The impact of climate change is predicted to be particularly intense in polar regions. Warmer and wetter conditions in the Arctic, where extensive moss dominated habitats are found, could lead to melting of permafrost and an increase in moss growth whilst forests decline. Our existing work has included developing innovative models which use the stable isotope composition of organic matter to provide information about moss growth. This work incorporated both moss preserved for thousands of years in Antarctic peat-moss banks, and desiccation-tolerant mosses that commonly grow on roofs and paths and are rapidly activated following a rain shower. Our previous work has shown that the stable isotope composition of carbon provides a reliable indicator of moss growing season, and the impact of climate change. However other naturally-occurring stable isotope signals in water (e.g 18O in water), associated with precipitation inputs and water vapour exchange, have until now been less well defined as markers of evaporative demand. In this proposal, we will increase our understanding of moss growth dynamics to include how plants respond to different evaporative conditions, how different types of moss grow, what conditions are best for the fixation of carbon dioxide from the atmosphere and growth through the synthesis of organic matter. These developments in moss physiology will be integrated with local weather conditions in models of moss growth that can be applied across large areas to predict periods of plant growth. We will carry out laboratory experiments in which moss growth is manipulated, monitored and measured, using isotope labels and growth responses under different temperature, humidity and drying regimes. We will work on moss species that grow in a range of habitats from wet bog Sphagnums, through hummock forming Polytrichales to desiccation tolerant Syntrichia. At the field scale, the same mosses will be regularly monitored in their natural environment, testing how the experimentally determined dynamics apply within an ecologically relevant setting. The combination of lab and field measurements will firstly allow us to determine the controls on moss organic matter 18O composition as climatic conditions vary. Secondly, remote sensing field measurements will be made from a distance of several metres using newly developed LIFT (laser induced fluouresence transient) technology. By understanding the link between moss growth dynamics and photosynthetic activation over this larger spatial scale we will establish a baseline that will allow remote sensing methodologies, such as measurements from aeroplanes and satellites, to be used to monitor moss performance in the future.

This project will advance our ability to quantify the influence of phosphorus limitation and temperature on plant tissue respiration. The carbon balance of an organism and of an ecosystem is strongly dependent on the balance between photosynthesis and respiration. Globally, respiration on land is at present very slightly smaller than photosynthesis, meaning that terrestrial ecosystems are thought to be a 'sink' for atmospheric carbon dioxide, slowing the continual rise in carbon dioxide concentration in the atmosphere. A large fraction of the total respiration from land is thought to come from trees, so understanding what determines plant respiration is central to understanding how the terrestrial component of the Earth system works. However, despite its importance, only a limited amount of data are available to help us quantify plant respiration over large regions of the world. For example, although we know that the most important nutrients for plant growth (nitrogen and phosphorus) limit plant metabolism, we have almost no information on how phosphorus deficiency limits plant respiration, and hence the carbon balance. We also know only a little about how plant respiration responds to temperature: currently our global models of terrestrial ecosystems make large assumptions about this that may be wrong. When we consider that: (i) 30% of the global land surface may be phosphorus-deficient; (ii) the global phosphorus supply may seriously decline in under 100 years; and (iii) global climatic warming is likely to increase plant respiration this century (but by how much we don't know), there is clearly a strong and urgent need to address this issue. We will make measurements of respiration on a wide range of plant species. We will first use controlled-environment chambers to control the supply of nutrients to plants. We will then couple this with field measurements made in selected forested regions where phosphorus and nitrogen are differentially limiting, in order to compare the data from our experimental work to real ecosystems. The choice of our fieldsites in tropical South America and New Zealand makes use of existing knowledge about likely phosphorus limitations and will allow us to also address the issue of how biodiversity affects the phosphorus-respiration relationship. Finally we will analyse our data to enable us to incorporate our findings into mathematical models used to calculate how the land surface and our climate interact. Our project will enable us: (i) to quantify how phosphorus deficiency affects respiration; (ii) to quantify the influence of phosphorus deficiency on the temperature dependence of plant respiration. We will be able to link our results to existing work on the relationship between plant tissue metabolism and nitrogen concentration, and to incorporate the results into site-specific and global modelling frameworks. The project is highly cost efficient to NERC, making use of international facilities and project partner time supplied at zero cost to this project. This work will also link directly into existing research programmes funded by NERC of which the project investigators are already a part. The project will fill a signficant gap in our understanding of global ecology and the functioning of the Earth system.