The effect of tree species on seasonal fluctuations in water-soluble and hot water-extractable organic matter at post-mining sites

Seasonal changes in the contents of water-soluble carbon (WSC) and hot water-extractable carbon (HWC) were investigated in the organic and underlying mineral horizons of soils in a common garden experiment at 40 years old post-mining sites. The sites were planted with alder, oak, or spruce or overgrown by a spontaneous succession dominated by willow. Sampling was performed at 2-month intervals from April 2013 until March 2014. Two major peaks in WSC in the mineral horizons were evident: one in early summer and another in late autumn or winter. The peaks were more pronounced at sites with deciduous trees than with spruce. According to liquid state H-1 NMR spectroscopy, hot-water extracts (HWE) from the mineral horizons had a higher relative content of aliphatic components in summer, while the winter samples had a larger relative abundance of carbohydrates. The results suggest that the peaks had different sources of carbon. RDA with variation partitioning showed that both tree species and season significantly affected the composition of HWE, but that tree species was most important, explaining 67.3% of data variability. However, the trends in temporal variation in concentrations and chemical composition were remarkably similar at the studied sites suggesting the changes were mainly induced by seasons. (C) 2016 Elsevier B.V. All rights reserved.