394-8 Soybean Gas Exchange and Chlorophyll Fluorescence As Affected By K Supply Under Ambient and Elevated CO2 Concentration.
Poster Number 519
See more from this Division: C02 Crop Physiology and MetabolismSee more from this Session: Crop Physiology and Metabolism: I
Wednesday, November 5, 2014
Long Beach Convention Center, Exhibit Hall ABC
Potassium (K) deficiency adversely affects many of the vital processes inside the plant such as water relation, photosynthesis, cell expansion, assimilates transport, and enzyme activation. The K availability in soil nutrients may exert a major control over the plant response to rising atmospheric carbon dioxide (CO2) . To evaluate the combined effects of K and CO2 on soybean gas exchange and chlorophyll fluorescence, plants were grown in controlled environment growth chambers with three levels of K supply (optimum, 5.0 mM; K-stress, 0.50 and 0.02 mM) under ambient (aCO2, 400 ppm) and elevated (eCO2 800 ppm) CO2. Photosynthesis (Pnet) and chlorophyll a fluorescence (Fvʹ/Fmʹ) were measured at ambient oxygen (O2 ≈21%) and low O2 (2%) exhibiting photo-respiratory (PR) and non photo-respiratory (NPR) conditions, respectively. At the lowest K supply, Pnet decrease by 68% but did not differ between the two higher K supply. Elevated CO2 increased Pnet by 11-25% across the K nutrition. Stomatal conductance consistently decreased due to K deficiency (45%) and eCO2 (37%). However, Fvʹ/Fmʹ was not affected by ether of the treatments. Both the photo-respiration (differences in Pnet at NPR vs. PR condition) and the day-respiration increased 50-150% under K deficiency across CO2 level. However, eCO2, decreased the photo-respiration by 54% but increased the day-respiration by 36%, when averaged across K supply. Compared to the optimum K supply, the maximum carboxylation efficiency (VCmax) and the maximum rate of photosynthetic electron transport (Jmax) either increased by 10-34% at 0.50 mM K or decreased by 30% at 0.02 mM K across CO2 levels. However, mesophyll conductance decreased markedly under K deficiency by 41-81% and eCO2 by 30%. Irrespective of the K supply, photosynthetic acclimations of soybean plants to CO2 enriched environments were evident from the reduced quantum yields and carboxylation efficiency of the photosynthetic processes. . The results from this study clearly indicated that the amount of available soil K will affect soybean photosynthetic processes independent of CO2 concentration. Moreover, the beneficial effect of eCO2 on photosynthesis will be offset by severe K deficiency.
See more from this Division: C02 Crop Physiology and MetabolismSee more from this Session: Crop Physiology and Metabolism: I