Format: ORAL

Patricia Rivera1, Tommaso Anfodillo2, Mark E. Olson3

1.Unidad de Recursos Naturales, Centro de Investigación Científica de Yucatán, A.C., Mérida, México 2. Department Territorio e Sistemi Agro-Forestali, University of Padova, Legnaro, Italy 3 Instituto de Biología, Universidad Nacional Autónoma de México, Mexico City, Mexico

The escalating global tree mortality crisis, with millions of trees succumbing to drought annually, impacts biodiversity conservation. The vulnerability of xylem conduits to drought-induced embolism is a critical factor in determining tree survival during hydric stress. If narrower xylem conduits are less vulnerable to embolism formation, then this vulnerability- diameter link would explain numerous well-established patterns. These include wider xylem conduits in moist environments and narrower conduits in drier environments, the consistent production of conduits that are well below the developmental possible maximum diameter of 700 m+, widening of the conduits from the tip to the base of the plant, in a way that keeps conductance optimal with height growth, the distribution of wide to narrow conduits in earlywood to latewood, and the differential leaf shedding between plants with wider and narrower conduits. All of these patterns require explanation, and if a vulnerability-diameter link is rejected, alternative explanations are required. As part of a possible explanation for these patterns, we provide data suggesting that the vulnerability-diameter link could involve the association between intervessel pit membrane thickness, vessel wall thickness, and vessel diameter. We show ways in which the vulnerability-pit membrane-wall thickness-vessel diameter associations could account for the link as well as why it is not found in some situations.