We aim to establish how DIN:TP ratios influence biomass, composition and elemental stoichiometry of phyto- and zooplankton communities, and to determine nutrient limiting factors of phytoplankton and consumer-driven nutrient regeneration responses.
Ecological effects of glacial dust deposition on remote Arctic lakes
We compare the ecological effects of glacially-derived dust on lakes along a gradient of dust deposition rates in SW Greenland and assess its role in regional carbon and aquatic community dynamics at a range of temporal (annual to centennial) and spatial scales (lake to regional landscape).
Impacts of climate warming and brownification on trophic dynamics and food webs of northern lakes
Effect of herbivory and climate on tundra vegetation
We will study the interactive effect of herbivores and climate on plant community composition and plant traits using two long term field experiments in the Fennoscandian tundra. We aim to improve the interpretation of the driving forces behind changes in NDVI observed in satellite images, and clarify the potential of herbivores to influence the climate via changes in the albedo of the tundra.
Effects of altered snow conditions on herbivory in an arctic ecosystem
Effects of altered snow conditions on herbivory in an arctic ecosystem
Copyright Gesche Blume-Wherry 2012
Project Summary
By the end of the century, an increase of global average temperatures with 1.4 - 5.8° is predicted as a result from increased greenhouse gas levels in the athmosphere. The climate scenarios for northern latitudes predict not only higher temperatures but also higher precipitation that may even create a greater and prolonged snow cover in some areas. The profound changes in temperature and snow conditions may change plant community composition and ecosystem functioning, and produce positive or negative feedbacks to climate via changes in the carbon cycle. Herbivory is a key process for the function of arctic ecosystems, as herbivores alter plant community composition, plant chemical composition, nutrient cycling, primary production and carbon storage.
The goal of this project is to study how altered snow conditions will affect plant-herbivore interactions in arctic ecosystems. We will thus study herbivory and plant chemical composition in a snow manipulation experiment along a natural gradient in snow cover. A combination of plant chemical analyses and ecological studies of herbivory in the field is essential in order to understand these complex interactions. We can, by running experiments along natural gradients, avoid many weaknesses commonly associated with both experiments and descriptive studies.
Effects of reindeer on plant and soil nutrient stoichiometry in Arctic tundra
Effects of reindeer on plant and soil nutrient stoichiometry in Arctic tundra
Project Summary
Herbivores directly and indirectly influence the structure and function of ecosystems throughout the world. Present conceptual models predict that herbivores have a positive effect on nutrient availability and primary productivity in nutrient rich environments and a negative one in nutrient poor environments. However, a recent meta-analysis did not support a positive relationship between plant nutrient availability and the effect of herbivores on nitrogen cycling in several grassland ecosystems. The reason for the shortcoming of present theories could be that they fail to incorporate the complex interactions regulating the release of nutrients from the soil organic matter by microbial decomposers.
In order to assess this shortcoming, a new stoichiometric explicit model of the nutrition of herbivores, plants and microbes was designed. In contrast to previous models, it includes delayed composition and stoichiometric constraints on decomposers similar to what we find in terrestrial ecosystems.
This project will focus on 1) testing predictions of the model in a reindeer-dominated tundra ecosystem and 2) further developing the model by adding key processes that operate in northern ecosystems (e.g. uptake of organic nutrients by plants, herbivore-mediated changes in plant community composition).
Collaborators
Johan Olofsson, Umeå University
Mehdi Cherif, Umeå University
Funding
The Kempe Foundation
Microbial use of phosphorus in soils
Microbial use of phosphorus in soils
Project Summary
Globally, phosphorus (P) together with nitrogen (N) is the most important nutrient element limiting plant growth. In boreal forest ecosystems, P limitation is found in groundwater discharge areas and recent studies also indicate that many alpine ecosystems may be P limited. In this project I will study microbial strategies to utilize phosphate and organophosphorus compounds and the effect of surface sorption. One method that will be used is measurement of microbial respiration using a respicond. This is a microbial bioassay for studying the availability of P to microorganisms.
Ongoing studies
In the first project we sampled six different South African forest soils. The soils were selected to represent a broad range of soil properties, especially concerning aluminium, iron and organic carbon content. The respiration results will be compared to the amount of P in the soil to show how much of the total P pool that microorganisms can utilise and how the microbial availability is affected by iron and aluminium concentrations in the soil. This way we can compare in detail how different soil properties interact with microbial available P determined in the bioassay.
In the second ongoing study we sampled 30 islands in Lake Hornavan and Lake Uddjaur, situated close to Arjeplog in the boreal forest of Northern Sweden. The time since the last major fire vary between the islands and the wildfires form a chronosequence which is closely correlated to island size and vegetation succession (Wardle et al. 1997). Earlier results indicate increasing phosphorus limitation over time since the last fire (Wardle et al, 2004). During this study we will compare the different P and N pools with microbial growth kinetics in relation to island size and humus depth.
