Data from: Endophytic-insect parasitic fungi translocate nitrogen directly from insects to plants

Most plants obtain nitrogen through nitrogen-fixing bacteria and microbial decomposition of plant and animal material. Most vascular plants are able to form close symbiotic associations with endophytic fungi. Metarhizium is a common plant endophyte found in a large number of ecosystems. This abundant soil fungus is also a pathogen to a large number of insects, a source of nitrogen. It is possible that endophytic capability and insect pathogenicity of Metarhizium are coupled to provide an active method of nitrogen transfer to plant hosts via fungal mycelia. In this study we used soil microcosms to test the ability of M. robertsii to translocate insect-derived nitrogen to plants. Insects were injected with 15N-labelled nitrogen, and we tracked the incorporation of 15N into amino acids in two plant species, haricot bean (Phaseolus vulgaris) and switchgrass (Panicum virgatum), in the presence of M. robertsii. These findings are evidence that active nitrogen acquisition by plants in this tripartite interaction may play a larger role in soil nitrogen cycling than previously thought.

绝大多数植物可通过固氮菌（nitrogen-fixing bacteria）以及动植物残体的微生物分解作用获取氮素。多数维管植物（vascular plants）能够与内生真菌（endophytic fungi）建立紧密的共生关联。绿僵菌（Metarhizium）是一类广泛分布于多种生态系统中的常见植物内生真菌，这类分布广泛的土壤真菌同时也是多种昆虫的病原菌，而昆虫本身是重要的氮素来源。绿僵菌的内生定殖能力与昆虫致病活性可能存在耦合机制，可通过真菌菌丝体（mycelia）向植物宿主主动转运氮素。本研究借助土壤微宇宙（soil microcosms）体系，检验了罗伯茨绿僵菌（Metarhizium robertsii，简称M. robertsii）将昆虫来源的氮素转运至植物的能力。实验中，研究人员向昆虫体内注射15N标记氮（15N-labelled nitrogen），并追踪了在罗伯茨绿僵菌存在的条件下，菜豆（haricot bean，学名Phaseolus vulgaris）与柳枝稷（switchgrass，学名Panicum virgatum）两种植物体内氨基酸（amino acids）对15N的掺入情况。本研究结果证实，在这类三方互作（tripartite interaction）中，植物主动获取氮素的过程在土壤氮循环（soil nitrogen cycling）中所发挥的作用可能远超此前的认知。