Micro-environmental conditions affect grass and shrub seedling emergence in denuded areas of the arid Patagonian Monte, Argentina

Abstract

Harsh micro-environments in bare soil patches generated by disturbance may affect the emergence of plant species in desert ecosystems. We evaluated the effects of litter addition on the emergence of perennial grass and evergreen shrub species under different conditions of UV radiation and soil water content in disturbed patches of bare soil. We sowed seeds of perennial grasses (Nassella tenuis and Poa ligularis), and shrubs (Atriplex lampa, Larrea divaricata and Schinus johnstonii) in microcosms containing blocks of upper soil (28cm depth) subjected to different levels of three factors: litter (bare soil without litter cover, high quality litter cover from undisturbed plant patches, and low quality litter cover from disturbed plant patches), UV radiation (near ambient and attenuated UV radiation), and soil water (5–15% and 15–25% of volumetric soil water content). The patterns of seedling emergence in relation to litter, UV radiation, and soil water content varied among species independently of life form. Seedling emergence of all species increased under exposure to UV radiation at all combinations of litter and soil water factors. High soil water content had an important positive effect on the emergence of N. tenuis and L. divaricata in combination with UV radiation and litter. In contrast, soil water content did not affect or affected negatively the emergence P. ligularis and A. lampa in combination with litter and UV radiation. The emergence of S. johnstonii occurred only under exposure to UV radiation mostly at high soil water content, independently of litter levels. These results highlight the importance of the combined effects of the presence and type of litter, soil water content, and UV radiation on seedling emergence of perennial grass and shrub species and consequently on the vegetation reestablishment processes at disturbed areas.