Subke Jens-Arne, Vallack Harry W, Magnusson Tord, Keel Sonja G, Metcalfe Daniel B, Högberg Peter, Ineson Phil
Stockholm Environment Institute, Department of Biology, University of York, York YO10 5DD, UK.
Section of Soil Science, Department of Forest Ecology and Management, Swedish University of Agricultural Sciences (SLU), SE-901 83, Umeå, Sweden.
New Phytol. 2009;183(2):349-357. doi: 10.1111/j.1469-8137.2009.02883.x. Epub 2009 Jun 3.
Physical diffusion of isotopic tracers into and out of soil pores causes considerable uncertainty for the timing and magnitude of plant belowground allocation in pulse-labelling experiments. Here, we partitioned soil CO(2) isotopic fluxes into abiotic tracer flux (physical return), heterotrophic flux, and autotrophic flux contributions following (13)CO(2) labelling of a Swedish Pinus sylvestris forest. Soil CO(2) efflux and its isotopic composition from a combination of deep and surface soil collars was monitored using a field-deployed mass spectrometer. Additionally, (13)CO(2) within the soil profile was monitored. Physical (abiotic) efflux of (13)CO(2) from soil pore spaces was found to be significant for up to 48 h after pulse labelling, and equalled the amount of biotic label flux over 6 d. Measured and modelled changes in (13)CO(2) concentration throughout the soil profile corroborated these results. Tracer return via soil CO(2) efflux correlated significantly with the proximity of collars to trees, while daily amplitudes of total flux (including heterotrophic and autotrophic sources) showed surprising time shifts compared with heterotrophic fluxes. The results show for the first time the significance of the confounding influence of physical isotopic CO(2)-tracer return from the soil matrix, calling for the inclusion of meaningful control treatments in future pulse-chase experiments.
在脉冲标记实验中，同位素示踪剂进出土壤孔隙的物理扩散给植物地下分配的时间和幅度带来了相当大的不确定性。在此，我们在对瑞典樟子松森林进行¹³CO₂标记后，将土壤CO₂同位素通量划分为非生物示踪剂通量（物理回流）、异养通量和自养通量贡献。使用现场部署的质谱仪监测了深层和表层土壤环带组合的土壤CO₂排放及其同位素组成。此外，还监测了土壤剖面内的¹³CO₂。发现脉冲标记后长达48小时内，土壤孔隙空间中¹³CO₂的物理（非生物）排放都很显著，且在6天内与生物标记通量的量相当。整个土壤剖面中¹³CO₂浓度的测量和模拟变化证实了这些结果。通过土壤CO₂排放的示踪剂回流与环带距树木的距离显著相关，而总通量（包括异养和自养源）的日振幅与异养通量相比显示出惊人的时间偏移。结果首次表明了土壤基质中物理同位素CO₂ - 示踪剂回流的混杂影响的重要性，这要求在未来的脉冲追踪实验中纳入有意义的对照处理。
