertebrates although the first plant annexin was reported early in 1989 from tomato （Lycopersicon esculentum）. To date， information on annexins in legumes， particularly forage legumes， is scarce. In this study， the phylogeny of annexins in Arabidopsis thaliana， Medicago truncatula and Medicago sativa， was analyzed. We then focused on investigating the expression pattern and biological functions of MtANN2 in root development and salt response. Quantitative RT-PCR demonstrated that MtANN2 was abundantly expressed in roots and was NaCl-inducible. RNA in situ hybridization showed a predominant expression of MtANN2 in the lateral root primordia. The loss-of-function mutantof AtANN2， the closest homolog of MtANN2 in Arabidopsis， displayed pleiotropic morphological abnormalities including dwarfism with fewer lateral roots and lower fresh weight， and the homozygous atann2 plants were hypersensitive to the salt treatment （100 mmol·L^-1）. The transgenic atann2 plants ectopically expressed MtANN2 were reminiscent of the wild type with similar fresh weight and the lateral root density between atann2 and Col-0. The results indicated that MtANN2 partly rescued the defects of atann2. Under the NaCl treatment， the germination rate and growth of the transgenic lines were similar to those of the wild type. Our molecular results suggest that MtANN2 is involved in root growth and salt response， and that the increase level of MtANN2 improves salt tolerance. Therefore， MtANN2 may serve as a potential target for breeding alfalfa tolerant to high salinity using the molecular approaches.

The role of a cytokinin signaling pathway type-B ARR transcription factor， LpARR10， in cadmium tolerance of perennial ryegrass

Qing ZHANG, Jing XING, Jia-ming YAO, Ting-chao YIN, Xin-ru HUANG, Yue HE, Jing ZHANG, Bin XU

2022, 31(5):  135-143.  DOI: 10.11686/cyxb2021097

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Cadmium （Cd） is one of the major elements causing heavy metal pollution in mining areas that can severely inhibit plant growth and development. It is known that cytokinin （CTK） can enhance plant Cd tolerance， but its underlying mechanism is still unclear. In this study， a CTK signal pathway gene， LpARR10， was cloned in perennial ryegrass that has six exons and encodes 598 amino acids. Evolutionary analysis indicated that LpARR10was clustered together with the Arabidopsis B-type ARR transcription factors （B-ARRs） and closely related to AtARR10 and AtARR12. Protein sequence analysis demonstrated that LpARR10 has typical functional domains of B-ARRs featured with a phosphate receptor domain， phosphorylation sites， and metal ion binding sites. Expression analysis showed that both CTK （25 μmol·L^-1 6-BA） and Cd （200 μmol·L^-1 CdCl₂） significantly promoted the transcription of LpARR10 in roots of perennial ryegrass after 0.5， 2， 6， 12， 24 and 48 h of treatment and in leaves after 2 and 6 h. When grown in MS medium， there was no significant difference in root length and fresh weight between transgenic lines and wild type plants. However， the root length and fresh weight of the transgenic lines were significantly higher than those of the wild type plants when grown in MS medium with Cd （180 μmol·L^-1 CdCl₂）. In conclusion， LpARR10 plays an important role in cytokinin-regulated plant Cd tolerance.

Vegetation community structure and diversity in a burned area of Picea asperata-Abies fabri forest on different aspects on the northeastern margin of the Qinghai-Tibetan Plateau

Xiao-lei ZHOU, Yue-e YAN, Jing ZHANG, Xu-jiao ZHOU, Yong-qin YAN, Fu-qiang YANG, Xue-ping CAO, An ZHAO, Yan-li ZHAO, Jing-yi SU

2022, 31(5):  144-155.  DOI: 10.11686/cyxb2021372

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In this study， we conducted field surveys to determine the composition and diversity of the plant community in a burned area of Picea asperata-Abies fabri forest on the northeastern margin of the Qinghai-Tibetan Plateau. Non-metric multidimensional scaling methods were used to analyze the data. Twenty-two families， 40 genera， and 46 species were identified in the burned areas. The dominant families were Compositae （11）， Ranunculaceae （6）， Apiaceae （4）， Polygonaceae （3）， Rubiaceae （2）， Gentianaceae （2）， Rosaceae （2）， and Caprifoliaceae （2）. Different communities were distributed on slopes with different aspects： a Cystopteris montana+Carex crebra+Ligularia botryodes community on the north-facing （N） slope， a C. crebra+C. montana+Fragaria vesca community on the northwest-facing slope， a C. crebra+ F. vesca+Fargesia spathacea community on the northeast-facing slope， and a C. crebra+F. vesca+L. botryodes community on the east-facing （E） slope. The community on the N slope had the highest Margalef’s richness index and Shannon-Wiener diversity values， while the community on E slopes had the highest Simpson’s dominance index. There were no significant differences in Pielou’s evenness index of vegetation among the four different slopes. A gradient distribution pattern of vegetation existed on the different slopes， and there was some overlap among community distributions. The extent of vegetation cover decreased from the cloudy slope （N） to the semi-sunny slope （E）. The slopes were ranked， from highest values of Margalef’s richness index and Shannon-Wiener diversity index to lowest， as follows： N>NW>NE>E.

The arthropod community structure in Reaumuria soongorica litter at the early stage of its decomposition in arid and semi-arid regions

Jia-yu JIANG, Xue LIAN, Xi-ming TANG, Ren-tao LIU, An-ning ZHANG

2022, 31(5):  156-168.  DOI: 10.11686/cyxb2021105

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Two desertified grasslands in semi-arid Yanchi County of Ningxia and in arid Urat Rear Banner of Inner Mongolia were selected as sites to study litter decomposition of Reaumuria soongorica. Litter bags were set up between shrub microhabitats beneath the shrub canopy and in the open spaces. The litter arthropod community composition and diversity were investigated， as well as the litter chemical composition and soil conditions. The objective of the present study was to explore the differences in litter arthropod community composition and diversity between shrub microhabitats in semi-arid Yanchi County and a more arid Urat site. It was found that： 1） There were 3 dominant taxa of litter arthropods beneath shrub canopy and 2 dominant taxa in the open spaces in semi-arid Yanchi； there were 3 dominant taxa in both microhabitats in arid Urat. There were 7 commonly occurring taxa beneath shrub canopy， and 3 found in the open spaces in semi-arid Yanchi； while there were 7 commonly occurring taxa beneath shrub canopy and 4 in the open spaces in arid Urat. Rare species were found in the open spaces only in semi-arid Yanchi， and beneath shrub canopy only， in arid Urat. 2） The abundance and species richness of litter arthropods was found to be significantly higher in the open spaces than beneath shrub canopy in semi-arid Yanchi， but followed the reverse distribution in arid Urat （P<0.05）. There were no significant differences in Shannon-Wiener index， Simpson index， Margalef index， and Pielou index between the two shrub microhabitats at either of the study sites. 3） The abundance of litter arthropods was found to be positively correlated with soil pH and negatively correlated with soil sand content. Species richness was negatively correlated with soil sand content in semi-arid Yanchi only （P<0.05）. The abundance of litter arthropods and species richness were uncorrelated with environmental factors in the arid area of Urat Rear Banner （P>0.05）. From the results of redundancy analysis and partial redundancy analysis showed that litter K content of litter was the main factor driving the distribution of litter arthropods in arid and semi-arid areas. In conclusion， both shrub microhabitats and climatic factors affected the abundance and group richness of litter deposition， while there was little effect on litter arthropod diversity. With increased aridity， there was a transition from an ‘overflow’ effect towards a ‘facilitative’ effect of shrubs on the distribution of litter arthropod abundance and species richness.

Effects of different concentrate supplement levels on rumen fermentation and microbial community structure of grazing yaks in the warm season

Dong-wen DAI, Kai-yue Pang, xun WANG, Ying-kui YANG, Sha-tuo CHAI, Shu-xiang WANG

2022, 31(5):  169-177.  DOI: 10.11686/cyxb2021091

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The aim of this research was to investigate the effects of different concentrate supplement levels on rumen fermentation and the rumen microbial community structure of grazing yaks in the warm season. Forty-eight male yaks with good body condition and similar body weight were randomly assigned to four groups （n=12）. Yaks in the control group were only grazed， while the three supplement groups received 0.5 （Ⅰ）， 1.5 （Ⅱ）， and 2.5 kg·d^-1 （Ⅲ） of concentrate， respectively. There was a 10-day pre-test period and the experimental period lasted 60 days. The experiment results showed that： 1） As concentrate supplementation level increased， the concentration of ruminal fluid total volatile fatty acids， propionic acid， butyric acid， isobutyric acid， valeric acid and isovaleric acid increased quadratically （P<0.05）， while ruminal pH， concentration of acetic acid and the acetic∶propionic acid ratio decreased quadratically （P<0.05） and the concentration of microbial protein in supplement groups Ⅱ and Ⅲ were significantly higher than those in the other two groups. 2） In total， 3138 operational taxonomic units （OTUs） were detected， and 1337 of those OTUs （42.61% of the total OTUs） were shared by all four treatment groups. The control treatment had 183 unique OTUs， while group Ⅲ had 106 unique OTUs. The number of microbial species， Chao1 index and Shannon index decreased with increasing concentrate supplementation level （P<0.05）. 3） At the phylum level， with increasing concentrate supplementation level， the relative abundance of Bacteroidetes increased quadratically （P<0.05）， while the relative abundance of Firmicutes decreased quadratically （P<0.05） and the relative abundance of Actinobacteria increased linearly （P<0.05）. At the genus level， with increased concentrate supplementation level， the relative abundances of Prevotella_1， Christensenellaceae_R-7 and Prevotellaceae_UCG-001 increased quadratically （P<0.05）， while relative abundance of Succiniclasticum andRuminococcaceae_UCG-005 decreased quadratically （P<0.05）. In conclusion， increasing the level of concentrate supplementation promoted rumen fermentation and increased the abundance of the some starch-degrading bacteria of grazing yaks in the warm season.

Effect of a Chinese medicine formula on the performance and physiological and blood biochemical parameters of hybrid Small-Tail Han sheep under heat stress

Juan-juan ZHAO, Da-lu CHE, Wei-ting GUO, Wei-tao ZHANG, Lian-chao LIU, Li-chen ZHAO, Yu-hong GAO, Xin-sheng SUN, Xue-mei LI, Yuan WANG

2022, 31(5):  178-189.  DOI: 10.11686/cyxb2021128

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Fattening sheep often suffer from heat stress. The objective of this study was to investigate the effects of a traditional Chinese medicine formula on the production performance， physiological parameters， and blood biochemical parameters of hybrid sheep （Small-Tail Han sheep×Inner Mongolian Fine Wool sheep） under heat stress. Four Chinese herbal medicines： Elsholtzia ciliata， Rheum palmatum， Magnolia officinalis， and Scutellaria baicalensis， were mixed at a ratio of 3∶3∶2∶2. The experiment included 240 hybrid late-sheep （average weight， 36.6±0.73 kg）， which were randomly assigned to four groups： the control （no formula） and three formula-fed groups （diets containing 0.5%， 1.0%， or 1.5% of the formula on a dry matter basis）. Each treatment group consisted of 60 sheep. The experiment lasted for 28 days， during which the temperature and humidity index in the shed averaged 79.68. The main results were as follows： 1） Compared with the control group， the formula-fed groups showed a significantly lower respiratory rate （P<0.05） and more time lying， particularly in the period from 12：00 to 16：00. The proportion of time lying was 13.38% to 19.15% higher in the formula-fed groups than in the control group. 2） In terms of production performance， the average daily feed intake was 1.05% to 7.21% higher in the three formula-fed groups than in the control （P<0.05）， and the average daily gain （ADG） was also significantly higher in the formula-fed groups than in the control （P<0.05）. Among the three formula-fed groups， the 0.5% formula group showed the highest ADG （12.12% higher than that of the control） and lowest feed-to-weight ratio （F/G） （14.68% lower than that of the control） （P<0.05）. 3） The sheep in the formula-fed groups showed increased thyroxine （T₄） levels and decreased cortisol （COR） levels， compared with those in the control （P<0.05）. In the 0.5% formula group， the T₄ concentration was 13.97% higher than that in the control （P<0.05）， and the COR concentration was 33.15% lower than that in the control （P<0.05）. There were significant differences （P<0.05） in urea nitrogen （BUN） and glucose （GLU） concentrations in serum between all the groups. Compared with the control group， the 0.5% formula group showed higher GLU （P<0.01） and lower BUN （P<0.05） concentrations in serum. 4） An economic benefit analysis showed that the benefit from weight gain increased by 7.50% to 13.91% as the dietary intake of the formula increased from 0.5% to 1.5%， and the largest net benefit was in the 0.5% formula group （4.85 yuan·d^-1·sheep^-1）. In summary， this Chinese medicine formula effectively alleviated heat stress in hybrid Small-Tail Han sheep， and its inclusion at 0.5% of the diet had the best results.

Progress in research on tall wheatgrass as a salt-alkali tolerant forage grass

Hong-wei LI, Qi ZHENG, Bin LI, Mao-lin ZHAO, Zhen-sheng LI

2022, 31(5):  190-199.  DOI: 10.11686/cyxb2021384

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Tall wheatgrass （Elytrigia elongata） is a perennial cool season forage grass that is tolerant to salt-alkali， waterlogging， and drought. It has been cultivated for more than half a century in the United States， Canada， Australia， and other countries. It has also been used as a distant hybridization parent for wheat genetic improvement in China since 1954. Although some tall wheatgrass varieties were introduced and grown as forage and sand-stabilizing plants in North China during the 1980s-1990s， it has not been cultivated as widely in China as in other countries. More than 10 varieties were certified and released in the United States， Canada， Australia， and other countries. However， no tall wheatgrass variety was certified and released in China currently. Li Zhen-sheng’s group has studied tall wheatgrass cultivated in Beijing， Caofeidian， Nanpi， Haixing， and Dongying， China for 8 years， and found that it grows well and is highly productive in saline and alkaline soils. On the basis of those findings， Li proposed a new concept of a “coastal grass belt”， wherein salt-alkali tolerant forage grass could be grown in coastal areas with saline and alkaline soils. There are 667000 hectares of saline and alkaline soils where it is unprofitable to grow cereal crops in the coastal Circum-Bohai sea region in China. In such areas， the cultivation of perennial forage grasses such as tall wheatgrass would not only meet the increasing local demands for hay， pasture， and silage， but also minimize soil erosion and salinization. However， the paucity of tall wheatgrass varieties and limited knowledge of cultivation techniques are major challenges. These issues must be addressed before tall wheatgrass can be used to create a “coastal grass belt” in China. Here， we review the results of studies on its tolerance to salt， drought， and waterlogging， and on forage quality， cultivars， and cultivation techniques. We also discuss the progress to date in using tall wheatgrass to create a “coastal grass belt”.

Determination of the nutrient digestibility of herbage consumed by grazing animals

You-shun JIN, Fu-jiang HOU

2022, 31(5):  200-212.  DOI: 10.11686/cyxb2021089

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Nutrient digestibility of herbage consumed by grazing livestock is one of the key indicators for grassland management， and is a function of both the biomass and nutritional quality of forage， and the health and production status of livestock. Nutrient digestibility of forage consumed by grazing livestock can be determined by direct or indirect methods. The direct methods include， among others， the total feces collection method， the indigestible marker method and near infrared spectroscopy （NIRS）. The indirect methods include in vivo or in vitro fermentation digestibility determinations， the forage quality prediction method and the climate prediction method. The total fecal collection method is a comparatively accurate method， provided that the feed dry matter intake and feces dry weight are accurately determined. However， it is time-consuming and laborious， and has a great impact on the grazing behavior. Moreover， it is difficult to reflect the spatial heterogeneity of forage supply in the pasture. The indigestible marker method estimates the nutrient digestibility according to the proportion of indigestible matter recovered and causes little disturbance to the grazing behavior of livestock. However， it is not easy to analyze for the indigestible marker， and the method is not suitable for wild grazing animals. The NIRS method has high efficiency， low labor intensity， low cost， and does not have any effects on livestock， so it can estimate the nutrient digestibility of forage consumed by grazing livestock on a large scale. However， NIRS requires a lot of directly measured calibration data to improve the prediction accuracy. The climate estimation method is fast， and therefore time-saving but is also less accurate. Climate estimation is therefore suitable for large spatial and temporal scales. The nutrient digestibility of forage consumed by grazing livestock is closely related to biological factors， environmental factors and social factors such as livestock class， grassland type， grazing methods employed， temperature and precipitation. Combined with remote sensing， unmanned aerial vehicle methods and artificial intelligence， the nutrient digestibility of forage consumed by grazing livestock can be accurately and quickly measured， providing support for grassland ecological restoration and livestock health and management.