Table of Content

20 October 2023, Volume 32 Issue 10

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An evaluation of a remote sensing method based on optimized triangular vegetation index （TVI） for aboveground shrub biomass estimation in shrub-encroached grassland

Zheng-yong XU, Bin SUN, Wang-fei ZHANG, Yi-fu LI, Zi-yu YAN, Wei YUE, Si-han TENG

2023, 32(10):  1-14.  DOI: 10.11686/cyxb2022488

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Shrub-encroachment onto grassland is becoming an important ecological problem in grassland ecosystems， and accurate estimation of the shrub above-ground biomass （AGB） in shrub-encroached grassland vegetation plays a significant role in research into regional ecosystem carbon cycles. Due to the dual effects of soil background noise and differences in vegetation growth structure characteristics， the traditional vegetation indices are extremely unstable for model-building involving shrub-encroached grassland AGB estimation. To solve this problem， in this study we developed a novel way by optimizing the triangular vegetation index （TVI） using Sentinel-2 remote sensing data for shrub-encroached grassland AGB estimation. The results showed that： 1） In the area dominated by herbaceous vegetation， TVI calculated using a combination of green， red-edge and near-infrared （R_{\mathrm{560}}， R_{\mathrm{705}} and R_{\mathrm{865}}） performed best with an R² of 0.684； in the area dominated by shrub vegetation， the TVI again performed best with R²= 0.368. 2） When analyzing the sensitivity of the 12 commonly used vegetation indexes to soil noise， the enhanced vegetation index （EVI） was the most sensitive to soil noise in the area dominated by herbaceous vegetation； in the area dominated by shrub vegetation， the modified soil adjusted vegetation index （MSAVI） was the most sensitive. 3） In the area dominated by herbaceous vegetation， the optimized vegetation index grassland triangular vegetation index （GTVI） performed better than TVI with the value of R_{\mathrm{C}\mathrm{V}}^{\mathrm{2}} （coefficient of determination cross validation） increased by 0.153 and the value of RMS{E}_{\mathrm{C}\mathrm{V}} decreased by 12.222 g·m^-2； in the area dominated by shrub vegetation， GTVI performed better than TVI and the R_{\mathrm{C}\mathrm{V}}^{\mathrm{2}} value increased 0.029， while the RMS{E}_{\mathrm{C}\mathrm{V}} （root mean square error cross validation） decreased 1.684 g·m^-2. 4） The estimation results acquired by GTVI showed the highest accuracy when compared with the results estimated by the commonly used 12 vegetation indices. The results of this study are expected to provide a scientific basis and reference AGB estimation in shrub-encroached grassland using vegetation indices extracted from remote sensing data.

Response of soil organic phosphorus mineralization to alpine meadow degradation and temperature

Hong-yu QIAN, Yu-lin PU, Shan-xin LANG, Yi-ran LI, Nan-ding ZHOU

2023, 32(10):  15-27.  DOI: 10.11686/cyxb2022469

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Clarification of the mineralization characteristics of organic phosphorus in degraded grassland soils at different temperatures can provide basic data and a theoretical framework for the scientific management of soil phosphorus nutrients during the ecological recovery of degraded grassland. In this research， an aerobic culture method at constant temperature and humidity was used to investigate the mineralization characteristics and temperature responses of organic phosphorus in non-degraded （ND） meadow， and lightly degraded （LD）， moderately degraded （MD） and heavily degraded （HD） soils on the Zoige Plateau. It was found that the mineralization rate of organic phosphorus showed no obvious change in the early stage （0-30 d）， increased rapidly in the middle stage （30-60 d）， and gradually stabilized in the late stage （60-120 d） when the four types of meadow soils were cultured at 5-15 ℃. Meadow degradation had no significant effect on soil organic phosphorus mineralization at low temperature （5-10 ℃）. However， soil organic phosphorus mineralization was significantly reduced in MD and HD soils at high temperature （≥15 ℃）. Compared with ND， the net mineralization rate of organic phosphorus in MD and HD soils decreased by 52.8% and 56.8%， respectively， at 15 ℃， and the constant B₀ of soil organic phosphorus mineralization decreased by 29.5% and 40.4%， respectively. Furthermore， the temperature sensitivity of soil organic phosphorus mineralization decreased gradually with increased severity of meadow degradation. For example， the temperature sensitivity coefficient y" of organic phosphorus mineralization in ND soil was significantly higher than that in MD and HD soils by 221.1% and 306.7%， respectively. In summary， the degradation of alpine meadow reduced the mineralization and temperature sensitivity of soil organic phosphorus， which would be predicted to result in further reduction of soil phosphorus availability， and exacerbate any problem of phosphorus limitation in degraded grassland ecosystems arising from ongoing global warming.

Interactive effect of fertilization and cutting on community dynamics and transgressive overyielding effect of grass pasture in the northern Tibetan Plateau

Juan-juan ZHOU, Wei WEI

2023, 32(10):  28-39.  DOI: 10.11686/cyxb2023014

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Establishing artificial grassland using native species is an effective measure to restore alpine degraded grassland in the northern Tibetan Plateau. Our objective was to provide the scientific basis for ecological restoration of degraded grassland. This study investigated the dynamics of community fluctuation in sown grassland of three different native species domesticated in the northern part of Tibet： Elymus nutans， Elymus tangutorum and Poa litwinowiana. We aimed to identify the optimal sowing combination， explore the possibility of transgressive overyielding effect compared with monocultures， net effect of biodiversity， and the response of individual species to fertilization and cutting of mixed-species grassland. The experiment used a split-plot design with 7 sowing combinations as main plots： Monocultures of E. nutans （S₁）， E. tangutorum （S₂） and P. litwinowiana （S₃）， the combinations of E. nutans+E. tangutorum （M₁）， E. nutans+P. litwinowiana （M₂）， E. tangutorum+P. litwinowiana （M₃） and E. nutans+E. tangutorum+P. litwinowiana （M₄）. Fertilization and cutting treatments were applied as sub-plot treatments. The sub-plots set 4 treatments： Fertilization treatment， cutting treatment， fertilization+cutting treatment combination and control （untreated）. The plots were planted in 2019 with 60 g·m^-2 fertilizer application of （NH₄）₂HPO₄， cut to 5 cm stubble height. It was found that swards of the different sowing combinations displayed obvious population dynamic changes through the growing season. Aboveground biomass peaked on September 20^th （the end of growing season）， and E. nutans was the dominant species of mixtures. The underground biomass accumulation reached its maximum value on August 20^th （booting stage）； The underground biomass of treatment M₄ was the highest （669.61 g·m^-2）. The combination of E. nutans+E. tangutorum+P. litwinowiana （M₄） had the highest productivity. A positive interaction between fertilization and cutting treatments resulted in high yield （3190.83 g·m^-2） in the fertilization+cutting treatment combination. Therefore， the mixed sowing of E. nutans+E. tangutorum+P. litwinowiana with fertilization and cutting is the recommended methodology for the establishment of sown grassland in the northern Tibetan Plateau. When tested using natural log response ratio （LNRR） analysis， E. nutans had the strongest competitiveness， followed by P. litwinowiana and E. tangutorum. The relative yield totals of M₁， M₂， M₃ （control and cutting treatments） and M₄ were all greater than 1.0， and thus all had over yielding compared to the respective monocultures. In M₄， M₁ （control and cutting treatments）， M₂ （cutting， fertilization and fertilization+cutting treatments）， the complementary effect and selection effects jointly contributed to the over yielding， while in M₁ （fertilization and fertilization+cutting treatments）， M₂ （control treatment） and M₃ （control and cutting treatments）， only the complementary effect was important and dominated the over yielding.

Comparative metabolomics analysis of root systems of two Dactylis glomerata cultivars in response to submergence stress

Bing-na SHEN, Pan-pan SHANG, Bing（student） ZENG, Lin-xiang LI, Xing-yun YANG, Lei BI, Yu-qian ZHENG, Ming-hao QU, Wen-wen LI, Xiao-li ZHOU, Jun RAO, Bing(teacher) ZENG

2023, 32(10):  40-57.  DOI: 10.11686/cyxb2022461

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Orchard grass （Dactylis glomerata） is a world famous temperate cold-season forage grass. In recent years， frequent floods in southern China have seriously affected forage crop production. In order to explore the response mechanism of orchard grass roots under submergence stress， the waterlogging-tolerant orchard grass cultivar ‘Dianbei’ （DB） and the waterlogging-sensitive orchard grass cultivar ‘Anba’ （AB） were studied. Two waterlogging treatments （8 and 24 h） were set up， and a non-waterlogging treatment was used as the control （0 h）. The morphology was observed and metabolomics analysis was performed on the seedling roots for 0， 8 and 24 h treatments. It was found that the root growth of the two varieties became weak and the roots became black after submergence stress treatment， and adventitious roots were produced by cultivar DB after treatment for 24 h. 120 differentially produced metabolites were identified in the DB_8h vs DB_0h comparison and 155 differentially produced metabolites were identified in the DB_24h vs DB_0h comparison， while 93 differentially produced metabolites were identified in the AB_8h vs AB_0h comparison and 118 differentially produced metabolites were identified in the AB_24h vs AB_0h comparison. Between cultivars， 80 differentially produced metabolites were identified in the DB_0h vs AB_0h comparison； 125 differentially produced metabolites were identified in the DB_8h vs AB_8h comparison and 48 significantly differentially produced metabolites were identified in the DB_24h vs AB_24h group. Six flavonoids involved in the metabolic pathway of flavonoid biosynthesis were found in the waterlogging-tolerant orchard grass cultivar DB， namely： Hesperidin， glycyrrhizin， apigenin， neohesperidin， naringin and naringenin； While four amino acids and their derivatives were found in the waterlogging-sensitive orchard grass cultivar， namely： O-phosphate-L-serine， L-glutamic acid， L-tyrosine and tryptophan. These amino acids are involved in the metabolic pathway of amyl-tRNA biosynthesis； Glycine， serine and threonine metabolism； Glucosinolate biosynthesis； Phenylalanine， tyrosine and tryptophan biosynthesis and the tryptophan metabolic pathway. Comparison of the differential metabolites of DB and AB under the same duration of flooding stress indicated that the main differentially produced metabolites present in DB were sucrose， isomaltose， alginate 6-phosphate， L-ornithine， L-histidine， D-ornithine and apigenin， and the metabolic pathways involved were ABC transport factor， starch and sucrose metabolism， β-alanine metabolism flavonoid biosynthesis and flavonoid and flavonol biosynthesis. These differentially produced metabolites may be responsible for the differences in waterlogging tolerance between the two species. The results provide a basis for resolving the differentially produced metabolites and metabolic pathways in orchard grass in response to submergence stress， and provide a reference for further studies on the molecular mechanisms of orchard grass metabolic regulation in response to submergence stress.

Differential covariation characteristics in functional traits of two ephemerals of Boraginaceae in the Gurbantunggut Desert， China

Xin-yue JIN, Li GONG, Meng-ting WANG, Ye TAO, Duo-qi ZHOU

2023, 32(10):  58-70.  DOI: 10.11686/cyxb2022476

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Ephemerals are a specialised plant group that have evolved to escape summer drought， but it is not clear whether the functional traits of different ephemeral species have the same or similar covariant characteristics. In this study， two species from the same family （Boraginaceae） but different genera widely distributed in the Gurbantunggut Desert， Xinjiang， China， Arnebia decumbens and Nonea caspica， were studied to answer this question. The data were obtained by field sampling and indoor measurement， and the differences in functional traits， allometric relationships among traits and trait covariance relationships of different species were systematically studied by reduced major axis regression， principal component analysis and plant trait network analysis. The results showed that the aboveground biomass （2.217 g·plant^-1）， whole plant biomass （2.407 g·plant^-1）， crown diameter （14.26 cm）， and crown diameter to height ratio （1.550） of N. caspica were significantly higher than A. decumbens （1.010 g·plant^-1， 1.145 g·plant^-1， 10.95 cm， and 1.138）， but the root-to-shoot ratio of the latter （0.147） was significantly greater than the former （0.091）. There were mostly significant allometric relationships （α≠1） among functional traits of the two species， e.g.， aboveground biomass allocation rates were higher than the belowground biomass （α=0.888 and 0.909）， but the biomass allocation was body size-dependent for them. The two species showed different phenotypic developmental patterns. For example， the height and crown diameter of A. decumbens grew at an equal rate （α=1.095）， while N. caspica increased crown diameter at a much higher rate than height （α=1.516）， resulting in the larger body size or ‘stumpy’ plant shape. Principal component analysis and plant trait network analysis revealed that differences in covariant characteristics among functional traits existed for the two species， and the hub traits and network topological parameters in the trait networks also differed. The study showed that even for ephemerals from different genera in the same family， the functional traits and trait association characteristics were not identical and showed a degree of species specificity.

Effects of slow-release N fertilizer on growth and water- and N- use efficiencies of forage sweet sorghum under three different irrigation regimes

Ren-shi MA, Cong-ze JIANG, Wei GAO, Zhong-li LI, Yu-ying SHEN, Xian-long YANG

2023, 32(10):  71-81.  DOI: 10.11686/cyxb2022489

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To investigate the water-saving and high-yield cultivation conditions for forage sweet sorghum （Sorghum bicolor）， an auto-weighed lysimeter experiment under greenhouse conditions was conducted to determine the effects of different water and nitrogen （N） supply conditions on growth， yield， and water- and N- use efficiencies of forage sweet sorghum. Three irrigation and three N fertilization regimes were tested in this study： maintaining soil moisture content at 30%-50% （I₁）， 50%-70% （I₂）， and 70%-90% （I₃） of field capacity， and using conventional urea at 200 kg·ha^-1 elemental N （U₂₀₀）， coated urea at 160 kg·ha^-1 elemental N （CU₁₆₀）， and coated urea at 120 kg·ha^-1 elemental N （CU₁₂₀）. It was found that increasing the irrigation amount significantly promoted plant height and stem diameter， and increased the total leaf area per plant. Compared with I₁， I₂ and I₃ increased the plant height by 9.5% and 15.4%， and increased the stem diameter by 2.4% and 27.6%， and increased the total leaf area per plant by 32.0% and 76.0%， respectively. With increase in the irrigation level， the fresh and dry weight of stems， leaves， and of the whole plant were increased significantly， as well as the stem-leaf ratio. Compared with I₁， I₂ and I₃ increased the whole plant fresh weight by 61.7% and 187.4%， and the dry weight by 55.7% and 129.8%， respectively. The N fertilization regimes also significantly affected the fresh and dry weight of stems， leaves and the whole plant. Compared with U₂₀₀， CU₁₆₀ increased the whole plant fresh weight by 13.9%， and increased the dry weight by 22.8%， respectively. The cumulative water consumption per plant and water- and N- use efficiencies increased significantly with increase in irrigation level. Compared with I₁， I₂ and I₃ increased water consumption by 52.1% and 108.4%， and increased the dry matter water use efficiency by 2.6% and 11.3%， and increased partial-factor productivity by 51.9% and 128.3%， respectively. The N fertilization methods significantly affected water- and N- use efficiencies. Compared with U₂₀₀， CU₁₆₀ increased the dry matter water use efficiency by 22.4%， while CU₁₆₀ and CU₁₂₀ increased the partial-factor productivity by 53.5% and 80.0%， respectively. Therefore， moderate irrigation and use of slow-release fertilizer with at a lower N application rate significantly promoted the efficient production of forage sweet sorghum plants， and enhanced water- and N- use efficiencies， compared with the I₃-U₂₀₀ treatment combination.

A multi-trait evaluation of the performance of 16 forage oat varieties in central and southern Heilongjiang Province

Feng LI, Wen-long LI, Xue LI, Zhong-juan ZHANG, Lin-po BAI, Yu-fei ZHAO, Ya TAO

2023, 32(10):  82-92.  DOI: 10.11686/cyxb2022473

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This research evaluated forage oat varieties for suitability for spring sowing in central and southern Heilongjiang Province to assist the sustainable development of animal husbandry in this region. Our study monitored and analyzed the growth period， lodging resistance， yield traits and nutritional quality of 16 domestic and foreign oat （Avena sativa） varieties， and compiled a multi-trait production performance score using the grey correlation method. The results were as follows： Time from sowing to cutting （milk maturity） for the 16 oat varieties ranged from 83-97 days， during which time Mengshi No.1， Qingyin No.1， Qingyin No.2， Charisma， Helios and Kona did not lodge. Values for plant height， hay yield， fresh yield， crude protein （CP）， neutral detergent fiber （NDF）， acid detergent fiber （ADF）， ether extract （EE）， water-soluble carbohydrates （WSC）， and relative feed quality （RFQ）， respectively， ranged from 96.40-131.13 cm， 7287.73-14635.76 kg·hm^-2， 19366.97-36905.00 kg·hm^-2， 8.61%-11.39% dry matter （DM）， 42.86%-57.84%DM， 23.52%-34.99%DM， 1.19%-1.88%DM， 3.52%-10.18%DM， and 128.28-208.78. There were significant differences among different varieties in all characteristics evaluated （P<0.05）， and the plant heights of Qingyin No.1， Qinghai sweet oats and Heibei were significantly greater than those of other varieties. The hay yields of Mengshi No.1， Kona， Baiyan No.7 and Dahan were significantly higher than those of other varieties； The CP content of Lanniao No.1 was significantly higher than that of other varieties； The NDF contents of Baiyan No.7， Mengshi No.1 and Lanniao No.1 were significantly lower than Charisma and Everleaf， and Mengshi No.1， Baiyan No.7， Souris and Lanniao No.1 had significantly lower ADF than Everleaf. The RFQ value of Baiyan No.7 was significantly higher than that of other varieties. Grey correlation analysis showed that the weighting coefficients for plant height， CP and NDF ranked the top three among all traits and were therefore important characteristics for evaluating oat productivity in this region. Baiyan No.7， Mengshi No.1， Kona， Qingyin No.2 and Qinghai sweet oat had higher grey scores and superior multi-trait performance， and are therefore recommended as suitable for sowing in Heilongjiang Province and similar areas.

Physiological and antioxidant enzyme gene expression differences between female and male Buchloe dactyloides plants under drought stress

Mu-ye LIU, Li-zhu GUO, Yue-sen YUE, Ju-ying WU, Xi-feng FAN, Guo-zeng XIAO, Ke TENG

2023, 32(10):  93-103.  DOI: 10.11686/cyxb2023019

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Drought is one of the important stress factors that restrict plant growth. At present， there are few studies on the physiological and molecular mechanisms of drought resistance of buffalo grass （Buchloe dactyloides） plants of different genders. To investigate the differences in the effects of drought stress on male and female buffalograss， we studied the ‘Texoka’ cultivar in terms of antioxidant enzyme activity and gene expression. The changes in relative water content （RWC）， chlorophyll （Chl） content， the maximum quantum yield of PSII （F_v/F_m） and antioxidant enzyme activities were determined under drought stress for 0， 7， 14 days and 7 days after re-watering. In addition， the expression levels of antioxidant enzyme coding genes of female and male buffalograss in response to drought stress were investigated using qRT-PCR. The results showed that the turf quality of female and male plants decreased with the duration of drought stress， but recovered after rewatering. The turf quality of female plants was better than that of male plants. RWC of both female and male plants decreased with increase in drought exposure time but showed recovered after rewatering. RWC of female plants was significantly higher than that of male plants on the 7th day of drought treatment. Chl of female and male buffalograss decreased during the drought-rehydration treatment. F_v/F_m showed the same trend during the drought-rehydration treatment， with a significant decrease on the 14th day of drought. There was no significant difference in Chl and F_v/F_m between female and male plants except on the 7th day， and the photosynthetic characteristics of both plants were similar after long-term drought stress and rewatering. The photosynthetic characteristics of both genders were similar under long-term drought stress and after re-watering. In detail， the activity of superoxide dismutase in female buffalograss was higher than that in male buffalograss at 7 and 14 d of drought stress and 7 d after re-watering. The activity of ascorbate peroxidase （APX） in female buffalograss was higher than in male plants indicating that APX accumulated faster in female buffalograss under drought stress. The activity of peroxidase of female and male buffalograss plants showed the same time course under drought stress， with no significant difference between them. The time course of catalase activity of female and male plants was completely opposite on the 7th day of drought. The expression of antioxidant enzyme genes in female buffalograss peaked after re-watering， which was inconsistent with the change of antioxidant enzyme activity. The expression of FeSOD， Zn/Cu-SOD and POD of male buffalograss peaked in each case on the 14th day of drought， and was in accordance with the pattern of antioxidant enzyme activities. The expression of APX and CAT in male seedlings decreased from the imposition of drought and increased after re-watering， but was inconsistent with the changes in antioxidant enzyme activities which needs further investigation. In general， physiological and transcriptional differences were found between female and male buffalograss in response to drought stress. The drought resistance of female buffalograss was stronger than male buffalograss. This study enriched our knowledge of the mechanism of antioxidant systems in buffalograss under drought stress， and provided reference data of potential ecological significance for the study of drought resistance strategies in dioecious plants.

Response to fertilization of leaf functional traits of grassland plants with different mycorrhizal status

Wen-jing WEI, Zhao-yong SHI, Meng-ge ZHANG, Shuang YANG, Wen-ya YANG

2023, 32(10):  104-114.  DOI: 10.11686/cyxb2022444

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In order to explore the effects of mycorrhizal status and fertilization on leaf traits of grassland plants， fertilization treatments were applied at 27 globally distributed grassland sites across four continents based on data made by Firn et al^［25］. The treatments included a control and full factorial combinations of nitrogen （N）， phosphorus （P）， and potassium （K）. After 3-4 years of nutrient addition， the leaf N， P and K contents and specific leaf areas （SLA） of dominant species in each plot were measured， and the mycorrhizal status of plants was determined based on published literature. On this basis， combined with the composition of dominant species， the grassland plants were divided into poaceous plants and non-poaceous species， and the responses of the two plant groups to difference in mycorrhizal status and fertilization treatments were further analyzed. It was found that mycorrhizal status was an important factor affecting the leaf traits of grassland plants. Especially for poaceous plants， the leaf nutrient content of non-obligate mycorrhizal （NOM） plants was significantly higher than that of obligate mycorrhizal （OM） plants. For non-poaceous grassland plants， the leaf traits of OM plants and NOM plants also showed some differences， but these were not significant overall. The effects of fertilization on the leaf traits of grassland plants were mainly to significantly increase the contents of N， P and K in leaves， but fertilization had little effect on SLA. Path analysis further showed that there was a significant positive correlation between fertilization and leaf nutrient content， while there was no significant correlation between fertilization and SLA. In addition， the leaf traits of OM and NOM plants in grassland were significantly affected by climatic factors and differed between treatment years. In conclusion， in poaceous plants， leaf traits were significantly affected by mycorrhizal status， while fertilization significantly increased the leaf nutrient content of grassland plants. The effects of climatic factors on the leaf traits of grassland plants and differences between years also merit further investigation.

An evaluation of the pathogenicity of Fusarium solani and disease resistance of alfalfa varieties

Bo CHEN, Yi-fan NIU, Xiao-yu LIU, Su-han ZHANG, Jun-peng NIU, Zhi-peng GUO, Chao-qi LIU, Yong-peng GUO, Yu-xia GUO

2023, 32(10):  115-128.  DOI: 10.11686/cyxb2022447

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The objective of this study was to evaluate the pathogenicity of a range of Fusarium solani isolates to various alfalfa varieties on two culture media， potato dextrose agar （PDA） and water agar （WA） medium. We used conventional tissue separation methods to isolate and purify the fungi from alfalfa roots， and the representative strains of the isolates were identified using both morphological and molecular techniques. We estimated the relative root length， relative seedling length， relative root to seedling ratio， relative germination rate and disease index at 14 d after inoculation with F. solani， and synthesized various indexes through membership functions. The results showed that F. solani was the pathogenic fungus causing alfalfa root rot. F. solani was pathogenic to 22 alfalfa varieties on both culture media， and the pathogenicity of F. solani on PDA medium was stronger than that on WA medium. The disease resistance of the 22 alfalfa varieties varied. ‘TARIMU 5S’ showed the strongest resistance， while ‘Zhongmu No.1’， ‘Bara310SC’， ‘OPTIMUS F3’ and ‘Golden-queen’ exhibited high-level resistance. ‘Zhonglan No.2’， ‘Sardi 7’， ‘Longmu 803’ and ‘Gannong No.3’ exhibited low-level resistance； ‘Paola’ had the weakest resistance.

Effects of dialectric barrier discharge plasma treatment on seed germination and physiological characteristics of Astragalus sinicus

Xiang LI, Meng ZHANG, Chun-zeng LIU, Yi-fei ZHU, Xiao-xin YE

2023, 32(10):  129-140.  DOI: 10.11686/cyxb2022437

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Poor seed germination and seedling performance when germinated in commonly encountered osmolyte concentrations are major constraints to expansion of Astragalus sinicus cultivation. The objective of this study was to test the potential use of an electrical discharge plasma treatment as a low-cost technology for sustainable A. sinicus cultivation. Two cultivars of A. sinicus （Ganzi 75-3-51 and Xinzi 1） were investigated in an indoor germination experiment in order to investigate the influences of various dielectric barrier discharge plasma treatments （7， 8 or 9 kV for 1， 3， 5 or 10 min） on A. sinicus seed germination， seedling growth， antioxidant enzyme activity and osmolyte concentrations. It was found that plasma treatments had no significant effects on the germination rate or germination potential of A. sinicus seed， but did raise the germination index and seed vigor index of both cultivars. Significant interactions between plasma and cultivar effects were observed for most traits indicating that the response patterns of the cultivars across the imposed plasma treatments were different. The growth of Ganzi 75-3-51 seedlings was promoted with lower-dose plasma treatment and inhibited with higher-dose plasma treatment. Xinzi 1 seedlings were sensitive to plasma treatment and high dose plasma treatment （9 kV with 10 min duration） significantly reduced the fresh weight of Xinzi 1 seedlings （the decrease， as compared with the controls was 20.5%）. The activities of superoxide dismutase and peroxidase of Ganzi 75-3-51 tended to rise initially and then decline with increase in voltage and treatment time. The antioxidant enzyme activity of Xinzi 1 showed a trend of increase with increased exposure time in the low-voltage plasma treatment （7 kV）， but wasn’t significantly changed by high-voltage plasma treatment. In addition， low dose plasma treatment enhanced the contents of soluble sugar and protein in seedlings of both A. sinicus cultivars. Though plasma treatment didn’t significantly affect the germination of tested A. sinicus cultivars in the current study， some plasma treatments did stimulate antioxidant enzyme activities， and promote starch and protein hydrolysis， thereby improving the seed vigor and growth of A. sinicus seedlings.

Effects of H₂O₂ immersion on seed germination and seedling growth of alfalfa under salt stress

Jiao-yun LU, Hong TIAN, He-shan ZHANG, Jun-bo XIONG, Yang LIU, Zhen-nan WANG

2023, 32(10):  141-152.  DOI: 10.11686/cyxb2022486

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Salt stress is one of the major abiotic stresses affecting the normal growth of plants worldwide. Exogenous H₂O₂ can alleviate the damage caused by salt stress on plants by altering the activity of plant peroxidase and osmotic regulatory substances. In this study， different salt stress concentrations （0， 0.6%， 1.2%， 1.8% NaCl） and H₂O₂ immersion seed treatments （0， 5， 100 μmol·L^-1 H₂O₂） were used to study the effects of H₂O₂ on seed germination， seedling growth， antioxidant enzyme activity and osmotic adjustment substances of alfalfa under the different salt stress concentrations. It was found that： 1） With successive increases in NaCl concentration， the germination rate， germination potential， germination index and vigor index of alfalfa seed progressively decreased. With increase in NaCl concentration， the fresh weight， dry weight and absolute water content of alfalfa seedlings aboveground and whole plant initially increased and then decreased at higher concentration， while the fresh weight， dry weight and absolute water content of roots continued to decrease across the tested concentration range. With increasing NaCl concentration， superoxide dismutase （SOD） activity and soluble protein content increased gradually， catalase （CAT） activity and malondialdehyde content increased initially and then decreased， peroxidase （POD） activity and soluble sugar contents were lower than those of seedlings without salt stress. 2） The germination potential， germination index and vigor index of alfalfa seed were improved by H₂O₂ immersion. The fresh weight， dry weight， root∶shoot， SOD and CAT activities， proline and soluble protein contents of alfalfa seedlings under the 5 μmol·L^-1 H₂O₂ immersion treatment were higher than those under the 100 μmol·L^-1 H₂O₂ and distilled water immersion treatments， while the malondialdehyde content of the 5 μmol·L^-1 H₂O₂ treatment was lower than that of 100 μmol·L^-1 H₂O₂ and distilled water immersion treatments. Multivariate analysis showed that salt stress inhibited seed germination and seedling growth of alfalfa， and that alfalfa seedlings resisted salt stress by increasing antioxidant enzyme activity and osmotic regulatory substance content. The salt resistance of alfalfa seeds and seedlings was improved by H₂O₂ immersion， and soaking seeds with 5 μmol·L^-1 H₂O₂ was better than soaking with 100 μmol·L^-1 H₂O₂.

Effects of Euphorbia jolkinii on physiology and endogenous hormone content of alfalfa seedlings

Gui-lian SHAN, Zu-yan MA, Jia-yi LI, Yang LIU, Yong XIE, Jia LIU, Xiao-hui CHU

2023, 32(10):  153-161.  DOI: 10.11686/cyxb2022455

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This research explored the effects of allelochemicals in Euphorbia jolkinii on alfalfa （Medicago sativa）seedlings using an indoor controlled experiment with the aim of providing information to support the replanting of improved forage species and restoration of degraded grassland where the poisonous herb has spread. We determined the effects of E. jolkinii on the morphology， physiology and endogenous hormone content of alfalfaseedlings. It was found that the addition of E. jolkinii reduced seedling root activity initially， and then blocked the synthesis of chlorophyll， gibberellic acid （GA）， zeatin （ZT） and indoleacetic acid （IAA）， with the ultimate effect of significant inhibition of alfalfa seedling growth. The addition of soil from the root zone of E. jolkinii plants promoted the synthesis of chlorophyll and improved the root activity of alfalfa on the one hand， and reduced the synthesis of GA， ZT， and IAA on the other hand， with the overall result was that there was no significant effect on the growth index of alfalfa seedlings in terms of seedling root length and fresh weight in treatments where root-zone soil was added. In summary， the allelochemicals contained in E. jolkinii can strongly inhibit the hormone synthesis of alfalfa seedlings， and thereby inhibit the growth of alfalfa seedlings but some amelioration through inoculation with E. jolkinii root-zone soil is possible.

Effects of dietary broad bean skin on growth rate， slaughter performance， organ development and meat quality of Hu sheep

Zhao WANG, Jing LIU, Hao YU, Peng LI, Wei-qiang NIU, Yong-jie WAN, Yan-li ZHANG, Da-gan MAO

2023, 32(10):  162-172.  DOI: 10.11686/cyxb2022472

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This study aimed to investigate the effect of a dietary broad bean skin supplement on growth rate， slaughter performance， organ development and meat quality of Hu sheep. Healthy 4-month-old male Hu sheep （n=60； 27.00±2.00 kg） were randomly divided into four treatment groups of 15 animals （3 replicates in each group and 5 sheep in each replicate） and fed diets containing 0% （control， Group C）， 10% （Group I）， 20% （Group II） and 30% （Group III） broad bean skin. The trial period was 60 days. Compared with the control group， the body weight， average daily feed intake and daily gain of Hu sheep in groups fed broad bean skin were very significantly increased （P<0.01）. In Group III， the carcass weight （19.62±0.73 vs 17.75±0.86 kg） and live weight before slaughter （37.22±1.01 vs 34.76±0.71 kg） were very significantly increased （P<0.01） compared to Group C while the area of eye muscle was significantly increased （35.84±2.47 vs 27.84±0.13 cm²， P<0.05）； The liver weight tended to be increased （670.00±73.37 vs 588.00±49.87 g， P=0.071）， the rumen weight （659.40±66.44 vs 548.00±75.48 g） and small intestine weight （1107.80±150.56 vs 901.00±41.32 g） were significantly increased （P<0.05）； The cross-sectional area of muscle fiber was extremely significantly lower （584.67±32.01 vs 832.90±53.48 μm²， P<0.01）； The glutamic acid content was very significantly increased （37.74±1.64 vs 13.19±3.38 mg·g^-1， P<0.01）； The contents of arginine （19.08±1.28 vs 11.25±2.39 mg·g^-1） and nonessential amino acids （118.44±1.98 vs 90.59±9.56 mg·g^-1） were significantly higher （P<0.05）， and the contents of valine （12.40±1.09 vs 7.98±1.61 mg·g^-1， P=0.086） and essential amino acids （135.25±3.51 vs 106.79±11.14 mg·g^-1， P=0.071） tended to increase. In summary， the addition of broad bean skin to the diet improved the growth rate， slaughter performance， gastrointestinal development， muscular fiber and amino acid composition of Hu sheep， and the data provide a scientific basis for ration formulation incorporating broad bean skin in the production of Hu sheep.

Screening of target genes related to milk fat in dairy cows regulated by alfalfa miR168b

Jing-ying JIA, Bao-bao LIU, Yun MA, Hong-juan DUAN, Xiao-yan CAI

2023, 32(10):  173-186.  DOI: 10.11686/cyxb2022449

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The alfalfa （Medicago sativa） miRNAs expressed significantly differently in the blood and milk of high-fat dairy cows and low-fat dairy cows and their potential target genes in dairy cows were screened out in order to lay a foundation for further exploring the regulation of milk fat level by alfalfa miRNAs at gene level. Firstly， the level of dairy herd improvement （DHI） was measured in milk of Holstein cows which had produced 4 fetuses and had the same dietary level. Three cows were selected from high-and low-milk-fat cows as duplicates and RT-qPCR was used to quantify alfalfa miRNAs in milk and blood of the dairy cows. After screening out differentially expressed miRNAs， the target genes were predicted and analyzed， and the target genes related to milk fat metabolism were screened according to the binding sites and quantitative results by miRNA-mRNA. The results were as follows： 1） Three high-fat dairy cows and three low-fat dairy cows were identified by their DHI score. The fat content in the milk of high-fat dairy cows was >4.2%， and that of low-fat dairy cows was <3.5%. 2） Alfalfa sourced novel-miR54， miR156f， miR166a， miR168b and miR168c-3p were detected in cow blood and milk. The expression level of miR168b in the blood of high-fat milk cows was extremely significantly lower than that in low-fat milk cows （P<0.01）， and similarly the expression level of miR168b in the milk of high-fat milk cows was significantly lower than that in low-fat milk cows （P<0.05）. 3） The high expression of mtr-miR168b in mammary epithelial cells inhibited the expression of adipogenic marker genes PPARγ， SCD1， CEBP/β and SREBP1. 4） GO and KEGG databases indicated 1834 and 296 target genes， respectively， predicted by mtr-miR168b. The predicted target genes were closely related to N-glycan biosynthesis （3.72%）， the cGMP-PKG signaling pathway （2.37%） and vascular smooth muscle contraction （2.37%） and the glycerophosphate metabolism pathway （1.69%） was also significantly enriched. 5） CPT1A and STARD7， two genes closely related to lipid metabolism， were also screened. A targeting relationship between miR-168b and CPT1A was confirmed by dual-luciferase report. In conclusion， mtr-miR168b can regulate milk fat production by inhibiting the expression of adipogenic marker genes in mammary epithelial cells， and this study identifies target genes for further verification of alfalfa miRNA regulation of milk fat percentage in dairy cows.

An evaluation of drought resistance of five forage legumes based on a quantile model

Zhan-jun WANG, Bo JI, Tong JI, Qi JIANG

2023, 32(10):  187-199.  DOI: 10.11686/cyxb2021048

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This research systematically analyzed the suitable water conditions for forage growth in order to screen high-quality drought resistant forages for arid areas. Five perennial leguminous forages （Astragalus melilotoides， Lespedeza potaninii， Lespedeza davurica， Coronilla varia， and Astragalus cicer） were studied， and agronomic traits （number of green leaves and plant height） were systematically analyzed. The trade-off relationship between plant growth and soil moisture supply， using the RMSD （root mean square distance） for plant size and soil moisture content as quantile model variables to determine the soil moisture threshold needed to maintain normal growth of plants， while recording a multivariate score of physiological indicators under drought stress. This drought resistance evaluation showed that： 1） The higher the drought stress， the greater the negative impact on the chlorophyll and plant height of the forage； However， a moderate drought can promote the growth and development of the forage. 2） With respect to the tolerance of different forages to drought stress， differences were found in the degree and scope of exposure， with the soil moisture thresholds of plant green leaves number for A. melilotoides， L. potaninii and A. cicer being 17%， 10% and 5%， respectively， while the soil moisture thresholds of plant height are A. melilotoides， 16%； L. potaninii， 14% and A. cicer 10% and quantile models for other variables failed the significance test. 3） From the evaluation and analysis of seven physiological indicators， the drought resistance of the five leguminous forage species was ranked： L. potaninii>L. davurica>C. varia>A. cicer>A. melilotoides. 4） Based on the combination of soil water content threshold and drought physiological evaluation， the selection of L. potaninii for severe drought can be used as the selective pasture for severe drought， and L. potaninii for moderate drought can be used as the selective pasture for moderate drought.

Research progress on vigor estimation for forage seeds

Qi-bo TAO, Xi-hu QIE, Qian ZHANG, Yu-xuan GAO, Ya-qi ZHANG, Rui-zhen ZHANG, Xiao-fei CHEN, Tian-xiu NIU, Xiao-tong SUN, Yu-ting NIE, Ya-ru LIU, Jia-qi HU, Shang-zhi ZHONG, Juan SUN

2023, 32(10):  200-225.  DOI: 10.11686/cyxb2023007

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High-quality forage seeds are fundamental materials for grass-husbandry industry development and ecological restoration in China. Seed vigor is an important aspect of evaluate seed quality. The efficient vigor estimation of forage seeds is of great importance for selection of high-quality seed lots for cultivated grassland establishment and improvement of natural grassland， and is therefore critical to ensuring food and ecological security. Numerous studies on diverse forage seed vigor estimation methods and their ability to predict field performance have been carried out and published. In this study， the concepts and methodologies for forage seed vigor estimation are summarized， with particular emphasis on the estimation principles and their application in forage seed vigor estimation of some of the more commonly used methods. Coverage of this review includes forage seed physical properties， germination and seedling growth characteristics， stress testing， physiological and biochemical indicators， and advanced technologies. Future prospects in this field are also identified and discussed， to provide necessary direction for the improvement of future research.

Chinese grassland insurance development model， practical difficulties and system construction

Tao QIN, Cai-xia ZHU, Jian-he WANG, Jin ZHANG

2023, 32(10):  226-246.  DOI: 10.11686/cyxb2022471

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Grassland is an important ecological security barrier， animal husbandry base and carbon reservoir carrier in China， and building a risk guarantee system with grassland insurance as the core is of great value for protecting the grassland ecological environment， promoting rural revitalization in pastoral areas and achieving the ‘dual carbon’ goal of peak carbon dioxide emissions before 2030 and carbon neutrality before 2060，and it plays a key role in global climate governance. Through literature review and qualitative comparative analysis， it is found that the United States， Canada and France， among others， have established different forms of grassland product insurance systems， with index insurance as the core mechanism to transfer forage risks. However， Chinese grassland insurance is currently in the exploration stages. A current pilot phase， has not yet established a product system that is aligned with Chinese national conditions. During the pilot work， many constraints have emerged. There are some difficulties in collecting premiums， the promotion of the system lacks uniformity， the product supply power is insufficient， there is no theoretical basis for determination of premium rates， and the cost of determining loss claims is too high. Therefore， China needs to improve the grassland insurance policy system and product system as soon as possible， and build a linkage mechanism for central and local premium subsidies. Improvement of the multi-level disaster risk protection system and innovation introduction should include： The development model of a “comprehensive insurance+index insurance”； Development of diversified insurance products to meet the diversified risk management needs of insured entities； Promotion of the process of grassland risk zoning and rate determination， and establishing a differentiated dynamic pricing mechanism； Formulation of unified technical standards for survey and loss assessment； Improvement of the underwriting claim mechanism； Improvement of the level of grassland insurance technology and enhancement of the innovation level； And increase in the service capabilities of insurance products.

Phenotype and biomass analysis of nodulation-deletion mutants in Melilotus albus

Sheng-sheng WANG, Zhen DUAN, Pei ZHOU, Ji-yu ZHANG

2023, 32(10):  247-256.  DOI: 10.11686/cyxb2022464

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In order to elucidate the mechanism of symbiotic nitrogen fixation of Melilotus， nodulation-deletion mutants Ma58， Ma61 and Ma62 induced by ethylmethane sulfonate （EMS）， and wild-type Ma389 of Melilotus albus were studied and the nodulation phenotypes and biomass were analyzed after inoculation with Sinorhizobium meliloti SM1021. It was found that mutants Ma58 and Ma61 did not form infection lines and nodule primordia， while mutant Ma62 did not form infection lines and only formed a few small white nodules which did not fix nitrogen. The root fresh/dry weight of the three mutants was significantly lower than that of the wild type in low nitrogen substrate for 30 d （P<0.05）， and the aboveground fresh/dry weight， root fresh/dry weight， plant height and root length were significantly lower than those of the wild type from 40 d （P<0.05）. However， no significant differences were found when plants were grown in a nitrogen-rich substrate， indicating that the mutant genes of the three mutants were related only to symbiotic nitrogen fixation. This study has identified genetic resources for the study of the symbiotic nitrogen fixation mechanisms of Melilotus.