Hippuric acid and benzoic acid inhibition of urine derived N2O emissions from soil

Atmospheric concentrations of the greenhouse gas nitrous oxide (N₂O) have continued to rise since the advent of the industrial era, largely because of the increase in agricultural land use. The urine deposited by grazing ruminant animals is a major global source of agricultural N₂O. With the first commitment period for reducing greenhouse gas emissions under the Kyoto Protocol now underway, mitigation options for ruminant urine N₂O emissions are urgently needed. Recent studies showed that increasing the urinary concentration of the minor urine constituent hippuric acid resulted in reduced emissions of N₂O from a sandy soil treated with synthetic bovine urine, due to a reduction in denitrification. A similar effect was seen when benzoic acid, a product of hippuric acid hydrolysis, was used. This current laboratory experiment aimed to investigate these effects using real cow urine for the first time. Increased concentrations of hippuric acid or benzoic acid in the urine led to reduction of N₂O emissions by 65% (from 17% to <6% N applied), with no difference between the two acid treatments. Ammonia volatilization did not increase significantly with increased hippuric acid or benzoic acid concentrations in the urine applied. Therefore, there was a net reduction in gaseous N loss from the soil with higher urinary concentrations of both hippuric acid and benzoic acid. The results show that elevating hippuric acid in the urine had a marked negative effect on both nitrification and denitrification rates and on subsequent N₂O fluxes. This study indicates the potential for developing a novel mitigation strategy based on manipulation of urine composition through ruminant diet.     

Relationships between abundance and body size: where do tourists fit?

Abstract.

• 1 The possible effects of the inclusion of ‘tourist’ species have been the cause of some concern in investigations of interspecific relationships between abundance and body size.
• 2 Data for adult beetles (Coleoptera) from oak trees in Britain are used to investigate the relationship of abundance to body size when tourists are and are not included.
• 3 For this particular assemblage, tourists do not fundamentally alter the basic statistics of the relationship between abundance and body size. However, they are not a random sample of the beetle assemblage. They have lower abundances and are also of smaller body size than other species.

     

The distribution of mammal body masses

How the diversity of organisms relates to their body sizes has long been a question of interest to biologists, an interest that has grown as data have become available from an increasing number of taxa at ever larger spatial scales. Here, we examine the form of this relationship for a large proportion of the global placental mammal fauna. In common with other large-scale assemblages, the frequency distribution of mammal body masses is strongly right-skewed, even after logarithmic transformation. The modal body mass is slightly lower than predicted by a recent energetic fitness model, but the exact modal value depends on the taxonomic inclusivity of the analyses. Moreover, threatened species are larger bodied than expected by chance, suggesting that extinct species may also have been so. Therefore, the loss of large-bodied species from the global mammalian fauna could potentially have lowered the mode of the distribution. However, this loss must be balanced against evidence that most mammal species for which body mass data were not available for our analyses are small-bodied, which may in turn raise the apparent mode of the distribution. Clearly, tests of explanations for patterns in body size frequency distributions will be complicated by the fact that present-day distributions may be significantly biased by species that are missing from them.     

Rhodopsin-like Protein from the Purple Membrane of <Emphasis Type="Italic">Halobacterium halobium</Emphasis>

HALOPHILIC bacteria require high concentrations of sodium chloride and lower concentrations of KCl and MgCl₂ for growth. The cell membrane dissociates into fragments of varying size when the salt is removed¹. One characteristic fragment—termed the “purple membrane” because of its characteristic deep purple colour—has been isolated in relatively pure form from Halobacterium halobium². We can now show that the purple colour is due to retinal bound to an opsin-like protein, the only protein present in this membrane fragment (see also ref. 3).     

European phenological response to climate change matches the warming pattern

Global climate change impacts can already be tracked in many physical and biological systems; in particular, terrestrial ecosystems provide a consistent picture of observed changes. One of the preferred indicators is phenology, the science of natural recurring events, as their recorded dates provide a high-temporal resolution of ongoing changes. Thus, numerous analyses have demonstrated an earlier onset of spring events for mid and higher latitudes and a lengthening of the growing season. However, published single-site or single-species studies are particularly open to suspicion of being biased towards predominantly reporting climate change-induced impacts. No comprehensive study or meta-analysis has so far examined the possible lack of evidence for changes or shifts at sites where no temperature change is observed. We used an enormous systematic phenological network data set of more than 125 000 observational series of 542 plant and 19 animal species in 21 European countries (1971–2000). Our results showed that 78% of all leafing, flowering and fruiting records advanced (30% significantly) and only 3% were significantly delayed, whereas the signal of leaf colouring/fall is ambiguous. We conclude that previously published results of phenological changes were not biased by reporting or publication predisposition: the average advance of spring/summer was 2.5 days decade⁻¹ in Europe. Our analysis of 254 mean national time series undoubtedly demonstrates that species' phenology is responsive to temperature of the preceding months (mean advance of spring/summer by 2.5 days°C⁻¹, delay of leaf colouring and fall by 1.0 day°C⁻¹). The pattern of observed change in spring efficiently matches measured national warming across 19 European countries (correlation coefficient r =−0.69, P <0.001).     

Spring photosynthesis in a cool temperate bog

In northern ecosystems, the onset and growth of spring photosynthesis may have an important influence on the annual carbon (C) budget, yet the controls have not been clearly identified, especially for peatlands. We used a 5‐year set of daily carbon dioxide (CO₂) exchange measurements derived from an eddy covariance tower located at Mer Bleue, an ombrotrophic bog near Ottawa, Canada, from March to May [day‐of‐year (DOY) 60–150], 1999–2003. We used half‐hourly measured net ecosystem exchange minus modelled ecosystem respiration to estimate daily photosynthesis, as gross ecosystem production (GEP). The onset of GEP in each year was closely related to the thinning and disappearance of the snow cover, occurring between DOY 86 and 101. GEP increased during the spring, reaching 10‐day average values of between 5 and 9 g CO₂ m^?2 day^?1 by the end of May. This increase was initially associated with moss activity (Sphagnum and Polytrichum), followed by the evergreen shrubs. Peat temperatures in the rooting zone (10–20 cm depth) and increases in shrub leaf nitrogen and chlorophyll a concentrations contributed to this rapid increase in GEP. Examination of moderate‐resolution imaging spectroradiometer (MODIS) images over several years revealed that the temporal resolution (16‐day composites) was inadequate to capture the onset of GEP but estimates of gross primary productivity and photosynthesis from MODIS 8‐day composites for the most part followed the pattern and magnitude of CO₂ exchange observed at the tower.     

Juvenile sex ratio in relation to breeding success in Capercaillie Tetrao urogallus and Black Grouse T. tetrix

We examined the relationship between breeding success and juvenile sex ratio in two gamebirds with differing degrees of sexual size dimorphism. We used breeding success as an indicator of the level of environmental stress the birds had experienced. Capercaillie Tetrao urogallus and Black Grouse T. tetrix wing samples were collected from hunters in northern Sweden during 1977-86. In both species, annual juvenile sex ratio (percentage of males) increased with annual breeding success, i.e. with reduced environmental stress. We attribute this to the higher energy requirements during growth, vulnerability to environmental stress, and mortality of juvenile males compared with females, especially under adverse conditions. Moreover, the relationship between breeding success and juvenile sex ratio was stronger in Capercaillie than in Black Grouse. This reflects the higher degree of sexual size dimorphism in Capercaillie, and consequent larger mortality difference between juvenile males and females.     

Dynamics of nitrous oxide in groundwater at the aquatic–terrestrial interface

Few data are available to validate the Intergovernmental Panel on Climate Change's (IPCC) emission factors for indirect emissions of nitrous oxide (N₂O). In particular the N₂O emissions resulting from nitrogen leaching and the associated groundwater and surface drainage (EF5-g) are particularly poorly characterized. In situ push–pull methods have been used to identify the fate of NO₃⁻ in the groundwater. In this study, we adapted a previously published in situ denitrification push–pull method to examine the fate of ¹⁵N₂O introduced into the subsoil–groundwater matrix. Enriched ¹⁵N₂O was manufactured, added to groundwater via a closed system in the laboratory, and then introduced into the groundwater–subsoil matrix in an upland-marsh transition zone of a salt marsh and a forested alluvial riparian zone. Conservative tracers (SF₆ and Br⁻) and ¹⁵N₂O were injected into the groundwater and left for 1–4 h after which the groundwater was sampled. Added ¹⁵N₂O behaved in a conservative manner at one site while the other site showed variability with some injections showing significant consumption (3–8 μg N₂O-¹⁵N kg⁻¹ soil day⁻¹) of ¹⁵N₂O. Our results show that the fate and dynamics of N₂O in groundwater are complex and variable and that these dynamics should be considered in the development of improved IPCC inventory calculations.