Extreme precipitation reduces the recent photosynthetic carbon isotope signal detected in ecosystem respiration in an old-growth temperate forest.

IF 3.5 2区 农林科学 Q1 FORESTRY
Haoyu Diao, Jiabing Wu
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引用次数: 0

Abstract

The successful utilization of stable carbon isotope approaches in investigating forest carbon dynamics has relied on the assumption that the carbon isotope compositions (δ13C) therein have detectable temporal variations. However, interpreting the δ13C signal transfer can be challenging, given the complexities involved in disentangling the effect of a single environmental factor, the isotopic dilution effect from background CO2 and the lack of high-resolution δ13C measurements. In this study, we conducted continuous in situ monitoring of atmospheric CO2 (δ13Ca) across a canopy profile in an old-growth temperate forest in northeast China during the normal year 2020 and the wet year 2021. Both years exhibited similar temperature conditions in terms of both seasonal variations and annual averages. We tracked the natural carbon isotope composition from δ13Ca to photosynthate (δ13Cp) and to ecosystem respiration (δ13CReco). We observed significant differences in δ13Ca between the two years. Contrary to in 2020, in 2021 there was a δ13Ca valley in the middle of the growing season, attributed to surges in soil CO2 efflux induced by precipitation, while in 2020 values peaked during that period. Despite substantial and similar seasonal variations in canopy photosynthetic discrimination (Δ13Ccanopy) in the two years, the variability of δ13Cp in 2021 was significantly lower than in 2020, due to corresponding differences in δ13Ca. Furthermore, unlike in 2020, we found almost no changes in δ13CReco in 2021, which we ascribed to the imprint of the δ13Cp signal on above-ground respiration and, more importantly, to the contribution of stable δ13C signals from soil heterotrophic respired CO2. Our findings suggest that extreme precipitation can impede the detectability of recent photosynthetic δ13C signals in ecosystem respiration in forests, thus complicating the interpretation of above- and below-ground carbon linkage using δ13CReco. This study provides new insights for unravelling precipitation-related variations in forest carbon dynamics using stable isotope techniques.

极端降水减少了在温带原始森林生态系统呼吸中检测到的近期光合作用碳同位素信号。
成功利用稳定碳同位素方法研究森林碳动态的前提是其中的碳同位素组成(δ13C)具有可检测的时间变化。然而,要解释δ13C 信号的传递可能具有挑战性,因为要分清单一环境因素的影响、背景 CO2 的同位素稀释效应以及缺乏高分辨率的δ13C 测量结果是非常复杂的。在本研究中,我们在 2020 年正常年和 2021 年潮湿年期间,对中国东北某温带原始森林的树冠剖面上的大气二氧化碳(δ13Ca)进行了连续的原位监测。这两年的季节变化和年平均气温条件相似。我们跟踪了从 δ13Ca 到光合作用(δ13Cp)和生态系统呼吸作用(δ13CReco)的天然碳同位素组成。我们观察到这两年的 δ13Ca 有明显差异。与 2020 年相反,2021 年的δ13Ca 在生长季中期出现了一个谷底,这是由于降水引起的土壤二氧化碳外流激增所致,而 2020 年的δ13Ca 值在这一时期达到峰值。尽管这两年冠层光合分辨力(Δ13Ccanopy)的季节变化巨大且相似,但 2021 年的δ13Cp 变异性明显低于 2020 年,这是因为δ13Ca 存在相应的差异。此外,与 2020 年不同的是,我们发现 2021 年的δ13CReco 几乎没有变化,我们将其归因于δ13Cp 信号对地面呼吸作用的影响,更重要的是,土壤异养生物呼吸的 CO2 对稳定的δ13C 信号的贡献。我们的研究结果表明,极端降水会阻碍森林生态系统呼吸作用中近期光合作用δ13C信号的可探测性,从而使利用δ13CReco解释地上和地下碳联系变得更加复杂。这项研究为利用稳定同位素技术揭示与降水相关的森林碳动态变化提供了新的见解。
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来源期刊
Tree physiology
Tree physiology 农林科学-林学
CiteScore
7.10
自引率
7.50%
发文量
133
审稿时长
1 months
期刊介绍: Tree Physiology promotes research in a framework of hierarchically organized systems, measuring insight by the ability to link adjacent layers: thus, investigated tree physiology phenomenon should seek mechanistic explanation in finer-scale phenomena as well as seek significance in larger scale phenomena (Passioura 1979). A phenomenon not linked downscale is merely descriptive; an observation not linked upscale, might be trivial. Physiologists often refer qualitatively to processes at finer or coarser scale than the scale of their observation, and studies formally directed at three, or even two adjacent scales are rare. To emphasize the importance of relating mechanisms to coarser scale function, Tree Physiology will highlight papers doing so particularly well as feature papers.
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