Increased vapor pressure deficit due to higher temperature leads to greater transpiration and faster mortality during drought for tree seedlings common to the forest–grassland ecotone

• Published in: The New phytologist Vol. 200; no. 2; pp. 366 - 374
• Main Authors: Will, Rodney E., Wilson, Stuart M., Zou, Chris B., Hennessey, Thomas C.
• Format: Journal Article
• Language: English
• Published: England New Phytologist Trust 01.10.2013; Wiley Subscription Services, Inc
• Subjects: Climate change; Drought; Droughts; Ecotones; Forest ecology; Forests; Gas exchange; Grasslands; Habitat selection; Hot Temperature; Measurement; Mortality; Photosynthesis - physiology; Plant Leaves - physiology; Plant species; Plant Transpiration - physiology; Plants; Regeneration; Regeneration (biological); Seedlings; Seedlings - physiology; Survival; Temperature; Transpiration; Trees; Trees - physiology; United States; Vapor Pressure; vapor pressure deficit (VPD); Vapors; Vapour pressure; Water - physiology; Water potential; Water temperature; Water use; Xylem; United States; mortality; vapor pressure deficit (VPD); transpiration; water potential; drought; seedlings
• ISSN: 0028-646X; 1469-8137
• DOI: 10.1111/nph.12321

Tree species growing along the forest–grassland ecotone are near the moisture limit of their range. Small increases in temperature can increase vapor pressure deficit (VPD) which may increase tree water use and potentially hasten mortality during severe drought. We tested a 40% increase in VPD due to an increase in growing temperature from 30 to 33°C (constant dewpoint 21°C) on seedlings of 10 tree species common to the forest–grassland ecotone in the southern Great Plains, USA. Measurement at 33 vs 30°C during reciprocal leaf gas exchange measurements, that is, measurement of all seedlings at both growing temperatures, increased transpiration for seedlings grown at 30°C by 40% and 20% for seedlings grown at 33°C. Higher initial transpiration of seedlings in the 33°C growing temperature treatment resulted in more negative xylem water potentials and fewer days until transpiration decreased after watering was withheld. The seedlings grown at 33°C died 13% (average 2 d) sooner than seedlings grown at 30°C during terminal drought. If temperature and severity of droughts increase in the future, the forest–grassland ecotone could shift because low seedling survival rate may not sufficiently support forest regeneration and migration.