Effects of Air Temperature, Relative Humidity and Photosynthetic Photon Flux on the Evapotranspiration Rate of Grafted Seedlings Under Artificial Lighting

Abstract

Four air temperature levels of 23, 25, 27 and 29C, three humidity levels of 85, 90 and 95%R.H. and two photosynthetic photon flux (PPF) levels of 30 and 50 jumol m-2 s-1 were provided to investigate the effects of air temperature, relative humidity and light intensity on the evapotranspiration rate (EVTR) of watermelon grafted seedlings. EVTR of grafted seedlings increased with increasing air temperature and the passage of time after grafting. Also EVTR increased with decreasing relative humidity. EVTR of grafted seedlings at dark period reduced by half of those at photoperiod. Effect of relative humidity on the EVTR of grafted seedlings was distinctly shown at relatively high PPF. As the vapor pressure deficit decreased, the graft-taking of grafted seedlings increased. Under the high humidity more than 90%, EVTR was gradually increased with days after grafting and thus the scion and rootstock were also smoothly joined together. It is required to control optimally the environment for decreasing the vapor pressure deficit and preventing the wilting of grafted seedlings under artificial lighting during first 2–3 days after grafting. And then it is suggested to lower the relative humidity and raise the PPF by steps for the robust joining of grafted seedlings.