Mediterranean trees vulnerability to climate change will not be minimized through hydraulic safety traits adjustments.

2021 ◽  
Author(s):  
Myriam Moreno ◽  
Guillaume Simioni ◽  
Jean-Marc Limousin ◽  
Jesus Rodriguez-Calcerrada ◽  
Julien Ruffault ◽  
...  
Keyword(s):  
Climate Change ◽  
Quercus Ilex ◽  
Pinus Halepensis ◽  
Rooting Depth ◽  
Quercus Pubescens ◽  
Widespread Species ◽  
Turgor Loss Point ◽  
Safety Margins ◽  
Significant Difference ◽  
Hydraulic Safety

<p><span>Climate change in the Mediterranean region leads to an intensification of summer droughts. These episodes of extreme water stress threaten the survival of tree species and, by the same token, would affect the structure and ecosystem services of woodlands. Indeed, in conditions of prolonged and intense drought, one of the major risks for trees is the hydraulic failure due to high embolism level. Xylem embolism risk depends essentially on various leaf and hydraulic traits including (i) the vulnerability of their xylem to cavitation, (ii) the turgor loss point (a surrogate for stomatal control) and (iii) their cuticular transpiration (gmin). The two former traits can be used to compute hydraulic safety margins (HSM). </span></p><p><span>In order to assess whether trees will survive future climatic conditions, it is necessary to quantify and assess the plasticity of these traits to intensified drought. In this study, we used three rainfall exclusion experiments established in mature forests in south-eastern France (Font-blanche, Puéchabon and O3HP experimental sites) to measure these traits and evaluate their ability to adjust to aggravated drought conditions for three Mediterranean widespread species: </span><span><em>Quercus ilex</em></span><span>, </span><span><em>Quercus Pubescens</em></span><span>, and </span><span><em>Pinus halepensis</em></span><span>. We performed pressure-volume curves of trees from rainfall exclusion and control plots to see if adjustments of gmin and leaf hydraulic traits involved in stomatal regulation occurred in these three species. Using the optical method and cavitron, we also quantified the plasticity of xylem vulnerability to cavitation by comparing the values of water potential leading to a 50% reduction in plant hydraulic conductance (P50). </span></p><p><span>Our results show that </span><span><em>Quercus pubescens</em></span><span> has the lowest HSM while </span><span><em>Quercus ilex</em></span><span> has the highest. In addition, gmin is higher for </span><span><em>Quercus pubescens</em></span><span> than for the other two species. All together these results suggest that </span><span><em>Quercus pubescens</em></span><span> is the most vulnerable to drought among the three studied. Globally, for most traits and species no significant difference was found between treatments. The only exception was for </span><span><em>Quercus ilex</em></span><span> that exhibited lower turgor loss point (Ψtlp) in the dry treatment. Drought acclimation for these species may rather depend on other traits, such as leaf area reduction or rooting depth. To integrate the role of these traits to estimate the historic and future mortality risk for these species, the use of hydraulic based models will be of interest. </span></p>

scholarly journals Large hydraulic safety margins protect Neotropical canopy rainforest tree species against hydraulic failure during drought

2019 ◽  
Vol 76 (4) ◽  
Author(s):  
Camille Ziegler ◽  
Sabrina Coste ◽  
Clément Stahl ◽  
Sylvain Delzon ◽  
Sébastien Levionnois ◽  
...  
Keyword(s):  
Tree Species ◽  
Turgor Loss Point ◽  
Canopy Tree ◽  
Hydraulic Failure ◽  
Xylem Vulnerability ◽  
Safety Margins ◽  
Hydraulic Safety ◽  
Dry Seasons ◽  
Canopy Tree Species ◽  
Embolism Resistance

Abstract Key message Abundant Neotropical canopy-tree species are more resistant to drought-induced branch embolism than what is currently admitted. Large hydraulic safety margins protect them from hydraulic failure under actual drought conditions. Context Xylem vulnerability to embolism, which is associated to survival under extreme drought conditions, is being increasingly studied in the tropics, but data on the risk of hydraulic failure for lowland Neotropical rainforest canopy-tree species, thought to be highly vulnerable, are lacking. Aims The purpose of this study was to gain more knowledge on species drought-resistance characteristics in branches and leaves and the risk of hydraulic failure of abundant rainforest canopy-tree species during the dry season. Methods We first assessed the range of branch xylem vulnerability to embolism using the flow-centrifuge technique on 1-m-long sun-exposed branches and evaluated hydraulic safety margins with leaf turgor loss point and midday water potential during normal- and severe-intensity dry seasons for a large set of Amazonian rainforest canopy-tree species. Results Tree species exhibited a broad range of embolism resistance, with the pressure threshold inducing 50% loss of branch hydraulic conductivity varying from − 1.86 to − 7.63 MPa. Conversely, we found low variability in leaf turgor loss point and dry season midday leaf water potential, and mostly large, positive hydraulic safety margins. Conclusions Rainforest canopy-tree species growing under elevated mean annual precipitation can have high resistance to embolism and are more resistant than what was previously thought. Thanks to early leaf turgor loss and high embolism resistance, most species have a low risk of hydraulic failure and are well able to withstand normal and even severe dry seasons.

scholarly journals Litter traits and rainfall reduction alter microbial litter decomposers: the evidence from three Mediterranean forests

2019 ◽  
Author(s):  
S Pereira ◽  
A Burešová ◽  
J Kopecky ◽  
P Mádrová ◽  
A Aupic-Samain ◽  
...  
Keyword(s):  
Quercus Ilex ◽  
Pinus Halepensis ◽  
Community Change ◽  
Mediterranean Forests ◽  
Quercus Pubescens ◽  
Forest Sites ◽  
Litter Traits ◽  
Drought Conditions ◽  
Rainfall Reduction ◽  
Total Bacteria

Abstract The objective of the study was to evaluate changes in microbial communities with the predicted arrival of new species to Mediterranean forests under projected intensification of water stress conditions. For that, litter from three Mediterranean forests dominated respectively by Quercus pubescens Willd., Quercus ilex L. and Pinus halepensis Mill. was collected, and placed to their ‘home’ forest but also to the two other forests under natural and amplified drought conditions (i.e. rainfall reduction of 30%). Quantitative PCR showed that overall, actinobacteria and total bacteria were more abundant in Q. pubescens and Q. ilex than in P. halepensis litter. However, the abundance of both groups was dependent on the forest sites: placement of allochthonous litter to Q. pubescens and P. halepensis forests (i.e. P. halepensis and Q. pubescens, respectively) increased bacterial and fungal abundances, while no effect was observed in Q. ilex forest. P. halepensis litter in Q. pubescens and Q. ilex forests significantly reduced actinobacteria (A/F) and total bacteria (B/F) to fungi ratios. The reduction of rainfall did not influence actinobacteria and bacteria but caused an increase of fungi. As a result, a reduction of A/F ratio is expected with the plant community change towards the dominance of spreading P. halepensis under amplified drought conditions.

Biomass of understory species of Pinus halepensis Mill. forests in the Kassandra Peninsula - Chalkidiki

1998 ◽  
Vol 63 ◽  
Author(s):  
P. Smiris ◽  
F. Maris ◽  
K. Vitoris ◽  
N. Stamou ◽  
P. Ganatsas
Keyword(s):  
Moisture Content ◽  
Aboveground Biomass ◽  
Quercus Ilex ◽  
Pinus Halepensis ◽  
Biomass Estimation ◽  
Regression Equations ◽  
Pistacia Lentiscus ◽  
Quercus Coccifera ◽  
Understory Species ◽  
Cistus Incanus

This  study deals with the biomass estimation of the understory species of Pinus halepensis    forests in the Kassandra peninsula, Chalkidiki (North Greece). These  species are: Quercus    coccifera, Quercus ilex, Phillyrea media, Pistacia lentiscus, Arbutus  unedo, Erica arborea, Erica    manipuliflora, Smilax aspera, Cistus incanus, Cistus monspeliensis,  Fraxinus ornus. A sample of    30 shrubs per species was taken and the dry and fresh weights and the  moisture content of    every component of each species were measured, all of which were processed  for aboveground    biomass data. Then several regression equations were examined to determine  the key words.

scholarly journals Impacts of Climate Change Interacting Abiotic Factors on Growth, aflD and aflR Gene Expression and Aflatoxin B1 Production by Aspergillus flavus Strains In Vitro and on Pistachio Nuts

Toxins ◽  
2021 ◽  
Vol 13 (6) ◽  
pp. 385
Author(s):  
Alaa Baazeem ◽  
Alicia Rodriguez ◽  
Angel Medina ◽  
Naresh Magan
Keyword(s):  
Climate Change ◽  
Gene Expression ◽  
Water Stress ◽  
Aspergillus Flavus ◽  
Aflatoxin B1 ◽  
Abiotic Factors ◽  
Pistachio Nuts ◽  
Significant Difference ◽  
Spoilage Fungi

Pistachio nuts are an important economic tree nut crop which is used directly or processed for many food-related activities. They can become colonized by mycotoxigenic spoilage fungi, especially Aspergillus flavus, mainly resulting in contamination with aflatoxins (AFs), especially aflatoxin B1 (AFB1). The prevailing climate in which these crops are grown changes as temperature and atmospheric CO2 levels increase, and episodes of extreme wet/dry cycles occur due to human industrial activity. The objectives of this study were to evaluate the effect of interacting Climate Change (CC)-related abiotic factors of temperature (35 vs. 37 °C), CO2 (400 vs. 1000 ppm), and water stress (0.98–0.93 water activity, aw) on (a) growth (b) aflD and aflR biosynthetic gene expression and (c) AFB1 production by two strains A. flavus (AB3, AB10) in vitro on milled pistachio-based media and when colonizing layers of shelled raw pistachio nuts. The A. flavus strains were resilient in terms of growth on pistachio-based media and the colonisation of pistachio nuts with no significant difference when exposed to the interacting three-way climate-related abiotic factors. However, in vitro studies showed that AFB1 production was significantly stimulated (p < 0.05), especially when exposed to 1000 ppm CO2 at 0.98–0.95 aw and 35 °C, and sometimes in the 37 °C treatment group at 0.98 aw. The relative expression of the structural aflD gene involved in AFB1 biosynthesis was decreased or only slightly increased, relative to the control conditions at elevated CO, regardless of the aw level examined. For the regulatory aflR gene expression, there was a significant (p < 0.05) increase in 1000 ppm CO2 and 37 °C for both strains, especially at 0.95 aw. The in situ colonization of pistachio nuts resulted in a significant (p < 0.05) stimulation of AFB1 production at 35 °C and 1000 ppm CO2 for both strains, especially at 0.98 aw. At 37 °C, AFB1 production was either decreased, in strain AB3, or remained similar, as in strain AB10, when exposed to 1000 ppm CO2. This suggests that CC factors may have a differential effect, depending on the interacting conditions of temperature, exposure to CO2 and the level of water stress on AFB1 production.

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