采伐对大兴安岭非连续冻土区毛赤杨沼泽碳源/汇的影响

Impact of harvesting on carbon source/sink of Alnus sibirica var. hirsuta swamps in Daxing’anling Mountains discontinuous permafrost region of northeastern China

【目的】气候变暖引起冻土退化将会增加冻土之上湿地的温室气体排放,但有关采伐干扰对冻土湿地温室气体排放有何影响仍不清楚。【方法】运用静态箱-气相色谱,相对生长方程等方法,测定寒温带大兴安岭冻土生境毛赤杨沼泽林4种不同采伐处理(对照(D)、轻度择伐15%(Qz)、重度择伐45%(Zz)及皆伐(J))的土壤呼吸年碳排放量(ACE)(CO2和CH4),植被净初级生产力(NPP)与年净固碳量(VNCS)及相关环境因子(土壤温度、水位、化冻深度、土壤碳氮含量、雪被厚度等),依据生态系统净碳收支平衡,揭示采伐干扰对冻土生境毛赤杨沼泽林生态系统碳源/汇的影响规律及其机制。【结果】(1) Zz和J显著降低土壤CH4年均通量(0.008~0.019 mg/(m2·h))52.6%~57.9%,而Qz与对照相近(-10.5%,P>0.05),且其季节动态趋势存在2种类型(D、Qz双峰型-低排放及Zz和J双峰型-低吸收)。(2) Qz、Zz和J显著降低土壤CO2年均通量(103.69~133.65 mg/(m2·h))14.4%~22.4%(P <0.05),且其季节动态趋势存在2种类型(D、Qz单峰型-峰值于夏末及Zz和J单峰型-峰值提前于盛夏)。(3)其土壤CH4通量受土壤温度、水位、雪被厚度综合控制,土壤CO2通量受土壤温度、土壤有机碳含量、化冻深度综合控制。(4) NPP(5.07~8.83 t/(hm2·a))和VNCS(2.10~3.83 t/(hm2·a))呈现随采伐强度增大而递减趋势,Qz与D相近(P> 0.05),Zz和J显著低于D 13.7%~36.9%和14.2%~43.5%(P <0.05),J又显著低于Zz 26.9%和34.2%(P <0.05)。(5)净生态系统碳收支(-0.42~1.30 t/(hm2·a))存在显著差异性,D、Qz、Zz均表现为碳的吸收汇,且Qz的汇强显著高于D和Zz 1.6和1.2倍(P <0.05),但J已转化为碳的排放源(-0.42 t/(hm2·a),P <0.05)。【结论】择伐干扰8年后寒温带冻土区毛赤杨沼泽林的碳汇功能已恢复,而皆伐后仍维持碳源,故在湿地碳汇管理中适宜采取择伐而应避免皆伐。

[Objective] Degradation of permafrost caused by climate warming will increase greenhouse gas emissions from wetlands above it, yet it is still unclear that how harvest disturbance affects greenhouse gas emissions from wetlands on frozen soil. [Method] Annual carbon emission fluxes(ACE)(CO2 and CH4),the net primary productivity(NPP) and annual net carbon sequestration of vegetation(VNCS) of four different harvest treatments(control-D, low intensity selective cutting 15%-Qz, high intensity selective cutting 45%-Zz and clear cutting-J) of Alnus sibirica var. hirsuta swamp were measured synchronously using the static chamber gas chromatography method and the relative growth equation, as well as related environmental factors(soil temperature, water level, thawing depth, soil carbon and nitrogen content, etc.) at Nanwenghe in Daxing’anling discontinuous permafrost region of northeastern China, in order to reveal the influence of harvesting disturbance on the carbon source/sink of the cold temperate forested wetlands according to the balance of net carbon budget of the ecosystem. [Result](1) Zz and J made the mean annual fluxes of CH4(0.008-0.019 mg/(m2·h)) significantly lower than D by 52.6%-57.9%(P < 0.05), Qz is close to the D(-10.5%, P > 0.05), and their seasonal dynamic trends took on two types(D, Qz bimodal-low emission;Zz and J bimodal-low absorption);(2) Qz, Zz and J all made the mean annual fluxes of CO2(103.69-133.65 mg/(m2·h)) significantly decreased by 14.4%-22.4%(P < 0.05) compared with control,their seasonal dynamic trends also existed two types(D, Qz unimodal type-peak at late summer;Zz and J unimodal type-peak advance to midsummer);(3) The soil CH4 flux was controlled by soil temperature, water level and snow thickness;soil CO2 flux was controlled by soil temperature, soil organic carbon content and freezing depth synthetically;(4) Both NPP(5.07-8.83 t/(ha·year)) and VNCS(2.10-3.83 t/(ha·year))showed a declining trend with increasing harvesting intensity, among them, NPP and VNCS of Qz were similar to those of D, Zz and J, made NPP and VNCS significantly decreased by13.7%-36.9% and14.2%-43.5% compared with control(P < 0.05), respectively, and those of J were significantly lower than that of Zz by 26.9% and 34.2%(P < 0.05);(5) Net ecosystem carbon budget(-0.42-1.30 t/(ha·year)) of four treatments existed significant differences. D, Qz and Zz were all carbon sinks, and the sink strength of Qz was significantly higher than that of D and Zz by 1.6 and 1.2 times(P < 0.05), but J had been converted into carbon source(-0.42 t/(ha·year), P < 0.05). [Conclusion] Therefore, after eight years of harvesting, Alnus sibirica var. hirsuta swamp had restored the carbon sink function at selective cutting site, while it still maintained the carbon source at clear cutting site in the cold temperate discontinuous permafrost region, so selective cutting should be adopted in the management of wetland carbon sinks and to avoid clear cutting.