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.

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.­

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.

Coral reefs are constructed of calcium carbonate (CaCO₃). Deposition of CaCO₃ (calcification) by corals and other reef organisms is controlled by the saturation state of CaCO₃ in seawater (Ω) and sea surface temperature (SST). Previous studies have neglected the effects of ocean warming in predicting future coral reef calcification rates.  In this study we take into account both these effects by combining empirical relationships between coral calcification rate and Ω and SST with output from a climate model to predict changes in coral reef calcification rates.  Our analysis suggests that annual average coral reef calcification rate will increase with future ocean warming and eventually exceed pre-industrial rates by about 35% by 2100. There is evidence however to suggest that different corals display different sensitivities to changes in Ω_arag and SST [Reynaud et al., 2003].  Considering that both these environmental parameters are likely to change considerably in the future, additional experiments on a variety of differing coral species will be crucial to obtain a better understanding of future coral reef stability.

The effect of three atmospheric CO₂ concentrations (ambient – 400 ppm, doubled – 800 ppm and tripled – 1200 ppm) has been studied (1) on the productivity of cottonwood tree (Populus deltoides Barr.), (2) on the activity of soil microbial biomass in rooting zone. It has been shown, that the total biomass of cottonwood trees increase under elevated CO₂ (2.61, 5.59 and 4 kg/tree for 400, 800 and 1200 ppm respectively). The highest production had the stem and coarse roots at 800 ppm (in 3 and 2 times higher as compared to ambient CO₂). Under 1200 ppm CO₂ we observed increased the roots biomass, but the biomass of leaves and branches was insignificant or didn’t changed at all. The shoot/root ratio changed as following: 400 ppm – 1.8, 800 ppm – 2.3, 1200 ppm – 1.4. The rate of С-СО₂ flux from soil samples being incubated for 70 days increased in the row 1200>800>400 ppm CO₂, the average values of CO₂ emission were 2.76, 2.33, 2.02 mg 100g^-1·day^-1, respectively. The largest amount of C microbial biomass (C_mb) was in the variant with triple CO₂ concentration (75.1 mg 100g^-1), and the lowest – under ambient concentration (53.7 mg 100g^-1).

The effect of CO₂ enrichment in raising the temperature was realized in the Open Top Chamber (OTC) experiment. The elevated CO₂ with this level of temperature raised grain yield and yield components of rice but varied greatly by year. The CO₂ enriched plot had lesser N, P, and K in grain, straw, and root but higher organic carbon (OC) in the root compared to the Ambient and the Field. The study indicated that this rise of temperature due to the elevated CO₂ could not adversely affect the yield.

In P. maximum the cumulative dry biomass production in two cuttings showed an increase of 59.24% and 43.17% in open top chambers (OTC) with elevated CO₂ (600±50 ppm) (C₆₀₀) and without elevated CO₂ (C_OTC) respectively over the open field grown corps (Ca). In S. hamata the dry matter increased by 39.79% under C₆₀₀ and 31.02% in C_OTC over Ca. The canopy photosynthesis (P_N x LAI) increased significantly in both the crop species with elevated CO_2. The increased rate of canopy photosynthesis indicated that there was higher assimilation of CO₂, which has intern maximum biomass production. The increase in fresh and dry matter accumulation in C₆₀₀ indicating that these crop species should be promoted for higher biomass production and carbon sequestration in the semi arid tropical environmental conditions.