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Hb2015 holmes-mineralization
- 1. The seasonal pattern of N mineralization in the Bartlett Experimental Forest Caitlin Holmes MELNHE Shoestring Arizona State University
- 2. Outline Soil N mineralization research Known effects of nutrient additions Nutrient manipulations results My research Objective Methods Expected Results
- 3. Background • N mineralization: amount of organic N that is transformed to plant usable NH4 and NO3 In the past, N mineralization has been tested at each site during the summer field season 21 days after nutrient manipulations.
- 4. Known Effects of Added Nutrients • Net N mineralization: – Increased in N plots – Had no effect in P plots – Decreased in N+P plots in mineral soil only
- 5. 0 1 2 3 4 5 6 7 Con N NP P NetNmineralization (mg/gsoil/21d) Mineral ab a b c Courtesy of Melany Fisk 0 50 100 150 200 250 300 350 Con N NP P NetNmineralization (mg/gsoil/21d) Oe a a ab b 0 10 20 30 40 50 60 70 80 90 Con N NP P NetNmineralization (mg/gsoil/21d) Oa a ab ab b Melany’s 2014 net N mineralization results
- 6. But what about before nutrient manipulations?
- 7. Seasonality of N mineralization • Seasonal pattern of N mineralization (Ross et al., 2004) • N mineralization in response to nutrients (Fisk and Fahey, 2001)
- 8. Is there a seasonal response of N mineralization to added N and P?
- 9. • Test N mineralization throughout the growing season to determine if there is a seasonal pattern • Observe whether responses to N and P are the same throughout the growing season Objective
- 10. Methods • Collect samples from old stands: C7, C8, C9 – Control, N, P, and N+P plots • Composite Oe, Oa, and mineral soil horizons from each plot • Test N mineralization: – Before fertilization – Twice after fertilization • Incubations and extractions with KCl Oe Oa Mineral
- 11. Expected Results • N mineralization will respond to N and P additions in the same way throughout the growing season • N mineralization will respond seasonally to treatments
- 12. Acknowledgements Thank you to Melany Fisk and Shinjini Goswami for their ongoing assistance with my project. An additional thanks to the Shoestring crew for their help in the field!
- 13. References • Fisk, M.C., and T.J. Fahey. 2001. Microbial biomass and nitrogen cycling response to fertilization and litter removal in young northern hardwood forests. Biogeochemistry 53: 201-223. • Ross, D.S., G.B. Lawrence, G. Fredriksen. 2004. Mineralization and nitrification patterns at eight northest USA forested research sites. Forest Ecology and Management 188: 317-335.
Editor's Notes
- First I’ll be introducing some of Melany Fisk’s data on soil N mineralization and then I’ll delve further into my research.
- Melany Fisk previously investigated the microbial response to added nutrients. She analyzed the impacts that nutrient manipulations had on the soil net N mineralization. In the past, impacts of nutrient manipulations have only been assessed during the middle of the field season after nutrient manipulations have been performed.
- Melany found that net N mineralization increased in N plots and decreased in N+P plots in mineral soil only.
- You can see here that there was a substantial decrease in the net N mineralization in the N+P treatment plot in mineral soil, but that N increased in all horizons.
- Studies have shown that there is a seasonal pattern to N mineralization, where N min was found to be highest in the middle of the growing season (July). Alternatively, Fisk and Fahey found higher N min earlier in the growing season, and a lower fraction of gross N min that as immobilized, which is concsistent with higher N availability.
- What we don’t know is whether or not there is a seasonal response of N mineralization to added N and P.
- I will test N mineralization over the growing season to trace the seasonal patterns of variation. In addition, I will examine whether the previously observed treatment effects extend over time.
- Old stands because synchronicity of N cycle more established
- It’s possible that there will be a seasonal response in N mineralization when N and P are added. This would mean that the responses to treatments are consistent with past data. The addition of nutrients will disrupt normal synchronicity of N cycle, but will ultimately have the same effect throughout the growing season. Offsets N cycle, don’t apply by mid June, already in full swing, initial swing, occelating curves Offset synchronicity