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The aim of this study was to examine the effects of elevated carbon dioxide [CO2] and ozone [O3] and their interaction on wood chemistry and anatomy of five clones of 3-year-old trembling aspen (Populus tremuloides Michx.). Wood chemistry was studied also on paper birch (Betula papyrifera Marsh.) and sugar maple (Acer saccharum Marsh.) seedling-origin saplings of the same age. Material for the study was collected from the Aspen Free-Air CO2 Enrichment (FACE) experiment in Rhinelander, WI, USA, where the saplings had been exposed to four treatments: control (C; ambient CO2, ambient O3), elevated CO2 (560ppm during daylight hours), elevated O3 (1.5 × ambient during daylight hours) and their combination (CO2 + O3) for three growing seasons (1998–2000). Wood chemistry responses to the elevated CO2 and O3 treatments differed between species. Aspen was most responsive, while maple was the least responsive of the three tree species. Aspen genotype affected the responses of wood chemistry and, to some extent, wood structure to the treatments. The lignin concentration increased under elevated O3 in four clones of aspen and in birch. However, elevated CO2 ameliorated the effect. In two aspen clones, nitrogen in wood samples decreased under combined exposure to CO2 and O2. Soluble sugar concentration in one aspen clone and starch concentration in two clones were increased by elevated CO2. In aspen wood, α-cellulose concentration changed under elevated CO2, decreasing under ambient 03 and slightly increasing under elevated O3. Hemicellulose concentration in birch was decreased by elevated CO2 and increased by elevated O3. In aspen, elevated O3 induced statistically significant reductions in distance from the pith to the bark and vessel lumen diameter, as well as increased wall thickness and wall percentage, and in one clone, decreased fibre lumen diameter. Our results show that juvenile wood properties of broadleaves, depending on species and genotype, were altered by atmospheric gas concentrations predicted for the year 2050 and that CO2 ameliorates some adverse effects of elevated O3 on wood chemistry. [ABSTRACT FROM AUTHOR]

Abstract Ecosystem fluxes of energy, water, and CO[sub 2] result in spatial and temporal variations in atmospheric properties. In principle, these variations can be used to quantify the fluxes through inverse modelling of atmospheric transport, and can improve the understanding of processes and falsifiability of models. We investigated the influence of ecosystem fluxes on atmospheric CO[sub 2] in the vicinity of the WLEF-TV tower in Wisconsin using an ecophysiological model (Simple Biosphere, SiB2) coupled to an atmospheric model (Regional Atmospheric Modelling System). Model parameters were specified from satellite imagery and soil texture data. In a companion paper, simulated fluxes in the immediate tower vicinity have been compared to eddy covariance fluxes measured at the tower, with meteorology specified from tower sensors. Results were encouraging with respect to the ability of the model to capture observed diurnal cycles of fluxes. Here, the effects of fluxes in the tower footprint were also investigated by coupling SiB2 to a high-resolution atmospheric simulation, so that the model physiology could affect the meteorological environment. These experiments were successful in reproducing observed fluxes and concentration gradients during the day and at night, but revealed problems during transitions at sunrise and sunset that appear to be related to the canopy radiation parameterization in SiB2. [ABSTRACT FROM AUTHOR]

Abstract We present the annual patterns of net ecosystem-atmosphere exchange (NEE) of CO[sub 2] and H2O observed from a 447 m tall tower sited within a mixed forest in northern Wisconsin, USA. The methodology for determining NEE from eddy-covariance flux measurements at 30, 122 and 396 m above the ground, and from CO[sub 2] mixing ratio measurements at 11, 30, 76, 122, 244 and 396 m is described. The annual cycle of CO[sub 2] mixing ratio in the atmospheric boundary layer (ABL) is also discussed, and the influences of local NEE and large-scale advection are estimated. During 1997 gross ecosystem productivity (947-18 g C m[sup -2] yr[sup -1] ), approximately balanced total ecosystem respiration (963±19 g C m[sup -2] yr[sup -1] ), and NEE of CO[sub 2] was close to zero (16±19 g C m[sup -2] yr[sup -1] emitted into the atmosphere). The error bars represent the standard error of the cumulative daily NEE values. Systematic errors are also assessed. The identified systematic uncertainties in NEE of CO[sub 2] are less than 60 g C m[sup -2] yr[sup -1] . The seasonal pattern of NEE of CO[sub 2] was highly correlated with leaf-out and leaf-fall, and soil thaw and freeze, and was similar to purely deciduous forest sites. The mean daily NEE of CO[sub 2] during the growing season (June through August) was -1.3 g C m[sup -2] day[sup -1] , smaller than has been reported for other deciduous forest sites. NEE of water vapor largely followed the seasonal pattern of NEE of CO[sub 2] , with a lag in the spring when water vapor fluxes increased before CO[sub 2] uptake. In general, the Bowen ratios were high during the dormant seasons and low during the growing season. Evapotranspiration normalized by potential evapotranspiration showed the opposite pattern. The seasonal course of the CO[sub 2] mixing ratio in the ABL at the tower led the seasonal pattern of NEE of CO[sub 2] in time: in spring, CO[sub 2] mixing ratios began to decrease prior to the onset of daily net uptake of CO[sub 2] by the forest, and in fall mixing ratios began to increase before the forest became a net source for CO[sub 2] to the atmosphere. Transport as well as local NEE of CO[sub 2] are shown to be important components of the ABL CO[sub 2] budget at all times of the year. [ABSTRACT FROM AUTHOR]