Abstract: Moisture in wood gives serious effect on wood utilization and processing, and moisture content of wood should therefore be adjusted to an appropriate range through drying. Conventional drying can be improved due to great energy consumption and considerable drying defects, while the industrialization of new energy-saving drying technologies such as heat pump drying and solar drying are far from perfection. Considering the source of water in wood and the physiological properties of water in trees, the present work discusses a new drying theory and technology for living trees, namely, physiological drying based on transpiration. The basic theory of physiological drying for living trees from the viewpoint of water and plant physiology are expounded. Three possible evaporation locations summarized from the researches on water evaporation in leaves are presented as:all the mesophyll cells and epidermis exposing into the inner air spaces, the most mesophyll cells and epidermal cells around the substomatal cavity nearby the stomatal pore, and other mesophyll and epidermal cells around the substomatal cavity. By analyzing the research on water transmission theory in plant, three potential water transport ways inner leaves are presented as:the symplastic pathway via plasmodesmata, the transcellular pathway by aquaporin and the apoplastic pathway through the non-suberized cell wall. Studies on the cohesion-tension theory(CT/CTT)widely used to explain the dynamics of long-distance water transport in xylem with the current arguments and some rising theories, such as the multi-force theory and watergate theory are reported. In addition, the common phenomenon of cavitation and embolism and its recover mechanics during the process of long-distance water ascent is discussed. On this basis, 4 focal points for further studies are suggested as:1) To explore the relationship between stomatal transpiration and cuticular transpiration when the trees were subjected to severe water stress in the process of physiological drying; 2) To locate the water evaporation points within leaves; 3) To understand the effect of the microstructure of pits on the process of long-distance water transportation in xylem and on the forming and recovering processs of the cavitation and embolism; 4) To reveal the mechanism of the formation and recovery of cavitation and embolism in physiological drying, and their effects on the long-distance water transportation.

Key words: living trees, physiological drying, transpiration, water, transmission, loss