Exotic grass litter modulates seasonal pulse dynamics of CO 2 and N 2 O, but not NO, in Mediterranean-type coastal sage
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Exotic grass litter modulates seasonal pulse dynamics of CO2 and N2O, but not NO, in Mediterranean-type coastal sage scrub at the wildland-urban interface Holly M. Andrews
&
G. Darrel Jenerette
Received: 7 February 2020 / Accepted: 16 September 2020 / Published online: 22 September 2020 # Springer Nature Switzerland AG 2020
Abstract Aims Mediterranean shrublands adjacent to urbanization experience nitrogen deposition and exotic grass invasions which likely have downstream consequences for carbon and nitrogen emissions from soils. We tested a hypothesis that soil wetting produces trace gas pulses modified by seasonal wetting history, grass litter availability, and cover type in these systems. Methods Over two seasons, we conducted 48-h wetting experiments and measured CO2, N2O, and NO pulses at an invaded, polluted California shrubland following grass litter addition to sites dominated by either an invasive grass (Schismus barbatus) or a native shrub (Erioginum fasciculatum). Results CO2 and N2O pulses consistently appeared 15 min post-wetting and diminished within 12 h; NO peaked later and remained elevated at 24 h. All pulses were stronger in the dry season than wet season. Grass litter amendments increased CO2 and dry-season N2O pulses without significantly modifying NO pulses. Grass cover reduced CO2 pulses compared to shrub cover.
Responsible Editor: Elizabeth M Baggs. H. M. Andrews (*) Department of Evolution, Ecology, and Organismal Biology, University of California at Riverside, Riverside, CA 92521, USA e-mail: [email protected] G. D. Jenerette Department of Botany & Plant Sciences, University of California at Riverside, Riverside, CA 92521, USA
Conclusions Our results support the hypothesis that shrubland soils produce stronger pulses of CO2, N2O, and NO during the dry season when wetting is less frequent. We show that invasive grass litter can provide a labile C source that stimulates CO2 and N2O, but not NO, emissions from shrubland soils. Keywords Soil rewetting . Grass invasion . Coastal sage scrub . Trace gas pulse . Plant litter Abbreviations CSS Coastal sage scrub C Carbon N Nitrogen CO2 Carbon dioxide N2O Nitrous oxide NO Nitric oxide
Introduction Carbon (C) and nitrogen (N) cycling in dryland soils are often described using a pulse-reserve model, whereby most nutrient processes occur in discrete “pulses” catalyzed by the wetting of dry soils (Collins et al. 2008; Loik et al. 2004; Ogle and Reynolds 2004; Reynolds et al. 2004). Pulses – rapid increases and subsequent decreases of nutrient fluxes – occur following soil wetting, when microbial communities recover their metabolic activities within minutes (Austin et al. 2004). Carbon dioxide (CO2) is the main product of soil
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microbial respiration and is a prominent trace gas pulse emitted when dry soils are rewetted, frequently described as the “Birch effect” (Birch 1958; Jarvis et al. 2007). However, increasing evidence suggests soil wetting produces pulses of other trace gases with additional consequences for ecosystem fun
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