Brown meets green: light and nutrients alter detritivore assimilation of microbial nutrients from leaf litter

Abstract

In aquatic detrital‐based food webs, research suggests that autotroph‐heterotroph microbial interactions exert bottom‐up controls on energy and nutrient transfer. To address this emerging topic, we investigated microbial responses to nutrient and light treatments during Liriodendron tulipifera litter decomposition and fed litter to the caddisfly larvae Pycnopsyche sp. We measured litter‐associated algal, fungal, and bacterial biomass and production. Microbes were also labeled with 14C and 33P to trace distinct microbial carbon (C) and phosphorus (P) supporting Pycnopsyche assimilation and incorporation (growth). Litter‐associated algal and fungal production rates additively increased with higher nutrient and light availability. Incorporation of microbial P did not differ across diets, except for higher incorporation efficiency of slower‐turnover P on low‐nutrient, shaded litter. On average, Pycnopsyche assimilated fungal C more efficiently than bacterial or algal C, and Pycnopsyche incorporated bacterial C more efficiently than algal or fungal C. Due to high litter fungal biomass, fungi supported 89.6–93.1% of Pycnopsyche C growth, compared to 0.2% to 3.6% supported by bacteria or algae. Overall, Pycnopsyche incorporated the most C in high nutrient and shaded litter. Our findings affirm others' regarding autotroph‐heterotroph microbial interactions and extend into the trophic transfer of microbial energy and nutrients through detrital food webs.

Detritivore physiology and growth benefit from algal presence during microbial leaf colonization

“…The presence of leaf‐associated aquatic hyphomycetes (a polyphyletic group of fungi), acts as the “peanut butter on the cracker” for detritivores (sensu Cummins 1974). These fungi enhance the nutrient content, are more readily assimilated than other microbes (Price et al 2021) and improve the fatty acid (FA) content (Arce Funck et al 2015) of the leaves, making it a food source of higher quality for detritivores.…”