Temporal Changes in Deciduous and Coniferous Stemflow Dissolved Organic Matter Composition

Stemflow is rainwater that runs down the trunk of trees and transport canopy derived dissolved organic matter (DOM) to the forest floor. The chemical composition of stemflow may create hot spots and hot moments of biogeochemical reactivity in the soil and water table. The amount and character of stemflow DOM throughout a 12-month period were analyzed to better understand the effect of phenophases (e.g., leafless, emergence, leafed, senescence for deciduous species and leafed-winter, emergence, leafed-spring/summer, senescence for pine) on tree-derived DOM composition. This study collected stemflow from four major species in the eastern United States, Betula lenta L. (sweet birch), Fagus grandifolia Ehrh. (American beech), Liriodendron tulipifera L. (yellow poplar), and Pinus rigida Mill. (pitch pine), on a monthly basis. A total of 157 samples were analyzed for organic carbon concentration, fluorescence, and light absorbance characteristics. Results from one of the absorbance characterizations, specific ultraviolet absorbance at 254nm, SUVA₂₅₄, indicated a change in DOM composition throughout the phenophases for the four species. American beech and sweet birch increase in SUVA₂₅₄ values with the lowest values occurring during emergence with progressively higher values from leafless to leafed and finally senescence phases. Pitch pine’s trend from smallest to largest values follows a different pattern beginning with leafed-winter, then leafed-spring/summer then emergence to senescence. Yellow poplar also demonstrates a different trend with no change occurring between emergence and the leafed phase with those two seasons having the smallest values, then progressively increasing in the leafless phase and then senescence. The fluorescence index (FI) values obtained demonstrate similar phenophase trends as the SUVA₂₅₄ analysis except for sweet birch. The FI values for sweet birch were highest and identical in emergence and leafed, while FI successively declined between senescence and leafless phenophases. These trends indicate species and season influence sources that alter the quantity and compositional characteristics of DOM, e.g., aromatic content, which varied greatly. We are building a parallel factor analysis (PARAFAC) model based upon the total fluorescence of stemflow DOM to further investigate these changes and provide a more in-depth analysis of its chemical components throughout the different phenophases of these four trees.

Funding note: This research was supported by funds from the US National Science Foundation (Award No. GCR-CMMI-1934887).