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8 results on '"Brown, Jamie R."'

1. Assessing the combined effect of Carbon-Water dynamics on hydrological processes in Brazil

Author

Brown, Jamie R C and Brown, Jamie R C

Abstract

Vegetation dynamics optimally adapt to given environmental conditions by maximising their net carbon profit. If we model these processes, can they help us understand hydrological fluxes across different climates? Furthermore, can this optimality modelling further our understanding on the sensitivity of carbon-water mechanisms in vegetation to changes in CO2? This thesis uses a vegetation optimality model across multiple biomes in Brazil to examine the extent to which it can answer these questions. Firstly, we examine the reliability and suitability of five high-resolution meteorological gridded products (ERA5-Land, GLDAS2.0, GLDAS2.1, the BNMD and MSWEPv2.2 (precipitation only)) for seven variables (precipitation, air temperature, wind speed, pressure, specific humidity, and downward shortwave and longwave radiation) against eleven flux towers spanning five biomes across Brazil. At the daily scale analysis showed that MSWEPv2.2 outperformed the others for precipitation whilst ERA5-Land showed the most consistency for all other variables. Secondly, we show that the Vegetation Optimality Model (VOM), is successfully able to reproduce patterns of evapotranspiration (ET) at several sites, with a stronger correlation at more seasonal sites (r values ranging 0.25 – 0.69 across sites). VOM is a developed model that attempts to quantify the physiological processes of a plant growth carbon-capture cost-benefit system through describing carbon-water dynamics. Results show the importance of root dynamics in the success of the model; the minimal calibration needed per site reflects the strong physiological understanding behind it. Finally, we show declines in ET across an increasing atmospheric CO2 gradient, with dampened impacts on hydrological processes through modelling long-term adaptations in vegetation (reductions from 0.7-6.0% over an increase of 77 ppm CO2). Overall, this thesis advances our knowledge in relation to the questions above i

Published
2023

8. Global Change Could Amplify Fire Effects on Soil Greenhouse Gas Emissions

Author

Niboyet, Audrey, Brown, Jamie R., Dijkstra, Paul, Blankinship, Joseph C., Leadley, Paul W., Le Roux, Xavier, Barthes, Laure, Barnard, Romain L., Field, Christopher B., and Hungate, Bruce A.

Subjects
2. Zero hunger, 13. Climate action, 15. Life on land
Abstract

Background Little is known about the combined impacts of global environmental changes and ecological disturbances on ecosystem functioning, even though such combined impacts might play critical roles in shaping ecosystem processes that can in turn feed back to climate change, such as soil emissions of greenhouse gases. Methodology/Principal Findings We took advantage of an accidental, low-severity wildfire that burned part of a long-term global change experiment to investigate the interactive effects of a fire disturbance and increases in CO2 concentration, precipitation and nitrogen supply on soil nitrous oxide (N2O) emissions in a grassland ecosystem. We examined the responses of soil N2O emissions, as well as the responses of the two main microbial processes contributing to soil N2O production – nitrification and denitrification – and of their main drivers. We show that the fire disturbance greatly increased soil N2O emissions over a three-year period, and that elevated CO2 and enhanced nitrogen supply amplified fire effects on soil N2O emissions: emissions increased by a factor of two with fire alone and by a factor of six under the combined influence of fire, elevated CO2 and nitrogen. We also provide evidence that this response was caused by increased microbial denitrification, resulting from increased soil moisture and soil carbon and nitrogen availability in the burned and fertilized plots. Conclusions/Significance Our results indicate that the combined effects of fire and global environmental changes can exceed their effects in isolation, thereby creating unexpected feedbacks to soil greenhouse gas emissions. These findings highlight the need to further explore the impacts of ecological disturbances on ecosystem functioning in the context of global change if we wish to be able to model future soil greenhouse gas emissions with greater confidence., PLoS ONE, 6 (6), ISSN:1932-6203

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