Photosynthetic acclimation to elevated CO₂ is dependent on N partitioning and transpiration in soybean

• Published in: Plant science (Limerick) 2009-11, Vol.177 (5), p.398-403
• Main Authors: Kanemoto, Kenji, Yamashita, Yumiko, Ozawa, Tomoko, Imanishi, Naomi, Nguyen, Nguyen Tran, Suwa, Ryuichi, Mohapatra, Pravat Kumar, Kanai, Syunsuke, Moghaieb, Reda E, Ito, Junki, El-Shemy, Hany, Fujita, Kounosuke
• Format: Article
• Language: English
• Subjects: Biological and medical sciences; carbon dioxide; dry matter accumulation; elevated atmospheric gases; Fundamental and applied biological sciences. Psychology; Glycine max; leaves; long term experiments; nitrogen; nitrogen content; nutrient partitioning; nutrient uptake; photosynthesis; plant-water relations; roots; soybeans; stems; stomatal conductance; transpiration
• ISSN: 0168-9452; 1873-2259
• DOI: 10.1016/j.plantsci.2009.06.017

Physiological processes that modulate photosynthetic acclimation to rising atmospheric CO₂ concentration are subjects of intense discussion recently. Apparently, the down-regulation of photosynthesis under elevated CO₂ is not understood clearly. In the present study, the response of soybean (Glycine max L.) to CO₂ enrichment was examined in terms of nitrogen partitioning and water relation. The plants grown under potted conditions without combined N application were exposed to either ambient air (38Pa CO₂) or CO₂ enrichment (100Pa CO₂) for short (6 days) and long (27 days). Plant biomass, apparent photosynthetic rate, transpiration rate and ¹⁵N uptake and partitioning were measured consecutively after elevated CO₂ treatment. Long-term exposure reduced photosynthetic rate, stomatal conductance and transpiration rate. In contrast, short-term exposure increased biomass production of soybean due to increase in dry weight of leaves. Leaf N concentration tended to decrease with CO₂ enrichment, however such difference was not true for stem and roots. A close correlation was observed between transpiration rate and ¹⁵N partitioned into leaves, suggesting that transpiration plays an important role on nitrogen partitioning to leaves. In conclusion existence of a feed back mechanism for photosynthetic acclimation has been proposed. Down-regulation of photosynthetic activity under CO₂ enrichment is caused by decreasing leaf N concentration, and reduced rate of transpiration owing to decreased stomatal conductance is partially responsible for poor N translocation.