Tracking senescence‐induced patterns in leaf litter leachate using parallel factor analysis (PARAFAC) modeling and self‐organizing maps

Abstract

In autumn, the dissolved organic matter (DOM) contribution of leaf litter leachate to streams in forested watersheds changes as trees undergo resorption, senescence, and leaf abscission. Despite its biogeochemical importance, little work has investigated how leaf litter leachate DOM changes throughout autumn and how any changes might differ interspecifically and intraspecifically. Since climate change is expected to cause vegetation migration, it is necessary to learn how changes in forest composition could affect DOM inputs via leaf litter leachate. We examined changes in leaf litter leachate fluorescent DOM (FDOM) from American beech (Fagus grandifolia Ehrh.) leaves in Maryland, Rhode Island, Vermont, and North Carolina and from yellow poplar (Liriodendron tulipifera L.) leaves from Maryland. FDOM in leachate samples was characterized by excitation-emission matrices (EEMs). A six-component parallel factor analysis (PARAFAC) model was created to identify components that accounted for the majority of the variation in the data set. Self-organizing maps (SOM) compared the PARAFAC component proportions of leachate samples. Phenophase and species exerted much stronger influence on the determination of a sample's SOM placement than geographic origin. As expected, FDOM from all trees transitioned from more protein-like components to more humic-like components with senescence. Percent greenness of sampled leaves and the proportion of tyrosine-like component 1 were found to be significantly different between the two genetic beech clusters, suggesting differences in photosynthesis and resorption. Our results highlight the need to account for interspecific and intraspecific variations in leaf litter leachate FDOM throughout autumn when examining the influence of allochthonous inputs to streams.

American beech leaf‐litter leachate chemistry: Effects of geography and phenophase

“…DIC/DOC and total bound N (TNb) was measured with an Elementar Vario‐Cube TOC Analyzer (Mount Holly, NJ, USA), while nitrate‐N and ammonium‐N were measured with a Bran & Luebbe AutoAnalyzer 3 (Model AA3, Buffalo Grove, IL, USA). A table of soil chemistry results can be found in the supplementary tables of Wheeler et al (). Fluorescence and UV‐visible absorbance analysis was conducted by the Watershed Sciences Research Group at the University of Delaware on a Horiba Aqualog © Benchtop Fluorometer for DOM (Kyoto, Japan).…”

“…In 2015, beech leaves were collected from four field sites in the eastern United States, spread across a distance of approximately 1,450 km and 8° of latitude, with elevations ranging from 47 to 1,400 m. More detailed sites descriptions can be found in Wheeler et al (). Leaves from North Carolina were collected in a beech‐dominated forest, 1,400 m elevation above mean sea level in the Blue Ridge Mountains near Boone (36°13'58” N, 81°41'48” W).…”

“…Fluorescence and UV‐visible absorbance analysis was conducted by the Watershed Sciences Research Group at the University of Delaware on a Horiba Aqualog © Benchtop Fluorometer for DOM (Kyoto, Japan). For more detailed information on instrumental analysis, see Wheeler et al (). The following indices were of particular interest for this study: percent humic‐like fluorescence, percent fulvic‐like fluorescence, percent protein‐like fluorescence, humification index (HIX), biological index (BIX), fluorescence index (FI), spectral slope ratio (S R ), and specific ultraviolet absorbance at 254 nm (SUVA 254 ).…”

“…Samples were refrigerated at 4°C until instrumental analysis could be completed. Wheeler et al (2017). Fluorescence and UV-visible absorbance analysis was conducted by the Watershed Sciences Research Group at the University of Delaware on a Horiba Aqualog Benchtop Fluorometer for DOM (Kyoto, Japan).…”

Effects of nitrogen fertilization and bioenergy crop type on topsoil organic carbon and total Nitrogen contents in middle Tennessee USA

“…Based on fluorescence excitation-emission matrix [32,53], the PAFRAC model was used to identify three components-C1 and C2 representing protein-like DOM and C3 representing humic-like DOM (S1 Table). Given that tyrosine-like DOM is found to be the first component to decrease in leaf leachate during the senescence [54], a high percent tyrosine-like DOM and low tryptophan-like DOM in a sample indicate more labile SOM to microbial degradation.…”