Table of Content

20 December 2018, Volume 27 Issue 12

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Effects of 7-year enclosure on an alpine meadow at the south-eastern margin of Tibetan Plateau based on community structure and soil physico-chemical properties

ZHOU Tian-yang, GAO Jing, WANG Jin-niu, SUN Jian, XU Bo, XUE Jing-yue, HE Jun-dong, XIE Yu, WU Yan

2018, 27(12):  1-11.  DOI: 10.11686/cyxb2018084

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Over-grazing on the Tibetan Plateau is a human disturbance that has occurred for a long time. It has seriously harmed the structure, function, and services of the alpine meadow ecosystem. Because of its simplicity and effectiveness, enclosure has been widely used for the restoration of deteriorated grassland. However, it can have positive and negative effects, so it is vital to assess the quality of grassland under enclosure systematically and scientifically. The aim of this study was to comprehensively assess the quality of an alpine meadow after 7 years of enclosure. The quality of the alpine meadow was analyzed by determining community biomass, species biodiversity, and soil physico-chemical properties. After 7 years of enclosure, most of the indexes related to soil physico-chemical properties had improved to a certain extent, but only nitrate N had increased significantly (by almost double). Community biomass and plant litter were 35.73% and 65.75% greater, respectively, in the enclosed area than in the grazed area. However, there was no significant difference in species diversity between the enclosed and grazed areas. A principal component analysis showed that the soil quality was better in the enclosed area than in the grazed area (mean comprehensive scores of 0.1 and -0.02, respectively). The effects of various factors on meadow quality were evaluated by analyzing the association between biomass weight values and certain indexes. The meadow quality was restored after 7 years of enclosure, and this was largely due to improved soil physico-chemical properties. In summary, enclosure plays a positive role in restoring deteriorated alpine meadow. Further studies should assess the restoration effect of enclosure on deteriorated grassland at regular intervals to understand the timing and duration of its restorative effects.

Spatial distribution characteristics of nitrogen and phosphorus in soil on the Gannan Plateau

ZHANG Yao-yao, LENG Ruo-lin, CUI Xia, SONG Qing-jie, XU Gang

2018, 27(12):  12-21.  DOI: 10.11686/cyxb2018085

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Recently, grassland degradation and ecosystem structural disorders caused by inappropriate use of grassland resources have become more common. Studies on the physical and chemical properties of soil are great significance for controlling grassland degradation, maintaining the balance of grassland ecosystems, and promoting the sustainable development of grassland animal husbandry. Soil nitrogen and phosphorus are important components of soil nutrients in grassland. The purpose of this study was to analyze the spatial distribution of soil total nitrogen and total phosphorus on the Gannan plateau. Using classical statistical and geostatistical methods, we focused on the vertical distribution of soil total nitrogen and total phosphorus, and variations in the nitrogen and phosphorus contents in soil among sampling areas on the basis of ground-measured data. After determining the characteristics of total nitrogen and total phosphorus contents at different elevations and different soil depths, we analyzed the correlations among total nitrogen, total phosphorus, N/P, C/N, soil organic matter, and soil moisture. The results showed that: 1) Total nitrogen content in the surface of grassland gradually decreased from southwest to northeast and from west to east of the study area. Similar to the distribution of total nitrogen content, total phosphorus content changed from southwest to northeast and from west to southwest. Total nitrogen and total phosphorus contents showed medium variability at the 0-40 cm soil depth. The variation in total nitrogen content was higher at 20-40 cm depth than at 0-20 cm depth. The variation in total phosphorus content increased with soil depth. The total nitrogen and total phosphorus contents gradually decreased with soil depth, but the total nitrogen and total phosphorus contents tended to be higher in the surface layer than in lower layers. The phenomenon of surface aggregation was common. 2) The total phosphorus content was significantly (P<0.01) correlated with total nitrogen content in the 0-10 cm, 10-20 cm, and 20-30 cm soil depths. The correlation coefficient progressively decreased with soil depth, and became insignificant in the deeper soil layers (30-40 cm). The N/P ratio was highly significantly correlated with total nitrogen content, but showed a weaker correlation with total phosphorus content. There were significant (P<0.05) positive correlations between soil organic matter content and total phosphorus content and the N/P ratio. The factors affecting soil organic matter content could be ranked, from strongest correlation to weakest, as follows: total nitrogen>N/P ratio>total phosphorus. Soil organic matter and soil moisture content were very significantly positively correlated in all soil layers. 3) The total nitrogen and total phosphorus contents in soil increased with increasing elevation. However, the coefficients of variation of total nitrogen and total phosphorus increased with soil depth at the same altitude.

Effects of different management strategies on soil organic carbon and nitrogen pools in arid areas and their influencing factors

JIANG La-mei, YANG Xiao-dong, YANG Jian-jun, HE Xue-min, LÜ Guang-hui

2018, 27(12):  22-33.  DOI: 10.11686/cyxb2018062

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The organic carbon content and total nitrogen content in soil and their dynamic balance are important indicators of the quality of soil and grassland. The aim of this study was to determine the effects of different management strategies on the quality of soil and grassland in the Xinjiang Aletai area. We analyzed soil in grasslands under three different management strategies (natural pasture, grazed pasture, and abandoned grassland), and determined soil organic carbon content, total nitrogen content, soil moisture, aggregate structure, pH, soil bulk density, and the relationships among these parameters. The soil carbon∶nitrogen ratio, total nitrogen content, organic carbon content, and total nitrogen reserves increased significantly with increasing soil depth (P<0.05). The soil total nitrogen contents and organic carbon contents in the 0-10 cm, 10-30 cm, and 30-50 cm soil layers were higher in natural grassland and grazed grassland than in abandoned grassland, but the soil carbon∶nitrogen ratio did not differ among the three types of grasslands. In the 0-10 cm, 10-30 cm, and 30-50 cm soil layers, soil conductivity and pH were significantly higher in grazed grassland than in natural grassland (P<0.05). In the 0-10 cm and 30-50 cm soil layers, the soil moisture content was significantly higher in grazed grassland than in abandoned grassland (P<0.05). The intermediate aggregate content differed significantly between abandoned grassland and the other two types of grasslands (P<0.05). Data for soil carbon content, nitrogen storage, and physical and chemical factors were used in correlation and canonical correlation analyses. In these analyses, the soil water content, aggregates, intermediate aggregates, micro aggregates, pH, and conductivity were explanatory variables, and soil nitrogen reserves and soil organic carbon reserves were the response variables. The explanatory factors explained up to 75.70% of the variation in soil nitrogen and soil organic carbon reserves, with soil moisture and aggregate structure showing strongest correlations with the response variables. We concluded that the soil carbon and nitrogen contents and reserves differed among the different management strategies, and that soil moisture content and soil aggregate structure were the main variables affecting soil carbon and nitrogen pools. Water content was strongly related to soil moisture and aggregate structure.

Profile distribution and dynamics of soil organic carbon and total nitrogen in the Horqin meadow wetland during the growing season

WANG Xue-qin, LIU Ting-xi, ZHANG Jun-yi, WANG Guan-li, DUAN Li-min

2018, 27(12):  34-44.  DOI: 10.11686/cyxb2018024

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Wetlands are highly productive ecosystems and serve as an important component of global carbon and nitrogen cycles. To better understand the functions of wetlands, more accurate estimations of soil organic carbon (SOC) and total nitrogen (TN) reserves in these environments are needed. In this study, soil samples were taken down to a depth of 100 cm twice a month from May to October 2016 and in August 2017 to analyze the profile distributions and dynamics of SOC and TN in the Horqin meadow wetland. The contents of SOC and TN, above- and below-ground biomass, and other soil physicochemical properties such as soil pH were determined. Our results showed that: 1) Both SOC and TN contents decreased significantly with soil depth in the surface layer (0-20 cm), but tended to remain relatively stable in the subsurface layer, ranging from 11.9 to 23.5 g·kg^-1 and from 0.66 to 1.50 g·kg^-1, respectively. 2) The monthly variations in SOC and TN contents were significant (except for TN content in the 40-60 cm layer), and the magnitude of variation first decreased and then increased with soil depth. The variations in SOC and TN densities (0-100 cm) were larger during the whole growing season than among years. The SOC density increased during the whole growing season, and ranged from 15.44 to 20.82 kg·m^-2, while the TN density decreased significantly in the early growth period and then tended to remain relatively stable, ranging from 1.01 to 1.16 kg·m^-2. 3) There was a significant positive correlation between SOC content and TN content (P<0.01). Vegetation and hydrology were the key factors affecting the distribution and variations of SOC and TN in the Horqin meadow wetland. The Horqin meadow wetland was found to be a potential carbon sink and nitrogen source during the growing season, but the carbon sink potential has not been fully evaluated on an inter-annual scale. The results indicated that grazing should be banned and nitrogen fertilizer inputs should be increased to enhance the wetland’s function.

Effect of rotation sequence on stability of soil organic carbon in dry-land oil flax

LIU Dong, CUI Zheng-jun, GAO Yu-hong, YAN Bin, ZHANG Zhong-kai, WU Bing

2018, 27(12):  45-57.  DOI: 10.11686/cyxb2018097

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The aim of this study was to determine the effects of the flax rotation sequence on the soil carbon pool in a dry?land oil flax cropping area. A field experiment was conducted in a typical semiarid gully area of the Loess Plateau from 2012 to 2016 to study the effects of six rotation sequences with different flax frequencies (fallow; PWFW: 25% flax, potato?wheat?flax?wheat; WFWP: 25% flax, wheat?flax?wheat?potato; FWPF: 50% flax, flax?wheat?potato?flax; WPFF: 50% flax, wheat?potato?flax?flax; FFFF: 100% flax, flax?flax?flax?flax). We measured soil aggregates, total organic carbon (TOC), particulate organic carbon (POC), microbial biomass carbon (MBC), and nitrogen (MBN) in all the treatments. A continuous cropping treatment served as the control. The results showed that the fallow treatment and a lower frequency of flax significantly increased the <0.25 mm soil aggregate content, TOC content, and POC content in the 0-30 cm soil layer. All of these parameters decreased with increasing flax frequency. The soil aggregate contents in the 25% flax treatments were 2.02%-4.04% higher and 9.56%-11.73% than those pre?sowing and in the fallow treatment, respectively. The SOC was 5.95%-7.48% higher in the 25% flax treatments than in the continuous cropping treatment. In the 50% flax treatments, the timing of the flax crop in the rotation sequence significantly affected soil SOC. The SOC content was significantly higher in the FWPF treatment than in the WPFF treatment. The treatments could be ranked, from highest soil SOC content in the 0-60 cm layer to lowest, as follows: fallow>pre?sowing≈25% flax>50% flax>100% flax. Compared with continuous cropping, rotation significantly increased the soil TOC and POC contents in the 0-10 cm soil layer, consistent with the phenomenon of surface enrichment. The treatments could ranked, from highest soil POC content to lowest, as follows: 25% flax≈fallow>50% flax>100% flax. In addition, crop rotation treatments significantly increased the soil MBC content. The soil MBC content in the 0-30 cm layer decreased gradually with increasing flax frequency. Compared with pre?sowing, fallow, and crop rotation treatments, continuous cropping significantly reduced the ratio of soil microbial C/N. The SOC and microbial biomass were significantly affected by the interaction between the 50% flax rotation sequence and soil depth. These results indicated that a fallow treatment could significantly improve the soil physical and chemical properties. The 25% flax rotation sequence could maintain the stability of soil aggregates and increase soil TOC, SOC, and POC contents. The 50% flax rotation sequence could improve the soil microbial biomass and the ratio of soil microbial C/N. Because the rotation sequence with 25% flax frequency could maintain the stability of SOC, it was identified as the ideal rotation sequence for dry?land oil flax crops.

Characteristics of inorganic phosphorus in lime concretion black soil under continuous straw-return and fertilization in a rice-wheat rotation area

ZHAO Qing-lei, XIN Cai-yun, WANG Yu, WANG Jia, LIU Qi-hua, LI Jing-ling, MA Jia-qing

2018, 27(12):  58-68.  DOI: 10.11686/cyxb2018280

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The aim of this study was to determine the effects of straw return and chemical fertilizer application on the inorganic phosphorus content in lime concretion black soil. Therefore, we conducted a multi-year field experiment with various straw return and fertilization treatments, and analyzed the profiles and accumulation characteristics of different forms of inorganic phosphorus in soil. The field experiment had six treatments: conventional fertilizer application+straw total return (HN₁); 50% of conventional fertilization+straw total return (HN₄); no fertilizer+straw total return (HN₀); conventional fertilization+straw removal (N₁); 50% of conventional fertilization+straw removal (N₄); and no fertilizer+straw removal (N₀). The results showed that under the same level of chemical fertilizer application, straw return significantly increased the contents of soil Ca₂-P and Fe-P by up to 219.05% and 51.35%, respectively, compared with those in the straw removal treatments. The proportions of Ca₂-P and Fe-P out of total inorganic phosphorus also increased significantly with straw return. In general, the Ca₈-P and Al-P contents decreased to some extent while Ca₁₀-P decreased significantly, and the total amount of inorganic phosphorus increased when straw was returned. The activation of inorganic phosphorus in soil with straw return and chemical fertilizer application decreased with decreasing amounts of fertilizer and increasing soil depth. The application of chemical fertilizers without straw return significantly reduced the contents of Ca₂-P, Ca₈-P, Al-P, and Fe-P in the soil. Compared with straw removal alone, straw removal+chemical fertilizer promoted the conversion and decomposition of potential phosphorus sources such as Ca₁₀-P. The main forms of inorganic P in soil were Ca-P (Ca₂-P, Ca₈-P, and Ca₁₀-P) and Fe-P. Under conventional fertilization conditions, straw return resulted in a rapid increase in Olsen-P content in soil. Under 50% conventional fertilization, straw return increased the Olsen-P content in surface soil. Returning straw to soil without fertilizer application did not significantly increase the Olsen-P content in soil. The correlations between soil Olsen-P and soil Ca₂-P, Ca₈-P, Al-P, and Fe-P reached significant or extremely significant levels, indicating that these four forms of inorganic P were closely related to soil Olsen-P, and may be important sources of available P in the soil. Therefore, the no-fertilizer and straw returning treatment could accelerate the depletion of inorganic P in soil. Together, the results showed that the rational application of straw and chemical fertilizers can improve the soil P supply by converting low-activity inorganic P into high-activity forms of inorganic P such as Ca₂-P and Fe-P.

spatial distribution characteristics of nitrogen and phosphorus in soil on the Gannan Plateau

SU Xin, LU Man, FENG Cheng?cheng, GUO Ying?lan, YUE Zhong?hui

2018, 27(12):  69-78.  DOI: 10.11686/cyxb2018049

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The aim of this study was explore the relationship between soil enzyme activity and plant community characteristics in degraded saline?alkali grasslands. Therefore, we conducted a field study to determine relationship between soil enzyme activity and plant community characteristics in different growing seasons in saline?alkali grassland on the Songnen Plain. The relationship between soil enzyme activity and plant community characteristics differed among the different growing seasons. There was a significant negative correlation between polyphenol oxidase activity and Shannon’s index (P<0.05). Peroxidase activity was negatively correlated with Simpson’s index, richness index, and Shannon’s index (P<0.05, P<0.01). Invertase activity was positively correlated with alkaline phosphatase activity and with the Pielou index (P<0.05). Stepwise regression analyses of soil enzyme activity and plant community characteristics indices in different months were conducted. The results showed that there were quantitative relationships between peroxidase activity and Shannon’s index, and between invertase activity and evenness index in May. In July, alkaline phosphatase activity was quantitatively related with Simpson’s index and with the Pielou index. In August, there was a quantitative relationship between polyphenol oxidase activity and Simpson’s index. The results of a canonical correspondence analysis (CCA) showed that only polyphenol oxidase activity was correlated with plant community characteristics during the whole growing season. In general, although soil enzyme activities showed certain correlative or quantitative relationships with plant community characteristics in different growing seasons, the strongest correlation was between polyphenol oxidase activity and the community characteristics index. This relationship can be used to evaluate changes in plant community characteristics of degraded saline?alkali grasslands.

Size?dependent reproductive allocation of Artemisia scoparia in different habitats on the desert steppe

CHEN Lin, LI Yue?fei, SU Ying, SONG Nai?ping, YANG Xin?guo, WANG Lei,BIAN Ying?ying, YANG Li?na

2018, 27(12):  79-93.  DOI: 10.11686/cyxb2018203

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The reproductive allocation of plants is an important factor in the theory of life history. The distribution of heterogeneous habitats is an important environmental factor affecting plant species on the desert steppe. To study the reproductive allocation strategies of plants on the desert steppe, we selected Artemisia scoparia growing in heterogeneous habitats (aeolian sandy soil, sierozem soil, and weathering bedrock) and evaluated the biomass characteristics of individuals of different sizes. We analyzed the relationships between biomass and biomass position, and evaluated the absolute inputs to reproductive organs and the characteristics of reproductive allocation. The results showed that aboveground biomass, underground biomass, reproductive organ biomass, vegetative organ biomass, number of reproductive bodies, and weight of reproductive bodies of A. scoparia were lower in plants growing on weathering bedrock than in plants growing in aeolian sandy soil and sierozem soil. There were no significant differences in aboveground biomass, number of reproductive bodies, weight of reproductive bodies, and single capitulum mass among different parts of single plant (P>0.05), suggesting that there was no difference in observed resource input in A. scoparia. The absolute input to reproductive organ biomass (lg R) increased as the size of the individual plant (lg V) increased (P<0.001), indicating that vegetative growth and resource input to reproduction in A. scoparia increased simultaneously. The reproductive thresholds of A. scoparia growing on weathering bedrock, aeolian sandy soil, and sierozem soil were 2.07, 1.96, and 1.99 g, respectively, and there was a negative correlation between reproductive allocation and individual size in the different habitats (P<0.05). There were negative correlations between single capitulum mass and individual size, and between single capitulum mass and the number of capitula on each plant. These differences reflected phenotypic plasticity in the resource allocation of A. scoparia, but there were no significant correlations between these trade?offs (P>0.05).

Effects of grazing on ecological stoichiometry of soil and dominant plants in desert grassland

AN Yu, AN Hui, LI Sheng-bing

2018, 27(12):  94-102.  DOI: 10.11686/cyxb2018039

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To determine the effect of grazing intensity on ecological stoichiometry characteristics, we evaluated the carbon (C), nitrogen (N), and phosphorus (P) contents in soil and dominant plants in desert grassland of Ningxia under different grazing intensities. The results showed that the C content and ratios of C∶N and C∶P in soil decreased with increasing grazing intensity, while the P content increased, and the N content and N∶P ratio decreased after an initial increase. The N contents in different dominant plants showed different responses to grazing intensity. The N contents in Glycyrrhiza uralensis, Oxytropis racemosa, Ixeris chinensis, and Cynanchum komarovii were significantly lower under moderate and heavy grazing intensities than under light grazing intensity and no grazing. The N contents in Lespedeza potaninii, Stipa breviflora, Pennisetum centrasiaticum, Oxytropis aciphylla, Corispermum hyssopifolium, Salsola collina, Euphorbia esula, and Peganum harmala were significantly higher under moderate and heavy grazing intensities than under light grazing intensity and no grazing. These results indicated that an appropriate grazing intensity could significantly increase the N content of some species. The trends in C∶N and C∶P ratios in the 13 dominant plants were opposite to the trends in N and P contents under different grazing intensities, and the effect of grazing on the N∶P ratio differed among the different dominant plant species. The P content and C∶P ratio of dominant plants were significantly positively correlated with the P content and C∶P ratio of soil, but there was no correlation between the C and N contents and the C∶N and N∶P ratios in dominant plants and those in soil. These findings indicated that the stoichiometric characteristics of plants were affected by the genetic characteristics of plants, and not directly determined by soil nutrient contents. This helps to explain why dominant plants have a relatively stable ability to adapt the extreme environment in desert grassland.

Arbuscular mycorrhizal fungi (AMF) enhance phytoremediation of strontium-contaminated soil by Sorghum bicolor seedlings

QI Lin, YANG Ying-bo, ZHANG Bo, ZHAO Wei, WANG Xiao-ling, LIU Yu-hua

2018, 27(12):  103-112.  DOI: 10.11686/cyxb2018333

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In this study, we determined the effects of arbuscular mycorrhizal fungi (AMF) on the ability of Sorghum bicolor to remediate soil polluted with strontium (Sr). Seedlings of S. bicolor were inoculated with Glomus geosporum, Glomus mosseae, Glomus versiforme, or Glomus diaphanum, to compare the effects of different AMF on the strontium accumulation capacity of S. bicolor. All the AMF had infection rates of >50%, and G. versiforme showed the highest infection rate (75%). The largest biomass increases were in plants inoculated with G. geosporum and G. mosseae. The shoot biomass and root biomass of seedlings inoculated with G. geosporum increased by 54.72% and 53.26%, respectively, compared with uninoculated seedlings. Sorghum seedlings showed significant mycorrhizal dependency (P<0.05), suggesting that AMF promoted their growth. Among the AMF, G. geosporum and G. mosseae significantly increased the biomass of sorghum seedlings, and the mycorrhizal dependencies of sorghum for these two AMF were 154.44% and 147.61%, respectively. The shoot and root Sr concentrations were significantly higher (P<0.05) in AMF-inoculated sorghum than in uninoculated seedlings, and the translocation factors of AMF-inoculated sorghum were all >1. The Sr concentrations were 30.18%-86.05% higher in G. geosporum-inoculated sorghum seedlings than in uninoculated seedlings. The total phosphorus and available phosphorus contents in sorghum seedlings were significantly (P<0.05) decreased by inoculation with G. geosporum, G. mosseae, and G. versiforme; the total phosphorus content was decreased by 15.89%-20.32%, and the available phosphorus content was decreased by 12.98%-18.49%. The activity of soil phosphatase was 21.43%-30.36% higher in AMF treatments than in controls (P<0.05). The soil invertase activities were 25.77%-28.87% higher in the G. geosporum, G. mosseae, and G. versiforme treatments than in controls. In conclusion, AMF enhanced the ability of S. bicolor to accumulate and tolerate Sr, and G. geosporum was the most effective AMF.

Relationship between organic acids secreted from rhizosphere phosphate?solubilizing bacteria in Trifolium pratense and phosphate?solubilizing ability

LI Hai?yun, YAO Tuo, ZHANG Rong, ZHANG Jie, LI Zhi?yan, RONG Liang?yan, LU Xiao?wen, YANG Xiao?lei, XIA Dong?hui, LUO Hui?qin

2018, 27(12):  113-121.  DOI: 10.11686/cyxb2018066

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This study represents a preliminary exploration of the relationship between organic acid secretion and the phosphate?dissolving ability of rhizosphere phosphate?solubilizing bacteria. Four strains of excellent phosphate?solubilizing bacteria were selected from Trifolium pratense and cultured in improved PKOC2 liquid medium. The pH, phosphate?solubilizing ability, and the types and quantities of organic acids secreted were dynamically monitored by molybdenum blue colorimetry and high performance liquid chromatography (HPLC). The results showed that the strains MHS7, MHS27, MHS30, and MHS49 all secreted lactic acid, oxalic acid, malic acid, fumaric acid, and succinic acid, and strain MHS30 also secreted tartaric acid. In strain MHS7, the phosphate?solubilizing ability was negatively correlated with pH (P>0.05). In strain MHS27, the phosphate?solubilizing ability was positively correlated with pH (P>0.05) and lactic acid content (P<0.05). In strain MHS30, the phosphate?solubilizing ability was negatively correlated with pH (P<0.05), and positively correlated with the amount of organic acids secreted (P<0.01) and the tartaric acid content (P<0.05). In strain MHS49, the phosphate?solubilizing ability was significantly positively correlated with the succinic acid content (P<0.05). The types and quantities of organic acids secreted differed among the four bacterial strains. The phosphate?solubilizing ability of phosphate?solubilizing bacteria was correlated with the total organic acids content, and was also influenced by the types and quantities of organic acids released. However, the effective increase in effective phosphorus content was not determined by the total organic acids content. There were diverse relationships between the phosphate?solubilizing ability of different bacterial strains and the types and amounts of organic acids they released. These findings suggested that different phosphorus?solubilizing pathways exist in different strains of phosphate?solubilizing bacteria.

Effects of water and nitrogen supply on growth and microclimate characteristics of alfalfa under drip irrigation

HU Wei, ZHANG Ya-hong, LI Peng, LIU Rui, CAI Wei, WANG Xiao-ju

2018, 27(12):  122-132.  DOI: 10.11686/cyxb2018050

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The overall aim of our research is to improve the microenvironment ecological factors of alfalfa and to recommend appropriate regulation of water and fertilizer use based on scientific evidence. In this study, the relationship between the amounts of inputs (irrigation and nitrogen fertilizer) and the growth and microclimate characteristics of alfalfa were investigated in a 2-year drip-irrigation field experiment in the Yellow River irrigation region of Ningxia. The results showed that the amounts of drip irrigation and nitrogen fertilizer significantly affected the plant height, leaf area, and yield of alfalfa. Compared with the no-fertilizer treatment, fertilization decreased the air temperature, soil temperature, and illumination within the alfalfa stand, but increased the relative humidity. The microenvironment of alfalfa varied among the different irrigation treatments. As the amount of irrigation increased, the relative humidity in the alfalfa stand gradually increased, and the cooling effects on air temperature and soil temperature became stronger. There were strong positive correlations between plant height and leaf area, grass biomass, and relative humidity. There were significant negative correlations between plant height and illumination, temperature, and soil temperature. Therefore, a reasonable decrease in the amount of irrigation and nitrogen fertilizer can not only maintain good growth of alfalfa, but also increase grass yield and improve grassland ecological conditions.

Effects of incorporating Chinese milk vetch on reductive material characteristics and greenhouse gas emissions in paddy soil

CHANG Dan-na, LIU Chun-zeng, LI Ben-yin, LÜ Yu-hu, PAN Zi-liang, GAO Song-juan,CAO Wei?dong

2018, 27(12):  133-144.  DOI: 10.11686/cyxb2018029

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A 28?day laboratory incubation experiment was conducted to explore the environmental impacts of incorporating Chinese milk vetch into paddy soil. Chinese milk vetch was incorporated into soil at rates of 0 (CK), 15000, 30000, and 45000 kg?ha (M1, M2, and M3, respectively), and the dynamic changes in reducing substances and greenhouse gas emissions in paddy soil were monitored. Incorporation of Chinese milk vetch significantly increased the total soil reducing substances, active reductive material, and the concentrations of iron and manganese ions (Fe2+ and Mn2+) in paddy soil, but decreased the soil redox potential (Eh). Compared with CK, the M1, M2, M3 treatments increased total soil reducing substances by 0.34, 0.80, 1.16 cmol?kg-1, respectively; increased the active reductive material content by 0.14, 0.35, and 0.52 cmol?kg-1, respectively; increased the average Fe2+ content by 87.91, 182.91, and 280.61 mg?kg-1, respectively; increased the average Mn2+ content by 10.12, 12.77, and 15.73 mg?kg-1, respectively, and decreased the average Eh by 32.88, 47.98, and 57.26 mV, respectively. The total reducing substances content peaked after 0.5 months of incubation. The Fe2+ content in the M3 treatment increased to >400 mg?kg-1, which may result in poisoning of rice seedlings. Incorporation of Chinese milk vetch significantly increased CO2 and CH4 emissions, but decreased N2O emissions, and ultimately increased the global warming potential. Compared with CK, the M1, M2, M3 treatments increased the average CO2 emission rate by 7.67, 12.48, and 20.54 mg?kg-1?d-1, respectively; increased the average accumulative emission of CO2 by 171.63, 293.42, and 498.45 mg?kg-1, respectively; increased the average CH4 emission rate by 0.04, 0.09, and 0.21 mg?kg-1?d-1, respectively; increased the average accumulative emission of CH4 by 0.36, 0.69, and 1.77 mg?kg-1, respectively; decreased the average N2O emission rate by 0.46, 0.64, and 0.72 μg?kg-1?d-1, respectively; and decreased the average accumulative emission of N2O by 10.00, 13.02, and 14.36 μg?kg-1, respectively. The global warming potential of the M1, M2, and M3 treatment was 1.59?times, 2.04?times, and 2.93?times higher, respectively, than that of CK. The CO2 and N2O emissions were mainly concentrated in the earlier period of incubation, while CH4 emissions were concentrated in the later period of incubation. The reducing substances content was positively correlated with CO2 and CH4 emissions, but negative correlated with N2O emissions. The results showed that incorporating Chinese milk vetch significantly increased the reducing substances content, enhanced CO2 and CH4 emissions, and decreased N2O emissions. Importantly, Chinese milk vetch incorporation increased the rice yield. Therefore, there is potential value in incorporating Chinese milk vetch into soil to maintain rice yield, but it should be incorporated at appropriate rates to reduce environmental impacts. Appropriate incorporation rates should be verified through pot and field experiments.

Effects of sowing methods on sowing quality growth and development of maize planted under full-film mulching in double-ridge burrows in Loess Plateau East of Gansu

ZHAO Gang, LI Shang-zhong, ZHANG Jian-jun, WANG Lei, DANG Yi, FAN Ting-lu, WANG Shu-ying^*, CHENG Wan-li

2018, 27(12):  145-155.  DOI: 10.11686/cyxb2018128

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The aim of this study was to clarify the effects of different sowing methods on the sowing quality, growth, and development of corn. Therefore, a 5-year field study was conducted in an arid area near Shangxiao, Zhenyuan County, in eastern Gansu Province. The cultivation pattern was full-film mulching in double-ridge burrows. The sowing quality, growth, and development of corn sown at various densities were determined. The density was controlled by increasing or decreasing row spacing and the amount of seeds sown. The results showed that sowing methods significantly (P<0.05) affected the rates of seedling emergence and survival of corn planted under full-film mulching in double-ridge burrows. Seedling emergence was 1.9% higher under single-seed sowing than under double-seed sowing, and rate of seedling survival was 100% higher under single-seed sowing with half-row spacing than under conventional sowing. Under three-seed sowing with multiple row spacing, light transmittance at the ears and stem bottoms was 10.7% and 4.6%, respectively, significantly higher than in other treatments. The photosynthetic rate during the jointing stage and dry matter accumulation at every growth stage did not differ significantly among the treatments. Under different treatments, the magnitude of changes in seed biomass, spike-stalk biomass, leaf biomass, subtending leaf biomass, and stem biomass amounted to 3.0%, 1.3%, 0.8%, 1.4% and 4.2%, respectively, but the sowing method did not affect dry matter accumulation and distribution. Indexes such as water use efficiency, yield, and water consumption varied significantly among the treatments (P<0.05). Water consumption did not vary significantly among treatments. Compared with the yields and water-use efficiencies under conventional sowing, those under single-seed sowing with half-row spacing were increased by 2.7% and 2.1%, respectively, and those under three-seed sowing with multiple spacing were increased by 1.2% and 2.5%, respectively. Under the cultivation pattern of full-film mulching in double-ridge burrows in an arid area in eastern Gansu Province, sowing methods affected the seedling emergence of corn, but did not affect corn yield or growth and development during later growth stages. Therefore, when mechanized sowing is used, methods such as single-seed sowing with half-row spacing can be chosen. When the sowing density is increased by 17% in terms of target density, such sowing methods as three-seed sowing with multiple-row spacing can be applied, with 2 seeds sown in each hole. This method can decrease the number of sowing holes by 50%.

Effects of vertical rotary sub-soiling on soil water characteristics and potato tuber yield in a semi-arid area of northwest China

ZHANG Xu-cheng, MA Yi-fan, YU Xian-feng, HOU Hui-zhi, WANG Hong-li, FANG Yan-jie

2018, 27(12):  156-165.  DOI: 10.11686/cyxb2018313

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The right tillage methods can improve the capacity of soil to supply water to crops and promote root development. This can result in better drought resistance of crops and higher productivity. Therefore, this is a promising strategy to increase the yield and water-use efficiency of potato (Solanum tuberosum) crops in a semiarid area. This study was conducted at the Dingxi Experimental Station of the Gansu Academy of Agricultural Sciences. The station is located in the northwest of Loess Plateau (Anding District, Dingxi, Gansu Province, 104°36' E, 35°35' N) at an altitude of approximately 1970 m. The field experiment was conducted under ridge-furrow planting and plastic-mulching conditions in 2016 and 2017. Potato (Longshu 10) was used as the material, and the three treatments included: 1) vertical rotary sub-soiling to 40 cm depth (VRT); 2) sub-soiling to 40 cm depth (DLT); and (3) traditional tillage to 15 cm depth (TT). The experimental design was a randomized block with three replicates, and the area of each plot was 10 m×6 m. The soil bulk density, soil total porosity, capillary porosity, soil saturation moisture content, capillary moisture content, field water capacity, soil wilted moisture content, total soil water content, and tuber yield were investigated. In addition, soil available water storage, evapotranspiration (ET), and water-use efficiency (WUE) were calculated to determine the effect of the different tillage treatments on soil water characteristics, potato tuber yield, and WUE. The results showed that VRT significantly decreased the soil bulk density; by 10.8%-25.3% and by 13.8%-24.8% as compared with DLT and TT, respectively. Compared with DLT and TT, VRT increased total soil porosity and capillary porosity by 12.3%-23.7% and 29.7%-46.6%, respectively, increased the soil saturation moisture content and capillary moisture content by 26.1%-54.4% and 38.8%-82.9%, respectively, and decreased the soil wilted moisture content by 11.0%-49.0%. Compared with the TT treatment, the DLT treatment resulted in lower soil bulk density and soil wilted moisture content, and higher soil saturation moisture content, capillary moisture content, total soil porosity, and capillary porosity. The optimized soil physical and hydrographic characteristics resulted in significant increases in soil available moisture in VRT (34.3%-136.9% higher than in DLT and 44.6%-575.2% higher than in TT). The soil available moisture content in the 20-40 cm soil layer was much higher in DLT than in TT. The significant increase in soil available water content in VRT resulted in increased potato plant growth (by 24.8%-156.8%), increased potato tuber yield (by 47.8%-41.0%), and increased WUE (by 18.9%-92.3% and 19.2%-26.6%), as compared with those in the DLT and TT treatments. The observed differences among the treatments were significant, and were greater in the drought year (2016) than in the normal year (2017). Consequently, VRT optimized the soil physical and hydrographic characteristics, increased soil available moisture, increased potato development and tuber yield, and improved WUE, with stronger effects in the drier year (2016). Thus, VRT is a promising method to improve drought resistance and increase the water-use efficiency of crops on the semiarid Loess Plateau.

Water- and fertilizer-use efficiency of cotton and Secale cereale cultivated under a multiple cropping pattern on the Haihe Plain

YOU Yong-liang, ZHAO Hai-ming, LI Yuan, WU Rui-xin, LIU Gui-bo, ZHAI Lan-ju

2018, 27(12):  166-176.  DOI: 10.11686/cyxb2018028

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The multiple cropping system on the Haihe Plain serves as an important overall driver of socio-economic development in the region. In this study, several multiple cropping patterns were established with different combinations of cotton and Secale cereale sown on four dates at Ren Town, Hebei Province, during 2011 to 2014. The feasibility of a multiple cropping pattern of cotton/S. cereale was analyzed in terms of yield, economic benefit, water-use efficiency, nutrient-use efficiency, and soil improvement. The results indicated that cotton/S. cereale multiple cropping was feasible. To reduce the influence on cotton yield, the best sowing date for S. cereale is around 20 October in the current year, and its harvest time should be at the end of April in the next year. Under these conditions, the economic benefit increased by 5470.1 yuan·ha^-1 according to our research. Compared with monoculture, the multiple cropping pattern improved water-use efficiency and water-economic-use efficiency by 16.49% and 56.54%, respectively. The multiple cropping pattern also improved soil quality; it increased soil organic matter by 5.71%, and decreased soil salinity by 23.72%, compared with monocropping. These results highlighted the importance of multiple cropping for socio-economic development in this region.

Effects of nitrogen fertilizer on community structure and nutritional quality of degraded grassland of Stellera chamaejasme under two different management measures

WANG Yu-qin, BAO Gen-sheng, SONG Mei-ling, YIN Ya-li, LIU Sheng-cai, YANG You-wu, YANG Ming, WANG Hong-sheng

2018, 27(12):  177-186.  DOI: 10.11686/cyxb2018179

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Fertilization is an effective management measure for the recovery of degraded grasslands. The aim of this study was to determine the effects of nitrogen fertilization on the community structure and nutritional quality of degraded alpine meadows of Stellera chamaejasme. We conducted a fertilization experiment with different amounts of nitrogen fertilizer [10 (N₁), 20 (N₂), 30 (N₃), 40 (N₄) kg·ha^-1], under two different management measures, clipping and prohibition of grazing. The density and above-ground biomass of S. chamaejasme were significantly lower under the two different management measures than in the control (P<0.05), and were decreased in the fertilization+prohibition of grazing treatments. In the area in which grazing was prohibited, the richness index was highest in N₄, but was not significantly different from that in CK (P>0.05). The Alatalo index was highest in N₁, and the Shannon-Wiener index was highest in the clipping+N₄ area. The Alatalo index was significantly higher in the clipping area than in the clipping+N₄ treatment (P<0.05), and the highest number of species was in the clipping area. The above-ground biomass was significantly higher in all the N-fertilization treatments than in CK (P<0.05). The above-ground biomass of the Cyperaceae was higher than that of the Gramineae. The total aboveground biomass and the biomass of functional groups did not differ significantly among the different fertilization treatments (P>0.05). Total biomass and the biomass of the Cyperaceae showed high rates of increase (47.21% and 48.24%, respectively). The highest rate of increase of the Gramineae was in the grazing-prohibition+N₄ treatment (119.35%). Overall, the nutrient contents of grass did not differ significantly (P>0.05) among the different fertilization treatments. However, the crude protein content was significantly higher in the grazing treatment than in the grazing+N₁ treatment. The crude ash content was significantly higher in the clipping+N₂ treatment than in CK, and the neutral detergent fiber content was significantly higher in the clipping treatment than in the clipping+N₂ treatment (P<0.05). The crude protein content per unit area did not differ significantly among the different fertilization treatments (P>0.05). The crude fat content per unit area was significantly higher in the grazing+N₄ treatment than in the grazing treatments and CK (P<0.05), and significantly higher in the clipping+N₁ treatment than in CK (P<0.05).

Effects of mixed sowing ratio and mowing period of Medicago sativa and Bromus inermis on silage quality in cold regions of north China

KUANG Xiao, JI Jing, LIANG Wen?xue, CUI Guo?wen, JI Guo?xu, CUI Xin, LIU Jian,HU Guo?fu

2018, 27(12):  187-198.  DOI: 10.11686/cyxb2018027

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The aim of this study was to determine optimal conditions for the production of silage from Medicago sativa and Bromus inermis. The two crops were sown at different proportions and both were mowed each year. Silage tests were carried out in the early flowering period and full?bloom period of first stubble, and in the full?bloom period of second stubble in the third year. The results for silage tests conducted at the flowering period of second stubble have been published previously. The nutritional indicators and fermentation indicators of silage made from mixed forages were determined. The forage quality and nutrient quality of silage were determined, and the optimal mixed sowing ratio was determined using grey system theory. We compared the silages produced in the above three periods, and found that the mixed sowing combination E1 (sowing rate: 9 kg?ha-1 M. sativa+30 kg?ha-1 B. inermis) performed best, especially silage produced in the full?bloom period of second stubble (fermentation indicators: pH 4.21, ammonia nitrogen/total nitrogen 3.94%, lactic acid 3.08%; nutritional indicators: crude protein 16.78%, crude fat 3.95%, neutral detergent fiber 61.02%, acidic detergent fiber 48.65%, soluble sugars 0.91%). The dry matter of the mixed forage combination was 6955.73 kg?ha-1. Considering the yield factors, under the production conditions of the E1 mixed forages, the highest yield of silage made in the early flowering period of first stubble+the full?bloom period of second stubble was 16337.13 kg?ha-1.

Promoter cloning and analysis of low temperature-induced expression of sikFBA4 from Saussurea involucrata

ZHANG Yao, LI Zhong-qing, WANG Ai-ying, ZHU Jian-bo

2018, 27(12):  199-207.  DOI: 10.11686/cyxb2017527

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Saussurea involucrata tolerates severe abiotic stresses, especially cold conditions. Therefore, it is a useful plant for studies on cold adaptability. Previous studies have shown that the cold tolerance of Lycopersicon esculentum was significantly improved by over-expressing sikFBA4. To further analyze sikFBA4, changes in its transcript levels under a 4 ℃ treatment were determined by qRT-PCR. Hi-Tail PCR was used to clone the promoter sequence of sikFBA4 from genomic DNA, and PlantCARE software was used to predict and analyze promoter elements in PsikFBA4. To evaluate the activity and study the expression characteristics of PsikFBA4, we constructed GUS gene reporter constructs for transient expression in Nicotiana tabacum leaves. The results showed that sikFBA4 was strongly induced by low temperature. Its transcript levels peaked at 1 hour of cold treatment before declining slowly. The bioinformatics analysis indicated that a low temperature response element was located at -1648 bp in the gene promoter. The result that GUS activity was regulated by PsikFBA4 in response to a cold treatment confirmed that PsikFBA4 is a cold-inducible promoter. These results provide a foundation for further research on the expression and regulation mechanism of sikFBA genes.

Research on forage resources in northwest China during the period of the Republic of China

CHEN Jia-jin, LU Yong, LI Qun

2018, 27(12):  208-218.  DOI: 10.11686/cyxb2018073

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Research on pasture resources in Northwest China in modern times represents the highest level of pasture science and technology, but few studies have tried to place current research in a wider context. In this study, we searched current and historical literature, using modern newspapers and periodicals as the main sources of information, and summarized the main achievements of modern pasture science and technology in China. Researchers and government officials have studied pasture resources in the Northwest China since the early 1930s. Research in Shaanxi Province has mainly been botanical studies on plant classification and the characteristics of herbage. Studies on soil and water conservation were mainly concentrated in Shaanxi, Gansu, and Qinghai provinces, and generally aimed to identify high-quality grass species that favored soil and water conservation. Studies on the role of herbage in animal husbandry focused on the distribution, varieties, quality, and storage of different types of herbage. The introduction of forage was another major area of research and achievement in northwest China. Many scholars such as Wang Dong and Ye Pei-zhong used the theories of western experimental science to conduct many forage cultivation experiments. At the same time, scientists in northwest China pioneered experimental research on the nutrition, preservation, and breeding of forage resources, many of which were the only ones in the country at that time. Forage grass science and technology have been promoted in northwest China, and the main areas of research have been resource characterization and the cultivation, breeding, and preservation of herbage.