Throughfall chemistry in a loblolly pine plantation under elevated atmospheric CO2 concentrations

Abstract

Accelerated tree growth under elevatedatmospheric CO2 concentrations may influencenutrient cycling in forests by (i) increasingthe total leaf area, (ii) increasing the supplyof soluble carbohydrate in leaf tissue, and (iii) increasing nutrient-use efficiency. Here wereport the results of intensive sampling andlaboratory analyses of NH 4 + , NO 3 − , PO 4 3− , H+, K+, Na+,Ca2+, Mg2+, Cl−, SO 4 2− , and dissolved organic carbon (DOC) in throughfallprecipitation during the first 2.5+ years of the DukeUniversity Free-Air CO2 Enrichment (FACE)experiment. After two growing seasons, a largeincrease (i.e., 48%) in throughfall deposition of DOCand significant trends in throughfall volume and inthe deposition of NH 4 + , NO 3 − , H+, and K+ can be attributed to the elevatedCO2 treatment. The substantial increase indeposition of DOC is most likely associated withincreased availability of soluble C in plant foliage,whereas accelerated canopy growth may account forsignificant trends toward decreasing throughfallvolume, decreasing deposition of NH 4 + ,NO 3 − , and H+, and increasing deposition of K+ under elevated CO2. Despiteconsiderable year-to-year variability, there wereseasonal trends in net deposition of NO 3 − ,H+, cations, and DOC associated with plant growthand leaf senescence. The altered chemical fluxes inthroughfall suggest that soil solution chemistry mayalso be substantially altered with continued increasesin atmospheric CO2 concentrations in the future.