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Linking microbial activity and soil organic matter transformations in forest soils under elevated CO 2
Author(s) -
Billings S. A.,
Ziegler S. E.
Publication year - 2005
Publication title -
global change biology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 4.146
H-Index - 255
eISSN - 1365-2486
pISSN - 1354-1013
DOI - 10.1111/j.1365-2486.2005.00909.x
Subject(s) - soil water , mineralization (soil science) , environmental chemistry , incubation , organic matter , soil organic matter , microbial population biology , chemistry , soil respiration , isotopic signature , ecosystem , soil carbon , nutrient , dissolved organic carbon , agronomy , ecology , biology , stable isotope ratio , bacteria , biochemistry , genetics , physics , quantum mechanics
Soil organic matter (SOM) dynamics ultimately govern the ability of soil to provide long‐term C sequestration and the nutrients required for ecosystem productivity. Predicting belowground responses to elevated CO 2 requires an integrated understanding of SOM transformations and the microbial activity that governs them. It remains unclear how the microorganisms upon which these transformations depend will function in an elevated CO 2 world. This study examines SOM transformations and microbial metabolism in soils from the Duke Free Air Carbon Enrichment site in North Carolina, USA. We assessed microbial respiration and net nitrogen (N) mineralization in soils with and without elevated CO 2 exposure during a 100‐day incubation. We also traced the depleted C isotopic signature of the supplemental CO 2 into SOM and the soils' phospholipid fatty acids (PLFA), which serve as biomarkers for living cells. Cumulative net N mineralization in elevated CO 2 soils was 50% that in control soils after a 100‐day incubation. Respiration was not altered with elevated CO 2 . C : N ratios of bulk SOM did not change with elevated CO 2 , but incubation data suggest that the C : N ratios of mineralized organic matter increased with elevated CO 2 . Values of SOM δ 13 C were depleted with elevated CO 2 (−26.7±0.2 vs. −30.2±0.3‰), reflecting the depleted signature of the supplemental CO 2 . We compared δ 13 C of individual PLFA with the δ 13 C of SOM to discern incorporation of the depleted C isotopic signature into soil microbial groups in elevated CO 2 plots. PLFA i15:0, a15:0, and 10Met18:0 reflected significant incorporation of recently produced photosynthate, suggesting that the bacterial groups defined by these biomarkers are active metabolizers in elevated CO 2 soils. At least one of these groups (actinomycetes, 10Met18:0) specializes in metabolizing less labile substrates. Because control plots did not receive an equivalent 13 C tracer, we cannot determine from these data whether this group of organisms was stimulated by elevated CO 2 compared with these organisms in control soils. Stimulation of this group, if it occurred in the elevated CO 2 plot, would be consistent with a decline in the availability of mineralizable organic matter with elevated CO 2 , which incubation data suggest may be the case in these soils.