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    20 January 2021, Volume 30 Issue 1
    Stratified data reconstruction based on spatial pattern of soil bulk density intemperate grasslands of Northern China
    Yu-xin QIAO, Hua-ping ZHONG, Hua-zhong ZHU, Xiao-ming SHAO, Yu-zhe Li
    2021, 30(1):  1-11.  DOI: 10.11686/cyxb2020056
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    The spatial patterns and stratification of soil bulk density in the temperate grassland of Northern China remain undefined because of the complex geographical conditions. In this study, we used measured data for soil bulk density available in reports of soil surveys of temperate grasslands of Northern China, and constructed a soil transfer function from the surface soil bulk density. Accordingly, we reconstructed vertically stratified bulk density data of the soil profile, and estimated the pattern of soil bulk density in the horizontal plane. In these analyses, the soil bulk density of the temperate grasslands of Northern China was typically high in the central and northwestern regions and low in the eastern and mountainous regions. The mean soil bulk density of grasslands was 1.50 g·cm-3. According to geographical divisions, the highest soil bulk density was in the South Xinjiang Basin (mean soil bulk density, 1.99 g·cm-3), and the lowest was in the Altai Mountains (mean soil bulk density, 1.03 g·cm-3). Based on data obtained from various types of grasslands, the soil bulk density was lowest in alpine meadow grassland (mean soil bulk density, 0.76 g·cm-3) and highest in temperate desert grassland (mean soil bulk density, 1.80 g·cm-3). The mean prediction error, root mean square deviation, relative error, and multiple correlation coefficient of soil bulk density data pertaining to the surface layer (0-10 cm) in the temperate grasslands of Northern China were 0.018, 0.223, 16.2%, and 0.5386, respectively.

    Community diversity, patterns of productivity, and factors influencing them in Stipa in Ningxia grassland
    Wan-di LIU, Xiao-wei LI, Wen-guang HUANG, Hui-cheng MA, Hong-ying MA, Wen-xiao WANG
    2021, 30(1):  12-23.  DOI: 10.11686/cyxb2020064
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    Species diversity and productivity are core indicators of grassland ecosystems and the fundamental factors for characterizing the services and functions of grassland ecosystems. The temperate grasslands in Ningxia are located in the transitional area between arid and semi-arid grasslands. Stipa is the dominant plant genus and it is sensitive to changes in water and heat. Therefore, in this study, we focused on the diversity of Stipa plant communities in Ningxia grasslands in the context of global climate change. A knowledge of the patterns of diversity and productivity, and the factors that influence them at the macro-scale, is not only of great value for research on ecological theory, but is also significant for the production and management of natural grasslands in Ningxia. In this study, 15 Stipa plant communities in the temperate grassland of Ningxia were studied in detail. Fifteen field observation plots were established along an environmental gradient, and the characteristics of the plant community, soil nutrient status, and climatic factors were measured. The spatial distribution patterns of plant community diversity and productivity, and the responses of plant communities to ecological factors were also determined. These analyses clarified the relationship between plant community species diversity and productivity. We found that: 1) The productivity of the Stipa community in Ningxia was significantly positively correlated with latitude and negatively correlated with altitude and longitude; species diversity was significantly negatively correlated with latitude and significantly positively correlated with altitude, but not significantly correlated with longitude; 2) The results of redundancy analyses showed that soil available nitrogen, annual average temperature, soil organic carbon, soil total nitrogen, annual average radiation, soil moisture, soil bulk density, soil total phosphorus, average annual precipitation, average monthly precipitation of the growing season, and average monthly precipitation of the dry season were the main factors affecting species diversity and productivity. Soil factors explained, respectively, 15.6%, 17.8%, and 19.8% of the variation in productivity, diversity, and overall interpretation, and hydrothermal factors explained, respectively, 13.8%, 37.9%, and 25.2% of the variation in the same factors, while the interaction between hydrothermal factors and soil factors explained, respectively, 68.7%, 39.6%, and 50.6% of the variation in the same factors. In general, water, heat, and soil factors were identified as the drivers of the productivity and diversity patterns of Stipa in Ningxia, but the sizes of their contributions to diversity and productivity differed, and showed certain trends. Community diversity and productivity tended to be positively correlated, but this was not statistically significant. The results of this study provide a theoretical basis for the production and management of natural grasslands in Ningxia.

    Characteristics of soil organic carbon and active organic carbon in typical natural grassland in Ningxia
    Bo JI, Jian-long HE, Xu-dong WU, Zhan-jun WANG, Ying-zhong XIE, Qi JIANG
    2021, 30(1):  24-35.  DOI: 10.11686/cyxb2020305
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    This research explored the variation and characteristics of soil carbon components across four major types of natural grassland (meadow steppe, warm steppe, steppe desert and desert steppe) in Ningxia typical temperate natural grassland. The carbon components were investigated soil organic carbon and active organic carbon (readily oxidized organic carbon, microbial biomass carbon and dissolved organic carbon) at 49 fixed sites, using both survey and direct sampling methods. It was found that soil organic carbon contents to 40 cm soil depth were, respectively, 34.23, 12.84, 5.76 and 3.82 g·kg-1, and the soil organic carbon storage was, respectively, 13.43, 5.75, 2.58 and 2.29 kg·m-2 in the four natural grassland categories. For the four grassland categories, the readily oxidized organic carbon content ranged from 0.75-7.43 g·kg-1, microbial biomass carbon content ranged from 102.52-554.77 mg·kg-1, and dissolved organic carbon content ranged from 69.66-89.61 mg·kg-1. The overall ranking was meadow steppe>warm steppe>steppe desert>desert steppe. The levels of readily oxidized organic carbon storage were 2.56, 1.44, 0.62 and 0.48 kg·m-2, respectively; soil microbial biomass carbon storage was 218.31, 170.50, 81.99 and 68.26 g·m-2, respectively, with meadow steppe significantly higher than the other grassland types (P<0.05). The soil dissolved organic carbon storage was 34.36, 35.21, 37.22 and 43.14 g·m-2, respectively, and the value for desert steppe was significantly larger than the other grassland types (P<0.05). The range of values in the four grassland types for readily oxidized organic carbon was18.42%-29.72%, with the warm steppe being the highest. The range of values for microbial biomass carbon was 1.54%-3.83%, and meadow steppe grassland was the lowest. The range of values for dissolved organic carbon was 0.23%-2.01%, with ranking desert steppe>steppe desert>warm steppe>meadow steppe, and with significant differences (P<0.05) between the four grassland types. Soil organic carbon storage showed a significant (P<0.05) or extremely significant (P<0.01) positive correlation with soil readily oxidized organic carbon storage, microbial biomass carbon storage, total nitrogen, total phosphorus and total potassium, and showed significant (P<0.05) or extremely significant (P<0.01) negative correlation with soil dissolved organic carbon storage, soil bulk density and pH values. In summary, soil organic carbon stability was lowest in desert grassland, while the activity and bioavailability of the soil organic carbon pool in warm grassland was the highest. The importance of the soil organic carbon storage of natural grassland in Ningxia should not be underestimated.

    Species diversity and soil nutrient changes of a Nitraria tangutorum shrub community in Qingtu Lake wetland
    Fu-gui HAN, Duo-qing MAN, Qing-zhong ZHENG, Yan-li ZHAO, Yu-nian ZHANG, Bin XIAO, Gui-quan FU, Juan DU
    2021, 30(1):  36-45.  DOI: 10.11686/cyxb2020353
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    This paper results from a study of species diversity and soil nutrient variation in a Nitrariatangutorum shrub community in Qingtu Lake Wetland. It was found that: 1) There were 15 species in the community, belonging to 6 families and 15 genera, including 7 genera of Chenopodiaceae, 3 genera of Tribulaceae, 2 genera of Asclepiadaceae, and 1 genus each from the Poaceae, Solanaceae and Lauraceae. 2) The highest importance value for N. tangutorum was 54.72 in heavy saline-alkali soil. Importance values for saline sandy soil, yellow silty sandy soil, gray-white silty sandy soil, and semi-fixed sandy soil were, respectively 35.00, 31.16, 22.22, and 15.65. 3) For Margalef richness index and Shannon-Weiner diversity index, there were significant differences (P<0.05) between gray-white silty soil and other soils; for Simpson diversity index, community dominance index and Pielou evenness index, there were no significant differences between soil categories (P>0.05); for Alatulo evenness index, there were significant differences (P<0.05). 4) The highest soil organic matter content was in wetland area, with the greatest concentration at 10-20 cm depth, and the lowest at 40-60 cm depth; the highest content of total phosphorus was in the upper part of the shrub dune, with the highest concentration at 5-10 cm depth, and the lowest at 40-60 cm depth; the highest content of total nitrogen was at the land among dune with the highest N content at 0-5 cm depth, and the lowest at 20-40 cm depth; 5) The soil water content in waterlogged and non-waterlogged land (dunes) increased gradually with increasing soil depth, to a maximum below 40-60 cm soil depth. The water content of Nitraria shrub dunes was increased when growing in waterlogged areas, and settlement of fine sand on the soil surface in waterlogged areas enhanced. The groundwater level at the study site has steadily risen from approximately -4.1 m in 2006 to -3.0 m in 2019, fitting the regression equation: Water depth=-0.0017X2+0.1275X-4.274, where X denotes year (R2=0.9804; P<0.05).

    The species diversity and community assembly of arbuscular mycorrhizal fungi in typical alpine grassland in Sanjiangyuan region
    Cong-cong LI, Ya-xing ZHOU, Qiang GU, Ming-xin YANG, Chuan-lu ZHU, Zi-yuan PENG, Kai XUE, Xin-quan ZHAO, Yan-fen WANG, Bao-ming JI, Jing ZHANG
    2021, 30(1):  46-58.  DOI: 10.11686/cyxb2020268
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    This study investigated the key processes driving arbuscular mycorrhizal (AM) fungal community changes in typical alpine grassland ecosystems, by systematically measuring AM fungal diversity and community composition in four typical grassland ecosystems of Sanjiangyuan National Park, based on the Illumina-Miseq high-throughput sequencing method. The ecosystems evaluated were: Alpine desert, alpine steppe, alpine meadow and alpine wetland. Ecological processes structuring the fungal communities were inferred according to phylogenetic patterns and species abundance distributions in different ecosystems. It was found that: 1) The dominant genus in alpine desert, alpine meadow and alpine wetland was Glomus, while the dominant genus in alpine steppe was Diversispora. 2) The OTU richness and phylogenetic diversity index of AM fungi in alpine wetland were significantly lower than those of the other three grassland ecosystem types. 3) There were significant differences in species composition and phylogenetic composition of AM fungal communities among different grassland types. Plant community composition, soil water content, and available N∶P were the main factors affecting the composition of the AM fungal community. Soil water content was the primary determinant of the species composition of the AM fungal community, and plant community composition was a key factor in determining the phylogenetic composition of the AM fungal community. 4) AM fungal communities were all phylogenetically clustered in the four grassland types. The phylogenetic structure of AM fungal communities in the different grassland types are clustered. In alpine deserts, AM fungal community assembly is determined by stochastic processes, while in alpine grasslands, alpine meadows and alpine wetlands, AM fungal community assemblage are determined by stochastic processes and weak responses to environmental filtering.

    Isolation, screening and beneficial effects of plant growth-promoting rhizobacteria (PGPR) in the rhizosphere of Leymus chinensis
    Jing MAN, Bo TANG, Bo DENG, Jia-huan LI, Yu-juan HE, Jia-liang ZHANG
    2021, 30(1):  59-71.  DOI: 10.11686/cyxb2020321
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    Plant growth-promoting rhizobacteria (PGPR) are a category of beneficial bacteria which colonize the plant rhizosphere and promote plant growth and development. In this study, PGPR strains with the capacity for nitrogen fixation, phosphate solubilization, ACC deaminase activity and IAA production were isolated and screened from the rhizosphere of Leymus chinensis in different regions, with a view to providing PGPR resources for the development of microbial fertilizers. Twenty strains possessing high nitrogenase activities (range 8.71 to 11.63 nmol C2H4 ·mL-1·h-1) were isolated from Lanxi, Xilinhot and Hulun Buir. Twenty six inorganic phosphorus solubilizing bacterial strains with ratios of the diameter of phosphate-solubilizing halo to colony diameter (D/d values) greater than 1.5 were identified. For these, the range of phosphate solubilization was 7.08-82.71 μg·mL-1. Thirty six organic phosphorus solubilizing bacteria with D/d values greater than 1.5 were also isolated with the range of phosphate-solubilization being 1.56-32.48 μg·mL-1. Sixty PGPR strains with ACC deaminase activities were screened and the range of activities observed were 0.04-64.31 μmol α-KA·mg-1 Pr·h-1. Thirty nine PGPR strains with high activities of nitrogenase, phosphate-solubilizing ability and ACC deaminase activity were further selected for determination of IAA production. The results showed that all 39 PGPR strains in this selection had the ability to secrete IAA, with the secretion amounts ranging from 3.27 to 48.97 μg·mL-1. Two strains (HPS14 and XPR2) which were observed to increase height and aboveground and belowground biomass of Leymus chinensis were screened out in an in vitro experiment. Compared with control plants (not inoculated with PGPR), the height, and aboveground and belowground dry weight of Leymus chinensis in a treatment inoculated with a PGPR strain named HPS14 were increased by 49.0%, 89.2% and 243.1%, respectively; and for plants inoculated with a PGPR strain named XPR2 were increased by 16.8%, 28.9% and 240.0%, respectively. 16S rRNA showed that these two strains belong to the species Inquilinus ginsengisoli and Phyllobacterium loti, respectively. These strains could be used for the development of microbial fertilizer.

    Effects of co-utilization of Chinese milk vetch and rice straw on the potassium cycle and potassium balance in a paddy soil
    Fan ZHANG, Qian YANG
    2021, 30(1):  72-80.  DOI: 10.11686/cyxb2020089
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    Rice straw return and planting green manure in winter are important ways to improve paddy soil fertility and reduce chemical fertilizer input. Chinese milk vetch (Astragalus sinicus) is the most important winter leguminous green manure crop. A typical crop rotation system in Hunan Province is: Chinese milk vetch-early rice-late rice. Many studies have shown that Chinese milk vetch can reduce chemical nitrogen fertilizer input in rice production. If the input of chemical potassium fertilizer in rice production can also be reduced, this will encourage the promotion and use of Chinese milk vetch. Here we report a 2-year field experiment on cultivation of Chinese milk vetch followed by double cropping of rice, in an acidic red yellow soil and an alkaline purple alluvial soil in Hunan, in which the effect of co-utilization of Chinese milk vetch and double cropping rice straw on the soil K cycle and balance were investigated. The experiments had the same treatments in two soil types, including winter fallow-rice-rice without rice straw return (FRR), Chinese milk vetch-rice-rice without rice straw return (MvRR), Chinese milk vetch-rice-rice with rice straw return (MvRR+St). The results indicated: 1) Compared with FRR and MvRR, the content of different soil K forms of the acidic red yellow soil were not influenced in MvRR+St, while the contents of available K and non-exchangeable K of the alkaline purple alluvial soil were significantly increased in MvRR+St. Compared to MvRR, the contents of water-soluble K, non-specifically absorbed K and specifically absorbed K of the alkaline purple alluvial soil in MvRR+St were significantly increased by 134.0%, 93.0% and 73.4%, respectively. 2) Compared with MvRR, the total K content and K uptake of Chinese milk vetch in the acidic red yellow soil in MvRR+St were significantly increased by 68.6% and 91.1%, respectively; the total K content and K uptake of Chinese milk vetch of the alkaline purple alluvial soil in MvRR+St were significantly increased by 56.4% and 81.2%, respectively. Compared with red yellow soil, the K uptake of Chinese milk vetch in alkaline purple alluvial soil was greater than that in acidic red yellow soil under the same treatment. 3) The yield and K uptake of early rice and late rice were not influenced by MvRR+St in the two typical paddy soils. 4) With the current potassium nutrient input in this study, the MvRR+St treatment had a K surplus in the two typical paddy soils (red yellow soil K surplus was 401.15 kg·ha-1, purple alluvial soil K surplus was 403.42 kg·ha-1). This shows that the co-utilization of Chinese milk vetch and rice straw can reduce the input of chemical potassium fertilizer in double cropping rice production. On the whole, the co-utilization of Chinese milk vetch and double cropping rice straw is beneficial to the K cycle and balance of paddy soils.

    Effects of controlled release nitrogen and urea ratio on nitrogen accumulation, transfer, and nitrogen-use efficiency of different summer maize varieties
    Jia-meng GUO, Ling-zhi HE, Dong-liang YAN, Zhuo LI, Yong-chao WANG, Rui-xin SHAO, Qing-hua YANG
    2021, 30(1):  81-95.  DOI: 10.11686/cyxb2020067
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    The overall aim of this research was to provide a theoretical foundation for matching nitrogen fertilizer types to maize varieties to improve the production of summer maize on the Huang Huai Hai Plain. Various combinations of nitrogen and controlled-release nitrogen (CRU) were applied to different varieties of summer maize, and the yield, nitrogen uptake pre-and post-silking, nitrogen-use efficiency, and economic benefits were determined. A 2-year field experiment with a split-spot randomized block design was conducted with nitrogen as the main plot and maize variety as the subplot. Nitrogen was applied at three levels: 0, 180,and 300 kg·ha-1, and at two ratios of CRU-urea (1∶2 and 2∶1-N from CRU∶N from urea), as well as a CRU-only treatment at the 180 kg·ha-1 level and a urea-only treatment at the 300 kg·ha-1 level. Thus, there were six treatments, as follows: N0 (CK, no nitrogen fertilizer), N180U (urea only), N180C1 (urea-N∶CRU-N=1∶2), N180C2 (urea-N∶CRU-N=2∶1), N180C (CRU only), and N300U (urea only). The two maize varieties were YH988 (low nitrogen-use efficiency) and ZD958 (high nitrogen-use efficiency). The results indicated that the one-off application of a mixture of CRU and urea at 180 kg N·ha-1 before sowing was able to satisfy the nitrogen demands of the summer maize system with the varieties YH988 and ZD958 on the Huang Huai Hai Plain. The highest yields of YH988 and ZD958 were in the N180C1 treatment and the N180C2 treatment, respectively (a one-off application of a mixture of CRU and urea at 1∶2 and 2∶1 at 180 kg·ha-1, respectively). The biomass increase and nitrogen uptake after the post-silking stage were higher in N180C1 (for YH988) and N180C2 (for ZD958) than in the other treatments. The cultivars YH988 and ZD958 showed the highest nitrogen partial productivity, nitrogen agronomic efficiency, nitrogen-use efficiency, and economic benefits in the N180C1 and N180C2 treatments, respectively. In summary, YH988 and ZD958 showed the highest yield, above-ground dry matter accumulation, and nitrogen accumulation after the post-silking stage in the N180C1 and N180C2 treatments. Therefore, the combination of nitrogen and CRU can improve the production of summer maize on the Huang Huai Hai Plain, and promote the synergistic improvement of yield and nitrogen-use efficiency.

    Effects of different tillage practices and nitrogen application rate on carbon dioxide emissions and carbon balance in rain-fed maize crops
    Peng QI, Xiao-jiao WANG, Yi-ming YAO, Xiao-long CHEN, Jun WU, Li-qun CAI
    2021, 30(1):  96-106.  DOI: 10.11686/cyxb2020136
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    Full-film double furrow sowing technology is one of the main production technologies of dryland maize on the Loess Plateau in recent years. Study of the influence of different tillage methods on soil CO2 emission from dryland maize farmland is highly relevant to understanding of carbon cycling, reducing emissions, and selection of appropriate management measures in farmland systems. This research evaluated the CO2 emission and carbon balance of dryland maize farmland under four tillage methods (subsoiling, no-tillage, rotary tillage and ploughing). combined with two commonly used nitrogen application rates (200 and 300 kg·ha-1) in field experiments. It was found that the variation in soil CO2 emission rate reflected variation in atmospheric temperature. The maximum and minimum values occurred around 12:00-14:00 and 4:00-6:00, respectively. The soil CO2 emission rate during the growth period showed a trend of initial increase and then decrease with increasing plant maturity. The pattern of variation in each treatment with time was basically the same. The peak soil CO2 emission rate appeared in the stem elongation, head emergence and flowering periods, and then decreased to the lowest rate in the ripening period. The total carbon emission and carbon emission efficiency over the entire growth period were significantly higher in the ploughing treatment than other treatments (P<0.05), and there were no significant differences (P>0.05) between the other tillage methods. The total soil CO2 emission at a fertilizer application rate of 300 kg·ha-1 was significantly higher than 200 kg·ha-1 P<0.05). The net ecosystem productivity and carbon sequestration potential of the maize field cropping system were significantly higher under subsoiling than other treatments (P<0.05), but the two nitrogen rates did not differ significantly (P>0.05). In conclusion, based on these results, the combination of subsoiling and the traditional nitrogen application rate (200 kg N·ha-1) is the preferred management mode for maize in the Loess Plateau arid region, from the perspective of carbon sequestration and emission reduction.

    Effects of different nitrogen levels on photosynthetic characteristics and drought resistance of switchgrass (Panicum virgatum
    Hai-feng HE, Cheng-hong YAN, Na WU, Ji-li LIU, Yu-han JIA
    2021, 30(1):  107-115.  DOI: 10.11686/cyxb2020069
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    This aim of this study was to determine the optimal nitrogen application rate for high-efficiency cultivation of switchgrass (Panicum virgatum) with good yields and quality in saline-alkali soil in Yinbei, Ningxia. Switchgrass was grown with different levels of nitrogen and its photosynthetic characteristics and drought resistance were analyzed. The P. virgatum cultivar ‘Cave-in-Rock’ was used as the experimental material, and four levels of nitrogen were applied in the field experiment, as follows: no added nitrogen (0 kg·ha-1, N0), low nitrogen (60 kg·ha-1, N60), medium nitrogen (120 kg·ha-1, N120) and high nitrogen (240 kg·ha-1, N240). The photosynthetic characteristics, contents of osmotic compounds, and activities of antioxidant enzymes in leaves of switchgrass at different growth stages were determined, and the drought resistance of switchgrass was evaluated by the multivariate membership function method. The results showed that with increase in nitrogen application levels, the relative chlorophyll content (SPAD value), net photosynthetic rate (Pn), stomatal conductance (Gs), and intercellular CO2 concentration (Ci) in switchgrass initially increased and then decreased, with peak values in the medium nitrogen (N120) treatment. Compared with the leaves of plants in the N0 treatment, those in the N60, N120, and N240 treatments showed increases of 4.73%, 18.71%, and 8.86%, respectively, in the SPAD value; increases of 5.55%, 17.02%, and 12.41%, respectively, in the Pn value; increases of 7.87%, 56.18%, and 39.33%, respectively, in Gs; and increases of 7.86%, 30.71%, and 13.81%, respectively, in Ci. The maximum transpiration rate was in the N240 treatment, and the leaf water-use efficiency gradually decreased with increasing nitrogen application levels. The results of the membership function analysis showed that the maximum average value of drought resistance indexes was in the N120 treatment. Therefore, application of nitrogen at an appropriate level (120 kg·ha-1) can improve the photosynthesis and drought resistance of switchgrass growing in saline-alkali soil.

    Yield and dynamic responses of yield components of adzuki bean to insolation, temperature and rainfall across five sowing dates
    Le-zheng WANG, Fang-jing HUA, Peng-peng CAO, Feng-ju GAO, Wen-rong XIA
    2021, 30(1):  116-129.  DOI: 10.11686/cyxb2020088
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    In order to optimize utilization of meteorological resources for high yield of adzuki bean, this research established a ‘sowing-date series’ of a late- and an early-maturing variety of adzuki bean and monitored light, temperature, rainfall and yield components through the crop development. Late-maturing Huaxiaodou (V1) and early-maturing Dehong 5261 (V2) were the varieties studied. Sowing dates were June 17 (T1), June 22 (T2), June 27 (T3), July 2 (T4), and July 7 (T5). The recorded responses of yield components to insolation, temperature, and rainfall through the crop development were analyzed. It was found that the yield, pod number per plant, and seed weight per plant initially increased then decreased, with ranking T2>T1>T3>T4>T5. The yield of V2 was significantly greater than V1. Seed number per pod and 100-seed weight were not significantly affected by sowing date. The days to maturity, mean leaf area index, and photosynthetic potential decreased gradually through the sowing date series whereas the harvest index increased. The meteorological factors affected the development of the two varieties differently. For V1, in the earlier growth stages, the effective accumulated temperature (AT) was significantly positively correlated with the yield, mean leaf area index, photosynthetic potential, and mean crop growth rate, and was significantly negatively correlated with mean net assimilation rate and harvest index. The rainfall was significantly positively correlated with pod number per unit area. The light was significantly positively correlated with mean leaf-area index, photosynthetic potential, and mean crop growth rate, and was significantly negatively correlated with mean net assimilation rate. In later growing stages, the AT was significantly positively correlated with mean crop growth rate, and light was significantly positively correlated with photosynthetic potential. For V2, in the earlier growth stages, the AT was significantly positively correlated with the yield, pod number per unit area, mean leaf-area index, photosynthetic potential, and mean crop growth rate, and was significantly negatively correlated with harvest index. The rainfall was significantly negatively correlated with mean leaf-area index and mean crop growth rate. Light was significantly positively correlated with days to maturity and photosynthetic potential. Yield was significantly negatively correlated with harvest index and seed number per pod. In the later growth stages of V2, the AT was significantly positively correlated with mean leaf area index, days to maturity and photosynthetic potential, and was significantly negatively correlated with harvest index, seed number per pod and 100-seed weight. Rainfall was significantly positively correlated with mean crop growth rate. Regression analysis between the yield and the distribution of meteorological factors between earlier and later growth stages revealed that, the optimum ratio of resource allocation between the earlier and later growth periods in V1 and V2, respectively were 1.86 and 1.45 for growing days; 2.27 and 1.49 for AT; 49.73 and 1.57 for rainfall; and 1.45 and 0.98 for light. In this experiment, sowing the early-maturing adzuki bean line V2 near to June 20 gave the optimum distribution ratio of light, temperature and rainfall, and resulted in high yield.

    Effects of exogenous melatonin on photosynthetic carbon assimilation and endogenous hormones in tobacco seedlings under drought stress
    Dong LI, Hong-tao SHEN, Yan-fang WANG, Yue-hua WANG, Li-jun WANG, Shi-min ZHAO, Ling LIU
    2021, 30(1):  130-139.  DOI: 10.11686/cyxb2020070
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    In order to elucidate the physiological mechanism of exogenous melatonin (MT) application in relieving drought stress on tobacco seedlings growth. The drought-tolerant variety ‘Yuyan No.6’ and drought-sensitive variety ‘Yuyan No.10’ were tested for their response following foliar-spraying with MT at concentration of 0.2 mmol·L-1 under normal water supply and drought stress. Parameters measured included seedlings growth, chlorophyll fluorescence parameters, photosynthetic carbon assimilation enzyme activity, and the contents of carbohydrates and endogenous hormones of the tobacco seedlings. The results showed that drought stress significantly inhibited the seeding growth of both tobacco cultivars, and the inhibiting effects in drought-sensitive ‘Yuyan No.10’ were greater than that in drought-tolerant ‘Yuyan No.6’. Exogenous melatonin application remarkably increased plant height, stem diameter, biomass, reduced the root-shoot ratio, increased maximal PSⅡ quantum yield (Fv/Fm), PSⅡ actual photochemical efficiency (ΦPSⅡ) and photochemical quenching coefficient (qP), decreased non-photochemical quenching coefficient (NPQ), enhanced the activities of sedoheptulose-1,7-bisphosphatase (SBPase) and ribulose-1,5-bisphosphate carboxylase (Rubisco), and increased the contents of soluble total sugar, sucrose, fructose, auxin (IAA), gibberellin (GA) and zeatin nucleoside (ZR), reduced the contents of starch and abscisic acid (ABA) of tobacco seedlings under drought stress. The changes in drought-sensitive ‘Yuyan No.10’ were greater than those in drought-tolerant ‘Yuyan No.6’. The results indicated that exogenous MT played an important role on enhancing the activity of photosynthetic carbon assimilation enzyme, regulating the metabolism of endogenous hormones and carbohydrates, relieving the damage of photosynthetic apparatus caused by drought stress, and strengthening the drought resistance of tobacco seedlings.

    A multivariate evaluation of agronomic straits and forage quality of 22 oat varieties in the Huang-Huai-Hai area of China
    Hui-xin JIANG, Shan-shan BAI, Bo WU, Jing-yi SONG, Guo-liang WANG
    2021, 30(1):  140-149.  DOI: 10.11686/cyxb2020386
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    This paper reports observations on the growth performance, forage yield and quality of 22 oat varieties planted in Huang-Huai-Hai area of China from 2018 to 2019, conducted to identify the most suitable oat varieties for this region. Multivariate evaluation was used to analyze the data gained from the experiment. It was found that the variation coefficients among the 22 oat varieties were more than 15% in the ratio of leaf/whole plant dry weight and spike/whole plant dry weight, and those were less than 10% in the ratio of stem/whole plant dry weight and plant height. Hence, the differences in growth pattern between varieties were mainly shown in the leaves and spikes. A cluster analysis of 13 growth and nutrient indexes was carried out, the results showed that 22 oat varieties could be clustered as four groups: The first group was the high quality group with high relative feed value (RFV), the second group was the poor quality group with low RFV, the third group was the high plant height group, and the fourth group was the high protein group with abundant leaves. The groups did not differ significantly in forage yield (P>0.05). However, there were significant differences in the proportion of plant parts and crude protein (CP), neutral detergent fiber, acid detergent fiber, acid detergent lignin and RFV (P<0.05). Correlation analysis showed that plant height, the ratio of leaf/whole plant dry weight and spike/whole plant dry weight were significantly positively correlated with hay yield, forage CP and RFV (P<0.05), which indicated that leaf and spike played an important role in oat forage quality. Using Grey correlation analysis, varieties Baylor, Souris, and Linna from group I, and ESK, Molasses and Haymaker from group IV had higher Equal-weighted correlation degree and Weighted correlation degree, and were identified as suitable for planting in the Huang-Huai-Hai area of China.

    Effects of cutting time and plant height of ‘Reyan No.4’ king grass on distribution of lactic acid bacteria and silage fermentation quality
    Xin-zhu CHEN, Jian-guo ZHANG
    2021, 30(1):  150-158.  DOI: 10.11686/cyxb2020079
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    In this study, we investigated the effects of cutting time and plant height on the distribution of lactic acid bacteria (LAB) and the fermentation quality of king grass (Pennisetum purpureum×Pennisetum typhoideum cv. ‘Reyan No.4’) silage. We analyzed the LAB distribution on, and characteristics of, king grass cut at different times (first, second, and third cuttings) and at different plant heights (1.0, 1.5, and 2.0 m), and evaluated the fermentation quality of silages produced from these materials. The results showed that with the increase in king grass height, the contents of dry matter (DM), neutral detergent fiber (NDF), and acid detergent fiber (ADF) increased significantly (P<0.05), and the crude protein (CP) content and pH value significantly decreased (P<0.05). The DM content in king grass was significantly higher (P<0.05) at the second cutting than at the first and third cuttings. At the first cutting, the contents of CP, water soluble-carbohydrate (WSC), and ADF were the highest, and the NDF content was the lowest. The fermentation quality of the silage produced from the second cutting was better than that of the silages produced from the first and the third cuttings. The fermentation quality of silage produced from 2.0 m high king grass was better than that of silages produced from 1.0 and 1.5 m high king grass. The number of LAB detected from king grass was significantly higher (P<0.05) at the second and third cuttings than at the first cutting. The highest number of LAB was detected from 2.0 m high king grass, but the number did not differ significantly among the three heights (P>0.05). The most abundant LAB on king grass were Lactobacillus plantarum and Weissella confusa. Two types of LAB were isolated from king grass at the first cutting and four types of LAB were isolated at the third cutting.

    Ruminal degradation characteristics of whole maize plant material before and after ensiling in beef cattle as determined in situ using the nylon bag method
    Tao-tao LIU, Si-wei WANG, Qiu-feng LI, Yu-feng CAO, Kun WANG, Li-juan WANG, Yi-zhao SHEN, Xue-li SUN, Mei-qi ZHANG, Jin-ling YAN, Jian-guo LI, Yan-xia GAO, Mei-mei WANG
    2021, 30(1):  159-169.  DOI: 10.11686/cyxb2020071
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    The overall aim of this research was to identify suitable varieties of corn to use as feed for cattle in Hebei Province. Therefore, we determined the rumen degradation characteristics in situ in beef cattle, by the nylon bag method of whole maize plant material before and after ensiling. A 2×3 two-factor experimental design was used, with three varieties of maize: 7367, 7377, and 7387. The nutrient composition and ruminal degradation characteristics of whole maize plant material before and after ensiling were determined using the nylon bag method. The main results were as follows: 1) Before ensiling, the contents of crude protein (CP) and non-protein nitrogen (NPN) were higher in 7377 than in 7367 and 7387 (P<0.05), and the contents of neutral detergent fiber (NDF) were lower in 7367 and 7377 than in 7387 (P<0.05). The acid detergent fiber (ADF) content was lower in 7367 than in 7377 and 7387 (P<0.05). Comparing silage made from each maize variety with the fresh material of the same variety, the contents of CP, ether extract (EE), crude ash (Ash), calcium (Ca), phosphorus (P), and NPN were increased in silages of all three maize varieties (P<0.05), while the NDF contents were decreased (P<0.05). The contents of CP and NPN were higher in 7367 silage than in 7377 silage and 7387 silage (P<0.05), and the contents of NDF and ADF were lower in 7367 silage and 7377 silage than in 7387 silage (P<0.05). 2) Before ensiling, the ruminal degradability of dry matter (DM), CP, NDF, and ADF differed significantly among the three maize varieties. The ruminal degradability of DM and NDF was higher in 7367 than in 7377 and 7387 (P<0.05). The ruminal degradability of CP was significantly higher in 7377 than in 7367 and 7387 (P<0.05). Ensilage significantly increased the proportions of rapidly degraded DM, CP, NDF, and ADF in all three maize varieties (P<0.05). In each maize variety, ensilage increased the proportion of rapidly degraded DM, CP, NDF and ADF (P<0.05) and decreased the slowly degraded proportions of these nutritional factors (P<0.05). For each maize variety, the ruminal effective digestibility of DM, CP, NDF, and ADF were higher in silage than in fresh whole plant material (P<0.05). The ruminal degrade ability of DM, CP and NDF and ADF was higher in 7367 silage than in 7377 silage and 7387 silage. The results show that ensilage can preserve the nutrient composition of these three maize varieties, and significantly improve ruminal degradation characteristics of DM, CP, NDF, and ADF. The nutritional status and ruminal degradation characteristics before and after ensilage were better in 7367 than in 7377and 7387. Thus, 7367 is the better variety to grow as feed for cattle in Hebei Province.

    Effects of cellulase treatment of buckwheat straw on fiber structure and meat quality of Tan sheep
    Shuang WU, Yu-xiang ZHOU, Rou JIA, Ya-dong JIN, Wan-zong YANG
    2021, 30(1):  170-180.  DOI: 10.11686/cyxb2020085
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    The aim of this study was to determine the effects of cellulase treatment on the fiber structure and nutrient composition of buckwheat straw, the quantity of microbes in fermented buckwheat straw, and the mutton quality of Tan sheep fed with the treated straw. This experiment was divided into two parts; the first part consisted of enzyme treatments, and the second part was a feeding test. The enzyme treatment experiment had three groups: the control group (unprocessed buckwheat straw), trial group Ⅰ (cellulase Ⅰ treatment of buckwheat straw), and trial group Ⅱ (cellulase Ⅱ treatment of buckwheat straw). Each group had three replicates. Buckwheat straw with enzymes was sealed and stored in a fermenting tank for 30 days and then sampled. The fiber structure, nutrient composition, and microorganism abundance in buckwheat straw before and after the enzyme treatments were analyzed. In the feeding experiment, 24 healthy 3-month-old Ningxia Tan sheep with similar body weight were randomly assigned to three groups (eight sheep/group).The ratio of basal diet to forage was 30∶70. The control group was fed basal diet+unprocessed buckwheat straw, trial group Ⅰ was fed basal diet+buckwheat straw treated with cellulose Ⅰ, and trial group Ⅱ was fed basal diet+buckwheat straw treated with cellulose Ⅱ. The preparation period was 15 d, and the formal experimental period was 60 d. At the end of the formal experimental period, five Tan sheep with approximately equal body weight were selected from each group and slaughtered after fasting for 24 hours. Then, the physicochemical indexes and nutrient contents of the mutton were determined. The main results were as follows: 1) The cell wall fibrous structure of untreated buckwheat straw remained intact, while that of buckwheat straw treated with cellulase was disrupted to different degrees; 2) The acid detergent fiber content of buckwheat straw in trial group Ⅰ and trial group Ⅱ was reduced by 18.71% and 13.78%, respectively, compared with that in the control group (P<0.05), and the neutral detergent fiber content of buckwheat straw in trial group Ⅰ and trial group Ⅱ was reduced by 19.75% and 17.81%, respectively, compared with that in the control group (P<0.05); 3) The contents of lactic acid bacteria were higher in the cellulase-treated groups than in the control (P<0.05), and the contents of molds were lower in the cellulase-treated groups than in the control (P<0.05); 4) Compared with mutton from sheep in the control group, mutton from sheep in trial group Ⅱ showed a significantly improved muscle cooked meat rate (P<0.05), and that from sheep in trial groups Ⅰ and Ⅱ showed a reduction in shear force by 9.31% and 11.84%, respectively (P<0.05); 5) The crude protein content of mutton from sheep in trial group Ⅰ and trial group Ⅱ was increased by 14.22% and 14.23%, respectively, compared with mutton from sheep in the control group (P<0.05). In summary, these results show that cellulase treatment can effectively degrade the fiber structure and improve the nutrient status of buckwheat straw, thereby enhancing its feed quality. Ultimately, this leads to better meat quality. Under these experimental conditions, treatment with cellulase Ⅰ provided the best improvement in the feed quality of buckwheat straw.

    Effect of simulated changes in rainfall patterns on characteristics of ramets and roots of Chloris virgata
    Lin YANG, Mo CHEN, Hai-yan LI, Yun-fei YANG
    2021, 30(1):  181-188.  DOI: 10.11686/cyxb2020066
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    As an important part of global climate change, changes in rainfall patterns will have different effects on various types of plants. Chloris virgata is one of the main pioneer species for the restoration of degraded saline-alkali grasslands. To design optimal ecological restoration strategies for degraded saline-alkali land in the background of global change, it is important to understand how the changes in rainfall patterns will affect the characteristics of ramets and roots of C. virgata. We determined the effects of several simulated rainfall patterns (decreased by 30%, unchanged, increased by 30%) and rainfall intervals (1 and 2 days) on the aboveground ramet and underground root morphological characteristics of C. virgata. It was found that: 1) The changes in rainfall pattern had almost no effect on the sexual reproduction characteristics of C. virgata. With increasing rainfall amount or increasing rainfall interval, vegetative reproductive characteristics tended to be enhanced. 2) Rainfall interval and rainfall amount had different effects on the roots of C. virgata. Rainfall interval had the greatest influence, although two factors were interdependent. When the rainfall amount was unchanged, the total root length, total root surface area, total root volume, and root diameter decreased significantly with increasing rainfall interval. 3) Both rainfall amount and rainfall interval affected biomass accumulation, with rainfall interval being more important. The root biomass, stem biomass, and total biomass significantly decreased with increasing rainfall interval, and the biomass of leaves and inflorescences showed a decreasing trend, but this was not statistically significant.

    Response of alfalfa root architecture and physiological characteristics to drought and rehydration
    Zhen-song LI, Li-qiang WAN, Shuo LI, Xiang-lin LI
    2021, 30(1):  189-196.  DOI: 10.11686/cyxb2020297
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    The objective of this research was to understand the response of alfalfa (Medicago sativa) root architecture and physiological characteristics to drought and rehydration regimes. Four water regime treatments were imposed on plants of the alfalfa cultivar Zhaodong in a pot experiment: normal water supply (CK), low water stress (LS), moderate water stress (MS) and severe water stress (SS). We studied the differences in root architecture and physiological indicators between treatments under rehydration after 4 weeks of drought treatment. It was found that drought treatment had an extremely significant (P<0.01) effect on root dry weight and root tip number and a significant effect on root length, root surface area, root volume and root density (P<0.05). Drought stress inhibited root growth, reduced root dry weight, root length, root surface area, root volume, root density, and the number of root tips, and promoted an increase in rooting depth. There was a significant difference in topological index between treatments (P<0.05), and drought induced a transformation of the alfalfa root system from dichotomous branching to herringbone branching. Drought stress resulted in an extremely significant (P<0.01) increase in the content of root malondialdehyde (MDA) and superoxide anion (O2-), and in the activities of superoxide dismutase (SOD) and glutathione (GSH). The content of abscisic acid (ABA) increased extremely significantly under drought stress (P<0.01). These physiological changes would have kept reactive oxygen species to low levels, and improved the drought resistance of alfalfa as a result of the drought-induced changes to physiological status and signal transduction pathways.

    Changes in morphological and physiological characteristics of Gymnocarposprzewalskii roots in response to water stress
    Hai-xia HUANG, Qi-qi YANG, Peng CUI, Gang LU, Guo-jun HAN
    2021, 30(1):  197-207.  DOI: 10.11686/cyxb2020057
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    Gymnocarpos przewalskii originates from the Tethys Sea, and is a Tertiary relic of the desert area in central Asia. This species is very important for research on xerophyte evolution. Using 1-year-old seedlings of G. przewalskii as the experimental materials, we evaluated the responses of root morphological and physiological characteristics to drought stress in a pot experiment. Four water treatments were established, comprising a gradient corresponding to a control and light, moderate, and severe water stress (soil water content controlled at 45%-50%, 30%-35%, 15%-20%, and 5%-10% of field capacity, respectively). The different soil water contents were maintained by regular weighing and re-watering pots to target weights. There were 10 replicates of each treatment. The seedlings were cultivated in pots in 2018 under these conditions, and the responses of the roots were analyzed. It was found that with increasing severity of drought stress, root length and root surface area significantly decreased. The root biomass decreased markedly under severe drought stress. Moderate and severe drought stress caused significant increases in the shoot:root ratio, specific root length, and specific root surface area of fine roots, and increased the ratio of bound water to free water. Drought stress led to a significant decrease in root vitality. As the soil water content decreased, proline content in roots initially decreased then markedly increased, while the soluble sugar and soluble protein content showed the reverse trend. Under drought stress, the concentrations of malondialdehyde, hydrogen peroxide, and the superoxide anion significantly increased, indicative of damage to the root membrane system. Root superoxide dismutase (SOD) activity markedly increased, peroxidase activity significantly decreased, and catalase (CAT) activity significantly increased under drought stress. In short, under drought stress, roots of G. przewalskii seedlings showed several morphological changes to increase their water-absorption efficiency, i.e., the shoot∶root ratio, specific root length, and specific root surface area of fine roots all increased. The physiological changes in response to drought stress were a decrease in metabolism to reduce water consumption, active accumulation of organic solutes to decrease cell osmotic potential, and increases in SOD and CAT activity to reduce cell membrane damage.

    Research progress on the physiological response of plants to low temperature and the amelioration effcectiveness of exogenous ABA
    Hong-tao XIANG, Dian-feng ZHENG, Ning HE, Wan LI, Man-li WANG, Shi-ya WANG
    2021, 30(1):  208-219.  DOI: 10.11686/cyxb2020091
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    Global climate change is producing abnormal, extreme weather and agricultural meteorological disasters linked to climate change now occur frequently. Sudden low temperature stress has become one of the most common abiotic stresses in agricultural production, and low temperature stress more generally has become one of the most common abiotic stresses in agricultural production in recent years. Low temperature stress interferes with plant growth and development, and can directly or indirectly affect physiological functions, cell membrane components and structure of the plant, thus reducing yield and quality, and seriously restricting agricultural production. Application of exogenous ABA at appropriate rates can alleviate the effects of low temperature stress on physicochemical processes. Here we systematically expound the effects of low temperature stress on the physicochemical processes of plants and clarify the mechanisms of plant responses to low temperature stress, including aspects of photosynthetic physiology, stress physiology, cell membrane components and cell structure, hormone levels, and gene expression. Furthermore, the positive effects of exogenous ABA in alleviating low temperature stress are analyzed. This paper discusses the research status and development trends with respect to the use of plant growth regulators for alleviation of low temperature stress. This topic is of great significance for stable production and preservation of agriculture, and also provides a theoretical basis for future research on plant cold resistance.