Maximum CO2 assimilation in young Eucalyptus plantations is higher than in Brazilian savanna trees during dry field seasons

Abstract

In terms of some specifics parameters, Eucalyptus and savanna trees were characterized by similar responses of resource use under field conditions. Remarkably, young eucalypt exhibited greater photosynthetic capacity, primarily in the dry season. Although a growing demand for paper and pulp is enhancing pressure for land use to increase eucalypt plantations in tropical savanna regions around the world, it has not been thoroughly characterized to date how eucalypt plantations perform in terms of energy, water and CO2 assimilation exchange compared to native savanna species. In this study, we performed an integrative analysis of diurnal changes in gas exchange, chlorophyll fluorescence (Fv/Fm) and water use efficiency of eucalypt and savanna species over a whole year in the Brazilian tropical savanna region in eastern Mato Grosso do Sul State. We also evaluated the response curves of net photosynthetic rate (A) in response to photosynthetic photon flux density in leaves of these species during both wet and dry seasons. Although dry season conditions led to decreases in all parameters, primarily in stomatal conductance (gs), Fv/Fm values remained above the level that causes photoinhibition. Young eucalypt exhibited mostly similar Amax values in wet and dry seasons, but adult eucalypt and savanna trees decreased their Amax by 83% and 69% in the dry season, respectively. Overall, all species were similar in photosynthetic terms and intrinsic water use efficiency (WUEi), as demonstrated via principal component analysis. Despite major differences between wet and dry seasons, eucalypt plantations and savanna woody species were characterized by similar responses of resource use efficiency under field conditions. Remarkably, young eucalypt was characterized by higher photosynthetic capacity, particularly during the dry season.