Abstract: Fiber saturation point(FSP)is an important concept in the field of wood science which was first proposed by Tiemann in 1906 and has been discussed in the literature for over 100 years. FSP has played an important role in wood-water relations, wood physical and mechanical properties and other research fields in wood science. Despite its importance and extensive study, the exact theoretical definition of the FSP and the correct way to measure the FSP are still debated because considerable progress has been made compared with the initial concept form of FSP. The research on wood-water relations has changed from qualitative description of the state and its locations of water in wood to the direction of water potential differences and water phase boundaries, and relevant new theoretical definitions and test methods of FSP have been presented in recent years. The research on FSP is relatively lagging behind in our country, there are rarely introductions to principles and test methods of FSP. In this paper, the development of FSP concept has been summarized, the advantages and disadvantages of test methods are analyzed systematically. The applications and further developments in wood-water relations, wood drying technology, modification effect are also summarized. According to the different research stages of wood-water relations, the concept of FSP could be divided into 4 types. The first type emphasizes that FSP could be defined from physical and mechanical properties, or locations of water in wood. The second type concept related FSP to the amount of water contained with the water saturated cell wall. The third type concept emphasizes the different combination forms between water and wood, which could result in different thermal phenomenon. The fourth type concept of FSP is based on solution thermodynamics that treats the FSP as a phase boundary, which attaching clear physical meaning to FSP. The test methods of FSP could be divided into 7 types, including extrapolation method, solute exclusion method,pressure plate measurement, differential scanning calorimetry method, centrifugal dehydration method, nuclear magnetic resonance method, and solution thermodynamics calculation method. The actual bound water content in cell wall could be determined from these methods except for extrapolation and solution thermodynamics calculation method. The actual bound water content is obviously higher than 30% which is traditionally considered as average value of FSP. The research on FSP could further play an important role in the analysis of shrinkage and swelling, working out wood drying schedule. It also could be applied in the evaluation of wood modification effect and the microstructure analysis after modification treatment. The chemical potentials expression of the wood-water relationship and wood moisture phase diagram based on the FSP thermodynamic concept would be an important research field of wood-water relations scientific evaluation system, and more attention should be paid in wood science and industry.

Key words: fiber saturation point, wood-water relations, concept evolution, test method, application