Print PageA theoretical framework of desertification has been developed within the Jornada Basin LTER in New Mexico where the importance of wind and water erosion increases as gap size increases that ultimately perpetuates desertification of arid grasslands. The loss of connectivity of vegetated patches and the subsequent increase in erosion results in the nonlinear expansion of shrubs across landscapes. 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”. We hypothesize that encroachment of mesquite into black grama dominated grasslands has caused a disruption to the positive feedback loop between soil biotic crusts, endophytic fungi, and black grama. 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 in order to identify changes in soil biotic communities across a desertification gradient at the Jornada LTER that included a relatively undisturbed grassland site on Otero Mesa, NM. 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 as well as serving as a proxy for relative soil biota community change. 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 a desertification gradient that includes the ecotone between the grassland and shrubland vegetation states.
Results/Conclusions
Nematode diversity decreases and becomes highly specialized within the Jornada grassland and mesquite duneland sites when compared with the ecotone between the two vegetation states. However, nematode diversity was highest at the undisturbed site but similar in composition to the Jornada grassland indicating similar soil biotic communities are associated with black grama grasslands. The partitioning of nematode communities also indicates that soil biotic communities are not driving vegetation dynamics but follow changes in vegetation and may aid in resilience of the system. Based on these shifts in species composition, we would expect the suite of soil microorganisms associated with different vegetation states to follow these same patterns, where changes in trophic structure may indicate shifts in soil biotic communities.
