Species-mixing alters root nutrient acquisition and leaf nutrient conservation strategies in plantation forests

Abstract Leaf nutrient conservation and root nutrient acquisition from soils are two critical mechanisms by which plants sustain their nutrition. Species mixing may affect these two strategies; however, few studies have investigated the changes in both strategies simultaneously, and the less on their associations. Here, we determined leaf nitrogen (N) resorption efficiency (LNRE), leaf phosphorus (P) resorption efficiency (LPRE) and six absorptive root traits of Manchurian ash ( Fraxinus mandshurica , a broad-leaved species) in the pure plantation and mixed-species plantations of Manchurian ash with coniferous species of Dahurian larch ( Larix gmelinii ), Korean pine ( Pinus koraiensis ) and Korean spruce ( Picea koraiensis ), respectively. Our aims were to explore leaf nutrient conservation and root nutrient acquisition strategies, as well as their associations. We found that the LNRE increased under mixing with coniferous species. However, the LPRE in mixed-species plantations was significantly lower than that of the pure Manchurian ash plantation, except when it was mixed with Korean spruce. Compared with the pure plantations, there were no significant differences in root diameter (RD), root tissue density (RTD), root N concentration (RN) and root P concentration (RP) in the mixed-species plantations, while root biomass (RB) and specific root length (SRL) varied with the mixed species. The simple and multiple regression analyses suggested that SRL was the best predictor for LNRE variation, and RTD for LPRE, respectively. The principal component analysis (PCA) showed a multi-dimensional root economic space across the pure and mixed-species plantations, where the root ‘collaboration’ dimension loaded at the first axis, characterized by a negative correlation between SRL and RD. Across the pure and mixed-species plantations, LNRE was not related to root nutrient acquisition strategy, while LPRE decreased with increased ‘outsourcing’ strategy along the ‘collaboration’ dimension of root economics space. Overall, our results suggest that mixing with coniferous species altered leaf nutrient conservation and root nutrient acquisition strategies of Manchurian ash. Specifically, ash tended to produce thicker, denser roots, and to rely more on ‘outsourcing’ nutrient foraging to mycorrhiza, while exhibiting reduced phosphorus resorption in leaves. These findings may deepen our understanding of the nutrient acquisition and conservation strategies of mixed-species plantations at the whole-plant level.