Table of Content

20 December 2020, Volume 29 Issue 12

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Aboveground biomass in grasslands in Qinghai Province estimated from MODIS data and its influencing factors

Hui-fang ZHAO, Xiao-dong LI, Dong ZHANG, Rui-xiang XIAO

2020, 29(12):  5-16.  DOI: 10.11686/cyxb2020240

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According to the principles of satellite remote sensing estimation， the relationships between vegetation index and biomass were analyzed to produce a method to assess biomass in Qinghai Province based on satellite data. These analyses were based on the normalized difference vegetation index （NDVI） monitored by the EOS/MODIS satellite， aboveground biomass measured on the ground， and meteorological monitoring data （temperature and precipitation）， and revealed the factors affecting aboveground biomass in Qinghai Province. We detected a significant positive correlation （P<0.01） between forage yield （aboveground biomass） and NDVI at ground monitoring sites in different grassland types during the grassland growing season. The average aboveground biomass in Qinghai Province tended to slightly increase from 2003 to 2017. The minimum average biomass was 2622 kg·ha^–1 in 2003， and the maximum average biomass was 3252 kg·ha^–1 in 2010. The aboveground biomass decreased gradually from the southeast to northwest. The areas with the highest biomass were in the southeastern part of Guoluo Prefecture， Yushu Prefecture，Huangnan Prefecture， and Haibei Prefecture， and the area with the lowest biomass was in the northwest of the Qaidam Basin. The aboveground biomass in most areas of Qinghai Province tended to remain unchanged or increase from 2003 to 2017. The grassland biomass significantly decreased in Qumalai， Dulan， and Gande. Against a background of high temperature and sufficient heat conditions， grassland in Qinghai Province was favorably affected by greater water availability resulting from increased precipitation. Greater water availability played a role in promoting the growth and development of grassland vegetation in alpine regions， which eventually led to an increase in NDVI and biomass in those regions.

Effects of short-term grazing exclusion on standing biomass and plant community diversity in sagebrush desert

Yu-xuan CUI, Zong-jiu SUN, Hui-xia LIU, Yi-qiang DONG

2020, 29(12):  17-26.  DOI: 10.11686/cyxb2020018

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This research explored the adaptation of plant communities in desert grassland to short-term grazing exclusion. Using a paired experimental design， we determined the effects of short-term grazing exclusion on aboveground biomass， litter， underground biomass， and diversity of plant communities in sagebrush desert grassland on northern slopes in different regions of the Tianshan Mountains. Compared with grazed plots， the ungrazed plots in sagebrush desert grassland in Xinyuan， Manas， Hutubi， and Qitai showed significant increases in aboveground living biomass （98.91%， 65.99%， 246.66%， and 91.91%， respectively）， but there was no significant change at the Bole site. After grazing exclusion， the aboveground living biomass of semi-shrubs increased significantly by 65.56% to 265.47%， and the size of the increase in the biomass of perennial herbs and annual herbs differed among different plots. Grazing exclusion promoted the accumulation of underground biomass in sagebrushdesert grassland at the Bole and Hutubi sites （increases of 65.16%-151.89%）， and this was mainly concentrated in the 0-5 cm soil layer. Grazing exclusion did not significantly affect litter accumulation in any of the plots. After grazing exclusion， the Shannon-Wiener index， Simpson’s index， and the Pielou index of the plant community in the Bole plots increased by 15.12%， 14.88%， and 11.54%， respectively； the Patrick index， Shannon-Wiener index， Simpson’s index， and the Pielou index of the plant community in the Xinyuan plots decreased significantly by 62.12%， 64.54%， 58.02%， and 34.81%， respectively； the Patrick index of the plant community in the Manas plots significantly decreased by 32.48% and the Pielou index increased significantly by 21.90%； and the Shannon-Wiener index and Simpson’s index in the Hutubi plots decreased by 73.21% and 68.69%， respectively. Grazing exclusion did not affect the diversity of the plant community in the Qitai plots. Our results show that short-term grazing exclusion promotes the accumulation of biomass in degraded Artemisia desert grasslands， but its impacts on plant community diversity vary from region to region.

Factors affecting the shear strength of root-soil complexes from three types of grass hedgerows in a karst area

Jiao-jiao QIANG, Zhe-hao YAN, Yun CHEN, Bing-hui HE, Han TANG, Xiao-hong LIU

2020, 29(12):  27-37.  DOI: 10.11686/cyxb2020034

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This research explored the differences in the shear strength of grass hedgerow root-soil complexes from a karst area， and the factors affecting this parameter. Three grass hedgerows， i.e.， Orychophragmus violaceus， Viciavillosa rothvar， and Ophiopogon bodinieri， were established on the upper， middle， and lower slopes of a karst bedding slope in Youyang， Chongqing. The shear strength of the complexes， the basic physical and chemical properties of the soil in the root zone， and the morphological and chemical indexes of the root system in the complexes were measured， and the cohesion and internal friction angle of the complexes were calculated. The main results were as follows： 1） Among the upper/middle slope composites， the O. bodinieri complex showed significantly higher shear strength than the O. violaceus and V. rothvar complexes （P<0.05）， but shear strength did not differ significantly among the three hedgerow complexes from the lower slope. Only the shear strength of the O. bodinieri complex differed significantly among different slope positions （middle slope>upper slope>lower slope） （P<0.05）； 2） The shear strength index was significantly higher for the O. bodinieri and V. rothvar complexes than for the O. violaceus complex. There were differences in the internal friction angle among complexes from the middle slope and in the cohesion of complexes at each position on the slope （P<0.05）. The cohesion and internal friction angle of the O. bodinieri complex and the cohesion of the V. rothvar complex were significantly higher at the middle slope than at the upper and lower slopes （P<0.05）. These parameters of O. violaceus complexes did not differ significantly among the three slopes； 3） Soil organic matter content was positively correlated with the cohesion of V. rothvar and O. bodinieri complexes （correlation coefficients of 0.91 and 0.83， respectively）， but not with the cohesion of O. violaceus complexes. There were significant or extremely significant positive correlations between the cohesion of the three hedgerow complexes and the root morphology index， and the highest correlation coefficient was 0.99. In conclusion， O. bodinieri complexes had the highest shear strength， and the optimal slope location was the middle slope. The shear strength of O. violaceus， V. rothvar， and O. bodinieri hedgerow complexes was mainly affected by cohesion.

Chemical weathering characteristics of calcareous soil under different land-use patterns in a Karst mountainous area

Peng-peng ZHOU, Ying-ge SHU, Zhong-liu CHEN, Qing-song CHEN

2020, 29(12):  38-49.  DOI: 10.11686/cyxb2020315

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We determined the chemical weathering characteristics of calcareous soil profiles under different land-use patterns ［cultivated land （CL）， wild grassland （WGL）， returning farmland to grassland （RFL） and forest and grass intercropping （FGL）］ in the Karst mountainous area. The distribution， migration， and enrichment of mineral elements in calcareous soil profiles were analyzed， and the chemical weathering characteristics of soil under different land-use patterns were determined by measuring the soil weathering degree， element leaching degree， migration degree， and residual degree. It was found that the main oxides in the limestone profile in the Karst mountainous area were SiO₂， Al₂O₃， and Fe₂O₃， with smaller amounts of other oxides （medium-variable elements）. Comparing soils from areas with different land-use patterns， WGL soil was richer in SiO₂， Al₂O₃， and MgO； FGL soil was richer in CaO and Na₂O； and CL soil was richer in Fe₂O₃， MnO， P₂O₅ and K₂O. The soil in the study area was in the middle chemical weathering stage， with a weak degree of aluminization. The chemical alteration coefficient of the soil in desert grassland was stronger under certain land-use patterns. Aluminization was strongest in FGL soil. Leaching of soil K， Na， and Ca was severe in the study area， and leaching of salt ions was more obvious in barren grasslands. The strength of leaching of salt ions was relatively low in FGL soil. Soils had relatively high Fe and Al contents， especially Al in FGL soil and Fe in RFL soil. The implementation of governance models such as returning farmland to grassland to increase vegetation cover will significantly affect soil protection. These findings provide a scientific basis and theoretical guidance for understanding the formation and evolution of lime soil in the Karst mountainous area， soil degradation mechanisms， soil management and land-use countermeasures， ecological restoration， and soil and water conservation in ecologically vulnerable Karst areas.

Traits correlated with lodging resistance of oat strains in the alpine region

Jing YANG, Wen-hui LIU, Guo-ling LIANG, Zhi-feng JIA, Kai-qiang LIU, Yan ZHANG, Rui WU, Yu-jie YANG

2020, 29(12):  50-60.  DOI: 10.11686/cyxb2020022

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The aim of this study was to identify the traits affecting the lodging resistance of oats （Avena sativa）. We analyzed 25 traits in lodging-resistant oat germplasm lines （QYJ301， QYJ386， QYJ322， QYJ986， QYJ211） and lodging-susceptible oat germplasm lines （QYJ272， QYJ224， QYJ288， QYJ320， QYJ280， QYJ055） from the alpine region. Several traits differed significantly （P<0.05） or extremely significantly （P<0.01） between the lodging-resistant group and the lodging-susceptible group， including plant height （lodging-resistant group： 103.00-117.40 cm； lodging-susceptible group： 125.80-144.18 cm）， ear length （lodging-resistant group： 17.82-21.94 cm； lodging-susceptible group： 23.82-27.10 cm）， height of center of gravity （lodging-resistant group： 50.24-56.34 cm； lodging-susceptible group： 56.70-59.24 cm）， ear height （lodging-resistant group： 84.54-95.46 cm； lodging-susceptible group： 98.80-117.08 cm）， internode length， stem diameter， stem position coefficient， lodging index， and mechanical properties. The oat germplasm lines with different lodging properties performed differently in terms of lodging resistance-related traits. Cluster analysis was performed for the 22 lodging-resistance related traits showing significant differences between resistant and susceptible oat resources. A relative distance of 10 was used to divide the 11 oat germplasm lines into two categories， namely the lodging-resistant group and the lodging-susceptible group. Plant height， ear length， height of center of gravity， ear height， stem position coefficient， and mechanical properties at the base of the stem all showed significant （P<0.05） or extremely significant （P<0.01） correlations with lodging index. Because these traits affect the lodging resistance of oats， they can be used as important indexes of lodging resistance.

Effects of machine sowing depth and amounts of seeds and fertilizer on lodging and yield of Tartary buckwheat

Hao-tian WU, Jiao NIE, Wen-juan YANG, Zhi-yong ZHANG, Kang-hong WU, Xiao-yu LI, Xiao-mei FANG, Ren-wu RUAN, Ze-lin YI

2020, 29(12):  61-72.  DOI: 10.11686/cyxb2020048

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Tartary buckwheat （Fagopyrum tataricum） belongs to the Polygonaceae， and originated in the southwest of China， northern India， Bhutan， and Nepal. Most Tartary buckwheat is grown in hilly and mountainous areas， where mechanized farming is still underdeveloped. Lodging is a serious problem in Tartary buckwheat grown in hilly and mountainous areas， and this greatly restricts the development of the Tartary buckwheat industry. Because the appropriate use of agricultural machinery can increase agricultural productivity， we conducted a field study to identify the optimal method for mechanical sowing and fertilization of Tartary buckwheat in hilly and mountainous areas. The field study consisted of an L₉3⁴ orthogonal experiment with three factors and three levels conducted in 2016 and 2017. Seeds of Youqiao 5， a moderately lodging-resistant Tartary buckwheat cultivar， were sown at a depth of 2 （A₁）， 3 （A₂）， or 4 cm （A₃）， at a rate of 16.8 （B₁）， 33.6 （B₂）， or 50.4 kg seeds·ha^-1 （B₃）， with fertilizer applied at 150 （C₁）， 300 （C₂）， or 450 kg·ha^-1 （C₃）. The lodging and yield of Tartary buckwheat were determined at different growth stages. Of the three factors， sowing depth had the strongest effect on lodging rate， followed by the amount of seeds and then the amount of fertilizer. As the sowing depth increased， the lodging period was delayed， and the lodging level and the lodging rate decreased and then increased. The lodging level and lodging rate increased as the amount of seeds and fertilizer increased. The length， diameter， fresh weight， and bending resistance of the second internode of the stem base gradually increased from flowering to maturity. Compared with sowing depth and amount of fertilizer， the amount of seeds had a greater effect on the diameter， fresh weight， and breaking force of the second internode of the stem， but not on the length of second internode. With increasing sowing depth， the diameter， fresh weight， and bending force of the second internode initially increased and then decreased， and the length of the second internode initially decreased and then increased. With increasing amounts of seeds sown， the diameter， fresh weight， and bending strength of the second internode decreased gradually， and the length of the second internode first decreased and then increased. With increasing amounts of fertilizer， the length， diameter， fresh weight， and bending resistance of the second internode increased gradually. The activity of 4-coumarate：CoA ligase （4CL）， phenylalanine ammonia-lyase （PAL）， and cinnamyl alcohol dehydrogenase （CAD） increased and then decreased from flowering to maturity， and the lignin content gradually increased. The lignin content and the activities of 4CL， PAL， and CAD in the second internode of the stem were most strongly affected by the amount of seeds sown， followed by sowing depth and then fertilizer amount. The lignin content and the activities of 4CL， PAL， and CAD first increased and then decreased with increasing sowing depth； gradually decreased with increasing amounts of seeds sown； and increased with increasing amounts of fertilizer. Yield， grain number per plant， and number of plants （but not 1000-grain weight） were most strongly affected by the amount of seeds sown， followed by sowing depth and then fertilizer amount. As the amount of seeds sown increased， the yield and number of plants increased， and the number of individual plant grains and 1000-grain weight decreased. As the amount of fertilizer increased， the yield and number of plants were not significantly affected， but the individual grain number and 1000-grain weight gradually increased. Overall， the combination of A₂B₂C₃ （sowing depth of 3 cm， seed sowing rate of 33.6 kg·ha^-1， fertilizer amount 450 kg·ha^-1） was found to be beneficial for growing Tartary buckwheat with a high yield and strong lodging resistance in hilly and mountainous areas.

Potential geographical distribution of Ambrosia trifida in Xinjiang under climate change

Qian-qian MA, Tong LIU, He-gan DONG, Han-yue WANG, Wen-xuan ZHAO, Rui-li WANG, Yan LIU, Le CHEN

2020, 29(12):  73-85.  DOI: 10.11686/cyxb2020040

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Determining the potential distribution of invasive species and their responses to climate change on a regional scale is of great significance for the early warning， specific prevention， and control of invasive species. Ambrosia trifida （giant ragweed） is a globally recognized invasive weed. This plant is now widely distributed in the Yili Valley in Xinjiang which locaded in Central Asian hub of the“Belt and Road”. To predict the potential spread of A. trifida in Xinjiang， a Maxent niche model was used to project its potential distribution under the current climate and the climate in the 2050s and 2070s under two climate change scenarios （RCP4.5 and RCP8.5）. The results indicated that the suitable habitat area of giant ragweed in Xinjiang could extend to 24.01×10⁴ km²， accounting for 14% of the total area of Xinjiang under the current climate conditions. Under the RCP4.5 scenario， its suitable habitat area was predicted to increase to 37.36×10⁴ km² and 39.23×10⁴ km² by the 2050s and 2070s， respectively. Under the RCP8.5 scenario， its suitable habitat area was predicted to increase to 39.45×10⁴ km² and 42.94×10⁴ km² by the 2050s and 2070s， respectively. Under the two future climate scenarios， the potential suitable habitat area will tend to increase and shift northwards， and the decreasing areas will be mainly concentrated in the Junggar Basin. Among all the environmental factors， precipitation and temperature made the strongest contributions to distribution， with total contribution rates of 40.1% and 56.0%， respectively. The individual factors making the strongest contributions to giant ragweed distribution were precipitation in the driest month （36.2%） and temperature seasonality （29.1%）. Farmland and construction land were identified as the areas with the highest risk of giant ragweed invasion. On the basis of these results， we suggest that management strategies should focus not only on predicted habitats， but also on farmland， grassland， and roadsides where there is sufficient water and strong disturbance by humans or animals.

Phenotypic variations among Leymus chinensis populations from different geographical areas and effects of variations on clonal propagation of the rhizome

Wu-yun BAI, Xiang-yang HOU, Zi-nian WU, Chun-yu TIAN, Yong DING

2020, 29(12):  86-94.  DOI: 10.11686/cyxb2020049

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Leymus chinensis is one of the most important forages in China， and it is widely distributed on the Eurasian steppes. Populations of L. chinensis show a high degree of phenotypic variation because of complex natural selection and the diverse environmental conditions in its wide habitat range. A common garden experiment was performed with 66 L. chinensis ramets from split geographical origins. We evaluated intraspecific variations of traits related to phenotype and reproduction of L. chinensis. Curve fitting and partial least squares regression analysis were used to analyze the effects of variable traits on the clonal propagation of L. chinensis rhizomes. The main conclusions were as follows： 1） The phenotypic and reproductive traits of L. chinensis from split geographical origins were significantly different. The environmental conditions in the original habitat had a profound and long-term effect on the phenotype and reproduction of L. chinensis. 2） The magnitude of variation differed among different traits. Leaf-related traits showed the smallest variations. Traits related to extravaginal ramets were more diverse than traits related to spatial expansion. 3） A linear relationship described the relationship between the comprehensive ability to grow clonally and the main variable traits of L. chinensis. 4） Stem height， plant height， leaf width， leaf size， and the production of multiple parent-type ramets through tillering had strong explanatory effects on the ability of L. chinensis rhizomes to grow clonally. In summary， the capacity for asexual propagation from the rhizome was strongest in L. chinensis plants with wide， large leaves. The plants with greater stem height， plant height， and strong tillering ability also showed a relatively strong capacity for asexual propagation.

Effects of arbuscular mycorrhizal fungi on ion absorption and distribution in Leymus chinensis under saline-alkaline stress

Ying-kui WANG, Yu-rong YANG, De-li WANG

2020, 29(12):  95-104.  DOI: 10.11686/cyxb2020036

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To explore the mechanism by which arbuscular mycorrhizal fungi （AMF） improve plants’ tolerance to saline-alkaline stress， we determined their effects on ion absorption and distribution in above- and below-ground plant parts in a pot experiment. The dominant species in Songnen grassland， Leymus chinensis， was used as the experimental material. Saline-alkaline stress increased the Na⁺ content and reduced the contents of K⁺， Ca²⁺， and Mg²⁺ in above-ground parts， enhanced Na⁺ transport from below-ground to above-ground parts， inhibited the transport of K⁺， Ca²⁺， and Mg²⁺， and altered above- and below-ground ion distribution in L. chinensis. Under saline-alkaline stress， AMF inhibited the absorption of Na⁺， promoted the absorption of K⁺， Ca²⁺， and Mg²⁺， and improved the ability of L. chinensis roots to retain Na⁺. The ion balance was maintained by the ion transport ratio and the cation transport selection ratio， and this improved the salt and alkali tolerance of L. chinensis.With increasing saline-alkaline stress， the hyphal colonization rate and hyphal density of AMF decreased significantly， but vesicle colonization increased. This helped the AMF store more saline-alkaline ions in the vesicles， thereby reducing the damage caused by saline-alkaline stress to L. chinensis roots. Therefore， under saline-alkaline stress， AMF enhanced the salt-alkali tolerance of L. chinensis by inhibiting absorption of Na⁺， by using the vesicle structure to help the root intercept Na⁺， and by promoting the absorption of K⁺， Ca²⁺， and Mg²⁺. The results suggest that the L. chinensis-AMF symbiosis has the potential to improve the health of grasslands affected by salinization-alkalization. In addition， these results provide insights into the mechanisms by which AMF enhance plants’ salt-alkali tolerance.

Effects of salt stress on seed germination and seedling growth of carnation

Yong HUANG, Meng GUO, Hong-rui ZHANG, Yan ZHOU, He-min LI, Zhi-ming GAO, Pan-pan WANG

2020, 29(12):  105-111.  DOI: 10.11686/cyxb2020027

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In this study， we determined the effects of salt stress on the seed germination， seedling growth， and physiological characteristics of carnation （Dianthus chinensis）. The results showed that 50 mmol·L^–1 NaCl had no significant effect on the germination of carnation seeds， while NaCl at 100， 150， 200 and 250 mmol·L^–1 significantly inhibited the germination of carnation seeds， and the inhibition became stronger with increasing NaCl concentrations. The stem diameter was significantly increased in the 50， 100 and 150 mmol·L^–1 NaCl treatments， unaffected in the 200 mmol·L^–1 treatment， and significantly decreased in the 250 mmol·L^–1 NaCl treatment， compared with the control. The leaf length， leaf width， root length， and dry weight per plant were not affected by NaCl at 50 mmol·L^–1， but were significantly inhibited by NaCl at higher concentrations. The contents of free proline， soluble protein， and malondialdehyde increased with increasing NaCl concentrations. The contents of soluble sugars and hydrogen peroxide and the activity of peroxidase first increased and then decreased with increasing NaCl concentrations. The highest soluble sugars content was in the 100 mmol·L^–1 NaCl treatment， and the highest hydrogen peroxide content and peroxidase activity were in the 150 mmol·L^–1 NaCl treatment. All the NaCl treatments significantly inhibited superoxide dismutase activity. Our results indicated that D. chinensis is partially salt tolerant. It can germinate and grow normally under 50 mmol·L^–1 NaCl stress， but NaCl at higher concentrations inhibits its seed germination and seedling growth.

Effects of Bacillus subtilis and three actinomycetes on seed germination and seedling growth of Bidens pilosa and Eclipta prostrata under salt stress

Ju-hong WANG, Sheng-jing SHI, Wen CHEN, Gui-mei GAN, Sai-na CHEN, Zhang-wei LI

2020, 29(12):  112-120.  DOI: 10.11686/cyxb2020068

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This research investigated the effects of Bacillus subtilis and actinomycetes on salt tolerance of plants. Specifically， the effects of B. subtilis and three actinomycetes （Roseosporus 2-5， Lavendulae 6-3 and Cinereus 1-6） on seed germination and seedling growth of Bidens pilosa and Eclipta prostrata under salt stress were studied using a petri dish method. It was found that： 1） B. subtilis and the three actinomycetes increased the seed germination rate of B. pilosa at salt concentrations of 25-75 mmol·L^-1， but the four microbial solutions had little effect on the seed germination rate of E. prostrata. 2） B. subtilis and the three actinomycetes had little effect on the root length of B. pilosa under salt stress， and had different degrees of growth promotion effect on the root length of E. prostrata. 3） The four microbial solutions had little effect on the stem length of B. pilosa， but significantly promoted intestinal stem growth of E. prostrata under salt stress， with B. subtilis and the 3 ascomycetes increasing the stem length of this species by 30.56%， 28.57%， 26.47% and 24.24%， respectively at 100 mmol·L^-1 salt concentration. 4） Treatment with B. subtilis and the three actinomycetes at the various salt concentrations reduced the dry weight of B. pilosa， compared to seedlings germinated in a sterile solution， but the dry weight of E. prostrata was increased to different degrees in the same conditions. In summary， B. subtilis and the three actinomycetes had significant growth promotion effects on seed germination rate of B. pilosa and root length， stem length and dry weight of E. prostrata under salt stress， which was beneficial to adaptation of B. pilosa and E. prostrata seedlings to salt stress.

Pathogenicity ofseed-borne fungi of Orychophragmus violaceus

Bo-wen XIAO, Wei FENG, Ting-yu DUAN

2020, 29(12):  121-130.  DOI: 10.11686/cyxb2020026

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Orychophragmus violaceus is an important ground cover， landscape， and green manure crop species. Seven species of seed-borne fungi in five genera were isolated from the seeds of O. violaceus， and their pathogenicity was determined in seed germination， in vitro leaf inoculation， and greenhouse potted plant tests. The seed-borne fungi were Alternaria alternata， Alternaria brassicicola， Alternaria tenuissima， Epicoccum nigrum， Fusarium incarnatum， Harzia acremonioides， and Ulocladium sp. The percentages of seed rot and seedling rot caused by the seed-borne fungi ranged from 16.50% to 68.50%. A. brassicicola and H. acremonioides caused the seed germination percentage to decrease by 18.18%-27.27%. All the fungi caused symptoms such as chlorosis and leaf rot when inoculated onto O. violaceus leaves in vitro： the disease incidence was 100%， the lesion area was 8.84%-99.38%， and the disease index was 22.50-95.00. In potted greenhouse-grown O. violaceus plants， the seed-borne fungi caused wilt， chlorosis， leaf spot， or leaf rot symptoms. The percentage of diseased seedlings was 100%， the diseased leaf rate was 41.56%-79.88%， and the disease index was 16.22-56.93. We compared various biochemical indexes between control plants （not inoculated with seed-borne fungi） and those infected with seed-borne fungi at 9 days after inoculation. Compared with the control plants， the infected plants showed 30.40%-204.15% increases in malondialdehyde content， -1.81%-82.87% and 18.78%-86.14% increases in peroxidase and superoxide dismutase activities， respectively， and 13.24%-37.85% reductions in SPAD value. The results of the pathogenicity tests showed that A. brassicicola and H. acremonioides had the strongest and weakest pathogenicity against O. violaceus， respectively.

Species and pathogenicity of seed-borne fungi in 32 varieties of alfalfa

Ting-yan MA, Yan-zhong LI

2020, 29(12):  131-139.  DOI: 10.11686/cyxb2020038

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Plant pathogens can spread over time and in space via seeds. The aims of this study were to determine whether the main alfalfa varieties currently grown in China harbor pathogens causing destructive diseases， for example， Verticillium alfalfae， and to provide data to support the safe introduction， transportation， and disease control of alfalfa. We collected seeds of 32 alfalfa varieties from Chinese alfalfa breeders and importers. The fungi were isolated by the potato dextrose agar plate method and then identified. The pathogenicity of the fungal strains isolated from Zhongmu No.3 against seeds and seedlings was determined. Fungi in 19 genera， including 20 species of V. alfalfae and other quarantine pathogens， were detected from the tested seeds. The main fungi on alfalfa seeds were Alternaria spp.， Penicillium spp.， and Aspergillus spp.， which are common in the environment. There were significant differences in the frequency of seed-borne fungi among different alfalfa varieties. The percentage of seeds harboring pathogenic fungi was 26.18%-67.54% without disinfection， and disinfection decreased the average percentage of fungi by 25.10%. In pathogenicity tests against seeds， the seed germination percentage was significantly decreased by Cladosporium sp.， Epicoccus nigrum， Acremonium sp. and Alternaria alternata. In pathogenicity tests against seedlings， Talaromyces sp.， Chaetomium globosum，Aspergillus flavus， Stenophyllium solani， and other fungi significantly inhibited the shoot and root growth of seedlings， causing them to wither and rot.

Detection of alfalfa mosaic virus and white clover mosaic virus in alfalfa and their effects on physiological and biochemical characteristics of alfalfa plants

Shou-feng CHENG, Qiao-lan LIANG, Lie-xin WEI, Xu-wen SANG, Yu-ling JIANG

2020, 29(12):  140-149.  DOI: 10.11686/cyxb2020030

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In this study， we screened alfalfa （Medicago sativa） varieties that are grown on a large scale in Gansu Province for the presence of alfalfa mosaic virus （AMV） and white clover mosaic virus （WCMV）， and determined the physiological and biochemical effects of these viruses on alfalfa plants. Twelve alfalfa varieties were cultivated in the laboratory for 30 days， and then viruses were detected using double antibody sandwich enzyme-linked immunosorbent assays. The effects of the viruses were determined by measuring the chlorophyll content， the activities of defensive enzymes， and the contents of soluble protein in alfalfa seedlings. The 12 alfalfa varieties could be divided into four groups： a non-infected group， an AMV-infected group， a WCMV-infected group， and an AMV/WCMV-infected group. Among all the plants， 66.7% were infected by one or both viruses （50% positive for AMV； 41.7% positive for WCMV， and 25% positive for AMV/WCMV）. Analyses of variance indicated that AMV/WCMV co-infection and single-virus infection significantly decreased the chlorophyll content and the soluble protein content in alfalfa plants， compared with uninfected plants （CK）. AMV/WCMV co-infection significantly decreased the chlorophyll content and the soluble protein content in alfalfa plants， compared with those infected with a single virus. Compared with uninfected plants and those infected by a single virus， plants co-infected with both AMV and WCMV showed significantly increased activities of defensive enzymes including peroxidase， polyphenol oxidase， and phenylalanine ammonia-lyase. Our findings show that infection with AMV and/or WCMV significantly affects the physiological and biochemical characteristics of different alfalfa varieties.

Correlations between arbuscular mycorrhizal fungi and distribution of main grassland types in Ningxia

Zhan-jun WANG, Kun MA, Hui-zhen CUI, Guang-wen LI, Hong-qian YU, Qi JIANG

2020, 29(12):  150-160.  DOI: 10.11686/cyxb2020186

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The aim of this study was to analyze the distribution and types of soil arbuscular mycorrhizal （AM） fungi in different grassland types in Ningxia. We selected areas with five vegetation types on the desert steppe （Pennisetum centrasiaticum+Glycyrrhiza uralensis， Stipa breviflora+Lespedeza potaninii+Artemisia scoparia， Artemisia arenaria， and S. breviflora） and dry steppe （Stipa bungeana+Leymus secalinus+Artemisia gansuensis）. These areas have been fenced since 2003. The soil AM fungi were analyzed by fatty acid fingerprinting and subjected to high-throughput sequencing using the Illumina platform. The correlations between soil AM fungal diversity and community composition， characteristics of grassland vegetation community， and soil environmental factors were determined. The results showed that there were significant differences in the soil AM fungal biomass characterized by neutral lipid fatty acids （16：1ω5c） in the steppe grassland soil of S. bungeana+L. secalinus+A. gansuensis， compared with the desert steppe soils of P. centrasiaticum+G. uralensis， S. breviflora+L. potaninii+A. scoparia， A. arenaria， and S. breviflora （P<0.01）. The values of the Shannon-Wiener index， Simpson’s index， Chao1 index， and Pielou index were higher for AM fungi in soil of S. bungeana+L. secalinus+A. gansuensis on the dry steppe than for soil AM fungi in soil from vegetation types on desert steppe （P<0.05）. We identified one phylum， three classes， four orders， seven families， eight genera， and 50 species of AM fungi. Glomus and Paraglomus were the dominant genera of AM fungi. Under the different classification levels， there were significant differences in the relative abundance of 11 kinds of AM fungi between the dry steppe and desert steppe soils. The results of nonmetric multidimensional scaling analysis showed that the spatial distribution of the soil AM fungal communities differed between the dry steppe and the desert steppe， and the AM fungal communities on the dry steppe were more diverse than those on the desert steppe. The AM fungal Shannon-Wiener index and Chao1 index were significantly positively correlated with the vegetation Shannon-Wiener index， species， total biomass， and the vegetation importance value， as determined by Pearson’s correlation analyses. The relative abundance of Claroideoglomus and Paraglomus was positively and significantly correlated with the contents of soil total nitrogen， total phosphorus， available nitrogen， organic matter， and available potassium. Our results indicate that differences in soil physical and chemical properties and the characteristics of vegetation types caused by rainfall distribution and elevation are the main factors affecting the diversity of soil AM fungi and the relative abundance of dominant soil AM genera in different grassland types.

Effect of nitrogen addition on soil bacterial diversity in alpine degraded grasslands of differing slope

Cheng-yi LI, Xi-lai LI, Yuan-wu YANG, Hong-lin LI, De-fei LIANG

2020, 29(12):  161-170.  DOI: 10.11686/cyxb2020109

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The aim of this study was to determine the effects of nitrogen addition on the bacterial community in soils in degraded alpine meadows with different slopes in Guoluo Prefecture， in the Sanjiangyuan Region. Degraded grasslands with different slopes were supplemented with nitrogen at three levels： low nitrogen （LN， 2 g N·m^-2）， medium nitrogen （MN， 5 g N·m^-2）， high nitrogen （HN， 10 g N·m^-2）， and the effects on soil bacterial diversity were determined. The 16s rDNA region of soil bacteria was sequenced and analyzed using Miseq PE250 sequencing technology. Actinomycota and Proteobacteria were the two main bacterial classes in the grassland soil in the study area. Individual phyla with extremely low abundance in soil and those with high abundance （>61.4%）， including unidentified bacterial genera， differed significantly between gentle slope and steep slope regions （P<0.05）. Different nitrogen addition levels did not significantly effect on the relative abundance of bacterial phyla and most bacterial genera in degraded alpine grassland， but had significant effects on some less abundant genera （P<0.05）. On both gentle and steep slopes， the overall soil microbial richness and diversity tended to initially decrease and then increase with increasing nitrogen addition. The HN treatment inhibited the decrease of soil bacterial richness and diversity. The effect of nitrogen addition on bacterial diversity was threshold-limited. Among the three treatments， the MN treatment significantly reduced soil bacterial richness and diversity （P<0.05）.

Nutritional value and fermentation quality of different oat varieties in the Hulunbuir area

Yan-zi XIAO, Li-jun XU, Xiao-ping XIN, Ren-qiqige WU, Lin SUN, Chao JIANG

2020, 29(12):  171-179.  DOI: 10.11686/cyxb2020138

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The aim of these experiments was to select suitable oat varieties to produce high-quality silage in Hulunbeier. In a regional field trial in 2018， ten oat varieties （Baler， Meili， Longyan No.2， Longyan No.3， Yanwang， Qinghai 444， Bayan No.3， Lena， Baiyan No.7， Qingyin No.1） were planted in a random block design at the National Field Scientific Observation and Research Station of the Hulunbeier Grassland Ecosystem， Chinese Academy of Agricultural Sciences. The oat plants were harvested at the ‘milky’ grain development stage， cut into 2 cm pieces， and stored in containers. After 60 days， the nutrient contents and fermentation index of the silages were determined. The dry matter （DM） yield was highest in Longyan No.2 （4905.45 kg·ha^-1）， and lowest in Qingyin No.1 （1773.65 kg·ha^-1）， and this difference was significant. The DM content of silages made from the ten oat varieties ranged from 30.73% to 45.47%. The DM content was highest in Longyan No.2 and lowest in Bayan No.3， and the difference between them was significant. The crude protein contents of Lena， Baylor， and Longyan No.2 were 12.63%， 12.46%， 12.41%， respectively， significantly higher than in the other varieties （P<0.05）. The acid detergent fiber content was significantly lower in Baler and Lena （25.11% and 26.11%， respectively） than in the other varieties （P<0.05）. The water soluble sugars （WSC） content ranged from 2.17% and 4.33% （average， 3.39%）. The WSC was highest in Baler and lowest in Yanwang， and differed significantly between these two varieties （P<0.05）. There were significant differences in fermentation quality among the ten different oat varieties （P<0.05）. Lena silage had the lowest pH， the highest lactic acid content （6.86%）， and the lowest contents of propionic acid， butyric acid， ammonia nitrogen， and total volatile fatty acids. The V-scores for the silages made from the ten oat varieties indicated that the fermentation quality of Longyan No.3， Lena， Longyan No.2， Qinghai 444， Meili， Qingyin No.1， Baiyan No.7， and Baler was excellent （V-scores>80）. Considering the yield， nutritional quality， and silage fermentation quality， Lena is a suitable oat variety for planting and processing into silage in the Hulunbuir area.

Effects of additives on fermentation quality of alfalfa silage

Cheng ZONG, Jian ZHANG, Tao SHAO, Zhi-hao DONG, Jun-feng LI, Lu TANG, Qi-fan RAN, Qin-hua LIU

2020, 29(12):  180-187.  DOI: 10.11686/cyxb2020158

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The objective of this study was to improve fermentation quality and inhibit the loss of unsaturated fatty acids from alfalfa silage. Alfalfa was ensiled without additives （control）， or with sodium benzoate， sodium caseinate， hexadecanoic acid， molasses， or propionic acid. After ensiling for 65 days， the fermentation quality and fatty acid contents of the various silages were evaluated. For the control silage， the pH was lower than 4.50， the lactic acid content was 54.25 g?kg^-1 DM， and the butyric acid content was lower than 5.00 g?kg^-1 DM. The Flieg score of the control silage was 64.33， indicative of good fermentation quality. Compared with the alfalfa material before ensiling， the silages showed significantly increased contents of linoleic acid （C18：2n6） and linolenic acid （C18：3n3） （P<0.05）. Compared with the control silage， silages fermented with hexadecanoic acid and sodium caseinate showed non-significant （P>0.05） and significant （P<0.05） reductions in lactic acid content， respectively； and silage fermented with sodium caseinate showed a significantly increased （P<0.05） butyric acid content. The silages fermented with hexadecanoic acid and sodium caseinate had Flieg scores lower than 50.00， indicative of poor fermentation quality. Compared with control silage， the silages fermented with sodium benzoate， propionic acid， and molasses showed increased lactic acid contents， decreased pH， and lower contents of ammonia nitrogen and acid detergent fiber. The Flieg scores were 70.33 for sodium benzoate-treated silage， 74.33 for propionic acid-treated silage， and 67.67 for molasses-treated silage， indicative of better fermentation quality than that of the control. Compared with the control silage， silages fermented with sodium benzoate and propionic acid showed increased C18：2n6 or C18：3n3 contents， while silage fermented with molasses had decreased contents of C18：2n6 and C18：3n3 （P<0.05）. In summary， sodium benzoate and propionic acid are suitable additives to produce high-quality alfalfa silage.

Distribution of ground-active arthropod community structure after introduction of Caragana korshinskii into Reaumuria soongorica shrubland on the Urat desert steppe， Inner Mongolia

Hai-tao CHANG, Ren-tao LIU, Wei CHEN, An-ning ZHANG, Xiao-an ZUO

2020, 29(12):  188-197.  DOI: 10.11686/cyxb2020019

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The introduction of Caragana korshinskii shrubs to degraded Reaumuria soongorica shrubland on the Urat desert steppe in Inner Mongolia is an important ecological restoration measure. It is important to determine how introduced C. korshinskii shrubs affect the structure and diversity of ground-active arthropod communities in natural R. soongorica shrublands to understand their roles in biodiversity conservation and the restoration of degraded ecosystems in this region. In this study， we determined the effects of introduced C. korshinskii and environmental factors on the composition of the ground-active arthropod community in R. soongorica microhabitats on the natural desert steppe by analyzing specimens collected in pitfall traps in spring， summer， and autumn in 2018. In total， 560 individual ground-active arthropods were captured， belonging to 23 families and 10 orders. The main groups were Tenebrionidae and Formicidae， accounting for 41.07% and 22.14% of all collected arthropods， respectively. There were 10 common groups accounting for 32.68% of all collected arthropods， and 11 rare groups accounting for 4.11%. The community composition of ground-active arthropods differed among R. soongorica shrubs， C. korshinskii shrubs， and bare microhabitats. For example， Lycosidae and Clubionidae were present only under C. korshinskii shrubs， and Aphodiidae and Neobisiidae were present only in bare microhabitats. There was no significant difference in the number of arthropods， groups， Shannon-Wiener index， and Simpson’s index among R. soongorica shrubs， C. korshinskii shrubs， and bare microhabitats （P>0.05）. The Jaccard index of ground-active arthropod communities ranged from 0.65 to 0.71， indicative of strong similarity among R. soongorica shrubs， among C. korshinskii shrubs， and among bare microhabitats. The results of redundancy analysis and partial redundancy analysis showed that soil pH was the main environmental factor affecting the distribution of ground-active arthropods. Our findings indicated that introduced C. korshinskii shrubs in the R. soongorica shrubland on the Urat desert steppe affected the community composition of ground-active arthropods. However， the introduced plants had little effect on the number of individuals and groups and on the diversity distribution of ground-active arthropods， indicating that introduced C. korshinskii shrubs have limited effects on the recovery of ground-active arthropod diversity.

Effect of seasonal transformation of flower morphology on reproduction of Viola philippica

Hui-fang SUN, Yan WEI, Zi-yan YAN, Cheng YAN

2020, 29(12):  198-204.  DOI: 10.11686/cyxb2020044

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Viola philippica is a garden plant with excellent ornamental characteristics， and there are large germplasm resources for this species. V. philippica forms different types of flowers during the growing season. The objective of this study was to determine how this variable florescence phenology affects the breeding system. V. philippica produces two kinds of flowers. In spring， it forms chasmogamous flowers with five petals and five calyxes. These flowers are produced in a mass-flowering pattern in a short period from mid- to late April. The flowers produced in summer and autumn are cleistogamous. They have no petals， and the sepals wrap the female parts and stamens. The cleistogamous flowers are produced in an extended flowering pattern from early May to the beginning of September. The average number of pollen grains per chasmogamous flower was 7053， and the pollen/ovule ratio （P/O） was 173.32-204.49. There were 179.2 pollen grains per cleistogamous flower， and the P/O value was 4.46-5.95. The results show that the breeding system of open flowers is heterozygous， partially compatible， and pollinated， while the closed flowers are fertilized. The style of chasmogamous flowers has a curved structure， and nectaries at the base of the dorsal part of the lower two stamens extend to the base of the petals. Bee pollinators press the stigma by colliding with the style， pushing the stamen arm in a lever motion to pollinate， thus promoting the separation of the appendages. The cleistogamous flowers show strict closed fertilization and do not require pollination. The seed setting rate and seed setting rate per individual plant are significantly higher for plants with cleistogamous flowers than for plants with chasmogamous flowers.