Initial soil responses to experimental warming in two contrasting forest ecosystems, Eastern Tibetan Plateau, China: Nutrient availabilities, microbial properties and enzyme activities

In order to understand the effects of projected global warming on soils in different land-use types, we compared the impacts of warming on soils in two contrasting forest ecosystems (a dragon spruce plantation and a natural forest) using the open-top chamber (OTC) method in the Eastern Tibetan Plateau of China. The OTC on average enhanced daily mean soil temperatures by 0.61 °C (plantation) and by 0.55 °C (natural forest) throughout the growing season, respectively. Conversely, soil volumetric moisture declined by 4.10% in the plantation and by 2.55% in the natural forest, respectively. Warming did not affect dissolved organic C (DOC) and N (DON) in the plantation but significantly increased them in the natural forest. Elevated temperature significantly increased net N mineralization rates and extractable inorganic N pools in both sites. Warming had no effects on microbial biomass C (MBC) and N (MBN) and their ratios (MBC/MBN) in the plantation and significantly increased MBC and MBN only late in the growing season in the natural forest. Warming did not affect basal respiration in the plantation but significantly increased it in the natural forest. No clear change was observed in metabolic quotient between warming regimes for both forest types. Experimental warming tended to increase invertase and urease in both forest soils. Measured pools related to N turnover generally showed significant interactions in warming, forest type and sampling date. Taken together, our results indicate that responses of soils to experimental warming depend strongly on forest managements and seasons.

Research highlights▶ Reforestation affects the pattern and magnitude of soil nitrogen turnover, and further influences the responses of soil nitrogen transformation to warming.