Anthropogenic N deposition and the fate of 15NO 3 − in a northern hardwood ecosystem

Human activity has substantially increased atmospheric NO ₃ ^– deposition in many regions of the Earth, which could lead to the N saturation of terrestrial ecosystems. Sugar maple (Acer saccharum Marsh.) dominated northern hardwood forests in the Upper Great Lakes region may be particularly sensitive to chronic NO ₃ ^– deposition, because relatively moderate experimental increases (three times ambient) have resulted in substantial N leaching over a relatively short duration (5–7 years). Although microbial immobilization is an initial sink (i.e., within 1–2 days) for anthropogenic NO ₃ ^– in this ecosystem, we have an incomplete understanding of the processes controlling the longer-term (i.e., after 1 year) retention and flow of anthropogenic N. Our objectives were to determine: (i) whether chronic NO ₃ ^– additions have altered the N content of major ecosystem pools, and (ii) the longer-term fate of ¹⁵NO ₃ ^– in plots receiving chronic NO ₃ ^– addition. We addressed these objectives using a field experiment in which three northern hardwood plots receive ambient atmospheric N deposition (ca. 0.9 g N m^–2 year^–1) and three plots which receive ambient plus experimental N deposition (3.0 g NO₃ ^–-N m^–2 year^–1). Chronic NO ₃ ^– deposition significantly increased the N concentration and content (g N/m²) of canopy leaves, which contained 72% more N than the control treatment. However, chronic NO ₃ ^– deposition did not significantly alter the biomass, N concentration or N content of any other ecosystem pool. The largest portion of ¹⁵N recovered after 1 year occurred in overstory leaves and branches (10%). In contrast, we recovered virtually none of the isotope in soil organic matter (SOM), indicating that SOM was not a sink for anthropogenic NO ₃ ^– over a 1 year duration. Our results indicate that anthropogenic NO ₃ ^– initially assimilated by the microbial community is released into soil solution where it is subsequently taken up by overstory trees and allocated to the canopy. Anthropogenic N appears to be incorporated into SOM only after it is returned to the forest floor and soil via leaf litter fall. Short- and long-term isotope tracing studies provided very different results and illustrate the need to understand the physiological processes controlling the flow of anthropogenic N in terrestrial ecosystems and the specific time steps over which they operate.     

Stable isotope views on ecosystem function: challenging or challenged?

Stable isotopes and their potential for detecting various and complex ecosystem processes are attracting an increasing number of scientists. Progress is challenging, particularly under global change scenarios, but some established views have been challenged. The IX meeting of the Spanish Association of Terrestrial Ecology (AAET, Úbeda, 18–22 October 2009) hosted a symposium on the ecology of stable isotopes where the linear mixing model approach of partitioning sinks and sources of carbon and water fluxes within an ecosystem was challenged, and new applications of stable isotopes for the study of plant interactions were evaluated. Discussion was also centred on the need for networks that monitor ecological processes using stable isotopes and key ideas for fostering future research with isotopes.     

Ostrich recruitment dynamics in relation to rainfall in the Mara–Serengeti ecosystem

Animal population dynamics can be driven by rainfall variability through its influence on habitat suitability, availability and nutritional sufficiency of forage. To understand how rainfall influences ostriches, we related changes in ostrich recruitment in the Mara–Serengeti ecosystem to rainfall. Over a 15-year period, monthly counts of ostriches were made and the number of hatchlings, chicks, hens, cocks, and the size of the groups in which they occurred were recorded. Breeding was bimodal with a major peak in February and a minor peak in October. Ostriches formed larger groups in the wet (4.41 ± 5.17 (mean ± SD), range 1–72, n = 672 groups) than in the dry (2.49 ± 2.70, range 1–29, n = 398) season. The number of hatchlings plus chicks per hen increased across the duration of the study period and with increasing annual and early wet-season rainfall, affecting forage availability and quality. Recruitment was highest at intermediate levels of the five-year average of the late wet-season rainfall, implying that a change in long-term rainfall and habitat suitability would move recruitment away from the optimum. Outstanding adaptations to life in arid environments could make ostriches more resilient than sympatric ungulates if food shortages and water stress became more frequent because of widening climatic variability.     

Variation in the methods leads to variation in the interpretation of biodiversity–ecosystem multifunctionality relationships

生物多样性常常和生态系统多功能性(生态系统同时提供多个生态系统功能的能力)正相关。然而,生物多样性与生态系统多功能性的关系是否依赖于生态系统功能的数目有诸多争议。其中,生物多样性对生态系统多功能性的影响或许不随生态系统功能数目的变化而变化,或者随生态系统功能数目的增多而增强。我们期望通过研究不同生态系统多功能性指数的统计原理来解决这些争议。 我们使用了模型模拟和一系列来自不同空间尺度(从局域到全球)和不同生物群系(温带和高寒草地、森林和干旱地)的经验数据。我们回顾了量化生态系统多功能性的三种方法,包括平均值法、加和法和阈值法。我们发现随着生态系统功能数目的增加,生物多样性与生态系统多功能性的关系要么不变,要么增强。这些结果可由平均和加和的多功能性指数的统计原理来解释。具体来讲,当利用生态系统功能的平均值计算多功能性指数时,由于多样性对多功能性的效应等于多样性对单个生态系统功能效应的平均值,所以不会随生态系统功能数目的变化而变化。同样的道理,当利用单个生态系统的加和值计算多功能性指数时,多样性的效应会随着生态系统功能数目的增加而增强。我们提出了一个改进的多功能性指数,将平均或加和多功能性指数转化为标准化的多功能性指数, 以便于对不同研究的结果进行比较。此外,我们提出了基于变量数值范围的标准化方法来解决阈值法的数学假象问题(多样性效应随生态系统功能数目的增加而增强)。我们的研究结果表明,量化多功能性指数的方法不同,结果也不同。因此,有必要加深对不同方法数理基础的理解。而标准化的多功能性指数为比较不同研究中的生物多样性与生态系统多功能性的关系提供了有效的方法。     

Measurements of nitrogen fixation in fababean at different N fertilizer rates using the 15N isotope dilution and ‘A-value’ methods

The ¹⁵N isotope dilution and A-value methods were used to measure biological nitrogen (N₂) fixation in field grown fababean (Vicia faba L.), over a 2-year period. Four N rates, 20, 100, 200 and 400 kg N ha^–1 were examined. The two isotope methods gave similar values of % N derived from the atmosphere (%Ndfa). With 20 kg N ha^–1, %Ndfa in fababean was about 85% in both years. Increasing the N rate to 100 kg N ha^–1 decreased N₂ fixation slightly to 75%. Further reductions in N₂ fixed to 60 and 43% occurred where 200 and 400 kg N ha^–1 were applied, respectively. Thus even higher rates of N than normally applied in farming practice could not completely suppress N₂ fixation in fababean.We also devised one equation for both the isotope dilution and A-value approaches, thereby (i) avoiding the need for different calculations for the ¹⁵N isotope methods, and (ii) showing once again that the isotope dilution and A-value methods are mathematically and conceptually identical.     

Residents’ valuation of ecosystem services in a Mediterranean coastal dune ecosystem: The case of the Ritoque dunes in central Chile

Coastal dunes provide a variety of cultural and ecological ecosystem services to local communities. However, most of these ecosystems are globally threatened by anthropic factors. Chile is home to important dune ecosystems such as the emblematic Ritoque coastal dunes located in the hotspot for biodiversity conservation in central Chile where there is a delicate relationship between conservation and human development interests, among local communities and authorities. Here, we performed a choice experiment study to determined willingness to implement conservation measures in the Ritoque dunes. In particular, we assessed residents’ preferences for improvements of the current state of local ecosystem services such as scenic beauty, biodiversity and archaeological sites. Residents showed preferences for improvements in Ritoque coastal dunes’ ecosystem services, and a high willingness to pay for protecting biodiversity and archeological sites, rather than for recreational infrastructure. Our study highlights the importance of place-based research that specifically addresses residents and stakeholders’ conservation priorities, which could be used to design and implement effective conservation management strategies for coastal ecosystems and coastal cities near them.     

Seasonal variation in stable C and N isotope ratios of the Rhone River inputs to the Mediterranean Sea (2004–2005)

The temporal variation in the stable carbon and nitrogen isotope ratios of particulate organic matter (POM) in the Rhone River was investigated on a monthly basis during a 2-year period (2004–2005). In spite of high month-to-month variation, interannually consistent seasonal trends appeared, with significantly lower δ¹³C (<?28.2‰) in spring than in the other seasons. In contrast, δ¹⁵N did not exhibit significant temporal variation. In spring and summer, high chlorophyll a and b concentrations were associated with low C/N values (<8) and a high percentage of organic carbon (%C) and organic nitrogen (%N), testifying to high development of autochthonous riverine phytoplankton (mainly diatoms and chlorophytes). In fall and winter, higher δ¹³C (>?27.2‰) and C/N (>8) values, and lower %C, %N, and chlorophylls concentrations indicated the predominance of allochthonous terrestrial detritus material in the river POM. The lower δ¹³C values recorded in spring–summer, when the phytoplankton biomass was high, were related to the lower carbon isotopic signatures of freshwater diatoms and chlorophytes compared to those of terrestrial plants. Overall, Rhone River POM was mainly composed of terrestrially derived material (90%), with autochthonous phytoplankton representing only 10% as a mean, in spite of a higher mean contribution of phytoplankton (27%) to river POM in summer.     

What can conservation strategies learn from the ecosystem services approach? Insights from ecosystem assessments in two Spanish protected areas

Biodiversity conservation strategies that overlook the interests of local people are prone to create conflicts. The ecosystem service approach holds potential for more comprehensively integrating the social dimension into decision-making in protected areas, but its implementation in conservation policies is still in its infancy. This research assesses the extent to which ecosystem services have been implemented in conservation strategies in protected areas. The study was conducted in two outstanding Spanish protected areas, covering a wetland (Doñana Natural and National Parks) and a Mediterranean mountain system (Sierra Nevada Natural and National Parks). Data were collected from deliberative workshops with managers and researchers, face-to-face surveys with users and a review of management plans. We found that, beyond intrinsic values of ecosystems and biodiversity, these areas provide multiple ecosystem services that deserve further attention to ensure their sustained delivery. Our research shows that environmental managers and researchers have different perceptions and priorities regarding ecosystem services management compared with ecosystem service users. Environmental managers and researchers in both protected areas perceived that human-nature relationships and ecosystem services are already widely included in management plans, if often not explicitly. We found that different ecosystem service categories receive uneven attention in management plans. These contained measures to manage provisioning and cultural services whereas measures for managing regulating services were perceived to be largely absent. We conclude by summarizing insights on how the ecosystem service approach may enhance the consideration of social interests in the management of management protected areas.     

Who dominates whom in the ecosystem? Energy flow bottlenecks and cascading extinctions

In this paper, we investigate the problem of secondary extinction in food webs through the use of dominator trees, network topological structures that reduce food webs to linear pathways that are essential for energy delivery. Each species along these chains is responsible for passing energy to the taxa that follow it, and, as such, it is indispensable for their survival; because of this it is said to dominate them. The higher the number of species a node dominates, the greater the impact resulting from its removal. By computing dominator trees for 13 well-studied food webs we obtained for each of them the number of nodes dominated by a single species and the number of nodes that dominate each species. We illustrate the procedure for the Grassland Ecosystem showing the potential of this method for identifying species that play a major role in energy delivery and are likely to cause the greatest damage if removed. Finally, by means of two indices that measure error and attack sensitivity, we confirm a previous hypothesis that food webs are very robust to random loss of species but very fragile to the selective loss of the hubs.     

Fish abundance and species richness across an estuarine–freshwater ecosystem in the Neotropics

We investigated the distributional patterns of shallow-water fish and their environmental correlates along a broad spatial scale encompassing estuarine and freshwater ecosystems. Marine-vagrant species were restricted to the sites under the influence of salinity intrusion, whereas estuarine-related and freshwater guilds were found along the entire estuarine–freshwater gradient. Primary- and secondary-freshwater fish guilds had the most widespread spatial distribution and comprised a major fraction of the total abundance and species richness. Abiotic factors correlated with fish abundance and composition along two main environmental axes, one related with variation in salinity, water transparency, and sediment granulometry and the other with the slope gradient. Species richness was significantly higher at the natural channel linking the estuarine- and freshwater-ecosystem, which probably was due to: (a) a steeper slope that favored the confluence of fish from the littoral (<2 m) and limnetic (>2 m) zones and (b) the sporadic inflow of saltwater that carried into this region several marine-related species. Although estuarine–freshwater ecotones are known to support few species, mainly salinity tolerant, our results suggest that habitat features and seasonal fish movement associated with salinity intrusion could lead to more diverse fish assemblages in this transitional zone.     

The spatial pattern and dispersion of Lygodium microphyllum in the Everglades wetland ecosystem

Since 1958, L. microphyllum (Old World Climbing Fern), which originated from the Old World Tropics, has become a nuisance exotic and has rapidly spread and is being established system-wide in extremely remote and undisturbed areas such as the Florida Everglades. Of particular concern is that L. microphyllum is disrupting, at an alarming rate, the flora and fauna of the native ecosystem at the same time that a major 8.4 billion dollar Everglades restoration program is trying to enhance these same attributes. This research utilized IKONOS satellite data to map L. microphyllum within the 58,000-ha Loxahatchee National Wildlife Refuge wetland in south Florida. Results show that approximately 11.6% of the tree/shrub vegetation within the impoundment has been infected by L. microphyllum. These data were then utilized to explore the spatial spread patterns of L. microphyllum within the Refuge. Results suggest that L. microphyllum is more likely to establish on the southeast side of a tree/shrub island and then spread to the northwest, which corresponds to the prevailing wind direction in south Florida. Spatial pattern analysis of L. microphyllum spread indicated that it is correlated with the density and spatial distribution of tree/shrub island vegetation. It appears that the dispersion of L. microphyllum is density dependent, which can be expressed as a logistic function and has a catastrophic threshold of 160 m of mean distance between tree/shrub islands in the Everglades. It is predicted that 38% (or 1910 ha) of tree/shrub islands in the Refuge will be invaded by L. microphyllum by 2012. Tree islands in the Everglades wetland could be considered similar to oceanic islands throughout the world that are notoriously vulnerable to biological invasions.     

Mapping the glycoxidation product Nε-carboxymethyllysine in the milk proteome

Milk processing leads to severe protein damage caused by the formation of nonenzymatic posttranslational modifications (nePTMs), such as glycation and glycoxidation. As a result, the technological and nutritional function of milk proteins can be critically altered. The present study investigated the protein-specific distribution of the glycoxidation product N(ε) -carboxymethyllysine (CML) in the proteome of processed milk. For this purpose, raw milk and heated milk were separated by 1-D or 2-DE. The distribution of CML in the milk proteome was examined by immunoblotting. The changes in the protein composition that occurred during heating were monitored by Coomassie staining. Relative modification rates were measured for the major milk protein fractions after 30 and 60 min of heating at 120°C and normalized to the content of the respective protein fraction in the samples. The highest glycoxidation rates were detected in the high molecular weight aggregates that are generated during heating. The casein fraction and the whey protein β-lactoglobulin were affected in a similar manner. The relevance of the results for industrial milk processing was confirmed by analyzing several commercial milk products accordingly. The presented approach allows nonenzymatic posttranslational modification mapping of the entire milk proteome.     

Manipulation of host behaviour by parasites: ecosystem engineering in the intertidal zone?

Understanding the influence of parasites on the community ecology of free-living organisms is an emerging theme in ecology. The cockle Austrovenus stutchburyi is an abundant mollusc inhabiting the sheltered shores of New Zealand. This species, which lives just few centimetres under the surface, plays a key role for many benthic invertebrate species, because in these habitats the cockle shell is the only available hard surface where invertebrates can establish. However, the behaviour of this cockle can be altered locally by a parasite, the trematode Curtuteria australis. Indeed, heavily infected cockles are unable to bury perfectly and typically lie entirely exposed at the surface of the mud. In this study, we investigated the ecological consequences of this behavioural alteration for two invertebrates species commonly associated with cockles, the anemone Anthopleura aureoradiata and the limpet Notoacmea helmsi. A field study first demonstrated that in both infected and non-infected populations of cockles, there was a negative relationship between the number of anemones and limpets found on cockles. In the laboratory, we showed that predation of limpets by anemones is possible when they share the same cockle shell. In a heavily infected population of cockles, limpets were significantly more frequent and more abundant on cockles manipulated by C. australis than on cockles with a normal behaviour. A colonization test conducted in natural conditions demonstrated that the predominance of limpets on manipulated cockles results from a direct habitat preference. Conversely, anemones were significantly less frequent and less abundant on manipulated cockles than on cockles manipulated by C. australis. A desiccation test revealed that, relative to limpets, they had a lower resistance to this physical stress. We discuss our results in relation to current ideas on ecosystem engineering by organisms.     

N,N,N′,N′-tetramethyl-p-phenylenediamine initiates the appearance of a well-resolved I peak in the kinetics of chlorophyll fluorescence rise in isolated thylakoids

Addition of N,N,N′,N′-tetramethyl-p-phenylendiamine (TMPD) to thylakoid membranes isolated from pea leaves initiates the appearance of peak I in the polyphasic rise of chlorophyll (Chl) fluorescence observed during strong illumination, making it similar to that observed in leaves or intact chloroplasts. This effect depends on TMPD concentration and incubation period of isolated thylakoids with TMPD. The resolution of I-peak in the presence of weak concentrations of TMPD which reduced the overlap between I- and P-peaks, resulted from a decreased reduction of both fast and slow plastoquinone (PQ) pools of the granal and stromal thylakoids, respectively, as TMPD effectively accepts electrons from reduced PQ. High concentrations of TMPD markedly decreased the J–I–P phase of fluorescence rise and greatly retarded the I–P step rise. Accumulation of oxidized TMPD in the thylakoid lumen accelerated the re-oxidation of the acceptor side of Photosystem II (PSII) as illustrated by a two-fold increase in the magnitude of the fast component and complete suppression of the middle component of the variable Chl fluorescence (F_v) decay in the dark. Evidently, exogenous addition of high concentrations of TMPD prevented the light-induced reduction of the slow PQ pool.     

Mother–embryo isotope fractionation in the pygmy devilray Mobula kuhlii cf. eregoodootenkee

We determined stable-isotope ratios for replicate muscle tissues in 13 gravid Mobula kuhlii cf. eregoodootenkee (110.4–120.4 cm disc width; W_D) and their embryos (7.0–42.3 cm W_D) and also yolks and histrotroph, to assess the potential implications for juvenile nutrition and habitat use. Irrespective of their development in the uterus, embryos had similar δ¹³C values in their muscle tissue as the mothers and both had greater values than in the histotroph. During gestation, δ¹³C values increased across all sample types. However, while embryo muscle tissue and the histotroph were associated with increasing ¹⁵N levels during embryonic development, this was depleted in the mothers’ muscle tissue and yolk. Although speculative, the observed variation in stable-isotope ratios might imply a dietary shift among gravid females during their early gestation. Irrespective of the underlying mechanisms, the results indicate neonates will have relatively greater δ¹⁵N values than post-partum females, which would probably confound juvenile foraging-ecology estimates.     

Parasites in the northern Wadden Sea: a conservative ecosystem component over 4 decades

We investigated potential changes in the metazoan endoparasite fauna in the northern Wadden Sea during the past 4 decades by compiling published studies, reports and original data. During the time considered, the parasite fauna has remained basically the same. Only a few changes in parasite species presence occurred that resulted from changes in host distribution and abundance. The introduction of potential host species had little effect on the parasite community because no alien parasites were concomitantly introduced and the native parasites show low prevalence and intensity in these novel hosts. Eutrophication and effects of phased-out hunting may not have had clear bottom–up or top–down effects on the parasite community because of various confounding factors. Parasites depending on several host species may only be subject to strong population changes if all hosts are affected in a unidirectional way. This, however, is rather unlikely to happen in a coastal ecosystem subject to multiple pressures. Hence, parasites appear to be a relatively conservative component of the northern Wadden Sea.     

Charcoal production in the Mopane woodlands of Mozambique: what are the trade-offs with other ecosystem services?

African woodlands form a major part of the tropical grassy biome and support the livelihoods of millions of rural and urban people. Charcoal production in particular is a major economic activity, but its impact on other ecosystem services is little studied. To address this, our study collected biophysical and social datasets, which were combined in ecological production functions, to assess ecosystem service provision and its change under different charcoal production scenarios in Gaza Province, southern Mozambique. We found that villages with longer histories of charcoal production had experienced declines in wood suitable for charcoal, firewood and construction, and tended to have lower perceived availabilities of these services. Scenarios of future charcoal impacts indicated that firewood and woody construction services were likely to trade-off with charcoal production. However, even under the most extreme charcoal scenario, these services were not completely lost. Other provisioning services, such as wild food, medicinal plants and grass, were largely unaffected by charcoal production. To reduce the future impacts of charcoal production, producers must avoid increased intensification of charcoal extraction by avoiding the expansion of species and sizes of trees used for charcoal production. This is a major challenge to land managers and policymakers in the area.This article is part of the themed issue ‘Tropical grassy biomes: linking ecology, human use and conservation’.     

Is the loss of Australian digging mammals contributing to a deterioration in ecosystem function?

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Do increased summer precipitation and N deposition alter fine root dynamics in a Mojave Desert ecosystem?

Climate change is expected to impact the amount and distribution of precipitation in the arid southwestern United States. In addition, nitrogen (N) deposition is increasing in these regions due to increased urbanization. Responses of belowground plant activity to increases in soil water content and N have shown inconsistent patterns between biomes. In arid lands, plant productivity is limited by water and N availability so it is expected that changes in these factors will affect fine root dynamics. The objectives of this study were to quantify the effects of increased summer precipitation and N deposition on fine root dynamics in a Mojave Desert ecosystem during a 2‐year field experiment using minirhizotron measurements. Root length density, production, and mortality were measured in field plots in the Mojave Desert receiving three 25 mm summer rain events and/or 40 kg N ha^?1 yr^?1. Increased summer precipitation and N additions did not have an overall significant effect on any of the measured root parameters. However, differences in winter precipitation resulting from interannual variability in rainfall appeared to affect root parameters with root production and turnover increasing following a wet winter most likely due to stimulation of annual grasses. In addition, roots were distributed more deeply in the soil following the wet winter. Root length density was initially higher under canopies compared to canopy interspaces, but converged toward the end of the study. In addition, roots tended to be distributed more deeply into the soil in canopy interspace areas. Results from this study indicated that increased summer precipitation and N deposition in response to climate change and urbanization are not likely to affect fine root dynamics in these Mojave Desert ecosystems, despite studies showing aboveground plant physiological responses to these environmental perturbations. However, changes in the amount and possibly distribution of winter precipitation may affect fine root dynamics.