Dissolved organic matter and inorganic nutrients released from forest leaf litter through leaching are important energy and nutrient sources that support the production of aquatic food webs. Leaf litter-derived dissolved organic carbon (DOC) is a critical energy source for aquatic heterotrophic microbes, and inorganic nitrogen and phosphorus can enhance primary production. In this study, we experimentally measured the release efficiencies and amounts of DOC, total dissolved nitrogen (TDN) and total dissolved phosphorus (TDP) of the leaf litter from 11 temperate tree species by soaking the leaf litter in water for 28 days. We found that the maximal release efficiency (% of element released per estimated mass of the element) was the highest for P and lowest for N. These efficiencies were species-specific. Additionally, the DOC:TDP, DOC:TDN, and TDN:TDP ratios varied among the leachate of different leaf litter species. DOC:TDP increased with the C:P ratio in leaf litter biomass but is considerably lower; TDN:TDP was lower than the N:P ratio in leaf litter biomass as well; DOC:TDN ratio was higher than the C:N ratio in leaf litter biomass. These results suggest that the ratios of DOC to dissolved N and P nutrients released into water are related to, but not the same as, the stoichiometry of leaf litter biomass. Based on these findings, we concluded that changes in the vegetation with different leaf litter stoichiometry can alter the relative importance of detrital and grazing food chains in aquatic ecosystems.

We examined 11 tree species commonly found in the mountainous areas of northeast Japan. These shed leaves were collected at Zao (N38.122, E140.451) on October 3, 2020, at Kawatabi (N38.745, E140.757) on October 15, 2020, and at Aobayama (N38.259, E140.837) on November 19, 2020, in Miyagi Prefecture, Japan (Fig. 1 and Table 1). All leaves were collected on top of other leaf litter on the ground and therefore did not directly come into direct contact with the soil.

The leaf litter was dried at room temperature (approximately 20°C) in paper bags until it was used for measuring its C, N, and P contents. Prior to the experiment, the C and N contents in the leaf litter were measured using an elemental analyzer (2400 Series II CHNS/O Analyzer, Perkin Elmer, Shelton, Connecticut). For estimating the P content in the leaf litter, the weighed amount of dry leaf litter was first combusted (420°C) for 2 h to turn the leaf litter into ash, which was suspended in 10 mL of distilled water. The mixture of ashes and distilled water was autoclaved with potassium persulfate for 30 min to oxidize organic phosphorus compounds and the total orthophosphate concentration was measured by the ascorbate-reduced molybdenum blue method (Murphy and Riley 1962, Menzel and Corwin 1965). We cut the dry leaf litter using scissors to mimic the initial decomposition process of detritivores and immersed the cut dried leaf litter into 1 L experimental bottles containing 800 mL distilled water. Two replicates of the leaching bottles were set up for each leaf litter species. These bottles were aerated and placed in dark incubators at 2°C for 28 days. The dry weight of leaf litter used for leaching incubation was 7–385 mg, depending on the tree species: for tree species with low leaf litter P, a larger amount of leaf litter was added into experimental bottles to ensure that the P in leachate would be the same concentration level and thus minimizing and equalizing measurement errors. During the experiment, we shook the bottles manually to mix the leachate once a day. On days 1, 3, 7, 14, 21, and 28, we sampled 50 mL of the supernatant of the leachate after all leaf litter had settled down to the bottom of the bottle and did not refill the bottle with new distilled water. These samples were used to measure the DOC, TDN, and TDP in the leachate. DOC and TDN in the litter leachate were measured using a TOC/TNb analyzer (multi N/C 3100, Analytik Jena GmbH, Jena, Germany). For TDP measurements, 10 mL of leaf litter leachate was autoclaved with potassium persulfate and measured using the ascorbate-reduced molybdenum blue method.

We saved the data of leaf litter stoichiometry and dissolved C, N, and P release as Excel files. R can be used to open and analyze the dataset.