COS 61-6 - Model-data integration of belowground function in tropical forests: Exploring root strategies for nutrient and water acquisition in highly diverse ecosystems

Abstract: Field ecologists recognize the importance of fine roots as the interface between plants and soil that can influence higher order ecosystem processes through biogeochemistry (carbon and nutrient cycling) and biogeophysical processes (water and energy fluxes). Hence, it seems clear that fine-root traits and functions should be included in ecosystem and Earth system models, but the scarcity of relevant root data and conceptual understanding has hindered integration of root function into models. Including fine-root traits and function in models of tropical forests presents some unique challenges. Tropical forests have the highest diversity in root morphological traits globally, and root dynamics and strategies respond to unique moisture fluctuations and nutrient conditions compared with most temperate forests, which have framed most modeling efforts.
Our goal has been to summarize the current knowledge of tropical root traits and function and suggest ways forward to advance their inclusion in models. We organize around three unique aspects of tropical forests that are particularly challenging for making model-data connections: the high plant diversity of tropical forests, responses to seasonal moisture variation, and nutrient dynamics driving root function in strongly weathered tropical soils.
Traditional modeling approaches for aboveground plant functional types are not directly relevant for representing root function in diverse tropical forests. We suggest using fine-root morphological and structural traits to create belowground plant functional types so that tropical forest trait variation and flexibility in their responses to intermittent water and nutrient scarcity can be better characterized in models. This effort must start with empirical understanding of how root trait syndromes relate to both water and nutrient acquisition, and their scales of variation. Assessing root function across tropical moisture gradients and manipulations could help us model dynamic root responses to changing climate. Strongly-weathered soils underlay the majority of moist and wet tropical forests, where fine roots have unique sets of strategies to acquire phosphorus or tolerate phosphorus scarcity. In tropical forests, water and nutrient availability are often separated in space and time, but not always, and many root traits are utilized for both water or nutrient uptake.
A frontier in ecosystem modeling is to bring together recent advances in soil hydrology, plant hydraulics, and plant nutrition modules under a coupled framework. Balanced teams of ecosystem modelers and tropical field ecologists to co-design and analyze experiments and observations are needed to tackle the above challenges.