Alfalfa regrowth is a complex process that is frequently constrained by deficits in water and N fertilisers after cutting. However, the transcriptomic regulatory networks and primary metabolic changes during regrowth are largely unknown. The alfalfa regrowth biomass responses to water deficiency and water deficiency supplied with N fertilisers and corresponding transcriptional and primary metabolic changes in new leaves and roots were systematically explored at 9 and 14 d after cutting. Water deficiency significantly decreased the alfalfa regrowth biomass. Integrated transcriptomic and metabolomic analysis demonstrated that osmoprotection related genes, sucrose and starch metabolic pathways, hormone biosynthesis and signalling pathways, and key transcription factors in new leaves and roots are responsible for alfalfa regrowth under water deficiency. Furthermore, alfalfa regrowth biomass was significantly improved in the presence of N fertilisers under water deficiency through multigene network coordination and metabolic pathway rearrangement. Interestingly, differentially expressed genes expression occurred predominantly in roots at 9 d after cutting, while it mainly occurred in the new leaves at 14 d after cutting. This study revealed the complex molecular mechanisms of alfalfa regrowth and provided theoretical support for optimal irrigation and N fertiliser strategies that will achieve maximum biomass of alfalfa in dryland farming areas.

Soybeans can simultaneously form tripartite symbiotic associations with arbuscular mycorrhizal fungi (AMF) and diazotrophs. However, no studies have explored whether soybean genotypes differing in their maturity groups (MGs) may have implications for the recruitment of rhizosphere soil AMF and diazotrophs. We investigated the diversity and community compositions of AMF and diazotrophs in three soybean genotypes differing in their maturity groups (MG) using high-throughput sequencing. The soybean MGs were MG1.4, MG2.2, and MG3.8, representing early, standard, and late maturity, respectively, for the study region. Soil chemical properties and yield-related traits were determined, and co-occurrence network patterns and drivers were also analyzed. The results obtained demonstrated that AMF richness and diversity were relatively stable in the three soybean genotypes, but noticeable differences were observed in diazotrophs, with late maturity being significantly higher than early maturity. However, there were differences in AMF and diazotrophic composition among different MG genotypes, and the changes in the proportion of dominant species in the community were necessarily related to MG genotypes. Co-occurrence network analysis showed that the positive correlation between AMF and diazotrophs gradually decreased in earlier MG genotypes than in the other later MG genotypes. The results of the structural equation model analysis showed that soil organic carbon, AMF, diversity of soil nutrients, and extracellular enzyme activities were important factors driving soybean yield change, with organic carbon accounting for more than 80% of the pathways analyzed. These results suggest that soybean genotype selection based on MG plays an important role in recruiting both AMF and diazotrophic communities, and in comparison to AMF, diazotrophs are more responsive to the different MG genotypes.

为研究紫花苜蓿叶片和根系对水分和外源氮(N)添加的响应规律,在温室条件下设置水分胁迫处理(WS)(35％±5％)田间持水量(field water capacity,FWC)和充分灌溉且未渍水(WW)(70％±5％)FWC两个水分梯度,每个水分梯度下设置0、5和10 mmol·L-13个N添加水平(Nn、Nm和Nh),研究了紫花苜蓿叶片和根系膜脂过氧化的程度及C、N特征对不同水分条件和外源N添加的响应规律.结果表明:WS和外源N提高了紫花苜蓿叶片丙二醛(MDA)含量,但对根系没有显著影响.WS和N添加未影响紫花苜蓿叶片C含量,但N添加提高了根系C含量.WS未改变紫花苜蓿叶片N含量,但提高了根系N含量.外源N添加不但提高了叶片N含量,还增加了根系N含量,但叶片N含量在WW处理下对外源N添加较为敏感,而根系N含量在WS处理下对外源N的添加较为敏感,这说明紫花苜蓿叶片和根系C、N状态对N添加的响应受土壤水分条件的调控.紫花苜蓿根系C/N较叶片更高,且对水分和外源N添加的响应更为敏感.WS处理显著提高了根系δ13C,对叶片δ13C无显著影响.外源N添加降低了叶片和根系δ15N,且在WS处理下根系δ15N显著降低,叶片中δ15N在WW处理下显著降低.总之,相比叶片,紫花苜蓿根系生理参数及C、N特征对水分和外源N添加采取了更为积极的策略,在生长中发挥着更重要的作用.该研究结果有助于全面掌握紫花苜蓿各器官对水分和外源N添加的响应策略,为我国旱作农业区紫花苜蓿制定精准的水肥管理制度提供了理论依据.

为探究不同秋眠类型紫花苜蓿根际与非根际土壤理化性质,本研究调查了关中地区种植5年不同秋眠类型紫花苜蓿再生期和休眠期根际与非根际土壤有机碳(Soil organic carbon,SOC)、全氮(Total nitrogen,TN)、全磷(Total phosphorus,TP)及土壤酶活性.结果表明:根际SOC、TN、土壤酶活性及化学计量比显著高于非根际土壤(P<0.05);TP在根际与非根际土壤中无显著差异(P>0.05);休眠期土壤SOC、TN、TP含量整体变化趋势表现为随着秋眠级数递增,养分含量逐渐升高,即强秋眠(D)<半秋眠(SD)<非秋眠(ND),而再生期的表现趋势正好相反.根际与非根际SOC与T N、蔗糖酶活性呈正相关;根际土壤T N与蔗糖酶、蛋白酶活性呈正相关,与脲酶活性呈负相关;非根际土壤TN与蔗糖酶活性呈正相关,与蛋白酶活性呈负相关.本研究结果将有助于进一步探究不同秋眠类型紫花苜蓿土壤营养物质循环与生产力之间的关系及根际土壤的微生态.

为进一步明确关中地区基于牧草种植和传统农作物生产对土壤理化性质的影响,本试验测定了单播紫花苜蓿(A)、玉米(M)、小麦(W)及套种紫花苜蓿和玉米(AM)四年后土壤碳氮含量、稳定性同位素、微生物生物量及酶活性.结果表明:紫花苜蓿根际土壤全氮(TN)、同位素氮(δ15N)、微生物生物量碳氮(MBC、MBN)及蔗糖酶(SUC)、脲酶(UR)和中性磷酸酶(NP)均显著高于小麦和玉米.此外,AM的根际土壤全碳(TC),TN和MBC显著高于单播作物.土壤TC和TN分别与δ15N,MBC和NP等呈极显著正相关(P＜0.01),且冗余分析中土壤C,N及微生物生物量分别解释了酶活性变化的50.86％和69.81％.因此,关中地区基于豆科牧草紫花苜蓿的种植模式能够实现C,N资源的高效利用与土壤的可持续生产.本研究从土壤理化性质的角度为关中地区落实"粮改饲"等政策,实现农业资源的高效利用提供理论依据.

为研究紫花苜蓿在叶片和根系水平上响应干旱胁迫的形态和生理的品种特异性规律,在温室内分析了干旱胁迫下WL363HQ和巨能7紫花苜蓿株高、分枝数、生物量及叶片和根系中丙二醛（MDA）、脯氨酸、抗氧化酶类物质、C、N含量、C/N、稳定性C同位素(δ 13 C)和稳定性N同位素(δ 15 N)。结果表明:干旱胁迫显著降低了供试品种地上部分和根系的干重及分枝数（P＜0.05）。干旱胁迫显著降低了巨能7的株高（P＜0.05）,但增加了巨能7的根冠比,而WL363HQ的结果与之相反,这说明干旱胁迫下供试品种的株高和根冠比具有品种特异性的规律。干旱胁迫增加了WL363HQ和巨能7叶片和根系中MDA和脯氨酸的含量及抗氧化酶物质的活性,且在器官水平也具有品种特异性规律。干旱胁迫下巨能7叶片的MDA含量显著增加（P＜0.05）,而在WL363HQ根系中的MDA含量也显著增加（P＜0.05）。干旱胁迫下WL363HQ叶片脯氨酸含量、POD和SOD活性,及根系SOD的活性均显著增加（P＜0.05）,而巨能7仅叶片SOD活性,根系脯氨酸含量、POD活性显著升高（P＜0.05）。尽管干旱胁迫对供试品种叶片和根系C、N含量无显著影响（P＞0.05）,但干旱胁迫显著提高了WL363HQ和巨能7紫花苜蓿根系的δ 13 C（P＜0.05）,且WL363HQ叶片的δ 15 N均显著高于巨能7（P＜0.05）。此外,干旱胁迫均显著提高了巨能7叶片和根系的C/N（P＜0.05）。干旱胁迫下供试品种C、N代谢参数并没有在叶片和根系中表现出较为明显的品种特异性规律,深层次的机制还有待进一步研究。本研究结果将为进一步掌握紫花苜蓿叶片和根系协同抗旱机制及抗旱丰产紫花苜蓿新品种的选育提供理论依据。