Breves reseñas biográficas

Breves notas biográficas de los autores participantes en el presente número

Effects of Nitrogen Deposition on the Abundance and Metabolism of Lichens: A Meta-analysis

Lichens are the key to nutrient cycling and trophic networks in many terrestrial ecosystems and are good bioindicators of air pollution, including nitrogen (N) deposition. Experimental studies have shown that N deposition can reduce the abundance of lichens and alter their thallus chemistry and metabolism, but we currently lack information about how widespread this effect is and what are the environmental factors modulating the response of lichens to N. We carried out a meta-analysis of the literature about the effects of experimental N fertilization on lichen abundance and metabolism. We found thirty-nine articles from thirty-one experimental sites that met our search criteria. These studies showed that the addition of N accelerates lichen metabolism in the short term and decreases their abundance in the medium–long term. Early senescence of lichens is proposed as a possible mechanism linking the two observed responses. Chlorolichens from regions with high precipitation (> 1000 mm) and with a background N deposition of mixed origin (agricultural and industrial) were the most affected by N, in terms of both abundance and metabolism. Structural equation modelling showed that the rate of N addition was the main factor in modulating the response of lichens to N in terms of metabolism, whereas isothermality played a very important role in modulating the lichen response to N in terms of abundance. Our meta-analysis identified that excess N deposition reduces lichen abundance and increases the metabolism of sensitive species, especially across European ecosystems; lichens from more climatically benign regions (that is, greater precipitation and isothermality) are the most affectedROH initiated this study being funded by a Juan de la Cierva-Incorporación Fellowship (JCI-2014-21252) from MINECO and finished it with the support of a Ramón y Cajal Fellowship (RYC-2017-22032) from MICIU. All data used in this study can be accessed from Ochoa-Hueso and Gutierrez-Larruga (2019)

Nitrogen deposition depletes the soil seed bank of a kermes oak thicket

Resumen de una presentación realizada en: I Simposio sobre Interacciones Planta-Suelo (ICA-CSIC, Madrid, 25-26 Febrero 2016)Aims: Nitrogen (N) deposition is a major driver of global change that can influence soil seed bank composition and abundance and seed germination. We investigated how eight years of simulated N deposition impacted the soil seed bank of a semiarid Mediterranean shrubland in Central Spain.Methods: The soil seed bank used in this study was collected from a kermes oak thicket located in the Nature Reserve El Regajal-Mar de Ontígola (Central Spain, 4o9’N, 3o29’W). Samples were collected on September 2014, following the spring/summer seed rain and prior to the onset of equinoctial rains. Consequently, we collected both transient and permanent seed banks without distinction. Three soil cores, 4.5 cm diameter and 4.0 cm deep, were collected from each of 24 plots that are fertilized since October 2007 (72 cores). Fertilization treatments corresponded to simulated N deposition rates of 0, 10, 20 and 50 kg N ha-1 year-1. Soils were incubated under semi-controlled conditions in a greenhouse and emerged plants were recorded.Results: During the course of the study, a total of 198 seedlings belonging to 21 species were recorded. When the number of germinated plants were compared among N treatments no significant differences were found (p<0.05). However, when the between-plot variations in soil variables were considered in the analysis, the highest N treatment had a significantly lower number of germinated seeds than the control (p<0.05). Soil organic matter, organic nitrogen and total nitrogen content masked the effects of nitrogen deposition on soil seed bank.Conclusions: N deposition can influence the emergence of soil seed bank species. However, the mechanism linked to this effect, alteration of seed emergence physiology or compositional shifts of the seed bank, remains unknown.Peer reviewe

Phosphorus and water supply independently control productivity and soil enzyme activity responses to elevated CO2 in an understorey community from a Eucalyptus woodland

Aims While it is well-established that nitrogen (N) availability regulates elevated [CO2] (eCO(2)) effects on plant growth and soil carbon (C) storage in N-limited environments, there are fewer studies investigating the role of phosphorous (P) supply on such responses in P-limited environments. In this study, we explored whether P fertilization influences the response of plant growth, soil enzyme activity and C fluxes to eCO(2), and determined how different levels of water availability regulate these processes. Methods We used soil collected from a temperate, P-limited Eucalyptus woodland containing the native soil seed bank to grow a potted replica of local understory communities. We exposed the emerging communities to eCO(2) under two contrasting water levels and two levels of P fertilization. We assessed plant biomass allocation, the rhizosphere activity of extracellular enzymes related to C, N and P cycles, and pot-level CO2 fluxes. Results The positive effects of eCO(2) on plant production and ecosystem C dynamics were strongly constrained by low levels of P availability. Enhanced water supply increased rhizosphere enzyme activity with minor impacts on plant biomass responses to eCO(2.) Our data also suggest that plant and microbial mechanisms that increase nutrient release from SOM may not be able to overcome this P limitation. Conclusions While current Earth System Models predict positive feedback responses of terrestrial ecosystems on C storage under eCO(2), here we emphasize the importance of accounting for the widespread phenomenon of P-limitation in such responses

Land use change of transhumant drove roads leads to soil quality degradation: a case study in Central Spain

Grassland soils, beyond their role as biodiversity reservoirs, actively contribute to the provision of numerous ecosystem services. In the Iberian Peninsula, drove roads, the traditional routes used for seasonal livestock movements in search of the most productive pastures, play a key role in the preservation of semi-natural grasslands and in the protection of the upper soil horizon. However, the absence of transhumant pastoralism has led to the degradation of these natural corridors, with unexplored consequences in terms of soil quality and functioning. To investigate the relationship between the conservation state of these livestock routes and soil characteristics, which had not been researched to date, we selected thirty sites within the Madrid drove road network in central Spain. We established three categories: (i) reference well-preserved drove roads and two degraded states: (ii) overgrown abandoned and (iii) eroded drove roads and collected soil samples at each state. We determined soil physicochemical variables like the percentage of C, total N and P, available K, pH and electrical conductivity. We also measured soil enzyme activity using fluorometric methods and assessed litter decomposition through the Tea Bag Index experiment. Our findings demonstrated that the preservation state of drove roads had a significant impact on soil fertility. The mean carbon percentage was up to ten times lower in eroded drove roads compared to reference sites, while nitrogen content was four times higher in reference sites, and phosphorus and potassium content were twice as high in reference drove roads compared to eroded sites. Litter decomposition rate was also half in eroded soils compared to reference sites. Although the nutrient content and litter decomposition of overgrown abandoned drove roads did not differ from reference sites, enzyme activity was significantly higher in reference soils compared to both degraded states. Arylsulfatase activity was six times higher in reference plots, which also showed twice as much phosphatase activity and up to four times as much β-xylosidase activity. Our results confirmed our hypothesis that drove roads suffering from erosion have the most degraded soils. Additionally, we found that both the excessive accumulation of biomass due to grazing abandonment and the loss of vegetation cover through erosion contribute to the loss of soil functionality within the Madrid drove road network. The lack of use and subsequent degradation of drove roads compromise both the stability of the soil ecosystem and the availability of nutrients for plants. Given the vast surface area covered by this network of corridors, the reintroduction of transhumant and local extensive grazing can be an important tool to improve soil characteristic

Biocrusts buffer against the accumulation of soilmetallic nutrients induced by warmingand rainfall reduction

The availability of metallic nutrients in dryland soils, many of which are essential for the metabolism of soil organisms and vascular plants, may be altered due to climate change-driven increases in aridity. Biocrusts, soil surface communities dominated by lichens, bryophytes and cyanobacteria, are ecosystem engineers known to exert critical functions in dryland ecosystems. However, their role in regulating metallic nutrient availability under climate change is uncertain. Here, we evaluated whether well-developed biocrusts modulate metallic nutrient availability in response to 7 years of experimental warming and rainfall reduction in a Mediterranean dryland located in southeastern Spain. We found increases in the availability of K, Mg, Zn and Na under warming and rainfall exclusion. However, the presence of a well-developed biocrust cover buffered these effects, most likely because its constituents can uptake significant quantities of available metallic nutrients. Our findings suggest that biocrusts, a biotic community prevalent in drylands, exert an important role in preserving and protecting metallic nutrients in dryland soils from leaching and erosion. Therefore, we highlight the need to protect them to mitigate undesired effects of soil degradation driven by climate change in this globally expanding biome. Eduardo Moreno-Jimenez et al. experimentally manipulate rainfall and temperature in a Mediterranean dryland to explore the association of biocrusts with essential metallic nutrients. They find that biocrusts-communities of lichens, bryophytes and cyanobacteria on the soil surface-can buffer against the effects of warming and reduced rainfall on metallic nutrient availability

Altered precipitation and root herbivory affect the productivity and composition of a mesic grassland

Background Climate change models predict changes in the amount, frequency and seasonality of precipitation events, all of which have the potential to affect the structure and function of grassland ecosystems. While previous studies have examined plant or herbivore responses to these perturbations, few have examined their interactions; even fewer have included belowground herbivores. Given the ecological, economic and biodiversity value of grasslands, and their importance globally for carbon storage and agriculture, this is an important knowledge gap. To address this, we conducted a precipitation manipulation experiment in a former mesic pasture grassland comprising a mixture of C-4 grasses and C-3 grasses and forbs, in southeast Australia. Rainfall treatments included a control [ambient], reduced amount [50% ambient] and reduced frequency [ambient rainfall withheld for three weeks, then applied as a single deluge event] manipulations, to simulate predicted changes in both the size and frequency of future rainfall events. In addition, half of all experimental plots were inoculated with adult root herbivores (Scarabaeidae beetles). Results We found strong seasonal dependence in plant community responses to both rainfall and root herbivore treatments. The largest effects were seen in the cool season with lower productivity, cover and diversity in rainfall-manipulated plots, while root herbivore inoculation increased the relative abundance of C-3, compared to C-4, plants. Conclusions This study highlights the importance of considering not only the seasonality of plant responses to altered rainfall, but also the important role of interactions between abiotic and biotic drivers of vegetation change when evaluating ecosystem-level responses to future shifts in climatic conditions.This work was partially supported by a Higher Degree Research Scholarship from the Hawkesbury Institute for the Environment at Western Sydney University. Additional funding came from a project grant to SAP and SNJ from the Hermon Slade Foundation (P00021516) and funding provided by Western Sydney University. The Western Sydney University Library provided financial assistance for open access publication fees. Documen

Protist Diversity Responses to Experimental N Deposition in Biological Crusts of a Semiarid Mediterranean Ecosystem

Biological soil crusts (BSC) are associations of different macro and microorganisms and aggregated soil particles located on the surface of soils in many different habitats. BSC harbour a diverse and complex community of ciliates and testate amoebae. These phagotrophic protists play an important role in C and N recycling in soil ecosystems but have not been frequently studied in BSC. In this context, the effects of three increasing N inputs on ciliates and testate amoebae in crusts from a semi-arid Mediterranean ecosystem were evaluated. A field experiment with artificial N-deposition was designed to mimic the effects caused by anthropogenic N depositions. The results have shown that the protist populations of these semi-arid Mediterranean environments have lower species richness than other soil environments. The increase in N produces a net loss of diversity in the populations studied and shifts in the community structure. It has also been shown that some ciliates and testate amoebae, due to their population responses to increased N concentrations, could potentially be used as bio-indicators of N contamination in these BSCs

Ecosystem coupling:A unifying framework to understand the functioning and recovery of ecosystems

Global change frequently disrupts the connections among species, as well as among species and their environment, before the most obvious impacts can be detected. Therefore, we need to develop a unified conceptual framework that allows us to predict early ecological impacts under changing environments. The concept of coupling, defined as the multiple ways in which the biotic and abiotic components of ecosystems are orderly connected across space and/or time, may provide such a framework. Here, we operationally define the coupling of ecosystems based on a combination of correlational matrices and a null modeling approach. Compared with null models, ecosystems can be (1) coupled; (2) decoupled; and (3) anticoupled. Given that more tightly coupled ecosystems displaying higher levels of internal order may be characterized by a more efficient capture, transfer, and storage of energy and matter (i.e., of functioning), understanding the links between coupling and functioning may help us to accelerate the transition to planetary-scale sustainability. This may be achieved by promoting self-organized order