Effects of simulated warming on soil DOC and DON concentrations in the alpine forest of western Sichuan based on altitudinal gradient experiment.

Abstract

In order to understand the effects of climate warming on the process of soil carbon and nitrogen in the alpine forest, intact soil columns were collected in the alpine fir forest, and dissolved organic carbon (DOC) and dissolved organic nitrogen (DON) concentrations in both soil organic layer (OL) and mineral soil layer (ML) placed at different altitudes were measured from May 2010 to April 2011 (the first incubation period) and from May 2011 to April 2012 (the second incubation period). The results indicated that both DOC and DON concentrations in OL and ML va-ried greatly during the sampling period. The DOC concentration in soil columns at the altitudes of 3300 and 3000 m increased 6.8 and 26.6 mg·kg-1 compared with that at 3600 m, respectively. The highest DOC concentrations in soil columns at the altitudes of 3600, 3300 and 3000 m were 408.0, 317.9 and 448.2 mg·kg-1, respectively, which were all detected in LG (late growth pe-riod) during the first incubation period, while the lowest concentrations were 33.1, 32.4 and 36.5 mg·kg-1, respectively, which were all detected in MG (mid growth period) during the second incubation period. Moreover, the DON concentration in soil columns at the altitudes of 3300 and 3000 m increased 2.3 and 30.4 mg·kg-1 respectively compared with that at 3600 m. The highest DON concentrations at the altitudes of 3600 and 3300 m were 65.9 and 64.6 mg·kg-1, which were both detected in MG in the first incubation period, while the lowest concentrations were 31.9 and 37.1 mg·kg-1, both detected in ET (early thawing period) in the second incubation period. Simulated warming increased the concentrations of DOC and DON in the OL, but decreased the concentration of DOC in ML and the ratio of DOC to DON in OL and ML. The ratio of DOC to DON was significantly positively related with DOC concentration and negatively related with DON concentration in OL, whereas the ratio of DOC to DON was significantly negatively related with DOC concentration and positively with DON concentration in ML. The results indicated that climate warming would increase the concentrations of DOC and DON in soils of the high-frigid forest by changing soil tempe-rature and freeze-thaw pattern, and in turn alter the process of soil carbon and nitrogen.