Responses of Legume Versus Nonlegume Tropical Tree Seedlings to Elevated CO2 Concentration  

Abstract

We investigated responses of growth, leaf gas exchange, carbon-isotope discrimination, and whole-plant water-use efficiency (W P ) to elevated CO 2 concentration ([CO 2 ]) in seedlings of five leguminous and five nonleguminous tropical tree species. Plants were grown at CO 2 partial pressures of 40 and 70 Pa. As a group, legumes did not differ from nonlegumes in growth response to elevated [CO 2 ]. The mean ratio of final plant dry mass at elevated to ambient [CO 2 ] (M E /M A ) was 1.32 and 1.24 for legumes and nonlegumes, respectively. However, there was large variation in M E /M A among legume species (0.92-2.35), whereas nonlegumes varied much less (1.21-1.29). Variation among legume species in M E /M A was closely correlated with their capacity for nodule formation, as expressed by nodule mass ratio, the dry mass of nodules for a given plant dry mass. W P increased markedly in response to elevated [CO 2 ] in all species. The ratio of intercellular to ambient CO 2 partial pressures during photosynthesis remained approximately constant at ambient and elevated [CO 2 ], as did carbon isotope discrimination, suggesting that W P should increase proportionally for a given increase in atmospheric [CO 2 ]. These results suggest that tree legumes with a strong capacity for nodule formation could have a competitive advantage in tropical forests as atmospheric [CO 2 ] rises and that the water-use efficiency of tropical tree species will increase under elevated [CO 2 ].

Two tropical conifers show strong growth and water-use efficiency responses to altered CO2concentration

“…There was no positive response to increasing c a in either of the two angiosperm species. The lack of a growth response of Tabebuia and Chrysophyllum to c a is consistent with previous experiments in which seedlings of tropical tree species were grown in unfertilized soil (Lovelock et al, 1998;Winter et al, 2000;Cernusak et al, 2011). The causes of differential responses of plants to elevated c a in greenhouse experiments have recently been revisited by Ali et al (2013).…”

“…Both Tabebuia and Chrysophyllum have been used extensively in previous ecophysiological work in Panama (e.g. Cernusak et al, 2008Cernusak et al, , 2011. All four genera form arbuscular mycorrhizal associations (Dickie and Holdaway, 2010).…”

Tropical forest responses to increasing atmospheric CO2: current knowledge and opportunities for future research

“…At the leaf level, g s typically declines in response to elevated c a (Wullschleger et al 2002;Ainsworth and Rogers 2007), although not always (Körner and Würth 1996;Keel et al 2007). Declining g s in response to elevated c a has been observed in seedlings and saplings of tropical tree species (Berryman et al 1994;Goodfellow et al 1997;Cernusak et al 2011b). An example of the response of g s to growth at elevated compared with ambient c a is shown in Fig.…”

Seed germination in <em>Ormosia macrocalyx</em>, an endangered tropical forest tree

“…Ormosia macrocalyx plays an important role in CO 2 uptake by the forest biomass, and the effect of carbon capture by forests provides an important opportunity in land management to increase the capacity of the soil to respond to disturbances that arise from the intense pressures of both land use and climate change (Banwart et al 2015). Cernusak et al (2011) found that O. macrocalyx can reach high nodulation rates (48.9 mg·g -1 ) on unfertilized soils and provided evidence for a positive relationship between N 2 fixation and nodule mass ratio, inferring that this tree has the highest rate of N 2 fixation relative to other leguminous species. They estimated the proportion of the plant N acquired by N 2 fixation to be about 84 %.…”