Initial responses of phosphorus biogeochemistry to calcium addition in a northern hardwood forest ecosystem

We measured changes in P pools and cycling 1 year after a Ca fertilization treatment at the Hubbard Brook Experimental Forest in central New Hampshire. We hypothesized that by increasing soil pH and available Ca, the treatment would change the amount of readily available P in the forest floor and the biogeochemical cycling of P in the forest ecosystem. One year after the Ca addition, significant increases occurred in soil pH (one pH unit), resin-sorbed P (2- to over 10-fold), and the microbial respiratory quotient (27%) in the Oe horizon of the treated watershed compared with a reference watershed. Additionally, we observed significant increases in foliar P concentrations (20-133% across six species) and in P retranslocation in the treated watershed between pre- and post-Ca-addition years (p < 0.05). Foliar P was strongly correlated (r = 0.74) with resin-sorbed P. Microbial biomass P, microbial C to P ratios, and available organic and inorganic P fractions were lower in the Oe horizon of the treatment watershed than in the reference watershed, but no differences were observed in soil solution or fine root P concentration. Apparently, by changing soil pH, Ca addition increased rates of P cycling in forest floor horizons at Hubbard Brook Experimental Forest.