Trophic ecology of citrus pests based on stable isotope analysis

Macrodactylus pumilio Burm. (Coleoptera: Scarabeidae) and Naupactus cervinus (Boh.) (Coleoptera: Curculionidae) are considered primary pests in citrus crops in Brazil, causing damage to plants and decreasing productivity. However, few studies investigate the ecology of these insects. In this context, the use of stable isotopes analysis (SIA) emerges as an alternative technique to conventional studies of behavioral ecology because it is faster and may explain feeding behavior based on the food source for each species. Field sampling and laboratory experiments were carried out to examine the changes of carbon and nitrogen stable isotope ratios (δ13C and δ15N) among pests and host plants (C3 citrus and C4 grasses), providing means to examine trophic interactions. Beetles were collected at the municipality of Gavião Peixoto, São Paulo State, identified and kept at 5 °C in saturated saline solution until the SIA. Two patterns for both species were found: δ13C value for N. cervinus was -23.6 ‰ and -13 ‰ for M. pumilio, indicating similarity between the results of δ13C of N. cervinus and citrus plants (-26 ‰) and dependence on grasses (-12 ‰) for M. pumilio individuals. The mean δ15N value was 4.3 and 5.8 ‰ for citrus plants and grass leaves, respectively, and the mean δ15N value was 4.4 ‰ for N. cervinus and 4.9 ‰ for M. pumilio. The results showed a higher affinity of N. cervinus for citrus roots since the larval stage compared with the alternative diet on M. pumilio

Environmental inferences by stable isotopes (13C and 18O) and ages of Amazonian Natural Forest Trees

Inferências qualitativas do passado climático recente (±500 anos) da bacia Amazônica, da qual não existem registros instrumentais dos principais parâmetros climáticos mais longos que 70 anos, foram levantadas com base na variação da razão isotópica de 13C e 18O da celulose isolada de árvores naturais. As idades das árvores de terra firme (e uma da várzea) das regiões de Boa Vista (RR), Manaus (AM) e Porto Velho (RO) foram estimadas por um novo método usando radiocarbono (14C), a partir de taxas de crescimento extrapoladas das atividades no CO2 atmosférico, encontrando árvores de 60 a 600 anos. A celulose, isolada pelo método de GREEN (1963), foi convertida a CO2 por reação com HgCl2 e purificado por uma versão modificada do método de RITTENBERG e PONTICORVO (1956), para análise de 18O por espectrometria de massa, com uma precisão melhor que ±0,4‰ V-SMOW. Para análise de 13C, a matéria orgânica foi oxidada a CO2 por combustão com CuO, com precisão melhor que ±0,2‰ PDB. Uma tendência de diluição do 13C do CO2 atmosférico, observada pela correspondente diluição no teor isotópico da celulose, detectada nos estudos similares do hemisfério norte, foi também encontrada nas árvores mais antigas e nas mais jovens que cresceram livres dos efeitos de tamponamento climático da floresta. Efeitos de juventude foram detectados em arvores que se desenvolveram sob a copa da floresta e um efeito associado de menor temperatura foi sugerido para explicar teores muito negativos na madeira. Três períodos de maior umidade relativa ar foram sugeridos pela análise da variação natural da razão isotópica de 18O na celulose com base nos atuais modelos interligando estas variáveis. Em 1700, 1600-50 e nas últimas décadas, a umidade relativa do ar teria sido até 9,4% maior que os outros períodos cobertos por estas árvores. Análises mais sistemáticas deverão ser implantadas para o refino destas inferências, se modo a complementar informações paleoclimáticas daquela região e confirmar evidências de outras áreas como a palinologia e estudos em sedimentos.Qualitative interpretations of recent past climate (±500 years) in the Amazon Basin - a region where no instrumental records for the main climate parameters exist over the last 70 years were surveyed based on the isotopic variation of the 13C and 18O contents in cellulose isolated from natural trees. Trees from terra firme and from várzea environments collected in the regions of Boa Vista (PR), Manaus (AM) and Porto Velho (RO) had their ages estimated by the radiocarbon method extrapolated from growth rates obtained from atmospheric CO2 activities. Tree ages from 60 to 600 years were found. Analysis of the 18O content by mass spectrometry was done on cellulose material isolated through the method described by GREEN (1963). ln this procedure the cellulose was converted to CO2 by a reaction with HgCl2 and purified by using method originally developed by RITTENBERG AND PONTICORVO (1956). The overall precision was better than ±0.4 ‰ V-SMOW. The 13C analysis on the organic matter was done on CO2 collected from an oxidation reaction by using CuO as a reagent. The analytical precision was better than ±0.2 ‰ PDB. A trend, in terms of isotopic dilution of 13C, similar to that observed in the Northern Hemisphere trees was also documented in the older trees in this study. For the younger individuals it was possible to show that they have grown without being influenced by the so-called climatic buffer effect in forests. Juvenile effect was detected in trees growing under the forest canopy and a temperature effect was postulated to explain isotopic depleted values observed in the wood. From the 18O, three periods of elevated relative humidity (near 1700; 1600-1850; recent decades) could be postulated. A more systematic study has been planned for the near future in association with research in the area of palynology and lake sediments, with the aim to corroborate these findings

Contribution of vegetation to the water cycle of the Amazon basin: An isotopic study of plant transpiration and its water source

Previous models which have been developed to explain the water cycle in the Amazon have been unable to locate or quantify sources of direct evaporation (E) in the evapotranspiration process of the basin (E + T). The proportion of water vapor generated by plant transpiration relative to the total forest vapor returned to atmosphere (T/(E + T)) remains unknown. An isotopic technique was developed to record this proportion at two sites in the Amazon basin with contrasting hydrological characteristics. The results show that plant transpiration accounts for the major source of water vapor to evapotranspiration flux. It was also observed that this proportion increased slightly during the dry season at a site in the eastern Amazon, whereas no effect was apparent at a site in the western Amazon where the dry season is less intense.A search for the source of water for plant transpiration was also conducted at an eastern Amazon site using a label pulse chase experiment. The results indicate different water uptake patterns between forest plants and abandoned pasture vegetation. Vines in the forest, as well as shrubs and grasses in the pasture, acquired labeled water from the surface very quickly three days after the soil was irrigated with deuterated water. Fourteen months after label application forest trees evidenced higher labeled water uptake when the label was deeper than 1 m depth in the soil. The roots of pasture grass acquired water deeper in the soil than the roots of shrubs, but neither could access the labeled water when it was deeper than 1 m. Water infiltration rates were consistent with the plant water uptake patterns, with higher values recorded for the pasture than for the forest.This study identifies plant transpiration as a major source of water vapor during the dry season and describes the important function of the eastern Amazon forests as a moisture reservoir (deep soil water) for the dry season

Trophic ecology of citrus pests based on stable isotope analysis

ABSTRACT: Macrodactylus pumilio Burm. (Coleoptera: Scarabeidae) and Naupactus cervinus (Boh.) (Coleoptera: Curculionidae) are considered primary pests in citrus crops in Brazil, causing damage to plants and decreasing productivity. However, few studies investigate the ecology of these insects. In this context, the use of stable isotopes analysis (SIA) emerges as an alternative technique to conventional studies of behavioral ecology because it is faster and may explain feeding behavior based on the food source for each species. Field sampling and laboratory experiments were carried out to examine the changes of carbon and nitrogen stable isotope ratios (δ13C and δ15N) among pests and host plants (C3 citrus and C4 grasses), providing means to examine trophic interactions. Beetles were collected at the municipality of Gavião Peixoto, São Paulo State, identified and kept at 5 °C in saturated saline solution until the SIA. Two patterns for both species were found: δ13C value for N. cervinus was -23.6 ‰ and -13 ‰ for M. pumilio, indicating similarity between the results of δ13C of N. cervinus and citrus plants (-26 ‰) and dependence on grasses (-12 ‰) for M. pumilio individuals. The mean δ15N value was 4.3 and 5.8 ‰ for citrus plants and grass leaves, respectively, and the mean δ15N value was 4.4 ‰ for N. cervinus and 4.9 ‰ for M. pumilio. The results showed a higher affinity of N. cervinus for citrus roots since the larval stage compared with the alternative diet on M. pumilio

Nitrogen availability patterns in white-sand vegetations of Central Brazilian Amazon

Addressing spatial variability in nitrogen (N) availability in the Central Brazilian Amazon, we hypothesized that N availability varies among white-sand vegetation types (campina and campinarana) and lowland tropical forests (dense terra-firme forests) in the Central Brazilian Amazon, under the same climate conditions. Accordingly, we measured soil and foliar N concentration and N isotope ratios (delta(15)N) throughout the campina-campinarana transect and compared to published dense terra-firme forest results. There were no differences between white-sand vegetation types in regard to soil N concentration, C:N ratio and delta(15)N across the transect. Both white-sand vegetation types showed very low foliar N concentrations and elevated foliar C:N ratios, and no significant difference between site types was observed. Foliar delta(15)N was depleted, varying from -9.6 to 1.6aEuro degrees in the white-sand vegetations. The legume Aldina heterophylla had the highest average delta(15)N values (-1.5aEuro degrees) as well as the highest foliar N concentration (2.1%) while the non-legume species had more depleted delta(15)N values and the average foliar N concentrations varied from 0.9 to 1.5% among them. Despite the high variation in foliar delta(15)N among plants, a significant and gradual (15)N-enrichment in foliar isotopic signatures throughout the campina-campinarana transect was observed. Individual plants growing in the campinarana were significantly enriched in (15)N compared to those in campina. In the white-sand N-limited ecosystems, the differentiation of N use seems to be a major cause of variations observed in foliar delta(15)N values throughout the campina-campinarana transect.CNPq, Brazil[PPI2-3105

Using stable isotopes to determine sources of evaporated water to the atmosphere in the Amazon basin

The return of water in vapor form from the land to the atmosphere, via plant transpiration and evaporation, is fundamental for the maintenance of the regional water cycle in the Amazon basin. Whereas transpiration, the dominant process, has the extensive vegetation cover as a large single source, evaporation can have several sources, and their relative importance and location are poorly known. The isotopic composition (δ 18O and δD) of water from various sources was used to see whether or not specific sources of water vapor to the atmosphere could be determined. It is well established that natural waters fall on a line called the meteoric water line (MWL; the regression of δ 18O × δD), with slope equal to eight and an intercept equal to ten. When a water body loses water via evaporation the slope become smaller than eight, typically 5–6. We estimated the slope of the regression of δ 18O × δD for several potential sources. We analyzed 1273 samples: 500 of rainfall, 409 of river water, 134 of lake water, 164 of soil water, 40 of throughfall and stemflow water, and 26 of shallow ground-water. We found that large rivers and lakes are likely contributors of evaporated water to the atmosphere. However, as they cover only a small area of the basin, other sources are needed. Probably, evaporated water originates from several small sources that were not detected by the isotopic composition of our data

Carbon and nitrogen stable isotope values, and C/N atomic values for <i>Mellopsis doucasae</i>.

<p>Mean ± standard deviation of (a) <i>δ</i>¹⁵N, (b) <i>δ</i>¹³C, and (c) C/N atomic values from the following treatments: Fuel Et. 15—preserved in fuel ethanol for 15 days; Fuel Et. 60—preserved in fuel ethanol for 60 days; Com.Et. 15—preserved in 92.8% commercial ethanol for 15 days; Com.Et. 60—preserved in 92.8% commercial ethanol for 60 days; Frozen 15—frozen for 15 days; Frozen 60—frozen for 60 days; Control—freshly processed material (highlighted in gray). Different letters indicate significant differences between treatment groups (P < 0.05). All preservation methods resulted in significant ¹⁵N depletion compared to controls.</p

Carbon and nitrogen stable isotope values, and C/N atomic values for <i>Phoremia</i> sp.

<p>Mean ± standard deviation of (a) <i>δ</i>¹⁵N, (b) <i>δ</i>¹³C, and (c) C/N atomic values from the following treatments: Fuel Et. 15—preserved in fuel ethanol for 15 days; Fuel Et. 60—preserved in fuel ethanol for 60 days; Com. Et. 15—preserved in 92.8% commercial ethanol for 15 days; Com. Et. 60—preserved in 92.8% commercial ethanol for 60 days; Frozen 15—frozen for 15 days; Frozen 60—frozen for 60 days; Control—freshly processed material (highlighted in gray). Different letters indicate significant differences between treatment groups (P < 0.05).</p

Land Use Influences Niche Size and the Assimilation of Resources by Benthic Macroinvertebrates in Tropical Headwater Streams.

It is well recognized that assemblage structure of stream macroinvertebrates changes with alterations in catchment or local land use. Our objective was to understand how the trophic ecology of benthic macroinvertebrate assemblages responds to land use changes in tropical streams. We used the isotope methodology to assess how energy flow and trophic relations among macroinvertebrates were affected in environments affected by different land uses (natural cover, pasture, sugar cane plantation). Macroinvertebrates were sampled and categorized into functional feeding groups, and available trophic resources were sampled and evaluated for the isotopic composition of 13C and 15N along streams located in the Cerrado (neotropical savanna). Streams altered by pasture or sugar cane had wider and more overlapped trophic niches, which corresponded to more generalist feeding habits. In contrast, trophic groups in streams with native vegetation had narrower trophic niches with smaller overlaps, suggesting greater specialization. Pasture sites had greater ranges of resources exploited, indicating higher trophic diversity than sites with natural cover and sugar cane plantation. We conclude that agricultural land uses appears to alter the food base and shift macroinvertebrate assemblages towards more generalist feeding behaviors and greater overlap of the trophic niches