Relationship between root water uptake and soil respiration: A modeling perspective

• Published in: Journal of geophysical research. Biogeosciences 2017-08, Vol.122 (8), p.1954-1968
• Main Authors: Teodosio, Bertrand, Pauwels, Valentijn R. N., Loheide, Steven P., Daly, Edoardo
• Format: Article
• Language: English
• Subjects: Carbon dioxide; Compensation; Computer simulation; Dynamics; Efflux; Estimation; Formulations; Groundwater table; Heat transfer; hydraulic redistribution; Mathematical models; Modelling; Moisture content; Rescaling; Richards equation; root water compensation; root water uptake; Scaling; Shallow water; Soil; soil carbon efflux; Soil dynamics; Soil moisture; soil respiration; Soil stresses; Soil surfaces; Soil water; Transpiration; Uptake; Vertical distribution; Vertical profiles; Water content; Water flow; Water potential; Water stress; Water table; Water uptake; Xylem
• ISSN: 2169-8953; 2169-8961
• DOI: 10.1002/2017JG003831

Soil moisture affects and is affected by root water uptake and at the same time drives soil CO2 dynamics. Selecting root water uptake formulations in models is important since this affects the estimation of actual transpiration and soil CO2 efflux. This study aims to compare different models combining the Richards equation for soil water flow to equations describing heat transfer and air‐phase CO2 production and flow. A root water uptake model (RWC), accounting only for root water compensation by rescaling water uptake rates across the vertical profile, was compared to a model (XWP) estimating water uptake as a function of the difference between soil and root xylem water potential; the latter model can account for both compensation (XWPRWC) and hydraulic redistribution (XWPHR). Models were compared in a scenario with a shallow water table, where the formulation of root water uptake plays an important role in modeling daily patterns and magnitudes of transpiration rates and CO2 efflux. Model simulations for this scenario indicated up to 20% difference in the estimated water that transpired over 50 days and up to 14% difference in carbon emitted from the soil. The models showed reduction of transpiration rates associated with water stress affecting soil CO2 efflux, with magnitudes of soil CO2 efflux being larger for the XWPHR model in wet conditions and for the RWC model as the soil dried down. The study shows the importance of choosing root water uptake models not only for estimating transpiration but also for other processes controlled by soil water content. Key Points A comparison of three root water uptake (RWU) models accounting for root water compensation and hydraulic redistribution was performed RWU models drive the vertical distribution of soil moisture affecting modeled soil CO2 dynamics and CO2 efflux from the soil surface Differences between models for the studied scenario were up to 20% for total transpiration and 14% for the soil CO2 efflux in 50 days