Swiss Federal Research Institute WSL, Zuercherstrasse 111, 8903 Birmensdorf, Switzerland.
Tree Physiol. 2010 Dec;30(12):1515-27. doi: 10.1093/treephys/tpq090. Epub 2010 Nov 12.
Forest ecosystems have a large carbon (C) storage capacity, which depends on their productivity and the residence time of C. Therefore, the time interval between C assimilation and its return to the atmosphere is an important parameter for determining C storage. Especially fine roots (≤2 mm in diameter) undergo constant replacement and provide a large biomass input to the soil. In this study, we aimed to determine the residence time of C in living fine roots and the decomposition rates of dead fine roots. Therefore, we pulse-labelled nine 20-year-old individual silver fir trees (Abies alba Miller; ∼70 cm tall) with ¹³CO₂ in situ to trace the assimilated C over time into the fine-root systems. Whole trees were harvested at different time points after labelling in autumn, biomass was determined and cellulose and starch of fine roots were extracted. Moreover, soil cores were taken and ingrowth cores installed, in which fine roots were genetically identified, to assess incorporation and remobilization of ¹³C in the fine roots of silver fir trees; litterbags were used to determine fine-root decomposition rates. The ¹³C label was incorporated in the fine-root system as cellulose within 3 days, with highest values after 30 days, before reaching background levels after 1 year. The highest δ¹³C values were found in starch throughout the experiment. ¹³C recovery and carbon mean residence times did not differ significantly among fine-root diameter classes, indicating size-independent C turnover times in fine roots of A. alba trees of ∼219 days. Furthermore, carbon was remobilized from starch into newly grown fine roots in the next spring after our autumn labelling. One year after installation, litterbags with fine roots revealed a decrease of biomass of ∼40% with relative ¹³C content in fine-root bulk biomass and cellulose of ∼50%, indicating a faster loss of ¹³C-labelled compounds compared with bulk biomass. Our results also suggest that genetic analysis of fine-root fragments found in soil and ingrowth cores is advisable when working in mixed forest stands with trees of similar fine-root morphology. Only then can one avoid dilution of the labelling signal by mistake, due to analysis of non-labelled non-target species roots.
森林生态系统具有较大的碳（C）储存能力，这取决于其生产力和 C 的停留时间。因此，C 同化和返回大气之间的时间间隔是确定 C 储存的一个重要参数。特别是细根（直径≤2 毫米）不断更新，为土壤提供大量生物质输入。在这项研究中，我们旨在确定活细根中 C 的停留时间和死细根的分解速率。因此，我们使用¹³CO₂在原地脉冲标记了 9 株 20 年生的白冷杉个体（Abies alba Miller；约 70 厘米高），以追踪随时间同化到细根系统中的 C。在秋季标记后不同时间点采集整株树，测定生物量，并提取细根的纤维素和淀粉。此外，采集土壤芯并安装生长芯，在其中鉴定银冷杉细根中的¹³C 的掺入和再移动；使用凋落物袋来确定细根分解速率。¹³C 标签在 3 天内被掺入细根系统的纤维素中，30 天后达到最高值，1 年后达到背景水平。整个实验过程中，淀粉的δ¹³C 值最高。¹³C 回收率和碳平均停留时间在细根直径类群之间没有显著差异，表明白冷杉细根的 C 周转率与大小无关，约为 219 天。此外，在我们秋季标记后的下一个春天，从淀粉中重新动员碳进入新生长的细根。安装一年后，含有细根的凋落物袋显示生物量减少了约 40%，细根总生物量和纤维素中的相对¹³C 含量减少了约 50%，这表明与总生物量相比，¹³C 标记化合物的损失更快。我们的研究结果还表明，在具有类似细根形态的树木的混交林分中工作时，对土壤和生长芯中发现的细根片段进行遗传分析是明智的。只有这样，才能避免由于分析非标记的非目标物种的根而错误地稀释标记信号。
