1. Soil enzymes are central to ecosystem processes because they mediate numerous reactions that are essential in biogeochemical cycles. However, how soil enzyme activities will respond to global warming is uncertain. We reviewed the literature on mechanisms linking temperature effects on soil enzymes and microbial communities, and outlined a conceptual overview on how these changes may influence soil carbon fluxes in terrestrial ecosystems.2. At the enzyme scale, although temperature can have a positive effect on enzymatic catalytic power in the short term (i.e. via the instantaneous response of activity), this effect can be countered over time by enzyme inactivation and reduced substrate affinity. At the microbial scale, short-term warming can increase enzymatic catalytic power via accelerated synthesis and microbial turnover, but shifts in microbial community composition and growth efficiency may mediate the effect of warming in the long term.3. Although increasing enzyme activities may accelerate labile carbon decomposition over months to years, our literature review highlights that this initial stage can be followed by the following phases: (a) a reduction in soil carbon loss, due to changing carbon use efficiency among communities or substrate depletion, which together can decrease microbial biomass and enzyme activity and (b) an acceleration of soil carbon loss, due to shifts in microbial community structure and greater allocation to oxidative enzymes for recalcitrant carbon degradation.Studies that bridge scales in time and space are required to assess whether there | 1379Functional Ecology FANIN et Al.

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While rodents frequently host ectoparasites that can vector zoonotic diseases, often little is known about their ectoparasite communities, even in places where hosts frequently interact with humans. Yosemite National Park is an area of high human-wildlife interaction and high potential zoonotic disease transfer. Nonetheless, relatively few studies have surveyed the flea communities on mammalian hosts in this area, and even fewer have characterized the environmental and host factors that predict infestation. We focused on two species, the alpine chipmunk ( Tamias alpinus ) and the lodgepole chipmunk ( T. speciosus ), which inhabit Yosemite and surrounding areas and can host fleas that vector plague. Because these hosts are exhibiting differential responses to environmental change, it is valuable to establish baselines for their flea communities before further changes occur. We surveyed fleas on these chipmunk hosts during three years (2013–2015), including in the year of a plague epizootic (2015), and documented significant inter-host differences in flea communities and changes across years. Flea abundance was associated with host traits including sex and fecal glucocorticoid metabolite levels. The average number of fleas per individual and the proportion of individuals carrying fleas increased across years for T. speciosus but not for T. alpinus . To better understand these patterns, we constructed models to identify environmental predictors of flea abundance for the two most common flea species, Ceratophyllus ciliatus mononis and Eumolpianus eumolpi . Results showed host-dependent differences in environmental predictors of flea abundance for E. eumolpi and C. ciliatus mononis , with notable ties to ambient temperature variation and elevation. These results provide insight into factors affecting flea abundance on two chipmunk species, which may be linked to changing climate and possible future plague epizootics.