Table of Content

20 January 2023, Volume 32 Issue 1

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Characteristics of temporal and spatial variation in landscape ecological risk in Gansu Province based on land use and cover

Yang-jing XIU, Meng-jing HOU, Jiao-yang TIAN, Tian-gang LIANG, Qi-sheng FENG

2023, 32(1):  1-15.  DOI: 10.11686/cyxb2021298

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Gansu Province has rich and diverse landscape types， which play a key role in the ecological security of Western China， and also provide important material bases and ecological services for local development. Due to the impact of climate change and unsustainable human activities， the security and stability of the ecological environment in some areas of Gansu Province has become severely challenged. Based on the climate change initiative-land cover （CCI-LC） data of European Aviation Administration， this study analyzes the characteristics of land use and cover change in Gansu Province from 2005 to 2019， using a ‘dynamic degree and transfer matrix’ methodology. By constructing the landscape ecological risk index and using the spatial autocorrelation analysis method， this study analyzes the spatial distribution characteristics of landscape ecological risk. It was found that： 1） From 2005 to 2019， the area of bare land decreased the most， with a change over the 15-year study period of 1.88%， followed by cultivated land， with a decrease of 2.31%； grassland area increased the most， with a five-year change （an annual increase） of 1.83%， followed by construction land， with an increase of 191.08%. 2） Among all land use and cover categories， the extent of change for construction land was the highest， and the rate of change remained at a consistently high level throughout the study period. The period with the highest overall extent of change was 2010-2019. 3） The land use/cover transfer matrix was mainly comprised of the transfer in and transfer out of cultivated land， forest land， grassland and bare land， as well as the transfer in of other land types to construction land. 4） The overall ecological risk value in 2019 was significantly higher than in 2005. Among the risk categories， the ‘low-risk’ category had the largest area， and the most frequent occurrence of transformation. Areas designated ‘medium risk’ and ‘high risk’ were comparatively small， they all have exhibited different degrees of growth. 5） From 2005 to 2019， Moran’s I remained at a high level. This index was positively correlated with the spatial distribution of landscape ecological risk and had a strong aggregation effect. The purpose of this study is to provide a scientific basis for land use planning and ecological risk control in Northwest China.

Analysis of grassland community-level plant functional traits and functional diversity at different times during restoration

Jiang-wen LI, Bang-yin HE, Cai LI, Hong-yan HUI, Bo LIU, Xiao-xi ZHANG, Hui FAN, Wen-yu SU

2023, 32(1):  16-25.  DOI: 10.11686/cyxb2022029

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Plant functional traits and functional diversity are important factors when evaluating the function of grassland ecosystems. In this study， we conducted a series of analyses of the understory grassland of Robinia pseudoacacia forests and abandoned grassland at different time points during restoration in the hilly and gully regions of the Loess Plateau. The community-level dynamics of plant functional traits and functional diversity were analyzed during vegetation restoration to explore how the grassland plant community and its functional traits change over time. The results showed that： 1） The understory grassland and abandoned grassland were both dominated by perennial weeds in the Asteraceae and Rosaceae； 2） During restoration， the understory grassland succeeded from a dicot-dominated community to a monocot-dominated community， while Asteraceae species were gradually replaced by Poaceae species. The abandoned grassland was always dominated by Asteraceae species， however， and showed a tendency to shrub encroachment. 3） The values of community-level leaf functional traits were higher in understory grassland than in abandoned grassland， while the values of community-level plant functional traits of coverage， density， and aboveground biomass were lower in understory grassland than in abandoned grassland. The values of species diversity and functional trait diversity were higher in abandoned grassland than in understory grassland， and abandoned grassland exhibited higher ecological benefits. These results provide a theoretical basis for the evaluation of grassland ecosystem functions in the hill and gully region of the Loess Plateau.

Vegetation responses to sand source and supply volume in Caragana microphylla shrubland

Ya-ling HU, Eerdun HASI, Liang MAN, Yi YANG, Ping ZHANG

2023, 32(1):  26-35.  DOI: 10.11686/cyxb2022003

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This research targeted Caragana microphylla nebkhas located in three sites in residual-depositional land （endogenous sand source）， downwind of alluvial fans and cultivated land （exogenous sand source） in the eastern sector of the northern foot of Yinshan Mountain. Three sampling areas were set up along a transect at each sample site， and three sample quadrats were set up in each sample area， making a total of 27 sample quadrats across the three sample sites. The aim was to investigate the vegetation of C. microphylla nebkhas and inter-dunes， and to study the plant community characteristics of the C. microphylla shrubland under the different sand sources and sand supply volumes. It was found that： 1） C. microphylla-Leymus chinensis was a ubiquitous plant species association of C. microphylla nebkhas at all three study sites， despite the different soil depositional processes. 2） The species number within nebkhas was much greater than that of inter-dune areas in the three sites， and the species number was maximized in nebkhas located downwind of the alluvial fans with the most sand. Comparing the three sites， the species similarity was the highest between the downwind of the alluvial fans and cultivated land （38%-42%）. The similarity between the nebkhas and inter-dunes at each site was the highest in the residual-depositional land （80%） and lowest in the cultivated land （53%）. 3） Six plant species appeared in all three sites： Stipa krylovii， L. chinensis， Cleistogenes squarrosa， Artemisia frigida， Allium tenuissimum and Salsola ruthenica. 4） In downwind direction， as the increase （residual-depositional land） or decrease （downwind of alluvial fans and cultivated land） of sand supply volumes， the species number increased initially and then decreased on the inter-dune area， while within nebkhas， the numbers of species near the sand source were higher in the downwind of the alluvial fans and cultivated land than that in residual-depositional site， and were gradually close to that in the residual-depositional land with the decrease of sand supply volume. In conclusion， the sand supply volume and sand source greatly influenced species diversity of C. microphylla shrubland， while the major plant species association categories were almost unaffected.

Study on above-ground biomass measurement of Caragana microphylla in shrub-encroached grassland

Rong RONG, Bin SUN, Zhi-tao WU, Zhi-hai GAO, Zi-qiang DU, Si-han TENG

2023, 32(1):  36-47.  DOI: 10.11686/cyxb2022201

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Shrub-encroached grassland has become an important vegetation landscape type in arid and semi-arid areas in China. The shrub-encroached grassland of Caragana microphylla in Inner Mongolia is the most typical example of this vegetation landscape type in China. To explore the best measurement method for above-ground biomass of C. microphylla， 17 typical plots were selected in the Bordered Yellow Banner and Zhengxiangbai Banner of Xilin Gol League， and the accuracy of above-ground biomass obtained using two direct measurement methods， “standard branch” and “standard quadrat” ， was compared. At the same time， the possibility of indirect measurement of above-ground biomass under noninvasive conditions was studied by using four directly measurable factors， i.e.， height and irregular canopy area obtained by real-time kinematic analyses and three derived complex factors. Using these factors， a model to estimate the above-ground biomass of C. microphylla shrub in the study area was established. It was found that： 1） The biomass predicted by the “standard branch” method （R=0.95， P<0.01） was more accurate and less destructive than that predicted by the “standard quadrat” method （R=0.84， P<0.01）. 2） In the correlation analysis of easy-to-measure factors， the single factors crown breadth， irregular crown area and irregular crown perimeter were strongly correlated， with correlation coefficients greater than 0.98 （P<0.01）， suggesting that they could be used to predict the above-ground biomass of C. microphylla. Height showed a general relationship with each of the single factors， with correlation coefficients ranging from 0.67 to 0.72 （P<0.05）. However， three-term complex factors derived from height improved the prediction accuracy. 3） Among the single factors， crown breadth （R=0.92， P<0.01） had the strongest correlation with biomass， while irregular volume （R=0.92， P<0.01） had the strongest correlation with the complex factors. An above-ground biomass prediction model of C. microphylla was established. It consisted of a linear function with crown breadth as an independent variable and a power function with irregular volume an independent variable. These results provide a scientific reference for the estimation of above-ground biomass based on an integrated “space-air-ground” method.

Effects of interplanting with different species of cover grass on soil evaporation， air humidity， and soil water storage in apple orchards on the North China Plain in spring

Wen-li QIN

2023, 32(1):  48-62.  DOI: 10.11686/cyxb2022163

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The aim of this study was to clarify how different species of cover grass affect soil evaporation， canopy air humidity， and soil water storage in an apple （Malus pumila） orchard in spring， and to determine how cover grasses affect the available water content in soil. A field experiment was conducted from 2019 to 2021 at the Wuluo Modern Agriculture Demonstration Garden， Wuyi County， Hebei. Changes in， and interactions among， the leaf area index （LAI） of the grass population， photosynthetically active radiation （PAR） transmittance， soil temperature， water evaporation， air relative humidity in the fruit tree canopy， soil water content， and water storage were evaluated when overwintering grasses ［February orchid （Orychophragmus violaceus）， hairy vetch （Vicia villosa）， and triticale （×Triticosecale Wittmack）］ and perennial grasses ［cocksfoot （Dactylis glomerata） and white clover （Trifolium repens）］ were planted between the apple tree rows. It was found that the soil evaporation in sod culture was 3.14 mm higher with overwintering grasses than with perennial grasses from April to May in 2021. The effects of overwintering grasses on soil evaporation differed between before and after returning to the field. Before returning to the field， overwintering grasses reduced soil evaporation by 20.5% compared with perennial grasses due to the rapid growth rate， large population LAI， low PAR transmittance， low temperature in 0-25 cm soil profile， and low soil water content. After overwintering grasses were returned to the field， the soil evaporation was 29.0% higher than in the plots with perennial grasses. There was a significant linear positive correlation between air relative humidity at 1 m height in the fruit tree canopy and reduced soil water storage in the 1 m soil profile. Compared with perennial grasses， overwintering grasses consumed 39.20 mm more stored soil water， and increased the air relative humidity by 15.5%. Compared with clear tillage， sod culture reduced soil evaporation by 27.80 mm， and increased stored soil water consumption by 52.50 mm. In conclusion， the ability of cover grasses to reduce soil evaporation in spring could not compensate for the consumption of soil water by grass growth， which ultimately resulted in reduced soil available water content. Compared with perennial grasses， overwintering grasses were more conducive to improve air humidity in orchards on the North China Plain in spring， but consumed a large amount of stored soil water. In practice， irrigation systems for apple orchards in spring should be optimized according to how different grass species affect the soil water content.

Effects of a cover crop on deep soil water and root characteristics in a dryland apple orchard on the Loess Plateau

Wei-jie LI, Li WANG, Jing-yong MA, Zi-kui WANG

2023, 32(1):  63-74.  DOI: 10.11686/cyxb2022009

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To clarify the interaction between soil water content and root distribution and provide information for orchard cover crop management in the Loess Plateau， the distribution of apple tree root systems and deep soil moisture contents in the presence or absence of a cover crop were investigated. The experiment was conducted in the apple orchard of Qingyang National Field Station of Grassland Agroecosystems. Two planting patterns were set up， namely， orchard with cover crop （Dactylis glomerata， planted in 2014） and orchard with clean tillage， with annual crop farmland as control. Soil moisture and fine root length density in 0-500 cm soil layer were measured at four locations in the tree rows and between the tree rows for two consecutive years in summer and the effects of cover crop on soil moisture deficit and fine root length density were determined. Soil moisture levels in 0-300 cm soil horizon of orchard with clean tillage decreased by 6.7%-8.3% （P<0.01） compared to the control farmland， while soil moisture in 300-500 cm soil layer was not significantly changed （P>0.05）； soil moisture levels in the whole profile of 0-500 cm of the cover crop treatment were on average 11.5%-12.3% lower than those of the clean tillage treatment. The water deficit in the 0-500 cm soil horizon of the control farmland was 163.9-172.1 mm after 6-7 years of cover crop planting， which was 3.2-4.2 times of that in the clean tillage orchard. In addition， the fine root length density of apple tree roots in the 0-100 cm soil layer was higher than that in deeper layers， and averaged 0.187 cm·cm^-3 in density. Cover crop promoted root length density in the 0-100 cm soil layer. The soil moisture content in the various soil horizons from 0-500 cm decreased with increase in fine root length density and the correlation coefficient was increased by the presence of a cover crop， and was higher in the dry season.In summary， long-term cover crop planting in apple orchards in the dryland area on the Loess Plateau promoted the growth of apple tree roots， reduced deep soil moisture and aggravated deep soil drying， which would have a negative effect on the production of apple trees and water cycling in the local agricultural ecosystem. Cover crop management in apple orchard should be reviewed to ensure sustainable water use.

Effect of multivariate flax rotation mode on soil aggregation characteristics and nitrogen content

Yong ZHANG, Hai-di WANG, Yu-hong GAO, Bing WU, Bin YAN, Yi-fan WANG, Zheng-jun CUI, Ze-dong WEN

2023, 32(1):  75-88.  DOI: 10.11686/cyxb2022020

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The aim of this study was to devise a planting system conducive to maintaining good physical and chemical properties of farmland soil in the arid area of Northwest China. Therefore， a field experiment was conducted to determine the effects of different planting patterns of flax （Linum usitatissimum） alone or with other crops， wheat （W， Triticum aestivum） and potato （P， Solanum tuberosum）， on soil properties. The experimental treatments consisted of 100% flax， 50% flax （Ⅰ）， 50% flax （Ⅱ） and 25% flax， with a fallow treatment as the control. Under the four flax planting frequencies， 100% flax （Cont F） consisted of flax only， 50% flax （Ⅰ） consisted of flax alongside W and P， planted with the following pattern： WFPF， FPFW， PFWF， FWFP； 50% flax （Ⅱ） consisted of flax alongside W and P planted with the following pattern： FWPF， WPFF， PFFW， FFWP； and 25% flax consisted of flax alongside W and P planted with the following pattern： WPWF， PWFW， WFWP， FWPW. The stability of farmland soil aggregates and the distribution of nitrogen under these 13 crop rotation systems were determined. We detected very significant negative correlations between soil aggregate mean weight diameter （MWD） and geometric mean diameter （GMD）， fractal dimension （D）， and percentage of aggregate destruction （PAD）. There were significant positive correlations between MWD and NH₄⁺-N content in the 0.5-1.0 mm particle size fraction and NO₃^--N content in the >2 mm particle size fraction. The nitrate ammonium nitrogen content increased with increasing soil aggregate stability. The planting frequency of 50% flax （Ⅰ） and potato stubble significantly increased the amount of soil aggregates in the >0.25 mm size class and macroaggregate MWD and GMD， and significantly reduced soil D， PAD， and soil erodibility. The FWFP treatment increased the amount of soil aggregates in the 0.25-2.00 mm size class， significantly increased soil aggregate MWD and GMD and erosion resistance， reduced soil D and PAD， and made the soil aggregate structure more stable. These results show that the FWFP rotation can significantly improve soil water content and soil stability and increase the contents of soil aggregates and their stability. This information is important for the sustainable development of flax cultivation in Northern China.

Effects of long-term monocropping on soil microbial metabolic activity and diversity in topsoil and subsoil horizons of Lycium barbarum fields

Tong PENG, Shao-lan MA, Cai-xia MA, Yan-fang SONG, Na GAO, Kai-le LI, Chuan-ji ZHANG, Jing-wen LI, Xiao-fan NA, Li-guang WANG

2023, 32(1):  89-98.  DOI: 10.11686/cyxb2021494

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The diversity and activity of soil microbial communities are essential for maintenance of the stability and function of the soil ecosystem. However， long-term monocropping of Lycium barbarum has caused biodiversity loss and alteration of soil microbial community composition. It is still unclear how such management affects soil microbial metabolic activity. This research explored the impacts of long-term monocropping on soil microbial metabolic activity in L. barbarum fields. We investigated the variation of microbial community-level physiological profiles （CLPP） in the topsoil （0-20 cm） and subsoil （20-40 cm） horizons of L. barbarum fields using Biolog EcoPlate methodology. Soil enzyme activities and abiotic properties were measured to explore the factors driving variation in CLPP. It was found that L.barbarum monocropping promoted the microbial metabolic activity of topsoil （P<0.05）， but did not affect that of the subsoil nor the metabolic diversity index of either soil horizon. With increase in stand age， the utilization rates of Tween 80 and itaconic acid increased in topsoil， while those of D-glucosaminic acid and phenylethylamine decreased significantly in subsoil （P<0.05）. The utilization of polymers significantly decreased with the increase in stand age in both soil depths （P<0.05）， indicating that long-term monocropping affects the ability of soil microorganisms to degrade complex organic matter. Variance partitioning analysis further suggested that soil abiotic properties and fungal abundance were the major factors driving the variation in soil microbial metabolic diversity in L. barbarum fields. The data show that long-term monocropping disturbed the metabolic activity and the decomposition rates of complex soil organic matter， particularly in the subsoil. We propose that the subsoil quality of L. barbarum fields should be monitored and supervised under monocropping.

Effects of salt stress on the growth， physiology， and biochemistry of five Bromus inermis varieties

Rui-qiang LI, Yu-xiang WANG, Yu-lan SUN, Lei ZHANG, Ai-ping CHEN

2023, 32(1):  99-111.  DOI: 10.11686/cyxb2022027

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The aim of this study was to compare the salt tolerance of different Bromus inermis varieties. Seedlings of five B. inermis varieties （L_1-5） were used as the experimental materials. According to the composition of soil salts in Xinjiang， two treatments were established； neutral salt （M salt） （NaCl∶Na₂SO₄∶Na₂CO₃=1∶4∶0） and alkaline salt （A salt） （NaCl∶Na₂SO₄∶Na₂CO₃=1∶1∶8）. When seedlings reached the three-leaf stage， each pot was irrigated with 2 L salt treatment solution with an electrical conductivity （EC） of 20 ms·cm^-1 at a one-time treatment. The control （CK） was irrigated with the same amount of tap water. After 30 days of treatment， the growth index， chlorophyll fluorescence characteristic parameters， malondialdehyde （MDA） content and osmoregulation substance content were measured. Then， correlation analysis， principal component analysis， and a membership function analysis were used to analyze and evaluate 13 indicators. The results showed that， other than maximum quantum efficiency （F_v/F_m） and potential quantum efficiency （F_v/F_o）， the other 11 indexes were strongly affected by salt stress， and the values of the indexes differed significantly among the five Bromus varieties （P<0.05）. The plant height， stem diameter， tiller number， aboveground biomass， root-crown ratio， MDA content， and proline content of the five B. inermis varieties showed different adaptive changes under different types of salt stress. The plant height of L₂ and L₄ was significantly higher in the A salt treatment than in the M salt treatment； the A salt treatment significantly increased the aboveground biomass of L₃， while the M salt treatment had no significant effect compared with CK. The MDA content of L₁， L₂， and L₅ increased more under the A salt treatment than under the M salt treatment， and the MDA content of L₂ was higher than that in the other lines under the A salt treatment. Salt stress seriously inhibited root development and the accumulation of soluble sugars in all B. inermis varieties. The underground biomass and soluble sugar contents in the five B. inermis varieties were decreased to varying degrees in the salt treatments compared with CK. A principal component analysis showed that osmotic adjustment substance content and growth indexes could be used as comprehensive indexes of the salt tolerance of B. inermis. According to the salt tolerance evaluation D value， L₄ has strong salt tolerance and L₅ has weak salt tolerance.

Young spike differentiation and reproductive pattern of Bromus inermis in different habitats

Ying-xia CHEN, Yu DU, Yu-xiang WANG, Bo ZHANG, Abduriherman ADILE

2023, 32(1):  112-121.  DOI: 10.11686/cyxb2022014

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In this study， we explored the effects of habitat on young spike differentiation and the reproductive pattern of Bromus inermis cv. Wusu No.1. We compared the process of young spike differentiation and flowering habits between plants in two growth environments： a desert oasis area and a high altitude area. The results showed that the young spike differentiation of B. inermis extended from the tillering stage to the heading stage， and could be divided into eight stages： the vegetative stage， elongation stage， single ridge stage， spikelet primordial stage， floret primordial stage， stamen primordial formation stage， stamen formation stage， and spike completion stage. Young spike differentiation started from the first branch primordium and floret primordium at the top of the growth cone. The primordia on the same branchlets and floret primordia developed from bottom to top. The flowering sequence of the whole spike was from top to bottom， and the flowering time was shorter on the lower branches than on the upper branches. The florets on the spikelets bloomed from bottom to top. Compared with the plants in the desert oasis area， those in the high altitude area differentiated young spikes later， had a shorter cycle， had higher contents of gibberellin， abscisic acid， and leaf soluble protein in the spike， lower cytokinin content and 1000-grain weight， and higher number of mature seeds per spike and seed yield per unit area. These results show that the high altitude area is more suitable for B. inermis seed production.

Resistance of quinoa seedlings under different salt-alkali stress levels

Hao-yu XU, Ying ZHAO, Qian RUAN, Xiao-lin ZHU, Bao-qiang WANG, Xiao-hong WEI

2023, 32(1):  122-130.  DOI: 10.11686/cyxb2021500

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This research explored the resistance mechanism of quinoa （Chenopodium quinoa） seedlings under different salt-alkali stress levels， to provide reference data for its breeding， introduction and cultivation. It was envisaged the research would overcome the planting limitation of quinoa arising from to land salinization in northwest China. In this study， neutral salts （NaCl， Na₂SO₄） and alkaline salts （NaHCO₃， Na₂CO₃） mixed in different proportions with a concentration of 200 mmol·L^-1 were used as stress treatments. These included： A） NaCl∶Na₂SO₄ =1∶1， B） NaCl∶Na₂SO₄∶NaHCO₃ =1∶2∶1， C） NaCl∶Na₂SO₄∶NaHCO₃∶Na₂CO₃ =1∶9∶9∶1， D） NaCl∶Na₂SO₄∶NaHCO₃∶Na₂CO₃ =1∶1∶1∶1， E） NaCl∶Na₂SO₄∶NaHCO₃∶Na₂CO₃ =9∶1∶1∶9. This series was designed to provide gradually increasing pH as stress treatments. There was also a control （CK） treatment. The effects of the different saline-alkali stress levels on the growth of white quinoa seedlings， the levels of osmotic regulators， the activity of antioxidant enzymes and the expression of NHX1a and NHX1b genes related to Na⁺ compartmentalization were analyzed. It was found that with increased stress time， the plant height of quinoa was suppressed， and the root length and root∶shoot were promoted. Compared with CK， the plant height under treatment E was decreased by 15.39%， and the root length under treatment C was increased by 35.97% and the root∶shoot was increased by 53.10%. Across the salt concentration series， the content of malondialdehyde （MDA） in leaves increased initially and then decreased， and was low under treatment E. The contents of soluble sugar， soluble protein and proline （Pro） increased first and then decreased under the treatment of components A， B and C， and increased continuously under the treatment of components D and E. The superoxide dismutase and ascorbate peroxidase activities in the leaves initially increased and then decreased， peroxide enzyme activity progressively declined， catalase activity increased initially and then plateaued. The expression of Na⁺ compartmentalization-related genes NHX1a and NHX1b in leaves decreased initially and then increased， and the gene expression ranked in order treatment E>D>B>C>A. The results showed that as the proportion of alkaline salt in the saline solution was increased， the damage to quinoa seedlings progressively intensified， but quinoa has capacity to improve its own tolerance through salt tolerance mechanisms such as osmotic regulation， antioxidant production， and salt tolerance-related gene expression.

Responses of leaf epidermis， anatomical structure and photosynthetic characteristics of Poa pratensis to different nitrogen application level

Wen-wu QIAN, Peng GUO, Hui-sen ZHU, Shi-min ZHANG, De-ying LI

2023, 32(1):  131-143.  DOI: 10.11686/cyxb2021498

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This study explored the response of leaf epidermal characteristics， anatomical structure and photosynthetic characteristics of Poa pratensis to nitrogen application level. Six P. pratensis varieties were used， including three introduced varieties from the United States： Merit， Jackrabbit and Park， two native wild populations from Shanxi： Yingxian and Hunyuan， and one P. pratensis strain， ‘Taihang’， bred from wild populations from Shanxi. The treatments comprised two nitrogen levels： N₁， 10 g·m^-2 （low nitrogen） and N₂， 40 g·m^-2 （normal nitrogen）. Freehand slicing and paraffin sectioning were used to prepare slides. The leaf upper and lower epidermal thickness， cell length∶width， cell density， stomatal index， stomatal length∶width， stomatal density， leaf thickness， sclerenchyma thickness， vascular bundle area， stomatal conductance， and net photosynthetic rate were measured using an optical microscope. It was found that the upper and lower epidermal thickness， leaf thickness， sclerenchyma thickness， vascular bundle area， stomatal conductance and net photosynthetic rate of P. pratensis leaves under the N₁ treatment were significantly lower than those under the N₂ treatment， while the stomatal size in N₁ was not significantly different from that under the N₂ treatment. Under the N₂ treatment， the leaf thicknesses of Jackrabbit and Park were significantly higher than those of Hunyuan and Yingxian. The leaf thickness of Park was the largest， reaching 173.39 μm. The leaf vascular bundle area of Jackrabbit was significantly higher than that of Hunyuan and Park. The net photosynthetic rate of Merit was the highest， reaching 17.23 μmol CO₂·m^-2·s^-1. This value was 45.16% higher than that of the lowest， Park. Correlation analysis showed that net photosynthetic rate was positively correlated with upper and lower epidermal thickness， sclerenchyma thickness， vascular bundle area and stomatal conductance. The N₁ （low） nitrogen treatment resulted in thinning of P. pratensis leaves， decreased vascular bundle area， and decreased stomatal conductance and net photosynthetic rate. Leaf stomatal conductance and net photosynthetic rates of P. pratensis var. ‘Taihang’ were higher than those of other varieties under the N₁ treatment， and ‘Taihang’ had lower sensitivity to low nitrogen.

Effect of root traits of Medicago sativa lines with fall dormancy on overwintering

Xiao-long WANG, Zhao YANG, Yong-cai LAI, Hong LI, Peng ZHONG, Yan-xia XU, Hua CHAI, Sha-sha LI, Yue WU, Min-chao SONG, Jing-ming ZHOU

2023, 32(1):  144-153.  DOI: 10.11686/cyxb2022016

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Alfalfa （Medicago sativa） varieties suitable for cultivation in western Heilongjiang Province were screened to explore the relationships among winter survival rate， root traits， and yield. Eight alfalfa varieties with different levels of fall dormancy from China and abroad were tested in a regional field experiment， which was established with a randomized block design. The yield， winter survival rate， and root traits （root crown diameter， root crown volume， root crown depth in soil， root length， main root diameter， number of root tips， lateral root diameter， lateral root position， lateral root number， and root biomass） were measured for each variety. The winter survival rates of Gongnong No.2， Caoyuan No.3， and Zhaodong alfalfa were all higher than 95%. The winter survival rate was significantly negatively correlated with root biomass （P<0.05； correlation coefficient， 0.762）； and positively correlated with root crown diameter and crown depth in soil （P<0.05； correlation coefficients of 0.797 and 0.756， respectively）. The winter survival rate was negatively correlated with the position of lateral roots （P<0.05； correlation coefficient， 0.712）. There was a significant positive correlation between yield and winter survival rate （P<0.01； correlation coefficient， 0.956）. The yields of Zhaodong， Caoyuan No.3， and Gongnong No.2 were 12746.73， 11921.24， and 11416.77 kg·ha^-1， respectively， which were significantly higher than those of other varieties （P<0.05）. A principal component analysis identified root crown diameter， root crown volume， root crown depth in soil， root length， main root diameter， lateral root diameter， lateral root number， and winter survival rate as important indexes to identify the cold resistance of alfalfa. On the basis of the results of a membership function analysis， the alfalfa varieties were ranked from most to least cold resistant as follows： Zhaodong>Gongnong No.2>Caoyuan No.3>Gold empress>Caribou>420>Sanditi>Sardi. Because of their high yields and winter survival rates， Zhaodong， Caoyuan No.3， and Gongnong No.2 were identified as the most suitable lines for cultivation in western Heilongjiang Province.

Response of soil nematode community structure and diversity to increased nitrogen in alpine meadows of northern Tibet

Yu-bao SHA, Ganjurjav HASBAGAN, Guo-zheng HU, Xue-xia WANG, Jun YAN, Shi-cheng HE, Qing-zhu GAO

2023, 32(1):  154-164.  DOI: 10.11686/cyxb2022165

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Soil nematodes play an important role in material cycling and energy transfer processes in alpine meadow ecosystems. Alpine meadow plants are extremely sensitive to nitrogen deposition， but the effect of increased nitrogen on the structure and diversity of the soil nematode community remains unclear. In this study， we conducted a simulated nitrogen deposition experiment in alpine meadows in Nagqu， Tibet， with four levels of nitrogen enrichment： 0 （CK）， 7， 20， and 40 kg N·ha^-1·yr^-1. Then， we investigated the effects of nitrogen enrichment on the structure and diversity of the soil nematode community. The results showed that： 1） Increased nitrogen significantly changed the soil nematode community composition in alpine meadows and reduced nematode diversity and evenness； 2） the N₂₀ and N₄₀ treatments significantly increased the relative abundance of bacterivore （Ba） taxa by 30.4% and 31.7%， respectively， compared with the control group； 3） The treatments could be ranked， from highest nematode diversity index and evenness index to lowest， as follows： N_ck>N₄₀>N₂₀>N₇. There were no significant differences in the plant parasite index， maturity index， and Wasilewska index （WI） among the treatments. The nematode channel ratio was greater than 0.5 and the WI was greater than 1 under different nitrogen enrichment conditions， indicating that the soil nematode taxa in the study area were mainly bacterivore nematodes， and that the main players in the mineralization pathway were bacterivore and fungivore nematodes； 4） The ammonia nitrogen content in soil was significantly and positively correlated with the total numbers of nematodes and bacterivores. This study clarified that the increase in the total number of soil nematodes in the alpine meadows of northern Tibet under nitrogen deposition is because of increased numbers of bacterivore nematodes. These results provide a reference for exploring how alpine meadow ecosystems in northern Tibet will respond to nitrogen deposition.

Comparative study on transformation systems of seashore paspalum using hpt and bar genes as selection markers

Kai JIANG, Xue-li WU, Yi-jun LIU, Yue MA, Yang SONG, Wen-jie LU, Zeng-yu WANG

2023, 32(1):  165-177.  DOI: 10.11686/cyxb2022189

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Seashore paspalum is a warm-season turfgrass with strong salt tolerance， and it has a wide range of potential applications. To establish an efficient and stable genetic transformation system for this plant， we used its mature seeds as explants， and determined the optimal selection pressures of hygromycin and glufosinate during callus subculture and the regeneration stage. After optimizing the genetic transformation conditions， we compared the transformation efficiency of hpt and bar genes as selection markers in Agrobacterium-mediated transformation of seashore paspalum. The results showed that the regeneration rate of callus decreased significantly after subculture for 36 weeks， and the highest regeneration rate was 67.9% after subculture for 48 weeks. The optimal concentration of hygromycin for screening was 120 mg·L^-1 at the subculture stage and 80 mg·L^-1 at the regeneration stage. The optimal concentration of glufosinate for screening was 1.2 mg·L^-1. Calli subcultured for 24 weeks were selected for Agrobacterium-mediated genetic transformation. The optimal transformation conditions were as follows： ultrasonic treatment of the explant for 20 min with bacterial solution （concentration OD₆₀₀=0.6） containing 100 μmol·L^-1 acetosyringone and 0.01% Silwet L-77， followed by vacuum treatment for 10 mins， then soaking for 30 mins and co-culturing for 2 days. Through screening multiple resistant calli and resistant regenerated seedlings， we obtained regenerated transgenic plants expressing each vector. Analyses by PCR confirmed that hpt and bar genes were successfully expressed in the respective transformed seashore paspalum materials. The average efficiency of GUS stable expression and PCR detection with hygromycin as the screening agent was 18.9%， and the highest transformation efficiency was 20.3%， which were higher than those obtained using glufosinate as the screening agent. Our results indicate that the hpt gene is more suitable as a selectable marker gene for the genetic transformation of seashore paspalum， as it achieves a higher transformation efficiency.

Cloning and identification of drought tolerance function of the LjbHLH34 gene in Lotus japonicus

Fu LIU, Cheng CHEN, Kai-xuan ZHANG, Mei-liang ZHOU, Xin-quan ZHANG

2023, 32(1):  178-191.  DOI: 10.11686/cyxb2022008

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Drought is an important environmental factor affecting plant growth and development. In this paper， we studied the drought tolerance function of the gene LjbHLH34， and conducted a preliminary analysis of its molecular mechanism in response to drought stress， in order to provide a theoretical basis for molecular breeding of Lotus japonicus drought resistance. In this study， the size of LjbHLH34 was found to be 711 bp and to encode 236 amino acids， belonging to the bHLH transcription factor family. Phylogenetic tree analysis showed that LjbHLH34 was closely related to AtbHLH34 and AtbHLH104 in the bHLH Ⅳ subfamily of Arabidopsis thaliana. The expression level of LjbHLH34 was the highest in the roots， the second highest in the leaves， and the lowest in the stems， suggesting that LjbHLH34 plays a role in multiple tissues of L. japonicus.LjbHLH34 gene expression was also induced by polyethylene glycol （PEG） and abscisic acid （ABA）. A yeast assay showed that LjbHLH34 had transcriptional activation activity， and a subcellular localization assay showed that LjbHLH34 was located in the nucleus. Under 200 mmol·L^-1 D-Mannitol stress， the root length of LjbHLH34 transgenic A. thaliana was significantly longer than that of the wild type. After drought treatment， the degree of withering of the wild-type was more obvious than transgenic Arabidopsis. At the same time， the relative water content and superoxide dismutase （SOD） activity of transgenic Arabidopsis were significantly higher than those of the wild-type， while malondialdehyde （MDA） accumulation was significantly lower than in the wild-type. qRT-PCR showed that the expression levels of stress-related genes AtCAT1， AtCAT3 and AtRD22 in transgenic lines were significantly increased after drought treatment. These results indicated that LjbHLH34 positively regulates drought resistance of plants.

Evaluation of forage yield and quality traits of 113 forage hexaploid triticale germplasm lines

Shan-shan WANG, Hai-tao GU, Hui-fang XIE, Shao-dong HE, Chang-bo GAN, Xiao-yong WEI, Guang-chao KONG

2023, 32(1):  192-202.  DOI: 10.11686/cyxb2022011

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Germplasm are important resources in genetic improvement and breeding， and forage yield and quality are key characteristics for triticale （×Triticosecale Wittmack） varieties for animal feeds. In this study， 113 triticale cultivars from 15 countries were planted in two years， and their forage yields and quality traits （fresh forage weight per plant， dry forage weight per plant， fresh-dry ratio， forage crude protein content， neutral detergent fiber content， acid detergent fiber content and relative feed value） were investigated and a comprehensive index of these traits was evaluated. It was found that forage yield and quality traits of the tested triticale germplasm lines differed significantly between cultivars and years. In two consecutive years， the range of values for measured traits was： fresh forage weight per plant， 36.000-111.560 g and 36.310-159.780 g； dry forage weight per plant， 12.000-27.000 g and 9.150-30.150 g； fresh-dry ratio， 2.380-4.370 and 2.610-6.210； forage crude protein content 6.894%-13.259% and 6.680%-14.304%； forage neutral detergent fiber content， 48.480%-74.850% and 53.850%-67.980%； forage acid detergent fiber content， 26.600%-42.780% and 29.000%-39.280%； and forage relative feed value， 69.650-128.150 and 79.840-113.170. The comprehensive index for the seven tested traits ranged from 1.974 to 2.075. The forage fiber quality factor， forage yield factor and comprehensive quality factor were the three most important principal components， with eigenvalues of 1.894， 1.618 and 1.419， respectively. These three principal components explained 82.198% of total data variation. Based on the dry forage weight per plant， crude protein content， and relative feed value， the 113 triticale germplasm lines could be placed into three groups： a higher forage yield and better forage quality group with 17 cultivars， a lower forage yield and good forage quality group with 50 cultivars， and an intermediate-yield and quality group with 46 cultivars. These results indicate that the 113 tested triticale germplasm lines exhibited rich genetic variation in yield and quality traits， which will facilitate forage triticale breeding and genetic improvement.

Research advances in disease resistance mechanism of herbaceous plants

Cai-xia ZHANG, Xiang-ling FANG

2023, 32(1):  203-215.  DOI: 10.11686/cyxb2021508

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Grass disease is one of the major limiting factors for the development of forage industries. At present， the development and utilization of resistant cultivar is the most economical and effective disease management strategies. Research on plant disease resistance mechanisms is essential for the development of resistant cultivar and the construction of eco-environmental friendly disease prevention and control measures. Plants form a variety of defense mechanisms when they are infected by pathogens. This study summarized the research advances relating to disease resistance mechanism， including tissue resistance， physiological and biochemical resistance， and molecular mechanism involving resistance genes and quantitative trait loci （QTLs） related to disease resistance traits. The major problems and opportunities for solutions in the research into resistance mechanisms of herbaceous plants are identified， which provides a theoretical basis for breeding of grass disease resistance.