Photosynthetic and stress tolerance change of Tamarixramosissima seedling under different water tables

Saplings of Tamarix ramosissima were planted in pots with simulated water tables（U1，U2，U3 andU4）of depth 1，2，3，4 m，respectively，to study the impacts of water tables on the photosynthetic characteristicsand stress tolerance of T. ramosissima. The results showed that the apparent quantum yield，dark respiration rate，carboxylation efficiency，photorespiration rate and maximum net photosynthetic rate decreased，in addition，theusing range of effective photosynthetic radiation and CO2 concentration reduced with water table lowering. Themaximum net photosynthetic rate of U1 was 25.24（±4.95）μmol/m2·s，and the maximum net photosynthetic rate ofU4 reduced by 88.99%， down to 2.78（±0.11）μmol/m2·s. Also，stomatal conductance of saplings declined and wateruse efficiency increased with water table lowering；CO2 enrichment reduced stomatal conductance of saplings，butsignificantly improved water use efficiency. With water table lowering，chlorophyll content of saplings significantlydecreased and MDA accumulated. Compared to U1，the chlorophyll contents of U2，U3 and U4 decreased by 4.6%，14.14% and 30.85%，MDA increased by 165%，256% and 225%. Drought stress increased gradually，however，T.ramosissima adapted to the effects of drought stress by improving regulating materials like proline，soluble sugarcontent and SOD，POD activity etc.