The influence of deciduous tree species on soil carbon dynamics and sequestration in temperate forests

温带森林储存了3000亿吨有机碳。在欧洲，每年有8亿吨碳固定在森林中，约40%在土壤中，约60%在生物生物量中。可持续林业的目标之一是保证和增加森林生态系统的碳汇功能。然而，控制这一过程的因素尚不完全清楚。本研究的主要目的是分析重要树种（Fagus sylvatica L., Quercus spec., Fraxinus excelsior L.）， pseudoplatanus L., Tilia cordata Mill.)的影响。云杉（Picea abies L. Karst）对森林碳固存的影响。该研究将解决以下具体目标：(1)虽然树种对土壤碳储量的影响已被充分记录，但土壤碳储量随时间的变化，即碳的固存，在很大程度上仍是未知的。在本研究中，我们将在丹麦普通园林试验中不同树种下的森林土壤中重新采样土壤C，该试验是在10年前的2004/2005年进行的。因此，可以直接量化土壤碳储量的可能变化。(2)树种对森林土壤碳储量和储量变化的影响机制尚不明确。因此，将在两年内测量土壤呼吸，并将其划分为来源，异养呼吸（有机物分解）和自养呼吸（根呼吸）。将检查这些来源在总土壤呼吸中的相对比例是否取决于树种，从而对森林地面的不同碳储量有所贡献。(3)在以往的树种效应研究中，碳储量的差异主要表现在土壤和生物量上。然而，物种之间土壤和生物量C储量的差异可能不是相互正相关的，即现有的研究不能得出关于森林总树种依赖的C平衡的结论。此外，微量气体一氧化二氮（N2O）和甲烷（CH4）也是相关的温室气体，它们的增温势分别是CO2的28倍和264倍。树种可能以不同于CO2排放的方式影响N2O排放和CH4吸收。在本研究中，温室气体总平衡（生物量和土壤）包括CH4吸收和N2O排放将在两年的时间内在树种水平上量化。将分析其他土壤特性，例如养分含量，以便在本资助期之后的后续项目中校准和验证现有的生物地球化学模型（例如Biome-BGC， Version Zalf）。

Temperate forests store 300 billion tons of organic carbon (C). In Europe, 800 million tons of C are fixed annually in the forest, ~40% in the soil and ~60% in the living biomass. One goal of sustainable forestry is to ensure and increase the C sink function of the forest ecosystem. However, the factors controlling this process are not yet fully understood. The main objective of the proposed study is to analyze the effect of important tree species (Fagus sylvatica L., Quercus spec., Fraxinus excelsior L., Acer pseudoplatanus L., Tilia cordata Mill. and Picea abies L. Karst.) on forest C-sequestration. The study will address the following specific objectives:(1) While the tree species effect on soil C stocks is well documented, the change in soil C stocks over time, i.e. the C sequestration, remains largely unknown. In the present study, the forest soil will be resampled for soil C under different tree species in Danish common garden experiments which were analyzed for C 10 years ago in 2004/2005. Thus, possible changes in soil C stocks can be directly quantified. (2) It remains unclear which mechanisms are responsible for the tree species effect on forest soil C stocks and stock changes. Thus, soil respiration will be measured over two years and partitioned into its sources, the heterotrophic respiration (decomposition of organic substances) and the autotrophic respiration (root respiration). It will be checked whether the relative proportions of these sources to the total soil respiration are dependent on tree species and thus contribute to different carbon stocks in the forest floor.(3) In previous studies of tree species effects, differences in C stocks were observed either in the soil or in the biomass. However, it is possible that differences between species in soil and biomass C stocks are not positively related to each other, i.e. the available studies do not allow drawing conclusions concerning a total tree species dependent C-balance of the forests. Furthermore, the trace gases nitrous oxide (N2O) and methane (CH4) are relevant greenhouse gases, too, as their warming potentials are 28 times (CH4) and 264 times (N2O) higher than that of CO2, respectively. Tree species may influence the N2O emission and CH4 uptake in a different way than the CO2 emission. In the present study the total greenhouse gas balance (biomass and soil) including the CH4 uptake and N2O emissions will be quantified at the tree species level over a period of two years.Additional soil properties, e.g. nutrient content, will be analyzed in order to enable calibration and validation of existing biogeochemical models (e.g. Biome-BGC, Version Zalf) in a follow-up project to be pursued subsequent to this funding period.