Nitrogen (N) additions often decrease soil respiration and increase soil organic carbon (C) stock. However, it is unclear how microbial substrates may shift with N additions and increasing temperature. Leveraging 12 years of N fertilization experiments and the associated shift in the dominant vegetation from C4to C3, we explored the δ13C‐CO2and temperature sensitivities of respired CO2and extracellular enzyme activities in control and fertilized soils. N additions increased cellulose‐decaying extracellular enzyme activity while respiration remained similar between the control and fertilized soils. Temperature sensitivity of cellulose‐decaying extracellular enzyme activity decreased with the N additions. The δ13C‐CO2data reveal that, as temperature increased, microbes in fertilized soils changed their dominant substrate from bulk soil organic C to plant litterfall. Our results suggest that long‐term N fertilization imposed C limitation on microbes, leading to enhanced microbial efforts to acquire C. This study highlights how long‐term N additions can promote the relative preservation of organic C in mineral soil while litterfall, the precursor to mineral‐associated C, is increasingly decayed as temperatures increase.
Warming‐induced changes in precipitation regimes, coupled with anthropogenically enhanced nitrogen (N) deposition, are likely to increase the prevalence, duration, and magnitude of soil respiration pulses following wetting via interactions among temperature and carbon (C) and N availability. Quantifying the importance of these interactive controls on soil respiration is a key challenge as pulses can be large terrestrial sources of atmospheric carbon dioxide (CO2) over comparatively short timescales. Using an automated sensor system, we measured soil CO2flux dynamics in the Colorado Desert—a system characterized by pronounced transitions from dry‐to‐wet soil conditions—through a multi‐year series of experimental wetting campaigns. Experimental manipulations included combinations of C and N additions across a range of ambient temperatures and across five sites varying in atmospheric N deposition. We found soil CO2pulses following wetting were highly predictable from peak instantaneous CO2flux measurements. CO2pulses consistently increased with temperature, and temperature at time of wetting positively correlated to CO2pulse magnitude. Experimentally adding N along the N deposition gradient generated contrasting pulse responses: adding N increased CO2pulses in low N deposition sites, whereas adding N decreased CO2pulses in high N deposition sites. At a low N deposition site, simultaneous additions of C and N during wetting led to the highest observed soil CO2fluxes reported globally at 299.5 μmol CO2 m−2 s−1. Our results suggest that soils have the capacity to emit high amounts of CO2within small timeframes following infrequent wetting, and pulse sizes reflect a non‐linear combination of soil resource and temperature interactions. Importantly, the largest soil CO2emissions occurred when multiple resources were amended simultaneously in historically resource‐limited desert soils, pointing to regions experiencing simultaneous effects of desertification and urbanization as key locations in future global C balance.
more » « less- PAR ID:
- 10410769
- Publisher / Repository:
- Wiley-Blackwell
- Date Published:
- Journal Name:
- Global Change Biology
- Volume:
- 29
- Issue:
- 11
- ISSN:
- 1354-1013
- Page Range / eLocation ID:
- p. 3205-3220
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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