Norma E. García-Calderón

Biogeography of testate amoebae in the soils of Mexico

We studied testate amoebae (testates) in the soils of coniferous and deciduous forests and in the wetland and aquatic habitats of Mexico. In 141 samples we found 205 taxa identified to the species or intraspecies level and 68 testate amoebae, which could not be identified to the species level. The highest species diversity of testates was found in the soils of the tropical rainforest (126 species and intraspecific taxa, including spp.) and in tropical wetlands (144 species and intraspecific taxa, including spp.). The study documented testate amoebae with a limited geographical distribution (genera Centropyxis, Cornuapyxis, Ellipsopyxis, Hoogenraadia, Planhoogenraadia, Apolimia, Certesella, Apodera, and Alocodera). We found that testate amoebae in the soils of Mexico had a high level of polymorphism and individual variability. We discuss the value of soil testate amoebae for defining biogeographical regions of Mexico.

Gas diffusivity in chinampas soils in Mexico City .

En este experimento de laboratorio medimos los coeficientes de difusion de gas (D) en nucleos inalterados de suelos antropogenicos de chinampas y probamos la validez de algunos modelos clasicos de difusion de gases para predecir la relacion de D al coeficiente de difusion de gas en aire libre (Do) como una funcion de la porosidad del suelo llena de aire (e). El horizonte A1 (0-7cm) de los suelos de chinampas alcanzo la difusividad de gas mas alta y una relacion lineal entre D/Do y e, y asi, el modelo de Penman mostro una prediccion adecuada para este subhorizonte. El modelo de Millington-Quick tuvo un D/Do similar en todo el rango de e para el subhorizonte A2 (7-18 cm) y a la e < 0,5 cm3 cm-3 para los subhorizontes A3 (18-30 cm) y A4 (30-50 cm). La difusividad de gas en suelos de chinampas fue menor que en suelos minerales, como predijeron los modelos D/Do(e), debido probablemente al contenido elevado de carbono organico del suelo. Los modelos predictivos podrian ser utilizados para la valoracion de la emision de gases de efecto de invernadero de los suelos de chinampas.

Composition of soil lipids in two, chinampas agroecosystems from Xochimilco and Tlahuac municipalities, Mexico

Abstract The Chinampas are important historically and represent a special agroecosystem that has been sustainable for many years. However, their agricultural potential has currently decreased mainly because of irrigation with waste water from Mexico City, leading to progressive salinity and alkalinity problems and the subsequent general alteration on the agroecosystem. Chemical composition of the main groups of lipid molecules in anthropogenic organic soil from Xochimilco and Tlahuac Municipalities (Mexico) were investigated. The analysis performed included physico‐chemical characteristics of the soil and the distribution analysis of free alkanes and fatty acids. The successive accumulation stages of organic materials in these anthropogenic organic soils represent a source of irregular distribution in organic carbon, likewise the concentration of lipid extracts differed noticeably with depth. There is a vertical variability, where hydromorphic environment has played a key role in this variability. The major compounds identified in the soil lipid extracts by gas chromatography‐mass spectrometry include series of linear and satured alkanes, fatty acids, as well as individual components such as sterols and hopanes. Most of the lipid components in these soil seem to have a biogenic origin (higher plants and microorganism biomass).

CO2 production in anthropogenic Chinampas soils in Mexico City .

We studied microbial-associated C2 production in anthropogenic chinampas soils. !e soils were constructed by the accumulation of materials such as organic matter and loamy lacustrine sediments in Pre-Hispanic cultures in Mexico. To study the temperature sensitivity of C2 production related to soil depth, moisture and oxygen availability, soil samples were collected at depths of 0-7, 7-18, 18-30, 30-40 and 40-50 cm. !e soil samples were incubated under aerobic and anaerobic conditions at controlled temperatures (-5, 0, 5, 10, 20, 30 °C) and soil moistures of 10, 30, 60 and 90% water-filled pore space. For all the soil depths, incubation temperatures and soil moistures, the mean rate of aerobic CO2 production was 58.0 mg CO2 kg-1 d-1 and that of anaerobic CO2 production 31.2 mg CO2 kg-1 d-1, with the highest rate found in the soil samples collected at a depth of 0-7 cm. A decrease in soil organic carbon content inhibited CO2 production more under anaerobic than aerobic conditions. The dependence of aerobic CO2 production on soil moisture increased at what constituted both unusually high and low temperatures for the study area. Since the response of CO2 production to temperature was lower under anaerobic than aerobic conditions, the increase in soil moisture content led to a decrease in the temperature sensitivity of CO2 production. !e response of microbial activity to other factors may be modified under what constitutes the limiting conditions for any of the factors considered, as follows: (i) when anaerobiosis increases in the soil, the limiting e#ect of substrate availability on microbial activity increases; (ii) the CO2 production rate becomes more dependent on soil moisture under temperature stress; (iii) the sensitivity of CO2 production to temperature is highest under drought stress.

Oribatid mites and springtails from a coffee plantation in Sierra Sur, Oaxaca, Mexico

The objective of this work was to compare the oribatid mite and springtail communities in three plots with different soil use - Coffee (CP), secondary vegetation or fallow fields (acahual, A) and a cloud mountain forest (CMF) - within a coffee plantation located in Santa Maria Huatulco, Oaxaca State, Mexico. In each plot 20 samples (10 of soil, 10 of litter) were taken and processed in Berlese funnels. The extracted fauna was preserved in 70% ethanol. A total of 3,031 oribatid mites belonging to 33 species, and 1,177 specimens of springtails belonging to 43 species, were collected. The number of species recorded was: 27 at CP (14 oribatids; 13 springtails), 44 at A (19 oribatids; 25 springtails) and 62 at CMF (32 for each group). A total of 26 oribatid and 27 springtail species was found in the soil, and 25 oribatid and 32 springtail species were found in the litter. The most abundant species were the oribatids Rostroztes foveolatus (Haplozetidae), Tectocepheus sp. (Tecocepheidae), Karenella sp. (Oppidae), Atropacarus (Hoplophorella) cf. fonseciai (Phthiracaridae), Epilohmannia pallida americana (Epilohmannidae), and the springtails Ceratophysella cf. gibbosa (Hypogastruridae), Mesaphorura sp. (Tullbergidae) and Proisotoma cf. minuta (Isotomidae). Fourteen families and 18 species of Oribatida species and 5 families and 34 species of Collembola were recorded for the first time for the State.