Oligotrophic Species Research Articles

Warm growing season activates microbial nutrient cycling to promote fertilizer nitrogen uptake by maize

The influence of nitrogen (N) inputs on soil microbial communities and N uptake by plants is well-documented. Seasonal variations further impact these microbial communities and their nutrient-cycling functions, particularly within multiple cropping systems. Nevertheless, the combined effects of N fertilization and growing seasons on soil microbial communities and plant N uptake remain ambiguous, thereby constraining our comprehension of the optimal growing season for maximizing crop production. In this study, we employed 15N isotope labeling, high-throughput sequencing, and quantitative polymerase chain reaction (qPCR) techniques to investigate the effects of two distinct growing seasons on microbial communities and maize 15N uptake ratios (15NUR). Our results showed that the warm growing season (26.6 °C) increased microbial diversity, reduced network complexity but enhanced stability, decreased microbial associations, and increased modularization compared to the cool growing season (23.1 °C). Additionally, the warm growing season favored oligotrophic species and increased the abundance of microbial guilds and functional genes related to N, phosphorus, and sulfur cycling. Furthermore, alterations in the characteristics of soil microbial keystone taxa were closely linked to variations in maize 15NUR. Overall, our findings demonstrate significant seasonal variations in soil microbial diversity and functioning, with maize exhibiting higher 15NUR during the warm growing season of the double cropping system.

Decoupled fungal and bacterial functional responses to biochar amendment drive rhizosphere priming effect on soil organic carbon mineralization

The application of biochar to soil is widely recognized as a promising strategy for enhancing the accumulation and stability of soil organic carbon (SOC), which is crucial in mitigating climate change. However, the influence of interactions between plants and biochar on soil microbial communities and their involvement in SOC mineralization and stability remains unclear. This understanding is essential for optimizing carbon (C) sequestration in systems involving plants, soil, and biochar. In this study, employing a 13C natural abundance approach, we investigated the effect of biochar on the maize rhizosphere priming effect (RPE) in paddy soil. We also examined alterations in microbial communities and functional genes related to C degradation and fixation. Over the 99 days of maize growth, biochar application increased RPE and total SOC while decreasing dissolved organic C. It also elevated soil pH, resulting in shifts in fungal and bacterial community structure, favoring oligotrophic species. Fungal and bacterial assemblies were dominated by deterministic and stochastic processes, respectively. While the abundance of fungal guilds varied irregularly, bacterial guilds were uniformly enriched under biochar-plant interactions. Functional traits such as ecoenzymatic activities, bacterial guilds, and functional genes predominantly affected RPE under biochar application. Bacterial functional genes associated with C degradation and fixation were concurrently enhanced with biochar application. Our results indicate that interactions between plants and biochar can enhance native SOC mineralization and accumulation in a short timeframe by modulating functional traits of soil microorganisms, particularly the bacterial community involved in C degradation and fixation.Graphical

Leveraging Bayesian network to reveal the importance of water level in a shallow lake ecosystem: A study based on Paleo-diatom and fish community

Lake ecological processes and nutrient patterns are increasingly affected by water level variation around the world. Still, the long-term effects of water level change on lake ecosystems and their implications for suitable lake level management have rarely been studied. Here, we studied the ecosystem dynamics of a mesotrophic lake located in the cold and arid region of northern China based on long-term paleo-diatom and fishery records. Utilizing a novel Copula-Bayesian Network model, possible hydrological-driven ecosystem evolution was discussed. Results show that increased nutrient concentration caused by the first water level drop in the early 1980s incurred a transition of sedimental diatoms towards pollution-resistant species, and the following water level rise in the mid-1980s brought about considerable external loading, which attributed to eutrophication and caused the miniaturization of fishery structure. In the 21st century, a continuous water level plummet further reduced the sediment diatom biomass and the fish biomass by altering nutrient concentration. However, with the implementation of the water diversion project in 2011, oligotrophic species increased, and the ecosystem developed for the better. From the perspective of water quality protection requirements and the ecological well-being of Lake Hulun, the appropriate water level should be around 542.42–544.15 m. In summary, our study highlights the coupling effect of water level and water quality on Lake Hulun ecosystem and gives shed to lake water level operation and management under future climate change and human activities.

Climatic variation of the last 29.000 years BP in the northern Santos basin (Rio de Janeiro Shelf) inferred by an alternation of cysts Tuberculodinium vancampoae and Operculodiniumcentrocarpum

During the transition from the Pleistocene to the Holocene, significant changes occurred on the Brazilian continental shelf. In this study, we investigated the environmental changes that occurred during this period through the quantification and classification of cosmopolitan dinoflagellate cysts. We used three cores collected in the northern part of the Santos Basin and analyzed a total of 42 samples. The results showed a predominance of cysts of O. centrocarpum, L. machaerophorum and T. vancampoae, whose occurrence was influenced by sea-level fluctuations during the Pleistocene-Holocene transition and by changes in ocean currents due to temperature variations. Oligotrophic species were established during the Late Pleistocene, followed by mixotrophic species from the Holocene. Analysis of the dinocysts showed the presence of colder waters due to upwelling and the entry of waters with lower salinity due to the formation of transitional estuarine systems. These environmental changes have contributed to the configuration of the current Brazilian coastal scenario.

Еколого-біоморфологічна характеристика мохоподібних торфово-болотного масиву Сира Погоня Рівненського природного заповідника (Україна)

Monitoring biodiversity and the state of mire ecosystems is particularly relevant today for the further planning of nature conservation management in such areas. Revision the taxonomic composition and determining the ecological and biomorphological features of the bryoflora of the peat massif Syra Pogonia RNR are relevant for assessing its current state and forecasting its dynamic dynamic trends. Research on bryophytes was carried out during 2020-2023 by collecting field materials, processing literary sources and critical analysis of herbarium collections. 68 species of bryophytes from 31 families and 39 genera we have identified in the mire massif of the Syra Pogonia of the Rivnenskyi Nature Reserve based on the results of our own field research and literary data. The families Sphagnaceae – 22,2%, Polytrichaceae – 11,8%, Mniaceae and Dicranaceae – 7,5% each, were found to be the most abundant in terms of species. An analysis of the ecological groups of mosses based on trophicity of the substrate revealed a predominance of mesotrophic (33,8%) and oligotrophic species (30,1%), as well as mesoeutrophic species (19,1%); a significant percentage (5,9%) of eutrophic species. Among the ecological groups based on moisture of the habitats, hygromesophytes and hygrophites predominate (35,3%); mesophytes and xeromesophytes account for 30,3% and 20,6% respectively. As a result of biomorphological analysis, the dominance of tall turfs (39,7%) and wefts (19,1%) life forms of mosses, which are associated with wet and oversaturated areas of mire and forest ecosystems, was established, but a large percentage of short turf (23,5%) were also found to be widespread on disturbed areas. A wide range of trophic and moisture content of habitats, as well as a variety of biomorphological spectra of bryophytes, were observed in the studied territory. The heterogeneity of the ecobiomorphological spectrum of mosses in the in the mire massif, particularly the significant presence of xeromesophytic and mesoeutrophic species with life forms of low turfs, indicates a negative trend towards meso- and eutrophication of certain sites of the oligotrophic bog.

Cultivating the Mediterranean Wild Edible Species Cichorium spinosum L. in Aquaponics: Functional and Growth Responses to Minimal Nutrient Supplementation

Aquaponics is a plant and fish co-cultivation system with high sustainability, yet sub-optimal concentrations of Fe and K often compromise crop yields. We cultivated the Mediterranean wild edible Cichorium spinosum L. (Greek name: stamnagathi) in an aquaponics setup following a minimal supplementation approach that focused on Fe and K. Stamnagathi and tilapia fish were co-cultivated under (i) solely Fe, (ii) Fe+K input and (iii) no-input Control treatments. We aimed to evaluate the feasibility of aquaponics for stamnagathi cultivation, identify the system’s bottlenecks, and propose optimization measures. Several plant’s growth and functional parameters were monitored throughout the 35-day experimental period, notably instantaneous gas exchange and photosynthetic capacity via light response curves, state and efficiency of the photosynthetic machinery, pigment content, and yield and morphometric assessments. Fish growth characteristics and survival rates remained unaffected. Fe deficiency was crucial in shaping the responses of Control stamnagathi, which showed inferior performance in terms of photochemistry, chlorophylls content, light use efficiency and, subsequently, photosynthetic activity. Fe and Fe+K-treated plants exhibited similarly high performance in all studied parameters and achieved 4.5- and 4-fold increased yields, respectively, compared to Control. The results demonstrate that aquaponics is an advantageous cropping system for stamnagathi and solely Fe supplementation is adequate to promote excellent performance and yield of this oligotrophic species.

Using Ellenberg’s indicator values in the analysis of the flora and vegetation of small mires in Karelia

Ecological analysis of the vascular plant flora and 20 associations on 63 small mid-boreal mires of Karelia was performed using Ellenberg’s indicator values for four ecological factors (light, moisture, substrate reaction, substrate nitrogen). The flora is mainly dominated by heliophilous (57 %), hygrophytic (84 %), acidophilous (58 %) and oligotrophic (72 %) species of vascular plants. Ordination of the syntaxa shows that the leading factors for the distribution of communities in the space of ecological gradient factors are substrate acidity and richness in nitrogen.

Decreasing nitrogen deposition rates: Good news for oligotrophic grassland species?

Several studies have found that increased nitrogen (N) deposition leads to a decline in species richness in semi-natural grasslands, mainly due to the loss of species typical of nutrient-poor soils. However, after reaching a peak around 1990, N deposition has decreased in Europe over the last 30 years. In this study, we investigated the changes in species number and composition of semi-natural grasslands during this period of declining N deposition. To this end, we compared the data from the first survey (2001-2005) of 147 grassland sites in Switzerland with those from the third survey (2011-2015). We further analysed the vegetation development of a specific hay meadow from 1992 to 2013. In this grassland, total vegetation cover and the cover of graminoid species decreased, while the cover of oligotrophic species increased. At the 147 grassland sites, total species number decreased at sites with still high levels of N deposition and it tended to increase at sites with low N deposition, i. e. below the critical load for N deposition. The number of oligotrophic grassland species increased at sites with a large decrease in N deposition and strong inclination. Thus, the results of this study indicate that the reduction of N emissions had a measurable positive effect on species diversity in these semi-natural grasslands. Most of the grasslands surveyed appear to be quite resilient against N deposition, i. e. they do not shift to an alternative low diversity state dominated by a few competitive species, and recovery of the species composition as a result of the decrease in N deposition seems possible, especially on steep slopes. Furthermore, the study underlines the importance of regular management of semi-natural, unfertilised, low-productivity grassland to maintain the diversity of oligotrophic grassland species.

Manganese availability modifies nitrogen eutrophication signals in acidophilous temperate forests

Increases in atmospheric nitrogen (N) deposition are known to alter the ground vegetation of forest ecosystems by promoting nitrophilic plant species and displacing nitrogen-sensitive, oligotrophic species. Though there are well-known indicator species for eutrophication, there is often no direct verifiable relationship between N deposition and the strength of the eutrophication signal in the vegetation. The key reason for this sometimes lacking or weak relationship is that significant amounts of plant-available reactive N (Nr) are provided from the decay and mineralization of organic matter in the course of N cycling within the forest. The relationship is further complicated as N mineralization is also influenced by external N inputs. It has been shown repeatedly that various soil parameters related to acidity can confound a close N deposition-vegetation relationship, because acidity exerts a strong influence on the decomposition of organic matter. To further improve the understanding of the complex relationships between soil variables and vegetation composition, we analyzed vegetation and soil chemistry in acidophilous broad-leaved temperate forests of southwestern Germany, dominated by beech and oak. Our results suggest that manganese (Mn) availability likely is another factor modifying the eutrophication signal of the ground vegetation. In our analyses, the eutrophication signal in the vegetation was strongly related to high exchangeable Mn concentrations from the soil matrix and high Mn concentrations in the soil solution, in some cases to a greater extent than to parameters that reflect soil acidity. This response may be attributed to the function of Mn as a cofactor in the Mn peroxidase of white-rot fungi, which are the initiators of the decomposition of lignified organic matter. Since Mn depletion following previous acidic deposition is common in Central European forests, such a disconnection of the eutrophication signal in the vegetation from atmospheric N deposition might be widespread in forests on acidic soils.

Diatom assemblage responses to multiple environmental stressors in a deep brackish plateau lake, SW China.

Eutrophication, climate change, water level fall, fish introduction, and salinity have been widely recorded to impact lake ecosystems around the world. However, the combined responding pattern in the lake ecosystem to the above multiple environmental stressors is not well understood. Here, we present diatom assemblage and geochemical indicators (total organic carbon (TOC), total nitrogen (TN), and total phosphorous (TP)) in lake sediment to investigate the long-term trends in the aquatic ecosystem in response to multiple environmental stressors in Lake Chenghai, a deep brackish lake located on Yunnan-Guizhou Plateau, SW China, during the past 80years. We identified 8 genera and 15 species of diatom reaching a relative abundance of ≥ 2% in at least one sample, with the dominant taxa such as Cyclotella rhomboideo-elliptica and Aulacoseira alpigena through the sediment core. There was a clear shift in the diatom community from oligotrophic species of C. rhomboideo-elliptica to eutrophic species such as Cyclotella meneghiniana and Cyclostephanos dubius becoming dominant since ca. 1998 CE. In addition, the changes in the fish introduction, water level, temperature, and salinity also resulted in the variation in abundance of planktonic and benthic diatoms. The increase in the abundance of diatoms of C. rhomboideo-elliptica since ca. 1986 CE may be related to the decline in water level and increasing fish production. For one thing, the decline in water level reduces the concentrations of benthic diatoms but increases the relative biomass of planktonic diatoms. For another, the increasing fish production results in the decrease in the zooplankton biomass, thus reducing the predation pressure on planktonic algae. Besides, some specific species such as C. meneghiniana may respond to the increased nutrient release and increased salinity since ca. 1998 CE. Combined, our findings demonstrate that trophic level is the main driver of diatom assemblage changes, and other environmental variables including water level, fish introduction, and climate warming also contribute to diatom community variation in this brackish plateau lake during the last 80years.

The invasive herb Lupinus polyphyllus can reduce plant species richness independently of local invasion age

The ecological impacts of invasive species may change or accumulate with time since local invasion, potentially inducing further changes in communities and the abiotic environment. Yet, time since invasion is rarely considered when investigating the ecological impacts of invasive non-native species. To examine the effect of time since invasion on the ecological impacts of Lupinus polyphyllus, a perennial nitrogen-fixing herb, we surveyed vascular plant communities in the presence and absence of L. polyphyllus in young, intermediate, and old semi-natural grassland sites (ca. 5, 10, 15 years representing both time since lupine invasion and plant community age). We analyzed vascular plant community composition, vascular plant species richness, and the cover of various ecological plant groups and L. polyphyllus. In contrast to our hypotheses, we found no change in the mean cover of L. polyphyllus (about 35%) with time since local invasion, and an ordination did not suggest marked changes in plant community composition. L. polyphyllus was associated with lower species richness in invaded plant communities but this effect did not change with time since invasion. Invaded plant communities were also associated with lower occurrence of generalist, oligotrophic (low-nutrient-adapted) and copiotrophic (nutrient-demanding) species but no temporal dynamics were detected. We conclude that even the intermediate cover of L. polyphyllus can reduce plant species richness, but the ecological impact caused by this invader might not dramatically change or accumulate with time since invasion.

Vegetation changes in the understory of nitrogen-sensitive temperate forests over the past 70 years

Since the industrial revolution, atmospheric nitrogen deposition has increased strongly and has been shown to alter nitrogen cycles, species composition and diversity in many ecosystems, including forests. At the same time, nitrogen removal from forests through biomass extraction via historical management techniques has decreased considerably. A proven tool to analyze the effects of long-term environmental changes are vegetation resurveys.In this study, we tested whether environmental changes resulting from atmospheric nitrogen deposition and altered forest management are reflected in the vegetation composition of temperate forest understories in six acidophilic and oligo-mesophilic forest types in south-western Germany. We compared historical surveys from 1950 to 1976 with surveys from 2017/18 and examined changes in the vegetation using NMDS ordinations and Ellenberg indicator values.While an increase in the number of nitrophilic species was detected in all forest types, only the acidophytic and oligotrophic Vaccinio-Abietetum and Luzulo-Quercetum forests (dominated by Abies alba (Mill.) and Quercus spec., respectively) exhibited a replacement of oligotrophic species by nitrophilic species, amounting to an overall trend of eutrophication.Despite the uncertainties resulting from different plot locations and the slow dynamics of forests, we demonstrate a significant trend in the understory vegetation composition, which is likely caused by atmospheric N deposition. Differences in the sensitivity of different forest types indicate an influence of geological and climatic site characteristics and historical land use on the effects of environmental changes.

Response of Aquatic Organisms Communities to Global Climate Changes and Anthropogenic Impact: Evidence from Listvennichny Bay of Lake Baikal

Simple SummaryLake Baikal is ranked first among the world’s lakes in terms of freshwater reserves (23,000 km3). It is a UNESCO World Heritage Site, and its biota is represented by unique fauna and flora, with endemics accounting for more than 60%. What is happening in the Baikal ecosystem in recent decades due to global climate change and anthropogenic impacts? In this paper, we studied this issue on the example of one of the few open bays on the western shore of Lake Baikal, as well as of some remote areas. It has been found that the plankton composition is dominated by thermophilic species; the role of endemic species in the formation of total biomass is decreasing, which confirms the ecosystem’s response to climate warming. As a result of human activity, filamentous algae bloom suppresses endemic algae species and reduces mollusk proportion. The coastal zone of Lake Baikal is taking on the features of common shallow freshwater lakes due to the predominance of cosmopolitan and widespread Palearctic species. It is necessary to monitor the Baikal ecosystem in the changing climate and to strengthen control over human activities on the shores of the lake.Recent studies have revealed how the freshwater biota of Lake Baikal responds to climate change and anthropogenic impacts. We studied phyto- and zooplankton, as well as phyto- and zoobenthos, in the open coastal waters of the southern basin of the lake and of Listvennichny Bay. A total of 180 aquatic organism taxa were recorded. The response of the Baikal ecosystem to climate change can be traced by changes in the species composition of planktonic communities of the lake’s open coasts in summer. The key species were thermophilic the Anabaena lemmermannii P. Richt. (Fij = +0.7) blue-green algae, the Asplanchna priodonta Gosse (Fij = +0.6) rotifers in 2016, the Rhodomonas pusilla (Bachm.) Javorn. (Fij = +0.5) cold-loving algae, and the Cyclops kolensis Lilljeborg (Fij = +0.9) copepods in the past century. The proportion of Chlorophyta decreased from 63% to 17%; the Cyanophyta increased from 3% to 11% in the total biomass of phytoplankton; and the proportion of Cladocera and Rotifera increased to 26% and 11% in the biomass of zooplankton, respectively. Human activity makes an additional contribution to the eutrophication of coastal waters. The Dinobryon species, the cosmopolitan Asterionella formosa Hass. and Fragilaria radians Kütz., dominated phytoplankton, and filamentous algae, Spirogyra, dominated at the bottom in the area with anthropogenic impact. The trophic level was higher than at the unaffected background site: the saprobity index varied from 1.45 to 2.17; the ratio of eutrophic species to oligotrophic species ranged from 1:2 to 3:1, and the ratio of mesosaprobiont biomass to endemics biomass ranged from 2:1 to 7:1. Currently, the boundaries of eutrophication zones of shallow waters in Lake Baikal are expanding, and its coastal zone has acquired features typical of freshwater bodies of the eutrophic type.

Biofouling by ultra-low pressure filtration of surface water: The paramount role of initial available biopolymers

Biofouling layer (i.e., biofilm) is an inevitable presence for the membrane filtration processes. In this study, we elucidated biofouling formation from the perspective of affecting the attachment of bacteria for the first time, whereby the role of initial available biopolymers was revealed. Results demonstrated that the presence of initial available biopolymers increased the abundance of the genus Caulobacter, which was capable of mineralizing biopolymers; whereas, for the typically oligotrophic species of Polynucleobacter, it exhibited low abundance. Greater concentrations of polysaccharides and proteins were accumulated in the biofouling layer, when provided with initial biopolymers, and the biofilm structure was more heterogeneous with larger pore size and higher thickness. Thereby, the corresponding filtration system exhibited greater permeability and better removal performance of organics. Collectively, the initial available biopolymers altered the attachment conditions for the bacteria, which subsequently impacted the bacterial community, and in turn biofilm composition, physical structure and filtration performance.

Multiple soil factors explain eutrophication signals in the understorey vegetation of temperate forests

AbstractQuestionsVegetation in forest understories is determined by a complex interplay of many different environmental factors, including light, water and nutrient availability. Changes in these conditions, especially changes in nitrogen (N) availability, have been widely discussed to cause shifts in species composition and loss of oligotrophic species. We examined whether nitrogen is the most important factor for the decline of nitrogen‐sensitive species in understorey communities, as measured by average Ellenberg N values and the share and number of nitrogen‐sensitive character species.LocationNine different oligo–mesotrophic types of temperate forest in southwest Germany.MethodsWe combined understorey vegetation and soil data from 135 forest stands. To study the importance of variables in explaining the vegetation gradients, we used random forest analyses and non‐metric multidimensional scaling (NMDS) ordinations combined with fitting of environmental vectors.ResultsWe detected strong differences between three examined forest type groups: eutrophication in the understorey vegetation of broad‐leaved forests on carbonate soils was strongly related to high canopy closure and low soil carbon/phosphorus (C/P) ratio. In broad‐leaved forests on acidic soil, base saturation played a major role, but the vegetation was also influenced by the C/N and C/P ratios. In coniferous forests on acidic soil, soil pH and organic layer depth were important, as were the C/N, C/P and N/P ratios.ConclusionOur results show that eutrophication in understorey forest vegetation is not monocausal. Rather, oligotrophic species of forest communities are reduced at sites with higher N or P availability and/or higher base saturation and soil pH. These conditions favor fast‐growing ubiquitous species in the competition for light and other limiting factors. Since these factors were of varying importance between the forest types examined, differences shaping the forest communities need to be regarded when evaluating the impact of environmental changes, for example through atmospheric nitrogen deposition.

Changes in vegetation structure and composition of a lowland mire over a sixty-five-year interval.

Mires are characterized by plant communities of high conservation and societal value, which have experienced a major decline in area in many parts of the world, particularly Europe. Evidence suggests that they may be particularly vulnerable to changes in climate and nutrient addition. Although they have been the focus of extensive paleoecological research, few attempts have been made to examine the dynamics of mire vegetation during the current era of anthropogenic environmental change.To assess long‐term change in the spatial structure and composition of a lowland mire community, in 2016 we resurveyed plots first surveyed in 1951. Measures of species richness and composition were compared between the two surveys, and changes in community composition were related to plant traits.Overall, mean species richness declined by 26%. The area of occupancy declined in 37% of species, which were primarily oligotrophic species typical of nutrient‐poor bog communities. Conversely, occupancy increased in 21% of species, especially those that were more tolerant of higher nutrient availability. These changes were associated with variation in plant functional traits, as indicated by an increase mean Ellenberg trait values for nitrogen and mean temperature, and a decline in values for precipitation. These results suggest that eutrophication and climate change have been key drivers of floristic change on this site. Synthesis. This investigation provides a rare assessment of the dynamics of a mire community over a multi‐decadal interval. Results indicate that substantial change has occurred in the composition of the community, and the distribution of species within it. The investigation provides evidence of the impact of environmental change on the composition and structure of a lowland mire community, and highlights challenges for its future conservation.

Detecting the drivers of functional diversity in a local lichen flora: a case study on the extinct volcano of Roccamonfina (southern Italy).

Current strategies for conservation reportedly suffer from an inadequate awareness of the drivers affecting lichen diversity, pointing to the need to fully develop a functional approach to lichen ecology. This study is an attempt to detect the drivers affecting functional diversity in the lichen flora of a volcanic Mediterranean area. Data on epiphytic lichen distribution were correlated with information coming from a GIS analysis. Species richness, functional diversity and indicator values of lichens species were analyzed as a function of altitude, bioclimatic patterns and land use patterns. Both taxonomic and functional diversity were found to increase with altitude, peaking at 600m a.s.l. and slightly decreasing at higher elevations. A filtering effect of altitude on lichen growth-forms was detected at increasing altitude, with foliose isidiate lichens replacing crustose lichens with sexual reproduction, cyanobacteria replacing Trentepohlia as photobiont, and oligotrophic species linked to partially shaded environments gradually replacing species indicating eutrophic conditions. Forest stations impacted by low impact traditional agriculture tended to express higher lichen diversity compared to either undisturbed broadleaved forests or intensive orchards. These data demonstrate the need to integrate traditional low-impact agricultural practices in protected areas. Moreover, they provide the evidence that reanalyzing past and recent lichenological censuses with the proposed analytical tools may help previewing and driving the evolution of endangered ecosystems.

Identifying diatom indicator species of nutrient enrichment: An in situ nutrient enrichment experiment in subtropical upland streams

Nutrients are a fundamental determinant of broad scale patterns in the benthic algal community of stream ecosystems. Excessive inputs of nutrients such as nitrogen and phosphorus into upland streams may result in significant impacts on benthic algal communities. In upland streams, diatoms are the most abundant and diverse taxonomic group in benthic algal communities. In this study, benthic algal biomass and diatom community responses to in situ nitrogen and phosphorus enrichment were investigated by conducting an in-stream nutrient diffusing substrate experiment at high and low ambient nutrient concentration sites. Nitrogen was found to be the primary limiting nutrient across all sites, regardless of the ambient nutrient concentrations. In general, enrichment relieved nutrient limitation, promoting the dominance of a smaller suite of eutrophic species in the community. This was particularly evident in the low ambient nutrient sites where oligotrophic species initially dominated the community. This study identified diatom species with competitive advantage under nutrient enriched conditions and further the understanding of diatom species competition for multiple nutrients. Five diatom nutrient trait groups differentiate nutrient generalists and specialists and identifies potential indicator species based on their responses to specific enrichment treatments.

Динамика изменения растительности нефте- и солезагрязненных олиготрофных грядово-мочажинных комплексных болот после рекультивации (Среднее Приобье, ХМАО – Югра)

Oligotrophic ridge-hollow and ridge-hollow-pool complex mires are widely distributed in the central part of West Siberia, including many oil fields of the Middle Pre-Ob region. The article considers the dynamics of re-vegetation of oil and salt-contaminated areas of these mire types subjected to reclamation. Survey materials for 2–3 years and 15 years after reclamation allow to identify the main trends in vegetation restoration in the short and medium term. The reversible oligotrophication of ridges manifests in a relative decrease in the participation of the meso-eutrophic species on contaminated mire sites. In the hollows, however, the similar trend can be traced only in relation to oil-contaminated sites, whereas in the salt-contaminated hollows, the strong eutrophic conditions last. In the medium-term perspective, most typical oligotrophic hollow species, with the exception of Eriophorum russeolum and Oxycoccus palustris, were unable to recover. In the course of dynamic changes in the vegetation, the leading role in recovery successions gradually passes to mesotrophic and eutrophic species possessing massive root systems and aerenchyma – Eriophorum angustifolium, Phragmites australis, Carex rostrata, etc. Restoration of the moss layer is several years behind that of the grass layer, and due to the lack of competition, the participation of liverworts in it is of great importance, especially in salt spills. At the same time, among mosses as in the case of vascular species mesotrophic components are the main dominant ones15 years after reclamation.

Long-term influence of hay-cutting on plant species richness, biodiversity and soil fertility in a Danish fen

We present a rare long-term management project of annual cutting, hay removal and plant species survey on a small Danish freshwater meadow (0.6 ha) for an extended period of 21 years. We evaluate whether disturbance by hay-cutting could reduce the dominance of tall grasses, increase species richness and change the representation of growth strategies and Ellenberg indicator values among species. We also evaluate whether hay removal could reduce soil fertility and increase the proportion of oligotrophic species. We found that species richness increased 3-fold over time accompanying a marked decline of vegetation height and proportion of tall, clonal grasses. Comparison with an adjacent un-cut area confirmed that species richness and evenness increased extensively in the plant community by hay-cutting. During the first ten years of the restoration period, species richness increased for both oligotrophic and eutrophic species, while during the latter 11 years only small oligotrophic species continued to increase. The proportion of Grime’s competitive C-strategies and Ellenberg’s N indices in the community declined over time in accordance with the 50% decrease of organic matter, total and exchangeable phosphorus in the soils. We conclude that long-term hay-cutting by disturbance and nutrient removal can markedly increase plant biodiversity as well as the representation of orchids and small species by breaking the dominance of tall grasses. Focused effort over decades can ensure a remarkable high biodiversity even in a small area, which will go unnoticed in common short-term experiments.