Title : Photosynthesis and Growth Responses of Mustard (Brassica juncea L. cv Pusa Bold) Plants to Free air carbon dioxide Enrichment (FACE)
Abstract:
Increased atmospheric [CO2] is likely to affect photosynthesis, plant growth and yield potential of plants. Mustard (Brassica juncea L.) is an important oil seed crop that is widely grown in India. Therefore, the impact of elevated [CO2] (585 ?mol mol-1) on pigment and protein content, chlorophyll a fluorescence, photosynthetic electron transport reactions, CO2 assimilation, biomass production and seed yield potential was measured in Brassica juncea cv Pusa Bold, grown inside free air carbon dioxide enrichment (FACE) rings installed on the campus of Jawaharlal Nehru University, New Delhi, India. Plants were grown for three consecutive winter seasons (2010—2013), in ambient (385 ?mol mol-1) or elevated [CO2] (585?mol mol-1), in open field conditions. Electron transport rate, photosystem I, photosystem II and whole chain electron transport rates increased by 3-5% in elevated [CO2]. However, the net photosynthesis rate increased by ≈50% in 3 growing seasons under elevated [CO2] condition. The stomatal conductance and transpiration rate decreased resulting in higher photosynthetic water use efficiency. The photosynthesizing surface, i.e. number of leaves per plant and leaf area index substantially increased leading to higher biomass and seed yield under elevated [CO2] condition. The quantum yield of photosynthetic CO2 assimilation measured at limiting light intensities, in ambient CO2 was 0.058 and it increased to 0.745 in high [CO2]. The ACi curve did not reveal any downregulation of Rubisco in mustard plants grown in elevated [CO2]. Acclimatory downregulation of photosynthesis and plant productivity was not observed in 3 consecutive growing years suggesting that in the absence of nutrient limitation, Brassica juncea is highly responsive to elevated CO2 whose yield potential shall increase in changing climatic conditions.
