The Forest-Atmosphere Carbon Transfer and Storage (FACTS-II) Project in northern Wisconsin is examining the interacting effects of elevated carbon dioxide (CO₂) and ozone (O₃) concentrations on the productivity, sustainability, and competitive interactions in a regenerating northern hardwood ecosystem. A key component of this project involves an examination of the micrometeorological feedback mechanisms that can alter atmospheric environments within and above vegetation layers exposed to elevated CO₂ and O₃ concentrations. This paper provides a brief summary of some of the observed forest micrometeorological responses to elevated CO₂ and O₃ concentrations at the FACTS-II study site over the 1999-2004 period.

We examined the photosynthetic and growth traits of two woody species (birch) that are dominant in northern Japan under elevated CO₂ concentration ([CO₂]), using a free air CO₂ enrichment (FACE) system. Our results suggest that it is necessary to consider not only leaf-level photosynthesis but also the entire plant physiology when using photosynthesis to evaluate the growth response of two birch saplings under elevated [CO₂].

The three cereal crops rice, maize and wheat cover over 75% of the total food production of Nepal. All the three crops rice, maize and wheat showed increased yield with doubling the CO₂ level but also followed a declined tendency at the elevated temperature. Among the three crops, maize was the most affected by the rise in temperature although increased CO₂ level could increase the crop yield. The Terai plains and the hills of Nepal were more affected. The mountains, on the other hand, showed a favorable tendency.

A highly controversial issue in global change research is the regulation of terrestrial carbon (C) sequestration by soil nitrogen (N) availability. The Third Assessment IPCC Report  predicts rising atmospheric CO₂ alone could stimulate terrestrial carbon (C) sequestration by 350 – 980 Pg (=10¹⁵ g) C in the 21^st Century. Sequestering 350 – 980 Gt C in terrestrial ecosystems requires 7.7 – 37.5 Pg (N) based on a stoichiochemical relationship that approximately 0.005 g N is required for 1 g C stored in long-lived plant biomass (i.e., wood) and 0.067 g N for 1 g C sequestered in soil organic matter (SOM).  Thus, to realistically predict future C sequestration in terrestrial ecosystems, we have to understand how closely C and N processes are coupled in response to rising C_a.­

The maximal specific growth rate of microorganisms from rhizospheres of Populus deltoides grown under normal CO₂ concentration in the atmosphere (400 ppm) was lower compared to the assessments made for plots under elevated CO₂ (800 and 1200 ppm). A similar conclusion was made for microbial communities from soil under winter wheat and sugar beets grown under 370 and 550 ppm CO₂ in the atmosphere. Three to four years fumigation of field plots with elevated CO₂ has been shown to result in the formation of rhizosphere microbial communities characterized by faster specific growth rates as compared to microbial community under control plants.

Extreme global model scenarios of complete preservation and degradation of biogenic particulate CaCO₃ (calcium carbonate) in open ocean waters which are supersaturated with respect to CaCO₃ were carried out. According to these experiments, the theoretical potential of upper ocean alkalinity controls for changing the atmospheric pCO₂ (CO₂ partial pressure) amounts to several hundred μatm on time scales of several 10⁴ years. Up to a timescale of 10³ years, however, the respective influence is minor as compared to an expected anthropogenic increase of the atmospheric pCO₂ in the order of 500-1000 μatm.

While rising atmospheric carbon dioxide (CO₂) is known to be an important contributor to radiative forcing of Earth’s climate, more direct effects of this gas on photosynthesis and plant water relations have been underway for more than a century, and likely have already contributed to important ecosystem changes. Experiments conducted in native and semi-natural grasslands in which ambient CO₂ concentrations have been artificially increased have shown that increasing CO₂ often increases photosynthesis, results in higher soil and plant water content, and can enhance plant water use efficiency, the ratio of plant biomass produced per unit water transpired back to the atmosphere. While these responses may appear beneficial, there are long-term responses of ecosystems to CO₂ such as alterations in the cycling and availability of critical plant nutrients like nitrogen (N) which are likely to change over time and may significantly alter CO₂-enhanced production and forage quality. Herein we discuss these phenomena and speculate on the implications and the importance for world grasslands.