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United States Department of Agriculture

Agricultural Research Service

Research Project: IMPACTS OF RISING ATMOSPHERIC CARBON DIOXIDE AND TEMPERATURE ON CROP GROWTH, REPRODUCTIVE PROCESSES, YIELD, AND SEED QUALITY Title: Vapor pressure deficit effects on leaf area expansion and transportation of soybean subjected to soil drying

Authors
item Fletcher, Andrew - UNIVERSITY OF FLORIDA
item Sinclair, Thomas - UNIVERSITY OF FLORIDA
item Allen, Leon

Submitted to: Soil and Crop Science Society of Florida Proceedings
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: July 2, 2008
Publication Date: December 1, 2008
Citation: Fletcher, A.L., Sinclair, T.R., Allen Jr, L.H. 2008. Vapor pressure deficit effects on leaf area expansion and transportation of soybean subjected to soil drying. Soil and Crop Science Society of Florida Proceedings. 67:15-20.

Interpretive Summary: Soil water deficit limits transpiration rate (TR) of plants whereas dry air (air with high leaf-to-air vapor pressure difference, VPD) increases TR. But the combined effects of soil water deficit and VPD on leaf growth (plant leaf area expansion, PLAE), are less defined. ARS and University of Florida scientists at Gainesville, Florida studied the combined effects of soil drying, VPD, and their interaction on TR and PLAE. They placed potted soybean plants in growth chambers maintained at either high VPD (weighted mean VPD of 2.08 kPa) or low VPD (mean VPD of 1.27 kPa). Control plants were maintained well-watered while treatment pots progressively dried over 12-14 d. Soil drying was quantified as the fraction transpirable soil water (FTSW) which could range from 1.0 (fully watered) to 0.0 (dry). Within each VPD, TR was similar to the well-watered controls until FTSW decreased to 0.25 and below. Also, PLAE was unaffected until FTSW decreased to 0.24 and below in both VPD treatments. These results showed that both decreasing FTSW and high VPD decreased PLAE, but that these two factors did not interact. Finally, the response of PLAE to the FTSW break point in was similar to the TR breakpoint—both at FTSW of about 0.25.

Technical Abstract: Effects of leaf-to-air vapor pressure difference (VPD) and soil water deficit on transpiration rate (TR) of plants are well understood but their effects on plant leaf area expansion (PLAE) are less defined. Both PLAE and TR are unaffected by soil drying until the fraction transpirable soil water (FTSW) decreases to about 0.25-0.35. High VPD increases TR and may decrease the expansion of leaves. This study examined the effect of soil drying, VPD, and their interaction on TR and PLAE. Potted soybean plants with 4 trifoliolate leaves were placed in growth chambers at either high VPD (weighted mean VPD = 2.08 kPa) or low VPD (mean VPD = 1.27 kPa). Control plants were maintained well-watered, while treatment pots progressively dried over 12-14 d. High VPD increased TR of well-watered controls by 24% over the low VPD treatment. Within each VPD, TR was similar to the well-watered controls until FTSW = 0.25. As FTSW declined PLAE was unaffected until FTSW = 0.24 in both VPD treatments. In control plants, high VPD resulted in progressive decreases in PLAE to only 43% of the low VPD plants by the end of the study. These results showed that both decreasing FTSW and high VPD decreased PLAE, but that these two factors did not interact.

Last Modified: 10/25/2014
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