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首页> 外文期刊>Global Biogeochemical Cycles >Ecological processes dominate the 13C land disequilibrium in a Rocky Mountain subalpine forest
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Ecological processes dominate the 13C land disequilibrium in a Rocky Mountain subalpine forest

机译：生态过程主导了落基山亚高山森林的13C土地失衡

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摘要

Fossil fuel combustion has increased atmospheric CO_2 by ≈ 115 μmol mol~(-1) since 1750 and decreased its carbon isotope composition (δ~(13)C) by 1.7-2‰(the 13C Suess effect). Because carbon is stored in the terrestrial biosphere for decades and longer, the δ~(13)C of CO_2 released by terrestrial ecosystems is expected to differ from the δ~(13)C of CO_2 assimilated by land plants during photosynthesis. This isotopic difference between land-atmosphere respiration (δ_R) and photosynthetic assimilation (δ_A) fluxes gives rise to the 13C land disequilibrium (D). Contemporary understanding suggests that over annual and longer time scales, D is determined primarily by the Suess effect, and thus, D is generally positive (δ_R>δ_A). A 7 year record of biosphere-atmosphere carbon exchange was used to evaluate the seasonality of δ_A and δ_R, and the 13C land disequilibrium, in a subalpine conifer forest. A novel isotopic mixing model was employed to determine the δ~(13)C of net land-atmosphere exchange during day and night and combined with tower-based flux observations to assess δ_A and δ_R. The disequilibrium varied seasonally and when flux-weighted was opposite in sign than expected from the Suess effect (D =-0.75 ± 0.21‰or -0.88 ± 0.10‰depending on method). Seasonality in D appeared to be driven by photosynthetic discrimination (Δ_(canopy)) responding to environmental factors. Possible explanations for negative D include (1) changes in Δ_(canopy) over decades as CO_2 and temperature have risen, and/or (2) post-photosynthetic fractionation processes leading to sequestration of isotopically enriched carbon in long-lived pools like wood and soil.
机译：自1750年以来，化石燃料燃烧使大气中的CO_2增加了约115μmolmol〜（-1），并使碳同位素组成（δ〜（13）C）降低了1.7-2‰（13C Suess效应）。由于碳在陆地生物圈中存储了数十年甚至更长的时间，因此陆地生态系统释放的CO_2的δ〜（13）C与光合作用过程中陆地植物吸收的CO_2的δ〜（13）C不同。陆地-大气呼吸（δ_R）和光合同化（δ_A）通量之间的同位素差异导致13C土地失衡（D）。当代的理解表明，在每年和更长的时间尺度上，D主要由Suess效应决定，因此D通常为正（δ_R>δ_A）。利用7年的生物圈-大气碳交换记录，评估了亚高山针叶林的δ_A和δ_R的季节性以及13C土地失衡。利用新颖的同位素混合模型确定白天和夜晚净陆地-大气交换的δ〜（13）C，并结合基于塔的通量观测值来评估δ_A和δ_R。不平衡随季节变化，通量加权的符号与Suess效应所预期的相反（D = -0.75±0.21‰或-0.88±0.10‰，取决于方法）。 D中的季节性似乎是由对环境因素作出响应的光合作用歧视（Δ_（冠层））驱动的。负D的可能解释包括（1）随着CO_2和温度的升高，几十年来Δ_（冠层）的变化，和/或（2）光合作用后的分馏过程导致了长寿命池（如木材和泥。

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