Biogeochemical models do not agree on a conceptual model of plant root nutrient acquisition, leading to large uncertainty in predicted biogeochemical-climate feedbacks. We reviewed plant and soil biogeochemical processes that affect uptake, surveyed relevant measurements, and analyzed three common modeling paradigms: relative-demand, thermodynamic flux-force, and capacity-based. Our results can inform the next generation of land models.
Our review shows that (1) plant photosynthesis and root nutrient acquisition are intrinsically asynchronous because of the physical and biological constraints imposed on plant carbon and nutrient use; (2) plant root nutrient acquisition can occur in the absence of photosynthesis and is a strong function of soil biogeochemistry; and (3) the capacity-based approach is best at integrating the essential biogeochemical processes identified in this review. Our review points out a clear pathway to improve nutrient cycle representations in terrestrial biogeochemical models.
Nutrient dynamics exert a strong control on ecosystem biogeochemistry and feedbacks with the climate. However, modelers have not agreed upon what conceptual approaches should be used to represent plant root nutrient acquisition. We analyzed three modeling paradigms of plant root nutrient acquisition and compared them against known plant biogeochemical principles and observed plant nutrient acquisition patterns. We found that the capacity-based approach best mechanistically accounts for the asynchrony between plant photosynthesis and plant root nutrient acquisition and for plant-soil-microbial nutrient interactions. We also recommend more empirical measurements of nutrient acquisition dynamics in different ecosystem types to develop more accurate model representations of these complex processes.