Table of Content

20 January 2020, Volume 29 Issue 1

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Temporal and spatial variations in natural grassland phenology in China over the last 30 years

NI Lu, WU Jing, LI Chun-bin, QIN Ge-xia, LI Zheng, KONG Jie

2020, 29(1):  1-12.  DOI: 10.11686/cyxb2019003

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Long-term monitoring of grassland phenology in large-scale areas by remote sensing is an important area of ecological research and a core part of global change research. Based on the GIMMS 3g Normalized Difference Vegetation Index (NDVI) of the 30-year (1986-2015) dataset, the Savitzky-Golay filtering method was employed to reconstruct the time series. A dynamic threshold method was used to extract phenological parameters of Chinese natural grassland (start of the growing season, SOS; end of the growing season, EOS; and length of the growing season, LOS). Then, 1998 was selected as the time demarcation point to analyze the temporal trends in evolution and spatial differentiation of grassland phenological characteristics in the two time periods. It was found that: 1) The national average annual SOS, EOS, and LOS were mainly concentrated around 100-140 days, 260-290 days, and 130-170 days, respectively; 2) Phenological trends have not changed significantly over the 30 years with a range of -0.3 to 0.3 d·yr^-1; 3) Before 1998, the SOS of grassland was 0.37 d·yr^-1 earlier and the EOS was 0.43 d·yr^-1 later on average, and there was a big difference in the area of grassland. After 1998, grassland phenology began to change. The SOS of grassland showed the largest change with an average advance of 0.28 d·yr^-1; 4) The phenological characteristics of alpine subalpine meadow, mountain grassland, flat grassland, and alpine subalpine flat grassland changed in a completely opposite direction after 1998. The time trends identified in this paper are consistent with observational data and the results of other studies.

An analysis of dynamic changes and their driving factors in marsh wetlands in the eastern Qinghai-Tibet Plateau

HOU Meng-jing, GAO Jin-long, GE Jing, LI Yuan-chun, LIU Jie, YIN Jian-peng, FENG Qi-sheng, LIANG Tian-gang

2020, 29(1):  13-27.  DOI: 10.11686/cyxb2019148

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Wetland degradation and ecosystem structural degeneration caused by climate change and unsustainable human activity have become more common since the middle of the 20th century. It is difficult to carry out a ground-based investigation because of complex spatial mosaic of grassland interspersed with bodies of water and marsh wetlands in the eastern part of the Qinghai-Tibet Plateau. We therefore used remote sensing technology to monitor real-time dynamic change in wetland distribution, to enhance understanding of the changes in the ecological environment of the Qinghai-Tibet Plateau. Using Landsat TM/ETM+/OLI images, the areas of marsh wetlands in the eastern Qinghai-Tibet Plateau were extracted by visual interpretation from 1991, 2000, 2010, and 2016 records. The area change of marsh wetlands, and direction and rate of movement were analyzed based on a dynamic transfer matrix methodology. Landscape indices at the patch level were used to quantify the spatial and temporal dynamics of the marsh wetlands. We also used the grey correlation method together with meteorological data and statistical information to analyze the factors driving marsh wetland change. It was found that: 1) The marsh wetlands are mainly distributed in the northeast of the study region. For the 1991, 2000, 2010 and 2016 analyses, the total marsh wetland areas were 6739.89, 6231.39, 5849.59 and 5649.35 km², respectively, meaning that a reduction in total area of 1090.54 km² was recorded during the 26 year study period; 2) The annual rate of wetland loss decreased gradually during the 26 years from -7.54% to -3.42%, and the lost marsh wetlands were mainly transformed into alpine grassland; 3) The number of patches increased initially and then decreased, while patch density continued to increase, indicating an increasing degree of fragmentation of the marsh wetlands. The largest patch index decreased initially and then increased slightly, while the landscape shape index increased initially and then decreased slightly, reflecting the decreasing dominance of marsh wetlands and the complexity of landscape shape. The splitting index increased initially and then decreased slightly, while the aggregation index decreased throughout the study period, reflecting a tendency for marsh wetlands to be fragmented and discrete; 4) Human factors are the primary reason for reduction of marsh wetland area in the eastern Qinghai-Tibet Plateau, followed by climatic factors. Specifically, the factors in order of influence were: Gross output value of animal product, gross domestic product, population increase, temperature and precipitation.

Change in factors influencing soil water holding capacity at microsites along a slope transect in alpine meadow in the eastern Qilian Mountains

MA Hai-xia, ZHANG De-gang, CHEN Jin, GUO Chun-xiu, DONG Yong-ping, MA Yuan, KANG Yu-kun, CHEN Lu, DU Kai, CHEN Jian-gang

2020, 29(1):  28-37.  DOI: 10.11686/cyxb2019113

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In order to provide reference data for water conservation modelling and to determine sustainable utilization and protection criteria for alpine meadow, factors influencing soil water holding capacity were assessed for microsites at different positions along a slope transect in the eastern Qilian Mountains. Five study plots at different altitudes (slope crest, 2990 m; upper slope, 2980 m; mid slope, 2970 m; lower slope, 2960 m and slope foot, 2950 m) were selected, and the soil particle size distribution (i.e. soil texture), soil moisture, soil bulk density, soil porosity and soil permeability were measured. Soil texture varied little between the slope crest, upper, mid, and lower slope or with soil depth at those sites (typically 8%-10% clay, 79%-83% silt, and 7%-11% sand); however, at the slope foot soil had 42% sand in the 0-10 cm soil layer, increasing with depth to 74% sand in the 30-40 cm soil layer, with corresponding reductions in silt and clay components. Soil field moisture capacity was negatively correlated with sand and clay content and positively correlated with silt content and was typically in the range 45%-55% for slope crest and upper, mid and lower slope positions, and was 40% for the 0-10 cm layer reducing to 21% for the 30-40 cm layer at the slope foot where soil had a higher sand content. Total soil porosity was generally similar to soil field moisture capacity, and showed a tendency to decrease with soil depth, while non-capillary porosity was somewhat variable with slope position and soil depth, and typically less than 8%. Infiltration rate decreased with increasing soil depth, but increased moving down the slope from crest to foot. At the slope crest, infiltration rates after 5 min testing were 1.2 mm·min^-1 for the 0-10 cm soil layer, decreasing to just over 0.2 mm·min^-1 in the 30-40 cm soil layer, while at the slope foot they were 4.4 mm·min^-1 for the 0-10 cm soil layer, decreasing to approximately 2.5 mm·min^-1 in the 30-40 cm soil layer. These data will assist with modelling of soil storage and release of water after rainfall events.

The biomass-diversity relationship depends upon soil pH variations in Inner Mongolian grasslands: Insight from comparison between gradient observations and manipulative experiments

LI Zi-yan, LIU Zun-chi, YAN Chuang, ZHANG Jing-jing, SHI Xin-rong, YUAN Zhi-you

2020, 29(1):  38-49.  DOI: 10.11686/cyxb2019177

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The relationship between biomass and diversity is a hot topic in ecological research. Although studies have found that this relationship is influenced by environmental factors, no study has tested the congruence of biomass-diversity responses to changing soil pH obtained from studies using an observational approach and studies using manipulative experiments in grasslands. Here, we combined manipulative and observational approaches to investigate the biomass-diversity relationship response to soil pH in Inner Mongolian grasslands. We found: 1) Along a natural transect, soil pH was mainly affected by soil and grassland types, and aridity index. The relationship between aboveground biomass and soil pH showed a U-shaped curve. Species richness showed a significant U-shaped curve in relation to soil pH. Diversity was positively correlated to aboveground biomass. 2) In the acid/alkaline addition experiments, the relationship between aboveground biomass and soil pH was characterized by a one-peak curve. This was also true for species richness in relation to soil pH. The biomass-diversity relationship depended on grassland types: A positive correlation could be found in desert grasslands, but not in typical/meadow grasslands. Our study suggested that the relationships between biomass and diversity in temperate grasslands were dependent upon the variations in soil pH. The observation that results from manipulative experiments were opposite to those from observational studies might be attributed to the fact that the observations along transects reflect the results of long-term adaptation. In contrast, results from manipulative experiments reflect the short-term response to environmental changes.

Photosynthetic responses to differences in soil moisture content of co-existing species in plant communities of abandoned land on the Loess Plateau

ZHOU Min, DU Feng, ZHANG Yun-yun, PAN Tian-hui

2020, 29(1):  50-62.  DOI: 10.11686/cyxb2019158

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Differences in environmental adaptability and relative competitive ability of co-existing species are two key factors driving community dynamics and succession. Photosynthetic responses are closely linked to adaptability and competitive ability. Therefore, it is useful to study the differences in photosynthetic characteristics of co-existing species to help understand the mechanisms of community succession. In this study, 10 co-existing plant species in middle secondary successional stages in Loess Plateau vegetation were studied. The species studied were Heteropappus altaicus, Artemisia scoparia, Artemisia sacrorum, Artemisia giraldii, Oxytropis glabra, Lespedeza dahurica, Bothriochloa ischaemum, Agropyron cristatum, Cleistogenes chinessis, and Cleistogenes songorica. Their photosynthetic rate, transpiration rate and water use efficiency under different water treatments (severe, moderate and mild water deficit) were measured in August, September and October, with the aim of categorizing the differences among these plant species in photosynthetic response to variation in soil moisture. The results showed that: 1) Under all water conditions, the diurnal variation of net photosynthetic rate of C. songorica, B. ischaemum, O. glabra and L. dahurica showed a diurnally unimodal curve, while A. cristatum and H. altaicus showed bimodal curves with an obvious midday depression of photosynthesis. The diurnal peak of C. songorica had the highest amplitude, while that of A. cristatum had the lowest. 2) The diurnal variation in transpiration rate of most species followed a single-peaked curve under all water conditions, with the main exception being C. chinessis and H. altaicus. Again, the peak of C. songorica had the largest amplitude, while O. glabra had the lowest. 3) There were significant inter-species and growing season differences in daily average net photosynthetic rate and transpiration rate (P<0.05), while differences in daily average water use efficiency were not obvious (P>0.05). Among the 10 co-existing species, C. songorica had the highest daily average net photosynthesis and transpiration rates. 4) With respect to the ecological successional sequence, the daily average water use efficiency of the early-succession species were relatively low, while values for the post-succession species were relatively high, meaning that the water use performance of the late-succession species was higher. Considering the arid conditions in this region of the Loess Plateau, and their likely impact on the succession process, the logical expectation is that late-succession species will, through their water use characteristics, gradually occupy a dominant position in their plant communities, and thus gradually replace the early-succession species in the arid and semi-arid hilly region of the Loess Plateau.

A study of the photosynthetic physiology of different forage triticale genotypes

ZHAO Fang-yuan, LIU Jing, DU Wen-hua, TIAN Xin-hui

2020, 29(1):  63-73.  DOI: 10.11686/cyxb2019339

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The aim of this research was to identify forage triticale genotypes with strong photosynthetic performance and elucidate the main factors influencing photosynthetic performance. The chlorophyll content and photosynthetic physiological index of 6 forage triticale genotypes were studied at different growth stages, and data analysed by analysis of variance and principal component analysis. It was found that parameters related to photosynthesis (except for stomatal limitation value) peaked during early development and then declined with advancing maturity. Values for chlorophyll content, transpiration rate, photosynthetic rate and intercellular CO₂ concentration peaked at the heading stage, while water use efficiency peaked at the flowering stage. The time trend for stomatal limitation value was opposite to that of other traits with the lowest value observed at the heading stage. The principal component analysis revealed that transpiration rate and stomatal traits most influenced the photosynthetic performance of forage triticale. Both C31 and C19 had relatively strong photosynthetic performance during the entire development cycle and were high-yielding. However, C19 showed an advantage of relatively high water use efficiency. This line can therefore be further used as a germplasm resource for drought resistance. The principal component analysis showed that transpiration rate and stomatal related factors had significant influence on the photosynthetic performance of forage triticale.

Effects of different planting configurations on yield of Avena sativa and Vicia sativa mixed plantings with soybean in alpine pastures

ZHU Ya-qiong, YU Hui, ZHENG Wei, LI Song-song, Naerkezi, LIU Yue-han, HAO Shuai, Ailifeire

2020, 29(1):  74-85.  DOI: 10.11686/cyxb2019184

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This research investigated the aboveground growth efficiency, together with belowground root morphological characteristics and spatial configuration for mixed plantings of the forages Avena sativa (As) and Vicia sativa (Vs), in trays of area 70 cm×45 cm, and 30 cm depth. The aim was to assess the competitive dynamics and the relative contribution of aboveground and belowground traits of the two species to the mixed cropping advantage in different plant spacings, and the nitrogen fixation, and nitrogen transfer and utilization efficiency of the different mixed cropping planting configurations, in order to clarify the inter-specific competition process. Four planting configurations with two monoculture controls were included in the experiment: As+Vs mixed within rows at 15 cm row spacing (T₁₅); As+Vs in alternate rows at 15 cm row spacing (Y₁₅); As+Vs in alternate rows at 15 cm spacing with a root barrier between (YZ₁₅); As+Vs in alternate rows at 30 cm row spacing (Y₃₀); monoculture As (CK₁); and monoculture Vs (CK₂). The results indicated that: 1) Forage yield was approximately 60% higher (P<0.05) for the T₁₅ and Y₁₅ planting configurations than for YZ₁₅ and Y₃₀, and this yield gain was reflected in higher land equivalent ratios (1.5, 1.4, 1.0 and 1.2 for T₁₅, Y₁₅, YZ₁₅ and Y₃₀, respectively). The aggressivity of As was substantially greater than that of Vs in all planting configurations. 2) The mixed cropping advantage of T₁₅ and Y₁₅ could be attributed partly to improved light utilization aboveground and partly to enhanced N fixation belowground and capture of legume-derived N by the more aggressive As. The relative contribution of aboveground and underground factors to the mixed-cropping advantage was about 22% and 78%, respectively. 3) Forage yield was positively correlated with the initial fluorescence efficiency (F) of the forage leaves and the capture of light energy per unit area (TR_o/CS_o) values (P<0.05). There was a significant positive correlation between forage yield and root morphological parameters and root configuration (P<0.01). 4) Because oats are strong competitors, they are also the main contributor to the advantages of mixed sowing. Therefore, in an environment of strong competition and high nutrient utilization efficiency, the T₁₅ and Y₁₅ planting configurations exhibited strong mixed planting advantages over CK₁ and CK₂, and LER ratios near 1.5.

Productivity and interspecific competition of maize intercropped with faba bean, soybean or pea

ZHAO Jian-hua, SUN Jian-hao, CHEN Liang-zhi

2020, 29(1):  86-94.  DOI: 10.11686/cyxb2019119

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A key factor for obtaining high yield and advantages of interspecific interaction when intercropping is the selection of compatible intercrop species. A field experiment was conducted with three intercropping species combinations: maize/faba bean (M/F), maize/soybean (M/S) and maize/pea (M/P), and the corresponding sole crops. Yield and biomass data for the three intercrop combinations and the four sole species were collected to define the effect of the three legume crops on the productivity and competition dynamics of the legumes when intercropped with maize. The results showed an obvious intercropping advantage for all three legumes intercropped with maize. Land equivalent ratio (LER) values averaged over two seasons were 1.38, 1.19, and 1.26 for M/F, M/S and M/P, respectively. The greatest harvest yield of intercropped maize was obtained from M/S intercropping. At harvest, the yield of maize intercropped with soybean (M/S) was 93.6% (2017) and 71.2% (2018) of sole maize (SM), respectively; Additionally, M/S produced more grains per ear than M/F or M/P. The aboveground biomass and average growth rate during the sampling stage of intercropped maize ranked: M/S>M/P>M/F. The aggressivity of soybean relative to maize (A_sm) decreased, and the aggressivity of faba bean relative to maize (A_fm) and of peas relative to maize (A_pm) increased during co-growth period. There was no significant difference in compensation effect (CE) between the three intercropping patterns during early growth of maize, and the average CE value over the two years was below 1. Therefore, based on the present study, maize intercropped with soybean is an efficient intercrop combination in the Hexi Corridor of Gansu Province.

Factors influencing nodulation and N fixation ability of alfalfa in a simulated alfalfa/maize intercropping system

ZHAO Ya-jiao, LIU Xiao-jing, TONG Chang-chun, WU Yong

2020, 29(1):  95-105.  DOI: 10.11686/cyxb2019383

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In this research, numbers of nodules, N fixation rate, and yield of alfalfa plants co-planted with maize in pots were measured at different N levels (N₂₁, N₂₁₀) and growth stages and with different types of partition between roots. Partition types were: pot with no barrier (A-T), pot with nylon mesh barrier (NA-T), and pot with plastic barrier (PA-T), and alfalfa alone (SA) was used as a control. It was found that nodulation, N fixation ability of alfalfa and N metabolite levels in the maize plants ranked in order (A-T)>(NA-T)>(PA-T). Total nodule numbers (TNN), total nodule weight (PNW) and nitrogen fixation capacity (PNF) in all stages and effective nodule numbers (ENN), ENN/TNN and nitrogenase activity (NA) in budding and flowering stages in pots A-T were significantly higher than corresponding values in NA-T pots which in turn were significantly higher than those with PA-T and sole alfalfa (SA) (P<0.05). TNN under N₂₁₀ was higher than N₂₁. The difference in TNN between plants with different root partition types was largest at the flowering stage. Parameters relating to nodulation and N fixed, except for TNN, were lower under N₂₁ than under N₂₁₀ at the branching stage, but were higher under N₂₁ than those under N₂₁₀ in the budding and flowering stages. The effect of the different root partition types on PNW and PNF was largest in flowering stage. However, the differences of all parameters expect TNN with different root partitions was largest shortly before flowering. The correlation between PNW and PNF was high (0.993). The conclusion was that nodule formation in alfalfa increased as the N concentration decreased, and that appropriate N addition promoted nodule growth and development during the branching stage. The N threshold for promoting nodule formation is also higher than that of nodule growth and development. The greater the degree of interaction between alfalfa and maize roots, the more the promotion of nodulation and N fixation of alfalfa. Hence, the root interaction was the main factor influencing nodulation and N fixation.

A metabolomics analysis of the effect of water deficit on the freezing tolerance of alfalfa (Medicago sativa)

XU Hong-yu, LI Xiang-lin

2020, 29(1):  106-116.  DOI: 10.11686/cyxb2018756

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This research examined the influence of water deficit on alfalfa freezing tolerance. Two treatments with alfalfa plants grown at 80% and 25% soil water holding capacity were set up, and the semilethal temperature (LT₅₀) determined and compared for the contrasting watering regimes. Metabolite levels in alfalfa crowns were analyzed using an LC-MS instrument. Results showed the freezing tolerance of alfalfa plants in water deficit (WD) to be superior to that of well-watered plants (WW), with higher total soluble sugar levels WD than WW. Compared with the WW treatment, WD plants displayed up-regulated glycerophospholipids and fatty acyls which are the main constituents of the plasma membrane and have a function of enhancing membrane fluidity and stability. Hence, the up-regulated compounds are very important to the capability to resist cold damage. In addition, from KEGG analysis of carbohydrate profiles of the two treatments, the up-regulation of D-maltose levels in WD plants appears to be another important contributing factor to the enhanced freezing tolerance in the WD plants.

Effect of exogenous salicylic acid on the antioxidant enzyme activities and fatty acid profiles in seashore paspalum under low temperature stress

ZHANG Xiang, YANG Yong, LIU Xue-yong, XIANG Zuo-xiang

2020, 29(1):  117-124.  DOI: 10.11686/cyxb2019293

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This research investigated the effect of exogenous salicylic acid (SA) on the cold tolerance of seashore paspalum (Paspalum vaginatum), cultivar “Platinum”. A pre-treatment of 1 mmol·L^-1 SA was applied to plants in pots and after 5 days, turf quality, leaf electrolyte leakage (EL), malondialdehyde (MDA) content, antioxidant enzyme activity (superoxide dismutase, SOD; peroxidase, POD; catalase, CAT), fatty acid content and an index of unsaturated fatty acid occurrence, were determined. There were three temperature treatments: optimal temperature (30 ℃/25 ℃, day/night), chilling (8 ℃/4 ℃) and freezing (2 ℃/-2 ℃), and four replicates for SA treated and untreated pots/swards. The results showed that turf quality was adversely affected, and leaf electrolyte leakage (EL), MDA content and SOD, POD and CAT activity were increased under the chilling and freezing temperature treatments. Pre-treatment with exogenous SA significantly alleviated the detrimental effect of chilling and freezing stress on the plant growth, turf quality, EL, MDA content and antioxidant enzyme activity. The saturated fatty acid content was increased, and unsaturated fatty acid content and the index of unsaturated fatty acid occurrence were decreased under chilling and freezing temperature treatments; while pre-treatment with exogenous SA diminished these chilling and freezing effects, compared to those seen in pots not receiving SA. These results indicate that one factor in the SA-enhanced cold tolerance of seashore paspalum is the maintenance and/or increase in unsaturated fatty acid content and the index of unsaturated fatty acid occurrence, which would in turn enhance membrane stability and contribute to the observed enhancement of chilling and freezing tolerance.

Physiological response of naked oat seedlings to exogenous hydrogen peroxide (H₂O₂) under cadmium stress

LIU Jian-xin, OU Xiao-bin, WANG Jin-cheng, LIU Rui-rui, JIA Hai-yan

2020, 29(1):  125-134.  DOI: 10.11686/cyxb2019178

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Cadmium (Cd) is one of the most toxic pollutants. In order to investigate the regulatory effect of the exogenous signaling molecule hydrogen peroxide (H₂O₂) on physiological responses of naked oat (Avena nuda) under Cd stress, a pot experiment was conducted in a greenhouse at the Longdong University Experimental Base from April to July 2017. Perlite was used as the culture substrate; the naked oat cultivar ‘Dingyou No.6’ was selected as the variety for testing. Four treatments were included: 1) Naked oat leaves were sprayed with distilled water, and roots fed with Hoagland’s nutrient solution (CK); 2) Naked oat leaves were sprayed with 5 mmol·L^-1 H₂O₂ solution, and the roots fed with Hoagland’s nutrient solution; 3) Leaves were sprayed with distilled water, and the roots were fed with Hoagland’s nutrient solution containing 50 mg·L^-1 Cd²⁺; 4) Leaves were sprayed with 5 mmol·L^-1 H₂O₂ solution, and the roots were fed with Hoagland’s nutrient solution containing 50 mg·L^-1 Cd²⁺. The effects of exogenous H₂O₂ on growth, reactive oxygen species (ROS) metabolism, photosynthetic parameters and activities of key enzymes involved in carbon assimilation were assessed. The results showed that foliar spraying of H₂O₂ significantly alleviated the decrease of root length, plant height, fresh weight and dry weight of naked oats seedlings under Cd stress. Spraying the Cd²⁺ stressed seedlings with H₂O₂ significantly decreased the contents of superoxide anion, H₂O₂, malondialdehyde and ascorbic acid and the activities of catalase, and it increased the activities of superoxide dismutase and ascorbate peroxidase and the glutathione, flavonoid, total phenol and proanthocyanidin levels in seedling leaves, but had little influence on peroxidase activity, chlorophyll a and chlorophyll b contents, chlorophyll a:b ratio, stomatal conductivity, and transpiration rate of leaves. Also, spraying H₂O₂ significantly alleviated the Cd inhibitory effects on carotenoid content, net photosynthetic rate, the activities of ribulose 1, 5-biphosphate carboxylase, sedoheptulose-1, 7-bisphosphatase, fructose-1, 6-bisphosphate aldolase and transketolase, and it decreased the intercellular CO₂ concentration in leaves. The above results indicate that exogenous H₂O₂ can reduce the oxidative damage induced by Cd stress through up-regulation of the ROS scavenging system, and increased activity of key enzymes of carbon assimilation, thus mitigating the inhibition of photosynthesis under Cd stress. In summary, H₂O₂ alleviates the inhibitory effects of Cd stress on the growth of naked oat seedlings and enhances the tolerance of naked oats to Cd stress.

Effects of salicylic acid and Epichloё on perennial ryegrass (Lolium perenne) under drought stress

MA Bi-hua, LIN Wei-hu, GAO Min, WANG Xing-di, TIAN Pei

2020, 29(1):  135-144.  DOI: 10.11686/cyxb2019103

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This greenhouse experiment studied the effects of different concentrations of salicylic acid (SA) on endophyte-infected (E+) and endophyte-free (E-) perennial ryegrass (Lolium perenne), under continuous drought stress for 15 days or well watered (Control). Measurements included leaf relative leaf water content, chlorophyll content, peroxidase (POD) activity, superoxide dismutase (SOD) activity, malondialdehyde (MDA) content, proline (Pro) and soluble sugar (SS) of the perennial ryegrass. Changes in physiological indices such as SS content were examined to determine the effects of SA and endophytic fungi on perennial ryegrass under drought stress. It was found that the relative water content, chlorophyll content, POD activity and SS content of E+ were significantly higher (P<0.05) than those of E- L. perenne plants under drought stress. The addition of exogenous SA increased the relative water content, chlorophyll content, POD and SOD activities, and Pro and SS contents, while decreasing MDA content. The present study showed that exogenous SA solutions of 0.25 and 0.50 mmol·L^-1 were best for enhancement of the drought tolerance of L. perenne. There was a significant (P<0.05) interaction effect between Epichloё endophyte and SA together on SOD activity, POD activity and chlorophyll content of perennial ryegrass. In summary, Epichloё endophyte and SA both improved the drought resistance of perennial ryegrass. Specifically, Epichloё endophyte and SA promoted osmotic adjustment and activity of oxygen radical scavenging system, and thereby increased the drought resistance of the host plant.

Isolation, identification and growth promotion of arbuscular mycorrhizal fungi (AMF) from Potentilla chinensis in degraded alpine grassland in the Qilian Mountains

GAO Ya-min, LUO Hui-qin, YAO Tuo, ZHANG Jian-gui, LI Hai-yun, YANG Yan-shan, LAN Xiao-jun

2020, 29(1):  145-154.  DOI: 10.11686/cyxb2019185

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An arbuscular mycorrhizal fungus (AMF) species was isolated from Potentilla chinensis growing in degraded alpine grassland in the Qilian Mountains, and the AMF growth promotion effect was then identified, with a view to potential future application to provide agricultural benefit. The AMF spores in soil were extracted by wet-screen decantation-sucrose centrifugation, and cultured by potting with oats. Morphological characteristics and 18S rRNA gene analysis were used to identify the AMF. With respect to morphological traits, the spore color of the isolated AMF ranged from white, through milky white, to yellowish brown, while spore shape ranged from ellipsoidal, through nearly spherical, to spherical. Spore diameter was 90-120 μm. The effective 18S sequence length was 673 bp. Compared by NCBI blast, the isolated AMF was 100% similar to Rhizophagus intraradices, so both the morphological and mRNA evidence were consistent with identification of the isolated AMF as R. intraradices (GenBank serial number MK311327). A culture test on oat seedlings was conducted with treatments: CK (not inoculated); A (inoculated with R. intraradices from a laboratory reference sample, AMF1); and B (inoculated with the isolated AMF, AMF2). The pot experiment showed that AMF2 increased the plant height, stem diameter and chlorophyll b content of oat seedlings by 10.70%, 21.43% and 2.60%, respectively. AMF1 had a weaker effect on the aboveground growth of oat seedlings. AMF2 also increased the total root length, root volume, and root surface area of the roots of the oats, and reduced the average diameter of the roots, especially the diameter roots less than 1.0 mm diameter. To summarise, AMF2, the isolated strain of R. intraradices demonstrated a strong growth promotion effect on oat seedlings. Thus AMF2 is a useful addition to the AMF strain library in China, and also shows potential for agricultural use in ecological restoration of degraded alpine grassland.

Effect of AM fungi on alfalfa responses to aphid stress

LI Ying-de, DING Ting-ting, DUAN Ting-yu

2020, 29(1):  155-162.  DOI: 10.11686/cyxb2019150

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Alfalfa (Medicago sativa) is widely planted around the world, and is one of the most important perennial forage legumes due to its high yield and good feed quality, including a high nitrogen content. The pea aphid (Acyrthosiphon pisum) is also important globally as an insect pest of many crops and forages. The pea aphid can cause serious production losses in alfalfa, and is also the major vector of many plant viruses. Arbuscular mycorrhizal (AM) fungi are very important soil microorganisms which can colonize plant roots of 80% of terrestrial plant species, and then form mutualistic symbioses with the roots in natural and agricultural ecosystems. The AM fungus generally confers growth and fitness benefits on its host plants and can promote host plant nutrient uptake. The AM fungus also plays important roles in plant defenses against both biotic and abiotic stress. The present study was designed to test the effect of two AM fungi, Rhizophagus intraradices and Claroideoglomus etunicatum, on alfalfa responses to pea aphid stress. It was found that AM fungi can regulate the plant response to aphids by promoting plant growth and nutrient uptake, changing plant defense enzyme activity, and concentration of plant hormone signaling substances. Presence of R. intraradices and C. etunicatum significantly increased the biomass, branch number and N and P content of alfalfa (P<0.05). In addition, R. intraradices significantly promoted peroxidase (POD) enzyme activity. Compared to plants with no mycorrhizal treatment, AM plants had higher catalase activity and salicylic acid (SA) concentration after aphid infestation (P<0.05). C. etunicatum significantly promoted POD activity (P<0.05). SA and nitric oxide (NO) concentration of alfalfa was increased after aphid infestation, and aphid infestation significantly inhibited superoxide dismutase (SOD) activity (P<0.05). AM fungal colonization further promoted root P content, POD and SOD activities, and SA concentration of aphid-infested plants, which suggests that AM fungi can alleviate pea aphid damage to alfalfa.

Isolation and identification of pathogenic Fusarium spp. causing maize ear rot and analysis of their toxin-producing genotype in Heilongjiang Province

WANG Bao-bao, BI Si-gang, XIAO Ming-gang, ZHANG Dong-ying, YAN Qiang, ZHANG Yan-yan, YANG Shu-long, ZHU Zhen-dong, DUAN Can-xing

2020, 29(1):  163-174.  DOI: 10.11686/cyxb2019198

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The present study was designed to systematically elucidate the main pathogenic Fusarium species causing maize ear rot and their distribution characteristics in Heilongjiang Province, and then formulate scientifically based and practical control measures for maize ear rot, so as to control mycotoxin occurrence in maize kernels. A total of 143 samples of maize cobs displaying ear rot were collected in 21 maize-producing areas in Heilongjiang Province in 2018. Fusarium spp. were isolated by the seed health test method and then identified by morphology and molecular characteristics. A total of 200 Fusarium isolates were obtained and 12 Fusarium species were identified and confirmed. The isolation frequency of F. graminearum and F. verticillioides was 33.00% and 16.00% respectively, followed by F. subglutinans, F. proliferatum, F. boothii, F. temperatum, F. andiyazi, F. incarnatum, F. sporotrichioides, F. poae, F. commune and F. asiaticum, with isolation rates of 13.00%, 13.00%, 12.50%, 7.50%, 2.50%, 2.00%, 1.00%, 1.00%, 1.00% and 0.50%, respectively. Toxin genotype analyses showed that F. asiaticum belong to the NIV-producing type, whereas F. graminearum and F. boothii contained three kinds of genotypes, among which 15-AcDON was the most abundant, followed by 3-AcDON, and the NIV type was the least common. The key fumonisin-producing fum1 gene was found in F. verticillioides, F. proliferatum, F. subglutinans, F. andiyazi, F. incarnatum, F. sporotrichioides, F. poae, while F. temperatum and F. commune did not carry the fum1 gene. The diversity of Fusarium species causing maize ear rot in Heilongjiang was relatively rich, F. graminearum and F. verticillioides were the predominant pathogens, and F. subglutinans, F. proliferatum and F. boothii were distributed relative widely, while F. temperatum and F. andiyazi had a relatively small distribution range. In this study, F. sporotrichioides, F. incarnatum, F. poae and F. commune were isolated from diseased maize ears in Heilongjiang Province for the first time. This study enhanced knowledge about the species of Fusarium causing maize ear rot in Heilongjiang.

Allelopathic effects of Hylotelephium erythrostictum flowers on three weed species and identification of potential allelochemicals

WANG Yu-xuan, TANG Zong-shou, CAO Meng-lin, LI Ya-xin, ZHANG Tian-bao, DU Hui-ling

2020, 29(1):  175-182.  DOI: 10.11686/cyxb2019308

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The allelopathic effects of various extracts from Hylotelephium erythrostictum flowers on germination and early growth of seeds of the ‘weeds’ species Echinochloa crusgalli, Amaranthus retroflexus, and Trifolium repens, were studied by laboratory bioassay. Petroleum ether, methylene chloride, ethyl acetate, N-butanol and aqueous extracts were prepared. The dichloromethane extract had a strong inhibitory effect on weed germination and growth, and the inhibitory effect increased with increasing concentration. The inhibition effect on the three tested weed species reached 100% at an extract test concentration of 10 g·L^-1. The methylene chloride extract also displayed strong allelopathic activity. GC-MS was used to analyze the chemical constituents of these extracts, and 18 compounds were initially identified, from which 5 potential allelopathic were screened out: dibutyl phthalate, methyl hexadecanoate, benzenemethonic acid, octadecanoic acid methyl ester, and phenol. For these five compounds, samples of analytical purity were obtained and used to test for allelochemical activity. The effect of dibutyl phthalate was weak, with the allelopathic inhibitory effect on T. repens germination only 14.1%, while the other four had strong inhibitory effects, and there were significant differences in allelopathic activities. T. repens was the most sensitive among the tested species, and methyl hexadecanoate, benzenemethonic acid and phenol had an inhibitory effect of 100% in this species. This study identifies compounds with allelochemical activity that might potentially be used as bioherbicides for H. erythrostictum.

Plant secondary metabolites of four rangeland plant species and their effects on the activities of detoxification enzymes of Oedaleus asiaticus in a steppe grassland

CHEN De-xia, LIU Xu, LUO Lin-hua, HUANG Xun-bing, LÜ Shen-jin, LI Guang-yue, ZHANG Ze-hua

2020, 29(1):  183-192.  DOI: 10.11686/cyxb2019128

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Oedaleus asiaticus Bey-Bienko, a significant grasshopper pest species occurring in north China, has specific food preferences and adaptations. To explore the identity of the plant metabolites responsible for food preference, we measured the content of flavonoids, phenols, alkaloids, terpenoids, and tannins in the grassland species Stipa krylovii, Cleistogenes squarrosa, Leymus chinensis, and Artemisia frigida. The growth and detoxification enzyme activity of O. asiaticus feeding on the above four plant species with their different secondary metabolite profiles were also analyzed. The grass S. krylovii had low levels of secondary metabolites, while the grass L. chinensis and the herb A. frigida possessed the highest contents of the five measured plant secondary metabolites. Grasshoppers feeding on S. krylovii with low secondary metabolite levels, had greater growth and decreased reactive oxygen species (ROS) concentration and digestive enzyme activity then those feeding on L. chinensis and A. frigida. In summary, S. krylovii was the most favorable host plant among the plants tested, and enhanced the performance of the grasshopper species O. asiaticus. This study shows that grasshopper feeding preference is linked to low levels of secondary metabolites, and this information could aid in grasshopper control.

An analysis of the response of the LpWRKY20 gene to abiotic stress and its role in drought resistance

YANG Liu-hui, YIN Hang, HUANG Qin-mei, ZHANG Yan-ni, HE Miao, ZHOU Yun-wei

2020, 29(1):  193-202.  DOI: 10.11686/cyxb2019318

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This research investigated the expression of the LpWRKY20 gene under different abiotic stresses, using quantitative reverse transcription PCR (qRT-PCR). The plant expression vector pBI121-LpWRKY20-GFP was transferred into tobacco by the leaf disc method and transgenic lines were obtained. The expression of this gene differed under different abiotic stresses. The phenotype of transgenic plants was better than that of wild plants under drought stress. The activities of superoxide dismutase and catalase of transgenic plants were higher than those of the wild type, and the ability to remove free radicals in vivo increased significantly over time. Tissue malondialdehyde level was lower than that of the wild type, indicating that the cell membrane of transgenic plants was less damaged and had a strong self-repairing ability. The change of phenotype and physiological indexes under drought conditions indicated that transgenic plants had strong drought resistance, and the preliminary conclusion was reached that the LpWRKY20 gene confers drought resistance.

Effects of inorganic N on the N accumulation and root morphology of a mining ecotype of Polygonum hydropiper

QING Yue, LI Ting-xuan, YE Dai-hua

2020, 29(1):  203-210.  DOI: 10.11686/cyxb2019117

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Excessive application of nitrogen (N) fertilizers increases the loss of N via runoff and leaching, resulting in a more serious eutrophication. In a previous study, we screened out a nitrogen-phosphorus enriched plant, the mining ecotype (ME) of Polygonum hydropiper. Studying the root morphology response to inorganic nitrogen addition could be expected to provide a theoretical basis for understanding the absorption and accumulation mechanism of nitrogen in the ME of P. hydropiper. Sand culture experiments were conducted to analyse the N accumulation and root morphology of the P. hydropiper ME supplied with different ammonium nitrogen (NH₄-N) concentrations (25, 50, 75 mg N·L^-1) and different nitrate nitrogen (NO₃-N) concentrations (25, 50, 75 mg N·L^-1). The P. hydropiper ME showed the greatest biomass and N accumulation at 50 mg N·L^-1. The biomass values of the P. hydropiper ME grown in 50 and 75 mg·L^-1 NO₃-N treatments were significantly higher than those in NH₄-N treatments; however, the P. hydropiper ME accumulated more N when grown in the NH₄-N than when grown in the NO₃-N treatments. The root growth of the P. hydropiper ME was greatly inhibited with increasing NH₄-N concentrations in solution. The root system of the P. hydropiper ME showed the greatest length, surface area, and volume when grown in 50 mg·L^-1 NO₃-N. The root growth of the P. hydropiper ME was greater in NH₄-N than in NO₃-N at 25 mg N·L^-1, but this difference was reversed at 50 and 75 mg N·L^-1. In summary, he appropriate NO₃-N concentration promoted the growth of the P. hydropiper ME and the development of lateral roots, resulting in enhanced absorption of N. High concentration of NH₄-N inhibited root growth, but did not reduce N accumulation in the plant.