Soil respiration in northern forests exposed to elevated atmospheric carbon dioxide and ozone

The aspen free-air CO 2 and O 3 enrichment (FACTS II–FACE) study in Rhinelander, Wisconsin, USA, is designed to understand the mechanisms by which young northern deciduous forest ecosystems respond to elevated atmospheric carbon dioxide (CO 2 ) and elevated tropospheric ozone (O 3 ) in a replicated, factorial, field experiment. Soil respiration is the second largest flux of carbon (C) in these ecosystems, and the objective of this study was to understand how soil respiration responded to the experimental treatments as these fast-growing stands of pure aspen and birch + aspen approached maximum leaf area. Rates of soil respiration were typically lowest in the elevated O 3 treatment. Elevated CO 2 significantly stimulated soil respiration (8–26%) compared to the control treatment in both community types over all three growing seasons. In years 6–7 of the experiment, the greatest rates of soil respiration occurred in the interaction treatment (CO 2  + O 3 ), and rates of soil respiration were 15–25% greater in this treatment than in the elevated CO 2 treatment, depending on year and community type. Two of the treatments, elevated CO 2 and elevated CO 2  + O 3 , were fumigated with 13 C-depleted CO 2 , and in these two treatments we used standard isotope mixing models to understand the proportions of new and old C in soil respiration. During the peak of the growing season, C fixed since the initiation of the experiment in 1998 (new C) accounted for 60–80% of total soil respiration. The isotope measurements independently confirmed that more new C was respired from the interaction treatment compared to the elevated CO 2 treatment. A period of low soil moisture late in the 2003 growing season resulted in soil respiration with an isotopic signature 4–6‰ enriched in 13 C compared to sample dates when the percentage soil moisture was higher. In 2004, an extended period of low soil moisture during August and early September, punctuated by a significant rainfall event, resulted in soil respiration that was temporarily 4–6‰ more depleted in 13 C. Up to 50% of the Earth’s forests will see elevated concentrations of both CO 2 and O 3 in the coming decades and these interacting atmospheric trace gases stimulated soil respiration in this study.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/45867/1/442_2006_Article_381.pd

Structure of the Kerguelen Plateau province from Seasat altimetry and seismic reflection data

The Kerguelen Plateau in the southern Indian Ocean stands 2−4 km above the adjacent sea floor and is 2,500 km long (Fig. 1)1,2. Seasat provided a unique data set for deriving the free-air gravity field of the region (Fig. 2)3−5. Here we report the results of a new analysis of the plateau province's structure employing both Seasat and newly-acquired multichannel seismic (MCS) data6,7 for ground truth. The northern sector is characterized by volcanism and a sedimentary basin; the southern sector by a broad anticlinal arch, major faulting, and a sedimentary basin; and the eastern sector by an abyssal basin (Labuan) and bounding ridge (William's). The three sectors argue for a more complex tectonic evolution of the feature than has been previously proposed

Can CO2 enrichment modify the effect of water and high light stress on biomass allocation and relative growth rate of cork oak seedlings?

To test whether the impact of an enriched-CO2 environment on the growth and biomass allocation of first-season Quercus suber L. seedlings can modify the drought response under shade or sun conditions, seedlings were grown in pots at two CO2 concentrations x two watering regimes x two irradiances. Compared to CO2, light and water treatment had greater effects on all morphological traits measured (height, stem diameter, number of leaves, leaf area, biomass fractions). Cork oak showed particularly large increases in biomass in response to elevated CO2 under low-watered (W-) and high-illuminated conditions (L+). Allocation shifted from shoot to root under increasing irradiance (L+), but was not affected by CO2. Changes in allocation related to water limitation were only modest, and changed over time. Relative growth rate (RGR) and net assimilation rate (NAR) were significantly greatest in the L+/W+ treatment for both CO2 concentrations. Changes in RGR were mainly due to NAR. Growth responses to increased light, water or CO2 were strongest with light, medium with water availability and smallest for CO2, in terms of RGR. The rise in NAR for light and water treatments was counterbalanced by a decrease in SLA (specific leaf area) and LMF (leaf mass fraction). Results suggest that elevated CO2 caused cork oak seedlings to improve their performance in dry and high light environments to a greater extent than in well-irrigated and low light ones, thus ameliorating the effects of soil water stress and high light loads on growth