TY - JOUR
T1 - The soil priming effect
T2 - Consistent across ecosystems, elusive mechanisms
AU - Liu, Xiao Jun Allen
AU - Finley, Brianna K.
AU - Mau, Rebecca L.
AU - Schwartz, Egbert
AU - Dijkstra, Paul
AU - Bowker, Matthew A.
AU - Hungate, Bruce A.
N1 - Funding Information:
We thank Jingran Sun, Zacchaeus Compson, and Jeff Propster for collecting soil and gas samples, Jamie Brown and Melanie Caron for soil and microbial C and N analyses, and Derek Sonderegger for help with statistical analyses and interpretation. This work was supported in part by the National Science Foundation, Division of Environmental Biology (grant number: DEB-1241094 ).
Publisher Copyright:
© 2019 Elsevier Ltd
PY - 2020/1
Y1 - 2020/1
N2 - Organic matter input to soils can accelerate the decomposition of native soil carbon (C), a process called the priming effect. Priming is ubiquitous and exhibits some consistent patterns, but a general explanation remains elusive, in part because of variation in the response across different ecosystems, and because of a diversity of proposed mechanisms, including microbial activation, stoichiometry, and community shifts. Here, we conducted five-week incubations of four soils (grassland, piñon-juniper, ponderosa pine, mixed conifer), varying the amount of substrate added (as 13C-glucose, either 350 or 1000 μg C g−1 week−1) and either with no added nitrogen (N), or with sufficient N (as NH4NO3) to bring the C-to-N ratio of the added substrate to 10. Using four different ecosystems enabled testing the generality of mechanisms underlying the priming effect. The responses of priming to the amount and C-to-N ratio of the added substrate were consistent across ecosystems: priming increased with the rate of substrate addition and declined when the C-to-N ratio of the substrate was reduced. However, structural equation models failed to confirm intermediate responses postulated to mediate the priming effect, including responses postulated to be mediated by stoichiometry and microbial activation. Specifically, priming was not clearly associated with changes in microbial biomass or turnover, nor with extracellular enzyme activities or the microbial C-to-N ratio. The strongest explanatory pathways in the structural equation models were the substrate, soil, and C-to-N ratio treatments themselves, with no intermediates, suggesting that either these measurements lacked sufficient sensitivity to reveal causal relationships, or the actual drivers for priming were not included in the ancillary measurements. While we observed consistent changes in priming caused by the amount and C-to-N ratio of the added substrate across a wide array of soils, our findings did not clearly conform to common models offered for the priming effect. Because priming is a residual flux involving diverse substrates of varying chemical composition, a simple and generalizable explanation of the phenomenon may be elusive.
AB - Organic matter input to soils can accelerate the decomposition of native soil carbon (C), a process called the priming effect. Priming is ubiquitous and exhibits some consistent patterns, but a general explanation remains elusive, in part because of variation in the response across different ecosystems, and because of a diversity of proposed mechanisms, including microbial activation, stoichiometry, and community shifts. Here, we conducted five-week incubations of four soils (grassland, piñon-juniper, ponderosa pine, mixed conifer), varying the amount of substrate added (as 13C-glucose, either 350 or 1000 μg C g−1 week−1) and either with no added nitrogen (N), or with sufficient N (as NH4NO3) to bring the C-to-N ratio of the added substrate to 10. Using four different ecosystems enabled testing the generality of mechanisms underlying the priming effect. The responses of priming to the amount and C-to-N ratio of the added substrate were consistent across ecosystems: priming increased with the rate of substrate addition and declined when the C-to-N ratio of the substrate was reduced. However, structural equation models failed to confirm intermediate responses postulated to mediate the priming effect, including responses postulated to be mediated by stoichiometry and microbial activation. Specifically, priming was not clearly associated with changes in microbial biomass or turnover, nor with extracellular enzyme activities or the microbial C-to-N ratio. The strongest explanatory pathways in the structural equation models were the substrate, soil, and C-to-N ratio treatments themselves, with no intermediates, suggesting that either these measurements lacked sufficient sensitivity to reveal causal relationships, or the actual drivers for priming were not included in the ancillary measurements. While we observed consistent changes in priming caused by the amount and C-to-N ratio of the added substrate across a wide array of soils, our findings did not clearly conform to common models offered for the priming effect. Because priming is a residual flux involving diverse substrates of varying chemical composition, a simple and generalizable explanation of the phenomenon may be elusive.
KW - Carbon use efficiency
KW - Microbial growth and respiration
KW - Nutrient limitation
KW - Soil carbon sequestration
KW - Soil organic matter decomposition
KW - Stable isotope tracer
UR - http://www.scopus.com/inward/record.url?scp=85074226958&partnerID=8YFLogxK
UR - http://www.scopus.com/inward/citedby.url?scp=85074226958&partnerID=8YFLogxK
U2 - 10.1016/j.soilbio.2019.107617
DO - 10.1016/j.soilbio.2019.107617
M3 - Article
AN - SCOPUS:85074226958
SN - 0038-0717
VL - 140
JO - Soil Biology and Biochemistry
JF - Soil Biology and Biochemistry
M1 - 107617
ER -