Physiological plasticity in eucalyptus clones in the vegetative stage contributes to drought tolerance

With the expansion of eucalyptus crops to areas with severe water limitations,physiological studies involving eucalyptus clones to identify those that are tolerant to water stress become important.The objective of this study was to assess morphological and physiological responses by eucalyptus clones subjected to drought stress and rehydration.The experiment consisted of three eucalyptus clones:VC865,I224 and I144 and two water regimes:control and water stress followed by rehydration,with six replicates.Leaf water potential,gas exchange,maximum quantum efficiency of photo systemⅡand plant height and stem diameter were evaluated under drought stress and rehydration.After6 d of rehydration,the number of leaves,leaf area and dry mass of root,leaf,stem and their total were evaluated.All clones showed intense reduction of gas exchange during the drought stress period,and only VC865 and 1144 showed rapid recovery with 3 d of rehydration.Clone 1224 showed greater reduction in height,stem diameter,number of leaves,water potential at midday(Ψ_(w)_(Midday)),and maximum quantum efficiency of photosystemⅡ(F_(v)/F_(m)).Clones VC865and T144 showed lower reductions inΨ_(wMidday)and F_(v)/F_(m) under stress.VC865 had lower reductions in leaf number,leaf area and higher leaf dry mass,while clone I144 had higher height and lower reduction in root dry mass under.Both these clones showed higher water use efficiency with 3d of rehydration.These different phenotypic plasticities gave the clones VC865 and 1144 efficient mechanisms of acclimatization to stress and more drought tolerance,enhancing their greater capacity for recovery after stress,which allowed lower dry mass reduction.Clone 1224,however,was more susceptible to drought stress,undergoing greater physiological damage with only partial recovery during rehydration.

Light intensity and hydrogel soil amendment differentially affect growth and photosynthesis of successional tree species

Global climate changes have increased temperatures,radiation indexes,and consequently,irregularities in rainfall in mainly tropical countries,considerably hindering plant establishment in recovering degraded areas.The objective of this study was to evaluate the growth and physiological characteristics of one species of each successional group:pioneer,secondary,and climax when subjected to different light intensities and hydrogel as a soil conditioner during rainy and dry periods.The experiment was conducted in the ecotone between Brazil’s two largest biomes,the Cerrado and the Amazon in the State of Maranh?o.The parameters consisted of three species:Guazuma ulmifolia Lam.(pioneer),Astronium fraxinifolium Schott(secondary),and Cariniana rubra Gardner ex Miers(climax).There were two light intensities:70%and 100%,and two planting conditions:with and without soil conditioner(hydrogel).Gas exchanges were higher during the rainy season;the pioneer and secondary species had greater heights and photosynthetic rates in the dry period;the climax species had the lowest gas exchange and lowest recovery as rainfall resumed.The pioneer and secondary species showed higher physiological plasticity,denoting better adaption to environments with high irradiance.Hydrogel improved the photosynthetic performance of these species in the dry season and in areas with 100%sunlight.