Abstract

Comparing the belowground allocation of assimilated carbon (C) to roots and mycorrhizal fungi across biomes can reveal specific plant nutrient acquisition strategies in ecosystems and allows to predict consequences of environmental changes. Three natural ecosystems (arid shrubland; coastal matorral; humid‐temperate forest) distinct in annual precipitation and vegetation cover and compositions were selected to conduct a 13 CO 2 pulse labeling of natural, woody vegetation to chase the allocation of assimilated C to arbuscular mycorrhiza (AM) and fine roots. Further, nitrogen (N) and phosphorus (P) availability, root traits, root colonization, and the extraradical AM mycelium (PLFA and NLFA 16:1 w5c) were analyzed to evaluate the efficiency of nutrient acquisition strategies. AM fungal colonization decreased with increasing aridity by up to 55% intraradical and by up to 90% extraradical. High root tissue densities and low specific root lengths indicated a slow and resource conservative acquisition by plants in the arid shrubland. Opposite traits and higher root N contents pointed to a fast nutrient acquisition by plants in the semiarid matorral. The expression of abundant acquisitive fine roots, however, comes at the cost of larger C investment, shown by high 13 C incorporation into root tissue by plants in the matorral. High root tissue densities and greater root diameter indicated that plants in the humid-temperate forest followed a resource-conservative strategy and greatly outsource their nutrient acquisition to AM fungi. This outsourcing provides an efficient pathway to compensate the low uptake capacity of thick and dense roots. These ecosystem-specific acquisition strategies and distinct mutualism with AM fungi across the biomes will likely affect the sensitivity of plants to abiotic and biotic stressors and, thus, ecosystem responses to future climatic and environmental changes.