153 research outputs found
L'aigua com a factor clau en l'ús eficient de la radiació per la vegetació terrestre
Un grup d'investigació, liderat pel Centre de Recerca Ecològica i Aplicacions Forestals (CREAF), ha analitzat els factors que influeixen en l'eficiència amb què la vegetació utilitza la radiació per a la captació del carboni atmosfèric en el procés de fotosÃntesi. L'ús que les plantes fan de la radiació que reben es troba determinat per variables climà tiques, però la prevalença que les precipitacions tenen sobre altres factors, com la temperatura, ha quedat demostrada grà cies a modernes tècniques d'anà lisi micrometeorològic i al processat de les dades recollides pel sensor MODIS, instal·lat en un satèl lit de la NASA. Els resultats exposats obliguen a reformular algunes de les afirmacions tradicionals sobre el funcionament dels ecosistemes.Un grupo de investigación, liderado por el Centre de Recerca Ecològica i Aplicacions Forestals (CREAF), ha analizado los factores que influyen en la eficiencia con que la vegetación usa la radiación para la captación del carbono atmosférico en el proceso de fotosÃntesis. El uso que las plantas hacen de la radiación que reciben se encuentra determinado por variables climáticas, pero la prevalencia que las precipitaciones tienen sobre otros factores, como la temperatura, ha quedado demostrada gracias a modernas técnicas de análisis micrometeorológico y al procesado de los datos recogidos por el sensor MODIS, instalado en un satélite de la NASA. Los resultados expuestos obligan a reformular algunas de las afirmaciones tradicionales sobre el funcionamiento de los ecosistemas
Caracterizacion de la fenologÃa de la vegetación a escala global mediante series temporales SPOT VEGETATION
Altres ajuts: Programes Copernicus, le Pôle Thématique Surfaces Continentales THEIA, GIOBIO (32-566) i LONGLOVE (32-594).La fenologÃa de la vegetación a escala global se caracterizó a partir de series temporales del Ãndice de área foliar (LAI) SPOT VEGETATION a 1-km de resolución espacial en el periodo 1999-2010. Los patrones espaciales de la fenologÃa estimada a partir de datos de satélite muestran una gran consistencia con la distribución de biomas y factores climáticos. La comparación de la fenologÃa SPOT VEGETATION con medidas in-situ para las fenofases del abedul común (Betula pendula) en Europa muestra un gran acuerdo en el gradiente latitudinal de temperatura con un descenso en la duración de la estación de crecimiento de 5 dÃas por grado de latitudWe characterized the phenology of the vegetation at the global scale from the mean seasonal leaf area index (LAI) estimated from 1-km SPOT VEGETATION time series for 1999-2010. The satellite-derived phenology was spatially consistent with the global distributions of climatic drivers and biome land cover. The rate of change of phenological leaf development from VEGETATION data and in-situ observations for the date of phenophases of European birch forests agreed very well with latitudinal temperature with a decrease in the length of season of approximately five days per degree of latitude
Les papallones com a bioindicadores dels hà bitats a Catalunya: l'exemple dels prats de dall i le pastures del Parc Natural dels Aiguamolls de l'EmpordÃ
El Parque Natural de los Aiguamolls de lÂ’EmpordÃ
(PNAE) es uno de los espacios protegidos más conocidos
y emblemáticos de Cataluña. Uno de sus
hábitats más localizados y amenazados son las denominadas
closes, prados de siega destinados a la producción
de forraje, rodeados de canales de desagüe e
inundados durante parte del invierno. Recientemente,
se ha demostrado que la comunidad vegetal más
tÃpicamente asociada con estos prados es la más rica
del Parque y la que alberga las especies más raras.
En este trabajo se utilizan datos de mariposas diurnas
(ropalóceros), obtenidos después de aplicar durante
17 años la metodologÃa del Butterfly Monitoring
Scheme, para evaluar el interés de conservación
de los principales ambientes del PNAE. Las closes
constituyen también para los ropalóceros el
hábitat más valuoso. La coincidencia en los resultados
obtenidos en dos grupos taxonómicos amplios
y que ocupan niveles tróficos distintos, sumada a la
alarmante regresión que han experimentado las
closes en los últimos 50 años y a su singularidad en
el área mediterránea, permiten considerarlas objetivamente
como uno de los hábitats más amenazados
del PNAE y del conjunto de Cataluña. En una segunda
parte del trabajo, se analizan las respuestas
de las mariposas frente al abandono de las closes y
a su recuperación a partir de antiguos cultivos intensivos.
Los cambios que experimentan las comunidades
de mariposas pueden pasar del todo desapercibidos
si los análisis se focalizan en indicadores
generales (p. ej., riqueza especÃfica y abundancia).
Contrariamente, se demuestra que la respuesta de
algunas especies potencialmente bioindicadoras
puede ser muy acusada, si bien es necesario conocer
su ecologÃa para poder interpretarla correctamente.
En concreto, se concluye que Plebejus argus representa
la mejor especie bioindicadora de las peculiares
condiciones ambientales propias de las
closes: las poblaciones responden con descensos
rapidÃsimos cuando estas condiciones se deterioran,
y también con aumentos progresivos cuando
el hábitat mejora. Además, se trata de una especie
muy sedentaria que se estructura en forma de
metapoblaciones, por lo cual el monitoreo de una
población local refleja también las condiciones
del paisaje de su entorno.Aiguamolls de l’Empordà Natural Park is one of
the most important protected wetland areas on the
Mediterranean coast. In this article, butterfly
assemblages were used to characterize and evaluate
the conservation value of the main habitat types in
this protected area. Butterfly data were obtained
from a number of transects walked as part of the
Catalan Butterfly Monitoring Scheme, which uses a
standardized methodology for monitoring butterflies.
Hay meadows flooded in winter (the so-called
closes) appeared always as the highest ranked
habitat in terms of conservation evaluation: they
have more butterflies and a slight tendency to
harbour more and generally rarer species. This
conclusion coincides with that of previous
investigations indicating that the most diverse and
rare plant communities in the whole Natural Park
are present in the closes, and highlights the
importance of traditionally managed hay meadows
for wildlife. However, these hay meadows are in
alarming decline and have become one of the most
threatened habitats in this area and the whole
Mediterranean region. In a second part of the
article, we analysed the responses of butterfly
communities once the closes are abandonned or
when they are recovered from former arable
fields. Changes may be completely overlooked if
the analyses are focussed on general patterns for
the whole community (e.g. species richness and
abundance). On the other hand, several individual
species showed strong population trends and some
of them may be considered as true bioindicators of
the narrow environmental conditions associated
with this kind of habitat. In particular, we suggest
that Plebejus argus represents an excellent
bioindicator of these traditionally managed hay
meadows: its populations always showed dramatic
decreases once the closes were abadonned,
overgrazed or invaded by exotic weeds, and
progressive increases once the quality of the
meadows improved. Moreover, this highly
sedentary species exists as metapopulations and,
therefore, the wealth of local populations also
reflects that of the surrounding landscape.El Parc Natural dels Aiguamolls de l'EmpordÃ
(PNAE) és un dels espais protegits més coneguts i
emblemà tics a Catalunya. Un dels seus hà bitats
més localitzats i amenaçats són les anomenades
closes, prats destinats a la producció de farratge,
envoltats per canals de desguàs i bosc de ribera,
inundats durant part de l'hivern i dallats periòdicament.
Recentment s'ha demostrat que la comunitat
vegetal més tÃpica de les closes és la més rica
del Parc i la que alberga les espècies més rares. En
aquest treball s'utilitzen dades de papallones
diürnes (ropalòcers), obtingudes després d'aplicar
durant 17 anys la metodologia del Butterfly Monitoring
Scheme, per avaluar l'interès de conservació
dels principals ambients del PNAE. Les closes
constitueixen l'hà bitat més valuós també per als
ropalòcers. La coincidència dels resultats per a
dos grups taxonòmics amplis que ocupen nivells
tròfics diferents, sumada a l'alarmant regressió
que han experimentat les closes en els darrers 50 anys i a la seva singularitat dins de l'à rea mediterrà nia,
permeten considerar-les objectivament
com un dels hà bitats més amenaçats del PNAE i
de tot Catalunya. En una segona part del treball,
s'analitzen les respostes de les papallones enfront
de l'abandonament de les closes i de la seva
recuperació a partir d'antics conreus intensius. Els
canvis que experimenten les comunitats de
ropalòcers poden passar del tot desapercebuts si
les anà lisis es focalitzen en indicadors generals (p.
ex., riquesa especÃfica i abundà ncia). Contrà riament,
es demostra que la resposta d'algunes espècies
potencialment bioindicadores pot ser molt
més acusada, encara que cal conèixer la seva ecologia
per poder-la interpretar correctament. En
concret, es conclou que Plebejus argus representa
la millor espècie bioindicadora d'unes condicions
ambientals pròpies de les closes empordaneses
tradicionals: les poblacions responen amb descensos
rapidÃssims quan les condicions òptimes es deterioren,
i també amb augments progressius quan
l'hà bitat millora. A més, es tracta d'una espècie
molt sedentà ria que s'estructura en forma de
metapoblacions, per la qual cosa el monitoratge
d'una població reflecteix també les condicions del
paisatge del seu entorn
Local interpretation of machine learning models in remote sensing with SHAP : the case of global climate constraints on photosynthesis phenology
Altres ajuts: the Fundación Ramón Areces grant CIVP20A6621Data-driven models using machine learning have been widely used in remote-sensing applications such as the retrieval of biophysical variables and land cover classification. However, these models behave as a 'black box', meaning that the relationships between the input and predicted variables are hard to interpret. Recent regression models that downscale sun-induced fluorescence (SIF) with MODIS and weather variables are an example. The impact of weather variables on the predicted SIF in these models is unknown. The explanation of such weather-SIF relationships would aid in the understanding of climate-related constraints on photosynthesis phenology since SIF is a proxy of gross primary productivity. Here, we used SHapley Additive exPlanations (SHAP) - a novel technique based on game theory - for explaining the contribution of input variables to the individual predictions in a machine learning model. We explored the capabilities of this technique with a weather-SIF model. The regression model predicted ESA-TROPOSIF measurements from ERA5-Land air temperature, shortwave radiation, and vapour-pressure-deficit (VPD) data. The SHAP values of the model were estimated at the start and end of the growing season for the entire globe. These values depicted the global constraints of the three climate variables on the photosynthetically active season and confirmed existing knowledge on the limiting factors of terrestrial photosynthesis with unprecedented spatial detail. Radiation was the limiting factor in tropical rainforest and VPD constrained the start and end of the growing season in tropical dryland ecosystems. In extra-tropical regions, temperature was the main limiting factor during the start of the growing season, but both temperature and radiation constrained photosynthesis at the end of the growing season. This technique may help future remote sensing studies that require the use of non-interpretable machine-learning regression models and explain how input variables contribute to the model prediction in a spatiotemporally explicit manner
Bidirectional interaction between phyllospheric microbiotas and plant volatile emissions
Due to their antimicrobial effects and their potential role as carbon sources, plant volatile organic compound (VOC) emissions play significant roles in determining the characteristics of the microbial communities that can establish on plant surfaces. Furthermore, epiphytic microorganisms, including bacteria and fungi, can affect plant VOC emissions in different ways: by producing and emitting their own VOCs, which are added to and mixed with the plant VOC blend; by affecting plant physiology and modifying the production and emission of VOCs; and by metabolizing the VOCs emitted by the plant. The study of the interactions between plant VOC emissions and phyllospheric microbiotas is thus of great interest and deserves more attention
A Novel Method to Simultaneously Measure Leaf Gas Exchange and Water Content
Understanding the relationship between plant water status and productivity and between plant water status and plant mortality is required to effectively quantify and predict the effects of drought on plants. Plant water status is closely linked to leaf water content that may be estimated using remote sensing technologies. Here, we used an inexpensive miniature hyperspectral spectrometer in the 1550–1950 nm wavelength domain to measure changes in silver birch (Betula pendula Roth) leaf water content combined with leaf gas exchange measurements at a sub-minute time resolution, under increasing vapor pressure deficit, CO2 concentrations, and light intensity within the measurement cuvette; we also developed a novel methodology for calibrating reflectance measurements to predict leaf water content for individual leaves. Based on reflectance at 1550 nm, linear regression modeling explained 98–99% of the variation in leaf water content, with a root mean square error of 0.31–0.43 g cm−2. The prediction accuracy of the model represents a c. ten-fold improvement compared to previous studies that have used destructive sampling measurements of several leaves. This novel methodology allows the study of interlinkages between leaf water content, transpiration, and assimilation at a high time resolution that will increase understanding of the movement of water within plants and between plants and the atmosphere
β-Ocimene, a key floral and foliar volatile involved in multiple interactions between plants and other organisms
β-Ocimene is a very common plant volatile released in important amounts from the leaves and flowers of many plant species. This acyclic monoterpene can play several biological functions in plants, by potentially affecting floral visitors and also by mediating defensive responses to herbivory. The ubiquity and high relative abundance of β-ocimene in the floral scents of species from most plant families and from different pollination syndromes (ranging from generalism to specialism) strongly suggest that this terpenoid may play an important role in the attraction of pollinators to flowers. We compiled abundant evidence from published studies that supports β-ocimene as a generalist attractant of a wide spectrum of pollinators. We found no studies testing behavioural responses of pollinators to β-ocimene, that could directly demonstrate or deny the function of β-ocimene in pollinator attraction; but several case studies support that the emissions of β-ocimene in flowers of different species follow marked temporal and spatial patterns of emission, which are typical from floral volatile organic compound (VOC) emissions that are involved in pollinator attraction. Furthermore, important β-ocimene emissions are induced from vegetative plant tissues after herbivory in many species, which have relevant functions in the establishment of tritrophic interactions. We thus conclude that β-ocimene is a key plant volatile with multiple relevant functions in plants, depending on the organ and the time of emission. Experimental behavioural studies on pure β-ocimene conducted with pollinating insects will be necessary to prove the assumptions made here
A broadband green-red vegetation index for monitoring gross primary production phenology
The chlorophyll/carotenoid index (CCI) is increasingly used for remotely tracking the phenology of photosynthesis. However, CCI is restricted to few satellites incorporating the 531nm band. This study reveals that the Moderate Resolution Imaging Spectroradiometer (MODIS) broadband green reflectance (band 4) is significantly correlated with this xanthophyll-sensitive narrowband (band 11) (R2 = 0:98, p < 0:001), and consequently, the broadband green-red vegetation index GRVI-computed with MODIS band 1 and band 4-is significantly correlated with CCI-computed with MODIS band 1 and band 11 (R2 = 0:97, p < 0:001). GRVI and CCI performed similarly in extracting phenological metrics of the dates of the start and end of the season (EOS) when evaluated with gross primary production (GPP) measurements from eddy covariance towers. For EOS extraction of evergreen needleleaf forest, GRVI even overperformed solar-induced chlorophyll fluorescence which is seen as a direct proxy of plant photosynthesis. This study opens the door for GPP and photosynthetic phenology monitoring from a wide set of sensors with broadbands in the green and red spectral regions
Divergent estimates of forest photosynthetic phenology using structural and physiological vegetation indices
The accurate estimation of photosynthetic phenology using vegetation indices (VIs) is important for measuring the interannual variation of atmospheric CO2 concentrations, but the relative performances of structural and physiological VIs remain unclear. We found that structural VIs (normalized difference VI, enhanced VI, and near-infrared reflectance of vegetation) were suitable for estimating the start of the photosynthetically active season in deciduous broadleaf forests using gross primary production measured by FLUXNET as a benchmark, and a physiological VI (chlorophyll/carotenoid index) was better at identifying the end of the photosynthetically active season for deciduous broadleaf forests and both the start and end of season for evergreen needleleaf forests. The divergent performances were rooted in the combined control of structural and physiological regulations of carbon uptake by plants. Most existing studies of photosynthetic phenology have been based on structural VIs, so we suggest revisiting the dynamics of photosynthetic phenology using physiological VIs, which has significant implications on global plant phenology and carbon uptake studies
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