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 fotosíntesi. L'ús que les plantes fan de la radiació que reben es troba determinat per variables climàtiques, però la prevalença que les precipitacions tenen sobre altres factors, com la temperatura, ha quedat demostrada gràcies a modernes tècniques d'anàlisi 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 fotosíntesis. 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 fenología 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 fenología de la vegetación a escala global se caracterizó a partir de series temporales del índice de área foliar (LAI) SPOT VEGETATION a 1-km de resolución espacial en el periodo 1999-2010. Los patrones espaciales de la fenología estimada a partir de datos de satélite muestran una gran consistencia con la distribución de biomas y factores climáticos. La comparación de la fenología 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 días 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 hàbitats a Catalunya: l'exemple dels prats de dall i le pastures del Parc Natural dels Aiguamolls de l'Empordà

El Parque Natural de los Aiguamolls de l’Empordà (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 típicamente 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 metodología 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 específica y abundancia). Contrariamente, se demuestra que la respuesta de algunas especies potencialmente bioindicadoras puede ser muy acusada, si bien es necesario conocer su ecología 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 rapidísimos 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'Empordà (PNAE) és un dels espais protegits més coneguts i emblemàtics a Catalunya. Un dels seus hàbitats 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 típica 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'hàbitat 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'àrea mediterrània, permeten considerar-les objectivament com un dels hàbitats 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 anàlisis es focalitzen en indicadors generals (p. ex., riquesa específica i abundància). Contràriament, 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 rapidíssims quan les condicions òptimes es deterioren, i també amb augments progressius quan l'hàbitat millora. A més, es tracta d'una espècie molt sedentària 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

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

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

Assessment of the response of photosynthetic activity of Mediterranean evergreen oaks to enhanced drought stress and recovery by using PRI and R690/R630

Agraïments: Chao Zhang gratefully acknowledges the support from the Chinese Scholarship Council.The photochemical reflectance index (PRI) and red-edge region of the spectrum are known to be sensitive to plant physiological processes, and through measurement of these optical signals it is possible to use non-invasive remote sensing to monitor the plant photosynthetic status in response to environmental stresses such as drought. We conducted a greenhouse experiment using Quercus ilex, a Mediterranean evergreen oak species, to investigate the links between leaf-level PRI and the red-edge based reflectance ratio (R690/R630) with CO2 assimilation rates (A), and photochemical efficiency (FV/FM and Yield) in response to a gradient of mild to extreme drought treatments (nine progressively enhanced drought levels) and corresponding recovery. PRI and R690/R630 both decreased under enhanced drought stress, and had significant correlations with A, FV/FM and Yield. The differential values between recovery and drought treatments of PRI (DPRIrecovery) and R690/R630 (DR690/R630recovery) increased with the enhanced drought levels, and significantly correlated with the increases of DArecovery, DFV/FMrecovery and DYieldrecovery. We concluded that both PRI and R690/R630 were not only sensitive to enhanced drought stresses, but also highly sensitive to photosynthetic recovery. Our study makes important progress for remotely monitoring the effect of drought and recovery on photosynthetic regulation using the simple physiological indices of PRI and R690/R630

Les plantes s'avisen del perill imminent

Les plantes envien senyals a l'atmosfera per comunicar-se amb altres plantes i amb els animals: quan una planta és atacada per un patogen o per un herbívor allibera certs compostos a l'aire que "avisen" les altres del perill imminent, de manera que puguin preparar-se per rebre'l. Són substàncies que activen el metabolisme defensiu de les plantes com l'emissió de compostos repel·lents contra els herbívors, de reclam pels parasitoides dels herbívors o la segregació d'antioxidants o estabilitzadors de les membranes cel·lulars. Investigadors de la UAB han investigat si el metanol podria comptar-se entre aquestes substàncies de comunicació ja que s'ha detectat que en la sega dels camps de cultiu o en l'atac per herbívors s'alliberen grans quantitats d'aquest compost a l'atmosfera detectables per les plantes de la rodalia.Las plantas envían señales a la atmósfera para comunicarse con otras plantas y con los animales: cuando una planta es atacada por un patógeno o por un herbívoro libera ciertos compuestos en el aire que "avisan" a las demás del peligro inminente, de manera que puedan prepararse para recibirlo. Son sustancias que activan el metabolismo defensivo de las plantas como la emisión de compuestos repelentes contra los herbívoros, de reclamo para los parasitoides de los herbívoros o la segregación de antioxidantes o estabilizadores de las membranas celulares. Investigadores de la UAB han investigado si el metanol podría estar entre estas sustancias de comunicación ya que se ha detectado que en la siega de los campos de cultivo o en el ataque por herbívoros se liberan grandes cantidades de este compuesto a la atmósfera detectables por las plantas de los alrededores

Removal of floral microbiota reduces floral terpene emissions

The emission of floral terpenes plays a key role in pollination in many plant species. We hypothesized that the floral phyllospheric microbiota could significantly influence these floral terpene emissions because microorganisms also produce and emit terpenes. We tested this hypothesis by analyzing the effect of removing the microbiota from flowers. We fumigated Sambucus nigra L. plants, including their flowers, with a combination of three broad-spectrum antibiotics and measured the floral emissions and tissular concentrations in both antibiotic-fumigated and non-fumigated plants. Floral terpene emissions decreased by ca. two thirds after fumigation. The concentration of terpenes in floral tissues did not decrease, and floral respiration rates did not change, indicating an absence of damage to the floral tissues. The suppression of the phyllospheric microbial communities also changed the composition and proportion of terpenes in the volatile blend. One week after fumigation, the flowers were not emitting b-ocimene, linalool, epoxylinalool, and linalool oxide. These results show a key role of the floral phyllospheric microbiota in the quantity and quality of floral terpene emissions and therefore a possible key role in pollination

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

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