Abstract
Understanding the effects of nitrogen (N) addition on dissolved carbon in boreal forest soils is essential for accurate evaluation of regional carbon balances. The objective of this study was to determine the effects of different levels and types of N addition on soil dissolved carbon concentration in a cold-temperate coniferous forest through an in-situ fertilization experiment. Simulated atmospheric N addition was applied in a factorial experiment with N addition level (control, 10, 20 and 40 kg of N ha−1yr−1) and N type (NH4Cl, KNO3 and NH4NO3) treatments. The experiment was conducted over the 2010 growing season (May-September) at the Kailaqi farm of Genhe Forestry Bureau, located in the northern Great Xin’an mountain range, northern China. Monthly N addition treatments were applied in three replicate plots per treatment (n = 36), and measurements of dissolved organic carbon (DOC) and dissolved inorganic carbon (DIC) were derived from monthly sampling of the organic and mineral soil horizons. There was a significant effect of N type, with the combined N source (NH4NO3) producing significantly higher DOC than the control (ambient addition) or the NH4Cl treatment in both the organic and mineral layers. The N addition treatment increased DIC in the organic layer at the low levels only, while N type did not have a significant effect. There was a significant interaction of the month and the N level treatment, as low level N addition tended to increase the content of soil DOC while high level N tended to inhibit soil DOC content, with these trends being most pronounced in the middle of the growing season. These results elucidate the importance of the type and timing of N additions to the dynamics of soil carbon pools.
Highlights
The amount of atmospheric nitrogen (N) has increased considerably in recent decades as a result of higher anthropogenic emissions, resulting in significant changes in carbon and N cycles in terrestrial ecosystems[1,2]
C decomposition is coupled with N availability, dissolved organic N (DON) decomposition resembles that of dissolved organic carbon (DOC), and DOC decomposition is fueled by N mineralization[9]
The highest DOC occurred in the combined NH4NO3 and KNO3 N addition type treatments (Fig. 1A)
Summary
The amount of atmospheric nitrogen (N) has increased considerably in recent decades as a result of higher anthropogenic emissions, resulting in significant changes in carbon and N cycles in terrestrial ecosystems[1,2]. C decomposition is coupled with N availability, dissolved organic N (DON) decomposition resembles that of DOC, and DOC decomposition is fueled by N mineralization[9] Despite these known connections, the effects of increasing N deposition on soil DOC concentrations remain unclear. Studies on soil dissolved carbon and its dynamics have been conducted in forest, grassland, wetland and agricultural ecosystems[14,15]. Long-term inputs of low-level N will increase N availability in boreal forest ecosystems, affecting regional soil CO2 emissions and the soil carbon balance[16]. The objective of this study was to determine the effects of different levels and types of N addition on soil dissolved carbon concentration in a cold-temperate coniferous forest through an in-situ fertilization experiment. We anticipate that our results will provide new insights into forest soil carbon dynamics in the context of N addition in northern forest ecosystems
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