Photosynthesis adaptation to long- and short-term water restriction in commercial plantlets of Eucalyptus grandis and hybrids with Red Gums

Eucalyptus grandis and Red-Gum hybrid plantlets differ in the photosynthetic responses to long and short-term water restriction, leading to different adaptation mechanisms to cope with stress.

Eucalypts are the most planted forest species in Uruguay and face frequent drought events, which impact plantlet's establishment. Information needs to be included regarding the behavior of promising clones in such conditions. This work aimed to analyze the effects of short and long-term water restriction (WR) on photosynthetic parameters and whether they enable the plant to cope with water shortage. One clone of Eucalyptus grandis (GG) and interspecific hybrids of E. grandis × E. camaldulensis (GC) and E. grandis × E. tereticornis (GT) were subjected to WR defined by soil water potential. At 6 and 16 weeks after treatment imposition, chlorophyll (%Chl) carotenoids (%Carot), maximum net assimilation rate (A_max), stomatal conductance (g_S), leaf transpiration rate (E), light saturation point (LSP) and quantum efficiency (ΦPSII) were assessed. Our results showed that the clones behaved differently. GG minimized water loss significantly to avoid the stress condition through strong stomatal regulation while GC and GT adapted their photosynthetic structure and thus were able to cope with water shortage. Unexpectedly, GT increased A_max significantly under short-term WR, suggesting an early adaptation mechanism to WR. In the long-term WR condition, both hybrids increased %Chl, ΦPSII and A_max while reducing g_S and water uptake. These results suggest that Red-Gum hybrids experienced a “priming” effect of a sublethal dose of WR that enabled them to cope with drought stress in the long term.