Critical loads of nitrogen deposition and critical levels of atmospheric ammonia for semi-natural Mediterranean evergreen woodlands

Nitrogen (N) has emerged in recent years as a key factor associated with global changes, with impacts on biodiversity, ecosystems functioning and human health. In order to ameliorate the effects of excessive N, safety thresholds such as critical loads (deposition fluxes) and levels (concentrations) can be established. Few studies have assessed these thresholds for semi-natural Mediterranean ecosystems. Our objective was therefore to determine the critical loads of N deposition and long-term critical levels of atmospheric ammonia for semi-natural Mediterranean evergreen woodlands. We have considered changes in epiphytic lichen communities, one of the most sensitive comunity indicators of excessive N in the atmosphere. Based on a classification of lichen species according to their tolerance to N we grouped species into response functional groups, which we used as a tool to determine the critical loads and levels. This was done for a Mediterranean climate in evergreen cork-oak woodlands, based on the relation between lichen functional diversity and modelled N deposition for critical loads and measured annual atmospheric ammonia concentrations for critical levels, evaluated downwind from a reduced N source (a cattle barn). Modelling the highly significant relationship between lichen functional groups and annual atmospheric ammonia concentration showed the critical level to be below 1.9 μg m−3, in agreement with recent studies for other ecosystems. Modelling the highly significant relationship between lichen functional groups and N deposition showed that the critical load was lower than 26 kg (N) ha−1 yr−1, which is within the upper range established for other semi-natural ecosystems. Taking into account the high sensitivity of lichen communities to excessive N, these values should aid development of policies to protect Mediterranean woodlands from the initial effects of excessive N

Seasonal changes in water sources used by woody species in a tropical coastal dune forest

AimsOur aim was to investigate the water sources used by woody species under contrasting water availability and the extent of water-sources-use differentiation among dominant woody species in a tropical coastal dune forest.MethodsWe sampled 15 woody species in a Brazilian restinga forest and, through Bayesian isotope mixing models, we estimated the proportion of water sources used. We tested whether water-sources-use was (i) different between contrasting water availability conditions; (ii) dependent on growth form, plant size or crown illumination; and (iii) influenced by stand density, evenness or biomass.ResultsWe found a seasonal variation in water-sources-use, but no vertical soil-water partitioning among woody species. In wetter periods, plants used mainly water from top-soil, as a shallow water table limited water uptake to top-soil layers recharged with rainwater. Contrastingly, during drier periods, with the absence of rain and a deeper water table, plants generally relied on deeper (50 cm) soil layers. Only under less-wet conditions, a greater evenness and density implied higher water-uptake depth heterogeneity among plants. However, changes in the main water-sources used by plants were neither evoked in more dense or diverse plots, nor induced by plant size.ConclusionsOur study shows that restinga species have dynamic shifts in water-uptake depth caused by seasonal water availability changes, influenced by the combined effect of insufficient moisture at shallow soil layers and water-table lowering in drier periods. These temporal shifts are common among species, implying that restinga woody community has a homogeneous strategy of water-resources acquisition. This study enhances our understanding of the effects that water variations can have on water-resource use in restinga forests437438624154CAPES - Coordenação de Aperfeiçoamento de Pessoal e Nível SuperiorCNPQ - Conselho Nacional de Desenvolvimento Científico e TecnológicoFAPESP – Fundação de Amparo à Pesquisa Do Estado De São Paulosem informação403710/2012-02003/12595-7; 2012/51509-8; 2012/51872-5PPG - Ecologia, Instituto de Biologia, Universidade Estadual de Campinas; Coordenacao de Aperfeicoamento de Pessoal de Nivel Superior (CAPES) - Cristina Antunes PhD scholarship [PROEX 0229083]; Fundacao para a Ciencia e a Tecnologia (FCT)Portuguese Foundation for Science and Technology [PTDC/AAC-CLI/118555/2010, UID/BIA/00329/2013]; Brazilian National Research Council/CNPq (PELD) [403710/2012-0]; British Natural Environment Research Council/NERCNERC Natural Environment Research Council; State of Sao Paulo Research Foundation/FAPESP as part of the project Functional Gradient within the BIOTA/FAPESP Program - The Biodiversity Virtual Institute [2003/12595-7, 2012/51509-8, 2012/51872-5]; State of Sao Paulo Research Foundation/FAPESP as part of the project PELD/BIOTA within the BIOTA/FAPESP Program - The Biodiversity Virtual Institute [2003/12595-7, 2012/51509-8, 2012/51872-5]; State of Sao Paulo Research Foundation/FAPESP as part of the project ECOFOR within the BIOTA/FAPESP Program - The Biodiversity Virtual Institute [2003/12595-7, 2012/51509-8, 2012/51872-5

Gas source isotope ratio mass spectrometry (IRMS)

Gas source isotope ratio mass spectrometry is usually referred to as isotope ratio mass spectrometry (IRMS) or stable-isotope ratio mass spectrometry (SIRMS). IRMS is a conventional method for measuring isotope ratios and has benefited from more than 65 years of research and development. Modern mass spectrometers are all based on gas source isotope ratio mass spectrometry field mass separators. More recently, the development of high-resolution sector field devices has added a new dimension to IRMS. Modern instruments achieve a high sample throughput, which is a prerequisite, e.g., for ecosystem studies where usually a large number of samples needs to be analysed and high precision is required. IRMS is used specifically for the measurement of stable-isotope ratios of a limited number of elements (C, H, N, O and S) after transfer into a gaseous species. Si, Cl, Br and Se can be added to the list even though their applications are limited compared to the other isotope systems. A concise overview of the technical background is given here as well as numerous applications of this technique in earth and geosciences, paleoclimate research, cosmochemistry, environmental sciences and life sciences

Competitive balance between the alien invasive Acacia longifolia and native Mediterranean species

Werner C, Peperkorn R, Maguas C, Beyschlag W. Competitive balance between the alien invasive Acacia longifolia and native Mediterranean species. In: Tokarska-Guzik B, Brock J, Brundu J, Child L, Daehler C, Pysek P, eds. Plant Invasions: Human perception, ecological impacts and management. Leiden, The Netherlands: Backhuys Publishers; 2008: 261-275

Progress and challenges in using stable isotopes to trace plant carbon and water relations across scales

Werner C, Schnyder H, Cuntz M, et al. Progress and challenges in using stable isotopes to trace plant carbon and water relations across scales. Biogeosciences. 2012;9(8):3083-3111.Stable isotope analysis is a powerful tool for assessing plant carbon and water relations and their impact on biogeochemical processes at different scales. Our process-based understanding of stable isotope signals, as well as technological developments, has progressed significantly, opening new frontiers in ecological and interdisciplinary research. This has promoted the broad utilisation of carbon, oxygen and hydrogen isotope applications to gain insight into plant carbon and water cycling and their interaction with the atmosphere and pedosphere. Here, we highlight specific areas of recent progress and new research challenges in plant carbon and water relations, using selected examples covering scales from the leaf to the regional scale. Further, we discuss strengths and limitations of recent technological developments and approaches and highlight new opportunities arising from unprecedented temporal and spatial resolution of stable isotope measurements