Table of Content

20 November 2019, Volume 28 Issue 11

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Plant community diversity in grazed Seriphidium semidesert grassland and its relationships with environmental factors

CHEN Yi-shi, SUN Hai-rong, LI Na-na, JIN Sheng-fei, CHE Zhao-bi, CAO Jia-min, LU Wei-hua

2019, 28(11):  1-11.  DOI: 10.11686/cyxb2018776

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This study investigated plant community species composition and biodiversity in grazed Seriphidium semidesert grassland, to explore the relationship between community structure and environmental factors. The results showed that: 1) Grazed grassland had an obvious grazing gradient by sheep, and the utilization of grassland was reasonable. A detrended correspondence analysis revealed eight plant communities in the grazed area. There were significant differences in species diversity indexes among plant communities, and there was heterogeneity among communities; 2) Six environmental variables (soil organic matter content, amount of feces, grazing intensity, litter biomass, altitude, and slope direction) were chosen by forward selection. The first axis of a detrended canonical correspondence analysis showed gradients of organic matter content, amount of feces, and grazing intensity, while the second axis showed gradients of litter biomass, altitude, and slope direction gradient among communities. The plant species and communities were distributed along gradients of environmental factors. Our results show that quantitative ecological methods provide more detailed information about ecological relationships between vegetation and the environment for grazed Seriphidium semidesert grassland.

Influence of herders’ livelihood capital on livelihood strategies in the Three-River Headwaters region

WU Ting-mei, WU Yuan, WANG Duo-bin, LIN Hui-long

2019, 28(11):  12-21.  DOI: 10.11686/cyxb2018784

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Herdsmen are the decision-making body of natural resource utilization in the Three-River Headwaters region. Therefore, studying their livelihood strategies is important for local ecological protection. This study was based on first-hand survey data from stratified random sampling. Herders’ livelihood strategies were classified as pure pastoral or diverse, and key livelihood capital indicators that affect the choice of livelihood strategies by herdsmen were analyzed using a binary logistic model. The results indicated that: 1) The livelihood capital status of herdsmen with different livelihood strategies showed significant differences, and diverse herders had better livelihood capital than pure herdsmen. 2) The key livelihood capital indicators affecting the choice of livelihood strategies of the herdsmen in the Three-River Headwaters region were grassland area, housing quality, annual family income, whether there were cadres in the circle of friends and relatives, and the distance from the place of residence to the market. 3) The livelihood activities and income structure of the herdsmen in the Three-River Headwaters region were single, and even diverse herders were not separated from grazing-based livelihood activities. Considering these key livelihood capital indicators, herdsmen can be actively and rationally guided to choose a livelihood strategy that is conducive to ecological protection. This represents a new direction for the improvement of the ecological environment in the Three-River Headwaters region in the future.

Changes in soil microbial biomass and structural differentiation over 5 years in a vegetable-pasture rotation field

LIN Dong, ZHANG De-gang, McCulley Rebecca L.

2019, 28(11):  22-31.  DOI: 10.11686/cyxb2019271

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The objective of this study was to analyze the interannual and seasonal changes in soil microbial biomass and community composition in a vegetable-pasture rotation field in a temperate agro-ecosystem. The pasture 1 to 5 years old after low-cost vegetable production were identified for sampling on an organic farm, compared with permanent pasture. The signature fatty acids in microorganisms were determined using a high-throughput phospholipid fatty acid identification method. Nonmetric multidimensional scaling ordination was used to analyze the structure of microbial communities. A multi-response permutation procedure (nonparametric multivariate analysis) was used to examine pairwise comparisons and group significant differences in the proportional abundance of fatty acid methyl esters among rotation year and season. The results showed that: 1) Soil total microbial biomass and the diversity of phospholipid fatty acids increased during the pasture rotation years, with a decrease in the Gram positive to Gram negative ratio, and an increase in the fungi to bacteria ratio. 2) Season significantly affected the ratio of special fatty acid methyl esters and the biomass of saprophytic fungi and anaerobes. The soil microbial community composition also varied among seasons. 3) The microbial community composition changed after 4 years of pasture growth and became more similar to that of permanent pasture. Carbon mineralization and particulate organic matter drove the structural differentiation of microbial communities.

Response of soil characteristics of different types of shrub patches to enclosure on eastern Qilian Mountain

LIU Yu-zhen, CAO Wen-xia, WANG Jin-lan, LI Wen, XIN Yu-qiong, WANG Shi-lin, WANG Xiao-jun

2019, 28(11):  32-45.  DOI: 10.11686/cyxb2019327

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Soil is one of the basic functional components of the alpine shrub ecosystem. This study aimed to provide scientific guidance for the restoration of the degraded alpine shrub ecosystem. A typical area of the alpine shrub ecosystem on eastern Qilian Mountain with and without enclosures was selected as the sampling site. We selected three typical shrubs (Rhododendron capitatum, Salix oritrepha, Potentilla fruticosa) for detailed analyses of their soil properties. We measured 10 soil physico-chemical properties: total nitrogen (TN), total phosphorus (TP), total potassium (TK), available nitrogen (AN), available phosphorus (AP), available potassium (AK), soil organic carbon (SOC), soil moisture (SM), bulk density (BD), and soil porosity (SP). We analyzed the relationships among soil physico-chemical properties of different distributed community types using various field and experimental methods and statistical analyses including one-way ANOVA, the Tukey-Kramer HSD test, and principal component analysis (PCA) across inside and outside enclosures. We also compared soils from under shrubs and outside the shrub canopy in this ecosystem. It was found that SM, SOC, TP, TK, and AN differed significantly between samples collected under shrubs and outside the shrub canopy, and SM, BD, SOC, TP, AN, and AP differed significantly between inside and outside enclosures. The PCA indicated that AN and SP contributed more to vegetation distribution than did other environmental factors in the fenced plots, and were important predictors of the distribution of different shrubs and plants inside fenced areas on eastern Qilian Mountain. The PCA also indicated that AN and TK contributed more than did the other environmental factors in the grazed plots, and were important predictors of the distribution of different shrubs and plants in grazed grassland on eastern Qilian Mountain. R. capitatum patches always had better soil physical and chemical properties, indicating that this plant has a strong anti-interference ability. The results of these analyses show that short-term enclosure can significantly increase the SM content and available nutrient content in soil in shrub patches, further confirming that fencing is the best way to restore degraded alpine shrub ecosystem.

Effects of drought on competition, growth, and resistance of the lawn species Zoysia tenuifolia to the invasive weed Imperata koenigii

ZENG Xiao-lin, LI Ying, LIU Jin-ping, YOU Ming-hong, HUANG Xi-ye, HUANG Liu

2019, 28(11):  46-59.  DOI: 10.11686/cyxb2018823

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In subtropical areas, there is frequent functional degradation of Zoysia tenuifolia lawn by invasion of Imperata koenigii during summer drought. To explore the relationship between these two species under drought, we planted Z. tenuifolia and I. koenigii in five different proportions (9∶1, 8∶2, 7∶3, 6∶4, 5∶5), and after 40 days of growth, imposed four different drought treatments (adequate water, mild drought, moderate drought, and severe drought). After 60 days of the drought treatments, competitive indicators including relative yield, total relative yield, attacking power, and competitive equilibrium index were determined for both plant species. We also analyzed growth indexes including plant height, tiller number, leaf number, biomass, and the root∶shoot ratio, as well as physiological indexes including superoxide dismutase (SOD), peroxidase (POD), and catalase (CAT) activities, and the contents of soluble sugars (SS), soluble protein (SP), proline (Pro), and malondialdehyde (MDA). These analyses allowed us to compare the effect of drought on the competition, growth, and resistance systems of the two plant species. The results showed that: 1) The degree of drought and proportion of I. koenigii significantly affected the aboveground and underground competition index of both plant species (P<0.05). Under mild drought conditions and with a small proportion of I. koenigii (≤30%), the underground attacking power index and competition balance index of Z. tenuifolia were both positive. Moderate and severe drought caused the loss of the interspecific competitiveness of Z. tenuifolia. When the proportion of I. koenigii was ≥20%, its antagonistic effect was strong enough to exclude Z. tenuifolia from the community. 2) Drought mainly affected the underground competitiveness of Z. tenuifolia, yet the invasion of I. koenigii mainly affected the aboveground competitiveness of Z. tenuifolia. The synergistic effect of drought and invasion of I. koenigii had a greater impact on the attacking power and balance index of underground parts of Z. tenuifolia than on its aboveground parts. When the degree of drought and the proportion of I. koenigii increased, the aboveground and underground competitiveness of Z. tenuifolia decreased to negative values. 3) Mild drought was beneficial for the growth of both plant species. Moderate and severe drought reduced the plant height, tiller number, leaf number, and biomass of Z. tenuifolia, but had little effect on I. koenigii. At proportions of >10% I. koenigii restricted the numbers of tillers and leaves of Z. tenuifolia, and at proportions of >20% I. koenigii reduced the biomass and root∶shoot ratio of Z. tenuifolia. The synergistic effect of drought and invasion of I. koenigii inhibited the growth and regeneration ability of Z. tenuifolia. 4) The SOD, POD, and CAT activities of Z. tenuifolia significantly increased with increasing drought severity (P<0.05). Mild drought decreased the CAT activity of I. koenigii but did not affect SOD activity. More than 10%, 20%, and 30% I. koenigii increased the SOD, CAT, and POD activity of Z. tenuifolia, respectively. The enzymes were ranked, from strongest response to drought to weakest, as follows: CAT>SOD>POD in Z. tenuifolia; and SOD>POD>CAT in I. koenigii. In both plant species, the proportion of I. koenigii had the strongest effect on SOD activity, followed by CAT and then POD activity. Drought affected the antioxidant enzyme system of Z. tenuifolia more than did the proportion of I. koenigii. 5) Mild drought increased SS and SP contents of Z. tenuifolia and the SP content of I. koenigii. Moderate and severe drought increased the contents of SS, SP, Pro, and MDA in both plants (P<0.05). More than 10% I. koenigii increased SS, SP, and MDA contents of Z. tenuifolia, and more than 20% I. koenigii increased Pro content of Z. tenuifolia. The synergistic effect of drought and proportion of I. koenigii aggravated the degree of injury in both plant species. The physiological indexes were ranked, from strongest response to habitat stress to weakest, as follows: SS>Pro>SP>MDA in Z. tenuifolia; and MDA>Pro>SS>SP in I. koenigii. Therefore, the basic requirements to maintain the health of Z. tenuifolia lawn are to avoid severe drought in summer and maintain the proportion of I. koenigii at less than 10%.

Effects of ridge-furrow rainwater harvesting on soil moisture, temperature, and alfalfa fodder yield in a semi-arid region of China

ZHOU Xu-jiao, WANG Qi, ZHANG Deng-kui, YIN Xin-wei, LI Xiao-ling, LIU Qing-lin, JIA Sheng-hai

2019, 28(11):  60-74.  DOI: 10.11686/cyxb2018787

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The aim of this study was to explore the suitability of the ridge-furrow rainwater harvesting system for the sustainable production of a perennial legume (alfalfa) in a semi-arid region of China. A field experiment was conducted to determine the effects of different ridge mulching materials (manually compacted soil, MCS; biodegradable film, BF; and plastic film, PF) and different furrow-to-ridge ratios (60∶30, 60∶45, and 60∶60) on soil moisture, temperature, alfalfa forage yield, and water use efficiency (WUE) in a completely randomized arrangement. Traditional flat planting (TFP) served as the control. Soil water storage at 0-3.0 m depth decreased as the alfalfa growth period progressed and the stand age increased over the consecutive alfalfa cultivation for 4-5 years. The treatments were ranked, from the highest soil water storage to the lowest soil water storage, as follows: PF>BF>MCS>TFP. The soil water storage increased with ridge width increasing. Soil desiccation in the surface layer (0-1.2 m) occurred in all treatments and aggravated as the alfalfa growth period progressed and the stand age increased, especially in TFP. The soil temperature on ridge tops differed significantly among treatments, but that at furrow bottoms did not. The soil temperature at ridge tops increased with ridge width increasing. Over the 2-year period, the average topsoil temperature on ridge tops increased by 0.68, 0.99, 1.49, 2.49, 3.05, 3.44, 3.44, 4.03 and 4.29 ℃ for MCS₃₀, MCS₄₅, MCS₆₀, BF₃₀, BF₄₅, BF₆₀, PF₃₀, PF₄₅, and PF₆₀ (where subscripts 30, 45, and 60 refer to ridge widths in cm), respectively, compared with that for TFP. Ridge-furrow rainwater harvesting increased soil moisture and temperature, which promoted alfalfa growth, development, and yield. Over the 2-year period, in MCS₃₀, MCS₄₅, MCS₆₀, BF₃₀, BF₄₅, BF₆₀, PF₃₀, PF₄₅, and PF₆₀, the average annual forage yield increased by 7.77%, 7.30%, 2.11%, 32.23%, 29.95%, 22.47%, 40.88%, 38.44%, and 28.37%, respectively, and the average WUE increased by 17.94, 26.16, 29.57, 17.35, 19.47, 17.85, 20.99, 22.66, and 20.63 kg·ha^-1·mm^-1, respectively, compared with those in TFP. Further research is needed to investigate the soil desiccation mechanism in the alfalfa root zone in ridge-furrow rainwater harvesting system.

Effects of nitrogen and phosphorus fertilizers combined application on diurnal variations of leaves photosynthetic characteristics in Festuca kryloviana

SHI Zheng-hai, LIU Wen-hui, ZHANG Yong-chao, QIN Yan, WEI Xiao-xing

2019, 28(11):  75-85.  DOI: 10.11686/cyxb2019149

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Nitrogen and phosphorous are the two basic elements needed for plant growth, we carried out this experiment with two different levels of nitrogen (0, 60 kg·ha^-1) and three difference levels of phosphorous (0, 60, 90 kg·ha^-1) addition treatments, to investigate the effect of fertilizer addition and daily light radiation on the photosynthetic characters on Festuca kryloviana by analysis the leaf gas exchanges parameters and chlorophyll fluorescence parameters. As the results shown, the photosynthetically active radiation increased and decreased in the daytime, the peak value was at 13:00 p.m. 2000 μmol·m^-2·s^-1, and which the effect on the photo index were more significant than the fertilizer addition. Net photosynthetic rate (P_n) increased first then decreased with the increasing photosynthetically active radiation and its value was the highest at 800-1000 μmol·m^-2·s^-1. The change of stomatal conductance (G_s), stomatal limited value (L_s), transpiration rate (T_r), water use efficiency (WUE) were consistent with P_n, but the intercellular CO₂ concentration (C_i) was opposite. After the nitrogen and phosphorus addition, G_s, L_s and T_r increased, and C_i decreased, indicated that the increase of P_n after fertilization were mainly by the increasing of the water and CO₂ exchange among the leaves and the environment. With the increasing of photosynthetically active radiation, the effective photochemical efficiency of PSⅡ (F_v'/F_m'), the actual photochemical efficiency of PSⅡ (Φ_PSⅡ) and the photochemical quenching coefficient (qP) were significantly reduced, the non-photochemical quenching coefficient (NPQ) increased significantly and the electron transport rate (ETR) increased first and then decreased, the scale was among the 400 to 800 μmol·m^-2·s^-1 and changed rapidly after 1200 μmol·m^-2·s^-1. Nitrogen and phosphorus fertilizers significantly increased F_v'/F_m', Φ_PSⅡ, qP and ETR. In particular, N₆₀P₉₀ treatment also increased the maximum photochemical efficiency of PSⅡ (F_v/F_m) and NPQ. In terms of light energy allocation and alleviate the light damage, versus thermal dissipation (D) and excess (E) were increased and the proportion of photosynthetic electron transport (P) decreased with the increasing of photosynthetically active radiation. The above results showed that from the photosynthetic characteristics of the leaves of F. kryloviana, the application of nitrogen and phosphorus fertilizers increased the leaves P_n through adjust G_s that enhancing of water and CO₂ exchange between the leaves and the environment and increased the activity of the PSⅡ and P by reducing the proportion of E.

Differences in physiological resistance traits of Angelica sinensis seedlings from uncultivated and cultivated fields in Min County

BAI Gang, GUO Feng-xia, CHEN Yuan, YUAN Hong-chao, XIAO Wan-jun

2019, 28(11):  86-95.  DOI: 10.11686/cyxb2019292

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Growing Angelica sinensis seedlings traditionally on uncultivated alpine meadow land causes habitat destruction, but it can show reduced productivity when grown in continuously cropped farmland. In this study, we compared wild-grown A. sinensis seedlings with those grown in pea-Astragalus alternate stubble in farmland in Min County, where is the plant’s geo-authentic habitats. Physiological indicators were measured at the end of the seedling stage, and the survival and early bolting rates were determined to evaluate differences in resistance between seedlings from uncultivated and cultivated fields. The results showed that there were no significant differences in relative conductivity, amino acid leakage rate, soluble protein and sugar contents, malondialdehyde content, autoxidation rate as well as superoxide dismutase, peroxidase, and catalase activities between the seedlings from the two fields. Compared with the field-grown seedlings, those from uncultivated field showed relatively lower amino acid leakage but higher catalase activity, leading to a 5.32% lower early bolting rate. Compared with the seedlings from uncultivated field, those grown in farmland exhibited lower relative conductivity, higher superoxide dismutase and peroxidase activities, lower malondialdehyde content, 3.33% lower incidence of root disease, 3.06% lower overwintering disease index, 7.52% higher re-greening power after transplantation, and 11.39% higher ratio of medicinal plants. Hence, seedlings of A. sinensis in Min County showed better resistance and lower autotoxicity when cultivated in a double-legume stubble field. Field management should be enhanced to include organic cultivation during the seedling-raising period. These findings provide a scientific and technical basis for the cultivation of A. sinensis seedlings as part of a field rotation system.

Effects of different quantities of straw mulch on oxidation resistance of dryland wheat at the grain-filling stage

WANG He-zheng, HUANG Ming, ZHANG Jun, MA Chao, WU Jin-zhi, LI You-jun, CHEN Ming-can, FU Guo-zhan

2019, 28(11):  96-104.  DOI: 10.11686/cyxb2018786

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The aim of this study was to elucidate the effects of straw mulching on active oxygen metabolism in wheat at the grain-filling stage. The overall aim of this research is to identify the most suitable straw mulching method for high-yield dryland cultivation of wheat in Western Henan Province. The wheat variety Yumai 49-198 was used as the experimental material, and was mulched with straw at five different rates [no mulching as the control (I), and 2000 (II), 4000 (III), 6000 (IV) and 8000 kg·ha^-1 (V)]. We determined the reactive oxygen species content in the flag leaf, antioxidant enzyme activity, contents of antioxidant compounds and osmotic regulators, and yield at different times (0, 10, and 20 days) after the heading stage of wheat. It was found that straw mulching decreased the contents of the superoxide free radical ($O^{-·}_{2}$), hydrogen peroxide (H₂O₂), and malondialdehyde (MDA) in the flag leaves of wheat after heading. Treatment IV had the strongest effect; at 20 days after heading, the 2-year average decrease in $O^{-·}_{2}$, H₂O₂, and MDA contents were 43.0%, 32.2%, and 30.4%, respectively, compared with the control. The contents of soluble sugars, amino acids, glutathione, and ascorbic acid, and the activities of superoxide dismutase, peroxidase, and catalase were increased by mulching; the highest 2-year average increases in these indexes were in treatment IV (28.3%, 120.5%, 110.5%, 11.6%, 44.7%, 47.6%, and 57.5%, respectively, compared with the control). The values of these indexes were higher in treatment IV than in the other mulching treatments, and differed significantly from the control. Within a certain range of straw mulching (2000-6000 kg·ha^-1), the increase or decrease in each index was proportional to the amount of mulching, but this relationship was less clear when the quantity of mulch exceeded a certain level. The results showed that an appropriate amount of straw mulch could improve the ability of wheat to scavenge reactive oxygen species, reduce the accumulation of reactive oxygen species, and increase yield. For wheat cultivated in the dryland ecological conditions of Western Henan, the best results were obtained by applying straw mulch at 6000 kg·ha^-1.

Effects of antioxidant priming on germination and seedling growth of aged seeds of smooth bromegrass

SUN Ming, WANG Si-qi, Aierken· Dawuti, MAO Pei-sheng

2019, 28(11):  105-113.  DOI: 10.11686/cyxb2018788

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The poor vigor of aged seeds is a technical problem that needs to be solved for the protection of plant germplasm resources and for agricultural production. In this study, an antioxidant priming technique was used to treat smooth bromegrass seeds aged for 16 days, to determine the suitable antioxidant and optimum priming conditions to postpone seed aging. Aged seeds were conditioned with ascorbic acid (AsA, 2 mmol·L^-1), glutathione (GSH, 0.25 mmol·L^-1), melatonin (MT, 100 μmol·L^-1), or water (WT), and then germination and seedling growth characteristics, and the activities of superoxide dismutase, peroxidase, and catalase were determined. There were differences in effectiveness among the priming treatments. All the priming treatments significantly (P<0.05) increased the germination percentage, germination potential, germination index, vigor index, leaf length, root length, and seedling weight, and significantly (P<0.05) decreased the mean germination time. Compared with WT, priming with antioxidants significantly increased the vigor index and seedling weight of aged seeds. Among the three antioxidants, GSH significantly (P<0.05) promoted the root length of seedlings, germination percentage, and germination potential, and resulted in the highest values for germination percentage and germination potential. Priming with water had no significant (P>0.05) effect on antioxidant enzyme activity in aged seeds. However, compared with water priming, antioxidant priming of aged seeds significantly (P<0.05) enhanced seed peroxidase activity, and priming with AsA and GSH significantly (P<0.05) increased seed catalase activity. The data for the eight indexes of germination and seedling growth in the priming treatments were subjected to a cluster analysis. This analysis showed that GSH had the strongest positive effect on the seed germination and seedling growth of smooth bromegrass. A principal component analysis showed that, of all the indexes, the germination percentage and germination potential best reflected the effect of priming on germination and seedling growth of aged seeds. Therefore, antioxidant priming, especially with GSH, can significantly enhance the vigor of aged smooth bromegrass seeds, although the repair of aging damage can take some time.

Isolation, screening, and growth-promoting characteristics of plant growth promoting rhizobacteria in the rhizosphere of Kobresia myosuroides and Polygonum viviparum in alpine meadow pasture

GAO Ya-min, YAO Tuo, LI Hai-yun, LUO Hui-qin, ZHANG Jian-gui, YANG Yan-shan, LIU Ting

2019, 28(11):  114-123.  DOI: 10.11686/cyxb2018754

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The aim of this study was to screen the rhizosphere of the dominant species in an alpine meadow (Kobresia myosuroides and Polygonum viviparum), for plant growth promoting rhizobacteria (PGPR) with excellent growth-promoting properties. The rhizosphere distribution pattern was also explored for later production and applications. We screened bacteria from root surface soil (RS), the root surface (RP), and roots (HP) by the plate coating method, then re-screened bacteria in selective media containing phosphorus (Pikovskaya medium, Mengjinna medium, nitrogen-free medium) by spot inoculation of nitrogen-fixing strains. For all strains, we determined phosphorus solubilization, nitrogenase activity, and secretion of phytohormones (indoleacetic acid, IAA; gibberellin, GA₃; trans-zeatin, t-Z). Then, strains were re-screened by molybdenum blue colorimetry, gas chromatography, and high performance liquid chromatography. The first screening step yielded 68 bacterial strains, and then the next step reduced the number to 43 nitrogen-fixing phosphatase-active PGPR strains. Among those 43 strains, 17 were able to dissolve inorganic phosphorus (phosphorus content: 9.39-94.79 μg·mL^-1); 22 were able to dissolve organic phosphorus (phosphorus content: 10.37-72.82 μg·mL^-1); 30 were able to biologically fix nitrogen [nitrogenase activity: 3.79-3193.07 nmol (C₂H₄)·h^-1·mL^-1]; 26 secreted IAA (0.24-69.98 μg·mL^-1); 32 secreted GA₃ (0.34-68.87 μg·mL^-1) and 36 secreted t-Z (0.11-47.59 μg·mL^-1). There were significantly more PGPR in the RP area than in the RS and HP areas, and more PGPR in the rhizosphere of P. viviparum than in that of K. myosuroides. The ability of PGPR to dissolve organic phosphorus was greater in the K. myosuroides rhizosphere than in the P. viviparum rhizosphere. The number of PGPR was inversely related to the ability to dissolve inorganic phosphorus in the rhizosphere. In the strains that secreted phytohormones, the most abundant was t-Z, followed by GA₃ and then IAA. The main phosphate-solubilizing strains (ZNRS2, SNRP2, ZKHP3, ZKRP1), nitrogen-fixing strains (SKRP2, SNHP1, ZNRS3), and phytohormone-producing strains (SKHP3, ZNHP2, ZKRS2, ZKRP1, ZKRP2) could be used for microbial fertilizer production and related research. The strain ZKRS2 had the strongest growth promoting effect, and should be studied in more detail.

Effects of perennial forage on characteristics of the soil fungal community in an apple orchard

QIAN Ya-li, WANG Xian-zhi, LAI Xing-fa, LI Jun-cheng, SHEN Yu-ying

2019, 28(11):  124-132.  DOI: 10.11686/cyxb2018824

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A 13-year-old apple orchard on the Longdong Loess Plateau was selected as the site for this study. High-throughput sequencing was used to analyze the soil fungi community structure and the genera present in the 0-10 cm soil layer when planted with three different forage species (orchard grass, white clover, and lucerne). The results showed that the alpha diversity of soil fungi was increased by 17.4%, 18.6%, and 27.0% in the orchard grass, white clover, and lucerne plantings, respectively, compared with that in the control (clean tillage). At the phylum level, the soil fungi community mainly comprised Ascomycota, Zygomycota, Basidiomycota, and Glomeromycota. The relative abundance of Zygomycota under the three forage species was increased by 196.2%, 169.8%, and 126.9%, respectively, compared with that in the control. At the genus level, the relative abundance of Fusarium in soil was higher in the three forages than in the control, and the relative abundance of Phoma in soil was higher in the white clover and lucerne plots than that in the control. The soil planted in orchard grass had abundant Thermomyces, which are associated with protein and carbohydrate degradation. Stachybotrys and Actinomucor, which secrete catabolic enzymes that decompose plant fibers and hemi-fibers, were present in the soil of the white clover treatment. The soil in the lucerne treatment contained Cladosporium and Botryosphaeria.

Test guidelines for distinctness, uniformity, and stability of new varieties of Vicia sativa-Testing characteristics and assessment of reference varieties

MIN Xue-yang, LIU Wen-xian, WANG Yan-rong, LIN Xiao-shan, QI Xiao, ZHANG Zheng-she, NIE Bin

2019, 28(11):  133-146.  DOI: 10.11686/cyxb2019303

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We used the general introduction to the examination of distinctness, uniformity, and stability (TG/1/3), guidelines to identify and conduct tests for distinctness, uniformity, and stability of common vetch (TG/32/7), and related documents developed by the International Union for the Protection of New Varieties of Plants (UPOV) as guidelines to study the core technical content of the common vetch DUS test guidelines, which include test characteristics and reference varieties. We collected 51 common vetch varieties from around the world and evaluated their characteristics in a 2-year field trial. We evaluated 31 test characteristics, including 23 UPOV common vetch DUS test characteristics, and eight new characteristics representative of the distinctness feature. The expression status, and the observation period/method/number of each characteristic were scientifically graded and accurately described. Finally, a total of 32 reference varieties (21 international varieties and 11 varieties from China) corresponding to 123 expression states were screened. We further complemented the expression states of “ground color of test” and “seed shape” in the UPOV common vetch DUS test guidelines. This study lays a technical foundation for the development of new common vetch varieties in accordance with DUS test guidelines in China. The establishment of these reference varieties and testing guidelines will be useful for the protection, validation, and breeding of common vetch in China.

Development of EST-SSR molecular markers and analysis of genetic diversity of erect milk vetch (Astragalus adsurgens)

GONG Wen-long, WANG Zan, ZHAO Gui-qin, MA Lin, WEI Bao, GONG Pan, LIU Xi-qiang

2019, 28(11):  147-158.  DOI: 10.11686/cyxb2018802

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Erect milk vetch (Astragalus adsurgens) is a perennial cross-pollinated legume forage with superior yield, high quality, and strong stress resistance. The lack of molecular markers has limited research on, and genetic breeding of, this species. The aim of this study was to develop a large set of expressed sequence tag-simple sequence repeat (EST-SSR) molecular markers to provide reference resources for the improvement and genetic diversity analysis of erect milk vetch accessions. First, RNA-seq sequencing of two erect milk vetch accessions (CF019650, CF020070) was performed by de novo transcriptome sequencing technology, and 151516 unigenes with a total length of 190587631 bp were obtained by splicing the sequencing data. A total of 39163 EST-SSR loci were detected from 30262 unigene sequences at a frequency of 25.85%, of which 6635 (21.93%) contained two or more SSRs, and 3514 (11.61%) were compound SSRs. Primer pairs (PPs) were designed for all EST-SSR loci (in total, 22367 EST-SSR PPs). In addition, 100 PPs were synthesized randomly and preliminarily screened in two accessions (CF019650, CF020070), and 90 of them were determined to be clear and stable EST-SSR markers. Fifty-one PPs were randomly selected to assess the genetic diversity of 27 erect milk vetch accessions. The average allele number, average polymorphism information content, average expected heterozygosity, and average observed heterozygosity values obtained using the 51 PPs were 8.750, 0.682, 0.719, and 0.730, respectively. Principal coordinate and cluster analyses revealed clear germplasm specificity in the genetic distribution of accessions with creeping and erect ecotypes, as well as a relatively high correlation between clusters and geographic origin. These newly developed EST-SSR molecular markers will be useful for the genetic improvement of, and genomic research on, erect milk vetch, and can be used in molecular marker-assisted breeding, quantitative trait loci mapping, and genetic variation analyses.

Expression analysis of SaLDC promoter from Sophora alopecuroides in Arabidopsis thaliana

LU Shan-shan, HONG Yuan-shu, LIU Ping

2019, 28(11):  159-167.  DOI: 10.11686/cyxb2018755

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Lysine decarboxylase (LDC) gene is the first key enzyme gene in oxymatrine (OMA) biosynthesis in Sophora alopecuroides. The promoter sequence (1260 bp, gene bank accession number: KY038928) upstream of the gene (SaLDC) encoding lysine decarboxylase was cloned from S. alopecuroides genomic DNA. Its promoter activity was evaluated by transient expression in S. alopecuroides callus. A bioinformatics analysis showed that the promoter sequence contains a TATA-box, a CAAT-box, and other cis-acting elements such as drought-responsive, light-responsive, defense-responsive, stress-responsive elements, methyl jasmonate-responsive element, and tissue-specific expression element. To further study the functionality of the SaLDC promoter, a plant expression vector with the SaLDC promoter sequence fused to the GUS reporter gene (encoding β-glucuronidase) was transferred into Arabidopsis thaliana by Agrobacterium. β-glucuronidase activity was quantified by GUS staining and quantitative assays. We detected GUS activity in T₂ transgenic A. thaliana seedlings at different growth stages and in tissues of the adult plants. During seedling growth, GUS activity in the leaves decreased. In adult plants, GUS activity was higher in the leaves and calyxes than in the roots, stems, petals and pods. The expression of GUS was induced by simulated drought (polyethylene glycol, PEG) stress and light in transgenic A. thaliana. Quantitative analyses showed that GUS activity increased significantly in the early stage of PEG stress (1-2 h) (P<0.05) and then decreased to a minimum at 8 h (P<0.01), to around 28.2% of its original level. All these results show that the SaLDC promoter confers tissue-specific and spatio-temporal-specific expression, and that the expression of this structural gene is regulated by light and drought stress.

Effects of oregano essential oil on nutrient degradability, rumen fermentation, and CH₄ production in sheep

ZHOU Rui, LIU Li-shan, WU Jian-ping, WEI Sheng, LANG Xia, WANG Cai-lian

2019, 28(11):  168-176.  DOI: 10.11686/cyxb2019124

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We evaluated the effects of oregano essential oil on the nutrient degradability, rumen fermentation, and CH₄ production of sheep in an in vitro fermentation system. The experiment had a single-factor design. Oregano essential oil (OEO) was added to the medium at four different levels: 0 (CON), 100 (EO₁), 400 (EO₂), 700 (EO₃), and 1000 mg·L^-1 (EO₄). Each group had four replicates. After fermentation for 48 h, nutrient degradability and fermentation parameters were measured. The total gas and CH₄ production were measured at 1, 3, 6, 9, 12, 18, 24, 36, and 48 h during fermentation. The main results were as follows: 1) Dry matter degradability (DMD), crude protein degradability (CPD), and neutral detergent fiber degradability (NDFD) were significantly increased in the EO₁ group (P<0.05), significantly decreased in the EO₄ group (P<0.05), and unaffected in the EO₂ group (P>0.05) compared with the CON group. The DMD was significantly higher in the EO₃ group than in the CON group (P<0.05). Addition of OEO did not affect the acid detergent fiber degradability (ADFD) (P>0.05); 2) Among all groups, the EO₁ group had the lowest pH but the highest concentrations of total volatile fatty acids (TVFA) and propionate. The acetate concentration was higher in the EO₁ group than in the EO₂, EO₃, and EO₄ groups (P=0.011), however, the percentage of acetate/TVFA was significantly lower in the EO₁ group than in the EO₃ and EO₄ groups (P<0.001), and the ratio of acetate/propionate was significantly lower in the EO₁ group than in the CON group (P<0.05). Compared with the CON group, all the EO groups showed significantly decreased concentrations of butyrate and NH₃-N, and lower butyrate/TVFA ratios (P<0.05); 3) The total gas production and CH₄ production after 36 h of fermentation decreased as the OEO dose increased. Compared with the CON group, the EO₁ group showed significantly decreased total gas production from 18 to 48 h of fermentation (P<0.05), and the EO₂, EO₃, and EO₄ groups showed significantly decreased total gas production and CH₄ production after 18 h of fermentation (P<0.05). Compared with the CON group, all EO groups showed significantly lower CH₄ production from 12 to 36 h of fermentation (P<0.05). In summary, supplementation with oregano essential oil can improve nutrient degradability, regulate rumen fermentation, and decrease total gas and CH₄ production; the optimal supplementation level is less than 100 mg·L^-1 in in vitro fermentation conditions.

Relationships between alfalfa leaf nutrient resorption and stoichiometric ratios of nitrogen, phosphorus, and potassium

WANG Zhen-nan, ZHAO Mei, YANG Yan, LI Fu-kuan, WANG Hui, LÜ Shen-jin

2019, 28(11):  177-183.  DOI: 10.11686/cyxb2018750

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Alfalfa is an excellent legume with strong environmental adaptability. Leaf nutrient resorption is an important mechanism to improve nutrient use efficiency and enhance environmental adaptability. It directly affects the nutrient concentration, and consequently, the stoichiometric ratio of elements in alfalfa. Many studies have focused on the nutrient resorption and ecological stoichiometric characteristics of alfalfa, but few have focused on the relationship between nutrient resorption and stoichiometric ratios. To explore this relationship, we measured the concentrations of carbon, nitrogen, phosphorus, and potassium in the mature and senescent leaves of seven alfalfa cultivars. Then, the characters and the relationships between resorption (including resorption efficiency and resorption proficiency) and stoichiometry were analyzed. It was found that the average nitrogen, phosphorus, and potassium resorption efficiencies of alfalfa were 42.7%, 42.4%, and 52.1%, respectively, lower than those of global terrestrial plants (62.1%, 64.9%, and 70.1%, respectively). On the basis of the relationship between nutrient resorption and stoichiometric ratios, we concluded that the growth of alfalfa stands was limited by phosphorus in our study region. The leaf resorption efficiencies were positively correlated with the stoichiometric ratios in senescent leaves, but the opposite conditions were detected in the mature leaves. Thus, there is a close link between nutrient resorption and stoichiometric ratios, and this relationship is significantly affected by the growth status of the leaf (mature vs. senescent).

Relationship between vegetation community and soil moisture in the loess region of northern Shaanxi Province

PUYANG Xue-hua, WANG Chun-chun, GOU Qing-ping, ZHAO Zhi-jie, HUANG Juan

2019, 28(11):  184-191.  DOI: 10.11686/cyxb2018775

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We analyzed the trend in soil water content in the 0-100 cm soil layer and its relationship with the species diversity of vegetation community. These analyses were conducted in three reference regions with different precipitation conditions; Baibao, Chaigou and Wangwazi, in Wuqi County, Shaanxi Province. The overall aim of these analyses was to obtain reference information to devise strategies for vegetation construction and landscape configuration in the local loess region. The results showed that the amount of precipitation in Wuqi County gradually decreased from southeast to northwest. There were 57 species of 47 genera in 20 families in the three reference regions, among which 38 species of 29 genera in 12 families were herbage, and 61.7% of the genera and 68.4% of the species were in the Asteraceae, Poaceae, Rosaceae, and Fabaceae. The soil water content in the 0-100 cm soil layer in Baibao, Chaigou and Wangwazi was 14.4%, 12.7%, and 8.7%, respectively. With decreasing precipitation in the three regions, the importance values of herbage varied significantly, but the composition of vegetation communities was similar among the three regions. The values of the species richness index, Shannon-Wiener index, Pielou index, and Simpson’s index of the vegetation community decreased from Baibao to Chaigou to Wangwazi. There was a significant positive correlation between soil water content and the species diversity index of the vegetation community. In conclusion, herbaceous species were the most abundant in the three reference regions. The soil moisture content in the 0-100 cm soil layer was significantly affected by the precipitation gradient, and was closely related to vegetation community characteristics.

Effects of boron foliar spray on grain-setting characteristics of Chinese milk vetch (Astragalus sinicus)

ZHENG Chun-feng, LIU Chun-zeng, LI Ben-yin, Lü Yu-hu, PAN Zi-liang, CAO Wei-dong

2019, 28(11):  192-199.  DOI: 10.11686/cyxb2018811

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Boron is an essential trace element for plant growth and development, with special functions in pollen tube elongation and the synthesis and transport of carbohydrates. The aim of this study was to determine the effect of applying boron as a foliar spray on flowering and the development of pods and grains, with an overall aim to increase the number of grains per pod and improve yield. The Chinese milk vetch cultivar “Xinzi No.1” was subjected to six different foliar application treatments; water (control) and borate solution (500 mg·L^-1, T₁; 1000 mg·L^-1, T₂; 2000 mg·L^-1, T₃; 4000 mg·L^-1, T₄; 6000 mg·L^-1, T₅), which were applied at the pre-flowering stage. When the plants reached the mature stage, the number of inflorescences, pods, grains per pod for different inflorescence positions (1 lowest on the raceme, 6 highest) and the number of plants and branches per unit area were determined using conventional test methods. The number of inflorescences and pods unit area, grain set rates of pods, and number of grains per pod for different inflorescence positions did not differ significantly between the control and the treatments, except for the T₃ treatment. In the 3rd to 6th inflorescence positions, the number of inflorescences per unit area was increased by 31.87%, 40.79%, 37.49%, and 44.99%, respectively; the number of pods per unit area was increased by 27.89%, 32.69%, 35.92% and 25.84%, respectively; the number of grains per pod was increased by 20.69%, 23.54%, 23.24%, and 22.03%, respectively; and the grain set rates of pods was increased by 2.95%, 2.56%, 3.49% and 4.51%, respectively, in the T₃ treatment as compared with the water control. However, these parameters in the 1st and 2nd inflorescence positions did not differ significantly between the T₃ treatment and the control. Further analyses showed that spraying boron at different concentrations had little effect on first-order branching and 1000-grain weight of Chinese milk vetch. Our results show that, when applied at the pre-flowering stage, a foliar application of boron (2000 mg·L^-1) can significantly increase the number of inflorescences, pods, and grains per pod per unit area at the 3rd to 6th inflorescence positions, thereby increasing the grain-setting rates of pods and increasing the grain yield of Chinese milk vetch.