Use of differential water sources by Prosopis flexuosa DC: a dendroecological study.

Abstract

In central-western Argentina, there is a pronounced water deficit gradient, from semiarid climate conditions with 500-mm rainfall/year to arid climate conditions with 80-mm rainfall/year. This climatic transition, governed by the rainfall gradient, occurs between the Arid Chaco and Monte phytogeographic regions and is evidenced by differences in vegetation type, structure, dynamics and tree growth. In turn, the availability of soil moisture, particularly access to the water table, modifies water use strategies by trees along this gradient. We analyzed how water availability, expressed as differences in accessibility to the water table, influences Prosopis flexuosa tree rings along a precipitation gradient. In this manner, we try to interpret the growth of species according to the use of differential water sources. P. flexuosa showed highly varying growth reactions (tree-ring width and hydraulic anatomic parameters) with climate, depending on the ecology of the site. Along the Arid Chaco- Monte gradient, the growth of P. flexuosa is more dependent on variations in rainfall in those areas where water depth is greater than root spread. The climate signal was hidden in those regions where the water table is accessible to the root system.