Contents Summary I. Introduction II. Comparison of various definitions and measurement techniques... more Contents Summary I. Introduction II. Comparison of various definitions and measurement techniques of minimum conductance III. Cuticular conductance IV. Contribution of stomata V. Environmental and ecological variation in minimum conductance VI. Use of minimum conductance in models VII. Conclusions Acknowledgements References SUMMARY: When the rate of photosynthesis is greatly diminished, such as during severe drought, extreme temperature or low light, it seems advantageous for plants to close stomata and completely halt water loss. However, water loss continues through the cuticle and incompletely closed stomata, together constituting the leaf minimum conductance (g ). In this review, we critically evaluate the sources of variation in g , quantitatively compare various methods for its estimation, and illustrate the role of g in models of leaf gas exchange. A literature compilation of g as measured by the weight loss of detached leaves is presented, which shows much variation in this...
<p>Modeling forest drought-induced mortality is critical for predicting the... more <p>Modeling forest drought-induced mortality is critical for predicting the impacts of climate change on ecosystems, natural resources, and global carbon- and water-cycles. The incorporation of mechanistic representations of how water moves through plants (i.e., plant hydraulics) in vegetation, land surface, and Earth system models has enabled estimating the degree of vascular damage that plants experience due to drought stress, with the possibility of mechanistically relating vascular stress to plant mortality. We used forest inventory data and a plant hydraulics model for predicting forest mortality across Western United States. We found that incorporating plant hydraulic model outputs of vascular damage and photosynthetic assimilation in generalized linear models and random forest models improved forest mortality predictions. Nevertheless, the variance explained by these models was relatively low. We use this study to highlight which are the challenges for predicting forest drought-induced mortality at landscape scales. We also propose future research lines that will help close existing knowledge gaps and improve mortality predictions.</p>
persal, until the seeds germinate and settle. The effect of small mammals, birds or ants on secon... more persal, until the seeds germinate and settle. The effect of small mammals, birds or ants on secondary seed dispersal has been addressed for many forest species included Pinaceae (Briggs et al., 2009) and Fagaceae (Herrera et al., 1994). Both primary and secondary dispersal constitute the 'basic' dispersal (Bontemps et al., 2013), which is the template for recruitment. Effective dispersal combines primary and secondary dispersal with establishment (Nathan & Muller-Landau, 2000), and ultimately determines population dynamics and colonization patterns.
Dutch elm disease (DED) spread across Europe and North America in the 20th century killing most n... more Dutch elm disease (DED) spread across Europe and North America in the 20th century killing most natural elm populations. Today, breeding programmes aim at identifying, propagating and studying elm clones resistant to DED. Here, we have compared the physiology and biochemistry of six genotypes of Ulmus minor of variable DED resistance. Leaf gas exchange, water potential, stem hydraulic conductivity and biochemical status were studied in 5-year-old trees of AB-AM2.4, M-DV2.3, M-DV2 9 M-CC1.5 and M-DV1 and 6-year-old trees of VA-AP38 and BU-FL7 before and after inoculation with Ophiostoma novo-ulmi. Leaf water potential and net photosynthesis rates declined, while the percentage loss of hydraulic conductivity (PLC) increased after the inoculation in susceptible trees. By the 21st day, leaf predawn and midday water potential, stomatal conductance to water vapour and net photosynthesis rates were lower, and PLC was higher in trees of susceptible (S) genotypes inoculated with the pathogen than in control trees inoculated with water, whereas no significant treatment effect was observed on these variables in the resistant (R) genotypes. Fourier transform infrared spectroscopy analyses revealed a different biochemical profile for branches of R and S clones. R clones showed higher absorption peaks that could be assigned to phenolic compounds, saturated hydrocarbons, cellulose and hemicellulose than S clones. The differences were more marked at the end of the experiment than at the beginning, suggesting that R and S clones responded differently to the inevitable wounding from inoculation and repeated sampling over the experimental course. We hypothesize that a weak activation of the defence system in response to experimental wounding can contribute to the susceptibility of some genotypes to O. novo-ulmi. In turn, the decline in shoot hydraulic conductivity and leaf carbon uptake caused by the infection further exacerbates tree susceptibility to the fungus.
Leaf water potential (ψleaf), typically measured using the pressure chamber, is the most importan... more Leaf water potential (ψleaf), typically measured using the pressure chamber, is the most important metric of plant water status, providing high theoretical value and information content for multiple applications in quantifying critical physiological processes including drought responses. Pressure chamber measurements of ψleaf (ψleafPC) are most typical, yet, the practical complexity of the technique and of the underlying theory has led to ambiguous understanding of the conditions to optimize measurements. Consequently, specific techniques and precautions diversified across the global research community, raising questions of reliability and repeatability. Here, we surveyed specific methods of ψleafPC from multiple laboratories, and synthesized experiments testing common assumptions and practices in ψleafPC for diverse species: (i) the need for equilibration of previously transpiring leaves; (ii) leaf storage before measurement; (iii) the equilibration of ψleaf for leaves on bagged br...
The low recruitment success of some endemic species under Mediterranean environmental conditions ... more The low recruitment success of some endemic species under Mediterranean environmental conditions is primarily the result of a low ability to create an efficient (highly conductive) and safe (able to maintain an intact water column under negative pressure) hydraulic system. Consequently, their lower resistance to drought-induced cavitation may induce mortality in seedlings and, during summer droughts, in mature individuals. In this study, the hydraulic safety (water potential at 50% loss of conductivity, P 50), hydraulic efficiency (specific conductivity, Ks) and xylem anatomy were compared between Rhamnus ludovicisalvatoris, an endemic species of the Balearic Islands whose distribution area is being reduced, and two populations of Rhamnus alaternus, which is widely distributed along the Mediterranean basin. R. ludovicisalvatoris was found to be more susceptible to drought-induced cavitation and less efficient at conducting water in comparison with R. alaternus. Moreover, R. ludovici-salvatoris demonstrated a lower vessel area, wood density and inter-vessel wall strength than R. alaternus. These results are in accordance with the lower ability of R. ludovici-salvatoris to recruit seedlings under Mediterranean conditions in comparison with R. alaternus; this may partially explain the reduction in the distribution area of R. ludovici-salvatoris.
External induction of resin secretion, based on the defence system of Pinus trees, has been perfo... more External induction of resin secretion, based on the defence system of Pinus trees, has been performed by humans since Classical times through various methods. The socioeconomic implication of this practice in Spain and the expansion of the Chinese market justify a new approach to tapping methodology and the effects of this activity on the tree. The resin yield of 561 Pinus pinaster trees in a stand in central Spain, tapped in 2012 using four different methods (mechanised or traditional tool, upwards or downwards), was analysed. An anatomical study was made of 13 trees (8 tapped and 5 controls) in another stand 13 km away with similar climate and soil conditions, tapped in 2011 using the same four methods. From each tapped tree, eight cores were taken at different locations and varying distances from the tapping wound. In each core, an analysis was made of growth ring, earlywood and latewood width, and axial canal frequency, area, mean size and location from one year before tapping to two years after (2010-2013). The highest mean annual resin yield was found for traditional tool upward tapping, which also induced the highest increase in axial canal frequency and area. The lowest yield was found for mechanised tapping, which showed no differences between the upward and downward directions. The strongest induction of systemic induced responses in terms of resin canal frequency and area was detected one year after tapping for upward tapping. This suggests the involvement of signalling processes that spread mainly upwards, and the importance of adaptive processes as a defence to periodic insect attacks for this forest tree.
Slow growth, branch dieback and scarce acorn yield are visible symptoms of decay in abandoned Que... more Slow growth, branch dieback and scarce acorn yield are visible symptoms of decay in abandoned Quercus pyrenaica coppices. A hypothetical root-to-shoot (R:S) imbalance provoked by historical coppicing is investigated as the underlying driver of stand degradation. After stem genotyping, 12 stems belonging to two clones covering 81 and 16 m 2 were harvested and excavated to measure above-and belowground biomass and nonstructural carbohydrate (NSC) pools. To study root system functionality, root connections and root longevity were assessed by radiocarbon analysis. Seasonality of NSC was monitored on five additional clones. NSC pools, R:S biomass ratio and fine roots-to-foliage ratio were higher in the large clone, whose centennial root system, estimated to be 550 years old, maintained large amounts of sapwood (51.8%) for NSC storage. 248 root connections were observed within the large clone, whereas the small clone showed comparatively simpler root structure (26 connections). NSC concentrations were higher in spring (before bud burst) and autumn (before leaf fall), and lower in summer (after complete leaf expansion); they were always higher in roots than in stems or twigs. The persistence of massive and highly interconnected root systems after coppicing may lead to increasing R:S biomass ratios and root NSC pools over time. We highlight the need of surveying belowground organs to understand aboveground dynamics of Q. pyrenaica, and suggest that enhanced belowground NSC storage and consumption reflect a trade-off between clonal vegetative resilience and aboveground performance.
High temperatures threaten tree survival and regeneration. A few pine species, such as Pinus ooca... more High temperatures threaten tree survival and regeneration. A few pine species, such as Pinus oocarpa and Pinus canariensis, resprout after complete defoliation, a likely consequence of evolving in volcanic environments. Pinus pinea and Pinus pinaster rely on other mechanisms to survive wildfires. We hypothesized that the needle water potential (Ψ) and needle osmotic potential (Ψs) would decrease more under hot wind in resprouting species, a strategy of needle sacrifice in accordance with the hydraulic segmentation hypothesis. We submitted two-year-old seedlings to a two-phase hot wind treatment, consisting of one hour at 39 °C followed by five minutes at 70 °C. Phase 2 killed all needles. In non-resprouting species, Ψ decreased steeply at the beginning of Phase 1 and remained between −2 MPa and −4 MPa afterward, maintaining the loss of stem hydraulic conductance below the 50% threshold. On average, resprouting species had 15% lower wood densities and kept 51% higher stem water conte...
In Mediterranean ecosystems, water shortage is the main factor constraining survival and growth o... more In Mediterranean ecosystems, water shortage is the main factor constraining survival and growth of plants. Xylem hydraulic properties are a key factor for the general function of plants as they exert a strong influence on water transport and therefore on the potential for carbon uptake. Resistance to cavitation has been considered a major character involved in drought tolerance. However, variation in cavitation vulnerability could be accompanied by a trade-off with other water transport and physiological traits. We investigated stem xylem vulnerability to cavitation in Pinus canariensis, the only endemic pine of the Canary Islands (Spain). We used the ‘Cavitron’ technique (Cochard 2002; Cochard et al. 2005) to construct xylem vulnerability curves.
In recent years, the use of wood has gained social interest, leading to a global increase in its ... more In recent years, the use of wood has gained social interest, leading to a global increase in its demand. Yet, this demand is often covered by the production of woods of low natural durability against biological deterioration. The main biological agents with the potential to attack the structural integrity of wood are wood-decay fungi, saproxylic beetles, termites, and marine molluscs and crustaceans. In most circumstances, fungi are the main wood-deteriorating agents. To attack the cell wall, wood-decay fungi combine a complex enzymatic mechanism with non-enzymatic mechanisms based on low-molecular-weight compounds. In some cases, the larvae of saproxylic beetles can also digest cell wood components, causing serious deterioration to wooden structures. The impact of subterranean termites in Europe is concentrated in the Southern countries, causing important economic losses. However, alien invasive species of voracious subterranean termites are expanding their presence in Europe. Wood...
Contents Summary I. Introduction II. Comparison of various definitions and measurement techniques... more Contents Summary I. Introduction II. Comparison of various definitions and measurement techniques of minimum conductance III. Cuticular conductance IV. Contribution of stomata V. Environmental and ecological variation in minimum conductance VI. Use of minimum conductance in models VII. Conclusions Acknowledgements References SUMMARY: When the rate of photosynthesis is greatly diminished, such as during severe drought, extreme temperature or low light, it seems advantageous for plants to close stomata and completely halt water loss. However, water loss continues through the cuticle and incompletely closed stomata, together constituting the leaf minimum conductance (g ). In this review, we critically evaluate the sources of variation in g , quantitatively compare various methods for its estimation, and illustrate the role of g in models of leaf gas exchange. A literature compilation of g as measured by the weight loss of detached leaves is presented, which shows much variation in this...
<p>Modeling forest drought-induced mortality is critical for predicting the... more <p>Modeling forest drought-induced mortality is critical for predicting the impacts of climate change on ecosystems, natural resources, and global carbon- and water-cycles. The incorporation of mechanistic representations of how water moves through plants (i.e., plant hydraulics) in vegetation, land surface, and Earth system models has enabled estimating the degree of vascular damage that plants experience due to drought stress, with the possibility of mechanistically relating vascular stress to plant mortality. We used forest inventory data and a plant hydraulics model for predicting forest mortality across Western United States. We found that incorporating plant hydraulic model outputs of vascular damage and photosynthetic assimilation in generalized linear models and random forest models improved forest mortality predictions. Nevertheless, the variance explained by these models was relatively low. We use this study to highlight which are the challenges for predicting forest drought-induced mortality at landscape scales. We also propose future research lines that will help close existing knowledge gaps and improve mortality predictions.</p>
persal, until the seeds germinate and settle. The effect of small mammals, birds or ants on secon... more persal, until the seeds germinate and settle. The effect of small mammals, birds or ants on secondary seed dispersal has been addressed for many forest species included Pinaceae (Briggs et al., 2009) and Fagaceae (Herrera et al., 1994). Both primary and secondary dispersal constitute the 'basic' dispersal (Bontemps et al., 2013), which is the template for recruitment. Effective dispersal combines primary and secondary dispersal with establishment (Nathan & Muller-Landau, 2000), and ultimately determines population dynamics and colonization patterns.
Dutch elm disease (DED) spread across Europe and North America in the 20th century killing most n... more Dutch elm disease (DED) spread across Europe and North America in the 20th century killing most natural elm populations. Today, breeding programmes aim at identifying, propagating and studying elm clones resistant to DED. Here, we have compared the physiology and biochemistry of six genotypes of Ulmus minor of variable DED resistance. Leaf gas exchange, water potential, stem hydraulic conductivity and biochemical status were studied in 5-year-old trees of AB-AM2.4, M-DV2.3, M-DV2 9 M-CC1.5 and M-DV1 and 6-year-old trees of VA-AP38 and BU-FL7 before and after inoculation with Ophiostoma novo-ulmi. Leaf water potential and net photosynthesis rates declined, while the percentage loss of hydraulic conductivity (PLC) increased after the inoculation in susceptible trees. By the 21st day, leaf predawn and midday water potential, stomatal conductance to water vapour and net photosynthesis rates were lower, and PLC was higher in trees of susceptible (S) genotypes inoculated with the pathogen than in control trees inoculated with water, whereas no significant treatment effect was observed on these variables in the resistant (R) genotypes. Fourier transform infrared spectroscopy analyses revealed a different biochemical profile for branches of R and S clones. R clones showed higher absorption peaks that could be assigned to phenolic compounds, saturated hydrocarbons, cellulose and hemicellulose than S clones. The differences were more marked at the end of the experiment than at the beginning, suggesting that R and S clones responded differently to the inevitable wounding from inoculation and repeated sampling over the experimental course. We hypothesize that a weak activation of the defence system in response to experimental wounding can contribute to the susceptibility of some genotypes to O. novo-ulmi. In turn, the decline in shoot hydraulic conductivity and leaf carbon uptake caused by the infection further exacerbates tree susceptibility to the fungus.
Leaf water potential (ψleaf), typically measured using the pressure chamber, is the most importan... more Leaf water potential (ψleaf), typically measured using the pressure chamber, is the most important metric of plant water status, providing high theoretical value and information content for multiple applications in quantifying critical physiological processes including drought responses. Pressure chamber measurements of ψleaf (ψleafPC) are most typical, yet, the practical complexity of the technique and of the underlying theory has led to ambiguous understanding of the conditions to optimize measurements. Consequently, specific techniques and precautions diversified across the global research community, raising questions of reliability and repeatability. Here, we surveyed specific methods of ψleafPC from multiple laboratories, and synthesized experiments testing common assumptions and practices in ψleafPC for diverse species: (i) the need for equilibration of previously transpiring leaves; (ii) leaf storage before measurement; (iii) the equilibration of ψleaf for leaves on bagged br...
The low recruitment success of some endemic species under Mediterranean environmental conditions ... more The low recruitment success of some endemic species under Mediterranean environmental conditions is primarily the result of a low ability to create an efficient (highly conductive) and safe (able to maintain an intact water column under negative pressure) hydraulic system. Consequently, their lower resistance to drought-induced cavitation may induce mortality in seedlings and, during summer droughts, in mature individuals. In this study, the hydraulic safety (water potential at 50% loss of conductivity, P 50), hydraulic efficiency (specific conductivity, Ks) and xylem anatomy were compared between Rhamnus ludovicisalvatoris, an endemic species of the Balearic Islands whose distribution area is being reduced, and two populations of Rhamnus alaternus, which is widely distributed along the Mediterranean basin. R. ludovicisalvatoris was found to be more susceptible to drought-induced cavitation and less efficient at conducting water in comparison with R. alaternus. Moreover, R. ludovici-salvatoris demonstrated a lower vessel area, wood density and inter-vessel wall strength than R. alaternus. These results are in accordance with the lower ability of R. ludovici-salvatoris to recruit seedlings under Mediterranean conditions in comparison with R. alaternus; this may partially explain the reduction in the distribution area of R. ludovici-salvatoris.
External induction of resin secretion, based on the defence system of Pinus trees, has been perfo... more External induction of resin secretion, based on the defence system of Pinus trees, has been performed by humans since Classical times through various methods. The socioeconomic implication of this practice in Spain and the expansion of the Chinese market justify a new approach to tapping methodology and the effects of this activity on the tree. The resin yield of 561 Pinus pinaster trees in a stand in central Spain, tapped in 2012 using four different methods (mechanised or traditional tool, upwards or downwards), was analysed. An anatomical study was made of 13 trees (8 tapped and 5 controls) in another stand 13 km away with similar climate and soil conditions, tapped in 2011 using the same four methods. From each tapped tree, eight cores were taken at different locations and varying distances from the tapping wound. In each core, an analysis was made of growth ring, earlywood and latewood width, and axial canal frequency, area, mean size and location from one year before tapping to two years after (2010-2013). The highest mean annual resin yield was found for traditional tool upward tapping, which also induced the highest increase in axial canal frequency and area. The lowest yield was found for mechanised tapping, which showed no differences between the upward and downward directions. The strongest induction of systemic induced responses in terms of resin canal frequency and area was detected one year after tapping for upward tapping. This suggests the involvement of signalling processes that spread mainly upwards, and the importance of adaptive processes as a defence to periodic insect attacks for this forest tree.
Slow growth, branch dieback and scarce acorn yield are visible symptoms of decay in abandoned Que... more Slow growth, branch dieback and scarce acorn yield are visible symptoms of decay in abandoned Quercus pyrenaica coppices. A hypothetical root-to-shoot (R:S) imbalance provoked by historical coppicing is investigated as the underlying driver of stand degradation. After stem genotyping, 12 stems belonging to two clones covering 81 and 16 m 2 were harvested and excavated to measure above-and belowground biomass and nonstructural carbohydrate (NSC) pools. To study root system functionality, root connections and root longevity were assessed by radiocarbon analysis. Seasonality of NSC was monitored on five additional clones. NSC pools, R:S biomass ratio and fine roots-to-foliage ratio were higher in the large clone, whose centennial root system, estimated to be 550 years old, maintained large amounts of sapwood (51.8%) for NSC storage. 248 root connections were observed within the large clone, whereas the small clone showed comparatively simpler root structure (26 connections). NSC concentrations were higher in spring (before bud burst) and autumn (before leaf fall), and lower in summer (after complete leaf expansion); they were always higher in roots than in stems or twigs. The persistence of massive and highly interconnected root systems after coppicing may lead to increasing R:S biomass ratios and root NSC pools over time. We highlight the need of surveying belowground organs to understand aboveground dynamics of Q. pyrenaica, and suggest that enhanced belowground NSC storage and consumption reflect a trade-off between clonal vegetative resilience and aboveground performance.
High temperatures threaten tree survival and regeneration. A few pine species, such as Pinus ooca... more High temperatures threaten tree survival and regeneration. A few pine species, such as Pinus oocarpa and Pinus canariensis, resprout after complete defoliation, a likely consequence of evolving in volcanic environments. Pinus pinea and Pinus pinaster rely on other mechanisms to survive wildfires. We hypothesized that the needle water potential (Ψ) and needle osmotic potential (Ψs) would decrease more under hot wind in resprouting species, a strategy of needle sacrifice in accordance with the hydraulic segmentation hypothesis. We submitted two-year-old seedlings to a two-phase hot wind treatment, consisting of one hour at 39 °C followed by five minutes at 70 °C. Phase 2 killed all needles. In non-resprouting species, Ψ decreased steeply at the beginning of Phase 1 and remained between −2 MPa and −4 MPa afterward, maintaining the loss of stem hydraulic conductance below the 50% threshold. On average, resprouting species had 15% lower wood densities and kept 51% higher stem water conte...
In Mediterranean ecosystems, water shortage is the main factor constraining survival and growth o... more In Mediterranean ecosystems, water shortage is the main factor constraining survival and growth of plants. Xylem hydraulic properties are a key factor for the general function of plants as they exert a strong influence on water transport and therefore on the potential for carbon uptake. Resistance to cavitation has been considered a major character involved in drought tolerance. However, variation in cavitation vulnerability could be accompanied by a trade-off with other water transport and physiological traits. We investigated stem xylem vulnerability to cavitation in Pinus canariensis, the only endemic pine of the Canary Islands (Spain). We used the ‘Cavitron’ technique (Cochard 2002; Cochard et al. 2005) to construct xylem vulnerability curves.
In recent years, the use of wood has gained social interest, leading to a global increase in its ... more In recent years, the use of wood has gained social interest, leading to a global increase in its demand. Yet, this demand is often covered by the production of woods of low natural durability against biological deterioration. The main biological agents with the potential to attack the structural integrity of wood are wood-decay fungi, saproxylic beetles, termites, and marine molluscs and crustaceans. In most circumstances, fungi are the main wood-deteriorating agents. To attack the cell wall, wood-decay fungi combine a complex enzymatic mechanism with non-enzymatic mechanisms based on low-molecular-weight compounds. In some cases, the larvae of saproxylic beetles can also digest cell wood components, causing serious deterioration to wooden structures. The impact of subterranean termites in Europe is concentrated in the Southern countries, causing important economic losses. However, alien invasive species of voracious subterranean termites are expanding their presence in Europe. Wood...
Uploads
Papers by Rosana Lopez