Paper Reviewed
Oliveira, M.F. and Marenco, R.A. 2019. Photosynthesis and biomass accumulation in Carapa surinamensis (Meliaceae) in response to water stress at ambient and elevated CO2. Photosynthetica 57: 137-146.

Climate models predict that portions of the Amazon will experience more frequent and more severe droughts in the future in consequence of CO2-induced climate change. The impact of such predictions on the growth and physiology of tropical trees, however, remains largely unexplored.

Hoping to provide some knowledge in this area, Oliveira and Marenco (2019) recently grew andiroba trees (Carapa surinamensis) under two CO2 concentrations and two watering regimes over a period of 163 days. Their work was conducted in controlled environments at the National Institute for Research in the Amazon in Manaus, Brazil. Atmospheric CO2 concentrations included 400 or 700 ppm and the two watering regimes represented well-watered (soil kept at 100% field capacity) and drought (soil kept at 50% field capacity) conditions.

Results indicated that drought reduced the light-saturated net photosynthetic rate by 33.5% at ambient CO2 conditions, whereas elevated CO2 increased this parameter by 64% and 152% when soil water capacity was maintained at 100% and 50%, respectively (see Figure 1a). Similarly, drought negatively impacted plant biomass, whereas elevated CO2 had a positive effect (a 24% increase at 100% soil water capacity and a larger 40% increase at 50% soil water capacity; see Figure 1b). Consequently, in the words of the authors, "elevated CO2 conditions negated the effect of water stress on light-saturated net photosynthesis' and also "mitigated the effect of water stress on biomass accumulation." And these findings are important because they show the ability of Carapa to "endure drought or to improve carbon uptake at elevated CO2 conditions."

Figure 1. Light-saturated net photosynthetic rate (PNsat; Panel A) and total plant dry matter (WT; Panel B) of Carapa grown for 163 days under treatment combinations of either 400 or 700 ppm CO2 and 50% or 100% soil water capacity. Source: Oliveira and Marenco (2019).