Comparison of Gas Exchange in Moringa oleifera and other Drought Tolerant Tree Species for Climate Change Mitigation under Semi-arid Condition of Northern South Africa

摘要

Climate change has modified rainfall and temperature patterns especially in semi-arid areas. One practical way to cope with this challenge is to plant trees that could have a great influence on environmental perturbations. Plants act as carbon sink minimize carbon dioxide (CO 2 ) from the atmosphere during photosynthesis and stores excess carbon as biomass in their parts. This study was conducted under semi-arid condition of northern South Africa to evaluate the physiological parameters of three drought tolerant tree species for their comparative tendency to mitigate climate change. An existing moringa (Moringa oleifera) trial, planted at a population of 5000 plants ha -1 was used in this study. The other two naturally growing tree species were mopane (Colophospermum mopane) and marula (Sclerocarya birrea) growing within the moringa trial vicinity were included in the study as a control. Eight trees from each species were tagged for data collection. The photosynthetic rate (A), stomatal conductance (gs), transpiration rate (E) and sub-stomatal CO 2 (Ci) measurements were measured using a fully- expanded leaf on the abaxial side of each selected leaf using a non-destructive method. Furthermore, three fully expanded leaves were sampled from one tree of each species to determine leaf stomatal density in each replication. The tree species differed significantly in gas exchange, although moringa showed highest activity of all the parameters measured. Stomatal density was also different among the species, being 281.8, 355.2 and 930.6 per unit area for marula, mopane and moringa species, respectively. Moringa maintained good leaf yield even under drought condition, indicated its potential to act as a good sink for CO 2 assimilation. The results strongly showed the superiority of moringa in capturing more carbon among the three species. Moringa can therefore be recommended for climate change mitigation in semi-arid areas of Limpopo province and possibly other areas.