Abiotic Amelioration Research Articles

Role of shrubs in the community assembly of biocrusts: the biotic and abiotic influences along a biocrust succession gradient

In water-limited areas, shrubs influence biological soil crust (biocrust) composition and diversity via soil microenvironment alterations and through modifying biotic interactions amongst biocrust taxa. However, the relative contributions of shrubs to biocrust succession and assembly via the biotic and abiotic influences are poorly known. The community composition of biocrusts and soil properties in the interspace and beneath the dominant shrub (Artemisia ordosica) along a biocrust succession sequence were investigated. Biocrust interspecific interactions at a small scale (within shrub) were evaluated based on the co-occurrence pattern using null models. A hypothetical multigroup structural equation model (SEM) was proposed to evaluate the influence of multiple variables on the biocrust richness and to investigate the path variance between successional stages. Along the biocrust succession, shrubs significantly increased the size of bare soil gap by 489%, decreased lichens by 43% and increased soil organic matter by 13%. In years 18, 31and 37, the paths in SEM explained 59% of the variation in richness, only the effect of abiotic amelioration was significant (0.62). In years 54 and 62, the shrubs had direct (0.37) and indirect effect (0.10) via species interaction to biocrust richness. Shrubs directly and indirectly affected the community assembly of biocrusts. Biocrust species interactions are an important driver of biocrust diversity and primarily affect late succession. The increasing influences of shrubs suggests a close relationship between shrub and biocrust components in arid or semiarid ecosystems, with shrubs playing an important role in regulating biocrust assembly and maintaining biocrust richness.

Comparing Direct Abiotic Amelioration and Facilitation as Tools for Restoration of Semiarid Grasslands

Abstract Desertification can be an irreversible process due to positive feedback among degraded plant and soil dynamics. The recovery of semiarid degraded ecosystems may need human intervention. In restoration practices, the abiotic conditions often need to be improved to overcome the positive plant–soil feedback loops. Using nurse‐plants to improve abiotic conditions for introduced individuals (facilitation) has been suggested as an alternative to direct abiotic amelioration. Here, we compared direct abiotic amelioration and facilitation as tools for restoration of semiarid grasslands in Spain. Seedlings and seeds of Lygeum spartum and Salsola vermiculata were planted and sown in a stably degraded semiarid area in Northeast Spain. Two levels of direct abiotic amelioration (ploughing and damming) and indirect abiotic amelioration through facilitation by Suaeda vera nurse shrubs were compared with a control with no amelioration treatment. The control treatment showed low plant establishment, confirming the practical irreversibility of the degraded state. Plant establishment was significantly higher in the three treatments with interventions than in the control treatment. The best treatment depended on the plant trait considered, but damming was in most cases better than plant facilitation. However, facilitation maintained the nutrient‐rich topsoil layer. Given the relative success of facilitation, revegetation using the facilitative effect of nurse‐plants would, in principle, be recommended for restoring semiarid grasslands. Direct abiotic amelioration would be needed under extreme degradation or harsh climatic conditions.