• Mineralization N/P driven by the of the dissolved inorganic compounds N/P in the ocean (“Redfield paradigm”)7

• Redfield-type ratios have been explored for microbes, soil, leaves, and litter8-10

• C/nutrient analyses on land demonstrate plant-litter-soil-microbe interactions11

Redfield Ratios & Ecological Stoichiometry Meta-analytical methods

References: 1. IPCC, Climate Change 2007: The Physical Science Basis. Contribution of Working Group I to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change S. Solomon et al., Eds. (2007). 2. P. M. Vitousek et al., Ecol Appl 20, 5–15 (2010). 3. B. A. Hungate et al., Science 302, 1512–1513 (2003). 4. J. J. Elser et al., Ecology Letters 10, 1135–1142 (2007). 5. Swift et al., Decomposition in Terrestrial Ecosystems (1979). 6. W. McGill, C. Cole, Geoderma 26, 267–286 (1981). 7. A. C. Redfield, American Scientist 46 (1958). 8. C. C. Cleveland, D. Liptzin, Biogeochemistry 85, 235–252 (2007). 9. M. McGroddy et al., Ecology 85, 2390–2401 (2004). 10. W. A. Reiners, American Naturalist, 59–73 (1986). 11. S. Manzoni et al., Ecol Monogr 80, 89–106 (2010). 12. S. C. Reed et al., New Phytologist 196, 173–180 (2012). 13. L. Vergutz et al., Ecol Monogr 82, 205–220 (2012). 14. R. Aerts, Oikos 80, 603–606 (1997). 15. C. Deutsch, T. Weber, Annu. Rev. Marine. Sci. 4, 113–141 (2012). 16. N. Gruber, J. L. Sarmiento, Global Biogeochem. Cycles 11, 235–266 (1997). 17. F. M. Monteiro, M. J. Follows, Geophys. Res. Lett. 39 (2012), doi:10.1029/2012GL050897. 18. K. K. Treseder et al., Biogeochemistry 109, 7–18 (2011).

• Forests sequester atmospheric CO21

• Nitrogen and phosphorus limit this process2-4

• How does net mineralization of N and P vary?5,6

Fig. 1. Nutrient dynamics during decomposition

• Compiled data from 78 separate studies (Fig. 2), 372 litterbag series (170 tropical, 202 temperate) and 1308 total observations of N and P mineralization (691 tropical, 617 temperate)

• MAT range: -2.9-26.7ºC; MAP range: 173 – 5050 mm

Fig. 4. Locations of compiled leaf litter nutrient mineralization data

• Calculated mineralization in 2 ways to understand short and long-term controls on mineralization

1. Mineralization from initial = Xt-X0 (longer-term) 2. Incremental mineralization = Xt-Xt-1 (short-term)Xi is the mass of N or P in the litterbag at any time i in the series

Fig. 2a: Hypothesis 1: Litter substrate regulation of N/P resupply Corollary: Mean N/P of net mineralization matches that of initial substrate

Fig 2b: Hypothesis 2: Substrate non-dependence of N/P resupplyCorollary: Decoupling between net mineralization N/P and litter substrate

N/P min. Tropics > N/P microbes > N/P min. Temperate

• Litter collected from field site and placed in mesh bags• Litterbags installed in field and retrieved at set time points• Chemistry measured at multiple time points to determine effects

of time on decomposition and mineralization

Fig. 3. Typical in situ litterbag experiment (Jughandle State Park)

Photo Credit: Joy CookinghamPhoto Credit: Tiff van Huysen

Hypotheses

Summary

Motivation

Fig. 6. Frequency distribution of the anomaly from perfect substrate-dependence Conclusion: Decomposers can alter N/P during decomposition; deviations tend towards a lower N/P of mineralization vs. litter (~70% of data points)

Fig. 7. Relationship between N/P of mineralization and decomposers (tropical: R2=0.41; n=170; p<0.001; temperate: R2=0.41; n=202; p<0.001)Conclusion: Temperate N/P mineralization < decomposer N/P < tropical N/P mineralization

Fig. 5. Relationship between mineralization and litter N/P calculated from (a) initial (Slope = 1.2, R2=0.31, n=372) and (b) incremental litter (slope = 0.9, R2=0.45, n=270)Conclusion: Strong coherence in N/P stoichiometry of leaf litter and mineralization

• Potential head-to-head competition between plants and microbes (via resorption and immobilization)12-14

• Similarities between terrestrial and oceanic environments: in general, organism N/P matches resupply N/P15-17; deviations tend towards lower N/P mineralization than substrate

• Globally coherent patterns can be incorporated into ecosystem models to improve predictions of global change18

Litterbag Experiments

*armarklein@ucdavis.edu

Acknowledgements: Joy Cookingham, Sara Enders, David Gonzalez, Tiff van Huysen, Jorge Izquierdo, Derrick Light, Daniel Liptzin, Kimberley Miller, Scott Morford, and Robert Norton for help compiling data and discussions; and the Andrew W. Mellon Foundation (to B.Z.H) and the U.C. Davis Graduate Student Research Award in Engineering & Computer Science (to A.R.M.) for funding.

Results & Conclusions

Implications

Nitrogen/phosphorus mineralization ratios across forests worldwideAlison R. Marklein* and Benjamin Z. Houlton (B13B-0491)

Ecology Graduate Group at the University of California, Davis

Question: Do microbes alter the N/P of mineralization along the litter-decay continuum in forests?Methods: Meta-analysis of litterbag experiments across global forestsResults : Net mineralization N/P matches litter N/P; deviations tend to have lower N/P of mineralization than substrates. In the tropics, P is scarce relative to microbial decomposer stoichiometry; the converse is true in temperate forestsImplications: Potential head-to-head competition for nutrients between plants and microbes; consistencies between average terrestrial and oceanic environments; potential improvements for nutrient mineralization dynamics in ecosystem models