Date from: Mycorrhizal identity of neighboring trees shapes seedling survival and plant-soil feedbacks through trait and light interactions

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) experiencing positive PSFs. PSFs are driven by
the difference between seedling performance in both con- and hetero-
specific 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 (three AM, two EM) in soils from six adult tree
species (three AM, three EM). Seedlings were grown for 12 weeks under
three light levels. Mycorrhizal colonization and defense/recovery traits
(phenolics, lignin, nonstructural carbohydrates) were assessed at three
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.