Dry Tropical Region Research Articles

Use of ethylenediurea for assessing the impact of ozone on mung bean plants at a rural site in a dry tropical region of India

A field study was conducted to evaluate the usefulness of ethylenediurea (EDU) in assessing the impact of ozone (O3) on mung bean plants (Vigna radiata L Malviya Janpriya) grown in a rural area of a dry tropical region of India. Mean monthly O3 concentrations varied between 52.9-64.5 ppb. Significant reductions in growth, yield, soluble protein, pigments, and ascorbic acid in non-EDU-treated plants were observed when compared with EDU-treated plants. This clearly showed that EDU treatment provided protection against negative effect of O3 on mung bean and therefore can be effectively used as a tool to assess phytotoxic O3 concentrations in rural areas.

Cambrian–Ordovician non-marine fossils from South Australia

Newly discovered trace and body fossils from the Grindstone Range Sandstone of South Australia reveal evidence of megascopic life on land during the Cambrian–Ordovician. Arthropod trackways (Diplichnites gouldi) are interpreted here to have formed on land. The most persuasive evidence for this view is that footprints vary in clarity along the length of the trackway as it traversed moist then dry silt, then biological soil crust. Compatible, though not diagnostic of walking on land is trackway symmetry, without one side buoyed up by current. The footprints bulge outward and are partially filled with miniature talus cones. Footprints also are alternate as in walking, rather than opposite as in sculling. Arthropod resting traces (Selenichnites sp. indet.) have 11 lateral furrows, and footprints are bundled into sets of 8–11, most like euthycarcinoids. No arthropod dwelling burrows were found in associated palaeosols, so the track maker was more likely amphibious than fully terrestrial. Associated trace fossils include a new ichnotaxon of burrow, Myrowichnus arenaceus gen. et sp. nov. Thallose impressions (Farghera robusta gen. et sp. nov.) have the radiating dichotomous form of lichens, algae and liverworts. All these trace and body fossils were found in weakly developed palaeosols. Other palaeosols in the same formation are evidence of terrestrial ecosystems of modest biomass, weathering, carbon sequestration and stability in dry tropical regions.

A comparative account of the microbial biomass-N and N-mineralization of soils under natural forest, grassland and crop field from dry tropical region, India

This study investigated microbial biomass-N (MB-N) and N-mineralization in soils of four different vegetation systems including forest (sal), mixed forest, savanna and cropland ecosystems in the Vindhyan region, India. A change was noted in the above region due to physiographic differences and anthropogenic disturbances. Annually the soil moisture (SM) content across the different study sites ranged from 7.5 to 24.3% being maximum in forest sites compared to savanna and cropland sites. The NH<sub>4</sub><sup>+</sup>-N, NO <sup>-</sup><sub>3</sub> -N and MB-N concentrations varied from 4.3 to 10.2 μg/g, 1.1 to 5.8 μg/g and 21.3 to 90.2 μg/g dry soil, respectively, with minimum values in the wet and maximum values in the dry season. The trend of seasonal variation in net N-mineralization was similar to that of moisture content but counter to the concentrations of inorganic-N and MB-N. The net N-mineralization rates at different investigated sites ranged from 4.5 to 37.6 μg/g month. Cultivation reduced the N-mineralization and MB-N by 58.5% and 63.5%, respectively. Experiments showed that the percentage contribution of MB-N to total-N was 8.01 to 19.15%. MB-N was positively correlated with the inorganic-N (<i>n</i> = 180,<i>r</i>.80,<i>P</I> < 0.001) but negatively with soil moisture (<i>n</i> = 180, <i>r</i> = 0.79, <i>P</I> < 0.001) and net N-mineralization rates (<i>n</i> = 180, <i>r</i> = 0.92, <i>P</I> < 0.0001). The higher N-mineralization and MB-N in the soil of forest ecosystem was reported compared to savanna and cropland and the order of soil MB-N levels and net N-mineralization followed the sequence: forest (sal) > mixed forest > savanna > cropland.

Atmospheric Deposition and Heavy Metal Contamination in an Organic Farming System in a Seasonally Dry Tropical Region of India

Increased consciousness about agricultural sustainability and health risks associated with agrochemicals has lead organic farming to be a globally emerging alternative farm practice. We report the effect of atmospheric deposition on soil quality and heavy metal contamination of agricultural produce under an organic farming system using wheat and corn as test crops. Data obtained in the open field (OFO) were compared with a plastic-covered glass-house-grown system (OFG). The results showed that depositions of Cd, Cu, Ni, Pb, and Zn increased with time. Soil porosity, water holding capacity, microbial biomass carbon (Cmic), substrate-induced respiration (SIR), alkaline phosphatase, and FDAase activity decreased, whereas the bulk density and contents of Cd, Cu, Ni, Pb, and Zn increased over time in open plots receiving atmospheric deposition. Concentrations of metals in grains in OFO crops exceeded the safe limits of Indian standards and were three to sixfold higher than those recorded in OFG plots. These results indicate that atmospheric deposition of heavy metals can have a destabilizing effect on soil fertility in organic farming and can greatly increase the dietary intake of toxic metals. This may have long–term implications for human health as well as for agricultural sustainability. The data presented here have particular concern for developing countries, where unprecedented urban–industrial growth and consequently increased input fluxes of heavy metals will continue for decades to come.

Water budget and the consequent duration of canopy carbon gain in a teak plantation in a dry tropical region: Analysis using a soil–plant–air continuum multilayer model

A soil–plant–air continuum multilayer model was used to numerically simulate canopy net assimilation ( A n), evapotranspiration (ET), and soil moisture in a deciduous teak plantation in a dry tropical climate of northern Thailand to examine the influence of soil drought on A n. The timings of leaf flush and the end of the canopy duration period (CDP) were also investigated from the perspective of the temporal positive carbon gain. Two numerical experiments with different seasonal patterns of leaf area index (LAI) were carried out using above-canopy hydrometeorological data as input data. The first experiment involved seasonally varying LAI estimated based on time-series of radiative transmittance through the canopy, and the second experiment applied an annually constant LAI. The first simulation captured the measured seasonal changes in soil surface moisture; the simulated transpiration agreed with seasonal changes in heat pulse velocity, corresponding to the water use of individual trees, and the simulated A n became slightly negative. However, in the second simulation, A n became negative in the dry season because the decline in stomatal conductance due to severe soil drought limited the assimilation, and the simultaneous increase in leaf temperature increased dark respiration. Thus, these experiments revealed that the leaflessness in the dry season is reasonable for carbon gain and emphasized the unfavorable soil water status for carbon gain in the dry season. Examining the duration of positive A n (DPA) in the second simulation showed that the start of the longest DPA (LDPA) in a year approached the timing of leaf flush in the teak plantation after the spring equinox. On the other hand, the end appeared earlier than that of all CDPs. This result is consistent with the sap flow stopping earlier than the complete leaf fall, implying that the carbon assimilation period ends before the completion of defoliation. The model sensitivity analysis in the second simulation suggests that a smaller LAI and slower maximum rate of carboxylation likely extend the LDPA because soil water from the surface to rooting depth is maintained longer at levels adequate for carbon gain by decreased canopy transpiration. The experiments also suggest that lower soil hydraulic conductivity and deeper rooting depth can postpone the end of the LDPA by increasing soil water retention and the soil water capacity, respectively.

The hosts and potential geographic range of Dothistroma needle blight

Dothistroma needle blight, one of the most important foliar diseases of Pinus spp., is caused primarily by the fungus Dothistroma septosporum (Dorog.) Morelet, and to a lesser extent by Dothistroma pini Hulbary. The potential distribution and abundance of Dothistroma spp. was determined by (i) developing a process-oriented model of potential distribution of Dothistroma spp. from known locations, (ii) compiling a comprehensive list of susceptible host species from existing scientific literature and (iii) determining the distribution of susceptible hosts in areas predicted to be suitable for range expansion of Dothistroma spp. Using these three sources of information regions at risk were identified as those that were predicted to be suitable for range expansion by Dothistroma spp. and included significant areas of susceptible host species. The process-oriented distribution model, CLIMEX was used to infer the climatic requirements of Dothistroma spp. from laboratory based measurements and 248 disease records in North America and Asia. When validated against 7594 disease observations from Europe, Africa, South America and Oceania, the model correctly predicted that all observations had a suitable climate for Dothistroma spp. The model indicated that the fungi can persist in climates ranging from sub-arctic through temperate, Mediterranean, continental, subtropical to dry tropical regions. The low level of disease detection in many regions projected to be climatically suitable may be due to the low occurrence of susceptible hosts. When areas that were not suitable for susceptible hosts were excluded results suggest that Dothistroma spp. could further extend their range into south east China, Vietnam, Ireland, Western Australia, Venezuela, Guyana, Suriname, Panama, Turkey, Albania and many countries bordering the Mediterranean Sea.

Forest Regeneration from Pasture in the Dry Tropics of Panama: Effects of Cattle, Exotic Grass, and Forested Riparia

Abstract We currently have the opportunity to restore one of the most threatened tropical ecosystems on the Pacific coast of Panama as a consequence of land use change. Factors that influence succession must be understood in order to capitalize on natural regeneration mechanisms. In this study, we determined the effects of exotic grass removal, cattle removal, proximity to forested riparian zones, and topography (upslope vs. downslope) on the initial stages of forest regeneration from pasture in a dry tropical region. After 3 years, basal area, stem density, and species richness of plants (trees, shrubs, vines, and herbs) were significantly and positively affected by exclusion of cattle, presence of exotic grass (no herbicide application), and presence of adjacent forested riparian zones (p < 0.01). Interactions between factors were not significant. Cattle foraged and stomped on vegetation, whereas herbicide application, although effectively removing grass, also killed tree and shrub sprouts, the major source of regrowth. Proximity to forested riparian zones had the greatest effect on species diversity. Shannon’s index for diversity (H) equaled 3.23 in plots adjacent to forested riparian zones as compared to 2.78 in plots not associated with these areas. Our recommendations during the early stages of forest succession are to (1) exclude cattle, (2) make site‐specific decisions about herbicide application based on the presence or absence of forested riparia and prevalence of coppicing, and (3) actively conserve and protect riparian zones, which function as a critical source of diverse propagules.

Phosphorus cycling in primary and secondary seasonally dry tropical forests in Mexico

• Primary forests in the seasonally dry tropical regions of Mexico are disappearing under land-use pressure, creating a mosaic of secondary forests of different ages. • In this study we measured the aboveground litterfall phosphorus (P) fluxes, litter-layer and soil P pools to compare the P cycles in primary and secondary seasonally dry tropical forests. Our hypothesis was that the previous agricultural land use of secondary forests would bring about a lower P flux in the litterfall, lower soil P pool, and higher nutrient resorption proficiency than in primary forests, as well as an increase of relative amounts of available P provided by the soil with forest aging. • The expected litterfall P flux increase in the secondary forest following a previous agricultural land use did not occur. Phosphorus return to the soil by aboveground litterfall was unaffected by the succession stage of the forest. In addition, the total soil P pool did not change with forest age. However, available soil P (bicarbonate P-inorganic and P-organic pools) and hydroxide inorganic P pools were higher in primary than in secondary forest soils. Phosphorus concentration in litterfall increased significantly with forest age, suggesting that P is cycled more efficiently (by a higher nutrient resorption proficiency) when soil available P is less abundant. Despite these differences among forests, the results of our study gave evidence that P requirements by plants in primary and secondary forests are sufficiently met by the accumulation of dissolved (water extractable) P in the forest floor during the dry season and by soil bicarbonate-P pools. • Our study on the effects of land cover change on P cycling, following the discontinuation of agricultural practices, leads to the conclusion that this ecosystem P dynamics will vary depending on the successional stage of the forests, and is strongly influenced by the seasonal rainfall pattern which determines plant-available P.

Understanding and managing groundwater and salinity in a tropical conjunctive water use irrigation district

Agricultural production around the world is increasingly being constrained by hydrological factors—such as over-extraction of groundwater in some locations, rising water tables in others, and worsening groundwater quality in general. One such area is the Lower Burdekin irrigation area in northern tropical Australia, where rising watertable levels and increasing salinity concentrations within alluvial deposits are causing concern. The aim of this study was to improve understanding of the processes driving trends in groundwater quantity and quality in Mona Park, a conjunctive water use irrigation district in the Lower Burdekin. The analysis is intended to enable land and water managers to explore alternative policy and management practices to help support the reversal in current trends, and to improve water table conditions in terms of both water quantity and quality. Key lessons that are applicable to the development of new irrigation schemes in wet–dry tropical regions elsewhere in the world are emphasised. This study demonstrated that simple qualitative methods that link historical developments and observed climatic and hydrological trends can support development of a robust understanding of groundwater behaviour. The results showed that to minimise groundwater accessions in wet–dry tropical regions, a large soil water deficit should be maintained in the unsaturated zone prior to the onset of the wet season to buffer against potentially large wet season recharge events, and that this strategy should be implemented from when irrigation is first commenced. It is very clear that groundwater systems under or down gradient from irrigated areas need to be managed adaptively, such that: (1) timely decisions are made in response to changes in watertable level and groundwater quality; and (2) suitable mechanisms are in place to ensure farmers have the financial incentives and flexibility to respond in the short-term. The work also demonstrated that the establishment of good baseline data prior to irrigation development, and long-term analysis (>30 years) involving various combinations of wet and dry periods, are required in order to build a comprehensive understanding of potential groundwater behaviour and adaptive management needs.

Assessing impact of industrialization in terms of LULC in a dry tropical region (Chhattisgarh), India using remote sensing data and GIS over a period of 30 years

The main focus of the paper is to assess the land use/ land cover (LULC) change in northern Chhattisgarh due to industrialization using remote sensing and Geographical Information System (GIS). The impact was assessed using an information extraction method applied to temporal satellite data (LANDSAT and IRS scenes) in GIS domain. For assessing the impact on natural resources, the classification scheme was restricted to (1) Forest patches ((a) completely cleared, (b) partially cleared, (c) least affected), (2) Non-Forest ((d) completely changed, (e) least changed), (3) Industrial/Mining area, and (4) River. Over the three decades 22.22% of forests have been completely cleared and converted to industrial setup. Another 25% is completely cleared and 10% is degraded. Around 4% of agricultural area is totally affected due to industrial activity. Random assessment of plant distribution (Trees, Shrubs and Herbs) indicates significant changes in the herb distribution directly related to distance gradient form the industrial/mining setup. Visual recording, socio-economic survey and satellite data also helped in delineation of extent of environmental pollution in forest and non-forest areas. The paper presents methodology for the environmental impact assessment.

Accumulation of heavy metals in dietary vegetables and cultivated soil horizon in organic farming system in relation to atmospheric deposition in a seasonally dry tropical region of India

Increasing consciousness about future sustainable agriculture and hazard free food production has lead organic farming to be a globally emerging alternative farm practice. We investigated the accumulation of air-borne heavy metals in edible parts of vegetables and in cultivated soil horizon in organic farming system in a low rain fall tropical region of India. The factorial design of whole experiment consisted of six vegetable crops (tomato, egg plant, spinach, amaranthus, carrot and radish) x two treatments (organic farming in open field and organic farming in glasshouse (OFG)) x seven independent harvest of each crop. The results indicated that except for Pb, atmospheric deposition of heavy metals increased consistently on time scale. Concentrations of heavy metals in cultivated soil horizon and in edible parts of open field grown vegetables increased over time and were significantly higher than those recorded in OFG plots. Increased contents of heavy metals in open field altered soil porosity, bulk density, water holding capacity, microbial biomass carbon, substrate-induced respiration, alkaline phosphatase and fluorescein diacetate hydrolytic activities. Vegetable concentrations of heavy metal appeared in the order Zn > Pb > Cu > Ni > Cd and were maximum in leaves (spinach and amaranths) followed by fruits (tomato and egg plant) and minimum in roots (carrot and radish). Multiple regression analysis indicated that the major contribution of most heavy metals to vegetable leaves was from atmosphere. For roots however, soil appeared to be equally important. The study suggests that if the present trend of atmospheric deposition is continued, it will lead to a destabilizing effect on this sustainable agricultural practice and will increase the dietary intake of toxic metals.

Water source partitioning among trees growing on shallow karst soils in a seasonally dry tropical climate

The sources of water used by woody vegetation growing on karst soils in seasonally dry tropical regions are little known. In northern Yucatan (Mexico), trees withstand 4-6 months of annual drought in spite of the small water storage capacity of the shallow karst soil. We hypothesized that adult evergreen trees in Yucatan tap the aquifer for a reliable supply of water during the prolonged dry season. The naturally occurring concentration gradients in oxygen and hydrogen stable isotopes in soil, bedrock, groundwater and plant stem water were used to determine the sources of water used by native evergreen and drought-deciduous tree species. While the trees studied grew over a permanent water table (9-20 m depth), pit excavation showed that roots were largely restricted to the upper 2 m of the soil/bedrock profile. At the peak of the dry season, the delta(18)O signatures of potential water sources for the vegetation ranged from 4.1 +/- 1.1 per thousand in topsoil to -4.3 +/- 0.1 per thousand in groundwater. The delta(18)O values of tree stem water ranged from -2.8 +/- 0.3 per thousand in Talisia olivaeformis to 0.8 +/- 1 per thousand in Ficus cotinifolia, demonstrating vertical partitioning of soil/bedrock water among tree species. Stem water delta(18)O values were significantly different from that of groundwater for all the tree species investigated. Stem water samples plotted to the right of the meteoric water line, indicating utilization of water sources subject to evaporative isotopic enrichment. Foliar delta(13)C in adult trees varied widely among species, ranging from -25.3 +/- 0.3 per thousand in Enterolobium cyclocarpum to -28.7 +/- 0.4 per thousand in T. olivaeformis. Contrary to initial expectations, data indicate that native trees growing on shallow karst soils in northern Yucatan use little or no groundwater and depend mostly on water stored within the upper 2-3 m of the soil/bedrock profile. Water storage in subsurface soil-filled cavities and in the porous limestone bedrock is apparently sufficient to sustain adult evergreen trees throughout the pronounced dry season.

Frugivory by Small Vertebrates Within a Deforested, Dry Tropical Region of Central America

ABSTRACTSmall vertebrates were inventoried within three habitat types in a degraded dry forest region of Panama. Animals were classified as frugivorous if they were observed foraging on fruit or if fecal samples contained mostly or exclusively seeds. Overall, we found that eight bat species and 21 bird species consumed fruit. The greatest numbers of birds were observed within live fences and bird species richness was greatest within riparian forests. Bat assemblages were not significantly different between habitats. The implication is that ecosystem services such as seed dispersal may still be functional in this landscape.

RETRACTED: Contrasting pattern of methanotrophs in dry tropical forest soils: Effect of soil nitrogen, carbon and moisture

Population dynamics of methane-oxidizing bacteria (MOB) was measured for 2 consecutive years for four forest and one savanna sites in seasonally dry tropical regions of India. The soils were nutrient-poor and well drained. These sites differed in vegetational cover and physico-chemical features of soils. There were significant differences in MOB population size during the 2 years (mean 0.40 and 0.48 x 10(5) cells g(-1) dry soil), and at different sites (mean 0.38-0.59 x 10(5) cells g(-1) dry soil). The mean population size of MOB was higher (P<0.05) in dry seasons than in the rainy season at all the sites. There was a significant season and site interaction, indicating that the effect of different seasons differed across the sites. There was a positive relation between soil moisture and MOB population size during summer (the driest period) and a negative relation during the rest of the year. The number of MOB was consistently higher for the Kotwa hill base site than rest of the sites having higher soil organic C and total N. The results suggested that in seasonally dry tropical forests the moisture, C and N status of the soil regulates the population size of MOB (methanotrophs) in the long term.

Experiments on Ecological Restoration of Coal Mine Spoil using Native Trees in a Dry Tropical Environment, India: A Synthesis

A series of experiments was conducted on the rehabilitation of mine spoil in a dry tropical region of India for determining the suitability of tree species for plantation, growth performance of selected indigenous species in monoculture and impact of the plantations on the restoration of biological fertility of soil. All of the 17 indigenous species examined could grow in the mine spoil and the growth of a majority of them could be improved by amending the mine spoil with NPK fertilizer. Direct seeding showed greatest height of Zizyphus jujuba and Pongamia pinnata on flat surface, and of Azadirachta indica on slope. In terms of diameter, Syzygium cumini performed best on flat surface and Terminalia arjuna on slope. Total biomass in plantations of selected native tree species on mine spoil at 5-yr age varied from 7.2 to 74.7 t ha−1, being minimum for Shorea robusta and maximum for Dendrocalamus strictus. Total net production ranged from 3.5 (for Shorea robusta) to 32.0 t ha−1 yr−1 (for Dendrocalamus strictus), respectively. Microbial biomass in the redeveloping soil was lower compared to that in natural forest soil but immobilization of soil C in microbial biomass was greater in the mine spoil than in the natural forest. The study indicated that net primary production of the plantations was a function of the amount of foliage, soil C was a function of the amount of litter fall and biomass C was a function of soil C. Plantation of trees significantly accelerated the soil redevelopment process on the mine spoil.

Seedling survival and growth of native tree species in pastures: Implications for dry tropical forest rehabilitation in central Panama

Our study tested the effects of herbicide application and cattle removal on the survival and growth of three native tree species planted in pastures within a deforested, dry tropical region of Panama. We investigated whether enrichment planting may be a potential, complementing reforestation tool with natural regeneration. Three economically valuable tree species were chosen for the study; Cedrela odorata L., Enterolobium cyclocarpum (Jacq.) Griseb, and Copaifera aromatica Dwyer. Planted seedlings were monitored for survival, root collar diameter and height growth in the presence or absence of two factors; (1) initial herbicide application and (2) cattle. After 16 months, subsamples of seedlings within each treatment were harvested and measured for dry masses and leaf areas. In the initial stages of development, C. odorata seedlings had the greatest growth rates with herbicide application whereas E. cyclocarpum seedlings had the greatest growth rates with cattle exclusion. The combination of these two factors yielded the best growth for both species. Of the three species, C. odorata had the lowest mortality rates (58%), and the greatest average dry mass ( μ = 403.7 g), leaf area ( μ = 169.3 m 2), diameter growth rate ( μ = 3.7 cm year −1) and height growth rate ( μ = 81.7 cm year −1) at 16 months. In addition, in the presence of cattle, C. odorata grew significantly better than E. cyclocarpum. To accelerate forest succession, herbicide should be applied initially and cattle removed before enrichment planting.

Estructura, composición y diversidad de la selva baja caducifolia del Cerro Verde, Nizanda (Oaxaca), México

En este estudio se describe la estructura, la composición florística y los patrones de diversidad de la selva baja caducifolia del Cerro Verde, localizado en Nizanda (Istmo de Tehuantepec, Oaxaca, México). En 30 parcelas de 100 m2 se censaron las plantas leñosas con DAP ??1 cm (estrato alto), y en cinco subcuadros de 4 m2 dentro de cada una se censaron las plantas con DAP &lt; 1 cm, pero con altura &gt; 30 cm (estrato bajo). Se encontraron 194 especies distribuidas en 52 familias. La riqueza de especies fue idéntica en ambos estratos (145 especies), y cada uno aportó de manera exclusiva ca. 25% de la riqueza total registrada. Leguminosae fue la familia más rica en especies (27), seguida por Asteraceae (20) y Euphorbiaceae (18). Las especies más frecuentes fueron Bursera simaruba + B. aff. cinerea (no distinguidas en el campo), Euphorbia schlechtendalii, Pilosocereus collinsii y Capparis verrucosa. La riqueza específica promedio por cuadro fue de 30 especies. Los índices basados en la riqueza y la abundancia de las especies (Berger-Parker = 0.20; Simpson = 0.09; [de Fisher = 9.47; Shannon = 2.78; equitatividad = 0.82) indican una alta diversidad y una consecuente baja dominancia en esta selva. Los valores extrapolados mostraron una densidad total (estratos alto + bajo) de 23,950 ind. ha-1 (830 ind. ha-1 con DAP ? 10 cm), una cobertura de 446.7%, y un área basal de 53 m2 ha-1. La altura promedio del 10% de los árboles más altos fue 9.1 m. La estructura de la selva baja del Cerro Verde es semejante a la de otras comunidades vegetales del trópico seco de México y denota un buen estado de conservación. Este hecho, aunado a su particular composición florística, enfatiza la pertinencia de su conservación formal.

Role of ethylene diurea (EDU) in assessing impact of ozone on Vigna radiata L. plants in a suburban area of Allahabad (India)

A field study was conducted to evaluate the suitability of ethylene diurea ( N-[2-(2-oxo-1-imidazolidinyl)ethyl]- N′-phenylurea; EDU) in assessing the impact of O 3 on mung bean plants ( Vigna radiata L. var. Malviya Jyoti) grown in suburban area of Allahabad city situated in a dry tropical region of India. EDU is a synthetic chemical having anti-ozonant property. Mean monthly O 3 concentration varied between 64 and 69 μg m −3 during the experimental period. In comparison to EDU-treated plants, non-EDU-treated plants showed significant reductions in plant growth and yield under ambient conditions. Significant favourable effects of EDU-application were observed with respect to photosynthetic pigments, soluble protein, ascorbic acid and phenol contents. EDU-treated plants maintained higher levels of pigments, protein and ascorbic acid in foliage as compared to non-EDU-treated ones. The study clearly demonstrated that EDU alleviates the unfavourable effects of O 3 on mung bean plants, and therefore can be used as a tool to assess the growth and yield losses in areas having higher O 3 concentrations.

Soil C and N dynamics in primary and secondary seasonally dry tropical forests in Mexico

The nature and size of soil carbon (C) and nitrogen (N) pools and turnover were compared in secondary and primary forests in a seasonally dry tropical region of Mexico. Total soil C and N, microbial biomass C and N, mineral (ammonium and nitrate) N pools and potential mineralization and nitrification were measured in samples collected during the dry and rainy seasons in early-, mid-, late-successional and primary forests. We hypothesized that the previous agricultural land use of secondary forests would result in lower soil C and N stocks than in primary forest soils, as well as in the seasonal dynamics changes of these two elements. The expected pattern of decreasing soil C and N after a previous agricultural land use did not occur. Soil C was unaffected by the successional stage of the forest. In addition, early- and mid-successional forests registered the highest total and mineral N pools and potential N transformations, whereas primary forests had the lowest N pools and potential cycling. The total soil C and N pools did not change with the sampling season. However, the nitrate pool decreased at the beginning of the rainy season in all forest soils, as did the ammonium pool in primary forests. A striking contrast of the effects of the rainfall (i.e., dry season versus rainy season) seasonality on the microbial biomass and its C:N ratio was observed among forests; late-successional and primary forests recorded the lowest values of both parameters at the beginning of the rainy season, whereas early- and mid-successional forests showed the highest values at this sampling date. Therefore, potential N transformations in all forests were the highest during the rainy season. Our study on the consequences of the land cover change on soils, following the discontinuation of agricultural practices, allows us to conclude that the nutrient dynamics in this ecosystem will vary depending on the successional stage of the forests. This work suggests that the full restoration of soil C and N dynamics will take ca. 60 years of secondary succession.

Intra- and interspecific host discrimination in arrhenotokous and thelytokous Eretmocerus spp.

Bemisia tabaci (Gennadius) is a serious pest of vegetable, ornamental, and agronomic crops throughout the world. To control B. tabaci, Eretmocerus eremicus Rose & Zolnerowich, and Eretmocerus mundus Mercet are considered the most effective parasitoids in dry tropical regions. In parasitoids, choosing the `right` hosts has direct consequences for their reproductive success and efficiency as biocontrol agent. Therefore, being able to discriminate a parasitized host from an unparasitized one would be important to prevent wasting time, eggs, and to reduce the mortality risk for their offspring. We evaluated intra- and interspecific host discrimination and the chance of super-parasitism or multi-parasitism in two populations of E. mundus (sexual and asexual) and E. eremicus. Different combinations and sequences of female introduction were carried out for the various populations and species. Experienced females avoided super-parasitism. However, naive females did lay eggs under hosts that were previously parasitized by conspecific females. E. eremicus females avoided to multi-parasitize hosts parasitized by E. mundus. However, E. mundus females did multi-parasitize the hosts that had been parasitized earlier by E. eremicus. In the case of super-parasitism, the outcome showed that neither of the E. mundus populations was stronger, whereas in the case of multi-parasitism E. mundus appeared stronger than E. eremicus. Since those populations and species are morphologically similar a molecular method had to be developed to identify the outcome of super- or multi-parasitism, which is presented in Appendix A.