Gas exchange characteristics of bald cypress (Taxodiumdistichum L.): evaluation of responses to leaf aging, flooding, and salinity

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Abstract
Bald cypress (Taxodium distichum L.) seedlings were subjected to flooding with saline water containing 0 to 8 parts per thousand (137 mequiv. L-1 NaCl) under controlled environment conditions. Imposition of flooding and salinity stresses was designed to simulate the increase in submergence and salinity level which Louisiana''s [USA] extensive cypress forests are currently experiencing as a result of rapid subsidence. The effect of flooding and salt water intrusion on subsequent stomatal behaviour and net photosynthesis for leaves developed before and after salt exposure were measured. Flooding and salinity resulted in a substantial decrease in stomatal conductance and net photosynthesis in both young and old leaves. Leaf aging did not significantly affect stomatal conductance and photosynthesis. Only plants flooded with freshwater and those flooded with low salinity concentration produced new leaves with improved stomatal conductance and net photosynthesis, which suggests some stomatal and photosynthetic acclimation to flooding and low salinity for bald cypress. Increase in salinity, however, caused more extensive impact and greater reductions of stomatal conductance and net photosynthesis in both leaf ages.