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    20 March 2023, Volume 32 Issue 3
    The diversity-Godron stability relationship of alpine grassland and its environmental drivers
    Shi-long LEI, Li-rong LIAO, Jie WANG, Lu ZHANG, Zhen-cheng YE, Guo-bin LIU, Chao ZHANG
    2023, 32(3):  1-12.  DOI: 10.11686/cyxb2022125
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    The diversity and stability of plant communities is of great significance to the function of ecosystems and their ability to provide services. Drawing on field investigation and analysis of data from 480 sample plots, the present study explored the relationship between plant diversity and stability of alpine wetland meadow, alpine meadow, alpine steppe and alpine desert steppe, and also elucidated their environmental drivers using significance analysis, regression analysis and structural equation modeling. It was found that the alpine steppe had higher plant diversity than the other three grassland types, and alpine meadow had the highest community stability. The relationship between species diversity and community stability was different in the four alpine grassland types. The community evenness was negatively correlated with community stability. Plant Shannon-Wiener diversity was negatively correlated with community stability in alpine meadow and alpine desert steppe, but in contrast plant richness was positively correlated with community stability in alpine wetland meadow and alpine steppe. Precipitation is the main factor affecting plant diversity and community stability in alpine grassland. Soil organic carbon, pH and ammonium nitrogen content also affected community stability through altering plant diversity. Taken together, climate and soil factors should be considered in the management of alpine grassland ecosystems, and different management measures should be formulated for different types of grassland.

    Effects of irrigation modes on forage yield, quality and water use of corn-legume intercropping systems in the Hexi irrigation area
    Mao-jian WANG, Wei SHI, Sheng-hua CHANG, Cheng ZHANG, Qian-min JIA, Fu-jiang HOU
    2023, 32(3):  13-29.  DOI: 10.11686/cyxb2022136
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    In 2019 and 2020 growing seasons a field experiment was set up in the Hexi region of Gansu with three crop planting configurations: Corn (Zea mays) monocropping (C), Corn-forage soybean (Glycine max) intercropping (CM) and Corn-laba bean (Dolichos lablab) intercropping (CL). In addition, to study their effects in combination with corn-legume intercropping on the yield, quality and crop water use, six irrigation regimes were imposed: severe water deficit (T1), late water deficit (T2), alternate water deficit (T3), late mild water deficit (T4), early mild water deficit (T5), and full irrigation (T6). The total hay yields of CM and CL treatments were, respectively, 6.48% and 9.47% higher than the yield of C in 2019 and 9.09% and 13.11% higher than C (P<0.05) in 2020, respectively. The acid detergent fiber (ADF) and neutral detergent fiber (NDF) contents of CM and CL treatments were significantly lower than those of the C treatment in both years, while the crude protein content, crude ash content and relative feeding value (RFV) of CM and CL treatments were significantly higher than those of the C treatment in both years. Compared with C, the RFVs of CM and CL treatments were increased, respectively, by 10.73% and 13.06% in 2019, and by 7.39% and 10.59% in 2020 (P<0.05). Compared with C, the water use efficiency (WUE) and irrigation production efficiency (IPE) of CL were increased, respectively, by 7.77% and 11.41% in 2019 and by 8.76% and 15.11% in 2020 (P<0.05). There was no significant difference in the total hay yield of T5 and T6 treatments in the two years. Compared with other treatments, the contents of crude protein and ether extract in treatment T5 were higher, while the contents of ADF and NDF were lower. In both years, the WUE and IPE of treatment T5 were significantly higher than those of T6, with increases of 22.14% and 48.34%, respectively, in 2019 and of 25.18% and 45.51% in 2020, compared with T6. Corn-laba bean intercropping can improve forage yield, quality and water use efficiency under mild water deficit conditions during the early crop growth stages. It can be recommended as a suitable management regime for cultivation of high-yield and high-quality forage crops and to achieve water use efficiency in the Hexi area.

    Effect of sowing rate on yield and forage quality of a Dolichos lablab-Sorghum bicolor mixture under drip irrigation in arid areas of Ningxia
    Teng-fei WANG, Bin WANG, Jian-qiang DENG, Man-you LI, Wang NI, Qin FENG, Yun-yun TUO, Jian LAN
    2023, 32(3):  30-40.  DOI: 10.11686/cyxb2022121
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    Effective planting methods can alleviate the problem of low forage yield and poor quality in arid areas of Ningxia. In this study, a mixture of Dolichos lablab and Sorghum bicolor was sown at five different seeding rates (S0: 0 kg·ha-1, S1: 16.5 kg·ha-1, S2: 33.0 kg·ha-1, S3: 49.5 kg·ha-1, S4: 66.0 kg·ha-1) and grown under drip irrigation. The agronomic traits of S. bicolor, the yield of the mixed sward, and the nutritional quality of forage were comprehensively analyzed in a two-year experiment. It was found that the seeding rate of the D. lablab-S. bicolor mixture significantly affected plant height, stem diameter, the stem strength at the first to the fourth internodes; The stem strength at the fifth to seventh internodes of S. bicolor; And the hay yield, crude protein yield, crude protein content, neutral detergent fiber content, acid detergent fiber content, and relative feed value of the mixed sward (P<0.05). Among these parameters, plant height, stem diameter of S. bicolor, and the hay yield and crude protein yield of the mixed sward first increased and then decreased with increasing seeding rate of the D. lablab-S. bicolor mixture. The highest values for total hay yield, crude protein yield, and relative feed value occurred in the S3 treatment (32.12 t·ha-1, 4.13 t·ha-1, and 117.30, respectively). The highest crude protein content of mixed forage (12.31%) was in the S4 treatment. According to the results of a principal component analysis, plant height, stem diameter, crude protein yield, total hay yield, strength of the stem at the first to fourth internodes, and the relative feed value of the mixed D. lablab-S. bicolor sward made the largest contributions to forage yield and quality. The treatments were ranked, from highest yield and quality to lowest, as follows: S3>S2>S4>S1>S0. Based on the yield and nutritional quality of the mixed swards, it is suggested that the optimum seeding rate of D. lablab and S. bicolor grown under drip irrigation in arid areas of Ningxia is 49.5 kg·ha-1.

    Changes in vegetation characteristics and soil enzyme activities under different treatments in semi-arid meadow grassland
    Zhi-ting WANG, Ting-xi LIU, Xin TONG, Li-min DUAN, Dong-fang LI, Xiao-yong LIU
    2023, 32(3):  41-55.  DOI: 10.11686/cyxb2022084
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    Different grassland development methods, for example, burning, fencing enclosure, and grazing, have different effects on vegetation and soil. To explore the influence of different grassland treatment methods on meadow grassland, several sites within Horqin meadow grassland were selected for study. Four grassland treatments were applied: Enclosure (UNM), enclosure+mowing (M), enclosure+burning (F), and grazing (G). The activities of soil urease, soil alkaline phosphatase, and soil sucrase as well as vegetation characteristics in the growing season were analyzed to explore the best treatment method for meadow grassland. It was found that: 1) Soil enzyme activity decreased with increasing soil depth, and the differences among different treatments gradually decreased as the soil depth increased. 2) Compared with UNM, G resulted in decreased vegetation height, coverage, aboveground biomass, and soil enzyme activity at different points, but a higher richness index. 3) Compared with UNM, M resulted in different compensatory abilities of species in a range of functional groups. In M, the compensatory ability of Poaceae was greater than that of Compositae. 4) Compared with UNM, F resulted in increased vegetation height, coverage, aboveground biomass, richness index, and activities of the three soil hydrolases at different points. 5) Compared with G, M resulted in increased vegetation height, coverage, aboveground biomass, richness index, and soil urease activity, but decreased sucrase and alkaline phosphatase activities. In conclusion, our results show that controlled burning is the best development treatment for meadow grassland in semi-arid areas.

    Soil nutrient and microbial activity responses to nitrogen and phosphorus addition in oats and arrowhead peas in monocrop and mixed sowings
    Le-le SU, Yan QIN, Zhao-min WANG, Yong-chao ZHANG, Wen-hui LIU
    2023, 32(3):  56-66.  DOI: 10.11686/cyxb2022181
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    Nitrogen and phosphorus are key nutrients for improving forage yield and quality. Nitrogen and phosphorus additions will change soil nutrient conditions and cause changes in microbial biomass and enzyme activities. This study investigated the response of soil microbial characteristics to different nitrogen and phosphorus treatments in oat and common vetch within different planting configurations. In this experiment in an alpine region, monocultures of oats (Avena sativa) or common vetch (Vicia sativa) and plots of oats mix-cropped with vetch in a 1∶1 seeding ratio were established, and four different nutrient addition treatments were applied: Nitrogen only, phosphorus only, nitrogen and phosphorus and zero added nutrients. Variation in soil microbial biomass carbon, nitrogen and phosphorus and their stoichiometric ratios, together with extracellular soil enzyme activities were the main focus of measurements. It was found that: 1) N only and P only had negative effects on soil microbial biomass in oat monocultures; P fertilizer application and combined nitrogen and phosphorus application had a positive effect on soil microbial biomass in vetch monocultures; Application of N fertilizer only resulted in increased soil microbial biomass carbon only in the mixed oat-vetch sowings, while the combined application of nitrogen and phosphorus decreased the microbial biomass carbon and microbial biomass nitrogen. 2) Added N only increased the activity of β-1,4-glucosidase (BG), while added P only increased the activity of acid phosphatase (AP). However, β-N-acetylglucosaminidase (NAG) and AP enzyme activities were increased in oat plots indicating that soil microorganisms can increase the nutrient acquisition ability by increasing the enzyme activities obtained by C, N and P. 3) For soils in this experiment, the soil microbial biomass (SMB) C∶N was lower than the national average, while the SMB N∶P was higher than the national average, and the soil N∶P enzyme activity ratio was greater than 1, indicating that the nitrogen availability restriction to soil microbial activity was greater than the phosphorus limitation at the test site. Therefore, in this experiment, the single application of nitrogen fertilizer inhibited the growth of soil microorganisms in the oat monoculture plots, but was beneficial to the growth of soil microorganisms in the mixed oat-vetch plots. Stoichiometric ratios indicate that microorganisms respond to changes in soil nutrient conditions by adjusting the nutrient content of the microbial biomass and the content of secreted extracellular enzymes.

    Morphological diversity and germplasm utilization potential of wild Elymus sibiricus
    Chun-yan LI, Yan WANG, Xin-rui LI, Ying-zhu LI, Ming-feng LI, Li-li CHEN, Xiong LEI, Li-jun YAN, Ming-hong YOU, Xiao-fei JI, Chang-bing ZHANG, Qi WU, Wen-long GOU, Da-xu LI, Jia-jun YAN, Shi-qie BAI
    2023, 32(3):  67-79.  DOI: 10.11686/cyxb2022132
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    This study investigated the morphological variation exhibited among, and genetic background of 104 wild populations of Elymus sibiricus. Data were collected on 23 morphological indexes and genetic diversity of 520 wild E. sibiricus from the 104 populations, representing different ecological types in the main distribution areas of wild E. sibiricus in China. Significant differences were found in morphological characteristics of E. sibiricus germplasm in different habitats, and the coefficient of variation for quantitative characters ranged from 9.49% to 49.56%. Results of a cluster analysis indicated that the 104 populations could be grouped into four categories with distinct morphological characteristics and development and utilization potential. Correlation analysis showed that some particular traits such as heading, plant height and flag leaf length of wild E. sibiricus were significantly correlated with altitude. Furthermore, a principal component analysis showed that five traits (plant height, heading or not, number of stem nodes, dry and fresh weight per plant, flag leaf length and width) accounted for 67.79% of the morphological diversity of E. sibiricus, and these traits were the main the main sources of morphological variation in E. sibiricus and could be used as an important reference index of morphological variation in E. sibiricus.

    Effects of nitrogen application rate on seed yield and nitrogen use efficiency of Elymus
    Tong-yao LI, Qing-ping ZHOU, You-jun CHEN, Yuan ZHAN, Hui WANG
    2023, 32(3):  80-90.  DOI: 10.11686/cyxb2022279
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    Nitrogen is one of the crucial macroelements contributing to the growth and development of gramineous (poaceous) plants. However, excessive nitrogen application will result in environmental pollution, increased production costs and a decrease in profitability. Based on the strong demand and the low seed yield of Elymus in the Qinghai-Tibet Plateau area, this study investigated the seed yields of two Elymus species under six nitrogen fertilizer application rates. The cultivars investigated were Elymusbreviaristatus cv. Tongdeand Elymus sibiricus cv. Qingmu No. 1. The six nitrogen application treatments in this study were 0, 45, 90, 135, 180 and 225 kg N·ha-1. The effects of nitrogen application on seed production and nitrogen use efficiency of Elymus were analyzed to provide reference data for seed production in Elymus. It was found that nitrogen application promoted the growth of both tested Elymus varieties. Forage vegetative growth was enhanced, including plant height, tillers per unit area, the seed yield and yield components such as fertile tillers per unit area, spikelets per ear, seeds per ear and 1000-seed weight. With increase in nitrogen application rate, the various yield indexes initially increased and then plateaued or decreased. As successive nitrogen increments were added, the agronomic use efficiency of E. sibiricus cv. Qingmu No. 1 initially increased and then decreased, while the agronomic use efficiency and differential N response of both cultivars gradually decreased. In this study, E. breviaristatus cv. Tongde and E. sibiricus cv. Qingmu No. 1 had seed yields of 712-1661 kg·ha-1 and 701-1626 kg·ha-1, respectively. In order to manage and reduce N fertilizer inputs, the recommended N fertilizer application rate was 135-180 kg·ha-1. Correlation analysis and pathway analysis showed that fertile tillers per unit area and seeds per ear contributed more to the increase of seed yield among seed yield components.

    Genome-wide identification and analysis of the DMP gene family in flax (Linum usitatissimum
    Wen LI, Li-rong ZHAO, Jian-ping ZHANG, Zi-gang LIU, Yan-ni QI, Wen-juan LI, Ya-ping XIE
    2023, 32(3):  91-106.  DOI: 10.11686/cyxb2022094
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    Members of the DMP genefamily are plant-specific membrane proteins that play an important role in plant reproductive development and senescence. Flax (Linum usitatissimum) is an important oil and cash crop in China. However, there are no reports on the distribution and functions of the DMP gene family in this flax species. We identified the members of the DMP gene family in flax using bioinformatics analyses, and determined their sequence characteristics, phylogeny, and duplication events. Transcriptome data and quantitative reverse-transcription polymerase chain reaction (qRT-PCR) analyses were used to analyze the transcriptional profiles of LuDMP genes in different tissues and organs and under stress treatments. Seventeen LuDMP genes, designated as LuDMP-1 to LuDMP-17, were identified from the Longya-10 cultivar by homology analysis, and were found to be unevenly distributed on nine chromosomes. Sequence characteristics analysis showed that only LuDMP-9LuDMP-16, and LuDMP-17 had an intron and the other members had none. All members of the LuDMP family contained many cis-acting elements related to hormone and stress responses in their promoter regions. The coding sequences encoded polypeptides with lengths ranging from 195 to 240 amino acids, molecular weights ranging from 20946 to 25830 Da, and theoretical isoelectric points ranging from 4.76 to 9.71. All LuDMP proteins were predicted to be hydrophobic with two to five transmembrane domains and four to eight motifs. Four motifs were present in all LuDMP proteins. Most LuDMP proteins were predicted to localize in the cell membrane. Three tandem duplication and eight segmental duplication gene pairs were identified in the LuDMP gene family, which has been under strong purification selection during the evolution of flax. Transcriptome analyses showed that most LuDMP members are specifically expressed in the fruit and stem. In a phylogenetic analysis, the 17 DMP proteins were divided into five subgroups. Subgroup III was the largest, with 11 members. The DMP proteins in each subfamily exhibited monocotyledon-specific or dicotyledon-specific clustering patterns. LuDMP-1 and LuDMP-7 in subgroup IV showed the highest homology with haploid induction genes in Arabidopsis and maize (Zea mays) and were located in the same evolutionary branch, with sequence homology higher than 67%. Moreover, these two genes showed the highest transcript levels in the mature anther, suggesting that they are candidate genes for inducing flax haploids. We cloned LuDMP-1 from Longya-10 (full-length coding sequence, 699 bp). The promoter regions of LuDMP-1/7 contained hormone- and stress-responsive elements, and both genes showed increased transcript levels under auxin (indole acetic acid, naphthalene acetic acid), gibberellin, polyethylene glycol, and high temperature and low temperature treatments. Their responses to low temperature and high temperature were the most obvious, with transcript levels increased to 260 times and 600 times that in the control, respectively. The results of this study lay a foundation for elucidating the functions of LuDMPs and identify genetic resources for haploid breeding of flax.

    Cloning of MsBBX24 from alfalfa (Medicago sativa) and determination of its role in salt tolerance
    Yuan WANG, Jing WANG, Shu-xia LI
    2023, 32(3):  107-117.  DOI: 10.11686/cyxb2022104
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    Salt stress is one of the main abiotic stress factors affecting plant growth and development. Members of the BBX family of transcription factors are known to play important regulatory roles in pigment accumulation, photomorphogenesis, seed development, and stress adaptation. To clarify the function of Medicago sativa (alfalfa) BBX genes, we used Primer Premier 5 to design specific primers according to the sequence of MsBBX24 in the NCBI database, and cloned MsBBX24 using the cDNA of alfalfa as the template. Bioinformatics software was used to analyze the sequence and structure of MsBBX24, and to compare MsBBX24 with related BBX24 sequences in other plants. A phylogenetic tree was constructed to analyze the evolutionary relationships among BBX24s. The transcriptional profile of MsBBX24 was analyzed by real-time quantitative polymerase chain reaction (qRT-PCR). An MsBBX24-overexpression vector was constructed by DNA digestion and ligation, and introduced into wild-type Arabidopsis by Agrobacterium-mediated transformation. The positive transgenic Arabidopsis plants were screened using the herbicide Basta and the presence of the transgene was confirmed by semi-quantitative RT-PCR. The salt tolerance of wild-type and transgenic Arabidopsis plants overexpressing MsBBX24 was analyzed on the basis of phenotypic characteristics and physiological indexes. The MsBBX24 coding sequence was 723 bp long, encoding a polypeptide of 240 amino acids with a predicted molecular weight of 30.58 kDa and theoretical isoelectric point of 7.74. MsBBX24 showed high homology with BBX24 of Cicer arietinum and Medicago truncatula. The results of qRT-PCR analyses showed that the transcript levels of MsBBX24 increased in response to salt stress (150 mmol·L-1 NaCl). The transgenic Arabidopsis plants showed increased tolerance to NaCl stress. Compared with the controls, the transgenic plants overexpressing MsBBX24 showed enhanced growth of seedling roots and lateral roots, a higher cotyledon greening rate, significantly reduced ion leakage, malondialdehyde content, and H2O2 content, increased contents of chlorophyll and proline, and higher peroxidase and superoxide dismutase activities. These results show that, under salt stress, MsBBX24 improves the antioxidant defense system to remove reactive oxygen species, thereby enhancing the salt tolerance of transgenic plants. Thus, MsBBX24 is an important candidate gene for breeding new salt-tolerant varieties of alfalfa.

    Changes in small intestinal morphology, digestive enzyme activity and antioxidant enzyme activities of female Tibetan sheep after substituting the maize component of a concentrate diet with palm meal
    Li ZHOU, Sheng-zhen HOU, Zhi-you WANG, Bao-chun YANG, Li-juan HAN, Lin-sheng GUI
    2023, 32(3):  118-127.  DOI: 10.11686/cyxb2022126
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    This experiment explored the effects on jejunum histomorphology, digestive enzyme activity, pH, lipopolysaccharide levels and antioxidant enzyme activity of substituting the maize component of a concentrate diet with palm meal in female Tibetan sheep. Well bred female Tibetan sheep aged 2-3 months with similar initial weight and in good health were randomly divided into four treatment groups of 30 animals, each comprising six replicate groups of 5 sheep. In the four treatment groups, 0%, 15%, 18% or 21% palm meal were fed to replace maize in the concentrate for a test period is 97 days. It was found that: 1) There were no significant differences in villus height, villus width, crypt depth, mucosal thickness and villus height∶crypt depth between the 0% and 15% maize groups (P>0.05); 2) The activities of α-amylase, cellulase, lipase and chymotrypsin in the jejunum in the 0% maize group were significantly lower than those in 15% maize group (P<0.05 or P<0.01). 3) The activities of glutathione peroxidase and catalase in the jejunum in the 0% maize group were significantly lower than those in the 15% and 18% maize groups (P<0.05), but did not differ significantly from the 21% maize group (P>0.05); 4) The jejunum concentrations of lipopolysaccharide in the 18% and 21% maize groups were significantly higher than in the 0% maize group (P<0.05 or P<0.01), but there was no significant difference compared with the 15% group (P>0.05). In conclusion, palm meal can partially replace maize to feed Tibetan ewes, and the recommended maize substitution rate is 15%.

    Effects of sodium salt stress on seed germination and seedling growth of three Chenopodiaceae annuals
    Wen-ting GUO, Guo-hua WANG, Qian-qian GOU
    2023, 32(3):  128-141.  DOI: 10.11686/cyxb2022123
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    In this study, we selected three typical Chenopodiaceae annuals (Bassia dasyphyllaSalsola ruthenica, and Halogeton arachnoideus) that grow in a typical desert-oasis ecotone in the Hexi Corridor and determined their responses to salt stress. We investigated the effects of different concentrations of salts (NaCl and NaHCO3, 0, 50, 100, 150 and 200 mmol·L-1) on their seed germination, seedling growth, and physiological characteristics. The results showed that: 1) Sodium salt stress significantly inhibited the seed germination and seedling growth of all three species. At the seed germination stage, the germination rate, germination power, and germination index decreased with increasing salt concentrations, but the seeds of all three species were able to recover germination after the removal of salt stress. At the seedling growth stage, the plant height, main root length, and fresh weight decreased with increasing salt concentrations. 2) The salts clearly affected the physiological characteristics of the three Chenopodiaceae annuals. As the concentration of the salts increased, the chlorophyll content of three plants showed a downward trend, while the malonaldehyde content showed an upward trend, and the free proline and soluble sugar contents initially increased and then decreased. Among these parameters, chlorophyll content was particularly important for seedling growth. 3) Under mild (50 mmol·L-1) and moderate (100, 150 mmol·L-1) salt stress conditions, the three plants adapted mainly through osmotic adjustment, and the contents of soluble sugars and free proline increased significantly to improve the water holding capacity and maintain normal plant growth through cell osmotic regulation. Under severe salt stress (200 mmol·L-1), the malonaldehyde content increased rapidly, chlorophyll decomposed more rapidly, osmotic adjustment was weakened, and there was a clear inhibitory effect of salts on plant growth. 4) In terms of individual adaptation strategies to severe salt stress, the three Chenopodiaceae annuals adapted to salt stress by reducing the distribution of resources to the roots and significantly decreasing the root∶shoot ratio. 5) Compared with NaCl, the alkaline salt NaHCO3 had stronger negative effects on the three Chenopodiaceae annuals. In addition, there were significant differences in the salt tolerance of different species among different growth stages. The species were ranked, from most to least salt tolerant, as follows: H. arachnoideus>B. dasyphylla>S. ruthenica.

    Acid-aluminum adaptability and tolerance evaluation of 44 alfalfa cultivars
    Zheng TIAN, Zheng-yu YANG, Zhong-jie LU, Ben LUO, Mao ZHANG, Rui DONG
    2023, 32(3):  142-151.  DOI: 10.11686/cyxb2022097
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    The aims of this study were to explore the range of adaptability of Medicago sativa cultivars in Guizhou to acid-aluminum conditions, and to determine which physiological factors are related to tolerance of these conditions. We selected 44 alfalfa varieties for a one-year field experiment. A genotype×environment interaction model was used to analyze the yield of alfalfa at two locations in one year, and five acid-tolerant and aluminum-adaptive varieties were identified: Algonquin, M. sativa cv. xinjiangdaye, Trifecta, Vernal and Medicago varia cv. Zhongmu No.1. Aluminum-acid stress experiments were carried out using the sensitive variety UC-1465 and the tolerant variety Algonquin. It was found that, under the same treatment, the electrical conductivity, relative aluminum content, and mortality rates were significantly lower in the tolerant alfalfa cultivar than in the sensitive alfalfa cultivar. The response of alfalfa plants to acid-aluminum stress was mainly reflected by significant (P<0.05) increases in citric acid, malic acid, acetic acid, tartaric acid, fumaric acid, and oxalic acid contents. The increased synthesis and secretion of malic acid may be an important factor in resistance to acid and aluminum stress.

    Response of the mitochondrial AsA-GSH cycle during alfalfa seed germination under low temperature stress
    Shou-jiang SUN, Yi-han TANG, Wen MA, Man-li LI, Pei-sheng MAO
    2023, 32(3):  152-162.  DOI: 10.11686/cyxb2022272
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    This study investigated the response to low temperature stress of the ascorbic acid-glutathione (AsA-GSH) cycle in radicle mitochondria of alfalfaMedicago sativa) seeds. Alfalfa seeds were germinated at two temperatures (10 or 20 ℃) and during imbibition antioxidant mechanisms, including hydrogen peroxide content, AsA-GSH cycle enzyme activity and antioxidant content were measured in radicle mitochondria imbibed for different times (6, 12 and 24 h). It was found that the H2O2 content of radicle mitochondria under low temperature (10 ℃) was higher than that under normal temperature (20 ℃) after 12 and 24 hours imbibition. The glutathione reductase (GR) activity of radicle mitochondria at 10 ℃ was lower than that at 20 ℃ after imbibition for 6, 12 and 24 h. After 12 and 24 h imbibition, the ascorbic acid (AsA) content of radicle mitochondria at 10 ℃ was lower than that at 20 ℃. After 24 h imbibition under low temperature stress, the glutathione (GSH) content of radicle mitochondria decreased significantly (P<0.05) compared with seeds imbibed at normal temperature. During imbibition under low temperature, the normal process of seed germination was inhibited by oxidative damage, mainly through decrease in the activities of GR, monodehydroascorbate reductase, and peroxidase and decreased levels of AsA and GSH in the AsA-GSH cycle, which led to the accumulation of H2O2 in the radicle mitochondria.

    Aboveground and belowground phenotypic characteristics of Cynodon dactylon lines differing in drought resistance and endogenous hormone response to drought stress
    Yi-long ZHANG, Qi-kun YU, Wen LI, Pei-ying LI, Zong-jiu SUN
    2023, 32(3):  163-178.  DOI: 10.11686/cyxb2022129
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    This study investigated the effects of drought stress on Cynodon dactylon lines varying in drought resistance, in order to identify patterns in morphological and ecophysiological traits and endogenous hormone levels correlated with drought resistance. It was anticipated this research would enhance understanding of drought resistance in C. dactylon and thereby provide a theoretical basis for use of exogenous hormones to regulate drought resistance in industry practice. Plants were established in pots made from PVC pipes then subjected to predetermined levels of water deficit for 10 days. The relative water content, relative conductivity, endogenous hormones [indole acetic acid (IAA), abscisic acid (ABA), gibberellin A3 (GA3), zeatin riboside (ZR), brassinolide (Br)], leaf characteristics (leaf length, leaf width, leaf area), root characteristics (total root length, root surface area, root volume, root average diameter, root dry weight, longest root length and root activity) were measured. The changes in endogenous hormone levels in leaves and roots of C. dactylon with different drought resistance and the correlations between phenotypic characteristics and hormones were analyzed. The results showed that with increased intensity of drought stress, leaf length, leaf width, leaf area and root average diameter of both drought-tolerant and intolerant C. dactylon were reduced, while the growth and development of roots was promoted. The content of ABA in leaves and roots was increased, and the contents of IAA, GA3, ZR and Br were decreased, and IAA∶ABA and GA3∶IAA ratios were inversely correlated with leaf indexes and root indexes. This showed that the leaf and root systems of C. dactylon root adopted contrasting survival strategies under drought stress: promotion of underground growth and reduction in aboveground growth. Drought-resistant C. dactylon exhibited comparatively better adaption to a water deficit stress environment by maintaining some growth, larger leaf area, a more developed root system and higher ZR∶ABA, GA3∶ABA, IAA∶ABA and Br∶ABA ratios under the same level of water deficit stress.

    Effect of arbuscular mycorrhizal fungi on the salt tolerance of Trifolium repens
    Yan-lan ZHAO, Xin-yi ZENG, Jin-chao GONG, Xiang-jun LI, Xu-xu LI, Shan LIU, Xin-quan ZHANG, Ji-qiong ZHOU
    2023, 32(3):  179-188.  DOI: 10.11686/cyxb2022101
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    Arbuscular mycorrhizal fungi (AMF) enter into symbiotic relationships with plants by forming mycorrhizal networks, and thus play critical roles in plant growth and resilience to environmental stresses. At present, it is still debated whether AMF affect the salt tolerance of clover (Trifolium repens). In this study, we explored the effect of AMF on T. repens plants under salt-stress conditions (NaCl at 150 mmol·L-1). It was found that, compared with a no-salt control, salt stress inhibited the growth and physiological indexes of T. repens. Under salt stress conditions, compared with uninoculated plants, those inoculated with AMF showed significantly increased plant height, dry weight, maximal photochemical efficiency of photosystem II, and relative water content, decreased malondialdehyde content and relative electric conductivity, and higher contents of soluble sugars and free proline (32.03% and 9.42% higher, respectively). Our results demonstrate that salt stress inhibits the growth of T. repens, and that AMF improve the salt stress tolerance of T. repens by enhancing stress resistance and decreasing the malondialdehyde content and ion leakage (relative conductivity) under salt stress.

    Effects of phosphorus application and inoculation with arbuscular mycorrhizal fungi and phosphorus-solubilizing bacteria on the photosynthetic characteristics and biomass of alfalfa
    Xuan-shuai LIU, Yan-liang SUN, Xiao-xia AN, Chun-hui MA, Qian-bing ZHANG
    2023, 32(3):  189-199.  DOI: 10.11686/cyxb2022081
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    This study explored the effects of inoculation with arbuscular mycorrhizal fungi (AMF) and phosphorus-solubilizing bacteria (PSB) on the photosynthetic characteristics and biomass of alfalfa under different phosphorous application levels. 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 16 treatments in total, consisting of four inoculation treatments [uninoculated control (CK, J0), single inoculation with Bacillus megaterium (Bm, J1), single inoculation with Funneliformis mosseae (Fm, J2), and double inoculation (Bm×Fm, J3)] and four phosphorus (P2O5) application levels [0 (P0), 50 (P1), 100 (P2) and 150 mg·kg-1 (P3)]. The net photosynthetic rate (Pn), transpiration rate (Tr), stomatal conductance (Gs), intercellular CO2 concentration (Ci), light energy use efficiency (LUE), water use efficiency (WUE), chlorophyll [Chl (a+b)] content, and biomass of alfalfa leaves were measured. Correlation analyses were conducted to clarify the relationship between each photosynthetic index and the biomass of alfalfa. The best combination of bacteria and phosphorus conditions in terms of biomass accumulation and photosynthetic characteristics of alfalfa was identified using a membership function analysis. It was found that, under the same inoculation treatment, the PnTrGs, LUE, WUE, Chl (a+b), and biomass all initially increased and then decreased with increasing phosphorus levels, with the maximum values in the P2 treatment. The values of these parameters were significantly higher in the phosphorus application treatments than in the no-phosphorus treatments (P<0.05). The value of Ci gradually decreased with increasing phosphorus levels, and its value was significantly lower in the phosphorus application treatments than in the no-phosphorus treatments (P<0.05). Under the same phosphorus application level, the PnTrGs, LUE, WUE, Chl (a+b), and biomass of leaves were significantly higher in alfalfa plants inoculated with AMF and PSB than in uninoculated plants (P<0.05). The parameters PnTrGs, LUE, WUE, and Chl (a+b) showed maximum values in the J3 treatment, while Ci showed the minimum value in J3 and was significantly lower in inoculated plants than in uninoculated ones (P<0.05). Correlation analyses showed that Ci was significantly negatively correlated with PnTrGs, LUE, WUE, Chl (a+b) and biomass (P<0.05), and the other parameters were significantly and positively correlated with each other (P<0.05). A multivariate evaluation ranked the treatments on the basis of the comprehensive membership function values, and the top three were J3P2>J2P2>J3P1. Therefore, a phosphorus application rate of 100 mg·kg-1 and double inoculation with AMF and PSB can significantly increase photosynthesis and the chlorophyll content of alfalfa leaves, thereby increasing the biomass of alfalfa.

    Comprehensive screening of Agropyron cultivars for tolerance to salt stress at the seedling stage
    Han MIAO, Lai WEI, Yan-ping YANG, Yong-he CHE
    2023, 32(3):  200-211.  DOI: 10.11686/cyxb2022083
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    Agropyron is a perennial grass in the Triticeae (Poaceae). It has the advantages of resistance to drought, cold, and salinity, so it is an excellent crop for saline-alkali land improvement. To provide a basis for the evaluation of salt tolerance of Agropyron, seedlings of two main Agropyron cultivars, Agropyron mongolicum cv. Mengnong No.1 and Agropyron cristatum×Agropyron desertorum cv. Hycrest-Mengnong, were exposed to salinity stress using five concentrations of seawater in a pot experiment in a greenhouse. Thirty days later, twelve indexes were investigated including root length (RL), shoot height, superoxide dismutase (SOD) activity, malondialdehyde content,and K+ content. The effects of salt stress on the seedling growth characteristics, K+/Na+, antioxidant enzyme activity, and contents of osmotic regulatory substances in the Agropyron materials were analyzed. The saline tolerance coefficient of each index under different seawater treatments was calculated, and then the salt tolerance of Agropyron at the seedling stage was comprehensively analyzed by a principal components analysis, subordinate function analysis, and regression analysis. All of the indexes except for the relative water content of the shoot showed significant differences (P<0.05) among the different salt stress treatments. A principal components analysis was conducted using ten indexes to evaluate the salt tolerance of the Agropyron at the seedling stage. A regression analysis identified three important factors in salt stress tolerance: An osmotic adjustment factor, a plant type factor, and a root system factor. The following mathematical evaluation model for Agropyron salt tolerance was established by regression analysis: D=0.833-0.018SOD-0.147SP-0.042SS-0.142Pro-0.004Na+-0.520 K+-0.076RL, where SP=soluble protein, SS=soluble sugars and Pro=proline. Using this equation, the salt tolerance of Agropyron germplasm resources could be quickly and accurately predicted on the basis of seven indexes: SOD, K+, Na+, SP, SS, Pro, and RL. These analyses revealed that the salt tolerance of Hycrest-Mengnong was higher than that of Mengnong No.1. The results of this study will be useful for promoting and managing the cultivation of grasses in salinized areas.

    Theoretical basis, technical principles and realization of grassland multifunctional objective management
    Chun-hui ZHANG, Liang ZHAO, Xin-quan ZHAO
    2023, 32(3):  212-223.  DOI: 10.11686/cyxb2022159
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    There are diverse grassland types, including protected grassland, grazed rangeland grassland and artificially sown grassland. Similarly, there is a diversity of biological resources linked to grassland use, such as animals, plants and microorganisms, and a diversity of ecosystem services and functions including regulating, provisioning, supporting and cultural functions. Drawing on the concept of ecosystem multifunctionality, this study summarizes the development process of grassland management, and puts forward the framework of grassland multifunctional objective management in the new era. This framework sets out the basic theory of maintaining the diversity of grassland types, biological resources and ecosystem services and functions and informs the transformational development of grassland utilization technologies relating to grassland animal, plant and microbial resources, the precise measurement of surface information and remote sensing inversion technology systems, the technical systems for accurate measurement of grassland herbivore utilization and grassland carrying capacity, the production technology systems to achieve feed supply and demand balance in grassland and animal husbandry, and the technical systems to simultaneously achieve improvement in grassland ecological function and the realization of ecological product value. In addition, this study explores the management path for multifunctional optimization of ecology, production and livelihood in grasslands while maintaining the multifunctional attributes of grassland, protecting the health and sustainable use of grassland, and realizing the goals of regional protection of nature, providing services to human populations and achieving sustainable development.

    Effects of particle size on Uraria crinita rumen in-vitro fermentation characteristics and microbial population in lambs
    Jing WANG, Ling-ying KONG, Jian-feng XU, Jing KANG, Zhen-feng SHEN, Ting LIU
    2023, 32(3):  224-233.  DOI: 10.11686/cyxb2022133
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    This study investigated the effect of difference in particle size on in vitro rumen fermentation and microbial population when Uraria crinita was used as the dietary fiber source for lambs. Six treatments were set up with differing U. crinita particle size (1.00, 2.36, 3.35, 4.75, 8.00 and 12.50 mm) as rumen fermentation substrates incubated 48 hours in vitro using Rusitec-s artificial rumen simulation. There were four replicates per treatment. The results showed that degradation rate of in vitro neutral detergent fiber degradability (IVNDFD), the molar ratios of butyrate, isobutyrate, valerate, isovaleric, and the copy number of Butyrivibrio fibrisolvens (B.f)in the 2.36 mm particle size treatment were significantly increased (P<0.05), while the number of total Methanogens (TMe) (P<0.05) was significantly decreased. Total bacteria number was positively correlated with ammonia nitrogen concentration and acetic acid molar ratio (R2 =0.84, P=0.038; R2 =0.88, P=0.021). B.f was positively correlated with propionate molar ratio (R2 =0.82, P=0.045), and negatively correlated with pH (R2 =-0.98, P=0.001). TMe were positively correlated with in vitro crude protein degradability (IVCPD) (R2 =0.91, P=0.012), and negatively correlated with in vitro dry matter degradability and IVNDFD (R2 =-0.86, P=0.027; R2 =-0.83, P=0.043). Methanobacteriaceae(Mba) was negatively correlated with pH (R2 =-0.90, P=0.015). These results describe how different particle sizes of U. crinita fermentation substrate affect the rumen microbial community structure and population numbers in lamb fermentation broth in vitro, resulting in changes in fermentation outcomes. Under the experimental conditions, the 2.36 mm particle size provided the best fermentation outcome for 3-month-old lambs.