F. Magnani - Academia.edu (original) (raw)
Papers by F. Magnani
Application of the 3-PGS model to assess carbon
IGARSS 2018 - 2018 IEEE International Geoscience and Remote Sensing Symposium, 2018
ESA's FLEX/Sentinel-3 tandem mission aims at mapping Sun-induced fluorescence (SIF) as a prox... more ESA's FLEX/Sentinel-3 tandem mission aims at mapping Sun-induced fluorescence (SIF) as a proxy to quantify photosynthetic activity of terrestrial vegetation. Due to the complexity of the mission concept and stringent requirements for the data processing algorithms, ESA developed a Phase A/B1 End-to-End Mission Performance Simulator (E2ES) tool to reproduce the expected mission performance and check the mission and instrument concepts. In the current Phase C/D, the E2ES concept must evolve to consolidate the whole data processing chain, providing an accurate figures of the whole mission error budget and serving as a roadmap for the future development of FLEX Ground Segment. This paper gives an overview of the activities involving the FLEX E2ES, from the conceptual development phase (Phase A/B1) to the implementation of the Ground Segment and operations (Phase C/D). Particularly, we will focus on the high-level description of the Level-2 data processing chain from an architecture and software design point of view.
The impact of carbon dioxide and other greenhouse gases on forest ecosystems. Report No.3 of the IUFRO task force on environmental change, 2001
A review of the modelling of response key plant and ecosystem processes to atmospheric CO2 concen... more A review of the modelling of response key plant and ecosystem processes to atmospheric CO2 concentrations and temperature is presented. An outline of the most frequently adopted modelling approaches, at different temporal and spatial scales, is also presented.
Journal of Silviculture and Forest Ecology, 2005
Abstract: Forest biomass provides a relevant fraction of world energy needs, not only in developi... more Abstract: Forest biomass provides a relevant fraction of world energy needs, not only in developing Countries. In Italy, several factors are presently contributing to a new interest for this resource, ranging from regulatory quotas for renewables to the increasing price of fossil fuel to the emergence of a European carbon stock exchange. This focus on renewable resources constitutes an important opportunity for the forest sector and for society by and large, but because of the potential dimensions of the emerging market it also requires new planning instruments, in order to avoid a sudden and widespread resumption of coppice management and a reduction of standing carbon stock in forest ecosystems, which would run contrary to the objectives of the Kyoto Protocol. An example of the future demand for biomasses in Central Italy is presented, based on the possible use of fuelwood in new coal-fired power plants by the ’co-firing’ technology.
Forest@ - Rivista di Selvicoltura ed Ecologia Forestale, 2005
Forest biomass provides a relevant fraction of world energy needs, not only in developing Countri... more Forest biomass provides a relevant fraction of world energy needs, not only in developing Countries. In Italy, several factors are presently contributing to a new interest for this resource, ranging from regulatory quotas for renewables to the increasing price of fossil fuel to the emergence of a European carbon stock exchange. This focus on renewable resources constitutes an important opportunity for the forest sector and for society by and large, but because of the potential dimensions of the emerging market it also requires new planning instruments, in order to avoid a sudden and widespread resumption of coppice management and a reduction of standing carbon stock in forest ecosystems, which would run contrary to the objectives of the Kyoto Protocol. An example of the future demand for biomasses in Central Italy is presented, based on the possible use of fuelwood in new coal-fired power plants by the 'co-firing' technology.
Stomatal, mesophyll conductance and biochemical limitations to photosynthesis as affected by drou... more Stomatal, mesophyll conductance and biochemical limitations to photosynthesis as affected by drought and leaf ontogeny in ash and oak trees
Geoscientific Model Development Discussions, 2014
Forest models are being increasingly used to study ecosystem functioning, through the reproductio... more Forest models are being increasingly used to study ecosystem functioning, through the reproduction of carbon fluxes and productivity in very different forests all over the world. Over the last two decades, the need for simple and "easy to use" models for practical applications, characterized by few parameters and equations, has become clear, and some have been developed for this purpose. These models aim to represent the main drivers underlying forest ecosystem processes while being applicable to the widest possible range of forest ecosystems. Recently, it has also become clear that model performance should not be assessed only in terms of accuracy of estimations and predictions, but also in terms of estimates of model uncertainties. Therefore, the Bayesian approach has increasingly been applied to calibrate forest models, with the aim of estimating the uncertainty of their results, and of comparing their performances. <br><br> Some forest models, considered to...
Forest@ - Rivista di Selvicoltura ed Ecologia Forestale, 2005
What role for afforestation in Italian strategies towards the Kyoto Protocol? Hints from a Kyoto ... more What role for afforestation in Italian strategies towards the Kyoto Protocol? Hints from a Kyoto forest in the Po Valley (Northern Italy). The carbon balance of an afforested area in the Emilia-Romagna floodplain has been monitored for a 4-year period. Detailed measurements covering both above-and below-ground components of biomass production and accumulation were complemented by eddy-covariance measurements at the ecosystem level. Experimental results have been extrapolated in time by means of a process-based ecosystem model, so as to better assess the potential role of afforestation towards the carbon-reduction goals of the Kyoto Protocol.
Imaging Spectrometry X, 2004
Proprietary and intellectual rights of University of Calgary, Canada are involved in the subject-... more Proprietary and intellectual rights of University of Calgary, Canada are involved in the subject-matter of this material and all manufacturing, reproduction, use, disclosure, and sales rights pertaining to such subject-matter are expressly reserved. This material is submitted for a specific purpose as agreed in writing, and the recipient by accepting this material agrees that this material will not be used, copied, or reproduced in whole or in part nor its contents (or any part thereof) revealed in any manner or to any third party, except own staff, to meet the purpose for which it was submitted and subject to the terms of the written agreement.
Photosynthetica, 2008
We analyzed the response of potted strawberry tree (Arbutus unedo L.) seedlings exposed to water ... more We analyzed the response of potted strawberry tree (Arbutus unedo L.) seedlings exposed to water stress by withholding water for 10 d (WS). Leaf water potential, net CO 2 assimilation, and stomatal conductance decreased with increasing water deficit. A 30 % reduction of chlorophyll (Chl) content in the antenna complexes was observed in WS-plants. Simultaneously, a decline of photochemical efficiency (F v /F m) occurred as a result of an excess of solar radiation energy when carbon assimilation was limited by stomata closure due to soil water deficit. The non-photochemical quenching of Chl fluorescence (Φ NPQ) significantly increased, as well as the leaf contents of zeaxanthin (Z) and antheraxanthin (A) at the expense of violaxanthin during the WS-period. Elevated predawn contents of de-epoxidized xanthophyll cycle components were associated with a sustained lowering of predawn photosystem 2 efficiency; this suggested an engagement of Z+A in a state primed for energy dissipation. Thus, the ability of strawberry trees to maintain the functionality of the xanthophyll cycle during the Mediterranean summer is an efficient mechanism to prevent irreversible damages to the photosynthetic machinery through thermal energy dissipation in the antenna and the reduction in photochemical efficiency.
Plant, Cell & Environment, 2000
plants as they do in animals (Nooden 1988). Rather, the explanation seems to be found in the shif... more plants as they do in animals (Nooden 1988). Rather, the explanation seems to be found in the shifting balance between photosynthesis, respiration and tissue turnover. Kira & Shidei (1967) first hypothesized that the decline in net primary production with stand age was due to the continuous increase in respiring tissues. Direct observations, however, have recently demonstrated that increasing sapwood respiration accounts for only a small proportion of the P a decline (Ryan & Waring 1992; Ryan et al. 1995). An increased below-ground allocation has also been proposed as a possible explanation, as a consequence of the reduced availability of nutrients that are increasingly immobilized in litter during stand development (Murty, McMurtrie & Ryan 1996). A greater fine root-to-foliage biomass ratio with age has indeed been often observed (
ABSTRACT The response of ecosystems to environmental factors, such as temperature and rainfall, i... more ABSTRACT The response of ecosystems to environmental factors, such as temperature and rainfall, is crucial to understand the impact of climate change on the terrestrial C cycle. Forest soil respiration represents the main pathway by which photosynthetically assimilated C is released to atmosphere; its intensity depends not only on soil environmental conditions, but also on the availability of organic substrates respired by roots and microorganisms. Several techniques have been applied to partition the autotrophic and heterotrophic components of soil respiration in boreal and temperate forests; there is a general lack of information, on the contrary, on the dynamics of soil CO2 efflux in Mediterranean ecosystems. The IPCC A1B scenario highlighted the importance of the Mediterranean area since it is expected to experience a temperature increase (from 2.2 °C to 5.1 °C) and a rainfall reduction ranging from -4 to -27% on annual basis. We used the tree-girdling technique together with periodic chamber-based measurements to study the partitioning of total soil respiration (Rs) into its autotrophic (Ra) and heterotrophic (Rh) components in a 60-year old forest in Central Italy (San Rossore) dominated by Pinus pinaster. This technique has been extensively used to block the flux of photosynthates from leaves to roots, thus stopping the autotrophic root respiration in the soil. We found that two weeks after the treatment soil respiration in the girdled plots decreased by 29% and remained stable over the period of analysis, suggesting that Rh dominates total soil respiration. The anomalous low rainfall regimen of May to October 2011 (102 mm cumulated rain) associated with average air temperatures (with a mean value of 19,6 °C over the period) gave us the opportunity to investigate the decoupled response of soil respiration to water and temperature. Time series analysis performed under this severe drought conditions showed overall low values of soil respiration with three clear peaks associated with water pulses from rain events. Both total and partitioned fluxes were indeed significantly correlated with soil water content (Rs: R2=0,63, p<0,001; Rh: R2=0,45, p<0,01; Ra: R2=0,70, p<0,001) while the response to soil temperature was evident only for Ra (R2=0,27, p<0,05) and no significant for Rh and Rs (R2=0,11, p>0,05 and R2=0,03, p>0,05, respectively). The relationship with photosynthesis was subsequently evaluated analyzing the time-lagged correlation between daily gross primary productivity (GPP) derived from eddy covariance measurements and total and partitioned soil CO2 efflux. The time lagged analysis showed that Ra was overall best correlated with GPP with a peak at 3 days of delay (r= 0,72, p<0,001) while Rs had a peak in the fraction of variance explained corresponding to 4 days of delay (r=0,66, p=0,001). These findings confirm that CO2 efflux from soil is strongly affected by environmental factors and substrates supplied by photosynthetic activity, but suggest that the effects they exert on autotrophic and heterotrophic fluxes follow different mechanisms and temporal dynamics.
Annals of Forest Science, 2013
HAL is a multidisciplinary open access archive for the deposit and dissemination of scientific re... more HAL is a multidisciplinary open access archive for the deposit and dissemination of scientific research documents, whether they are published or not. The documents may come from teaching and research institutions in France or abroad, or from public or private research centers. L'archive ouverte pluridisciplinaire HAL, est destinée au dépôt et à la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d'enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.
Trees, 1998
mThe present study was carried out to elucidate the response mechanisms of 50-year-old Pinus hale... more mThe present study was carried out to elucidate the response mechanisms of 50-year-old Pinus halepensis Mill. trees to a long-term and severe drought. The amount of water available to trees was artificially restricted for 12 months by covering the soil with a plastic roof. Over the short term a direct and rapid impact of drought was evident on the water relations and gas exchanges of trees: as the soil dried out in the Spring, there was a concurrent decrease of predawn water potential; transpiration was strongly reduced by stomatal closure. Seasonal changes in the water volume fractions of twig and stem xylem were observed and interpreted as the result of cavitation and refilling in the xylem. When droughted trees recovered to a more favourable water status, refilling of embolized xylem was observed; twig predawn water potentials were still negative in the period when the embolism was reversed in the twig xylem. A few months after the removal of the covering, no differences in whole plant hydraulic resistance were observed between droughted and control trees. Needle and shoot elongation and stem radial growth were considerably reduced in droughted trees; no strategy of trees to allocate carbon preferentially to the stem conducting tissues was apparent throughout the experiment. An after-effect of the drought on growth was observed.
Trees, 2007
In this study, tree hydraulic conductance (K tree) was experimentally manipulated to study effect... more In this study, tree hydraulic conductance (K tree) was experimentally manipulated to study effects on short-term regulation of stomatal conductance (g s), net photosynthesis (A) and bulk leaf water potential (Y leaf) in well watered 5-6 years old and 1.2 m tall maritime pine seedlings (Pinus pinaster Ait.). K tree was decreased by notching the stem and increased by progressively excising the root system and stem. Gas exchange was measured in a chamber at constant irradiance, vapour pressure deficit, leaf temperature and ambient CO 2 concentration. As expected, we found a strong and positive relationship between g s and K tree (r = 0.92, P = 0.0001) and between A and K tree (r = 0.9, P = 0.0001). In contrast, however, we found that the response of Y leaf to K tree depended on the direction of change in K tree : increases in K tree caused Y leaf to decrease from around-1.0 to-0.6 MPa, but reductions in K tree were accompanied by homeostasis in Y leaf (at-1 MPa). Both of these observations could be explained by an adaptative feedback loop between g s and Y leaf , with Y leaf prevented from declining below the cavitation threshold by stomatal closure. Our results are consistent with the hypothesis that the observed stomatal responses were mediated by leaf water status, but they also suggest that the stomatal sensitivity to water status increased dramatically as Y leaf approached-1 MPa.
Plant, Cell and Environment, 1995
ABSTRACT
Application of the 3-PGS model to assess carbon
IGARSS 2018 - 2018 IEEE International Geoscience and Remote Sensing Symposium, 2018
ESA's FLEX/Sentinel-3 tandem mission aims at mapping Sun-induced fluorescence (SIF) as a prox... more ESA's FLEX/Sentinel-3 tandem mission aims at mapping Sun-induced fluorescence (SIF) as a proxy to quantify photosynthetic activity of terrestrial vegetation. Due to the complexity of the mission concept and stringent requirements for the data processing algorithms, ESA developed a Phase A/B1 End-to-End Mission Performance Simulator (E2ES) tool to reproduce the expected mission performance and check the mission and instrument concepts. In the current Phase C/D, the E2ES concept must evolve to consolidate the whole data processing chain, providing an accurate figures of the whole mission error budget and serving as a roadmap for the future development of FLEX Ground Segment. This paper gives an overview of the activities involving the FLEX E2ES, from the conceptual development phase (Phase A/B1) to the implementation of the Ground Segment and operations (Phase C/D). Particularly, we will focus on the high-level description of the Level-2 data processing chain from an architecture and software design point of view.
The impact of carbon dioxide and other greenhouse gases on forest ecosystems. Report No.3 of the IUFRO task force on environmental change, 2001
A review of the modelling of response key plant and ecosystem processes to atmospheric CO2 concen... more A review of the modelling of response key plant and ecosystem processes to atmospheric CO2 concentrations and temperature is presented. An outline of the most frequently adopted modelling approaches, at different temporal and spatial scales, is also presented.
Journal of Silviculture and Forest Ecology, 2005
Abstract: Forest biomass provides a relevant fraction of world energy needs, not only in developi... more Abstract: Forest biomass provides a relevant fraction of world energy needs, not only in developing Countries. In Italy, several factors are presently contributing to a new interest for this resource, ranging from regulatory quotas for renewables to the increasing price of fossil fuel to the emergence of a European carbon stock exchange. This focus on renewable resources constitutes an important opportunity for the forest sector and for society by and large, but because of the potential dimensions of the emerging market it also requires new planning instruments, in order to avoid a sudden and widespread resumption of coppice management and a reduction of standing carbon stock in forest ecosystems, which would run contrary to the objectives of the Kyoto Protocol. An example of the future demand for biomasses in Central Italy is presented, based on the possible use of fuelwood in new coal-fired power plants by the ’co-firing’ technology.
Forest@ - Rivista di Selvicoltura ed Ecologia Forestale, 2005
Forest biomass provides a relevant fraction of world energy needs, not only in developing Countri... more Forest biomass provides a relevant fraction of world energy needs, not only in developing Countries. In Italy, several factors are presently contributing to a new interest for this resource, ranging from regulatory quotas for renewables to the increasing price of fossil fuel to the emergence of a European carbon stock exchange. This focus on renewable resources constitutes an important opportunity for the forest sector and for society by and large, but because of the potential dimensions of the emerging market it also requires new planning instruments, in order to avoid a sudden and widespread resumption of coppice management and a reduction of standing carbon stock in forest ecosystems, which would run contrary to the objectives of the Kyoto Protocol. An example of the future demand for biomasses in Central Italy is presented, based on the possible use of fuelwood in new coal-fired power plants by the 'co-firing' technology.
Stomatal, mesophyll conductance and biochemical limitations to photosynthesis as affected by drou... more Stomatal, mesophyll conductance and biochemical limitations to photosynthesis as affected by drought and leaf ontogeny in ash and oak trees
Geoscientific Model Development Discussions, 2014
Forest models are being increasingly used to study ecosystem functioning, through the reproductio... more Forest models are being increasingly used to study ecosystem functioning, through the reproduction of carbon fluxes and productivity in very different forests all over the world. Over the last two decades, the need for simple and "easy to use" models for practical applications, characterized by few parameters and equations, has become clear, and some have been developed for this purpose. These models aim to represent the main drivers underlying forest ecosystem processes while being applicable to the widest possible range of forest ecosystems. Recently, it has also become clear that model performance should not be assessed only in terms of accuracy of estimations and predictions, but also in terms of estimates of model uncertainties. Therefore, the Bayesian approach has increasingly been applied to calibrate forest models, with the aim of estimating the uncertainty of their results, and of comparing their performances. <br><br> Some forest models, considered to...
Forest@ - Rivista di Selvicoltura ed Ecologia Forestale, 2005
What role for afforestation in Italian strategies towards the Kyoto Protocol? Hints from a Kyoto ... more What role for afforestation in Italian strategies towards the Kyoto Protocol? Hints from a Kyoto forest in the Po Valley (Northern Italy). The carbon balance of an afforested area in the Emilia-Romagna floodplain has been monitored for a 4-year period. Detailed measurements covering both above-and below-ground components of biomass production and accumulation were complemented by eddy-covariance measurements at the ecosystem level. Experimental results have been extrapolated in time by means of a process-based ecosystem model, so as to better assess the potential role of afforestation towards the carbon-reduction goals of the Kyoto Protocol.
Imaging Spectrometry X, 2004
Proprietary and intellectual rights of University of Calgary, Canada are involved in the subject-... more Proprietary and intellectual rights of University of Calgary, Canada are involved in the subject-matter of this material and all manufacturing, reproduction, use, disclosure, and sales rights pertaining to such subject-matter are expressly reserved. This material is submitted for a specific purpose as agreed in writing, and the recipient by accepting this material agrees that this material will not be used, copied, or reproduced in whole or in part nor its contents (or any part thereof) revealed in any manner or to any third party, except own staff, to meet the purpose for which it was submitted and subject to the terms of the written agreement.
Photosynthetica, 2008
We analyzed the response of potted strawberry tree (Arbutus unedo L.) seedlings exposed to water ... more We analyzed the response of potted strawberry tree (Arbutus unedo L.) seedlings exposed to water stress by withholding water for 10 d (WS). Leaf water potential, net CO 2 assimilation, and stomatal conductance decreased with increasing water deficit. A 30 % reduction of chlorophyll (Chl) content in the antenna complexes was observed in WS-plants. Simultaneously, a decline of photochemical efficiency (F v /F m) occurred as a result of an excess of solar radiation energy when carbon assimilation was limited by stomata closure due to soil water deficit. The non-photochemical quenching of Chl fluorescence (Φ NPQ) significantly increased, as well as the leaf contents of zeaxanthin (Z) and antheraxanthin (A) at the expense of violaxanthin during the WS-period. Elevated predawn contents of de-epoxidized xanthophyll cycle components were associated with a sustained lowering of predawn photosystem 2 efficiency; this suggested an engagement of Z+A in a state primed for energy dissipation. Thus, the ability of strawberry trees to maintain the functionality of the xanthophyll cycle during the Mediterranean summer is an efficient mechanism to prevent irreversible damages to the photosynthetic machinery through thermal energy dissipation in the antenna and the reduction in photochemical efficiency.
Plant, Cell & Environment, 2000
plants as they do in animals (Nooden 1988). Rather, the explanation seems to be found in the shif... more plants as they do in animals (Nooden 1988). Rather, the explanation seems to be found in the shifting balance between photosynthesis, respiration and tissue turnover. Kira & Shidei (1967) first hypothesized that the decline in net primary production with stand age was due to the continuous increase in respiring tissues. Direct observations, however, have recently demonstrated that increasing sapwood respiration accounts for only a small proportion of the P a decline (Ryan & Waring 1992; Ryan et al. 1995). An increased below-ground allocation has also been proposed as a possible explanation, as a consequence of the reduced availability of nutrients that are increasingly immobilized in litter during stand development (Murty, McMurtrie & Ryan 1996). A greater fine root-to-foliage biomass ratio with age has indeed been often observed (
ABSTRACT The response of ecosystems to environmental factors, such as temperature and rainfall, i... more ABSTRACT The response of ecosystems to environmental factors, such as temperature and rainfall, is crucial to understand the impact of climate change on the terrestrial C cycle. Forest soil respiration represents the main pathway by which photosynthetically assimilated C is released to atmosphere; its intensity depends not only on soil environmental conditions, but also on the availability of organic substrates respired by roots and microorganisms. Several techniques have been applied to partition the autotrophic and heterotrophic components of soil respiration in boreal and temperate forests; there is a general lack of information, on the contrary, on the dynamics of soil CO2 efflux in Mediterranean ecosystems. The IPCC A1B scenario highlighted the importance of the Mediterranean area since it is expected to experience a temperature increase (from 2.2 °C to 5.1 °C) and a rainfall reduction ranging from -4 to -27% on annual basis. We used the tree-girdling technique together with periodic chamber-based measurements to study the partitioning of total soil respiration (Rs) into its autotrophic (Ra) and heterotrophic (Rh) components in a 60-year old forest in Central Italy (San Rossore) dominated by Pinus pinaster. This technique has been extensively used to block the flux of photosynthates from leaves to roots, thus stopping the autotrophic root respiration in the soil. We found that two weeks after the treatment soil respiration in the girdled plots decreased by 29% and remained stable over the period of analysis, suggesting that Rh dominates total soil respiration. The anomalous low rainfall regimen of May to October 2011 (102 mm cumulated rain) associated with average air temperatures (with a mean value of 19,6 °C over the period) gave us the opportunity to investigate the decoupled response of soil respiration to water and temperature. Time series analysis performed under this severe drought conditions showed overall low values of soil respiration with three clear peaks associated with water pulses from rain events. Both total and partitioned fluxes were indeed significantly correlated with soil water content (Rs: R2=0,63, p<0,001; Rh: R2=0,45, p<0,01; Ra: R2=0,70, p<0,001) while the response to soil temperature was evident only for Ra (R2=0,27, p<0,05) and no significant for Rh and Rs (R2=0,11, p>0,05 and R2=0,03, p>0,05, respectively). The relationship with photosynthesis was subsequently evaluated analyzing the time-lagged correlation between daily gross primary productivity (GPP) derived from eddy covariance measurements and total and partitioned soil CO2 efflux. The time lagged analysis showed that Ra was overall best correlated with GPP with a peak at 3 days of delay (r= 0,72, p<0,001) while Rs had a peak in the fraction of variance explained corresponding to 4 days of delay (r=0,66, p=0,001). These findings confirm that CO2 efflux from soil is strongly affected by environmental factors and substrates supplied by photosynthetic activity, but suggest that the effects they exert on autotrophic and heterotrophic fluxes follow different mechanisms and temporal dynamics.
Annals of Forest Science, 2013
HAL is a multidisciplinary open access archive for the deposit and dissemination of scientific re... more HAL is a multidisciplinary open access archive for the deposit and dissemination of scientific research documents, whether they are published or not. The documents may come from teaching and research institutions in France or abroad, or from public or private research centers. L'archive ouverte pluridisciplinaire HAL, est destinée au dépôt et à la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d'enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.
Trees, 1998
mThe present study was carried out to elucidate the response mechanisms of 50-year-old Pinus hale... more mThe present study was carried out to elucidate the response mechanisms of 50-year-old Pinus halepensis Mill. trees to a long-term and severe drought. The amount of water available to trees was artificially restricted for 12 months by covering the soil with a plastic roof. Over the short term a direct and rapid impact of drought was evident on the water relations and gas exchanges of trees: as the soil dried out in the Spring, there was a concurrent decrease of predawn water potential; transpiration was strongly reduced by stomatal closure. Seasonal changes in the water volume fractions of twig and stem xylem were observed and interpreted as the result of cavitation and refilling in the xylem. When droughted trees recovered to a more favourable water status, refilling of embolized xylem was observed; twig predawn water potentials were still negative in the period when the embolism was reversed in the twig xylem. A few months after the removal of the covering, no differences in whole plant hydraulic resistance were observed between droughted and control trees. Needle and shoot elongation and stem radial growth were considerably reduced in droughted trees; no strategy of trees to allocate carbon preferentially to the stem conducting tissues was apparent throughout the experiment. An after-effect of the drought on growth was observed.
Trees, 2007
In this study, tree hydraulic conductance (K tree) was experimentally manipulated to study effect... more In this study, tree hydraulic conductance (K tree) was experimentally manipulated to study effects on short-term regulation of stomatal conductance (g s), net photosynthesis (A) and bulk leaf water potential (Y leaf) in well watered 5-6 years old and 1.2 m tall maritime pine seedlings (Pinus pinaster Ait.). K tree was decreased by notching the stem and increased by progressively excising the root system and stem. Gas exchange was measured in a chamber at constant irradiance, vapour pressure deficit, leaf temperature and ambient CO 2 concentration. As expected, we found a strong and positive relationship between g s and K tree (r = 0.92, P = 0.0001) and between A and K tree (r = 0.9, P = 0.0001). In contrast, however, we found that the response of Y leaf to K tree depended on the direction of change in K tree : increases in K tree caused Y leaf to decrease from around-1.0 to-0.6 MPa, but reductions in K tree were accompanied by homeostasis in Y leaf (at-1 MPa). Both of these observations could be explained by an adaptative feedback loop between g s and Y leaf , with Y leaf prevented from declining below the cavitation threshold by stomatal closure. Our results are consistent with the hypothesis that the observed stomatal responses were mediated by leaf water status, but they also suggest that the stomatal sensitivity to water status increased dramatically as Y leaf approached-1 MPa.
Plant, Cell and Environment, 1995
ABSTRACT