Pregitzer Kurt, Loya Wendy, Kubiske Mark, Zak Donald
Ecosystem Science Center, School of Forest Resources and Environmental Science, Michigan Technological University, 1400 Townsend Ave., Houghton, MI, 49931, USA.
Oecologia. 2006 Jun;148(3):503-16. doi: 10.1007/s00442-006-0381-8. Epub 2006 Feb 18.
The aspen free-air CO2 and O3 enrichment (FACTS II-FACE) study in Rhinelander, Wisconsin, USA, is designed to understand the mechanisms by which young northern deciduous forest ecosystems respond to elevated atmospheric carbon dioxide (CO2) and elevated tropospheric ozone (O3) in a replicated, factorial, field experiment. Soil respiration is the second largest flux of carbon (C) in these ecosystems, and the objective of this study was to understand how soil respiration responded to the experimental treatments as these fast-growing stands of pure aspen and birch + aspen approached maximum leaf area. Rates of soil respiration were typically lowest in the elevated O3 treatment. Elevated CO2 significantly stimulated soil respiration (8-26%) compared to the control treatment in both community types over all three growing seasons. In years 6-7 of the experiment, the greatest rates of soil respiration occurred in the interaction treatment (CO2 + O3), and rates of soil respiration were 15-25% greater in this treatment than in the elevated CO2 treatment, depending on year and community type. Two of the treatments, elevated CO2 and elevated CO2 + O3, were fumigated with 13C-depleted CO2, and in these two treatments we used standard isotope mixing models to understand the proportions of new and old C in soil respiration. During the peak of the growing season, C fixed since the initiation of the experiment in 1998 (new C) accounted for 60-80% of total soil respiration. The isotope measurements independently confirmed that more new C was respired from the interaction treatment compared to the elevated CO2 treatment. A period of low soil moisture late in the 2003 growing season resulted in soil respiration with an isotopic signature 4-6 per thousand enriched in 13C compared to sample dates when the percentage soil moisture was higher. In 2004, an extended period of low soil moisture during August and early September, punctuated by a significant rainfall event, resulted in soil respiration that was temporarily 4-6 per thousand more depleted in 13C. Up to 50% of the Earth's forests will see elevated concentrations of both CO2 and O3 in the coming decades and these interacting atmospheric trace gases stimulated soil respiration in this study.
美国威斯康星州莱茵兰德的白杨自由空气二氧化碳和臭氧富集（FACTS II-FACE）研究旨在通过一项重复、析因的田间试验，了解北方年轻落叶林生态系统对大气二氧化碳（CO₂）浓度升高和对流层臭氧（O₃）浓度升高的响应机制。土壤呼吸是这些生态系统中第二大的碳（C）通量，本研究的目的是了解在这些快速生长的纯白杨林和桦木+白杨林接近最大叶面积时，土壤呼吸如何对实验处理作出响应。在臭氧浓度升高的处理中，土壤呼吸速率通常最低。在所有三个生长季节中，与对照处理相比，二氧化碳浓度升高显著刺激了两种群落类型的土壤呼吸（8%-26%）。在实验的第6至7年，土壤呼吸速率在交互处理（CO₂ + O₃）中最高，且该处理中的土壤呼吸速率比二氧化碳浓度升高处理高15%-25%，具体取决于年份和群落类型。其中两个处理，即二氧化碳浓度升高处理和二氧化碳浓度升高+臭氧处理，用贫¹³C的二氧化碳进行熏蒸，在这两个处理中，我们使用标准同位素混合模型来了解土壤呼吸中新碳和旧碳的比例。在生长季节的高峰期，自1998年实验开始以来固定的碳（新碳）占土壤总呼吸的60%-80%。同位素测量独立证实，与二氧化碳浓度升高处理相比，交互处理中呼吸出的新碳更多。2003年生长季节后期的一段土壤湿度较低的时期，导致土壤呼吸的同位素特征与土壤湿度较高时的采样日期相比，¹³C富集了4‰-6‰。2004年，8月和9月初出现了一段持续的土壤湿度较低的时期，期间有一次显著降雨事件，导致土壤呼吸的¹³C暂时贫化了4‰-6‰。在未来几十年里，地球上高达50%的森林将面临二氧化碳和臭氧浓度的升高，而在本研究中，这些相互作用的大气痕量气体刺激了土壤呼吸。
