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

FERNÁNDEZ, MARGARITA M.; PÉREZ-MÉNDEZ, NÉSTOR; VAN DOORN, LIZA; FIORONI, FACUNDO; MARTÍNEZ, LUCÍA; EISSENSTAT, DAVID; KAYE, MARGOT; MARRERO, HUGO J.; GARIBALDI, LUCAS A.

Congreso; 2024 ESA Annual Meeting; 2024

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