Experimental nitrogen and phosphorus enrichment stimulates multiple trophic levels of algal and detrital-based food webs: a global meta-analysis from streams and rivers

Anthropogenic increases in nitrogen (N) and phosphorus (P) concentrations can strongly influence the structure and function of ecosystems. Even though lotic ecosystems receive cumulative inputs of nutrients applied to and deposited on land, no comprehensive assessment has quantified nutrient-enrichment effects within streams and rivers. We conducted a meta-analysis of published studies that experimentally increased concentrations of N and/or P in streams and rivers to examine how enrichment alters ecosystem structure (state: primary producer and consumer biomass and abundance) and function (rate: primary production, leaf breakdown rates, metabolism) at multiple trophic levels (primary producer, microbial heterotroph, primary and secondary consumers, and integrated ecosystem). Our synthesis included 184 studies, 885 experiments, and 3497 biotic responses to nutrient enrichment. We documented widespread increases in organismal biomass and abundance (mean response = +48%) and rates of ecosystem processes (+54%) to enrichment across multiple trophic levels, with no large differences in responses among trophic levels or between autotrophic or heterotrophic food-web pathways. Responses to nutrient enrichment varied with the nutrient added (N, P, or both) depending on rate versus state variable and experiment type, and were greater in flume and whole-stream experiments than in experiments using nutrient-diffusing substrata. Generally, nutrient-enrichment effects also increased with water temperature and light, and decreased under elevated ambient concentrations of inorganic N and/or P. Overall, increased concentrations of N and/or P altered multiple food-web pathways and trophic levels in lotic ecosystems. Our results indicate that preservation or restoration of biodiversity and ecosystem functions of streams and rivers requires management of nutrient inputs and consideration of multiple trophic pathways.     

Diversity of axonal growth-promoting receptors and regulation of their function.

Growth-promoting receptors for substrate-bound molecules are usually found to belong to the integrin, immunoglobulin, or cadherin families of glycoproteins. New members of each of these families have been identified in the past year, and advances have been made in our understanding of their functional regulation.     

Abundance and size change of Hannaea baicalensis in Lake Baikal

Hannaea baicalensis is a benthic pennate diatom that predominantly grows at depths of less than a metre attached to rocks and filamentous algae in Lake Baikal, Russia. This narrow zone at the edge of the lake is subject to frequent wave action and lake level fluctuations, which combine with other factors to affect seasonal abundance. During ice cover from January to May in 2008, when lake levels decreased from 42 to 14 cm above datum, H. baicalensis cell abundance remained low (0.39 × 10⁶ cells cm^–2). The main period of net cell increase occurred in autumn, when there was a period of stable lake level (±10 cm changes in water depth) that coincided with the return of nutrients during autumn overturn. Cell abundance reached 1.52 × 10⁶ cells cm^–2 on 31 October. Alongside the changes in abundance, cyclic size changes in cell apical lengths were found (40 to 144 µm), which were associated with timing of the length of the life cycle. Size decline occurred in both spring and autumn, with an average decrease in apical length of 36 µm per year. It took two years for the mean apical length of a single cohort to decrease from 128 µm to 56 µm, which was then below the threshold (< 65 µm) for initiation of size regeneration.     

Associations between Green Space and Health in English Cities: An Ecological,Cross-Sectional Study

Green space has been identified as a modifiable feature of the urban environment and associations with physiological and psychological health have been reported at the local level. This study aims to assess whether these associations between health and green space are transferable to a larger scale, with English cities as the unit of analysis. We used an ecological, cross-sectional study design. We classified satellite-based land cover data to quantify green space coverage for the 50 largest cities in England. We assessed associations between city green space coverage with risk of death from all causes, cardiovascular disease, lung cancer and suicide between 2002 and 2009 using Poisson regression with random effect. After adjustment for age, income deprivation and air pollution, we found that at the city level the risk of death from all causes and a priori selected causes, for men and women, did not significantly differ between the greenest and least green cities. These findings suggest that the local health effects of urban green space observed at the neighbourhood level in some studies do not transfer to the city level. Further work is needed to establish how urban residents interact with local green space, in order to ascertain the most relevant measures of green space.     

Influence of fulvic acid on bacteriophage adsorption and complexation in soil.

The effect of fulvic acid, the major fraction of natural soluble organic matter, on the adsorption of MS2 bacteriophage to soil was investigated in controlled laboratory experiments. Batch experiments together with scanning electron microscopy-energy-dispersive X-ray analysis showed that fulvic acid complexed phage, which prevented its adsorption to soil. Phage strongly adsorbed to soil in the absence of fulvic acid. Phage which was complexed with fulvic acid was not irreversibly inactivated and could become viable under proper conditions, illustrating the importance of assay and elution procedures in the recovery of virus from aqueous solutions.     

Xylem pressure potential and chlorophyll fluorescence as indicators of freezing survival in black locust and Western hemlock seedlings

Xylem pressure potential was determined using the Scholander pressure chamber on stems of cold hardened and non-hardened black locust (Robinia pseudoacacia L.) seedlings following freezing to various nonlethal and lethal temperatures and subsequent thawing. Correlation was found between immediate xylem pressure potential and long-term seedling survival. Chlorophyll fluorescence transients were monitored using needles of western hemlock (Tsuga heterophylla (Raf.) Sarg.) seedlings following freezing to various non-lethal and lethal temperatures and subsequent thawing. Immediate and repeatable differences in fluorescence transients correlated with long-term seedling survival. Methodology is described and correlations discussed relative to using either chlorophyll fluorescence or xylem pressure potential as an immediate indicator of long-term freezing survival in woody plant seedlings.     

Neotropical tadpoles influence stream benthos: evidence for the ecological consequences of decline in amphibian populations

1. Few studies have assessed the role of tadpoles in tropical streams, although they are often abundant and conspicuous components of these systems. Moreover, amphibian populations are declining around the globe, particularly stream‐dwelling species in tropical uplands, and the ecological consequences of these losses are not understood. 2. We chose a stream in the central Panamanian highlands, which has an intact fauna of stream‐breeding anurans, to examine the ecological consequences of amphibian losses. This site differs dramatically from sites in nearby western Panama and Costa Rica where anuran diversity and abundance have declined greatly in the last two decades. 3. We used an underwater electric field to create tadpole exclosures in runs, so that we could evaluate their influence on sediment dynamics and the abundance and community structure of algae and aquatic insects. Tadpoles reduced total sediments and both organic and inorganic fractions on substrata. Tadpoles also reduced algal abundance on substrata by approximately 50% and decreased algal biovolume. Gut content analyses showed that tadpoles consumed algae and sediments and we could see that algae and sediments were also displaced through bioturbation. 4. Atelopus zeteki, Rana warszewitschii, and Hyla spp. were the dominant larval anurans responsible for the effects observed. Visual surveys indicated that the densities of these taxa ranged from 23 (R. warszewitschii and Hyla spp. combined) to 43 m^?2 (A. zeteki) in runs. 5. The abundance of baetid mayflies was lower in tadpole exclosures compared with controls, and this was attributed to tadpoles facilitating mayfly feeding by removing sediments and exposing underlying periphyton. 6. Tadpoles affect the abundance and diversity of basal resources and other primary consumers, and thus influence food web dynamics and energy flow in these tropical streams. Catastrophic decline in stream‐breeding anuran populations will influence the structure and function of neotropical stream ecosystems.     

Inhibition of tyrosine phosphorylation potentiates substrate-induced neurite growth.

Protein tyrosine kinases (PTKs) have major roles in signal transduction and growth control. There are several lines of evidence implicating PTKs in the regulation of axon growth, and this has led to the suggestion that they are centrally involved in the transduction of neuronal growth signals. To test this idea, we assayed the effect of the compounds genistein and lavendustin, specific inhibitors of PTKs, on neurite growth. We find that genistein greatly reduces phosphotyrosine in neurons, as expected from its action on other cells. Surprisingly, administration of genistein or lavendustin potentiated substrate-induced neurite growth in at least several different neuronal types. Stimulation of neurite growth by genistein was abolished by vanadate, providing additional evidence that inhibition of PTKs is responsible for this effect. The potentiation of growth is rather general, in that it occurs on several different extracellular matrix substrates and on two different cell adhesion molecules. Both the initiation of neurite growth and the rate of neurite elongation appear to be potentiated. Our results do not provide evidence for models of substrate-induced signal transduction that involve PTKs as a positive and necessary step, but suggest that such kinases play a regulatory role in neurite elongation.