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Abstract Global climate change is projected to intensify soil drying-rewetting (DRW) events with extended drought, especially in arid and semiarid ecosystems. However, the extent to which the soil DRW with intensified drought can alter soil respiration (R s) in forests is still under debate, and subsequent legacy effects on R s are not well understood. Here, we conducted a 180-d soil incubation experiment to investigate how soil DRW with different drought intensities alter the R s in poplar (Populus simonii) and Mongolian pine (Pinus sylvestris var. mongolica) plantations. The incubation experiment included four 30-d cycles of 1) constant moisture treatment (control), 2) DRW with 10-d drying and 20-d rewetting (DRW 10-20) or 3) DRW with 20-d drying and 10-d rewetting (DRW 20-10), and then an extended 60-d incubation under constant moisture. During the four DRW cycles, the direct C release with respiration of Mongolian pine soils (27 g C·m−2 in DRW 10-20 and 140 g C·m−2 in DRW 20-10 , respectively) decreased to a much lower extent than that of poplar soils (228 g C·m−2 in DRW 10-20 and 498 g C·m−2 in DRW 20-10 , respectively). R s did not significantly change during the extended 60-d incubation in the DRW 10-20 treatment compared to control treatment. However, the respired CO 2 were increased by 68 g C·m−2 in the poplar soils and 19 g C·m−2 in the Mongolian pine soils in the DRW 20-10 treatment, which approximately compensated for 14% of the decreases of total respiration during four DRW cycles. This legacy effect induced by the DRW with intensified drought was attributed to the higher amount of remaining substrates and soil microbial biomass. Our study highlights that DRW can cause both direct and legacy effects on R s , but the effects vary with drought intensity and forest type. Highlights • Soil respiration was measured during four drying-rewetting (DRW) cycles and an extended incubation. • DRW with longer drought decreased more soil respiration than with mild drought. • Extended incubation compensated for 14% of the drought-induced soil respiration reduction. • The DRW effects on soil respiration varied with drought intensity and forest type. [ABSTRACT FROM AUTHOR]

Abstract: The combustion of fossil fuels and fertilizer use has increased the amount of biologically available N over the last 150 years. Future rates of atmospheric N deposition may slow organic matter decay and alter microbial community composition and function. However, our understanding of how anthropogenic N enrichment may alter the physiological mechanisms by which soil microorganisms assimilate and cycle N in soil are largely unknown. Since 1994, we have experimentally increased NO3 deposition to replicate (n = 4) northern hardwood forest stands across a 500-km climatic gradient in the Great Lakes region of North America. Our goal was to examine how functional genes mediating N-cycle processes in soil microbial communities have responded to experimental N deposition using the functional gene microarray, GeoChip 4.0. Experimental N deposition decreased the abundance and richness of key protein-coding genes in Archaea and Bacteria responsible for N fixation, ammonification, denitrification and assimilatory nitrate reduction; the same was true for bacterial genes mediating nitrification and dissimilatory nitrate reduction. However, the extent to which experimental N deposition decreased abundance and richness was site-specific, which was revealed by a significant site by treatment interaction. Experimental N deposition also caused a community composition shift via dispersion (increased β-diversity) in archaeal and bacterial gene assemblages. In combination, our observations suggest future rates of atmospheric N deposition could fundamentally alter the physiological potential of soil microbial communities. [Copyright &y& Elsevier]