Soil microbes alter plant fitness under competition and drought

Plants exist across varying biotic and abiotic environments, including variation in the composition of soil microbial communities. The ecological effects of soil microbes on plant communities are well known, whereas less is known about their importance for plant evolutionary processes. In particular, the net effects of soil microbes on plant fitness may vary across environmental contexts and among plant genotypes, setting the stage for microbially mediated plant evolution. Here we assess the effects of soil microbes on plant fitness and natural selection on flowering time in different environments. We performed two experiments in which we grew Arabidopsis thaliana genotypes replicated in either live or sterilized soil microbial treatments, and across varying levels of either competition (isolation, intraspecific competition, or interspecific competition) or watering (well-watered or drought). We found large effects of competition and watering on plant fitness as well as the expression and natural selection of flowering time. Soil microbes increased average plant fitness under interspecific competition and drought, and shaped the response of individual plant genotypes to drought. Finally, plant tolerance to either competition or drought was uncorrelated between soil microbial treatments suggesting that the plant traits favoured under environmental stress may depend on the presence of soil microbes. In summary, our experiments demonstrate that soil microbes can have large effects on plant fitness, which depend on both the environment and individual plant genotype. Future work in natural systems is needed for a complete understanding of the evolutionary importance of interactions between plants and soil microorganisms.

植物广泛分布于多样的生物与非生物环境中，其中也涵盖土壤微生物群落组成的差异。土壤微生物对植物群落的生态效应已被广泛阐明，但人们对其在植物演化过程中的重要性却知之甚少。具体而言，土壤微生物对植物适合度（plant fitness）的净效应可能随环境背景与植物基因型的不同而发生变化，从而为微生物介导的植物演化奠定了基础。本研究旨在探究不同环境下土壤微生物对植物适合度以及开花时间自然选择的影响。本研究开展了两组实验：将拟南芥（Arabidopsis thaliana）不同基因型的植株分别置于活土壤微生物与灭菌土壤微生物处理组中培养，并设置不同梯度的竞争条件（隔离、种内竞争或种间竞争）或水分条件（正常浇水或干旱胁迫）。研究结果显示，竞争与水分条件对植物适合度以及开花时间的表达与自然选择均存在显著影响。土壤微生物可在种间竞争与干旱胁迫条件下提升植株的平均适合度，并调控不同植物基因型对干旱的响应。最后，不同土壤微生物处理组间，植物对竞争或干旱的耐受性并无相关性，这表明环境胁迫下植物的优势性状可能依赖于土壤微生物的存在。综上，本研究实验证实土壤微生物对植物适合度存在显著影响，且这种影响同时依赖于环境条件与植物个体基因型。未来需在自然生态系统中开展相关研究，以全面阐明植物与土壤微生物互作的演化重要性。