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Growth, gas exchange, leaf nitrogen and carbohydrate concentrations in NAD‐ME and NADP‐ME C 4 grasses grown in elevated CO 2
Author(s) -
LeCain Daniel R.,
Morgan Jack A.
Publication year - 1998
Publication title -
physiologia plantarum
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.351
H-Index - 146
eISSN - 1399-3054
pISSN - 0031-9317
DOI - 10.1034/j.1399-3054.1998.1020218.x
Subject(s) - panicum virgatum , panicum , biology , andropogon , poaceae , botany , photosynthesis , chloris gayana , agronomy , bioenergy , dry matter , ecology , renewable energy
Plants with the C 4 photosynthetic pathway have predominantly one of three decarboxylation enzymes in their bundle sheath cells. Within the grass family (Poaceae) bundle sheath leakiness to CO 2 is purported to be lowest in the nicotinamide adenine dinucleotide phosphate‐malic enzyme (NADP‐ME, EC 1.1.1.40) group, highest in the NAD‐ME (EC 1.1.1.39) group and intermediate in the phosphoenolpyruvate carboxykinase (PCK, EC 4.1.1.32) group. We investigated the hypothesis that growth and photosynthesis of NAD‐ME C 4 grasses would respond more to elevated CO 2 treatment than NADP‐ME grasses. Plants were grown in 8‐1 pots in growth chambers with ample water and fertilizer for 39 days at a continuous CO 2 concentration of either 350 or 700 µl l −1 . NAD‐ME species included Bouteloua gracilis Lag. ex Steud (Blue grama), Buchloe dactyloides (Nutt.) Engelm. (Buffalo grass) and Panicum virgatum L. (Switchgrass) and the NADP‐ME species were Andropogon gerardii Vittman (Big bluestem), Schizachyrium scoparium (Michx.) Nash (Little bluestem), and Sorghastrum nutans (L.) Nash (Indian grass). Contrary to our hypothesis, growth of the NADP‐ME grasses was generally greater under elevated CO 2 (significant for A. gerardii and S. nutans ), while none of the NAD‐ME grasses had a significant growth response. Increased leaf total non‐structural carbohydrate (TNC) was associated with greater growth responses of NADP‐ME grasses. Decreased leaf nitrogen in NADP‐ME species grown at elevated CO 2 was found to be an artifact of TNC dilution. Assimilation (A) vs intercellular CO 2 (C i ) curves revealed that leaf photosynthesis was not saturated at 350 µl l −1 CO 2 in any of these C 4 grasses. Assimilation of elevated CO 2 ‐grown A. gerardii was higher than in plants grown in ambient CO 2 . In contrast, B. gracilis grown in elevated CO 2 displayed lower A, a trait more commonly reported in C 3 plants. Photosynthetic acclimation in B. gracilis was not related to leaf TNC or nitrogen concentrations, but A:C i curves suggest a reduction in activity of both phosphoenolpyruvate (PEP) carboxylase (EC 4.1.1.31) and ribulose‐1,5‐bisphosphate carboxylase/oxygenase (Rubisco, EC 4.1.1.39). Some adaptation of stomatal functioning was also seen in B. gracilis and A. gerardii leaves grown in elevated CO 2 . Our study shows that C 4 grasses have the capacity for increased growth and photosynthesis under elevated CO 2 even when water and nutrients are non‐limiting. While it was the NADP‐ME species which had significant responses in the present study, we have previously reported significant growth increases in elevated CO 2 for B. gracilis .