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Universidade de Sao Polo (2012)

Microgramma squamulosa (Kaulf.) de la Sota e Pleopeltis hirsutissima (Raddi) de la Sota : estratégias contrastantes de uso da água em um ambiente epifítico

Marques Barbosa Joyce

Titre : Microgramma squamulosa (Kaulf.) de la Sota e Pleopeltis hirsutissima (Raddi) de la Sota : estratégias contrastantes de uso da água em um ambiente epifítico

Microgramma squamulosa (Kaulf.) de la Sota and Pleopeltis hirsutissima (Raddi) de la Sota : two epiphytes with contrasting water use strategies

Auteur : Marques Barbosa Joyce

Université de soutenance : Universidade de Sao Polo

Grade : Mestre em Ciencias 2012

Résumé
In land plants the resistance to drought can be accomplished by two main strategies. One involves mainly dehydration avoidance mechanisms and the other is based on the ability to withstand drought at the tissues and down to subcellular levels. The former is found on the desiccation sensitive plants (DS) and the last describes the desiccation tolerant plants (DT). The metabolic costs of the desiccation tolerance mechanisms are probably high, at least when considering the cessation of photosynthesis during anabiosis - a condition that is absent in drought avoidance strategies. The coexistence of drought avoiders and desiccation tolerant plants in the same substrate and condition can rise some questions about the relative advantages of each strategy when submitted to similar water regime. We ask whether desiccation tolerant plants have a compensatory carbon gain under a watering regime that induces frequent anabiosis or cumulative damage in drought avoidance have a detrimental effect comparable to the costs of the desiccation tolerance. An analysis of the epiphytic plant community associated to the trees of the CUASO urban landscape showed a very frequent co-occurring species pair including the desiccation sensitive Microgramma squamulosa and a desiccation tolerant Pleopeltis hirsutissima, both cryptogams of the same plant family. These species were thoroughly examined regarding the patterns of light, water and carbon dynamics together with pigments concentration during cycles of natural drought and wet climate field conditions. These observations were complemented with experimental induction of different water and light regimes. The results showed no sign of chronic stress in both plants living at the same condition but allowed us to identify large distinctions in resource use patterns. A compensatory carbon assimilation was not found in P.hirsutissima. Both species have similar CO2 assimilation values. Experimental induction of drought in different light regimes allowed to verify a relative advantage in desiccation tolerant P.hirsutissima in comparison to the desiccation sensitive M.squamulosa under high irradiance values. Furthermore, light curve analysis suggest that they share the same tree but their niches differ in light intensity regime allowing the high frequency of co-occurrence observed in the field

Mots clés  : Chlorophyll fluorescence ; Desiccation tolerance ; Drought stress ; Epífitas ; Epiphytes ; Estresse hídrico ; Fluorescência da clorofila ; Fotossíntese ; Photosynthesis ; Tolerância à dessecação ; Ecologia : Ecossistemas Terrestres e Aquáticos

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Page publiée le 13 janvier 2016, mise à jour le 11 septembre 2018