Different response of earlywood vessel features of Fraxinus mandshurica to rapid warming in warm-dry and cold-wet areas

Abstract

Xylem anatomical features are constantly adapting to changing environmental conditions, and are directly related to the key functions and physiological processes of trees. However, little is known about the responses of xylem to recent rapid warming in many areas. Based on the anatomical features of the xylem of Fraxinus mandshurica Rupr. from 14 sites in two contrasting areas (warm-dry and cold-wet) of northeast China, the plasticity response and adaptation strategies of radial growth, earlywood vessels (EWV), and hydraulic features of F. mandshurica to climate change were studied. Results showed that, compared with the cold-wet area, F. mandshurica in warm-dry area had wider rings, larger vessel area, higher number of vessels (VN), larger hydraulic diameters (Dh) and higher theoretical tree-ring hydraulic conductivity (Kh). On the contrary, the vessel density (VD), percentage of EWV (PC) and xylem-specific theoretical hydraulic conductivity (Ks) in warm-dry area was lower than those in cold-wet area. In these two areas, the RW, mean vessel area (MVA), total vessel area (TVA), VN, Dh, and Kh were significantly positively correlated with temperature, and negatively correlated with winter moisture. However, the PC, VD, and Ks were inversely related to climate factors in the two areas. F. mandshurica can adjust the density and proportion of EWV by changing the configuration of earlywood and latewood to cope with the interannual climate change and balance the hydraulic efficiency and safety. Rapid warming significantly increased the growing season length and hydraulic efficiency of F. mandshurica in warm-dry and cold-wet areas, thus maximizing carbon fixation. This provides a potential physiological explanation for the growth increase and range expansion of the main broadleaf tree species in temperate zone of northeast China in recent years. F. mandshurica in warm-dry areas benefits greatly from continuous climate warming, but the risk of hydraulic failure may increase.