Implications of the mesophyll conductance to CO 2 for photosynthesis and water‐use efficiency during long‐term water stress and recovery in two contrasting E ucalyptus species

• Published in: Plant, cell and environment cell and environment, 2014-11, Vol.37 (11), p.2470-2490
• Main Authors: CANO, F. JAVIER, LÓPEZ, ROSANA, WARREN, CHARLES R.
• Format: Article
• Language: English
• ISSN: 0140-7791; 1365-3040
• DOI: 10.1111/pce.12325

Water stress ( WS ) slows growth and photosynthesis ( A n ), but most knowledge comes from short‐time studies that do not account for longer term acclimation processes that are especially relevant in tree species. Using two E ucalyptus species that contrast in drought tolerance, we induced moderate and severe water deficits by withholding water until stomatal conductance ( g sw ) decreased to two pre‐defined values for 24 d, WS was maintained at the target g sw for 29 d and then plants were re‐watered. Additionally, we developed new equations to simulate the effect on mesophyll conductance ( g m ) of accounting for the resistance to refixation of CO 2 . The diffusive limitations to CO 2 , dominated by the stomata, were the most important constraints to A n . Full recovery of A n was reached after re‐watering, characterized by quick recovery of g m and even higher biochemical capacity, in contrast to the slower recovery of g sw. The acclimation to long‐term WS led to decreased mesophyll and biochemical limitations, in contrast to studies in which stress was imposed more rapidly. Finally, we provide evidence that higher g m under WS contributes to higher intrinsic water‐use efficiency (i WUE ) and reduces the leaf oxidative stress, highlighting the importance of g m as a target for breeding/genetic engineering. Recent years have seen increasing interest in mesophyll conductance ( g m ) as a key component of plant carbon balance, especially under water deficit. Exposure of E ucalyptus spp. to long‐term water deficit highlighted the important role of g m in provoking higher intrinsic water use efficiency ( iWUE ) and lower leaf oxidative stress of water stressed plants. Additionally we discuss potential sources of error that may bias estimation of g m and developed new equations to simulate the effect of resistance to refixation of CO 2 on estimates of g m . Commentary: Mesophyll Conductance with a Twist: A comment on “Implications of the mesophyll conductance to CO2 for photosynthesis and water use efficiency during long‐term water stress and recovery in two contrasting Eucalyptus species”