Lina M. Mercado
University of Exeter
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Featured researches published by Lina M. Mercado.
Nature | 2009
Lina M. Mercado; Nicolas Bellouin; Stephen Sitch; Olivier Boucher; Chris Huntingford; Martin Wild; Peter M. Cox
Plant photosynthesis tends to increase with irradiance. However, recent theoretical and observational studies have demonstrated that photosynthesis is also more efficient under diffuse light conditions. Changes in cloud cover or atmospheric aerosol loadings, arising from either volcanic or anthropogenic emissions, alter both the total photosynthetically active radiation reaching the surface and the fraction of this radiation that is diffuse, with uncertain overall effects on global plant productivity and the land carbon sink. Here we estimate the impact of variations in diffuse fraction on the land carbon sink using a global model modified to account for the effects of variations in both direct and diffuse radiation on canopy photosynthesis. We estimate that variations in diffuse fraction, associated largely with the ‘global dimming’ period, enhanced the land carbon sink by approximately one-quarter between 1960 and 1999. However, under a climate mitigation scenario for the twenty-first century in which sulphate aerosols decline before atmospheric CO2 is stabilized, this ‘diffuse-radiation’ fertilization effect declines rapidly to near zero by the end of the twenty-first century.
Philosophical Transactions of the Royal Society B | 2008
Chris Huntingford; Rosie A. Fisher; Lina M. Mercado; Ben B. B. Booth; Stephen Sitch; Phil P. Harris; Peter M. Cox; Chris D. Jones; Richard A. Betts; Yadvinder Malhi; Glen R. Harris; Mat Collins; Paul R. Moorcroft
Simulations with the Hadley Centre general circulation model (HadCM3), including carbon cycle model and forced by a ‘business-as-usual’ emissions scenario, predict a rapid loss of Amazonian rainforest from the middle of this century onwards. The robustness of this projection to both uncertainty in physical climate drivers and the formulation of the land surface scheme is investigated. We analyse how the modelled vegetation cover in Amazonia responds to (i) uncertainty in the parameters specified in the atmosphere component of HadCM3 and their associated influence on predicted surface climate. We then enhance the land surface description and (ii) implement a multilayer canopy light interception model and compare with the simple ‘big-leaf’ approach used in the original simulations. Finally, (iii) we investigate the effect of changing the method of simulating vegetation dynamics from an area-based model (TRIFFID) to a more complex size- and age-structured approximation of an individual-based model (ecosystem demography). We find that the loss of Amazonian rainforest is robust across the climate uncertainty explored by perturbed physics simulations covering a wide range of global climate sensitivity. The introduction of the refined light interception model leads to an increase in simulated gross plant carbon uptake for the present day, but, with altered respiration, the net effect is a decrease in net primary productivity. However, this does not significantly affect the carbon loss from vegetation and soil as a consequence of future simulated depletion in soil moisture; the Amazon forest is still lost. The introduction of the more sophisticated dynamic vegetation model reduces but does not halt the rate of forest dieback. The potential for human-induced climate change to trigger the loss of Amazon rainforest appears robust within the context of the uncertainties explored in this paper. Some further uncertainties should be explored, particularly with respect to the representation of rooting depth.
Tellus B | 2007
Lina M. Mercado; Chris Huntingford; J.H.C. Gash; Peter M. Cox; Venkata Jogireddy
The Joint UK Land Environment Simulator (JULES) (which is based on MetOffice Surface Exchange Scheme MOSES), the land surface scheme of the Hadley Centre General Circulation Models (GCM) has been improved to contain an explicit description of light interception for different canopy levels, which consequently leads to a multilayer approach to scaling from leaf to canopy level photosynthesis. We test the improved JULES model at a site in the Amazonian rainforest by comparing against measurements of vertical profiles of radiation through the canopy, eddy covariance measurements of carbon and energy fluxes, and also measurements of carbon isotopic fractionation from top canopy leaves. Overall, the new light interception formulation improves modelled photosynthetic carbon uptake compared to the standard big leaf approach used in the original JULES formulation. Additional model improvement was not significant when incorporating more realistic vertical variation of photosynthetic capacity. Even with the improved representation of radiation interception, JULES simulations of net carbon uptake underestimate eddy covariance measurements by 14%. This discrepancy can be removed by either increasing the photosynthetic capacity throughout the canopy or by explicitly including light inhibition of leaf respiration. Along with published evidence of such inhibition of leaf respiration, our study suggests this effect should be considered for inclusion in other GCMs.
Philosophical Transactions of the Royal Society B | 2011
Lina M. Mercado; S. Patiño; Tomas F. Domingues; Nikolaos M. Fyllas; Graham P. Weedon; Stephen Sitch; Carlos A. Quesada; Oliver L. Phillips; Luiz E. O. C. Aragão; Yadvinder Malhi; A. J. Dolman; Natalia Restrepo-Coupe; Scott R. Saleska; Timothy R. Baker; Samuel Almeida; Niro Higuchi; Jon Lloyd
The rate of above-ground woody biomass production, WP, in some western Amazon forests exceeds those in the east by a factor of 2 or more. Underlying causes may include climate, soil nutrient limitations and species composition. In this modelling paper, we explore the implications of allowing key nutrients such as N and P to constrain the photosynthesis of Amazon forests, and also we examine the relationship between modelled rates of photosynthesis and the observed gradients in WP. We use a model with current understanding of the underpinning biochemical processes as affected by nutrient availability to assess: (i) the degree to which observed spatial variations in foliar [N] and [P] across Amazonia affect stand-level photosynthesis; and (ii) how these variations in forest photosynthetic carbon acquisition relate to the observed geographical patterns of stem growth across the Amazon Basin. We find nutrient availability to exert a strong effect on photosynthetic carbon gain across the Basin and to be a likely important contributor to the observed gradient in WP. Phosphorus emerges as more important than nitrogen in accounting for the observed variations in productivity. Implications of these findings are discussed in the context of future tropical forests under a changing climate.
New Phytologist | 2017
Alistair Rogers; Belinda E. Medlyn; Jeffrey S. Dukes; Gordon B. Bonan; Susanne von Caemmerer; Michael C. Dietze; Jens Kattge; Andrew D. B. Leakey; Lina M. Mercado; Ülo Niinemets; I. Colin Prentice; Shawn P. Serbin; Stephen Sitch; Danielle A. Way; Sönke Zaehle
Accurate representation of photosynthesis in terrestrial biosphere models (TBMs) is essential for robust projections of global change. However, current representations vary markedly between TBMs, contributing uncertainty to projections of global carbon fluxes. Here we compared the representation of photosynthesis in seven TBMs by examining leaf and canopy level responses of photosynthetic CO2 assimilation (A) to key environmental variables: light, temperature, CO2 concentration, vapor pressure deficit and soil water content. We identified research areas where limited process knowledge prevents inclusion of physiological phenomena in current TBMs and research areas where data are urgently needed for model parameterization or evaluation. We provide a roadmap for new science needed to improve the representation of photosynthesis in the next generation of terrestrial biosphere and Earth system models.
Philosophical Transactions of the Royal Society A | 2011
Chris Huntingford; Peter M. Cox; Lina M. Mercado; Stephen Sitch; Nicolas Bellouin; Olivier Boucher; Nicola Gedney
Many atmospheric constituents besides carbon dioxide (CO2) contribute to global warming, and it is common to compare their influence on climate in terms of radiative forcing, which measures their impact on the planetary energy budget. A number of recent studies have shown that many radiatively active constituents also have important impacts on the physiological functioning of ecosystems, and thus the ‘ecosystem services’ that humankind relies upon. CO2 increases have most probably increased river runoff and had generally positive impacts on plant growth where nutrients are non-limiting, whereas increases in near-surface ozone (O3) are very detrimental to plant productivity. Atmospheric aerosols increase the fraction of surface diffuse light, which is beneficial for plant growth. To illustrate these differences, we present the impact on net primary productivity and runoff of higher CO2, higher near-surface O3, and lower sulphate aerosols, and for equivalent changes in radiative forcing. We compare this with the impact of climate change alone, arising, for example, from a physiologically inactive gas such as methane (CH4). For equivalent levels of change in radiative forcing, we show that the combined climate and physiological impacts of these individual agents vary markedly and in some cases actually differ in sign. This study highlights the need to develop more informative metrics of the impact of changing atmospheric constituents that go beyond simple radiative forcing.
Geophysical Research Letters | 2015
A. Rap; D. V. Spracklen; Lina M. Mercado; C. L. Reddington; James M. Haywood; Rich Ellis; Oliver L. Phillips; Paulo Artaxo; Damien Bonal; N. Restrepo Coupe; Nathalie Butt
Atmospheric aerosol scatters solar radiation increasing the fraction of diffuse radiation and the efficiency of photosynthesis. We quantify the impacts of biomass burning aerosol (BBA) on diffuse radiation and plant photosynthesis across Amazonia during 1998–2007. Evaluation against observed aerosol optical depth allows us to provide lower and upper BBA emissions estimates. BBA increases Amazon basin annual mean diffuse radiation by 3.4–6.8% and net primary production (NPP) by 1.4–2.8%, with quoted ranges driven by uncertainty in BBA emissions. The enhancement of Amazon basin NPP by 78–156 Tg C a−1 is equivalent to 33–65% of the annual regional carbon emissions from biomass burning. This NPP increase occurs during the dry season and acts to counteract some of the observed effect of drought on tropical production. We estimate that 30–60 Tg C a−1 of this NPP enhancement is within woody tissue, accounting for 8–16% of the observed carbon sink across mature Amazonian forests.
Scientific Reports | 2016
Chris Huntingford; Lina M. Mercado
The recent Paris UNFCCC climate meeting discussed the possibility of limiting global warming to 2 °C since pre-industrial times, or possibly even 1.5 °C, which would require major future emissions reductions. However, even if climate is stabilised at current atmospheric greenhouse gas (GHG) concentrations, those warming targets would almost certainly be surpassed in the context of mean temperature increases over land only. The reason for this is two-fold. First, current transient warming lags significantly below equilibrium or “committed” warming. Second, almost all climate models indicate warming rates over land are much higher than those for the oceans. We demonstrate this potential for high eventual temperatures over land, even for contemporary GHG levels, using a large set of climate models and for which climate sensitivities are known. Such additional land warming has implications for impacts on terrestrial ecosystems and human well-being. This suggests that even if massive and near-immediate emissions reductions occur such that atmospheric GHGs increase further by only small amounts, careful planning is needed by society to prepare for higher land temperatures in an eventual equilibrium climatic state.
Functional Ecology | 2017
Simon M. Smart; Helen C. Glanville; Maria del Carmen Blanes; Lina M. Mercado; Bridget A. Emmett; David Leonard Jones; B. J. Cosby; R.H. Marrs; Adam Butler; Miles R. Marshall; Sabine Reinsch; Cristina Herrero-Jáuregui; J. G. Hodgson
1. Reliable modelling of above-ground Net Primary Production (aNPP) at fine resolution is a significant challenge. A promising avenue for improving process models is to include response and effect trait relationships. However, uncertainties remain over which leaf traits are correlated most strongly with aNPP. 2. We compared abundance-weighted values of two of the most widely used traits from the Leaf Economics Spectrum (Specific Leaf Area and Leaf Dry Matter Content) with measured aNPP across a temperate ecosystem gradient. 3. We found that Leaf Dry Matter Content (LDMC) as opposed to Specific Leaf Area (SLA) was the superior predictor of aNPP (R2=0.55). 4. Directly measured in situ trait values for the dominant species improved estimation of aNPP significantly. Introducing intra-specific trait variation by including the effect of replicated trait values from published databases did not improve the estimation of aNPP. 5. Our results support the prospect of greater scientific understanding for less cost because LDMC is much easier to measure than SLA.
Nature | 2013
Chris Huntingford; Lina M. Mercado; Eric Post
An innovative assessment of climate change calculates the year in which ongoing warming will surpass the limits of historical climate variability. Three experts explain this calculations significance compared with conventional approaches, and its relevance to Earths biodiversity. See Article p.183 Projections of warming are now a fixture of climate modelling exercises. Camilo Mora et al. have used an ensemble of these simulations to estimate when ongoing warming will exceed the bounds of historical climate variability. Depending on assumptions regarding future emissions in greenhouse gasses, this will occur sometime in the mid to late twenty-first century. This landmark event is likely to occur first in the tropics, where historical variability is low, and where biodiversity is highest. The new projections suggest that the often economically challenged areas in the tropics will face the highest burden of rapidly adapting to the biological effects of climate change. In an accompanying News & Views Forum, three climatologists discuss the significance of these results.