Nutrient imbalances in agricultural practices

Posted by Michelle:

I came across a policy discussion relating to nutrients (primarily N) in agricultural processes. The original article appeared in Science in June, with responses in the most recent issue (30 October 2009). The idea of reclaiming N in human waste for agriculture is not new, but obviously a topic that makes people uncomfortable. I had not realized that in urban centers alone, the N in human waste is equal to the amount of N fixed for agricultural purposes. What follows then is the problem of distribution, in other words, how do we get urban N to agricultural areas? Talk about recycling!

http://www.sciencemag.org/cgi/content/full/326/5953/665-a?sa_campaign=Email/toc/30-October-2009/10.1126/science.326_665a

Stoichiometry jobs! (well, RA-ships actually)

Posted by Jim:

I don’t usually do job ads on the blog, but this came in from Amy Rosemond (Univ of Georgia) and I thought I would post it here.

xxxxxx

Five graduate student assistantships (3 Ph.D. and 2 M.S.) are available as part of a newly funded project examining the responses of detritus-based stream food webs to concentrations and ratios of dissolved nitrogen and phosphorus. Two Ph.D. positions will be based at the University of Georgia and will focus on detrital carbon dynamics and responses of predatory salamanders, respectively. A third Ph.D. position will be based at the University of Alabama and will examine macroinvertebrate food web responses. Both M.S. positions will be based at Coastal Carolina University and will focus on microbial responses to N:P gradients using field and laboratory experiments. All fieldwork will be based at the Coweeta Long term Ecological Research site in Otto, North Carolina. We are looking for students with a holistic view of ecological ramifications of nutrient enrichment, strong interest in integrating a stoichiometric perspective across taxonomic groups, significant research experience and demonstrated communication skills. The positions will start in Summer or Fall 2010, with microbial positions starting as early as January 2010. The successful candidates will receive full tuition waivers and competitive stipends. For more information, contact Amy Rosemond (rosemond@uga.edu) or John Maerz (jmaerz@warnell.uga.edu) for the UGA positions, Jon Benstead (jbenstead@bama.ua.edu) for the UA position, or Vlad Gulis (vgulis@coastal.edu) for the two CCU positions.

 

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Genetic basis of P sensitivity in Daphnia

Wiley InterScience :: JOURNALS :: Ecology Letters.

Posted by Jim:

Our long-time collaborators Puni Jeysasingh, Bob Sterner, and Larry Weider have published a nifty paper showing how the genotype for Pgi (a gene controlling phosphoglucose isomerase, an enzyme involved in energy processing) is closely linked to an animal’s sensitivity to poor stoichiometric food quality (high C:P in algae).  Pgi homozygotes outcompete pgi heterozygotes because they are energetically INEFFICIENT, which is an advantage when food has high C:P ratio (C in excess).  The discovery is quite remarkable, as Pgi has long been used as some kind of “neutral” marker for identifying different populations of Daphnia.  So, it’s quite a coincidence that Pgi seems to be closely involved in how Daphnia copes with poor food quality.

Members of the Elser group should read this paper immediately.

Protected: Agouron Nitrogen meeting (day 4)

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Ecology and global change in alpine regions

Posted by Michelle:

I attended the International School on Alpine Ecology and Global Change hosted by the University of Innsbruck. There were talks by 21 researchers from 7 institutions in Europe and North America. The conference covered topics in both terrestrial and aquatic ecology. Participants included 20 graduate students and post docs from difference institutions in Europe, Asia, North and South America. The conference was held two hours outside of Innsbruck, Austria in the alpine ski village of Obergurgl. The facility was amazing; lunch and dinner consisted of 3 to 5 courses! I feel quite spoiled…

While the researcher presentations were all interesting, I want to share a few take-aways:

Christian Körner, Switzerland:
Many alpine plants respond more to photoperiod than to temperature. There has been must discussion that plants are limited by the opportunity to “escape” changes in temperature or solar radiation by colonizing higher in mountains. Such limitations will not be a significant problem for plants because microclimates are so highly variable within small spatial areas and because of the opportunity for plants to colonize laterally (e.g. north facing slopes) around mountains. The greatest risk to alpine plants is continued land use (mainly grazing) practices.

Richard Bardgett, UK:
Large herbivores (e.g. moose, caribou, cattle) can alter ecosystem productivity through selective grazing and fecal return. Removal of deer for example, led to shift from N to P limitation in regenerating woodlands.

David Livingstone, Switzerland:
Air temperatures in the Alps are increasing at a rate 2x that of the global mean. Such increases in regional will alter circulation patterns in lakes by increasing the thermal stability (differences in temperatures between the epilimnion and hypolimnion). This may shift dimictic lakes to monomictic lakes

Ruben Sommaruga, Austria:
In high elevation clear lakes, many organisms obtain screening compounds for protection against UV radiation. While phytoplankton and cyanobacteria can synthesize these compounds, zooplankton obtain them through their diet. There are 2 main types of UV screening pigments: carotinoids and mycosporine-like amino acids (MAA). There is evidence that increases in available N (such as through atmospheric deposition) may increase MAA production as a UV screening mechanism. This may benefit zooplankton because unlike carotinoids, MAA is colorless and may help the zooplankton evade predation.

Rolf Vinebrooke, Canada:
In mesocosm experiments, water warming treatments suppressed zooplankton abundance, especially in daphnia-dominated systems. This treatment did not change total phytoplankton biomass, but resulted in a shift in the community composition to less edible species (i.e. higher C:N, C:P). Interestingly, zooplankton also responded negatively to increases in DOC, perhaps do to a “toxic” effect of aromatic carbon compounds.

The conference ended with a day-long hike in the Tyrolean Alps along the outflow of the Rotmoos glacier. There were demonstrations of equipment to measure water potential and transpiration of plants. We also gathered and compared invertebrates between a glacial and mountain stream.

If you are interested in hearing more about the conference, let me know.

Glacial outflow from Rotmoos

Chemostat Update:

Posted by Amisha:

Christie and I worked on the alkaline phoshatase (AP) assay and here’s the data from our first trial. We tested AP activity of Synechocystis sp. PCC6803 cells and spent medium growing at different N:P ratios by measuring p-nitrophenol production from p-nitrophenyl phosphate. Our P-limited cultures (N:P of 53) exhibited the highest level of AP activity (great!), followed by the cultures growing at an N:P of 16. Iron-limited (N:P of 16 with 100 times less Fe than the other cultures) and N-limited (N:P of eight) cultures had very little cellular or extracellular AP activity.

Daphnia, Mutations, and Diseases.. oh my!

Posted by Becky:

Here’s a spiffy article I came across last week all the way from the University of Toronto. I can’t seem to link the article directly, so sorry about that!

The effect of pathogens on selection against deleterious mutations in Drosophila melanogaster

J A D E N E A . Y O U N G , C H R I S T O P H E R P . Y O U R T H & A N E I L F . A G R A W A L

Department of Ecology & Evolutionary Biology, University of Toronto, Toronto, ON, Canada

Abstract

In natural populations, fitness is reduced by both deleterious mutations and parasites. Few studies have examined interactions between these two factors, particularly at the level of individual genes. We examined how the presence of a bacterial pathogen, Pseudomonas aeruginosa, affected the selection against each of eight deleterious mutations in Drosophila melanogaster. We found that mutations tended to become more deleterious in the presence of disease. This increase in the average selection was primarily due to three genes with the

remainder showing little evidence of change.

( Young et al.)