Abiotic factors inv olv ed in the facilitation between woody and succulents [Factores abióticos involucrados en la facilitación entre leñosas y suculentas en el altiplano mexicano]
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We studied physiological and morphological characteristics of woody seedlings (nurses) and succulents (protected) which are distributed in an environmental gradient in the Mexican Plateau. Species from the mesic extreme of the gradient (Acacia schaffneri, A. farnesiana, Opuntia jaliscana) and from the xeric extreme (A. schaffneri, Prosopis laevigata, O. streptacantha) were chosen. 24-week-old seedlings were subjected for 90 days to varying levels of radiation (high = 2133 mol m-2 d-1, low = 166 mol m-2 d-1), available moisture (high = 60%25, low = 30%25) and fertility (high = canopy soil, low = open area). We assessed relative growth rate and its components: morphological (leaf area ratio) and physiological (net assimilation rate), as well as the quantum efficiency of photosystem II (φPSII), and the electron transport rate. Succulent seedlings had higher relative growth rate and leaf area ratio than woody ones. Most of the evaluated species grew more under high radiation and high humidity conditions. The canopy soil favored the growth of succulent species, but woody seedlings had the highest net assimilation rate. The results suggest that succulent seedlings showed ecophysiological functioning of protected species, best adapted to establish under the canopy of nurse plants. Woody species showed ecophysiological characteristics of nurses better adapted to open areas.
