Patagonian steppe plants grow under a combination of factors conducing to a similar number of stresses: low water and nutrient availability, low temperature, high grazing pressure and strong and highly frequent wind. Under these factors plants can adapt at physiological, morphological and/or biochemical level. Previous studies that contribute to the knowledge of the structure and functioning of this ecosystem did not focalize on wind influence over vegetation, been this factor poorly studied.

This study was carried out in the Argentinean Patagonian steppe (45 57’ S; 67 31’ W) in two dominant patagonian shrubs, Colliguaja integerrima and Berberis heterophylla. The objective of this study was determinate the effects of different wind expositions (leeward and windward) on the morpho-physiological traits at leaf scale. The variables measured were stomatal pore index, leaf thickness, leaf succulence, specific leaf area, leaf lamina density, leaf size, leaf water potential, turgor loss point, solutes, leaf capacitance, leaf hydraulic conductance and leaf dry matter content. All variables were measured at windward (SW) and leeward (NE) for each individual (n=10 per specie) during the spring season of 2009.

Results/Conclusions

Leaves at windward experienced wind velocities up to two fold higher than leaves at leeward (mean maximum wind velocity: 56 km h^-1 and 24.5 km h^-1 respectively).  Stomatal pore index, leaf specific area, leaf capacitance, percent of solutes, leaf density were lower in windward than leeward for both species. For example stomatal pore index was 0.04 and 0.045 at windward and leeward respectively for B. heterophylla and leaf capacitance varied from 50 mmol m^-2 MPa^-1 at windward to 200 mmol m^-2 MPa^-1 at leeward for C. integerrima. On the other hand, leaves more exposed to wind have higher thickness and stomatal density and exhibited higher turgor loss point than leaves less exposed. Thickness was 0.06 mm in leaves exposed of B. heterophylla and 0.042 mm in leaves at leeward. Leaf size, leaf dry mass content and succulence were relatively constant in the plant. These results suggest that the high wind velocity common in Patagonian steppe could affect gas exchange reducing total exchange area of CO₂ per leaf and consequently growth rate of shrubs.