Global variation of plant nitrogen acquisition strategies and their responses to decreasing nitrogen availability.

Abstract

Plants employ three N acquisition strategies to support productivity: root uptake from soils, symbiotic fixation, and resorption from senescing leaves. However, their global variation and coordination remain poorly understood. Here, we compile 3,193 field observations and use machine learning to map the three strategies and quantify their relative contributions. We estimate that global nitrogen uptake, fixation, and resorption amount to 559.2 ± 56.5 (mean ± standard deviation), 125.5 ± 7.2, and 279.3 ± 5.0 Tg N yr^-1, respectively, representing 58%, 13%, and 29% of total plant N acquisition. Their global variations are primarily determined by temperature and water conditions. Nitrogen uptake dominates globally, especially in warm, humid low-latitude regions, while resorption is more prevalent in arid and cold environments. In contrast, fixation contributes relatively little, with some hotspots in tropical regions and northern high latitudes. Notably, we find significant shifts in N acquisition strategies-from uptake to fixation and resorption-along gradients of decreasing nitrogen availability. These results suggest a spatially coordinated adjustment of plant nitrogen acquisition strategies in response to changing N conditions and offer insights into how coordinated nitrogen strategies shape terrestrial nitrogen cycling and its coupling with the carbon sink.