Nutrient Cycling In Ecosystems Research Articles

Relationship between herbivory and leaf traits in mangroves on Iriomote Island, southern Japan

Relationship between herbivory and leaf traits in mangroves on Iriomote Island, southern Japan

Chronic anthropogenic disturbance alters litter decomposition and nutrient concentrations and stocks across a Caatinga dry forest chronosequence

Litter decomposition plays a key role in the cycling and storage of nutrients in terrestrial ecosystems. However, very little is known about decomposition processes and their underlying drivers in tropical dry forests, particularly in human-modified landscapes. Here, we evaluate decomposition rates and nutrient concentrations and stocks in the litter of a Caatinga dry forest chronosequence, in northeast Brazil. Litter decomposition was monitored for a year across forest stands of varying ages and old-growth forests. The litter decomposition rate was highly variable across forest stands, although on average decomposition occurred slowly, with approximately 50% of the initial litter mass still present after one year. The decomposition rate is responsive to forest type and negatively affected by chronic disturbance. Litter nutrient concentration decreased along the decomposition process, exhibiting a nutrient-specific mineralization rate. Response to drivers was also nutrient specific, with precipitation and chronic disturbances playing prominent roles. Nutrient stocks in the remaining litter were higher in old-growth forests, and final stocks of certain nutrients also responded to multiple drivers. Our results suggest that the Caatinga dry forest experiences a slow rate of litter decomposition and mineralization, although rates exhibit considerable variability across forest stands and environmental conditions. Thus, chronic disturbance plays a role by either facilitating or reducing litter decomposition, mineralization rate, and the stocks transferred to the soil. Consequently, these factors have implications for nutrient availability, including goat consumption and subsequent loss of nutrients.

Nitrogen and phosphorus allocation in bark across diverse tree species

Understanding of nitrogen (N) and phosphorus (P) allocation patterns among various plant organs and tissues is crucial for gaining insights into plant growth and life-history strategies, as well as ecosystem nutrient cycles. However, there is limited information available regarding allocation strategies for N and P in bark (i.e., all tissues external to the vascular cambium), which is an indispensable and specialized secondary tissue system. This study presents analyses of a newly compiled and comprehensive data set comprising 1246 pairwise N-P observations across 335 tree species spanning 557 independent sampling sites worldwide. The aim is to explore the interspecific N and P stoichiometry of bark. The global geometric means for bark N and P concentrations, as well as N:P ratios, were 3.88 mg/g, 0.2 mg/g, and 19.38, respectively. However, these values varied significantly among different functional plant-groups and biomes. Across all 335 species, the N vs. P scaling exponent was 0.69 for bark, which is similar to the 2/3-power scaling relationship observed in leaves and twigs. However, the bark N vs. P scaling exponent differed among functional plant-groups, biomes, and local sites, indicating the absence of a “canonical” scaling exponent. The interactions of soil total N and P collectively accounted for the most significant variation in the bark scaling exponent among local sites. The results indicate that there is no “canonical” bark N vs. P scaling exponent, and that soil nutrient content is the most important factor influencing N and P allocation strategies in bark. These findings may hold significant implications for predicting plant nutrient allocation strategies in response to environmental changes.

Phylogeny, taxonomy, and biogeography of the Sphaeriinae (Bivalvia: Sphaeriidae)

Abstract The subfamily Sphaeriinae is a diverse and ecologically significant group of freshwater invertebrates, playing a keystone role in the energy flow and nutrient cycling in aquatic ecosystems. Despite a long history of its study, the taxonomic structure and species content of this group are a matter of ongoing disputes between malacologists. We clarify the taxonomy, distribution, and evolutionary biogeography of the Sphaeriinae around the world based on the largest dataset of DNA sequences of these clams ever accumulated, which includes the data on specimens collected from various continents and countries around the globe. Our 16S rRNA and two-locus phylogenies reveal that the Sphaeriinae is a monophyletic group, containing at least seven genus-level clades: Sphaerium Scopoli, 1777, Pisidium C. Pfeifffer, 1821 (s.s.), Euglesa Jenyns, 1832, Odhneripisidium Kuiper, 1962, Conventus Pirogov & Starobogatov stat. nov., 1974, ‘Pisidium’ sterkianum group, and Hindupisidium Vinarski & Bespalaya gen. nov. Our 16S rRNA phylogenetic tree contains 80 well-supported clades corresponding to the putative species-level taxa. Four species new to science are described here: Euglesa kolymensis Bespalaya, Aksenova & Bolotovsp. nov., Euglesa kyrgyzica Bespalaya, Aksenova, Kondakov & Palatovsp. nov., Euglesa moroccana Bespalaya, Vinarski, Aksenova, Mabrouki, Kondakov & Palatovsp. nov., Odhneripisidium caucasus Bespalaya, Vinarski, Aksenova, Kondakov & Palatovsp. nov. Our fossil-calibrated phylogeny and generalized biogeographic model indicate that the most recent common ancestor of the Sphaeriidae could have originated somewhere within a broad area covering China near the Lower Cretaceous boundary.

Stoichiometric imbalances between soil microorganisms and their resources regulate litter decomposition

Abstract Litter decomposition is dependent on the requirements of decomposer communities and their ability to acquire energy and nutrients from their substrates (i.e. litter) and the surrounding environment (i.e. soil). However, knowledge about whether and how stoichiometric imbalance (i.e. the differences in C:N:P ratios between microorganisms and their substrates) regulate litter decomposition rates and whether it can be compensated by soil resources have rarely been evaluated, and even less across different decomposition stages over time. In this study, we conducted a reciprocal litter transplantation experiment using a stoichiometric gradient along the forest‐steppe ecotone to evaluate mechanisms underlying litter‐microbe‐soil interactions at different moments during litter breakdown. We measured the C:N:P stoichiometry of litter, soil, microbes, enzyme ratios and soil microbial community composition (via metabarcoding) after 6 and 12 months of litter decomposition. We found that the stoichiometric imbalances between soil microorganisms and litter substrate controlled decomposition rates directly during the early phase of decomposition. In contrast, the stoichiometric imbalances between soil microorganisms and soil substrate regulated decomposition rates during the later phase of decomposition, but this was an indirect effect mediated via shifts in the saprophytic fungal community composition and enzyme allocation. These findings highlight that the stoichiometric imbalance between soil microorganisms and litter substrates can be partly compensated by the local soil resources over the course of the decomposition process. We conclude that the stoichiometric imbalance between soil microorganisms and their resources is a key mechanism that should not be ignored when predicting soil C and nutrient cycling in terrestrial ecosystems. Read the free Plain Language Summary for this article on the Journal blog.

Empirical measurements of ammonium excretion in kelp forest fishes: Effects of body size, taxonomy and trophic guild

Fishes and other consumers excrete metabolic waste products, including dissolved nutrients rich in nitrogen, which is an essential nutrient for primary production. Relatively little is known about the magnitude and variability of nutrients excreted by fishes in kelp forest ecosystems and whether consumer-derived nutrients are important for supporting kelp productivity. In this study, the supply of ammonium (NH4+) excreted by the dominant fishes (30 species representing ∼85% of total fish biomass) was investigated on nearshore rocky reefs in California. Using rapid field incubations, the amount of excreted dissolved ammonium was measured as a function of body size (n = 460 individuals) and predictive models were developed relating mass to excretion rates at the family-level. Mass-specific excretion rates ranged from 0.08 to 3.45 μmol·g−1·hr−1, and per capita ammonium excretion rates ranged from 5.9 to 2765 μmol·individual·hr−1. Ammonium excretion scaled with fish body mass to the ¾ power, as predicted by the metabolic theory of ecology; mass-specific excretion rates were higher in smaller fishes, but larger fishes contributed more ammonium per individual. When controlling for body size, ammonium excretion rates were greatest among surfperch (Embiotocidae), damselfish (Pomacentridae), and wrasses (Labridae), and the general trophic groups of planktivores and micro-carnivores. When body size differences were considered, the greatest mean excretion rates per individual were observed in larger-bodied species, such as California Sheephead (Semicossyphus pulcher) and Lingcod (Ophiodon elongatus). Empirical estimates of nutrient excretion by fishes, among the first measured in temperate kelp forests, were consistent with those in other aquatic systems. Ultimately, empirically derived excretion rates are the first step to quantifying the relative importance of consumers to nutrient cycling in kelp forest ecosystems.

Karacabey Kıyı Subasar Ormanlarında Kızılağaç ve Dişbudak yeşil yapraklarının biyokimyasal bileşimi üzerinde tuzlu su girişinin etkisi

Coastal forested wetlands provide substantial benefits to society, such as wave attenuation, erosion control, biodiversity support, and carbon sequestration. Many of these unique coastal ecosystems have been drained for various reasons, while those that remain are now threatened by salt water intrusion and sea level rise due to climate change. In this study, we aimed to investigate the effects of soil salinity on the biochemical components of the fresh leaves of alder (Alnus glutinosa L. Gaertn) and ash tree (Fraxinus angustifolia Vahl.) which are the dominant tree species in Karacabey coastal forested wetland next to the Sea of Marmara in Türkiye. For this purpose, fresh leaf and soil samples of alder and ash trees were collected from three zones (Z1: 0-1 km, Z2: 1 to 2 km and Z3: 2 to 3 km) from the inner border (Z3) of the forested wetland to the coastline (Z1) of the Sea of Marmara. The fresh leaf samples were analyzed for photosynthetic pigments (chlorophyll a, chlorophyll b and carotenoids), anthocyanin, xanthophylls, free amino acids, total nitrate, proline, total polyphenols, total soluble tannins, total phenolic compounds, glucose, sucrose and total carbohydrates. The soil samples were analyzed for soil pH, electrical conductivity and soil texture. The results showed that the soil salinity decreased from the coastline (Z1) towards the inner border (Z3). Similarly, mean photosynthetic pigments and anthocyanin, xanthophyll also decreased from the Z1 towards Z3, whereas mean total polyphenols and total soluble tannin concentrations increased for the both tree species. The other biochemical compounds showed either an increase or a decrease according to the tree species. These pioneer results illustrate the important point that biotic or abiotic environment in which tree grows significantly change the specific biochemical components in the fresh leaves of alder and ash trees in the coastal forested wetlands. In turn, these changes may result in variation in nutrient cycling, carbon cycling, and organic matter turnover rates in these forest ecosystems.

Seasonal variation of gross ecosystem productivity of periphyton in three post-mining lakes in the Czech Republic, Europe

We investigated the seasonal variation of gross ecosystem productivity (GEP) of periphyton biomass in three post-mining lakes in the Czech Republic. These lakes were established as part of recultivation efforts after coal mining activities and resulted in a unique series of anthropogenic oligotrophic lakes of gradual successional age. Periphyton is ubiquitous in aquatic habitats and performs numerous environmental functions such as nutrient cycling and self-purifying of aquatic ecosystems. Well-developed periphyton mat can be formed within a few weeks, so it can quickly become the dominant of littoral zone of newly established lakes. In studied post-mining lakes, the highly developed periphytic community covers the littoral zone of each lake to the depth of 2m (Bešta et al. 2022, Konopáčová et al. 2023) Fig. 1. We aimed to shed some new light on the processes controlling the dynamics of primary productivity in oligotrophic lakes. The accurate estimation of primary productivity is crucial for understanding the functioning of aquatic ecosystems, as primary productivity serves as the primary source of autochthonous carbon in these systems. In addition to phytoplankton, periphyton can significantly contribute to primary productivity in littoral zones, known for their high productivity and biodiversity. Conducting in situ measurements provides the most accurate means of inferring the metabolic activity of primary producers in littoral zones. We conducted detailed seasonal in-situ periphyton gross primary production (GPP) measurements in three post-mining lakes with different successional ages (Čapková et al. 2022). GPP and NPP of periphytic biomass were determined using direct in-situ measurement of O2 fluxes. O2 production and consumption were measured over 5 hours of in-situ light and dark gas-tight glass bottle incubation. Bottles were filled with the lake water from the corresponding depth, and a similar amount of periphytic biomass was enclosed Fig. 2. We used the Fibox3 fibre-optic oxygen meter coupled with a PSt3 oxygen sensor (PreSens, Regensburg, DE) to measure changes in O2 concentration. The O2 fluxes were normalized to periphytic biomass in each bottle (measured as total organic carbon). Data were corrected for O2 concentration changes in dark and light gas-tight bottles containing lake water without periphytic communities. This setup enabled us to monitor online oxygen flux, therefore, insights into metabolic activities. The primary productivity was measured in real-time, allowing us to capture the quantitative effect of various environmental drivers on periphyton productivity, i.e. phosphorus concentration and light intensity, as they are known to play significant roles in primary productivity. We showed that the primary production of periphyton mats exhibited seasonal variations, with higher productivity observed in spring compared to other seasons. This observation could be attributed to the occurrence of winter/spring upwelling events and vertical mixing, which resupply nutrients from the deeper strata. Furthermore, the physiological activity of periphyton was strongly influenced by the seasonal changes in light intensity, temperature, and nutrient concentration. We provided the first insight into the seasonal variation of primary productivity of the periphyton assemblage dominating the littoral zone of newly established post-mining lakes. We stress the importance of periphyton in aquatic ecosystems, particularly in anthropogenic oligotrophic lakes.

Disentangling carcass size and climate effects on soil biogeochemistry during decomposition

When an animal dies the decomposition of its carcass releases multiple compounds that become available to soil microbiota altering soil biogeochemistry. This zone of affected substrate is characterized by significant changes to numerous soil biogeochemical parameters including pH, conductivity, microbial respiration rates, dissolved organic carbon (DOC), C/N ratios, carbon and nitrogen stable isotopes (δ13C and δ15N), and major/trace elemental concentrations. Although the effects of animal decomposition on these parameters have been recorded for various organisms and in a variety of ecosystems several knowledge gaps remain, including: the effect of carcass size; and decomposition effects in prairie ecosystems (i.e., semi-arid climates). the effect of carcass size; and decomposition effects in prairie ecosystems (i.e., semi-arid climates). Here, we investigate how soil biogeochemical parameters are affected by the decomposition of a horse carcass (~660 kg) in a prairie ecosystem in comparison to beavers (~18 kg) in a temperate forest. Three parameters were identified as significantly influenced by carcass size: conductivity, DOC, and microbial respiration rate. Average soil conductivity underneath the horse carcass was three to fifteen times higher than control soils and reached a maximum at 1114 ADD, while maximum soil conductivity values were observed after 160 ADD in beaver-associated soils. Maximum DOC concentrations were observed after 160 ADD in beaver-associated soil (67 ± 40 mg C gdw-1) and after 1114 ADD in horse-associated soil (326 ± 115 mg C gdw-1). Microbial respirations rates were both greater in horse-associated soil and longer-lasting compared to beaver-associated soil. Respiration rates were greatest in two of the three horse-associated soils after 1114 ADD (~733 µg CO2-C gdw-1 day-1), which significantly differs compared to beaver-associated soils (300 ± 90 µg CO2-C gdw-1 day-1 at 160 ADD). Taken together, these results demonstrate that larger carcasses result in a greater release of decomposition products, including C, and greater stimulation of soil heterotrophic communities. Other measured biogeochemical indicators of decay suggest a mixed influence due to carcass size and climate, notably δ15N values of the soil, and major element concentrations. Climate was revealed to be more important in controlling changes to pH and gravimetric moisture than carcass size, with baseline soil conditions and type playing critical roles. Additionally, in semi-arid regions such as western South Dakota, the role of wet-dry cycles on carcasses undergoing decomposition may help to explain the pulses observed with C concentrations and C cycling. This study provides the first direct comparison of soil biogeochemistry associated with the decomposition of two different sized taxa decayed in two different climates. Attempting to normalize climate data using ADD was found to be an imperfect system that does not account for all climate variables affecting decomposition. Unravelling patterns in decomposition can better help to constrain nutrient cycling in modern and ancient ecosystems.

Fine‐root turnover and leaf litterfall of Salsola passerina facilitate soil restoration in Alxa steppe desert of northwest China

Nutrient cycling in desert ecosystems is heavily reliant on the fine root turnover and litter decomposition processes of dominant plant species. Based on field investigations and laboratory experiments, we explored fine root production (FRP) and turnover of Salsola passerina in Alxa steppe desert, and assessed fine root and leaf litter input and its correlation with soil C and N stocks, and then compared the variability of soil physicochemical properties at the site below and the interspace of S. passerina canopy. Results showed that fine root biomass dynamics of S. passerina were consistent with soil water content. Annual FRP of S. passerina was 243.3 g m−2 yr−1 and the turnover rate was 2.0 per year. S. passerina contributed 172.2 g C m−2 and 6.8 g N m−2 to soil from its fine root senescence and leaf litter input annually. Compared to the canopy interspace, the soil texture and fertility beneath the shrubs significantly improved, while the soil salinity decreased. The results indicated that the activities of desert shrub growth provided the degraded soil with abundant nutrients through fine root turnover and litter decomposition processes, which promoted soil texture and nutrition heterogeneity at the stand scale, and played an important role in degraded dryland restoration.

Multi-Scale Altitudinal Patterns of Soil and Litter Invertebrate Communities in a Warm Temperate Deciduous Broadleaf Forest

The diversity and spatial patterns of soil invertebrates are the cornerstones for understanding their ecological functions, which are crucial to maintaining nutrient cycling and soil health in forest ecosystems. Based on a continuous altitudinal gradient (1020–1770 m) composed of 119 plots, this study analyzed the spatial patterns of invertebrate communities in temperate mountain forest litter and soil using multi-scale ordination. The results indicate that along the altitudinal gradient, the invertebrate communities in both litter and soil layers exhibit “patches” at a scale of approximately 33 plots that are mainly composed of Mesostigmata and Apterogasterine oribatid mites. In the litter layer, at the 11-plot scale, an aggregation of Onychiuridae is also formed, while in the soil layer, there are “patches” represented by Diadocidiidae at the 33-plot scale. The positive–negative associations among invertebrate taxa also shift between the litter and soil layers, as well as among “patches”. Our study confirms that the richness of invertebrates in temperate-forest litter is higher and forms multi-scale assembly “patches” despite the higher abundance of invertebrates in the soil layer. Future studies should delve deeper into the aggregation mechanisms of these specific taxa and may require higher sampling densities to reveal the multi-scale spatial patterns of soil invertebrates.

Effects of transforming multiple ecosystem types to tree plantations on soil microbial biomass carbon, nitrogen, phosphorus and their ratios in China

Tree plantations (thereafter plantations) is considered to be one of the most common land use changes that may have significant effects on soil microbial biomass, but the broader patterns and underlying drivers remain unclear. Here, we quantified the effects of transforming shrublands, secondary forests, primary forests, grasslands, deserts, and croplands to plantations on the concentrations of soil microbial biomass carbon (MBC), microbial biomass nitrogen (MBN), microbial biomass phosphorus (MBP) and their ratios (i.e., MBC: MBN, MBC:MNP and MBN:MBP) based on 2107 paired observations from 107 studies using meta-analysis across China. We found that (1) transforming grasslands into plantations significantly increased MBC, MBN, and MBP concentrations by 81.1, 75.3, and 65.4 %, respectively, while transforming primary forests to plantations significantly decreased soil MBC, MBN, and MBP concentrations by −29.2 -34.7, and − 50.6 %, respectively; (2) ecosystem transformation effects were seldom affected by plantation type, mycorrhizal association, plantation year, or soil depth; and (3) the impacts of climate, species richness, and soil properties on ecosystem transformation effects depended on former ecosystem type. Overall, our results clearly showed how ecosystem transformation affected soil MBC, MBN, MBP, and MBC:MBN, MBC:MBP, and MBN:MBP ratios, which plays a crucial role in nutrient cycling in ecosystems and evaluate sustainability of forest management.

Litter decomposition and nutrient release are faster under secondary forests than under Chinese fir plantations with forest development

In terrestrial ecosystems, leaf litter is the main source of nutrients returning to the soil. Understanding how litter decomposition responds to stand age is critical for improving predictions of the effects of forest age structure on nutrient availability and cycling in ecosystems. However, the changes in this critical process with stand age remain poorly understood due to the complexity and diversity of litter decomposition patterns and drivers among different stand ages. In this study, we examined the effects of stand age on litter decomposition with two well-replicated age sequences of naturally occurring secondary forests and Chinese fir (Cunninghamia lanceolata) plantations in southern China. Our results showed that the litter decomposition rates in the secondary forests were significantly higher than those in the Chinese fir plantations of the same age, except for 40-year-old forests. The litter decomposition rate of the Chinese fir initially increased and then decreased with stand age, while that of secondary forests gradually decreased. The results of a structural equation model indicated that stand age, litter quality and microbial community were the primary factors driving nutrient litter loss. Overall, these findings are helpful for understanding the effects of stand age on the litter decomposition process and nutrient cycling in plantation and secondary forest ecosystems.

A dataset of litter decomposition residual mass and nutrient concentrations under nitrogen and phosphorus addition in subtropical plantations (2016–2019)

The increase in atmospheric nutrient deposition resulted from human activities and changes of natural factors have a dramatically influence on the ecosystem nutrient cycling. The subtropical plantations in the South of China account for more than 40% of the national plantation area, which have become the central zone of nutrient deposition. Therefore, the scientific understanding of nutrient cycling process in plantations is the basis of coping with global climate changes and ensuring the construction of national ecological civilization. According to the unified specification of Chinese Ecosystem Research Network, and on the basis of the long-term observation of the field plots of Qianyanzhou Ecological Research Station, Jiangxi (referred to as Qianyanzhou Station), we integrated residual mass and nutrient concentrations of leaf and absorptive roots of Pinus massoniana and Schima superba plantations under different treatments (control, lower nitrogen addition, higher nitrogen addition, phosphorus addition, adding both higher nitrogen and phosphorus) from 2016 to 2019. The production and sharing of this dataset can help to provide basic data support for the dynamic study of litter decomposition as well as for the stock of soil carbon pool under the background of global changes. Additionally, it can promote the sustainable development of subtropical plantations.

A dataset of monthly and yearly litterfall production in different succession stages of evergreen broad-leaved forests in Tiantong (2008 – 2018)

Litter production is an important part of the matter cycle of forest ecosystems, which plays an important role in maintaining forest soil fertility and promoting ecosystem nutrient cycling. Additionally, it serves as an important indicator for the quantification of ecosystem function such as forest productivity and carbon balance. The data in the dataset are from two observation plots in Zhejiang Tiantong National Forest Ecosystem National Observation and Research Station. The community succession types in the above two pilots belong to the middle-late stage and mature stage of evergreen broad-leaved forest succession, respectively. The projected area of each plot is 50 m × 50 m. There are 27 litter traps of 0.5 m2 in each plot. We collected and counted the data in terms of litter components, i.e. branches, leaves, flowers (fruits), bark and debris). The dataset includes the monthly and annual production of each component and the total amount of litter in the two plots from 2008 to 2018. The data have been checked against the original paper records, as well as the dynamic trend of data in the same period, so as to ensure data quality control and accuracy assessment. This dataset can provide basic information for understanding the changes of ecosystem structure and function during the succession process of evergreen broad-leaved forests. Moreover, it can also provide data support for studying the impact of regional climate change on the forest ecosystem and the assessment of carbon balance in the zone of evergreen broad-leaved forests.

Interkingdom network analyses reveal microalgae and protostomes as keystone taxa involved in nutrient cycling in large freshwater lake sediment.

Few studies have explored the role of interkingdom interactions between bacteria and microeukaryotes in nutrient cycling in lake ecosystems. We conducted sediment sampling from 40 locations covering Hongze Lake and analyzed their chemical properties. Intra- and interkingdom networks were constructed using 16S and 18S rRNA gene amplicon sequencing. Microeukaryotic intranetworks were more complex in spring than in autumn, while no clear variation in the complexity of bacterial intranetworks was found between autumn and spring. Larger and more complex bacterial-microeukaryotic bipartite networks emerged in spring than in autumn, correlated with lower carbon, nitrogen, and phosphorus levels in spring, likely resulting in intense microbial competition. Bacteria and microeukaryotes played different topological roles in interkingdom networks, with microeukaryotes contributing to the networks' greater complexity. Seven keystone modules were identified in spring and autumn nutrient cycling. Importantly, keystone taxa in these modules belonged to photoautotrophic microalgae or predatory protostomes, indicating that these organisms are key drivers in lake sediment nutrient cycling. Our results suggested that nutrient content variation in autumn and spring changes interkingdom networks' topological structure between bacteria and microeukaryotes. Microalgae and protostomes are essential in freshwater lake nutrient cycling and may be targeted to modulate nutrient cycling in large freshwater ecosystems.

'Phototaxis' in the absence of light? Locomotory patterns in unionid mussels.

Locomotion in benthic invertebrates can strongly affect habitat selection and ecosystem nutrient cycling. In the case of freshwater mussels, the drivers of locomotion are largely unresolved. Our aim was to assess the influence of light presence and intensity on the locomotory behaviour of freshwater mussels in controlled laboratory experiments. The species investigated in our study were Anodonta anatina and Unio pictorum, two widely distributed mussels in European lentic and lotic inland waters. At low algal concentrations, known to be associated with more frequent locomotory activities, we found that both species moved primarily in the absence of light (72.7% of all movements across experiments). However, the movements of both species were directed towards the light source, resembling a net-positive 'phototactic' response but in the absence of light. The distance to the light source, which was negatively correlated to light intensity, had a positive effect on the distance covered in locomotory activities by A. anatina but not by U. pictorum. Intraspecific variation in shell size had no impact on movement distance, indicating that the energetic costs of movement were not a limiting factor. We suggest that the observed movement towards brighter locations helps to enhance food quantity and quality, whilst movement in darkness mitigates predation risks.

Effects of rock lithology and soil nutrients on nitrogen and phosphorus mobility in trees in non-karst and karst forests of southwest China

The primary productivity of terrestrial plants is widely limited by nitrogen (N) and phosphorus (P), and the mobility of N and P in plants is the key to predicting plant growth and development. Non-karst and karst forests soil have different nutrient supply capacities due to the difference in soil parent material, but the effect mechanism of the two soil nutrient conditions on the N and P mobility process of trees remains unclear. In this study, forests dominated by three typical tree species, Eucalyptus maideni, Pinus yunnanensis, and Quercus franchetii were selected as the research objects in non-karst and karst areas of southwest China to investigate the effects of soil nutrient conditions on plants’ N and P foraging, transportation and resorption. The results showed that the rock lithology had significant effects on the soil nutrients, plants’ N and P foraging, transportation, and resorption. The soil total N and P concentrations, soil organic carbon concentration, and pH were higher in karst forests than those in the non-karst forests, but the green leaves N and P concentrations exhibited opposite characteristics. The root foraging potential for N and P in non-karst forests was significantly higher than that in karst forests. The N resorption efficiency of trees in karst forests was higher than that in non-karst forests, but the P resorption efficiency was lower than that in non-karst forests. The trade-offs of foraging, transportation and resorption of trees were adjusted according to changes in nutrient conditions, but the trade-offs of the three processes were not continuous in non-karst and karst forests. Compared with non-karst forests, the decreased degree of root nutrient foraging potential in karst forests was greater than the transportation factor and resorption efficiency. The slow-growing Quercus franchetii among the three typical forests showed better adaptability to foraging, transportation, and resorption of N and P in karst areas. The results revealed the response of different forests’ N and P mobility patterns of trees to different nutrient conditions in non-karst and karst areas, which was helpful to improve the prediction and mechanistic understanding of nutrient cycling in local forest ecosystems.

Orchid Diversity at Three Elevations in the Mountain Sandstone Plateaus of the Cordillera del CóndorEcuador

Orchids comprise one of the largest families of flowering plants and have important roles in the total biomass, water balance, and nutrient cycling of tropical ecosystems; however, they are also one of the most endangered plant taxa. Because their diversity is strongly coupled to environmental factors, we hypothesize that local elevation can affect the diversity of these organisms. The purpose of this research was to compare the orchid species diversity at 1200, 1400, and 1700 m of elevation, corresponding to a sandstone plateau of the Cordillera del Cóndor that hosts a great orchid diversity. For each elevation, three plots of 0.1 ha were established. Each plot was subdivided into 25 subplots, and 8 were randomly selected, wherein all orchid species were counted and identified. The results obtained revealed the existence of 119 species belonging to 54 genera and a total of 867 individuals. The greatest diversity of species was found at an elevation of 1700 with 63 species, followed by 1400 m with 52 species, with the least diversity at an elevation of 1200 m with 39 species. Orchid composition differed significantly among the three elevations related to more humidity at higher elevations (e.g., 1700 m). More importantly, twenty-one species were the best candidate indicators of environmental conditions (e.g., Maxillaria grayi, Elleanthus oliganthus, Maxillaria mapiriensis, Stelis pittieri, Stelis ortegae) in this region. We conclude that orchid communities in sandstone plateau forests in the Shagmi Range of the Cordillera del Cóndor are mainly limited by elevation.

In situ method for the determination of nutrient acquisition and its hormonal regulation in the spiral valve of two chondrichthyan fishes.

Chondrichthyans play an important role in nutrient cycling of many marine ecosystems, yet little is known about their nutritional physiology particularly relating to nutrient acquisition in the spiral valve intestine. This unique organ poses challenges for examining nutrient transport physiology using traditional reductionist methods owing to its scroll-like morphology. Thus, we established a method for the characterization of nutrient uptake rates in two representative chondrichthyans, the Pacific spiny dogfish (Squalus suckleyi) and the Pacific spotted ratfish (Hydrolagus colliei). We validated a dual-cannulation method wherein perfusate was circulated through the vasculature of the spiral valve via the anterior and posterior intestinal arteries, and [14C]glucose or [3H]oleic acid was accumulated from the static spiral valve lumen into the anterior and posterior intestinal veins. Radiotracer accumulated at a stable rate in the venous effluent in comparison with measures of mucosal disappearance. Interestingly, similar anterior and posterior glucose uptake was observed in dogfish, yet significantly more oleic acid was accumulated in the posterior veins of ratfish. Further validation of the preparation in dogfish demonstrated sodium dependence of glucose transport as well as an effect of bovine insulin administration to the arterial circulation. Each of these manipulations resulted in significant differences in glucose handling between the anterior and posterior veins, suggestive of heretofore unknown heterogenous functions along the intestine. This preparation demonstrates a new and reliable method for the measurement of nutrient acquisition and regulation thereof in a unique digestive organ. Furthermore, it presents avenues for investigation of differential functional along the spiral valve.NEW & NOTEWORTHY We describe a novel dual cannulation method for investigating radiolabeled nutrient uptake from a unique organ, the spiral valve. Furthermore, we identify functional differences in nutrient transport along the length of the spiral valve which consists of a homogenous gross morphology. Finally, this method reveals a useful way in which to manipulate the arterial supply to better understand postprandial physiology as it varies with metabolites and endocrine factors.