Table of Content

20 February 2019, Volume 28 Issue 2

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Soil physicochemical and biological characteristics of Tamarix ramosissima Nebkhas in different degradation degree

DING Ai-qiang, XÜ Xian-ying, ZHANG Wen, LIU Jiang, FU Li, FU Gui-quan

2019, 28(2):  1-11.  DOI: 10.11686/cyxb2018159

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Fifteen indicators of soil physicochemical properties, enzyme activity and microbial quantity were measured in a space-time substitution experiment, to characterize the changes in soil properties in nebkhas formed in association with Tamarix ramosissima within the transition zone from oasis to desert in the Minqin Lake region. With increasing degradation, bulk density increased, organic matter and cation exchange capacity increased in the early stages, and later decreased; soil moisture, total salt content, and electric conductivity decreased, while pH remained unchanged. The pattern of change in the profile with increasing soil depth was that bulk density increased, while soil moisture content, organic matter, and cation exchange capacity decreased, while total salt content and electrical conductivity were highest in the 5-10 cm soil layer. The abundance of soil microorganisms, and soil enzyme activity decreased with increase in degradation status and with soil depth. All soil physicochemical properties and soil biological characteristics, except individual index, showed statistically significant differences,while the relationship between degenerative state or soil depth needs to be researched. In conclusion, the soil physicochemical properties and biological characteristics were adversely affected in the degraded nebkhas. Therefore, vegetation and soil factors should be considered together when planning restoration of degraded nebkhas.

Effects of mulching on soil environment and water utilization by roots of Lycium barbarum

XU Sheng-rong, ZHANG En-he, MA Rui-li, WANG Qi, LIU Qing-lin, HUANG Yu-fang

2019, 28(2):  12-22.  DOI: 10.11686/cyxb2018162

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Lycium barbarum (Wolfberry), is the main commercial crop in arid land in northwestern China. This research aimed to improve knowledge of the water uptake characteristics of L. barbarum, in order to increase the water use efficiency of the root system. A mulching experiment was conducted at the Gulang agricultural demonstration area, Gansu province (37.30° N, 103.29° E). The experiment included four mulching treatments: plastic mulching (PM), fabric mulching (FM), stalk mulching (SM), and an un-mulched control (CK). Hydraulic conductivity of the canopy and root, and soil micro-environment were monitored in four year old seedlings of the ‘Ningqi 1’ variety of L. barbarum. It was found that the hydraulic conductivity of the canopy and roots was increased by mulching. The greatest increase occurred with PM, which had values 109.7% and 102.8% of CK. The root system absorbed water mainly in the 30-100 cm soil depth in the CK plants. Soil moisture increase in 0-30 cm was found to decrease the utilization rate by plants of deeper soil moisture. Depletion of the deep soil moisture was 81.81% in CK, compared to 47.06% in the PM treatment. WUE was lowest in the PM treatment and highest in the SM treatment. By contrast, the soil moisture content at 0-150 cm was increased by mulching, and was highest in the PM treatment. For soil average temperature, the treatments ranked PM>FM>CK>SM. soil organic carbon, microbial biomass, and microbioal diversity index were enhanced in SM (14.69 mg·g^-1, 618.8×10⁶ CFU·g^-1 and 3.13 H, respectively), compared to other treatments, while the soil organic carbon of the PM treatment was the lowest (97.98% of CK). The soil temperature, soil moisture content with the hydraulic conductivity and water use efficiency showed significant correlations. It suggested that the root water use efficiency in L. barbarum is affected by the mulching material used. Promotion of plant growth and improvement of the soil environment was more pronounced in the SM treatment with other mulching materials, It is possible to increase the water use efficiency of roots by stalk mulching.

Factors influencing leaf nitrogen and phosphorus stoichiometry in plant species of Ningxia grasslands

LI Ming-yu, HUANG Wen-guang, YANG Jun-long, LI Xiao-wei

2019, 28(2):  23-32.  DOI: 10.11686/cyxb2018459

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Nitrogen (N) and phosphorus (P) cycles control plant growth and development, community structure and function of grassland ecosystems. In order to define patterns of change in leaf N and P stoichiometry in Ningxia grasslands, and their main driving factors, leaf N and P contents were determined for 409 dominant plant species at 111 sampling sites. The geographic distribution of leaf stoichiometry patterns was analyzed in relation to the climatic factors, mean annual temperature (MAT) and mean annual precipitation (MAP), as well as altitude and latitude of the sampling site. The arithmetic means for leaf N and P content of Ningxia grassland plants were 22.47 and 1.83 mg·g^-1, respectively, and the mean N∶P ratio was 14.24. The growth of Ningxia grassland plants was limited by N and P. Leaf N and N∶P ratio increased with the increasing latitude and MAT, and with decreasing altitude and MAP. Leaf P increased with increase in MAP, while leaf N and P both increased with increased longitude. Spatial distribution and hydrothermal conditions explained 70.83% of the variance for leaf N, leaf P and N∶P ratio, indicating that the hydrothermal environment is the main driving factor for the Leaf N and P stoichiometry of Ningxia grassland plants. The results provide a theoretical basis for the management and improvement of productivity in Ningxia grassland.

Distribution of newly fixed carbon of Nitraria tangutorum in the plant-soil system

LI Xin-le, BAO Fang, WU Bo, CAO Yan-li, LIU Ming-hu, DUAN Rui-bing

2019, 28(2):  33-40.  DOI: 10.11686/cyxb2018561

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Characterizing the carbon turnover in terrestrial ecosystems is critical for understanding and predicting carbon dynamics in ecosystems. We used in situ ¹³C pulse labeling to track photosynthetic carbon fluxes of Nitraria tangutorum from shoot to root and soil in the Ulanbuh Desert. The objectives of this study were: 1) To determine the transfer dynamics of newly photosynthesized carbon to different carbon pools including leaves, stems, roots, soil, and respiration. 2) To quantify the allocation rate of newly fixed carbon among different carbon pools. 3) to estimate the carbon budget of a N. tangutorum desert ecosystem. It was found that the distribution of ¹³C-newly fixed carbon in leaves, stems, and roots of N. tangutorum and in soil was significantly different in different labeling periods. The ¹³C abundance value in leaves and stems rose rapidly to the highest value after labeling for 1 h, at which point the ¹³C abundance value was 520.1‰ and 592.5‰, 14 and 20 times higher than the control, respectively. Thereafter, the ¹³C abundance value gradually decreased with time until it stabilized. The labeled ¹³C was found in the roots and soil after labeling 18 h, and the ¹³C abundance values reached 9.5‰ and -23.8‰, respectively. The amount of newly fixed carbon lost through shoot respiration and soil respiration reached a maximum after labeling for 1 h and 18 h, respectively. At the end of the labeling period, about 35.59% of labeled carbon was transferred to the shoots, 16.67% was retained in root, 31.92% was lost as respiration (shoot respiration+soil respiration) and 15.82% remained in the soil. In the three carbon pools, i.e., shoot, root, and soil pools, shoots consistently had the highest proportion of ¹³C in the plant-soil system during the 32 days. Based on the ¹³C partitioning pattern and biomass production, we estimate a total of 2895.6 kg C·ha^-1·yr^-1 was fixed by these desert plants during the vegetation growth season. This study suggests that N. tangutorum plays an important role in carbon sequestration in the carbon cycle of desert ecosystems.

Effects of water and nitrogen supply under drip irrigation on the production performance rate and water and nitrogen use efficiency of alfalfa

HU Wei, ZHANG Ya-hong, LI Peng, WANG Xiao-ju, ZHANG Peng, HE Yi, KANG Xin-yun

2019, 28(2):  41-50.  DOI: 10.11686/cyxb2018231

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The effects of water and nitrogen supply on the growth, yield and water and nitrogen use efficiency of alfalfa were investigated to find out the best combination of water and nitrogen in the production of alfalfa and to provide scientific reference data for actual production under drip irrigation in the Yellow River irrigation region of Ningxia. A field experiment using a split-plot design was used. There were four irrigation levels (W₁, 480 mm; W₂, 550 mm; W₃, 620 mm; W₄, 690 mm) in main plots and four nitrogen levels (N₀, 0; N₁, 60 kg·ha^-1; N₂, 120 kg·ha^-1; N₃, 180 kg·ha^-1) in sub-plots. The results showed that water and nitrogen supply had different effects on the plant height and stem diameter of alfalfa for each harvest. The plant heights of first and second cutting of alfalfa increased with increased nitrogen application rate and with increased irrigation supply, and the stem diameter at the first cutting was increased with increased irrigation rate. The yields of alfalfa hay at the first and second cutting increased with increased irrigation rate. Applied nitrogen significantly increased the alfalfa hay yield at the first and fourth cuttings and over the whole growth season. The irrigation effect, the nitrogen application effect, and the irrigation and nitrogen interaction for hay yield were all extremely significant (P<0.01). The irrigation water use efficiency (IWUE) and water use efficiency (WUE) were decreased with increased irrigation rate, and were increased by nitrogen application. The treatment W₄N₀ had the lowest IWUE and WUE.Alfalfa nitrogen use efficiency (ANUE) showed different patterns with different nitrogen fertilizer and irrigation rates. In the W₁, W₂ and W₃ treatments, ANUE was greatest in the N₂ treatment and reduced at higher or lower N application rates, while in the W₄ treatment, ANUE was decreased with increased nitrogen application rate. Nitrogen partial factor productivity (PFPN) was decreased significantly with the increase of nitrogen application rate. ANUE was decreased by irrigation at lower water application rates but was increased by irrigation at higher application rates, while PFPN showed the opposite pattern with highest PFPN at intermediate irrigation rates, indicating that irrigation at an appropriate rate can improve the ANUE and PFPN of alfalfa. From these results, to optimize hay yield while conserving water and fertilizer resources, W₃N₂ (620 mm, 120 kg·ha^-1) was indicated as the best irrigation and fertilizer treatment combination for alfalfa under drip irrigation in this region. The study provides valuable information for improving management of alfalfa in the Yellow River irrigation region of Ningxia.

An evaluation of smallholder seed threshing and cleaning technologies in seed production of Cleistogenes songorica cv. ‘Tenggeli’

TAO Qi-bo, JIA Cun-zhi, WANG Yan-rong, LI Xin-yong, HAN Yun-hua, BAI Meng-jie

2019, 28(2):  51-60.  DOI: 10.11686/cyxb2018135

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Cleistogenes songorica ‘Tenggeli’ is a new “wild” grass cultivar registered by the Chinese Herbage Variety Registration Board in 2016 (Registration No: 499), which has excellent drought tolerance and soil stabilization capacity, and so plays an important role in ecological regeneration, landscaping, and grassland restoration in arid and semiarid areas. However, there is an urgent need to accelerate seed multiplication and to develop feasible seed threshing and cleaning techniques. Based on a preliminary trial we conducted at an experimental station in Yuzhong County, Gansu Province, further research was carried out in Minqin County in the Hexi Corridor, Gansu Province, to evaluate the suitability of the seed threshing and cleaning techniques developed, for use by smallholder farmers. For naturally dried seed-heads, 45-55 passes under a 50 kg roller resulted in the highest harvest rate (up to 78% of total seed present), without loss of seed quality. The optimum airflow velocity for seed cleaning was 4.5 m·s^-1, and seed purity attained with this airflow velocity and two passes over a sieve, was up to 86%. These data are of great importance for C. songorica ‘Tenggeli’ seed production, as improved seed availability will enhance the extension process and the user adoption of this important new cultivar.

Effects of surface-layer accumulated temperature on major growth traits of spring maize when un-mulched or under clear or black plastic film mulches

SUN Shi-jun, JIANG Hao, CHEN Zhi-jun, ZHU Zhen-chuang, ZHANG Xu-dong, CHI Dao-cai

2019, 28(2):  61-72.  DOI: 10.11686/cyxb2018493

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The objective of this research was to study the effects of surface-layer accumulated temperature on major growth traits of spring maize under different colored plastic film mulching in the rain-fed region of Northeast China. Field experiments with three film mulching treatments: no mulch (M₀), colorless transparent plastic film mulch (M₁) and black plastic film mulch (M₂), were conducted.Slogistic equation was used to fit the progression of maize plant height, leaf area index, and dry matter accumulation as a function of surface-layer accumulated temperature.It was found that the average rate of maize plant height increase ranked M₂>M₁>M₀ during early growth, M₂>M₀>M₁during stem elongation, and M₀>M₂>M₁ during grain development. The treatment rankings for accumulation rate of maize leaf area index followed those of plant height during early growth and grain development stages, but ranked M₂>M₁>M₀ during stem elongation. The black film (M₂) treatment significantly increased the duration of dry matter accumulation during the stem elongation stage and reached the stem elongation growth phase earlier than other treatments, and so contributed to improved maize yield. There was a significant relationship between maximum dry matter accumulation rate, the accumulated temperature at which the inflexions of the dry matter accumulation curves occurred, other parameters of the Slogistic equation, and maize yield. The results show that film mulching had the greatest impact on maize development during the early growth stage.Transparent plastic film accelerated leaf senescence,while the black plastic film treatment had the largest dry matter accumulation rate and the highest yield.Results from this research into the effect of mulching treatment options on the growth dynamics of maize and on maize yield can be used to improve resource use efficiency and output of maize production systems.

Evaluation on production performance and economic benefit of the single alfalfa filed interplanting different forage crops in summer

LI Yuan, ZHAO Hai-ming, YOU Yong-liang, WU Rui-xin, LIU Gui-bo

2019, 28(2):  73-87.  DOI: 10.11686/cyxb2018541

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On the Haihe plain, the traditional 3-5 cutting of alfalfa are difficult to achieve in wet growing seasons. To explore this problem, two field experiments were conducted from 2011 to 2016 to analyze the production performance and economic benefit of interplanting alfalfa with various forage crops in summer. Five different forage crops were evaluated: silage maize, Sorghum bicolor×Sorghum sudanense, Dolichos lablab, fodder soybean, and forage millet. The results indicated that there were no significant differences between 30-30 cm and 20-40 cm row spacing treatments (P>0.05). The hay yield of the first two cuts of alfalfa for the second year when alfalfa was interplanted with S. bicolor×S. sudanense was significantly lower than for alfalfa alone (P<0.05). The total feed equivalent units when interplanting silage maize with alfalfa were significantly higher than for alfalfa alone (P<0.05); but the total economic benefits were not significantly different (P>0.05). The average solar energy use efficiency, water use efficiency, and land equivalent ratio when interplanting silage maize and alfalfa in summer were significantly higher than for alfalfa alone (P<0.05. Other research into the yield performance for alfalfa interplanted with silage corn showed that there were no significant differences (P>0.05) in the first two cuts between 30-30 cm and 20-40 cm row spacing treatments for hay yield, total feed equivalent units, total economic benefit, average solar energy use efficiency, water use efficiency, land equivalent ratio. Considering all the results, the optimal planting details for alfalfa interplanted with silage maize are as follows: the alfalfa field is planted in autumn using alternate wide and narrow row spaces of 20 and 40 cm. The silage corn is interplanted in the wide row space after the second cut of alfalfa is harvested in second year. The plant density of silage maize was less than 60000 plants·ha^-1 and the maize is harvested with alfalfa at the end of September, after which the alfalfa overwinters normally. The following year silage maize is replanted as the above. The interplanting methodology developed in this study is more easily implemented than the traditional 3-5 cuts of alfalfa in wet growing seasons and enhances solar, water and land resource use efficiency with the promise of corresponding economic benefits.

Molecular typing and biotype classification of rhizobia of Medicago sativa

KANG Wen-juan, SHI Shang-li, MIAO Yang-yang

2019, 28(2):  88-101.  DOI: 10.11686/cyxb2018160

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This study aimed to classify biotypes in the same rhizobium species according to their phenotypic characteristics and the symbiotic efficiency between the alfalfa variety and rhizobium strain, and so to provide a knowledge base for breeding rhizobia that are effective symbiotic partners with alfalfa. Rhizobium strains were isolated from different plant parts of five Medicago sativa varieties in three cultivation regions of Gansu province. 16S rRNA sequencing, multilocus sequence typing (MLST), numerical taxonomy analysis based on phenotypic characteristics and symbiotic efficiency determination were used to achieve rhizobia biotype classification. Of 78 rhizobia strains in a preliminary screening, 20 were assigned to Rhizobium radiobacter by 16S rRNA sequencing and MLST analysis. Seven phenotypic clusters were formed based on numerical taxonomy analysis of phenotypic characteristics. Seedlings of the five M. sativa varieties were inoculated with the 20 R. radiobacter strains, and shoot dry weights, which contributed the most to the symbiotic efficiency between alfalfa and rhizobium, for varieties inoculated with each strain were compared using Duncan’s multiple range test. The symbiotic efficiency of strains was designated A, B, or C when the shoot dry weight of inoculated plants was, respectively, significantly higher than, not significantly different from, or significantly lower than that of non-inoculated control plants.The designated symbiotic efficiency of each rhizobia was combined according to the order of M. sativa cv. Gannong No.3, Gannong No.9, Longzhong, Qingshui, and WL168HQ, and six kinds of symbiotic combination patterns were formed.The 20 R. radiobacter strains were divided into 14 biotypes according to phenotypes and symbiotic patterns. For M. sativa cv. WL168HQ, Gannong No.3, and Longzhong many rhizobium biotypes were found, while the rhizobia of M. sativa cv. Gannong No.9, and Qingshui were monotypic. In conclusion, rhizobia of the same species (R. radiobacter) could be classified into biotypes using information on phenotypic characteristics and symbiotic patterns, and some alfalfa varieties were found to host a number of rhizobium biotypes.

Isolation of heavy metal-tolerant Sinorhizobium meliloti and the effect on copper uptake of alfalfa, perennial ryegrass and Sorghum bicolor plants grown on copper-contaminated soil

YAN Jing, XIA Li, SHENG Xia-fang, HE Lin-yan

2019, 28(2):  102-111.  DOI: 10.11686/cyxb2018131

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This research was aimed at improvement of the adaptability and performance of plants used for phytoremediation in marginal lands subject to heavy metal contamination, The use of rhizobia to increase biomass productivity is an exciting new development in the phytoremediation of contaminated sites. In the present study, a heavy-metal-tolerant rhizobia strain was isolated from nodules of alfalfa (Medicago sativa) plants grown in copper (Cu) mine tailings in Nanjing. A greenhouse experiment was conducted to evaluate the potential role of this rhizobium strain in encouraging plant growth, Cu uptake and soil remediation by three plant species: M. sativa, Lolium perenne and Sorghum bicolor. The strain of Sinorhizobium meliloti (designated D10) was isolated from root nodules of alfalfa, and was Cu-Pb-Cd-tolerant. Symbiotic association was successfully established between S. meliloti D10 and M. sativa in the current research. It was found that the biomass production of the three species ranked in order: S. bicolor>L. perenne>M. sativa. Inoculation of S. meliloti D10 significantly increased the biomass of M. sativa and S. bicolor, with a 28.6%-78.1% greater biomass for inoculated vs. uninoculated plants. Among the tested plants, S. bicolor accumulated the greatest amounts of Cu. Further, inoculation of S. meliloti D10 resulted in a significant increase in Cu uptake in S. bicolor and M. sativa of 50.4%-111.8% of the uninoculated control. The beneficial impacts of S. meliloti D10 colonization on plant growth and Cu uptake of the three tested species was associated with both improved water-soluble sugar content and increased urease activity. The experiment provided evidence of the potential for use of these plant species in combination with S. meliloti D10 for ecological remediation of metalliferous mine tailings.

An analysis of genetic control of flowering time in alfalfa with QTL mapping of active loci

HE Fei, ZHANG Fan, ZHANG Tie-jun, KANG Jun-mei, LONG Rui-cai, YANG Qing-chuan, MA Chun-hui

2019, 28(2):  112-120.  DOI: 10.11686/cyxb2018154

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In order to explore the genetic basis for flowering date variation in alfalfa, a QTL mapping population was set up comprising 152 F₁ hybrids of 2 parent plants with contrasting maturity dates, and the QTL loci associated with flowering date were identified. A low-yielding early-maturing alfalfa variety was used as the pollen parent and a high-yield late-maturing variety was used as the seed parent. In 2015 and 2016, the date of initial flowering was recorded for the 152 F₁ hybrids and the 2 parent plants, and genotyping of the 154 single plants was carried out using GBS sequencing technology. The SNP markers generated were used to construct a linkage map, and QTL ici Mapping software and phenotypic data were used for QTL positioning of flowering time. A major gene and poly gene inheritance model was then used to build up the optimal genetic model for control of initial flowering time. The analysis indicated two major gene model-additive effect as the optimum genetic model for controlling date of initial flowering. The major gene heritability reached 99.0% in 2015, while it was 98.5% in 2016. The pollen-parent linkage map comprised 1386 cM and the average marker spacing was 3.2 cM. The female-parent linkage map covered 798.73 cM with an average marker spacing of 8.07 cM. Two main QTLs were found in both year’s data sets, with phenotypic variation accounted for being 12.13% and 11.02% respectively. In summary, date of initial flowering is largely determined by two major genes with additive effects. The initial time of flowering is mainly controlled by two QTL sites.

Effects and trade-offs of shading and drought on clonal growth, and sexual reproduction in Arthraxon hispidus

XU Xiao-xia, LIU Jin-ping, YOU Ming-hong, ZHANG Xiao-jing, XIE Rui-juan

2019, 28(2):  121-132.  DOI: 10.11686/cyxb2018130

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Arthraxon hispidus, is a wild grass with potential for development as a turf plant for sloping ground. In this study, 20 treatments were set up by a factorial combination of five shade levels (0, 10%, 30%, 50%, 70%) and four drought levels (adequate moisture, mild drought, moderate drought and severe drought). The purpose was to study the combined effects of shade and drought on growth of A. hispidus, and identify trade-offs between clonal growth and sexual reproduction. Various data, including clonal growth traits, number of seed-heads, and biomass structure were gathered, and differences in cloning efficiency index (CEI), reproductive allocation (RA), reproductive efficiency index (REI), reproduction index (RI) and ratio of breeding (RR) under the 20 treatments were analyzed. It was found that: 1) Shade and drought stress had significant effects on clonal daughter ramet number and CEI. Moderate and severe drought and over 10% shading significantly reduced daughter ramet number. Drought had no effect on CEI and shade decreased CEI, and a shade x CEI interaction (P<0.01) was observed, expressed as a reduced daughter ramet and genet number, and reduced CEI. 2) Shading and drought had significant effects on flower spike numbers and floret numbers of mother ramets, daughter ramets and genets, reproductive organ biomass (ROB), non-reproductive organ biomass (NROB) and total biomass (TB) (P<0.05). Light and moderate drought or 10%-30% shade or the combination of mild shade and mild drought significantly increased flower spike number and floret number of mother ramets, and of daughter ramets and genets. Mild drought or 10% shading or the combination stress of mild drought and light shade all significantly increased TB and ROB. Moreover, a synergistic interaction between shade and drought strongly increased flower spike number and floret number of genets, and TB, ROB and NROB. The effect of drought on TB and NROB was followed, and shading had greater influence on ROB. 3) Shading and drought significantly (P<0.05) affected RA, REI, RI and RR: mild and moderate drought or 10% shading significantly increased the genet reproductive parameters, but severe drought or more than 30% shading significantly reduced reproductive parameters (P<0.05). Compared with either single stress, the combined stresses of light shading and mild drought promoted sexual reproduction. Mild drought alleviated reduction in sexual reproduction observed under moderate and severe shading. Reproductive parameters typically displayed a synergistic effect, with shading the larger effect, and the drought effect smaller. 4) A. hispidus displayed an altered balance between clonal growth and sexual reproduction, depending on the degree of shading and drought. Greater than 30% shade prolonged the period of clonal growth by 10-34 days. 5) Under all 20 treatment combinations of shading and drought, A. hispidus maintained both clonal and sexual reproduction concurrently. Adequate water and light promoted clonal growth. Light and moderate drought, and mild shade alone or in combination with drought were treatments that promoted sexual reproduction.

An evaluation of agronomic traits and genetic diversity among 51 oat germplasm accessions

WANG Jian-li, MA Li-chao, SHEN Zhong-bao, LIU Jie-lin, ZHU Rui-fen, HAN Wei-bo, ZHONG Peng, DI Gui-li, HAN Gui-qing, GUO Chang-hong

2019, 28(2):  133-141.  DOI: 10.11686/cyxb2018679

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This research aimed to objectively evaluate the genetic diversity of oat germplasm resources for important agronomic traits, and to provide key data for use in oat breeding programs in the Heilongjiang region. A total of 51 oat germplasm accessions from different sources were planted in Harbin at the High Latitude Grass and Science Institute, Heilongjiang Academy of Agricultural Sciences. Genetic diversity indices for the various accessions were calculated, and cluster analysis and a principal component (PC) analysis were carried out to investigate patterns of genetic diversity across accessions for agronomic characters. The index of genetic diversity was high for all traits, with the highest being for the length of the main spike (1.517), followed by plant height (1.448) and seed weight of the main spike (1.414). The largest coefficient of trait variation was for spikelet number of the main spike (34.8%), followed by seed weight of the main spike (33.1%), and tiller number per plant (27.4%). Based on cluster analysis, nine quantitative traits could be used to classify plants into four groups. Plants in germplasm group 1, contained no obviously attractive traits, while group II contained the germplasm that could be used as parents of short-stemmed varieties. The germplasm in group III typically had greater stem length and increased tiller number, compared to others. In contrast, the germplasm in group IV was suitable for breeding cultivars with large grain size, multiple panicle and spikelet numbers .According to principle component analysis, the first three main component (seed yield factor, till factor, plant height factor) made the contribution of 70.09% to variation.

An analysis of genetic diversity and linked agronomic traits of Heshangtou wheat in northwest China

ZHANG Yan-jun, GOU Zuo-wang, WANG Xing-rong, LI Yue, QI Xu-sheng

2019, 28(2):  142-155.  DOI: 10.11686/cyxb2018124

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Key aims of this study were: 1) to better understand the genetic structure of the Heshangtou wheat landrace from northwestern China, and 2) to explore the link between genetic markers and agronomic traits. A collection of 43 germplasm lines from different regions in northwest China was genetically characterized using 150 simple sequence repeat (SSR) marker loci, which were evenly distributed across the 21 chromosomes of wheat. Concurrently, 19 agronomic traits were recorded for the same germplasm lines at two test sites, and a general linear model (GLM) was used to analyze the association between molecular markers and phenotypic traits. A total of 151 allelic variants were detected using 45 pairs of polymorphic SSR markers. The number of alleles in each marker ranged from 2 to 6, with an average of 3.36, and the polymorphic information content (PIC) varied from 0.044 to 0.771. It was found that the genetic diversity among the 19 agronomic traits assessed in this way was significantly higher than that of quality traits. The agronomic traits (except for shell color) exhibited varying degrees of correlation. Population genetic structure analysis classified the 43 germplasm lines into 8 subgroups. Correlation analysis showed that 11 SSR markers were significantly associated with particular agronomic traits, and the extent to which phenotypic variation was explained by single markers ranged from 8.89%-24.74%. Some of the markers identified may be useful for marker-assisted selection in wheat breeding.

Effects of complex saline-alkali stress on seed germination and seedling antioxidant characteristics of Chenopodium quinoa

ZHAO Ying, WEI Xiao-hong, HE Ya-long, ZHAO Xiao-fei, HAN Ting, YUE Kai, XIN Xia-qing, SU Mei-fei, MA Wen-jing, LUO Qiao-juan

2019, 28(2):  156-167.  DOI: 10.11686/cyxb2018181

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The saline-alkali conditions in many parts of Northern China constitute a soil factor causing significant restrictions to quinoa development. In order to better understand the adaptive physiology of quinoa under saline-alkali stress, this research focused on quinoa seed germination, antioxidant enzyme activities and isozyme characteristics. A set of 20 different alkali-saline plant stress conditions were simulated by mixing two neutral (NaCl and Na₂SO₄) and alkaline (NaHCO₃ and Na₂CO₃) salts with soil in different proportions (A, NaCl∶Na₂SO₄=1∶1. B, NaCl∶Na₂SO₄∶ NaHCO₃=1∶2∶1. C, NaCl∶Na₂SO₄∶NaHCO₃∶Na₂CO₃=1∶9∶9∶1. D, NaCl∶Na₂SO₄∶NaHCO₃∶Na₂CO₃=1∶1∶1∶1. E, NaCl∶Na₂SO₄∶NaHCO₃∶Na₂CO₃=9∶1∶1∶9) and at concentrations of (50, 100, 150 and 200 mmol·L^-1). Several germination and physiological indices, such as the germination percentage, germination index, germination energy were measured, and the activities of SOD, POD, CAT and GR were also analysed, and isoenzymic zymograms prepared. It was found that the five different saline-alkali stress formulations all decreased quinoa germination percentage, germination index and germination energy. With increasing saline-alkali concentration, germination was decreased dramatically (P<0.05). Compared to the control, saline-alkali stress induced higher activities of SOD and GR under treatments A and B, and lower activity of SOD under treatments C, D, and E, while GR activity was significantly increased at 50 mmol·L^-1 salt concentration. The activity of POD was the highest when the concentration of saline-alkali solution was 50 mmol·L^-1; with increased salt concentration, POD activity fell to levels 4 times lower than control, and CAT activity also decreased. SDS-PAGE revealed that saline-alkali stress induced significant changes to isomer ratios of antioxidant enzymes (SOD, POD, CAT, GR), including new isoforms. These results indicate that salt-alkaline stress inhibited seed germination of quinoa. For Na₂SO₄ and NaHCO₃ on the germination inhibition of quinoa seeds was more obvious. The threshold of salt tolerance was 50 mmol·L^-1 in this study, and salt concentration was the main determinant of the degree of inhibition, with the composition of the salt solution being a minor factor.

Effect of γ-aminobutyric acid on photosynthetic characteristics and carbohydrate metabolism under high temperature stress in perennial ryegrass

WANG Ri-ming, WANG Zhi-qiang, XIANG Zuo-xiang

2019, 28(2):  168-178.  DOI: 10.11686/cyxb2018167

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The aim of this research was to elucidate the effects of exogenous γ-aminobutyric acid (GABA) on high temperature stress metabolism, plant growth, photosynthetic and chlorophyll fluorescence characteristics, carbohydrate content and gene expression levels of key enzymes associated with sugar metabolism. The material studied was a heat sensitive cultivar (Pinnacle) of perennial ryegrass (Lolium perenne) under high temperatures (35/30 ℃ light/dark) in growth chambers for 15 d. It was found that heat stress inhibited plant growth, increased leaf electrolyte leakage and decreased carbohydrate and chlorophyll content, photosynthesis rate. The gene expression levels of key enzymes associated with sugar metabolism were initially up-regulated and subsequently decreased under heat stress. Exogenously applied GABA significantly alleviated the damage effect of heat stress on plant growth and enhanced the chlorophyll content and carbohydrate content under high temperature. The leaf net photosynthetic rate (P_n), stomatal conductance (G_s), transpiration rate (T_r), carboxylation efficiency (CE), maximum assimilation (A_max), photochemical efficiency (F_v/F_m), maximum velocity of carboxylation (V_cmax), maximum electron transfer rate (J_max), photochemical quenching (qP), electron transport rate (ETR) and actual photochemical efficiency of PSII (Φ_PSⅡ) significantly increased while leaf stomatal limitation (Ls), compensation point (CP) and none photochemical quenching (NPQ) significantly decreased after application of GABA under heat stress. To summarize, exogenous application of GABA reduced leaf stomatal and non-stomatal limitations to photosynthesis and alleviated the inhibition of PSII reaction centers, leading to an enhancement in light and dark reactions of photosynthesis and in photosynthetic potential. Expression levels of key genes for sugar metabolism were also enhanced. These physiological changes acted cumulatively to confer a higher tolerance to heat stress in perennial ryegrass.

Progress in application of the CENTURY model for prediction of soil carbon levels in different ecosystems

WANG Xu-yang, LI Yu-qiang, LIAN Jie, LUO Yong-qing, NIU Ya-yi, GONG Xiang-wen

2019, 28(2):  179-189.  DOI: 10.11686/cyxb2018126

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The CENTURY model, designed to predict soil C, N, P, and S dynamics in a range of ecosystems, is one of the most famous biogeochemical models in the world. The research reported here systematically examines the operating mechanisms and processes of the CENTURY model, and research data on results of soil organic carbon were analyzed and collated for grassland, farmland and forest ecosystems using this model. It was found that soil texture and soil nutrient levels are key factors influencing the application of the CENTURY model in grassland ecosystems, and that the model has high predictive accuracy in desert grassland. Agricultural management is one of the factors most strongly affecting soil organic carbon (SOC) simulation accuracy. The SOC simulation accuracy was higher in intercrop systems than in monocrop scenarios. CENTURY had structural defects in simulating soil organic matter in the litter layer of forest ecosystems; hence the CENTURY model performs better in the simulation of grassland and farmland systems than when simulating forest ecosystems. Since the CENTURY model was originally developed for work on grassland ecosystems, its model parameters are more universally applicable to grassland ecosystems in different regions. Excessive human intervention would increase the uncertainty factor in CENTURY modeling of agro-ecosystems, potentially resulting in instable simulation results. The simulation accuracy could be substantially improved through collecting data on and accurately accounting for historical farm system and management methodologies practiced, when performing the simulation. The simulation results for forest ecosystems can be used for the formulation of management measures. In addition, scaling up from single-point simulation to the regional level could be achieved by the integration of CENTURY model results into a GIS approach.

Effects of enclosure on the soil organic carbon and its active components in desert steppe grassland

YU Shuang, TAO Li-bo, XÜ Dong-mei, XÜ Ai-yun, LIU Jin-long

2019, 28(2):  190-196.  DOI: 10.11686/cyxb2018164

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This experiment used spatially distributed sites which had been fenced for 0, 3, 5, 7 and 10 years in desert steppe grassland in Yanchi County of Ningxia, to form a time series, for field and laboratory study of soil C dynamics. Variables measured included: total soil organic carbon (SOC), soil particulate organic carbon, soil dissolved organic carbon and soil readily oxidizable organic carbon for 10 cm increments of soil depth to 40 cm at each site. The results revealed significant differences (P<0.05) in total organic carbon at 5-10 cm, 10-20 cm and 20-40 cm soil depth, linked to the number of years of grazing exclusion. The SOC content ranged from 2.24 g·kg^-1 to 4.52 g·kg^-1, and in general increased with increased enclosure time. Thus, values were higher in desert steppe grasslands of 7 and 10 years grazing exclusion. There were no significant effects of grazing exclusion on soil particulate organic carbon (P>0.05). The contents of soil dissolved organic carbon were highest in grazed grassland (0.59, 0.49 and 0.56 g·kg^-1, respectively, for 0-5 cm, 5-10 cm and 20-40 cm soil depths). Values decreased initially after grazing exclusion, (with lowest values recorded after 5-7 years), and then increased with longer duration of exclusion. The soil readily oxidizable organic carbon content was highest (2.48 g·kg^-1) in desert steppe grassland subject to 7 years grazing exclusion. In summary, 7 years is a recovery point in the process of natural restoration and succession of degraded desert steppe by grazing exclusion.

Effects of flooding and planting density on the photosynthesis of Hemarthria compressa and Cynodon dactylon cottage seedlings

LI Xiao-xue, LI Chang-xiao, SONG Hong, YUAN Zhong-xun

2019, 28(2):  197-206.  DOI: 10.11686/cyxb2018134

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This research aimed to investigate the photosynthetic responses of Cynodon dactylon and Hemarthria altissima under different flooding conditions and to identify a suitable planting pattern. On April 29, 2016, a pot experiment was set up with a replacement series design in which H. altissima (H) and C. dactylon (C) were planted at seven ratios (H₀C₁₂, H₂C₁₀, H₄C₈, H₆C₆, H₈C₄, H₁₀C₂, and H₁₂C₀) under three water treatments, including normal growth water condition (CK), flooding at 10 cm above the soil surface (SF) and flooding at 2 m above the soil surface (TF). The flooding and density treatments had significant (P<0.05) effects on net photosynthetic rate (P_n) of H. altissima and C. dactylon. Under the CK water treatment, the P_n of H. altissima with the H₂C₁₀ ratio was greater than that with the monoculture, and the P_n of C. dactylon significantly decreased under the mixed intercropping conditions when compared with that under the monoculture conditions (P<0.05). Under the SF treatment, the P_n of H. altissima with the H₈C₄ planting ratio was greater than that at other planting densities, while the P_n of C. dactylon in monoculture was lower than that achieved under mixed intercropping (P<0.05). Compared with the CK treatment, the P_n of H. altissima significantly decreased (P<0.05) under the TF water treatment regime. Taking photosynthetic efficiency of the two species into consideration, the results suggested that a mixed intercropping pattern with a planting ratio of H₂C₁₀ should be adopted in high-altitude areas where no water flooding occurs, and the H₈C₄ ratio should be adopted in areas where the soil surface is flooded. The monoculture of H₁2C₀ is the optimal choice for low-altitude areas where complete flooding often takes place.

Effect of boiling and extraction on dry matter digestibility and intestine-digestible crude protein levels in plant residue following Chinese medicinal herb preparation

TIAN Xiu-e, WAN Mei-jiao, WANG Yong-jun, ZHANG Yang

2019, 28(2):  207-215.  DOI: 10.11686/cyxb2018158

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The aim of this study was to assess the effects of boiling and extraction on dry matter digestibility and intestine-digestible protein content of plant residue from production of Chinese herbal medicines. This information is relevant to assessing the usefulness of these residues for animal feeding. Using a mobile nylon bag technique, various digestive degradation kinetic parameters were determined for processing residues of Astragalus (Astragalus membranaceus), malt (Hordeum vulgare) and Licorice (Glycyrrhiza uralensis). Parameter estimates obtained for the three plant materials included: the effective degradability (ED) in the rumen of the main dry matter (DM) nutritive components (crude protein, neutral and acid detergent fiber; CP, NDF, ADF, respectively), the small intestine digestibility (Idg), and their rumen non-degradable dry matter (UDDM) and non-degradable protein (U_DP) for both raw plant materials and after boiling and extraction. It was found that: 1) The ED_DM and ED_CP of the three tested residues after boiling and extraction were significantly lower than those of the untreated raw materials (P<0.05), while ED_NDF and ED_ADF were significantly higher than the untreated materials (P<0.05); 2) The Idg_UDDM and Idg_UDP after boiling and extraction, of the three tested Chinese herbal medicine preparation residues, were significantly higher than those of the untreated raw materials (P<0.05); 3) Boiling significantly increased the DDM of all 3 tested residues (P<0.05), and also the Idg_CP, and Idg_CP/CP of malt extract residue (P<0.05), but significantly reduced Idg_CP, and Idg_CP/CP of licorice extract residues and the Idg_CP of Astragalus extract residues (P<0.05). These results indicate that it is not necessary to boil these feeds unless there is a special requirement to do so. Malt extract residues have good nutritional potential as a high-quality refined feed; Astragalus and licorice extraction residues have nutritional potential as a quality roughage.