Despite the essential role of micronutrients in plant metabolic processes and carbon cycle, the mechanisms by which micronutrients regulate plant community traits remain poorly understood. Here, we used a long-term experiment to explore the potential mechanisms of plant community micronutrients and traits along a precipitation gradient. Our results showed that plants shifted toward lateral growth and asexual reproduction over time. From 1985 to 2022, the plant community Fe content increased by 18.8% in the north but declined by 25.2% in the south of the typical steppe. Furthermore, plant community growth and reproduction were sensitive to both micronutrient contents and uptake efficiencies in the north of the typical steppe. While plant community Mn and Zn contents enhanced growth longitudinally, Zn and Fe uptake efficiencies hindered sexual reproduction. Furthermore, soil moisture and GDP per capita were the key drivers of micronutrient variation in the north and south of the typical steppe, respectively. Precipitation fluctuations primarily regulated community traits across all sites. In the arid site, micronutrient-driven shifts in reproduction stabilized the soil carbon stock by balancing biomass allocation. These findings can help us to better understand the coupling of plant micronutrients, traits, and soil carbon stocks, thereby providing the basis for a scientific grassland conservation strategy under global change scenarios.

Zygophyllum xanthoxylum is a xerophytic shrub with potential for forage production and as a genetic resource for stress tolerance, yet knowledge for optimising its seed production remains limited. A 5-year field experiment investigated the effects of phosphorus (P) application (0, 60, 120 and 180 kg ha -1 ) and GA 3 foliar spraying (0, 100 and 200 mg L -1 ) on seed yield, components, quality and nutrient use efficiency. Seed yield exhibited a parabolic response to both factors. The optimal combination — 120 kg ha -1 P + 100 mg L -1 GA 3 — increased yield 2.44-fold (averaging 1020.91 kg ha -1 across three seasons) and improved seed quality. Maximum nutrient use efficiency occurred at 60 kg ha -1 P + 200 mg L -1 GA 3 , revealing a trade-off between yield maximisation and resource efficiency. Structural equation modeling identified reproductive branches per plant (RBP) as the dominant yield driver (effect = 0.82), with P, GA 3 and yield components together explaining 90% of the variation in seed yield, positioning RBP as a target for genetic improvement and seed production management. Interannual variation highlighted the sensitivity of seed production to climatic factors, underscoring the need for climate-resilient strategies. These findings establish a framework for optimising seed production in Z. xanthoxylum and demonstrate that integrated nutrient-hormone management is an effective strategy for overcoming seed production constraints in xerophytic shrubs, with practical implications for ecological restoration and forage production in arid lands.

Abstract Ongoing human activities and climate change threaten global grasslands, where plant nutrients are essential for ecosystem stability. However, long-term assessments (1985–2022) of above- and below-ground nutrient trade-offs remain limited. Here, we conducted a 37-year study along the precipitation gradient (267–441 mm) to investigate the dynamics and trade-offs of plant carbon (C), nitrogen (N) and phosphorus (P). Our study found that with increasing local precipitation, above-ground C, N and P contents increased, while below-ground C content declined. The long-term response of plant nutrients varied spatially; the drier north (267 mm) and central region (334 mm) showed increased above-ground C but decreased N and P over time, whereas the opposite pattern occurred in the wetter south (441 mm). Additionally, the trade-off values of plant C, N and P stocks increased with local precipitation, and temporal stability of the N and P trade-off values was lowest in the drier north. Finally, precipitation fluctuation, fertilizer input and per capita GDP were identified as the key drivers of plant above- and below-ground nutrient dynamics in the northern, central and southern regions, respectively. With increasing local precipitation, the effect of climate on trade-off values shifts from negative to positive, whereas the effect of human activities shifts from positive to negative. Our findings highlight that the long-term response of plant nutrients is regulated by local precipitation patterns, through which the precipitation gradient has reshaped plant nutrient regulation by shifting the dominant driver from climatic to human activities factors.

Enhancing alfalfa seed yield is essential for its comprehensive utilization in the forage, ecological, energy, and food sectors. Optimal irrigation and nutrient management are widely acknowledged as key factors in the arid and semiarid regions. However, the synergistic effects of drip irrigation and micronutrient application, particularly boron, on alfalfa seed production in these areas remain insufficiently understood. To address this gap, we conducted a three-year field experiment to investigate the impact of four irrigation frequencies (2, 3, 4, and 5 times, with 50 mm per application) and four boron concentrations (0, 0.3 %, 0.6 % and 0.9 %) on seed yield, water use efficiency (WUE), and economic benefits in alfalfa. Our results revealed a negative parabolic relationship between seed yield and both irrigation amount and boron concentration. The highest seed yields were achieved with three irrigations (150 mm) combined with a 0.6 % boron application, except for the year of 2021. In 2022and 2023, this optimal treatment resulted in seed yields of 931.28 kg/hm2 and 983.98 kg/hm2, representing a 3.22-fold and 2.08-fold increase compared to the control, respectively. This treatment also produced the highest WUE, with an average value of 2.31 kg/hm2/mm from 2021 to 2023, reflecting a 2.92-fold increase over the control. Furthermore, seed yield exhibited a strong positive correlation with all key yield components (P < 0.001). The structural equation model identified the number of reproductive branches per plant as the most significant contributor to seed yield. These findings provide valuable insights into the effects of irrigation and boron application on alfalfa seed yield and offer practical guidance for optimizing agronomic practices aimed at improving seed production in alfalfa and similar crops.

Population dynamics may fluctuate dramatically over time in response to changing climate conditions. Thus, assessing how trade-offs in growth and reproduction of plant population respond to climate change may be key for predicting and conserving complex communities, especially in the context of different precipitation. Here, using a long-term experiment along the precipitation gradient, we investigated trade-offs in growth and reproduction of dominant species, Artemisia capillaris and companion species, Aster altaicus, as well as their climate-driven mechanisms. The impact of A. capillaris and A. altaicus on community above-ground biomass (AGB) and species richness (SR) were also evaluated. Our findings indicate that, over the past 37 years, A. capillaris exhibited lateral growth and asexual reproduction across the three sites. In contrast, A. altaicus tended to grow vertically and reproduce sexually, with a significant increase in its AGB. Moreover, the influence of climate fluctuation, characterized by variations in temperature and precipitation over specific time scales, on the two populations diminished from north to south. Long-term average climate, reflecting mean temperature and precipitation, and current climate conditions during the sampling year primarily influenced changes in A. capillaris and A. altaicus in south, respectively. Additionally, from north to south, the contribution of A. altaicus to community AGB and SR increased, while the contribution of A. capillaris to community AGB and SR decreased. Community AGB increased as the coupling index between A. capillaris and A. altaicus intensified. These findings can help us to better understand the coupling of plant traits, populations and communities, aid in the protection of grasslands under future climate change scenarios.

Artemisia sphaerocephala, a xerophyte shrub from the Compositae family, has gained significant attention in ecological restoration and various industries. However, limited knowledge of agricultural practices for its seed production hinders the development and use of this species. In a 5-year field experiment, we investigated the effects of four surface drip irrigation treatments (W0, W1, W2, and W3 with 0, 80, 160, and 240 mm, respectively) on seed yield, quality, and water use efficiency (WUE) in A. sphaerocephala. Higher irrigation levels significantly increased seed yield, with annual averages of 37, 85, 140, and 195 kg/ha for W0, W1, W2, and W3, respectively. Additionally, increased irrigation improved germination percentage and reduced median water potential (). However, the effect of irrigation on WUE varied from year to year. Therefore, we recommend total irrigation of 240 mm, distributed as 80 mm each during winter, regreening, and full flowering stages, to optimize A. sphaerocephala seed production, particularly in arid regions. A structural equation model identified seeds per flower (SF) as the most significant contributor to seed yield, highlighting SF as a key trait for breeding programs aimed at improving A. sphaerocephala seed yield. Our study provides valuable insights for implementing effective agronomic measures to enhance seed yield in A. sphaerocephala and similar semi-shrubs.

Soil nutrients are essential for ecosystem function and food production. However, the long-term dynamics and ecological drivers of soil macro- and microelements, as well as their relationships, remain virtually unknown, especially in varying precipitation contexts. Here, we conducted a long-term experiment in typical steppes to explore the universal and differential mechanisms of soil macro- and microelements along the precipitation gradient. Our results showed decreases in soil Zn and Fe stocks, alongside increases in Cu, SOC, and STN stocks over time. From north to south, the temporal stability of SOC, STN, Cu and Zn stocks generally increased. Additionally, compared to the humid site, soil macronutrients showed stronger coupling with micronutrients at the arid site, especially Fe, followed by Mn, Zn, Cu. The sensitivity of soil macro- and microelements to climate change and human activities were correlated with the local background precipitation. Precipitation fluctuation, GDP per capita and current precipitation were significant factors contributing to the variation in soil macro- and microelements stock in the north, center and south. Climate explained 46%, 19%, and 16% of nutrient coupling variation in the north, center, and south sites, respectively. Across all sites, human activities explained 74% of variation. Altogether, our findings provide an overview of long-term soil macro- and microelement distribution, their coupling relationships, and driving factors under different precipitation contexts, which is important for grassland management and food production in future global change scenarios.

Soil ecological stoichiometry play vital roles in regulating structure and function of grassland ecosystems. However, the long-term dynamics of soil nutrient elements and their underlying driving mechanisms remain poorly understood, particularly in the context of changing precipitation patterns. Here, we conducted a longterm experiment to assess temporal-spatial dynamics and mechanisms of soil ecological stoichiometry along the precipitation gradient. Over the past 37 years, our results indicated a significant overall increase in soil organic carbon (SOC) and total nitrogen (STN) contents, accompanied by a decrease in soil total phosphorus (STP) content across the three sites. The sensitivity of SOC, STN, C:P, and N:P to climate change decreased significantly as local precipitation increased, while the sensitivity of SOC, STN, and C:N to local precipitation declined significantly over time. From north to south, STP content increased on average by 1.03 %, 1.16 % and 1.68 % in 1985, 2002 and 2022, respectively. Additionally, the coupling strength of SOC, STN and STP decreased with increasing local precipitation from 1985 to 2002. Furthermore, the interaction between climate and soil properties explained 18 % and 22 % of the variation in temporal stability and contents of SOC, STN and STP, climate was the most critical factor affecting spatial stability of SOC, STN and STP. Among them, average precipitation, plant phylogenetic diversity and soil moisture were key indicators of temporal-spatial variability in soil C:N:P stoichiometry. Our findings provide an overview of biogeographical nutrient cycles under different temporal and spatial contexts, which is critical for grassland management and conservation in future global change scenarios.

Sainfoin has gained considerable attention in the forage, medicinal, and food industries due to its exceptional nutritional profile and rich bioactive compounds. However, knowledge of agricultural practices for its seed production, particularly in arid and semiarid regions, remains limited. We conducted a three-year field experiment from 2021 to 2023 to evaluate the effects of four irrigation frequencies (2, 3, 4, and 5 applications of 50 mm each) and four boron concentrations (0, 0.3 %, 0.6 % and 0.9 %) on seed yield, quality, water use efficiency (WUE) and economic benefits in sainfoin. Our findings revealed a negative parabolic relationship between seed yield and both irrigation amount and boron concentration. The highest yields were achieved with four irrigations (200 mm) combined with a 0.6 % boron application, resulting in seed yield of 696.69 kg/hm2 in 2021, 1200.94 kg/hm2 in 2022, and 1687.91 kg/hm2 in 2023. This optimal combination also exhibited superior WUE and economic benefits compared to other treatments. Higher irrigation frequency increased seed dimensions (length, width, and height), but it had a negative impact on both germination percentage and speed. The impact of boron on seed quality varied with irrigation levels. All yield components, except for 1000-seeds weight, showed significant positive correlations with seed yield (P < 0.001). A structural equation model indicated that the number of reproductive branches per plant was the most significant contributor to seed yield. Our findings enhance the understanding of the mechanisms underlying seed yield responses to irrigation and boron application in sainfoin, offering valuable insights for agronomic practices aimed at improving seed yield in sainfoin and similar crops.

Lespedeza potaninii Vass is a highly drought-resistant China native legume plant, which plays an important role in animal husbandry and ecological restoration. However, there are few reports on the agricultural practices of its seed production. We evaluated the effect of four plant densities (33,333, 44,444, 66,666, and 133,333 plants ha(-1)) and five phosphate fertilizer rates (0, 45, 90, 135, and 180 kg ha(-1)) on seed yield, seed yield components and agronomic traits from the year 2020-2022. Correlation and structural equation model (SEM) analyses were used to determine the contribution of yield components to seed yield per plant. Year, plant density, phosphorus fertilizer rate and their interaction (P<0.05) significantly influenced the seed yield of L. potaninii Vass. The maximum average seed yield over 3 years (570 kg ha(-1)) occurred at the plant density of 44,444 plants ha(-1) and phosphate fertilizer rate of 90 kg/ha. All the yield components, except 1000-seed weight, were significantly correlated with seed yield per plant. The racemes per stem, florets per raceme and pods per raceme had significant positive correlation, and stems per square meter and biomass had significant negative correlation with seed yield per plant. Increasing phosphorus fertilizer increased seed yield per plant. However, increasing plant density decreased seed yield per plant. Our findings enable further understanding of the mechanism of seed yield response to plant density and phosphorus fertilization in L. potaninii Vass and provide a reference for appropriate agronomic measures to improve seed yield of L. potaninii Vass and similar shrubs.

Shortage of high-quality seeds of native species, particularly for xerophyte shrubs, have severely limited grass-land restoration in the arid region of China. However, little attention has been devoted to improving seed yield and quality in the xerophyte shrub. We conducted a three-year field experiment from 2019 to 2020 to investigate the effects of four irrigation treatments (i.e., W0: non-irrigated control; W1: irrigation at winter; W2: irrigation at winter and regreening; W3: irrigation at winter, regreening, and peak flowering) via subsurface drip irrigation on the seed yield and quality of Hedysarum fruticosum, a dominant leguminous shrub in the desert areas of China. The results showed that seed yield increased as irrigation frequency increased regardless of growth season. The yearly average seed yields were 98.0, 107.7, 179.3, and 265.5 kg hm-2 for W0, W1, W2, and W3 irrigation, respectively. Seed yield decreased in each subsequent growth year in all irrigation treatments, and the variation in seed yield each year was the highest in W0 and lowest in W3 irrigation. Compared to 2019, the seed yield of W0 decreased by 47 % and 66 %, but yields of the W3 irrigation treatment decreased by 8 % and 19 % in 2020 and 2021, respectively. Meanwhile, irrigation significantly affected seed yield components; the number of florets and pods per stem under the W3 irrigation treatment was two to three times that of W0 irrigation for three years. The structural equation model revealed that pods per stem had the largest direct positive effect on seed yield (path factor p = 0.44), followed by seeds per pod (path factor p = 0.36). Irrigation treatments affected seed germination percentage and seed size, which increased as irrigations times increased. A similar water use effi-ciency was achieved in W0 and W3 in three years, and W1 treatment had the lowest water use efficiency. In conclusion, we recommend W3 treatment to increase seed yield and quality, especially in arid regions. Future breeding objectives and agronomic practice for H.fruticosum should pay more attention to increasing pods per stem. Our study can be used as a reference for taking appropriate agronomic measures to improve the seed yield of H.fruticosum and similar shrubs.

Long-term observations have shown that structure and function of grasslands have changed due to climate change over the past decades. However, little is known about how grasslands respond to climate change along the precipitation gradient, and potential mechanisms remain elusive. Here, we utilize a long-term experiment in typical steppe to explore universal and differential mechanisms of community and functional groups assembly along the precipitation gradient. Our results indicated that the sensitivity of community and functional groups assembly to climate change was related to local precipitation. The strength of the positive effects of climate change on aboveground biomass, species richness, and their relationship of community decreased modestly with local precipitation. The mechanism behind this was the change in plant community composition of the precipitation-induced, annuals that was more responsive to climate change decreased as increased local precipitation. Furthermore, current and past climate both drove community and functional group assembly, and the role of past climate diminished with increasing local precipitation. Among them, climate fluctuation, average climate and current climate were the most critical climate indicators affecting community and functional groups assembly in low, medium and high precipitation sites, respectively. In conclusion, climatic change do not always exert identical effects on grasslands along the precipitation gradient. This could be critical importance for improving our ability to predict future changes in grassland ecosystems.

本研究从种质资源收集、品种选育、种子生产和质量管理等方面总结了我国草种业发展取得的成就,分析了面临的挑战,提出了建设草种强国的建议.我国已初步建立了完整的草种业体系,已成为世界草种质资源保存大国,自1987年实施品种审定制度以来,已审定通过了651个草类植物新品种,在利用乡土植物优异基因和内生真菌创制新种质等方面,取得了突出成果.所育成品种基本可满足一般生产需求.种子田常年保有面积10万hm2左右,年产种子约10万t.已在全国建立了5个部级检验中心,并在品种审定、特异性、一致性和稳定性(DUS)测试,种子立法等方面建成了较为完整的质量管理体系.面临的挑战是种质资源收集不及我国现有饲草种质资源数的50％,对已有种质资源评价、鉴定工作不足,缺少用于生态修复的草种和草坪草品种.根据国家生态修复规划,每年需草种7万t,目前缺口巨大,每年进口草种5万t左右,主要是高质量商品草和草坪草用种.质量管理体系中缺少种子认证.建议进一步加强种质资源收集、评价与利用;加强乡土草、草坪草及放牧型牧草选育;建立大规模草种生产基地及成果转化渠道;完善种子质量管理体系及提高对草的认识,从科技创新、人才培养、发展政策等方面予以支持.

Melilotus species are used as green manure and rotation crops worldwide and contain abundant pharmacologically active coumarins. However, there is a paucity of information on its genome and coumarin production and function. Here, we reported a chromosome-scale assembly of Melilotus albus genome with 1.04 Gb in eight chromosomes, containing 71.42% repetitive elements. Long terminal repeat retrotransposon bursts coincided with declining of population sizes during the Quaternary glaciation. Resequencing of 94 accessions enabled insights into genetic diversity, population structure, and introgression. Melilotus officinalis had relatively larger genetic diversity than that of M. albus. The introgression existed between M. officinalis group and M. albus group, and gene flows was from M. albus to M. officinalis. Selection sweep analysis identified candidate genes associated with flower colour and coumarin biosynthesis. Combining genomics, BSA, transcriptomics, metabolomics, and biochemistry, we identified a beta-glucosidase (BGLU) gene cluster contributing to coumarin biosynthesis. MaBGLU1 function was verified by overexpression in M. albus, heterologous expression in Escherichia coli, and substrate feeding, revealing its role in scopoletin (coumarin derivative) production and showing that nonsynonymous variation drives BGLU enzyme activity divergence in Melilotus. Our work will accelerate the understanding of biologically active coumarins and their biosynthetic pathways, and contribute to genomics-enabled Melilotus breeding.

Developmental signals and environmental stresses regulate carbon distribution in the vegetative and reproductive organs of plants and affect seed yield. Cleistogenes songorica is a xerophytic grass with great potential application value in ecological restoration. However, how carbohydrate transport and distribution during grain filling affect the seed yield of C. songorica under water stress is not clear. The present study showed that the soluble sugar and starch contents of cleistogamous (CL) spikes and chasmogamous (CH) spikes were significantly higher at the milk stage, which was attributed to a significantly higher seed number and seed yield per spike under water stress conditions than under well-watered conditions (P < 0.01). RNA-seq data revealed a total of 54,525 differentially expressed genes (DEGs) under water stress conditions, but only 3744 DEGs were shared among all comparison groups. Weighted gene co-expression network analysis showed that the transport and distribution of carbohydrates were regulated by ABA-responsive genes (CsABA8OX1_1, CsABA8OX1_2, CsABA8OX2_1, CsABA8OX2_2, CsNCED3, CsNCED1_1, CsNCED1_2 and CsNCED4_1) and sugar transport and starch synthesis genes (CsSUS1, CsSUS2, CsSUS3, CsAGP1, CsAGP4, CsAGP5, CsSSS1 and CsSBE5) under water stress conditions. These genes jointly regulated carbohydrate remobilization in sources (stems, leaves and sheaths) to promote grain filling and improve seed yield. The present study helped to clarify the phenotypic, metabolic and transcriptional response mechanisms of vegetative organs, such as stems and leaves, and reproductive organs, such as CL spikes and CH spikes, to promote carbohydrate redistribution under water stress, and it provides theoretical guidance for improving seed yields.

Polyamine and ethylene pathway genes (PEGs) are widely involved in regulating plant abiotic stresses. However, the PEGs in Cleistogenes songorica have not yet been thoroughly studied. In the present study, 17 polyamine-, 12 ethylene- and 6 S-adenosylmethionine (SAM)- related genes were identified at the genome-wide level in C. songorica. Phylogenetic analysis showed that genes in the ethylene and polyamine pathways and SAM family genes were not clearly separated. Promoter regions of these genes were rich in stress-related cis-regulatory elements. Several PEG and SAM genes coexpressed together and were responsive to abiotic stress treatment. In particular, qRT-PCR analysis showed that the expression of CsSAMDC2 increased under salt, dehydration and ABA treatment conditions. Arabidopsis plants transformed with CsSAMDC2 driven by a stress-inducible RD29A or constitutive promoter 35S exhibited enhanced dehydration tolerance and maintained higher chlorophyll content and photosynthetic capacity. The expression of CsSAMDC2 was generally higher in lines harboring RD29A:: CsSAMDC2 compared to 35 S::CsSAMDC2 lines under drought stress treatment. Seed germination of RD29A:: CsSAMDC2 or 35 S::CsSAMDC2 transgenic plants under salt stress treatment was superior to their wild-type counterparts, and the leaves of the transgenic plants exhibited a more compact structure. In addition, under salt stress, application of ABA improved lateral root development of RD29A::CsSAMDC2 Arabidopsis plants. The qRT-PCR analysis indicated that the expression of well-known abiotic stress-responsive genes AtPEGs, AtERF1 and AtRD29A, increased in both RD29A::CsSAMDC2 and 35 S::CsSAMDC2 transgenic Arabidopsis after drought, salt stress and salt stress plus ABA treatments. Our results suggest that CsSAMDC2 enhances drought and salt tolerance in Arabidopsis and therefore may contribute to abiotic stress tolerance in forage and food crops.

The genetic adaptations to harsh climatic conditions in high altitudes and genetic basis of important agronomic traits are poorly understood in Elymus sibiricus L. In this study, an association population of 210 genotypes was used for population structure, selective sweep analysis, and genome-wide association study (GWAS) based on 88,506 single nucleotide polymorphisms (SNPs). We found 965 alleles under the natural selection of high altitude, which included 7 hub genes involved in the response to UV, and flavonoid and anthocyanin biosynthetic process based on the protein-protein interaction (PPI) analysis. Using a mixed linear model (MLM), the GWAS test identified a total of 1,825 significant loci associated with 12 agronomic traits. Based on the gene expression data of two wheat cultivars and the PPI analysis, we finally identified 12 hub genes. Especially, in plant height traits, the top hub gene (TOPLESS protein) encoding auxins and jasmonic acid signaling pathway, shoot apical meristem specification, and xylem and phloem pattern formation was highly overexpressed. These genes might play essential roles in controlling the growth and development of E. sibiricus. Therefore, this study provides fundamental insights relevant to hub genes and will benefit molecular breeding and improvement in E. sibiricus and other Elymus species.

研究性教学是一种以问题为导向、以学生为主体,旨在提升学生创造性与实践能力的教学新模式,是满足当前社会对创新人才培养需求和学生全面发展内在需求的一种重要途径.本文以兰州大学草类植物种子学课程的本科教学为例,从教学内容的优化、研究性教学专题的选择、教学模式的创新、教学方法以及教学考核等角度,系统论述了研究性教学在草类植物种子学教学中的应用;并进一步基于研究性教学在实际应用中可能存在的问题进行了分析和讨论,给出了相应参考建议.

针对青藏高原草地畜牧业生产缺少优良豆科牧草的现状,从国际干旱地区农业研究中心(ICARDA)引进了育种材料,开展了春箭筈豌豆新品种选育.采用单株选择与混合选择相结合的方法,历时12年,育成"兰箭3号"春箭筈豌豆新品种.新品种显著的特性是早熟和种子产量高.在海拔3000 m的甘肃省甘南藏族自治州夏河县,连续多年的测定表明,平均生育期为100 d,生育期范围为92～106 d,平均种子产量为2023 kg·hm-2.比对照品种333/A生育期短13 d,种子产量高174.9％.新品种牧草产量也较高,平均2769 kg·hm-2,与对照品种相近.在陇东黄土高原夏播,作为短期轮作作物,牧草产量达3214 kg·hm-2,比对照品种高14.3％.新品种可作为青藏高原地区的优良豆科牧草品种,也可用作传统农耕区的短期轮作或绿肥作物品种.

Fusarium oxysporum f. sp. medicaginis (Fom) and Rhizoctonia solani (Rs) are the major soil-borne fungal pathogens that pose severe threats to commercial alfalfa production in China. However, the effects of Fom and Rs co-infection on alfalfa and whether co-infection alters disease resistance responses among diverse varieties remain unknown. A collection of 80 alfalfa varieties (Medicago sativa) originated from seven countries were used to study the effects of Fom and Rs co-infection on alfalfa and host resistance responses. The co-infection resulted in more severe disease and reductions in growth and biomass allocation across varieties in comparison with either single infection by Fom or Rs; in addition, root morphology was much more strongly altered by the co-infection. Principal component analysis based on all plant traits showed that varieties under the co-infection were related to the single infection by Rs, being separated from Fom, and hierarchical clustering found differential response patterns among varieties upon co-infection compared with either single infection, with most varieties being highly susceptible to the co-infection. Furthermore, varieties that were most resistant to either single infection were not effective to co-infection, and there was no individual variety with resistance to both pathogens singly and co-infected. This study reveals for the first time that the co-infection by Fom and Rs alters disease resistance responses among diverse alfalfa varieties and provides useful information for developing alfalfa varieties with resistance to the co-occurrence of different soil-borne pathogens.