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.