Table of Content

20 December 2016, Volume 25 Issue 12

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CONTENTS

Responses of aboveground net primary productivity of the typical steppe to climate change-a simulation based on the CENTURY Model

WANG Song, GENG Yuan-Bo, MU Yue

2016, 25(12):  4-13.  DOI: 10.11686/cyxb2016044

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The CENTURY model was used to simulate the dynamic changes in aboveground net primary productivity (ANPP) in the typical steppe of Inner Mongolia, based on meteorological data from 1953 to 2014 and measured data from 1998 to 2013. The overall aim was to analyze the correlation between dynamic changes in ANPP and meteorological factors. The main findings were as follows: 1) the trends in the measured values were highly consistent with those in the simulated values of ANPP at the research site from 1998 to 2013 (Pearson’s correlation coefficient, 0.79; root-mean-square error, 25.92 g/m²). These results indicated that the CENTURY model has good applicability in the typical steppe in Xilinhaote, Inner Mongolia. 2) The sensitivity analysis indicated that the main parameters of the model are soil physicochemical properties, the potential growth coefficient of grassland plants, and the most suitable and the highest temperature for plant growth at the research site. The determination of these parameters affected the accuracy of the model simulation results. 3) From 1953 to 2014, the temperature in Xilinhaote, Inner Mongolia, significantly increased (P<0.01) because of the significant rise in the annual average minimum temperature. The precipitation showed significant interannual fluctuations (variable coefficient, 30.2%). 4) The simulated ANPP at the research site showed a declining trend from 1953 to 2014, but the trend was not significant (P>0.05). Correlation analyses showed that precipitation was the most important factor affecting the changes in ANPP (correlation coefficient between annual precipitation and ANPP=0.959; P<0.01). Temperature was weakly correlated with ANPP.

Effects of alfalfa green manure on rice production and greenhouse gas emissions based on a DNDC model simulation

GAO Xiao-Ye, YUAN Shi-Li, LV Ai-Min, ZHOU Peng, AN Yuan

2016, 25(12):  14-26.  DOI: 10.11686/cyxb2016038

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The denitrification and decomposition (DNDC) model simulates carbon and nitrogen cycles on the basis of biogeochemical processes, and it has been widely used to simulate greenhouse gas emissions in rice (Oryza sativa) paddy fields. However, few studies have used the DNDC model to simulate the effects of green manure on paddy fields in southern China. In this study, we applied four management scenarios, including a control (no N fertilizer, no green manure), N fertilizer (200 kg/ha), alfalfa (Medicago sativa)+N (3000 kg DM/ha+200 kg N/ha), and broad bean (Vicia faba)+N (3000 kg DM/ha+200 kg N/ha), to investigate the effects of green manure on rice production and greenhouse gas emissions. The overall aim of the study was to establish the relationships between green manures and production and greenhouse gas emissions by using the DNDC model. The results showed that the average grain yields in the two years were 41.85%, 29.81%, and 25.36% higher in the alfalfa+N, broad bean+N, and N fertilizer treatments, respectively, than in the control. The most pronounced increase in CH₄ emissions was in the broad bean+N treatment, which had a high C/N. The greenhouse gas intensity (GHGI) was not significantly different between the alfalfa+N, control, and N-fertilizer scenarios. Through adjusting the cropping parameters in the DNDC model, the simulated values and observed values for grain yield were quite similar, and the R² value between them in a correlation analysis was 0.89 (relative mean deviation, -0.8%). Air temperature, CO₂ concentration, soil organic carbon, and the soil clay fraction were all sensitive to CH₄ and N₂O emissions. Temperature, CO₂ concentration, and soil organic carbon were all positively related to CH₄ and N₂O emissions, while the soil clay fraction was negatively related to CH₄ emissions. These results indicated that the localized DNDC model could accurately simulate the effects of alfalfa green manure on rice grain yield and greenhouse gas emissions.

Variations in soil carbon and nitrogen stable isotopes and density among different alpine meadows

QUAN Xiao-Long, DUAN Zhong-Hua, QIAO You-Ming, PEI Hai-Kun, CHEN Meng-Ci, HE Gui-Fang

2016, 25(12):  27-34.  DOI: 10.11686/cyxb2016116

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As a new technology, stable isotope analysis has developed rapidly in the field of ecology in recent decades. However, this technology has not been used widely in studies on alpine meadows. The abundance of stable isotopes and the densities of carbon and nitrogen in soils (0-30 cm) of different alpine meadows at the headwater region of the Yellow River were measured with Isoprime100. The soil δ¹³C ranged from -25.42‰ to -24.20‰. The soil δ¹⁵N ranged from 3.37‰ to 4.69‰, which is significantly higher than that in the atmosphere. The abundance of both δ¹³C and δ¹⁵N in soil increased with soil depth. The soil δ¹³C abundance was significantly lower in mix-seeded pasture soil than in soils of heavily and lightly degraded meadows (P<0.05), while the abundance of δ¹⁵N was significantly higher in mix-seeded pasture soil than in soils of heavily and lightly degraded meadows (P<0.05). The soil C∶N ratio ranged from 7.89 to 9.97. There was a significant (P<0.01) positive correlation between soil organic carbon content and total nitrogen content, and the relationship could be expressed by the following regression equation: TN(%)=0.0963×SOC (%)+0.0336 (R²=0.9619). The soil organic carbon density in the 0-30 cm soil layer in the lightly degraded meadow, severely degraded meadow, and mix-seeded pasture was 7.14, 6.67, and 6.46 kg/m², respectively, and the total nitrogen density was 0.83, 0.77, and 0.75 kg/m², respectively. Plant absorption and growth facilitated the outputs of ¹²C and ¹⁴N, leaving the heavier ¹³C and ¹⁵N isotopes in the soil. Vigorous growth and higher above ground biomass in the mix-seeded pasture consumed more soil ¹⁴N, resulting in higher concentrations of δ¹⁵N in the soil. Alpine meadow degradation and establishment of mix-seeded pastures may significantly reduce the soil carbon and nitrogen density, and this change will be mainly restricted to the 0-20 cm soil layer.

Effects of different management measures on soil microbial biomass in an alpine meadow

JIANG Yong-Mei, YAO Tuo, LI Jian-Hong, CHEN Long, LIU Huan, LIU Ting, TIAN Yong-Liang, ZHANG Biao, GAO Ya-Min

2016, 25(12):  35-43.  DOI: 10.11686/cyxb2016055

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In this study, soil microbial biomass characteristics were monitored during 2011-2014 in Maqu alpine meadows under four different management strategies: non-fenced, enclosed, enclosed with fertilization, and enclosed and sowing. Soil microbial biomass carbon (SMBC), soil microbial biomass nitrogen (SMBN), and soil microbial biomass phosphorus (SMBP) were analyzed using the chloroform fumigation extraction method. The results showed that in the same year, the different management measures were ranked, from highest soil microbial biomass in the 0-20 cm soil layer to lowest, as follows: enclosed+sowing>enclosed+fertilization>enclosed>non-fenced, and from highest soil microbial biomass in the 20-40 cm soil layer to lowest, as follows: enclosed+fertilization>enclosed+sowing>enclosed>non-fenced. In the same year, soil microbial biomass in the 0-20 cm soil layer was always greater (1.22 to 3.39 times greater) than that in the 20-40 cm soil layer. With the same management measure and soil depth (0-20 cm or 20-40 cm), soil microbial biomass increased from 2011 to 2012, peaking in 2012 and decreased again afterwards, except for SMBC in the 0-20 cm soil layer in the non-fenced treatment. With the same management measures, the annual variation in soil microbial biomass in the 0-20 cm soil layer was greater than that in the 20-40 cm soil layer. The soil microbial biomass was negatively correlated with temperature, and significantly positively correlated with precipitation. The management measures were ranked, from highest soil quality composite index to lowest, as follows: enclosed+sowing>enclosed+fertilization>enclosed>non-fenced. The results showed that enclosure+sowing is a better soil management measure than the other three strategies for soil restoration and improvement. Consequently, enclosure+sowing should be applied for ecological restoration of Maqu alpine meadows.

Dynamics of soil carbon and nitrogen sequestration and sequestration rate following long-term fencing of grasslands and abandoned farmlands

LI Jian-Ping, CHEN Jing, XIE Ying-Zhong

2016, 25(12):  44-52.  DOI: 10.11686/cyxb2016231

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Determining the effects of different vegetation restoration measures on soil organic carbon (SOC) and total soil nitrogen (TSN) can increase our understanding of carbon and nitrogen cycling in terrestrial ecosystems, which play important roles in moderating the global greenhouse effect. In this study, we evaluated carbon and nitrogen cycling in fenced grassland and abandoned farmland on the Loess Plateau, using grazed grassland and alfalfa farmland as the control and reference sites, respectively. We analyzed SOC storage, TSN storage, SOC sequestration, TSN sequestration, and their sequestration rates in grassland that had been fenced for 14 years and in abandoned farmland (0-300 cm soil depth). The results showed that SOC storage was significantly increased in 14-year-fenced grassland and abandoned farmland, compared with the reference and control sites. The mean values of SOC storage were similar in 14-year-fenced grassland and abandoned farmland; at 0-200 cm depth soil, STN storage in 14-year-fenced grassland was not significantly higher than that in grazed grassland, but at 0-300 cm soil depth, the STN storage was significantly higher in the 14-year-fenced grassland than in abandoned farmland (P<0.05). The amount of SOC sequestration and its rate were significantly higher in abandoned farmland than in fenced grassland. The SOC sequestration in abandoned farmland was almost completely limited to the 0-140 cm depth soil. At 0-100 cm soil depth, the amount of STN sequestration and its rate were significantly higher in abandoned farmland than in fenced grassland, but at 0-300 cm soil depth, the amount of STN sequestration and its rate were significantly lower in abandoned farmland than in fenced grassland. Therefore, 14 years of fencing of grassland and abandoned farmland could significantly increase SOC, but not TSN storage. Compared with fenced grassland, abandoned farmland had a higher SOC sequestration capacity and sequestration rate.

Plasticity of plant morphology and biomass allocation of Leymus chinensis under different phosphorus conditions

GUO Feng-Hui, HOU Xiang-Yang, DING Yong, LI Xi-Liang, WU Zi-Nian, WANG Zhen, HU Jing, LI Xin-Le, MA Wen-Jing, ZHAO Jin-Bo

2016, 25(12):  53-62.  DOI: 10.11686/cyxb2016061

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Changes in plant morphology and biomass allocation are the main factors in the natural grassland degradation process. Studying the responses of plant morphology and biomass allocation under different conditions could help to reveal the mechanism of grassland degradation. We conducted a pot experiment and evaluated the morphological responses and biomass accumulation and allocation of Leymus chinensis under different phosphorus (P) conditions. The treatments consisted of 0, 30, 90, and 180 mg P₂O₅/kg added to soil to provide four different P-availability conditions for cultivation of L. chinensis. The results showed that: 1) plant biomass and height were reduced under low-P availability, and were significantly increased under higher-P availability. Plant height, leaf biomass, stem biomass, root biomass, and total biomass were 14%, 50%, 51%, 79%, and 63% lower, respectively, under low-P availability than under high-P availability. 2) Plant morphology and biomass allocation showed different responses to P availability. Biomass accumulation was the most sensitive to P conditions, and morphology was the least sensitive; the plasticity indexes were 0.58, 0.31, and 0.19, respectively, for biomass accumulation, allocation, and morphology. The most sensitive single trait indicator was root dry mass with the plasticity index of 0.79. 3) The correlations between aboveground dry mass and leaf width, internode number, and plant height were all significant. Understanding the responses of L. chinensis to different P conditions can help to reveal the mechanisms of vegetation succession and degradation in the grassland ecosystem.

Ecological stoichiometry characteristics of common species in mountain meadows at different stages of degraded succession in the Kanas Scenic Area

TANG Gao-Rong, ZHENG Wei, WANG Xiang, ZHU Ya-Qiong, WU Yan-Feng

2016, 25(12):  63-75.  DOI: 10.11686/cyxb2016047

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The overall aim of this research was to analyze nutrient cycling and the ecosystem stability mechanisms of mountain meadows. We analyzed the stoichiometry characteristics of carbon (C), nitrogen (N), and phosphorus (P) in three common species (Poa pratensis, Carex pediformis, Achillea millefolium) and soil in mountain meadows at different stages of degradation in the Kanas Scenic Area, Xinjiang Uygur Autonomous Region. The results showed that: 1) the importance values, coverage, density, and biomass of the three species increased with increasing degrees of degradation of the mountain meadows, but the average plant height and chlorophyll content of leaves decreased. 2) The C, N, and P contents of common species decreased with increasing degradation. The C∶N of P. pratensis increased from community Ⅰ to Ⅱ and then decreased. The C∶N of other common species increased with increasing degradation. The N∶P of three common species ranged from 14 to 16 in communityⅠ. In other communities, the N∶P exceeded 16 in P. pratensis, but was lower than 14 in A. millefolium and C. pediformis. 3) There was a positive relationship between chlorophyll content and leaf N content. There was no correlation between coverage and the stoichiometric ratio of leaves and soil. The significance of correlations between plant height, density, biomass, and stoichiometric ratios depended on the species and habitats. 4) There were positive, significant, linear correlations between C, N, P contents in soil and in leaves. Plant growth in non-degraded meadows was mainly restricted by soil N and P or not restricted, and it was mainly restricted by soil N in degraded meadows. Together, these results show that soil nutrient stoichiometry has important effects on vegetation recovery in mountain meadows.

Relationships between biological nitrogen fixation and leaf resorption of nitrogen, phosphorus, and potassium in the rain-fed region of eastern Gansu, China

DUAN Bing-Hong, LU Jiao-Yun, LIU Min-Guo, YANG Mei, WANG Ya-Ya, WANG Zhen-Nan, YANG Hui-Min

2016, 25(12):  76-83.  DOI: 10.11686/cyxb2016235

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Leaf nutrient resorption is influenced by many factors, and is one of the most important strategies to enhance nutrient use efficiency and adaptability in adverse environmental conditions. The aim of this study was to explore the relationship between biological nitrogen fixation (BNF) and leaf nutrient resorption. We analyzed lucerne (Medicago sativa cv. Longdong) stands of different ages (2, 4, 7, 11, and 14 years since establishment) in the rain-fed region of eastern Gansu, China. Plant samples were taken at the early flowering stage to measure the concentrations of nitrogen and δ¹⁵N, phosphorus, and potassium in green and senesced leaves. The resorption efficiencies of N and P (NRE and PRE, respectively) first increased and then decreased with stand age, while the changes in potassium resorption efficiency (KRE) showed a different pattern. The NRE ranged from 28.4% to 43.4% with an average of 36.5%, and PRE ranged from 38.1% to 68.2% and averaged 52.6%. The highest NRE and PRE were in the 7-year-old stand. The KRE values of 2-, 11-, and 14-year-old lucerne stands ranged from 23.0% to 27.5%, while they were less than zero in the 4- and 7-year-old stands. As the stands aged, the K, N, and P resorption proficiencies (KRP, NRP, and PRP, respectively) showed different patterns of change from those of resorption efficiencies. The percentage of N derived from the atmosphere (%Ndfa) tended to decrease first and then increase with stand age, and averaged 51.0%, with the minimum value in the 7-year-old stand. There were negative correlations between %Ndfa and NRE, PRE, and KRP, but few relationships between %Ndfa and KRE, NRP, and PRP. These results suggested that there is a close link between nutrient resorption and BNF in lucerne and that BNF affects NRE, PRE, and KRP.

Effect of early weaning of calves on the grazing behavior of female yaks in the Qinghai Lake Area

LIU Pei-Pei, ZHANG Jiao-Jiao, LIU Shu-Jie, DONG Quan-Min, ZHENG Wen-Ming, ZHAO Suo-Nan, ZHOU Yu-Qing, JING Xiao-Ping, HU Rui, SHAO Ya-Qun, PEI Zhao-Xi, DING Lu-Ming

2016, 25(12):  84-93.  DOI: 10.11686/cyxb2016056

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The aim of this research was to study the effect of early calf weaning on the grazing behavior of female yaks. Twenty-six yak dams with calves were used in this experiment. Thirteen yak dams weaned their calves early, and the other 13 did not (control). Three randomly selected yak dams from each group were tagged with a GPS3300 from August 22 to November 15, 2015. The experiment included three periods: weaning inchoate (1st to 15th day after weaning), weaning metaphase (16th to 38th day after weaning), and weaning anaphase (59th to 82nd day after weaning). The weaning inchoate period was divided into phase I (1st to 6th day after weaning) and phase Ⅱ (7th to 15th day after weaning). The results showed that: 1) the daily moving distance of the early weaning group was higher than that of the control group in phase Ⅰ of the weaning inchoate period (P<0.01), but there was no significant difference during the other three phases (P>0.05). The daily moving distance of the early weaning and control groups differed among the four phases. The early weaning group’s daily moving distance was significantly higher than that of the control group on the weaning day. The early weaning and control group showed different daily grazing patterns in the different weaning phases. 2) The grazing space distribution pattern was not significantly different between the early weaning and control group in weaning inchoate phase Ⅰ, weaning inchoate phase Ⅱ, and weaning metaphase. The early weaning and control groups’ grazing ranges were larger in weaning metaphase than in the weaning inchoate phases. The grazing space distribution pattern differed between the two groups in weaning anaphase. These results indicate that early weaning can affect the grazing behavior of yaks in the short term, but the dams soon adapt to the absence of their calves. The yak dams with calves and those without calves should graze separately in periods of forage shortage.

Effect of biological additives on ultrastructure and fiber content of Leymus chinensis silage

YANG Hong, ZHANG Qing, HOU Jian-Jian, YU Zhu

2016, 25(12):  94-101.  DOI: 10.11686/cyxb2016059

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The aim of this study was to determine the effects of adding the cellulose (CEL) and Lactobacillus casei (LC) separately or together on the quality of Leymus chinensis silage. Chopped L. chinensis was supplemented with 1060 U/g cellulose, 1×10⁵ CFU/g fresh matter L. casei, or both (LC+CEL). Chopped L. chinensis with no additives served as the control. Three replicates of each treatment were weighed and chopped into 0.5 L plastic buckets, and these mini silos were stored at ambient temperature for 45 days. The ultrastructure of stems, fermentation quality, and nutrient composition of the L. chinensis silage were analyzed. The pH in the LC+CEL mixture was 3.86, which was significantly lower than those in the LC and the CEL treatments (P<0.05), but the lactic acid and acetic acid contents in the LC+CEL mixture were significantly higher than those in the LC and the CEL treatments (P<0.05). The LC+CEL mixture showed significantly decreased neutral detergent fiber (43.9 g/kg), acid detergent fiber (22.3 g/kg), cellulose (28.5 g/kg), and hemicellulose (21.6 g/kg) contents, and increased water soluble carbohydrates (20.5 g/kg) and lactic acid (29.2 g/kg) contents after 45 days of fermentation. Compared with the control (no additives), all of the treatments showed significantly lower neutral detergent fiber and acid detergent fiber contents, and significantly higher water soluble carbohydrates and organic acids contents (P<0.05). Overall, the LC+CEL mixture performed better in terms of degrading fiber to water soluble carbohydrates and organic acids than did either LC or CEL, but all of the treatments performed better than the control. The biological additives degraded the different tissues to varying degrees, with greater degradation of parenchyma tissue and less degradation of lignified tissue.

Effects of NO₃^--N/NH₄⁺-N ratio on the nutritional quality and feeding values of alfalfa

YU Tie-Feng, LIU Xiao-Jing, HAO Feng, FAN Jun-Jun

2016, 25(12):  102-110.  DOI: 10.11686/cyxb2016051

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The effects of different ratios of NO₃^--N/NH₄⁺-N (1/7,1/3,3/5,5/5,5/3,3/1,7/1) on alfalfa (Medicago sativa cv. Gannong No.3) in terms of its nutritional quality and feeding values were studied in an outdoor rain-protected chamber. Alfalfa plants were cultivated in sand with an optimum nitrogen supply (210 mg/L). The results indicated that under the ratio of NO₃^--N/NH₄⁺-N (5/3), the contents of crude protein (CP), total protein (TP), digestible dry matter (DDM) and dry matter intake (DMI) were significantly higher than their respective values in the other treatments (P<0.05), while the contents of neutral detergent fiber (NDF) and acid detergent fiber (ADF) were significantly lower than their respective values in the other treatments (P<0.05). Thus, the 5/3 ratio was determined to be the best ratio for nutrient accumulation. From the perspective of microelement nutrition analysis, mixed nitrogen mainly with NH₄⁺-N was more beneficial for the accumulation of iron, manganese, and molybdenum, and the adaptation ratios were 1/3, 1/7, and 3/5, respectively. Mixed nitrogen mainly with NO₃^--N was more beneficial for the accumulation of zinc, and the adaptation ratio was 3/1. In the relative feeding values analysis, the RFV value in the 5/3 treatment was significantly higher than those in the other treatments (P<0.05), and the RFV of all treatments was greater than 100. Referring to the classification standard of alfalfa grass products in America, the nutritional quality in all treatments was at least level 2, with that in the 5/3 and 7/1 treatments reaching level 1. When alfalfa was grown in an environment of available nitrogen mainly with NO₃^--N and the ratio of NO₃^--N/NH₄⁺-N was closer to 5/3, the alfalfa crop had good nutritional quality.

Effects of increased atmospheric temperature and CO₂ concentration during crop growth on the rumen degradability of wheat straw

HE Xiang-Yu, MU Chun-Long, CAI Min, WU Yan-Ping, YANG Yu-Xiang, MAO Sheng-Yong, CHENG Yan-Fen, ZHU Wei-Yun

2016, 25(12):  111-118.  DOI: 10.11686/cyxb2016053

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This experiment was conducted to investigate the effects of increasing atmospheric temperature and CO₂ concentration during crop growth on the rumen degradability of wheat straw. The experiment consisted of a control group (wheat plants grown with a mean temperature of 10.5 ℃ and a CO₂ concentration of 413 μmol/mol) and three treatments: elevated CO₂ (CO₂ group, wheat plants grown with a CO₂ concentration of 500 μmol/mol); an elevated temperature group (TEM group, wheat plants grown under a 2 ℃ increase in temperature); and a CO₂ and temperature group (CO₂+TEM group, wheat plants grown with elevated temperature and CO₂ concentration). At harvest, the wheat straw was collected and the in situ degradability was monitored in three fistulated Holstein dairy cows. The results showed that the proportion of rapidly degraded dry matter (DM) was significantly greater in the TEM group than in the control group (P<0.05). The slowly degraded proportion and rumen degradability of acid detergent fiber (ADF) were significantly decreased in the TEM group compared with the control group (P<0.05). In the CO₂ group, the rumen degradability of DM, organic matter (OM), neutral detergent fiber (NDF), and ADF was significantly decreased (P<0.05), and the effective degradability of DM, OM, and NDF was significantly decreased also (P<0.05). In the CO₂+TEM group, the rumen degradability of DM, OM, NDF, and ADF was significantly decreased (P<0.05), and the slowly degraded proportion and the effective degradability of DM, OM, and ADF was significantly decreased also (P<0.05). The treatments were ranked, from highest rumen degradability of DM, OM, NDF, and ADF to lowest, as follows: control group>TEM group>CO₂ group>CO₂+TEM group. These results showed that increased temperature and CO₂ concentration significantly decreased the in situ degradation of DM, OM, NDF, and ADF, and resulted in decreased nutritional value of wheat straw. The lowest nutritional value of wheat straw was in the CO₂+TEM group.

Fermentation quality and microbial characteristics of Amaranthus hypochondriacus-corn mixed silage

TAO Ya, LI Feng, GAO Feng-Qin, XU Chun-Cheng, SUN Qi-Zhong

2016, 25(12):  119-129.  DOI: 10.11686/cyxb2016187

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The fermentation quality and microbial characteristics of mixed silage made from Amaranthus hypochondriacus and corn were evaluated in this study. The two components (A. hypochondriacus and corn) were mixed at five different ratios: 10∶0 (T₁), 7∶3 (T₂), 5∶5 (T₃), 3∶7 (T₄), and 0∶10 (T₅). After 60 days of fermentation, the silage quality was evaluated, and its nutritional composition, microbial community structure, quantity of lactic acid bacteria, and proportion of fresh material and silage were analyzed. The overall aim was to find a practical use for A. hypochondriacus materials. The results showed that the fermentation quality of A. hypochondriacus was poor. With the addition of corn, the pH value and NH₃-N to total nitrogen ratio decreased significantly, and the dry matter (DM) and total acid content increased. When the proportion of corn in the mixture exceeded 50%, the fermentation quality was significantly improved. The lactic acid to acetic acid ratio, which is one of the main factors affecting fermentation quality, was affected by the succession of dominant lactic acid bacteria species and their quantities in silage. Enterococcus, Lactococcus, and Leuconostoc species, which have a strong ability to produce acids, were the main species at the start of fermentation, and Lactobacillus was the main group of lactic acid bacteria in the stable phase.

Identification and study on the effects of plant growth promoting rhizobacteria of Carex enervis

LIU Ting, YAO Tuo, CHEN Jian-Gang, MA Wen-Bin, LIU Huan, MA Cong-Yu, JIANG Yong-Mei

2016, 25(12):  130-139.  DOI: 10.11686/cyxb2016026

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Six plant growth-promoting rhizobacteria were isolated from Carex enervis. We analyzed the six strains to evaluate their phosphate solubilization (by molybdenum blue colorimetry), nitrogen fixation (by the acetylene reduction assay), and hormone secretion (by high performance liquid chromatography). The two strains with the strongest P solubilization and N fixation abilities were identified by analyses of their 16S rDNA sequences. The results showed that the phosphate solubilization capacity of the six strains ranged from 298.17 to 554.67 mg/L (in strain TPRS3). Four strains were able to fix nitrogen, with nitrogenase activity ranging from 170.19 to 456.87 nmol C₂H₄/(mL·h) (in strain TPRS19), while strains TPRS3 and TPRS12 lacked nitrogenase activity. All six strains secreted hormones (indole acetic acid (IAA), ranging from 8.20 to 86.36 mg/L; gibberellin (GA₃) ranging from 26.36 to 135.90 mg/L; and trans-zeatin (t-Z), ranging from 9.55 to 141.68 mg/L). Strain TPRS19 secreted the largest amount of IAA (86.36 mg/L), strain TPRS5 secreted the largest amount of GA₃ (135.90 mg/L), and TPRS2 secreted the largest amount of t-Z (141.68 mg/L). Strains TPRS3, TPRS5, TPRS12, and TPRS19 could secrete all three hormones simultaneously. Strain TPRS5 was identified as Bacillus subtilis and TPRS19 was identified as Enterobacter cloacae. These strains have the potential for use as microbial fertilizers.

Biological characteristics of Laetisaria fuciformis and Limonomyces roseipellis and their responses to different fungicides

ZHANG Wu, HU Mei-Jiao, GAO Zhao-Yin, LI Min, LIU Guo-Dao, NAN Zhi-Biao

2016, 25(12):  140-149.  DOI: 10.11686/cyxb2016058

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Red thread and pink patch, caused by the fungi Laetisaria fuciformis and Limonomyces roseipellis, respectively, are important diseases of many turfgrass species worldwide. In this study, we analyzed the biological characteristics of these two pathogens and evaluated their responses to 14 different fungicides. The results showed that L. fuciformis and Li. roseipellis grew well at pHs ranging from 5 to 7, and the optimal pH value was 6. The hyphae of both pathogens lost viability in agar plugs that were incubated at 50 ℃ for 10 min. The optimal carbon and nitrogen sources for L. fuciformis and Li. roseipellis were soluble starch and L-glutamine, respectively. The optimal medium for L. fuciformis was oatmeal agar (OMA) and that for Li. roseipellis was potato dextrose agar (PDA) or potato sucrose agar (PSA). Among the 14 fungicides, diniconazole had the strongest inhibitory effects on L. fuciformis and Li. roseipellis with EC₅₀ values of 0.113 mg/L and 0.282 mg/L, respectively. The fungicide with the weakest inhibitory effects was 15% metalaxyl·10% propamocarb, with EC₅₀ values of 121.522 and 214.532 mg/L for L. fuciformis and Li. roseipellis, respectively. The results provide a scientific basis for understanding the basic biology of these pathogens, and may be useful for the development of new management strategies.

Growth and functional trait responses of Alhagi sparsifolia seedlings to water and nitrogen addition

HUANG Cai-Bian, ZENG Fan-Jiang, LEI Jia-Qiang

2016, 25(12):  150-160.  DOI: 10.11686/cyxb2016093

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A 2-year pot experiment was conducted to study the effects of water and nitrogen additions on the growth and leaf and fine root traits of Alhagi sparsifolia seedlings, and to investigate the functional trait relationships between leaves and fine roots. The experiment was a completely randomized design with three water levels [drought, 30%-35% field capacity (FC); middle water level, (60%-65% FC); high water level, (80%-85% FC)] and four nitrogen (N) levels (no, low, middle, and high N level). The results showed that the biomass and the leaf and fine root traits of A. sparsifolia were significantly affected by the interaction between water and N treatments. However, the responses of different functional traits to water and N differed depending on the plant growth stage. For 1-year-old A. sparsifolia, there was no significant difference in the total root biomass between the drought and low-N treatment (51 mg N/kg) and the middle water treatment, but the total root biomass was higher in both of those treatments than in the other treatments. The maximum values of leaf N concentration (LNC) and specific leaf area (SLA) and the minimum value of leaf tissue density (LTD) were in the drought and middle-N treatment (102 mg N/kg). The maximum specific fine root length (SRL) value and very low fine root tissue density (RTD) values were in the drought and high-N treatment (306 mg N/kg). For 2-year-old A. sparsifolia, the maximum values of leaf, fine root, shoot, and belowground biomass were in the middle water and N-supply treatment. The maximum SLA and minimum LTD were in the control (drought and no N), whereas maximum SRL and very low RTD values were in the drought and low-N treatment. Leaf biomass was significantly and positively correlated with total root biomass at two growth stages, but there was no correlation between leaf and fine root traits. For the same organ, SLA was positively related to LNC, but negatively correlated with LTD. There was a negative correlation between SRL and RTD. The responses of leaf and root traits to different water and N supplies were not synchronized. The linkages between above- and below-ground growth were mainly reflected by the consistent variations in leaf and root biomass.

Protective effect of exogenous nitric oxide against oxidative damage in pumpkin seedlings under chilling stress

WU Xu-Hong, LV Cheng-Min, FENG Jing-Min

2016, 25(12):  161-169.  DOI: 10.11686/cyxb2016052

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The effects of exogenous nitric oxide on growth and oxidative damage in pumpkin seedlings under low temperature stress were studied. Seedlings of two pumpkin cultivars, ‘Yinhui 2’ and ’Qingli’, were sprayed with the nitric oxide donor, sodium nitroprusside (SNP: 100 μmol/L) and their growth, chloroplast pigment content, organic osmoregulation substances content, and active oxygen metabolism under chilling stress were analyzed. Chilling stress significantly inhibited the growth of pumpkin seedlings as a result of increased active oxygen accumulation and lipid peroxidation, decreased photosynthetic pigment content, and reduced osmotic adjustment ability. Under normal growth conditions, the SNP treatment significantly increased the activities of superoxide dismutase (SOD), peroxidase (POD), ascorbate peroxidase (APX), and glutathione reductase (GR), and also significantly increased shoot dry weight, root dry weight, and the H₂O₂, free amino acid, glutathione, and carotene contents. Under chilling conditions (8 ℃ days/5 ℃ nights), seedlings sprayed with 100 μmol/L SNP showed significantly increased plant growth and dry matter accumulation and significantly increased SOD, POD, APX and GR activities in leaves, and reduced accumulation of H₂O₂ and malondialdehyde (MDA). Exogenous SNP application increased the glutathione, chlorophyll, carotenoid, ascorbate, soluble protein, and total amino acid contents. Under chilling stress, exogenous SNP application reduced the accumulation of H₂O₂ and MDA, and protected membrane stability by increasing antioxidant enzyme activities and the contents of organic osmoregulation and antioxidant substances. These physiological changes protected the stability of cell membrane structure, and maintained carbon and nitrogen metabolism in the seedlings under chilling conditions, thereby increasing the cold resistance of pumpkin. Under these conditions, Yinhui 2 was more responsive than Qingli to exogenous SNP.

Introduction of AtSOS pathway genes into tall fescue to improve salt tolerance

MA Dong-Mei, QIN Chu, NI Xing, XU Xing, GUO Ling-Na

2016, 25(12):  170-179.  DOI: 10.11686/cyxb2016195

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Our research group is aiming to genetically engineer tall fescue to improve its salt tolerance, so that it can be used as a salt-tolerant turf grass to improve the soil in salt-contaminated environments. To this end, a regeneration system was established for tall fescue. Using embryogenic calli as the experimental materials, three salt tolerance-related AtSOS pathway genes from Arabidopsis thaliana (AtSOS1, AtSOS2, AtSOS3) were introduced in different combinations into the genome of the tall fescue cultivar‘Arid3’ by Agrobacterium-mediated transformation. The transgenic plants showed increased salt tolerance. Genomic DNA was extracted from the transgenic tall fescue plants, and PCR detection, Southern blotting, and RT-PCR analyses were conducted. The tall fescue plants transformed with different AtSOS gene combinations and wild-type plants were subjected to salt treatment, with three replicates for each line. The physiological and biochemical indexes, plant height, and Na⁺, K⁺, and chlorophyll contents were determined. Under salt stress, the superoxide dismutase (SOD), peroxidase (POD), hydrogen peroxidase (CAT) activities were significantly higher in the transgenic plants than in the control plants, and the malondialdehyde (MDA) and proline (Pro) contents were lower than those in the control plants. In the NaCl treatment, the Na⁺ and K⁺ contents in leaves were increased in transgenic and in wild-type plants. Most of the transgenic plants and wild-type plants showed reduced plant height and chlorophyll content under salt treatment, however, the chlorophyll content of transgenic plants harboring AtSOS1-AtSOS2-AtSOS3 was higher than that in control plants. These results demonstrate that the introduction of AtSOS pathway genes into tall fescue can increase its Na⁺ content under salt stress, alleviate the symptoms of salt stress, and improve its salt tolerance.

Cloning and transient expression of the GGPPS gene promoter from the energy plant Taraxacum kok-saghyz

LI Yong-Mei, FENG Yu-Jie, CAO Xin-Wen, ZHAO Li-Jing, ZHU Jian-Bo, YAN Jie

2016, 25(12):  180-187.  DOI: 10.11686/cyxb2016034

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Based on the known sequence of GGPPS, which encodes geranylgeranyl pyrophosphate synthase, the GGPPS promoter sequence was amplified from the root of the perennial herb Taraxacum kok-saghyz by thermal asymmetric interlaced PCR (TAIL-PCR) using nested specific primers. Analyses of the full-length 1131-bp fragment by PlantCare and PLACE software showed that the promoter sequence contained basic cis-acting elements, multiple organ-specific expression elements, and a number of stress-related cis-acting elements. The promoter sequence was designated as pTkGGPPS (GenBank: KT901796). The plant expression vector pCAMBIA1304-pTkGGPPS-GFP was constructed using this sequence to replace the CaMV 35S promoter sequence in the plasmid of pCAMBIA1304 with GFP as the reporter gene. The construct was transformed into onion epidermal cells using Agrobacterium tumefaciens, and the promoter successfully drove expression of the GFP gene. The cloning and transient expression of the GGPPS gene promoter from T. kok-saghyz provides a reference for further studies on the mechanisms and tissue-specificity of rubber synthesis.

Study on forest ecological dynamic security in Gansu Province

CHEN Dao-Jun, QU Wang-Long, LI Yu-Cai, WU Xiao-Zhou, GOU Shu-Ping

2016, 25(12):  188-193.  DOI: 10.11686/cyxb2016287

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The aims of this study were to analyze forest ecology security in Gansu Province, and to identify the main factors that positively and negatively affect the security of forest ecology. The ultimate aim is to improve forest management and the ecological function of forests in this region. Based on the Pressure-State-Response (PSR) model, we established an index system for the ecology of forests in Gansu Province. The security of forest ecology was determined by dynamic and quantitative evaluations using the entropy weight method and the ecological security index method, using data from the annual forest resource continuous inventory and the Statistical Yearbook for Gansu Province. The results showed that forest health has improved in Gansu Province during the period of 2006 to 2015. Also, a comprehensive evaluation of the overall ecological security of forest ecosystems showed an increasing trend from year to year, and the security of the forest ecological system has improved greatly. We discuss countermeasures and forest management strategies based on these results.

Research on the introduction of alfalfa into China during the Han Dynasty

SUN Qi-Zhong, LIU Qian, TAO Ya, XU Li-Jun

2016, 25(12):  194-205.  DOI: 10.11686/cyxb2016033

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Alfalfa is not only an excellent forage worldwide, but is also a symbol of the cultural exchange between China and western regions, being regarded as a dazzling bright pearl on the Silk Road. Although alfalfa has more than 2000 years of cultivation history in China, scholars in pratacultural science, agricultural history, and Chinese history have different opinions on when this plant spread into China. This article reviews the literature and interrelates the time when Alfalfa was introduced in China based on previous studies. We considered the times when Zhang Qian travelled to western regions and when envoys came to China, with an aim to identify similar ideas and explain the differences among the various theories. There are several ancient books that describe the origin and history of alfalfa, but there are opposing views on when it was introduced into China. The proposed introduction times are: 1) 139 or 138 BC, 129 BC, 126 BC, or 119-115 BC; 2) when Zhang Qian visited western regions in 102-101 BC; 3) an uncertain time; 4) after Zhang Qian’s death or another later time. By analyzing the existing texts, we eliminated the first and second proposed introduction times. The third view requires further historical data to confirm when Zhang Qian visited western regions, because there is a lack of direct historical evidence that Zhang Qian brought back alfalfa seeds. It is possible that alfalfa and ‘sweats blood’ (Ferghana) horses entered China at the same time. Further analyses of historical data are required to validate or disprove these theories.

Advances in research on grass endophytes in agricultural systems and applications in forage breeding

TIAN Pei, ZHANG Guang-Ming, NAN Zhi-Biao

2016, 25(12):  206-220.  DOI: 10.11686/cyxb2016049

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The Epichloё endophyte forms mutually beneficial associations with its hosts, which enhance their survival under abiotic and biotic stresses. Modern techniques in molecular biology, genomics, proteomics, metabolomics, and bioinformatics have accelerated research on endophytes. The diversity of secondary metabolites and the genes related to their biosynthesis have been identified and the molecular mechanisms of mutualism between the Epichloё endophyte and its hosts have been clarified. These endophytes are widely utilized in agriculture as they are animal-safe grass endophytes that improve the growth and stress resistance of their hosts, leading to increased pasture persistence, sustainability, and production. Thus, several Epichloё endophytes have been developed and commercialized. In this paper, we review recent research on the interactions between grasses and endophytes, and the effects of endophytes on livestock and on microbial and pasture ecosystems. We also discuss the selection of endophyte strains and forage breeding based on multidisciplinary research.