Climatic and Geochemical Controls on Soil Carbon at the Continental Scale: Interactions and Thresholds. Issue 3 (26th March 2021)

• Record Type: Journal Article
• Authors: Yu, Wenjuan; Weintraub, Samantha R.; Hall, Steven J.
• Is Part Of: Global biogeochemical cycles. Volume 35:Issue 3(2021)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2021-03-26
• Subjects: climate -- National Ecological Observatory Network (NEON) -- poorly crystalline mineral -- soil geochemistry -- soil organic carbon -- subsoil; Biogeochemical cycles -- Periodicals; Electronic journals; 577.1405
• DOI: 10.1029/2020GB006781
• Languages: English
• ISSNs: 0886-6236

Abstract

Abstract: Previous studies found conflicting results on the importance of temperature and precipitation versus geochemical variables for predicting soil organic carbon (SOC) concentrations and trends with depth, and most utilized linear statistical models. To reconcile the controversy, we used data from 2574 mineral horizons from 675 pits from National Ecological Observatory Network sites across North America, typically collected to 1 m depth. Climate was a fundamental predictor of SOC and played similarly important roles as some geochemical predictors. Yet, this only emerged in the generalized additive mixed model and random forest model and was obscured in the linear mixed model. Relationships between water availability and SOC were strongest in very dry ecosystems and SOC increased most strongly at mean annual temperature < 0°C. In all models, depth, oxalate‐extractable Al (Alox ), pH, and exchangeable calcium plus exchangeable magnesium were important while silt + clay, oxalate‐extractable Fe (Feox ), and vegetation type were weaker predictors. Climate and pH were independently related to SOC and also interacted with geochemical composition: Feox and Alox related more strongly to SOC in wet or cold climates. Most predictors had nonlinear threshold relationships with SOC, and a saturating response to increasing reactive metals indicates soils where SOC might be limited by C inputs. We observed a mostly constant relative importance of geochemical and climate predictors of SOC with increasing depth, challenging previous statements. Overall, our findings challenge the notion that climate is redundant after accounting for geochemistry and demonstrate that considering their nonlinearities and interactions improves spatial predictions of SOC. Key Points: The importance of climate for predicting soil carbon (C) emerged only in nonlinear statistical models, which captured threshold effects of predictors Geochemical and climatic predictors of soil C both remained important in deeper soils Climate and pH predicted soil C directly and via interactions with soil geochemical composition