Jérôme Ngao

• Ph.D.
• Researcher at French National Institute for Agriculture, Food, and Environment (INRAE)

Photosynthetic carbon assimilation rates are highly dependent on environmental factors such as light availability and on metabolic limitations such as the demand for carbon by sink organs. The relative effects of light and sink demand on photosynthesis in perennial plants such as trees remain poorly characterised. The aim of the present study was t...

Key message Scots pines developed for several years on volcano slopes showed a dwarf phenotype and a larger hydraulic safety margin than downslope trees, such that hydraulic safety was prioritized over growth. Abstract The ability of trees to survive and naturally regenerate under increasing drought conditions will depend on their capacity to vary...

The ability of trees to survive and naturally regenerate in increasing drought conditions will depend on their capacity to vary key hydraulic and morphological traits that increase drought tolerance. Despite many studies investigating variability in these drought-tolerant traits, there has been limited investigation into this variability under recu...

This study presents the coupling of TEB (Town Energy Balance) and Surfatm models developed for energy exchange estimates for urban impervious and vegetation surfaces, respectively. Once coupled, the TEB-Surfatm model allows the estimate of radiative, sensible (H), and latent heat (LE) fluxes in urban areas accounting for urban vegetation. The model...

Trees participate in mitigating the urban heat island phenomenon thanks to their transpiration and shading. This cooling potential is highly dependent on leaf area. Nevertheless, leaf traits potentially vary across different land management practices in urban settings, thereby challenging the models used to estimate thermal budgets. The present stu...

Herbivore insects have strong impacts on leaf gas exchange when feeding on the plant. Leaf age also drives leaf gas exchanges but the interaction of leaf age and phloem herbivory has been largely underexplored. We investigated the amplitude and direction of herbivore impact on leaf gas exchange across a wide range of leaf age in the apple tree–appl...

In this study, we measured the feed value, the freeze tolerance, and the drought tolerance of leaves from 14 woody plant species occurring in Auvergne. Analyses of leaf composition and digestible organic matter in vitro showed that white mulberry (Morris alba) and black elder (Sambucus nigra) have a high potential nutritional value, equivalent to t...

Urban trees provide many ecosystem services, including carbon sequestration, air quality improvement, storm water attenuation and energy conservation, to people living in cities. Provisioning of ecosystem services by urban trees, however, may be jeopardized by the typically poor quality of the soils in urban areas. Given their well-known multifunct...

Green Infrastructure is a nature-based-solution with the potential of mitigating the harmful and even deadly consequences of climate change and urbanisation in our urban areas. In particular, urban trees provide us with multiple ecosystem services, such as storm water control, carbon sequestration, soil health and temperature regulation. When suppo...

This research is investigating the trade-offs between the multiple ecosystem services of trees Trees are naturally sustainable as circular systems, providing multiple ecosystem services to mitigate and adapt to climate change Urban trees are nature-based solutions that provide us with multiple ecosystem services, such as stormwater control, carbon...

Urban trees play a key role in mitigating environmental problems in cities, but they often face harsh environmental conditions as they generally grow in sealed soils that have small rooting space and low water availability. In this context, rapid monitoring and assessment of tree health status is critical to maintain urban trees and secure the prov...

The aim of this paper is to investigate the minimal level of detail of the tree geometry reconstruction required to enable an accurate estimate of the evaporative cooling effect of an individual tree. The Functional Structural Plant Modeling approach, which links the 3D tree structure to its functioning, is used to investigate the impact of the lev...

In apple trees, external (temperature and water stress) and internal (hormonal signaling, carbon source-sink relationships) factors are assumed to affect floral induction and, consequently, to determine the regular or biennial fruiting behavior. Nevertheless, no clear consensus exists on the role of each factor and on the level of plant organizatio...

Trees in urban areas face harsh environmental conditions. Ectomycorrhizal fungi (EcM) form a symbiosis with many tree species and provide a range of benefits to their host through their extraradical hyphal network. Although our understanding of the environmental drivers and large scale geographical variation of EcM communities in natural ecosystems...

Heavy metals in urban soils may impose a threat to public health and may negatively affect urban tree viability. Vegetation spectroscopy techniques applied to bio-indicators bring new opportunities to characterize heavy metal contamination, without being constrained by laborious soil sampling and lab-based sample processing. Here we used Tilia tome...

Les îlots de chaleur urbains impactent fortement le confort thermique de la population urbaine et sont parfois renforcés par des vagues de chaleur. Pour minimiser ce phénomène, la végétalisation des villes s'avère nécessaire. Or, la manière dont la végétation interagit avec le milieu urbain n'est pas encore tout à fait bien comprise. L'analyse de s...

Determining the main factors causing urban tree decline is becoming essential for sustaining their health and survival. Understanding responses of tree growth to urban environments and climate change throughout tree life span is thus necessary. To explore these questions, a dendrochronological study exploring past climate-tree growth relationships...

In plants, carbon source–sink relationships are assumed to affect their reproductive effort. In fruit trees, carbon source–sink relationships are likely to be involved in their fruiting behavior. In apple, a large variability in fruiting behaviors exists, from regular to biennial, which has been related to the within-tree synchronization vs desynch...

Various models have been developed to predict tree growth and architecture over years, but few of them are capable of simulating 3D geometry development and shoot typology from a pre-existing crown geometry. In this study, we developed an approach for simulating 3D apple tree structure by combining 3D digitizing data with topological rules adapted...

Abstract The influence of drought intensity on spatial variability of leaf temperature was explored by the RATP model. We aimed at specifically determining (i) whether the spatial variability of leaf temperature was similar for the whole crown and for the top-viewed crown parts, and (ii) if the spatial variability at these two levels was comparable...

Presentation for the ISHS Orchard system symposium

Les micro-climats urbains et l'influence de la végétation font l'objet depuis 2013 d'une campagne de mesure spécifique sur l'agglomération de Strasbourg. Cette campagne comprend d'une part une réseau météorologique classique réparti sur l'ensemble de la ville, mais aussi des sites dédiés spécifiquement à l'étude détaillée des bilans radiatif et d'é...

L’équipe TRIO du laboratoire ICube (UMR 7357 Université de Strasbourg-CNRS) mène depuis 2013 un projet de recherche qui a pour objectif de comprendre et de modéliser la réponse de la zone urbaine de Strasbourg aux conditions imposées par le climat, en particulier lors de paroxysmes climatiques (canicules et périodes de grand froid). L’objectif cent...

Trees can potentially have a positive effect on the thermal urban climate due to their 3D spatial structure, their ability to intercept light and to evaporate water. Experimental and modelling works done since twenty years enabled to verify and quantify this potential at different scales: from the street to the city through the neighborhood. More p...

In a context of global climate change, mitigating the “urban heat island” effect is becoming an urging necessity with respect to human health. Among the different mitigating strategies, increasing the vegetated surface areas, such as trees and lawns, is thought to induce a cooling effect by increasing the latent heat flux (E) from the transpiring p...

Water availability is widely recognized as being an essential factor for tree survival, growth and for maximizing their ability in mitigating urban heat islands (UHI) through evapotranspiration. In urban areas, where the ground surface is highly impervious and the trees are not regularly irrigated, the reduction of precipitation infiltration into t...

Presentation for the X International Symposium on Modelling in Fruit Research and Orchard Management

Freezing stress is one of the most important limiting factors determining the ecological distribution and production of tree species. Assessment of frost risk is, therefore, critical for forestry, fruit production, and horticulture. Frost risk is substantial when hazard (i.e., exposure to damaging freezing temperatures) intersects with vulnerabilit...

Our objective was to quantify the production of ectomycorrhizal (ECM) hyphae throughout the growing season. For this purpose, we used ingrowth mesh bags (30 μm mesh filled with 40 g sand) in top soils of Fagus sylvatica, Quercus petraea and Pinus pinaster forests in France. Installations were done at three or four different growth phases at each si...

a b s t r a c t The aim of this study was to determine the amplitude and the driving factors of the spatial variability in soil CO 2 efflux in a young European beech forest. Soil CO 2 efflux was measured in 2003 and 2004 in seven beech plots differing in terms of soil type and leaf area index. After eliminating temporal fluctuations due to soil tem...

• Context The carbon isotope composition of the CO2 efflux (δ13CE) from ecosystem components is widely used to investigate carbon cycles and budgets at different ecosystem scales. δ13CE, was considered constant but is now known to vary along seasons. The seasonal variations have rarely been compared among different ecosystem components. • Aims We a...

Belowground carbon allocation is an important component of forest carbon budget, affecting tree growth (competition between aboveground and belowground carbon sinks), acquisition of belowground resources (nutrients and water) that are often limiting forest ecosystems and soil carbon sequestration. Total belowground carbon flow can be estimated usin...

Soil CO2 efflux is the main source of CO2 from forest ecosystems and it is tightly coupled to the transfer of recent photosynthetic assimilates belowground and their metabolism in roots, mycorrhiza and rhizosphere microorganisms feeding on root-derived exudates. The objectives of our study were to assess patterns of belowground carbon allocation am...

Soil CO2 efflux is the main source of CO2 from forest ecosystems and it is tightly coupled to the transfer of recent photosynthetic assimilates belowground and their metabolism in roots, mycorrhiza and rhizosphere microorganisms feeding on root-derived exudates. The objectives of our study were to assess patterns of belowground carbon allocation am...

• Phloem is the main pathway for transferring photosynthates belowground. In situ(13) C pulse labelling of trees 8-10 m tall was conducted in the field on 10 beech (Fagus sylvatica) trees, six sessile oak (Quercus petraea) trees and 10 maritime pine (Pinus pinaster) trees throughout the growing season. • Respired (13) CO(2) from trunks was tracked...

Temporal dynamics of C isotopic composition (delta13C) of CO2 and leaf litter was monitored during a litter decomposition experiment using Arbutus unedo L., as a slow decomposing model substrate. This allowed us (1) to quantify isotopic discrimination variation during litter decomposition, and (2) to test whether selective substrate use or kinetic...

Soil and trunk respiration are the major sources of carbon from forest ecosystems to the atmosphere and they account for a large fraction of total ecosystem respiration. The amount of photosynthate allocated to respiration affects the growth of the tree and the potential for carbon sequestration of forest ecosystems. This study, aiming at understan...

Above ground litter decomposition is the result of three interlinked processes: leaching, fragmentation and catabolism. Litter decomposition estimates are most commonly based on measurements of mass loss from litter residues, confined in mesh bags. This method provides a rough estimate of leaching and catabolism, while preventing fragmentation from...

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In fast-growing tree plantations, decomposition of leaf litter is considered as a key process of soil fertility. A three-month field experiment, spanning both rainy and dry seasons, was conducted to determine how changes in litter decomposition affect the main parameters of litter quality-namely, the concentrations of phenolic and non-phenolic carb...

The uncertainties of ecosystem response to global climate changes illustrate the need to improve knowledge of ecosystem functioning, in particular to explain the carbon (C) stock and fluxes variations and the abiotic and biotic factors driving such variations. Trunk CO2 efflux (RT) is a major component of total CO2 forest ecosystem efflux, but in c...

Trunk CO2 efflux is a major component of total CO2 forest ecosystem efflux but its determinism is still poorly understood. This CO2 flux could originate from different carbon sources (respiration of newly assimilates or reserves; xylem sap flow dissolved CO2). These potential CO2 sources of the ecosystem vary at a diurnal and seasonal time scale. T...

• Water and carbon fluxes, as measured by eddy covariance, climate, soil water content, leaf area index, tree biomass, biomass increment (BI), litter fall and mortality were monitored for 10 successive years in a young beech stand in Hesse forest (north-eastern France) under contrasting climatic and management conditions. • Large year-to-year varia...

Disentangling the autotrophic and heterotrophic components of soil CO2 efflux is critical to understanding the role of soil system in terrestrial carbon (C) cycling. In this study, we combined a stable C-isotope natural abundance approach with the trenched plot method to determine if root exclusion significantly affected the isotopic composition (δ...

This study aims to assess the effects of corrections for disturbances such as an increased amount of dead roots and an increase in volumetric soil water content on the calculation of soil CO2 efflux partitioning. Soil CO2 efflux, soil temperature and superficial soil water content were monitored in two young beech sites (H1 and H2) during a trenchi...

Earthworm relationships with vegetation have received extensive attention, and earthworm density has been shown to be related to vegetation types or plant species. However, the factors involved are rarely known. In Congo, we studied the effect of Chromolaena odorata (L) R.M. King & H. Robinson, which invades eucalypt plantations, on soil invertebra...

Methods involving stable isotopes have been successfully applied since decades in various research fields. Tracing 13C natural abundance in ecosystem compartments greatly enhanced the understanding of the C fluxes in the plant-soil-atmosphere C exchanges when compartments present different C isotopic signatures (i.e. atmospheric CO2 vs photosynthet...

Different soil CO2 efflux measurement systems and methodologies were used to estimate the annual soil respiration of different forest sites. To allow comparison between these annual values, this study aimed to cross-calibrate five soil CO2 efflux (RS) closed dynamic chamber systems, and compare the in situ measurement methodologies. We first assess...

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Le but de cette thèse est de séparer les composantes de la respiration de l'écosystème (RECO) et d'en dégager les facteurs majeurs influençant sa variabilité dans deux hêtraies. La respiration du sol (RS) et ses composantes autotrophe et hétérotrophe représentent la majeure part de RECO. Le flux de CO2 issu de la décomposition des débris ligneux et...

The contribution of leaf litter decomposition to total soil CO2 efflux (FL/F) was evaluated in a beech (Fagus sylvatica L.) forest in eastern France. The Keeling-plot approach was applied to estimate the isotopic composition of respired soil CO2 from soil covered with either control (−30.32‰) or 13C-depleted leaf litter (−49.96‰). The δ13C of respi...

Soil respiration was measured for six years from June 1996 to December 2001 in order to investigate both seasonal and interannual variations in a young beech forest in North Eastern France (Hesse forest). Soil respiration exhibited pronounced seasonal variations that clearly followed the seasonal changes in soil temperature (T) and soil water conte...

Eucalypt litter, which decomposes slowly, exhibits a high content of phenolic compounds, and the disappearance of these compounds during decomposition is expected to improve faunal consumption, litter decomposition and incorporation into the soil. The aim of this study was to measure the disappearance rate of the phenolic compounds in eucalypt litt...