Decomposition of Pine and Oak Litters as Affected by Their Lignin and Mineral Concentrations

Abstract

Tree litter chemistry such as lignin, nitrogen (N), calcium (Ca), phosphorus (P) and manganese (Mn) affects litter decomposition and ultimately alters the soil carbon (C) and nutrient dynamics. Specifically, it is well known that the ratio of lignin to N (lignin/N) is a key factor affecting litter decomposition; i.e., litter with low lignin and high N concentrations decomposes fast as compared to litter with high lignin and low N. However, no comprehensive study on the effects of various chemistry as well as lignin/N on the litter decomposition is available. To fill the research gap, this study investigated the variations in the decomposition of pine and oak litters with different chemistry. Split plot design with tree species as a main plot (pine and oak) and litter chemistry (e.g., low vs. high lignin/N) as a sub-plot were laid out in triplicates. Litter samples (1.5 g on the dry basis) were mixed with soils (30 g) and incubated for 45 days, and CO2 emission was monitored periodically. Litter addition increased the cumulative CO2 emissions (Ccum) by 16 times over the control soil without litter regardless of litter species and chemistry. The litters applied to the soil were decomposed by more than 20% of the initial during the incubation period. Regardless of species, the Ccum was higher for litter with high lignin/N than with low lignin/N in contradiction to the previous studies. These results suggest that CO2 emissions from litter decomposition may not be explained solely by the lignin/N of litters but should be deciphered by considering mineral concentration as well as lignin/N. Comparing two pine litter with different chemistry, decomposability of pine litter with high Ca and Mn concentration was greater than the other one due to the role of essential co-factor of Ca and Mn in ligninolytic enzyme. However, for two oak litter with different chemistry, P rather than Ca and Mn found to contribute to litter decomposition. Therefore, this study highlights the necessity of comprehensive understanding of the effects of various chemistry as well as lignin/N of litter on the decomposition of litter. Daily CO2 emission rate (large figures) and cumulative CO2 emission (small figures) of soils amended with litters of pine and oak with different litter chemistry during 45-days incubation.