Microclimate for Cryptomeria japonica seedlings in treeshelters - Mitigation of severe condition by seedling transpiration

We studied the microclimate inside treeshelters to examine how they affected growth of Japanese cedar (Cryptomeria japonica) seedlings in western Japan. Air temperature (T), relative humidity (RH), and photosynthetic active radiation (PAR) were measured inside and outside of commonly used design of tubular treeshelters made of translucent polypropylene at a nursery throughout a year. Vapor pressure deficit (VPD) was calculated from T and RH data. Results indicated that the inside T and VPD above the seedling foliage were extremely higher than ambient air. However, T within the seedling foliage showed 2.7 degrees C higher than ambient T even though 10.3 degrees C higher above the foliage in August. The VPD within seedling foliage was lower than ambient VPD in summer, and increased with decreasing RH when the precipitation was low. Microclimate in an empty treeshelter showed higher T and VPD than those in treeshelter with seedling. These results indicated that high T and VPD were mitigated by transpiration from needle leaves of seedling, and Japanese cedar seedlings could grow in treeshelters at sufficient water supply.