J. Peñuelas | UAB-CREAF - Academia.edu (original) (raw)

Papers by J. Peñuelas

Plant Science, 2014

A long-term experimental drought to simulate future expected climatic conditions for Mediterranea... more A long-term experimental drought to simulate future expected climatic conditions for Mediterranean forests, a 15% decrease in soil moisture for the following decades, was conducted in a holm oak forest since 1999. Net photosynthetic rate, stomatal conductance and leaf water potential were measured from 1999 to 2013 in Quercus ilex and Phillyrea latifolia, two co-dominant species of this forest. These measurements were performed in four plots, two of them received the drought treatment and the two other plots were control plots. The three studied variables decreased with increases in VPD and decreases in soil moisture in both species, but the decrease of leaf water potential during summer drought was larger in P. latifolia, whereas Q. ilex reached higher net photosynthetic rates and stomatal conductance values during rainy periods than P. latifolia. The drought treatment decreased ca. 8% the net photosynthetic rates during the overall studied period in both Q. ilex and P. latifolia, whereas there were just non-significant trends toward a decrease in leaf water potential and stomatal conductance induced by drought treatment. Future drier climate may lead to a decrease in the carbon balance of Mediterranean species, and some shrub species well resistant to drought could gain competitive advantage relative to Q. ilex, currently the dominant species of this forest.

Soil Biology and Biochemistry, 2014

ABSTRACT We investigated the effect of soil microclimate on the structure and functioning of soil... more ABSTRACT We investigated the effect of soil microclimate on the structure and functioning of soil microbial communities in a Mediterranean Holm-oak forest subjected to 10 years of partial rain exclusion manipulations, simulating average drought conditions expected in Mediterranean areas for the following decades. We applied a high throughput DNA pyrosequencing technique coupled to parallel measurements of microbial respiration (RH) and temperature sensitivity of microbial respiration (Q10). Some consistent changes in the structure of bacterial communities suggest a slow process of community shifts parallel to the trend towards oligotrophy in response to long-term droughts. However, the structure of bacterial communities was mainly determined by short-term environmental fluctuations associated with sampling date (winter, spring and summer) rather than long-term (10 years) shifts in baseline precipitation. Moreover, long-term drought did not exert any chronic effect on the functioning of soil microbial communities (RH and Q10), emphasizing the functional stability of these communities to this long-term but mild shifts in water availability. We hypothesize that the particular conditions of the Mediterranean climate with strong seasonal shifts in both temperature and soil water availability but also characterized by very extreme environmental conditions during summer, was acting as a strong force in community assembling, selecting phenotypes adapted to the semiarid conditions characterizing Mediterranean ecosystems. Relations of climate with the phylogenetic structure and overall diversity of the communities as well as the distribution of the individual responses of different lineages (genera) to climate confirmed our hypotheses, evidencing communities dominated by thermotolerant and drought-tolerant phenotypes.

Remote Sensing of Environment, 2004

... 2001. View Within Article. 3.2. NDVI assessment of treatment, annual and seasonal biomass cha... more ... 2001. View Within Article. 3.2. NDVI assessment of treatment, annual and seasonal biomass changes. 3.2.1. Community. Plant biomass ...

Plant Biology, 2008

Research on biogenic volatile organic compound (BVOC) emissions has mainly focused on native spec... more Research on biogenic volatile organic compound (BVOC) emissions has mainly focused on native species in natural ecosystems. However, much of the ozone and aerosol formation occurs in city atmospheres due to BVOC emissions by local urban vegetation. Plant composition of urban habitats is often dominated by non-native ornamental plant species, for which only limited data on BVOC emissions are available. To gain insight into the influence of ornamental vegetation on the urban atmospheric reactivity in Barcelona, Spain, we studied volatile isoprenoid emissions in 11 widespread ornamental tree species (three conifers and nine angiosperms). We found significant monoterpene emissions in all studied species, with normalized emission potentials (T = 30°C, photosynthetic photon flux density (PPFD) = 1000 lmolAEm)2 AEs)1) ranging between 0.2 to 110 lgAEg)1 (dry weight) h)1. Depending on species, the emissions were dominated by aand b-pinene, myrcene, aand b-phellandrene, carene, limonene and eucalyptol. These data demonstrate that ornamental plants may significantly contribute to the BVOC load in urban atmospheres and also underscore the importance of broadleaf angiosperms as significant monoterpene emitters.

Perspectives in Plant Ecology, Evolution and Systematics, 2013

Plants produce and emit a large variety of volatile organic compounds that play key roles in inte... more Plants produce and emit a large variety of volatile organic compounds that play key roles in interactions with abiotic and biotic environments. One of these roles is the attraction of animals (mainly insects) that act as vectors of pollen to ensure reproduction. Here we update the current knowledge of four key aspects of floral emissions: (1) the relative importance and interaction of olfactory signals and visual cues, (2) the spatial and temporal patterns of emission in flowers, (3) the attractive and defensive functions of floral volatiles and their interference, and (4) the effects of global change on floral emissions and plant-pollinator interactions. Finally, we propose future lines of research in this field that need to be addressed or investigated further.

International Journal of Remote Sensing, 1995

... GAMON, JA, FIELD, C B., GOULDEN, M. L., GRIFFIN, K. L., HARTLEY, A. E., JOEL, G., PENUELAS, J... more ... GAMON, JA, FIELD, C B., GOULDEN, M. L., GRIFFIN, K. L., HARTLEY, A. E., JOEL, G., PENUELAS, J., and VALENTINI, R., 1995, Relationship between NDVI ... LORENZEN, B., and JENSEN, A., 1989, Changes in leaf spectral properties induced in barley by cereal powdery mildew ...

International Journal of Remote Sensing, 1996

... indicator of water status and yield under mild and very mild water stress conditions. ... C.,... more ... indicator of water status and yield under mild and very mild water stress conditions. ... C., 1994, Reflectance indices associated with physiological changes in nitrogen-and water-limited sunflower ... J., FILELLA, I., and SAVE, R., 1995, Assessing signals of gerbera water status inthe ...

International Journal of Remote Sensing, 1997

ABSTRACT

International Journal of Remote Sensing, 1997

ABSTRACT

Global Ecology and Biogeography, 2009

Aim To test whether the onset of spring growth in European shrublands is advanced in response to ... more Aim To test whether the onset of spring growth in European shrublands is advanced in response to the warmer conditions projected for the next two decades by climate models, and, if there is a change, whether it differs across Europe. ... Location The studied sites spanned a ...

Crop Science, 1995

Nitrogen deficiencies can seriously reduce yield and economic returns for farmers. Remote sensing... more Nitrogen deficiencies can seriously reduce yield and economic returns for farmers. Remote sensing could provide inexpensive, largearea estimates of N status and be used to monitor N status since leaf chlorophyll (Chi) A content is mainly determined by N availability. The objective was to determine if remote sensing of wheat (Triticum aestivum L.) Chi A content would provide a rapid estimation of wheat N status. We measured the reflectance of a wheat crop submitted to five different fertilization treatments throughout the growth cycle. We tested several empirical reflectance indices of pigment content: reflectance at 550 nm (R550), reflectance at 680 nm (R680), three parameters of the red edge [wavelength ()."), amplitude in the first derivative of the reflectance spectra (dR re), and sum of amplitudes between 680 and 780 nm in the first derivative of the reflectance spectra (£dR 680. 78 o nm)], and pigment simple ratio (PSR) and normalized pigment chlorophyll index (NPCI) (indices of carotenoid/Chl ratio). We also measured leaf Chi A and N content, and leaf area index. There were significant correlations between canopy Chi A content and R550, R680, and all the red edge parameters. The NPCI and PSR followed phenological evolution of the carotenoids/Chl A ratio and separated the different treatments. By discriminant analysis based on the pigment indices reflectance at 430 nm (R430), R550, R680, X re , dR,e, and NPCI, each reflectance spectrum can be assigned to a different N status class. Thus, the use of these optical techniques offers a potential for assessing N status of wheat.

Atmospheric Chemistry and Physics, 2009

Large uncertainties exist in our knowledge of regional emissions of non-methane biogenic volatile... more Large uncertainties exist in our knowledge of regional emissions of non-methane biogenic volatile organic compounds (BVOC). We address these uncertainties through a two-pronged approach by compiling a state of the art database of the emissions potentials for 80 European forest species, and by a model assessment and inter-comparison, both at the local and regional scale, under present and projected future climatic conditions. We coupled three contrasting isoprenoid models with the ecophysiological forest model GOTILWA+ to evaluate leaf and ecosystem isoprenoid emissions, build an emissions inventory for European forests, and to consider model behaviour in present climate and under projected future climate change conditions. Hourly, daily and annual isoprene emissions as simulated by the models were evaluated against flux measurements. The validation highlighted a general model capacity to capture gross fluxes but inefficiencies in capturing short term variability. A regional inventory of isoprenoid emissions for European forests was created using each of the three modelling approaches. The models agreed on an average European emissions budget of 1.03 TgC a −1 for isoprene and 0.97 TgC a −1 for monoterpenes for the period 1960-1990, which was dominated by a few species with largest aerial coverage. Species contribution to total emissions depended both on species emission potential and geographical distribution. For projected future climate conditions, however, emissions budgets proved highly model dependent, illustrating the current uncertainty associated with isoprenoid emissions responses to potential future conditions.

Agricultural and Forest Meteorology, 1998

We developed a method to estimate live fine fuel moisture LFFM by ground-based, high-resolution p... more We developed a method to estimate live fine fuel moisture LFFM by ground-based, high-resolution plant reflectance Ž. measurements in the visible and near infrared regions. NDVI and WI R rR were the reflectance indices used because 970 900

Agricultural and Forest Meteorology, 1992

Remotely measured canopy temperature of greenhouse strawberries as indicator of water status and ... more Remotely measured canopy temperature of greenhouse strawberries as indicator of water status and yield under mild and very mild water stress conditions. Agric. For. Meteorol., 58: 63-77. Strawberry plants were submitted to mild and very mild water stress regimes in a tunnel (simple semicircular greenhouse) by planting them in two plots fertirrigated when the soil matric potential reached-0.07 MPa and-0.01 MPa, respectively. The plants were monitored for water stress by measuring the foliage temperature with a hand-held infrared thermometer. Parallel to this, weather variables, the difference between leaf and air temperature, the derived crop water stress index (CWSI), the soil matric potential, the leaf water potential, the photosynthetic gas exchange rates, the transpiration rates, photosynthetic pigments, sugars, starch, canopy structure and accumulated yield were measured. The wet treatment (WT) presented a higher yield and higher leaf area index (LAI). In WT, leaves were disposed mostly in a monolayer oriented to the south, whereas in dry treatment (DT) leaves were distributed in a multilayer pattern and oriented to the north. During the hotter part of cloudless days and before irrigation took place, the canopy temperature of WT was about 3 °C less than that of DT. Accumulated stress degree days (SDD) were then higher in DT. WT presented lower average CWSI values, between 0.045 and 0.54, while those of DT were between 0.32 and 0.70. It was concluded that leaf temperature, its difference with air temperature (8 T) and the derived indices, such as SDD and CWSI, are useful for the assessment of even these mild and very mild water stresses in strawberries under protected conditions. Regression analysis showed that under the very mild water stress conditions tested in WT, the contribution of air vapor pressure deficit to variation in leaf water potential was significant. This did not happen under the mild water stress of DT.

Communications Biology, 2020

The drivers of global change, including increases in atmospheric CO2 concentrations, N and S depo... more The drivers of global change, including increases in atmospheric CO2 concentrations, N and S deposition, and climate change, likely affect the nutritional status of forests. Here we show forest foliar concentrations of N, P, K, S and Mg decreased significantly in Europe by 5%, 11%, 8%, 6% and 7%, respectively during the last three decades. The decrease in nutritional status was especially large in Mediterranean and temperate forests. Increasing atmospheric CO2 concentration was well correlated with the decreases in N, P, K, Mg, S concentrations and the increase of N:P ratio. Regional analyses indicated that increases in some foliar nutrient concentrations such as N, S and Ca in northern Europe occurred associated with increasingly favourable conditions of mean annual precipitation and temperature. Crucial changes in forest health, structure, functioning and services, including negative feedbacks on C capture can be expected if these trends are not reversed.

Annals of Botany, 2003

Summer leaf senescence in Pistacia lentiscus L. plants serves to remobilize nutrients from the ol... more Summer leaf senescence in Pistacia lentiscus L. plants serves to remobilize nutrients from the oldest leaves to the youngest ones, and therefore contributes to plant survival during the adverse climatic conditions typical of Mediterranean summers, i.e. water de®cit superimposed on high solar radiation and high temperatures. To evaluate the extent of photo-and antioxidative protection during leaf senescence of this species, changes in carotenoids, including xanthophyll cycle pigments, and in the levels of ascorbate and a-tocopherol were measured prior to and during summer leaf senescence in 3-year-old plants grown under Mediterranean ®eld conditions. Although a chlorophyll loss of approx. 20 % was observed during the ®rst stages of leaf senescence, no damage to the photosynthetic apparatus occurred as indicated by constant maximum ef®ciencies of photosystem II photochemistry. During this period the de-epoxidation state of the xanthophyll cycle, and lutein, neoxanthin and ascorbate levels were kept constant. At the same time b-carotene and a-tocopherol levels increased by approx. 9 and 70 %, respectively, presumably conferring photo-and antioxidative protection to the photosynthetic apparatus. By contrast, during the later stages of leaf senescence, characterized by severe chlorophyll loss, carotenoids were moderately degraded (neoxanthin by approx. 20 %, and both lutein and b-carotene by approx. 35 %), ascorbate decreased by approx. 80 % and a-tocopherol was not detected in senescing leaves. This study demonstrates that mechanisms of photo-and antioxidative protection may play a major role in maintaining chloroplast function during the ®rst stages of leaf senescence, while antioxidant defences are lost during the latest stages of senescence.

Geoscientific Model Development Discussions, 2014

Since 70 % of global forests are managed and forests impact the global carbon cycle and the energ... more Since 70 % of global forests are managed and forests impact the global carbon cycle and the energy exchange with the overlying atmosphere, forest management has the potential to mitigate climate change. Yet, none of the land-surface models used in Earth system models, and therefore none of today's predictions of future climate, accounts for the interactions between climate and forest management. We addressed this gap in modelling capability by developing and parametrising a version of the ORCHIDEE land-surface model to simulate the biogeochemical and biophysical effects of forest management. The most significant changes between the new branch called ORCHIDEE-CAN (SVN r2290) and the trunk version of ORCHIDEE (SVN r2243) are the allometric-based allocation of carbon to leaf, root, wood, fruit and reserve pools; the transmittance, absorbance and reflectance of radiation within the canopy; and Published by Copernicus Publications on behalf of the European Geosciences Union. 2036 K. Naudts et al.: A vertically discretised canopy description for ORCHIDEE ORCHIDEE-CAN outperformed the trunk regarding its ability to reproduce large-scale spatial patterns as well as their inter-annual variability over Europe. Depending on the data stream, ORCHIDEE-CAN had a 67 to 92 % chance to reproduce the spatial and temporal variability of the validation data.

Annals of Botany, 2005

Background and Aims Natural regeneration of white spruce (Picea glauca) after disturbance has bee... more Background and Aims Natural regeneration of white spruce (Picea glauca) after disturbance has been reported to be very poor. Here a study was made to determine whether C compounds released from understorey species growing together with white spruce could be involved in this regeneration failure, either by (1) changing soil nutrient dynamics, (2) inhibiting germination, and /or (3) delaying seedling growth. Methods Foliage leachates were obtained from two shrubs (Ledum palustre and Empetrum hermaphroditum) and one bryophyte (Sphagnum sp.) with high phenolic compound concentrations that have been reported to depress growth of conifers in boreal forests, and, as a comparison, one bryophyte (Hylocomium splendens) with negligible phenolic compounds. Mineral soil from a white spruce forest was amended with plant leachates to examine the effect of each species on net N mineralization. Additionally, white spruce seeds and seedlings were watered with plant leachates to determine their effects on germination and growth. Key Results Leachates from the shrubs L. palustre and E. hermaphroditum contained high phenolic compound concentrations and dissolved organic carbon (DOC), while no detectable levels of C compounds were released from the bryophytes Sphagnum sp. or H. splendens. A decrease in net N mineralization was determined in soils amended with L. palustre or E. hermaphroditum leachates, and this effect was inversely proportional to the phenolic concentrations, DOC and leachate C/N ratio. The total percentage of white spruce germination and the growth of white spruce seedlings were similar among treatments. Conclusions These results suggest that the shrubs L. palustre and E. hermaphroditum could negatively affect the performance of white spruce due to a decrease in soil N availability, but not by direct effects on plant physiology.

Vegetation History and Archaeobotany, 2008

The palaeoenvironment of a former coastal lagoon in the south eastern Iberian Peninsula (San Rafa... more The palaeoenvironment of a former coastal lagoon in the south eastern Iberian Peninsula (San Rafael, Almeria, Spain) were inferred from one core analyzed for particulate organic matter content (POM) together with its C/N, d 13 C, d 15 N to depict the biogeochemical record from the Late Glacial to the Holocene. The results, complemented by previously reported pollen assemblages, indicate the appearance of a freshwater lagoon at 7300 B.P. (uncalibrated 14 C age), its salinization at 6200 B.P. and its disappearance at 4400 B.P. The period of existence of the lagoon coincided with a period of wetter conditions as inferred from terrestrial vegetation. The lagoon's salinization was not related to a decrease in precipitation but to a stronger maritime influence since there were no parallel changes in terrestrial vegetation. Salinization caused an increase in d 13 C, associated with a higher relative presence of C 4 plants, and an increase in d 15 N, due to a decrease in plant N demand. The late period of the lagoon, from about 5100 to 4400 B.P., shows a progressive drying and salinization not detected in isotopes but reflected in a decrease in POM, and in the pollen records. Increases in d 15 N were related to increases in salinity within the lagoon, and are indicative of a more open N cycle, because the absence of changes in terrestrial vegetation rules out changes in the catchment area as the cause for changes in d 15 N.

Russian Journal of Plant Physiology, 2009

We tested the effect of forecasted soil drought and warming climate conditions for the next decad... more We tested the effect of forecasted soil drought and warming climate conditions for the next decades on emission rates of isoprenoids by mediterranean shrublands. We measured isoprenoid emissions by whole dominant mediterranean woody plants (Erica multiflora L. and Globularia alypum L.) inhabiting the studied shrublands. Monoterpene emissions were detected in both species, but isoprene was emitted only by E. multiflora. Maximum emission rates were found during the hottest periods (except for G. alypum , in which they occurred in autumn), and minimum emission rates in winter in E. multiflora. Terpene emission rates ranged from 0.08 μ g/(g dry wt h) in winter in E. multiflora to 8.8 μ g/(g dry wt h) in G. alypum in autumn. In E. multiflora , the terpene emission rates decreased in response to soil drought only in summer, but increased in response to warming in spring and autumn. Isoprene emissions ranged from 0.1 μ g/(g dry wt h) in spring to 4.4 μ g/(g dry wt h) in summer. The effect of the treatments was only detected in autumn when soil drought and warming had a negative effect on isoprene emission rates. These data might improve our knowledge of isoprenoid emissions at the canopy level and in response to climate change, soil drought, or warming.

Plant Science, 2014

A long-term experimental drought to simulate future expected climatic conditions for Mediterranea... more A long-term experimental drought to simulate future expected climatic conditions for Mediterranean forests, a 15% decrease in soil moisture for the following decades, was conducted in a holm oak forest since 1999. Net photosynthetic rate, stomatal conductance and leaf water potential were measured from 1999 to 2013 in Quercus ilex and Phillyrea latifolia, two co-dominant species of this forest. These measurements were performed in four plots, two of them received the drought treatment and the two other plots were control plots. The three studied variables decreased with increases in VPD and decreases in soil moisture in both species, but the decrease of leaf water potential during summer drought was larger in P. latifolia, whereas Q. ilex reached higher net photosynthetic rates and stomatal conductance values during rainy periods than P. latifolia. The drought treatment decreased ca. 8% the net photosynthetic rates during the overall studied period in both Q. ilex and P. latifolia, whereas there were just non-significant trends toward a decrease in leaf water potential and stomatal conductance induced by drought treatment. Future drier climate may lead to a decrease in the carbon balance of Mediterranean species, and some shrub species well resistant to drought could gain competitive advantage relative to Q. ilex, currently the dominant species of this forest.

Soil Biology and Biochemistry, 2014

ABSTRACT We investigated the effect of soil microclimate on the structure and functioning of soil... more ABSTRACT We investigated the effect of soil microclimate on the structure and functioning of soil microbial communities in a Mediterranean Holm-oak forest subjected to 10 years of partial rain exclusion manipulations, simulating average drought conditions expected in Mediterranean areas for the following decades. We applied a high throughput DNA pyrosequencing technique coupled to parallel measurements of microbial respiration (RH) and temperature sensitivity of microbial respiration (Q10). Some consistent changes in the structure of bacterial communities suggest a slow process of community shifts parallel to the trend towards oligotrophy in response to long-term droughts. However, the structure of bacterial communities was mainly determined by short-term environmental fluctuations associated with sampling date (winter, spring and summer) rather than long-term (10 years) shifts in baseline precipitation. Moreover, long-term drought did not exert any chronic effect on the functioning of soil microbial communities (RH and Q10), emphasizing the functional stability of these communities to this long-term but mild shifts in water availability. We hypothesize that the particular conditions of the Mediterranean climate with strong seasonal shifts in both temperature and soil water availability but also characterized by very extreme environmental conditions during summer, was acting as a strong force in community assembling, selecting phenotypes adapted to the semiarid conditions characterizing Mediterranean ecosystems. Relations of climate with the phylogenetic structure and overall diversity of the communities as well as the distribution of the individual responses of different lineages (genera) to climate confirmed our hypotheses, evidencing communities dominated by thermotolerant and drought-tolerant phenotypes.

Remote Sensing of Environment, 2004

... 2001. View Within Article. 3.2. NDVI assessment of treatment, annual and seasonal biomass cha... more ... 2001. View Within Article. 3.2. NDVI assessment of treatment, annual and seasonal biomass changes. 3.2.1. Community. Plant biomass ...

Plant Biology, 2008

Research on biogenic volatile organic compound (BVOC) emissions has mainly focused on native spec... more Research on biogenic volatile organic compound (BVOC) emissions has mainly focused on native species in natural ecosystems. However, much of the ozone and aerosol formation occurs in city atmospheres due to BVOC emissions by local urban vegetation. Plant composition of urban habitats is often dominated by non-native ornamental plant species, for which only limited data on BVOC emissions are available. To gain insight into the influence of ornamental vegetation on the urban atmospheric reactivity in Barcelona, Spain, we studied volatile isoprenoid emissions in 11 widespread ornamental tree species (three conifers and nine angiosperms). We found significant monoterpene emissions in all studied species, with normalized emission potentials (T = 30°C, photosynthetic photon flux density (PPFD) = 1000 lmolAEm)2 AEs)1) ranging between 0.2 to 110 lgAEg)1 (dry weight) h)1. Depending on species, the emissions were dominated by aand b-pinene, myrcene, aand b-phellandrene, carene, limonene and eucalyptol. These data demonstrate that ornamental plants may significantly contribute to the BVOC load in urban atmospheres and also underscore the importance of broadleaf angiosperms as significant monoterpene emitters.

Perspectives in Plant Ecology, Evolution and Systematics, 2013

Plants produce and emit a large variety of volatile organic compounds that play key roles in inte... more Plants produce and emit a large variety of volatile organic compounds that play key roles in interactions with abiotic and biotic environments. One of these roles is the attraction of animals (mainly insects) that act as vectors of pollen to ensure reproduction. Here we update the current knowledge of four key aspects of floral emissions: (1) the relative importance and interaction of olfactory signals and visual cues, (2) the spatial and temporal patterns of emission in flowers, (3) the attractive and defensive functions of floral volatiles and their interference, and (4) the effects of global change on floral emissions and plant-pollinator interactions. Finally, we propose future lines of research in this field that need to be addressed or investigated further.

International Journal of Remote Sensing, 1995

... GAMON, JA, FIELD, C B., GOULDEN, M. L., GRIFFIN, K. L., HARTLEY, A. E., JOEL, G., PENUELAS, J... more ... GAMON, JA, FIELD, C B., GOULDEN, M. L., GRIFFIN, K. L., HARTLEY, A. E., JOEL, G., PENUELAS, J., and VALENTINI, R., 1995, Relationship between NDVI ... LORENZEN, B., and JENSEN, A., 1989, Changes in leaf spectral properties induced in barley by cereal powdery mildew ...

International Journal of Remote Sensing, 1996

... indicator of water status and yield under mild and very mild water stress conditions. ... C.,... more ... indicator of water status and yield under mild and very mild water stress conditions. ... C., 1994, Reflectance indices associated with physiological changes in nitrogen-and water-limited sunflower ... J., FILELLA, I., and SAVE, R., 1995, Assessing signals of gerbera water status inthe ...

International Journal of Remote Sensing, 1997

ABSTRACT

International Journal of Remote Sensing, 1997

ABSTRACT

Global Ecology and Biogeography, 2009

Aim To test whether the onset of spring growth in European shrublands is advanced in response to ... more Aim To test whether the onset of spring growth in European shrublands is advanced in response to the warmer conditions projected for the next two decades by climate models, and, if there is a change, whether it differs across Europe. ... Location The studied sites spanned a ...

Crop Science, 1995

Nitrogen deficiencies can seriously reduce yield and economic returns for farmers. Remote sensing... more Nitrogen deficiencies can seriously reduce yield and economic returns for farmers. Remote sensing could provide inexpensive, largearea estimates of N status and be used to monitor N status since leaf chlorophyll (Chi) A content is mainly determined by N availability. The objective was to determine if remote sensing of wheat (Triticum aestivum L.) Chi A content would provide a rapid estimation of wheat N status. We measured the reflectance of a wheat crop submitted to five different fertilization treatments throughout the growth cycle. We tested several empirical reflectance indices of pigment content: reflectance at 550 nm (R550), reflectance at 680 nm (R680), three parameters of the red edge [wavelength ()."), amplitude in the first derivative of the reflectance spectra (dR re), and sum of amplitudes between 680 and 780 nm in the first derivative of the reflectance spectra (£dR 680. 78 o nm)], and pigment simple ratio (PSR) and normalized pigment chlorophyll index (NPCI) (indices of carotenoid/Chl ratio). We also measured leaf Chi A and N content, and leaf area index. There were significant correlations between canopy Chi A content and R550, R680, and all the red edge parameters. The NPCI and PSR followed phenological evolution of the carotenoids/Chl A ratio and separated the different treatments. By discriminant analysis based on the pigment indices reflectance at 430 nm (R430), R550, R680, X re , dR,e, and NPCI, each reflectance spectrum can be assigned to a different N status class. Thus, the use of these optical techniques offers a potential for assessing N status of wheat.

Atmospheric Chemistry and Physics, 2009

Large uncertainties exist in our knowledge of regional emissions of non-methane biogenic volatile... more Large uncertainties exist in our knowledge of regional emissions of non-methane biogenic volatile organic compounds (BVOC). We address these uncertainties through a two-pronged approach by compiling a state of the art database of the emissions potentials for 80 European forest species, and by a model assessment and inter-comparison, both at the local and regional scale, under present and projected future climatic conditions. We coupled three contrasting isoprenoid models with the ecophysiological forest model GOTILWA+ to evaluate leaf and ecosystem isoprenoid emissions, build an emissions inventory for European forests, and to consider model behaviour in present climate and under projected future climate change conditions. Hourly, daily and annual isoprene emissions as simulated by the models were evaluated against flux measurements. The validation highlighted a general model capacity to capture gross fluxes but inefficiencies in capturing short term variability. A regional inventory of isoprenoid emissions for European forests was created using each of the three modelling approaches. The models agreed on an average European emissions budget of 1.03 TgC a −1 for isoprene and 0.97 TgC a −1 for monoterpenes for the period 1960-1990, which was dominated by a few species with largest aerial coverage. Species contribution to total emissions depended both on species emission potential and geographical distribution. For projected future climate conditions, however, emissions budgets proved highly model dependent, illustrating the current uncertainty associated with isoprenoid emissions responses to potential future conditions.

Agricultural and Forest Meteorology, 1998

We developed a method to estimate live fine fuel moisture LFFM by ground-based, high-resolution p... more We developed a method to estimate live fine fuel moisture LFFM by ground-based, high-resolution plant reflectance Ž. measurements in the visible and near infrared regions. NDVI and WI R rR were the reflectance indices used because 970 900

Agricultural and Forest Meteorology, 1992

Remotely measured canopy temperature of greenhouse strawberries as indicator of water status and ... more Remotely measured canopy temperature of greenhouse strawberries as indicator of water status and yield under mild and very mild water stress conditions. Agric. For. Meteorol., 58: 63-77. Strawberry plants were submitted to mild and very mild water stress regimes in a tunnel (simple semicircular greenhouse) by planting them in two plots fertirrigated when the soil matric potential reached-0.07 MPa and-0.01 MPa, respectively. The plants were monitored for water stress by measuring the foliage temperature with a hand-held infrared thermometer. Parallel to this, weather variables, the difference between leaf and air temperature, the derived crop water stress index (CWSI), the soil matric potential, the leaf water potential, the photosynthetic gas exchange rates, the transpiration rates, photosynthetic pigments, sugars, starch, canopy structure and accumulated yield were measured. The wet treatment (WT) presented a higher yield and higher leaf area index (LAI). In WT, leaves were disposed mostly in a monolayer oriented to the south, whereas in dry treatment (DT) leaves were distributed in a multilayer pattern and oriented to the north. During the hotter part of cloudless days and before irrigation took place, the canopy temperature of WT was about 3 °C less than that of DT. Accumulated stress degree days (SDD) were then higher in DT. WT presented lower average CWSI values, between 0.045 and 0.54, while those of DT were between 0.32 and 0.70. It was concluded that leaf temperature, its difference with air temperature (8 T) and the derived indices, such as SDD and CWSI, are useful for the assessment of even these mild and very mild water stresses in strawberries under protected conditions. Regression analysis showed that under the very mild water stress conditions tested in WT, the contribution of air vapor pressure deficit to variation in leaf water potential was significant. This did not happen under the mild water stress of DT.

Communications Biology, 2020

The drivers of global change, including increases in atmospheric CO2 concentrations, N and S depo... more The drivers of global change, including increases in atmospheric CO2 concentrations, N and S deposition, and climate change, likely affect the nutritional status of forests. Here we show forest foliar concentrations of N, P, K, S and Mg decreased significantly in Europe by 5%, 11%, 8%, 6% and 7%, respectively during the last three decades. The decrease in nutritional status was especially large in Mediterranean and temperate forests. Increasing atmospheric CO2 concentration was well correlated with the decreases in N, P, K, Mg, S concentrations and the increase of N:P ratio. Regional analyses indicated that increases in some foliar nutrient concentrations such as N, S and Ca in northern Europe occurred associated with increasingly favourable conditions of mean annual precipitation and temperature. Crucial changes in forest health, structure, functioning and services, including negative feedbacks on C capture can be expected if these trends are not reversed.

Annals of Botany, 2003

Summer leaf senescence in Pistacia lentiscus L. plants serves to remobilize nutrients from the ol... more Summer leaf senescence in Pistacia lentiscus L. plants serves to remobilize nutrients from the oldest leaves to the youngest ones, and therefore contributes to plant survival during the adverse climatic conditions typical of Mediterranean summers, i.e. water de®cit superimposed on high solar radiation and high temperatures. To evaluate the extent of photo-and antioxidative protection during leaf senescence of this species, changes in carotenoids, including xanthophyll cycle pigments, and in the levels of ascorbate and a-tocopherol were measured prior to and during summer leaf senescence in 3-year-old plants grown under Mediterranean ®eld conditions. Although a chlorophyll loss of approx. 20 % was observed during the ®rst stages of leaf senescence, no damage to the photosynthetic apparatus occurred as indicated by constant maximum ef®ciencies of photosystem II photochemistry. During this period the de-epoxidation state of the xanthophyll cycle, and lutein, neoxanthin and ascorbate levels were kept constant. At the same time b-carotene and a-tocopherol levels increased by approx. 9 and 70 %, respectively, presumably conferring photo-and antioxidative protection to the photosynthetic apparatus. By contrast, during the later stages of leaf senescence, characterized by severe chlorophyll loss, carotenoids were moderately degraded (neoxanthin by approx. 20 %, and both lutein and b-carotene by approx. 35 %), ascorbate decreased by approx. 80 % and a-tocopherol was not detected in senescing leaves. This study demonstrates that mechanisms of photo-and antioxidative protection may play a major role in maintaining chloroplast function during the ®rst stages of leaf senescence, while antioxidant defences are lost during the latest stages of senescence.

Geoscientific Model Development Discussions, 2014

Since 70 % of global forests are managed and forests impact the global carbon cycle and the energ... more Since 70 % of global forests are managed and forests impact the global carbon cycle and the energy exchange with the overlying atmosphere, forest management has the potential to mitigate climate change. Yet, none of the land-surface models used in Earth system models, and therefore none of today's predictions of future climate, accounts for the interactions between climate and forest management. We addressed this gap in modelling capability by developing and parametrising a version of the ORCHIDEE land-surface model to simulate the biogeochemical and biophysical effects of forest management. The most significant changes between the new branch called ORCHIDEE-CAN (SVN r2290) and the trunk version of ORCHIDEE (SVN r2243) are the allometric-based allocation of carbon to leaf, root, wood, fruit and reserve pools; the transmittance, absorbance and reflectance of radiation within the canopy; and Published by Copernicus Publications on behalf of the European Geosciences Union. 2036 K. Naudts et al.: A vertically discretised canopy description for ORCHIDEE ORCHIDEE-CAN outperformed the trunk regarding its ability to reproduce large-scale spatial patterns as well as their inter-annual variability over Europe. Depending on the data stream, ORCHIDEE-CAN had a 67 to 92 % chance to reproduce the spatial and temporal variability of the validation data.

Annals of Botany, 2005

Background and Aims Natural regeneration of white spruce (Picea glauca) after disturbance has bee... more Background and Aims Natural regeneration of white spruce (Picea glauca) after disturbance has been reported to be very poor. Here a study was made to determine whether C compounds released from understorey species growing together with white spruce could be involved in this regeneration failure, either by (1) changing soil nutrient dynamics, (2) inhibiting germination, and /or (3) delaying seedling growth. Methods Foliage leachates were obtained from two shrubs (Ledum palustre and Empetrum hermaphroditum) and one bryophyte (Sphagnum sp.) with high phenolic compound concentrations that have been reported to depress growth of conifers in boreal forests, and, as a comparison, one bryophyte (Hylocomium splendens) with negligible phenolic compounds. Mineral soil from a white spruce forest was amended with plant leachates to examine the effect of each species on net N mineralization. Additionally, white spruce seeds and seedlings were watered with plant leachates to determine their effects on germination and growth. Key Results Leachates from the shrubs L. palustre and E. hermaphroditum contained high phenolic compound concentrations and dissolved organic carbon (DOC), while no detectable levels of C compounds were released from the bryophytes Sphagnum sp. or H. splendens. A decrease in net N mineralization was determined in soils amended with L. palustre or E. hermaphroditum leachates, and this effect was inversely proportional to the phenolic concentrations, DOC and leachate C/N ratio. The total percentage of white spruce germination and the growth of white spruce seedlings were similar among treatments. Conclusions These results suggest that the shrubs L. palustre and E. hermaphroditum could negatively affect the performance of white spruce due to a decrease in soil N availability, but not by direct effects on plant physiology.

Vegetation History and Archaeobotany, 2008

The palaeoenvironment of a former coastal lagoon in the south eastern Iberian Peninsula (San Rafa... more The palaeoenvironment of a former coastal lagoon in the south eastern Iberian Peninsula (San Rafael, Almeria, Spain) were inferred from one core analyzed for particulate organic matter content (POM) together with its C/N, d 13 C, d 15 N to depict the biogeochemical record from the Late Glacial to the Holocene. The results, complemented by previously reported pollen assemblages, indicate the appearance of a freshwater lagoon at 7300 B.P. (uncalibrated 14 C age), its salinization at 6200 B.P. and its disappearance at 4400 B.P. The period of existence of the lagoon coincided with a period of wetter conditions as inferred from terrestrial vegetation. The lagoon's salinization was not related to a decrease in precipitation but to a stronger maritime influence since there were no parallel changes in terrestrial vegetation. Salinization caused an increase in d 13 C, associated with a higher relative presence of C 4 plants, and an increase in d 15 N, due to a decrease in plant N demand. The late period of the lagoon, from about 5100 to 4400 B.P., shows a progressive drying and salinization not detected in isotopes but reflected in a decrease in POM, and in the pollen records. Increases in d 15 N were related to increases in salinity within the lagoon, and are indicative of a more open N cycle, because the absence of changes in terrestrial vegetation rules out changes in the catchment area as the cause for changes in d 15 N.

Russian Journal of Plant Physiology, 2009

We tested the effect of forecasted soil drought and warming climate conditions for the next decad... more We tested the effect of forecasted soil drought and warming climate conditions for the next decades on emission rates of isoprenoids by mediterranean shrublands. We measured isoprenoid emissions by whole dominant mediterranean woody plants (Erica multiflora L. and Globularia alypum L.) inhabiting the studied shrublands. Monoterpene emissions were detected in both species, but isoprene was emitted only by E. multiflora. Maximum emission rates were found during the hottest periods (except for G. alypum , in which they occurred in autumn), and minimum emission rates in winter in E. multiflora. Terpene emission rates ranged from 0.08 μ g/(g dry wt h) in winter in E. multiflora to 8.8 μ g/(g dry wt h) in G. alypum in autumn. In E. multiflora , the terpene emission rates decreased in response to soil drought only in summer, but increased in response to warming in spring and autumn. Isoprene emissions ranged from 0.1 μ g/(g dry wt h) in spring to 4.4 μ g/(g dry wt h) in summer. The effect of the treatments was only detected in autumn when soil drought and warming had a negative effect on isoprene emission rates. These data might improve our knowledge of isoprenoid emissions at the canopy level and in response to climate change, soil drought, or warming.