Xylem vessel traits predict the leaf phenology of native and non‐native understorey species of temperate deciduous forests

Abstract

Summary Non‐native understorey woody species have been shown to extend leaf display and inhabit vacant phenological niches in early spring and late autumn when growing with native counterparts in temperate deciduous forests across the world. Despite the potential competitive advantages, extended leaf duration also subjects non‐native species to possible hydraulic risks associated with maintaining leaves during periods of increased frost probability. It remains unclear how non‐native species are able to maintain xylem function within this context. Leaf phenology in temperate deciduous trees has been shown to be a function of xylem anatomy, with earlier bud break associated with smaller xylem vessels due to the presumed resistance of smaller vessels to freezing‐induced cavitation. We examined relationships between leaf phenology and xylem vessel traits across 82 native and non‐native understorey deciduous woody species common to eastern U.S. deciduous forests. We hypothesized that non‐native species possess xylem vessel traits associated with maximum hydraulic safety during frost‐prone spring and autumn leaf display without compromising rapid growth rate. Larger metaxylem vessels in non‐native species were associated with both faster spring growth and delayed autumn leaf fall compared to native species. Non‐native species also had smaller latewood vessel diameter, latewood vessel area percentage and a higher proportion of solitary vessels in the entire secondary xylem cross section compared to natives, potentially increasing their resistance to freezing‐ and/or drought‐induced cavitation in autumn, thus allowing for delayed autumn leaf fall. Native and non‐native species exhibited similar dates of spring bud break and leaf emergence, consistent with similar xylem vessel size and vessel area percentage within metaxylem and earlywood. Within both groups, species with earlier bud and leaf emergence had a higher total percentage of vessel area within metaxylem and earlywood. This suggests understorey species need sufficient water to support their early spring growth at the risk of freezing‐induced cavitation. Our study suggests xylem vessel properties, along with cross‐sectional spatial xylem vessel distribution, reflect the capacity of non‐native plants to thrive in a new environment and deepen our understanding of the physiological mechanisms of successful invasions of non‐native understorey woody plant species.

Stems matter: Xylem physiological limits are an accessible and critical improvement to models of plant gas exchange in deep time

“…Particularly in the roots, this xylem morphological paradigm may have allowed the Marratialean tree fern Psaronius (Figure 9) to supply developing fiddleheads with water before sufficient stem and leaf xylem had grown to supply their fully developed form. This may be analogous to the function of narrow latewood conduits in some modern temperate taxa that support subsequent year leaf flush when wide earlywood conduits have been embolized (White, 1992;Gullo et al, 1995;Yin et al, 2016). Interestingly, this strategy may have ceased to be viable as seasonally humid tropics became arid at the Permo-Carboniferous boundary, when Marratialean tree ferns were replaced by coniferophytes like the cordaitaleans (Wilson et al, 2017).…”

‘… we really don’t know [buds] at all …’

“…Is the extent of preformation and rate of deployment of preformed organs related to other plant traits, such as xylem structure (e.g. Lauri et al ., 2008; Yin et al ., 2015)? What factors determine how many bud scales vs preformed leaves will be made?…”

Impacts of Invasive Species on Forest and Grassland Ecosystem Processes in the United States

“…Xylem anatomy can also confer greater water use by invasive species compared to native species in vernal and autumnal windows in deciduous forests. Among 82 native and nonnative understory, deciduous, woody species common to eastern US deciduous forests, invasive species had xylem traits that conferred higher freezing resistance or droughtinduced cavitation resistance in autumn, thus promoting delayed autumn leaf fall and continued carbon gain when native species were dormant (Yin et al 2016) (see Box 3.1).…”