Irene Sánchez-Gallen

ROOT PRODUCTIVITY IN A LOWLAND TROPICAL RAIN FOREST IN MEXICO

Fine root productivity was estimated in a lowland tropical rain forest at Los Tuxtlas (SE Mexico) and examined in relation to climatic factors. Two root diameter classes were defined (class I,<1 mm; class II, 1–3 mm). Total root productivity was estimated to 1.95 t ha−1 year−1, a value which is lower than those reported from other rain forest sites. Significant differences in root dry weight were found among months and between diameter classes throughout the year. Class I monthly means formed two groups: one corresponding to the months of highest precipitation, and the other to the relatively dry season. Class II monthly means also formed two groups, although these were unrelated to the regional precipitation pattern. A multiplicative regression model of productivity on precipitation was significant for both root classes when rainfall data of the previous month were used, while a linear regression model was significant only for class I roots when temperature data of two months before were used; these results suggest a delay in the effect of climatic conditions on root productivity. While the seasonal pattern of root productivity is clearly related to the annual rainfall distribution, the low total annual productivity may be related to the very high soil fertility at Los Tuxtlas.

Research on arbuscular mycorrhizae in Mexico: an historical synthesis and future prospects

This review analyzes the historical development and advances of the research on arbuscular mycorrhizal fungi (AMF) in Mexico, as well as the prospects for future research. AMF-research has been focused on studying both diversity and functionality in several ecosystems of Mexico, but mainly in the tropical dry and rainy ecosystems, and the agricultural systems. In Mexico, 95 species of AMF have been recorded, representing 41% of the known species worldwide. The functional effects of AMF colonization have been examined in approximately 10% of the known host plants, but greenhouse studies continue to dominate over those conducted under field conditions. Even though research to date has been at the organismic level, further effort is needed due to the high plant diversity in Mexico. Studies on AMF biomass under field conditions and more taxonomic determination are required based on morphological features, biochemical determinations (fatty acids) and molecular tools. In addition, ecophysiological and ecological in situ studies would help in understanding the relationships among AMF, soil fauna, nutrients, and host plants. The contribution of AMF to ecosystemic processes is a priority line of research that requires an integrated approach (inter- and multidisciplinary) in order to define the role of AM symbioses for biogeochemical models. The creation of a Mexican mycorrhizal research network has and will help to identify the main challenges. Generating similar research protocols, and sharing databases and experience will assist mycorrhizologists working under the diverse financial and ecological contexts that is to be found in Mexico and Latin America.

Analyses of Ecophysiological Traits of Tropical Rain Forest Seedlings under Arbuscular Mycorrhization: Implications in Ecological Restoration

The tropical rain forest is losing forest coverage at a rate of 2% annually, which has contributed to an increase in carbon emissions and has reduced carbon sequestering. The causes of deforestation are primarily anthropogenic, including forest exploitation, clearing for crop and livestock use, and the development of urban infrastructure, among others. The direct result of the deforestation process is fragmentation, which can increase population mortalities and reduce reproduction rates. These changes also produce alterations in soil microbiota, of which two of the most important components are the mycorrhiza-forming fungi and nitrogen-fixing bacteria. Facing rapid rain forest deterioration, restoration ecology practices are extremely necessary, as they allow ecosystem recuperation. One of the principal objectives of restoration programs should be the facilitation of system function reestablishment, maintaining long-term stability.

What Can the Arbuscular Mycorrhizal Fungi Community Tell Us About Plant Biodiversity Loss

The multiple changes of land use in the humid tropics have resulted in a landscape that is very heterogeneous with a high degree of fragmentation and disturbance whose first consequence is the plant biodiversity loss. Current analysis shows that there is a relationship between the organisms in the soil and the plants which are related in such a way that aboveground changes can have a strong and negative impact on organisms belowground. However, these impacts depend on a multiplicity of factors that need to be identified to understand the responses of these organisms at community level and propose comprehensive strategies for restoration of damaged ecosystems. Our studies have focused on the role of arbuscular mycorrhizal fungi (AMF) forming a mutualistic association with many plant species, and we have found that their richness and spore number respond to changes in the vegetation cover and the replacement of the original vegetation by cultivated plants or pastures altering, in addition, its composition, although edaphic variables are equally important such as nitrogen concentration, pH, and organic matter.

Dynamics and conservation of the flora of the desert scrub of the Ecological Reserve of the Pedregal de San Angel (D. F., Mexico)

The xerophytic scrub located on the lava field produced by the Xitle volcano has been almost completely destroyed by the urban sprawl of Mexico City. The Pedregal de San Angel Ecological reserve (1.77 km2) offers protection to one of the most important remnant portions. Despite such protection status, this plant community is presently still affected by invasion of exotic species, pollution, illegal extraction of selected species, and recurrent fires. The aim of this study was to update the floristic knowledge of the reserve and to analyze possible changes in the floristic richness and composition that have taken place in the last 50 years. Out of the total 337 species that are included in the present checklist (193 genera, 74 families), 152 species had already been reported by Rzedowski (1954) in a pioneer study that covered the entire lava field (80 km2). Contrastingly, 166 species recorded by him for this xerophytic scrub were not encountered in this study, although 21 of them do occur in another ecological reserve (Lomas del Seminario) located on the same lava field but at a higher elevation. The analysis of the distribution of species of the present checklist by vegetation type showed that only 34 of them occur exclusively in xerophytic scrub, whereas the remaining also occur in other plant communities. The information provided in this study is expected to serve as the basis for future monitoring studies aimed at assessing the dynamics of this flora through time.