Drought promotes early leaf abscission regardless of leaf habit but increases litter phosphorus losses only in evergreens

Abstract

Drought can alter leaf senescence and nutrient resorption, but whether these alterations are consistent between trees of contrasting leaf habits remains unclear. We conducted an experiment for 2 years with potted saplings to compare leaf habit and drought effects on leaf abscission dynamics and nutrient resorption proficiency in two evergreen and two deciduous Nothofagus (Nothofagaceae) species from southern temperate forests. A global meta-analyses has found similar nitrogen (N) proficiency between leaf habits, and greater phosphorus (P) proficiency for evergreens; however, it is unclear whether these differences are attributable to phylogeny or leaf habit. Leaf habit had no effect on either N or P resorption proficiency, but drought significantly decreased P resorption proficiency, particularly in evergreens. Additionally, drought reduced spring relative growth and promoted significantly earlier leaf abscission in both leaf habits. In evergreens, reduced P proficiency along with a non-significant trend of higher litter mass under drought led to increased litter P content. Thus, leaf P resorption proficiency of evergreens appeared to be hindered by drought, whereas drought-induced senescence was efficient in reducing P losses in deciduous saplings. Our findings suggest that nutrient cycling and species composition in strongly P-limited environments could change under sustained, moderate drought conditions.