Chronic phosphorus enrichment and elevated pH suppresses Quercus spp. leaf litter decomposition in a temperate forest

The potential of excessive nitrogen (N) suppressing litter decay in is widely recognized. The role of phosphorus (P) in plant litter decay is less understood and is generally assumed to have a weak influence in decomposition outside tropical or wetland ecosystems. Based on the "microbial mining" hypothesis that suggests the availability of limiting nutrients is the driving mechanism of decay, P could have a strong influence on carbon (C) cycling in low-P ecosystems. The objective of this study was to determine if increasing P availability will influence the decomposition of leaf litter in a low-P temperate forested ecosystem. If the availability of a limiting nutrient is a driving mechanism mediating decay, then increasing the availability of P in a low-P environment should inhibit decay. The experiment was held in a low-P mixed mesophytic forest in the unglaciated Alleghany Plateau (USA). Since 2009, P availability has been increased either directly by phosphate fertilizer and/or indirectly by raising soil pH. Starting in 2012 and for three consecutive years, Quercus spp. leaf litter bags were deployed and harvested at least every year for three years for temporal replication. After three years, elevating pH and/or P litter mass loss was similar to 52% and significantly (P < 0.001) lower than the control at 73% mass loss. The mean residence time (MRT; k yr(-1)) for the control was 2.1 years, but elevating P with pH increased MRT to 5.3 years. Results support the "microbial phosphorus mining" hypothesis that P has the potential to inhibit decay for Quercus spp. leaf litter in temperate forests and potentially increase soil C.