Modest Residual Effects of Short-Term Warming, Altered Hydration, and Biocrust Successional State on Dryland Soil Heterotrophic Carbon and Nitrogen Cycling

Colin Tucker,Sasha C. Reed,Scott Ferrenberg

doi:10.3389/fevo.2020.467157

Abstract

Biological soil crusts (biocrusts) on the Colorado Plateau may fuel carbon (C) and nitrogen (N) cycling by soil heterotrophic organisms throughout the region. Late successional moss and lichen biocrusts in particular can increase soil C and N availability, but some data suggest these biocrust types will be replaced by early successional cyanobacterial biocrusts as the region undergoes rapid warming. In this study, we evaluated the short-term interactive effects of biocrust successional state and elevated temperature on soil heterotrophic C and N cycling (specifically, respiration, N2O emissions, microbial biomass C and N, and soluble C and N), using a two-phase approach consisting of an 87-day greenhouse mesocosm phase followed by a short-term (2-day) laboratory incubation phase. We found that biocrust successional state, as well as exposure to warmer temperatures during the mesocosm phase, had subsequent significant effects on the amount and temperature sensitivity of soil heterotrophic C and N cycling in laboratory incubations. Late successional biocrusts increased C and N cycling relative to early successional crusts, while warming reduced both the magnitude and the temperature sensitivity of C and N cycling. The inhibiting effect of warming was most evident in soils from beneath late successional biocrusts, suggesting that an overall effect of climate warming may be a marked shift in the soil C and N cycles in the region.

Highlights

Biological soil crusts are fundamental members of dryland ecosystems (Weber et al, 2016b), and affect ecosystem functions of dryland soils in ways that vary with biocrust community composition and exposure to altered climate (e.g., Belnap et al, 2016; Reed et al, 2016)
An improved understanding of these linkages is critical considering that altered biocrust function as a result of warming may induce a cascade of changes related to soil fertility (Beraldi-Campesi et al, 2009), plant community structure (Havrilla et al, 2019), C storage and efflux (Darrouzet-Nardi et al, 2015, 2018), hydrology (Eldridge et al, 2020), and soil stability (Gao et al, 2020) - all of which could have substantial negative effects on dryland function
Values are for soil respiration, soil N2O efflux, microbial biomass C (MBC), microbial biomass N (MBN), K2SO4-extractable dissolved organic C (DOC), and K2SO4-extractable total dissolved N (TN)

Summary

Introduction

Biological soil crusts (biocrusts) are fundamental members of dryland ecosystems (Weber et al, 2016b), and affect ecosystem functions of dryland soils in ways that vary with biocrust community composition and exposure to altered climate (e.g., Belnap et al, 2016; Reed et al, 2016). An improved understanding of these linkages is critical considering that altered biocrust function as a result of warming may induce a cascade of changes related to soil fertility (Beraldi-Campesi et al, 2009), plant community structure (Havrilla et al, 2019), C storage and efflux (Darrouzet-Nardi et al, 2015, 2018), hydrology (Eldridge et al, 2020), and soil stability (Gao et al, 2020) - all of which could have substantial negative effects on dryland function. Predicting soil biogeochemistry in response to altered climate in these landscapes will require an improved understanding of soil biogeochemical pools and fluxes associated with biocrust and climate-induced changes to their community composition

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Conclusion