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The rate of metabolic processes demanding energy in tree stems changes in relation with prevailing climatic conditions. Tree water availability can affect stem respiration through impacts on growth, phloem transport or maintenance of diverse cellular processes, but little is known on this topic. Here we monitored seasonal changes in stem CO2 efﬂux (Fs), radial growth, sap ﬂow and non-structural carbohydrates in trees of Quercus ilex in a Mediterranean forest stand subjected since 2003 to either partial (33%) throughfall exclusion (E) or unchanged throughfall (C). Fs increased exponentially during the day by an effect of temperature, although sap ﬂow attenuated the increase in Fs during the day time. Over the year, Fs also increased exponentially with increasing temperatures, but Fs computed at a standard temperature of 15 ◦C (Fs15) varied by almost 4-fold among dates. Fs15 was the highest after periods of stem growth and decreased as tree water availability decreased, similarly in C and E treatments. The decline in Fs15 was not linked to a depletion of soluble sugars, which increased when water stress was higher. The proportion of ecosystem respiration attributed to the stems was highest following stem growth (23.3%) and lowest during the peak of drought (6.5%). High within-year variability in Fs15 makes unadvisable to pool annual data of Fs vs. temperature to model Fs at short time scales (hours to months) in Mediterranean-type forest ecosystems. We demonstrate that water availability is an important factor governing stem CO2 efﬂux and suggest that trees in Mediterranean environments acclimate to seasonal drought by reducing stem respiration. Stem respiratory rates do not seem to change after a long-term increase in drought intensity, however.

Auteurs, date et publication :

Auteurs Jesús Rodríguez-Calcerrada

Publication : Agricultural and Forest Meteorology

Date : 2025

Pages : 12

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#CNRS #FORET Puechabon

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Auteurs Andre Obregon , Christine Gehrig-Downie , S Robbert Gradstein , Jörg Bendix

Publication : Remote sensing of environment

Date : 2025

Volume : 155

Pages : 312-324

Catégorie(s)

#CNRS #FORET Nouragues

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Auteurs Pierre-Jean G Malé , Jean-Baptiste Ferdy , Céline Leroy , Olivier Roux , Jérémie Lauth , Arthur Avilez , Alain Dejean , Angélique Quilichini , Jérôme Orivel

Publication : Evolutionary Biology

Date : 2025

Volume : 41

Issue : 1

Pages : 22-28

Catégorie(s)

#CNRS #FORET Nouragues

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Auteurs Traci L Grzymala , Kipling W Will

Publication : ZooKeys

Date : 2025

Issue : 416

Pages : 77

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#⛔ No DOI found #CNRS #FORET Nouragues

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The airborne plant pathogenic bacterium Pseudomonas syringae is ubiquitous in headwaters, snowpack and precipitation where its populations are genetically and phenotypically diverse. Here, we assessed its population dynamics during snowmelt in headwaters of the French Alps. We revealed a continuous and signiﬁcant transport of P. syringae by these waters in which the population density is correlated with water chemistry. Via in situ observations and laboratory experiments, we validated that P. syringae is effectively transported with the snow melt and rain water inﬁltrating through the soil of subalpine grasslands, leading to the same range of concentrations as measured in headwaters (102–105 CFU l−1). A population structure analysis conﬁrmed the relatedness between populations in percolated water and those above the ground (i.e. rain, leaf litter and snowpack). However, the transport study in porous media suggested that water percolation could have different efficiencies for different strains of P. syringae. Finally, leaching of soil cores incubated for up to 4 months at 8°C showed that indigenous populations of P. syringae were able to survive in subalpine soil under cold temperature. This study brings to light the underestimated role of hydrological processes involved in the long distance dissemination of P. syringae.

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Auteurs Caroline L. Monteil , François Lafolie , Jimmy Laurent , Jean-Christophe Clement , Roland Simler , Yves Travi , Cindy E. Morris

Publication : Environmental Microbiology

Date : 2025

Volume : 16

Issue : 7

Pages : 2038-2052

Catégorie(s)

#CNRS #Lautaret #UGA

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