Physiological responses of young Brazil nut (Bertholletia excelsa) plants to drought stress and subsequent rewatering

Abstract

The Brazil nut tree (Bertholletia excelsa Bonpl.) is widely distributed in the Amazon region. It is subject to different rainfall regimes, particularly in El Niño years. Here, we demonstrate how biomass growth, gas exchange and biochemical traits of young B. excelsa plants were affected by imposed drought stress and subsequent rehydration. Four-month-old young plants were acclimated in a greenhouse for 15 days and received daily irrigation, after this period they were separated into two treatment: well-watered (control plants, WW) and water deficit (drought-stressed plants, DS). After 58 days of water deficit, the net photosynthetic rate (Pn) of the plants in the DS treatment regime reached values close to zero, water use efficiency significantly increased, and midday leaf water potential (Ѱleaf) reached a mean value of −4.7 MPa. The recovery of Pn and Ѱleaf to control levels was re-established after 16 days of rehydration. The DS treatment regime led to lower level of biomass (37%) when compared to plants in the WW treatment regime. The DS treatment plants had higher leaf concentrations of total soluble sugars, whereas the starch content was higher in the WW treatment regime. Our results suggest that (i) B. excelsa has a high physiological plasticity with respect to drought stress and (ii) the recovery of physiological traits was followed by the recovery of the absolute growth rates of the DS plants in the short term. These ecophysiological responses demonstrate the strong potential of this species for establishment in forest plantations in the Amazon region and its resilience during drought events.