Table of Content

20 September 2023, Volume 32 Issue 9

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Spatiotemporal dynamic variation of temperate grassland classes in Inner Mongolia in the last 20 years

Zhi-gui YANG, Jian-guo ZHANG, Jin-rong LI, Hong-yan YU, Li CHANG, Shu-hua YI, Yan-yan LYU, Yu-zhuo ZHANG, Bao-ping MENG

2023, 32(9):  1-16.  DOI: 10.11686/cyxb2022405

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Grassland classification is essential for rational utilization and effective protection of grassland resources and also crucial for maintaining sustainable development of grassland ecosystems. There has been considerable achievement in documenting spatio-temporal changes in land use types， but few reports on the spatio-temporal dynamic variation of grassland classes at the regional scale. Hence， this study explored the spatio-temporal variation of temperate grassland classes in Inner Mongolia. Several grassland class identification methods were constructed based on remote sensing vegetation index， meteorology， soil， topography， unmanned aerial vehicle （UAV） data and machine learning algorithms. Then the spatio-temporal variation was analyzed based on the optimal classification method. It was found that： 1） Among all the remote sensing classification characteristics and indexes evaluated， the importance values of precipitation and normalized difference vegetation index （NDVI） for grassland classification were higher than those of other indexes in the study area， and the cumulative contribution of the importance values of first 18 classification characteristics and indexes was more than 85%； 2） The random forest （RF） model gave the highest classification accuracy and was superior to other methods in grassland class identification in Inner Mongolia， with an overall accuracy of 82.16% and Kappa coefficient of 0.76； 3） In the past 20 years， the transition between grassland classes in Inner Mongolia has been intense， and has mainly occurred through transition among the classes typical steppe， desert steppe and desert. Compared with the grassland types in the 1980s， the grassland types in 2000-2009 changed from wet to dry， while the grassland types in 2010-2019 changed from dry to wet. The results of this study provide a scientific evaluation of the changes in grassland type in Inner Mongolia under global climate change and as a result of human activities， and provide a theoretical basis and technical support for planning sustainable grassland development in Inner Mongolia.

Factors influencing undergrowth herbaceous diversity of Cunninghamialanceolata plantations in southern mountainous areas

Zi-qi FENG, Wen-yi SUN, Xing-min MU, Peng GAO, Guang-ju ZHAO, Shuai CHEN

2023, 32(9):  17-26.  DOI: 10.11686/cyxb2022419

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Analysis of the factors influencing understory herbaceous diversity in Chinese fir plantations can provide a theoretical basis for the sustainable management of forests in China’s southern mountain area. Based on the data collected from 115 Chinese fir plantations， the relationship between environmental factors， stand structure and herb diversity in Chinese fir plantations was investigated using correlation analysis， variance decomposition analysis and a structural equation model. The maximum entropy model was used to simulate the potential geographical distribution of understory plant diversity in Chinese fir plantations. The results showed that： 1） The interpretation rates of the single effect of climate factors and the common effect of climate and terrain factors were 19.31% and 12.34%， respectively. 2） Mean annual precipitation and canopy cover had significant effects on understory herb diversity （P<0.01）， and the total influence coefficients were 0.72 and -0.49， respectively. Altitude， annual temperature， soil organic matter and total nitrogen content had significant effects on understory plant diversity （P<0.05）， and the total influence coefficients were -0.33， 0.17， 0.23 and 0.34， respectively. 3） The main environmental factors and their contribution rates of understory herb diversity in Chinese fir plantation were： mean annual precipitation （37.1%）>altitude （19.5%）>mean annual temperature （15.2%）>soil organic matter （8.9%）>soil total nitrogen （7.5%）， and the cumulative contribution rate was 88.2%. 4） Understory herbaceous diversity was greater in areas with mean annual precipitation ≥1650 mm， mean annual temperature 18-22 ℃， mid-low altitude （510-680 m）， and soil organic matter content ≥20 g·kg^-1.

Effects of biodiversity on primary productivity and its mechanism in artificially sown clonal plant communities of the Sanjiangyuan region

Zeng-hui LIU, Su-jin LU, Yu-xin WANG, Chun-hui ZHANG, Xin YIN

2023, 32(9):  27-38.  DOI: 10.11686/cyxb2022446

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Clonal plants have unique ways to compete and reproduce， and their unique traits may lead to a particular biodiversity-productivity relationship in communities they form. However， this issue has rarely been studied. In this research， a biodiversity experiment was set up using three clonal species （Elymus nutans， Medicago ruthenica and Potentilla anserine） in monocultures and mixtures. There were three replicates， E. nutans was used as the fixed species in all mixtures and the effects of biodiversity on productivity were assessed over two years. We found that the net biodiversity effects （NE） were significant in nearly all mixtures in our experiment， attributable to strong trait-independent complementary effects （TICE）， although there was no positive linear relationship between species richness and aboveground biomass. The strong TICE was predominantly caused by the complementary utilization of aboveground vertical space， while a secondary cause was the enhancement of light absorption capacity of the understorey species P. anserine. Meanwhile， the dominance of E. nutans increased over time and with increasing species richness， whereas P. anserine displayed the opposite tendencies， resulting in an increase in trait-dependent complementary effect （TDCE） and dominance effect （DE） for communities where P. anserine was present. However， the contributions of those two mechanisms to NE were limited. Furthermore， all those effects increased with time. The results of this study indicate that clonal species display a different biodiversity-productivity relationship from the normally positive linear pattern， due to the complementary use of aboveground vertical space.

Long-term grazing disturbance reduced plant diversity in Stipa breviflora desert steppe

Min ZHAO, Kun ZHAO, Yun-bo WANG, Guo-mei YIN, Si-bo LIU, Bao-long YAN, Wei-jun MENG, Shi-jie LYU, Guo-dong HAN

2023, 32(9):  39-49.  DOI: 10.11686/cyxb2022381

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The improvement of plant diversity is one of the manifestations of the restoration of degraded grassland. Overgrazing is the main cause of grassland degradation， and there is still controversy over grazing prohibition and grazing for the restoration of grassland plant diversity. In this study， Stipa breviflora desert steppe was selected as the object. During the peak of plant growth in August 2017， plant species， density， frequency and coverage were observed under different grazing intensities （no grazing， light grazing， moderate grazing and heavy grazing） in the enclosed steppe for 13 years （2004-2017）. The relative dominance of plant species， functional groups and plant diversity index were analyzed. The results show that： with the increase of grazing intensity， the Patrick richness index， Shannon-Wiener diversity index and Simpson dominance index showed a decreasing trend， and no grazing exclusion was significantly higher than heavy grazing （P<0.05）. Pielou evenness index under moderate grazing was the highest， and was significantly higher than heavy grazing （P<0.05）. Shannon-Wiener diversity index and Simpson dominance index were extermely negative correlated with the important value of S. breviflora， but extermely positive correlated with the important value of Artemisia frigida （P<0.01）. The relative dominance of dominant plants determined the level of plant diversity. By studying the effects of grazing intensity on plant diversity and its mechanism， we concluded that no grazing is one of the ideal ways to restore plant species diversity of degraded grassland in S. breviflora desert steppe， and light grazing will not change the stability of community.

Quantitative classification and ordination analysis of typical plant communities in Altay Prefecture of Xinjiang

Jin-juan SU, Yong-ping LIU, Li-yan LIU, Tian-zhong WU, Mei WANG

2023, 32(9):  50-67.  DOI: 10.11686/cyxb2022420

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To provide a theoretical basis for plant community protection and ecological restoration in Altay Prefecture of Xinjiang， the types and distribution of plant communities in Altay Prefecture of Xinjiang were studied， and the main environmental factors affecting the distribution of local communities were determined. Based on the field survey data in Altay Prefecture， taking the species importance value as the index， two-way indicator species analysis （TWINSPAN） and canonical correspondence analysis （CCA） were used to study the composition of plant communities and the dominant factors affecting community classification in Altay Prefecture. The results showed that： 1） A total of 322 species of vascular plants were recorded in 163 quadrats， belonging to 51 families and 207 genera， among which dicotyledonous plants were dominant. Asteraceae， Poaceae， Chenopodiaceae and Rosaceae were the dominant families in the study area. 2） Based on the TWINSPAN classification method， the plants in Altay Prefecture were divided into 17 associations， and the herbaceous plant communities were the majority. The vegetation types were mainly desert steppe and meadow steppe， as well as deciduous broad-leaved forest and evergreen coniferous forest. 3） CCA ordination showed that altitude was the main environmental factor affecting the distribution of local plant communities， followed by climate and soil factors.

Altitude and plant community jointly regulate soil stoichiometry characteristics of natural grassland in the Baluntai area on the southern slope of the middle Tianshan Mountains， China

Guo-liang YU, Zi-jing MA, Zi-li LYU, Bin LIU

2023, 32(9):  68-78.  DOI: 10.11686/cyxb2022412

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Exploring the altitudinal characteristics of soil stoichiometry is important for understanding the stoichiometric distribution of natural grassland soil in high altitude areas and improving soil nutrient conditions. In this research， the soil and plant communities at an altitude of 2200-3550 m in the Baluntai area on the southern slope of the middle Tianshan Mountains were studied. The variation of soil carbon， nitrogen， phosphorus and potassium stoichiometry along an altitude gradient was examined by one-way ANOVA and one-way Kruskal-Wallis tests. Correlation between soil stoichiometry data was explored by Pearson correlation analysis. The correlation between soil stoichiometry and soil physical and chemical properties and plant diversity was tested by redundancy analysis （RDA）. Significance tests were used to determine which factors had significant effects on soil stoichiometry. After removing the collinearity of independent variables， stepwise regression analysis was used to determine the optimal regression equation to determine the stoichiometry of single soils using the akaike information criterion. In this way the factors stoichiometry were found in each case. The results showed that： 1） Soil organic carbon， total nitrogen， available nitrogen content， carbon-phosphorus ratio， carbon-potassium ratio， nitrogen-phosphorus ratio and nitrogen-potassium ratio increased gradually with increase in altitude， while soil total phosphorus， total potassium， available phosphorus， available potassium content， carbon-nitrogen ratio and phosphorus-potassium ratio did not change significantly. 2） There were strong positive correlations between soil organic carbon content and all stoichiometric ratios except phosphorus-potassium ratio and between total nitrogen content and all stoichiometric ratios except carbon-nitrogen ratio， while the correlation between total phosphorus， total potassium content and organic carbon， total nitrogen content and stoichiometric ratio was not significant. 3） Altitude， soil salinity and Margalef richness index of the shrub layer are the main factors affecting soil stoichiometric characteristics. Soil carbon， nitrogen， phosphorus and potassium contents were also higher in areas with lower shrub species richness.

Study on soil enzyme activities under shrub encroachment gradients in alpine grassland

Dong ZHANG, Chen HOU, Wen-ming MA, Chang-ting WANG, Zhuo-ma DENGZENG, Ting ZHANG

2023, 32(9):  79-92.  DOI: 10.11686/cyxb2022421

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Shrub encroachment is an important ecological process that affects soil material cycling in grasslands. This study investigated the effect of different shrub encroachment gradients on soil enzyme activity， compared to grassland with no shrubs present， under three common shrub species on the eastern margin of the Qinghai-Tibetan Plateau： Spiraea alpina， Caragana microphylla and Potentilla fruticosa. Soil physical and chemical properties and sucrase， urease， polyphenol oxidase， glucosidase， protease and cellulase activities were analysed in 0-10 cm， 10-20 cm， 20-40 cm， 40-60 cm and 60-80 cm soil horizons with different shrub encroachment gradients （no shrubs， lightly and heavily shrub covered）. It was found that the pH and soil organic carbon （SOC） contents were significantly higher and the soil water content （SWC） and total nitrogen （TN） were significantly lower （P<0.05） in the 0-20 cm soil layer of the shrub-covered grassland than when no shrubs were present. Similarly， the activities of protease， glucosidase， cellulase， urease and sucrase were significantly lower in shrub-covered than in grassland with no shrubs （P<0.05）. The activity of polyphenol oxidase was not significantly different between shrub encroachment and no shrubs， and the activity of soil enzymes decreased with deepening of the soil layer at different shrub encroachment gradients. The main explanatory factor for the variation in soil enzyme activity across the different shrub encroachment gradients and soil depths was SWC， which explained 41.2%， 50.5%， 37.1%， 41.5% and 26.0%， respectively， of the variation in activities of the five above-mentioned soil enzymes. Structural equation modeling （SEM） showed that different shrub encroachment gradients mainly affected SOC， pH and SOC∶TN， but not SWC and TN， and that different shrub encroachment gradients could indirectly affect sucrase， urease， glucosidase， protease， polyphenol oxidase and cellulase activities by affecting pH and SOC content. SWC is still the main factor affecting the activities of the six enzymes. SWC directly and positively influenced the activities of the six enzymes， and also negatively influenced soil pH and positively influenced SOC to further influence TN and thus enzyme activities. Therefore， reduction of soil enzyme activity due to the invasion of grassland shrubs in the study area is beneficial for soil organic carbon sequestration.

Effects of simulated warming on growth characteristics of Bromus inermis

Ke GONG, Gui-li JIN, Wen-hao LIU, Jian MA, Zhi-biao LIU, Jia-xin LI, Ying LI

2023, 32(9):  93-103.  DOI: 10.11686/cyxb2022410

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The growth characteristics exhibited by wild forage grasses at different growth stages in the context of increasing global temperatures and the increased frequency of extreme weather occurrences are important elements in exploring the response patterns of forage grasses to warming. In this study， three temperature-increasing treatments （CK， W₁， W₂） were applied to three growth stages （germination， seedling and reproduction） by field simulation device （open-top chambers， OTC） to determine germination index， seedling growth index， trait index and biomass， respectively， using Bromus inermis in Xinjiang. The results showed that W₂ temperature increase significantly increased emergence energy and emergence rate by 1.38 and 1.49 times compared to CK， respectively （P<0.05）； W₁ and W₂ temperature increase inhibited seedling leaf length and root length by 9.9% and 43.3%， respectively， with the inhibitory effect of W₁ temperature increase on leaf length and root length being more obvious. W₁ temperature increase inhibited reproductive growth and enhanced inputs to nutritional organs in B. inermis， while reproductive growth was more dominant under W₂ temperature increase. The above- and below-ground biomass growth patterns gradually changed from anisotropic to isotropic during the seedling stage； the isotropic growth pattern was maintained throughout the reproductive stage. In summary， the three growth stages of B. inermis responded differently to the temperature increase， and seedling emergence and reproductive growth were promoted， but seedling growth was suppressed； and from the time of rooting， B. inermis prefers to accumulate the energy of the underground part， which is used to ensure its survival and sexual reproduction in a warmed environment. The results of the study can be used as a reference for understanding the adaptability of B. inermis in different growth stages in response to temperature increase.

Dry matter yield and spatial distribution characteristics of phosphorus in alfalfa under bacterial-phosphorus coupling

Xuan-shuai LIU, Yan-liang SUN, Chun-hui MA, Qian-bing ZHANG

2023, 32(9):  104-115.  DOI: 10.11686/cyxb2022431

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This study explored the effects on the P content of various organs and parts of alfalfa and soil available P content， of inoculation with arbuscular mycorrhizal fungi （AMF） and phosphorus-solubilizing bacteria （PSB） in different proportions with and without phosphorus （P） application. The ultimate aim of this research was to provide a theoretical basis for improving the efficiency of phosphorus fertilizer utilization for the production of high-quality， high-yielding alfalfa by formulating a scientifically based and appropriate fertilization system. A pot experiment was conducted with a randomized block design. There were 10 treatments in total， consisting of five inoculation ratios （AMF∶PSB） treatments ［3∶7 （J₁）， 4∶6 （J₂）， 5∶5 （J₃）， 6∶4 （J₄） and 7∶3 （J₅）］ and two phosphorus （P₂O₅） application levels ［0 （P₀） and 100 mg·kg^-1 soil （P₁）］. The plant P content， soil P content， dry matter yield of alfalfa and P use efficiency were measured. Correlation analyses were conducted to clarify the relationship between the alfalfa plant P content， soil P content， dry matter yield， and P use efficiency. The best combination of bacteria and phosphorus conditions for promoting alfalfa growth was identified using a membership function analysis. It was found that， under the same inoculation conditions， the contents of plant P， stem P， leaf P， flower P， root P， upper 1/3 plant P of aboveground part， middle 1/3 plant P of aboveground part， lower 1/3 plant P of aboveground part， rhizosphere soil available P， non-rhizosphere soil available P and the dry matter yield were all significantly greater in the P₁ treatments than in the P₀ treatments （P<0.05）. Under the same P application conditions， the plant P， stem P， leaf P， flower P， root P， upper 1/3 plant P of aboveground part， middle 1/3 plant P of aboveground part， lower 1/3 plant P of aboveground part were all significantly greater in the J₅ treatment than in the J₁， J₂， J₃ and J₄ treatments （P<0.05）， and the dry matter yields of J₁， J₂， J₃ and J₄ treatments were significantly greater than that of the J₅ treatment （P<0.05）. The P content of each organ of alfalfa ranked： flower>leaf>root>stem； the P content of each plant fraction ranked： upper 1/3 plant of aboveground part>middle 1/3 plant of aboveground part>lower 1/3 plant of aboveground part and the soil available P content ranked： rhizosphere soil>non-rhizosphere soil. Across the bacterial-P coupling treatments， the total dry matter yield and P use efficiency of alfalfa both reached their maximum values （49.31 g·pot^-1 and 27.23%， respectively） in the J₄P₁ treatment. Correlation analysis showed that the P content of alfalfa plants， rhizosphere soil P content， non-rhizosphere soil P content， P use efficiency and total dry matter yield were positively correlated with each other. Among these， total dry matter yield was highly significantly positively correlated with rhizosphere soil available P content and P use efficiency （P<0.01）， and was significantly positively correlated with non-rhizosphere soil available P content （P<0.05）. According to the ranking of membership function values， the top three were J₁P₁， J₃P₁ and J₄P₁. Therefore， a phosphorus application rate of 100 mg·kg^-1 P （P₂O₅） and double inoculation of AMF and PSB in the ratio 3∶7 can greatly improve alfalfa P nutrition level， thereby increasing the dry matter yield.

Screening and adaptability evaluation of early maturing oats in alpine regions of the Qinghai-Tibetan Plateau

Chun-yan REN, Guo-ling LIANG, Wen-hui LIU, Kai-qiang LIU, Jia-lei DUAN

2023, 32(9):  116-129.  DOI: 10.11686/cyxb2022414

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In order to select and breed early-maturing Avena sativa varieties with high yield and quality adapted to the high altitude region of the Qinghai-Tibetan Plateau， 595 oat germplasm lines planted in the Xining area were classified for maturity twenty two early-maturing oat lines with excellent yield were selected and evaluated for adaptability in 2 experimental sites in Haibei and Huangzhong. Early maturing oat lines with good production performance were selected for grain trait comparison， providing a theoretical basis for selecting and breeding early-maturing oats suitable for planting and promotion in the high altitude region of the Qinghai-Tibetan Plateau. It was found that： 1） Early-maturing oats mainly have a shorter duration of stem elongation and post-flowering maturation growth stages， and thus the whole reproductive period is shortened. The average hay yield of mid-season maturing and late-season maturing oat lines was higher （4744.8 and 4999.9 kg·ha^-1， respectively） while the average grain yield of mid-maturing oat lines was the highest （3186.9 kg·ha^-1）. 2） Among the 22 early-maturing oat resources screened， the average forage yield was higher at the Haibei test site （10209.5 kg·ha^-1）， and the average grain yield was higher in the Huangzhong test site （2640.6 kg·ha^-1）. The average maturity date of oats at the Haibei test site at an altitude of 3100 m was 15.3 d later than at the Huangzhong test site at an altitude of 2700 m， and the maturation time of more than 116 d meant that the Haibei site could not be used for grain production. 3） The seed germination performance of oats grown at the Huangzhong test site was much higher than that of those grown at the Haibei test site. Lines QYJ 782 and QYJ 797 had good germination performance at both test sites. Based on multivariate analysis of oat yield and seed trait data， lines QYJ 782 and QYJ 797 are suitable for planting in the area surrounding lake in Qinghai province at an altitude of about 3100 m. They are able to mature successfully and forage yield and seed yield is significantly better than the currently promoted varieties. These lines can therefore be recommended for use in the region.

Evaluation of resistance to Colletotrichum cereale and analysis of loss in a field of fifteen imported oat cultivars

Yong-hong SHI, Peng GAO, Zhi-hong FANG, Xiang ZHAO, Wei HAN, Jiang-ming WEI, Lin LIU, Jin-zhen LI

2023, 32(9):  130-142.  DOI: 10.11686/cyxb2022424

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Oat （Avena sativa） varieties of high quality and high yield are introduced from other countries and such imports are important to the development of forage-based livestock husbandry in China. However， anthracnose diseased caused by Collectotrichum cereale outbreaks in commercial oat crops is a significant problem with imported varieties. In this study， a total of 15 imported oat varieties were screened for high resistance to anthracnose disease. Simultaneously， we examined the oat yield reduction and quality loss caused by anthracnose. Four resistant varieties were identified： Titan， Everleaf， Souris and Monte. All other varieties were found to be susceptible to anthracnose. The leaf dry weight， stem dry weight， ear dry weight and plant height of the diseased plant of the highly susceptible “Kona” feed oat showed a linear downward trend in proportion to the degree of disease incidence. The forage yield reduction was 7.5%-28.1%， and the regression equation between the yield reduction and mean disease index score was y=0.3023x+1.6822 （R²=0.9837， P<0.05）. In this equation， y represents the forage yield reduction of mean disease index score （x） of units. The contents of crude protein， total amino acid， crude ash and phosphorus of moderately and severely diseased plants were significantly （P<0.05） lower than those of healthy plants by 7.2%， 26.5%， 9.0% and 12.8% and by 11.1%， 44.5%， 16.0% and 20.8% respectively. The content of acid detergent fiber in moderately diseased plants increased significantly （P<0.05） by 6.4% compared with healthy plants. The content of neutral and acid detergent fiber in severely diseased plants increased significantly （P<0.05） 11.9% and 10.0% compared with healthy plants， respectively. The reduction in feeding value was 3.2%-15.9%， and the regression equation between the reduction in feeding value and the mean disease index was y=0.1812x+0.5032 （R²=0.9963， P<0.05）. In this equation， y represents the forage yield reduction of mean disease index score （x） of units. Hence， the resistant varieties Titan， Everleaf， Souris and Monte are recommended for planting in areas with serious anthracnose. In addition timely and scientifically effective control measures should be implemented. The next step is to screen for superior germplasm with strong disease resistance among local varieties used in China.

Effects of exogenous melatonin on root development and physiological and biochemical characteristics of maize seedlings under drought stress

Ying JIANG, Hui-hong ZHANG, Chang WEI, Zheng-yang XU, Ying ZHAO, Fang LIU, Ge-zi LI, Xue-hai ZHANG, Hai-tao LIU

2023, 32(9):  143-159.  DOI: 10.11686/cyxb2022480

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This research studied the effect of spraying exogenous melatonin on drought resistance of maize seedlings， and explored the mechanism of melatonin alleviation of drought stress in maize variety Zhengdan 985. A hydroponic experiment was conducted， using polyethylene glycol （PEG-6000） to simulate drought stress. The effects of melatonin at different concentrations （0， 10， 50， 100 μmol·L^-1； MT₀， MT₁₀， MT₅₀， MT₁₀₀， respectively） on the growth， root configuration and diameter characteristics， photosynthetic characteristics， antioxidant capacity and osmotic content of maize seedlings under drought stress were studied. Multivariate analysis of the maize seedling drought resistance under the various treatments was undertaken using the subordinate function value method. Compared with the treatment without melatonin， spraying 50 μmol·L^-1 melatonin had the best effect， and significantly increased plant height， aboveground fresh and dry weight， underground fresh and dry weight， stem tolerance index and root tolerance index of the seedlings. The total root length （RL）， root surface area （SA）， root volume （RV） and root tip number （RT） of maize seedlings were also increased significantly by melatonin application. The RL of the finest diameter category （0-0.5 mm） and the SA and RV of the second diameter category （0.5-1.0 mm）， were also significantly increased. Across the treatments， the proportions of total RL and SA （82.40% and 47.32%， respectively） in the （0-0.5 mm） diameter range were highest in the 50 μmol·L^-1 melatonin treatment. In this treatment， compared to the control， shoot malondialdehyde （MDA） levels were decreased by 20.17% （P<0.05）， shoot soluble protein content was maximized， the soluble protein content of underground parts was increased by 49.14%， and leaf photosynthetic rate （P_n） and stomatal conductance （G_s） were increased by 85.83% and 32.81%， respectively. The activities of superoxide dismutase （SOD）， peroxidase （POD）， catalase （CAT） and ascorbate peroxidase （APX） in shoots and underground organs were also significantly increased. The order of drought resistance of the four treatments under drought stress was MT₅₀>MT₁₀>MT₁₀₀>MT₀. Exogenous application of 50 μmol·L^-1 melatonin effectively regulated the activities of antioxidant enzymes and osmotic regulation in the aboveground and underground parts of maize seedlings， reduced the MDA content， increased the photosynthetic capacity， and beneficially regulated the soluble protein content， ascorbate （AsA） content， glutathione （GSH） content， SOD activity， POD activity， APX activity and CAT activity in the aboveground and underground parts of maize seedlings. The biomass and elongation of maize seedlings were increased， the detrimental effect of drought stress on root configuration was reduced， and the drought resistance of maize seedlings was improved. These results provide a theoretical basis for revealing the mechanism of melatonin alleviation of drought stress.

Comparison of photosynthetic-CO₂ response process and models of Leymus chinensis under differing nitrogen addition and mowing conditions

Si-qi YANG, Ya-jing BAO, Jia-qi YE, Shuai WU, Meng ZHANG, Meng-ran XU, Yu ZHAO, Xiao-tao LYU, Xing-guo HAN

2023, 32(9):  160-172.  DOI: 10.11686/cyxb2022401

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Photosynthesis of plants is affected by grassland management practices such as nitrogen addition and mowing. In this research， the photosynthetic-CO₂ response process of the dominant species， Leymus chinensis， was determined in a controlled field experiment exploring the interaction between nitrogen addition （0， 2， 5， 10， 20 and 50 g N·m^-2·yr^-1） and mowing （mown and unmown） in an Inner Mongolian meadow steppe. Leaf photosynthetic-CO₂ response curves were fitted using a rectangular hyperbolic model， a non-rectangular hyperbolic model， a modified rectangular hyperbolic model and a Michaelis-Menten model in order to define photosynthetic trait responses of L. chinensis to nitrogen addition and mowing. It was found that the initial carboxylation efficiency and photorespiration rate of the non-rectangular hyperbolic model were closest to the measured values. The modified rectangular hyperbola model provided the best fit for CO₂ saturation point， CO₂ compensation point and maximum net photosynthetic rate， and the modified rectangular hyperbolic model the highest goodness of fit. Moderate nitrogen addition increased the net photosynthetic rate， water use efficiency， maximum net photosynthetic rate， initial carboxylation efficiency and CO₂ saturation point， and decreased the CO₂ compensation point， and thereby improved the CO₂ use efficiency of L. chinensis. With the increase of CO₂ concentration， the net photosynthetic rate of L. chinensis with nitrogen concentration of 20 g N·m^-2·yr^-1 with mowing increased， and higher maximum net photosynthetic rate， CO₂ saturation point and water use efficiency was observed， together with a lower CO₂ compensation point. In conclusion， the non-rectangular hyperbolic model and the modified rectangular hyperbolic model were more suitable for fitting L. chinensis CO₂ response curves defining responses to nitrogen addition and mowing. In this experiment conducted on an Inner Mongolian steppe， the photosynthetic capacity of L. chinensis was most efficiently increased by applying 20 g N·m^-2·yr^-1 with mowing. This treatment combination is beneficial to carbon sequestration of the grassland ecosystem.

Functional identification of iron transport of LcZIP1 in Leymus chinensis

Yan KANG, Yao-hui WANG, Tian-hui NIU, Zhe TENG, Zhi QI, Jia YANG

2023, 32(9):  173-180.  DOI: 10.11686/cyxb2022402

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Leymus chinensis is an important native forage grass， which is widely distributed in the Inner Mongolian steppe grasslands of China. However， the molecular mechanism of mineral uptake in L. chinensis is not yet well understood， although it is known from systematic study in many model plants and crops that zinc-regulated transporter/iron-regulated transporter-like proteins （ZIP transporters） are involved in the uptake and allocation of essential trace elements and heavy metal ions. In this study we found that the Lc206852 gene screened from the L. chinensis transcriptome database was homologous with Zn²⁺ transporter AtZIP1 in Arabidopsis thaliana. Transmembrane domain analysis using TMHMM Server v. 2.0 indicated that Lc206852， referred to hereafter as LcZIP1， had 9 transmembrane domains， which were closely related to ZIP proteins of plants of the genus Brachypodium. Expression of LcZIP1-GFP in leaf epidermal cells of tobacco and leaf protoplasts of L. chinensis showed that LcZIP1 resided in the endoplasmic reticulum. Real time PCR analysis found that LcZIP1 was responsive to zinc and iron nutrition， and that excess Zn or Fe and^{Fe deficiency induced LcZIP1 expression in roots at transcription level. The yeast （Saccharomyces cerevisiae） complementation test showed that expression of LcZIP1 stimulated growth of the ‘iron uptake-deficient’ yeast mutant ?fet3/?fet4 under Fe deficient conditions. Functional characterization of LcZIP1 willprovide an opportunity for crop improvement by mineral nutrition enhancement in the future.}

Study on sampling strategy of Potentilla anserina in the wild based on SSR molecular markers

Tian TIAN, Jun-qiao LI, Bin MA, Xin-ci WANG, Jun-ru QU

2023, 32(9):  181-197.  DOI: 10.11686/cyxb2022441

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In this study， a SSR molecular marker method was used to evaluate sampling strategies of Potentilla anserina in Qinghai， Gansu， Sichuan， and the Tibetan Autonomous Region. The research aim was to provide a theoretical basis for future research on P. anserina sampling and breeding. The P. anserina was randomly selected at the sampling site as the first sample， then take samples at 1， 2， 3， 4， 5， 10， 15， 20， 25， 30， 40， 50， 60， 80， 90， 100， 120， 150， 160， 200， 250， 300， 400， 500， 1000， 1500， 2000， 2500， 5000， 10000， 15000， 20000， 30000， 40000， 50000 m from the first sample. 20 SSR primer loci were used for PCR amplification of 210 wild individuals from 6 populations， and the amplified fragment length was determined using capillary electrophoresis. SSR data were analyzed using POPGENE， NTSYS and GenAIEx 6.5 software packages. The result showed that： 1） The genetic variation was mainly founded in the population ［estat variance （Est.Var）=12.745， 84%］， and the variation among populations is low （Est.Var=2.477， 16%）. 2） The genetic diversity among the six populations is variable. Qilian County was found to have the highest genetic diversity ［average heterozygosity（H）=0.2797， Shannon-Weiner index （I）=0.4287］， and Henan County had the lowest genetic diversity （H=0.2273， I=0.3542）. This indicates that the genetic variation among the six populations is relatively low， so it is suggested to increase the interval during sampling. 3） When collecting individual P. anserina samples in the same population， the shortest sampling distance is 5 km. If there are small mountains， sampling can be carried out across the mountains. Sampling between different populations can be divided into two situations： 1） When there is a larger mountain range with a height of 1000-1500 m， samples of the P. anserina population can be collected on either side of the mountain range to establish population variation. 2） In the plains where there is no large mountain range for isolation， the sampling distance to establish P. anserina population variation is not less than 100 km.

A study of genetic diversity in centipedegrass populations in Henan based on SSR markers

Yi-nan JI, Xue-feng REN, Tian-tian GOU, Guo-zhang ZANG, Yi-qi ZHENG

2023, 32(9):  198-212.  DOI: 10.11686/cyxb2022409

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Based on SSR molecular markers， this study analyzed the genetic diversity of centipedegrass populations in Henan. Ninety nine alleles were detected with the primers， the polymorphic information content of the primers was 0.53-0.88， and the percentage of polymorphic bands was 98.75%， showing that the selected primers had high polymorphism. Analysis of molecular variance （AMOVA） showed that genetic differentiation of centipedegrass in Henan occurred mainly within populations （86.96%） and showed frequent gene exchange among populations. Cluster analysis and a Mantel test showed that there was no correlation between geographic and genetic distance. The analysis of population genetic structure showed that 141 populations evaluated were divided into 3 subgroups， which was consistent with the results of principal coordinate analysis （PCoA）. Redundancy analysis （RDA） showed that precipitation in the driest month was the main factor affecting the population structure of centipedegrass in Henan. Four outlier loci were detected by combining FDIST2 and BayeScan， and the detection rate of outlier loci was 4.04%. Some loci associated with environmental factors were detected by environmental correlation analysis. In future， we can carry out further transcriptomics research， annotate gene functions， and systematically reveal the adaptive evolutionary mechanism of centipedegrass.

Expression characteristics and protein kinase activity analysis of the SikCDPK1 gene in Saussurea involucrata

Yu-ling LIU, Xin-xia ZHU, Xin-hua LYU, Hui SUN

2023, 32(9):  213-221.  DOI: 10.11686/cyxb2022386

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The SikCDPK1 gene in the extreme habitat plant Saussurea involucrata can significantly improve the low temperature and drought tolerance of genetically modified tobacco. In order to further explore the expression characteristics and protein kinase activity of SikCDPK1 gene， real-time quantitative PCR was used to detect the expression level of SikCDPK1 gene in different tissues and organs of S. involucrata and the induced response mode of signal molecules CaCl₂， abscisic acid， gibberellin， salicylic acid and hydrogen peroxide， while Kinase-Glo? technology was used to detect the activity of SIKCDPK1 protein kinase， and the green fluorescent protein （GFP） fusion protein expression method was used to carry out the subcellular localization of SIKCDPK1 protein. The SikCDPK1 gene was found to be expressed in roots， stems， leaves， seeds， young stems and young leaves of S. involucrata and expression was induced by CaCl₂， abscisic acid， gibberellin， salicylic acid， hydrogen peroxide， but the response mode was different. Kinase activity analysis showed that SIKCDPK1 had kinase catalytic activity when Ca²⁺ was present， and SIKCDPK1 had almost no kinase activity after adding the Ca²⁺ chelating agent ethylene glycol tetraacetic acid. SIKCDPK1 kinase activity increased with increase in Ca²⁺ concentration， and SIKCDPK1 kinase activity reached 1/2 of the maximum activity when Ca²⁺ concentration （K_0.5） was 48.7 nm. When HisⅢ was used as the substrate， the Km value of SIKCDPK1 reached 43.8 μg·mL^-1， and SIkCDPK1 protein was localized to the nucleus. In summary， the expression of the SikCDPK1 gene had no obvious tissue specificity， and could respond to the induction of signaling molecules Ca²⁺， abscisic acid， gibberellin， salicylic acid， hydrogen peroxide. Ca²⁺ is required for SIKCDPK1 to exert protein kinase activity， and SIKCDPK1 mainly functions in the nucleus.

Screening low-nutrient-tolerant lactic acid bacteria and their effects on the fermentation quality of silages from poor materials

Jing TIAN, Cai-xia CAO, Li-ying HUANG, Juan-yan WU, Jian-guo ZHANG

2023, 32(9):  222-230.  DOI: 10.11686/cyxb2022395

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Herbage with low water-soluble carbohydrate （WSC） content or low counts of lactic acid bacteria （LAB） is difficult to ensile. Sugars or LAB are usually added to improve the fermentation quality of silage， but the cost is relatively high. In this study， low-nutrient and acid-tolerant LAB were screened by adjusting the glucose content （0.002， 0.02， 0.2， 2 and 20 g·L^-1） and pH （4.0 and 4.5） of the medium， and inoculating them to stylo （Stylosanthes guianensis） and sudan grass （Sorghum sudanense） with poor ensiling conditions to investigate the silage fermentation quality. Ten low-nutrient-tolerant LAB strains were obtained. Low-nutrient and acid-tolerant strains SCLN₁ and HT₁， and an acid-tolerant strain LM₁ with relatively weak tolerance to low nutrient conditions were also obtained. SCLN₁ was identified Lactobacillus plantarum by 16S rDNA and physiological and biochemical characteristics， and LM₁ and HT₁ stored in the laboratory were identified as Leuconostoc mesenteroides and Lactobacillus rhamnosus， respectively. After ensiling for 60 days， uninoculated stylo and sudan grass silages had poor fermentation quality， with pH higher than 5.0， lactic acid less than 2% DM， and ammonia nitrogen （NH₃-N） reached up to 30.50% TN and 29.01% TN， respectively. Inoculation with LAB significantly improved the fermentation quality of silages of the two tested forage species， especially inoculation with SCLN₁. For stylo and sudan grass silages， inoculation with SCLN₁ alone significantly decreased pH values （from 5.36 and 5.19 to 4.67 and 4.10， respectively） and NH₃-N content （from 30.50% TN and 29.01% TN to 11.24% TN and 12.69% TN， respectively） and increased lactic acid content （from 2.00% DM and 1.82% DM to 4.16% DM and 8.29% DM， respectively）. The effect of inoculation with SCLN₁ alone was significantly better than that of inoculation with LM₁ and HT₁ alone or mixed with SCLN₁.

Analysis of the genetic structure of Tibetan yak populations based on mtDNA COX3

Yu-qi ZHE, Zhi-juan WU, Ji-kun WANG, Jin-cheng ZHONG, Zhi-xin CHAI, Jin-wei XIN

2023, 32(9):  231-240.  DOI: 10.11686/cyxb2022475

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This study explored the genetic diversity， phylogenetic evolution， and genetic relationship between Pali yak， Jiali yak， Leiwuqi yak， Gongbujiangda yak， Sibu yak， Sangri yak and Jiangda yak. Coding sequences （CDS） of the mitochondrially-encoded cytochrome c oxidase subunit Ⅲ gene （COX3） were determined in 140 individuals from seven groups of Tibetan yak by PCR and direct sequencing. DNAMAN， DNASP 5.1， and MEGA 7.0 software programs were used to analyze COX3 polymorphisms and haploid diversity， and a phylogenetic tree was constructed. The COX3 CDS sequence was shown to be 781 bp in all seven Tibetan yak groups， with 55 sites of variation. Tibetan yak COX3 showed 11 haplotypes and average haplotype diversity （H_d） and nucleotide diversity （P_i） levels of 0.665 and 0.00480， respectively， indicating a rich genetic diversity. Phyletic evolution analysis constructed a network relationship chart dividing the 11 haplotypes into two clusters， suggesting that the Tibetan yak can be categorized as the Leiwuqi yak line and a second yak line. Thus， Tibetan yaks may be descended from two separate maternal lineages. They can also be divided into three haplotype groups： domestic yak （Bos grunniens）， Bos primigenius， and Bos taurus. Hap_2， Hap_3， Hap_4， Hap_6， Hap_7， Hap_8， Hap_10， and Hap_11 belong to the Bos grunniens line， Hap_5 and Hap_9 to B. primigenius and B. taurus lines， and Hap_1 to the Bos mutus line. Although Tibetan yak have mixed matrilineal origins， they appear to be greatly influenced by domestic yak. These findings provide a theoretical basis for understanding the evolution of Tibetan yak， and in planning their conservation and utilization of genetic resources.