“Litter Decay and Leaching from the Forest Floor in Pinus Contorta (Lodgepole Pine) Ecosystems” Journal of Ecology 74 (1986): 525-545.
Yavitt, Joseph B. and Timothy J. Fahey
Department of Botany, University of Wyoming, Laramie, Wyoming 82071-3165, U.S.A.
SUMMARY
- The dynamics of organic matter and nutrient elements in the forest floor of Pinus contorta spp. Latifolia (lodgepole pine) forests in Wyoming, U.S.A., were investigated by combining three related measurements: leaching of the forest floor; longterm decay of leaf litter; and steady-state residence times in the forest floor.
- Elemental fluxes (g m-2 yr-1) resulting from leaching by spring snowmelt were: Ca = 1.35, Mg = 0.30 K = 0.65, N = 0.46, P = 0.022 and C = 8.3 Over 95% of the N flux was in organic forms.
- Most of the organic compounds were acidic, and anions of theses organic acids were the principal mobile species accompanying cation Flux; smaller, but important contributions were SO4 and HCO3. The chemical nature of the dissolved organic compounds changed as snowmelt proceeded, with polyphenolics and carbohydrate (leached from the fresh litter) being important in the early stages, and polymeric acid compounds (fulvic and humic acids)dominating in the later stages.
- About 35% of the original mass of leaf remained after 84 – 96 months Potassium and magnesium were lost rapidly from leaf litter, whereas there was temporary immobilization of Ca. Nitrogen accumulated in decaying leaves for 72 months, reaching 180% of the original content before net mineralization and release occurred. Relatively small changes in P content of leaf litter were noted during the decay process. The loss of soluable organic constituents (polyphenols, carbohydrates, lipids) was more rapid than for solid residues (holocellulose, lignin).
- The combination of approaches enabled several features of organic matter and nutrient dynamics in the forest floor, which would not be apparent using any of the methods in isolation, to be deduced: (i) about 30% of annual C release from the forest floor resulted from leaching of organic compounds; (ii) over 20% of the leaching flux for Ca and Mg was attributed to release from 01 litter, compared with less than 10% for K; (iii) high amounts of organic-N leaching from forest-floor layers, combined with rapid accumulation in 0- to 8-year-old litter, indicated rapid translocation of N from subsurface layers to 01 litter via heterotrophs; and (iv) leaching of polyphenols from the forest floor was 50% lower than the apparent loss from 01 litter, suggesting chemical transformation and changes in solubility of these compounds during litter decay. An association of this phenomenon with protein accumulation observed in the 02 horizon is postulated.
INTRODUCTION
It is well known that the forest floor plays an important role in nutrient accumulation and flux in forest ecosystems. In the temperate zone massive organic horizons (10 – 30 cm deep) often a accumulated during stand development, and this detritus stores substantial amounts of nutrients which eventually become available for plant uptake. The rate of nutrient release from organic horizons to the mineral soil is controlled by many complex, interacting modification to prevent hydrolysis of organic-N compounds (White & Gosz 1981). Total N was determined as ammonium following a micro-Kjeldah digestion (Jackson 1958).
