Phosphorus-nitrogen feedbacks maintain balanced availability in hardwood forest soils Tera Ratliff 11-July-2012

Time (millions of years)Total Soil Nutrients Walker and Syers, 1976 US Forest Service Identifying the processes underlying limitations to productivity help us understand forest ecosystem response to change

Resource Optimization High C:N:P High N:P P-limiting Investment in phosphatse N:P Low N:P N-limiting Investment in decomposition N:P Low C:N:P C-limiting Investment in C-mineralizing enzymes C:N:P

Resource optimization in response to N and P fertilization When N is high, organisms allocate to P Do N and P equilibrate over the long-term? Marklein and Houlton, 2011 Response Ratio = Mean outcome of treatment: mean outcome of control

Pretreatment (2008 to 2009) soil collection MELNHE plots Cores divided into Oe and Oa Resin strips buried in-situ (2010) C9 -1-A PO 4 -

N and P availability covary in forests of varying ages in the northern hardwoods N availability appears to promote P availability via phosphatase production.

Conclusions Tight coupling of N and P could contribute to colimitation at the ecosystem level Resource optimization could work to prevent P- limitation in the short-term by increasing investment when N is high Mechanisms of P redistribution from slowly available pools are of interest for understanding long-term effects of anthropogenic changes in N and P availability

Questions? Acknowledgments Many people have helped in carrying out this project, so many thanks to Kevan Minick, Mark Dempsey, Brittany Coyne, Stephanie Bailey, Carrie Rose Levine, members of the Fisk Lab, and collaborators at HBEF for assistance in the field and laboratory.