Coordinated responses of plant hydraulic architecture with the reduction of stomatal conductance under elevated CO₂ concentration
2018
Hao, Guang-You | Holbrook, N Michele | Zwieniecki, Maciej A. | Gutschick, Vincent P | BassiriRad, H. (Hormoz) | Oren, Ram
Stomatal conductance (gₛ) generally decreases under elevated CO₂ concentration (eCO₂) and its sensitivity varies widely among species, yet the underlying mechanisms for these observed patterns are not totally clear. Understanding these underlying mechanisms, however, is critical for addressing problems regarding plant–environment interactions in a changing climate. We examined gₛ, water transport efficiency of different components along the whole-plant hydraulic system and allometric scaling in seedlings of six tree species grown under ambient and eCO₂ treatments (400 and 600 ppm, respectively). Growth under eCO₂ caused gₛ to decrease in all species but to highly variable extents, ranging from 13% (Populus tremuloides Michx.) to 46% (Gymnocladus dioicus (L.)). Accompanying this significant decrease in gₛ, substantial changes in plant hydraulic architecture occurred, with root hydraulic conductance expressed both on leaf area and root mass bases overall exhibiting significant decreases, while stem and leaf hydraulic efficiency either increased or showed no consistent pattern of change. Moreover, significant changes in allometry in response to eCO₂ affected the whole-plant water supply and demand relations. The interspecific variation in gₛ response among species was not correlated with relative changes in stem and leaf hydraulic conductance but was most strongly correlated with the relative change in the allometric scaling between roots and leaves, and to a lesser extent with the intrinsic root hydraulic conductance of the species. The results underscore that allometric adjustments between root and leaf play a key role in determining the interspecific sensitivity of gₛ responses to eCO₂. Plant hydraulics and their associated allometric scaling are important changes accompanying gₛ responses to eCO₂ and may play important roles in mediating the interspecific variations of leaf gas exchange responses, which suggests that mechanistic investigations regarding plant responses to eCO₂ need to integrate characteristics of hydraulics and allometric scaling in the future.
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