冻融作用对我国东北湿地土壤碳排放与土壤微生物的影响

Effects of freeze-thaw cycles on soil microbial biomass carbon and carbon emissions from wetland soils,Northeast China

通过室内模拟冻融实验,探讨了冻融强度(-5和-15℃)和循环次数(0、1、5、10和15次)对我国东北连续多年冻土和季节性冻土湿地二氧化碳(CO2)、甲烷(CH4)产生以及土壤微生物生物量碳(MBC)的影响。结果表明,不同冻融条件下,2种冻土中CO2、CH4排放速率及MBC均表现为:在第1次冻融循环后有所降低,随后随着循环次数的增加,呈现先增高后降低并趋于稳定的趋势。总体上,循环次数显著影响2种冻土CO2、CH4排放和MBC。与对照和小幅度冻融循环相比,大幅温度波动显著促进2种冻土土壤碳排放,但冻融强度对MBC影响不大。实验期间,FTC(-15℃)处理中,连续多年冻土CO2累积排放量(679.99 mg·kg-1)高于季节性冻土(454.32 mg·kg-1),而对CH4累积排放量来说,在FTC(-5℃)处理时,连续多年冻土达到334.49μg·kg-1,略高于其他处理;而在FTC(-15℃)处理时,季节性冻土则最高(600.07μg·kg-1),可能意味着冻融过程中2种冻土产甲烷菌的温度敏感性具有一定差异。本研究为科学评估全球气候变化对我国东北主要冻土区的土壤碳周转提供了数据支持。

A laboratory experiment was conducted to assess the effects of the freezing-thawing cycles （FTCs） on soil microbial biomass carbon （MBC） , and CO2 and CH4 emissions from wet- land soils in the continuous permafrost zone （TQ） and seasonally frozen region （JC） of Northeast China. Soil samples were incubated at different frost intensities [ ＋5 （ control）, -5, and - 15 ℃ for 12 h respectively, and then thawed at ＋5 ℃ for 12 h. These freeze-thaw cycles were repeated for 0, 1, 5, 10, and 15 times. The results showed that the CO2 and CH4 emission rates and MBC of two types of soil decreased after the first freeze-thaw incubatidn, and presented an increase and then decrease pattern and then trended to be stable with the increases of cycling times. Compared with the control （5 ℃ ） and low frost intensity （-5 ℃ ） treatments, high frost intensity （-15 ℃ ） significantly promoted CO2 and CH4 emissions but did not significantly influence MBC. At -15℃, the cumulative CO/emissions from TQ soil reached 679.99 mg · kg-1 after 15 FTCs, which was about 50% higher than that of JC soil （ 454.32 mg· kg-1 ）. The highest cumulative CH4 emission from TQ soil was 334.49 μg· kg-1 at -5 ℃ after 15 FTCs, while this value was 600.07 μg · kg-1 at -15℃ for JC soil. The temperature sensitivities of methanogens might be different between these two frozen soils during the freezing-thawing cycles. Our results provide scientific data for the assessment of global climate change on soil carbon turnover in the main permafrost regions of Northeast China.