The Decomposition Difference between Aboveground and Belowground : Insights from a Long-Term Study of Contrasting Litter Types

Increasing evidence showed that litter positioning (above- vs. below-ground) would substantially influence decomposition process especially in drylands. However, it is not clear how positioning interacts with litter quality and incubation period controlling a long-term decomposition process. A litterbag experiment was carried out for more than three years with 11 litter types decomposing both on the surface soil and buried in the soil in a semiarid temperate steppe. Comparing to litter on the surface, the buried litter decomposed 23% faster until day 542, then the predominance of belowground decomposition weakened or disappeared at the end of this study (day 1282). The catch-up time (the time needed for litter at aboveground to reach the same level of accumulative decomposition as the litter in belowground) was negatively correlated with initial litter quality. Specifically, high-quality litter in belowground lost this predominance more quickly, while low-quality litter in belowground kept this predominance longer until the midterm or late stages. Comparing to the concentration of nitrogen (N) and phosphorus (P) of the aboveground counterparts, the high-quality litter in belowground generally had lower N and P concentration, and they generally increased with decomposition time, whether showing an early decrease or not, indicating their slower release than overall mass loss. Besides, more N and P released in belowground and from high-quality litter. Specifically, aboveground decomposition showed almost no net P release during initial two-year decomposition for most litter types. Our results demonstrated that above- and belowground decomposition are distinctly different in the pattern of mass loss and nutrient dynamics especially for P. However, the final mass loss and N loss seems to be similar between above- and belowground decomposition. This is different from earlier studies with experiment duration less than 2 years. Such results highlight the value of long-term observations disentangling the complex interactions of multiple factoring affecting litter decomposition. Even with similar final decomposition outcome for C and N, our results showed that burial of litter can accelerate carbon turnover and facilitate N release, which finally speed up nutrient cycling in dryland ecosystems