COS 67-7
Xylem vessel traits predict leaf phenology of 83 native and exotic woody understory species
Exotic plant species can possess traits that allow them to potentially outcompete co-occurring native species. Exotic species exert a competitive advantage by occupying vacant phenological niches when growing with native species to exploit temporally available resources, such as water, sunlight, nutrients, and pollinators. In particular, leaf phenology, the timing of leaf emergence and senescence, plays an important role in invasion success. In this study, we explored the relationship between leaf phenology and stem xylem anatomy of 83 exotic and native woody understory species including 35 exotic and 48 native species, belonging to 24 genera that are common to Eastern US deciduous forests. We monitored leaf phenology during the growing season in 2010, and examined xylem vessel characteristics in both earlywood and latewood. We aimed to 1) test the hypothesis that early- and latewood xylem anatomy would predict leaf out and leaf fall respectively within native-status, and 2) evaluate which vessel traits predict leaf phenology across three types of xylem porosity. We also examined the degree to which seasonal C gain was correlated with xylem vessel traits under the different leaf phenological strategies observed in exotic and native species.
Results/Conclusions
Exotic species had both smaller average vessel diameter and a smaller proportion of the entire xylem cross section occupied by latewood vessels compared to the natives, increasing the resistance to freezing-induced cavitation in late fall/winter, and thus perhaps resulting in delayed leaf fall. Leaf duration was positively correlated to the proportion of solitary vessels in an entire xylem cross section, indicating a trade-off between hydraulic efficiency and leaf duration. Across all species, earlier bud and leaf emergence in the spring was associated with a higher proportion of the entire xylem cross section occupied by vessels in earlywood. This suggests understory species need plenty of water to support their early spring growth at the risk of freezing-induced cavitation. We also found annual C gain was positively correlated to average vessel diameter across the entire xylem cross section, in which total C gain in spring and summer was determined by average vessel diameter in earlywood. This study indicates the cross-sectional spatial vessel distribution, along with individual xylem vessel properties, reflects the acclimation ability of exotic plants to a new environment, and could help better understand the physiological mechanisms of successful invasions of exotic plant species.