Response of five dry tropical tree seedlings to elevated CO 2 : impact of seed size and successional status

Abstract

2 area, Stomatal conductance, Transpiration, Water use efficiency Abstract. The impact of seed size and successional status on seedling growth under elevated CO was 2 studied for five dry tropical tree species viz. Albizia procera, Acacia nilotica, Phyllanthus emblica, Terminalia arjuna and Terminalia chebula. Seedlings from large (LS) and small seeds (SS) were grown at two CO levels (ambient and elevated, 700-750 ppm). CO assimilation rate, stomatal conductance, 2 2 water use efficiency and foliar N were determined after 30 d exposure to elevated CO . Seedlings were 2 harvested after 30 d and 60 d exposure periods. Height, diameter, leaf area, biomass and other growth traits (RGR, NAR, SLA, R:S) were determined. Seedling biomass across species was positively related with seed mass. Within species, LS seedlings exhibited greater biomass than SS seedlings. Elevated CO2 enhanced plant biomass for all the species. The relative growth rate (RGR), net assimilation rate (NAR), CO assimilation rate, R:S ratio and water use efficiency increased under elevated CO . However, the 2 2 positive impact of elevated CO was down regulated beyond 30 d exposure. Specific leaf area (SLA), 2 transpiration rate, stomatal conductance declined due to exposure to elevated CO . Fast growing, early 2 successional species exhibited greater RGR, NAR and CO assimilation rate. Per cent enhancement in 2 such traits was greater for slow growing species. The responses of individual species did not follow functional types (viz. legumes, non-legumes). The enhancement in biomass and RGR was greater for large-seeded species and LS seedlings within species. This study revealed that elevated CO could cause 2 large seeded, slow growing and late successional species to grow more vigorously.