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United States Department of Agriculture

Agricultural Research Service

Title: The Interactive Effects of Elevated CO2 and Ozone on Leaf Thermotolerance in Field-Grown Glycine Max (Soybean)

Authors
item Sasmita, Mishra - THE UNIVERSITY OF TOLEDO
item Heckathorn, Scott - THE UNIVERSITY OF TOLEDO
item Barua, Deepak -
item Wang, Dan - THE UNIVESITY OF TOLEDO
item Joshi, Puneet -
item Hamilton, William - WASHINGTON AND LEE UNIVER
item Frantz, Jonathan

Submitted to: Journal of Integrative Plant Biology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: August 15, 2008
Publication Date: October 1, 2008
Repository URL: http://hdl.handle.net/10113/32336
Citation: Sasmita, M., Heckathorn, S.A., Barua, D., Wang, D., Joshi, P., Hamilton, W., Frantz, J. 2008. The Interactive Effects of Elevated CO2 and Ozone on Leaf Thermotolerance in Field-Grown Glycine Max (Soybean). Journal of Integrative Plant Biology. 50:1396-1405.

Interpretive Summary: Human activity is increasing atmospheric CO2, which is increasing both average global temperatures and heat waves. Laboratory studies have shown that elevated CO2 can increase tolerance of photosynthesis to heat waves in most crop plants. However, human-caused increases in ground-level ozone, which causes oxidative stress and damages photosynthesis, may offset benefits of elevated CO2 during heat waves. In this study, we determined the effects of elevated CO2 and O3 on the heat tolerance of leaves of field-grown soybean. Experiments were conducted on plants grown at normal (~380 ppm) or enriched (~550ppm) CO2 and/or ambient or elevated ozone at the University of Illinois Soybean Free Air Concentration Enrichment (SoyFACE) site (Illinois, USA). Photosynthetic electron transport was measured in attached leaves heated in the field and in heated detached leaves under ambient CO2 and ozone. Heat stress decreased electron transport and ozone made this decrease more pronounced. Elevated CO2 prevented ozone-related decreases during heat stress. However, elevated CO2 improved electron transport only when no ozone stress was present. CO2 and ozone effects on electron transport during heat stress were dependant on the amount of light that was given to the leaves. Heat stress decreased chlorophyll content, especially under elevated CO2; similar trends were seen for light-harvesting pigments. Neither CO2 nor ozone had any effect on production of proteins that help plants tolerate heat stress. Heat stress increased two anti-oxidant proteins, while the increase in CO2 and ozone tended to decrease one of those proteins. Soluble sugar content within the leaves was not affected by heat stress, but increased in elevated CO2. Together, these results indicate that elevated CO2 provides plants modest protection of photosynthesis during heat stress in soybean; high CO2 limits damage during heat stress under elevated O3, but this protection is not due to increased production of heat-stress-protection proteins. This information will help in predicting the general stress response of many crop plants to climatic change during crop production.

Technical Abstract: Human activity is increasing atmospheric CO2, which is increasing both mean global temperatures and acute heat stress (heat waves). Laboratory studies have shown that elevated CO2 can increase tolerance of photosynthesis to acute heat stress in C3 plants. However, human-caused increases in ground-level ozone (O3), which causes oxidative stress and damages photosynthesis, may offset benefits of elevated CO2 during heat waves. In this study, we determined the effects of elevated CO2 and O3 on the heat tolerance of leaves of field-grown Glycine max (soybean). Experiments were conducted on plants grown at ambient or 550ppm CO2 and/or ambient or 1.2 x ambient O3 at the University of Illinois Soybean Free Air Concentration Enrichment (SoyFACE) site (Illinois, USA). Photosynthetic electron transport (Pnet) was measured in attached leaves heated in situ and in heated detached leaves under ambient CO2 and O3; biochemical assays were conducted on leaves of plants heated in the lab. Heat stress decreased Pnet and O3 exacerbated this decrease. Elevated CO2 prevented O3-related decreases during heat stress, but only increased Pet under ambient O3 in the field. CO2 and O3 effects on Pnet during heat stress were light dependent. Heat stress decreased chlorophyll content, especially under elevated CO2; similar trends were seen for carotenoids. Neither CO2 nor O3 had any effect on production of heat-shock proteins (HSP 70, HSP 60, and small HSP) during heat stress. Heat stress increased catalase (excluding in elevated O3) and Cu/Zn-SOD content, but not Mn-SOD; CO2 and O3 tended to decrease catalase and did not affect Mn- or Cu/Zn-SOD. Soluble carbohydrate content was unaffected by heat stress, but increased in elevated CO2. Together, these results indicate that modest protection of photosynthetic metabolism during heat stress by elevated CO2 is observed in G. max in field-grown plants under ambient O3, as in the lab, and high CO2 limits damage during heat stress under elevated O3, but this protection is likely related to decreased photorespiration and stomatal conductance rather than increased production of heat-stress adaptations.

Last Modified: 7/30/2014
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