Effects of elevated pH and phosphorus fertilizer on soil C, N and P enzyme stoichiometry in an acidic mixed mesophytic deciduous forest

Long-term additions of lime and/or phosphate fertilizer caused an indirect and/or direct increase in the availability of P in mixed mesophytic deciduous forest soil on the unglaciated portion of the Allegheny Plateau, southeast Ohio, USA. As expected, the activities of extracellular phosphatases declined across all treatments (by 23-65%), in both organic and mineral soil horizons. In contrast, there were few effects of P availability on either C or N acquiring extracellular enzyme activities. However, enzyme vector analysis showed the relative activity of phosphatases decreased with respect to N-acquiring enzymes (vector angles fell 4-30%) and the relative activity of C acquisition increased (vector lengths rose 9-51%) relative to the activities of both N and P acquiring enzymes. Thus, the overall ecoenzymatic stoichiometry of extracellular enzymes was altered by P availability. Also, the relative contribution of phosphodiesterase declined relative to phosphomonoesterase by an average of 16 +/- 16% as overall phosphatase activity declined, suggesting a reduction in the relative contribution of the less efficient enzyme as P demand decreased. Finally, contrary to expectations, the relative contribution of leucine aminopeptidase to total N acquiring enzyme activity did not increase with pH, but showed a bimodal relationship to soil NH4+ concentration. In summary, phosphatase activity declined with increased P availability but with little response in C or N acquiring activity suggesting emerging co-limitations by C and/or N in this ecosystem.