A functional approach to understanding the mechanisms of flood tolerance and survival in Amazonian wetland trees

Overview

Wetlands presently cover more than 800,000 km2 of the Amazon basin, an area almost four times larger than the UK(1). These habitats have extensively covered Amazonian lowlands for the last twenty million years (2), and currently host over half of the 6000+ known Amazonian tree species(3), showing high species endemism (4) and being a major component of the Amazon carbon cycle (5). Nevertheless, Amazonian wetlands remain severely understudied when compared to upland terrestrial forests, while being highly endangered by increasing recurrence of extreme hydrological events (6) and by expansion of hydropower enterprises that disrupt natural flooding cycles (7). If you take this project, you will be the first to apply modern functional ecology to understand the responses of Amazon wetland tree communities along inundation gradients, providing an entirely new perspective on the mechanisms of tropical plant adaptation to hydrological extremes. Your results will have direct and significant implications for understanding the evolution of Amazon plant diversity in the past and for improving future predictions of how Amazonian ecosystems will respond to climatic and anthropogenic changes.

Wetland environments are usually regarded as requiring adaptations leading to organism specialization, but it is possible that these same environments may select for higher tolerances to extremes (8). For example, adaptations to overcome root anoxia induced by flooding may be functionally similar to adaptations to survive droughts, enabling wetland-adapted species to also tolerate dryer conditions (9). Therefore, if we combine this knowledge with the prevalence of Amazonian wetlands through deep time and the large proportion of Amazon flora adapted to flooding, it is reasonable to expect a considerable contribution of Amazonian wetlands to the assembly and evolution of Amazon plant biota, and to its future resilience to climatic change. Nevertheless, studies on the effects of flooding on Amazonian trees to date have been focused mainly on documenting empirical changes in species composition or describing adaptations to inundation (10,11). There is thus a pressing need for advancing the current state-of-art by incorporating functional ecology approaches to elucidate the overarching mechanisms determining the assembly and maintenance of wetland tree diversity and its susceptibility to environmental extremes and changes. Currently, we are aware of only one study using a functional trait approach to study Amazon wetland ecosystems (12.)

The main objectives of this project are therefore to: 1) Produce the first analysis of functional assembly mechanisms in relation to flood tolerance strategies and responses to flood disturbances in Amazon wetland tree communities; 2) Improve the current mechanistic understanding of growth vs. flood tolerance strategies in these trees, including biophysical, physiological and/or genetic aspects of plant adaptation and tolerance; 3) Discuss the implications of the observed results for the evolution of the Amazon plant biota and/or the future resilience of Amazonian forest ecosystem to environmental changes.

Within these central themes, you will be free to complement the core functional approach with ecophysiological, genomic, remote sensing, biogeochemical, dendrochronological and/or statistical modelling and simulation methods, according to your interests and strengths.

Click on an image to expand

Image Captions

River.jpg – “Boat travel along the many channels of the Mamiraua Sustainable Reserve, Brazil. Edges of floodplain forest patches are visible at both sides” – photo by Thiago Silva.

Forest.jpg – “View from within an Amazonian floodplain forest during the dry season, in the Mamiraua Sustainable Reserve, Brazil” – photo by Thiago Silva.

Methodology

The first element of your PhD work will be a comprehensive literature review and/or meta-analysis of existing functional trait data for tropical wetland forests, to 1) establish a baseline of expectations for wetland functional composition in relation to the worldwide plant functional spectra, 2) propose a standardized set of functional traits directly related to flood tolerance, and protocols for their measurement, and 3) delineate the main research questions of your thesis. This work is likely to lead to a first publication/chapter within your dissertation.

You will then lead fieldwork to obtain the first ever measurements of plant functional traits along an explicit hydrological gradient in the Amazonian eutrophic floodplain forests. You will be able to work at the Mamiraua Sustainable Development Reserve in the Central Amazon, the largest Brazilian protected area dedicated to wetland conservation and both a UNESCO World Heritage site and a RAMSAR wetland conservation site. The MSDR offers one of the best fieldwork infrastructures in the Brazilian Amazon, including floating research stations, several boats and a vetted pool of locally trained field guides. You should expect to spend between two and four weeks at the field on your first year, with possible return on following years if necessary.

Our research group has been monitoring 18 fully-inventoried wetland forest plots in the MSDR since 2018, distributed along a continuous flooding gradient. By taking advantage of these existing plots, you will be able to sample functional traits and additional variables of interest. Within the broader context of the overarching research theme, we also expect to take high-precision topographic measurements of ground elevation using differential GPS and obtain 3D laser scans of forest structure using innovative scanning sensors developed by CSIRO in Australia. This data will be used to characterize changes in plant architecture and to determine individual flooding height for each inventoried tree with unprecedented precision, enabling the reconstruction of the past flooding regime using historical data and a network of water level loggers operating in the reserve. We also plan to preserve tissue material for further genetic and isotope analysis. All of this data will be freely available to be then incorporated on your thesis work as you see fit. Finally, you will then define your approach to analyse the resulting data using suitable modern analytical statistical approaches, and report your findings in the form of peer-reviewed manuscripts and conference presentations.

Project Timeline

Year 1

During year 1, you will perform an in depth-review of the published literature and existing global trait databases to compile functional trait information for tropical wetland trees, ideally leading to a manuscript establishing baseline expectations for tropical wetland functional composition, and proposing a standardized set of functional traits related to flood tolerance. You will also participate on specific training courses focused on trait-based plant ecology. At the end of Year 1, you will conduct your fieldwork at the selected Amazon site.

Year 2

During year 2, you will work on the submission of your review paper and on the processing and analysis of the collected data, including training activities on advanced analytical methods related to the approaches you have defined for your thesis research. You will then work on analysing your data focusing towards a second manuscript/ dissertation chapter focusing on the functional ecology aspect of your project. You will also be expected to participate on a relevant conference to present preliminary results and gather feedback on your analyses. Part of this work may be taken as a research placement within an UK or international research institution, according to the methodological approach selected for the project. The project current has partners in the UK, USA and Brazil.

Year 3

During year 3, you will finalize your second manuscript/chapter and then develop your work towards the additional scientific questions defined for your project. By the end of year 3, you will participate on an international level conference to present and receive feedback from the overall results of you thesis. The international research placement may be considered for year 3 instead of year 2, as well.

Year 3.5

You will use this time to finalise your analyses in the form of a third manuscript/chapter and assemble your overall thesis document, as well as focus on training for job/grant applications and higher education teaching, which are annually offered by University of Stirling.

Training
& Skills

Throughout the PhD any training needs will be continually assessed between the successful candidate and the supervisory team. There will be the opportunity to attend specific training events, including IAPETUS2 training events and choices among the 50+ training courses offered annually by the Postgraduate Researcher Skills Development Program of University of Stirling, including data analysis, coding, software training, scientific writing, scientific presentation and outreach, preparation for the job market, and higher education teaching. Formal training activities will be complemented by active supervision through regular meetings of the supervisory team with the student, starting with weekly meetings with the main supervisor and monthly meetings with the supervisory committee on year 1, progressing to meetings scheduled as needed as the candidate becomes more independent. In accordance to the progress of the thesis work, the candidate may also spend short periods working directly with the main supervisors or selected collaborators, at their home institutions in the UK or abroad. The candidate will also participate on the regular meetings of the Ecosystem Change research group of the Division of Biological and Environmental Sciences, of which you will be a member, attend the weekly departmental seminars, as present their work as well. Progress will be formally evaluated annually in the PGR review process of the University of Stirling.

References & further reading

1. Hess, L. L. et al. Wetlands of the Lowland Amazon Basin: Extent, Vegetative Cover, and Dual-season Inundated Area as Mapped with JERS-1 Synthetic Aperture Radar. Wetlands 35, 745-756 (2015).
2. Hoorn, C. et al. Amazonia Through Time: Andean Uplift, Climate Change, Landscape Evolution, and Biodiversity. Science 330, 927-931 (2010).
3. Luize, B. G. et al. The tree species pool of Amazonian wetland forests: Which species can assemble in periodically waterlogged habitats? PLoS One 13, e0198130 (2018).
4. Albernaz, A. L. et al. Tree species compositional change and conservation implications in the white-water flooded forests of the Brazilian Amazon. Joutnal of Biogeography. 39, 869-883 (2012).
5. Melack, J. M., Novo, E., Forsberg, B. R., Piedade, M. T. & Maurice, L. Floodplain ecosystem processes. In: Amazonia and Global Change 186, 525-542 (2009).
6. Barichivich, J. et al. Recent intensification of Amazon flooding extremes driven by strengthened Walker circulation. Science Advances 4, eaat8785 (2018).
7. Resende, A. F. et al. Massive tree mortality from flood pulse disturbances in Amazonian floodplain forests: The collateral effects of hydropower production. Sci. Total Environ. 659, 587-598 (2019).
8. Morin, X. & Lechowicz, M. J. Geographical and ecological patterns of range size in North American trees. Ecography 34, 738-750 (2011).
9. Parolin, P. et al. Drought responses of flood-tolerant trees in Amazonian floodplains. Annals of Botany 105, 129-139 (2010).
10. Wittmann, F. et al. Tree species composition and diversity gradients in white-water forests across the Amazon Basin. Journal of Biogeography. 33, 1334-1347 (2006).
11. Parolin, P. Submerged in darkness: adaptations to prolonged submergence by woody species of the Amazonian floodplains. Annals of Botany 103, 359-376 (2009).
12. Mori, G. B. et al. Trait divergence and habitat specialization in tropical floodplain forests trees. PLoS One 14, e0212232 (2019).

Further Information

For further information, please contact Dr. Thiago Silva by email at thiago.sf.silva@stir.ac.uk or by phone at +44 798 888 6891 (mobile).

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