Nitrogen ecophysiology of Heron Island, a subtropical coral cay of the Great Barrier Reef, Australia.

Coral cays form part of the Australian Great Barrier Reef. Coral cays with high densities of seabirds are areas of extreme nitrogen (N) enrichment with deposition rates of up to 1000 kg N ha y. The ways in which N sources are utilised by coral cay plants, N is distributed within the cay, and whether or not seabird-derived N moves from cay to surrounding marine environments were investigated.

Transport, storage and mobilization of nitrogen by trees and shrubs in the wet/dry tropics of northern Australia.

Xylem sap from woody species in the wet/dry tropics of northern Australia was analyzed for N compounds. At the peak of the dry season, arginine was the main N compound in sap of most species of woodlands and deciduous monsoon forest. In the wet season, a marked change occurred with amides becoming the main sap N constituents of most species.

Can the nitrogenous composition of xylem sap be used to assess salinity stress in Casuarina glauca?

It is predicted that dryland salinity will affect up to 17 Mha of the Australian landscape by 2050, and therefore, monitoring the health of tree plantings and remnant native vegetation in saline areas is increasingly important. Casuarina glauca Sieber ex Spreng. has considerable salinity tolerance and is commonly planted in areas with a shallow, saline water table.

Impact of point source pollution on nitrogen isotope signatures (δN) of vegetation in SE Brazil.

This study presents novel evidence that N natural abundance can be used as a robust indicator to detect pollutant nitrogen in natural plant communities. Vegetation from the heavily polluted industrial area of Cubatão in São Paulo State, SE Brazil, was strongly N depleted compared to plants at remote sites. Historic herbarium samples from Cubatão were significantly less N depleted than extant plants, indicating that N depletion of vegetation is associated with present-day nitrogen pollution in Cubatão.

N natural abundance of fossil peat reflects the influence of animal-derived nitrogen on vegetation.

δN signatures of fossil peat were used to interpret past ecosystem processes on tectonically active subantarctic Macquarie Island. By comparing past vegetation reconstructed from the fossil record with present-day vegetation analogues, our evidence strongly suggests that changes in the δN signatures of fossil peat at this location reflect mainly past changes in the proportion of plant nitrogen derived from animal sources. Associated with uplift above sea level over the past 8,500 years, fossil records in two peat deposits on the island chronicle a change from coastal vegetation with fur and elephant seal disturbance to the existing inland herbfield.

Subantarctic Macquarie Island - a model ecosystem for studying animal-derived nitrogen sources using N natural abundance.

Plants collected from diverse sites on subantarctic Macquarie Island varied by up to 30‰ in their leaf δN values. N natural abundance of plants, soils, animal excrement and atmospheric ammonia suggest that the majority of nitrogen utilised by plants growing in the vicinity of animal colonies or burrows is animal-derived. Plants growing near scavengers and animal higher in the food chain had highly enriched δN values (mean = 12.

Root adaptation and nitrogen source acquisition in natural ecosystems.

The capacity for nitrate reduction, as measured by nitrate reductase activity (NRA), was generally low for a range of plant communities in Australia (coastal heathland, rainforest, savanna woodland, monsoon forest, mangrove, open Eucalyptus forest, coral cay open forest) and only a loose relationship existed between NRA and leaf nitrogen concentration. This suggests that nitrate ions are not the sole nitrogen source in these communities. Based on (15)N labeling experiments, we found a range of tree species exhibiting a pronounced preference for uptake of ammonium over nitrate.

The deposition of atmospheric ammonia and its effects on plants.

Across Europe, total nitrogen deposition is increasing and, of this total, atmospheric ammonia can contribute up to 50-80%. Average deposition of ammonia in the UK is likely to be around 15-20 kg ha yr , while in The Netherlands, which has some of the highest rates of deposition, this value is likely to be between 40 and 50 kg ha yr . It is argued that because of the processes of assimilation and nitrification this ammonia is an acidifying pollutant.

Photosynthesis in relation to leaf nitrogen and phosphorus content in Zimbabwean trees.

CO assimilation in relation to light intensity and the relationship between leaf nitrogen and phosphorus concentrations and CO assimilation in 14 species of ecologically important Zimbabwean trees were examined. Eight of the species are members of the Fabaceae (Leguminosae). In the majority of Zimbabwean climax woodlands, the dominant trees are non-nodulating members of the sub-family Caesalpinioideae.