Tornillo pecan orchard soil CO2 efflux spatial variation

Spatial variability in soil CO2 efflux across landscapes is an important feature of the "Critical Zone" within dryland ecosystems. In dryland critical zones, resources are often distributed in patches or resource islands. Although this is particularly true in natural settings, the significance of spatial variability in CO2 efflux and its patterns also extends to dryland agriculture. In both irrigated and unirrigated systems, human management practices can significantly impact both organic and inorganic carbon cycling processes, highlighting the importance of studying CO2 efflux in these systems. We examined the spatial patterns of soil CO2 efflux and quantified the magnitude and scale of spatial autocorrelation using geostatistical techniques in a flood-irrigated pecan orchard and a creosote bush shrubland. Moreover, we explored some of the associated factors that may drive spatial variability in soil CO2 efflux. Our results indicated that while CO2 efflux was autocorrelated at short distances, it was quite variable and difficult to predict at larger scales across the study sites. Furthermore, the level of spatial autocorrelation varied depending on water availability, with weaker patterns at intermediate water levels at the flood-irrigated site. We also found that CO2 efflux had shorter ranges of autocorrelation compared to tree diameter and electrical conductivity. Tree diameter, proximity to the nearest tree and electrical conductivity did show some association with soil CO2 efflux, but the correlations were weak. Overall, this research provides evidence that electrical conductivity, tree diameter and proximity to the nearest tree are weak predictors of spatial variability in soil CO2 efflux and that there are likely other unmeasured factors that control spatial variation in soil CO2 efflux at these sites.