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Comprehension of the benefits involved in mutualisms is crucial to disentangle the role of interactions in the structure and functioning of populations, communities and ecosystems. In ant-plant mutualisms, benefits provided by plants to ants are immediately recognizable, but reverse benefits are less obvious, conditional and accumulate over longer time spans. Here we tested the hypothesis that the ant Azteca muelleri simultaneously provides multiple benefits to its host plant (Cecropia glaziovii), ultimately increasing plant performance. We planted seedlings and experimentally prevented ant colonization for half of them. Over 4.5 years we quantified the effects of ant presence or absence on plant growth, herbivory levels, fungal infection, fertilization via ant debris and changes in defense strategies. Ant colonization increased plant height by 125% compared to ant-free plants. Such an improvement in plant performance can be explained because plants with ants faced less herbivory, lower prevalence of pathogenic fungi, invested less in foliar trichomes and had more foliar nitrogen. We thus confirmed that ant mutualists provide cumulative benefits including nutritional benefits, effective defense and lower investment into other defenses – which result in increased plant growth. We highlight the importance of long-term experiments that simultaneously evaluate a multiplicity of potential ant effects to better understand their relative contribution to the performance of the mutualistic partner.

Land use changes in tropical forests intensified during the 20th century, mainly caused by deforestation for agricultural uses, which had an overwhelming influence on bird communities. However, there is a knowledge gap on how these historical anthropogenic changes have impacted habitat use and diet of tropical birds. On this regard, isotopic analysis can be useful since δ13C and δ15N values provides information of habitat and food resource use, and also isotopic niche of species. Here, we aimed to evaluate whether changes in landscape composition caused by centenary anthropogenic impacts have influenced the isotopic signatures and niche widths of birds in a Neotropical biodiversity hotspot, the Atlantic Forest, in southeastern Brazil. Our results showed that all bird guilds (frugivore, granivore, insectivore, nectarivore, omnivore) presented a large reduction (28-70%) in niche width from the twentieth century until contemporary. These reductions are likely associated with historical impacts (e.g. fragmentation and habitat loss), which are responsible for a decrease in the availability of food resources. There was also a reduction in the mean values of δ15N over the years in all guilds, which might be related to the expansion of agricultural areas and the increment in use of synthetic nitrogen fertilizers. Albeit some of the analyzed species are considered diet and habitat generalists, all of them showed to have been strongly influenced by anthropogenic actions throughout the years. Since these birds perform ecological functions in fragmented areas, we suggest an increase in conservation actions that ensure they do not vanish in the near future.

The origin of the organic matter was assessed in two estuaries in Eastern Amazon, Brazilian Northern Coast, under different hydrodynamic conditions. The isotopic composition ( δ 13 C; δ 15 N) and the elementary ratio (C/N) were determined in the sediments, in the suspended particulate material (SPM), as well as in the phytoplankton, plants and oysters. The ( δ 13 C) values have indicated that the sedimentary organic matter is a terrestrial–marine mix composed of terrigenous organic matter (75%) in the Para River estuary, as well as of marine organic matter (60%) in the Mocajuba River estuary. The estimates of sources recorded through δ 13 C data were partially confirmed through the correlation ( δ 15 N) versus C/N, which reflects the action of diagenetic and biological processes on the organic matter composition control. On the other hand, the high carbon content ( δ 13 C) found in Para River estuary samples is conclusive because it shows isotopic changes due to the anthropogenic processes in the region.

This study investigated two estuaries on the northern coast of Brazil submitted to different anthropic activities. The main objective was to assess the use of oysters (Crassostrea gasar and Paxyodon ponderosus) and phytoplankton as bioindicators of environmental contamination. Water, sediments, phytoplankton and oysters were chemically analyzed by ICP-OES and ICP-MS. The source for metal bioaccumulation in oysters and phytoplankton was assessed using BSAF (Biota Sediment Accumulation Factor) and the isotropic relations of stable carbon ( δ 13 C and δ 15 N). The oyster-sediment BSAF showed bioaccumulation of Mn, Cu, Zn, Se, Sr, As, Cd and Ba, which was supported by the correlations of Fe, Mn, Cu, Zn, Se, Sr, Al, Ba and Pb with the isotopes ( δ 15 N and δ 13 C), which confirmed bioaccumulation as well as biodilution and biomagnification in oysters and phytoplankton. That reflects the efficiency of organisms in bioconcentrating metals and their capacity as bioindicators of contamination.

Made available in DSpace on 2018-11-26T16:27:44Z (GMT). No. of bitstreams: 0 Previous issue date: 2016-03-15 Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) CIRAD USP-COFECUB AGREENIUM (Plantrotem project) SOERE F-ORE-T Agence Nationale de la Recherche Adaptive strategies to improve tree water-use efficiency (WUE) are required to meet the global demand for wood in a future drier climate. A large-scale throughfall exclusion experiment was set up in Brazil to study the interaction between water status and potassium (K) or sodium (Na) availability on the ecophysiology of Eucalyptus grandis trees. This experiment focused primarily on the changes in aboveground net primary production, stand water use, phloem sap and leaf delta C-13, net CO2 assimilation and stomatal conductance. The correlations between these response variables were determined to gain insight into the factors controlling water-use efficiency in tropical eucalypt plantations. The intrinsic WUE in individual leaves (the ratio of net CO2 assimilation to stomatal conductance) was estimated at a very short time scale from the leaf gas exchange. Sap flow measurements were carried out to assess the WUE for stem wood production (the ratio of wood biomass increment to stand water use). Averaged over the two water supply regimes, the stemwood biomass 3 years after planting was 173% higher in trees fertilized with K and 79% higher in trees fertilized with Na than in trees with no K and Na addition. Excluding 37% of the throughfall reduced stemwood production only for trees fertilized with K. Total canopy transpiration between 1 and 3 years after planting increased from about 750 to 1300 mm y(-1) in response to K fertilization with a low influence of the water supply regime. K fertilization increased WUE for stemwood production by approx. 60% with or without throughfall exclusion. There was a strong positive correlation between phloem sap delta C-13 and short-term leaf-level intrinsic WUE. Whatever the water and nutrient supply regime, the gas exchange WUE estimates were not correlated with WUE for stemwood production. Phloem sap delta C-13 and leaf delta C-13 were therefore not valuable proxies of WUE for stemwood production. The allocation pattern in response to nutrient and water supply appeared to be a major driver of WUE for stemwood production. In areas with very deep tropical soils and annual rainfall

Recycling of respiratory CO 2 was calculated with a previously developed model using stable isotope ratios and concentration values of ambient CO 2 . Measurements were taken at two different tropical forests in the Amazon basin during the dry season. One forest (Reserva Ducke) was characterized by a closed canopy with lower wind speeds, while the other (Fazenda Vitoria) had a relatively open canopy and higher wind speeds. The closed canopy forest had up to 39% of its respiratory CO 2 recycled at 18 m above the forest floor. Percent recycling in this forest was related to wind speed at the date of collection. Calculations of recycling on the open canopy forest gave values rnaging from 0 to negative. This forest may have ambient CO 2 contamination from charcoal kilns in a nearby town. Thus, calculations of recycling based on isotopic composition of ambient CO 2 for this forest may be incorrect.

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 (δ18O 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 δ18O × 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 δ18O × 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.

Whole-body protein kinetics was measured with 15N-glycine in five young adult male volunteers. Each subject participated twice, being his own control. They received a Brazilian rice and bean diet with usual Brazilian protein intake of 0.8 g/kg/d, but low (−30%) or high (+30%) in non-protein calories. The subjects were fed, at random, for 7–8 days the low or high calorie diet. During the last three days samples of food, feces and urine were collected for nitrogen balance. On the last day, rates of nitrogen flux, protein synthesis and degradation in the whole body were estimed from 15N excretion in urinary ammonia and total urea (excreted plus retained within the body) during a 9-h period after administration of oral single dose of 15N-glycine. During the kinetic study the subjects received 112 of the total food intake hourly. The results were for the low and high calorie intakes respectively: nitrogen balance, mg/kg/d, 2±21 (mean±SD) and 24±16 (p

A critical factor in estimating the contribution of tropical deforestation to nutrient mobilization and to CO2 build-up in the atmosphere is the amount of biomass available to burn. The biomass data for Brazil, a major site for deforestation, are few and of uncertain accuracy. Recent international agreements, however, require national inventories of sources and sinks for atmospheric greenhouse gases; such inventories will need better estimates of biomass and their uncertainties. To provide additional information on biomass uncertainty and on forest structure in southwestern Amazonia, a region of active deforestation, we measured in 1988 the diameter, bole and canopy heights of 474 trees covering a total of 1 ha (10 000 m2) in the Ecological Station of the Samuel Hydroelectric Reservoir in Rondonia (845′S, 63°23′W). Using allometric equations based on destructively sampled trees, we estimated the largest biomass component, standing alive aboveground biomass (SAAB), as 285 Mg (dry weight) ha−1. Fallen trunks and litter were 30 Mg and 10 Mg ha−1, respectively. The sum of these components, 325 Mg ha−1, is an underestimate of the total biomass because the biomass of roots, vines, shrubs, and small trees was not measured. Measurement error of SAAB is ± 20%, ± 57 Mg ha−1 about the mean (95% confidence interval), as derived by a Monte Carlo simulation. The SAAB distribution among trees is highly skewed: 3% of the trees contain 50% of the SAAB. For forests of similar distributions, sampling units typically used for biomass estimates (less than 2000 m2) will usually produce biomass estimates significantly different from those of larger units. Based on subsamples of our data, sampling units of 1000 m2 or smaller had at least a 75% chance of being outside the confidence interval of the global mean (228–342 Mg ha−1) derived from Monte Carlo simulation. To improve estimates of SAAB in similar forests a sampling program should focus on emergent and large canopy trees, the dominant contributors to biomass.