Table of Content

20 January 2022, Volume 31 Issue 1

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Grassland phenology extraction for Xinjiang Province and trend analysis using MODIS data

Ren-ping ZHANG, Jing GUO, Xiao-fang MA, Wei-yong GUO

2022, 31(1):  1-12.  DOI: 10.11686/cyxb2020510

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There are two important steps when monitoring vegetation phenology by remote sensing. The first is separation of ‘vegetation data’ from ‘noise’ such as cloud cover in the MODIS satellite data so as to obtain the best possible estimate or “reconstruction” of the normalized difference vegetation index （NDVI） and its changes over the time period of interest. The second is the extraction of estimates of vegetation phenology parameters from the reconstructed NDVI data. The comparative merits or demerits of different available NVDI reconstruction and vegetation phenology extraction methods and their suitability in different regions are still little-studied. It is necessary to carry out a comparative analysis of different methods and to compare results with field data to identify the optimal remote sensing extraction methodology for a particular region. Here we report a comparison of four extraction methods to extract the start of season （SOS） date for grassland in Xinjiang from 2001 to 2019. The four methods compared were： the asymmetric Gaussian function fitting method （asymmetric gaussian， A-G）， the double logistic function fitting method （double logistic， D-L）， Savitzky-Golay filter method （S-G） and the land cover dynamic product （MCD12Q2）. Through comparison of the extraction results obtained by the four methods， the optimal model for extracting SOS was found， and the regional variation and change over the 19-year study period in the SOS in Xinjiang Province were evaluated. The main conclusions were as follows： 1） The A-G extraction method provided the best estimate of the SOS for Xinjiang grassland. The correlation （R=0.879） between A-G estimates of SOS and the SOS recorded at field-measured points was higher and the root mean square error （RMSE=16.395 d） was smaller. Spatially， the standard deviation for SOS measured by the A-G method was less than 30 d for 82.19% of the area evaluated， compared with 76.53% and 67.98% for D-L and S-G methods， respectively. The MCD12Q2 method had a smaller standard error but there were large areas of terrain where no estimate of SOS could be provided. 2） Over the 19 years for which data were evaluated， the SOS in Xinjiang occurred as early as the 60th and as late as the 140th day of the year， with obvious regional differences， SOS being earlier in the north and later in the south. In the north of Junggar Basin and Ili river valley， the SOS was earlier than the 80th day， while in the Altai Mountain， central Tianshan Mountain and Kunlun Mountain the SOS was later than the 140th day. The SOS of different grassland types had obvious differences. For example， SOS of alpine meadow and alpine grassland was the latest， while SOS of temperate deserts was the earliest. 3） From 2001 to 2019， SOS in Xinjiang showed interannual variation of approximately 15 days between early and late years， with a trend over time to later SOS in lowland meadow， temperate desert and alpine desert， and earlier SOS in temperate grassland， alpine grassland and alpine meadow.

Effects of nitrogen addition on soil carbon and nitrogen and biomass change in different grassland types in Inner Mongolia

Xiao-yu HAN, Ning GUO, Dong-dong LI, Ming-yang XIE, Feng JIAO

2022, 31(1):  13-25.  DOI: 10.11686/cyxb2020483

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In this research we studied the nitrogen responses of grassland plant communities in meadow steppe， typical steppe and desert steppe grasslands of Inner Mongolia. A gradient of seven nitrogen addition treatments was set up， namely： CK （0 g N·m^-2·yr^-1）， N₁ （5 g N·m^-2·yr^-1）， N₂ （10 g N·m^-2·yr^-1）， N₃ （15 g N·m^-2·yr^-1）， N₄ （20 g N·m^-2·yr^-1）， N₅ （25 g N·m^-2·yr^-1）， N₆ （30 g N·m^-2·yr^-1）， One-way ANOVA and correlation analyses were used to evaluate the difference in vegetation biomass and soil carbon and nitrogen in the different grassland types under the different rates of nitrogen addition， and relate these to other factors of influence. It was found that： 1） Nitrogen addition did not significantly affect the underground biomass of any of the three grassland types （P>0.05）， but significantly increased aboveground biomass in meadow and desert steppe （P<0.05）. As a preliminary assessment based on these results， the N₃ treatment is the approximate response saturation threshold. At this level of nitrogen addition， the average biomass increase of the three Inner Mongolian grassland types was 29.66%， compared to CK. The response to added nitrogen was most obvious in the dry desert steppe grassland. Nitrogen application significantly reduced the root∶shoot ratio in the meadow steppe grassland （P<0.05） and significantly increased the root∶shoot ratio of the typical steppe grassland under the N₃ treatment （P<0.05）， but had no significant effect in desert steppe grassland （P>0.05）. 2） The soil carbon and nitrogen contents of 0-10 cm and 10-30 cm soil layers were analyzed to determine the effects of nitrogen addition on soil organic carbon and total nitrogen content in the three grassland types and it was found that in the meadow steppe grassland nitrogen addition had no significant effect on these parameters （P>0.05）. However， for the typical steppe and desert steppe grasslands， effects of added nitrogen on soil carbon and nitrogen content were significant （P<0.05）， and the 0-10 cm soil layer response was more obvious. 3） The aboveground biomass was significantly correlated with soil C∶N ratio， annual precipitation and nitrogen application （P<0.01）； underground biomass and total biomass were significantly correlated with soil total nitrogen content， organic carbon content， soil C∶N ratio， annual mean temperature and annual average precipitation （P<0.01）. Overall， the biomass and soil carbon and nitrogen contents of the grassland ecosystem in the three types of grassland responded differently to nitrogen fertilization. This means that nutrient addition should be considered as a tool in grassland restoration and management.

Effects of different restorative measures on soil carbon and nitrogen and their component fractions in a degraded desert steppe

Xing WANG, Shuang YU, Dong-mei XU, Ke-chen SONG

2022, 31(1):  26-35.  DOI: 10.11686/cyxb2020517

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This research investigated the impact of three restorative measures on soil carbon and nitrogen fractions in historically overgrazed desert steppe grassland in Yanchi County， Ningxia. The restorative measures investigated were deep tillage+reseeding （SR）， shallow tillage+reseeding （QR） and grazing exclusion （i.e. enclosure） （F）. Traditional grazing was taken as the control （CK）. Measurements made included soil organic carbon （SOC）， total nitrogen （TN）， particulate organic carbon （POC）， readily oxidizable organic carbon （ROC）， microbial biomass carbon （MBC）， nitrate nitrogen （NO₃^--N）， ammonium nitrogen （NH₄⁺-N） and microbial biomass nitrogen （MBN） for the 0-10 cm， 10-20 cm， 20-30 cm and 30-40 cm soil layers. It was found that： 1） For the QR treatment， soil SOC content （5.50-9.93 g·kg^-1）， soil TN content （0.17-0.23 g·kg^-1）， soil ROC content （0.53-0.99 g·kg^-1） and soil MBN content （62.82-73.20 mg·kg^-1） were generally higher than in other treatments. 2） Soil MBC content （386.00-481.80 mg·kg^-1） and the proportions of each component of carbon and nitrogen in SOC and TN were generally higher in the F treatment. 3） Soil POC， NH₄⁺-N and NO₃^–-N contents were decreased under the various restorative treatments compared with the CK treatment. 4） The contents of POC， NH₄⁺-N and NO₃^--N in each soil horizon were also decreased under the various restorative measures， compared with the CK treatment. Correlation analysis showed that SOC content was significantly positively correlated with TN and ROC content （P<0.01）， and significantly negatively correlated with MBC content （P<0.05）. Based on soil carbon and nitrogen fixation and preservation data， shallow tillage+reseeding was the most effective restorative measure for the degraded desert steppes in this study.

Effects of different organic ∶inorganic nitrogen addition ratios on nitrogen distribution and transformation in a grassland soil

Meng-han WANG, Li-li DONG, Fu-cui LI, Lie-bao HAN, Xiang WANG

2022, 31(1):  36-46.  DOI: 10.11686/cyxb2021104

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Increase in nitrogen （N） deposition has become one of the most important phenomena of global change， and has significantly affected the soil nitrogen cycle in many grasslands. This experiment studied the effects of inorganic versus organic forms of N addition on the soil N cycle， in a six-year N addition experiment carried out in meadow steppe grassland in Inner Mongolia. Inorganic N （IN） was added as NH₄NO₃， while organic N （ON） was added as urea and glycine mixed in equal proportions， based on their N concentrations. The ratios of IN∶ON used as treatments were 10∶0 （N₁）， 7∶3 （N₂）， 5∶5 （N₃）， 3∶7 （N₄）， 0∶10 （N₅） and 0∶0 （CK）. Soil N was fractionated into light fractions and heavy fractions. Additionally， a short-term incubation was conducted to assess potential N mineralization. Our results showed that soil total N content was not affected by the form of N addition. Nitrogen addition significantly increased soil nitrate and mineral N concentrations in the 0-20 cm soil layer， and this effect was most pronounced in the N₄ （IN∶ON=3∶7） treatment. Compared with the control treatment， soil mineral N increased by 1332% in the N₄ treatment. The N concentration of light fractions in the 0-10 cm soil horizon was increased by 91% and the N concentration of heavy fractions in the 0-20 cm horizon was increased by 44% both under N₁ treatment （IN∶ON=10∶0）. However， the percentage of N concentrations in light fractions and heavy fractions was not affected by different forms of N addition. The data also indicated that N addition increased the nitrification rate while decreasing the ammonization rate in the 10-20 cm soil horizon， but it did not affect the soil net N mineralization rate. Therefore， the effects of changing the IN∶ON addition ratio on the form and turnover of nitrogen in these grassland soils are complex.

Effects of different land-use patterns on soil active organic carbon in Stipa baicalensis steppe in Inner Mongolia

Jia-qiang JING, Ren-qi-li-mo-ge SA, Jie QIN, Hai-fang ZHANG, Ming LI, Dian-lin YANG

2022, 31(1):  47-56.  DOI: 10.11686/cyxb2020477

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Soil active organic carbon can accurately reflect soil nutrient availability and characterize changes in soil quality. It is one of the key indicators for research into sustainable grassland management measures. Here we report a field experiment carried out on Stipa baicalensis steppe in Inner Mongolia， in which grazing， grazing exclusion （i.e. enclosure） and mowing treatments were used to explore the effects of the different land use patterns on soil organic carbon （SOC） and active organic carbon. It was found that SOC content， soil microbial biomass carbon （MBC） content and soil readily oxidizable organic carbon （ROC） content under the different land use patterns all ranked： grazing exclusion>mowing>grazing. The ranking for soil dissolved organic carbon （DOC） content was grazing>exclusion>mowing. There was a very significant correlation between soil MBC， ROC and SOC （P<0.01）. Soil ROC and MBC were significantly correlated with total nitrogen and total phosphorus （P<0.01）. Grazing exclusion and mowing promoted the improvement of soil SOC， MBC and ROC， and grazing had an accumulative effect on DOC. Grazing exclusion and mowing enhanced the stability of soil SOC. Active organic carbon was closely related to soil organic carbon and soil physical and chemical properties and sensitively reflected changes in the level of soil organic carbon.

Effects of shrub encroachment on soil aggregate ecological stoichiometry and enzyme activity in alpine grassland

Wen-ming MA, Chao-wen LIU, Qing-ping ZHOU, Zhuo-ma DENGzeng, Si-hong TANG, Diliyaer·mohetaer, Chen HOU

2022, 31(1):  57-68.  DOI: 10.11686/cyxb2020478

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Shrub encroachment is one of the key factors affecting soil organic carbon storage in alpine grassland. In this study， we compared soil properties with and without shrub encroachment in grasslands at the eastern margin of Qinghai-Tibetan Plateau. Soil parameters measured included the contents of organic carbon， total nitrogen， total phosphorus， and total potassium， and activities of sucrase， urease， phosphatase， catalase， protease and glucosidase， as well as the ecological stoichiometry characteristics of soil aggregates of various sizes. Our results showed that： 1） The contents of organic carbon， total nitrogen and total phosphorus in different sized aggregates decreased after shrub encroachment and were higher in large aggregates （0.053-0.25 mm） in size. 2） The C∶N， C∶P and N∶P ratios in soil aggregates increased after shrub encroachment. The maximum C∶N ratio was observed in the >2 mm aggregates. The maximum C∶P and N∶P ratios were observed in the 0.053-0.25 mm aggregates， and the minimum values were observed in <0.002 mm and 0.002-0.053 mm aggregates（P>0.05）. 3） Urease， sucrase， phosphatase， catalase and β-D glucosidase activities were elevated mainly in >0.25 mm aggregates at grassland and shrub encroachment. After shrub encroachment， sucrase activity increased， while the protease and phosphatase activities decreased. 4） Urease and β-D glucosidase activities were positively correlated with soil organic carbon and total nitrogen， sucrase and catalase activities were positively correlated with total potassium contents， and protease and phosphatase activities were positively correlated with total phosphorus. Soil biogenic materials are mainly concentrated in large aggregates in this region. However， large aggregates are easily broken by external interference， which shows that the phenomenon of shrub encroachment is not conducive to the sequestration of organic carbon in this area.

Biomass allocation， water use characteristics， and photosynthetic light response of four Commelinaceae plants under different light intensities

Qing XUE, Bin CHEN, Xiao-mei YANG, Yu-jia YANG, Zi-wei LI, Shan BO, Miao HE

2022, 31(1):  69-80.  DOI: 10.11686/cyxb2021250

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The aim of this study was to explore the effects of different light intensities on the biomass allocation， water use characteristics， and photosynthetic light response of Commelinaceae plants. The experimental materials were ramets of Commelina purpurea， Tradescantia fluminensis ‘Variegata’， Tradescantia zebrina， and Tradescantia fluminensis ‘Vairidia’. These materials were subjected to light at five different intensities， which were obtained using a shading net. It was found that， as the light intensity decreased （shading intensity 25%-75%）， the aboveground biomass of the four plants initially increased and then decreased （P<0.05）. The total biomass also increased and then decreased as the light intensity decreased， except that of C. purpurea， which showed no significant change. The effects of different light intensities on biomass allocation and the crown∶root ratio of the four plants were diverse， however， the proportion of the stem to total biomass tended to increase in all four plants as the light intensity decreased. The midday water potential increased with decreasing light intensity， and was strongly related to the trend in the water loss rate. Both C. purpurea and T. zebrina showed low rates of water loss. As the amount of photosynthetically active radiation increased， the net photosynthetic rates of the four plants first increased and then gradually stabilized. As the light intensity decreased， the maximum net photosynthetic rate， apparent quantum efficiency， and light saturation point of the four plants tended to first increase and then decrease. Compared with T. fluminensis ‘Variegata’ and ‘Vairidia’， C. purpurea and T. zebrina showed higher values for maximum net photosynthetic rate， apparent quantum efficiency， and light saturation point， and a lower dark respiration rate. The water use efficiencies of C. purpurea and T. zebrina did not differ significantly among the light intensity treatments， but were higher than those of T. fluminensis ‘Variegata’ and ‘Vairidia’. Together， the results suggest that these four plants are able to make more effective use of weak light resources by adjusting their morphology， biomass allocation， and photosynthetic light responses in weak light （shade density of 25%-75%）. Our results show that C. purpurea and T. zebrina are better able to cope with low light intensity than are T. fluminensis ‘Variegata’ and ‘Vairidia’.

Response and sensitivity of photosynthesis of Stipa tianschanica in desert steppe to developing soil drought process

Zuo-tian YIN, Yu-hui WANG, Guang-sheng ZHOU, Quan-hui MA, Xiao-di LIU, Bing-rui JIA, Yan-ling JIANG

2022, 31(1):  81-94.  DOI: 10.11686/cyxb2020502

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Terrestrial ecosystem carbon budgets are sensitive to extreme climate events. To understand the carbon budget response in Stipa tianschanica desert steppe to extreme drought process， a manipulative experiment involving extreme soil extreme drought process was conducted under a rainout shelter. A range of characteristic parameters of S. tianschanica were measured and analyzed， and sensitivity to drought of the various parameters was also evaluated. It was found that water use efficiency （WUE） showed a significant exponential relationship with soil water content （SWC）. Stomatal conductance （G_s），maximum carboxylation rate （V_cmax） and triose phosphate utilization rate （TPU）showed significant liner relationships with SWC. There were also significant quadratic relationships between other carbon exchange parameters and SWC. CO₂ exchange activities of S. tianschanica at leaf scale were more sensitive to soil drought. Light-saturated net photosynthetic rate （A_sat）， transpiration rate （E）， maximum electron transfer rate （J_max）， photochemical efficiency of PSⅡ in the light （F_v'/F_m'）， actual photochemical efficiency of PSⅡ in the light （Φ_PSII） and net ecosystem CO₂ exchange （NEE） showed clear thresholds of soil moisture. G_s， WUE， V_cmax， TPU， ecosystem respiration （R_e） and gross ecosystem production （GEP） began to decrease when SWC started to decline， while E， NEE and J_max exhibited rapid rates of change under drought condition. 14.73% and 7.85% were two critical SWC at which the inhibition of leaf photosynthesis changed from stomatal limitation to non-stomatal limitation and the ecosystem shifted from sink to source， respectively. In conclusion， carbon exchange of S. tianschanica ecosystem was significantly related to SWC and carbon sink was significantly inhibited under extreme soil moisture deficit.

Effects of regulated deficit irrigation on the soil environment and forage growth of mixed-species forage plantings in China’s high-cold desert area

Jing-hai WANG, Guang LI, Min-hua YIN, Guang-ping QI, Yan-xia KANG, Yan-lin MA

2022, 31(1):  95-106.  DOI: 10.11686/cyxb2020476

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In the high-cold desert area of China， forage production is limited by the traditional planting patterns used and by the low natural productivity of the landscape. The purpose of this study was to explore a promising irrigation regime to increase forage yield and achieve efficient use of water and soil resources. For a mixed-sowing of oats （Avena sativa） and vetch （Vicia sativa）， a field experiment was conducted to analyze the effects of seven patterns of regulated deficit irrigation on the soil moisture， soil temperature， and soil nutrient levels of the forage crop， as well as the plant height， stem-leaf ratio， yield， and water and nitrogen use efficiency of the mixed-species forage crop. The seven irrigation patterns were： mild water deficit at jointing stage （BW₁， soil moisture at 65%-75% of field capacity； SM% FC）， moderate water deficit at jointing stage （BW₂， 55%-65% SM% FC）， severe water deficit at jointing stage （BW₃， 45%-55% SM% FC）， mild water deficit at flowering stage （KW₁， 65%-75% SM% FC）， moderate water deficit at flowering stage （KW₂， 55%-65% SM% FC）， severe water deficit at flowering stage （KW₃， 45%-55% SM% FC）， and full irrigation during all crop growth stages （QW₀， 75%-85% SM% FC）. It was found that： 1） The average soil water storage decreased with the increasing water deficit. Under the same water deficit conditions， there was no significant difference between the average soil water storage at jointing stage and at flowering stage. 2） The average soil temperatures of water deficit treatments were significantly higher than those of the full irrigation treatment. At the same level of water deficit， the average soil temperature was significantly higher in treatments with water deficit at the jointing stage than those with water deficit at the flowering stage. 3） Compared with levels before sowing， the soil nutrient contents of all treatments were reduced after harvest. The treatment KW₁ significantly increased soil available nitrogen content， while moderate or severe water deficit inhibited the absorption of soil available phosphorus and potassium by the forage crops. 4） Under the same irrigation pattern， the plant height， stem-leaf ratio， and yield of oats were significantly higher than those of vetch. The water consumption of the seven irrigation regimes was 386.1-502.6 mm. Compared with the treatment QW₀， the treatment KW₂ reduced the irrigation amount by 20.6%， had a statistically equal forage yield， and achieved a higher water use efficiency （31.5 kg·ha^-1·mm^-1）， irrigation water use efficiency （81.0 kg·ha^-1·mm^-1）， nitrogen absorption efficiency （0.99 kg·kg^-1）， and partial productivity of nitrogen fertilizer （191.1 kg·kg^-1）. In conclusion， moderate water deficit during the flowering stage was a water-saving， yield-increasing， and highly efficient water management regime for the tested oat-vetch forage crop at this site in a high-cold desert area.

Combined ploughing and tilling to improve degraded alfalfa （Medicago sativa） stands in a semi-arid region

Bin WANG, Man-you LI, Xin-pan WANG, Xiu DONG, Jun-bao PANG, Jian LAN

2022, 31(1):  107-117.  DOI: 10.11686/cyxb2021216

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Degraded alfalfa （Medicago sativa） stands in semi-arid regions have a low forage yield and poor forage quality， but may be improved by management methods such subsoiling. We conducted a 3-year field experiment with a single factor randomized block design to study the restorative effects on soil physical and chemical properties of subsoiling combined with shallow rotary tilling： plowing to 30 cm+tilling to 5 cm （S₁Q₁）， plowing to 30 cm+tilling to 10 cm （S₁Q₂）， plowing to 40 cm+tilling to 5 cm （S₂Q₁）， plowing to 40 cm+tilling to 10 cm （S₂Q₂）， plowing to 50 cm+tilling to 5 cm （S₃Q₁）， plowing to 50 cm+tilling to 10 cm （S₃Q₂） and control （CK）. Production performance and forage quality of degraded alfalfa grassland were determined， and a principal component analysis （PCA） was used to evaluate the improvement effects of the treatments. It was found that plowing with shallow rotary tilling reduced the soil bulk density， increased soil porosity， and led to significant increases in the plant height， branch number， and leaf∶stem ratio of alfalfa. Among the treatments， S₂Q₁ reduced the soil bulk density in the 0-40 cm soil layer， and S₂Q₂ increased the branch number， hay yield， and crude protein content in alfalfa， and reduced the neutral and acid detergent fiber contents. The results of the PCA indicated that the treatments had larger effects on alfalfa hay yield， leaf∶stem ratio， and crude protein content， and smaller effects on the forage relative feeding value and neutral detergent fiber content. The S₂Q₂ treatment with deep loosening by plowing and shallow tilling led to a high alfalfa hay yield （6505.44 kg·ha^-1） and crude protein content （20.74%）. The treatments were ranked， from largest effects on the multivariate performance score for alfalfa forage to smallest， as follows： S₂Q₂，S₁Q₂，S₂Q₁，S₃Q₂，S₁Q₁，S₃Q₁，CK. Therefore， plowing to 40 cm+tilling to 10 cm was found to be the most effective treatment for improving degraded alfalfa stands in this semi-arid area.

Genome-wide identification of the alfalfa TCP gene family and analysis of gene transcription patterns in alfalfa （Medicago sativa） under drought stress

Na WEI, Yan-peng LI, Yi-tong MA, Wen-xian LIU

2022, 31(1):  118-130.  DOI: 10.11686/cyxb2021189

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Alfalfa （Medicago sativa） is the most important legume forage in the world. However， its yield and geographical distribution are often influenced by drought. Transcription factors play important regulatory roles in alfalfa’s response to drought stress. Teosinte branched 1/cycloidea/pro-liferating cell factors （TCP） is a plant-specific transcription factor with important functions in plant growth， development， and stress resistance. However， its distribution and potential function in the response to drought stress have not been reported. To explore the responses of functional genes to drought stress in alfalfa， we identified members of the TCP gene family in alfalfa using bioinformatic methods. Further analyses were conducted to clarify the phylogeny and determine their gene structure， chromosome location， collinearity， and transcriptional patterns under drought stress. Our analyses identified 40 MsTCP genes that were unevenly distributed among the 20 chromosomes in the alfalfa genome. Among the MsTCP genes， 17 pairs were paralogous genes arising from gene fragment replication events. In a phylogenetic analysis， MsTCP genes formed two large branches and clustered into three subfamilies （PCF， CIN， and CYC/TB1）. Conserved domain analyses revealed that members in the same branch of the phylogenetic tree contain TCP domains with the same number of amino acids， and that the members of the same subfamily have similar conserved motifs and gene structures. Analyses of transcriptome data from alfalfa under drought stress revealed four MsTCP genes （MsTCP23， MsTCP27， MsTCP29， and MsTCP33） that may be involved in the drought response. The results of qRT-PCR analyses confirmed that these four genes were significantly up-regulated in roots and leaves of plants under a simulated drought （polyethylene glycol） treatment， providing further evidence that they participate in the drought response. These results lay the foundation for further research on the response to drought stress in alfalfa， and will be useful for generating new varieties of drought-resistant alfalfa using genetic engineering technology.

Genome-wide development and utilization of LTR retrotransposon-based IRAP markers in Medicago truncatula

Xiao-fan YIN, Na WEI, Shu-wen ZHENG, Wen-xian LIU

2022, 31(1):  131-144.  DOI: 10.11686/cyxb2020481

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Due to the narrowing of genetic differences between alfalfa （Medicago sativa） varieties， it is more difficult to identify phenotypes by traditional morphological methods. In the process of alfalfa breeding， molecular markers can greatly improve the breeding efficiency and variety identification. Reverse transcriptional transposon long terminal repeat sequence （LTR） are widely distributed in plant genomes. Molecular markers based on LTR are characterized by rich polymorphism and high information content， and are widely used in species identification and germplasm resource diversity evaluation. In this study， a large number of inter-retrotransposon amplified polymorphism （IRAP） markers were identified and designed at the genome-wide level in Medicago truncatula and used to analyze the genetic diversity of 40 alfalfa germplasm lines from within China and abroad. This approach produced 431 IRAP primers according to the design standards and the chromosomal location， from which 69 pairs of IRAP primers were obtained. A total of 325 alleles were amplified by 37 pairs of polymorphic primers； The average number of alleles was 8.8 per marker. Percentage of polymorphic bands （PPB） ranged from 50% to 100% with a mean of 79.9%. The polymorphic information content （PIC） ranged from 0.34 to 0.88， with an average of 0.69. Based on the genetic similarity coefficient （GS）， unweighted pair-group method with arithmetic means （UPGMA） was used for cluster analysis of the tested varieties. With 0.82 as the threshold， 40 samples of the tested germplasm lines could be divided into 4 categories. The grouping results were relatively consistent with geographic distribution information and STRUCTURE analysis of the 40 lines. In this study， IRAP molecular markers were developed at the whole genome level in M. truncatula for the first time and then evaluated and applied to investigate germplasm lines of alfalfa. A large number of the IRAP molecular markers obtained could provide technical support for the identification， protection and genetic background analysis of alfalfa varieties.

Analysis of differentially expressed genes in relation to tiller development and plant height based on transcriptomic sequencing of two tall fescue cultivars

Zhi-min YANG, Rui XING, Yun-jia DING, Li-li ZHUANG

2022, 31(1):  145-163.  DOI: 10.11686/cyxb2020486

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Tiller number and plant height are important agronomic traits for grasses. Identification of genes controlling tiller development and plant height is of great significance for molecular assisted breeding of forage and turfgrass. In this study， two varieties of tall fescue （Festuca arundinacea） 'Kentucky-31' （K31） and 'Regenerate' were used to construct transcriptome maps and explore the differentially expressed genes （DEGs） regulating shoot growth and development. Transcriptomic sequencing was performed based on Illumina HiSeq 2500×Miseq 300， the data obtained were assembled de novo and a total of 77872 unigenes were obtained. The obtained unigenes were then blasted against the non-redundant protein （NR）， universal protein （Uniprot）， gene ontology （GO）， kyoto encyclopedia of genes and genomes （KEGG） and cluster of orthologous groups （COG） databases， and 59927， 40213， 44447， 15146 and 13767 unigenes， respectively， were successfully annotated. A total of 1573 up-regulated DEGs and 1441 down-regulated DEGs were detected in 'Regenerate' when compared to 'K31'. GO enrichment analysis found that DEGs are mainly enriched in biological processes such as cell and cell component and macromolecular complex assembly. A total of 42 differentially expressed transcription factors were noted among the identified DEGs， mainly belonging to teosinte branched 1， cycloidea， proliferating cell factors （TCP）， WRKY and auxin response factor （ARF） families. DEGs relating to eight plant hormone categories were also annotated， including auxin， cytokinin， abscisic acid， gibberellin， ethylene， brassinosteroids， salicylic acid and jasmonic acid. The expression pattern of DEGs verified by real-time PCR was consistent with RNA-Seq， indicating the RNA sequencing results were accurate. This study has advanced the transcriptome knowledge for tall fescue， obtained a preliminary identification of the candidate genes controlling plant height and tiller development， and provided theoretical support for further research on gene function and molecular breeding.

Identification and functional analysis of lncRNA167 and its cleavage product miR167c in Medicago truncatula

Jia-ju ZHANG, Jie YU, Ming-na LI, Jun-mei KANG, Qing-chuan YANG, Rui-cai LONG

2022, 31(1):  164-180.  DOI: 10.11686/cyxb2020501

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Long non-coding RNA （lncRNA） is a class of functional RNA molecules with a length of more than 200 nucleotides， which plays important roles in various biological regulation processes and response to biological and abiotic stresses. lncRNAs often interacts with microRNAs （miRNAs）. In this study， a salt stress induced lncRNA （Mt-lncRNA167） obtained by high-throughput sequencing was identified to be a precursor of miRNA. The chromosome location of Mt-lncRNA167 coincided with that of miR167c， a member of miR167 family in Medicago truncatula. Mt-lncRNA167 was predicted to play a role as a cleavage precursor of Mt-miR167c. The online software analysis showed that auxin response factor 6/8 （ARF6/8） were two target genes of Mt-miR167c. The expression pattern analysis showed that Mt-lncRNA167 mainly expressed in leaves. Mt-lncRNA167 and Mt-miR167c responded to 100 mmol·L^-1 NaCl， 5% PEG 6000， and 4 ℃ cold stress， which was consistent with the prediction of their promoter cis-acting elements. Under salt， drought and low temperature stresses， the expression patterns of Mt-lncRNA167 and Mt-miR167c were almost the same， which were contrary to the expression patterns of target genes ARF6/8. Mt-lncRNA167 and Mt-miR167c overexpressing Arabidopsis thaliana showed fertility defect phenotypes， such as short fruit pod and filament， anther deformity， and low pollen activity. The results of germination rate under salt and drought stress showed that the resistance of Mt-lncRNA167 and Mt-miR167c overexpressing A. thaliana plants was better than that of wild type plants. In addition， the hypocotyls of Mt-lncRNA167 and Mt-miR167c overexpressing A. thaliana plants were significantly longer than that of the wild type plants. In conclusion， Mt-lncRNA167 was predicted to be the precursor of Mt-miR167c， while Mt-miR167c inhibited the expression of ARF6/8. The regulatory network of Mt-lncRNA167-Mt-miR167c-ARF6/8 may play an important role in stress tolerance and developmental regulation of M. truncatula.

Identification and expression characteristics of a cation/H⁺ exchanger gene family in Medicago truncatula

Tong WU, Yun-miao LIU, Jun JIN, Wei-feng DONG, Xiao-xi CAI, Ming-zhe SUN, Bo-wei JIA, Xiao-li SUN

2022, 31(1):  181-194.  DOI: 10.11686/cyxb2021237

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The CPA （cation proton antiporter） superfamily regulates intracellular ion and pH homeostasis by transporting proton and monovalent metal ions. Cation/H⁺ exchangers （CHX） belong to cation proton antiporter 2 （CPA2） superfamily. CPA2 members contain an Na⁺/H⁺ exchanger domain at the N terminus， which plays an important role in maintaining ion balance and flower organ development. In this study， CHX family genes from Medicago truncatula were systematically analyzed using bioinformatics， and a total of 47 non-redundant MtCHXs were identified by genome-wide screening. Chromosome location analysis showed that MtCHXs were distributed on 8 different chromosomes. Homology analysis indicated that alfalfa was closely related to Arabidopsis， but far removed from rice （Oryza sativa）. According to their evolutionary relationship， the 47 MtCHXs were further divided into 5 groups， andgene structure and motif of MtCHX genes within each group were conserved. In addition， analysis of the cis-acting element revealed that the MtCHXs gene promoter contained numbers of light-responsive elements， hormone-responsive elements， drought， low temperature and wound responsive elements. Further analysis of expression characteristics indicated that MtCHXs were highly expressed in reproductive organs and responded to abiotic stresses such as drought and low temperature.

Effect of topdressing after cutting on alfalfa growth and production

Rui-zhi XU, Xiao-juan WU, Hui-min YANG

2022, 31(1):  195-204.  DOI: 10.11686/cyxb2021265

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Fertilization is one of the important management measures in alfalfa （Medicago sativa） production， but the comparative effect of different topdressing regimes after cutting alfalfa and the optimal fertilization management plan are not clear. Hence， the aim of this research was to investigate the effects on the growth and production of alfalfa， of topdressing time and different combinations of N and P fertilizer applied to stimulate regrowth after cutting. The treatments comprised a complete factorial combination of two application times ［on the day the cut was made （T₀） and 7 d after cutting （T₁）］， three levels of N fertilizer （0， 25 and 50 kg·ha^-1 N， designated N₀， N₂₅ and N₅₀， respectively） and three levels of P fertilizer （0， 30， 60 kg·ha^-1 P₂O₅， designated P₀， P₃₀ and P₆₀， respectively）， with three replicates （54 plots in total）. The alfalfa variety was “Longdong” and the experiment was conducted in the establishment year. It was found that： 1） Topdressing after the first cut promoted the growth of the second crop of alfalfa. The highest alfalfa growth was achieved by applying a small amount of P fertilizer immediately after cutting （T₀N₀P₃₀）， and it was 20.53% higher than the control treatment （T₀N₀P₀）. In addition， topdressing after cutting could increase the alfalfa leaf∶stem. This effect was most evident in the high N-low P treatment combinations （N₅₀P₀ and N₅₀P₃₀） with topdressing at T₁. 2） The yield of the second crop of alfalfa differed significantly （P<0.05） between the various treatments. The highest hay and crude protein yields were 3.58 and 0.94 t·ha^-1， respectively， and these occurred with application of a large amount of N and P fertilizer immediately after cutting （T₀N₅₀P₆₀）， which were significantly different from that of the treatment after 7 days. Topdressing after cutting had no significant effects on alfalfa second cut acid detergent fiber， neutral detergent fiber or relative feeding values （P>0.05）. 3） Root length， root surface area， root volume and root biomass per cm³ of soil in the second cut were significantly affected by N and P topdressing （P<0.05）. The highest values of root length density （2.66 mm·cm^-3） were observed in the no-fertilizer （N₀P₀） treatments； the highest root surface area density （7.75 mm²·cm^-3）^{was observed in treatment T₀N₂₅P₃₀ and the highest root volume densities were observed in T₁N₂₅P₃₀ treatments. Root biomass was rather variable across treatments but was higher than other treatments where no fertilizer was applied （T₀N₀P₀ and T₁N₀P₀）_. In summary， in rainfed agricultural area of Longdong Loess Plateau， topdressing N and P fertilizer after cutting promoted alfalfa regrowth in the establishment year. In practice， a small amount of P₂O₅ or a combination of 50 kg·ha-1 N and 60 kg·ha-1 P₂O₅ can be applied as soon as possible after cutting.}

Comparison of 30 maize （Zea mays） varieties for food and feed in the Yanmenguan area

Xin-ming WU, Zhi-hong FANG, Hui-wu CHI, Hui-li JIA, Jian-ning LIU, Yong-hong SHI, Xue-min WANG

2022, 31(1):  205-216.  DOI: 10.11686/cyxb2021255

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The aim of this study was to select varieties of silage maize （Zea mays） suitable for cultivation in the Yanmenguan area from 30 maize varieties from different ecological zones. The 30 varieties were planted with a randomized block experiment design， and the agronomic traits， biological yield， and nutritional quality of each variety were measured and analyzed. The 30 tested varieties were divided into four groups in a cluster analysis， and the main characteristics of each group were analyzed and summarized. It was found that： 1） Two silage maize varieties， Yuqing No.3 and Quchen No.9 had higher biomass and hay yield， a high value for ear height， and better stay-green performance than that of other varieties， but these two varieties had lower nutritional quality than the grain and forage maize varieties. 2） The grain and forage maize varieties Tunyu 661 and Xianyu 1225 showed low hay yield， but high starch content （>30%）. 3） The biological yield was significantly positively correlated with the number of green leaves， green leaf weight， plant height， stem diameter， stem weight， and ear weight. Based on field performance and multi-trait evaluation results， Quchen No.9， Jindan 65， and Xiandan 405 were identified as the most suitable silage maize varieties for cultivation in the Yanmenguan area.

Research progress on plant coumarin biosynthesis pathway and the genes encoding the key enzymes

Zhen DUAN, Fan WU, Qi YAN, Ji-yu ZHANG

2022, 31(1):  217-228.  DOI: 10.11686/cyxb2020485

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Coumarins， the important secondary metabolites of plants， derive from phenylpropanoids metabolism pathway， have a variety of biological activities and play an important role in plant growth and development and stress response. Here， the research progress of coumarin biosynthesis pathway and the genes encoding the key enzymes involved in coumarin biosynthesis were reviewed， and the phylogenetic evolution of the UDP-glucosyltransferase （UGT） gene family were analyzed. Moreover， the current research issues on coumarin biosynthesis were summarized and the future research directions were prospected in order to provide references for studying the coumarin biosynthesis and follow-up research.

Characteristics of chlorophyll and photosynthesis in leaves and their response to nutrients during aging of Elymus sibiricus

Yong-chao ZHANG, Guo-ling LIANG, Yan QIN, Wen-hui LIU, Zhi-feng JIA, Yong LIU, Xiang MA

2022, 31(1):  229-237.  DOI: 10.11686/cyxb2020514

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In this study， we investigated the changes in leaf chlorophyll content and photosynthesis parameters of Elymus sibiricus cv. Qinghai No.1 in response to fertilization and aging. E. sibiricus is distributed and used widely in the grassland of Qinghai province on the Qinghai-Tibetan plateau. Three field experiments were set up： 1） a time series of plots from one to six years old without any treatments， 2） fertilizer addition to six-year-old plots， 3） annual fertilizer addition to field plots for six years since 2015. From 2015，sowings were carried out in May of each year. The seeding rate was 2.25 g?m^-2 in row with 30 cm in spacing between rows and 15 m² （3 m×5 m） per plot. The chlorophyll content of leaves was measured at the flowering stage for 10 randomly chosen plants from the flag leaf down to the third leaf， using a SPAD analyzer from Konica Minolta， Inc. The photosynthesis parameters of the flag leaf were recorded from 10：30 to 11：30 am in a sunny day at the flowering stage （July-August） with a LI-COR LI-6400XT portable photosynthesis meter. It was found that chlorophyll content was decreased from the three years of age， but increased again at six years of age. In the age-series of E. sibiricus cv. Qinghai No.1， the net photosynthesis rate decreased， intercellular CO₂ concentration increased， stomatal conductance and transpiration rate decreased significantly at three years of age， and remained unchanged thereafter from three to six years of age. When nitrogen and phosphorous fertilizer was applied to previously unfertilized six-year-old field plots of E. sibiricus cv. Qinghai No.1， the relative chlorophyll content （which varied in different parts of leaves from 33.30% to 48.23%）， and the net photosynthesis rate increased， and signs of ageing were reversed. The highest net photosynthesis rate observed （10.77 μmol·m^-2·s^-1） occurred at the nitrogen level of 60 kg?ha^-1. In the long-term fertilizer addition field， low level nitrogen addition （45 kg·ha^-1） enhanced chlorophyll content， while phosphorous addition had no significant effect. An intermediate nitrogen addition level （60 kg·ha^-1） with phosphorous resulted in six-year-old plants retaining a high net photosynthesis rate.

Analysis of genetic variation in agronomic traits of half-sib families of Melilotus albus in the second generation of recurrent selection

Peng-lei WANG, Zhuan-zhuan YAN, Li-juan GAO, Qian MA, Xi-fang ZONG, Sheng-sheng WANG, Ji-yu ZHANG

2022, 31(1):  238-245.  DOI: 10.11686/cyxb2020487

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This research formed part of a program to breed a new cultivar of Melilotus albus with high quality， high yield and low coumarin content. In pursuit of this goal， we conducted a second recurrent selection at two sites， of 25 half-sib families of M. albus，on the basis of the first recurrent selection. Significant genotypic variation （P<0.05） between half-sib families were found for plant height， dry weight， fiber content and coumarin content， and there were significant genotype×environment interactions （P<0.05） between the two locations for most traits， including dry weight， plant height and stem diameter. The predicted genetic gain of dry weight and plant height traits were 4.3% and 2.6%， respectively， based on genotypic variance. The correlation analysis showed that the stem diameter was significantly positively correlated with dry weight and plant height （P<0.01）， and the crude protein concentration was significantly negatively correlated with neutral detergent fiber and acid detergent fiber levels （P<0.01）. Principal component analysis was used to show the relationship among agronomic traits and the performance of the half-sib families. The 25 half-sib families were divided into four groups by cluster analysis. Among these four groups， the third group had relatively high dry weight and crude protein， as well as lowest coumarin content. This second recurrent selection of 25 half-sib families will provide useful germplasm for breeding new lines of M. albus.