Controls on Soil Organic Carbon Partitioning and Stabilization in the California Sierra Nevada

Abstract

There is a critical need to quantify the role of soil mineral composition on organic carbon (C) stabilization in forest soils. Here, we address this need by studying a matrix of forest ecosystems and soil parent materials with the objective of quantifying controls on the physical partitioning and residence time of soil organic carbon. We sampled soil profiles across a climate gradient on the western slope of the California Sierra Nevada, focusing on three distinct forest ecosystems dominated by ponderosa pine, white fir, or red fir, on three igneous parent materials that included granite, andesite, and basalt. Results indicated that short-range order mineral phases were the dominant factors accounting for the variation in soil carbon content and residence time. The results further suggested an interaction between ecosystem fire regime and the degree of soil weathering on the partitioning, chemical composition, and residence time of C in density separated soil physical fractions. These results suggest a link between the degree of soil weathering and C storage capacity, with a greater divergence in storage capacity and residence time in the Inceptisols, Entisols, and Andisols of the white fir and red fir ecosystems relative to minimal variation in the highly weathered Ultisols and Alfisols of the ponderosa pine ecosystem.

Rock weathering controls the potential for soil carbon storage at a continental scale

“…Local studies have shown that PCMs are correlated with SOC stocks across soils of different ages, climates, and parent materials (Dahlgren et al 1997;Torn et al 1997;Chadwick et al 2003;Masiello et al 2004;Heckman et al 2009;Rasmussen et al 2018b). More expansive, continental scale data syntheses indicate that PCMs play a major role in SOC storage in humid climates (Rasmussen et al 2018a;Kramer and Chadwick 2018;von Fromm et al 2020).…”

“…Studies of soil age gradients show that PCMs accumulate during the initial stages of weathering and then decline as primary minerals (e.g., feldspars) are exhausted and PCMs ripen into less reactive crystalline secondary minerals (e.g., phyllosilicate clays) (Torn et al 1997;Masiello et al 2004;Garcia Arredondo et al 2019). Across rock types, PCMs are most abundant in soils formed from volcanic parent materials rich in feldspars and glass with feldspar-like composition (Heckman et al 2009;Rasmussen et al 2018b). Furthermore, studies of climate gradients show that PCMs are most abundant in humid climates, where the potential for weathering is highest (Dahlgren et al 1997;Chadwick et al 2003).…”

“…Based on this simple set of relationships, PCMs should be most abundant where primary mineral weathering is actively occurring-and by implication, it is in these environments that PCMs have the greatest potential to influence soil carbon storage (Wang et al 2018;Rasmussen et al 2018b). Notably, this relationship emphasizes the weathering rate as the proximate control on PCM stocks, rather than the weathering state (i.e., time integrated loss of elements or minerals).…”

How will a drier climate change carbon sequestration in soils of the deciduous forests of Central Europe?

“…The change in litter quality due to the drier climate can also affect the speed of litter decomposition (Santonja et al 2015). This transient increase in soil C storage from tree mortality is expected to be mostly particulate, plant-derived C, rather than mineral-associated organic matter (MAOM), which is determined both by mineralogy and climate as well as detrital inputs (Rasmussen et al 2018). Certainly, maximum soil C storage capacity will change as new equilibrium levels develop, and in forests, these new equilibrium levels might take decades or centuries to form, given the longevity of trees and rates of response to a slowly changing climate.…”

Soil organic carbon is not just for soil scientists: measurement recommendations for diverse practitioners

“…Clay mineral composition is highly correlated with SOC content at broad scales (Poeplau et al 2015), a feature incorporated into SOC modeling efforts (Sulman et al 2014). However, other studies have suggested that specific clay minerals might be more explanatory of SOC stabilization (Percival et al 2000, Sanderman et al 2014, Yeasmin et al 2017, Rasmussen et al 2018 b ), and that the type of mineral present in a given environment may determine the availability of mineral‐associated organic matter to biological degradation (Mikutta et al 2007). In particular, the influence of short‐range order (SRO) Fe‐ and Al‐oxides and (oxy)hydroxides (largely ferrihydrite and nano‐crystalline goethite, allophane, imogolite, proto‐imogolite, and amorphous gibbsite) on the total amount, resilience, and molecular structure of soil organic matter has been observed in many studies (Torn et al 1997, Masiello et al 2004, Rasmussen et al 2005, Hernández et al 2012, Hall and Silver 2015, Coward et al 2017, Rasmussen et al 2018 a ).…”