Seasonal variation in net ecosystem CO2 exchange of a Brazilian seasonally dry tropical forest.

Forest ecosystems sequester large amounts of atmospheric CO2, and the contribution from seasonally dry tropical forests is not negligible. Thus, the objective of this study was to quantify and evaluate the seasonal and annual patterns of CO2 exchanges in the Caatinga biome, as well as to evaluate the ecosystem condition as carbon sink or source during years. In addition, we analyzed the climatic factors that control the seasonal variability of gross primary production (GPP), ecosystem respiration (Reco) and net ecosystem CO2 exchange (NEE). Results showed that the dynamics of the components of the CO2 fluxes varied depending on the magnitude and distribution of rainfall and, as a consequence, on the variability of the vegetation state. Annual cumulative NEE was significantly higher (p < 0.01) in 2014 (-169.0 g C m-2) when compared to 2015 (-145.0 g C m-2) and annual NEP/GPP ratio was 0.41 in 2014 and 0.43 in 2015. Global radiation, air and soil temperature were the main factors associated with the diurnal variability of carbon fluxes. Even during the dry season, the NEE was at equilibrium and the Caatinga acted as an atmospheric carbon sink during the years 2014 and 2015.

Croton blanchetianus modulates its morphophysiological responses to tolerate drought in a tropical dry forest.

An understanding of variations in morphophysiological leaf traits of plant models in dry tropical forests is essential for quantifying C fluxes from forest ecosystems in response to climate changes. The present study evaluated the influences of seasonal rainfall and different light conditions on the gas exchange, nutrients, organic compounds and morphological traits in Croton blanchetianus Baill. trees within a fragment of Caatinga forest. Stomatal conductance (gs) and net photosynthesis (PN) demonstrated variations within the diurnal cycle, with maximum values at approximately midday and minimum values at predawn. The PN and the diurnal integrated CO2 assimilation were lower during the dry season than in the rainy season. Water use efficiency was positively correlated with PN (r=0.73) during the dry season only. However, the correlation between PN and gs was observed during the rainy season only (r=0.60). Thus we demonstrated that C. blanchetianus has a remarkable ability to adapt to global climatic changes and could be considered a model in studies exploring water relationships in woody plants; consequently, this species may be important in future reforestation studies.