Ecological significance of phyllosphere leaf traits on throughfall hydrology, biogeochemistry, and leaf litter among Quercus species in the southeastern United States

Background/Question/Methods

Forest ecosystems support the majority of terrestrial biodiversity and productivity, which are in large part regulated by biogeochemistry. Biogeochemical cycling in forest ecosystems are strongly influenced by 1) the quantity and quality of litterfall, 2) canopy cover and its regulation of water throughfall quantity and chemistry, and 3) the phenology of these processes. In particular, Quercus (oak) is a dominant species in many forest ecosystems across the United States that contribute vital ecosystem services through water and nutrient cycling. Quercus species display large interspecific variation in leaf chemistry, the timing and duration of leaf fall, and the subsequent impact of canopy-derived hydrology and biogeochemical fluxes. Given, the prevalence, persistence, and diversity of Quercus leaves in forest ecosystems, it is likely that this species strongly mediate nutrient cycling when present.

The objective of this study was to determine the (1) interspecific temporal distribution of Quercus leaf fall and (2) quantify canopy-derived nutrients contributed to forest ecosystems in an oak-hickory forest in Mississippi. Beginning in Fall 2014, canopy litterfall was collected weekly to quantify changes in canopy leaf area index (LAI) and timing of species-specific leaf fall rates. Throughfall quantity and chemistry were measured during individual storm events under each of the five focal Quercus species Q. shumardii, Q. alba, Q. pagoda, Q. stellata, and Q. falcata), and two non-Quercus species (C. glabra and C. ovata).

Results/Conclusions

During the winter, Q.shumardii had the highest leaf retention although non-oak species had a higher leaf retention in general. Quercus shumardii also had the lowest average C:N amounts (43.99 mg L^-1) in leaf litter content compared to the other Quercus species. Non-oak species had a considerably lower average C:N ratio ( Carya spp. 32.58 mg L^-1) which positively correlated with longer leaf retention. As leaves were lost, throughfall depths generally increased in all species but were highest in Q. shumardii, Q alba, and C. glabra. The average total nitrogen content of throughfall was highest in Q. shumardii (1.44 mg L^-1) and Q. stellata (1.65 mg L^-1) compared to other Quercus and non-Quercus species. This research demonstrates that Quercus species, such as Q. shumardii, facilitate greater water and nutrient input to the forest floor compared to non-Quercus species during winter months when forests are most resource limited. Continuing the study of leaf retention in Quercus species could further the understanding of important nutrient cycling components in hardwood forests.