Sensitivity of four ecological models to adjustments in fine root turnover rate

Abstract

A B S T R A C TLarge uncertainties surrounding root-specific parameters limit model descriptions of belowground processes and ultimately hinder understanding of belowground carbon (C) dynamics and terrestrial biogeochemistry. Despite this recognized shortcoming, it is unclear which processes warrant attention in model development, given the computational cost of additional model complexity. Here, we tested the sensitivity of four models to adjustments in fine root turnover in forested systems: CENTURY, ED2, MC1, and LANDCARB. In general, faster root turnover rates resulted in lower total system carbon (C) and within model changes ranged from 1% to 38% following 100-year simulations. However, the underlying mechanisms driving these changes differed among models as some expressed lower net primary productivity (NPP) with faster turnover rates and others had similar NPP but large shifts in C allocation away from wood to fine roots. Based on these findings we expect that different model responses to changes in fine root turnover will be determined by (1) whether C is allocated to fine roots as fixed portion of NPP or to maintain a fixed biomass ratio between fine roots and leaves or stems and (2) whether soil nutrient and water uptake is a function of both resource availability and fine root biomass or based on resource availability alone. These results suggest that better constrained estimates of fine root turnover will represent a valuable improvement in many terrestrial biosphere models.

Underestimation of boreal soil carbon stocks by mathematical soil carbon models linked to soil nutrient status

“…A higher amount of more recalcitrant fine roots compared to more labile leaves (Xia et al, 2015) heavily increased the soil carbon sequestration in CENTURY model simulations, which was in line with McCormack et al (2015). Though, the contribution of fine roots to SOC stabilization is still not settled due to the significant role of mycorrhizal fungi in SOC accumulation (Averill et al, 2014;Orwin et al, 2011).…”

Evaluating CENTURY and Yasso soil carbon models for CO2 emissions and organic carbon stocks of boreal forest soil with Bayesian multi‐model inference

“…The exponential temperature function used by Kelly et al () resulted in smaller summer CO 2 emissions and larger SOC than that of the Gaussian function of Adair et al (). Although CENTURY has been found to be sensitive to litter input from the fine roots (McCormack et al, ), its SOC did not increase abruptly after trenching. The difference in CENTURY SOC development after trenching was a result of more gradual litter transfer between the carbon pools than for the Yasso07 and Yasso15 models.…”

Modelling fine root biomass of boreal tree stands using site and stand variables

“…Fine roots represent one of the largest litter inputs to the soil, especially in boreal forests (Vogt et al, 1986;Lehtonen, 2005;Clemmensen et al, 2013;Leppälammi-Kujansuu et al, 2014;Ojanen et al, 2014). Unfortunately, the quantity of fine roots and their lifespan are poorly known (Brunner et al, 2013) compared to aboveground compartments, and this may lead to severe uncertainties in ecosystem simulation models and C budget estimates (Peltoniemi et al, 2006;Strand et al, 2008;Smithwick et al, 2014;McCormack et al, 2015a). In order to estimate litter input from fine roots to soil, it is necessary to estimate both the quantity and the lifespan of fine roots; in this study we improve the fine root quantity estimation.…”