• Energy Research

Flood-tolerant tree species of the Amazonian floodplain forests are subjected to an annual dry period of variable severity imposed when low river-water levels coincide with minimal precipitation. Although the responses of these species to flooding have been examined extensively, their responses to drought, in terms of phenology, growth and physiology, have been neglected hitherto, although some information is found in publications that focus on flooding.The present review examines the dry phase of the annual flooding cycle. It consolidates existing knowledge regarding responses to drought among adult trees and seedlings of many Amazonian floodplain species.Flood-tolerant species display variable physiological responses to dry periods and drought that indicate desiccation avoidance, such as reduced photosynthetic activity and reduced root respiration. However, tolerance and avoidance strategies for drought vary markedly among species. Drought can substantially decrease growth, biomass and photosynthetic activity among seedlings in field and laboratory studies. When compared with the responses to flooding, drought can impose higher seedling mortality and slower growth rates, especially among evergreen species. Results indicate that tolerance and avoidance strategies for drought vary markedly between species. Both seedling recruitment and photosynthetic activity are affected by drought,For many species, the effects of drought can be as important as flooding for survival and growth, particularly at the seedling phase of establishment, ultimately influencing species composition. In the context of climate change and predicted decreases in precipitation in the Amazon Basin, the effects of drought on plant physiology and species distribution in tropical floodplain forest ecosystems should not be overlooked.

Abstract Large floodplains are complex ecosystems at the land–water boundary. Because of rainy and dry seasons, most tropical floodplains are subjected to annual water-level fluctuations. During typical low-water periods, extensive areas of the floodplains are dry. However, relatively small geomorphological differences within the boundaries of the floodplains result in comparatively large differences in the length and depth of inundation and, in turn, the establishment of distinct plant communities, called macrohabitats. The specific ecological conditions of these macrohabitats have to be taken into consideration in the development of sustainable management methods and protection measures. Extreme floods and droughts have very strong effects on flora and fauna. The low hydrological buffer capacity of floodplains makes them vulnerable to anthropogenic changes in hydrology and to the impacts of global climate change. This study presents a macrohabitat classification system that has been applied to three large Brazilian floodplains: the forested Amazonian varzeas and igapos, and the savanna floodplains of the upper Paraguai River (Pantanal of Mato Grosso). Examples are provided to demonstrate the applicability of this system in comparative inter- and intra-wetland studies and therefore its utility in assessing environmental changes, including those arising from global climate change. Our approach can also be used to guide the implementation of sustainable management methods and as a focal point for the development of environmental legislation.

Abstract Tropical floodplain forests are productive and diverse ecosystems for which there is scant data on biomass, carbon sequestration, and potential abiotic and human drivers. We used a regression approach to test the effects of seasonal flood duration, forest age, and livestock activity on aboveground biomass (AGB) and annual biomass accumulation (ABA) in 49 plots of 0.1 ha in secondary floodplain forests of the Lower Amazon over nine years. AGB averaged 226 ± 87 Mg ha−1 among forests 30–120 years old. An intermediate peak model explained spatial variation in AGB, peaking in moderately flooded (70–140 d y−1) forests. Flood duration was the key explanatory factor for AGB across all plots. In contrast, forest age and its interaction with flood duration affected net ABA, which declined from 10.3 ± 4.3 to −6.2 ± 11.1 Mg ha−1 y−1 with increasing age. Tree diameter growth comprised 95 ± 4% of total ABA, which declined with increasing flood duration and increasing forest age. Overall, forests had a high capacity to capture carbon, accumulating 16.4 ± 7.1 Mg ha−1 y−1 in AGB, but had high turnover of biomass at 76 ± 81% of AGB per year. There was no strong evidence for differences in biomass accumulation due to livestock activity. We fill a major geographical gap for ground-based data on biomass of flooded forests, which comprise 11% of the Amazon Basin, and also provide an example of community-based monitoring for carbon storage in human-dominated tropical floodplain ecosystems.

We grew leaves of Montrichardia arborescens in four microcosm chambers with different temperatures and CO2 concentrations simulating the scenarios of expected climate change. These leaves were used to feed shredders (Phylloicus) and to assess the effects of changes in leaf quality on their consumption. We also evaluated the effect of detritus conditioning by microorganisms on leaf consumption. We hypothesized that leaves of plants grown under different environmental conditions could offer substrata of different qualities to microorganisms colonizing them, and, consequently the shredder consumption rate would differ according to leaf conditioning. The microcosm chambers for plant growth simulated three different combined air temperature and CO2 scenarios, relative to the real-time (control) current conditions in Manaus-Brazil. The leaf consumption experiment was performed only in the control chamber. Specific leaf area was positively affected by predicted climate change, while tannins were detected only in leaves of plants grown in chambers simulating a changed climate. Other leaf detritus parameters were similar in all chambers. Shredders showed higher consumption rates in leaves developed under mild and intermediate conditions in relation to control. Shredder consumption was similar in conditioned and unconditioned treatments. Thus, shredder consumption was influenced more by the intrinsic quality of leaves than by microorganism conditioning, but we were not able to show effects of climate change on leaf quality that could explain differences in shredder consumption.

Abstract. The Amazon Basin plays key roles in the carbon and water cycles, climate change, atmospheric chemistry, and biodiversity. It has already been changed significantly by human activities, and more pervasive change is expected to occur in the coming decades. It is therefore essential to establish long-term measurement sites that provide a baseline record of present-day climatic, biogeochemical, and atmospheric conditions and that will be operated over coming decades to monitor change in the Amazon region, as human perturbations increase in the future. The Amazon Tall Tower Observatory (ATTO) has been set up in a pristine rain forest region in the central Amazon Basin, about 150 km northeast of the city of Manaus. Two 80 m towers have been operated at the site since 2012, and a 325 m tower is nearing completion in mid-2015. An ecological survey including a biodiversity assessment has been conducted in the forest region surrounding the site. Measurements of micrometeorological and atmospheric chemical variables were initiated in 2012, and their range has continued to broaden over the last few years. The meteorological and micrometeorological measurements include temperature and wind profiles, precipitation, water and energy fluxes, turbulence components, soil temperature profiles and soil heat fluxes, radiation fluxes, and visibility. A tree has been instrumented to measure stem profiles of temperature, light intensity, and water content in cryptogamic covers. The trace gas measurements comprise continuous monitoring of carbon dioxide, carbon monoxide, methane, and ozone at five to eight different heights, complemented by a variety of additional species measured during intensive campaigns (e.g., VOC, NO, NO2, and OH reactivity). Aerosol optical, microphysical, and chemical measurements are being made above the canopy as well as in the canopy space. They include aerosol light scattering and absorption, fluorescence, number and volume size distributions, chemical composition, cloud condensation nuclei (CCN) concentrations, and hygroscopicity. In this paper, we discuss the scientific context of the ATTO observatory and present an overview of results from ecological, meteorological, and chemical pilot studies at the ATTO site.

Climate change may affect the chemical composition of riparian leaf litter and, aquatic organisms and, consequently, leaf breakdown. We evaluated the effects of different scenarios combining increased temperature and carbon dioxide (CO2) on leaf detritus of Hevea spruceana (Benth) Müll. and decomposers (insect shredders and microorganisms). We hypothesized that simulated climate change (warming and elevated CO2) would: i) decrease leaf-litter quality, ii) decrease survival and leaf breakdown by shredders, and iii) increase microbial leaf breakdown and fungal biomass. We performed the experiment in four microcosm chambers that simulated air temperature and CO2 changes in relation to a real-time control tracking current conditions in Manaus, Amazonas, Brazil. The experiment lasted seven days. During the experiment mean air temperature and CO2 concentration ranged from 26.96 ± 0.98ºC and 537.86 ± 18.36 ppmv in the control to 31.75 ± 0.50ºC and 1636.96 ± 17.99 ppmv in the extreme chamber, respectively. However, phosphorus concentration in the leaf litter decreased with warming and elevated CO2. Leaf quality (percentage of carbon, nitrogen, phosphorus, cellulose and lignin) was not influenced by soil flooding. Fungal biomass and microbial leaf breakdown were positively influenced by temperature and CO2 increase and reached their highest values in the intermediate condition. Both total and shredder leaf breakdown, and shredder survival rate were similar among all climatic conditions. Thus, low leaf-litter quality due to climate change and higher leaf breakdown under intermediate conditions may indicate an increase of riparian metabolism due to temperature and CO2 increase, highlighting the risk (e.g., decreased productivity) of global warming for tropical streams.

Abstract Tropical peatlands are among the most carbon-dense terrestrial ecosystems yet recorded. Collectively, they comprise a large but highly uncertain reservoir of the global carbon cycle, with wide-ranging estimates of their global area (441 025–1700 000 km2) and below-ground carbon storage (105–288 Pg C). Substantial gaps remain in our understanding of peatland distribution in some key regions, including most of tropical South America. Here we compile 2413 ground reference points in and around Amazonian peatlands and use them alongside a stack of remote sensing products in a random forest model to generate the first field-data-driven model of peatland distribution across the Amazon basin. Our model predicts a total Amazonian peatland extent of 251 015 km2 (95th percentile confidence interval: 128 671–373 359), greater than that of the Congo basin, but around 30% smaller than a recent model-derived estimate of peatland area across Amazonia. The model performs relatively well against point observations but spatial gaps in the ground reference dataset mean that model uncertainty remains high, particularly in parts of Brazil and Bolivia. For example, we predict significant peatland areas in northern Peru with relatively high confidence, while peatland areas in the Rio Negro basin and adjacent south-western Orinoco basin which have previously been predicted to hold Campinarana or white sand forests, are predicted with greater uncertainty. Similarly, we predict large areas of peatlands in Bolivia, surprisingly given the strong climatic seasonality found over most of the country. Very little field data exists with which to quantitatively assess the accuracy of our map in these regions. Data gaps such as these should be a high priority for new field sampling. This new map can facilitate future research into the vulnerability of peatlands to climate change and anthropogenic impacts, which is likely to vary spatially across the Amazon basin.