Lignin in particle-size fractions of native grassland soils as influenced by climate

The turnover of soil organic carbon (SOC) in grasslands can be predicted as a function of climate, plant lignin content, texture, and kinetically defined C pools. Particle-size fractionation has been used to identify soil C pools, This study was conducted to investigate influences of climate on the dynamics of lignin in particle-size fractions. Composite samples mere taken from the top 10 cm of 18 native grassland sites along temperature and precipitation transects from Central Saskatoon, Canada, to South Texas, Lignin-derived phenols were determined in the <2 mu m (clay), 2- to 20-mu m (silt), 20- to 250-mu m (fine sand) and 250- to 2000-mu m (coarse sand) size separates. With decreasing particle size the concentration of lignin-derived phenols decreased significantly from 72 g kg(-1) SOC in the coarse sand fractions to 12 g kg(-1) SOC in the clay fractions, Increasing phenolic acids to aldehyde ratios indicated that side chain oxidation proceeded as particle size decreased, Moreover, these ratios decreased in fractions <250 mu m with increasing mean annual temperature (MAT) at the sites, This suggests that the degree of lignin decomposition decreased with increasing MAT, possibly because there was a lack of additional C sources, such as saccharides of root litter, which are needed for the cometabolic decay of lignin.