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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]

Terrestrial soil denitrification is of great importance for closing the nitrogen (N) cycle, yet the current understanding of soil denitrification response to N fertilization remains uncertain. While there has been a focus on factors controlling N 2 O fluxes from agricultural soils because of its global warming effect, much less is known about factors controlling total denitrification losses, yet these can be sufficiently large to affect N use efficiency. Here, we collated 353 observations from 74 papers and conducted a global-scale meta-analysis to explore the effects of N fertilization on agricultural soil denitrification (N 2 O + N 2 ) where the acetylene inhibition technique was used. Relative to the control, N fertilization significantly increased soil denitrification by an average of 174%, although the magnitude of this increase differed significantly across environmental and soil conditions. Soil denitrification was more responsive to N fertilization in grasslands than in croplands. The changes in soil denitrification increased exponentially when the rates of synthetic N fertilizer application ≤ 250 kg N ha − 1 , but above this threshold, there were no further increases. The responses of soil denitrification to N fertilization were negatively correlated with soil clay content, C:N ratio, and bulk density. The comparable responses of soil N 2 O emissions (165%) and denitrification to N fertilization resulted in a small insignificant decrease of the N 2 O:N 2 ratio. Organic fertilizer applied with and without synthetic N fertilizer can contribute to lower N 2 O emissions probably by facilitating the last step of soil denitrification to N 2 production. Taken together, we conclude that these findings can provide important insights on regulating soil denitrification, which might contribute to improvement of N use efficiency and elimination of its negative impacts in agro-ecosystems. [ABSTRACT FROM AUTHOR]

Manure application mitigates land degradation and improves soil fertility. Despite many individual studies on manure effects, a comprehensive overview of its consequences for a broad range of soil properties is lacking. Through a meta-analysis of 521 observations spanning the experiments from days after pulse addition up to 113 years with continues manure input, we quantified and generalized the average responses of soil biochemical properties depending on climate factors, management, soil, and manure characteristics. Large increase of pools with fast turnover (microbial carbon (C) and nitrogen (N): +88% and +84%, respectively) compared to stable organic matter pools (+27% for organic C, and +33% for total N) reflects acceleration of C and N cycles and soil fertility improvement. Activities of enzymes acquiring C-, energy-, N-, phosphorus- and sulfur were 1.3–3.3 times larger than those in soil without manure for all study durations included. Soil C/N ratio remained unaffected, indicating the stability of coupled C and N cycles. Microbial C/N ratio decreased, indicating a shift towards bacterial domination, general increase of C and N availability and acceleration of element cycling. Composted manure or manure without mineral fertilizers induced the greatest increase compared to non-composted manure or manure with mineral fertilizers, respectively, in most biochemical properties. The optimal manure application rate for adjusting proper soil pH was 25 Mg ha−1 year−1. Among manure types, swine manure caused the greatest increase of N-cycle-related properties: microbial N (+230%), urease (+258%) and N -acetyl-β-D-glucosaminidase (+138%) activities. Manure application strategies should avoid P and N losses and pollution via runoff, leaching or gaseous emissions due to fast mineralization and priming of soil organic matter. In conclusion, manure application favors C accumulation and accelerates nutrient cycling by providing available organic substances and nutrients and thus increasing enzyme activities. Unlabelled Image • Manure effects on soil biochemical properties were identified using meta-analysis • Manure-only application was differentiated from application of manure with mineral fertilizers • Averaging of enzyme activities should be avoided as it disregards specific functions of individual enzymes • Optimal manure application rate for adjusting best soil pH is 25 Mg ha−1 year−1 • Swine manure caused the greatest increase of N-cycle-related properties. [ABSTRACT FROM AUTHOR]