Seasonal Dynamics of Soil C[O.sub.2] Concentration and C[O.sub.2] Fluxes from the Soil of the Former Lake Texcoco, Mexico

Seasonal changes of the soil C[O.sub.2] concentration and the rate of C[O.sub.2] fluxes emission from the soil formed on the sediments of the former Lake Texcoco, which occupied a significant part of the Mexico Valley until the mid-17th century, were studied. The soils (Fluvic Endogleyic Phaeozems) were characterized by a low C[O.sub.2] fluxes rate, which is related to their high alkalinity. The mean values of soil respiration were 6.0- 14.1 mg C/([m.sup.2] h) depending on vegetation type, which corresponds to 60-157 g C/([m.sup.2] yr). The contribution of plants to the C[O.sub.2] fluxes insignificantly varied by seasons and depended on the species composition of vegetation. The soil C[O.sub.2] concentration and soil respiration in eucalypt (Eucalyptus globulus Labill.) plantation were two times higher than those in the grass-subshrub area, the ground cover of which consisted of Distichlis spicata (L.) Greene and Suaeda nigra (Raf.) J.F. Macbr. species. This can be related to the significant volumes of gas production during the respiration of eucalypt roots and associated rhizosphere community. The contribution of the root systems of grass cover to the soil C[O.sub.2] fluxes in eucalypt plantation slightly varied within the year and was equal to 24% on the average. In the grass-subshrub area, its value varied from 41% in the cold season to 60% in the warm season. The spatial variability of soil C[O.sub.2] concentration and its flux rate to the atmosphere was due to the differences in plant species composition and hydrothermal conditions, and their temporal trend was closely related to the seasonal accumulation of plant biomass and soil temperature. Keywords: C[O.sub.2] concentration, soil respiration, saline soil, Eucalyptus globulus, Distichlis spicata, temperature, soil water content