Enhanced Plant P and Unchanged Soil P Stocks After a Quarter-Century of Experimental Warming in Arctic Tundra

Phosphorus (P) availability may limit or co-limit plant and microbial life in multiple ecosystems, including Arctic tundra. Although current global carbon (C) models focus on the coupling between soil nitrogen (N) and C, ecosystem P response to climate warming may also influence the global C cycle. We propose multiple mechanisms through which permafrost soils in the Arctic may see either enhanced or reduced P availability under climate warming including changing litter inputs through plant community change, changing plant-microbial dynamics, altered rates of mineralization of soil organic P through increased microbial activity, and newly exposed mineral-bound P via deeper thaw. We investigated the effect of long-term experimental warming on plant, multiple soil and microbial C, N, and P pools, and microbial extracellular enzyme activities, in Alaskan tundra plots underlain by permafrost. We show that 25 years of experimental summer warming increases community-level plant P through changing community composition to favour relatively P-rich plant species. However, despite associated increases in P-rich litter inputs, we found only a few responses in the belowground pools of P available for plant and microbial uptake, including a weak positive response for citric acid-extractable PO4 in the surface soil and a decrease in microbial biomass P. Further, we found no change in soil P stocks, paralleling a lack of change in soil C and N stocks. Thus we found weak, neutral or negative belowground P responses to warming despite enhanced litter P inputs which is consistent with a growing number of studies in arctic tundra that find no long-term response of soil C and N stocks to warming.