Naomi Levine

Overview of the Large-Scale Biosphere–Atmosphere Experiment in Amazonia Data Model Intercomparison Project (LBA-DMIP)

Publisher: Elsevier BV

Date: 12-2013

DOI: 10.1016/J.AGRFORMET.2013.04.030

The Microbiological Drivers of Temporally Dynamic Dimethylsulfoniopropionate Cycling Processes in Australian Coastal Shelf Waters

Publisher: Frontiers Media SA

Date: 15-06-2022

DOI: 10.3389/FMICB.2022.894026

Abstract: The organic sulfur compounds dimethylsulfoniopropionate (DMSP) and dimethyl sulfoxide (DMSO) play major roles in the marine microbial food web and have substantial climatic importance as sources and sinks of dimethyl sulfide (DMS). Seasonal shifts in the abundance and ersity of the phytoplankton and bacteria that cycle DMSP are likely to impact marine DMS (O) (P) concentrations, but the dynamic nature of these microbial interactions is still poorly resolved. Here, we examined the relationships between microbial community dynamics with DMS (O) (P) concentrations during a 2-year oceanographic time series conducted on the east Australian coast. Heterogenous temporal patterns were apparent in chlorophyll a (chl a ) and DMSP concentrations, but the relationship between these parameters varied over time, suggesting the phytoplankton and bacterial community composition were affecting the net DMSP concentrations through differential DMSP production and degradation. Significant increases in DMSP were regularly measured in spring blooms dominated by predicted high DMSP-producing lineages of phytoplankton ( Heterocapsa , Prorocentrum , Alexandrium , and Micromonas ), while spring blooms that were dominated by predicted low DMSP-producing phytoplankton ( Thalassiosira ) demonstrated negligible increases in DMSP concentrations. During elevated DMSP concentrations, a significant increase in the relative abundance of the key copiotrophic bacterial lineage Rhodobacterales was accompanied by a three-fold increase in the gene, encoding the first step of DMSP demethylation ( dmdA ). Significant temporal shifts in DMS concentrations were measured and were significantly correlated with both fractions (0.2–2 μm and & μm) of microbial DMSP lyase activity. Seasonal increases of the bacterial DMSP biosynthesis gene ( dsyB ) and the bacterial DMS oxidation gene ( tmm ) occurred during the spring-summer and coincided with peaks in DMSP and DMSO concentration, respectively. These findings, along with significant positive relationships between dsyB gene abundance and DMSP, and tmm gene abundance with DMSO, reinforce the significant role planktonic bacteria play in producing DMSP and DMSO in ocean surface waters. Our results highlight the highly dynamic nature and myriad of microbial interactions that govern sulfur cycling in coastal shelf waters and further underpin the importance of microbial ecology in mediating important marine biogeochemical processes.

Rapid reductions in population size drive evolutionary divergence in diatoms

Publisher: Cold Spring Harbor Laboratory

Date: 27-09-2022

DOI: 10.1101/2022.09.25.509407

Abstract: Unicellular photosynthetic marine microbes, or phytoplankton, make up the base of marine food webs and drive global nutrient cycles. Despite their key roles in ecology and biogeochemistry, we have a limited understanding of how the basic features of their demographics along with dynamic environments affect trait evolution. A key feature of diatom ecology is frequent extreme reductions in population size, both as part of their bloom-and-bust growth dynamics, and as a result of living within ocean currents. Here, we use experimental evolution to understand which metabolic pathways and functions readily ersify in diatom populations following population bottleneck events. We subjected replicate populations of six genetically distinct diatom strains to population bottlenecks and then subsequently allowed them to evolve as large populations in the absence of environmental change. Phylogenies and global expression of orthologs were generally strain-specific, indicating that vertical (inherited) evolutionary constraints largely determine the occupation of specific locations in the transcriptional landscape (i.e. tran-scape). Following bottlenecks and subsequent evolution as large populations, transcriptional networks of most populations returned to those of the ancestral population. However, at least one replicate population per lineage migrated in the tran-scape, demonstrating that evolutionary changes in gene expression patterns and transcriptional relationships can be driven by population bottlenecks even in the absence of environmental change. Importantly, the orthologs dominating transcriptional ersification resided in common, central metabolic pathways. These data advance our understanding of constraints and patterns of transcriptional relationships underlying trait evolution in microbes that drive global food webs and elemental cycles.

Multivariate trait analysis reveals diatom plasticity constrained to a reduced set of biological axes

Publisher: Springer Science and Business Media LLC

Date: 25-10-2021

DOI: 10.1038/S43705-021-00062-8

Abstract: Trait-based approaches to phytoplankton ecology have gained traction in recent decades as phenotypic traits are incorporated into ecological and biogeochemical models. Here, we use high-throughput phenotyping to explore both intra- and interspecific constraints on trait combinations that are expressed in the cosmopolitan marine diatom genus Thalassiosira . We demonstrate that within Thalassiosira , phenotypic ersity cannot be predicted from genotypic ersity, and moreover, plasticity can create highly ergent phenotypes that are incongruent with taxonomic grouping. Significantly, multivariate phenotypes can be represented in reduced dimensional space using principal component analysis with 77.7% of the variance captured by two orthogonal axes, here termed a ‘trait-scape’. Furthermore, this trait-scape can be recovered with a reduced set of traits. Plastic responses to the new environments expanded phenotypic trait values and the trait-scape, however, the overall pattern of response to the new environments was similar between strains and many trait correlations remained constant. These findings demonstrate that trait-scapes can be used to reveal common constraints on multi-trait plasticity in phytoplankton with ergent underlying phenotypes. Understanding how to integrate trait correlational constraints and trade-offs into theoretical frameworks like biogeochemical models will be critical to predict how microbial responses to environmental change will impact elemental cycling now and into the future.

Multitrait diversification in marine diatoms in constant and warmed environments

Publisher: Cold Spring Harbor Laboratory

Date: 10-04-2022

DOI: 10.1101/2022.04.08.487611

Abstract: Phytoplankton are photosynthetic marine microbes that affect food webs, nutrient cycles, and climate regulation. Their roles are determined by a correlated set of phytoplankton functional traits including cell size, chlorophyll content, and cellular composition. Here, we explore how interrelated trait values and correlations evolve. Because both chance events and natural selection contribute to phytoplankton trait evolution, we used population bottlenecks to ersify six genotypes of Thalassiosirid diatoms. We then evolved them in two environments where natural selection could act on this ersity. Interspecific variation and within-species evolution were visualized for nine traits and their correlations using reduced axes (a trait-scape). Shifts in both trait values and correlations, resulting in movement of evolving populations on the trait-scape, occurred in both environments, and were more frequent under environmental change. Which trait correlations evolved was strain-specific, but greater departures from ancestral trait correlations were associated with lower population growth rates. There was no single master trait that could be used to understand multitrait evolution. Instead, repeatable multitrait evolution occurred along a major axis of variation defined by several diatom functional traits and trait relationships. Because trait-scapes capture changes in trait correlations and values together, they offer an insightful way to study multitrait variation.

Ecosystem heterogeneity and diversity mitigate Amazon forest resilience to frequent extreme droughts

Publisher: Wiley

Date: 22-05-2018

DOI: 10.1111/NPH.15185

Abstract: The impact of increases in drought frequency on the Amazon forest's composition, structure and functioning remain uncertain. We used a process- and in idual-based ecosystem model (ED2) to quantify the forest's vulnerability to increased drought recurrence. We generated meteorologically realistic, drier-than-observed rainfall scenarios for two Amazon forest sites, Paracou (wetter) and Tapajós (drier), to evaluate the impacts of more frequent droughts on forest biomass, structure and composition. The wet site was insensitive to the tested scenarios, whereas at the dry site biomass declined when average rainfall reduction exceeded 15%, due to high mortality of large-sized evergreen trees. Biomass losses persisted when year-long drought recurrence was shorter than 2-7 yr, depending upon soil texture and leaf phenology. From the site-level scenario results, we developed regionally applicable metrics to quantify the Amazon forest's climatological proximity to rainfall regimes likely to cause biomass loss > 20% in 50 yr according to ED2 predictions. Nearly 25% (1.8 million km

Do dynamic global vegetation models capture the seasonality of carbon fluxes in the Amazon basin? A data‐model intercomparison

Publisher: Wiley

Date: 29-08-2016

DOI: 10.1111/GCB.13442

Abstract: To predict forest response to long-term climate change with high confidence requires that dynamic global vegetation models (DGVMs) be successfully tested against ecosystem response to short-term variations in environmental drivers, including regular seasonal patterns. Here, we used an integrated dataset from four forests in the Brasil flux network, spanning a range of dry-season intensities and lengths, to determine how well four state-of-the-art models (IBIS, ED2, JULES, and CLM3.5) simulated the seasonality of carbon exchanges in Amazonian tropical forests. We found that most DGVMs poorly represented the annual cycle of gross primary productivity (GPP), of photosynthetic capacity (Pc), and of other fluxes and pools. Models simulated consistent dry-season declines in GPP in the equatorial Amazon (Manaus K34, Santarem K67, and Caxiuanã CAX) a contrast to observed GPP increases. Model simulated dry-season GPP reductions were driven by an external environmental factor, 'soil water stress' and consequently by a constant or decreasing photosynthetic infrastructure (Pc), while observed dry-season GPP resulted from a combination of internal biological (leaf-flush and abscission and increased Pc) and environmental (incoming radiation) causes. Moreover, we found models generally overestimated observed seasonal net ecosystem exchange (NEE) and respiration (R

Understanding water and energy fluxes in the Amazonia: Lessons from an observation‐model intercomparison

Publisher: Wiley

Date: 03-03-2021

DOI: 10.1111/GCB.15555

Abstract: Tropical forests are an important part of global water and energy cycles, but the mechanisms that drive seasonality of their land‐atmosphere exchanges have proven challenging to capture in models. Here, we (1) report the seasonality of fluxes of latent heat (LE), sensible heat ( H ), and outgoing short and longwave radiation at four erse tropical forest sites across Amazonia—along the equator from the Caxiuanã and Tapajós National Forests in the eastern Amazon to a forest near Manaus, and from the equatorial zone to the southern forest in Reserva Jaru (2) investigate how vegetation and climate influence these fluxes and (3) evaluate land surface model performance by comparing simulations to observations. We found that previously identified failure of models to capture observed dry‐season increases in evapotranspiration (ET) was associated with model overestimations of (1) magnitude and seasonality of Bowen ratios (relative to aseasonal observations in which sensible was only 20%–30% of the latent heat flux) indicating model exaggerated water limitation, (2) canopy emissivity and reflectance (albedo was only 10%–15% of incoming solar radiation, compared to 0.15%–0.22% simulated), and (3) vegetation temperatures (due to underestimation of dry‐season ET and associated cooling). These partially compensating model‐observation discrepancies (e.g., higher temperatures expected from excess Bowen ratios were partially ameliorated by brighter leaves and more interception/evaporation) significantly biased seasonal model estimates of net radiation ( R n ), the key driver of water and energy fluxes (LE ~ 0.6 R n and H ~ 0.15 R n ), though these biases varied among sites and models. A better representation of energy‐related parameters associated with dynamic phenology (e.g., leaf optical properties, canopy interception, and skin temperature) could improve simulations and benchmarking of current vegetation–atmosphere exchange and reduce uncertainty of regional and global biogeochemical models.

Global Perspectives on Observing Ocean Boundary Current Systems

Publisher: Frontiers Media SA

Date: 08-08-2019

DOI: 10.3389/FMARS.2019.00423

Inter-annual variability of carbon and water fluxes in Amazonian forest, Cerrado and pasture sites, as simulated by terrestrial biosphere models

Publisher: Elsevier BV

Date: 12-2013

DOI: 10.1016/J.AGRFORMET.2013.05.015

Terrestrial and marine perspectives on modeling organic matter degradation pathways

Publisher: Wiley

Date: 28-07-2015

DOI: 10.1111/GCB.12987

Abstract: Organic matter (OM) plays a major role in both terrestrial and oceanic biogeochemical cycles. The amount of carbon stored in these systems is far greater than that of carbon dioxide (CO2 ) in the atmosphere, and annual fluxes of CO2 from these pools to the atmosphere exceed those from fossil fuel combustion. Understanding the processes that determine the fate of detrital material is important for predicting the effects that climate change will have on feedbacks to the global carbon cycle. However, Earth System Models (ESMs) typically utilize very simple formulations of processes affecting the mineralization and storage of detrital OM. Recent changes in our view of the nature of this material and the factors controlling its transformation have yet to find their way into models. In this review, we highlight the current understanding of the role and cycling of detrital OM in terrestrial and marine systems and examine how this pool of material is represented in ESMs. We include a discussion of the different mineralization pathways available as organic matter moves from soils, through inland waters to coastal systems and ultimately into open ocean environments. We argue that there is strong commonality between aspects of OM transformation in both terrestrial and marine systems and that our respective scientific communities would benefit from closer collaboration.

Mechanisms of water supply and vegetation demand govern the seasonality and magnitude of evapotranspiration in Amazonia and Cerrado

Publisher: Elsevier BV

Date: 06-2014

DOI: 10.1016/J.AGRFORMET.2014.02.008

University Of Southern California

Location: United States of America

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Discovery Projects - Grant ID: DP230100657

Start Date: 2023

End Date: 12-2025

Amount: $392,000.00

Funder: Australian Research Council

Discovery Projects - Grant ID: DP170101925

Start Date: 2017

End Date: 12-2020

Amount: $589,000.00

Funder: Australian Research Council

Special Research Initiatives - Grant ID: SR200100008

Start Date: 08-2021

End Date: 12-2027

Amount: $20,000,000.00

Funder: Australian Research Council