Abstract
The effects of CO2 enrichment on plant growth and on nitrogen partitioning were examined using soybean [Glycine max (L.) Merr. cv. Clark] leaflets. Plants were grown from single seeds in matching controlled environment chambers. Continuous ambient CO2 partial pressures were from 38 to 40 Pa and elevated CO2 treatments were 68 to 70 Pa. Total above ground biomass, total leaf area and specific leaf weight of soybean were increased 78%, 58% and 33%, respectively, in response to CO2 enrichment when measured 25 days after sowing. Total chlorophyll (a+b) was 25% greater in third trifoliolate soybean leaflets in response to CO2 enrichment but total soluble protein did not differ between treatments. These and other measurements indicated that soybean plants were nitrogen sufficient in this study. Variations of total soluble amino acids were observed in soybean leaflets and these were enhanced by CO2 enrichment when measurements were performed mid-day. However, concentrations of total amino acids were similar in both CO2 treatments by end of the photoperiod. Glycine was lower in the elevated compared to the ambient CO2 treatment suggesting that rates of photorespiration were diminished by elevated CO2. Alanine increased 20% in response to CO2 enrichment. Overall, changes of soluble amino acids in response to CO2 enrichment were smaller than in other crop species and a temporal shift occurred in the daily accumulation of amino acids in soybean leaflets.
Highlights
Photosynthetic capacity frequently decreastional to the change in CO2 concentration
The hypothesis of this study older plants were watered with nutrient soluand tobacco leaves decreased in response to was that soluble amino acid metabolism in tion twice daily to ensure nutrient sufficiency elevated CO2 treatments both in season-long soybean leaflets would respond to CO2 enrich- and to avoid drought
When measured 25 DAS total above ground biomass, total leaf area and specific leaf weight (SLW) increased (P≤0.01) by 78%, 58% and 33%, respectively, in the elevated compared to the ambient CO2
Summary
Photosynthetic capacity frequently decreastional to the change in CO2 concentration. supplemental CO2 was only provided during daylight hours and it is likely that nocturnal CO2 levels alter dark respiration rates and plant growth rates of soybean.[18]. Environmental Growth Chamber Corp., Chagrin Falls, OH, USA) essentially as described previously.[11] Plants were seeded in 1.8 dm[3] plastic pots filled with vermiculite, the air temperature was 27±1°C and the PPFD was 850±40 μmol m–2 s–1. Varying watered once daily with a complete mineral ously in CO2 enriched atmospheres.[1,2] For environmental conditions can obscure the nutrient solution containing 12 mM nitrate example, net CO2 assimilation rates, photosyn- responses of leaf metabolites to specific treat- and 2.5 mM ammonium. 19 d-old or thetic proteins and Chl(a+b) of wheat, barley ments.[19] the hypothesis of this study older plants were watered with nutrient soluand tobacco leaves decreased in response to was that soluble amino acid metabolism in tion twice daily to ensure nutrient sufficiency elevated CO2 treatments both in season-long soybean leaflets would respond to CO2 enrich- and to avoid drought. Ambient and elevated field studies and in controlled environments.[3,4,5,6,7,8,9,10] ment when using twice ambient CO2 partial chamber air CO2 partial pressures were 38±10
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