Carbon Sequestration and Water Productivity in Olive grove

El olivar constituye uno de los principales sistemas agrícolas en el área Mediterránea, y puede desempeñar un papel muy importante en el ciclo biogeoquímico como sumidero de gases de efecto invernadero (GEI). Sin embargo, la capacidad de fijar CO2 en diferentes condiciones ambientales por parte de las cubiertas de olivar es casi desconocida. Por otra parte, la elevada productividad del agua en el olivar ha provocado que la práctica del riego en este cultivo se haya generalizado en los últimos años, llegando a convertirse en el más importante de la agricultura española de regadío, cuya sostenibilidad se ve amenazada de forma creciente por la escasez de recursos hídricos. Esta situación evidencia la necesidad de profundizar en el estudio del efecto del estrés hídrico en el intercambio de gases y en la productividad del agua en el olivar. Dada la dificultad de extrapolar resultados obtenidos a partir de medidas en hoja, sería de gran utilidad el disponer de herramientas que permitiesen realizar estas medidas a escala árbol en condiciones de campo. Un método adecuado para medir el intercambio de gases en árboles individuales es el uso de cámaras. Sin embargo, hay una dificultad práctica en el diseño, construcción y operación de cámaras lo suficiente grandes como para incluir un árbol entero. El mayor reto de esta tesis fue el desarrollo de una herramienta capaz de medir el flujo de gases en árboles con volúmenes de copa de 20 a 30 m3 en campo. Para ello se diseñó una cámara de cierre transitorio con ventanas y techos móviles para mantener la cubierta del árbol acoplada al ambiente mientras está abierta. Partiendo de unas condiciones naturales, mediante cierres transitorios se mide simultáneamente la variación en la concentración de CO2 y vapor de agua por el intercambio de gases del árbol en el ambiente confinado por la cámara en un periodo de tiempo determinado. Los test realizados permitieron el desarrollo de un procedimiento estándar para medir el intercambio de gases en olivos.Para caracterizar las variaciones diurnas y estacionales de las tasas de fotosíntesis a nivel de cubierta y el efecto del estrés hídrico en el intercambio de carbono y vapor de agua, se midió la asimilación neta de CO2 (An), la transpiración (E) y la eficiencia en la transpiración (WUE) de olivos adultos en un periodo de 2 años en una parcela de olivar en Córdoba (España) con dos tratamientos de riego: control sin estrés hídrico (CI) y riego deficitario controlado (RDI). Independientemente del tratamiento de riego, la evolución de la conductancia estomática a lo largo del día presentó los valores máximos por la mañana temprano (8:00-9:00 GMT), disminuyendo de forma gradual desde ese momento hasta la puesta de sol. Mientras que la asimilación neta mostró un patrón similar al de la conductancia, la transpiración alcanzó sus valores máximos a primera hora de la tarde, como resultado del efecto conjunto de la conductancia de la cubierta y la demanda evaporativa (DPV). La asimilación neta (An) diaria varió estacionalmente con valores extremos de 9.6 g CO2 m-2 d-1 en diciembre de 2006 y 22 g CO2 m-2 d-1 en septiembre de 2007, para el tratamiento CI. El estrés hídrico redujo significativamente la An diaria en el tratamiento RDI. La WUE instantánea varió de forma dramática desde valores de 30 g CO2 L-1 a primera hora del día hasta 2.7 g CO2 L-1 al final de la tarde, siguiendo la típica relación inversa con el DPV. Aunque las diferencias en los valores instantáneos de WUE entre los dos tratamientos de riego fueron muy pequeñas, el déficit hídrico provocó un aumento notable en la WUE diaria, como resultado de un mayor control estomático en los periodos del día con mayor demanda evaporativa (DPV). Las medidas permitieron la calibración de un modelo de conductancia basado en la relación conductancia-asimilación que contribuyó a evaluar el efecto del estrés hídrico en la WUE. La mejora de la WUE en el RDI sugiere el uso de estrategias de riego deficitario como método eficiente para maximizar la acumulación de biomasa y la productividad en un escenario de escasez de agua cuando el estrés hídrico se concentra en el verano (VPD alto). Sin embargo, los límites de déficit hídrico para evitar efectos secundarios negativos (reducción en el índice de cosecha, la senescencia foliar, etc.) deben ser definidos.En último lugar, se presentan las primeras medidas de respiración a nivel de árbol en un estudio centrado en comprender cómo los patrones de respiración de la planta y el suelo de una parcela de olivar regulan la capacidad para el secuestro de carbono y cómo la respiración de los árboles responden a la temperatura, fenología y composición específica de órganos de la planta. Los resultados obtenidos en una serie de experimentos indicaron que; la respiración del suelo fue un componente importante de la respiración a nivel de ecosistema a pesar de que estuvo fuertemente limitada en el suelo seco. La respiración de raíces, micorrizas, y organismos descomponedores (respiración heterótrofa) en suelos permanece desconocida y requieren ser estudiadas. Mientras que la respiración del suelo fue constante, la respiración de la planta varió de forma proporcional a la temperatura. Este patrón hizo que la respiración del suelo fuera el mayor contribuyente de la respiración a nivel de ecosistema cuando la temperatura del aire fue inferior a 20 ºC. Los componentes de mantenimiento y crecimiento de la respiración fueron determinados en un experimento con olivos jóvenes sometidos a periodos prolongados de oscuridad y podas selectivas. Aproximadamente el 30% de la respiración de las plantas fue asignada a su componente de crecimiento y el 70% a la de mantenimiento, cuya dependencia con la temperatura fue determinada empíricamente para sus diferentes órganos. El coeficiente específico de mantenimiento (la tasa de respiración por unidad de masa de un órgano determinado a una temperatura de referencia) medido en frutos fue similar al de hojas, siendo para ramas el más bajo. En experimentos similares con árboles adultos, la respiración del tronco representó el 6% de la respiración total de la planta. Los resultados obtenidos indicaron que generalmente la respiración específica de un árbol está más relacionada a su masa foliar que a su masa total o su área foliar ya que las hojas fueron los principales contribuyentes a la respiración de las planta. El coste de mantenimiento tan reducido encontrado en madera estructural indica que la respiración de la cubierta se ve afectada mínimamente por diferencias en la biomasa leñosa

Planted or Natural Pine Forests, Which One Will Better Recover after Drought? Insights from Tree Growth and Stable C and H Isotopes

Increasing intensity and frequency of droughts are leading to forest dieback, growth decline and tree mortality worldwide. Reducing tree-to-tree competition for water resources is a primary goal for adaptive climate silviculture strategies, particularly in reforested areas with high planting density. Yet, we need better insights into the role of stand type (i.e., natural forests versus plantations) on the resilience of pine forests to droughts across varying time scales. In this study, we combined dendrochronological data and stable C (δ13C) and H (δ2H) isotopes measured in tree-ring wood as well as in specific wood chromatographically isolated compounds to investigate contrasting responses to drought of natural versus planted stands of two representative pine species, i.e., Pinus pinaster and Pinus nigra in southeastern Europe. Natural stands exhibited about two-fold increase in tree-ring growth in average (basal area at 20 years-BAI20) as compared to planted stands. A response function analysis showed contrasting seasonal growth patterns for both species, which were related to monthly mean temperature and precipitation. Both stand type and species variables influenced growth resilience indices. Both pine species revealed contrasting resilience patterns among forest types; whereas planted stands seemed to be less sensitive to yearly droughts as determined by a higher recovery index (CRc) for P. pinaster, the contrary was found in the case of P. nigra. On the other hand, while resistance CRT and resilience CRS indices were higher for planted than natural forests in the case of P. pinaster, little differences were found for P. nigra. Beyond comparisons, carbon stable isotopes shed lights on the role of forest types in dry sites, being δ13C consistently lower in natural than in planted forests for both pine species (p < 0.05). We concluded that planted forest assimilated more carbon as per unit of water used than natural stands in response to droughts. Both δ13C and δ2H isotopic signals were positively correlated for both species for planted forests. However, a lack of correlation was evidenced for natural stands. Consistent with δ13C observations, δ2H concentrations in woody phenolic compounds (guaiacol and oleic acid) revealed contrasting patterns among forest types. This puts forward that δ2H concentrations in woody phenolic compounds (rather than in woody tree ring) accounts for other confounding factors in tree ring formation that can be associated with forest type. Our results highlight the value of stable isotope approaches versus conventional dendrochronological tools in drought studies and call for the consideration of forest type as an endogenous aspect defining the vulnerability of pine forests to climate

Winds induce CO2 exchange with the atmosphere and vadose zone transport in a karstic ecosystem

Research on the subterranean CO dynamics has focused individually on either surface soils or bedrock cavities, neglecting the interaction of both systems as a whole. In this regard, the vadose zone contains CO-enriched air (ca. 5% by volume) in the first meters, and its exchange with the atmosphere can represent from 10 to 90% of total ecosystem CO emissions. Despite its importance, to date still lacking are reliable and robust databases of vadose zone CO contents that would improve knowledge of seasonal-annual aboveground-belowground CO balances. Here we study 2.5 years of vadose zone CO dynamics in a semiarid ecosystem. The experimental design includes an integrative approach to continuously measure CO in vertical and horizontal soil profiles, following gradients from surface to deep horizons and from areas of net biological CO production (under plants) to areas of lowest CO production (bare soil), as well as a bedrock borehole representing karst cavities and ecosystem-scale exchanges. We found that CO followed similar seasonal patterns for the different layers, with the maximum seasonal values of CO delayed with depth (deeper more delayed). However, the behavior of CO transport differed markedly among layers. Advective transport driven by wind induced CO emission both in surface soil and bedrock, but with negligible effect on subsurface soil, which appears to act as a buffer impeding rapid CO exchanges. Our study provides the first evidence of enrichment of CO under plant, hypothesizing that CO-rich air could come from root zone or by transport from deepest layers through cracks and fissures.These data were funded by the Andalusian regional government project GEOCARBO (P08-RNM-3721), including European Union ERDF funds, with support from Spanish Ministry of Science and Innovation projects SOILPROF (CGL2011-15276-E), CARBORAD (CGL2011-27493), and GEISpain (CGL2014-52838-C2-1-R). This research was supported by a Marie Curie International Outgoing Fellowship within the 7th European Community Framework Programme, DIESEL project (625988).Peer Reviewe

Sun-induced chlorophyll fluorescence and photochemical reflectance index improve remote-sensing gross primary production estimates under varying nutrient availability in a typical Mediterranean savanna ecosystem

Este estudio investiga las diferentes actuaciones de ópticas sobre los índices para estimar la producción primaria bruta (GPP) del estrato herbáceo de una sabana mediterránea con diferente disponibilidad de nitrógeno (N) y de fósforo (P). La fluorescencia de la clorofila inducida por el sol sobre el rendimiento calculado en 760 nm (FY760), escala de índice de reflectancia fotoquímica (sPRI), MERIS terrestre (índice de clorofila MTCI) y el índice de vegetación de diferencia normalizada (NDVI) fueron calculadas desde cerca de la superficie y las mediciones de espectroscopia de campo recolectados se hicieron utilizando espectrómetros de alta resolución espectral, que abarcan las regiones del infrarrojo cercano visible. La GPP fue medida utilizando cámaras de dosel en las mismas localidades muestreadas por los espectrómetros. Hemos probado si la eficiencia del uso de los modelos de luz (LUE) impulsados por cantidades de teledetección (RSMs) pueden hacer un mejor seguimiento de los cambios en la GPP causada por fuentes de nutrientes en comparación con aquellos impulsados exclusivamente por datos meteorológicos (MM). En particular, comparamos los espectáculos de diferentes formulaciones de RSM -basándose en la utilización de FY760 o sPRI como proxy para LUE y NDVI MTCI o como una fracción de la radiación fotosintéticamente activa absorbida (APAR f)- con las clásicas de MM. Los resultados mostraron mayor GPP en la N -parcelas experimentales fertilizadas durante el período de crecimiento. Estas diferencias en la GPP desaparecieron en el período de secado, cuando los efectos de la senescencia enmascarada contiene diferencias de potencial debido a la planta N. Por consiguiente, MTCI estaba estrechamente relacionada con la media de la planta N, contenida a través de tratamientos (r2 D 0:86, p < 0:01), porque estaba mal relacionados con GPP (r2 D 0:45, p < 0:05). Por el contrario sPRI y FY760 se correlacionaban bien con GPP durante todo el período de medición. Los resultados revelaron que la relación entre el GPP y FY760 no es única en los tratamientos, pero no se ve afectada por la disponibilidad de N. Los resultados de un análisis de validación cruzada mostró que el MM (AICcv D 127, MEcv D 0:879) superó a RSM (AICcv D 140, MEcv D 0:8737,) cuando la humedad del suelo fue utilizada para restringir la dinámica estacional de LUE. Sin embargo, el análisis residual demostró que las predicciones de GPP con MM son inexactas cuando no revela explícitamente unas variables climáticas en cambios relacionados con el parámetro de nutrientes LUE. Estos resultados sugieren que RSM es un medio valioso para diagnosticar los efectos inducidos por los nutrientes en la actividad fotosintética.This study investigates the performances of different optical indices to estimate gross primary production (GPP) of herbaceous stratum in a Mediterranean savanna with different nitrogen (N) and phosphorous (P) availability. Sun-induced chlorophyll fluorescence yield computed at 760 nm (Fy760), scaled photochemical reflectance index (sPRI), MERIS terrestrial-chlorophyll index (MTCI) and normalized difference vegetation index (NDVI) were computed from near-surface field spectroscopy measurements collected using high spectral resolution spectrometers covering the visible near-infrared regions. GPP was measured using canopy chambers on the same locations sampled by the spectrometers. We tested whether light-use efficiency (LUE) models driven by remote-sensing quantities (RSMs) can better track changes in GPP caused by nutrient supplies compared to those driven exclusively by meteorological data (MM). Particularly, we compared the performances of different RSM formulations – relying on the use of Fy760 or sPRI as a proxy for LUE and NDVI or MTCI as a fraction of absorbed photosynthetically active radiation (f APAR) – with those of classical MM. Results showed higher GPP in the N-fertilized experimental plots during the growing period. These differences in GPP disappeared in the drying period when senescence effects masked out potential differences due to plant N content. Consequently, although MTCI was closely related to the mean of plant N content across treatments (r2 D 0:86, p < 0:01), it was poorly related to GPP (r2 D 0:45, p < 0:05). On the contrary sPRI and Fy760 correlated well with GPP during the whole measurement period. Results revealed that the relationship between GPP and Fy760 is not unique across treatments, but it is affected by N availability. Results from a cross-validation analysis showed that MM (AICcv D 127, MEcv D 0:879) outperformed RSM (AICcv D 140, MEcv D 0:8737) when soil moisture was used to constrain the seasonal dynamic of LUE. However, residual analyses demonstrated that GPP predictions with MM are inaccurate whenever no climatic variable explicitly reveals nutrient-related changes in the LUE parameter. These results suggest that RSM is a valuable means to diagnose nutrient-induced effects on the photosynthetic activity.Trabajo financiado por: Alexander von Humboldt Foundation y la Max Planck Research AwardpeerReviewe

Nutrients and water availability constrain the seasonality of vegetation activity in a Mediterranean ecosystem

Anthropogenic nitrogen (N) deposition and resulting differences in ecosystem N and phosphorus (P) ratios are expected to impact photosynthetic capacity, that is, maximum gross primary productivity (GPP). However, the interplay between N and P availability with other critical resources on seasonal dynamics of ecosystem productivity remains largely unknown. In a Mediterranean tree–grass ecosystem, we established three landscape-level (24 ha) nutrient addition treatments: N addition (NT), N and P addition (NPT), and a control site (CT). We analyzed the response of ecosystem to altered nutrient stoichiometry using eddy covariance fluxes measurements, satellite observations, and digital repeat photography. A set of metrics, including phenological transition dates (PTDs; timing of green-up and dry-down), slopes during green-up and dry-down period, and seasonal amplitude, were extracted from time series of GPP and used to represent the seasonality of vegetation activity. The seasonal amplitude of GPP was higher for NT and NPT than CT, which was attributed to changes in structure and physiology induced by fertilization. PTDs were mainly driven by rainfall and exhibited no significant differences among treatments during the green-up period. Yet, both fertilized sites senesced earlier during the dry-down period (17–19 days), which was more pronounced in the NT due to larger evapotranspiration and water usage. Fertilization also resulted in a faster increase in GPP during the green-up period and a sharper decline in GPP during the dry-down period, with less prominent decline response in NPT. Overall, we demonstrated seasonality of vegetation activity was altered after fertilization and the importance of nutrient–water interaction in such water-limited ecosystems. With the projected warming-drying trend, the positive effects of N fertilization induced by N deposition on GPP may be counteracted by an earlier and faster dry-down in particular in areas where the N:P ratio increases, with potential impact on the carbon cycle of water-limited ecosystems.The authors acknowledge the Alexander von Humboldt Foundation for supporting this research with the Max-Planck Prize to Markus Reichstein. Yunpeng Luo and Mirco Migliavacca gratefully acknowledge financial support from the China Scholarship Council. Gerardo Moreno acknowledges financial support from the grant agreement IB16185 of the Regional Government of Extremadura

Chlorophyll Fluorescence Detection with a High-Spectral Resolution Spectrometer through in-filling of the O2-A band as function of Water Stress in Olive Trees

2nd International Workshop on Remote Sensing of Vegetation Fluorescence, 17-19 Nov. 2004, Montreal, CanadaA high spectral resolution spectrometer of 0.065 nm FWHM in the 680-770 nm range was used for collecting spectral measurements in an orchard of olive trees in Spain under 3 different water stress treatments. The measurements were conducted as part of validation efforts for the FluorMOD project funded by the European Space Agency (ESA) to advance the science of vegetation fluorescence simulation. Diurnal steadystate chlorophyll fluorescence was measured from leaves in the field during summer 2004 using the PAM-2100 fluorometer to study the effects of water stress on chlorophyll fluorescence. Water potential, photosynthesis, and stomatal conductance on trees were also measured in a weekly basis to track the effects of water stress on the tree status and functioning. Infrared Apogee sensors were placed on top of the trees for diurnal thermal data collection, studying the effects of water stress on the tree temperature as an indicator of stress. The Ocean Optics HR-2000 spectrometer was used to measure irradiance and radiance spectra from above tree crowns under different stress conditions. The spectral measurements of irradiance with a cosine corrector and crown radiance with bare fibre were acquired from a pole 7 m in height to collect nadir radiance from the top of tree crowns. Analysis in the red edge covering the 680-770 nm range enabled the study of the chlorophyll fluorescence in-filling in the O2-A band at 760 nm. Results of the spectral analysis and simulation using the FluorMOD radiative transfer model demonstrate that water stress effects on steady-state fluorescence are detectable at the tree level in the O2-A band from reflectance spectra due to the in-filling effects.The development of the FluorMODgui interface has been carried out in the frame of the ESA-project Development of a Vegetation Fluorescence Canopy Model, ESTEC contract no. 16365/02/NL/FF. Within the same project, the leaf and canopy fluorescence models FluorMODleaf and FluorSAIL were developed and provided by R. Pedrós and S. Jacquemoud of LED, University of Paris, I. Moya, Y. Goulas and J. Louis of LURE, University of Paris-South, and Wout Verhoef, National Aerospace Laboratory NLR.Peer reviewe

Short- and mid-term tillage-induced soil CO2 efflux on irrigated permanent- and conventional-bed planting systems with controlled traffic in southern Spain

Use of permanent beds combined with controlled traffic (PB) has been proposed as an alternative planting system for reducing soil erosion and compaction while increasing soil organic carbon (SOC) in irrigated, annual-crop based systems in Mediterranean conditions. The objective of this study was to characterise, in space (beds and furrows with and without traffic) and time (hours, days, and weeks), soil CO2 efflux in PB compared with conventionally tilled bed planting (CB) and with a variant of PB in which subsoiling was performed in trafficked furrows (DPB). The three treatments were combined with controlled traffic. Tillage resulted in abrupt CO2 effluxes that lowered rapidly within hours. However, in CB, soil CO2 effluxes increased again significantly 12 days after tillage compared with PB or DPB. These differences were due to higher emissions from beds than from furrows where the soil had been compacted during the harrowing that formed the beds. In DPB, CO2 effluxes increased in furrows with traffic after subsoiling and the effect was maintained during the study despite subsequent traffic. Soil CO2 efflux increased with soil temperature (measured concomitantly) except after soil tillage. Tillage reduced SOC in both CB and DPB compared with PB. © CSIRO 2013.Peer Reviewe

A large closed canopy chamber for measuring CO2 and water vapour exchange of whole trees

A transient-state chamber was developed to measure canopy gas exchange of single trees in the field. The chamber, with a volume of 41.6 m3, is designed to enclose a medium-size orchard tree; chamber top and windows can be left open, causing minimum disturbance to the tree environment. Transitory closures allow simultaneous measurement of CO2 exchange and transpiration of the enclosed tree. The chamber was tested during a 2-year study in an olive orchard submitted to different irrigation treatments: control with no water stress (CI) and regulated deficit irrigation (RDI). Leakage had a minimal impact on flux calculations (0.8% min-1); adsorption was not detectable. Maximum increases in canopy temperature of 0.58 °C min-1 for CI and 1.3 °C min-1 for RDI generated very small effects on fluxes. Changes in the transpiration rate induced by the chamber's modification of the canopy environment were evaluated by continuous sap flow measurements with heat pulse gauges inserted in the trunk of two trees enclosed by chambers. Results showed a sap flow decrease of about 8% after 180 s of chamber closure. The artificial turbulence generated by fans into the chamber to facilitate air mixing did not alter the transpiration rate. The enclosure had a very small impact on the tree canopy conductance (Gc). The initial lag and mixing time was estimated as 30 s; the optimal duration of the calculation window was 70 s. Hourly carbon assimilation (A), transpiration (E), and water use efficiency (WUE) for two olive trees in the field subjected to different levels of water stress were measured. © 2009 Elsevier B.V. All rights reserved.This work was funded by projects AGL-2004-05717 of Ministerio de Educación y Ciencia of Spain and P08-AGR-4202 of Junta de Andalucía.Peer Reviewe

Water deficit effects during olive tree Inflorescence and flower development

International Symposium on Olive Irrigation and Oil QualityAn initial step for achieving good fruit production is the formation of a sufficient number of flowers capable of pollination, fertilization and fruit set. We examined the influence of the time of water stress on floral development and quality by withholding water supply during successive periods from winter dormancy until flowering and initial fruit set. The experiments were carried out with three-year-old 'Picual' olive trees growing in a soil peat mixture in 50-L pots, in which control periods were irrigated to replace evapotranspirative loss and soil water content was monitored continuously. Inflorescences and flowers were evaluated at different levels of morphogenetic organization, including inflorescence, ovary and ovule development, and final fruit number and weight determined. Stress during winter dormancy produced no lasting effect and the plants recovered rapidly in response to rewatering. Water deficit during inflorescence development reduced many different flowering parameters, including inflorescence number, flower number, imperfect flower number and percentage, and ovule development, whereas prior to bloom it produced mild or no effects. When water deficit occurred during flowering and initial fruit set, the petals of many flowers dried closed and abscised as a unit, exposing a senescent stigma which was no longer receptive to pollination. Fruit production closely followed flowering parameters, with fruit number low either when flower number was reduced or fertilization inhibited. Fruit size increased with low crop load but not enough to compensate for yield reduction.Peer Reviewe

Effects of water supply on carbon and water exchange of olive trees

Little information is available on carbon exchange of olive orchards despite their agronomical and ecological importance. Measurements of CO 2 and water vapour exchange were performed during 2006 and 2007 with large closed chambers in an olive orchard in Cordoba (Spain) under two irrigation regimes, full and regulated deficit irrigation.Canopy assimilation was higher for full (10.8-21.3gCO 2m -2day -1) than for deficit irrigation (5.1-17.4gCO 2m -2day -1). Forty-five percent of gross assimilation was lost in respiration being root respiration less than 30% of total respiration. Water use efficiency (WUE) typically decreased from maximum values around 30gCO 2L -1 soon after sunrise to 2-7gCO 2L -1 in the afternoon when vapour pressure deficit typically exceeded 5kPa. While water stress improved instantaneous WUE only slightly, the effect was dramatic for daily values. The measurements allowed the calibration of a model coupling canopy conductance and assimilation that showed a seasonal variation in the parameters suggesting changes in the physiology of olive trees. The improvement of WUE in olive trees under water stress supports the adoption of deficit irrigation in olive orchards although further research is required to prevent negative side effects. © 2012 Elsevier B.V.The authors gratefully acknowledge the financial support of the Ministerio de Educación y Ciencia of Spain (project AGL2004-05717), Consejeria de Ciencia e Innovación Junta de Andalucia (project P08-AGR-04202), and of the European Regional Development Fund (ERDF).Peer Reviewe