Mycorrhizal identity of neighbouring trees shapes seedling survival and plant–soil feedbacks through trait and light interactions

Abstract Plant–soil feedbacks (PSF) play a central role in determining forest community dynamics, with trees associated with arbuscular mycorrhizal fungi (AMF) often experiencing negative PSFs, while those associated with ectomycorrhizal fungi (EMF) experience positive PSFs. PSFs are driven by the difference between seedling performance in both conspecific and heterospecific soil, and thus the mycorrhizal match or mismatch of the heterospecific soil to the focal seedling could drive PSFs. Furthermore, functional traits and light environments could influence seedling responses. To understand how mycorrhizal type and seedling functional traits influence PSFs, we conducted a greenhouse experiment with five temperate tree species (3 AM, 2 EM) in soils from six adult tree species (3 AM, 3 EM). Seedlings were grown for 12 weeks under three light levels. Mycorrhizal colonization and defence/recovery traits (phenolics, lignin, non‐structural carbohydrates) were assessed at 3 weeks, and survival was measured over 12 weeks. AM seedlings generally experienced negative PSFs, with lower survival in AM‐cultured soils, while EM seedlings had positive PSFs and higher survival in EM soils. However, negative PSFs in AM trees and positive PSFs in EM trees occurred only when the heterospecific tree culturing the soil had a mismatched mycorrhizal type relative to the focal seedling PSFs occurred under all light levels, but their magnitude was strongest at low light, where AM seedlings showed the most negative PSFs and EM seedlings the most positive. Mycorrhizal colonization and functional trait values increased under high light and were often elevated in conspecific soils (with the exception of non‐structural carbohydrates). These enhancements in traits tended to neutralize PSFs in both AM and EM seedlings. Mycorrhizal type match/mismatches between adults and seedlings influenced seedling survivorship and PSFs, likely shaping seedling recruitment patterns and long‐term forest composition, diversity, and resilience. Read the free Plain Language Summary for this article on the Journal blog.