Effects of Soil Water and Salt Contents on Photosynthetic Characteristics

One year old seedlings of baldcypress(Taxodium distichum L.) were grown in a pot under greenhouse conditions with varying soil water levels and soil salt(NaCl) (alone and in combination) levels to determine photosynthetic characteristics.There were 20 different treatments of soil water and salt contents,and the time of treatment was 100 days.The results were as follows:(1)The net photosynthetic rate,stomatal conductance,chlorophyll a concentration,chlorophyll b concentration,and chlorophyll content decreased with increasing of soil content at varying soil water content,while intercellular CO_2 concentration and chlorophyll a/b increased,but transpiration rate and respiration rate had no unanimous changing tendency;(2)The net photosynthetic rate decreased with decreasing of soil water content at varying soil salt contents,and the water treatment of W_3 among five soil water levels had a highest intercellular CO_2 concentration,chlorophyll a concentration and chlorophyll content,but stomatal conductance,transpiration rate,respiration rate,chlorophyll b concentration and chlorophyll a/b had no unanimous changing tendency;the decreasing of net photosynthetic rate of baldcypress at the soil condition of salt stress and higher water content was caused by non-stomatal limitation,but it was caused at the soil condition of drought by stomatal limitation and non-stomatal limitation;The decreasing of chlorophyll content also was one of the cause of the decreasing of net photosynthetic rate under salt stress.