Forest soil CO2 flux:: uncovering the contribution and environmental responses of ectomycorrhizas
Forest soil CO2 flux:: uncovering the contribution and environmental responses of ectomycorrhizas
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DOI：
10.1111/j.1365-2486.2007.01383.x
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发表时间：
2007-08-01
影响因子：
11.6
通讯作者：
Ineson, Phil
中科院分区：
文献类型：
--
作者：
Heinemeyer, Andreas;Hartley, Iain P.;Ineson, Phil
森林在全球碳循环中发挥着关键作用，被认为是一个重要的、持续的碳汇。然而，森林中的碳固存对全球气候变化的反应仍然是一个主要的不确定性，对土壤二氧化碳排放的来源和环境反应的了解尤其不足。例如，尽管外生菌根真菌(EM)的生物量很大，但它们对森林土壤二氧化碳排放的贡献以及对环境驱动因素变化的反应迄今尚未在实地进行量化。它们的活动通常被简单地包括在“自养”的根呼吸项中。采用菌根网领设计，建立了一套多路连续的土壤呼吸测量系统，对根部、根外菌根菌丝和土壤异养呼吸3种主要的土壤CO2外排组分进行了监测，结果表明，菌根菌丝呼吸在插领后1个月内显著增加，此后保持显著稳定。秋季土壤CO2通量可分为近60%的异养型、25%的EM菌丝型和15%的根际通量。因此，根外EM菌丝体对土壤二氧化碳通量的贡献比根部大得多。虽然EM菌丝呼吸对土壤水分的降低有强烈的反应，并且似乎高度依赖于同化物的供应，但它并不直接对土壤温度的变化做出反应。主要是土壤异养通量组分导致了通常观察到的与温度的指数关系。我们的结果强烈表明，对土壤呼吸的准确模拟，特别是在森林生态系统中，需要明确地考虑菌根菌丝体及其对特定环境因素的动态响应。此外，我们认为，在森林生态系统中，菌根二氧化碳通量分量代表着一个溢出的二氧化碳分流，通过这个分流，多余的植物碳可以直接返回到大气中，从而限制了在二氧化碳增加的情况下树木预期的碳固存。
Forests play a critical role in the global carbon cycle, being considered an important and continuing carbon sink. However, the response of carbon sequestration in forests to global climate change remains a major uncertainty, with a particularly poor understanding of the origins and environmental responses of soil CO2 efflux. For example, despite their large biomass, the contribution of ectomycorrhizal (EM) fungi to forest soil CO2 efflux and responses to changes in environmental drivers has, to date, not been quantified in the field. Their activity is often simplistically included in the 'autotrophic' root respiration term. We set up a multiplexed continuous soil respiration measurement system in a young Lodgepole pine forest, using a mycorrhizal mesh collar design, to monitor the three main soil CO2 efflux components: root, extraradical mycorrhizal hyphal, and soil heterotrophic respiration.Mycorrhizal hyphal respiration increased during the first month after collar insertion and thereafter remained remarkably stable. During autumn the soil CO2 flux components could be divided into similar to 60% soil heterotrophic, similar to 25% EM hyphal, and similar to 15% root fluxes. Thus the extraradical EM mycelium can contribute substantially more to soil CO2 flux than do roots. While EM hyphal respiration responded strongly to reductions in soil moisture and appeared to be highly dependent on assimilate supply, it did not responded directly to changes in soil temperature. It was mainly the soil heterotrophic flux component that caused the commonly observed exponential relationship with temperature. Our results strongly suggest that accurate modelling of soil respiration, particularly in forest ecosystems, needs to explicitly consider the mycorrhizal mycelium and its dynamic response to specific environmental factors. Moreover, we propose that in forest ecosystems the mycorrhizal CO2 flux component represents an overflow 'CO2 tap' through which surplus plant carbon may be returned directly to the atmosphere, thus limiting expected carbon sequestration from trees under elevated CO2.