Plant species-specific litter decomposition rates are directly affected by tropospheric ozone. Analysis of trends and modelling

Litter decay is an important component of nutrient cycling processes in forest ecosystems, and its decomposition rates reflect functional adaptations among species. In this framework, tropospheric ozone (O3), which is recognised as a significant phytotoxic air pollutant, is one of the most important factors affecting forest health, and its effects on vegetation are species-specific. We used an O3-free air controlled exposure facility (O3-FACE) to quantify the effect of O3 fumigation (ambient air vs 1.4 × ambient air) on litter decay rates of leaves from three Quercus species: Q. ilex L., Q. pubescens Wild. and Q. robur L. Results demonstrate different trends over time and decomposition rates of residual dry mass, lignin, cellulose and acid-detergent fibre variables between control and treated litters. Analysis of decay rate k(t) trends showed species-specific differences, even within the same O3 treatment. Single exponential Olson’s model demonstrated to be useful to correctly predict mass loss over time M(t) in Q. ilex litter (M(t)modM(t)meas=0.967,R2=0.935) of independently collected data from a field study when a function k(t) over time (k(t)=1(a+b×tc)) was included. These results suggest that species-specific decomposability may be correlated with ecological growth strategy (deciduous vs evergreen) and structural characteristics of leaves. The species-specific effect of ozone on the decomposition rates could have remarkable effects on the carbon cycle within forest ecosystems.