Acclimation of the photosynthetic machinery of the rubber tree clone FX 3864 by water stress cycles
Name: JESSILY MEDEIROS QUARESMA
Publication date: 14/07/2016
Advisor:
Name |
Role |
|---|---|
| JOSÉ EDUARDO MACEDO PEZZOPANE | Advisor * |
| PAULO CEZAR CAVATTE | Co-advisor * |
Examining board:
| Name |
Role |
|---|---|
| JOSÉ EDUARDO MACEDO PEZZOPANE | Advisor * |
| PAULO CEZAR CAVATTE | Co advisor * |
| TALITA MIRANDA TEIXEIRA XAVIER | External Examiner * |
Summary: The rubber tree is a native Amazon species commercially exploited for its latex, which is used for the production of natural rubber. However, studies in Brazil have shown that the productivity of the rubber trees can be affected by climatic variation in the environments in which the culture is inserted, mainly as to water limitation, and report that plants subjected to successive water stress are able to develop faster acclimation responses, enhancing their performance when subjected again to the same stress. So the purpose of the study was to test the hypothesis that clonal seedlings of the rubber tree FX 3864 submitted to three water stress cycles are able to present much more evident acclimation responses than plants subjected to just one cycle. Ecophysical and microclimate variables were monitored throughout the whole experiment, which was conducted in a greenhouse in the town of Jerônimo Monteiro, ES. The experiment lasted 167 days (October 2015 to April 2016) and the seedlings were grafted 47 days before the treatments initiated. The experimental design was completely randomized (CRD). The treatments consisted of cycles of water deficiency (WD): control (regularly irrigated plants); 1C (plants subjected to one cycle); 2C (plants subjected to two cycles); and 3C (plants subjected to three cycles). Each cycle of WD was characterized by two phases, the first phase with plant dehydration by withholding irrigation until the net assimilation rate (A) of the plants reached zero (A ≤ 0), and the second phase with the replacement of water substrate to near field capacity (FC). After the rehydration of the plants, when the rate of A reached 90% of the rate of the control plants, a new cycle of water deficiency was initiated. The results showed that the plants of treatment 3C obtained higher rates of A, stomatic conductance (gs), and transpiration (E) and instantaneous efficiency in the use of water (by the relationship of A/E) during the third cycle of WD, ending the cycle with 25% of available water (AW) in the substrate, in relation to the plants of 2C and 1C. The water status of the 3C plants, observed by the relative water content (RWC) to the end of the third cycle of WD, remained similar to the control plants, indicating a higher maintenance of turgor in the plant cells. The 1C plants were affected by WD, because even with 44% AW in the substrate, the fluid status within the cells was significantly reduced, and consequently the physiological processes. As to the photosynthetic pigments, the plants of treatment 3C accumulated higher levels of chloroplastid pigments, especially chlorophyll and carotenoids in relation to plants 2C and 1C. Therefore, we concluded that the plants subjected to three cycles of WD acclimated their photosynthetic machinery throughout the water stresses to which they were subjected, unlike the plants subjected to one WD cycle, because one single cycle promoted severe damage to their metabolism causing severe reduction in their physiological rates and consequent leaf abscission.
