Vessel, intervessel pits and vessel-to-fiber pits have significant impact on hydraulic function under different drought conditions and re-irrigation

Abstract

Although xylem embolism is a key process during drought-induced tree mortality, its relationship to xylem anatomy remains debated. We subjected Syzygium aromaticum to different degrees of drought treatments for three years, followed by short-term and high-intensity drought stress, and then re-irrigation to explore the influence of anatomical structures on hydraulic function. We found that vessel area, vessel diameter, and pit membrane area (APM) of intervessel pits significantly reduced after long-duration severe drought stress, while the APM of vessel-to-fiber pits increased. These variations had a strong effect on hydraulic conductivity and embolism. Drought-adapted plants had higher embolism resistance when exposed to short-term and high-intensity drought stress. Unexpectedly, under extreme drought stress, some exudations presented on the vessel-to-fiber pit membrane, and the aperture area of intervessel pits and vessel-to-fiber pits in each organ decreased by 29–44% and 0.7–30%, respectively. Pit membrane and aperture, especially the intervessel pits, were associated with hydraulic efficiency and embolism resistance under different drought conditions and re-irrigation. These findings suggest that the intervessel pits have a substantial impact on hydraulic function, and the fibers around vessels also play an essential role in embolism resistance. Our study makes an addition to the developing knowledge on xylem plasticity, vessel traits, and their effect on hydraulic function.