Fine‐root turnover patterns and their relationship to root diameter and soil depth in a ¹⁴C‐labeled hardwood forest

Abstract

Summary• Characterization of turnover times of fine roots is essential to understanding patterns of carbon allocation in plants and describing forest C cycling. We used the rate of decline in the ratio of 14 C to 12 C in a mature hardwood forest, enriched by an inadvertent 14 C pulse, to investigate fine-root turnover and its relationship with fine-root diameter and soil depth.• Biomass and ∆ 14 C values were determined for fine roots collected during three consecutive winters from four sites, by depth, diameter size classes ( < 0.5 or 0.5 -2 mm), and live-or-dead status.• Live-root pools retained significant 14 C enrichment over 3 yr, demonstrating a mean turnover time on the order of years. However, elevated ∆ 14 C values in dead-root pools within 18 months of the pulse indicated an additional component of live roots with short turnover times (months). Our results challenge assumptions of a single live fine-root pool with a unimodal and normal age distribution.• Live fine roots < 0.5 mm and those near the surface, especially those in the O horizon, had more rapid turnover than 0.5 -2 mm roots and deeper roots, respectively.

High organic inputs explain shallow and deep SOC storage in a long-term agroforestry system – combining experimental and modeling approaches

“…This could be linked to an overestimation of C input from tree fine root mortality. Indeed, a constant root turnover was considered along the soil profile, but several authors reported a decrease in the root turnover with increasing soil depth (Germon et al, 2016;Hendrick and Pregitzer, 1996;Joslin et al, 2006). However, the sensitivity analysis showed that the model was not sensitive to this parameter (Fig.…”

The decomposition of ectomycorrhizal fungal necromass

“…Thus, there is potential for a species' litter decomposition to be controlled largely by location in the soil profile. For example, there are slower turnover and decomposition rates of root litter at deeper depths in the soil profile (Gill and Burke, 2002;Joslin et al, 2006;McCormack et al, 2010). Recently, Schweigert et al (2015) traced the fate of 13 C-labeled Laccaria bicolor biomass amendments in an in vitro soil bioreactor experiment.…”

The effect of vertically resolved soil biogeochemistry and alternate soil C and N models on C dynamics of CLM4

“…CLM4 calculates root distributions for plant water uptake based on a double-exponential function (Zeng, 2001); in principle, however, the vertical profiles of root C and N inputs to soil need not be identical to those of plant water uptake from soil due to differing root lifetimes (Joslin et al, 2006;Riley et al, 2009) for different types of roots. Thus, one hypothesis is that C inputs are proportional to the root profiles used in the water uptake calculations.…”

“…Because of the dependence of soil heterotrophic respiration and the resulting CO 2 release on environmental conditions, climate change may lead to potentially large positive feedbacks with the atmosphere (Jenkinson et al, 1991). The current generation of coupled carbon-climate models have high uncertainty in the magnitude of carbon cycle feedbacks (Friedlingstein et al, 2006;Arora et al, 2013), and a dominant source of this uncertainty is associated with SOM sensitivity to environmental change (Jones et al, 2003). In addition to a direct role in the global C cycle through SOM decomposition and CO 2 production, SOM plays a crucial role in soil nutrient feedbacks -in particular, C-N couplings -because decomposing SOM provides mineralized N for vegetation growth.…”