A new theory of plant-microbe nutrient competition resolves inconsistencies between observations and model predictions

Terrestrial plants assimilate anthropogenic CO2 through photosynthesis and synthesizing new tissues. However, sustaining these processes requires plants to compete with microbes for soil nutrients, which therefore calls for an appropriate understanding and modeling of nutrient competition mechanisms in Earth System Models (ESMs). Here, we survey existing plant-microbe competition theories and their implementations in Earth System Models (ESMs). We found no consensus regarding the representation of nutrient competition and that observational and theoretical support for current implementations are weak. To reconcile this situation, we applied the Equilibrium Chemistry Approximation (ECA) theory to plant-microbe nitrogen competition in a detailed grassland 15N tracer study and found that competition theories in current ESMs fail to capture observed patterns and the ECA prediction simplifies the complex nature of nutrient competition and quantitatively matches the 15N observations. Since plant carbon dynamics are strongly modulated by soil nutrient acquisition, we conclude that (1) predicted nutrient limitation effects on terrestrial carbon accumulation by existing ESMs may be biased and (2) our ECA-based approach may improve predictions by mechanistically representing plant-microbe nutrient competition.

陆地植物可通过光合作用同化人为源二氧化碳，并合成新生组织。然而，维持这些生理过程需要植物与微生物竞争土壤养分，因此有必要在地球系统模型（Earth System Models, ESMs）中合理理解并建模养分竞争机制。本研究综述了现有植物-微生物竞争理论及其在地球系统模型中的实现方案，发现当前关于养分竞争的表征尚未达成共识，且现有实现方案的观测与理论支撑均较为薄弱。为解决这一问题，我们将平衡化学近似（Equilibrium Chemistry Approximation, ECA）理论应用于一项详细的草地15N示踪试验中的植物-微生物氮竞争研究，结果显示：当前地球系统模型中的竞争理论无法重现观测到的养分动态模式，而平衡化学近似的预测结果简化了养分竞争的复杂本质，并定量吻合15N观测结果。鉴于植物碳动态受土壤养分获取强烈调控，我们得出两点结论：（1）现有地球系统模型对养分限制影响陆地碳固存的预测可能存在偏差；（2）我们基于平衡化学近似的方法可通过从机理上表征植物-微生物养分竞争，改善相关预测效果。