Coping with warming and drying climate: Xylem adjustment in four temperate diffuse-porous tree species in northeastern China

The xylem anatomy of diffuse-porous tree species in temperate forests affects their water transport efficiency and drought resistance, thereby affecting their growth and survival. However, it remains unclear how xylem anatomical traits of different diffuse-porous species respond and adapt to warming and drying climate. Here, we assessed the main climate factors driving xylem anatomy of four dominant diffuse-porous tree species (Acer mono, Betula platyphylla, Populus davidiana, and Tilia amurensis) in the temperate forests of northeastern China. We identified distinct vessel patterns among the four species: A. mono and B. platyphylla exhibited larger, sparse vessels, whereas P. davidiana and T. amurensis displayed more small vessels. All xylem anatomical traits were categorized into three distinct clusters largely representing vessel number, vessel size and vessel density. Drought, caused by rising temperatures and declining precipitation, affected xylem formation, while the growth of the four species did not benefit from warming despite the rather low annual mean temperature of 3.0 degrees C. A. mono is mostly influenced by prior-year climate, and B. platyphylla has low climate sensitivity, while P. davidiana and T. amurensis respond promptly to current-year drought. Under continuously increasing warming conditions, A. mono and B. platyphylla adopted a more "conservative strategy" of reducing the vessel number, size, and density. Populus davidiana showed increased hydraulic safety at the expense of efficiency, while T. amurensis prioritized hydraulic efficiency. Our findings suggest that the ability of these species to persist under future climate scenarios will largely depend on their hydraulic strategies and the balance between growth and water use. Our results contribute to developing forest management practices dealing with preserving ecosystem stability and species diversity of temperate forests in the face of future climate change.