Objective This paper aims to clarify the differences in the anatomical characteristics of the xylem of trees in different habitats and the growth changes of the xylem of trees under warm and dry climate conditions.
Method The relatively dry and relatively wet habitat sampling sites were set up in mixed coniferous forests in Muling City, Heilongjiang Province of northeastern China, and Pinus koraiensis, Quercus mongolica, and Tilia amurensis were sampled. Micro-sections were cut with a rotary microtome to obtain the anatomical parameters of the xylem.
Result The mean vessel area and vulnerability index of Q. mongolica in the relatively dry habitat increased significantly, but the theoretical xylem-specific hydraulic conductivity of Q. mongolica did not differ significantly between the two habitats. From relatively wet habitat to relatively dry habitat, mean vessel area, vulnerability index, and theoretical xylem-specific hydraulic conductivity of T. amurensis were significantly reduced. Among the three tree species, only the mean tracheid area and vulnerability index of P. koraiensis did not differ significantly in the two habitats, and at the same time, theoretical xylem-specific hydraulic conductivity was significantly increased in the relatively dry habitat. The tree-ring widths of P. koraiensis, Q. mongolica and T. amurensis in relatively dry habitat were all significantly positively correlated with the Palmer drought severity index (PDSI) of the growing season, and the sensitivity decreased when the water content of soil rose. The theoretical xylem-specific hydraulic conductivity of Q. mongolica in the relatively dry habitat was significantly negatively correlated with the PDSI from November of the previous year to October of the current year. The tree-ring widths and mean vessel area of T. amurensis in the relatively dry habitat were significantly positively correlated with the lowest temperature in the previous non-growing season (PNG).
Conclusion At the beginning of the growing season, drought was an important factor that restricted the tracheid area and theoretical xylem-specific hydraulic conductivity of P. koraiensis in the Muling area. In the future, P. koraiensis may feel the change of climatic conditions in northeast China more strongly. T. amurensis reduces theoretical xylem-specific hydraulic conductivity in relatively dry habitats to improve hydraulic safety. The growth and mean vessel area of Q. mongolica in the relatively dry habitat were greater than that in the relatively wet habitat, so future warm and dry climate conditions may be more beneficial to the growth of Q. mongolica but there was also a risk of cavitation to it. Clarifying whether drought stress due to global warming will alter tree growth is critical to adjusting current silvicultural practices, which is better for mixed coniferous forests to cope with future warming and drying climatic conditions.