PARENT SESSION
Oral Session # 8: Plant Ecology I: Physiology and Function I.
Presiding: E Hamerlynck
Monday, August 4. 8:00 AM to 11:30 AM, SITCC Meeting Room 200.
Competition between NAD-ME and NADP-ME C4 grasses across a nitrogen gradient.
Keelin, Cheryl1, O'Brien, Sean1, Taub, Daniel*,1, 1 Southwestern University, Georgetown, Texas
ABSTRACT- There are three distinct biochemical variants of C4 photosynthesis, each performed by different C4 plant species. These three variants are called the NAD-ME, NADP-ME and PCK variants, after the bundle sheath decarboxylation enzyme used in each pathway. Some previous research has suggested that there may be differences amongst species using the different pathways in responses to nitrogen, but very little work has been done to explore this possibility. In this study we examined the competitive interactions of NAD-ME and NADP-ME species across a nitrogen gradient under greenhouse conditions. We grew three NAD-ME grass species and three NADP-ME grass species in every pairwise combination of an NAD-ME and an NADP-ME species (nine combinations in all), as well as each species individually. Plants were grown in pots at five different levels of IBDU nitrogen fertilizer for six weeks, following which the aboveground biomass was collected, dried and weighed. In monoculture, all species showed a positive growth response to nitrogen. There were significant differences amongst the species in the slope of the regression of aboveground biomass on nitrogen supply, but there was no consistent pattern of differences between the C4 variants. In six of the nine pairwise competition treatments, the NAD-ME species increased as a proportion of aboveground biomass as nitrogen supply increased. This provides qualified support to the hypothesis that NAD-ME species are superior competitors to NADP-ME species under high nitrogen fertility conditions.
Key words: nitrogen, C4 photosynthesis, competition, grass