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.

Mesophyll thickness and sclerophylly among Calotropis procera morphotypes reveal water-saved adaptation to environments

Calotropis procera(Aiton)Dryand(Apocynaceae)is a native species in tropical and subtropical Africa and Asia.However,due to its fast growing and drought-tolerant,it has become an invasive species when it was introduced into Central and South America,as well as the Caribbean Islands.Currently,C.procera displays a wide distribution in the world.Invasiveness is important,in particular,because many invasive species exert a high reproductive pressure on the invaded communities or are highly productive in their new distributed areas.It has been suggested that a very deep root system and a high capacity to reduce stomatal conductance during water shortage could allow this species to maintain the water status required for a normal function.However,the true mechanism behind the successful distribution of C.procera across wet and dry environments is still unknown.C.procera leaves were collected from 12 natural populations in Brazil,Colombia and Mexico,ranging from wet to dry environments during 2014–2015.Many traits of morphology and anatomy from these distinct morphotypes were evaluated.We found that C.procera leaves had a considerable capacity to adjust their morphological,anatomical and physiological traits to different environments.The magnitude of acclimation responses,i.e.,plasticity,had been hypothesized to reflect the specialized adaptation of plant species to a particular environment.However,allometric models for leaf area(LA)estimation cannot be grouped as a single model.Leaves are narrower and thicker with low amounts of air spaces inside the leaf parenchyma in wet environments,while they are broader and thinner with a small number of palisade cell layers in dry environments.Based on these,we argue that broader and thinner leaves of C.procera dissipate incident energy at the expense of a higher rate of transpiration to survive in environments in which water is the most limiting factor and to compete in favorable wet environments.