Effects of soil biota disturbance on inorganic carbon dynamics in renewable energy developments

Background/Question/Methods

Renewable 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. Vegetation removal may systemically alter SIC pools because respired CO₂ is the carbon source during SIC formation. We sought to understand how removal of creosote bush scrub affects soil carbon (C) pools. We hypothesized that vegetation plays a significant role in maintaining both SIC and soil organic C pools and that disturbance to the vegetation and soil biota will change CO₂ flux, increasing C loss from SIC sources. 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. Two sets of points were sampled in the disturbed area, one set that will remain bare and the other prior to planting creosote bush seedlings. An incubation experiment was conducted to determine potential flux from disturbed and undisturbed soils and potential C sources contributing to C loss. Each soil underwent two treatments, control (unwatered) and water addition at 25°C with three replicates per soil. Flux and isotopic composition (δ¹³C) of CO₂were measured continuously for each replicate.

Results/Conclusions

There was no significant CO₂ flux from any control (unwatered) replicates. CO₂ flux from water-treated 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 (bare and pre-seedling) 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 intact soils (shrub canopy and interspace), 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 (bare and pre-seedling) 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. The vegetation and soil biota play important roles in desert carbon balance. Disturbances, such as vegetation removal to accommodate renewable energy developments, may negatively impact the soil biota, potentially leading to unintended increased soil C losses from the SIC pool.