Environmental controls on the light use efficiency of terrestrial gross primary production

Gross primary production (GPP) by terrestrial ecosystems is a key quantity in the global carbon cycle. The instantaneous controls of leaf-level photosynthesis are well established, but there is still no consensus on the mechanisms by which canopy-level GPP depends on spatial and temporal variation in the environment. The standard model of photosynthesis provides a robust mechanistic representation for C3 species; however, additional assumptions are required to “scale up” from leaf to canopy. As a consequence, competing models make inconsistent predictions about how GPP will respond to continuing environmental change. This problem is addressed here by means of an empirical analysis of the light use efficiency (LUE) of GPP inferred from eddy covariance carbon dioxide flux measurements, in situ measurements of photosynthetically active radiation (PAR), and remotely sensed estimates of the fraction of PAR (fAPAR) absorbed by the vegetation canopy. Focusing on LUE allows potential drivers of GPP to be separated from its overriding dependence on light. GPP data from over 100 sites, collated over 20 years and located in a range of biomes and climate zones, were extracted from the FLUXNET2015 database and combined with remotely sensed fAPAR data to estimate daily LUE. Daytime air temperature, vapor pressure deficit, diffuse fraction of solar radiation, and soil moisture were shown to be salient predictors of LUE in a generalized linear mixed-effects model. The same model design was fitted to site-based LUE estimates generated by 16 terrestrial ecosystem models. The published models showed wide variation in the shape, the strength, and even the sign of the environmental effects on modeled LUE. These findings highlight important model deficiencies and suggest a need to progress beyond simple “goodness of fit” comparisons of inferred and predicted carbon fluxes toward an approach focused on the functional responses of the underlying dependencies

Variation in bulk-leaf ¹³C discrimination, leaf traits and water-use efficiency–trait relationships along a continental-scale climate gradient in Australia

© 2017 John Wiley & Sons Ltd Large spatial and temporal gradients in rainfall and temperature occur across Australia. This heterogeneity drives ecological differentiation in vegetation structure and ecophysiology. We examined multiple leaf-scale traits, including foliar 13C isotope discrimination (Δ13C), rates of photosynthesis and foliar N concentration and their relationships with multiple climate variables. Fifty-five species across 27 families were examined across eight sites spanning contrasting biomes. Key questions addressed include: (i) Does Δ13C and intrinsic water-use efficiency (WUEi) vary with climate at a continental scale? (ii) What are the seasonal and spatial patterns in Δ13C/WUEi across biomes and species? (iii) To what extent does Δ13C reflect variation in leaf structural, functional and nutrient traits across climate gradients? and (iv) Does the relative importance of assimilation and stomatal conductance in driving variation in Δ13C differ across seasons? We found that MAP, temperature seasonality, isothermality and annual temperature range exerted independent effects on foliar Δ13C/WUEi. Temperature-related variables exerted larger effects than rainfall-related variables. The relative importance of photosynthesis and stomatal conductance (gs) in determining Δ13C differed across seasons: Δ13C was more strongly regulated by gs during the dry-season and by photosynthetic capacity during the wet-season. Δ13C was most strongly correlated, inversely, with leaf mass area ratio among all leaf attributes considered. Leaf Nmass was significantly and positively correlated with MAP during dry- and wet-seasons and with moisture index (MI) during the wet-season but was not correlated with Δ13C. Leaf Pmass showed significant positive relationship with MAP and Δ13C only during the dry-season. For all leaf nutrient-related traits, the relationships obtained for Δ13C with MAP or MI indicated that Δ13C at the species level reliably reflects the water status at the site level. Temperature and water availability, not foliar nutrient content, are the principal factors influencing Δ13C across Australia

Scaling leaf respiration with nitrogen and phosphorus in tropical forests across two continents

Leaf dark respiration (Rdark) represents an important component controlling the carbon balance in tropical forests. Here, we test how nitrogen (N) and phosphorus (P) affect Rdark and its relationship with photosynthesis using three widely separated tropical forests which differ in soil fertility. Rdark was measured on 431 rainforest canopy trees, from 182 species, in French Guiana, Peru and Australia. The variation in Rdark was examined in relation to leaf N and P content, leaf structure and maximum photosynthetic rates at ambient and saturating atmospheric CO2 concentration. We found that the site with the lowest fertility (French Guiana) exhibited greater rates of Rdark per unit leaf N, P and photosynthesis. The data from Australia, for which there were no phylogenetic overlaps with the samples from the South American sites, yielded the most distinct relationships of Rdark with the measured leaf traits. Our data indicate that no single universal scaling relationship accounts for variation in Rdark across this large biogeographical space. Variability between sites in the absolute rates of Rdark and the Rdark : photosynthesis ratio were driven by variations in N- and P-use efficiency, which were related to both taxonomic and environmental variability

The nature of weather and climate impacts in the energy sector

The power sector’s meteorological information needs are diverse and cover many different distinct applications and users. Recognising this diversity, it is important to understand the general nature of how weather and climate influence the energy sector and the implications they have for quantitative impact modelling. Using conceptual examples and illustrations from recent research, this chapter argues that the traditional ‘transfer function’ approach that is common to many industrial applications of weather and climate science—whereby weather can be directly mapped to an energy impact—is inadequate for many important power system applications (such as price forecasting and system operations and planning). The chapter concludes by arguing that a deeper understanding of how meteorological impacts in the energy sector are modelled is required

Coordination of photosynthetic traits across soil and climate gradients

"Least-cost theory" posits that C3 plants should balance rates of photosynthetic water loss and carboxylation in relation to the relative acquisition and maintenance costs of resources required for these activities. Here we investigated the dependency of photosynthetic traits on climate and soil properties using a new Australia-wide trait dataset spanning 528 species from 67 sites. We tested the hypotheses that plants on relatively cold or dry sites, or on relatively more fertile sites, would typically operate at greater CO2 drawdown (lower ratio of leaf internal to ambient CO2 , Ci :Ca ) during light-saturated photosynthesis, and at higher leaf N per area (Narea ) and higher carboxylation capacity (Vcmax 25 ) for a given rate of stomatal conductance to water vapour, gsw . These results would be indicative of plants having relatively higher water costs than nutrient costs. In general, our hypotheses were supported. Soil total phosphorus (P) concentration and (more weakly) soil pH exerted positive effects on the Narea -gsw and Vcmax 25 -gsw slopes, and negative effects on Ci :Ca . The P effect strengthened when the effect of climate was removed via partial regression. We observed similar trends with increasing soil cation exchange capacity and clay content, which affect soil nutrient availability, and found that soil properties explained similar amounts of variation in the focal traits as climate did. Although climate typically explained more trait variation than soil did, together they explained up to 52% of variation in the slope relationships and soil properties explained up to 30% of the variation in individual traits. Soils influenced photosynthetic traits as well as their coordination. In particular, the influence of soil P likely reflects the Australia's geologically ancient low-relief landscapes with highly leached soils. Least-cost theory provides a valuable framework for understanding trade-offs between resource costs and use in plants, including limiting soil nutrients

Whole animal experiments should be more like human randomized controlled trials

Beverly S. Muhlhausler, Frank H. Bloomfield, Matthew W. Gillma

Understanding and modelling wildfire regimes: An ecological perspective

Funder: H2020 European Research Council; doi: http://dx.doi.org/10.13039/100010663; Grant(s): Global Change 2.0: Unlocking the past for a cleare, Re-inventing Ecosystem And Land-surface Models, gr, SCATAPNUT, grant number 681885Abstract Recent extreme wildfire seasons in several regions have been associated with exceptionally hot, dry conditions, made more probable by climate change. Much research has focused on extreme fire weather and its drivers, but natural wildfire regimes—and their interactions with human activities—are far from being comprehensively understood. There is a lack of clarity about the ‘causes’ of wildfire, and about how ecosystems could be managed for the co-existence of wildfire and people. We present evidence supporting an ecosystem-centred framework for improved understanding and modelling of wildfire. Wildfire has a long geological history and is a pervasive natural process in contemporary plant communities. In some biomes, wildfire would be more frequent without human settlement; in others they would be unchanged or less frequent. A world without fire would have greater forest cover, especially in present-day savannas. Many species would be missing, because fire regimes have co-evolved with plant traits that resist, adapt to or promote wildfire. Certain plant traits are favoured by different fire frequencies, and may be missing in ecosystems that are normally fire-free. For example, post-fire resprouting is more common among woody plants in high-frequency fire regimes than where fire is infrequent. The impact of habitat fragmentation on wildfire crucially depends on whether the ecosystem is fire-adapted. In normally fire-free ecosystems, fragmentation facilitates wildfire starts and is detrimental to biodiversity. In fire-adapted ecosystems, fragmentation inhibits fires from spreading and fire suppression is detrimental to biodiversity. This interpretation explains observed, counterintuitive patterns of spatial correlation between wildfire and potential ignition sources. Lightning correlates positively with burnt area only in open ecosystems with frequent fire. Human population correlates positively with burnt area only in densely forested regions. Models for vegetation-fire interactions must be informed by insights from fire ecology to make credible future projections in a changing climate.</jats:p

Containing the burden of infectious diseases is everyone’s responsibility.:A call for an integrated strategy for developing and promoting hygiene behaviour change in home and everyday life

Across the world, health agencies recognize the profound impact of infectious disease on health and prosperity. Equally, they recognize that prevention is central to fighting infection, and that hygiene in home and everyday life (HEDL) is a key part of this. A current driver is the part that hygienei plays in tackling antibiotic resistance, but it also reflects growing numbers of people at greater risk of infection being cared for in the community. Sustaining the quality of state-funded healthcare requires that the public take greater responsibility for their own health, including protecting themselves and their families against infection. Hygiene must be must be everyone’s responsibility. However, if we are to be successful in promoting hygiene as part of public health, there are barriers which need to be overcome. A key issue is the need to balance evidence of the health benefits of hygiene against possible risks, such as environmental impacts and toxicity issues. Another issue is the role of microbes in human health and whether we have become “too clean”. Lack of a unified voice advocating for hygiene means these issues have tended to take precedence. Another barrier to change is public confusion about the need for hygiene and the difference between hygiene and cleanliness. To address this, we must work together to provide the public with a clear, consistent restatement of the importance of hygiene, and to change public perceptions about hygiene and good hygiene practice. This paper is unique because it examines these issues in an integrated manner and focuses on making achievable, constructive recommendations for developing an effective and sustainable approach. The paper lays out a risk management strategy for hygiene in home and everyday life which gives hygiene appropriate priority within the context of environmental and other health concerns. This “targeted hygiene” approach needs to be placed at the heart of a multimodal prevention strategy, alongside vaccination and other interventions. Based on the findings of this paper, we issue a call to action to national and international policy makers, health agencies and health professionals to recognize the need for an integrated, family-centredii approach to hygiene, and provide effective leadership to achieve this. This paper shows that many of the components of a behaviour change strategy are already in place, but need to be integrated rather than developed independently. We also issue a call to scientists, health professionals, environmental and regulatory agencies, immunologists, microbiomists, the private sector (hygiene appliance and product manufacturers) and the media to work together, through innovative research and communication policies. A collaborative effort is vital if we are to overcome barriers to change and action integrated behaviour change programmes that really work. The report represents the consensus views of an international, interdisciplinary group of experts in the field of infection prevention and hygiene. We recognise that this paper leaves many questions unanswered and would welcome further dialogue with stakeholders on how to develop policy. The aim of this paper is to provide a sound basis for such dialogue. At the 2016 launch of the European Human Biomonitoring Initiative, the EU commissioner for food safety said the followingiii which encapsulates the aim of this report. “We must collectively recognise that risk and uncertainty are part and parcel of every decision we take. We need to engage people in a serious and rational debate. But in this world of information overload – from old media and new – information, misinformation, opinions, prejudices, truths, half-truths and un-truths all compete for public attention. We need better communication of science so that people can be better informed about risk assessment and management decisions

Historical changes in the stomatal limitation of photosynthesis: empirical support for an optimality principle

The ratio of leaf‐internal (ci) to ambient (ca) partial pressure of CO2, defined here as χ, is an index of adjustments in both leaf stomatal conductance and photosynthetic rate to environmental conditions. Measurements and proxies of this ratio can be used to constrain vegetation models uncertainties for predicting terrestrial carbon uptake and water use. We test a theory based on the least‐cost optimality hypothesis for modelling historical changes in χ over the 1951‐2014 period, across different tree species and environmental conditions, as reconstructed from stable carbon isotopic measurements across a global network of 103 absolutely‐dated tree‐ring chronologies. The theory predicts optimal χ as a function of air temperature, vapour pressure deficit, ca and atmospheric pressure. The theoretical model predicts 39% of the variance in χ values across sites and years, but underestimates the inter‐site variability in the reconstructed χ trends, resulting in only 8% of the variance in χ trends across years explained by the model. Overall, our results support theoretical predictions that variations in χ are tightly regulated by the four environmental drivers. They also suggest that explicitly accounting for the effects of plant‐available soil water and other site‐specific characteristics might improve the predictions

Towards a target label-free suboptimum oligonucleotide displacement-based detection system

A novel method for the future development of label-free DNA sensors is proposed here. The approach is based on the displacement of a labelled suboptimum mutated oligonucleotide hybridised with the immobilised biotin-capture probe. The target fully complementary to the biotin-capture probe can displace the labelled oligonucleotide causing a subsequent decrease of the signal that verifies the presence of the target. The decrease of signal was demonstrated to be proportional to the target concentration. A study of the hybridisation of mutated and complementary labelled oligonucleotides with an immobilised biotin-capture probe was carried out. Different kinetic and thermodynamic behaviour was observed for heterogeneous hybridisation of biotin-capture probe with complementary or suboptimum oligonucleotides. The displacement method evaluated colourimetrically achieved the objective of decreasing the response time from 1 h for direct hybridisation of 19-mer oligonucleotides in the direct enzyme-linked oligonucleotide assay (ELONA) to 5 min in the case of displacement detection in the micromolar concentration range