Vegetation and precipitation shifts interact with soil depth to change dryland carbon and nitrogen storage

Dr David Huber1,2,3, Dr Kathleen Lohse3, Ms Amy Commendador3, Dr Bruce Finney3, Dr Ken Aho3, Dr Mark Seyfried2, Dr. Matthew Germino4

1CSIRO-Adelaide, Urrbrae, Australia, 2USDA-ARS, Boise, United States, 3Idaho State University, Pocatello, United States, 4USGS, Boise, United States

Dryland ecosystems are experiencing shifts in precipitation and plant community composition, which alter the cycling and storage of soil carbon (C) and nitrogen (N). We measured profile soil organic C (SOC), total N (TN), and associated stable isotopes following 20 years manipulating 1) plant community (native shrub vs. exotic bunchgrass), 2) water availability [ambient, or doubling of annual rainfall in the dormant (DORM) or growing (GROW) season], and 3) soil depth (deep 2 m or shallow 0.5 m soils). Under both native shrubs and exotic bunchgrass, GROW increased profile SOC pools ~70% vs. ambient controls. DORM decreased SOC pools slightly under native shrubs and increased SOC for bunchgrass, primarily in the topsoil. Regardless of vegetation treatment, GROW increased SOC pools for interplant microsites. Contrasting soil depth treatments, profile SOC and TN pools were 1.56 and 1.23× greater, respectively, in shallow compared to deep soil treatments, with significant interactions between soil thickness × vegetation. Profile δ13C values, which integrate the long-term soil moisture status, were enriched in deep vs. shallow treatments and show greater water stress in deep soils. Similarly, profile δ15N values in shallow treatments were enriched vs. deep and show greater water availability in shallow treatments leading to enhanced N loss. Our study shows precipitation seasonality can interact with changes in plant community composition to alter soil biogeochemical processes in drylands. We provide evidence that soil thickness as a control volume has an important influence on the surface soil biogeochemical response to changes in climate and vegetation. Our findings could improve adaptive management decisions and help identify landscape control points that regulate ecosystem resilience.


Dr. Huber is a Soil Biogeochemist whose research integrates biology, soil physics, and isotope ecology to study dryland processes affected by climate and land-use change. David is a CSIRO Postdoctoral Fellow in terrestrial isotope geochemistry. A new arrival from the US, he is a former Postdoctoral Associate with the Agricultural Research Service and Reynolds Creek Critical Zone Observatory where he modelled antecedent environmental controls on soil and ecosystem respiration. He received his PhD in Soil Biogoechemistry from Idaho State University, and his M.S. in Soil Physics at Colorado State University.

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