Search

Abstract Reduced belowground carbon (C) allocation by plants exposed to ozone may change properties and activities of the microbial community in soils. To investigate how soil microbial biomass and extracellular enzyme activities respond to elevated ozone, we collected soils from a temperate grassland after four years of ozone exposure under fully open-air field conditions. We measured soil microbial biomass, the metabolism of low molecular weight C substrates and hydrolytic extracellular enzyme activities in both bulk soil and isolated aggregates to assess changes in microbial activity and community function. After four years of elevated ozone treatment, soil total organic C was reduced by an average of 20% compared with ambient condition. Elevated ozone resulted in a small but insignificant reduction (4–10%) in microbial biomass in both bulk soil and isolated aggregates. Activities of extracellular enzymes were generally not affected by elevated ozone, except β -glucosidase, whose activity in bulk soil was significantly lower under elevated ozone than ambient condition. Activities of β -glucosidase, leucine aminopeptidase and acid phosphatase were higher in microaggregates (<0.25 mm) as compared to macroaggregates (>0.25 mm). Elevated ozone had no effects on mineralization rates of low molecular weight C substrates in both bulk soil and isolated aggregates. We therefore conclude that the size and activity rather than function of the soil microbial community in this semi-natural grassland are altered by elevated ozone. Graphical abstract Unlabelled Image Highlights • A temperate grassland was exposed to ozone for 4 years under field conditions. • Soil total carbon and β-glucosidase activity were decreased under elevated ozone. • Neither ozone nor its interaction with aggregate size affected microbial activities. • Elevated ozone could alter the size and activity of soil microbial community. [ABSTRACT FROM AUTHOR]

Abstract: The estimation of nitrous oxide (N2O) emissions based on specific cropping systems is important for accurate national N2O budgets. Intensively managed vegetable cultivation is responsible for large N2O emissions in mainland China. However, little information can be obtained on the nationwide estimation of direct N2O emissions from vegetable fields. Estimates of fertilizer-induced direct N2O emissions from vegetable fields in mainland China were thus obtained by compiling and analyzing reported data in peer-reviewed journals and research reports. The results indicated that the seasonal N2O emissions from vegetable fields significantly increased with nitrogen (N) fertilizer application (p < 0.0001). According to the ordinary least squares (OLS) model, the fertilizer-induced emission factor (EF) and background emissions of N2O were estimated to be 0.55 ± 0.05% and 1.067 ± 0.277 kg N ha−1 yr−1, respectively. The EF was reduced and the background emission of N2O increased when the measurement duration was prolonged from ≤100 d to >100 and ≤200 d. Comparable results were obtained by the maximum likelihood (ML) model, with an EF of 0.49 ± 0.06% and background N2O emissions of 1.228 ± 0.189 kg N ha−1 yr−1. Based on the OLS-derived parameters, the fertilizer-induced direct emissions and background emissions of N2O were estimated to be 66.95 Gg N and 19.63 Gg N, respectively, in 2009, and the annual N2O emissions were much higher in the provinces of Shandong, Henan, Hebei and Sichuan. The estimated N2O emissions from vegetable fields accounted for 21.4% of the total direct N2O emissions from Chinese croplands, with large uncertainties. Therefore, the EF and background emissions of N2O for each cropping system, particularly for intensively managed vegetable fields, should be specifically determined for accurate national N2O inventories. [Copyright &y& Elsevier]