Lignin in Particle‐Size Fractions of Native Grassland Soils as Influenced by Climate

Abstract

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 were 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 −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 μm 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.