Table of Content

20 June 2020, Volume 29 Issue 6

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Spatio-temporal characteristics of grassland net primary productivity (NPP) in the Tarim River basin

CUI Bo-chao, ZHENG Jiang-hua, TUERXUN·Hasimu, DUAN Su-su, DU Meng-jie

2020, 29(6):  1-13.  DOI: 10.11686/cyxb2019427

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We analyzed spatio-temporal changes in grassland net primary productivity (NPP) in the Tarim River basin, based on an improved light use efficiency model (Carnegie-Ames-Stanford approach model, CASA) and moderate resolution imaging spectroradiometer (MODIS) data from 2006 to 2016. To study the temporal pattern, spatial characteristics, spatial stability and the time trend in grassland NPP were used to formulate a simple linear regression model, and derive the coefficient of variation and the Hurst index. The model analyses the temporal variation in grassland NPP in the Tarim River basin from 2006 to 2016. This analysis of the temporal pattern over the 11 years showed that the grassland NPP was variable with 64.1% of the total area, showing increased NPP and for 35.9% of the total area exhibiting falling NPP in the past 11 years. Overall, the grassland NPP of the Tarim basin was 1.31×10¹¹ g C·m^-2·yr^-1. The main growing season for grassland in the basin is from June to August each year, and NPP during this period accounts for 47.3% of the total annual NPP. A geographic gradient of decreasing grassland NPP from northwest to southeast was observed for these 2006-2016 Tarim River basin data. In the whole basin, the average annual grassland NPP estimated by the CASA model for 2006-2016, was 13.62 g C·m^-2·yr^-1. The altitudinal change in grassland NPP for the 11 years followed a “decreased-raised-lowered” pattern with increasing altitude, and also some smaller features related to latitude and longitude. The coefficient of variation of grassland NPP over the 11 years ranged from 0.19 to 3.17, in various localities, which indicated the grassland NPP has obvious spatial differentiation. The land area for which the coefficient of variation of grassland NPP is less than 0.5 accounts for 94.6% of the total surveyed land area. Areas of high NPP fluctuation include the Kaikong river basin, the Aksu river basin, the Yarkant river basin, the Hetian river basin, the Tarim River main stream basin, and the Qarqan river basin. The Hurst index of grassland NPP for the 11 years ranged from 0.10 to 0.97 and the mean value was 0.57. This indicates the grassland NPP is expected to maintain the same change-trend in the future. In summary, the patterns of spatio-temporal change in grassland NPP showed that the health status of the grassland ecosystem is improving in the majority of the Tarim River basin, but deteriorating in some local areas.

Numerical taxonomic study of morphological characteristics of species in Glycyrrhiza hybrid zones

CHEN Wen-qing, LU Jia-hui, WANG Qian-qian, XIN Qian, XU Ying

2020, 29(6):  14-26.  DOI: 10.11686/cyxb2019418

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In this study, the morphological characters of Glycyrrhiza specimens from nine regions of Xinjiang and Gansu Provinces where natural hybrids occur were classified by numerical taxonomic study to identify the parent species and hybridization type in different geographic areas where hybrids occur. Following field investigation and specimen collection, data on morphological traits were measured and recorded. After the numerical data collection, principal component analysis was carried out to identify the most important traits for classification purposes, and 29 traits were evaluated by R-cluster. The parental species and their hybrids in the different areas of hybrid occurrence were classified by operational taxonomic unit scatter and Q clustering. Principal component analysis result shows that Among the first three principal components, degree of legume inflation, upper limit of foliolate , lower limit of foliolate, presence of legume glandular hair, compound leaf length, no. of seeds per pod, compound rachis length, leaflet margin morphology, infructescence length, infructescence length:width ratio, leaflet length:leaflet width ratio, and leaflet width all are above 0.7, meaning that these twelve characters play an important role in taxonomic study on Glycyrrhiza species. The 29 traits could be classified into 2 categories: the first, mainly comprising leaflet and inflorescence traits, and the second, mainly comprising legume and compound leaf traits. The correlation coefficient between scores of the two categories of traits was 1, indicating that these trait groupings occur in conjunction and have high relevance as taxonomic indicators. Glycyrrhiza accessions (n=344) were classified into groups as follows: A, Glycyrrhiza inflata; B, The hybrid of G. inflata and Glycyrrhiza uralensis; C, G. uralensis; D, Glycyrrhiza glabra; E, the hybrid of G. inflata and G. glabra. A variation of G. inflata includes plants from Alaer and Korla in Xinjiang, and Guazhou and Minqin in Gansu Provinces, which are gathered into one branch, as these populations of G. inflata are less genetically differentiated. Plants of group C from Minqin, Zhangye in Gansu and from Korla, Yanqi, and Bohu in Xinjiang, were divided into two branches, as intravarietal genetic differentiation had occurred. Group D representing G. glabra. includes G. glabra and Glycyrrhiza glabra var. glandulosa from Alaer, Xinjiang, as G. glabra var. glandulosa is a variety of G. glabra. Nine geographic areas where natural interspecific hybrids occur could be divided into three categories: Alar and Turpan in Xinjiang Province are interspecific hybridization areas of G. inflata and G. glabra; Yanqi and Korla in Xinjiang and Guazhou in Gansu are interspecific hybridization areas of G. inflata and G. uralensis; Shanshan in Xinjiang is a mixed hybridization area of G. inflata, G. glabra and G. uralensis. All hybrid specimens of Glycyrrhiza examined, have distinctive and different inter-species combinations of morphological features. This study laid the foundation of morphological taxonomy for the utilization of medicinal Glycyrrhiza germplasm resources and the formation ofhybrid species.

Meta-analysis of alfalfa yield and WUE response to growing ages in China

CAI Lu, WANG Lin-lin, LUO Zhu-zhu, LI Ling-ling, NIU Yi-ning, CAI Li-qun, XIE Jun-hong

2020, 29(6):  27-38.  DOI: 10.11686/cyxb2019404

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In order to explore optimal alfalfa stand age in different environments, a meta-analysis was conducted to determine how yield and water use efficiency (WUE) of alfalfa (Medicago sativa) change with stand age in China. A total of 80 articles published before May 2019 were chosen from domestic and foreign journals (including 1496 available comparisons of yield and 220 available comparisons of WUE). Each article abstracted included data on annual precipitation, fertilization practices and water regime. Site annual rainfall was classified as <200 mm, 200-400 mm, 400-800 mm or ≥800 mm. Fertilization practice was recorded as fertilization or no fertilization, and water regime was classified as irrigation or rainfall. The analytical steps in each case consisted of a heterogeneity test, a comprehensive effect size calculation, a publication bias test, and influence factor analysis. It was found that forage yield and WUE of alfalfa were highest in three-five and six-eight year old stands, and then decreased gradually. Also, the yield and WUE decline in older stands of alfalfa may be related to reduction in soil water storage and soil fertility and their interaction. Based on the forage yield and WUE data examined in this study, peak performance occurs in three-five year old stands in arid regions, semi-arid regions and humid regions, but can extended to six-eight year old stands in semi-humid regions. The data indicate that alfalfa stand peak performance and longevity are more effectively extended by fertilization than by irrigation.

Yield and nutrient concentration in common green manure crops and assessment of potential for nitrogen replacement in different regions of China

YANG Ye-hua, ZHANG Song, WANG Shuai, LIU Zheng-lan, FANG Lin-fa, ZHANG Xue-liang, LIU Rui, ZHANG Jian-wei, ZHANG Yu-ting, SHI Xiao-jun

2020, 29(6):  39-55.  DOI: 10.11686/cyxb2019397

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Green manure is considered a clean source of organic fertilizer. It plays an important role in enhancing soil fertility and the substitution of chemical fertilizer. Quantifying green manure yield and nutrient concentration at the regional level can provide a theoretical basis and supporting data for green manure application and fertilizer replacement. This study, by searching the China National Knowledge Infrastructure (CNKI) database and related books, collected 3431 data, including information on 17 different common green manure crops across China. The green manure yield and nutrient concentration data from across China were systematically analyzed and compared, and the nitrogen fertilizer replacement effect was evaluated for different regions of China. It was found that the average yield of fresh green manure in China was 38.0 t·ha^-1 (moisture content was 81.0% on average), but a wide range (0.7-186.7 t·ha^-1) was noted. The average yields of ryegrass, erect milkvetch, Stylosanthes, and red clover were higher than 43 t·ha^-1, and significantly higher than other green manure species. The average nitrogen concentration of 17 kinds of common green manures was 28.0 g·kg^-1 (in the hay). The nitrogen concentration of common vetch, vetch, alfalfa, burclover, and white clover were all above 30.0 g·kg^-1, and this was significantly higher than other green manure types. The average phosphorus concentration of different common green manure crops was 7.0 g·kg^-1, and vetch and February orchid contained greater phosphorus concentration (above 8.0 g·kg^-1) than other green manures. The average potassium concentration of different common green manure crops was 25.3 g·kg^-1, and the February orchid and milk vetch were highest with a potassium concentration of more than 32.0 g·kg^-1. The average accumulation of nitrogen, phosphorus and potassium of green manure crops was 214.4 kg N·ha^-1, 48.4 kg P₂O₅·ha^-1 and 165.1 kg K₂O·ha^-1. There were significant differences in the accumulation of nitrogen, phosphorus and potassium in different common green manures, among which the accumulation of nutrients was the highest in erect milkvetch, ryegrass, red clover, alfalfa, and Stylosanthes, above 250.0 kg N·ha^-1, 50.0 kg P₂O₅·ha^-1 and 191.7 kg K₂O·ha^-1, respectively. Linking the nutrient accumulation data with regional climatic data, our further analysis found that: milk vetch is most suitable for planting in the southern hilly valley and interplanting zone; common vetch is suitable for planting in the northeast grain rotation area and the Yangtze River Basin; vetch is suitable for planting in the rice-cotton complex intercropping area of the Yangtze River Basin; alfalfa is most suitable for planting in the coastal multiple cropping area; white and red clover are most suitable for planting in the grain-grass intercropping area of the southwest mountainous hills and the northeast grain and grass rotation area; and ryegrass is most suitable for planting in rice-grass multiple cropping area. According to the nitrogen fixation potential assessment of the yield, nitrogen fixation amount and planting area of major leguminous green manure in different regions, the current planting area of green manure in China is about 4.49 million ha, equivalent to the production of 400-810 thousand tons of nitrogen fertilizer. If we estimate the potential area of green manure fertilizer in China at 46 million ha, this is equivalent to the production of 4.0-8.28 million tons of nitrogen fertilizer. Thus, leguminous green manure fertilizer has a high potential of fertilizer replacement. In formulating regional recommendations for green manure crop production, the green manure crop with strong adaptability and performance in each region should be identified and promoted.

Application of ¹³C stable isotope labeling in the partitioning of ecosystem respiration in a Leymus chinensis steppe in Inner Mongolia, China

LI Ru-xia, GENG Yuan-bo

2020, 29(6):  56-70.  DOI: 10.11686/cyxb2019424

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Grassland ecosystem respiration, of which the main components are soil respiration and aboveground plant respiration, plays an important role in the global carbon cycle and climate change. Also, different ecosystem respiratory components have different response mechanisms to environmental changes. In order to explore the contribution of grassland respiration to greenhouse gas emissions, we used a ¹³C natural stable isotope labeling method and a ¹³C pulse labeling method, combined with the static chamber-Keeling plot method, to distinguish the components of grassland ecosystem respiration in Leymus chinensis steppe. The research was conducted in the Xilin River Basin of Inner Mongolia and we then evaluated the two stable isotope methods according to partitioning results. It was found that: 1) ¹³C natural labeling and ¹³C pulse labeling methods gave significantly similar results when samples were from the same habitat, as defined by soil temperature and soil water content. Thus, the partitioning results obtained by the two methods are comparable. 2) Compared with the ¹³C natural labeling method, the pulse labeling method significantly improved the δ¹³C value of ecosystem respiration, soil respiration and above-ground plant respiration (P<0.05). 3) The partitioning results of the ¹³C natural labeling method and the ¹³C pulse labeling method expressed by F_s/F_eco (ratio of soil respiration flux to ecosystem respiratory flux), were (75.2±4.3)% and (73.8±2.9)%, respectively, in 2011, and (89.2±2.0)% and (89.1±1.4)% in 2012. The statistical analysis indicated that there was no significant difference between partitioning results of the ¹³C natural labeling method and the ¹³C pulse labeling method in different years (2011: P=0.567; 2012: P=0.674). These results imply that under natural conditions, the potential differences among δ¹³C in ecosystem respiration components were enough to differentiate ecosystem respiration. This discovery can improve the efficiency of ecosystem respiration partitioning research using the isotope labeling method. Further, this information will facilitate more insightful study of the ecosystem carbon cycle process.

Effects of litter quality and soil enzyme activity on litter decomposition rate in typical grassland subject to nitrogen addition

YUE Ke-xin, GONG Ji-rui, YU Shang-yuan, BAOYIN Taogetao, YANG Bo, WANG Biao, ZHU Chen-chen, ZHANG Zi-he, SHI Jia-yu

2020, 29(6):  71-82.  DOI: 10.11686/cyxb2019417

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Global atmospheric nitrogen (N) deposition has increased in recent years, affecting key processes of the carbon (C) cycle in terrestrial ecosystems. Litter decomposition is one of the key processes in the carbon cycle. We conducted a litter bag experiment at N addition rates ranging from 0 to 25 g·m^-2·yr^-1 in the typical temperate grasslands of Inner Mongolia. The effects of N addition on decomposition of litter samples were investigated by measuring the decomposition rate, quality index and soil enzyme activity of litter in different stages of decomposition. Our results showed that dry weight loss of litter mainly occurs in the growing season, which accounts for 91.3% of the total mass loss. N addition increased the rate of dry weight loss in the growing season, while decreasing the rate of dry weight loss in the non-growing season. N addition promoted litter decomposition by increasing the activity of β-glucosidase and reducing the content of cellulose and tannin in the first growing season. In the first non-growing season, low-N treatments enhanced urease activity, decreased lignin:N ratio, and accelerated decomposition, while high-N treatments inhibited the activity of polyphenol oxidase, thereby reducing the decomposition rate of lignin. High-N treatment promoted leucine aminopeptidase activity, improved N:P ratio, and facilitated the decomposition of litter in the second growing season. During the whole decomposition process, N addition reduced the content of tannin and cellulose, while showing a trend toward increased lignin content. This result may indicate that during decomposition, litter C showed a release pattern while phosphorus showed an immobilization-release pattern. In addition, the contents of calcium, manganese and N in litter increased with the progression of decomposition, showing an enrichment phenomenon. Our results indicate that the quality of litter samples and soil enzyme activity were the main factors influencing litter decomposition, and the dominant factors differ at different stages of the decomposition process. These results will provide a theoretical basis for understanding of the key processes of the grassland carbon cycle under different levels of N deposition in the future.

Effects of AM fungi on growth and rhizosphere soil enzyme activities of Salvia miltiorrhiza

JIA Hong-mei, FANG Qian, ZHANG Shu-hua, YAN Zhu-yun, LIU Min

2020, 29(6):  83-92.  DOI: 10.11686/cyxb2019494

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This research studied the effects of different arbuscular mycorrhiza (AM) fungi on the growth of Salvia miltiorrhiza and the activities of soil enzymes, with the aim of identifying new methodology for improving soil properties using S. miltiorrhiza. Plantlets of S. miltiorrhiza were tissue cultured with a single strain (8 strains were tested) or mixed strains of symbiotic AM fungi (35 combinations were tested) to determine the yield of medicinal parts of S. miltiorrhiza after co-culture with AM fungi. In addition, rhizospheric soil of the cultured S. miltiorrhiza plants was collected to measure the activities of invertase, phosphatase and urease enzymes in the soil. It was found that the tested AM fungi were able to successfully colonize the S. miltiorrhiza plantlets to form mycorrhizal fungal associations, but the mycorrhizal dependence of S. miltiorrhiza differed for different AM fungi. All 8 tested AM fungi were able to coexist with S. miltiorrhiza plantlets to form mycorrhizal structures, with the colonization percentage generally high (54.83%-89.97%). S. miltiorrhiza showed no mycorrhizal dependence on Acaulospora laevis or Glomus tenebrosum. After inoculation with AM fungi, the biomass and fresh weight of most S. miltiorrhiza test plants increased, indicating that inoculation with AM fungi had a promotional effect on the root accumulation of S. miltiorrhiza. Different AM treatment groups affected the biomass production of S. miltiorrhiza differently (P<0.05). Among the single strain treatments, treatment 34 (G) had the best effect, while among the mixed strain treatments, [name the AMS in this treatment] (Treatment 20) (ACE) had the most significant promotion effect on dry matter accumulation of S. miltiorrhiza. Similarly, different AM fungi affected soil enzyme activity differently (P<0.05). Among the single strain treatment groups, the G. tenebrosum group most increased the activity of invertase and phosphatase, and the Glomus formosanum group most increased urease activity. In the mixed strain treatment group, Treatment 20 most increased the activity of urease and sucrase, while treatment 17 (ABD) most increased the activity of phosphatase. Cluster analysis of the 35 treatment combinations yielded three groups based on the degree of growth promotion: strong growth promotion, low growth promotion and no growth promotion. Considering the achieved infection rate, mycorrhizal dependency, plant yield and soil enzyme activity, mixed inoculation with [name AM strains] has strong growth-promoting effects and so would be the best candidate treatment for the development of fungicides. However, Treatment 20 was overall the best combination, and this treatment resulted in some improvement in rhizosphere soil fertility, improved soil microenvironment. This research provides a theoretical basis for alleviating obstacles to continuous cropping of S. miltiorrhiza.

Quantification of soil nutrient levels and enzyme activities in different grassland categories in karst mountains

HUANG Yu-fan, SHU Ying-ge, XIAO Sheng-yang, CHEN Meng-jun

2020, 29(6):  93-104.  DOI: 10.11686/cyxb2019519

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In order to explore the soil properties of different grassland categories (wild grassland, farmland reverting to grassland, forest-grass intercropping land) in karst mountains, this study focuses on the changes in soil enzyme activity and soil nutrient content of different grasslands in Guizhou province. As expected, it was found that soil enzyme activity and soil nutrient content decrease with increasing soil depth. The ranking for catalase and phosphatase activities in the three grassland categories was: forest-grass intercropping land>wild grassland>farmland reverting to grassland. The ranking for urease activity in the 0-10 cm soil layer was as for phosphatase and catalase, while urease activities in the soil layer below 10 cm ranked: forest-grass intercropping land>farmland reverting to grassland>wild grassland, and the invertase activities ranked: wild grassland>forest and grass intercropping land>farmland reverting to grassland. The protease activity ranked: forest-grass intercropping land>farmland reverting to grassland>wild grassland. The soil polyphenol oxidase activity in the three grassland categories varied. The soil nutrient levels in the forest-grass intercropping land were higher than those of wild grassland and farmland reverting to grassland. It was found that the correlation between soil nutrient levels and soil enzyme activities differed in different grassland categories, being sometimes positive and sometimes negative. In summary, with the gradual restoration of surface vegetation and associated increase in biodiversity, the soil enzyme activities and soil nutrient levels in the forest grass intercropping land were higher, and the ecological environment in the karst mountain area is shown to have been gradually improved.

Effects of continuous nitrogen application on bacterial community structure and denitrification in the rhizosphere of potato

LI Zhi-long, LUO Chao-yue, QIU Hui-zhen, FU Xiao, DENG De-lei, ZHANG Chun-hong, SHEN Qi-rong

2020, 29(6):  105-116.  DOI: 10.11686/cyxb2019381

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A five-year field experiment was conducted at Dingxi in the Gansu Province of China from 2013 to 2018 to determine the effects of continuous application of different nitrogen rates on bacterial community structure and denitrification mechanisms. The experiment had six nitrogen application rates, namely: No nitrogen application (control, N₀), 75 kg N·ha^-1 (N₇₅), 150 kg N·ha^-1 (N₁₅₀), 225 kg N·ha^-1 (N₂₂₅), 300 kg N·ha^-1 (N₃₀₀) and 375 kg N·ha^-1 (N₃₇₅). It was found that nitrate ($NO_{3}^{-}$-N) content and nitrite reductase activity significantly increased with increasing nitrogen application rates. Treatment N375 increased $NO_{3}^{-}$-N content by 86.87%-856.12% when compared with the other treatments. Results from high-throughput sequencing showed that N375 significantly reduced the Alpha diversity of the bacterial community and changed the bacterial community composition of the rhizosphere. The control increased the relative abundance of Proteobacteria and thick-walled bacteria by 1.66%-26.53% and 22.59%-85.52%, respectively when compared with the nitrogen treatments. The relative abundance of nirK and nirS increased with increasing nitrogen application rates. Treatment N375 increased the relative abundance of nirK and nirS by 116.26% and 28.24%, respectively when compared with the control. Pearson correlation analysis showed that the relative abundance of nirK was significantly and positively correlated with $NO_{3}^{-}$-N while soil pH was negatively correlated with the abundance of nirK and nirS. The accumulation of $NO_{3}^{-}$-N and the reduction of soil pH due to the high nitrogen application rate changed the bacterial community structure and nirK and nirS abundance.

Effect of anthracnose infection on alfalfa yield and quality in the Shaerqin area

ZHANG Li-li, SHI Min, LI Yan-zhong

2020, 29(6):  117-126.  DOI: 10.11686/cyxb2019546

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Anthracnose caused by Colletotrichum americae-borealis is a serious disease of alfalfa (Medicago sativa), which has been widespread in Inner Mongolia in recent years. This study evaluated the resistance of 44 alfalfa varieties to anthracnose in the Shaerqin area of Inner Mongolia, in order to determine the anthracnose effect on alfalfa yield and quality. We also evaluated the disease severity in three alfalfa varieties: Hunter river, Magnum 2 and Reindeer. Yield loss assessments were performed to evaluate the effects of anthracnose on nutritional content and amino acid content in the variety reindeer. The results showed that there were differences in resistance to anthracnose among the 44 tested alfalfa varieties. The tested varieties were classified as having high susceptibility (13 varieties), moderate susceptibility (14 varieties), moderate resistance (13 varieties), or high resistance (1 variety). Hunter river, Reindeer, and Magnum 2 were among the highly susceptible varieties and should not be grown in this area. Compared with healthy plants, the plant dry weight of severely affected Hunter river, Magnum 2 and Reindeer varieties was reduced by 6.72%-27.24% (P<0.05), and yield was significantly reduced by 6.795-37.39% (P<0.05). Compared with lightly diseased plants, the yields of severely susceptible Reindeer, Magnum 2 and Hunter river decreased significantly by 0.49% to 21.06% (P<0.05). The contents of neutral detergent fiber and acid detergent fiber were, respectively, 20.57% and 15.79% higher in severely diseased plants than in healthy plants (P<0.05), while other indicators such as crude fat and crude protein were significantly lower (34.53% and 16.52%, respectively) than those in healthy plants (P<0.05). Anthracnose reduced the amino acid contents of the tested alfalfa varieties (P<0.05). For example, methionine, isoleucine, lysine, cysteine and histidine contents were reduced by 54.21%-85.88%. A regression equation was established with anthracnose severity as the independent variable and values of the various quality indexes as the dependent variables. Crude fat, neutral detergent fiber, threonine, leucine, alanine, and tyrosine showed a significant negative correlation and a good fit. In summary, when anthracnose is severe, the disease not only significantly reduces the yield, but also affects crop nutritive quality. Therefore, anthracnose should be controlled.

Isolation and identification of an anthracnose pathogen on Vicia sativa

WANG Qiong, DUAN Ting-yu, NAN Zhi-biao

2020, 29(6):  127-136.  DOI: 10.11686/cyxb2019299

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Anthracnose in Vicia sativa is an important fungal disease affecting leaves and stems. This research combined morphological and multiple gene phylogenetic analyses, using gene sequences of an internal transcribed spacer region, actin, chitin synthase 1 and glyceraldehyde-3-phosphate dehydrogenase to identify an anthracnose pathogen (WQ) isolated from leaves and stems of vetch plants (cv. Lanjian No.2) in Xiahe County, Gansu Province. Koch’s postulates were applied to identify pathogenicity of the strains. It was found that colonies of the fungus on potato dextrose agar (PDA) were flat, with surface dark gray-olivaceous to olivaceous-black, white margin, covered by short floccose whitish aerial mycelium, reverse gray-olivaceous to iron-gray. Conidia were hyaline, unicellular, (17.5-25.0) μm×(3.75-5.00) μm, and slightly falcate. Multiple-gene phylogenetic analysis indicated that the isolate WQ and a strain of CBS 128.57 were clustered into one clade, with a confidence level of 70%. The strains (WQ) could infect V. sativa leaves through wounds. It was confirmed that the pathogen was Colletotrichum spinaciae. This is the first report of C. spinaciae on V. sativa in China. A host range test showed that C. spinaciae exhibited high pathogenicity to Onobrychis viciifolia and Avena sativa, and moderate pathogenicity to four V. sativa cultivars, and low pathogenicity to Medicago sativa and Trifolium repens. However, Colletotrichum spinaciae had no pathogenicity to Lolium multiflorum.

Protective effects of Flavobacterium succinicans on perennial ryegrass under shade stress

ZHOU Han-yang, SUN Peng-yue, YU Xin-rong, ZHOU Yu, ZHANG Zhi-wei, GAO Jin-zhu, ZHAO Dong-hao, LUO Yi-lan, HU Tian-ming, FU Juan-juan

2020, 29(6):  137-143.  DOI: 10.11686/cyxb2019391

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This study aimed to investigate the effects of the plant growth-promoting rhizobacteria Flavobacterium succinicans DSM4002 (FS) on plant growth and physiological characteristics of perennial ryegrass under different shade stress treatments (0, 20%, 40%, 60% and 80%). The combined effects of DSM4002 inoculation and various levels of shade stress on the plant morphology, malondialdehyde (MDA) content, superoxide anion free radical ($O_{2}^{·-}$) levels, antioxidant enzyme activities, and non-enzyme antioxidant contents, were assessed. It was found that shade stress significantly inhibited the growth of perennial ryegrass seedlings while FS treatment alleviated the growth inhibition caused by shade stress. MDA accumulation increased with increasing shade stress. However, FS inoculation significantly reduced MDA and $O_{2}^{·-}$levels under shade stress, compared with shade treatment alone. Treatments of 20% shade+FS, 40% shade+FS, 60% shade+FS, and 80% shade+FS resulted in decreases in $O_{2}^{·-}$ levels of 4.47%, 29.75%, 44.57% and 49.84%, respectively. Additionally, shade stress resulted in a change in antioxidant enzyme activities and non-enzyme antioxidant concentrations, while FS inoculation further improved the activities of superoxide dismutase, catalase, and glutathione reductase, and increased levels of reduced ascorbate and reduced glutathione. Peroxidase and ascorbate peroxidase activities were unchanged by FS. In conclusion, inoculation with FS stimulated the antioxidant defense mechanisms, preventing the accumulation of reactive oxygen species, thus enhancing shade tolerance in perennial ryegrass. The present study indicates that F. succinicans DSM4002 has a great potential to improve plant adaptation to stress.

Physiological response of continuously cropped pea seedlings to inoculation with compound rhizobia preparations

YANG Ning, MA Shao-ying, MA Lei, ZHANG Xu-hui, WANG Na, LI Sheng, CHAI Qiang

2020, 29(6):  144-152.  DOI: 10.11686/cyxb2019502

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Continuous cropping poses a serious threat to the sustainability of agricultural production, especially in leguminous crops. In this experiment, pea varieties ‘Dingwan 8’ and ‘Longwan 6’ were inoculated with preparations of pea-rhizobium strains ‘ACCC15657’ and ‘ACCC15735’ and alfalfa-rhizobium strains ‘Da99’ were used as microbial materials. The experiment involved planting continuously cropped pea seedlings in pots, and evaluation of the effects of different rhizobial preparations on aboveground biomass, activities of superoxide dismutase (SOD), catalase (CAT), peroxidase (POD), and concentrations of proline (Pro), soluble sugars (SS) and malondialdehyde (MDA). It was found that, compared to continuous crop planting without rhizobial inoculation (CK), in ‘Longwan 6’ seedlings, inoculation with a single rhizobium, ‘ACCC15735’, significantly reduced MDA content, while inoculation with two rhizobia, ‘ACCC15657’+‘ACCC15735’, significantly increased plant aboveground biomass, shoot Pro concentration, and SOD, POD and CAT activities. Inoculation with three rhizobia, ‘Da99’+‘ACCC15657’+‘ACCC15735’, significantly increased the soluble sugar concentration. In ‘Dingwan 8’, seedlings, compared to CK, when inoculated with the two rhizobia ‘ACCC15657’+‘ACCC15735’, the POD activity and MDA content were significantly lower, while the SOD activity and Pro concentration were significantly improved. When inoculated with three rhizobia, ‘DA99’+‘ACCC15657’+‘ACCC15735’, the aboveground biomass, the CAT activity and the soluble sugar content were significantly increased. Multivariate analysis showed that the average score under each treatment with rhizobia inoculation was higher than CK. The average value of the multivariate score was highest (indicating the strongest resilience to continuous cropping) in ‘Dingwan8’ seedlings when inoculated with the rhizobial combination ‘DA99’+‘ACCC15657’+‘ACCC15735’, and was highest in ‘Longwan 6’ seedlings when inoculated with ‘ACCC15657+ACCC15735’ was the highest. In summary, inoculation with rhizobial preparations improved the resilience of pea seedlings to the deleterious effects of continuous cropping, and the effect of inoculation with compound rhizobial preparations was superior to that of using a single rhizobium strain.

Impacts of different paddy soils on nodule growth characteristics of Chinese milk vetch

LIU Fang, CHEN Zhen, XU Wen, CHU Zhi-ying, GUAN Yong-xiang, WU Gui-cheng, HUAN Jing, SUN Zheng-guo

2020, 29(6):  153-161.  DOI: 10.11686/cyxb2019356

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Nodule growth characteristics of Chinese milk vetch (CMV) differ in response to different soil physical and chemical properties, especially in different paddy soils. This study aimed to analyze the relationship between nodule characteristics of CMV and soil physical and chemical properties in CMV used in crop rotations with rice in Taihu and Ning-zhen rice growing regions. Correlation analysis and path analysis were used to associate differences in nodule characteristics with particular soil conditions in rice stubble. It was found that root nodule number, nodule weight and nitrogenase activity of milk vetch in rice-CMV crop rotations were affected by soil conditions. Nodule number per plant and the nitrogenase activity in Kunshan sample point were high (86.24·plant^-1, 1362.73 nmol C₂H₄·min^-1·g^-1, respectively), while corresponding values for Danyang sample point were low (1.13·plant^-1, 9.25 nmol C₂H₄·min^-1·g^-1, respectively). Path coefficients for nitrate nitrogen, total nitrogen, organic matter and available phosphorus were generally strongly correlated with nodule number, and organic matter, nitrate nitrogen and available phosphorus were positively correlated (P₂=1.629, P₁=0.633, P₄=0.448) but total nitrogen negatively correlated (P₅=-1.138, P represents direct path coefficient of factors). Soil organic matter, nitrate nitrogen and available phosphorus had the greatest positive influence on nodule number, whereas high soil total nitrogen reduced nodule number. There is a synergistic relationship between root nodule characteristics and the soil environment. In practice, appropriate organic fertilizer and phosphate fertilizer should be used to improve the nitrogen fixation capacity in CMV, rather than nitrogen fertilizer.

Soil quality assessment by principal component analysis in Glycyrrhiza uralensis stands of differing ages

LIU Jiang, LV Tao, ZHANG Li-xin, YE Li-na, LIU Xiang-yang, DAI Xiang-rong, WANG Wei-wei, DING Ru

2020, 29(6):  162-171.  DOI: 10.11686/cyxb2019380

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In this research, the impact of Glycyrrhiza uralensis planting on soil quality was elucidated using principal component analysis on data from G. uralensis stands of different ages, to include a time dimension. It was found that: 1) After planting G. uralensis, soil average infiltration rate, total porosity, available N, available P, organic matter, enzyme activities (urease, phosphatase, polyphenol oxidase and dehydrogenase) and proportion of bacteria significantly increased, while soil bulk density, fungi number and its proportion markedly decreased and other indexes did not change significantly. 2) With increased G. uralensis stand age, significant increases in soil moisture content, pH, available N, organic matter, soil enzyme activities (urease, phosphatase, invertase and dehydrogenase), number of bacteria, number and proportion of actinomycete were observed, while available K and proportion of bacteria were markedly decreased. After establishment, available P initially increased but then decreased with age in older stands. Visibly obvious changes in soil average infiltration rate, field capacity, bulk density, total porosity and proportion of fungi were not quantified . Among soil microbial groups in G. uralensis stands, actinomycetes had the greatest comparative abundance, followed by bacteria and fungi. 3) A significant, positive correlation between number of bacterial and actinomycete was found, and also a similar relationship between those two groups and activities of urease, phosphatase and invertase. Negative correlation between fungi and bacteria, actinomycete, all enzymes were universally insignificant. Enzyme activities, besides polyphenol oxidase, were significantly and positively correlated with each other. 4) Soil quality of 3-year-old stands of G. uralensis was similar to that of fields of 4-year-old stands, and overall soil quality in fields of G. uralensis increased with stand age. Multivariate evaluation of results using principal component analysis showed that, in contrast to shifting sandy land, the soil quality of fields of 3-year-old and 4-year-old G. uralensis showed marked improvement.

Fractal features of soil and their relationship with soil fertility under three shrub species in Otindag sandy land

DONG Xue, HAO Yu-guang, XIN Zhi-ming, DUAN Rui-bing, HUANG Ya-ru, LI Xin-le, MA Yuan, LIU Fang

2020, 29(6):  172-181.  DOI: 10.11686/cyxb2019401

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Amygdalus pedunculata, Caragana microphylla and Caragana stenophylla are common, widely distributed shrubs in Otindag sandy land. This research studied the soil properties beneath these three shrub species. The vertical distributions of soil particle mechanical composition, soil volume fractal dimension and soil nutrients in the 0-60 cm soil depth were analyzed to explore the relationship between soil fractal characteristics and soil fertility after, grassland colonization by shrubs, to assist understanding of the mechanisms of spread and survival and of shrub vegetation in desert steppe. It was found that there are significant differences in the morphology of the three common shrubs, which result in different particle size characteristics of the soil deposited under the shrub through interception of the sand flow. The proportions of clay and silt content and the fractal dimension differed significantly among the different plant species (P<0.05). Soil fractal dimension also differed significantly (P<0.05), as follows: C. microphylla (2.346)>C. stenophylla (2.259)>A. pedunculata (2.149)>bare sandy (2.057). Soil fractal dimension was correlated with particle diameter and proportions of <0.25 mm particles included clay and silt (<0.05 mm), very fine sand (0.05-0.1 mm) and fine sand (0.1-0.25 mm). The 0.1 mm particle size was the critical size that determined soil fractal dimension under shrubs in this study area. The greater the proportion of particles < 0.1 mm diameter (such as the clay and silt, very fine sand), the higher soil fractal dimension was. There was significant positive correlation between soil organic matter content, soil total nitrogen content and soil fractal dimension (P<0.01). Soil organic matter content decreased with increasing soil depth, and total nitrogen and total phosphorus fluctuated with soil layer. The differences in soil organic matter and total nitrogen content among species were significant (P<0.05), but the difference in total phosphorus content was not significant. The soil structure and fertility of shrub-covered land were significantly improved compared with values for bare sand sites. The soil improvement associated with the different species ranked: C. microphylla>C. stenophylla>A. pedunculata.

Anther structures and tapetum development types of 19 species of Asteraceae

WANG Rui, HU Yue, CUI Hong-an, NIU Jia-rui, LI Ya-dong, MIAO Fang

2020, 29(6):  182-190.  DOI: 10.11686/cyxb2019414

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Anther structure and tapetum developmental type is important for systematic classification and understanding of the evolution of the Asteraceae. In this work, anther structures and tapetum development types of 19 species in 19 genera of the Asteraceae were investigated by paraffin sections, hematoxylin integral staining, aniline-saffron integral staining and microscopic observation. It was found that the anther structures of all species examined consist of four clinandria except for one containing two. The anther wall consists of four layers of cells, namely: the epidermis, endothecium, middle layer and the tapetum layer. The middle layer cells disintegrate in the meiocyte period. During formation of pollen grains, the endothecium thickens in a U-shaped manner initially, followed by band-shaped thickening. The microspore mother cells have two types of cytokinesis, a continuous type and a simultaneous type. The majority of the microspore tetrads are tetrahedral. The tapetum has two types, an amoeboid type, characteristic of the Carduoideae, and a glandular type, a feature of the Cichorioideae. From an evolutionary perspective, a progression of three tapetal developmental types is evident: the amoeboid tapetum of the Heliantheae, a transitional type from amoeboid tapetum to glandular tapetum and glandular tapetum in the Lactuceae. The morphologies of the amoeboid tapetum are obviously different among the various species. The developmental type and morphology of the tapetum are important characteristics in Asteraceae classification.

Physiological role of γ-aminobutyric acid in protecting the photosynthetic system of maize seedlings under drought stress

WANG Yong-chao, ZHANG Ying-lei, YAN Dong-liang, HE Ling-zhi, LI Zhuo, YAN Bo-wen, SHAO Rui-xin, GUO Jia-meng, YANG Qing-hua

2020, 29(6):  191-203.  DOI: 10.11686/cyxb2019377

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This research aimed to clarify the physiological role of γ-aminobutyric acid (GABA) in the protection of the photosynthetic system of maize seedlings under drought stress. The maize variety studied was Zheng Dan 958, and the exogenous application of GABA at a concentration of 1 mmol·L^-1 was used tested in a hydroponic culture experiment where drought stress was simulated by adding PEG-6000. The experiment comprised four treatments: Blank control (CK), 1 mmol·L^-1 GABA treatment (G), 20% PEG (PEG-6000) simulated drought stress (D), 20% PEG (PEG-6000) simulated drought stress and 1 mmol·L^-1 GABA treatment (DG). It was found that: Application of 1 mmol·L^-1 exogenous GABA significantly improved the activities of superoxide dismutase, peroxidase and catalase and decreased the malondialdehyde, superoxide anion and hydrogen peroxide concentrations of leaf tissue. Leaf relative conductivity was also reduced. Furthermore, exogenous GABA significantly increased the content of soluble protein, soluble sugar and proline in leaves under drought stress, thereby improving the water retention capacity of cells. Exogenous application of GABA significantly reduced the chlorophyll fluorescence F₀ value; and improved the F_v, F_m and F_v/F_m values, thereby reducing photochemical damage in leaves. Compared with the D treatment, SPAD, P_n, T_r and G_s of the DG treatment were increased by 8.25%, 7.69%, 9.13% and 7.38%, respectively in 5th day after stress. In addition, C_i was decreased by 2.93%. In summary, exogenous GABA improved the drought resistance in leaves by reducing oxidative damage and increasing the capacity for cell water retention, thereby protecting the photosynthetic system in maize seedlings.

Unlocking the potential of nodal propagation by raising plantlets from the longer stem segments of perennial forage maize at the tasseling stage

YAN Xu, WU Zi-zhou, LI Ying-zheng, LI Xiao-feng, HE Ru-yu, YANG Chun-yan, LI Yang, ZHOU Yang, SHI Jian-zhong, EBENEZER Kofi Sam, HE Jian-mei, RONG Ting-zhao, TANG Qi-lin

2020, 29(6):  204-213.  DOI: 10.11686/cyxb2019426

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Novel perennial forage maize cultivar (‘Yucao No.6’, Yu6), an allopolyploid containing genomes of Zea mays, Tripsacum dactyloides and Zea perennis, is a palatable, sterile, high-tillering and productive C₄ grass. By virtue of sterility, it is limited to vegetative propagation. In comparison with ramet division as a propagation method, little is known about the performance of plants propagated from stem segments and the clonal potential of stem. The aim of this study was to clarify the field performance of plants derived from stem segments and the ability of stem to produce new plants. Field trials were performed to investigate the effect of propagule type on the developmental morphology and above-ground biomass (AGB) of Yu6 over two years, and to evaluate the effects of sowing time, nodal position and stem segment size on the regeneration of aboveground stem fragments from Yu6 in a field setting. Results showed that the establishment mortality (12.5%) of ramet division was higher than that (2.5%) of stem division in the establishment year, and that both types of propagules could safely overwinter (100% overwintering rate in the first winter after planting). We found slight advantages in plant height (PH), grass length (GL), basal circumference (BC), tiller number (TN), AGB for stem propagation compared to ramet division, and no propagule-related difference in stem to leaf ratio (SLR) in the establishment year, except that stem diameter (SD) was significantly greater in stem propagated plants during the tillering stage. There was no significant difference in plant characteristics (PH, GL, BC, TN, SD and SLR) and AGB between the propagule types in the second year following planting, but the second-year metrics (except SLR and SD) were significantly higher than the first year. Sowing date and nodal position had a significant effect on the survival rate, multiplication rate and plantlet size. However, the effect of stem segment size on these parameters was non-significant. Of the treatment combinations, the longer stem segment of the basal and middle stems at the tasseling stage showed the best plantlet regeneration performance. Briefly, use of stem propagation can enhance the propagation opportunities for perennial forage maize, and increase the success rate of establishment without compromising forage production performance. The most effective propagation methodology was the raising of plantlets from the longer stem segments of perennial forage maize at the tasseling stage. Adoption of this methodology could increase the popularity and use of perennial forage maize.

Selection of suitable silage maize varieties in the Bijie region based on yield, agronomic and nutritional evaluation

LOU Fen, LI Xiao-dong, SHANG Yi-shun, WU Jia-hai, ZHANG Rong, GAN Xiao-bo, XIONG Jun, CHEN Guang-ji, LI Shi-ge, PEI Cheng-jiang

2020, 29(6):  214-224.  DOI: 10.11686/cyxb2019485

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Animal husbandry is widely practiced to reduce poverty in Guizhou Province, and forage shortage is one of the major factors restricting the development of the industry in Guizhou, especially in Bijie region. In the present study, eight agronomic traits (growth period, biological yield, water content, plant height, panicle height, panicle weight, panicle length and leaf number) were analyzed in 35 silage maize varieties or lines, which were representative of the range of different varieties grown in the Bijie region. Among the selected varieties, Jinyu 908, Qingyu 1587, Qianyu 3 and Qianqing 4546 were early-maturing varieties (or lines); while Jinyu 818, GX276, L667 and Zhuqing 1 were late-maturing varieties (or lines). Yields of Jinyu 818, Qianyu 3, Jinyu 908, Qingyu 1587, L667, GX276, Qianqing 4546 and GX254 were significantly higher than those of the ‘reference’ line, Zhuqing 1. Eight nutritional traits, including dry matter, crude protein, crude fat, neutral detergent fiber, acid detergent fiber, crude ash, calcium and phosphorus, were also measured in the 35 silage corn varieties (or lines). In addition, the relative feeding value (RFV) and digestible energy (DE) were obtained by regression equation. Relative feeding value ranged from 94.81 to 200.10. Interestingly, the RFV of waxy maize lines was superior to that of non waxy maize lines. The differences between varieties or lines in DE were similar to those of RFV, and Qian-Nuo 868 and Jinyu 838 were the best lines. Based on multivariate evaluation of the yield, dry matter, RFV and DE data, the most suitable silage maize varieties or lines in the Bijie region were Jinyu 818, Qianyu 3, GX276, Jinyu 908, Qianqing 4546 and L667. Our study provides technical information to support the selection of silage maize varieties with superior performance potential to assist the development of grassland and livestock industry in Bijie region of Guizhou Province. Selection of superior crop varieties will potentially make a significant contribution to poverty reduction in this region.