TY - JOUR
T1 - Continental-scale patterns of extracellular enzyme activity in the subsoil
T2 - An overlooked reservoir of microbial activity
AU - Dove, Nicholas C.
AU - Arogyaswamy, Keshav
AU - Billings, Sharon A.
AU - Botthoff, Jon K.
AU - Carey, Chelsea J.
AU - Cisco, Caitlin
AU - Deforest, Jared L.
AU - Fairbanks, Dawson
AU - Fierer, Noah
AU - Gallery, Rachel E.
AU - Kaye, Jason P.
AU - Lohse, Kathleen A.
AU - Maltz, Mia R.
AU - Mayorga, Emilio
AU - Pett-Ridge, Jennifer
AU - Yang, Wendy H.
AU - Hart, Stephen C.
AU - Aronson, Emma L.
N1 - Publisher Copyright: © 2020 The Author(s). Published by IOP Publishing Ltd.
PY - 2020/10
Y1 - 2020/10
N2 - Chemical stabilization of microbial-derived products such as extracellular enzymes (EE) onto mineral surfaces has gained attention as a possibly important mechanism leading to the persistence of soil organic carbon (SOC). While the controls on EE activities and their stabilization in the surface soil are reasonably well-understood, how these activities change with soil depth and possibly diverge from those at the soil surface due to distinct physical, chemical, and biotic conditions remains unclear. We assessed EE activity to a depth of 1 m (10 cm increments) in 19 soil profiles across the Critical Zone Observatory Network, which represents a wide range of climates, soil orders, and vegetation types. For all EEs, activities per mass of soil correlated positively with microbial biomass (MB) and SOC, and all three of these variables decreased logarithmically with depth (p < 0.05). Across all sites, over half of the potential EE activities per mass soil consistently occurred below 20 cm for all measured EEs. Activities per unit MB or SOC were substantially higher at depth (soils below 20 cm accounted for 80% of whole-profile EE activity), suggesting an accumulation of stabilized (i.e. mineral sorbed) EEs in subsoil horizons. The pronounced enzyme stabilization in subsurface horizons was corroborated by mixed-effects models that showed a significant, positive relationship between clay concentration and MB-normalized EE activities in the subsoil. Furthermore, the negative relationships between soil C, N, and P and C-, N-, and P-acquiring EEs found in the surface soil decoupled below 20 cm, which could have also been caused by EE stabilization. This finding suggests that EEs may not reflect soil nutrient availabilities deeper in the soil profile. Taken together, our results suggest that deeper soil horizons hold a significant reservoir of EEs, and that the controls of subsoil EEs differ from their surface soil counterparts.
AB - Chemical stabilization of microbial-derived products such as extracellular enzymes (EE) onto mineral surfaces has gained attention as a possibly important mechanism leading to the persistence of soil organic carbon (SOC). While the controls on EE activities and their stabilization in the surface soil are reasonably well-understood, how these activities change with soil depth and possibly diverge from those at the soil surface due to distinct physical, chemical, and biotic conditions remains unclear. We assessed EE activity to a depth of 1 m (10 cm increments) in 19 soil profiles across the Critical Zone Observatory Network, which represents a wide range of climates, soil orders, and vegetation types. For all EEs, activities per mass of soil correlated positively with microbial biomass (MB) and SOC, and all three of these variables decreased logarithmically with depth (p < 0.05). Across all sites, over half of the potential EE activities per mass soil consistently occurred below 20 cm for all measured EEs. Activities per unit MB or SOC were substantially higher at depth (soils below 20 cm accounted for 80% of whole-profile EE activity), suggesting an accumulation of stabilized (i.e. mineral sorbed) EEs in subsoil horizons. The pronounced enzyme stabilization in subsurface horizons was corroborated by mixed-effects models that showed a significant, positive relationship between clay concentration and MB-normalized EE activities in the subsoil. Furthermore, the negative relationships between soil C, N, and P and C-, N-, and P-acquiring EEs found in the surface soil decoupled below 20 cm, which could have also been caused by EE stabilization. This finding suggests that EEs may not reflect soil nutrient availabilities deeper in the soil profile. Taken together, our results suggest that deeper soil horizons hold a significant reservoir of EEs, and that the controls of subsoil EEs differ from their surface soil counterparts.
KW - N-acetylglucosaminidase
KW - a-glucosidase
KW - acid phosphatase
KW - critical zone
KW - ecological stoichiometry
KW - extracellular enzymes
KW - microbial ecology
KW - phospholipid fatty acids
KW - subsoil
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U2 - 10.1088/1748-9326/abb0b3
DO - 10.1088/1748-9326/abb0b3
M3 - Article
SN - 1748-9318
VL - 15
JO - Environmental Research Letters
JF - Environmental Research Letters
IS - 10
M1 - 1040A1
ER -