N Deposition Alters Decomposition and C Cycling in the San Bernardino Mountains
Abstract
N deposition levels in the San Bernardino Mountains are amongst the highest in the country. Increased N levels can have considerable effects on decomposition and other components of the C cycle, however, these effects are not well understood, particularly, in xeric ecosystems. Two sites along an anthropogenic N deposition gradient were used for this study. At each site, there were N addition treatments of 50 and 150 kg N/ha/yr. Heterotrophic respiration rates from microcosm incubations showed that N addition levels of 50 kg/ha/yr increased respiration in the O horizon at both sites. However, the 150 kg/ha/yr treatment exhibited decreased respiration, suggesting that at high amendment levels, N depressed microbial decomposition. Radiocarbon signatures of the CO2 respired from the Oa decreased significantly with N amendment at both sites, suggesting that the isotopic composition of the tissue produced, and decomposed, differed from that of background N deposition. Beta-glucosidase activity in the Oa horizon increased with N amendment at the highly polluted site, but not at the less polluted site. Polyphenol oxidase activity decreased with N addition at the low pollution site, but not at the highly polluted site. Both of these changes suggest that the source of respiration shifted from older more recalcitrant substrates (i.e. lignin), to younger more labile substrates (i.e. cellulose) in response to N amendment. Therefore, the material being decomposed was younger, explaining the decrease in 14C values.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2006
- Bibcode:
- 2006AGUFM.B23F..03N
- Keywords:
-
- 0428 Carbon cycling (4806);
- 0469 Nitrogen cycling;
- 0470 Nutrients and nutrient cycling (4845;
- 4850);
- 0478 Pollution: urban;
- regional and global (0345;
- 4251)