Table of Content

20 May 2017, Volume 26 Issue 5

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Orignal Article

Quantitative assessment of relative roles of climate change and human activities on grassland net primary productivity in the Three-River Source Region, China

ZHANG Ying, ZHANG Chao-Bin, WANG Zhao-Qi, YANG Yue, ZHANG Yan-Zhen, LI Jian-Long, AN Ru

2017, 26(5):  1-14.  DOI: 10.11686/cyxb2016420

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The Three-River Source Region (TRSR), a region with key importance for the ecological security of China, has been affected by climate change and by changes in human activities driven by a series of ecological restoration projects in recent decades. In this study, we analyzed land use and cover change (LUCC) in the TRSR and the consequent changes in grassland net primary productivity (NPP). For this analysis, we used the CASA (Carnegie-Ames-Stanford Approach) model, a climatic production model, and land use data for the study area from 2001 and 2012, which were derived from the MODIS global land cover product. The contributions of LUCC, land management measures, and climate change to NPP variations were analyzed quantitatively. The results showed that, during the 12 years, the net increase in grassland area was 6749 km², and the average NPP and total NPP of grassland decreased by 5.47% and 5.00%, respectively. New grassland contributed 1293.12 Gg C (Gg=10⁹ g) to total NPP, while the loss of grassland led to a decrease of 215.42 Gg C. The climatic total NPP of grasslands decreased by 20.27% and the anthropogenic total NPP increased by 41.51%. These results indicate that climate conditions have negatively affected vegetation growth, whereas human activities have favorably affected vegetation recovery. The contributions of climate change, LUCC, and improved management measures to the variation in total NPP were -165.28 Tg C, 2.22 Tg C, and 140.03 Tg C, respectively. Therefore, improving grassland management measures can significantly reduce grassland deterioration due to climate change.

Spatial distribution and chemical properties of marsh wetland soil in the Heihe Nature Reserve

BAI Na, WANG Li, KONG Dong-Sheng

2017, 26(5):  15-28.  DOI: 10.11686/cyxb2016269

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The aim of this study was to analyze the spatial distribution of soils with different chemical properties in the marsh wetland of the Heihe Nature Reserve, Zhangye. A field study was conducted in the marsh wetland, and soil samples were collected for chemical analyses in the laboratory. Using spatial distribution instead of time succession, descriptive statistics and linear regressions of data were used to explore the distribution of available nutrients, organic matter, soil total salt content, and pH in the marsh soils. The soil organic matter levels significantly increased with increasing soil depth. As the soil depth increased, the available nitrogen content showed a clear vertical differentiation, first increasing and then decreasing. Available phosphorus, available potassium, and total salt content showed the same distribution patterns; that is, significant accumulation in surface soils. There was no significant difference in the spatial distribution of pH, but soil in this region is alkaline to strongly alkaline. Soil organic matter and pH showed a weak negative correlation, because pH indirectly affects the soil organic matter content by inhibiting growth. The total salt content was strongly correlated with available potassium. The variability coefficients of total salt, soil organic matter, available nitrogen, available phosphorus, and available potassium had medium values, while that of pH had a low value. The marsh wetland in Heihe is deteriorating because of a lack of soil and water conservation in arid and semiarid regions. Long-term experimental research to monitor changes in soils in sensitive areas is required for their protection and restoration.

Effects of plateau pika (Ochotona crzoniae) disturbances on plant species diversity and aboveground plant biomass in a Kobresia pygmaea meadow in the Qinghai Lake Region

JIN Shao-Hong, LIU Tong, PANG Xiao-Pan, YU Cheng, GUO Zheng-Gang

2017, 26(5):  29-39.  DOI: 10.11686/cyxb2016391

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A field survey was carried out to determine the effects of plateau pika disturbances on plant species diversity and productivity in a Kobresia pygmaea meadow in the Qinghai Lake Region. A random stratified paired sampling design was used to select a disturbed area containing burrow entrances and plateau pika simultaneously, and an undisturbed area without burrow entrances or plateau pika. The field experiment was conducted in early May, 2015. The dominant plant was the same in the disturbed and undisturbed areas, but its degree of dominance was lower in the disturbed area than in the undisturbed area. Ten plots (25 m×25 m) were randomly placed with at least 25 m distance between plots. Each plot was fenced to exclude other wild herbivores. In each plot, vegetation was sampled in three subplots on the diagonal (each 1 m×1 m, with at least 10 m distance between subplots). The results showed that plateau pika disturbances had different effects on species diversity and plant functional groups. Plateau pika disturbances increased the richness index of weeds and plant species richness, and decreased the plant evenness index, the richness index of Cyperaceae, and the evenness index of Gramineae (P<0.05). In disturbed areas, plant species richness and evenness and the richness index of weeds gradually increased with increasing plateau pika disturbance levels, while the evenness index of Gramineae decreased. Plateau pika disturbances significantly reduced the total community biomass (P<0.05), but the trends in the changes of biomass differed among functional groups. Plateau pika disturbances significantly decreased the biomass of Cyperaceae, Gramineae, and Leguminosae, but increased the biomass of weeds (P<0.05). With increasing plateau pika disturbance levels, the biomass of Cyperaceae and Leguminosae decreased, the biomass of weeds increased, and the biomass of Gramineae first increased and then decreased. These results suggested that analyses of plant diversity cannot replace analyses of plant functional diversity when trying to understand the responses of alpine meadows to plateau pika disturbances.

Effects of belt-spacing of artificial Caragana intermedia stands on the ecology of woodland on the Desert Steppe

ZHOU Jing-Jing, MA Hong-Bin, ZHOU Yao, CAI Yu-Rong, WU Xing-Wang, SU Ting-Ting, JIA Xi-Yang

2017, 26(5):  40-50.  DOI: 10.11686/cyxb2016387

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The spacing of Caragana intermedia belts in plantations can markedly affect the ecology of the surrounding woodland. In this study, we evaluated the changes in the woodland habitat after cutting C. intermedia forests with different spacings of C. intermedia belts. The study site was a forest grassland on the desert steppe with C. intermedia belts planted with 4 m, 6 m, and 8 m spacings. The soil physical and chemical properties, air temperature, wind speed, and amount of wind erosion were evaluated to determine the effects of different belt spacings of C. intermedia forest after stumping (cutting) C. intermedia plants to a stubble height of 0 cm in April 2015. The main findings were as follows: 1) The forest grassland with 8 m spacing of C. intermedia belts showed the highest proportion of perennial herbaceous species, vegetation coverage, and vegetation density (P<0.05), but vegetation coverage did not differ significantly between the 4 m and 6 m C. intermedia belt-spacing treatments. There was no difference in aboveground biomass and species diversity among the three treatments (P>0.05). 2) As the belt spacing increased, the soil fine particle content, soil organic matter content, total nitrogen content, available phosphorus content, and available potassium content tended to increase. The soil water content was highest in the forest with 6 m belt spacing, and lowest in the forest with 4 m belt spacing. 3) The average air temperature was highest in the forest with 4 m belt spacing, and lowest in the forest with 8 m belt spacing, while wind speed showed the opposite trend. Wind erosion of soil was highest in the forest with 6 m belt spacing (P<0.05), and lowest in the forests with 4 m and 8 m belt spacings. 4) Correlation analyses indicated that plant diversity was positively correlated with soil organic matter content, soil total nitrogen content, and soil fine particle content, and that soil organic matter content was positively correlated with soil fine particle content and vegetation coverage. These results indicate that C. intermedia forests with 8 m belt spacing have the advantages of increased vegetation diversity, better soil quality, and lower soil wind erosion of the surrounding forest grassland.

Effect of nitrogen treatments on growth of the invasive plant Xanthium strumarium, the native plant Xanthium sibiricum, and their reciprocal crosses

XUN Zhi-Feng, BAI Long, QU Bo, XU Yu-Feng, LI Guang-Hai, ZHAN Zhong-Lang, SHI Jiu-Yao

2017, 26(5):  51-61.  DOI: 10.11686/cyxb2016217

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The effect of soil nutrients on the invasion of alien plants is a hot topic in invasion biology research, but few studies have focused on the effects of soil nutrients on the characteristics of reciprocally crossing plants. In this study, we analyzed the differences in biomass accumulation and distribution, growth characteristics, and photosynthetic characteristics of the invasive plant Xanthium strumarium, the native plant Xanthium sibiricum, and their reciprocal crosses (Xst♀×Xsi♂ and Xsi♀×Xst♂) under different nitrogen treatments, to explore the relationship between invasion and soil nutrient status. The stem diameter, total leaf area, total biomass, root biomass, root biomass ratio, and root mass/crown mass ratio of X. strumarium, X. sibiricum, and their reciprocal crosses (Xst♀×Xsi♂) increased significantly (P<0.05) and the leaf area to root mass ratio decreased significantly (P<0.05) with increasing nitrogen levels in the soil. The net assimilation rate of X. strumarium was significantly higher than that of X. sibiricum (P<0.05), but its specific leaf area was significantly lower than that of X. sibiricum (P<0.05). The relative growth rate, net assimilation rate, and mean leaf area ratio were higher in the male progeny than in the female progeny (P<0.05), and the biomass index and growth index were higher in Xst♀×Xsi♂ plants than in Xsi♀ × Xst♂ plants. We concluded that: 1) when nutrients are limited, X. strumarium distributes more biomass to the root, possibly as an ecological strategy to adapt to nutrient-heterogenous environments during invasion. 2) Compared with the hybrid progenies of X. sibiricum, those of X. strumarium show stronger growth and increased reproductive ability, which are properties that will further strengthen their invasiveness.

Allelopathic effects of artemisinin on pasture grasses

WEI Li-Ben, XIA Zhi-Lin, YIN Jie, YUAN Ling

2017, 26(5):  62-69.  DOI: 10.11686/cyxb2016252

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Artemisia annua, which grows in many parts of Chongqing, releases artemisinin, which can inhibit the growth of surrounding plants. To identify pasture grasses that can grow in areas with abundant A. annua, we conducted a pot experiment to study the effects of artemisinin on grass growth. We evaluated the growth, physiology, antioxidant enzyme activity, and nutrient uptake of three pasture grasses (Lolium perenne, Trifolium repens, and Vicia villosa) growing in soil with artemisinin at different concentrations (0, control; 6,12,24,36 mg/kg soil). Artemisinin significantly affected the growth of all three pasture grasses, and the effects differed depending on the artemisinin concentration and the grass species. At 6 mg/kg, artemisinin led to significant decreases in growth indexes and the degree of inhibition increased with increasing artemisinin concentrations. Compared with their respective controls, L. perenne, T. repens, and V. villosa plants grown with artemisinin at 36 mg/kg showed 76.83%, 90.10%, and 65.09% decreases in biomass, respectively, and 47.82%, 38.76% and 44.49% decreases in plant height, respectively. Artemisinin had a negative allelopathic effect on all three pasture grasses, with the strongest effect on T. repens, followed by L. perenne and then V. villosa, indicating that V. villosa was the least sensitive to artemisinin. Therefore, V. villosa may be the most adaptable of the three tested grasses to growth in areas of Chongqing with abundant A. annua. In addition, artemisinin significantly reduced the chlorophyll content, root vigor, nitrate reductase activity, photosynthetic rate, root nutrient uptake, and nitrogen assimilation in all of the tested grasses. As a result, the uptake of nitrogen, phosphorus, and potassium by pasture grasses was decreased by more than 80%. The activity of protective oxidases in pasture grasses varied in response to artemisinin, with superoxide dismutase showing increased activity, peroxidase showing decreased activity, and catalase showing no significant change in activity. However, artemisinin greatly increased the malondialdehyde content in all three pasture grasses, suggesting that more oxyradicals were produced or less oxyradicals were eliminated, leading to cell membrane damage.

Efficient double cropping pattern of photoperiod-sensitive sorghum-sudangrass hybrids in summer after winter wheat

HE Chun-Gui, HE Zhen-Fu, WANG Fei

2017, 26(5):  70-80.  DOI: 10.11686/cyxb2016247

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We evaluated double-cropping patterns of photoperiod-sensitive sorghum-sudangrass hybrids after a winter wheat crop in the Longdong dryland area, Gansu province. We conducted a field experiment with three dibbling methods (no tillage or mulching, tillage without mulching, tillage with plastic mulching), three varieties [Monster, BJM, and Big kahuna (BMR)], and two cutting treatments (once or twice). The phenology, agronomic traits, and grass yield of the varieties were compared among these treatments. In the once-cut treatment (before the early frost), plant height, stem diameter, number of internodes, number of leaves, plant fresh weight, leaf weight per plant, stem weight per plant, and number of tillers showed highly significant differences among varieties (P<0.01); plant height and number of internodes showed significant differences among dibbling modes (P<0.05); and number of leaves, plant fresh weight, leaf weight per plant, stem weight per plant, and number of tillers showed highly significant differences among dibbling modes (P<0.01). The variety×dibbling mode interaction was significant only for leaf weight (P<0.05). For each variety, the fresh grass yield (65% moisture) was higher in the once-cut than in the twice-cut treatment. The average yield across the three varieties was 3.21 times higher in the once-cut treatment than in the two-cuts treatment. There were highly significant differences in grass yield in the first cut, the second cut, and the sum of two cuts among the three varieties in the two-cuts treatment (P<0.01). The grass yield also differed significantly among the three varieties in the once-cut treatment (P<0.05). The difference in grass yield among dibbling modes was highly significant in both cutting treatments (P<0.01). The variety×dibbling mode interaction was highly significant for grass yield in both cutting treatments (P<0.01). In the once-cut treatment, the average fresh grass yield of all three varieties in the plastic-mulching treatment was 62.21% higher than that in the no tillage without mulching treatment, and 36.45% higher than that in the tillage without mulching treatment. The fresh grass yield averaged across the three varieties in the tillage without mulching treatment was 21.08% higher than in the no tillage without mulching treatment. Under these conditions in the Longdong dryland area, the best combination of cultivation practices for photoperiod-sensitive sorghum-sudangrass hybrids after a winter wheat crop is tillage with plastic mulching, the BJM variety, with one cutting event. If growers prefer to conduct two or more cuttings, then the Monster variety combined with tillage with plastic mulching is preferable.

Effects of nutrient addition on leaf traits of six plant species in a Stipa baicalensis grassland in Inner Mongolia, China

LIU Hong-Mei, LI Jie, YU Li, HUANGFU Chao-He, YANG Dian-Lin

2017, 26(5):  81-91.  DOI: 10.11686/cyxb2016242

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Nutrient addition is an effective management measure for recovery of degraded grassland. Stipa baicalensis grassland is a type of meadow steppe that plays an important role in livestock husbandry in China. We conducted a field experiment to explore the mechanisms underlying variation in plant leaf traits in a mature typical steppe ecosystem in Inner Mongolia where nutrients have been added since 2010. The experiment had a randomized block design with six blocks of eight treatments: CK (control, no nutrient addition), N (N addition only, 100 kg/ha), P (P addition only, 100 kg/ha), K (K addition only, 100 kg/ha), NP (mixed N and P addition, 100 kg/ha each), NK (mixed N and K addition, 100 kg/ha each), PK (mixed P and K addition, 100 kg/ha each), and NPK (mixed N, P, and K addition, 100 kg/ha each). We selected six dominant and sub-dominant plant species for analyses: S. baicalensis, Leymus chinensis, Achnatherum sibiricum, Melissitus ruthenica, Serratulay amatsutanna, and Filifolium sibicum. Together, these species account for >90% of the total community aboveground biomass. We investigated variations in specific leaf area (SLA), leaf chlorophyll content, leaf N content, and leaf P content of the six plants under different nutrient treatments, to determine their responses to variations in soil physical and chemical properties. In all six plant species, the SLA, chlorophyll content, and leaf nutrient contents varied among different nutrient treatments, but the scope and direction of changes differed among plant species. A correlation analysis demonstrated that leaf SLA was positively correlated with leaf chlorophyll content and leaf N content (P<0.01), and with leaf P content (P<0.05). Leaf chlorophyll content was positively correlated with leaf N content and soil NH4+-N (P<0.01). Leaf N content was positively correlated with soil pH (P<0.01). Leaf P content was positively correlated with soil P, soil available P, and soil pH (P<0.01). Our results indicate that there is a very low leaf N content, and that plant growth is N-limited in the S. baicalensis grassland in Inner Mongolia, China. Different species had different responses to N addition. Differences in soil nutrients may be one important reason for the observed variations in leaf structure and leaf nutrient contents.

Effect of water stress on root growth of alfalfa seedlings and on nitrogen- and phosphorus- use efficiencies after water stress

DING Xiao-Qing, FAN Zi-Han, SHEN Yi-Xin

2017, 26(5):  92-99.  DOI: 10.11686/cyxb2016409

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A pot experiment was conducted to assess the effects of soil moisture on the root growth of alfalfa (Medicago sativa) and its nutrient-use efficiency after water stress. Two alfalfa cultivars (Sadie 7 and Icon) were grown under low- (deficiency), appropriate- (CK), or high- (water logging) soil moisture treatments for 20 days before restoring soil moisture to the CK level. The nitrogen- and phosphorus-use efficiencies of the plants were determined by applying nitrogen (urea: 0.336 g/pot) or phosphorus (superphosphate: 1.51 g/pot) at the end of the soil moisture treatment. Root growth differed significantly (P<0.05) among the three soil moisture treatments. Taproot elongation was significantly inhibited by water logging. The taproot diameter, surface area, and volume were lower in water-stressed plants than in CK plants. The taproot was significantly shorter under low soil moisture conditions than in the CK. The growth rate of the root system was significantly lower in the low- and high-soil-moisture treatments than in the CK, and the root system in the high-soil-moisture treatment showed the poorest recovery after removal of water stress. Root growth was inhibited under water stress conditions, and the absorption and utilization of nitrogen and phosphorus were significantly (P<0.05) lower after low- and high-soil-water stress than in CK because of slow recovery of the root system. Increasing the nitrogen and phosphorus supply significantly improved root growth. Together, these results suggested that maintaining soil moisture at an appropriate level and fertilizing with nitrogen and phosphate after soil stress are important to promote the growth of alfalfa roots and increase the forage yield.

Effects of exogenous inorganic salts and thiamine on the regrowth of defoliated alfalfa

ZHAO Wei, LI Ya-Ge, WANG Xin, LI Tao

2017, 26(5):  100-108.  DOI: 10.11686/cyxb2016429

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Grazing integrates multiple processes including bruising, defoliation, and the deposition of saliva, which may affect the regrowth of forage grasses. In this study, alfalfa plants defoliated at different intensities were treated with exogenous inorganic salts and with thiamine (treatment groups), and deionized water and sheep saliva (control groups). The aim of this study was to determine whether a herbivorous animal’s (sheep) saliva, especially its components (inorganic salts and thiamine) positively affect alfalfa regrowth. We also analyzed how the defoliation and sheep saliva interaction induced compensatory regrowth, and evaluated the morphological and physiological differentiation of defoliated alfalfa after treatment with inorganic salts and thiamine. Our results showed that, compared with alfalfa in the defoliation-only treatment, that in the saliva+defoliation treatment showed significantly better regrowth due to an effective ingredient in saliva (thiamine). Compared with defoliated alfalfa treated with exogenous inorganic salts, that treated with thiamine grew better, as indicated by the significantly greater aboveground biomass, 4.3-7.9-times greater stem/leaf ratio, and 1.56-times higher total tiller number at the 80% defoliation level. The physiological characteristics of defoliated alfalfa did not vary widely among treatments. In all treatments, the chlorophyll content of defoliated alfalfa was close to 49.3 mg/g. At the 20% defoliation level, alfalfa plants treated with sheep saliva and with water showed significantly increased soluble sugars contents in the roots, compared with those in the inorganic salts and thiamine treatments. Treatment with inorganic salts led to a progressive increase in peroxidase activity as the defoliation intensity increased, while treatment with thiamine did not affect peroxidase activity. These results increase our understanding of the functional mechanism of the alfalfa response to herbivore grazing. These results provide a reference for improving the status of artificial grassland and for improving the agricultural efficiency of cultivated forage grasses. The results of this study provide theoretical support for the development of ecologically sound grazing regimes.

Effects of cutting frequency on cadmium uptake and physiological responses of Medicago sativa under cadmium stress

LI Na, SUN Ning-Xiao, SONG Gui-Long, PUYANG Xue-Hua, ZHOU Shu-Qiong, ZHAO Ke-Qi, JIANG Kai

2017, 26(5):  109-117.  DOI: 10.11686/cyxb2016419

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Alfalfa (Medicago sativa) is a promising plant species for phytoremediation in soils polluted by heavy metals. This species has been reported to have a high growth rate and great potential for cadmium (Cd) accumulation. Alfalfa plants must be cut several times to reduce soil Cd concentrations to acceptable levels. Therefore, the aim of this study was to evaluate the effects of one, two, and three cuttings on the growth, Cd content, and physiological characteristics of alfalfa plants grown in Cd-contaminated soil. Alfalfa plants were grown in soil containing no Cd (control) and Cd at three concentrations (10, 25, 50 mg/kg) and cut once, twice, or three times. A higher number of cutting events promoted the growth rate and biomass accumulation in the shoot. The highest average shoot growth rate was 61.6 mg/(plant·d) in the three-cuttings treatment, but root growth was significantly lower in this treatment (P<0.05) than in the other treatments and the control. Over the whole growth cycle, cutting twice or three times improved the Cd uptake rate in the root and Cd accumulation in the shoot, thus increasing Cd enrichment in alfalfa plants. The highest Cd accumulation was 75.98 μg/plant in the 25 mg/kg Cd treatment with two cuttings. The relative electrical conductivity and malondialdehyde (MDA) contents were lower in the two-cuttings and three-cuttings treatments than in the single cutting treatment, but the proline contents were higher, which improved the tolerance of alfalfa to Cd toxicity under Cd stress. We concluded that in soil containing Cd at ≤ 25 mg/kg, two cuttings can significantly improve the repair efficiency of alfalfa plants growing in Cd-polluted soil.

Effects of inorganic salts on the growth and total flavonoid content of Glycyrrhiza uralensis callus

LIU Fu-Zhi, YANG Xiu-Yan

2017, 26(5):  118-126.  DOI: 10.11686/cyxb2016239

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In this study, five kinds of inorganic salts were added to Murashige and Skoog (MS) culture medium to determine their effects on the growth rate, physiological indexes, and secondary metabolite contents of licorice (Glycyrrhiza uralensis) callus. The hypocotyledonary axis of sterile licorice seedlings was used as the experimental material. The culture medium consisted of MS+6-benyzlaminopurine (0.5 mg/L)+2,4-dichlorophenoxyacetic acid (0.5 mg/L)+naphthalene acetic acid (0.5 mg/L)+kinetin (0.4 mg/L)+agar (8 g/L)+sugar (30 g/L). Tissue culture and ultraviolet spectrophotometry methods were used to study the effects of inorganic salts at various concentrations in the culture medium on the growth and characteristics of licorice callus. Increasing amounts of KNO₃ and MnSO₄·4H₂O in the medium increased the biomass of licorice callus. Increasing concentrations of CaCl₂·2H₂O in the medium led to increased accumulation of soluble sugars and total flavonoids. The highest peroxidase activity was in callus in medium containing 2533 mg/L KNO₃. Callus growth and total flavonoid content increased significantly as the KH₂PO₄ concentration increased from 170 mg/L to 226 mg/L. The presence of MgSO₄·7H₂O in the MS medium promoted licorice callus growth and flavonoid synthesis. However, callus growth and total flavonoid synthesis were affected by the interactions among various inorganic salts. The results of an orthogonal test and range analysis indicated that the optimal combination of salts for growth and secondary product accumulation in licorice callus was as follows: MgSO₄·7H₂O 493 mg/L; MnSO₄·4H₂O 7 mg/L; KNO₃ 2533 mg/L; KH₂PO₄ 170 mg/L; and CaCl₂·2H₂O 733 mg/L.

Effect of salt stress on the accumulation and distribution of sugars in Jerusalem artichoke (Helianthus tuberosus) plants

ZHAN Wen-Yue, LI Hui, KANG Jian, YIN Xiao-Ming, LIANG Ming-Xiang

2017, 26(5):  127-134.  DOI: 10.11686/cyxb2016227

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A pot experiment was conducted to determine the effects of salinity on the accumulation and distribution of sugars in Jerusalem artichoke (Helianthus tuberosus cv. Nanyu No. 1). The tuber, stem, and leaf showed differences in sugar accumulation under salt stress, as determined by high-performance liquid chromatography coupled with evaporative light scattering detection. At 140 DAP (days after planting), the contents of fructose, glucose, and sucrose were 72.67%, 78.31%, and 39.40% lower, respectively, in the stems of salt-treated plants than in those of control plants; and 67.08%, 60.91%, and 30.07% lower, respectively, in the tubers of salt-treated plants than in those of control plants. The contents of fructose, glucose, and sucrose in the leaves did not differ significantly between salt-treated and control plants. At 220 DAP, the contents of fructose, glucose, and sucrose had hardly changed in the tuber, but the glucose content in the stem was 139.22% lower in the salt-treated plants than in the control plants, and sugars were not detected in the leaves at this stage. Generally, there was a low degree polymerization of fructans in the tubers and stems of Jerusalem artichoke. Compared with the control, the salt-treated plants at 140 DAP showed different contents of 1-kestose, nystose, and 1F-fructofuranosylnystose in the tuber and stem. The sugar content in leaves was very low in salt-treated plants at this stage, similar to that in the control. At 220 DAP, 1-kestose, nystose, and 1F-fructofuranosylnystose were barely detectable in the stems of salt-treated plants, while the contents of 1-kestose and 1F-fructofuranosylnystose in the tubers had not changed significantly. The results implied that sugars in the stem and leaves were gradually transferred to the tuber as it developed. Salt stress induced an osmotic adjustment followed by sugar accumulation in the tuber. Salt stress affected the accumulation and distribution profiles of sugars in Jerusalem artichoke, and greatly reduced fructan accumulation in aboveground tissues, especially the stem.

Effect of exogenous nitric oxide on active oxygen metabolism and mineral contents in oat seedlings under lanthanum stress

LIU Jian-Xin, WANG Jin-Cheng, LIU Xiu-Li

2017, 26(5):  135-143.  DOI: 10.11686/cyxb2016241

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The pollution of agricultural systems by rare earth elements has become one of the most serious environmental deterioration problems worldwide. The signaling molecule nitric oxide (NO) is involved in the plant response to heavy metals. The aim of this study was to investigate the regulating effect of exogenous NO on the physiological response of oat seedlings to lanthanum (La) stress. We conducted a hydroponic experiment in which the exogenous NO donor sodium nitroprusside (SNP) was applied to oat seedlings under a 20 mmol/L La³⁺ treatment and plant growth, active oxygen metabolism, and the absorption of minerals were investigated. The root length, plant height, and dry weight of oat seedlings were significantly lower in La³⁺ -stressed seedlings than in control seedlings. Compared with control plants, those treated with La³⁺ showed significantly increased active oxygen (O2·- and H₂O₂) and malondialdehyde (MDA) contents in roots and leaves, decreased activities of superoxide dismutase (SOD), catalase (CAT), and peroxidase (POD), and increased ascorbate peroxidase (APX) activity and ascorbic acid (AsA) and glutathione (GSH) contents. Addition of 100 μmol/L SNP to oat seedlings under La³⁺stress significantly alleviated the La³⁺-inhibition of growth. Compared with La³⁺-treated seedlings, those treated with La³⁺ + SNP showed reduced contents of O2·-, H₂O₂, MDA, AsA, and GSH in roots and leaves, and increased activities of SOD, CAT, POD, and APX. Seedlings under La³⁺stress showed increased La and copper (Cu) accumulation in the roots and leaves, but decreased absorption of potassium (K), calcium (Ca), magnesium (Mg), iron (Fe), zinc (Zn), and manganese (Mn). Compared with La³⁺-treated seedlings, those treated with La³⁺ + SNP showed significantly lower La translocation from roots to leaves, increased absorption of K, Ca, Mg, Fe, increased Cu uptake, lower Zn and Mn contents in roots, and higher Zn and Mn contents in leaves. Consequently, exogenous NO could alleviate the oxidative damage and growth inhibition of oat seedlings under La³⁺ stress by increasing the activities of antioxidant enzymes and altering La translocation and mineral absorption.

Flower and anther characteristics of two male sterile lines of cauliflower, a dual-purpose vegetable and forage crop

TAO Xing-Lin, XIE Zhi-Jun, ZHU Hui-Xia, LIU Ming-Xia, ZHANG Jin-Wen, HU Li-Min

2017, 26(5):  144-154.  DOI: 10.11686/cyxb2016439

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The aim of this study was to analyze the morphological characteristics and cytological characteristics of anther development in two male sterile lines of cauliflower (Brassica oleracea var. botrytis). The cauliflower cytoplasmic male sterile line 09-R9, the maintainer line 09-24, and the temperature-sensitive genetic male sterile line GS-19 were used as the test materials, and morphological and cytological techniques were used to study anther development. There were differences between the two male sterile lines in fertility transition, flower morphology, and anther development. The three lines showed variations in fertility under different temperature treatments. The sterility of 09-R9 and 09-24 was not affected by temperature; 09-R9 was always sterile, and 09-24 was completely fertile. GS-19 was affected by temperature, and was sterile at high temperature (20 ℃) but fertile at a lower temperature (15 ℃). The buds and anthers were smaller in GS-19 than in 09-R9. Sterile plants differed from fertile plants, and there were significantly fewer flowers on sterile plants than on fertile plants. Microstructural observations showed that the anthers abortive stages and types differed between the two male sterile lines. 09-R9 formed a normal-shaped pollen sac at the early anther stage, but the materials within pollen sacs gradually disintegrated as buds developed, and the pollen sacs finally disappeared. The development of anthers was blocked before the formation of the pollen mother cell, so this line showed an abortive-type sterility without pollen sacs. The anther development of GS-19 showed differentiation of the pollen mother cell and normal pollen sac formation, but this line produced very small amounts of non-viable pollen and no viable pollen. In this line, the pollen mother cells did not undergo meiosis to form tetrads, but formed pseudo microspores with abnormal pollen exines. As the anthers developed, the pseudo microspores gradually decayed until only the empty shells remained. The anther development of GS-19 was blocked between the pollen mother cell stage and the tetrad stage, and so it was an abortive-type sterility of the pollen mother cell. These ultrastructural observations revealed the similarities and differences in anther abortion between the male sterile lines 09-R9 and GS-19 under high-temperature conditions.

Functional analysis of the stay-green gene ZjSGR from Zoysia japonica using transgenic Nicotiana tabacum

TAN Peng-Hui, YUAN Li-Li, FAN Bo, YU An-Dong, DONG Di, TENG Ke, CHAO Yue-Hui

2017, 26(5):  155-162.  DOI: 10.11686/cyxb2016492

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In green plants, SGR is a key gene with roles in chlorophyll degradation, plant development, senescence, and responses to abiotic stresses. In this study, the coding domain sequence of ZjSGR from Zoysia japonica was inserted into the 3302Y vector, yielding the plant expression vector 35S::ZjSGR:YFP, by DNA recombination technology. The construct was introduced into tobacco plants by Agrobacterium tumefaciens-mediated transformation. The transgenic plants were confirmed to harbor the construct by PCR, and qRT-PCR analyses confirmed that ZjSGR was successfully heterologously expressed in the transgenic tobacco plants. The transgenic plants showed a rapid yellowing phenotype corresponding to a lower chlorophyll content and lower photosynthetic rate. Subcellular localization analyses showed that ZjSGR was localized in the chloroplasts in stably transformed tobacco plants. Transmission electron microscope analyses revealed that the chloroplasts in transgenic plants showed retarded development and decomposition processes. Analyses of gene transcript levels by qRT-PCR showed that the transcript levels of SAG113, SAG12, NECD, and AAO3 were higher in ZjSGR-overexpressing tobacco plants than in control plants. The results of this study highlight the important roles of ZjSGR in controlling chlorophyll degradation and senescence in plants.

Distribution and rDNA-ITS sequence analysis of endophyte symbionts of Bothriochloa ischaemum at a copper tailings site

CAO Miao-Wen, JIA Tong, JING Ju-Hui, CHAI Bao-Feng

2017, 26(5):  163-172.  DOI: 10.11686/cyxb2016271

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Tailing ponds are special growth environment for plants. Soils at such sites contain high concentrations of heavy metals, which affect the physiology and ecology of plants. The aim of this study was to evaluate the endophytic fungi resources at a copper mine tailings site, and to explore whether different endophytic fungi can restore diversity by altering the physical and chemical properties of soil. Therefore, we studied endophytic fungi of Bothriochloa ischaemum growing in the Shibahe tailings pools at the Tongkuangyu Mine, a copper tailings site. B. ischaemum is the dominant species growing at this site, and it grows in several sub-dams with different recovery times. To investigate the endophytic fungi infection rate of B. ischaemum, we collected live plants and separated the endophyte from the sheath, and observed and described the characteristics and spore morphology of each fungus. We also selected 16 strains and amplified the 5.8S-ITS region for sequencing and phylogenetic analysis. Based on their phenotypes, the endophytes from B. ischaemum growing in four different sub-dams with different recovery times were separated into different groups. Most endophyte colonies were white, and the growth rate ranged from 5.515 and 12.548 mm/d. The endophytes produced spherical or oval/near oval spores, with sizes ranging from 2.085 μm to 7.072 μm. Sequence analyses showed that there were three different sequences among the 16 kinds of colonies, belonging to the genera Gibberella, Fusarium, and Penicillium. The smallest genetic distance was between the sub-dam with 30-years recovery and that with 5-years recovery. The largest genetic distance was between the sub-dam with 45-years recovery and that with 15-years recovery. At copper tailings sites, different soil environments at different stages of restoration might lead to a wide diversity of endophytes infecting B. ischaemum. The results of this study provide a theoretical basis for enriching endophyte resources, and reveal some of the ecological functions of endophytes associated with B. ischaemum at a copper tailings site.

Isolation and screening of inorganic phosphate-solubilizing bacteria and their effect on the growth of Bromus cartharticus

SHU Jian-Hong, WANG Pu-Chang, LI Xian-Gang, WANG Xiao-Li, LI Xiao-Dong

2017, 26(5):  173-180.  DOI: 10.11686/cyxb2016215

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We screened rhizosphere microorganisms of bromegrass (Bromus cartharticus) and isolated bacteria with phosphate-solubilization activity. The isolated bacteria were further analyzed to quantify their phosphorus-solubilization activity, indole acetic acid (IAA) secretion capacity, and their ability to promote the growth of bromegrass. The isolated microorganisms showed differences in their ability to utilize different inorganic phosphate substrates. All the selected strains had phosphate solubilization activity with calcium phosphate as the phosphorus source, whereas only strains Br1, Br7 and Br8 were able to solubilize phosphate with aluminum phosphate as the phosphorus source. Strain Br7 had the strongest phosphate-solubilization ability. Strains Br4, Br8, Br17, and Br24 secreted relatively large amounts of IAA, and IAA secretion was enhanced when exogenous tryptophan (an IAA precursor) was added. Analyses of the medium pH indicated that all eight isolated strains were acid-producing bacteria. The root length, root number, plant height, and total biomass of bromegrass inoculated with these isolated strains were measured. Strains Br8, Br13, Br17, and Br24 strongly affected root growth, resulting in a shorter main root but more abundant roots. Strains Br7, Br8, Br13, and Br24 increased bromegrass plant height and biomass. These results indicate that strain Br24 has great potential to improve the growth of bromegrass in Guizhou province.

Isolation and identification of an inorganic phosphorus-solubilizing bacterium RW8 and its growth-promoting effect on white clover (Trifolium repens)

CAI Lu, WANG Xiao-Li, CHEN Yin, WANG Zi-Yuan, LI Xiao-Dong

2017, 26(5):  181-188.  DOI: 10.11686/cyxb2016282

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Nine strains of inorganic phosphorus-solubilizing bacteria were isolated from the rhizosphere of white clover (Trifolium repens), and each strain was identified to the genus and species level based on its phenotypic and cytological characteristics. The growth-promoting effect of each strain on white clover was also analyzed. Strain RW8, which showed the strongest phosphorus-solubilizing activity, was selected based on analyses of the size and ratio of its plaques and colonies. Scanning electron microscopy observations revealed that RW8 was Bacillus brevis, a flagellated bacterium. Colonies of RW8 were opaque and had a smooth surface. In NCBI blast searches, the 16S rDNA sequence of RW8 showed 99.5% homology with that of Enterobacter sp. A Biolog analysis suggested that RW8 had high similarity (0.610) with Enterobacter cloacae. In a phosphorous-dissolving assay, RW8 produced 424.85 μg/mL dissolved phosphorus, which was possibly related to its strong organic acid production (12.30 μg/mL). RW8 strongly affected the biomass distribution to roots in white clover seedlings. Root elongation and the fresh weight and dry weight of roots were lower in RW8-colonized plants than in control plants, although the differences were not statistically significant. However, the seedling biomass (dry weight and fresh weight) of RW8-colonized white clover was significantly greater than that of control plants (P<0.05), and this phenomenon was not a result of indole acetic acid production by the bacterium. Further research is required to determine the precise mechanism of its growth-promoting effect.

Expression of β-glucosidase genes bglA, bglB, and bgl from Bacillus polymyxa in Escherichia coli

WANG Yan, MA Ya-Ru, WAN Xue-Rui, WANG Chuan, WU Run, LIU Gui-Lin, LIU Yuan-Zi, WU Zi-Xiang

2017, 26(5):  189-196.  DOI: 10.11686/cyxb2016220

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To improve the enzyme activity of β-glucosidase, two β-glucosidase genes from Bacillus polymyxa were introduced separately (bglA and bglB) and together (bgl) into the pET-28a vector and expressed in Escherichia coli C41. The three recombinant strains were designated as EA, EB, and co-expression EAB. Strains EA and EB were mixed at ratios of 1∶1, 1∶2, and 2∶1 and their total β-glucosidase activity was compared with those of each single enzyme group, the co-expression strain, and mixed expression strains. The results of SDS-PAGE analyses showed that both BglA and BglB were 50 ku, and the size of these proteins in the EA and EB mixed cultures was also 50 ku. The size of Bgl in the co-expression strain EAB was 100 ku. These results indicated that a Bgl complex was able to form in cells, but not in vitro. In an enzyme activity assay, the activity of Bgl from the co-expression strain was not significantly different from that of bgl in B. polymyxa, but it was significantly higher than those of BglA in EA and BglB in EB (P<0.05). The results of Congo red staining also showed that the enzyme activity of Bgl was significantly higher than those of BglA and BglB. This study lays the foundation for the construction of artificial assemblies, and for the integration of biological technologies in cellulose processing.

Nutritional value of ramie and its ruminal degradability

WEI Jin-Tao, YANG Xue-Hai, YAN Nian-Dong, XIONG Chang-Cai, WANG Hong-Wu, CHEN Fang, ZHANG Nai-Feng, DIAO Qi-Yu

2017, 26(5):  197-204.  DOI: 10.11686/cyxb2016223

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The aim of this study was to investigate the nutrient components and ruminal degradability characteristics of ramie. Common nutrition components, amino acids composition, and anti-nutrient (e.g., tannin) contents were determined for seven ramie samples containing different proportions of stubble, and the ruminal degradability was estimated using three male Boer goats fitted with permanent rumen fistula. The average crude protein (CP) content of the seven stubble samples was 19.57%. The CP content decreased with increasing proportions of stubble, but the CP content in sample 7, which had the highest proportion of stubble, was slightly higher than that in sample 6, which had a slightly lower proportion of stubble. The average total amino acids content was 16.40%, accounting for 83.80% of CP. The average Lys and Thr contents were 0.84% and 0.82%, respectively. The average content of tannin, the main anti-nutrient in ramie, was 0.67%. The ruminal degradability of ramie dry matter, CP, organic matter, neutral detergent fiber, and acid detergent fiber increased with longer digestion time; the effective degradability of these nutrients was 47.00%, 35.53%, 44.29%, 57.68% and 38.59%, respectively. In conclusion, ramie has a high protein content, high-quality CP, and high rumianl degradability of some nutrients. Therefore, it is a good forage for ruminants.

Effect of dietary Perilla frutescens seed intake on rumen fermentation characteristics, apparent nutrient digestibility, and growth performance of Hu sheep

DENG Kai-Ping, WANG Feng, MA Tie-Wei, WANG Zhen, YU Xiao-Qing, DING Li-Ren, TAO Xiao-Qiang, FAN Yi-Xuan

2017, 26(5):  205-212.  DOI: 10.11686/cyxb2016254

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The objective of this study was to evaluate the effect of the amount of Perilla frutescens seed (PFS) in the diet on the serum biochemical parameters, rumen fermentation characteristics, apparent nutrient digestibility, and growth performance of Hu sheep. Sixty male Hu lambs aged 2 months and weighing on average (23.02±1.36) kg were randomly divided into four groups and fed on diets containing varying proportions of PFS: 0% (control), 5% (5%PFS), 10% (10%PFS) and 15% (15%PFS) for 70 days. At 21 days before the end of the feeding experiment, four lambs were randomly selected from each experimental group for a 7-day digestion and metabolism experiment. At the end of the feeding period, lambs were weighed to calculate average daily gain (ADG). Blood and rumen fluid samples were collected for analysis. Volatile fatty acids (VFA), ammonia nitrogen (NH₃-N), total protein (TP), urea nitrogen (UN), glucose (Glu), growth hormone (GH), and insulin-like growth factors 1 (IGF-1) were quantified in the samples using gas chromatography, colorimetric, automatic biochemical analyzer, and ELISA methods. The results showed that the amount of PFS did not significantly affect growth performance (dry matter intake, ADG, and feed/gain ratio), blood biochemical indices (TP, UN, Glu, GH and IGF-1), rumen pH, or the concentrations of acetic acid, propionic acid, and total VFA (P>0.05). With increasing dietary PFS, the concentrations of acetic acid, butyric acid, and total VFA tended to decrease, whereas the concentration of propionic acid tended to increase. Compared with the control group, the 15%PFS group showed significantly decreased NH₃-N content and acetate∶propionate ratio (P<0.01) in the rumen fluid. The amount of PFS did not affect the apparent digestibility of ether extract (EE) and neutral detergent fiber (NDF) (P>0.05). However, the apparent digestibility of dry matter (DM), organic matter (OM), and NDF decreased with increasing amounts of PFS in the diet. The apparent digestibility of DM and OM was lower in the 15%PFS group than in the other groups (P<0.05). Compared with the control group, the 10%PFS group showed significantly increased apparent digestibility of crude protein (CP) (P<0.01), while the 15%PFS group showed a significant decrease in this parameter (P<0.01). In conclusion, 10% PFS in the diet is the appropriate level of supplementation for Hu sheep.

Associative effects of cornstalk, millet straw, and corn stalk on silage digestibility in vitro

LI Yan, HAN Xiao-Min, LI Jian-Guo, LI Qiu-Feng, GAO Yan-Xia, CAO Yu-Feng, LI Yun-Qi

2017, 26(5):  213-223.  DOI: 10.11686/cyxb2016276

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We investigated the associative effects of cornstalk (CS), millet straw (MS), and corn stalk silage (CSS) on silage digestibility using an in vitro rumen fermentation system. A single factor experiment was designed with CS and MS to identify the best CS-MS combination, then CSS was added in combination with CS-MS. First, CS and MS were tested at ratios of 100∶0, 80∶20, 60∶40, 50∶50, 40∶60, 20∶80 and 0∶100, with three replicates. Gas production (GP), rate of dry matter loss (DML), pH, microbial crude protein (MCP), ammonia nitrogen (NH₃-N), and volatile fatty acids (VFA) were measured for all the CS-MS combinations, and the single factor associative effects index and multiple factors associative effects index of different combinations were calculated. The results showed that GP and DML differed among the various combinations significantly (P<0.05) or extremely significantly (P<0.01). However, pH did not differ among the various combinations (P>0.05). The MCP yield differed significantly (P<0.05) or extremely significantly (P<0.01) among the different CS-MS combinations. The MCP yields of CS-MS combinations decreased with decreasing proportions of CS, while the MCP yields of the CS-MS-CSS (CS∶MS=60∶40) combinations increased with increasing proportions of CSS. There were significant (P<0.05) or extremely significant (P<0.01) differences in NH₃-N concentrations among the various combinations, ranging from 17.35 mg/dL to 24.63 mg/dL. There were significant (P<0.05) or extremely significant differences (P<0.01) of VFA yield among the various combinations. In conclusion, the CS-MS ratio of 60∶40 and the CS-MS-CSS combination at the ratio of 12∶8∶80 produced the largest associative effects in this study.

A bibliometric analysis of international grassland agroecology research

YANG Jing-Ning, SHEN Yu-Ying, WANG Yan-Rong

2017, 26(5):  224-234.  DOI: 10.11686/cyxb2016218

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Grassland agroecology research covers diverse subjects in biology, agriculture, and geography. In recent years, research on grassland agroecology has intensified in many countries and research institutions around the world. In this study, we used Thomson Data Analyzer and UCINET for data mining, and conducted a quantitative analysis of grassland agroecology research papers listed in the SCIE database from 1996 to 2015. We explored the annual trends, the distribution of scientific research strength, major research areas and hotspots, and international cooperations in grassland agroecology research from 1996 to 2015. The objectives of this study were to assess the current status of grassland agroecology research worldwide, to identify the international influences on this area of research by analyzing and comparing characteristic features of published papers, and to provide directions for future research. The number of grassland agroecology research papers has shown an average growth rate of 8% over the past 20 years. This field of research involves multiple disciplines, such as agriculture, environmental science and ecology, plant science, biodiversity and conservation, geology and so on. In addition to grassland and agriculture, protection of species and the environment have become more popular topics. The United States, the United Kingdom, and other developed countries have a stronger overall influence on grassland agroecology research. The United States is the most prominent country in international cooperative research, and has established strong research relationships with other major countries. The Chinese Academy of Sciences is very active in this field, and has published many more papers than the French National Institute for Agricultural Research (INRA), University of Saskatchewan, and other institutions. However, the research quality and the influence of the Chinese Academy of Sciences, as well as its capacity for international cooperation, should be improved.