新鲜出炉的Nature，来一睹为快吧！——CO2增高作用下的一个成熟林的碳归趋

点击上方蓝色字体，关注我们

大气二氧化碳浓度增高(eCO₂)可以促进植物的碳吸收和生长，因此，通过减缓大气CO₂浓度的增加速度为气候变化提供了重要的负反馈。虽然从幼龄林收集的证据普遍表明，CO₂施肥效应强烈影响生物量增长，但成熟林对eCO₂是否有类似的响应尚不清楚。在成熟的树木和林分中，eCO₂增加光合吸收，但对生长无显著影响，这给在eCO₂下固定的额外碳的动态留下了一个悬而未决的问题。本研究首次使用一个成熟林的生态系统尺度的开放式空气CO₂浓度增高实验(FACE)的数据，建立了一个生态系统碳收支综合研究，来追踪森林碳在为期4年的eCO₂暴露下的动态。结果表明，虽然周围环境+150 ppm的eCO₂处理(+38%)通过初级生产总量诱导增加12% (+247g C m^-2 yr^-1)的碳吸收，这一额外的碳吸收并未导致生态系统水平的固碳增加。相反，大部分额外的碳通过几个呼吸通量被排放回大气，增加的土壤呼吸仅贡献了总吸收盈余的50%。该研究结果对以下主流观点提出了质疑：①森林作为碳汇的能力在eCO₂作用下普遍增强；以及②依靠CO₂施肥效应作为增加森林和造林项目碳汇的驱动力来缓解气候变化战略的有效性。

Figure 1. A comprehensive carbon budget under ambient and elevated CO2 treatment in a mature forest ecosystem. Diamond boxes are gross primary production for overstorey (GPPo) and understorey (GPPu), respectively. Squared boxes are carbon stocks (g C m-2 ), including overstorey leaf (Col), stem (Cstem), coarse root (Ccroot), fineroot (Cfroot), understorey aboveground (Cua), leaf litter (Clit), soil (Csoil), microbe (Cmicr), aboveground insect (Cins), and mycorrhizae (Cmyco). Unboxed variables are carbon fluxes (g C m-2 yr-1), including net primary production of overstorey leaf (NPPol), stem (NPPstem), coarse root (NPPcroot), fineroot (NPPfroot), and understorey aboveground (NPPua), overstorey leaf consumption by insects (NPPins), respiration fluxes of overstorey leaf (Rol), stem (Rstem), root (Rroot), understorey aboveground (Rua), growth (Rgrow), insect (Rins), heterotroph (Rhetero), and soil (Rsoil), and volatile carbon emission (VC), frass production (Frass), dissolved organic carbon (DOC), and soil methane net  uptake (CH4). Solid arrow lines are fluxes entering a pool, dotted arrow lines are fluxes leaving a pool. Blue italic values are means ± one standard deviation of the ambient CO2 treatment  (n=3), whereas red values are means ± one standard deviation of the elevated CO2 treatment (n=3). All values are normalized by a linear mixed-model with plot-specific pre-treatment leaf area index as a covariate to account for pre-existing differences. Summary of variable definitions and data availability is provided in Extended Data Table 1.

Figure 2. The fate of additional carbon fixed under elevated CO2 (eCO2) in a mature forest ecosystem. a) Column “GPP” represents the total eCO2-induced increases in overstorey and understorey gross primary production (GPPo and GPPu, respectively), “NPP + Ra” represents the sum of net primary production and autotrophic respiration response, “R + ΔCpools” represents the sum of ecosystem respiration and carbon storage  response. b) The relative contributions of individual NPP fluxes to the aggregated NPP response to eCO2, including NPP responses of overstorey leaf (NPPol), twigs, barks and seeds (NPPother), fineroot (NPPfroot), and understorey aboveground (NPPua); c) The relative contributions of individual respiratory fluxes to the aggregated R response to eCO2, including respiration responses of stem (Rstem), root (Rroot), understorey aboveground (Rua), and soil heterotroph (Rhetero); and d) The relative contributions of individual change in carbon storage to the aggregated ΔCpools response to eCO2, including changes in pool of overstorey leaf (ΔCol), stem (ΔCstem), understorey aboveground (ΔCua), fineroot (ΔCfroot), and soil (ΔCsoil).Variables with an absolute mean CO2 effect of < 5 gCm-2yr-1 are excluded from the figure for better visual clarification. Individual CO2 responses are reported in Extended Data Figure 4. Each color represents the CO2 response of a flux variable, point indicates the net sum of all variables for a column, and the grey error bar represents one standard deviation of the estimated column sum at the plot-level (see Methods). The CO2 effect is estimated using a linear mixed-model analysis with plot-specific pre-treatment leaf area index as a covariate to account for pre-existing differences (see Methods). The un-normalized response is provided in Extended Data Figure 3, which generally agrees with findings present in this figure, but 796 with less statistical precision.

Figure 3. Estimates of net ecosystem production (NEP) under ambient and elevated CO2 treatment at EucFACE. Positive values indicate ecosystem net carbon uptake by the ecosystem. “In - Out” calculates NEP based on the difference between total influxes and total outfluxes. “NPP - Rhetero” calculates NEP based on the difference between net primary production (NPP) and heterotrophic respiration (Rhetero). “∆Cpools” derives NEP based on incremental changes in all ecosystem carbon pools. Colored bars indicate treatment means based on each method (n=3), with blue representing ambient and red representing elevated CO2 treatment. Individual dots are plot-level NEP, derived based on different methods (see Methods). Values are normalized by a linear mixed-model with plot-specific pre-treatment leaf area index as a covariate to account for pre-existing differences. Horizontal dotted line indicates NEP equals zero.

 想要了解更多，一定要去下载原文阅读噢 ↓↓↓

https://doi.org/10.1101/696898 

往期回顾

 每天/学习/多/一点     温/顾/而/知新

     欢迎同行进微信群探讨有关生态与环境的学术问题 ↓↓↓

扫描二维码

获取更多精彩

生态笔记

喜欢就点“在看”