Soil organic carbon stability in forests: Distinct effects of tree species identity and traits

Abstract

Rising atmospheric CO2 concentrations have increased interest in the potential for forest ecosystems and soils to act as carbon (C) sinks. While soil organic C contents often vary with tree species identity, little is known about if, and how, tree species influence the stability of C in soil. Using a 40 year old common garden experiment with replicated plots of eleven temperate tree species, we investigated relationships between soil organic matter (SOM) stability in mineral soils and 17 ecological factors (including tree tissue chemistry, magnitude of organic matter inputs to the soil and their turnover, microbial community descriptors, and soil physicochemical properties). We measured five SOM stability indices, including heterotrophic respiration, C in aggregate occluded particulate organic matter (POM) and mineral associated SOM, and bulk SOM δ15N and ∆14C. The stability of SOM varied substantially among tree species, and this variability was independent of the amount of organic C in soils. Thus, when considering forest soils as C sinks, the stability of C stocks must be considered in addition to their size. Further, our results suggest tree species regulate soil C stability via the composition of their tissues, especially roots. Stability of SOM appeared to be greater (as indicated by higher δ15N and reduced respiration) beneath species with higher concentrations of nitrogen and lower amounts of acid insoluble compounds in their roots, while SOM stability appeared to be lower (as indicated by higher respiration and lower proportions of C in aggregate occluded POM) beneath species with higher tissue calcium contents. The proportion of C in mineral associated SOM and bulk soil ∆14C, though, were negligibly dependent on tree species traits, likely reflecting an insensitivity of some SOM pools to decadal scale shifts in ecological factors. Strategies aiming to increase soil C stocks may thus focus on particulate C pools, which can more easily be manipulated and are most sensitive to climate change.

The linkage of 13C and 15N soil depth gradients with C:N and O:C stoichiometry reveals tree species effects on organic matter turnover in soil

“…In contrast to the d 13 C depth gradients, d 15 N increased consistently throughout the soil profile following a curve that is typical for N-limited forest ecosystems dominated by EM fungi (Hobbie and Ouimette 2009). The clearly higher d 15 N values under beech and Douglas fir compared to oak and pine are in accordance with observations made in a common garden experiment in Poland (Angst et al 2019). With increasing depth and ongoing decomposition, SOM becomes preferentially 15 N-enriched due to microbial activity coupled with an increasing proportion of 15 Nenriched microbial derived compounds (Lerch et al 2011).…”

Forest Management and Climate Change Mitigation: A Review on Carbon Cycle Flow Models for the Sustainability of Resources

“…Conflicts of interest may arise between carbon fixation and other forest functions. These may have different characteristics, and they have been previously described by several authors as follows [55,56]: Applying a management model that can balance these conflicts requires grounded knowledge of the reactions of forests to different forestry options. The further elimination of greenhouse gases from the atmosphere by increasing forests as sinks can be considered a short-term goal.…”

Can Carbon Sequestration in Tasmanian “Wet” Eucalypt Forests Be Used to Mitigate Climate Change? Forest Succession, the Buffering Effects of Soils, and Landscape Processes Must Be Taken into Account

“…is subsoil difference may reflect different SOM stabilisation mechanisms in subsoils under the two forest types, as observed in forests elsewhere [54] and in agricultural systems [55]. In the uppermost (A1) horizon at Eleven Road under mixed forest, most C was held in the oPOM<20 fraction, but under rainforest, most was held in the clay fraction.…”