Water use eficiency and nitrogen use in arid ecosystems (Telteca) by stable isotopes

ARANIBAR J. N; MEGLIOLI P.A; VILLAGRA P. E.; GUEVARA A.

San Juan

Congreso; II Reunión Conjunta de las Sociedades de Biología de la Republica Argentina; 2011

In arid ecosystems, water is the main resource that regulates primary productivity. Plants have different adaptations to optimize water use such as stomatal conductance and photosynthesis regulation as a function of local meteorological conditions. Nutrient use is optimized based on environment availability and metabolic requirements. We explored water and nutrient uses on phreatophic woodlands in Telteca in different environmental conditions (dunes/groundwater coupled interdune valleys), (after/before rainfalls), (disturbance/non-disturbance woodlands). We analyzed foliar carbon (C) and nitrogen (N) total concentration and their stable isotope compositions as indicators of nitrogen use strategies and water use efficiency. Prosopis flexuosa presented the highest water use efficiency among C plants in dry periods, both in dunes and interdune valleys. Trees in livestock posts had lower water use efficiency than in relatively undisturbed woodlands. We found no clear evidence of atmospheric N2 fixation, except in some seedlings of P. flexuosa. High foliar C:N ratios were observed prior to senescence in woodlands, indicating N conservation mechanisms, whereas lower C:N ratios were observed in livestock posts, indicating a higher N availability. We conclude that foliar stable isotope composition indicate an environment regulated by local meteorological conditions and disturbances.