Slope exposure and forest stand type as crucial factors determining the decomposition rate of herbaceous litter on a reclaimed spoil heap

Abstract

Chemical composition of plant litter, properties of the soil, and climatic conditions are the major factors determining rate of organic matter decomposition. Although the process of decomposition in degraded areas plays a significant role in accumulation of soil organic carbon (SOC), this issue is poorly studied. SOC content is a crucial factor determining the success of land restoration. We measured rates of decomposition of the grass Calamagrostis epigejos, the dicotyledonous N-fixer Medicago sativa, the dicotyledonous non-N-fixing Cirsium arvense and cellulose paper as a standard carrier in forest stands on a reclaimed spoil heap of the opencast lignite mine in Bełchatów (central Poland). We considered the 10 cm topsoil particle size distribution and pH as factors that can affect the rate of organic matter decomposition and soil organic carbon content. Rate of litter decomposition was slowest for the grass (mean half decay time 2.6 years), while the N-fixing litter was not decomposed faster than the dicotyledonous non-N-fixing litter (mean half decay time of both species 0.9 years). Cellulose was decomposed most quickly (mean half decay time 0.8 years). Decomposition rate was faster under the canopy of Robinia pseudoacacia (deciduous N-fixing tree species, mean half decay time 0.9 years), whereas the rate of decomposition under Pinus sylvestris (coniferous canopy) was not slower than under Betula pendula (deciduous non-N-fixing tree species, mean half decay time under both species 1.5 years). Irrespective of litter type, decomposition was faster on the northern slope (mean half decay time 0.9 years) than on the southern slope (1.6 years). The plots where decomposition was faster (under R. pseudoacacia and on the northern slope) were characterized by higher SOC content (1.95% and 1.96%, respectively) than the plots under B. pendula (1.15%), P. sylvestris (1.29%), and those located on the southern slope (0.97%).