This document summarizes a study examining how soil respiration and litterfall in northern hardwood forests are controlled by nutrient availability. The study measured soil CO2 fluxes and collected fine litterfall from treatment plots with different nitrogen and phosphorus additions across 13 forest stands from 2008-2019. Preliminary results found that nitrogen addition lowered soil respiration in nitrogen-poor sites from 2011-2013. While apparent trends were observed, the authors note that statistical analysis is still needed and fertilization effects on litterfall may be more complicated. Next steps include further statistical analysis and exploring why nutrient additions did not significantly impact soil respiration rates.

1. Litterfall and soil respiration
fluxes in the MELNHE study
Thomas Mann, Ruth Yanai, Tim Fahey, Melany Fisk

2. N
P
P
P
N
Allocation of resources

3. N
N
N
P
P
P
N
P
N
P
N
P N
P
N
P
N
P N
Allocation of resources

4. How are soil respiration and litterfall
controlled by nutrient availability?

5. Hypotheses
● N addition will lower soil
respiration
● N and P addition will increase
litterfall mass

6. Methods
Soil respiration (2008-2019)
● Soil CO2 fluxes are measured at 5-7
locations within each treatment plot
across all 13 stands
Litterfall mass (2008-2019)
● Fine litter (excluding twigs) is
collected from 5 litter baskets
placed in each treatment plot of
every stand

7. Results
Pre-treatment
○ Soil respiration was lowest in N-
rich sites
Image source: Bae et al., 2015

8. Results
Pre-treatment
○ Soil respiration was lowest in N-
rich sites
Image source: Kang et al., 2016
2011-2013
○ N addition lowered soil
respiration in N-poor sites

9. Adj R2: 0.5822

10. Adj R2: 0.6074

12. Adj R2: 0.2631

13. Adj R2: 0.2359

14. Conclusions
● Apparent trends
○ Soil respiration may not have responded to nutrient additions
○ Fertilization effects on litterfall may be complicated!
● Next steps
○ Statistical analysis
○ Explore explanations for lack of treatment effect on soil respiration
■ Consider N mineralization and pretreatment fertility
■ Uncertainty analysis

15. Questions, comments,
or suggestions are welcome!
Please feel free to email me at thmann@esf.edu.
Many thanks to the dozens of folks who have been involved in the collection,
processing, and analysis of this data over the history of the MELNHE project! The
MELNHE Project is funded by USDA NIFA (2019-67019-29464) and NSF (DEB-
1637685) . For more information, please visit www.esf.edu/melnhe