Table of Content

20 August 2023, Volume 32 Issue 8

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Spatio-temporal changes in grassland fractional vegetation cover in Inner Mongolia from 2000 to 2020 and a future forecast

Hui-long ZHANG, Xiu-chun YANG, Dong YANG, Ang CHEN, Min ZHANG

2023, 32(8):  1-13.  DOI: 10.11686/cyxb2022370

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Inner Mongolia is an important green ecological barrier in northern China， and grassland degradation in this region is of great concern. Fractional vegetation cover （FVC） is one of the most direct indicators of grassland ecological status. At present， it is still a challenge to build an accurate FVC estimation model for dynamic analysis of a large region over a long period of time. In this study， we used a large ground survey dataset， MODIS remote sensing data， and meteorological data from 2000 to 2020， and applied the random forest model for FVC partition modeling and prediction. The Sen+Mann-Kendall trend analysis method and Hurst index method were used to analyze the spatio-temporal changes in the FVC and its future trends. The main results were as follows： 1） The precision of each partition of the random forest model was better than that of the whole region， which effectively reduced the impact of spatial heterogeneity. 2） In Inner Mongolia， the grassland FVC generally showed a spatial pattern of being high in the east and low in the west， with obvious spatial differences. 3） In the past 21 years， the FVC of grassland in Inner Mongolia showed a fluctuating upward trend overall， the area of increased FVC was larger than the area of decreased FVC， and the magnitude of the extremely significant increase and significant increase was greater than that of the extremely significant decrease and significant decrease. 4） In the future， the grassland FVC in Inner Mongolia will generally improve. The area of FVC growth is larger than the area of FVC decrease， and the area with extremely significant growth and significant growth accounts for a high proportion （25.9%） of the total area. It is predicted that vegetation growth will develop well in the future.

Spatio-temporal evolution of grassland ecosystem service value in Inner Mongolia under multi scenario simulation

Xue-min LI, Tong-ning LI, Zhi-yu WU, Zhen-guo WU

2023, 32(8):  14-27.  DOI: 10.11686/cyxb2022358

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This research explored the ecosystem service value spatio-temporal evolution mechanisms caused by grassland use change under multiple scenarios. Such information is important for improving grassland ecosystem service value and maintaining regional ecological security. We first measured and analyzed the changes in different types of grassland use and grassland ecosystem service value in Inner Mongolia from 2010 to 2020 based on the comprehensive sequential classification of grassland （CSCS） and the estimation method of ecosystem service value （ESV）. Next， we used the PLUS model to simulate the utilization of various types of grassland under sustainable development， grassland protection and balanced development scenarios， and estimated the service value of the grassland ecosystems. Last， we compared and analyzed the aggregation of grassland ecosystem service values under the three scenarios based on hot spot analysis and spatial grid tools. We found that： 1） The service value of grassland ecosystems in Inner Mongolia shows an increasing trend， with a total increase of 10.14 billion CNY from 2010 to 2020， with the main contributions being from hilly desert grassland and hilly meadow grassland. 2） As assessed in 2020， the service value of grassland ecosystems under the three simulation scenarios of continuous development， grassland protection and balanced development has increased in varying degrees， among which the ecosystem service value of western grassland under the grassland protection scenario has increased the most. 3） The localities of high and low grassland ecosystem service value under the three simulation scenarios are characterized by wide distribution and aggregation， and the high value localities typically show a decentralized aggregation around small areas. The results provide a scientific basis for planning the restoration of grassland ecosystem balance and ecological security in the study area.

Integrating MODIS and Landsat data to reconstruct the Landsat NDVI of a typical region in the Qinghai Lake Basin and changes in the intra-annual NDVI maximum

Fang LI, Guang-jun WANG, Hai-bo DU, Meng LI, Si-hai LIANG, Hong-ming PENG

2023, 32(8):  28-39.  DOI: 10.11686/cyxb2022385

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The normalized difference vegetation index （NDVI） can provide accurate information about vegetation cover and growing status， and the changes in NDVI over a period of time are important indicators of vegetation growth on a global， national， or regional scale. However， there are two main problems to address： First， the spatial resolution of existing NDVI long-time-series products is coarse， so these data can only be used on a large scale， and not on a fine scale. Second， NDVI data obtained from medium-resolution images at different times， such as Landsat images， are greatly influenced by seasonal and inter-annual changes in vegetation as well as the quality of the ecological environment. To solve these two problems， we used the enhanced spatial and temporal adaptive reflectance fusion model （ESTARFM）， which integrates MOD09Q1 and Landsat data， to predict and interpolate the Landsat NDVI for the annual growing season. Then， the Logistic model was used to reconstruct NDVI curves covering vegetation growth seasons from 2001 to 2020. The date corresponding to the annual maximum of Landsat NDVI was obtained from the MODIS daily NDVI data. After reconstructing the curve， we introduced the date parameter to solve the optimal intra-annual NDVI maximum pixel by pixel. Finally， we used the annual maximum of Landsat NDVI to analyze the vegetation growth status and evaluate the change in vegetation in a typical local area near the Buha River in the Qinghai Lake basin. The results show that： 1） The annual maximum of Landsat NDVI was fitted after combining the MODIS and Landsat data. Most （98.5%） of the pixels in the results were within the triple root mean square error （RMSE）， indicative of high precision of the model. 2） When assessing vegetation growth status， the annual maximum value of Landsat NDVI was able to capture detailed changes in vegetation and reduced the errors caused by time differences in the Landsat data. 3） The spatial distribution of the maximum NDVI of vegetation in the study area was high in the north and south and low in the middle. The inter-annual variation first decreased and then increased， and vegetation growth showed an increasing trend. The annual maximum NDVI in the Kobresia and forb meadow in the Qinghai Lake Basin showed a decreasing trend and fluctuated sharply. Further studies should be conducted to investigate these changes in more detail.

Mechanism of herbaceous community assembly in a burned area of Picea asperata-Abies fargesii forest on the northeastern margin of the Qinghai-Tibetan Plateau

Xin-yi YANG, Fu-qiang YANG, Xu-jiao ZHOU, Ming-jun WANG, Hai-xia HUANG, Song-song LU, Xiao-wei ZHANG, Wei-bo DU, Xu-hu WANG, Qing TIAN, An ZHAO, Wan-peng HE, Xiao-lei ZHOU

2023, 32(8):  40-47.  DOI: 10.11686/cyxb2022442

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Many competing theories exist with respect to the mechanisms behind plant community assembly. Niche theory and neutral theory are among the two most widely proposed mechanisms. In this study， we focused on herbaceous communities at different successional stages in a burned area of Picea asperata-Abies fargesii forest on the northeastern margin of Qinghai-Tibetan Plateau. We aimed to elucidate the mechanism of community assembly through calculation of dispersal-niche continuum index （DNCI） and modified stochasticity ratio （MST）. Results show that， 1） DNCI between communities of 5， 15， 23 years and Climax were -22.6169， -21.7507 and -8.2594， respectively. These values were all significantly less than 0， and indicate that the main driving effect of herbaceous community assembly at different succession stages was the dispersal process； 2） MST values of both the 5 yr-Climax group and the 23 yr-Climax group were above the 50%， which indicated that the stochastic process dominated the community assembly in both groups. For the 15 yr-Climax group， the MST value of 15 yr was 0.6664， and the MST value of Climax vegetation was 0.4927， indicating that the plant community assembly of 15 yr is dominated by stochasticity， while the assembly of Climax community is deterministic； since the MST value of 15 yr is much higher than 50%， and the MST value of Climax is close to the threshold of 50%， it can also be shown that the community assembly of the 15 yr-Climax group is still dominated by stochasticity. In conclusion， in a burned area of P. asperata-A. fargesii forest on the northeastern margin of the Qinghai-Tibetan Plateau， stochasticity dispersal dominated the herbaceous community assembly.

Ecological stoichiometry characteristics of soil aggregates in alpine meadows with differing degrees of degradation

Lin-zhi LI, De-gang ZHANG, Yuan MA, Zhu-zhu LUO, Dong LIN, Long HAI, Lan-ge BAI

2023, 32(8):  48-60.  DOI: 10.11686/cyxb2022483

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The stability of alpine meadow ecosystems is closely related to soil structural integrity and nutrient retention. This research sought to clarify the effects of degradation on soil nutrient status and nutrient stoichiometric changes of soil aggregates in alpine meadows with differing degrees of degradation. The research was conducted at the Jinqianghe alpine meadow in Tianzhu County， Gansu Province. Soils with four differing degrees of degradation were selected： No degradation （ND）， light degradation （LD）， moderate degradation （MD） and severe degradation （SD）. Soil samples from the 0-30 cm soil layer were used to study the soil aggregate nutrient status and stoichiometric changes in these four degradation categories by the dry-sieving method. It was found that the organic carbon and total nitrogen in soil aggregates in alpine meadow increased initially and then decreased with increasing degradation， while soil aggregate total phosphorus exhibited a ‘V’-shaped distribution with increasing degradation. The highest contents of organic carbon， total nitrogen and total phosphorus in soil aggregates were in peds 0.25-0.50 mm in size. The C∶N of soil aggregates decreased with increasing degradation. C∶P and N∶P of soil aggregates increased initially and then decreased with increasing degree of deterioration. C∶N， C∶P and N∶P of soil aggregates decreased gradually with increase in soil depth. The results reveal the distribution characteristics of soil aggregate nutrient content and ecological stoichiometry in soils with different degrees of degradation， and thus provide information relevant to the restoration and development of alpine meadow. The composition of soil aggregates is the key factor affecting the nutrient content of soil aggregates. From the perspective of ecological stoichiometry， N and P are the main nutrient limiting factors in the process of alpine meadow degradation.

Distribution of heavy metals and their effects on enzymatic activity in soil of artificial Hippophae rhamnoides forests of different ages near abandoned mines in Shuanglonggou

Da-cheng SONG, Hao WU, Li-de WANG, Fei WANG, Yu-kai ZHANG, Xue-cheng ZHAO

2023, 32(8):  61-70.  DOI: 10.11686/cyxb2022374

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In this study， we investigated the distribution of heavy metals derived from mining activities in forest soils， how they are affected by vegetation， and how they affect soil enzyme activity. The study sites consisted of two artificial Hippophae rhamnoides forests with different ages （2， 10 years） and a control （wasteland）， which were located near abandoned mines in Shuanglonggou， Haxi. We investigated the temporal and spatial substitution of heavy metals in the soil and the activity of four enzymes （sucrase， alkaline phosphatase， catalase and urease） in soil of forests of different ages located near abandoned mines. The heavy metal contents in soil were generally similar between the forests of different ages， but the contents of vanadium （V）， manganese （Mn）， nickel （Ni）， copper （Cu）， strontium （Sr）， and barium （Ba） were 4.21%-26.84% lower in forest soils than in CK soil. The concentrations of V， Mn， Sr， and Ba increased with soil depth， and the concentrations of Cu and Ni were relatively higher in surface soil. The activities of soil enzymes were higher in the more mature forest， with sucrase， alkaline phosphatase， catalase， and urease activities being 12.89%-255.29% higher in the 10-year-old forest soil than in the CK soil. There was a strong negative correlation between the regional heavy metal content and the activity of soil enzymes. Strontium was identified as the main driving factor for differences in soil enzymatic activity among sites. This research provides a reference for the treatment of soil around abandoned mines in Qilian Mountain and other similar areas.

Slope protection by different types of vegetation and ground coverings： A case study on the silty subgrade slope of the Haian-Qidong Expressway

Feng-hou SHI, Yue NI, Cheng-can YANG, Ya-ru ZHAO, Hong-xiang FU

2023, 32(8):  71-81.  DOI: 10.11686/cyxb2022376

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The aim of this study was to explore the feasibility of protecting slopes by planting vegetation with or without ground coverings， and to select the best protection strategy for this purpose. The site selected for this research was the silty subgrade slope of the Haian-Qidong Expressway in Jiangsu Province. Different types of vegetation were planted on slopes of <2 m， 2-4 m， and >4 m in height， and different materials were used to cover the soil surface. We determined the effects of the covering materials on the growth and protection effect of the vegetation. In addition， we monitored the above-ground growth and root growth of five plant species. The results showed that the use of a fiber mat or a straw layer as ground coverings encouraged plant growth and improved their protection capacity. Compared with the straw curtain， the fiber blanket showed better ground coverage. Slope protection by vegetation alone was not suitable for slopes of >4 m in height， because the coverage and uniformity of protective plants in this slope section were poor， serious stratification occurred， and alluvial soil was still visible on the slope surface. Compared with plant growth after mixed sowing of multiple grasses and flowers， plant growth was better after mixed sowing of seeds of multiple grass and shrub species， mixed sowing of multiple grass species， and sowing seeds of a single grass species. The plant cover and uniformity was significantly better after mixed planting of grasses and shrubs than after other planting patterns. The combination of grasses and shrubs mutually promoted their growth， resulting in the best slope protection effect. We evaluated five plant root indicators， and found that the indexes of total root length， root surface area， and root volume were higher for Amorpha fruticosa， Lespedeza bicolor， and Cynodon dactylon than for Paspalum notatum and Magnolia multiflora. The suitability of plants for particular areas and their root growth characteristics can be used as the criteria for selection as protective plants. In general， the protection approach of mixed sowing of multiple grass and shrub seeds as well as a fiber blanket as a ground cover was suitable for protection of the silty subgrade slope of the Haian-Qidong Expressway. This approach was suitable for protection of slopes <4 m in height. The mixture of A. fruticosa， L. bicolor and C. dactylon grew best， and formed a strong plant root system that contributed to slope protection.

Study on shear strength of root-soil composite of Dolichos lablab and Medicago sativa in purple soil region

Yan WEI, You-bin LIU, Xiao-hong LIU, Yun CHEN, Zhe-hao YAN, Yi-zhi DU

2023, 32(8):  82-90.  DOI: 10.11686/cyxb2022392

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To clarify the effects of plant root systems on soil shear strength in purple soil sloping farmland， Dolichos lablab and Medicago sativa were planted and sampled. Their root morphological traits， fiber contents and biomechanical traits were measured. The shear strengths of root-soil composites were measured simultaneously. Correlation analysis and multiple stepwise regression analysis were used to analyze the relation between root traits （including fiber content） and soil cohesion， and root traits and soil internal friction. It was found that： 1） Under 100， 200， 300， and 400 kPa vertical pressure， root-soil composite shear strengths of D. lablab and M. sativa were greater than CK by 1.18%-63.81% （P<0.05）. Similarly， the soil cohesion with plant roots was 141.30%-189.74% greater than CK. 2） For the dominant root diameter class ≤0.5 mm， root parameters were the same for D. lablab and M. sativa. For root diameter classes >0.5 mm and ≤1.0 mm， the root length density， root surface area density and root volume ratio of D. lablab were significantly greater than those of M. sativa. 3） Soil cohesion in the root-soil composite showed a significantly positive relationship with root length density （R²>0.710， P<0.01）， and could be predicted well by root length density and ultimate elongation in a linear regression equation. Generally， D. lablab was better than M. sativa for root enhancement of soil shear strength in purple soil sloping farmland.

Types， grades， and utilization of grassland resources in 52 counties of Hunan Province

Hu-cheng XING, Xian-fang WANG, Qing ZHOU, Jing-cai YAN, Yu-cheng JIE

2023, 32(8):  91-103.  DOI: 10.11686/cyxb2022359

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After 40 years of continuous development， there have been substantial changes in the types， area， and distribution of grassland resources in Hunan Province. The data obtained in the grassland survey in the 1980s no longer reflect the current situation of grassland resources. To scientifically allocate ecological functions and production functions to grassland resources， it is necessary to understand their current situation. To this end， a grassland resources sample plot survey was conducted in 52 counties of Hunan Province in 2018. A total of 3030 sample plots were selected， and the longitude， latitude， altitude， slope aspect， slope position， grassland type， grassland grade， grassland level， coverage， grassland yield， degree of rocky desertification， extent of degradation， and grassland utilization of each sample plot were investigated. Based on the 2018 dataset， the rangeland in the 52 counties was divided into four grassland classes： Warm-temperate shrub tussock， tropical shrub tussock， lowland meadow， and up-land meadow. The majority of the plots （78.44%） were tropical shrub tussock plots， while 16.63% of the plots were lowland meadow and 4.93% of the plots were warm-temperate shrub tussock and up-land meadow. There were 35 types of grassland within the four grassland classes. The grassland types F05 （Imperata cylindrica）， G01 （Phragmites australis）， and G02 （P. australis and Scirpus triqueter） accounted for the largest proportions. Across the 52 counties， 94.47% of the rangeland was below 300 m above sea level （a.s.l.）， 4.54% was between 300 m and 800 m a.s.l.， and 0.99% was above 800 m a.s.l. The majority of rangeland （76.83%） was distributed on the sunny and semi-sunny slopes； 71.10% was distributed above the middle of the slope， and 14.58% was located on the shores of rivers， lakes， reservoirs， and ponds. A large proportion of plots （76.15%） contained grade III pastures， and these pastures were divided into eight levels. Among all the sample plots， 57.68% contained level 1 pastures. The utilization rate of rangeland was low， with 67.78% of rangeland not in use. The hay yield of rangeland was higher. The proportion of plots with a hay yield of 1000-5000 kg·ha^-1 was 42.78%， that with a hay yield of 5000-20000 kg·ha^-1 was 41.40%， and that with a hay yield of >20000 kg·ha^-1 was 11.93%. The grassland area in the 52 counties had decreased significantly since the 1980s. The rangeland vegetation cover was generally good， with average cover of 81.53%. The majority of rangeland sample plots （94.38%） showed no rocky desertification. The areas affected by rocky desertification were concentrated in the Wuling Mountain area， the Hengshao Basin， and the cities of Chenzhou and Yongzhou. The proportion of plots with degraded grassland was 12.73%， and grassland degradation was a significant problem in seven cities （Shaoyang， Yongzhou， Xiangxi， Chenzhou， Loudi， Zhangjiajie and Hengyang）. This inventory provides a reference for the development and utilization of grassland resources in Hunan Province.

Effects of hybrid turf strengthening methods on the quality and safety performance of football field turf

Wei-hao DOU, Gui-long SONG, Lie-bao HAN, Jia-bao CHEN, Xiao-hui YANG, Yong-qiang QIAN, Bo-kun ZOU, Yu-feng CHEN, Xiao-hong LIANG

2023, 32(8):  104-114.  DOI: 10.11686/cyxb2022377

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Reinforced hybrid turf is one of the most effective turf construction technologies to improve the quality and sports performance of football field turf. Reinforced hybrid turf is divided into three types： Fiber-reinforced hybrid turf， carpet hybrid turf， and stitched hybrid turf. In this study， natural turf （control， CK）， fiber-reinforced hybrid turf （sand+0.4% coconut fibre）， carpet hybrid turf， and plant fibre hybrid turf were subjected to a long-term sustained moderate traffic treatment， and their apparent quality， playing quality， and safety performance were evaluated and compared. The three kinds of reinforced hybrid turfs performed better than did CK， but to varying degrees. The apparent quality and sports performance of the reinforced turfs were better than those of CK， indicating that reinforcement can effectively slow down the decline in the apparent quality and sports quality of turf under sustained moderate traffic. Among the various turfs， the stitched hybrid turf performed better in terms of turf coverage， turf rotation friction， and rebound performance； And the fiber hybrid turf performed better in terms of normalized difference vegetation index， turf density， turf surface hardness， and head injury criterion. Compared with CK， the carpet hybrid turf performed better in terms of turf density， rotational friction， and rebound performance， but these effects were not significant or stable. The results show that these three kinds of reinforced hybrid turf are effective solutions to improve and stabilize the apparent quality and playing quality of turf. The use of appropriate reinforced hybrid turf will ensure that turf safety performance meets the relevant international standards and requirements.

Effects of Onobrychis viciifolia and Bromus inermis grass mixture sowing and deficit irrigation on grassland water use and production performance

Yan-xia KANG, Yuan-bo JIANG, Guang-ping QI, Min-hua YIN, Yan-lin MA, Jing-hai WANG, Qiong JIA, Zhong-xia TANG, Ai-xia WANG

2023, 32(8):  115-128.  DOI: 10.11686/cyxb2022451

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Improving the productivity of artificially sown grasslands would relieve the pressure on natural grasslands， maintain the balance between regional forage supply and demand， and promote the healthy development of the local livestock industry. In this research， three artificial pasture sowing strategies were investigated： Bromus inermis （B）， Onobrychis viciifolia （O）， and sainfoin mixed with B. inermis （M）， combined with four deficit irrigation treatments defined in terms of field capacity （θ_FC）： Adequate irrigation （W₀， 75%-85% θ_FC）， mild water deficit （W₁， 65%-75% θ_FC）， moderate water deficit （W₂， 55%-65% θ_FC）， and severe water deficit （W₃， 45%-55% θ_FC）， were applied to investigate the influence on evapotranspiration， yield and quality， and water use efficiency in grassland. The entropy-weighted TOPSIS and entropy-weighted gray correlation methods were applied separately to provide a multivariate evaluation of the treatment effects. It was found that： 1） The evapotranspiration of the pastures ranked first cut>second cut>third cut， and decreased with increasing water deficit. The total evapotranspiration of M was 2.20% less than O and 6.21% greater than B； 2） Forage yield progressively decreased with increasing water deficit level， with no significant difference between W₁ and W₀. The total yield of M was 16.88% and 103.32% greater than O and B， respectively. The land equivalent ratio of M under the four irrigation treatments ranged from 1.38 to 1.65， and the yield proportion of sainfoin in M tended to decrease with increasing water deficit； 3） The mild water deficit improved forage quality and water use efficiency （WUE）. The average crude protein content of M was 21.95% higher than B， and the average acid detergent fiber and neutral detergent fiber contents were， respectively， 1.40% and 3.64% lower than O. Compared with B and O， the average WUE， irrigation WUE， and crude protein water use efficiency increased by 91.17% and 19.07%， 83.17% and 24.47%， and 137.31% and 11.39%， respectively. In conclusion， from the multivariate evaluations， we concluded that M with W₁ had the best overall production effect and can be recommended as a suitable planting management pattern for artificial grassland in the Gansu Hexi Corridor and similar ecological zones.

Effect of alfalfa on the yield and sucrose metabolism of rice in an alfalfa-rice rotation system

Rui XU, Zheng WANG, Yi-ming WANG, Lian-tai SU, Li GAO, Peng ZHOU, Yuan AN

2023, 32(8):  129-140.  DOI: 10.11686/cyxb2022389

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The alfalfa-rice crop rotation system can improve soil quality， increase rice yield， and reduce nitrogen fertilizer input. The aim of this study was to investigate the physiological and molecular mechanisms underlying the effect of alfalfa to promote the yield of rice in this type of crop rotation. We conducted an experiment in which rice plants were grown with soil from a ryegrass crop （control 1）， soil from an alfalfa crop （control 2）， and soil and green manure from an alfalfa crop （alfalfa treatment）. Compared with the two controls， the alfalfa treatment significantly increased the number of tillers， biomass， seed yield， and nitrogen， phosphorus， and potassium contents in leaves of rice plants at the heading stage. The net photosynthetic rate of rice plants at the tillering stage， heading stage， and harvest stage was 16.99%， 27.22%， and 40.99% higher， respectively， in the alfalfa treatment than in control 1； and 16.88%， 37.99%， and 33.51% higher， respectively， in the alfalfa treatment than in control 2. The transcript levels of five key genes involved in sucrose metabolism （OsAGPS1， OsAGPL1， OsMEX1， OsSPS1， and OsSUS5） in the leaves （day and night） and roots differed significantly between the treatment and the controls. Compared with control 1， the alfalfa treatment resulted in up-regulation of OsAGPS1， OsAGPL1， OsMEX1， OsSPS1， and OsSUS5 （by factors of 2.45， 2.96， 1.29， 1.66， and 6.04， respectively） at night in leaves at the tillering stage， while only OsMEX1 and OsSPS1 were up-regulated in leaves during the daytime. OsMEX1 was significantly down-regulated during nighttime in leaves at the heading stage and harvesting stage in the alfalfa treatment. In roots， OsAGPL1， OsMEX1， and OsAGPS1 were significantly up-regulated at the tillering or heading stage in the alfalfa treatment. Correspondingly， the activity of sucrose phosphate synthase and soluble starch synthase in leaves at tillering stage， as well as the contents of starch， sucrose， and soluble sugars in new leaves and leaf sheaths were significantly increased， while sucrose and soluble sugar contents in old leaves were significantly decreased in the alfalfa treatment compared with the two controls. These results indicate that alfalfa green manure and soil can change the distribution of starch， sucrose， and soluble sugars in leaves and sheaths of rice plants grown in a rotation system by affecting the contents of N， P， K in leaves and the circadian expression pattern of key genes in the sucrose metabolic pathway at the tillering stage， thereby increasing rice yield.

Nitric oxide regulation of secondary metabolite accumulation in Medicago sativa seedlings under drought stress

Bao-qiang WANG, Wen-jing MA, Xian WANG, Xiao-lin ZHU, Ying ZHAO, Xiao-hong WEI

2023, 32(8):  141-151.  DOI: 10.11686/cyxb2022252

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The aim of this study was to determine the effects of nitric oxide （NO） on the accumulation of metabolites and the activities of key metabolic enzymes in leaves and roots of drought-stressed alfalfa （Medicago sativa）. The NO donor sodium nitroprusside and the NO scavenger carboxy-2-phenyl-4，4，5，5-tetramethylimidazolineoxyl-l-oxyl-3-oxide （c-PTIO） were applied as foliar sprays to potted alfalfa plants under simulated drought conditions （using polyethylene glycol-6000）. The contents of total phenols， flavonoids， lignans， and anthocyanins increased and then decreased in the leaves and roots of alfalfa during the drought treatment， while the activities of phenylalanine aminolytic enzymes and polyphenol oxidase increased. These trends were promoted by application of exogenous NO， which increased the total phenolic content by 33.08% and led to higher phenolic contents during the late stages of drought stress， thereby reducing drought-induced damage. In contrast， application of the NO inhibitor c-PTIO inhibited the accumulation of phenolic compounds and reduced the activity of key metabolic enzymes in drought-stressed alfalfa seedlings. Thus， exogenous NO promoted the accumulation and retention of secondary metabolites and increased antioxidant enzyme activity in alfalfa to levels higher those under drought stress alone. This greatly reduced the severity of drought damage in alfalfa plants， and improved their drought tolerance. These findings improve our understanding of the plant response to drought stress， and highlight the potential use of an NO donor as a tool to improve the drought tolerance of alfalfa.

A comprehensive evaluation of cold resistance and the physiological response of Elymus sibiricus genotypes

Wen-wei LIU, Xin LIU, Ying-xia LEI, Qing-ping ZHOU, Zhi-feng LIU, Pei WANG

2023, 32(8):  152-163.  DOI: 10.11686/cyxb2022365

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In this study， we screened for Elymus sibiricus genotypes with strong cold resistance， and investigated the mechanism of cold resistance. In a pot experiment， 43 wild-type E. sibiricus germplasm lines were subjected to a freezing treatment at -4 ℃， and the relative electrical conductivity， chlorophyll content， and maximum photochemical efficiency were determined. The data were subjected to a multivariate membership analysis to evaluate the cold resistance of these diverse lines. On the basis of this analysis， a cold-resistant genotype （I-1-4-1） and a cold-sensitive genotype （09-244） were selected. Chilling （4 ℃） and freezing treatments （-4 ℃） were applied to I-1-4-1 and 09-244. The differences in leaf relative water content， cell membrane permeability， osmotic substance content， antioxidant system capacity， and chlorophyll fluorescence parameters between I-1-4-1 and 09-244 under cold stress were analyzed. Under -4 ℃ freezing stress， the chlorophyll content， maximum photochemical efficiency of photosystem II， actual photochemical efficiency， photochemical quenching coefficient， and non-photochemical quenching coefficient were higher in I-1-4-1 than in 09-244， indicating that I-1-4-1 could maintain efficient photosynthesis. Under -4 ℃ freezing stress， the superoxide anion and hydrogen peroxide contents in the leaves were lower in I-1-4-1 than in 09-244， while catalase activity was higher in I-1-4-1 than in 09-244， indicating that I-1-4-1 had a stronger ability to scavenge reactive oxygen species compared with 09-244. The relative electrical conductivity and malondialdehyde content were lower in I-1-4-1 than in 09-244， indicating that the membrane system of I-1-4-1 was less damaged under freezing stress. In addition， I-1-4-1 was better able to adapt to cell dehydration induced by freezing stress by accumulating more free proline to improve osmoregulation. Two principal components were extracted by a principal component analysis. Their cumulative contribution to explaining the variation in cold resistance was >85%. The first principal component was mainly related to photosynthesis and cell membrane permeability， and the second principal component was mainly related to osmotic regulation substances. These results provide reference data for the evaluation of cold resistance and the selection of cold-resistant germplasm resources of E. sibiricus.

Effects of storage time on the fermentation quality， bacterial community composition， and functional profile of sweet sorghum silage

Jie ZHAO, Xue-jing YIN, Si-ran WANG, Zhi-hao DONG, Jun-feng LI, Yu-shan JIA, Tao SHAO

2023, 32(8):  164-175.  DOI: 10.11686/cyxb2022384

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In this study， we aimed to evaluate the chemical composition， fermentation quality， microbial community， and functional shifts of sweet sorghum （SS） during ensiling. SS harvested at the hard dough stage was naturally ensiled for 1， 3， 7， 15， 30， and 60 days. After opening the silo， SS silage （SSS） was randomly sampled for analyses of chemical composition， fermentation parameters， and microbial abundance. Fresh， 7-day， and 60-day SSS were further subjected to high-throughput sequencing and Kyoto Encyclopedia of Genes and Genomes （KEGG） functional prediction analyses. After 60 days of ensiling， SSS displayed homolactic fermentation as characterized by a lack of butyric acid， a low pH value， a high lactic acid concentration， and a high ratio of lactic to acetic acid. Enterobacter （26.0%） and Pantoea （25.7%） were the most common genera in fresh SS， while Leuconostoc （34.1%） and Lactococcus （31.6%） were dominant in 7-day SSS and were subsequently replaced by Lactobacillus （73.5%） in 60-day SSS. A heatmap constructed using Spearman’s correlation coefficient values showed that Lactobacillus was positively related to the lactic acid concentration and negatively related to the pH value. The KEGG metabolic profiles differed substantially between before and after ensiling. The ensiling process downregulated the metabolism of amino acids， energy， cofactors and vitamins， but upregulated the metabolism of nucleotides and carbohydrates. Overall， high-throughput sequencing combined with KEGG functional prediction analyses further confirmed the succession of cocci-shaped lactic acid bacteria to rod-shaped lactic acid bacteria during the SS ensilage process， and revealed trends of up-regulated carbohydrate metabolism and down-regulated amino acid metabolism. A thorough knowledge of the changes in bacterial community dynamics and functional shifts of SS during ensiling is important for understanding the fermentation mechanism and may contribute to the production of high-quality SSS.

Cloning of TB1 from Hordeum bogdanii and the effect of endophytic fungi on its expression

Dan HAN, Feng LONG, Sheng CHEN, Meng-fei HU, Dong WANG, Shui-hong CHEN

2023, 32(8):  176-185.  DOI: 10.11686/cyxb2022369

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The tillers of the Poaceous crop plant Hordeum bogdanii develop from non-elongating internodes at the base of the stem， form adventitious roots， and can survive independently of the main stem. The yield of H. bogdanii is mainly increased by tillering， which is regulated by both endophytic fungi and genes of the host. To explore the effect of endophytic fungi on the tiller-related gene TB1 in the host plant， the TB1 gene of H. bogdanii was cloned by RT-PCR， sequenced， and then analyzed using bioinformatic methods. The transcript levels of TB1 were determined by PCR using SYBR Green fluorescent dye. These PCR analyses were conducted for H. bogdanii with endophytic fungi （E+） and without endophyte fungi （E-） growing in Wensu County， Xinjiang and Tsaidam Basin， Qinghai. The full-length coding sequence of the TB1 gene clonedfrom H. bogdanii was 804 bp， encoding a polypeptide consisting of 267 amino acid residues. The TB1 gene had no promoter and did not encode a polyA tail. A subcellular localization analysis predicted that TB1 localizes in the vacuole. The TB1 protein， which belongs to the TCP family， has no transmembrane domains and no signal peptide， so it is not a transmembrane protein. It was predicted to be an unstable protein. The TB1 gene of H. bogdanii showed the highest homology （96.72%） with TB1 of Hordeum vulgare subsp.， and was located in the same branch as TB1 from H. vulgare subsp. in the phylogenetic tree. The transcript profiles of TB1 in the roots， stems， and leaves were similar between plants growing in Wensu County and those growing in the Tsaidam Basin. Endophytic fungi significantly reduced the expression of TB1 at the base of stems （the tillering site）. These results show that endophytic fungal infection affects the expression of the host’s TB1 gene， thereby regulating tillering. These findings provide a theoretical foundation for further research on the tillering mechanism of H. bogdanii.

Functional characterization of Cyperus esculentus CeWRKY transcription factors in response to abiotic stress

Xian-fei SHI, Yu GAO, Xu-sheng HUANG, Ya-li ZHOU, Gui-ping CAI, Xin-ru LI, Run-zhi LI, Jin-ai XUE

2023, 32(8):  186-201.  DOI: 10.11686/cyxb2022150

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Cyperus esculentus is a new type of forage and oil crop， with its overground leaves providing high-quality herbage and its underground tubers accumulating high levels of oleic acid-enriched oils. C. esculentus also possesses strong tolerance against various stresses. WRKY transcription factor （TF） is one group among the large superfamily of transcription factors involved in growth and development， tissue metabolism， stress response and other physiological processes in the plant. However， there is limited knowledge about the WRKY family members and their functions in C. esculentus. Here， a total of 67 CeWRKY transcription factors were identified by mining transcriptome data. Phylogenetic analysis showed that CeWRKYs were classified into three groups which we designated I， Ⅱ and Ⅲ. CeWRKYs have both the typical WRKY domain and a zinc finger domain. Seven CeWRKYs exhibited mutation in the WRKY domains， which may be related to their functional divergence. The sequence length， molecular weight， and isoelectric point of CeWRKY proteins are predicted to vary greatly. CeWRKY proteins are predicted to be hydrophilic proteins without a transmembrane structure. These proteins were predicted to be localized in the nucleus. Temporal and spatial expression of CeWRKY genes were detected during C. esculentus tuber development.Different CeWRKY genes displayed differential expression patters in C. esculentus seedlings in response to different stresses. The expression profile of the CeWRKY8 gene changed significantly in C. esculentus seedlings exposed to drought， salt， or alkali stresses. This CeWRKY8 may be a major regulator of stress response in C. esculentus. The present study establishes the essential framework for complete understanding of the diverse biological function of CeWRKY transcription factors and molecular mechanisms mediating stress response in C. esculentus， providing a scientific pathway for developing new varieties of C. esculentus with high quality， enhanced biomass yield and strong stress resistance.

Studies on the regulation of seed aging by reactive oxygen species and telomeres

Shou-jiang SUN, Pei-sheng MAO, Li-ru DOU, Zhi-cheng JIA, Ming SUN, Wen MA, Cheng-ming OU, Juan WANG

2023, 32(8):  202-213.  DOI: 10.11686/cyxb2022417

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Seeds enable plants to survive in harsh environmental conditions and can transmit genetic information from their parents to the next generation. Seed vigor is an important character in agriculture， which directly affects the field emergence rate and crop yield. However， due to seed aging， seed vigor decreased during storage. In order to effectively protect genetic resources and reduce the huge economic losses caused by seed aging to agricultural production， it is necessary to explore the mechanism of seed aging in order to understand the causes of seed aging and a series of important events that occur in the aging process. During seed storage， high temperature and humidity are the two main factors to accelerate seed aging. The oxidative damage caused by reactive oxygen species （ROS） is the main reason. ROS can interact with any biological macromolecule， leading to protein damage， lipid peroxidation， chromosomal telomere structure abnormality and various cell components damage caused by DNA damage. In addition， ROS may also induce programmed cell death， leading to seed aging. At the initial stage of imbibition， the seeds will repair some damage， but if they cause great damage to key structures， they will fail to repair， and the seeds will lose their vitality permanently， so they cannot germinate normally in a relatively short time. The exact mechanism of seed aging has not been fully studied. Based on this， this study mainly reviewed the generation and elimination of ROS during seed aging， the influence of ROS on biological macromolecules， the response of chromosome telomere system to seed aging， and the research progress of genes related to seed aging， which is of great significance for understanding the causes of seed aging and analyzing the mechanism of seed aging.

Effect of fencing and grazing on soil macro- and meso-arthropod diversity in alpine grassland ecosystems in the Qilian Mountains in the fall

Ji-liang LIU, Wen-zhi ZHAO, Yong-zhen WANG, Yi-lin FENG, Jin-xian QI, Yong-yuan LI

2023, 32(8):  214-221.  DOI: 10.11686/cyxb2022383

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Overgrazing and climate change are resulting in the degradation of alpine grasslands in the Qilian Mountains. Preventing grazing by fencing can restore the degraded alpine grassland ecosystem. However， long-term prevention of grazing will affect the structure and function of above- and below-ground ecosystems in alpine grasslands. In this research， we studied typical alpine grassland in the Hulu watershed of the Qilian Mountains， in which fenced （FH） and grazed alpine grassland habitats （GH） formed a gradient of grazing management. In autumn 2021， soil macro- and meso-arthropods were collected in the long-term FH and GH areas of alpine grassland by pitfall trapping and an improved Tullgren funnel method， and were identified and counted. The soil macro- and meso-arthropod community composition differed significantly between the FH and GH areas of alpine grassland in the fall， and soil meso-arthropod diversity was more sensitive than macro-arthropod diversity to grazing management. Compared with GH areas， the FH areas showed higher values of group richness and Shannon-Wiener index of soil macro-arthropods， and the activity density of soil macro-arthropods was significantly higher in FH areas than in GH areas. Compared with soil macro-arthropods， soil meso-arthropods responded differently to grazing management of alpine grassland. Their values of contrast density， group richness， Shannon-Wiener index， and Acarina/Collembola （A/C） were lower in FH areas than in GH areas. These results show that different soil arthropod taxa respond differently to grazing management of alpine grassland， and this affects the assemblages of soil macro- and meso-arthropods. Furthermore， prevention of grazing in alpine grassland significantly decreased the activity density of centipedes， spiders， and beetles， and reduced the activity density of ants and the density of springtails. In short， soil arthropod communities and major taxa in alpine grassland are sensitive to fencing and grazing management， and their changes in abundance and diversity can be used to indicate grazing management intensity in alpine grassland.