移栽自不同纬度的落叶松(Larix gmelinii Rupr.)林的春季土壤呼吸

Vernal soil respiration of Larix gmelinii Rupr.forests transplanted from a latitudinal transect

以往的土壤呼吸(RS)研究大多集中于生长季,而对非生长季RS的认知甚少。常见于中高纬度地区的春季土壤冻融交替是影响陆地生态系统碳循环的关键事件,是RS年内变化格局的转折期。但是春季冻融交替期间RS的动态规律及其机理过程尚缺乏了解。研究以我国北方森林的优势类型——兴安落叶松(Larix gmelinii Rupr.)林为对象,在其自然分布区内,将地处4个纬度(处理)的8年生兴安落叶松林生态系统整体移至其分布区的南缘,以模拟气候暖化对RS及其组分的影响。在春季土壤冻融交替时期,采用红外气体分析法和根系排除法测定了移栽自不同纬度的落叶松林的RS和异养呼吸(RH)及其相关的环境因子。研究结果表明:RS与温度的耦联关系随土壤解冻进程而变化。在解冻初期和中期,RS的日进程与温度解耦联,但在土壤完全解冻后却强烈地依赖于土壤温度。从整个土壤解冻过程看,4个处理的RS和RH与土壤温度和含水量相关极显著(R2=0.569～0.743,P<0.001)。解冻的初期和中期的RS基本上来自RH组分,土壤根际呼吸(RR)到4月底才出现。RS和RH均受到实验处理、解冻时期及其交互作用的显著影响。RS和RH的平均值随着解冻的进程而增大,而且RS与RH之间的差异也随之增大。RS波动在0.50～3.30μmolCO2m-2s-1之间;而RH则波动在0.52～3.04μmolCO2m-2s-1之间。在相同气候条件下,4个处理RS有随着纬度的增加而增加的趋势,而且RS对土壤温度的响应程度也随纬度增加而增加。研究结果意味着土壤解冻期间来自纬度较高的兴安落叶松林的R对气候变暖方案的响应可能更为强烈。

Alternate freezing and thawing in springs, commonly occurring in mid- and high latitudes, is an important event in carbon cycles of terrestrial ecosystems, and also a temporal transition period in seasonal dynamics of soil respiration （Rs ）. However, few field studies on Rs and involved mechanistic processes during this period exist. We developed a latitudinal transect, comprising of 4 sites across the distribution range of boreal Dahurian larch （Larix gmelinii Rupr. ） in northeastern China in the fall of 2004. The sites were matched as well as possible to have the same stand characteristics （8-year-old plantations） and site conditions. Four 10 x 10 m2 larch forest plots （trees ＋ understory ＋ ground cover ＋ soil A and B horizons） at each site were transplanted to Mao＇ershan Forest Ecosystem Research Station-the southern boundary of the Dahurian larch distribution range （127°30′ E, 45°20′ N ）. The experiment was a completely randomized design including 4 treatments （sites） by 4 replicate plots. We used root exclusion method and an infrared gas exchange analyzer to measure Rs and heterotrophic respiration （RH） for the transplanted larch forest ecosystems during the soil freezing and thawing period （ between March and May 2006）. The temperature dependency of Rs was related to soil thawing stages. The diurnal patterns of Rs and R, did not differ significantly among the treatments, but did in various thawing periods. The diurnal patterns of Rs and R, were independent of soil temperature before the soil was completely thawed when they were strongly temperature - dependent. Pooling all data across the whole soil thawing process, we found that the Rs and R, were significantly affected by soil temperature and water content across the 4 treatments （R^2 = 0. 569 - 0. 743, P 〈 0. 001 ）. The soil surface CO2 flux was predominantly composed of RM up till the end of April when the rhizospheric respiration （ RR ） occurred. The treatment, thawing period, and their interaction significantly affected both RS and RH. The mean values of Rs and RH, and their differences increased with the soil thawing proceeding. During the soil thawing process, the RS and RH varied from 0.50 - 3.30 μmolCO2m^-2 s^ -1 and 0.52 - 3.04 μmolCO2 m^-2 s^-1, respectively. Under the same climate conditions, the RS and its sensitivity to soil temperature tended to increase with the latitude. Our results suggest a stronger response of vernal soil respiration for more northern Larix gmelinii forests under climate warming scenarios.