Responses of drylands woody vegetation to elevated CO2: review of
consequences and research needs.
Abstract
Global changes such as elevated carbon dioxide [eCO2] and warming
have been described as the most serious environmental threats to our
planet. Elevated CO2 may have important consequences on forested
ecosystems. Although, the impact is worse in dryland ecosystems as
atmospheric changes increase aridity and change soil fertility, but it
remains unknown. The study aiming at understanding the effects of eCO2
and its consequences on Hashab (Acacia senegal) as a dryland C3 tree
species with substantial ecological and economic roles. We
quantitatively reviewed and discussed over 50 papers on the literature
about CO2 elevation (eCO2) effects on C3 plant and ecosystems to
understand how eCO2 will affect dryland C3 species of sub-Saharan
Africa. We found in the literature that, for C3 species generally eCO2
increases photosynthesis rate and reduces stomatal conductance but with
increased plant leaves’ area leading to release water. Water loss due to
stomatal conductance is unavoidable in dryland ecosystems. More seeds
can be produced in eCO2 but with mostly correlated seed low quality
which may limit seedling recruitment. Seedlings, as the most responsive
stage to eCO2, may respond by enhancing growth and biomass production or
experience photosynthesis down regulation and/or photorespiration. The
results suggested that A. senegal, as a C3 and leguminous species will
respond to eCO2 by two scenarios; 1) positively through enhancing growth
and biomass or; 2) a negative photosynthetic acclimation that could be
due to physiological dysfunction that resulted in metabolic compulsions.
The responses need to be further investigated under different ecological
conditions to feedback the global changes and ecosystem monitoring
including changes of species composition is recommended.