Effects of Vegetation Removal and Soil Disturbance on Soil Organic and Inorganic Carbon Dynamics in California Desert Ecosystems

Abstract:

Solar energy developments are projected to be deployed over desert wildland areas with deep soil inorganic carbon (SIC) deposits, which often involves elimination of deep-rooted vegetation. This land cover change may systemically alter SIC pools since respired CO₂ is the carbon (C) source during SIC formation. We sought to understand how removal of creosote bush scrub affects soil C pools. We hypothesized that vegetation is important for maintaining SIC and soil organic C (SOC) pools and that disturbance to the vegetation and soil will change CO₂ flux with increased losses from SIC. Soils were collected from sites that had intact creosote bush scrub habitat adjacent to disturbed, bare areas where the native vegetation had been previously removed. Samples were taken from beneath shrub canopies and interspaces in intact areas, and from random points in the disturbed area. Soils were analyzed for SIC, SOC, microbial and labile C, and δ¹³C. Soils were also incubated to determine the potential CO₂ flux from disturbed and undisturbed soils along with the sources of CO₂. Three replicates per soil underwent a control and water addition treatment and flux and δ¹³C of CO₂ were measured continuously. Control replicates yielded no significant CO₂ flux. CO₂ flux from watered soils was higher beneath shrub canopy (18.57µmol g soil^-1 day^-1±1.86) than the interspace soils (0.86 µmol g soil^-1 day^-1±0.17). Soils collected from bare areas had an intermediate flux (5.41 µmol g soil^-1 day^-1±2.68 and 3.68 µmol g soil^-1 day^-1±0.85, respectively) lying between shrub canopy and interspace soils. There was no significant difference between the δ¹³C values of CO₂ from shrub canopy and interspace soils, both of which had a very low δ¹³C values (-22.60‰±0.64 and -23.88‰±0.89, respectively), resembling that of organic C. However, the isotopic values of CO₂ from disturbed soils were significantly higher (-16.68‰±1.36 and -15.22‰±2.12, respectively) suggesting that these soils effluxed a greater proportion of CO₂ from an inorganic source than intact soils. Microbial and labile C were highest under shrub canopy, intermediate in interspaces, and lowest in bare areas. Vegetation removal to accommodate renewable energy developments may negatively impact soil C, potentially leading to unintended increased soil C losses from the SIC pool.