The effects of surface albedo and initial lignin concentration on photodegradation of two varieties of Sorghum bicolor litter

Decomposition of plant litter exposed to solar radiation appears to be a significant contributor to carbon cycling in some ecosystems. One factor that may influence incident solar radiation exposure on litter is surface albedo. Snow and soils with high reflectivity may enhance photodecomposition, especially in litter that stands upright for extended periods. We examined the influence of different surface albedos on the photodegradation of two varieties of sorghum (Sorghum bicolor) litter for 200-d, in southern Minnesota using litterbags made of material with a high transmittance of ultraviolet radiation (UV; 280–400 nm). One of these cultivars was a brown-midrib double mutant (DM) which had reduced levels of lignin compared to the wild type (WT). After 200-d sorghum litter had lost > 50% of its initial mass, and litter that was exposed to a high UV/high visible surface albedo had lost 1.4 and 2.5% more mass than litter exposed to a low UV/high visible and low UV/low visible surface albedo, respectively. Mass loss patterns agreed with initial litter chemistry, as DM litter had higher initial N, neutral detergent fiber (NDF) solubles and holocellulose:lignin ratios and lower lignin:N ratios than WT litter. Mass loss appears to be related to increased loss of hemicellulose and NDF soluble concentrations and not to lignin concentrations. Our results demonstrate that surface albedo has a small but significant effect on photodecomposition of sorghum litter.

Influence of initial chemistry on decomposition of foliar litter in contrasting forest types in British Columbia

We compare rates of decay of foliar litters of British Columbia tree species in two field studies, and assess which initial litter chemistry parameters best predict the decay rates. Nutrient concentrations, tannins, and carbon fractions (based on proximate analysis and nuclear magnetic resonance spectroscopy) were measured in fresh litter of 14 tree species in one experiment and seven species in a second experiment. Each study was replicated in a different site in order to assess the transferability of results. Broadleaf litters decayed faster than needle litters only during the first year; thereafter, they decayed slower. Lignin concentration was a good predictor of mass loss only during the first year and only in one of the two experiments, which may have resulted from all foliar litters having high lignin concentrations (>170 mg·kg–1). Litter chemistry effects on first-year decay were consistent and transferable among sites. None of the initial litter chemistry parameters were good predictors of mass remaining after 4 or 5 years, because mass loss of most litters was similar by this time. The convergence in mass losses of litters after 4–5 years despite initial differences indicates that decomposition estimates extrapolated from early rates or initial chemistry may not accurately predict long-term decay.

Predicting long-term patterns of mass loss, nitrogen dynamics, and soil organic matter formation from initial fine litter chemistry in temperate forest ecosystems

Long-term decomposition data are presented for several types of foliar and fine root litter in different stands in Wisconsin and Massachusetts, U.S.A. Changes in mass remaining as well as nitrogen and carbon fraction (extractives, cellulose, lignin) concentration are reported. Three models were developed for describing change in mass remaining with time: a litter-specific exponential decay function (statistical fit of data for each litter type), a generalized exponential decay function (k predicted from initial litter chemistry), and a carbon fraction model that calculates the weight loss of each carbon fraction individually as a function of current carbon chemistry regardless of litter type. The exponential decay function fits all litter data well for the portion of decomposition described here, but would not be appropriate for modeling longer term decomposition. Both the generalized and carbon fraction models predicted weight loss accurately. All litter types had similar carbon fraction chemistries at the end of the first phase of decomposition described here and also exhibited a narrow range of changes in nitrogen concentration per unit weight loss. It is concluded that the length of time required to convert litter into soil organic matter and the chemistry of the material produced by this process can be predicted from initial litter chemistry and (or) relatively short-term litter decay data. Key words: immobilization, mineralization, humus, lignin, cellulose, extractives.