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A case study Does long-term forest N enrichment enhance microbial P limitation? a case study Farrah Fatemi, Ivan Fernandez, Kevin Simon, David Bryan Dail,

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Presentation on theme: "A case study Does long-term forest N enrichment enhance microbial P limitation? a case study Farrah Fatemi, Ivan Fernandez, Kevin Simon, David Bryan Dail,"— Presentation transcript:

1 a case study Does long-term forest N enrichment enhance microbial P limitation? a case study Farrah Fatemi, Ivan Fernandez, Kevin Simon, David Bryan Dail, Lindsey Rustad, Stephen Norton

2 Globally, N deposition is still a problem Galloway et al Biogeochem 70:

3 Forest N enrichment may enhance P limitation N enrichment Can we detect a shift towards enhanced microbial P limitation in N-enriched soils? Magnitude of nutrient demand relative to supply

4 An Ecological Observatory The Bear Brook Watershed in Maine (BBWM)

5 WEST BEAR (treated) EAST BEAR (reference) 36 kg -1 ha -1 yr -1 N as (NH 4 ) 2 SO 4 The BBWM: A long-term N-enrichment experiment 8 kg -1 ha -1 yr -1 N WBSW WB has been experimentally acidified with N and S since 1989 EB receives ambient deposition of N and S EBHW EBSW WBHW

6 Watershed scale studies Q1 -Are there signs of enhanced microbial P limitation due to the whole-watershed, long-term N enrichment and acidification? phosphatases Bioavailable P Phosphatase activity Microbial biomass Insoluble organic P

7 Q2- What is the microbial response to P additions? P addition experiments: field and lab incubations C Control (H 2 O)Phosphorus P N - enriched reference soil phosphatase activity N mineralization soil respiration

8 Watershed scale results: soil phosphatase activity p= 0.04 p= 0.08 HardwoodsSoftwoods

9 HardwoodsSoftwoods Watershed scale results: microbial biomass Watershed scale results: microbial biomass So, phosphatase activity per unit microbial biomass is the same in reference and N-enriched soils HardwoodsSoftwoods Microbial biomass is higher in the reference watershed p=0.13 p=0.08

10 Results from P additions: phosphatase response EBHWWBHWEBSWWBSW P addition in the field decreased phosphatase activity +P

11 Results from P additions: Laboratory incubation HardwoodsSoftwoods Soil respiration N mineralization HardwoodsSoftwoods

12 SUMMARY A1- No, phosphatase activity data show no significant differences in microbial P demand Q1- Are there signs of enhanced microbial P limitation due to long-term N enrichment? Q2- What is the microbial response to P additions? A2- * soil phosphatase activity decreases * N mineralization and soil respiration do not respond significantly

13 Conclusions Extent of mirobial P limitation is not greater in N- enriched soils Phosphatase results highlight importance of considering microbial biomass in interpreting enzyme activity as an indicator of P limitation

14 The University of Maine: - Department of Plant, Soil and Environmental Sciences - Graduate Program in Ecology and Environmental Sciences - Climate Change Institute The National Science Foundation Thanks to many who helped with research design, field research and laboratory efforts! Acknowledgements


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