Does drought control emergence and survival of grass seedlings in semi-arid rangelands? An example with a Patagonian species

P. A. CIPRIOTTI, P. FLOMBAUM, O. E. SALA, AND M. R. AGUIAR

JOURNAL OF ARID ENVIRONMENTS

Año: 2008 vol. 72 p. 162 - 174

0140-1963

Current climate change models for arid ecosystems challenge our ability to understand the effects of droughts on plantpopulation dynamics. In a sandy soil plant community from the Patagonian steppe, we studied soil water dynamics and itseffects on grass regeneration. Our hypothesis was that a decrease in precipitation would not change soil water dynamics ofthe top soil layer where most of the seeds and seedling roots are located. First, we simulated soil water dynamics with abalance model (DINAQUA) for different years and soil layers, in two different periods related to the emergence andsurvival of plants. Then, we performed a manipulative field experiment in which we generated a drought gradient byintercepting 0%, 25%, 50%, and 80% of the precipitation for two different microsites (vegetated and bare soil). Wequantified drought effects on emergence, survival, and biomass of seedlings using a native grass (Bromus pictus Hook). Soilwater content in the top soil layer at the end of growing season was a 61% less than mid and bottom soil layers,independently of the climatic condition of the year. The simulations suggested that drought reduces the maximum depth ofwater infiltration, but available water for plants in the top layer where seedlings have their roots, was not modified, inagreement with our field experiment measurements. Consistently, the emergence (51%), survival (65%), and biomass(15 g/ind) of seedlings were not affected by drought levels. However, there is a positive microsite effect on biomass(36%), indicating a facilitative role of adult plants on grass seedlings. We interpreted these results as indicative that seedgermination and seedling recruitment will not be heavily impacted by increasing water deficit in the Patagonian steppe.