Data from: Isotopic methods for non-destructive assessment of carbon dynamics in shrublands under long-term climate change manipulation

1.Long-term climate change experiments are extremely valuable for studying ecosystem responses to environmental change. Examination of the vegetation and the soil should be non-destructive to guarantee long-term research. In this paper, we review field methods using isotope techniques for assessing carbon dynamics in the plant-soil-air continuum, based on recent field experience and examples from a European climate change manipulation network.

2.Eight European semi-natural shrubland ecosystems were exposed to warming and drought manipulations. One field site was additionally exposed to elevated atmospheric CO2. We evaluate the isotope methods that were used across the network to evaluate carbon fluxes and ecosystem responses, including: 1) analysis of the naturally rare isotopes of carbon (13C and 14C) and nitrogen (15N); 2) use of in-situ pulse labelling with 13CO2, soil injections of 13C- and 15N-enriched substrates, or continuous labelling by Free Air Carbon dioxide Enrichment (FACE) and 3) manipulation of isotopic composition of soil substrates (14C) in lab-based studies.

3.The natural 14C signature of soil respiration gave insight into a possible long-term shift in the partitioning between the decomposition of young and old soil carbon sources. Contrastingly, the stable isotopes 13C and 15N were used for shorter-term processes, as the residence time in a certain compartment of the stable isotope label signal is limited. The use of labelled carbon-compounds to study carbon mineralization by soil microorganisms enabled to determine the long-term effect of climate change on microbial carbon uptake kinetics and turnover.

4.Based on the experience with the experimental work, we provide recommendations for the application of the reviewed methods to study carbon fluxes in the plant-soil-air continuum in climate change experiments. 13C-labelling techniques exert minimal physical disturbances, however, the dilution of the applied isotopic signal can be challenging. In addition, the contamination of the field site with excess 13C or 14C can be a problem for subsequent natural abundance (14C and 13C) or label studies. The use of slight changes in carbon and nitrogen natural abundance does not present problems related to potential dilution or contamination risks, but the usefulness depends on the fractionation rate of the studied processes.

1. 长期气候变化试验对于研究生态系统对环境变化的响应具有极高价值。为保障长期研究的可持续性，对植被与土壤的观测需采用非破坏性方式。本文基于近期野外工作经验与欧洲气候变化操控网络的相关案例，综述了利用同位素技术（isotope techniques）评估植物-土壤-空气连续体（plant-soil-air continuum）碳动态的野外方法。
2. 该网络共包含8个欧洲半自然灌丛生态系统，均接受增温与干旱操控处理，其中1个野外样地额外施加了大气CO₂浓度升高处理。本文评估了该网络中用于测定碳通量（carbon fluxes）与生态系统响应的同位素方法，具体包括：1) 碳（¹³C、¹⁴C）与氮（¹⁵N）天然稀有同位素分析；2) 采用¹³CO₂原位脉冲标记（in-situ pulse labelling）、¹³C与¹⁵N富集底物土壤注入法，或通过自由空气CO₂富集（Free Air Carbon dioxide Enrichment, FACE）技术进行连续标记；3) 实验室研究中对土壤底物（¹⁴C）的同位素组成进行操控。
3. 土壤呼吸的天然¹⁴C信号特征，可揭示年轻与老旧土壤碳源分解分配模式可能发生的长期偏移。与之相对，稳定同位素¹³C与¹⁵N则多用于短期过程研究，因为稳定同位素标记信号在特定生态组分中的驻留时间有限。利用标记碳化合物研究土壤微生物的碳矿化（carbon mineralization）过程，可明确气候变化对微生物碳吸收动力学与周转的长期影响。
4. 基于本试验的工作经验，本文针对气候变化试验中植物-土壤-空气连续体碳通量研究的上述综述方法，提出了应用建议。¹³C标记技术对样地的物理干扰极小，但施加的同位素信号易出现稀释问题，这会对研究造成挑战。此外，过量¹³C或¹⁴C对野外样地的污染，会干扰后续天然丰度（¹⁴C与¹³C）分析或标记试验。利用碳、氮天然丰度的微小变化开展研究，不会面临潜在稀释或污染风险相关的问题，但该方法的有效性取决于研究过程的分馏速率（fractionation rate）。