Dynamics of organic carbon losses by water erosion after biocrust removal

In arid and semiarid ecosystems, plant interspaces are frequently covered by communities of cyanobacteria, algae, lichens and mosses, known as biocrusts. These crusts often act as runoff sources and are involved in soil stabilization and fertility, as they prevent erosion by water and wind, fix atmospheric C and N and contribute large amounts of C to soil. Their contribution to the C balance as photosynthetically active surfaces in arid and semiarid regions is receiving growing attention. However, very few studies have explicitly evaluated their contribution to organic carbon (OC) lost from runoff and erosion, which is necessary to ascertain the role of biocrusts in the ecosystem C balance. Furthermore, biocrusts are not resilient to physical disturbances, which generally cause the loss of the biocrust and thus, an increase in runoff and erosion, dust emissions, and sediment and nutrient losses. The aim of this study was to find out the influence of biocrusts and their removal on dissolved and sediment organic carbon losses. One-hour extreme rainfall simulations (50 mm h-1) were performed on small plots set up on physical soil crusts and three types of biocrusts, representing a development gradient, and also on plots where these crusts were removed from. Runoff and erosion rates, dissolved organic carbon (DOC) and organic carbon bonded to sediments (SdOC) were measured during the simulated rain. Our results showed different SdOC and DOC for the different biocrusts and also that the presence of biocrusts substantially decreased total organic carbon (TOC) (average 1.80±1.86 g m-2) compared to physical soil crusts (7.83±3.27 g m-2). Within biocrusts, TOC losses decreased as biocrusts developed, and erosion rates were lower. Thus, erosion drove TOC losses while no significant direct relationships were found between TOC losses and runoff. In both physical crusts and biocrusts, DOC and SdOC concentrations were higher during the first minutes after runoff began and decreased over time as nutrient-enriched fine particles were washed away by runoff water. Crust removal caused a strong increase in water erosion and TOC losses. The strongest impacts on TOC losses after crust removal occurred on the lichen plots, due to the increased erosion when they were removed. DOC concentration was higher in biocrust-removed soils than in intact biocrusts, probably because OC is more strongly retained by BSC structures, but easily blown away in soils devoid of them. However, SdOC concentration was higher in intact than removed biocrusts associated with greater OC content in the top crust than in the soil once the crust is scraped off. Consequently, the loss of biocrusts leads to OC impoverishment of nutrient-limited interplant spaces in arid and semiarid areas and the reduction of soil OC heterogeneity, essential for vegetation productivity and functioning of this type of ecosystems.This work was partially supported by several research projects: COSTRAS (RNM 3614), funded by the Consejería de Innovación, Ciencia y Empresa (Junta de Andalucía) including ERD (European Union of Regional Development) Funds, BACARCOS (CGL2011–29429) funded by Spanish national Plan for Research, Development and Innovation and including European Union of Regional Development Funds ERDF funds

Descomposición de hojarasca en la leguminosa Adenocarpus decorticans: pérdida de peso y dinámica de los nutrientes

Se ha estudiado la pérdida de peso y la liberación de N, P, K, Mg y Ca de la hojarasca de Adenocarpus decorticans Boiss. en la Sierra de los Filabres (Almería). Tras 828 días de incubación en el campo, la pérdida de peso inicial fue del 70%. La tasa de descomposición estimada a partir de la aplicación del modelo exponencial simple es de -0.82 el primer año, -0.62 el segundo año y -0.53 para el conjunto del periodo. La liberación de nutrientes sigue la secuencia K>Mg>Ca> P>N. Todos los elementos presentan liberación neta al cabo de 1.5 años. Las tasas de liberación de nutrientes estimadas a partir de ajustes exponenciales simples son: -0.31 (N), -1.69 (K). -0.96 (Mg) y -0.68 (Ca). La rápida liberación de N en esta especie es consistente con el carácter mesófilo de sus hojas y el bajo valor inicial del índice C/N en la hojarasca.Rates of weight loss and release of N, P, K, Mg and Ca from decomposing leaf litter were measured in Adenocarpus decorticans Boiss. growing in Sierra de los Filabres (Almería, Spain). Decomposition rate calculated from a simple exponential model was -0.82 during the first year. -0.62 during the second year and -0.53 for the overall period. The order of element mobility from decomposing leaf litter was K>Mg>Ca>P>N. All elements showed net release after 1.5 years. Rates of nutrient release calculated from exponential models were: -0.31 (N), - 1.69 (K), -0.96 (Mg) y -0.68 (Ca). Fast N mineralization in Adenocarpus leaf litter was attributed to the low C/N ratio combined to the mesophyllous character of its leaves.El presente trabajo ha sido realizado gracias a la financiación de la CEE (No. EV4V-0109-E) y de ICONA-CSIC a través del proyecto LUCDEME

Leaf and canopy boundary layer conductances of two semiarid species (Retama sphaerocarpa L. Boiss, and Stipa tenacissima L.)

La conductancia aerodinámica a escala de copa en dos especies dominantes del área de Rambla Honda (Almería), Retama sphaerocarpa L. Boiss y Stipa tenacissima L., ha sido calculada en condiciones naturales a partir de la medida de la evaporación directa de copas saturadas de agua. R. sphaerocarpa es un arbusto perenne de copa abierta, con cladodios cilíndricos localizados en tallos que se distribuyen de forma aleatoria. S. tenacissima es una gramínea perenne de densa copa, con hojas que se enrollan sobre sí mismas en los periodos de estrés hídrico. La conductancia aerodinámica a escala foliar fue calculada a partir de réplicas foliares artificiales y extrapolada posteriormente al conjunto de la copa. Los resultados de este estudio permiten incidir en la relevancia del efecto barrera entre las hojas de la copa, el cual ejerce una influencia significativa sobre la velocidad del viento y, en consecuencia sobre la conductancia aerodinámica. La comparación de los dos especies refleja una mayor interferencia entre las hojas de Stipa, produciendo una menor conductancia aerodinámica que en Retama. La comparación de los dos métodos de estima de conductancia aerodinámica a nivel de copa muestran que ésta no es simplemente la suma de las conductancias aerodinámicas foliares individuales en Stipa. Sin embargo en Retama, la interacción entre cladodios no es significativa y por tanto, esta extrapolación puede considerarse una aproximación válida.Canopy boundary layer conductance was calculated in the field by measuring the evaporation from artificially wet canopies of two main semi-arid species found in the Rambla Honda (Almena, South East of Spain), Retama sphaerocarpa (L.) Boiss. and Stipa tenacissima L. R. sphaerocarpa is a leafless perennial shrub having cylindrical cladodes arranged on randomly orientated stems constituting an open canopy. In contrast S. tenacissima is a perennial tussock grass having a dense canopy and leaves that can roll during periods of water stress. Values of leaf boundary layer conductance, taken from a previous study on the same species, obtained by the construction of cylindrical leaf replicas were extrapolated to the canopy. The results from the current study emphasise the importance of shelter effects influencing wind speed and then boundary layer conductance. The comparison between the two species reflects the interaction between leaves in Stipa, sheltering each other, producing a lower boundary layer than for R. sphaerocarpa. Our results showed that the extrapolation from a leaf to the whole of the canopy is not simply the addition of leaf boundary layer conductances in dense canopies as S. tenacissima. However for R. sphaerocarpa the interaction between leaves is not significant and the extrapolation from a leaf to the whole canopy is possible.This work has been funded by a postdoctoral grant of the Consejo Superior de Investigaciones Científicas (C.S.I.C.) of Spain, at The Institute of Ecology and Resource Management of The University of Edinburgh and the MEDALUS II project (Mediterranean Desertification and Land Use) funded by the European Community under its Environment Programme contract number EV5V CT92-0164. It was also partially funded by the Natural Environment Research Council project number GR3/8169 and the British Council in Spain

Non-rainfall water inputs: a key water source for biocrust carbon fixation

Links between water and carbon (C) cycles in drylands are strongly regulated by biocrusts. These widespread communities in the intershrub spaces of drylands are able to use non-rainfall water inputs (NRWI) (fog, dewfall and water vapour) to become active and fix carbon dioxide (CO2), converting biocrusts into the main soil C contributors during periods in which vegetation remains inactive. In this study, we first evaluated the influence of biocrust type on NRWI uptake using automated microlysimeters, and second, we performed an outdoor experiment to examine how NRWI affected C exchange (photosynthesis and respiration) in biocrusts. NRWI uptake increased from incipient cyanobacteria to well-developed cyanobacteria and lichen biocrusts. NRWI triggered biocrust activity but with contrasting effects on CO2 fluxes depending on the main NRWI source. Fog mainly stimulated respiration of biocrust-covered soils, reaching net CO2 emissions of 0.68 μmol m-2 s-1, while dew had a greater effect stimulating biocrust photosynthesis and resulted in net CO2 uptake of 0.66 μmol m-2 s-1. These findings demonstrate the key role that NRWI play in biocrust activity and the soil C balance in drylands.This work has been supported by the following projects: REBIOARID (RTI2018-101921-B-I00), funded by the FEDER/Science and Innovation Ministry-National Research Agency through the Spanish National Plan for Research and the European Union including European Funds for Regional Development, the RH2OARID (P18-RT-5130) funded by Junta de Andalucía and the European Union including European Funds for Regional Development and the BIOCOST project funded by the Biodiversity Foundation of the Ministry for the Ecological Transition. S.C. and E.R.C. were supported by a UAL-Hipatia postdoctoral fellowship funded by Plan Propio of the University of Almería

Seasonal transpiration pattern of Phragmites australis in a wetland of semi-arid Spain

Transpiration rates were measured in a flooded population of Phragmites australis ssp. altissima in a wetland located in ‘El Hondo’ Natural Park (southeastern Spain) during the growing season of 2000. The heat balance method for measuring sap flow was used to calculate the rate of water transpiration on a whole-stem basis. Four series of measurements were carried out in selected weeks in May, June, August and October. Structure, biomass and leaf area index of the reed population were simultaneously quantified in order to scale transpiration on a plot-area basis. Overall, transpiration flux was high during the sampling period and showed a typical diurnal pattern with a maximum at about midday. Mean transpiration was highest at the end of June coinciding with the peak of reed growth and with the maximum leaf area both at individual and plot scales. Rates decreased abruptly in October, in parallel with the advanced foliar senescence. The variation of both midday and integrated daily transpiration is significantly related to that of the air temperature on clear days. Cloudy and rainy days exert a pronounced effect on water loss by decreasing transpiration. Our results highlight the potential use of the sap-flow method to measure transpiration in reed ecosystems and the relevance of this flux for the water balance in wetlands in semi-arid environments. Thus, it is suggested that water management in these areas could be favoured by acquiring high-quality experimental data.This work has been funded by the Generalitat Valenciana (project GV99-43-1-03), the CICYT project ‘Modelización del balance de energía en áreas espacialmente heterogéneas de clima semiárido’ (ref. CLI99-0835-C02-02), by the Spanish National R&D Programme on Climate and by a short-visit grant funded by the Generalitat Valenciana (INV00-16-8) to the University of Alicante for the second author

Role of dewfall in the water balance of a semiarid coastal steppe ecosystem

Dewfall is widely recognized as an important source of water for many ecosystems, especially in arid and semiarid areas, contributing to improve daily and annual water balances and leading to increased interest in its study in recent years. In this study, occurrence, frequency and amount of dewfall were measured from January 2007 to December 2010 (4 years study) to find out its contribution to the local water balance in a Mediterranean semiarid steppe ecosystem dominated by scattered tussocks of Stipa tenacissima (Balsa Blanca, Almería, SE Spain). For this purpose, we developed a dewfall measurement method, ‘The Combined Dewfall Estimation Method’ (CDEM). This method consists of a combination of the potential dewfall model, i.e. the single-source Penman–Monteith evaporation model simplified for water condensation, with information from leaf wetness sensors, rain gauge data, soil surface temperature and dew point temperature. To assess the reliability of the CDEM, dewfall was measured in situ using weighing microlysimeters during a period of 3 months. Daily micrometeorological variables involved in a dewfall event were analysed in order to assess the significance of dewfall at this site. Dewfall condensation was recorded on 78% of the nights during the study period. Average monthly dewfall duration was 9.6 ± 3.2 h per night. Average dewfall was 0.17 ± 0.10 mm per night and was mostly dependent on dewfall duration. Dewfall episodes were longer in late autumn and winter and shorter during spring. Annual dewfall represented the 16%, 23%, 15% and 9% of rainfall on 2007, 2008, 2009 and 2010, respectively. Furthermore, when a wet period was compared to a dry one, the dewfall contribution to the water balance at the site was found to be 8% and 94%, respectively. Our results highlight the relevance of dewfall as a constant source of water in arid ecosystems, as well as its significant contribution to the local water balance, mainly during dry periods where it may represent the only source of water at the site.This work received financial support from several different research projects: the PROBASE (CGL2006-11619/HID), BACARCOS (CGL2011-29429) and CARBORAD (CGL2011-27493), funded by the Ministerio de Ciencia e Innovación; the GEOCARBO(RNM3721), GLOCHARID and COSTRAS (RMN-3614) projects funded by Consejería de Innovación, Ciencia y Empresa (Andalusian Regional Ministry of Innovation, Science and Business) and European Union funds (ERDF and ESF). OU received a JAE Ph.D. research grant fromthe CSIC

Plan de mejora y seguimiento del Grado de Ciencias del Mar 16-17

En el presente trabajo se expone la memoria del seguimiento de la titulación del Grado de Ciencias del Mar de la Universidad de Alicante, para el curso 2016-17. Tras la reacreditación del Grado, se repasan las propuestas de mejoras planteadas y se revisa el programa docente/formativo con el propósito de seguir avanzando en la coordinación de los contenidos, metodologías aplicadas, evaluación y guías docentes. La metodología seguida incluye principalmente el análisis de las actas de las reuniones establecidas en cada semestre por la Facultad de Ciencias. Estas reuniones, dos como mínimo para cada semestre del grado, quedan integradas por: a) el/la coordinador/a de semestre; b) profesorado responsable de las asignaturas de ese semestre; c) coordinador del grado; d) representante del alumnado del curso (delegado/a); y e) vocal de la titulación. Los resultados de la presente memoria ponen de manifiesto las propuestas de mejora establecidas con el propósito de seguir avanzando en la implementación del Grado en Ciencias del Mar de la Universidad de Alicante