The mobilization and transport of newly fixed carbon are driven by plant water use in an experimental rainforest under drought.

Non-structural carbohydrates (NSCs) are building blocks for biomass and fuel metabolic processes. However, it remains unclear how tropical forests mobilize, export, and transport NSCs to cope with extreme droughts. We combined drought manipulation and ecosystem 13CO2 pulse-labeling in an enclosed rainforest at Biosphere 2, assessed changes in NSCs, and traced newly assimilated carbohydrates in plant species with diverse hydraulic traits and canopy positions.

Effects of drought and recovery on soil volatile organic compound fluxes in an experimental rainforest.

Drought can affect the capacity of soils to emit and consume biogenic volatile organic compounds (VOCs). Here we show the impact of prolonged drought followed by rewetting and recovery on soil VOC fluxes in an experimental rainforest. Under wet conditions the rainforest soil acts as a net VOC sink, in particular for isoprenoids, carbonyls and alcohols.

Leaf-level metabolic changes in response to drought affect daytime CO2 emission and isoprenoid synthesis pathways.

In the near future, climate change will cause enhanced frequency and/or severity of droughts in terrestrial ecosystems, including tropical forests. Drought responses by tropical trees may affect their carbon use, including production of volatile organic compounds (VOCs), with implications for carbon cycling and atmospheric chemistry that are challenging to predict. It remains unclear how metabolic adjustments by mature tropical trees in response to drought will affect their carbon fluxes associated with daytime CO2 production and VOC emission.

Deep roots mitigate drought impacts on tropical trees despite limited quantitative contribution to transpiration.

Deep rooting is considered a central drought-mitigation trait with vast impact on ecosystem water cycling. Despite its importance, little is known about the overall quantitative water use via deep roots and dynamic shifts of water uptake depths with changing ambient conditions. Knowledge is especially sparse for tropical trees.

Tracing plant source water dynamics during drought by continuous transpiration measurements: An in-situ stable isotope approach.

The isotopic composition of xylem water (δ ) is of considerable interest for plant source water studies. In-situ monitored isotopic composition of transpired water (δ ) could provide a nondestructive proxy for δ -values. Using flow-through leaf chambers, we monitored 2-hourly δ -dynamics in two tropical plant species, one canopy-forming tree and one understory herbaceous species.

Chiral monoterpenes reveal forest emission mechanisms and drought responses.

Monoterpenes (CH) are emitted in large quantities by vegetation to the atmosphere (>100 TgC year), where they readily react with hydroxyl radicals and ozone to form new particles and, hence, clouds, affecting the Earth's radiative budget and, thereby, climate change. Although most monoterpenes exist in two chiral mirror-image forms termed enantiomers, these (+) and (-) forms are rarely distinguished in measurement or modelling studies. Therefore, the individual formation pathways of monoterpene enantiomers in plants and their ecological functions are poorly understood.

Ecosystem fluxes during drought and recovery in an experimental forest.

Severe droughts endanger ecosystem functioning worldwide. We investigated how drought affects carbon and water fluxes as well as soil-plant-atmosphere interactions by tracing CO and deep water HO label pulses and volatile organic compounds (VOCs) in an enclosed experimental rainforest. Ecosystem dynamics were driven by different plant functional group responses to drought.

Microbial Communities and Interactions of Nitrogen Oxides With Methanogenesis in Diverse Peatlands of the Amazon Basin.

Tropical peatlands are hotspots of methane (CH) production but present high variation and emission uncertainties in the Amazon region. This is because the controlling factors of methane production in tropical peats are not yet well documented. Although inhibitory effects of nitrogen oxides (NO ) on methanogenic activity are known from pure culture studies, the role of NO in the methane cycling of peatlands remains unexplored.

Rainforest-to-pasture conversion stimulates soil methanogenesis across the Brazilian Amazon.

The Amazon rainforest is a biodiversity hotspot and large terrestrial carbon sink threatened by agricultural conversion. Rainforest-to-pasture conversion stimulates the release of methane, a potent greenhouse gas. The biotic methane cycle is driven by microorganisms; therefore, this study focused on active methane-cycling microorganisms and their functions across land-use types.

Empirical evidence for resilience of tropical forest photosynthesis in a warmer world.

Tropical forests may be vulnerable to climate change if photosynthetic carbon uptake currently operates near a high temperature limit. Predicting tropical forest function requires understanding the relative contributions of two mechanisms of high-temperature photosynthetic declines: stomatal limitation (H1), an indirect response due to temperature-associated changes in atmospheric vapour pressure deficit (VPD), and biochemical restrictions (H2), a direct temperature response. Their relative control predicts different outcomes-H1 is expected to diminish with stomatal responses to future co-occurring elevated atmospheric [CO], whereas H2 portends declining photosynthesis with increasing temperatures.

Belowground changes to community structure alter methane-cycling dynamics in Amazonia.

Amazonian rainforest is undergoing increasing rates of deforestation, driven primarily by cattle pasture expansion. Forest-to-pasture conversion has been associated with increases in soil methane (CH) emission. To better understand the drivers of this change, we measured soil CH flux, environmental conditions, and belowground microbial community structure across primary forests, cattle pastures, and secondary forests in two Amazonian regions.

Highly sampled measurements in a controlled atmosphere at the Biosphere 2 Landscape Evolution Observatory.

Land-atmosphere interactions at different temporal and spatial scales are important for our understanding of the Earth system and its modeling. The Landscape Evolution Observatory (LEO) at Biosphere 2, managed by the University of Arizona, hosts three nearly identical artificial bare-soil hillslopes with dimensions of 11 × 30 m (1 m depth) in a controlled and highly monitored environment within three large greenhouses. These facilities provide a unique opportunity to explore these interactions.

Methanogens and Methanotrophs Show Nutrient-Dependent Community Assemblage Patterns Across Tropical Peatlands of the Pastaza-Marañón Basin, Peruvian Amazonia.

Tropical peatlands are globally important carbon reservoirs that play a crucial role in fluxes of atmospheric greenhouse gases. Amazon peatlands are expected to be large source of atmospheric methane (CH) emissions, however little is understood about the rates of CH flux or the microorganisms that mediate it in these environments. Here we studied a mineral nutrient gradient across peatlands in the Pastaza-Marañón Basin, the largest tropical peatland in South America, to describe CH fluxes and environmental factors that regulate species assemblages of methanogenic and methanotrophic microorganisms.

Author Correction: Biotic soil-plant interaction processes explain most of hysteretic soil CO efflux response to temperature in cross-factorial mesocosm experiment.

An amendment to this paper has been published and can be accessed via a link at the top of the paper.

Biotic soil-plant interaction processes explain most of hysteric soil CO efflux response to temperature in cross-factorial mesocosm experiment.

Ecosystem carbon flux partitioning is strongly influenced by poorly constrained soil CO efflux (F). Simple model applications (Arrhenius and Q) do not account for observed diel hysteresis between F and soil temperature. How this hysteresis emerges and how it will respond to variation in vegetation or soil moisture remains unknown.

Methane emissions from tree stems: a new frontier in the global carbon cycle.

Tree stems from wetland, floodplain and upland forests can produce and emit methane (CH ). Tree CH stem emissions have high spatial and temporal variability, but there is no consensus on the biophysical mechanisms that drive stem CH production and emissions. Here, we summarize up to 30 opportunities and challenges for stem CH emissions research, which, when addressed, will improve estimates of the magnitudes, patterns and drivers of CH emissions and trace their potential origin.

Isoprene emission structures tropical tree biogeography and community assembly responses to climate.

The prediction of vegetation responses to climate requires a knowledge of how climate-sensitive plant traits mediate not only the responses of individual plants, but also shifts in the species and functional compositions of whole communities. The emission of isoprene gas - a trait shared by one-third of tree species - is known to protect leaf biochemistry under climatic stress. Here, we test the hypothesis that isoprene emission shapes tree species compositions in tropical forests by enhancing the tolerance of emitting trees to heat and drought.

Phytogenic biosynthesis and emission of methyl acetate.

Acetylation of plant metabolites fundamentally changes their volatility, solubility and activity as semiochemicals. Here we present a new technique termed dynamic (13) C-pulse chasing to track the fate of C1-3 carbon atoms of pyruvate into the biosynthesis and emission of methyl acetate (MA) and CO2 . (13) C-labelling of MA and CO2 branch emissions respond within minutes to changes in (13) C-positionally labelled pyruvate solutions fed through the transpiration stream.

Floral CO(2) emission may indicate food abundance to nectar-feeding moths.

As part of a study of the roles of the sensory subsystem devoted to CO(2) in the nectar-feeding moth Manduca sexta, we investigated CO(2) release and nectar secretion by flowers of Datura wrightii, a preferred hostplant of Manduca. Datura flowers open at dusk and wilt by the following noon. During the first hours after dusk, when Manduca feeds, the flowers produce considerable amounts of nectar and emit levels of CO(2) that should be detectable by moths nearby.