Wind effect on mechanics and hydraulics traits across the canopy of cold desert shrubs

IOGNA PA; BUCCI SJ; SCHOLZ FG; GOLDSTEIN G

Conferencia; 7 Plant Biomechanics International Conference; 2012

Wind is an environmental factor that affects plant development. Stems within the canopy exposed to different wind intensities could express different phenotypes in relation to hydraulics and mechanical traits. Wood density has been related with vessel anatomical properties, and in accordance with the Hagen-Poiseuille law, with the water transport efficiency. The objetive was to evaluate the relationship between the hydraulic characteristics and the mechanical resistance of stems within the plant under the influence of wind stress. Four dominant patagonian steppe shrubs were chossen: Colliguaja integerrima, Berberis microphylla, Acantholippia seriphioides and Fabiana patagonica. Vessel diameter and density, hydraulic conductivity (ks), wood density and flexural rigidity (FR) of stems naturally exposed to wind within the same individual (windward and leeward) were measured. In all species FR was higher at windward, indicating that stems more exposed to wind are stiffer than protected stems. This suggests that this mechanical trait exhibite intraindividual phenotipic plasticity induced by wind across the studied Patagonian shrubs. However wood density only showed significant changes between exposures in C. integerrima, being exposed stems denser. There was no specific pattern in the response of ks to wind exposure across species. Two species (C. integerrima and A. seriphiodes) had lower ks at windward than at leeward. While in A. seriphiodes lower ks was consistent with the lower vessel diameter (P< 0.01) and density, in C. integerrima low ks was correlated with the lower vessel density (P< 0.1) of higher diameter. These results put in evidence a “tradeoff” between mechanical safety and hydraulic efficiency where stems under wind stress give priority to rigid instead of efficient water transport systems. On the other hand, F. patagonica exhibited higher ks at windward than leeward, wich was related to a higher density (P< 0.01) of smaller vessels (P< 0.01) and B. microphylla had higher ks at windward as a result of an increase in vessel diameter (P< 0.01) despite the decrease in vessel density. At difference of C. integerrima and A. seriphiodes, these species did not exhibite a “tradeoff” between conductivity and mecanical resistance due to stems with higher hydraulic capacity showed also higher resistance to bend with the wind at windward. A possible explanation could be that a small change in vessel traits that would affect hydraulic conductivity have no effects on stiffness of the stems.