Abstract:

Background & Aims: Plant photosynthetic products enter soil primarily through litter and root inputs, providing material and energy for belowground food webs. As a key component of soil biodiversity, protists play a crucial role in microbial regulation. However, the effects and mechanisms of litter and root inputs on the structure and diversity of soil protist communities remain unclear. 

Method: Based on a six-and-a-half-year resource manipulation experiment including litter removal and root deprivation at the Baotianman Forest Ecosystem Research Station, eDNA metabarcoding was used to analyze the responses of four protist functional groups (bacterivores, eukaryvores, omnivores, and detritivores) to changes in plant resource inputs. 

Results: Litter removal significantly reduced the richness of all protist functional groups, with declines ranging from 33.7% to 47.7% (P < 0.05). Litter removal exerted strong bottom-up negative effects on richness of protists by reducing bacterial and fungal richness. Specifically, bacterivores and eukaryvores were primarily associated with declines in bacterial richness, detritivores were mainly linked to reductions in fungal richness, whereas omnivores were jointly driven by decreases in both bacterial and fungal richness. The effects of root deprivation were relatively weaker, and the impacts of the two root resource types differed markedly among protist functional groups. Tree root deprivation exerted direct negative effects on the richness of multiple protist groups (except detritivores), while indirectly exerting positive effects on eukaryvores and detritivores by increasing soil moisture. By comparison, shrub root deprivation mainly promoted fungal richness, thereby indirectly exerting positive effects on omnivores and detritivores. Litter and root resources jointly regulate soil protist diversity through distinct pathways, and the differential responses of protist functional groups to these two plant resource inputs are closely linked to their contrasting effects on soil properties and microbial resources. 

Conclusions: These findings reveal the diverse responses of protists to changes in plant resource inputs and highlight their crucial roles in linking aboveground and belowground processes, maintaining micro-food web stability, thereby providing new insights into the functional mechanisms of protists in soil ecosystems.

Key words: DIRT, functional groups of protists, environmental DNA, soil foodweb, warm temperate deciduous broad leaved forest