From roots to leaves: multifunctional outcomes of nutrient enrichment in Patagonian woodlands

FERNANDEZ, MARGARITA; PÉREZ-MENDEZ, NÉSTOR; VAN DOORN, LIZA; FIORONI, FACUNDO; MARTÍNEZ, LUCÍA C.; EISSENSTAT, DAVID; KAYE, MARGOT; MARRERO, HUGO; GARIBALDI, LUCAS A.

Conferencia; ESA 2024 Annual meeting; 2024

Nutrient enrichment disrupts plant-animal interactions and ecosystem functioning globally. Yet, the mechanisms of bottom-up turnover on root symbiosis and trophic cascades remain understudied in woodlands. Here, we performed a full-factorial field experiment to evaluate the interactive effects of nutrient addition (nitrogen, phosphorus, and/or potassium) on several ecosystem components and functions of Patagonian woodlands. While N is expected to increase primary productivity in temperate areas, its interaction with other nutrients could drive antagonistic responses at different trophic levels in the mid-long term. We studied root symbiosis and herbivory response using two species with contrasting functional traits: Berberis microphylla (understory evergreen shrub) and Nothofagus antarctica (deciduous tree). We tested the relative importance of litter quality and soil nutrient conditions after fertilization on litter decomposition by microarthropods using a litterbag experiment with N. antarctica litter. Using generalized mixed effects models, we tested the effect of nutrient addition on root symbiosis, foliar traits, decomposition rates, herbivory frequency, and soil biota community structure. Nutrient addition selectively disrupted ecological interactions and decreased diversity at different trophic levels. We observed that N and P addition reduced root colonization by arbuscular mycorrhizas on B. microphylla and colonization by ectomycorrhiza on N. antarctica roots. K addition decreased ectomycorrhiza colonization and contributed to the loss of morphotypes. Similarly, adding N and P decreased the evenness of detritivore and fungivore microarthropods important for litter decomposition. The role of changes in foliar traits after nutrient addition was contrasting for herbivory and decomposition. After two and six years, N and P foliar concentrations increased significantly. We observed a 41% decrease in insect herbivory in the evergreen species when we added N, potentially mediated by leaf size and leaf density changes. However, K addition diluted the effect of N. On the contrary, we observed increased herbivory frequency in the deciduous species by adding all nutrients. While litter quality and foliar traits significantly impacted herbivory, microsite nutrient availability changes were more important for litter decomposition. In general, recalcitrant litter in unfertilized conditions decomposed faster, but N and P addition suppressed decomposition by microarthropods. Our results prove that managing soil nutrient availability is relevant for ecological interaction and ecosystem services provision in Patagonian woodlands. Effective strategies for sustainable management and resilience to global change stressors in Patagonia should consider community-level changes. Further understanding of the relationship between multitrophic biodiversity and ecosystem service provision under nutrient enrichment is needed for sustainable management.