Table of Content

20 May 2018, Volume 27 Issue 5

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The effects of different restoration practices on temperate grassland ecosystems in the Beijing-Tianjin Sand Source Control Project

LI Yu-zhe, FAN Jiang-wen, YU Hai-ling

2018, 27(5):  1-14.  DOI: 10.11686/cyxb2017471

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The grasslands of Northern China are an important ecological barrier preventing and controlling desertification; there has been a long history of large ecological restoration projects in this area. In order to understand the impacts of various restoration projects on species composition, productivity and species diversity of grassland communities, this study focused on the grasslands of the Beijing-Tianjin Sand Source Control Project, evaluating the effects of four typical restoration practices and their combinations: Fencing to exclude grazing animals, over sowing, small watershed conservation and basic ranch by comparing areas in and out of the Project area and discusses the driving mechanism of any differences. All of the engineering based restoration measures tended to increase the height and cover of communities; the restoration of grazing excluded steppe provided the best example of this. The prevalence of species from Gramineae and Cyperaceae increased while weeds decreased. The constructive species of communities changed from shorter species such as Stipa sareptana var. krylovii, Cleistogenes squarrosa and Thymus serpyllum to taller perennial Poaceae species such as Stipa grandis, Leymus chinensis and Achnatherum sibiricum. All of the engineered restoration measures tended to increase the above-ground biomass but below-ground biomass in typically management areas planted with artificial fodder decreased significantly, which led to a significant drop in overall community biomass; the overall biomass, above-ground biomass and below-ground biomass increased significantly where grazing was excluded. The ratio of the biomass of C₃ plants and perennial plants tended to increase. None of the engineered restoration measures increased the abundance of species in communities but all tended to decrease the evenness of species; the Shannon-Wiener index in supplementary grass planted and typical grazed areas decreased significantly. The results showed that long-term engineering measures restored the vegetation cover and productivity of grassland and increased fodder quality which helped stabilize sand, increased carbon sequestration fodder availability. However, engineering intervention may result in reduced species diversity of vegetation communities in a long term.

The C, N and P stoichiometry of dominant species in different land use types in a desert-oasis ecotone of the Southern Taklimakan Desert

ZHOU Xiao-bing, TAO Ye, ZHANG Yuan-ming

2018, 27(5):  15-26.  DOI: 10.11686/cyxb2017242

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The natural plants in a desert-oasis ecotone play an important role in protection of the ecological environment of the oasis. Understanding of how human activities like land use affect the natural plants is crucial for the evaluation of structure and function of the ecotone. Ecological stoichiometry is widely used in identification of nutrient deficiency and evaluation of ecosystem stability. Three species in the south region of the Taklimakan Desert, Tamarix ramosissima, Alhagi sparsifolia and Karelinia caspia were selected to study the effects of land use types and intensities on total carbon (C), nitrogen (N), phosphorus (P), C∶N, C∶P and N∶P of plant leaves. In this study, the average elemental content of the three species was 385.94 mg·g^-1, 13.62 mg·g^-1, 1.49 mg·g^-1, 30.33, 294.01 and 9.69, respectively for C, N, P, C∶N, C∶P and N∶P. Compared to other communities in arid lands or in global scale terrestrial ecosystems, plant C and P contents were normal, while N content was lower than in other regions. The land use types, intensities and their interactions significantly affect most indicators. The plant C, N, P and their ratios were significantly different among different desert sites of the ecotone. The plant nutrient levels also differed after cultivation. For example, plant C usually decreased, while N and P increased after cultivation. The more intensive the cultivation activity, the greater the magnitude of N and P increase observed. The nutrient changes also depended on species. Correlation between soil nutrient and plant nutrient levels was not significant in T. ramosissima, and K. caspia, while plant N and P of the three species were closely correlated. Generally, plants collected from the southern region of the Taklimakan Desert were lacking N, but the deficiency was partially alleviated under certain land uses. Along with the changes in intensity of the land use in this region, we speculated that the plant stoichiometry would vary in different magnitudes.

Effect of cover cropping on soil greenhouse gas emissions during summer fallow under manipulated rainfall

GE Xiao-rong, WANG Jun, ZHANG Qi, FU Xin, LI Zhi-peng

2018, 27(5):  27-38.  DOI: 10.11686/cyxb2017263

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Cover cropping during the summer fallow period has various ecological benefits in dryland farming systems. However, its effect on greenhouse gas (CO₂, N₂O and CH₄) emissions is not well known. A rainfall-manipulated winter wheat pot experiment was carried out to investigate the effects of cover cropping on soil greenhouse gas emissions during summer fallow under different rainfall patterns. Two rainfall treatments (ambient and 50% ambient) and different cover crops (ryegrass 21.4 kg·ha^-1, Changwu soybean at a rate of 82.5 kg·ha^-1, ryegrass 10.7 kg·ha^-1 plus Changwu soybean 41.25 kg·ha^-1 and a no crop control) were compared in a completely randomized design. Soil CO₂, N₂O and CH₄ fluxes were measured using a static chamber gas chromatograph. Both CO₂ and N₂O were emitted but the soil acted as a weak sink for CH₄.The effects of both rainfall pattern and cover cropping were significant for soil greenhouse gas emissions during the summer fallow period. Compared with ambient rainfall, 50% rainfall decreased daily mean CO₂ and N₂O flux by 33% and 17.9% respectively, but had no effect on CH₄ flux when averaged across all cover crops. Compared with the control, ryegrass, Changwu soybean and the ryegrass/soybean mixed increased the daily mean CO₂ flux by 140.8%, 135.6% and 137.7%, and decreased the daily mean N₂O flux by 8.0%, 21.8% and 27.4%, respectively. There was no significant difference among different cover crops in CO₂ flux, the differences in N₂O flux between ryegrass with other two cover cropping treatments were significant. The daily mean CH₄ uptake in Changwu soybean was lower by 65.8%, 63.7% and 68.9% compared with those in the fallow control, ryegrass and mixed, respectively. Averaged across cover crops, the average global warming potential was 26.1% lower while greenhouse gas intensity was 47.2% higher under 50% compared to ambient rainfall. Averaged across rainfall patterns, the global warming potential was 67.9%, 65.5% and 67.8% higher in ryegrass, Changwu soybean and the ryegrass/soybean mixed respectively than the fallow control. Compared with ryegrass and the ryegrass/soybean mixed, Changwu soybean had a higher shoot biomass and a lower green house gas intensity, indicating that Changwu soybean is more suitable for cover cropping during the summer fallow period in the dryland areas of the Loess Plateau.

Effects of straw and biochar on soil organic carbon and its active components

LI Jia-cheng, GAO Ming, TIAN Dong, HUANG Rong, XU Guo-xin

2018, 27(5):  39-50.  DOI: 10.11686/cyxb2017261

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The objective for this study was to provide a scientific basis for incorporation of straw and biochar into purple using the principle of ‘equivalent carbon’. The effects straw and biochar on soil organic carbon (SOC) and active carbon fractions were studied at the Experimental Farm of Southwest University. Five treatments including control (no organic material added, CK), straw (CS), straw plus decomposition agent (CSD), biochar (BC), 50% straw and 50% biochar (CSBC) were used (in maize season and rape season). SOC increased significantly in all treatments including added carbon, ranging from 31.26% to 107.82% but SOC content in the BC and CSBC treatments were significantly higher than the CS and CSD treatments, indicating a greater ability to sequester carbon sequestration from biochar. Soil active organic carbon reached the highest content during maize filling stage and rape pod ripening period. Microbial biomass carbon (MBC), dissolved organic carbon (DOC) and readily oxidizable carbon (ROC) in different treatment were ranked CSD>CD>CSBC>BC>CK, during the maize season. The MBC, DOC and ROC content of straw and biochar related treatments ranged from 125.53-172.02 mg·kg^-1, 102.73-79.07 mg·kg^-1 and 2.00-6.01 g·kg^-1, respectively. Microbial entropy, the DOC∶SOC and ROC∶SOC ratio for CS and CSD treatments were significantly higher than that in BC and CSBC treatments. Compared with the control, CS and CSD treatments significantly improved the soil ROC∶SOC ratio. However, BC and CSBC treatments were 14.33%-18.38% lower than that of the CK. In summary, straw and straw with added decomposition agent was able to promote the transformation of active carbon, able to be directly used by microorganisms. These treatments also increased SOC and soil fertility. Compared with straw, biochar resulted in lower soil microbial activity. However, the higher stability of SOC in biochar treatments stimulated the accumulation of SOC.

Effects of nitrogen on leaf functional traits and population characteristics of the artificial grassland Elymus nutans in Northern Tibet

LUO Wen-rong, LI Wen-han, Ganjurjav H, YAN Yu-long, LI Yu, CAO Xu-juan, HE Shi-cheng, DANJIU Luo-bu, GAO Qing-zhu, HU Guo-zheng

2018, 27(5):  51-60.  DOI: 10.11686/cyxb2017266

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Anitrogen addition experiment was performed at the Department of Agriculture Environmental Science Experiment Station in Nagqu town, Northern Tibet, from 2015 to 2016. Urea solution was sprayed on each replicated plot using five treatments: 0 g·m^-2 (CK), 7 g·m^-2 (N₁), 15 g·m^-2 (N₂), 30 g·m^-2 (N₃), 40 g·m^-2 (N₄), 50 g·m^-2 (N₅). The study focused on the response of Elymus nutans leaf functional traits and population characteristics to these different nitrogen application rates. The results showed: 1) The leaf area and specific leaf area of E. nutans increased with nitrogen application. Nitrogen application also significantly increased tiller number (P<0.05), while the leaf photosynthetic rate showed no significant response; 2) Under different nitrogen treatments, tassel density increased to some extent but the reproductive height was not significantly impacted. The trophic height increased significantly (P<0.05); the largest increase was 32.87 cm at N₅, 111.29% higher than CK. Coverage increased rapidly at first and then stabilized in the saturated state, rising from 43.67% to 100%. With increasing nitrogen rates, biomass increased significantly (P<0.05), and the higher the nitrogen the higher the biomass, with the largest increase occurring in the N₅ treatment, 303.18% (587.89 g·m^-2) higher than the control group (145.81 g·m^-2); 3) Correlation analysis showed that there was a significant correlation between the biomass and reproductive height, trophic height, and coverage when loaded on nitrogen application as a single factor (P<0.01). These results indicate that population characteristics rather than leaf functional traits are the key factors to improve the productivity of E. nutans grassland undergoing nitrogen application.

Effects of nitrogen fertilizer level on non-structural carbon and nitrogen metabolite levels in oats grown in sandy desert soil

YU Hua-rong, GUO Yuan, ZHU Ai-min, LU Fu-ying, WANG Le, ZHANG Yu-xia

2018, 27(5):  61-72.  DOI: 10.11686/cyxb2017255

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This study was located at Kezuozhong near Tongliao City, in the Inner Mongolia Autonomous Region of China, and investigated the effects of nitrogen fertilizer application on non-structural carbon and nitrogen metabolite levels in leaves of oats (Avena sativa) grown in a desert environment. Nitrogen fertilizer was applied as urea at 70, 140, 210 and 280 kg·ha^-1 elemental N, and with a no-N treatment as a control (designated N₇₀, N₁₄₀, N₂₁₀, N₂₈₀, and N₀, respectively). Separate fertilizer applications comprising 15%, 40%, 25%, and 20% of the total, respectively, were made at seedling, tillering, jointing, and heading stages of crop development. Soluble sugar, starch, amino acid, soluble protein (SP) content and nitrate reductase activity (NR) were measured for leaf samples collected from various positions at the booting, heading and grain filling growth stages. Sucrose content and activity of sucrose synthase (SS) were also measured at the grain filling stage.It was found that nitrogen fertilizer significantly (P<0.01) reduced the carbohydrate content (including soluble sugars, starches and glucose), with the size of the reduction in proportion to the quantity of N applied. Conversely, free amino acid levels in leaves were increased by N fertilizer and were highest in the N₂₈₀ treatment at booting and heading stages, and were also high in the N₂₁₀ nitrogen treatment at the watery dough stage of grain fill.Similarly, SP content was significantly higher in N-treated plants than in the control (P<0.01) and varied across growth stages, with highest values recorded in the N₂₁₀ treatment at the booting stage, and in the N₂₈₀ treatment at the heading stage. In terms of variation within the plant, SP concentration in the upper leaves was the highest in the N₂₁₀ treatment, while in the middle and lower leaves SP was the highest in N₂₈₀ nitrogen treatment in the watery dough stage. At grain filling stage, in the N₇₀ treatment, SS activities were 3.61, 6.50, and 13.44 μg·g^-1 FW·h^-1, respectively, for upper, middle and lower leaves, and corresponding values for NR activities were 81.6, 84.8, 76.2 μg·g^-1 FW·h^-1. SS and NR activities were significantly decreased (P<0.01 and P<0.05 for SS and NR, respectively) with application of N at higher rates than N₇₀.Topdressing of N fertilizer had no obvious influence on the nitrate-nitrogen content in the oat leaves. The C∶N ratios were largest in the N₀ treatment at the booting stage, being respectively 9.00, 5.70 and 1.48 for upper, middle, and lower leaves. However, the C∶N values of the upper leaves of N₂₁₀and the middle and lower leaves of the N₂₈₀ treatment nitrogen were maximized at the heading and filling stages.This study provides comprehensive data on developmental changes in carbon and nitrogen contents, on activities of key enzymes in carbon and nitrogen metabolism and on yield characteristics of oats grown in a desert soil, and will assist understanding of the coordination of carbon and nitrogen metabolism.

Effects of simulated elevated CO₂ concentration and precipitation change on carbon and nitrogen characteristics of Reaumuria soongorica

LIU Sheng-tong, CHONG Pei-fang, JI Jiang-li, ZENG Ji-juan

2018, 27(5):  73-84.  DOI: 10.11686/cyxb2017256

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Atmospheric CO₂ concentrations are predicted to increase from approximately 350 μmol·mol^-1today to over 700 μmol·mol^-1in the late 21st century. In the future, elevated CO₂ levels are likely to have profound effects on precipitation. This change would seriously affect the desert ecosystem, altering the carbon and nitrogen allocations of desert plants and so leading to changes in ecosystem structure and function. Although many studies have examined the effects of precipitation and CO₂, the interactions between precipitation changes and CO₂ in desert plants have attracted little attention to date. In order to assess the possible effect of global climate change on desert ecosystems, a pot experiment was conducted to study the interaction of elevated CO₂ concentrations and changing precipitation with organic carbon, total nitrogen, C/N, organic carbon accumulation (absorption), and total nitrogen accumulation (absorption) in the roots, stems and leaves of Reaumuria soongorica, a dominant species on desert steppe in the arid regions of China. The main experiment included three CO₂ concentrations (350, 550 and 700 μmol·mol^-1) and five precipitation conditions (natural precipitation as control [W₀], precipitation minus 30% [-W₂], precipitation minus 15% [-W₁], precipitation plus 15% [+W₁], and precipitation plus 30% [+W₂]). The main results are as follows: 1) At the same precipitation treatment, organic carbon in root, stem and leaf were significantly increased and total nitrogen decreased by elevated CO₂. The rise of organic carbon contents in roots was highest at 13.33% under 700 μmol·mol^-1 CO₂ concentration and -W₂ precipitation. Total nitrogen contents in leaves were lowest at 56.31% under 700 μmol·mol^-1 CO₂ concentration and +W₁ precipitation. C/N, organic carbon and total nitrogen accumulation (absorption) in root, stem and leaf were significantly increased by elevated CO₂. 2) At the same CO₂ concentrations, organic carbon and total nitrogen in roots and stems significantly increased with raised precipitation levels. The largest increase in organic carbon in leaves was 11.56% under +W₂ precipitation and 550 μmol·mol^-1 CO₂ concentration. The largest decrease in total nitrogen in leaves was 40.16% under precipitation +W₂ and 700 μmol·mol^-1 CO₂ concentration. C/N, organic carbon and total nitrogen accumulation (absorption) in root, stem and leaf were affected significantly by precipitation. 3) Under the interactive effects of elevated CO₂ and changing precipitation conditions, organic carbon contents and C/N were allocated mostly to roots, total nitrogen, organic carbon accumulation and total nitrogen accumulation (absorption) mostly to leaves. These results suggest that in the future, with CO₂ concentration and precipitation changes, the growth states of R. soongorica will be decided by the interactive effects of CO₂ concentration and precipitation changes on carbon and nitrogen. Elevated CO₂ concentration can relieve the inhibition of drought on the carbon and nitrogen absorbed and used of R. soongorica, and moist conditions can reinforce the impact of these elements.

Evaluation of the adaptability of triticale genotypes using membership function and GGE-Biplot analysis

LIU Jing, SONG Qian, TIAN Xin-hui, DU Wen-hua, LIU Han-cheng

2018, 27(5):  85-96.  DOI: 10.11686/cyxb2017241

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In order to screen triticale genotypes and areas potentially suitable for cultivating triticale, hay yield, nutritional value (crude protein, neutral detergent fiber, and acid detergent fiber content), and dry matter digestibility of 4 triticale genotypes (new lines P₂ and P₄; cultivars Shida No.1 and Zhongsi 1048) at the flowering stage were assessed at six sites (Lintao, Maqu, Xiahe, Hezuo, county of Mati and Kangle in Sunan) in Gansu province from 2014 to 2015. Only Lintao had irrigation, all other sites depended on rainfall. Data were analyzed using ANOVA, membership function and GGE (within genotypes and the interaction between the genotype and environment) biplots. Genotype P₂ had the highest hay yield (12.94 t·ha^-1) and nutritional value (0.67) and performed well in Lintao and Maqu; P₄ obtained higher hay yield (10.90 t·ha^-1) and nutritional value (0.5) than that of the controls, Shida No.1 and Zhongsi 1048. Both Shida No.1 and Zhongsi 1048 displayed low productivity or nutritional values at all sites. Highest yields were obtained at Lintao (14.13 t·ha^-1) and the highest nutrition value (0.51) at Maqu; Maqu also had high hay yield (14.07 t·ha^-1) and nutritional evaluation value (0.50). Yields were generally poor at other sites. This study demonstrated a simple and effective method for evaluating hay yield, nutritional quality and suitable area’s for triticale production and offers a theoretical basis for identification of superior genotypes and extension of triticale production.

Productivity and nutritional value of 28 alfalfa varieties in the Yanmenguan area of Shanxi province

ZHENG Min-na, LIANG Xiu-zhi, HAN Zhi-shun, KANG Jia-hui, CHEN Yan-ni

2018, 27(5):  97-108.  DOI: 10.11686/cyxb2017408

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Twenty-eight alfalfa (Medicago sativa) varieties were studied in Yanmenguan, Shanxi province. The growth rate, leaf∶stem ratio, plant height and hay yield were measured by conventional methods in two consecutive years. In addition, herbage nutritional qualities were measured by near infrared reflectance spectroscopy. Key results were: 1) The growth rate of M. sativa cv. Adrendin were the highest at 2.78 and 3.19 cm·d^-1 in 2015 and 2016 respectively. The leaf∶stem ratio of M. sativa cv. WL363HQ was the highest at 0.84 and 0.97 in 2015 and 2016 respectively. 2) The plant height of M. sativa cv. WL298HQ was the highest at 54.90 cm in 2015; The plant height of M. sativa cv. Magnum VII was the highest at 84.27 cm in 2016. The hay yield of M. sativa cv. Lumu No.2 was the highest at 6961.81 kg·hm^-2 in 2015, and the hay yield of M. sativa cv. Magnum VII was the highest at 8587.63 kg·hm^-2 in 2016. 3) The crude protein, crude ash and ether extract of M. sativa cv.Victorian were the highest at 26.80%, 10.20% and 2.34%; The dry matter percent of Zhaodong was the highest at 94.55%; The acid detergent fiber and neutral detergent fiber of M. sativa cv. Concept were the lowest at 27.18% and 33.31%, respectively. The rumen undegradable protein of M. sativa cv. Ladak was the highest at 22.27%. The dry matter digestibility of M. sativa cv. Concept was the highest at 79.93%. In this evaluation, M. sativa cv. Victorian, M. sativa cv. Concept, M. sativa cv. WL298HQ, M. sativa cv. SK3010 and M. sativa cv. Magnum VII, outperformed other varieties, which indicates that these five varieties are suitable for use in the Yanmenguan region of Shanxi province.

Impact of sewage sludge and indole butyric acid on growth and drought tolerance of Poa pratensis under drought stress

CAO Yun-xin, YU Fang-fang, BAI Mei, CHANG Zhi-hui

2018, 27(5):  109-119.  DOI: 10.11686/cyxb2017246

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Biosolids contains a wealth of nutrients and biologically active substances (BAS) and is useful for soil improvement and as fertilizer following appropriate treatment. The purpose of this research was to study the effects of sewage sludge obtained from Jiuxianqiao sewage treatment plant in Beijing and exogenous auxin on the growth and drought tolerance of kentucky bluegrass (Poa pratensis). A split plot trial design was used with main plot treatments being moisture availability (well-watered and drought stress). Subplots included treatments of sewage sludge, 2 μmol·L^-1 endogenous indole butyric acid (IBA) and a control. Three months after establishment watering in the drought stress plots was stopped until the soil water content fell to 25% of field capacity. Subsequently irrigation commenced again for a month, with held again until 25% field capacity and then fully irrigated for another month. The well-watered treatments were fully irrigated for the duration of the study. Turf quality, wilt rating, leaf relative water content, chlorophyll and carotenoids content, proline content, ABA content, IAA content and MDA (malondiadehyde) content of all treatments were measured at every beginning and end of drought stress. Sewage sludge and endogenous IBA improved turf quality and leaf chlorophyll content under well-watered conditions, and increased leaf IAA content (P<0.05); sewage sludge had a more lasting effect than IBA. Both sewage sludge and IBA enhanced the turf quality, leaf relative water content and chlorophyll content (P<0.05) under the drought stress. At the end of drought stress, the proline contents of control, sewage sludge and IBA treatments were respectively 433, 385 and 254 μg·g^-1, ABA content was 1.74, 0.68 and 0.70 μg·g^-1, respectively and MDA content 62.39, 40.08 and 25.38 nmol·g^-1, respectively. Proline, ABA and MDA contents of sewage sludge and IBA treatments were significantly lower than that of the control (P<0.05). The study indicated that both sewage sludge and IBA could promote the growth of Kentucky Bluegrass; sewage sludge raised drought resistance while IBA enhanced drought tolerance.

Effects of biochar amendment and arbuscular mycorrhizal inoculation on maize growth and physiological biochemistry under cadmium stress

LI Ji-wei, YUE Fei-xue, WANG Yan-fang, ZHANG Ya-mei, NI Rui-jing, WANG Fa-yuan, FU Guo-zhan, LIU Ling

2018, 27(5):  120-129.  DOI: 10.11686/cyxb2017447

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To explore the synergistic effects of biochar and arbuscular mycorrhizal fungi (AM) on plant grown in cadmium (Cd) contaminated soil, we conducted a pot experiment to investigate the effect of wheat-straw biochar amendment and AM inoculation (Glomus intraradices BEG 141) on maize (Zea mays) growth and physiological biochemistry characteristics with soil contaminated with 0, 3 or 6 mg Cd·kg^-1 soil. The results showed that applying either biochar or AM inoculant alone or in combination all significantly increased maize growth, photosynthetic pigment content, photosynthesis and antioxidant enzymatic activities while decreasing intercellular CO₂ concentration (C_i) and MDA content. Compared with biochar application and AM inoculation, AM inoculation alone was effective at alleviating Cd stress and facilitating maize growth while biochar alone was more effective at inducing soil alkalinization. Amending soil with biochar and AM inoculant together produced the largest increase in maize growth and physiological biochemistry characteristics. This effect was additive, with 43.87% and 79.10% greater plant height and biomass, 33.09%,45.04% and 31.27% higher net photosynthetic rate (P_n), transpiration rate (T_r) and stomatal conductance (G_s), and 51.42%, 82.91% and 43.96% higher superoxide dismutase (SOD), peroxidase (POD) and catalase (CAT) activity, respectively, at a 6 mg·kg^-1 Cd contamination rate. In general, biochar and AM inoculation alone or in combination all improved maize growth and alleviated Cd toxicity. Biochar addition in combination with AM inoculation application was the most effective treatment but AM inoculation alone was more effective than biochar for increasing the resistance of Cd toxicity and improving maize growth in Cd-contaminated soil.

Role of NO-mediated Ca²⁺ signaling in regulation of photosynthesis and resistance to osmotic stress in alfalfa seedlings

ZHAO Ying, YI Qin, WEI Xiao-hong, XIN Xia-qing, HAN Ting, YUE Kai, WANG Fang-lin

2018, 27(5):  130-140.  DOI: 10.11686/cyxb2017235

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The nitric oxide (NO) and Ca²⁺ transduction pathways have been implicated in mediating stress response and tolerance in plants. However, little is known about the interaction between NO and Ca²⁺ signals, in regulation of photosynthesis and antioxidant capacity of alfalfa seedlings under drought stress. This research aimed to explore the mechanism by which Ca²⁺ signaling mediated by nitric oxide (NO) in Medicago sativa seedlings regulates photosynthesis and antioxidant enzyme activity under osmotic stress. Solutions with:(i) differing osmotic potentials obtained using poly ethylene-glycol-6000 (PEG); (ii) a nitric oxide donor sodium nitroprusside (SNP); (iii) an exogenous Ca²⁺ signaling donor, calcium chloride (CaCl₂); (iv) an NO blocker (methylene blue, MB); and (v) a Ca²⁺ channel blocker (LaCl₃), were pre-sprayed onto the leaves of alfalfa seedlings in different combinations. The effect of the NO-mediated Ca²⁺ signaling on the photosynthetic pigment content, gas exchange parameters, antioxidant enzyme activity, on the levels of malondialdehyde (MDA) and proline, and on the peroxidase (POD) isoenzyme electrophoresis atlas were studied in leaves of alfalfa under osmotic stress simulated by 15% PEG. Results show that the photo-physiological characteristics of alfalfa seedling were significantly affected by osmotic stress. NO and Ca²⁺ application alleviated the decrease of chlorophyll a, carotenoid contents and the total chlorophyll contents, increased net photosynthetic rate (P_n), stomatal conductance (G_s) and stomatal limited value (L_s), but reduced intercellular CO₂ concentration (C_i) in alfalfa seedling leaves. Furthermore, compared to SNP or CaCl₂ treatment alone, SNP and CaCl₂ treatments applied together significantly increased the activities of SOD, POD, CAT and the content of proline by 39.29%, 30.41%, 56.24% and 45.59%, respectively, and decreased the content of MDA by 45.59%. The POD is ozymeprofile exhibited the greatest band number and strongest enzyme activity on the fourth day, and new band appeared after combined NO and Ca²⁺ treatment. Interestingly, when exogenous Ca²⁺was added together with MB, the promotional activity of Ca²⁺was inhibited.In addition, La³⁺ inhibited the promotional effect of NO. This indicated that in leaves of alfalfa seedlings under osmotic stress, Ca²⁺ mediated signaling transduction pathways, when induced by NO, helped to maintain antioxidant activity and prevent damage to photosynthesis systems.

Effects of interaction between Ca²⁺ salt and drought stress on seed germination and seedling physiology of oats

ZHANG Yu-jun, ZHAO Li-li, WANG Pu-chang, CHEN Chao

2018, 27(5):  141-152.  DOI: 10.11686/cyxb2017433

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The research aimed to study the adaptation mechanisms of oats (Avena sativa) to exposure to soil environments with high levels of calcium salts and drought, as in karst areas. PEG-6000 was used to set up solutions with 0 (CK), -0.2, -0.4, -0.6, -0.8, -1.2 MPa osmotic potential, to simulate a range of drought environments in karst areas. Similarly, calcium chloride (CaCl₂) solutions of 0 (CK), 50, 100, 150, 200 mmol·L^-1 were prepared to provide exogenous calcium and simulate the range of soil calcium environments in karst areas. The effects of low osmotic potential and Ca²⁺ exposure singly and their interaction effect on the seed germination characteristics and seedling physiological characteristics of oats were studied. Both low and medium levels of osmotic stress and exposure to elevated Ca²⁺, singly or in combination, promoted the germination of oat seeds and enhanced the activities of superoxide dismutase, catalase, peroxidase and glutathione peroxidase in seedlings. This was especially true in seedlings subjected to 100 mmol·L^-1 CaCl₂ and -0.6 MPa PEG interactive stress,where the germination rate increased significantly by 42.17% compared with the CK treatment. Two-way ANOVA showed that the effect of salt-drought interaction stress on oats was more significant than that of either single stress (P<0.05). Through comprehensive data analysis, oat tolerance of the stressors tested was found to be as follows: interaction stress>single PEG stress>single CaCl₂ stress.The exposure levels tolerated by oats under CaCl₂, PEG and interaction stresses, were 100 mmol·L^-1, -0.6 MPa, 100 mmol·L^-1 CaCl₂+-0.6 MPa PEG, respectively. The above results show that in karst mountain areas, medium-low concentrations of Ca²⁺ and ormoderate drought typical in these areas can promote seed germination and seedling growth of oats. This study provides reference information for the introduction and cultivation of oats in karst areas and for further research into breeding for stress resistance.

Effects of rhizosphere soil extraction from alfalfa-corn and alfalfa-wheat fields on alfalfa seed germination and seedling physiology and growth

YIN Guo-li, WU Fang, TAO Rong, SHI Shang-li, CAI Zhuo-shan

2018, 27(5):  153-161.  DOI: 10.11686/cyxb2017401

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To provide references for the study of alfalfa-corn and alfalfa-wheat rotation systems, the allelopathic effects of rhizosphere soil extraction from alfalfa-corn and alfalfa-wheat fields on the seed germination, seedling physiology and growth indexes of Medicago sativa cv. Gannong No.3 were investigated. Soil extraction from a five-year alfalfa field served as control (CK). Four rotation treatments were investigated: five-year alfalfa-corn (AC), five-year alfalfa-wheat (AW), five-year alfalfa-corn-corn (ACC), and five-year alfalfa-wheat-wheat (AWW). Three soil extraction concentrations (10, 50 and 160 g·L^-1) were applied and seed germination and seedling growth rates were determined. The results showed that: 1) Seed germination percentages for all the rotation treatments under the three concentrations increased significantly compared with CK, with allelopathic indexes exceeding zero. Seed germination percentages under treatment AWW with soil extraction concentrations of 10, 50 and 160 g·L^-1were the highest at 29.22%, 68.09% and 54.24% more than CK respectively (P<0.05). There were also significant differences between AWW and the other rotation treatments. The germ and radical lengths of each treatment except for ACC increased as soil extraction concentrations went up and were significantly higher than that of CK (P<0.05). Under the same concentration, the germ length of treatment AWW significantly increased compared with AC, ACC, AW, and the radical length was significantly higher than that of AC and AW (P<0.05). However, the radical length of AWW was not significantly larger than that of ACC (P>0.05). 2) The soluble sugar content and superoxide dismutase activity of alfalfa seedlings in each rotation treatment were significantly enhanced with increasing soil extraction concentrations (P<0.05). The malondialdehyde content and catalase activity in treatments AC and ACC were significantly promoted, while in treatment AW and AWW the catalase activity weakened significantly (P<0.05) and the malondialdehyde content decreased at first and then increased.

Study of the semipermeable characteristics of Sorghum bicolor×Sorghum sudanense seeds

SUN Qiu-jin, LÜ Yan-yan, HAN Yun-hua, WANG Yan-rong

2018, 27(5):  162-169.  DOI: 10.11686/cyxb2017218

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This study examines seed semipermeable properties and solutes leakage, investigating the testing of seed vigor by exploring the relationship between the presence of a semipermeable layer and electrical conductivity.In order to provide a scientific basis for seed quality evaluation, three Sorghum bicolor×Sorghum sudanense varieties were tested using measurements of water imbibition rate, electrical conductivity, tetrazolium salt uptake, and the fluorescent tracers technique. The results showed that the seed coat of Sorghum bicolor×Sorghum sudanense readily imbibed water, while showing poor permeability for tetrazolium salts and electrolytes. Intact seeds exhibited less strong staining with tetrazolium salt (5%, 0%, and 2% for Jicao No.2, Jicao No.8 and Jicao No.008, respectively) and there was no significant difference in the electrical conductivity of seeds with different germination rates (P>0.05). After puncturing, all seeds were strongly stained (100%) and electrical conductivity was significantly negatively correlated with germination rate (P<0.01). The seed coat permeability of the three Sorghum bicolor×Sorghum sudanense varieties to fluorescent tracers were different. Jicao No.8 and Jicao No.008 seed coats were not permeable to fluorescein. Lanthanum nitrate tracer combined with X-ray dispersive energy analysis revealed that a semipermeable layer was presented in the seed coverings of Sorghum bicolor×Sorghum sudanense. This is one of the main causes of differences in seed coat semipermeability, and its inhibition of electrolytes leakage resulted in the failure of electroconductivity tests to assess seed vigor.

Effect of PEG priming on the cellular and mitochondrial structure and oxidation resistance of aged oat seed embryos

XIA Fang-shan, DONG Qiu-li, MAO Pei-sheng, WANG Ming-ya, CHEN Ling-ling, CHENG Hang

2018, 27(5):  170-177.  DOI: 10.11686/cyxb2017240

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This study was designed to explore the effect of PEG priming on the seed germination, seedling growth, cellular and mitochondrial ultrastructure and oxidation resistance of aged oat (Avena sativa) seed embryos. Seeds with ultra-dry moisture content (4%) were deteriorated for 48 d at 45 ℃, and primed with either 0 (distilled water) or -1.2 MPa of PEG-6000 for 12 h at 20 ℃ under darkness conditions. Analysis was then undertaken to determine the seed germination percentage, germination index, mean germination time, seedling vigor index, cellular and mitochondrial ultrastructure and their superoxide dismutase (SOD), ascorbate peroxidase (APX), glutathione reductase (GR) and malondiadehyde (MDA). The results showed that the activities of cellular and mitochondrial SOD, APX and GR were increased by PEG priming in the embryo of ultra-dried and aged oat seeds. The activities of cellular SOD, APX and GR increased by 26.7%, 20.9% and 26.9% respectively. The activities of mitochondrial SOD, APX and GR increased by 19.2%, 19.4% and 17.1%. MDA contents declined by 28.3% and 13.7%, maintaining cellular and mitochondrial structures and hence promoting seed germination and seedling growth. However, the opposite changes were observed in seeds tested with distilled water priming. The ultrastructure and oxidation resistances showed a close and collaborative relationship between embryonic cells and their mitochondria in ultra-dried and aged oat seeds during the priming process, with the role of mitochondria more important than that of the embryonic cells.

Development of SSR markers based on transcriptome sequence and analysis of genetic diversity in Sorghum sudanense

ZHU Yong-qun, PENG Dan-dan, LIN Chao-wen, NIE Gang, XU Wen-zhi, HUANG Lin-kai, LUO Fu-xiang, PENG Jian-hua, ZHANG Xin-quan

2018, 27(5):  178-189.  DOI: 10.11686/cyxb2017420

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Sudangrass (Sorghum sudanense) is a poaceous forage with comparatively high yield and quality, and a lack of molecular markers for quality has been a limiting factor for the sudangrass breeding. EST-SSR markers based on the transcriptome sequence of sudangrass were developed and used to study the genetic diversity of 34 accessions of sudangrass and 2 accessions of Sorghum and further to validate the applicability of SSR primers. A total of 17548 SSR sites were identified from 80686 unigenes. These SSR sites were distributed in 13574 sequences at a frequency of 16.82%. The mononucleotide, dinucleotide, and trinucleotide repeat categories were, respectively, 38.59%, 19.18% and 39.09% of the total SSRs. The number of repeat units of the SSRs ranged from 5 to 23. Randomly selected pairs of primers (n=300) were validated and the success rate of amplification was 73.67%, resulting in 54 pairs of effective primers generated, for a total of 275 alleles. Of these, 205 (73.05%) were polymorphic. The average genetic diversity, as measured by the polymorphic information content, was 0.41, and the genetic similarity coefficient ranged from 0.3922 to 0.9022. Tested materials were classified into three groups based on UPGMA cluster analysis, and the clustering results were found to be related to geographic origin. Results of our study suggest the development of SSR markers based on transcriptome data could be used to analyse the genetic diversity and identify variation of germplasm resources in sudangrass or similar species, contributing to marker-assisted breeding.

Effect of moisture, bale density and CaO on storage life and quality of alfalfa hay

CHENG Qi-ming, GE Gen-tu, YIN Qiang, LIU Li-ying, FAN Wen-qiang, JIANG Xiao-wei, LU Qiang, BAO Jian, JIA Yu-shan

2018, 27(5):  190-200.  DOI: 10.11686/cyxb2017262

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The effect of bale density (50 kg·m^-3, 100 kg·m^-3, 150 kg·m^-3, 200 kg·m^-3), moisture content (14%-16%, 19%-21%, 24%-26%, 29%-31%) and addition of CaO (0%, 1%, 2%, 3%) to alfalfa hay bales were assessed to help identify the optimum conditions for storage of alfalfa hay bales. Nutrient content, feed value and in vitro digestibility of alfalfa bales stored for 360 days were analyzed using an orthogonal experimental design with three factors to determine optimum storage conditions. Experiment 1: The nutritional composition and feeding value, through different experimental treatments of the effect on alfalfa hay nutrition was initially assessed; treatments A₁₀ (density 100 kg·m^-3, moisture content 24%-26% and fungicide 3%), A₁₂ (density 200 kg·m^-3, moisture content 24%-26% and fungicide 1%), A₁₄ (density 100 kg·m^-3, moisture content 29%-31% and fungicide 2%) and A₁₅ (density 150 kg·m^-3, moisture content 29%-31% and fungicide 1%) resulted in relatively small dry matter (DM) losses with high feed value after 360 days. Experiment 2: The four best treatments were screened with A₁ (density 50 kg·m^-3, moisture content 14%-16% and fungicide 0) and A₁₆ (density 150 kg·m^-3, moisture content 29%-31% and fungicide 0) were used as controls. In vitro digestion was also assessed. The results showed that treatment A₁₄ had the highest gas production rate of 53.13 mL, significantly higher than the control treatments (P<0.05). The pH of A₁₄ bales was lower than other treatments at all times, with a mean pH of 6.64. The highest TVFA content of 61.05 mol·L^-1 occurred in A₁₄, significantly higher than other treatments (P<0.01). Degradation losses for crude protein and DM were 81.21% and 66.84% respectively, significantly higher than other treatments (P<0.01). Consideration of nutritional composition, feeding value and in vitro digestibility revealed that alfalfa hay with relatively high moisture (29%-31%), medium density (100 kg·m^-3) with 2% CaO added was superior to other treatment combinations.

Evaluating the associate effect of alfalfa hay and millet stalks with Nylon-bag technique

ZHUANG Er-lin, WANG Hui-juan, TIAN Xiu-e, WAN Mei-jiao, ZHANG Yang, WANG Yong-jun

2018, 27(5):  201-209.  DOI: 10.11686/cyxb2017247

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This study aimed to investigate the optimal proportion of millet stalks in a mixed diet of millet stalks and alfalfa hay. Five small-tailed Han sheep with permanent rumen fistulae were selected as experimental animals and a 5×5 Latin square design was set up with five individual sheep as replicates to test each of five dietary mixtures. All five diets were composed of a 40∶60 mixture of concentrate and roughage. However, the roughage varied in the proportion of millet stalks and alfalfa hay (0∶100, 100∶0, 25∶75, 50∶50, 75∶25, for diets Ⅰ, Ⅱ, Ⅲ, Ⅳ, and Ⅴ, respectively). The digestibility and effective degradability (ED) of major nutrition composition in diets were measured using Nylon-bag technique. ED_DM and ED_CP were used as the primary assessment index to calculate an associate effects index (AEI); ED_NDF and ED_ADF were used as a secondary index to reveal the mechanism of the associative effect between millet stalks and alfalfa hay. It was found that: 1) The ED of DM, CP, NDF and ADF was significantly increased with increasing proportion of alfalfa hay (P<0.05). 2) The AEI of groups Ⅲ, Ⅳ, and Ⅴ was 0.8%, 4.0% and 3.7%, respectively, when the ED_DM was the only evaluation index, while the AEI of groups Ⅲ, Ⅳ, and Ⅴ, was 2.5%, 3.5% and 3.1%, respectively, when the ED_CP was the only evaluation index. Thus, diet Ⅳ was the best. 3) In diets Ⅲ, Ⅳ, and Ⅴ the respective contributions of CF to the AEI_DM were 101.55%, 68.75% and 55.41%.

Effects of different starter NDF levels on the growth performance, rumen environments and serum biochemical parameters of calves

REN Chun-yan, BI Yan-liang, DU Han-chang, YU Bo, TU Yan, GUO Yan-li, DIAO Qi-yu

2018, 27(5):  210-218.  DOI: 10.11686/cyxb2017526

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The objective of this study was to determine the effects of different starter neutral detergent fiber (NDF) levels on the growth performance, rumen environments and serum biochemical parameters of calves. Sixty newborn Holstein calves (24 females and 36 males) with body weight (42±2.5) kg were randomly assigned to four treatment groups (A, B, C and D), with each group made up of nine males and six females. Each calf was housed individually in a 1.5 m×3.4 m calves island at the experimental farm. Each group was fed one of four starters with different NDF levels of alfalfa hay and oat hay. The NDF levels of the starters were 10%, 15%, 20% and 25%, respectively. The calves were weaned at 70 days of age and the experiment lasted for 112 days. The results were as follows. During 0-42 and 70-112 days of age, the average daily gains were 46.59, 39.79, 117.13 g·d^-1 and 35.33, 153.29, 145.93 g·d^-1 respectively higher in group B than in groups A, C and D (P<0.05). During 70-112 days of age, the starter intake was significantly higher by 255.20, 252.48 and 392.27 g·d^-1 in groups B, C and D than in group A (P<0.05). The A and B starters improved feed conversion ratios (P<0.05). 2) At 35 and 70 days of age, rumen pH was significantly higher in group C than in groups A, B and D (P<0.05). At 112 days of age, rumen pH was greater for groups A and B than C and D (P<0.05), and the ammonia nitrogen concentration was decreased by 16.72%, 44.19% and 52.10% more in groups B, C and D respectively than in group A (P<0.01). 4) The proportion of acetate was significantly higher in groups C and D than in groups A and B (P<0.01). The propionate ratio was significantly higher by 4.24%, 3.18% and 6.43% in group B than in groups A, C and D (P<0.05). The acetate to propionate ratio of group B was lower than the other groups (P<0.05). 5) No significant differences were observed in contents of total protein, glucose and urea nitrogen in serum (P>0.05). In conclusion, starters with approximately 15% NDF could increase Holstein calves’ average daily weight gains and improve their feed conversion ratio and rumen environments, while they do not affect their serum biochemical parameters.

Woody-plant encroachment in grasslands: a review of mechanisms and aftereffects

WANG Ying-xin, CHEN Xian-jiang, LOU Shan-ning, HU An, REN Jin-fei, HU Jun-qi, ZHANG Jing, HOU Fu-jiang

2018, 27(5):  219-227.  DOI: 10.11686/cyxb2017233

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Woody-plant encroachment in grasslands has been a much-studied topic in ecology and animal husbandry over the past few decades. This paper clarifes the causes and consequences of this encroachment by reviewing recent progress in the study of invasion stages, invasion mechanisms, the impacts of this encroachment on grassland ecosystems and their aftereffects. The means of woody-plant encroachment include both anthropophyte and natural invasion. In general, this encroachment divides into three stages: dispersal, colonizing and establishing and diffusing. The causes of encroachment have been identified as fire suppression, climate change, changes in nutrient availability and over grazing. These factors effect encroachment through changing plant coverage, soil water use efficiency and allelopathy. We conclude that woody-plant encroachment changes many interfaces in grassland ecosystems and influences the ecological and hydrological processes that lead to grassland degradation and desertification.