No country for new seeds: food and environmental security implications of Mexico's intended ban on GM crops.

An intended generalized ban on the "introduction and use of transgenic seeds" has been announced by the Mexican government, which, unlike the other agricultural programs under this administration, lacks a budget and rules of operation. In this policy brief we consider scenarios of implementing such an intended ban, de-regulating the use of genetically modified crops, or an intermediate scenario under the existing biosafety regulations. We recommend maintaining the status quo given its potential contributions to food and environmental security, in addition to a better economic outlook. However, a greater impulse needs to be given by the federal government to foment the domestic development of GM crops that are pertinent for Mexican agri-food needs, in addition to funding the development and implementation of various agro-ecological practices that increase biodiversity in food production units.

A δ(15)N assessment of nitrogen deposition for the endangered epiphytic orchid Laelia speciosa from a city and an oak forest in Mexico.

Atmospheric nitrogen deposition poses a major threat to global biodiversity. Tropical epiphytic plants are especially at risk given their reliance on atmospheric sources of nutrients. The leaf, pseudobulb, and root carbon and nitrogen content, C:N ratio, as well as the nitrogen isotopic composition were studied for individuals of Laelia speciosa from a city and from an oak forest in Mexico. The nitrogen content of leaves was similar between the city and the oak forest, reaching 1.3 ± 0.2 % (dry mass). The δ(15)N of leaves, pseudobulbs, and roots reached 5.6 ± 0.2 ‰ in the city, values found in sites exposed to industrial and vehicular activities. The δ(15)N for plant from the oak forest amounted to -3.1 ± 0.3 ‰, which is similar to values measured from sites with low industrial activities. Some orchids such as Laelia speciosa produce a single pseudobulb per year, i.e., a water and nutrient storage organ, so the interannual nitrogen deposition was studied by considering the ten most recent pseudobulbs for plants from either site formed between 2003 and 2012. The C:N ratio of the ten most recent pseudobulbs from the oak forest, as well as that of the pseudobulbs formed before 2010 for plants in the city were indistinguishable from each other, averaging 132.4 ± 6.5, while it was lower for the two most recent pseudobulbs in the city. The δ(15)N values of pseudobulbs from the oak forest averaged ‒4.4 ± 0.1 ‰ for the entire series. The δ(15)N ranged from 0.1 ± 1.6 ‰ for the oldest pseudobulb to 4.7 ± 0.2 ‰ for the pseudobulb formed in the city from 2008 onwards. Isotopic analysis and the C:N ratio for L. speciosa revealed that rates of nitrogen deposition were higher in the city than in the forest. The δ(15)N values of series of pseudobulbs showed that it is possible to track nitrogen deposition over multiple years.

Changes in Coleopteran assemblages over a successional chronosequence in a Mexican tropical dry forest.

Coleopterans are the most diverse animal group on Earth and constitute good indicators of environmental change. However, little information is available about Coleopteran communities' responses to disturbance and land-use change. Tropical dry forests have undergone especially extensive anthropogenic impacts in the past decades. This has led to mosaic landscapes consisting of areas of primary forest surrounded by pastures, agricultural fields and secondary forests, which negatively impacts many taxonomic groups. However, such impacts have not been assessed for most arthropod groups. In this work, we compared the abundance, richness and diversity of Coleopteran morphospecies in four different successional stages in a tropical dry forest in western Mexico, to answer the question: How do Coleopteran assemblages associate with vegetation change over the course of forest succession? In addition, we assessed the family composition and trophic guilds for the four successional stages. We found 971 Coleopterans belonging to 107 morphospecies distributed in 28 families. Coleopteran abundance and richness were greatest for pastures than for latter successional stages, and the most abundant family was Chrysomelidae, with 29% of the individuals. Herbivores were the most abundant guild, accounting for 57% of the individuals, followed by predators (22%) and saprophages (21%) beetles. Given the high diversity and richness found throughout the successional chronosequence of the studied tropical dry forest, in order to have the maximum number of species associated with tropical dry forests, large tracts of forest should be preserved so that successional dynamics are able to occur naturally.

Influence of Land Use on the C and N Status of a C4 Invasive Grass in a Semi-Arid Region: Implications for Biomonitoring.

Biomonitoring of atmospheric pollution is an increasingly accepted practice. However, most existing biomonitors are usually epiphytic species from mesic environments. This work assessed the suitability of buffelgrass (Cenchrus ciliaris), an invasive C4 grass in northwestern Mexico, as a biomonitor, by means of the spatial distribution of the carbon and nitrogen content and isotopic signatures for grass samples collected from urban, agricultural, and natural areas throughout the state of Sonora. We found the highest tissue carbon content of 45.6% (on a dry weight basis) and highest nitrogen content of 3.31% for buffelgrass from the Yaqui Valley. We also found the lowest δ13C of -15.9‰, and the highest δ15N of 16.7‰ in the same region. In contrast, the lowest carbon and nitrogen content of 39.4 and 1.49% were found for Bahía de Kino and Río Sonora mountains, respectively. The lowest δ15N of 2.18‰ and the highest δ13C of -13.7‰ were measured for two remote locations. These results show the influence that pollutant emissions, including agriculture and transportation, have on elemental and isotopic composition of vegetation. Buffelgrass is most adequate for tracking carbon and nitrogen emissions in arid environments and for determining alterations on nitrogen soil reactions, as a first approximation for saturation.

Isotopic biomonitoring of anthropic carbon emissions in a megalopolis.

Atmospheric pollution has become a serious threat for human health and the environment. However, the deployment, operation and maintenance of monitoring networks can represent a high cost for local governments. In certain locations, the use of naturally occurring plants for monitoring pollution can be a useful supplement of existing monitoring networks, and even provide information when other types of monitoring are lacking. In this work, we (i) determined the tissue carbon content and the δ13C values for the epiphytic CAM bromeliad Tillandsia recurvata and the relationship of both parameters with the existing CO concentrations in the Valley of Mexico basin and (ii) mapped the spatial distribution of such elemental and isotopic composition for this plant within the basin, in order to assess its potential as an atmospheric biomonitor of carbon monoxide, a pollutant with important repercussions on public health. The CO concentrations in the basin ranged from 0.41 ppm at rural locations to 0.81 ppm at urban sites. The carbon content of T. recurvata, which averaged 42.9 ± 0.34% (dry weight), was not influenced by the surrounding CO concentration. In contrast, the δ13C depended on the sites where the plants were collected. For example, the values were -13.2‰ in rural areas and as low as -17.5‰ in an urban site. Indeed, the isotopic values had a positive linear relationship with the atmospheric CO concentrations. Given the close relationship observed between the isotopic composition of T. recurvata with the CO concentrations in the Valley of Mexico, the δ13C values can be useful for the detection of atmospheric carbonaceous emissions.

Drying protocol does not alter plant δ13C and δ15N: a baseline survey for ecological studies.

Drying protocols might alter the isotopic signatures of plant samples given that high temperatures can volatilize various organic compounds or delay the halting of physiological processes at lower drying temperatures. We thus evaluated the effect of four drying protocols on the carbon and nitrogen isotopic signatures for 23 species of plants. In particular, leaves were either freeze-dried, placed in a herbarium drying stove (ca. 50°C), in a gravity convection oven (80°C), or microwaved (900 W) in 2-minute pulses, until constant weight. For each species, neither treatment led to significantly different δ13C values, which ranged from -31.7 to -12.4‰. The δ15N values of 21 of the species considered were not affected by the drying protocols, ranging from -11.6 to -8.8‰. For Tillandsia makoyana, significant differences were observed between the freeze dried and the microwaved samples and between the freeze dried samples and those dried at 50°C for Macroptilium gibbosifolium.

Characterization of nitrogen deposition in a megalopolis by means of atmospheric biomonitors.

An increase of nitrogen deposition resulting from human activities is not only a major threat for global biodiversity, but also for human health, especially in highly populated regions. It is thus important and in some instances legally mandated to monitor reactive nitrogen species in the atmosphere. The utilization of widely distributed biological species suitable for biomonitoring may be a good alternative. We assessed the suitability of an ensemble of atmospheric biomonitors of nitrogen deposition by means of an extensive sampling of a lichen, two mosses, and a bromeliad throughout the Valley of Mexico, whose population reaches 30 million, and subsequent measurements of nitrogen metabolism parameters. In all cases we found significant responses of nitrogen content, C:N ratio and the δ15N to season and site. In turn, the δ15N for the mosses responded linearly to the wet deposition. Also, the nitrogen content (R2 = 0.7), the C:N ratio (R2 = 0.6), and δ15N (R2 = 0.5) for the bromeliad had a linear response to NOx. However, the bromeliad was not found in sites with NOx concentrations exceeding 80 ppb, apparently of as a consequence of excess nitrogen. These biomonitors can be utilized in tandem to determine the status of atmospheric nitrogenous pollution in regions without monitoring networks for avoiding health problems for ecosystems and humans.

Biomonitors of atmospheric nitrogen deposition: potential uses and limitations.

Atmospheric nitrogen deposition is the third largest cause of global biodiversity loss, with rates that have more than doubled over the past century. This is especially threatening for tropical regions where the deposition may soon exceed 25 kg of N ha-1 year-1, well above the threshold for physiological damage of 12-20 kg of N ha-1 year-1, depending on plant species and nitrogenous compound. It is thus urgent to monitor these regions where the most diverse biotas occur. However, most studies have been conducted in Europe, the USA and recently in China. This review presents the case for the potential use of biological organisms to monitor nitrogen deposition, with emphasis on tropical plants. We first present an overview of atmospheric chemistry and the nitrogen metabolism of potential biomonitors, followed by a framework for monitoring nitrogen deposition based on the simultaneous use of various functional groups. In particular, the tissue nitrogen content responds to the rate of deposition, especially for mosses, whose nitrogen content increases by 1‰ per kilogram of N ha-1 year-1. The isotopic signature, δ15N, is a useful indicator of the nitrogen source, as the slightly negative values (e.g. 5‰) of plants from natural environments can become very negative (-11.2‰) in sites with agricultural and husbandry activities, but very positive (13.3‰) in urban environments with high vehicular activity. Mosses are good biomonitors for wet deposition and atmospheric epiphytes for dry deposition. In turn, the nitrogen saturation of ecosystems can be monitored with trees whose isotopic values increase with saturation. Although given ecophysiological limitations of different organisms, particular studies should be conducted in each area of interest to determine the most suitable biomonitors. Overall, biomonitors can provide an integrative approach for characterizing nitrogen deposition in regions where the deployment of automated instruments or passive monitoring is not feasible or can be complementary.

Responses to simulated nitrogen deposition by the neotropical epiphytic orchid Laelia speciosa.

Potential ecophysiological responses to nitrogen deposition, which is considered to be one of the leading causes for global biodiversity loss, were studied for the endangered endemic Mexican epiphytic orchid, Laelia speciosa, via a shadehouse dose-response experiment (doses were 2.5, 5, 10, 20, 40, and 80 kg N ha(-1) yr(-1)) in order to assess the potential risk facing this orchid given impending scenarios of nitrogen deposition. Lower doses of nitrogen of up to 20 kg N ha yr(-1), the dose that led to optimal plant performance, acted as fertilizer. For instance, the production of leaves and pseudobulbs were respectively 35% and 36% greater for plants receiving 20 kg N ha yr(-1) than under any other dose. Also, the chlorophyll content and quantum yield peaked at 0.66 ± 0.03 g m(-2) and 0.85 ± 0.01, respectively, for plants growing under the optimum dose. In contrast, toxic effects were observed at the higher doses of 40 and 80 kg N ha yr(-1). The δ (13)C for leaves averaged -14.7 ± 0.2‰ regardless of the nitrogen dose. In turn, δ (15)N decreased as the nitrogen dose increased from 0.9 ± 0.1‰ under 2.5 kg N ha(-1)yr(-1) to -3.1 ± 0.2‰ under 80 kg N ha(-1)yr(-1), indicating that orchids preferentially assimilate NH4 (+) rather than NO3 (-) of the solution under higher doses of nitrogen. Laelia speciosa showed a clear response to inputs of nitrogen, thus, increasing rates of atmospheric nitrogen deposition can pose an important threat for this species.