Table of Content

20 August 2017, Volume 26 Issue 8

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Vulnerability of herder households under the framework of sustainable livelihoods in the grassland of Northern China

DING Wen-Qiang, LI Ping, YIN Yan-Ting, HOU Xiang-Yang

2017, 26(8):  1-11.  DOI: 10.11686/cyxb2016414

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We developed an evaluation system based on the Delphi method to assess the vulnerability of herder households under the framework of sustainable livelihoods in the grassland regions in northern China. The herder households’ livelihood capital conditions were measured in the meadow steppe, typical steppe, desert steppe, sandy steppe, and desert and mountain steppe regions of northern China. The characteristics of differentiation were also explored at household and regional scales. In the two rounds of expert opinion of the herders, the coefficients of coordination were 0.445 and 0.692 (P<0.01). The livelihood capital of the herders in northern China was lower, indicating that these herders were vulnerable (mean vulnerability index, 0.2990). The herders were clustered into two groups by the K-means clustering method. The data were analyzed by an F-test and the F-value was significant, confirming that the herders could be divided into two groups on the basis of their vulnerability index. The herders’ human capital, natural capital, physical capital, financial capital, and social capital stock were significantly lower in the more vulnerable group than in the less vulnerable group. On the whole, the householders’ vulnerability tended to decrease from west to east at the county or regional scales. The regions were ranked, from most vulnerable herder households to least vulnerable, as follows: mountain steppe>steppe desert>desert steppe>sandy steppe>meadow steppe>typical steppe.

Interspecific associations in Dactylis glomerata communities in different regions and altitudes on the northern slope of Tianshan Mountain

ZHANG Xian-Hua, CHEN Ai-Ping, ZHU Jin-Zhong, LI Hai-Qi

2017, 26(8):  12-23.  DOI: 10.11686/cyxb2016390

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The aim of this research was to identify the interspecific associations of Dactylis glomerata and to identify changes in community stability related to altitude. D. glomerata communities in different regions and altitudes on the northern slope of Tianshan Mountain were analyzed using the adjacent lattice method to identify and compare the dominant species. The interspecific associations of D. glomerata and changes in community stability related to altitude were determined by calculating association indexes and spearman’s RAML correlation coefficients, and by conducting variance tests and χ² tests. The results showed that: 1) the overall association of the D. glomerata community changed from a positive implicative association to a negative association as the altitude increased from 1800 m to 2200 m. The stability of the D. glomerata communities gradually weakened with increasing altitude. 2) The association coefficient and association index were weak for most pairs of species, and most of the species pairs showed weak or no interspecific associations. 3) D. glomerata showed a positive implicative association with a species in some cases, and a negative association with the same species in other cases. The associations were related to the environmental factors in different regions and at different altitudes.

Soil nutrients and carbon management indexes in the rhizosphere versus non-rhizosphere area of different plant species in desert grassland

ZHANG Yi-Fan, CHEN Lin, LI Xue-Bin, LI Yue-Fei, YANG Xin-Guo

2017, 26(8):  24-34.  DOI: 10.11686/cyxb2017077

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The main plant species used in the Ningxia Desert Grassland Vegetation Restoration Project are Caragana korshinskii, Artemisia ordosica, Stipa breviflora, and Agropyron mongolicum. The aim of this study was to explore the effects of different types of vegetation restoration on soil nutrients and carbon pool management index (CPMI) characteristics. We collected rhizosphere and non-rhizosphere soil from the surface (0-5 cm), subsurface (5-10 cm), and deep (10-15 cm) soil layers, and determined soil total carbon (C_r), active organic carbon (C_A), carbon pool index (CPI) and CPMI. For all four plant species, soil nutrients decreased with increasing soil depth, and these decreases were greater in the rhizosphere soil than in the non-rhizosphere soil. The content of available potassium (AK) in the rhizosphere and non-rhizosphere of the C. korshinskii community was 130.81 and 111.96 mg/kg, respectively. The soil AK content showed a “fat island” aggregation effect on the desert steppe, and showed significant differences among the different communities (P<0.05). 2) The total organic carbon content in soil ranged from 2.09 to 17.11 g/kg, and was higher in the rhizosphere soil than in the non-rhizosphere soil. The vertical distributions of C_r and C_A in the soil profile were similar, and showed a “poly table” effect. The carbon pool activity in the surface layer of the C. korshinskii and A. mongolicum community was 38.41% and 29.54% higher, respectively, than that in the deep layer. The four vegetation types could be ranked, from highest carbon pool activity to lowest, as follows: A. mongolicum>A. ordosica>C. korshinskii>S. breviflora. Vegetation restoration significantly improved the distribution of soil organic matter and the quality of the soil carbon pool, and increased the soil carbon sink function of the desert grassland. 3) The soil CPMI was significantly correlated with soil nutrient content in the desert grassland, and pH was negatively correlated with C_r, C_A, CPI, and CPMI (correlation coefficients of -0.661, -0.437, -0.661, and -0.410, respectively). The soil CPMI was significantly or extremely significantly positively correlated with other soil nutrients (P<0.05; P<0.01). Higher soil N, P, and K contents promoted the soil carbon pool turnover rate, and significantly improved soil quality and productivity. These results show that CPMI serves as an effective index when evaluating soil quality and soil management practices.

Variations in soil organic carbon content and distribution during natural restoration succession on the desert steppe in Ningxia

XU Dong-Mei, XU Xin-Zhong, WANG Guo-Hui, TAO Li-Bo

2017, 26(8):  35-42.  DOI: 10.11686/cyxb2016440

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Fencing (enclosure) is one of the strategies used to promote the natural restoration of ecological communities on the desert steppe in Ningxia. To explore the effects of enclosure on soil organic carbon and its distribution, field studies were conducted at sites with 3, 5, 7, and 10 years of enclosure. Soil samples were collected to determine the total organic carbon concentration and its distribution at different soil depths and in soil aggregates. The results showed that the soil organic carbon concentrations were higher in 7-year and 10-year enclosed grasslands than in those enclosed for shorter times, except at 0-5 cm depth. The concentrations of soil organic carbon were lower in the 0-5 cm and 5-10 cm soil layers than in the 10-20 cm and 20-40 cm soil layers. The soil organic carbon concentrations in soil aggregate particles at 0-10 cm depth were highest in the 3-year enclosed grassland, while those at 10-40 cm depth increased with longer enclosure times. The maximum soil organic carbon contents were in aggregates with 1-0.5 mm and 0.5-0.25 mm diameters. Aggregates of <0.25 mm, >5 mm or <0.25 mm, and >5 mm made the largest contributions to soil organic carbon content at 0-10 cm depth, 10-20 cm depth and 20-40 cm depth, respectively. The contribution of aggregates to soil organic carbon content decreased with increasing enclosure times. As the soil depth increased, the contribution of aggregates to soil organic carbon content decreased, but the contributions of macroaggregates to soil organic carbon content increased. In conclusion, enclosure was beneficial for carbon sequestration. The restoration of the ecosystem on the degraded desert steppe appeared to undergo a transition at the 7th year of enclosure.

Effects of nitrogen and phosphorus addition on litter decomposition on the Stipa baicalensis steppe

LI Wen-Ya, QIU Xuan, BAI Long, YANG Dian-Lin

2017, 26(8):  43-53.  DOI: 10.11686/cyxb2016383

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Litter decomposition is one of the main pathways of nutrient cycling and energy flow in grassland ecosystems. Nutrient limitation is the major factor limiting production on the warm steppe. In this study, the effects of nutrient addition on litter decomposition were investigated to provide a theoretical reference for nutrient management, restoration, and construction of grassland ecosystems. On the Stipa baicalensis steppe in Inner Mongolia, the leaves, stems, and roots of S. baicalensis (Sb), Leymus chinensis (Lc) and Artemisia frigida (Af) were placed in mesh bags to measure decomposition in different treatments: CK (no fertilization), fertilization with N (ammonium nitrate), P (triple superphosphate), or NP (mixed ammonium nitrate and triple superphosphate). The residual rates of all three plants were significantly lower in the N, P, and NP treatments than in the CK, indicating that N and P addition promoted decomposition. During the decomposition process, N was released from leaves and roots at an early stage and enriched at later stages, whereas N in stems showed an enrichment-release-enrichment pattern. The leaves, stems, and roots released P and C continuously during decomposition. The residual rate of P decreased as the plant organs decomposed. The 95% decomposition time of S. baicalensis, L. chinensis, and A. frigida was 3.32-3.77 years, 2.95-3.96 years, and 2.64-4.89 years, respectively. The decomposition responses to fertilizers differed among plant organs and among plant species.

Responses of species diversity and aboveground biomass to nitrogen addition in fenced and grazed grassland on the Loess Plateau

ZHAO Jie, LI Wei, JING Guang-Hua, WEI Lin, CHENG Ji-Min

2017, 26(8):  54-64.  DOI: 10.11686/cyxb2017064

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Nitrogen addition can increase the aboveground biomass of the plant community in grasslands. However, it can also lead to a loss of species diversity, but the mechanisms involved in this process are unclear. The objective of this study was to explore the effects of nitrogen addition on aboveground biomass, species diversity, community composition, and the relationship between species richness and aboveground biomass in long-term fenced grassland and grazed grassland on the semi-arid Loess Plateau. We focused on the differences and similarities in the grassland responses under these two typical management systems, and tried to identify the the ecological mechanisms underlying these responses. We added nitrogen at different rates [0, 5, 10, 20, 40, 80 g CO(NH₂)₂/(m²·yr)] to long-term fenced grassland and grazed grassland. After 3 years of treatment, we measured aboveground biomass, calculated species diversity indexes (species richness, Shannon-Wiener index, and Pielou index) and analyzed the relationship between species diversity and productivity using regression analyses. The results showed that, in the long-term fenced grassland, nitrogen addition significantly increased the aboveground biomass and decreased species diversity, while the grazed grassland showed similar but weaker responses to nitrogen addition. The species diversity in fenced and fertilized grassland decreased as the litter biomass increased, and also increased with greater light penetration. In comparison, species diversity in grazed and fertilized grassland decreased slowly and did not change significantly with greater light penetration. The Shannon-Wiener index was significantly negatively correlated with above-ground productivity in fenced and fertilized grassland, but no such relationship existed in grazed grassland. These results indicated that grazing can relieve the negative effect of fertilization on species diversity. Therefore, grazing is a reasonable grassland management method to retain species diversity while increasing the community aboveground biomass by fertilization.

Effects of different management strategies on the number of soil nitrogen microorganism groups in an alpine meadow

ZHANG Jian-Gui, JIANG Yong-Mei, YAO Tuo, GAO Ya-Min, LI Hai-Yun, LAN Xiao-Jun, TIAN Yong-Liang, LI Jian-Hong, ZHANG Ying

2017, 26(8):  65-73.  DOI: 10.11686/cyxb2016433

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Understanding the micro-mechanisms of soil nitrogen formation can provide useful information about the growth and recovery of microorganisms in an alpine meadow. In this study, soil samples were collected from the alpine meadow in Maqu from sites under four types of management; unfenced, enclosed, enclosed with fertilization, and enclosed with sowing. The number of soil nitrogen microorganism groups was determined by the plate colony count and MPN (most probable number) methods. The number of nitrogen bacterial groups decreased with increasing soil depth at all sites. The number of nitrogen bacterial groups was significantly higher in the 0-10 cm and the 10-20 cm soil layers (P<0.05) than in the 20-30 cm soil layer (1.23-4.03 times and 1.11-2.25 times that in the 20-30 cm soil layer, respectively). There were also significant differences in abundance among the microorganism groups. The groups were ranked, from most abundant to least abundant, as follows: ammonifiers>denitrifying bacteria>nitrifiers>aerobic nitrogen-fixing bacteria (aerobic NFB)>anaerobic nitrogen-fixing bacteria (anaerobic NFB). In the same soil layer, there were significant differences in the abundance of bacterial groups among the different management strategies. The nitrogen bacterial groups were most abundant in the enclosed fertilized grassland and enclosed sown grassland, less abundant in enclosed grassland, and least abundant in the unfenced grassland. The amounts of ammonium nitrogen and nitrate nitrogen decreased with increasing soil depth in all treatments, and were significantly higher in enclosed fertilized grassland and enclosed sown grassland (P<0.05) than in enclosed grassland and unfenced grassland. These results show that, in the alpine meadow, the number and types of soil microorganisms and the contents of different forms of nitrogen can be increased by enclosure with sowing and enclosure with fertilization.

Water consumption characteristics and yields of fodder oat under different irrigation and nitrogen fertilization regimes in the northwest oasis irrigation area

FENG Fu-Xue, MU Ping, ZHAO Gui-Qin, CHAI Ji-Kuan, LIU Huan, CHEN Guo-Dong

2017, 26(8):  74-84.  DOI: 10.11686/cyxb2017074

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Irrigation and fertilization are the two most important methods to increase crop growth and yield. Understanding the water consumption characteristics and grain yield of oat (Avena sativa) under different water-nitrogen (N) regimes is useful to optimize oat cultivation. In the 2014-2015 oat growing seasons, field experiments were conducted with three irrigation levels and three N application rates to study the effects of the water-N interaction on soil water consumption in the 0-150 mm layer, soil evaporation, grain yield, and water use efficiency (WUE) of the oat variety ‘Longyan 3’. The three irrigation amounts were 270 (I₁), 337.5 (I₂), and 405 mm (I₃) and the three N application rates were 90 (N₁), 120 (N₂), and 150 kg/ha (N₃). The soil evaporation and the proportion of soil evaporation (E) to evapotranspiration (E/ET) decreased and then increased during the growing period. Under the same N application rate, E and its proportion of E/ET increased with increasing amounts of irrigation from the jointing to the filling stage, but decreased from the filling to the harvest stage. The oat water consumption and grain yield under a fixed N application rate were positively related to the amount of irrigation, whereas WUE was negatively related to the amount of irrigation. The highest grain yield of oat was in N₃I₃ (5466.0-5727.5 kg/ha), followed by N₃I₂ (5428.5-5678.5 kg/ha), and then N₁I₁ (4504.5-4804.3 kg/ha). The highest WUE was in N₃I₂ [(12.11-12.82 kg/(mm·ha)], followed by N₃I₁ [12.04-12.63 kg/(mm·ha)], and then N₁I₃ [9.79-10.58 kg/(mm·ha)]. The water-nitrogen interaction had significant effects on WUE and oat yield. Our results suggest that N application at 150 kg/ha combined with irrigation at 337.5 mm is a water-saving method to cultivate oat with high-yields in the Northwest Oasis area.

Allelopathic effects of an aqueous extract of Melilotus officinalis on Lolium multiflorum and Sorghum sudanense

WANG Jing-Yi, YAO Dan-Dan, ZHAO Guo-Qi, WU Cai-Xia, MA Qian-Bo, XU Jun, TANG Chen-Yang

2017, 26(8):  85-92.  DOI: 10.11686/cyxb2017113

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The aqueous extract of Melilotus officinalis is known to inhibit weed growth. To study in detail the allelopathic inhibition of grass growth and elucidate the allelopathic mechanism, an aqueous extract of M. officinalis was applied to seeds and seedlings of Lolium multiflorum and Sorghum sudanense and its effects on their growth were evaluated by measuring several important physiological and biochemical indexes. The aqueous extract of M. officinalis significantly (P<0.05) reduced the germination rate, root length, root dry weight, stem length, stem and leaf dry weight of both test species, compared with their respective controls. The aqueous extract of M. officinalis significantly reduced the chlorophyll content and increased the starch and soluble protein contents (P<0.05) of both test species. Treatment with the aqueous extract of M. officinalis significantly (P<0.05) increased the soluble sugars content in S. sudanense and significantly (P<0.05) reduced the soluble sugars content in L. multiflorum. The catalase activity in S. sudanense treated with the M. officinalis extract differed significantly (P<0.05) from that of its control, but returned to control levels after 8 days. The peroxidase activity in S. sudanense treated with the M. officinalis aqueous extract first decreased and then increased.

Autotoxicity of water extracts of the root and bulb of Lilium davidii var. unicolor salisb

HUANG Yu-Fang, ZHANG En-He, ZHANG Xin-Hui, WANG Hui-Zhen, WANG Qi, LIU Qing-Lin, SHI Yu-Qian

2017, 26(8):  93-103.  DOI: 10.11686/cyxb2016411

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Autotoxicity is one of the main problems in the continuous cropping of Lanzhou lily. The aim of this study was to determine the mechanism of the autotoxic effect of Lanzhou lily and identify the organic compounds responsible for its autotoxicity. Water extracts of the root and bulb were applied to young lily plants at different concentrations (10, 50, 100, and 150 mg/mL) to test their effects on early development. Spectrophotometry and titration methods were used to measure various physiological indexes in the seedlings, and gas chromatography-mass spectrometry was used to identify compounds in the extracts. The extracts inhibited seedling growth in a concentration-dependent manner. As the concentrations of the extracts increased, the activities of superoxide dismutase, peroxidase, and catalase first increased and then decreased, and the malondialdehyde content and relative conductivity decreased. The contents of proline and soluble sugars increased significantly when the extracts were applied at concentrations greater than 100 mg/mL. Twenty-three and 14 compounds were identified in chloroform extracts of the root and bulb, respectively, including indane, naphthalene, 2,4-bis(1,1-dimethylethyl)-phenol, 2-methoxy-4-vinylphenol, vanillin, dodecanoic acid, 4-hydroxy-3, 5-dimethoxy-benzaldehyde, tetradecanoic acid, phenyl isocyanate, 1, 4-benzenedicarboxylic acid, and bis(2-ethylhexyl) ester. Most of the identified substances are known to be allelopathic. These results showed that water extracts of the root and bulb of Lanzhou lily showed autotoxic effects on lily seedling growth.

Effects of temperature on flower bud differentiation, pigment contents, and photosynthesis of male and female Humulus scandens

GUO Hai-Yan, DUAN Jing, LIU Jin-Ping, YOU Ming-Hong, XIE Rui-Juan

2017, 26(8):  104-112.  DOI: 10.11686/cyxb2016425

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In this study, we evaluated the effects of temperature on the physiology of male and female plants of the dioecious climbing herb, Humulus scandens. Seeds of H. scandens were sown in pots, and the pots were moved to artificial climate incubators set at 15, 20, or 25 ℃ when the seedlings had one to two true leaves. These temperatures were selected based on the average temperatures of the areas where the wild resource are concentrated. We determined the duration of vegetative growth, growth accumulated temperature, number and characteristics of leaves, pigment contents, biomass, and photosynthetic parameters of the male and female seedlings. The effects of temperature on photosynthetic production, net photosynthetic rate (P_n), photosynthetic efficiency, transpiration rate (T_r), intercellular CO₂ concentration (C_i), and gas exchange (G_s) were also analyzed. The results showed that, 1) temperature and gender had significant effects on growth duration and accumulated temperature (P<0.01). Flower buds differentiated earlier in male plants than in female plants at all three temperatures (P<0.05). Flower bud differentiation was affected by temperature and was optimal at 20 ℃. Growth accumulated temperature differed between males and females, but was not related to growth duration. Temperature significantly affected all of the measured leaf traits (P<0.05), with the strongest effect on leaf number per plant>leaf area per leaf>leaf width>leaf length. The pigment contents did not differ significantly between males and females (P>0.05). Temperature significantly affected the contents of all pigments except for chlorophyll b (P<0.05) with the strongest effect on carotenoids>chlorophyll (a+b)>chlorophyll a/b>chlorophyll a>chlorophyll b. Pigment contents were significantly lower at 20 ℃ than at the other temperatures. Photosynthetic parameters differed significantly between males and females and among temperatures (P<0.05). The temperature affected photosynthetic parameters in the order P_n>C_i>T_r>G_s. The parameters P_n, C_i, and T_r were mainly affected by temperature, but G_s was mainly affected by gender. The biomass and root biomass distribution were significantly higher in female plants than in male plants (P<0.05). Temperature significantly affected biomass accumulation and allocation in the following order: root>leaf>stem (P<0.01). Biomass per plant significantly decreased as the temperature decreased (P<0.05). The highest biomass allocation to the root and stem was at 25 ℃ and the highest biomass allocation to leaves was at 15 ℃.

Effects of elevated carbon dioxide concentration on the growth and antioxidant system in tall fescue under heat stress

YU Jing-Jin, FAN Ning-Li, LI Ran, YANG Zhi-Min

2017, 26(8):  113-122.  DOI: 10.11686/cyxb2017093

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The gradual increases in the atmospheric CO₂ concentration and temperature are the two primary characteristics of global climate change. However, the rising atmospheric CO₂ concentration could alleviate the negative effects of heat stress. Therefore, the aim of this study was to explore the mitigating effects of elevated CO₂ on the growth and antioxidant system a perennial grass under heat stress. Tall fescue (Festuca arundinacea cv. ‘Barlexas’) was exposed to either ambient CO₂ concentration (400 μmol/mol) or elevated CO₂ concentration (800 μmol/mol) under optimal growth temperature (25/15 ℃ day/night) or elevated temperature (35/25 ℃ day/night) conditions. After 28 days of the experimental treatment, heat stress caused a significant reduction in relative growth rate (RGR), leaf net photosynthetic rate (P_n), number of green leaves, antioxidant enzyme activities [(superoxide dismutase, (SOD), catalase (CAT), peroxidase (POD), and ascorbate peroxidase (APX)], as well as an increase in electrolyte leakage (EL), and the contents of malondialdehyde (MDA) and reactive oxygen species (ROS) (H₂O₂ and O₂^-·). Elevated CO₂ mitigated these negative effects of heat stress in tall fescue. Compared with plants grown under heat stress and ambient CO₂, those grown under heat stress and elevated CO₂ had lower leaf EL and MDA contents (72% and 39% lower, respectively); the P_n, F_v/F_m, and number of green leaves were increased by 1.74-fold, 17%, and 1.65-fold, respectively; and the ROS contents were significantly lower (H₂O₂ and O₂^-· contents decreased by 46% and 31%, respectively). These results demonstrated that elevated CO₂ can improve the heat tolerance of tall fescue through increased photosynthetic capacity, cellular membrane stability, and decreased ROS accumulation.

Alleviation of cadmium toxicity in Corydalis yanhusuo seedlings by exogenous calcium or potassium

ZHANG Jing, YU Shun-Hui, QI Jun-Sheng, LIANG Ke-Zhong, CHEN Shu-Hong, LIU Lei, CHEN Hua-Hua, LU Ya-Ping

2017, 26(8):  123-130.  DOI: 10.11686/cyxb2016386

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In this study, we explored the alleviating effects of exogenous calcium (Ca²⁺) and potassium (K⁺) on Corydalis yanhusuo seedlings under cadmium (Cd) stress. Seedlings of C. yanhusuo were grown in soil containing Cd (0-25 mg/kg) and their plant height, biomass and physiological characteristics, heavy metal content, and medicinal quality were determined. At all levels of Cd stress, the optimal concentrations of exogenous Ca²⁺ and K⁺ to alleviate Cd stress were 100 and 200 mg/kg, respectively. Under low-Cd and high-Cd stress, the addition of 100 mg/kg Ca²⁺ increased the soluble sugars content in seedlings, increased the activities of superoxide dismutase (SOD), peroxidase (POD) and catalase (CAT), and decreased the malondialdehyde (MDA) content, compared with those in plants without exogenous Ca²⁺ treatment. There were no changes in these parameters in plants under low-Cd stress treated with K⁺ at 200 mg/kg. Under all levels of Cd stress, the addition exogenous Ca²⁺ and K⁺ at the optimal concentrations decreased the rate of micronucleus formation in the roots, indicating that there was a significant alleviation of Cd poisoning. Under Cd stress (especially high-Cd stress at 25 mg/kg), exogenous Ca²⁺ and K⁺ alleviated Cd poisoning of seedlings and relieved chromosomal damage by increasing the antioxidant capacity of C. yanhusuo seedlings. Exogenous Ca²⁺ and K⁺ also affected Cd accumulation in above-ground and below-ground parts of the plant, but the effects were complex. Under 25 mg/kg Cd stress, the tetrahydropalmatine content increased by 27.52% after adding exogenous Ca²⁺, indicating a significant increase in the medicinal quality of C. yanhusuo. Therefore, when growing C. yanhusuo in soil contaminated with Cd, the addition of an appropriate amount of Ca²⁺ can alleviate Cd poisoning via its effects on the activity of antioxidant enzymes. This leads to a decrease in the Cd content in tubers, thereby improving their medicinal quality. These results provide a theoretical basis for the safe and efficient cultivation of high-quality C. yanhusuo in Cd-contaminated soil.

Trehalose alleviates the negative effects of salinity on the growth and physiological characteristics of maize seedlings

TIAN Li-Xin, QU Dan-Yang, BI Wen-Shuang, XIE Teng-Long, LI Jing

2017, 26(8):  131-138.  DOI: 10.11686/cyxb2017156

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The aim of this study was to investigate the effects of exogenous trehalose on the growth of maize seedings under salt stress. We evaluated the plant biomass, chlorophyll content, membrane lipid peroxidation, antioxidant enzyme activities, and contents of osmotic adjustment substances in maize seedlings (variety Zhengdan 958) in the control (no NaCl) and under salinity stress (150 mmol/L NaCl) with and without trehalose treatment. The results showed that, compared with the control, salt-stressed seedlings showed significantly lower dry weight, fresh weight, leaf area, chlorophyll content, and antioxidant enzyme activities, and significantly higher malondialdehyde (MDA) content, proline (Pro) content, soluble protein content, and membrane permeability. Among the salt-stressed maize seedlings, those treated with 10 mmol/L trehalose showed significantly increased biomass and chlorophyll content, decreased MDA content, Pro content, and membrane permeability, increased superoxide dismutase (SOD) and peroxidase (POD) activities, and increased soluble protein contents. These results indicated that exogenous trehalose could alleviate the negative effects of salinity stress on maize seedlings, and increase the resistance of maize seedlings to salinity stress.

Effect of cotyledon damage on the early growth of Sophora alopecuroides seedlings

LIU Ying, ZHAO Yu, CUI Dong, LENG Jia-Ming, DONG Fang-Hui

2017, 26(8):  139-145.  DOI: 10.11686/cyxb2017052

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The aim of these experiments was to determine the effects of cotyledon damage on the growth of Sophora alopecuroides, a native invasive species in the Ili River Valley of Xinjiang. To simulate cotyledon predation, cotyledons were cut with different degrees of severity (excision of half a cotyledon, half of two cotyledons, one cotyledon, 1.5 cotyledons, and two cotyledons) or left uncut (control), and the growth of the seedlings was evaluated. The mortality rate, plant height, and leaf area strongly depended on the degree of cotyledon damage. There were no significant differences in seedlings’ taproot length among the damaged and non-damaged treatments. Compared with the control, the seedlings with 1.5 and two damaged cotyledons formed significantly fewer and shorter lateral roots, while those with half or one damaged cotyledon showed no significant difference in lateral root formation. Cotyledon damage significantly decreased the stem biomass, leaf biomass, and total biomass of seedlings, but had only small effects on the root biomass and root∶shoot ratio. As the severity of cotyledon damage increased, biomass allocation to the stem was unaffected, biomass allocation to the root significantly increased, and biomass allocation to the leaf significantly decreased. These results indicate that cotyledon damage is a bottleneck in seedling establishment and population regeneration.

Seed germination and physiological characteristics of Chenopodium quinoa under salt stress

YANG Hong-Wei, LIU Wen-Yu, SHEN Bao-Yun, LI Chao-Zhou

2017, 26(8):  146-153.  DOI: 10.11686/cyxb2016394

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In this study, we evaluated the effects of different concentrations of NaCl on seed germination and seedling growth of Chenopodium quinoa. Seeds and seedlings of C. quinoa were exposed to different concentrations of NaCl, and seed germination, physiological indexes, and biochemical indexes were determined. The germination percentage, germination energy, germination index, and vigor index of C. quinoa seeds decreased as the concentration of NaCl increased. When the concentration of NaCl was 3.0%, none of the quinoa seeds germinated. As the concentration of NaCl increased, the leaf water content decreased, the contents of soluble sugars, proline, malondialdehyde, relative conductance, and O₂^-· production rate increased, and the activities of superoxide dismutase, peroxidase, and catalase increased and then decreased. The plant height and stem diameter decreased as the NaCl concentration increased, but root lengths increased and then decreased. The longest root length was in the 1.8% NaCl treatment. In conclusion, seedling growth of C. quinoa was promoted by low concentrations of NaCl, but inhibited by high concentrations of NaCl. The threshold of salt tolerance was 1.8% NaCl.

Evaluation of the salt resistance of the Cynodon dactylon germplasm from Xinjiang during the seed germination period

CHAI Yan, SUN Zong-Jiu, LI Pei-Ying, BADEMU Qiqige, ZHANG Xiang-Xiang, YANG Jing

2017, 26(8):  154-167.  DOI: 10.11686/cyxb2016428

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The aim of these experiments was to determine the differences in salt resistance among Cynodon dactylon germplasm collected from Xinjiang. The relative germination rate, relative germination energy, germination index, and the length of the radical and plumule of 50 C. dactylon accessions were measured with the paper germination method under 0 (control), 0.4%, 0.8%, 1.2%, and 1.6% NaCl stress. Then, a synthetic evaluation of salt-resistance was conducted using the cluster analysis method. As the salt concentration increased, the relative germination rate, relative germination energy, and germination index of C. dactylon significantly decreased, and the length of the radical and plumule first increased then decreased, and peaked at 0.4% NaCl. As the salt concentration increased, the variation coefficient of all indexes increased. The variation coefficient under 1.6% salt stress was more than 2.0 times that in the control (no NaCl). The semi-lethal NaCl concentration for the C. dactylon germplasm was 1.28% (variation coefficient, 45.66%) and 1.2% NaCl was the optimum concentration to evaluate the salt tolerance of C. dactylon. The comprehensive cluster analysis of 50 Xinjiang C. dactylon accessions identified Cd012 as the most salt-tolerant accession; Cd019, Cd021, Cd020, and Cd054 as moderately salt-tolerant accessions; and Cd001, Cd033, Cd035, Cd057, and Cd059 as salt-sensitive accessions.

Transcriptome profiling analysis of the phosphate-solubilizing mechanism of the white clover rhizosphere strain RW8

LI Xiao-Dong, WANG Xiao-Li, CHEN Xi, CAI Lu, ZENG Qing-Fei, SHU Jian-Hong, CAI Yi-Ming

2017, 26(8):  168-179.  DOI: 10.11686/cyxb2016399

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We conducted transcriptome sequencing of the white clover (Trifolium repens) rhizosphere phosphorus-solubilizing bacterium RW8 to explore its gene expression profiles. Cells of RW8 were cultured in three different media: one containing insoluble phosphorus (group A), one containing soluble phosphorus (group B), and one lacking phosphorus (group C). Compared with group B cells, group A cells showed 4782 and 447 up- and down-regulated genes, respectively, and group C cells showed 3630 and 209 up- and down-regulated genes, respectively. The up-regulated genes in Groups A and C had similar gene ontology annotations. The main subcategories in the biological process category were metabolic process, cellular process, single-organism process, response to stimulus, localization, and biological regulation. In the cell components category, the main subcategories were cell part, membrane, membrane part, and macromolecular complex. In the molecular function category, the main subcategories were catalytic, binding, and transporter. A metabolic pathway analysis showed that several metabolic pathways were significantly enriched in groups A and C, including 2-oxocarboxylic acid metabolism, alpha-linolenic acid metabolism, C5-branched dibasic acid metabolism, fatty acid metabolism, glycine-serine-threonine metabolism and valine-leucine-isoleucine biosynthesis. Ten differentially expressed genes in three different groups were analyzed by quantitative real-time polymerase chain reaction (qRT-PCR). The transcriptional patterns detected by qRT-PCR were similar to those detected in the transcriptome sequencing analyses. The composition and concentrations of organic acids were detected by high performance liquid chromatography (HPLC). The lactic acid, succinic acid, and citric acid concentrations were significantly higher in group A and group C than in group B. The fumaric acid and malic acid concentrations were much higher in group C than in groups A and B, and did not differ significantly between groups A and B. The concentration of α-ketoglutaric acid was higher in group A than in group B, and did not differ significantly between groups C and B.

Differences in soil bacterial community composition among three forage-crop rotations on the Longdong Loess Plateau

LIANG Zhi-Ting, DENG Jian-Qiang, WANG Zi-Kui, SHEN Yu-Ying, WANG Xian-Zhi

2017, 26(8):  180-191.  DOI: 10.11686/cyxb2017048

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We analyzed the composition of the soil bacterial community in two topsoil layers (0-10 cm and 10-20 cm) under three crop-forage rotation models; winter wheat-fallow-soybean (W-F-S), winter wheat-forage rapeseed-common vetch (W-R-V), and winter wheat/fallow-lucerne (W/F-L-L). The soil bacterial community was analyzed by sequencing 16S rRNA gene amplicons. The results indicated that the dominant phyla in the topsoil were Proteobacteria and Acidobacteria under all three rotation models. The dominant genera in the topsoil under the three rotation models were Rhodoplanes, Gemmata, Nitrospira, Bradyrhizobium, Adhaeribacter, and Balneimonas. The bacterial communities in the topsoil under the W-F-S rotation sequence were dominated by Janthinobacterium and Lysobacter, which were related to the prevention and control of soybean cyst nematode, and were closely associated with soil-borne pathogen resistance under the W-F-S rotation. The dominant genus in topsoil in the W-R-V rotation was Erwinia, which was related to rapeseed, and that in the W/F-L-L rotation sequence was Sphingomonas, which was indicative of no- or low-tillage during alfalfa planting. The rotations could be ranked, from highest bacterial alpha-diversity to lowest, as follows W-F-S>W/F-L-L>W-R-V in the 0-10 cm topsoil layer; and W-R-V>W/F-L-L>W-F-S in the 10-20 cm topsoil layer. This study reveals the mechanisms by which nitrogen fixation is promoted and soil-borne pathogens are inhibited in various crop-forage rotation systems, from the perspective of the bacterial community composition and function. The results of this study have important theoretical value for maintaining a healthy soil ecological environment and for establishing successful forage-crop rotation systems on the Longdong Loess Plateau.

Effects of probiotics on the growth performance, organ relative weight, and intestine development of weaned piglets

LI Xue-Li, WANG Chao, YU De-Fu, DING Li-Ren, ZHU Wei-Yun, HANG Su-Qin

2017, 26(8):  192-199.  DOI: 10.11686/cyxb2016438

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The objective of this study was to investigate the effects of probiotics on the growth performance, relative organ weight, and intestinal development of weaned piglets, to determine whether probiotics can ease the weaning transition. A total of 144 Suhuai weaned piglets (9.34±0.33 kg) at an age of 28 days were randomly assigned to three groups; control group (basal diet), antibiotics group (basal diet+antibiotics), and probiotic group (basal diet+probiotic). Each group had six replicates, with eight piglets per replicate. The experiment started at 32 days after birth and ended at 59 days after birth. At 59 days, one piglet from each replicate was slaughtered for sampling. Compared with the control, the probiotic treatment significantly increased the average daily gain (ADG) and average daily feed intake (ADFI), and decreased the feed/gain ratio (F/G) and diarrhea rate after weaning (P<0.05). It also significantly increased ADG of the spleen and improved villus development in the duodenum, and reduced the villus height/crypt depth (V/C) of the duodenum, jejunum, and ileum after weaning (P<0.05). Compared with the control, the probiotic treatment significantly decreased the pH of the cecum and colon. A correlation analysis showed that the increased ADG was associated with increased relative weight of the liver. The increased ADFI was strongly related to the increased relative weight of the duodenum and spleen and the increased V/C of the jejunum. The decreased F/G was correlated with the increased relative weight of the colon. The decreased diarrhea rate was correlated with the increased relative weight of the duodenum and spleen, and with the increased V/C of the duodenum and jejunum. The findings imply that a probiotic can relieve weaning stress in piglets by improving their growth performance and decreasing the diarrhea rate via their effects on small intestine morphology, organ relative weight, and gastrointestinal pH. Probiotics could be used as alternatives to antibiotics during the weaning of piglets.

Characteristics of the plant-root system and its relationships with soil organic carbon and total nitrogen in a degraded sandy grassland

LUO Yong-Qing, ZHAO Xue-Yong, WANG Tao, LI Yu-Qiang

2017, 26(8):  200-206.  DOI: 10.11686/cyxb2016378

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Plants are the key component of ecosystems in terms of matter exchange and energy flux. The aboveground and belowground biomasses affect carbon and nitrogen feedback processes differently in the plant-soil system. In this study, the plant characteristics, soil organic carbon (SOC), soil total nitrogen (TN), and their relationships were investigated in four different habitats in the Horqin Sandy Land; mobile dune, semi-fixed dune, fixed dune, and fenced grassland. These four habitats represent four consecutive stages of the restoration process. The results showed that plant aboveground biomass and belowground biomass varied among the habitats. Aboveground biomass initially increased and then decreased during the restoration process, while the belowground biomass showed an exponential increase during restoration. The root to shoot ratio was significantly higher in fenced grassland than in the other three habitats. Similarly to biomass, the length and surface area of plant roots significantly increased during restoration, but there was no obvious trend in the change in root volume, although it differed significantly among the four habitats. Both the contents and storage of SOC and TN increased during the restoration process. The contents of both SOC and TN were higher in the 0-10 cm soil layer than in the 10-20 cm soil layer, however, their rates of increase were higher in the 10-20 cm soil layer than in the 0-10 cm soil layer. Both the aboveground biomass and belowground biomass showed significant linear relationships with SOC and TN storage, while the regression coefficient was higher for belowground biomass than for aboveground biomass. From the perspective of plant root morphology, root length and root surface area were more strongly related than root biomass to SOC and TN. In conclusion, plant roots were more strongly related to SOC and TN than was aboveground biomass. Therefore, root activities may be an important factor for carbon and nitrogen accumulation in soil, especially in barren soils in environments with strong winds and sand-moving processes.

Nutritional quality of four important herbage species in summer grazing grassland in the alpine zone, west Tianshan Mountain

ZHANG Fan-Fan, HE Hai-Xiu, YU Lei, LU Wei-Hua, ZHANG Qian-Bing, MA Chun-Hui

2017, 26(8):  207-215.  DOI: 10.11686/cyxb2016389

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The aim of this study was to evaluate the nutritional quality of four important herbage species growing in summer alpine pasture in the western region of Tianshan Mountain. We determined the nutritive value, digestibility, and parameters of in vitro gas production for four typical herbages (Kobresia capillifolia, Carex stenocarpa, Alchemilla sibirica, and Sanguisorbs alpina) growing in summer pasture on Shaertao mountain (2800-3400 m above sea level), west Tianshan. The contents of crude fiber and crude fat did not differ significantly among the four herbage species (P>0.05). C. lasiocarpa had the highest contents of acid detergent fiber (P=0.048) and neutral detergent fiber (P=0.005). A. sibirica had the highest content of crude ash (P=0.037) and the longest delay time (P=0.005). S. alpina had the highest contents of crude protein (P<0.0001), calcium (P=0.001), and phosphorus (P=0.004), the most digestible organic matter (P=0.003), and the highest metabolic energy (P=0.067) and gas production rate (P=0.079). K. capillifolia had the highest dry matter content (P=0.001). The results of a principal component analysis based on the 14 main indexes of nutritional quality indicated that the four herbages were ranked, from highest nutritional value to lowest, as follows: S. alpine>A. sibirica>K. capillifolia>C. stenocarpa.

Nitrogen and phosphorus ecological stoichiometry in different-aged alfalfa stands in southeast Shandong

WANG Hui, MIAO Fu-Hong, SUN Juan, LIU Hong-Qing, YANG Guo-Feng

2017, 26(8):  216-222.  DOI: 10.11686/cyxb2016436

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The main aim of this study was to explore the stoichiometry of nitrogen (N) and phosphorus (P) in alfalfa stands of different ages and cutting frequencies in the southeast Shandong area. We analyzed N and P contents and their stoichiometric ratios in the leaf and stem of alfalfa plants in stands of different ages (2, 3, 4, and 5 years). The leaf and stem N and P contents of alfalfa differed significantly among different stand ages and cutting frequencies. The leaf and stem N and P contents were higher in the 3-year-old alfalfa stand than in alfalfa stands of other ages. The leaf and stem N∶P ratios were highest in the 4-year-old alfalfa stand and lowest in the 3-year-old alfalfa stand. The leaf and stem N and P contents of alfalfa first increased and then decreased with increased cutting frequency, reaching a maximum at the third cut (except the stem N content of 3-year-old alfalfa). The leaf N∶P ratio in 2-year-old and 4-year-old alfalfa stands first decreased and then increased with cutting, while the stem N∶P ratio first decreased and then increased with cutting (except in the 5-year-old stand), and showed the minimum value at the fourth cut. The N and P contents and the N∶P ratios in the leaf and stem were affected significantly by stand age and the cutting frequency. The N contents in the leaf and stem were positively correlated with the N∶P ratio. The P contents in the leaf and stem were negatively correlated with the N∶P ratio. These results show that the nutrient limiting alfalfa growth shifted from N to P as the stands aged.