Alexandra Rodríguez

Spatial pattern and scale of leaf N and P resorption efficiency and proficiency in a Quercus robur population

Leaf nutrient resorption allows plants to lower their dependence on current soil nutrients, thereby influencing ecosystem-level processes such as litter decomposition and soil nutrient availability. Among different factors controlling nutrient resorption are the availability of plant resources such as nutrients, water or light. The heterogeneous spatial distribution of these resources in natural environments may influence the spatial pattern of nutrient resorption. The spatial variability of leaf N and P resorption efficiency and proficiency and their relationship to the spatial pattern of soil and light resources were evaluated by using descriptive statistics and geostatistics in a Quercus robur L. (pedunculate oak) population. Resorption efficiency and resorption proficiency were significantly higher for P than for N. Levels of N resorption proficiency indicated incomplete resorption in all individuals. However, 80% of individuals exhibited intermediate or complete levels of P resorption. Resorption efficiency and proficiency of leaf N and P showed spatial dependence at the studied scale, with the spatial distribution of P showing higher range (autocorrelation distance) than that of N. The spatial pattern and scale of nutrients in senesced leaves differed from that in green leaves, with senesced leaves having a higher spatial range but lower percentage of variance explained by distance. All soil variables and the light availability index showed spatial dependence at the examined spatial scale. However, only soil water content and extractable-P were significantly correlated with resorption proficiency and efficiency, although these relationships explained a low percentage (<5%) of total variance. The spatial dependence for resorption variables has important implications for sampling design because nearby individuals cannot be considered independent samples. It may also have implications for ecosystem-level processes related to litter quality, which might also exhibit spatial dependence.

Wildfire changes the spatial pattern of soil nutrient availability in Pinus canariensis forests

Abstract• Soil resources are heterogeneously distributed in terrestrial plant communities. This heterogeneity is important because it determines the availability of local soil resources. A forest fire may change the spatial distribution of soil nutrients, affecting nutrition and survival of colonizing plants. However, specific information on the effects of ecosystem disturbance on the spatial distribution of soil resources is scarce.• We hypothesized that, on a short-term basis, wildfire would change the spatial patterns of soil N and P availability. To test this hypothesis, we selected two Pinus canariensis forests burned in 2005 and 2000, respectively, and a third forest that was unburned since at least 1990 (unburned). We incubated ionic exchange membranes (IEMs) in replicated plots to estimate soil N and P availability and characterized the spatial pattern using SADIE (Spatial Analysis by Distance Indices).• Mineral N, NO3-N and PO4-P availability, and aggregation and cluster indices for all nutrients were higher in the 2005 wildfire plots than in the 2000 wildfire and unburned plots.• Our results suggest that surviving plants or new individuals becoming established in a burned area would find higher soil resources, but also higher small-scale heterogeneity in nutrients, which may have a major impact on the performance of individual plants and on the forest structure and dynamics.Résumé• Les ressources du sol sont distribuées de manière hétérogène dans les communautés végétales terrestres. Cette hétérogénéité est importante car elle détermine la disponibilité locale des ressources du sol. Un feu de forêt peut changer la répartition spatiale des éléments nutritifs du sol, affectant la nutrition et la survie des plantes colonisatrices. Cependant, des informations précises sur les effets des perturbations des écosystèmes sur la répartition spatiale des ressources du sol sont rares.• Nous avons émis l’hypothèse qu’à court terme, un feu de forêt pourrait modifier les modèles de répartition spatiale de disponibilité de N et P dans le sol. Pour tester cette hypothèse, nous avons sélectionné deux forêts de Pinus canariensis qui ont brûlé respectivement en 2005 et 2000, et une troisième forêt qui n’a brûlé depuis au moins 1990 (non brûlée). Nous avons incubé des membranes échangeuses d’ions (IEMs) dans plusieurs parcelles pour estimer la disponibilité du sol en N et P et nous avons caractérisé le modèle spatial en utilisant SADIE (Analyse spatiale en fonction d’indices de distance).• N-minéral, N-NO3, disponibilité en PO4-P, agrégation et indices de cluster ont été plus élevés dans les parcelles incendiées en 2005 que dans celles incendiées en 2000 et les parcelles non brûlées.• Nos résultats suggèrent que les plants survivants ou les plants en cours d’installation dans une zone brûlée, auront accès à des ressources plus abondantes, mais seront également confrontés à une hétérogénéité plus importante dans la disponibilité en éléments nutritifs. Cette dernière peut avoir un impact majeur sur la performance individuelle des plants et sur la structure et la dynamique forestières.

Changes in net N mineralization rates and soil N and P pools in a pine forest wildfire chronosequence

The concern that climate change may increase fire frequency and intensity has recently heightened the interest in the effects of wildfires on ecosystem functioning. Although short-term fire effects on forest soils are well known, less information can be found on the long-term effects of wildfires on soil fertility. Our objective was to study the 17-year effect of wildfires on forest net mineralization rates and extractable inorganic nitrogen (N) and phosphorus (P) concentrations. We hypothesize that (1) burned forest stands should exhibit lower net mineralization rates than unburned ones; (2) these differences would be greatest during the growing season; (3) differences between soil variables might also be observed among plots from different years since the last fire; and (4) due to fire-resistant geochemical processes controlling P availability, this nutrient should recover faster than N. We used a wildfire chronosequence of natural and unmanaged Pinus canariensis forests in La Palma Island (Canary Islands). Soil samples were collected during winter and spring at 22 burned and unburned plots. We found significantly higher values for net N mineralization and extractable N pools in unburned plots. These differences were higher for the winter sampling date than for the spring sampling date. Unlike extractable N and N mineralization rates, extractable P levels of burned plots exhibited a gradual recovery over time after an initial decrease. These results demonstrate that P. canariensis forest soils showed low resilience after wildfires, especially for N, and that this disturbance might induce long-term changes in ecosystem functioning.

Long-term decrease of organic and inorganic nitrogen concentrations due to pine forest wildfire

Abstract• Growing concerns about fires and the increase of fire frequency and severity due to climate change have stimulated a large number of scientific papers about fire ecology. Most researchers have focused on the short-term effects of fire, and the knowledge about the long-term consequences of fires on ecosystem nutrient dynamics is still scarce.• Our aim was to improve the existing knowledge about the long-term effects of wildfires on forestlabile N concentrations. We hypothesized that fires may cause an initial decline in organic and inorganic N availability, and in the amount of microbial biomass-N; this should be followed by the recovery of pre-fire N concentrations on a long-term basis. We selected a fire chronosequence in Pinus canariensis forests on La Palma Island (Canary Islands, Spain). These forests are under low anthropogenic atmospheric deposition, and forest management is completely lacking; wildfires are therefore the only significant disturbance. Soil samples were collected during the winter and spring at 22 burned and unburned plots.• Fire produced a significant decrease in microbial biomass N, mineral N and dissolved organic N. Almost 20 y after fire, pre-fire levels of N concentrations had not recovered.• These results demonstrate that P. canariensis forest soils have a lower resilience against fire than expected. The magnitude of these observed changes suggests that pine forest wildfires may induce long-term (2 decades) changes in soil and in plant primary production.Résumé• Les préoccupations grandissantes au sujet des incendies, de l’augmentation de leur fréquence et de leur gravité attribuable aux changements climatiques ont stimulé la production d’un grand nombre d’articles scientifiques sur l’écologie des incendies. La plupart des chercheurs ont mis l’accent sur les effets à court terme de l’incendie, et les connaissances sur les conséquences à long terme des incendies sur la dynamique des éléments nutritifs de l’écosystème sont encore rares.• Notre objectif est d’améliorer les connaissances actuelles sur les effets à long terme des incendies sur les concentrations labiles d’azote en forêt. Nous avons émis l’hypothèse que les incendies peuvent provoquer une baisse initiale de l’azote organique et de la disponibilité de l’azote inorganique, et de la quantité de biomasse microbienne azotée, ce qui devrait être suivie par la récupération des concentrations d’azote d’avant le feu sur une base de long terme. Nous avons sélectionné une chronoséquence d’incendies dans des forêts de Pinus canariensis sur l’île de La Palma (îles Canaries, Espagne). Ces forêts sont situées sous de faibles dépôts atmosphériques d’origine anthropique, et la gestion des forêts est totalement absente ; les feux de forêt sont donc les seules perturbations importantes. Des échantillons de sol ont été recueillis au cours de l’hiver et du printemps dans 22 parcelles brûlées et non brûlées.• L’incendie a produit une diminution significative de la biomasse microbienne azotée, de l’azote minéral et de l’azote organique dissous. Presque 20 ans après l’incendie, les niveaux de concentrations d’azote d’avant le feu n’ont pas été récupérés.• Ces résultats montrent que les sols forestiers de P. canariensis ont une résilience contre le feu plus faible que prévu. L’ampleur des changements observés suggère que les feux dans les forêts de pin peuvent induire des changements à long terme (2 décades) dans les sols et dans la production primaire des plants.

Spatial pattern and variability in soil N and P availability under the influence of two dominant species in a pine forest

The presence of a legume in a nitrogen (N)-limited forest ecosystem may not only create “islands of N fertility” but also affect the phosphorus (P) availability. The main objective of this study was to compare the effect of a pine (Pinus canariensis) and a leguminous (Adenocarpus viscosus) species on the spatial pattern and variability of different labile organic-N (microbial biomass-N [MB-N] and dissolved organic-N [DON]), as well as inorganic-N (IN) and –P fractions (NH4-N, NO3-N, and PO4-P), in a forest soil of the Canary Islands (Spain). Assuming some litter quantity and quality differences between these two species, we expected to find higher soil labile organic-N concentrations under isolated individuals of P. canariensis than under isolated individuals of A. viscosus. We also expected to find higher concentrations and spatial dependence (percentage of total variance explained by spatial autocorrelation) of NO3-N beneath A. viscosus than beneath P. canariensis canopies, and higher spatial scaling of soil variables under the influence of P. canariensis canopies than under the presence of A. viscosus individuals. Moreover, we tested whether the soil variables measured under isolated individuals of both species showed a different spatial variability than the same soil variables measured under overlapping pine canopies inside a pine forest. To test these hypotheses, soil samples under isolated mature individuals of each species were collected in the winter and summer, whereas under a pine forest canopy, the sampling was performed only in the winter. The winter MB-N and DON concentrations were significantly higher beneath the pine individual, whereas the winter NO3-N, NO3-N-to-IN ratio, and PO4-P were significantly higher under the leguminous individual; these differences were not observed in the summer samples. We found higher spatial ranges under the pine than under the legume canopy in the winter sampling, and the spatial dependence of NO3-N was twice as high beneath the legumes as under the pines at both sampling dates. The soil spatial variability was higher (up to 17 times higher) under isolated individuals than inside the pine forest. The results of this study suggest that both the morphological and physiological characteristics of P. canariensis and A. viscosus, as well as the spatial pattern of P. canariensis, may influence the spatial pattern and variability of soil resources.

Ivermectin residues disrupt dung beetle diversity, soil properties and ecosystem functioning: An interdisciplinary field study

Ivermectin is the most common endectocide used to control parasites affecting livestock. Short-term physiological and behavioural effects of ivermectin on dung beetles may have long-term consequences for beetle populations and ecosystem functioning. Long-term effects of the use of ivermectin can be estimated by comparing dung assemblages and ecosystem functions in areas with conventional ivermectin-treated livestock and environmentally similar areas in which livestock are not treated with veterinary medical products (organic farming). In this study, we investigated both short-term and long-term effects of the administration of ivermectin on the characteristics of dung beetle assemblages and the services they provided in a protected area (Doñana National Park, SW Spain). We examined short-term dung colonization, dwelling, relocation, and disaggregation rates and the associations between these processes and the key assemblage parameters of species richness, abundance, biomass and functional diversity. Furthermore, we analysed changes in soil physical-chemical properties and processes. Short-term differences were observed in the total amount of dung relocated by dung beetles at different colonization vs. emigration stages, suggesting that dung beetles in this area were affected by the recent treatments of livestock with ivermectin. Moreover, short-term effects could also be responsible for the significant differences in dung spreading rates between sites. Conventional use of ivermectin disrupted ecosystem functioning by affecting species richness, abundance and biomass. The decrease in diversity parameters was related to a reduction in the functional efficiency, which resulted in the long-term accumulation of dung on the ground and considerable changes in soil functionality.

Frontiers in Ecosystem Science

In this final chapter, a few examples of areas that seem poised for rapid progress, and that show the vitality of the field, are offered. Some of these areas are urbanization, global change, restoration ecology, and the integration of humans into ecosystems.

Comparing the use of leaf and soil analysis as N and P availability indices in a wildfire chronosequence

Two types of measures have traditionally been used to monitor changes after disturbances in the nutrient availability of forest ecosystems: (1) soil nutrient pools and transformation rates and (2) foliar nutrient content. We used a wildfire chronosequence in natural and unmanaged Pinus canariensis forests to determine which kind of measure is more effective in discriminating between disturbed and undisturbed plots and to determine whether the different availability indices provide comparable and consistent results within the chronosequence and between different sampling dates. The results showed that (1) foliar N and P concentrations were the variables that best discriminated between the plots of the chronosequence, (2) the various soil N availability indices neither showed steady relationships nor predicted the plant nutrient availability, and (3) P availability indices showed steady relationships and predicted plant nutrient availability. Due to the changing nature of the soil N pools, repeated sampling over a long period of time could yield results different from those presented here. However, the large sampling effort required would favor the use of foliar nutrient concentrations as the most desirable first approach to the community’s nutritional status, especially when time or budget constraints are relevant.