[Measurement and research status of stable hydrogen isotopes in tree-ring lignin methoxyl groups]

The primary hydrogen (H) source for all organic compounds in the biosphere is from water, and then participates in biogeochemical cycles through photosynthesis and plant physiological metabolism. As a new proxy of paleoclimate and paleoenvironment, stable hydrogen isotope ratios in wood lignin methoxyl groups (δ²H_LM) show great advantages in the studies of paleoclimatic change and have been used to reconstruct precipitation stable hydrogen isotope ratios and paleoclimate signals in many regions. Based on the lignin application mechanism and analysis method of δ²H_LM, we evaluated the stability and effectiveness of δ²H_LM-measurement method from lignin content and lignin monomer composition, and expounded the tree lignin methoxyl groups' stable isotope proxies of current research outcomes. In the middle latitudes, the tree-ring δ²H_LM had great potential in recording temperature signals and precipitation stable hydrogen isotope ratios. However, the study of tree-ring δ²H_LM was still in its infancy as evidenced by following reasons: 1) The study area was limited to the middle latitude of the northern hemisphere, and the study subjects were limited to conifer species; 2) To compensate for the limitation of hydrogen isotopic records of nitrocellulose, high resolution tree-ring δ²H_LM would be studied; 3) The potential of tree-ring δ²H_LM utilization in plant physiology and forest ecology remained to be exploited.