Tracing the fate of plant and fine root litter over 10 years in a coniferous forest soil

Background/Question/Methods

The fate of plant litter in ecosystems partially determines soil carbon (C) storage and nutrient availability. Differential plant allocation to roots or leaves can lead to different nutrient availability and carbon storage when tissue decomposability differs. The depth of plant inputs can also affect the fate of litter because soil horizons differ in their mineralogy, structure, climate, and microbial communities. We incubated ¹⁵N and ¹³C-labelled Pinus ponderosa needle and fine root litter in the Blodgett Experimental Forest in Northern California for 10 years. Using a two-way factorial design, needle and root litter were placed into O and A soil horizons. In 2001, litter was placed into either horizon within soil microcosms (10.2 cm diameter x 24 cm long PVC) without using litter bags. After 0.5, 1, 1.5, 4.5, and 10 years, the soil microcosms were collected from the field. Isotopes were used to measure the percent recovery of the litter C and nitrogen (N) in the bulk soil of the O and A horizons. The soils from the 4.5-year ad 10-year collection were further fractionated into density classes (free light, occluded light, and heavy fractions).

Results/Conclusions

We tested whether litter quality (root or needle) or soil horizon affected decomposition. After 10 years, more root litter (about 40%) was retained in the soil than needle litter (about 25%). After 4.5 years, more needle C and N than root C and N were found in the densest soil fraction, which was further evidence the needle litter had decomposed faster. There were no significant differences in the amount of litter retained in the O and A horizons.