Influence of night humidity on the distribution of calcium and sap flow intomato plants

Dry or humid night conditions were imposed to determine the distribution df calcium (Ca) and sap flow in tomato (Lycopersicon esculentum Mill.) plants . Radioisotopic Ca-45 was fed to assess the Ca distribution in a tomato pla nt treated with different night humidities on different branches. The amoun t of sap transported from root to shoot was measured by a heat-balance sap- flow gauge. More than 95% of the sap was transported to the shoots during t he daytime for 12 hours, while only negligible amount were transported at n ight. High nigh-time humidity considerably enhanced sap flow during the nig ht due presumably to generated root pressure. However, high night-time humi dity reduced the distribution of Ca-45 compared to low night-time humidity imposed in tomato branches.