Características morfofisiológicas de plantas jovens de Hevea brasiliensis (Willd. Ex Adr de Juss.) Muell. Arg.) submetidas a diferentes ambientes lumínicos e ao estresse hídrico

Abstract

The rubber tree (Hevea brasiliensis) is Amazonian rainforest tree species. Its bark has laticiferous vessels from which latex are extracted. Currently production overcomes demand, so there is a need for plantation expansion and employment of more efficient management techniques. In order to achieve it, knowing the eco-physiological requirements regarding the availability of resources such as CO 2 , water, nutrients and light can contribute decisively to the global production of rubber plantations. However, it should be noted that climatic changes or even limitations of primary resources during planting almost always impose stressful conditions on plantations, in particular, problems related to the light environment (low or high irradiance) and the availability of water. The aims of this study was investigate morphophysiological and biochemical changes caused on rubber tree seedlings growing under different light intensities and water deficiency as well as analyze their rehydration capacity. The experiments were conducted at Laboratory of Plant Physiology and Biochemistry - INPA. The results showed that the variation of light availability affected the photosynthetic performance of rubber tree seedlings. Plants subjected to low irradiance (47.5 ± 8.2 μmol photon m -2 s -1 ) showed low photosynthetic rates, higher pigment contents, greater leaf area and specific leaf area. On the other hand, under higher irradiation conditions, moderate (257.5 ± 49.3 μmol photon m -2 s -1 ) or high irradiation (642.7 ± 116.9 μmol photon m -2 s -1 ) it was verified higher photosynthetic rates, smaller leaf area and specific leaf area, lower performance indexes, as well as lower values of the quantum photosystem yield. The light capture related results indicate that may have happen photoinhibitory effects over moderate and high irradiance treatments. Although the intermediate irradiance treatment has suffered photoinhibition, it is possible that they were fully reversible, since this treatment had greater biomass accumulation, greater growth in height and higher survival. Farther, it was found that physiological mechanisms were former activated under different light intensities being the morphological ones activated later. So, it is indicated moderate shadowing over this species as soon as it is planted. It was verified that this specie tolerated until 32 days without irrigation, when photosynthesis got close to 0 μmol m -2 s - 1. There was neither alteration on performance index, on photosystem quantum yield, on photosynthetic pigment contents nor on the leaf area. But, an efficient osmotic control must be stressed, probably, influenced by soluble sugar and proline contents. The photosynthesis recovery occurred about 20 days after irrigation be re-established. We conclude that young plants of H.brasiliensis present moderate physiological plasticity in face of different light intensities and water deficiency.