Beyond N and P fertilization: Tropical ground hexapod communities are tied to micronutrients

Human-induced inputs of nitrogen (N) and phosphorous (P) disrupt global biogeochemical cycles and life itself. And yet there is no consensus on whether micro- or macronutrients are the main drivers of soil community assemblages. Tropical forests allow us to trace the response of nutrients on highly weathered soils, where previous studies have already shown N and P limitation. To address this, we conducted an N, P and NP field fertilization experiment in two French Guiana tropical rainforests (the Nouragues and Paracou forests) to study the response of metabarcoded ground-dwelling Hexapoda communities to macronutrients, while also assessing the impact of micronutrient availability (calcium (Ca), potassium (K), magnesium (Mg) and sodium (Na)). We assessed the importance of these nutrients through their impact on the abundance, richness, and composition of ground hexapod communities using linear models, canonical correlation analyses and analyses of variance. Our findings revealed that experimental fertilization with nitrogen and/or phosphorous did not drive ground hexapod community structure. In contrast, Ca, Mg and Na were positively associated with hexapod abundance. Ca, K and Mg positively correlated with OTU richness. And Ca and Na shaped community composition. Our results argue against the widespread assumption that macronutrient imbalances drive ground-dwelling hexapods, and we suggest that micronutrients need much more attention to properly assess the impact of nutrient imbalances and excessive fertilization in soils.