TY - JOUR
T1 - Decoupled stoichiometric, isotopic, and fungal responses of an ectomycorrhizal black spruce forest to nitrogen and phosphorus additions
AU - Mayor, Jordan R.
AU - Mack, Michelle C.
AU - Schuur, Edward A.G.
N1 - Funding Information:
This study was supported by an NSF Doctoral Dissertation award ( DGE-0221599 ), a Forest Fungal Ecology Research Award from the Mycological Society of America , and an International Association of GeoChemistry Student Research Grant to JRM; DOE and NSF grant funding to EAGS and MCM; and the logistical support of the Bonanza Creek LTER and Chapin laboratory at University of Alaska, Fairbanks. Dominique Ardura, Jason Curtis, Cathy Curtis, Rady Ho, Martin Lavoie, Dat Nyguen, Rachel Rubin, Emily Tissier provided invaluable field or laboratory assistance. Kathleen Treseder and Steve Allison kindly provided sporocarp δ 15 N values for years 3 and 4 of the experiment. Erland Bååth facilitated soil PLFA analyses. Jack Putz, Matt Cohen, and two anonymous reviewers provided invaluable comments that greatly improved the manuscript.
Publisher Copyright:
© 2015 Elsevier Ltd.
PY - 2015/9/1
Y1 - 2015/9/1
N2 - Many northern forests are limited by nitrogen (N) availability, slight changes in which can have profound effects on ecosystem function and the activity of ectomycorrhizal (EcM) fungi. Increasing N and phosphorus (P) availability, an analog to accelerated soil organic matter decomposition in a warming climate, could decrease plant dependency on EcM fungi and increase plant productivity as a result of greater carbon use efficiency. However, the impact of altered N and P availability on the growth and activity of EcM fungi in boreal forests remains poorly understood despite recognition of their importance to host plant nutrition and soil carbon sequestration. To address such uncertainty we examined above and belowground ecosystem properties in a boreal black spruce forest following five years of factorial N and P additions. By combining detailed soil, fungal, and plant δ15N measurements with in situ metrics of fungal biomass, growth, and activity, we found both expected and unexpected patterns. Soil nitrate isotope values became 15N enriched in response to both N and P additions; fungal biomass was repressed by N yet both biomass and growth were stimulated by P; and, black spruce dependency on EcM derived N increased slightly when N and P were added alone yet significantly declined when added in combination. These findings contradict predictions that N fertilization would increase plant P demands and P fertilization would further exacerbate plant N demands. As a result, the prediction that EcM fungi predictably respond to plant N limitation was not supported. These findings highlight P as an under appreciated mediator of the activity of denitrifying bacteria, EcM fungi, and the dynamics of N cycles in boreal forests. Further, use of δ15N values from bulk soils, plants, and fungi to understand how EcM systems respond to changing nutrient availabilities will often require additional ecological information.
AB - Many northern forests are limited by nitrogen (N) availability, slight changes in which can have profound effects on ecosystem function and the activity of ectomycorrhizal (EcM) fungi. Increasing N and phosphorus (P) availability, an analog to accelerated soil organic matter decomposition in a warming climate, could decrease plant dependency on EcM fungi and increase plant productivity as a result of greater carbon use efficiency. However, the impact of altered N and P availability on the growth and activity of EcM fungi in boreal forests remains poorly understood despite recognition of their importance to host plant nutrition and soil carbon sequestration. To address such uncertainty we examined above and belowground ecosystem properties in a boreal black spruce forest following five years of factorial N and P additions. By combining detailed soil, fungal, and plant δ15N measurements with in situ metrics of fungal biomass, growth, and activity, we found both expected and unexpected patterns. Soil nitrate isotope values became 15N enriched in response to both N and P additions; fungal biomass was repressed by N yet both biomass and growth were stimulated by P; and, black spruce dependency on EcM derived N increased slightly when N and P were added alone yet significantly declined when added in combination. These findings contradict predictions that N fertilization would increase plant P demands and P fertilization would further exacerbate plant N demands. As a result, the prediction that EcM fungi predictably respond to plant N limitation was not supported. These findings highlight P as an under appreciated mediator of the activity of denitrifying bacteria, EcM fungi, and the dynamics of N cycles in boreal forests. Further, use of δ15N values from bulk soils, plants, and fungi to understand how EcM systems respond to changing nutrient availabilities will often require additional ecological information.
KW - <sup>15</sup>N
KW - Boreal forest
KW - Denitrification
KW - Ectomycorrhizae
KW - Picea mariana
KW - Stoichiometry
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U2 - 10.1016/j.soilbio.2015.05.028
DO - 10.1016/j.soilbio.2015.05.028
M3 - Article
AN - SCOPUS:84934974654
SN - 0038-0717
VL - 88
SP - 247
EP - 256
JO - Soil Biology and Biochemistry
JF - Soil Biology and Biochemistry
ER -