Gas exchange, biomass allocation and water-use efficiency in response to elevated CO 2 and drought in andiroba (Carapa surinamensis, Meliaceae)

Abstract

Prolonged droughts are predicted for some parts of the Amazon; however, it is still unclear how Amazonian trees will respond to water stress under the ongoing increase in CO 2 concentration. The aim of this study was to assess the effect of elevated CO 2 (eCO 2 ) and drought on photosynthetic rates, water-use efficiency, and biomass allocation in andiroba (Carapa surinamensis). The plants were grown in pots at ambient (400 ppm CO 2 ) and eCO 2 (700 ppm) at two water regimes, soil at 50% field capacity, FC (drought) and soil at 100% FC for 163 days. We measured light saturated photosynthesis on a mass basis (A sat-mass ), stomatal conductance to CO 2 on a mass basis (g sCO2-mass ), whole-plant water-use efficiency (WUE P ), biomass accumulation, specific leaf area (SLA) and total leaf area. At eCO 2 , A sat-mass increased 28% in well-watered plants and 93% under drought, whereas g sCO2-mass declined 39% in well-watered plants at eCO 2 , with no effect of drought on g sCO2-mass at eCO 2 . The total biomass gain improved 73% at eCO 2 and over CO 2 levels it was reduced (54%) by drought. WUE P improved (188%) at eCO 2 in well-watered plants and 262% under drought. SLA declined 23% at eCO 2 , but the effect of drought on SLA was null. On the contrary, total leaf area was greatly reduced (67%) by drought, but it was not affected by eCO 2 . The large increase in total biomass and the substantial improvement in WUE P under eCO 2 , and the sharp decline in leaf area under water stress widen our knowledge on the physiology of this important species for the forest management of large areas in the Amazon region. © SISEF.