利用海拔差异模拟增温对高山森林土壤溶解性有机碳和有机氮含量的影响

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

在2010年5月—2011年4月和2011年5月—2012年4月2个培养周期内,采用原状土柱野外控制试验,利用海拔梯度变化研究了温度增加对川西高山森林土壤溶解性有机碳(DOC)和有机氮(DON)动态的影响.结果表明:经模拟增温处理(降低海拔)的土壤有机层和矿质土壤层DOC和DON含量在2个连续培养周期内的各关键时期均呈现明显的动态变化.海拔3300和3000 m样地比海拔3600 m样地土层DOC含量分别增加6.8和26.6 mg·kg^(-1).海拔3600、3300和3000 m样地土层DOC含量均在第1个培养周期的生长季末最高,分别为408.0、317.9和448.2 mg·kg^(-1),在第2个培养周期的生长季节中期最低,分别为33.1、32.4和36.5 mg·kg^(-1).与海拔3600 m样地相比,海拔3300和3000 m样地土层DON含量分别增加2.3和30.4 mg·kg^(-1).除海拔3000 m样地以外,海拔3600和3300 m样地土层DON含量在第1个培养周期内的生长季节中期最高,分别为65.9和64.6 mg·kg^(-1),在第1个培养周期内的融化期最低,分别为31.9和37.1 mg·kg^(-1).模拟增温处理增加了样地内土壤有机层DOC和DON含量,降低了矿质土壤层DOC含量、土壤有机层及矿质土壤层DOC/DON值.土壤有机层DOC/DON值与DOC含量呈显著正相关,与DON含量呈显著负相关;矿质土壤层DOC/DON值与DOC含量呈显著负相关,与DON含量呈显著正相关.未来全球气候变暖可能通过影响高寒森林土壤温度和冻融循环格局,增加整个土层DOC和DON含量,进而影响高寒森林土壤碳、氮循环过程.

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 varied 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 period） during the first incubation period,while the lowest concentrations were 33.1,32.4 and 36.5mg·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 37.1mg·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 temperature and freeze-thaw pattern,and in turn alter the process of soil carbon and nitrogen.