Elaeagnus angustifolia in the Mid Valley of Río Negro, Argentina.

1. Elaeagnus angustifolia in the Mid Valley of Río Negro, Argentina. Animal preference related to foliar anatomy. Klich, M.G. (1) and Fernández, O.A. (2) (1) guadalupeklich@gmail.com. http://mgklich.wordpress.com Escuela de Veterinaria, UNRN. Choele Choel, ARGENTINA (2) ofernan@criba.edu.ar. Departamento de Agronomía, CERZOS, UNS, Bahía Blanca, Buenos Aires. ARGENTINA Elaeagnus angustifolia L. (Russian olive) is a foreign shrubby species becoming naturalized and invasive in the Mid Valley of Río Negro of Argentina, covering densely extensive areas along the valleys The region is semiarid subjected to a great daily and seasonal temperature range, average values fluctuate from 6.83 ºC in the coldest month (July) to 23.02 ºC in the hottest month (January); the average annual precipitation is 300 mm. The study field locates at the northern margin of the River (39º 30´ S, 65º 30´ W). After a long drought and under moderate grazing pressure cattle was able to consume some particular plant parts leaving other untouched, becoming under the circumstance an important animal fodder alternative. This study was conducted to find the relation between anatomical leaves characteristics, determined by optical and scanning electro microscope, and animal preference. Upper leaves, exposed to higher solar irradiance and lower air humidity, are smaller, slender and thicker than the other inferior strata. Leaves color varies from silvery-grey green in the upper strata, to dark green in the lower one. LowerUpper Animals eat the leaves from branches placed at a middle level, from 1 to 2.8 m high. Upper sun-leaves that can not be reached by cattle (from 2.8 m up) are also consumed if branches are cut and made available to the animals. The lower leaves (up to 1 m) remain untouched even when food is scarce. 50 µm 50 µm The silvery leaves from the upper branches have only peltate hairs that, in the abaxial leaf surface, are arranged to form two or three layers of their flattened multicellular shields (g.h.i). The epidermis of middle stratum leaves have several hair layers, the external ones composed by hairs totally branched or stellate and the internal layer formed by peltate hairs with the cells of the shield partially joined (d,e,f). Lower leaves have branched hairs, the rays of adjacent trichomes overlapping, and exhibit an abaxial woolly appearance (a,b,c). E. angustifolia presents foliar morphological and anatomical variability within the canopy of single trees, product of adaptive evolution to develop and function in habitats marked by strong variations of solar radiation, air temperature and humidity. Pubescence and distribution of epidermal indumentum seems to affect palatability and cattle preference.