Recent Trends in the Land Carbon Cycle

Land ecosystems absorb about a quarter of all human emissions of carbon (C) by fossil fuel burning and land use change. This percentage varies greatly within years due to the land ecosystem response to climate variability and disturbance. Significant uncertainties remain in our knowledge of the magnitude and spatio-temporal changes in the land C sinks. The aims of my thesis are 1) to evaluate the capacity of different dynamic global vegetation models (DGVMs) to reproduce the fluxes and stocks of the land C cycle and 2) to analyse the drivers of change in the land C over the last two decades (1990-2009). In the first part of this thesis I evaluated the DGVM results over two regions: the Northern Hemisphere (NH) and the Tropics. Over the NH DGVMs tend to simulate longer growing seasons and a greater positive leaf area index trend in response to warming than that observed from satellite data. For the tropical region we found a high spatial correlation between the DGVMs and the observations for C stocks and fluxes, but the models produced higher C stocks over the non-forested areas. In the second part I studied the processes controlling the regional land C cycle. The findings can be summarized as: (1) the land CO2 sink has increased over the study period, through increases in tropical and southern regions with negligible change in northern regions; (2) globally and in most regions, the land sinks are not increasing as fast as the growth rate of excess atmospheric CO2 and (3) changes in water availability, particularly over the dry season, played a fundamental role in determining regional trends in NPP. My work seeks to improve our understanding of the relationship between the C cycle and its drivers, however considerable research is needed to understand the role of additional processes such as land use change, nitrogen deposition, to mention just a few.University of ExeterConsejo Nacional de Ciencia y TecnologíaConsejo Estatal de Ciencia y Tecnologia de MichoacánSecretaria de Educacion Public

Process Oscillations in Continuous Ethanol Fermentation with Saccharomyces cerevisiae

Based on ethanol fermentation kinetics and bioreactor engineering theory, a system composed of a continuously stirred tank reactor (CSTR) and three tubular bioreactors in series was established for continuous very high gravity (VHG) ethanol fermentation with Saccharomyces cerevisiae. Sustainable oscillations of residual glucose, ethanol, and biomass characterized by long oscillation periods and large oscillation amplitudes were observed when a VHG medium containing 280 g/L glucose was fed into the CSTR at a dilution rate of 0.027 h1. Mechanistic analysis indicated that the oscillations are due to ethanol inhibition and the lag response of yeast cells to ethanol inhibition. A high gravity (HG) medium containing 200 g/L glucose and a low gravity (LG) medium containing 120 g/L glucose were fed into the CSTR at the same dilution rate as that for the VHG medium, so that the impact of residual glucose and ethanol concentrations on the oscillations could be studied. The oscillations were not significantly affected when the HG medium was used, and residual glucose decreased significantly, but ethanol maintained at the same level, indicating that residual glucose was not the main factor triggering the oscillations. However, the oscillations disappeared after the LG medium was fed and ethanol concentration decreased to 58.2 g/L. Furthermore, when the LG medium was supplemented with 30 g/L ethanol to achieve the same level of ethanol in the fermentation system as that achieved under the HG condition, the steady state observed for the original LG medium was interrupted, and the oscillations observed under the HG condition occurred. The steady state was gradually restored after the original LG medium replaced the modified one. These experimental results confirmed that ethanol, whether produced by yeast cells during fermentation or externally added into a fermentation system, can trigger oscillations once its concentration approaches to a criterion. The impact of dilution rate on oscillations was also studied. It was found that oscillations occurred at certain dilution rate ranges for the two yeast strains. Since ethanol production is tightly coupled with yeast cell growth, it was speculated that the impact of the dilution rate on the oscillations is due to the synchronization of the mother and daughter cell growth rhythms. The difference in the oscillation profiles exhibited by the two yeast strains is due to their difference in ethanol tolerance. For more practical conditions, the behavior of continuous ethanol fermentation was studied using a self-flocculating industrial yeast strain and corn flour hydrolysate medium in a simulated tanks-in-series fermentation system. Amplified oscillations observed at the dilution rate of 0.12 h1 were postulated to be due to the synchronization of the two yeast cell populations generated by the continuous inoculation from the seed tank upstream of the fermentation system, which was partly validated by oscillation attenuation after the seed tank was removed from the fermentation system. The two populations consisted of the newly inoculated yeast cells and the yeast cells already adapted to the fermentation environment. Oscillations increased residual sugar at the end of the fermentation, and correspondingly, decreased the ethanol yield, indicating the need for attenuation strategies. When the tubular bioreactors were packed with ½” Intalox ceramic saddles, not only was their ethanol fermentation performance improved, but effective oscillation attenuation was also achieved. The oscillation attenuation was postulated to be due to the alleviation of backmixing in the packed tubular bioreactors as well as the yeast cell immobilization role of the packing. The residence time distribution analysis indicated that the mixing performance of the packed tubular bioreactors was close to a CSTR model for both residual glucose and ethanol, and the assumed backmixing alleviation could not be achieved. The impact of yeast cell immobilization was further studied using several different packing materials. Improvement in ethanol fermentation performance as well as oscillation attenuation was achieved for the wood chips, as well as the Intalox ceramic saddles, but not for the porous polyurethane particles, nor the steel Raschig rings. Analysis for the immobilized yeast cells indicated that high viability was the mechanistic reason for the improvement of the ethanol fermentation performance as well as the attenuation of the oscillations. A dynamic model was developed by incorporating the lag response of yeast cells to ethanol inhibition into the pseudo-steady state kinetic model, and dynamic simulation was performed, with good results. This not only provides a basis for developing process intervention strategies to minimize oscillations, but also theoretically support the mechanistic hypothesis for the oscillations

The dry season intensity as a key driver of NPP trends

We analyze the impacts of changing dry season length and intensity on vegetation productivity and biomass. Our results show a wetness asymmetry in dry ecosystems, with dry seasons becoming drier and wet seasons becoming wetter, likely caused by climate change. The increasingly intense dry seasons were consistently correlated with a decreasing trend in net primary productivity (NPP) and biomass from different products and could potentially mean a reduction of 10–13% in NPP by 2100. We found that annual NPP in dry ecosystems is particularly sensitive to the intensity of the dry season, whereas an increase in precipitation during the wet season has a smaller effect. We conclude that changes in water availability over the dry season affect vegetation throughout the whole year, driving changes in regional NPP. Moreover, these results suggest that usage of seasonal water fluxes is necessary to improve our understanding of the link between water availability and the land carbon cycle

Modelling carbon stock and carbon sequestration ecosystem services for policy design: a comprehensive approach using a dynamic vegetation model

Ecosystem service (ES) models can only inform policy design adequately if they incorporate ecological processes. We used the Lund-Potsdam-Jena managed Land (LPJmL) model, to address following questions for Mexico, Bolivia and Brazilian Amazon: (i) How different are C stocks and C sequestration quantifications under standard (when soil and litter C and heterotrophic respiration are not considered) and comprehensive (including all C stock and heterotrophic respiration) approach? and (ii) How does the valuation of C stock and C sequestration differ in national payments for ES and global C funds or markets when comparing both approach? We found that up to 65% of C stocks have not been taken into account by neglecting to include C stored in soil and litter, resulting in gross underpayments (up to 500 times lower). Since emissions from heterotrophic respiration of organic material offset a large proportion of C gained through growth of living matter, we found that markets and decision-makers are inadvertently overestimating up to 100 times C sequestrated. New approaches for modelling C services relevant ecological process-based can help accounting for C in soil, litter and heterotrophic respiration and become important for the operationalization of agreements on climate change mitigation following the COP21 in 2015

RECCAP2 Future Component: Consistency and Potential for Regional Assessment to Constrain Global Projections

This is the final version. Available from Wiley via the DOI in this record. Data Availability Statement: All CMIP6 model output datasets analyzed during this study are available online at https://esgf-node.llnl.gov/search/cmip6/ and code required to reproduce figures is available at https://github.com/ChrisJones-MOHC/RECCAP2Future_2023 (ChrisJones-MOHC, 2023) and Zenodo at https://doi.org/10.5281/zenodo.8420250.Projections of future carbon sinks and stocks are important because they show how the world's ecosystems will respond to elevated CO2 and changes in climate. Moreover, they are crucial to inform policy decisions around emissions reductions to stay within the global warming levels identified by the Paris Agreement. However, Earth System Models from the 6th Coupled Model Intercomparison Project (CMIP6) show substantial spread in future projections—especially of the terrestrial carbon cycle, leading to a large uncertainty in our knowledge of any remaining carbon budget (RCB). Here we evaluate the global terrestrial carbon cycle projections on a region‐by‐region basis and compare the global models with regional assessments made by the REgional Carbon Cycle Assessment and Processes, Phase 2 activity. Results show that for each region, the CMIP6 multi‐model mean is generally consistent with the regional assessment, but substantial cross‐model spread exists. Nonetheless, all models perform well in some regions and no region is without some well performing models. This gives confidence that the CMIP6 models can be used to look at future changes in carbon stocks on a regional basis with appropriate model assessment and benchmarking. We find that most regions of the world remain cumulative net sources of CO2 between now and 2100 when considering the balance of fossil‐fuels and natural sinks, even under aggressive mitigation scenarios. This paper identifies strengths and weaknesses for each model in terms of its performance over a particular region including how process representation might impact those results and sets the agenda for applying stricter constraints at regional scales to reduce the uncertainty in global projections.European Union’s Horizon 2020European Union’s Horizon 2020European Union’s Horizon 2020Joint UK BEIS/Defra Met Office Hadley Centre Climate ProgrammeCarbonWatch-NZ Endeavour Research ProgrammeSão Paulo Research FoundationSão Paulo Research FoundationSão Paulo Research FoundationNational Science FoundationAndrew Carnegie Fellow ProgramCNPqKorea Ministry of EnvironmentNatural Environment Research Council (NERC)Natural Environment Research Council (NERC)National Environmental Science Progra

The ecology of peace : preparing Colombia for new political and planetary climates

ABSTRACT: Colombia, one of the world’s most species-rich nations, is currently undergoing a profound social transition: the end of a decadeslong conflict with the Revolutionary Armed Forces of Colombia, known as FARC. The peace agreement process will likely transform the country’s physical and socioeconomic landscapes at a time when humans are altering Earth’s atmosphere and climate in unprecedented ways. We discuss ways in which these transformative events will act in combination to shape the ecological and environmental future of Colombia. We also highlight the risks of creating perverse development incentives in these critical times, along with the potential benefits – for the country and the world – if Colombia can navigate through the peace process in a way that protects its own environment and ecosystems

The carbon cycle in Mexico: Past, present and future of C stocks and fluxes

We modeled the carbon (C) cycle in Mexico with a process-based approach. We used different available products (satellite data, field measurements, models and flux towers) to estimate C stocks and fluxes in the country at three different time frames: present (defined as the period 2000–2005), the past century (1901–2000) and the remainder of this century (2010–2100). Our estimate of the gross primary productivity (GPP) for the country was 2137±1023 TgC yr$^{-1}$ and a total C stock of 34 506±7483 TgC, with 20 347±4622 TgC in vegetation and 14 159±3861 in the soil. Contrary to other current estimates for recent decades, our results showed that Mexico was a C sink over the period 1990–2009 (+31 TgC yr$^{-1}$) and that C accumulation over the last century amounted to 1210±1040 TgC.We attributed this sink to the CO$_{2}$ fertilization effect on GPP, which led to an increase of 3408±1060 TgC, while both climate and land use reduced the country C stocks by -458±1001 and -1740±878 TgC, respectively. Under different future scenarios, the C sink will likely continue over the 21st century, with decreasing C uptake as the climate forcing becomes more extreme. Our work provides valuable insights on relevant driving processes of the C cycle such as the role of drought in drylands (e.g., grasslands and shrublands) and the impact of climate change on the mean residence time of soil C in tropical ecosystems

Evaluation of Land Surface Models in Reproducing Satellite Derived Leaf Area Index over the High-Latitude Northern Hemisphere. Part II: Earth System Models

Abstract: Leaf Area Index (LAI) is a key parameter in the Earth System Models (ESMs) since it strongly affects land-surface boundary conditions and the exchange of matter and energy with the atmosphere. Observations and data products derived from satellite remote sensing are important for the validation and evaluation of ESMs from regional to global scales. Several decades ’ worth of satellite data products are now available at global scale which represents a unique opportunity to contrast observations against model results. The objective of this study is to assess whether ESMs correctly reproduce the spatial variability of LAI when compared with satellite data and to compare the length of the growing season in the different models with the satellite data. To achieve this goal we analyse outputs from 11 coupled carbon-climate models that are based on the set of new global model simulations planned in support of the IPCC Fifth Assessment Report. We focus on the average LAI and the length of the growing season on Northern Hemisphere over the period 1986–2005. Additionally we compare the results with previous analyses (Part I) o

Global annual dry-season length (left) and precipitation rate (right).

<p>Legend and methodology follows <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0190304#pone.0190304.g001" target="_blank">Fig 1</a>. The data employed is on a monthly resolution, but the figure is displayed in days for a better visualization.</p