Publication Date:
2013-05-16
Description:
Climate change may alter forest composition by differentially affecting the responses of faster- and slower-growing tree species to drought. However, the combined effects of rising atmospheric CO 2 concentration ([CO 2 ]) and temperature on drought responses of trees are poorly understood. Here, we examined interactive effects of temperature (ambient, ambient + °C) and [CO 2 ] (290, 400 and 650mu;l l –1 ) on drought responses of Eucalyptus saligna Sm. (faster-growing) and E . sideroxylon A. Cunn. ex Woolls (slower-growing) seedlings. Drought was imposed via a controlled reduction in soil water over 1–2 weeks, re-watering seedlings when leaves visibly wilted. In ambient temperature, the effect of drought on the light-saturated net photosynthetic rate ( A sat ) in E . saligna decreased as [CO 2 ] increased from pre-industrial to future concentrations, but rising [CO 2 ] did not affect the response in Eucalyptus sideroxylon . In contrast, elevated temperature exacerbated the effect of drought in reducing A sat in both species. The drought response of A sat reflected changes in stomatal conductance ( g s ) associated with species and treatment differences in (i) utilization of soil moisture and (ii) leaf area ratio (leaf area per unit plant dry mass). Across [CO 2 ] and temperature treatments, E . saligna wilted at higher soil water potentials compared with E . sideroxylon . Photosynthetic recovery from drought was 90% complete 2 days following re-watering across all species and treatments. Our results suggest that E . saligna (faster-growing) seedlings are more susceptible to drought than E . sideroxylon (slower-growing) seedlings. The greater susceptibility to drought of E . saligna reflected faster drawdown of soil moisture, associated with more leaf area and leaf area ratio, and the ability of E . sideroxylon to maintain higher g s at a given soil moisture. Inclusion of a pre-industrial [CO 2 ] treatment allowed us to conclude that susceptibility of these species to short-term drought under past and future climates may be regulated by the same mechanisms. Further, the beneficial effects of rising [CO 2 ] and deleterious effects of elevated temperature on seedling response to drought were generally offsetting, suggesting susceptibility of seedlings of these species to short-term drought in future climates that is similar to pre-industrial and current climate conditions.
Print ISSN:
0829-318X
Electronic ISSN:
1758-4469
Topics:
Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
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