A theoretical framework of desertification has been developed within the Jornada Basin LTER that involves the rate of change and magnitude of wind and water erosion affected by spatial variation in the distribution of gap size changes from high connectivity of vegetated patches in grasslands to low connectivity of vegetated patches in shrublands. With increased connectivity, increased retention also occurs where soil biotic interactions should be working at a high degree. Accumulating evidence suggests that connectivity between many small bare soil patches and vegetated areas may occur via hyphal networks that dominate decomposition and N transformation processes through symbiotic associations with producers and soil biotic crusts in a “fungal loop”. This fungal loop may provide an unexplored source of connectivity at the patch scale between plant species in a single community.
We hypothesize that encroachment of mesquite into black grama dominated grasslands has caused a disruption to the positive feedback loop between soil biotic crusts, DSF, and black grama (we collectively call this feedback-loop a soil biofeedback) where a loss of connectivity has occurred. Based upon the number of emerging studies identifying the importance of soil biota in semi-arid regions, this study utilized the highly specialized feeding behavior and physiology of nematode stylus/mouthparts as indicators of change. Specific nematode genera have been identified to feed/prey upon all three of the root, fungal and bacterial energy channels with plant roots belowground that have important ecosystem level effects. Utilizing the specificity in feeding behaviors, this study asserts that food web theory plays an integral role in regulating productivity, stability, and structure through the mechanisms of soil biofeedbacks by examining the associated changes in nematode community structure associated with the differing vegetation states of desertification.
Results/Conclusions
Our results show that as desertification increases, there are significant losses in nematode species diversity and significant trophic differences among grassland sites, mesquite dunelands, and the ecotone between the two. Based on these shifts in species composition, we would expect the suite of soil microorganisms associated with different vegetation to follow these same patterns, where changes in trophic structure may indicate shifts in soil biotic communities. The loss of connectivity associated with desertification has caused the nematode population to become much more heterogeneous in the shrublands opposed to the grassland and the ecotone, indicating that the same drivers and processes that affect vegetation patterns in arid systems may also play a role in disrupting biotic interactions between the vegetation and soil.