Effects of elevated concentrations of atmospheric CO2 and tropospheric O3 on leaf litter production and chemistry in trembling aspen and paper birch communities

Abstract

Human activities are increasing the concentrations of atmospheric carbon dioxide ([CO2]) and tropospheric ozone ([O3]), potentially leading to changes in the quantity and chemical quality of leaf litter inputs to forest soils. Because the quality and quantity of labile and recalcitrant carbon (C) compounds influence forest productivity through changes in soil organic matter content, characterizing changes in leaf litter in response to environmental change is critical to understanding the effects of global change on forests. We assessed the independent and combined effects of elevated [CO2] and elevated [O3] on foliar litter production and chemistry in aspen (Populus tremuloides Michx.) and birch-(Betula papyrifera Marsh.) aspen communities at the Aspen free-air CO2 enrichment (FACE) experiment in Rhinelander, WI. Litter was analyzed for concentrations of C, nitrogen (N), soluble sugars, lipids, lignin, cellulose, hemicellulose and C-based defensive compounds (soluble phenolics and condensed tannins). Concentrations of these chemical compounds in naturally senesced litter were similar in aspen and birch-aspen communities among treatments, except for N, the C:N ratio and lipids. Elevated [CO2] significantly increased C:N (+8.7%), lowered mean litter N concentration (-10.7%) but had no effect on the concentrations of soluble sugars, soluble phenolics and condensed tannins. Elevated [CO2] significantly increased litter biomass production (+33.3%), resulting in significant increases in fluxes of N, soluble sugars, soluble phenolics and condensed tannins to the soil. Elevated [O3] significantly increased litter concentrations of soluble sugars (+78.1%), soluble phenolics (+53.1%) and condensed tannins (+77.2%). There were no significant effects of elevated [CO2] or elevated [O3] on the concentrations of individual C structural carbohydrates (cellulose, hemicellulose and lignin). Elevated [CO2] significantly increased cellulose (+37.4%) input to soil, whereas elevated [O3] significantly reduced hemicellulose and lignin inputs to soil (-22.3 and -31.5%, respectively). The small changes in litter chemistry in response to elevated [CO2] and tropospheric [O3] that we observed, combined with changes in litter biomass production, could significantly alter the inputs of N, soluble sugars, condensed tannins, soluble phenolics, cellulose and lignin to forest soils in the future.

Litter fall production and decomposition in a fragment of secondary Atlantic Forest of São Paulo, sp, southeastern Brazil

“…This phytotoxic pollutant may cause oxidative stress in the plants (FERREIRA;DOMINGOS, 2012;APRO et al, 2012) and changes in the mineral elements flux (MAYER, 1983), which can be responsible for the foliage fall. Liu et al (2005), in a FACE study, found higher litter production in an elevated [CO 2 ] + elevated [O 3 ] treatments, showing that the negative effect of ozone was offset by the positive effect of CO 2 . The authors also found small changes in litter chemistry caused by elevated O 3 combined with carbon dioxide, which influenced litter production rates and had potential to significantly alter stand-level chemical inputs to soil.…”

Carbon-nitrogen feedbacks in the UVic ESCM

“…The reason for choosing this setup is to allow flexible root and leaf C/N ratios in order to avoid immediate N deficiency stress when enhancing C acquisition rates. It has been shown that root C/N ratios (Pendall et al, 2004;Gai-ping et al, 2006) as well as leaf C/N ratios (Liu et al, 2005) can increase in Free Air CO 2 Experiments experiments (FACE), though the interdependence between changes in root and leaf C/N ratios still needs investigation.…”

Variability of above-ground litter inputs alters soil physicochemical and biological processes: a meta-analysis of litterfall-manipulation experiments

“…Terrestrial ecosystems are undergoing simultaneous changes in climate and biogeochemical cycles, and those changes could affect plant net primary production (NPP) positively or negatively. Changes such as elevated CO 2 , nitrogen deposition (Xia and Wan, 2008) and temperature increases (Raich et al, 2006) were found to enhance plant productivity, whereas elevated O 3 (Liu et al, 2005), drought (Zhao and Running, 2010) and acid deposition (Irving and Miller, 1981) generally decreased productivity. These changes in primary production could alter both the quality and quantity of above-ground litter inputs to soil (Liu…”