Quantification and FTIR characterization of dissolved organic carbon and total dissolved nitrogen leached from litter: a comparison of methods across litter types

Background and aims Quantification and characterization of dissolved organic matter (DOM) leached from leaf litter in the laboratory may well depend on the method used to leach the litter. However, we lack a comparative assessment of the available methods. Here, we test how: i) four commonly used methods to leach plant litter, ii) cutting of the litter, and iii) litter species affect the quantity and composition of dissolved organic carbon (DOC) and total dissolved nitrogen (TDN) leached using fourier transform mid-infrared spectroscopy (FTIR). Methods We tested how soaking litter in water, dripping water over litter, and shaking litter in two different volumes of water affected leaching of both cut and whole leaves of alfalfa (Medicago sativa), ash (Fraxinus excelsior), big bluestem grass (Andropogon gerardii), oak (Quercus macrocarpa) and pine (Pinus ponderosa) litter. We measured DOC and TDN on the leachate to quantify how much DOM was leached by each method. We used the DOC: TDN ratio and FTIR to analyze the composition of the DOM leached. Results The leaching method and cutting had an impact on the amount of DOM leached from the litter. The amount of DOM leached was also affected by the litter species and its interaction with leaching method and cutting. FTIR analysis identified the same main functional groups of plant litter leachates across all of the litter species. Leaching method, cutting and litter type affected the concentration of the leachate and the resolution of the FTIR spectral data but not the relative contribution of the main functional groups. Conclusions Methods of leaching should be chosen consistently with experimental objectives and type of litter examined. The leaching method, cutting of the litter and litter species should be taken into consideration when comparing data on DOM amounts obtained from different leaching methods but the leachate consists of similar functional group components across method, cutting and litter species.