Phil Ineson

Global Warming and Terrestrial Ecosystems: A Conceptual Framework for Analysis

raise global mean temperature over the next century by 1.0–3.5 °C (Houghton et al. 1995, 1996). Ecologists from around the world have begun experiments to investigate the effects of global warming on terrestrial ecosystems, the aspect of global climate change that attracts the most public attention (Woodwell and McKenzie 1995, Walker and Steffen 1999). The effort to understand response to warming builds on a history of investigations of the effects of elevated CO 2 on plants and ecosystems (Koch and Mooney 1996, Schulze et al. 1999). There are important differences, however, between increases in atmospheric CO 2 and temperature change, both in the temporal and spatial patterns of change and in how they affect ecosystems. The scientists involved in temperature change research have had to face new technical and conceptual challenges in designing and interpreting their experiments (Schulze et al. 1999). In this paper we describe these challenges and present a conceptual framework for interpreting experimental results and predicting effects of warming on ecosystems.

Nitrogen and cation mobilization by soil fauna feeding on leaf litter and soil organic matter from deciduous woodlands

Abstract Decomposing oak litter was incubated in laboratory microcosms and the effects of adding a variety of soil animals upon nitrogen and cation release were monitored. Various groups of macrofauna caused a marked increase in ammonium release with smaller increases in calcium, potassium and sodium leaching. Microfauna also had significant but much less marked effects upon nitrogen and cation release. The effects of different grazing intensities of the millipede Glomeris marginata on a variety of forest organic substrates show that the animals amplified existing patterns of nutrient release.

Effect of collembolan grazing upon nitrogen and cation leaching from decomposing leaf litter

Abstract Fragmented oak litter was incubated in the laboratory for 4 months with and without collembola. The effects of the animals upon fungal standing crop and leaching of inorganic nitrogen and cations was monitored over this period. The results showed that the fungal standing crop was higher in the presence of small numbers of animals than in litter lacking animals, yet at higher grazing intensities the fungal standing crop fell markedly. Significant increases in the leaching of ammonium, nitrate and calcium occurred as a consequence of animal grazing, but potassium and sodium losses from the litter were unaffected.

The role of Eriophorum vaginatum in CH4 flux from an ombrotrophic peatland

Vegetation composition was found to be an important factor controlling CH4 emission from an ombrotrophic peatland in the UK, with significantly greater (P < 0.01) CH4 released from areas containing both Eriophorum vaginatumL. and Sphagnum, than from similar areas without E. vaginatum. Positive correlations were observed between the amount of E. vaginatum and CH4 emission, with the best predictor of flux being the amount of below-ground biomass of this species (r2 = 0.93). A cutting experiment revealed that there was no significant difference (P > 0.05) in CH4 flux between plots with E. vaginatum stems cut above the water table and plots with intact vegetation, yet there was a 56% mean reduction in CH4 efflux where stems were cut below the water table (P < 0.05). The effect of E. vaginatum on CH4 release was mimicked by the presence of inert glass tubes. These findings suggest that the main short-term role of E. vaginatum in the ecosystem is simply as a conduit for CH4 release. The longer-term importance of E. vaginatum in controlling CH4 fluxes through C substrate input was suggested by the positive correlation between the night-time CO2 and CH4 fluxes (r2 = 0.70), which only occurred when the vegetation was not senescent.

ELEVATED CO2 AFFECTS FIELD DECOMPOSITION RATE AND PALATABILITY OF TREE LEAF LITTER: IMPORTANCE OF CHANGES IN SUBSTRATE QUALITY

could be related to changes in tissue quality resulting from growing the plants at higher CO2 concentrations, with C-to-N ratios and lignin contents being significantly increased. The elevated CO2 treatment also aAected the rate of consumption of ash leaf litter by Oniscus asellus L. (Isopoda: Oniscoidea), with significantly less (ˇ16%) material being consumed for litter derived from the high CO2 regime. Our results indicate that changes in litter quality, which we may expect under elevated CO2, may aAect litter palatability for soil fauna. # 1998 Elsevier Science Ltd. All rights reserved

Quantification of soil carbon inputs under elevated CO2: C3 plants in a C4 soil

The objective of this investigation was to quantify the differences in soil carbon stores after exposure of birch seedlings (Betula pendula Roth.) over one growing season to ambient and elevated carbon dioxide concentrations. One-year-old seedling of birch were transplanted to pots containing ‘C4 soil’ derived from beneath a maize crop, and placed in ambient (350 μL L−1) and elevated (600 μL L−1) plots in a free-air carbon dioxide enrichment (FACE) experiment. After 186 days the plants and soils were destructively sampled, and analysed for differences in root and stem biomass, total plant tissue and soil C contents and δ13C values. The trees showed a significant increase (+50%) in root biomass, but stem and leaf biomasses were not significantly affected by treatment. C isotope analyses of leaves and fine roots showed that the isotopic signal from the ambient and elevated CO2 supply was sufficiently distinct from that of the ‘C4 soil’ to enable quantification of net root C input to the soil under both ambient and elevated CO2. After 186 days, the pots under ambient conditions contained 3.5 g of C as intact root material, and had gained an additional 0.6 g C added to the soil through root exudation/turnover; comparable figures for the pots under elevated CO2 were 5.9 g C and 1.5 g C, respectively. These data confirm the importance of soils as an enhanced sink for C under elevated atmospheric CO2 concentrations. We propose the use of ‘C4 soils’ in elevated CO2 experiments as an important technique for the quantification of root net C inputs under both ambient and elevated CO2 treatments.

Short‐term dynamics of abiotic and biotic soil 13CO2 effluxes after in situ 13CO2 pulse labelling of a boreal pine forest

Physical diffusion of isotopic tracers into and out of soil pores causes considerable uncertainty for the timing and magnitude of plant belowground allocation in pulse-labelling experiments. Here, we partitioned soil CO(2) isotopic fluxes into abiotic tracer flux (physical return), heterotrophic flux, and autotrophic flux contributions following (13)CO(2) labelling of a Swedish Pinus sylvestris forest. Soil CO(2) efflux and its isotopic composition from a combination of deep and surface soil collars was monitored using a field-deployed mass spectrometer. Additionally, (13)CO(2) within the soil profile was monitored. Physical (abiotic) efflux of (13)CO(2) from soil pore spaces was found to be significant for up to 48 h after pulse labelling, and equalled the amount of biotic label flux over 6 d. Measured and modelled changes in (13)CO(2) concentration throughout the soil profile corroborated these results. Tracer return via soil CO(2) efflux correlated significantly with the proximity of collars to trees, while daily amplitudes of total flux (including heterotrophic and autotrophic sources) showed surprising time shifts compared with heterotrophic fluxes. The results show for the first time the significance of the confounding influence of physical isotopic CO(2)-tracer return from the soil matrix, calling for the inclusion of meaningful control treatments in future pulse-chase experiments.

Aerobically isolated bacteria associated with the gut and faeces of the litter feeding macroarthropods Oniscus asellus and Glomeris marginata

Abstract Bacteria were isolated from the food, guts and faeces of the litter feeding macroarthropods Oniscus asellus and Glomeris marginata. Bacterial counts showed that bacterial growth was enhanced both in the guts and faeces of these animals. Significant differences in the biochemical capabilities of the isolates derived from litter, gut populations and faeces were noted, with the ability to grow facultatively anaerobically being associated with gut and faecal populations. Similarly, the ability to degrade uric acid was a common attribute of the faecal isolates from both macroarthropods. The results suggest that grazing by soil animals can cause a marked increase in litter bacterial activity even in acid soils, where fungi normally dominate decomposer activity.

Links between methane flux and transcriptional activities of methanogens and methane oxidizers in a blanket peat bog

The relationship between biogeochemical process rates and microbial functional activity was investigated by analysis of the transcriptional dynamics of the key functional genes for methanogenesis (methyl coenzyme M reductase; mcrA) and methane oxidation (particulate methane monooxygenase; pmoA) and in situ methane flux at two peat soil field sites with contrasting net methane-emitting and -oxidizing characteristics. qPCR was used to quantify the abundances of mcrA and pmoA genes and transcripts at two soil depths. Total methanogen and methanotroph transcriptional dynamics, calculated from mcrA and pmoA gene : transcript abundance ratios, were similar at both sites and depths. However, a linear relationship was demonstrated between surface mcrA and pmoA transcript dynamics and surface flux rates at the methane-emitting and methane-oxidizing sites, respectively. Results indicate that methanotroph activity was at least partially substrate-limited at the methane-emitting site and by other factors at the methane-oxidizing site. Soil depth also contributed to the control of surface methane fluxes, but to a lesser extent. Small differences in the soil water content may have contributed to differences in methanogen and methanotroph activities. This study therefore provides a first insight into the regulation of in situ, field-level surface CH(4) flux at the molecular level by an accurate reflection of gene : transcript abundance ratios for the key genes in methane generation and consumption.

The effects of nitrogen fertilisation and elevated CO2 on the lipid biosynthesis and carbon isotopic discrimination in birch seedlings (Betula pendula)

The effects of nitrogen (N) fertilisation and elevated [CO2] on lipid biosynthesis and carbon isotope discrimination in birch (Betula pendula Roth.) transplants were evaluated using seedlings grown with and without N fertiliser, and under two concentrations of atmospheric CO2 (ambient and ambient+250 μmol mol-1) in solar dome systems. N fertilisation decreased n-fatty acid chain length (18:0/16:0) and the ratios of α-linolenate (18:2)/linoleate (18:1), whereas elevated [CO2] showed little effect on n-fatty acid chain length, but decreased the unsaturation (18:2+18:1)/18:0. Both N fertilisation and elevated [CO2] increased the quantity of leaf wax n-alkanes, whilst reducing that of n-alkanols by 20–50%, but had no simple response in fatty acid concentrations. 13C enrichment by 1–2.5‰ under N fertilisation was observed, and can be attributed to both reduced leaf conductance and increased photosynthetic consumption of CO2. Individual n-alkyl lipids of different chain length show consistent pattern of δ13C values within each homologue, but are in general 5–8‰ more depleted in 13C than the bulk tissues. Niether nitrogen fertilisation and elevated CO2 influenced the relationship between carbon isotope discrimination of the bulk tissue and the individual lipids.