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No effect of warming and watering on soil nitrous oxide fluxes in a temperate sitka spruce forest ecosystem

2020-10-08, Zou, Junliang, Osborne, Bruce A.

Soil fluxes of nitrous oxide (N2O) play an important role in the global greenhouse gas budget. However, the response of soil N2O emissions to climate change in temperate forest plantations is not yet well understood. In this study, we assessed the responses of soil N2O fluxes to experimental warming with or without water addition, using a replicated in situ heating (~2°C above ambient) and water addition (170 mm) experiment in a temperate Sitka spruce plantation forest over the period 2014–2016. We found that seasonal fluxes of N2O during the year were highly variable, ranging from net uptake to net emissions. Seasonal variations in soil N2O fluxes were not correlated with either soil temperature or soil moisture. In addition, none of the individual warming/watering treatments, or their interactions, had significant effects on soil N2O fluxes and N-related soil properties. Overall, our results suggest that despite future increases in temperature, soil N2O emission may remain largely unchanged in many temperate forest ecosystems that are often N-limited.

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Spatially Related Sampling Uncertainty in the Assessment of Labile Soil Carbon and Nitrogen in an Irish Forest Plantation

2021-02-28, Zou, Junliang, Osborne, Bruce A.

The importance of labile soil carbon (C) and nitrogen (N) in soil biogeochemical processes is now well recognized. However, the quantification of labile soil C and N in soils and the assessment of their contribution to ecosystem C and N budgets is often constrained by limited information on spatial variability. To address this, we examined spatial variability in dissolved organic carbon (DOC) and dissolved total nitrogen (DTN) in a Sitka spruce forest in central Ireland. The results showed moderate variations in the concentrations of DOC and DTN based on the mean, minimum, and maximum, as well as the coefficients of variation. Residual values of DOC and DTN were shown to have moderate spatial autocorrelations, and the nugget sill ratios were 0.09% and 0.10%, respectively. Distribution maps revealed that both DOC and DTN concentrations in the study area decreased from the southeast. The variability of both DOC and DTN increased as the sampling area expanded and could be well parameterized as a power function of the sampling area. The cokriging technique performed better than the ordinary kriging for predictions of DOC and DTN, which are highly correlated. This study provides a statistically based assessment of spatial variations in DOC and DTN and identifies the sampling effort required for their accurate quantification, leading to improved assessments of forest ecosystem C and N budgets.