Nitrogen deposition and decreased precipitation altered nutrient foraging strategies of three temperate trees by affecting root and mycorrhizal traits

Abstract

Roots of nearly all plants have symbiotic relationships with mycorrhizal fungi. The root-mycorhizosphere serves an important role in both nutrient acquisition required for the plant growth, and soil carbon cycling of terrestrial ecosystems. The identification of root-mycorhizosphere traits that can be linked to nutrient acquisition is quite indispensable, especially for understanding and predicting plants nutrient acquisition strategies and ecosystem processes under climate change. Nonetheless, tree roots and mycorrhizal fungi traits variations are still rarely quantified synchronously in previous studies, which lead to an important knowledge gap in our understanding of how climate change will affect nutrient foraging strategies and soil carbon cycling. Thus, we conducted a decreased precipitation and N addition experiment to simulate climate change scenarios. Traits of root orders and mycorrhizal fungi that related to nutrient foraging were examined under different treatments across three coexisting mycorrhizal temperate tree species. N addition significantly increased individual root length, individual root surface area and mean root diameter in low root orders (the first root order or the first to third root orders), while it decreased or did not change these traits in high root orders (the fourth and fifth root orders). N addition tended to decrease branching intensity in all root orders across all species. Decreased precipitation significantly increased individual root length and individual root surface area of low order roots (the first and second root orders), while decreased or unchanged these traits in others root orders across all species. Specific root length was significantly increased in the first to fifth root orders with decreased precipitation and decreased in the second to fifth root orders with N addition (except Pinus koraiensis). Moreover, N addition significantly decreased total hyphae length, and significantly increased the mean hyphae diameter. Decreased precipitation significantly increased the total hyphae length and the total hyphae surface area compared with the control. Across all species, N addition, decreased precipitation and their interaction led to significantly decreased mycorrhizal colonization. The impacts of N addition and decreased precipitation on mycorrhizal fungi traits also were mediated by tree species. These results indicated that N addition and decreased precipitation significantly changed fine root and mycorrhizal morphological traits, which would alter the below-ground foraging strategies. These results indicate that the variation in root morphology by order under treatments suggests that roots at different branch order positions have different morphological structure and physiological functions. The trait patterns we found support the hypothesis that under climate change, plants attempt to improve resource acquisition.