Decomposition in the Santa Catalina Mountains: A study of the effects of litter type and invertebrate exclusion among plant biomes across an elevation gradient

Background/Question/Methods

Annual CO₂ input into the atmosphere through decomposition of organic carbon is nearly 10 times that of annual fossil fuel emissions. The three key drivers of decomposition, climate, litter quality, and the decomposer community, have been assumed to rank in that order of decreasing importance. However, recent studies have found that invertebrates can have a larger impact on decomposition than litter quality or precipitation in certain ecological contexts. To quantify the influence of invertebrate communities in litter decomposition relative to climate and litter quality, I am conducting a litter bag study in the Santa Catalina Mountains where many of the world’s temperate biotic communities occur in climatically structured elevation zones. Currently, 1,680 litter bags have been placed at 35 sites along the elevation gradient; seven sites in five plant biomes: mixed conifer, pine, oak woodland, grassland, and desert scrub. At each site, I am utilizing a 2 x 2 factorial design with two litter quality treatments (Raphia farinifera and Laurus nobilis, low and high quality treatments, respectively), and two invertebrate treatments (control and invertebrates suppressed by naphthalene). The experiment began in July 2011, and four litter bags have/will be collected from each site at months 4, 8, and 12.

Results/Conclusions

Initial findings from the first litter bag collection (November 2011) reveal that litter quality had the largest impact on decomposition. The high quality litter, Laurus nobilis, decomposed ~ 20% faster than the low quality litter, Raphia farinifera, in all plant biomes. Significant differences in decomposition among biomes were also observed, but decomposition rates were not correlated with elevation. Litter decomposition was fastest in the grassland (1330 – 1645 m in elevation) and mixed conifer (2442 - 2777 m) biomes and slowest in the desert scrub (1045 - 1130 m) and oak (2000 - 2200 m) biomes, despite temperature and litter humidity being strongly correlated with elevation. Invertebrate suppression did not influence decomposition rates. However, invertebrates are more likely to affect decomposition at later stages after liable substrates have been removed. This decomposition study in the Santa Catalina Mountains currently shows that early decomposition processes in these temperate plant biomes are driven primarily by differences in litter quality. I found no relationship between decomposition rates and temperature or litter humidity, suggesting that biome-specific details may also be important to understand these processes. Subsequent litter bag collections will help provide an organized framework for understanding the drivers of decomposition in different ecological contexts.