SUCCESSIVE EPISODES OF WATER DEFICIENCY RESULT IN ACLIMATIZATION OF THE PHOTOSYNTHETIC MACHINERY?

With the advance of commercial silviculture into non-traditional regions, characterized by lower rainfall and higher potential evapotranspiration rates, there is a demand for ecophysiological studies of forest species under water deficiency. To test the hypothesis that rubber tree seedlings subjected to successive previous drought cycles develop the ability to acclimatize the photosynthetic machinery, master's student Jessily Medeiros Quaresma evaluated the ecophysiology of the FX 3864 clone under soil water limitation conditions, after previously passing through drought stress cycles.

The results indicate that plants of the rubber tree clone FX 3864, when previously subjected to more than one cycle of water deficiency, are able to maintain cell hydration status for longer periods and develop photosynthetic machinery ability to effectively overcome water restriction that may occur again, achieving thereby an acclimation condition. Thus, from a practical point of view, submitting rubber tree seedlings in the early stages of development to controlled periods of moderate drought may contribute to improving hardening in nurseries and therefore increasing their ability to withstand subsequent drought events more quickly, reducing plant mortality rates in the field without excessive production losses.

The differential of the study developed by master's student Jessily is the use of ecophysiological indicators to demonstrate seedling acclimation. The results suggest that successive cycles of water deficiency may have generated a "stress memory" in the plants, triggering alterations in physiological responses and possibly biochemical and metabolic responses, resulting in acclimation. This "stress memory" favored carbon balance, with maintenance of leaf turgescence and improvement of plant ability to absorb water from the substrate even in low water availability levels. Further studies are still needed to establish the molecular mechanisms by which plants store information about stress exposure caused by biotic and abiotic variables.

More details can be found in the complete dissertation of the student on our website and in the article: Scientia Forestalis