Plant growth responses to elevated atmospheric CO2 are increased by phosphorus sufficiency but not by arbuscular mycorrhizas

Capturing the full growth potential in crops under future elevated CO₂ (eCO₂) concentrations would be facilitated by improved understanding of eCO₂ effects on uptake and use of mineral nutrients. This study investigates interactions of eCO₂, soil phosphorus (P), and arbuscular mycorrhizal (AM) symbiosis in Medicago truncatula and Brachypodium distachyon grown under the same conditions. The focus was on eCO₂ effects on vegetative growth, efficiency in acquisition and use of P, and expression of phosphate transporter (PT) genes. Growth responses to eCO₂ were positive at P sufficiency, but under low-P conditions they ranged from non-significant in M. truncatula to highly significant in B. distachyon Growth of M. truncatula was increased by AM at low P conditions at both CO₂ levels and eCO₂×AM interactions were sparse. Elevated CO₂ had small effects on P acquisition, but enhanced conversion of tissue P into biomass. Expression of PT genes was influenced by eCO₂, but effects were inconsistent across genes and species. The ability of eCO₂ to partly mitigate P limitation-induced growth reductions in B. distachyon was associated with enhanced P use efficiency, and requirements for P fertilizers may not increase in such species in future CO₂-rich climates.Iver Jakobsen, Sally E. Smith, F. Andrew Smith, Stephanie J. Watts-Williams, Signe S. Clausen and Mette Grønlun

Cosmological constant and the fate of the DDM theory

We investigate the impact of the non-zero cosmological constant on the classical decaying dark matter theory developed by the late Dennis Sciama. In particular, we concentrate on the change in relevant values of cosmological parameters in comparison to the high-precision estimates given by Sciama (1997). It is shown that the appropriate changes in resulting parameter values are such to make the DDM concept less plausible. This is in complete agreement with recently reported observational results detrimental to this theory.Comment: 4 pages, 2 eps figures, uses AA latex styl

Technical Note: Mesocosm approach to quantify dissolved inorganic carbon percolation fluxes

Dissolved inorganic carbon (DIC) fluxes across the vadose zone are influenced by a complex interplay of biological, chemical and physical factors. A novel soil mesocosm system was evaluated as a tool for providing information on the mechanisms behind DIC percolation to the groundwater from unplanted soil. Carbon dioxide partial pressure (<i>p</i>CO₂), alkalinity, soil moisture and temperature were measured with depth and time, and DIC in the percolate was quantified using a sodium hydroxide trap. Results showed good reproducibility between two replicate mesocosms. The <i>p</i>CO₂ varied between 0.2 and 1.1%, and the alkalinity was 0.1–0.6 meq L⁻¹. The measured cumulative effluent DIC flux over the 78-day experimental period was 185–196 mg L⁻¹ m⁻² and in the same range as estimates derived from <i>p</i>CO₂ and alkalinity in samples extracted from the side of the mesocosm column and the drainage flux. Our results indicate that the mesocosm system is a promising tool for studying DIC percolation fluxes and other biogeochemical transport processes in unsaturated environments