Thematic network CONSIDER (EVK2-CT-2002-20012)
Third periodic report (deliverable 44, DoW)
”Climate Change and soil biodiversity”
University of Reading, Centre for Agri-Environmental Research, Reading, UK (August 23-26 2005)
Introduction
CONSIDER deals with the most important anthropogenic activities that pose a threat
towards, or are being implemented to mitigate loss in, soil biodiversity. Threats are
habitat fragmentation and destruction and global climate change, whereas mitigation
activities include land abandonment and environmentally-friendly agriculture.
CONSIDER addresses these four topics, initially at each their workshop. To further
strengthen the focus of discussions, CONSIDER will perform, during the course of its
workshops, assessments or experiments at existing field experiments of relevance to
the theme of the workshop.
The impact of climate change was the topic of workshop 4 of CONSIDER,
hosted by the University of Reading on August 23-26 2005. The global temperature is
predicted to increase by 3.5oC over the next century as a consequence of increasing
atmospheric concentrations of greenhouse gases alone (IPCC 1996). On top of the
temperature increase precipitation patterns and its seasonality will also change and the
frequency of catastrophic events will be higher. Earlier emphasis was on the effects of
changing global climate on vegetation distribution and dynamics, with major shifts in the
boundaries of ecological systems being predicted (3). However, the close relationship
between vegetation change and soil carbon (1) supports the notion that there could be
major effects of global climate change on soil biodiversity, with a commensurate impact
on ecosystem functioning. At present, our knowledge is fragmentary and often based on
correlative studies. We need more comparative data especially between different
components of the soil system, to understand global climate effects on soil biodiversity.
There is now a growing literature on the local effects of climate change on vegetation
composition and dynamics, though far less is known about the direct or indirect
(mediated via the vegetation) effects of climate change on other trophic levels. For
example, in grasslands, both the abundance and diversity of invertebrates above ground
have been shown to change in response to experimental manipulations aimed to mimic
the predictions of Global Change Models (2), though little is known about the effects on
below ground taxa (6). However, it is almost certain that differences in the availability of
organic resources will modify soil microbial community diversity and other constituents
of food webs, influenced by bottom up control (5).
The aim of this workshop was therefore to pull together existing knowledge and to
recognise the potential threats to soil biodiversity of global climate change. In so
doing, we will identify key areas where future research activity should be targeted. It
is appropriate that the close interaction between vegetation above ground and soil
biodiversity is recognised. These interactions recognise engineers (of soil structure,
microclimate and hydrological fluxes), providers of nutrient resources, such as the
microbial and other components of subterranean food webs, as well as those
organisms directly interacting with the plant, such as mutualists and antagonists. We
aim to explore the links between species diversity and functional group diversity as
exemplified in (4).
The topics were arranged into the four themes (i) linkages between diversity in
vegetation and diversity in soil (ii) evidence for the relationship between soil organic
matter and soil biodiversity, (iii) interactions between heterogeneous inputs and the
stability versus variability of populations in time and space, and (iv) multitrophic
interactions at the living plant.
(i) Linkages between diversity in vegetation and diversity in soil.
Most of the presentations at the workshop focussed on experimental studies seeking to
quantify the impacts of climate change on soil biodiversity and below-ground
processes, and the identity of the drivers behind such changes. It was concluded that
changes in plant communities are likely to have a bigger impact than the direct effects
of climate change on soil biota.
Increases in atmospheric CO2 concentrations result in increased net primary
productivity (NPP). Studies have shown that elements of the soil biota can respond
either positively or negatively to shifts in NPP resulting from climate change, thus
creating difficulties in making generalisations. Groups deriving energy directly from
the plant (herbivores, protozoa and nematodes in rhizosphere) expected to respond
positively. Decomposers (saprophytic fungi, bacteria, microarthropods) do not
respond, as they experience CO2 levels greater than global change scenarios – For this
latter group, climate change effects are likely to be mediated primarily through
changes in litter quality resulting from the direct effects of climate on the composition
of the plant community.
The prevailing temperature affects the development rate, fecundity and number of
generations per year for most elements of the soil biota. However, the soil
environment is buffered from the extremes of temperature experienced above ground,
so the impacts of temperature changes resulting from climate change are likely to be
less significant than for above ground organisms. The workshop discussed problems
surrounding interpretation of experimental studies, in particular the fact that direct
effects of changes in temperature are difficult to disentangle from indirect effects
mediated through soil moisture.
Several presentations at the workshop focussed on studies demonstrating effects of
temperature changes on the abundance and community composition of below ground
taxa. In general, increases in average temperatures are likely to boost population
sizes. However, it is likely that increases in the frequency of extreme events will also
be important. The most significant impacts are likely to occur in alpine and polar
areas. In these stressed environments, levels of soil biodiversity are low and
consequently there is little redundancy in ecosystem service provision by belowground organisms. It is therefore considered that the impacts of climate change will
be greatest (7).
Soil biota are especially sensitive to changes in soil moisture, although most work on
climate change responses has focussed on CO2 and temperature changes. Populations
of fungi and bacteria are regulated by moisture, so levels of precipitation and
evapotranspiration, with consequent effects on fungivores and bacterivores. Soil
fauna depend on humid conditions and are susceptible to desiccation. The movement
of many elements of the soil biota is facilitated by water, so changes in moisture
influence their distribution and access to resources. The workshop discussed a
number of presentations describing the effects of experimental manipulations of soil
moisture on soil biodiversity.
(ii) Relationship between soil organic matter and soil biodiversity (WP2)
Increases in NPP as a result of climate change may increase organic matter inputs to
soils. However, changes in soil temperature and precipitation will tend to speed
decomposition processes and reduce soil organic matter content. Recent scenario
modelling execises highlight that impacts of climate change on soil organic matter
and carbon sequestration in the soil cannot be considered in isolation from the impacts
of changing land use and developments in agricultural technology (8).
The workshop discussed a number of studies on the inter-relationship of plant
diversity, litter decomposition and the diversity of elements of the soil biota involved
in the decomposition process. In particular, a study of enchytraeids, a keystone
component of the soil fauna of soils important in terrestrial carbon storage, was
discussed. In this study, species-specific responses to climate change manipulations
were found. Changes in the size of enchytraeid communities can impact strongly
upon C cycling in these systems through their influence on the release of dissolved
organic carbon in the soil solution. Therefore, the response of this group of soil biota
to climate change might result in a significant biotic feedback to climate change (9)
(iii) Interactions between heterogeneous inputs and stability/variability of
populations in time and space
Investigation of the impacts of climate change on soil biodiversity and below-ground
processes requires explicit consideration of spatial and temporal scale. Climate
change is manifest over large spatial and temporal scales, but can lead to phenomena
occurring in small patches over much shorter time scales. Generalisations about the
impact of climate change on the heterogeneity of resources for soil biota cannot
reliably be made. Increases in NPP might be expected to lead to decreased
heterogeneity in litter inputs, whilst increases in disturbance of the vegetation caused
by extreme events are likely to have the opposite effect.
The workshop discussed the issues surrounding the dilemma that experimental studies
on the likely impacts of climate change, by their very nature, operate over much
shorter time scales and smaller spatial scales than the phenomena of concern. In
addition, both small-scale spatial heterogeneity and variations in weather conditions
between years reduce the power of field experimental studies to detect responses.
Finally, experimental studies typically do not allow differentiation of behavioural
responses from population responses.
Shifts in the European range of many species are expected as a result of climate
change. There is also an increased likelihood of the establishment of alien species.
The rates of change in climatic condition are likely to be too great to allow many
elements of the soil biota to respond. The problem is likely to be greatest for species
with limited capacity for dispersal, and species associated with patchy habitats. The
workshop heard presentations on work from two situations likely to experience
significant climate change impacts on soil biodiversity. Changes in temperature will
affect the soil biodiversity alpine habitats, with altitudinal shifts in species
distributions threatening taxa restricted to high altitudes and which have limited
capacity for dispersal. The workshop heard evidence for colonisation of polar areas
by taxa typical of lower latitudes. Such colonisation events are likely to enhance the
soil biodiversity of areas with very species-poor soil biota. However, at a local scale,
increases in the frequency of freeze-thaw cycles may result in the loss of some taxa
(10).
(iv) multitrophic interactions at the living plant
Soil food web components are regulated by both bottom-up (resource control) and
top-down (predation-control) forces. As outlined above, different components of soil
biodiversity have been shown to respond either positively or negatively to shifts in
NPP resulting from climate change, thus creating difficulties in developing general
principles about the response of soil biota to climate change. Top-down effects can
be important in soil food-webs, creating negative feed-backs which may partially
counter bottom-up effects (11).
Discussion at the workshop focussed primarily on the decomposer food chain, and the
effects of changes in the quantity and quality of plant litter. However, a number of
recent studies have shown the ways in which changes in temperature and soil
moisture can affect multitrophic interactions involving the living plant, for example,
between below- and above- ground herbivores. One such study, carried out at an
experimental site visited by the delegates on a field trip during the workshop, was
discussed. In this, interactions between soil-dwelling beetle larvae and leaf miners
showed different responses in different plant species (12). The mechanism of the
interaction, whether mediated by changes in plant nutritional quality or induced
defences, can explain these contracting results
References
1 Jobbágy EG, Jackson RB (2000) The vertical distribution of soil organic carbon and its relation to climate
and vegetation. Ecological Applications 10: 423 436.
2 Masters, G.M. & Brown, V.K. (1997). Host plant mediated interactions between spatially separated
herbivores: effects on community structure. In: Multitrophic Interactions in Terrestrial Systems. (Eds.)
Gange A.C. & Brown V.K. pp. 217-237. Blackwell Scientific Publications, Oxford.
3 Smith T.M., Shugart H.H., Bonan G.B. and Smith J.B. (1992b) Modelling the potential reponse of
vegetation to global climate change. Advances in Ecological Research 22, 93-116.
4 Swift M.J., Andren O., Brussaard L., Briones M., Couteaux M.M., Ekschmitt K., Kjoller A., Loiseau P.
and Smith P. (1998). Global change, soil biodiversity, and nitrogen cycling in terrestrial ecosystems:
three case studies. Global Change Biology 4, 729-743.
5 Wardle, D. A.; Barker, G. M.; Bonner, K. I., and Nicholson, K. S. (1998) Can comparative approaches
based on plant ecophysiological traits predict the nature of biotic interactions and individual plant
species effects in ecosystems? Journal of Ecology, 86, 405-420.
6 Wolters V., Silver W.L., Bignell D.E., Coleman D.C., Lavelle P., Van der Putten W.H., De Ruiter P.,
Rusek J., Wall D.H., Wardle D.A., Brussaard L., Dangerfield J.M., Brown V.K., Giller K.E, Hooper
D.U., Sala O., Tiedje J., and Van Veen J.A. (2000) Effects of global changes on above- and belowground biodiversity in terrestrial ecosystems: Implications for ecosystem functioning. Bioscience 50,
1089-1098.
7 Ruess, L., Schmidt, I.K., Michelsen, A. & Jonasson, S. (2001) Manipulations of a microbial based soil
food web at two arctic sites - evidence of species redundancy among the nematode fauna? Applied
Soil Ecology, 17, 19-30
8
Smith, J., Smith, P., Wattenbach, M., Zaehle, S., Hiederer, R., Jones, R.J.A., Montanarella, L.,
Rounsevell, M.D.A., Reginster, I. & Ewert, F. (2005) Projected changes in mineral soil carbon of
European croplands and grasslands, 1990-2080. Global Change Biology, 11, 2141-2152
9 Cole L., Bardgett R.D., Ineson P., Adamson J.K. (2002) Relationships between enchytraeid worms
(Oligochaeta), climate change, and the release of dissolved organic carbon from blanket peat in
northern England. Soil Biology & Biochemistry, 34, 599-607
10 Coulson, S.J., Leinaas, H.P., Ims, R.A. & Sovik, G. (2000) Experimental manipulation of the winter
surface ice layer: the effects on a High Arctic soil microarthropod community. Ecography, 23, 299306
11
Wardle DA, Verhoef HA, Clarholm M (1998) Trophic relationships in the soil microfood-web:
predicting the responses to a changing global environment. Global Change Biology, 4, 713-727
12 Staley, J.T, (2006). Effects of climate change on plant:insect trophic interactions. PhD dissertation,
University of Reading.
Abstracts of talks at workshop 4.
Gabor Bakonyi (Szent Istvan University, Department of Zoology and Ecology, 2100
Godollo, Pater K. u.1. Hungary)
Are there any effects of global changes on the soil nematode community
structure?
Nematodes are key factors in important soil processes such as decomposition,
mineralization or nutrient cycling. Therefore global change inducing alteration of the
nematode community structure can have a considerable influence on ecosystem
functioning. However, it is not clear whether small but long-term changes in soil
temperature and/or moisture have any significant effect on the nematode community
structure. A field experiment has been performed in a mosaic of open sand grassland
and Juniper-Poplar woodland (VULCAN Project www.vulcanproject.com). Soil
temperature and moisture have been modified according to global changes expected
in the near future. Because of the mosaic nature of the experimental field microsite
effect has been found strong and able to mask moderate temperature or soil moisture
effect. The experiment has shown that nematode communities on bare soil are more
vulnerable to global changes than those under fescue and poplar soil. Multivariate
structure of the nematode community seems to be a sensitive measure of minute
changes in soil temperature and moisture. Nematode genera having high density are
better indicators of the changes than low density ones.
Liliane Ruess (Institute of Soil Science, University of Hohenheim, Emil-WolffStraße 27, 70599 Stuttgart, Germany)
Effects of simulated climate change on nematodes and microorganisms in
subarctic soils
Arctic terrestrial ecosystems are strongly dominated by temperature, and global
warming is expected to have a particularly strong impact at high latitudes. The Arctic
will therefore be an important region for early detection of global change. The
performed at experiments used two contrasting field sites, a dwarf shrub dominated
tree-line heath (450 m a.s.l.) and a high altitude fellfield (1150 m a.s.l.) at Abisko,
Swedish Lapland. In a first study the long term effects of simulated climate change on
soil micro-organisms and nematode populations were investigated. Soil temperature
was enhanced by using passive greenhouses, with or without NPK fertilizer addition.
Warming strongly increased nematode population density after 8 growing seasons, in
particular in combination with fertilization. Additionally, microbial biomass C and
active fungal biomass was greater in the heath soil, which was reflected by an
increase in bacterial and fungal feeding nematodes. Elevated soil temperature
apparently will lead to higher grazing pressure on microorganisms, contributing to
elevated net N and P mineralization rates and plant nutrient availability.
Nutrient limitation is a major constrain to plant production and carbon storage in
arctic ecosystems. We increased the influx of nutrients and energy in the soil over 4
growing seasons by NPK fertilization and addition of labile carbon (sugar).
Additionally, two bactericides (penicillin, streptomycin) and a fungicide (benomyl)
were applied to manipulate the bacterial and fungal component of the soil. Generally,
antibiotics did not alter nematode population structure, which corresponds to the lack
in respond of target organisms (i.e. microbes). Nutrient enhancement by fertilization
alone and in combination with carbon led to an increase in the abundance of
competitive dominant nematode species, whereas the fungicide benomyl was a strong
toxin to most nematodes.
Overall, the environmental manipulations (i.e. warming, nutrient enhancement,
fungicide application) led to an increase of general opportunists and a decrease of Kstrategists, which was reflected in a reduction in the maturity index. Similarly, species
number, richness and diversity declined, most pronounced in treatments with
benomyl. In contrast to the distinct changes in species structure, the trophic structure
was only moderately affected. Relating these findings to the estimates of functional
properties at the sites (e.g. microbial biomass, plant growth) suggests considerable
redundancy among the nematode fauna. The impact of the perturbations was most
severe at the climatically harsh high altitude fellfield, probably as a result of the lower
initial biodiversity (i.e. redundancy) at that site and indicates that the influence of
climate change will be more pronounced in systems already stressed by extreme
climatic conditions.
Claus Beier (Risø National Laboratory, Roskilde, Denmark)
Field scale climate change experiments - what about biodiversity?
CLIMAITE is a research centre to investigate how climatic changes will affect
biological processes and natural ecosystems. Climaite is based on the climate changes
predicted for Denmark in 2075. CO2 concentration, temperature and precipitation are
manipulated to simulate the climate predicted for Denmark in 70 years time. The
treatments started in the autumn 2005. The project will contribute to a more
comprehensive understanding of the effects of climatic changes on biological
processes and the functioning of natural ecosystems. The research deals with structure
(plant distribution) and function (ecophysiology) of the plant cover, as well as with
soil biota (micro-organisms and fauna) divided into rhizosphere organisms and
decomposers in the bulk soil. The project will provide important information relevant
to future political decisions and societal actions that may be taken in response to
climate change. Climaite also contributes to the education of new researchers and the
dissemination of knowledge about climatic effects on biological processes to the
general public. The project involves a consortium of six research groups from Risø
National Laboratory, University of Copenhagen, Royal Veterinary and Agricultural
University and the National Environmental Research Institute.
Field trip to the long-term climate change experimental site at Wytham, near
Oxford
The workshop participants visited the field site of a long-term climate change
experiment established under NERC’s TIGER (Terrestrial Initiative in Global
Environmental Research) programme. The experiments, ongoing since the early
1990s, were established to examine the effects of different climate change scenarios
on soil, plant and invertebrate biodiversity. Local climate is manipulated to simulate
either wetter or drier summers (as predicted by Global Change Models) separately and
in factorial combination with an elevated winter soil temperature of 30C. There are
five replicates of each of the four experimental treatments and a control (with ambient
local climate).
Most Significant Results to Date
1. After six years of manipulation, the treatments have significantly altered the
grassland community, unlike the unresponsive nature to date of Buxton, our sister
site.
2. Warmer winters promoted plant growth early in the year, resulting in an increased
demand for limited soil water resources during the spring. This, combined with a
naturally low rainfall in late spring, led to a drought, the effects of which were
intensified by summer droughting. Deep-rooted herb species (e.g. Pastinaca sativa –
Wild Parsnip) persist under such conditions while shallow-rooted species (particularly
grasses) have declined or indeed been lost from plots. In contrast, plots subjected to
supplemented summer rainfall show an increase in grasses (e.g. Trisetum flavescens –
Yellow Oat-grass) at the expense of annual herbs (e.g. Crepis capillaris – Smooth
Hawk's-beard). However, in the short-term at least, perennial herbs (e.g. Ranunculus
repens – Creeping Buttercup) have persisted alongside the vigorous grasses.
Additionally, there have been individual plant developmental responses to the warmer
winters. For example, Viola hirta (Hairy Violet) and Hypericum perforatum
(Perforate St. John's-wort) had their phenology advanced by the warmer conditions.
3. Invertebrate responses are, predictably, more complex, showing both direct and
indirect (host-plant mediated) responses to climate manipulation. Generally,
invertebrate groups track the vegetation responses; except under drought where plant
nutritional quality becomes important and can lead to population increases (e.g. leafminer populations increase in droughted plots while their host plants decline).
Additionally, the timing of insect activity is modified. For example, the spittlebug
Philaenus spumarius responded directly to warmer winters, with an earlier egg hatch
(by seven days) and consequent earlier development into adults.
4. Warmer winters may lead to spring droughts, which are strengthened by dry summers. Water is the
key to the responses of the ecosystem: grasses dominate with increased rainfall, while deep-rooted herb
species persist under drought. Invertebrates track these changes, except under drought, where plant
nutritional quality is more important and insect populations show an increase instead of the predicted
decline. The timing of insect activity is modified, as is the size of their populations – in the extreme,
leading to insect outbreaks.
Veronika Řezáčová (Institute of Microbiology, Academy of Sciences of the Czech
Republic, 142 20 Prague, Czech Republic Fax: +420-2-41062384 E-mail:
strver@seznam.cz)
The Effect of Elevated Atmospheric CO2 Concentration on Soil Microfungi
The current increase in atmospheric CO2 concentration is widely considered to be one
of the most important environmental long term changes. This change is predicted to
increase carbon input to the soil via increase of net primary production. I had been
testing the hypotheses that elevated CO2 increased the abundance of soil microfungi
when nitrogen level also increased; and caused changes in their species composition.
We focused on humic substances utilizers. To use these hypothesis, we analysed soil
samples from the 10 years running field experiment. The assumed increase in
microfungal abundance was indeed proved at elevated atmospheric CO2 concentration
under conditions of a synchronous higher input of nitrogen of 560 kg/ha/year. When
nitrogen input to the soil was 140 kg/ha/y the elevated atmospheric CO2 concentration
decreased abundance of microfungi. Humic substances utilizers were not affected by
CO2 at all. Community structure of microfungi, both the species composition and
relative abundance of particular species was affected by elevated atmospheric CO2
concentration.
Barbara Drigo, Johannes A. van Veen , Etienne Yergeau & George A. Kowalchuk
(Netherlands Institute of Ecology (NIOO-KNAW), Heteren)
Impact of increased atmospheric Carbon Dioxide on microbial community
dynamics associate with rhizosphere carbon flow
Within the framework of a national programme on global change and biodiversity, we
aim to investigate the impact of elevated atmospheric CO2 levels on the composition
and functioning of microbial communities in soil. In particular, the effects on the
natural control of below-ground plant pathogens of dune plants by microbial
antagonists will be studied. In the first experiment, we grew Carex arenaria (a nonmycorrhizal plant species) and Festuca rubra (a mycorrhizal plant species) in three
dune soils under controlled soil temperature and moisture conditions, while subjecting
the aboveground compartment to defined atmospheric conditions differing in CO2
concentrations (350 and 700 ppm).
Using PCR-DGGE and Q-PCR, we examined the abundance and diversity of both
broad microbial groups, such as bacteria, actinomycetes and fungi, as well as the
dynamics of specific groups, such as Pseudomonas, Burkholderia and Bacillus, in the
Carex rhizosphere. Multi-variate analysis of the DGGE profiles showed a significant
influence of the elevated CO2 on the total, bacterial community and fungal community
as well as on the specific groups of Burkholderia and Pseudomonas spp. However, no
significant effects were found for actinomycetes and bacilli suggesting that the plantdriven impact of elevated CO2 on the short term is towards species, which are known
to be successful colonizers of the rhizosphere and strong competitors for root
exudates.
K. Deiglmayr (1), L. Philippot (2), D. Tscherko (3), E. Kandeler (3)
(1) University of Hohenheim, Institute of Crop Production and Grassland Research,
Stuttgart, Germany
(2) INRA, Laboratory of Soil Microbiology and Geochemistry, Dijon, France
(3) University of Hohenheim, Institute of Soil Science, Stuttgart, Germany
The Response of Nitrate-Reducing Microorganisms to Climate Change –
Two Case Studies
Linking the structure of soil microbial communities with its function in soil processes
is a big challenge for current research in soil microbiology. In the presented two case
studies the dissimilatory nitrate-reducing community was investigated as model
community, since both the molecular technique to target this functional group and the
method for studying its specific enzyme activity were well established. The first
experiment investigated the effect of elevated atmospheric CO2. Rhizosphere soil was
sampled in monocultures of Lolium perenne and Trifolium repens at two different
nitrogen fertilization levels (140 kg N ha-1 a-1 and 560 kg N ha-1 a-1) and under two
pCO2 atmospheres (360 ppm and 600 ppm) at the Swiss FACE (Free Air Carbon
dioxide Enrichment) site. Directly extracted soil DNA was analyzed by RFLP-PCR
by using degenerated primers for the narG gene encoding the active site of the
membrane-bound nitrate-reductase. The corresponding enzyme activity of the nitrate
reductase was determined colorimetrically after 24 hours of anaerobic incubation. The
narG RFLP-fingerprints showed that only season and pH of the sampled site affected
the composition of the nitrate-reducing community. In contrast, the nitrate reductase
activity decreased significantly with carbon dioxide enrichment most probably due to
limited nitrate availability.
The second experiment investigated microbial succession in a glacier foreland of the
Central Alps, which has evolved - with accelerating rate - over the last 150 years due
to rising temperatures. Rhizospheric soil of Poa alpina was sampled in five replicates
along a gradient from 25 to 130 years of soil formation in August during the
flowering stage and in September 2004 after the first snowfalls. The community
structure showed only a small shift over the 100 years of soil formation and the two
sampling dates. However, analysis of clone libraries of the early and late succession
pointed to a decrease in diversity with increasing succession age. We assume that in
the early succession, the selective pressure on the nitrate reducers was relatively lower
compared to the late stage; hence a higher diversity could persist in this sparse
environment. The activity of the nitrate-reducing community, conversely, proved to
increase significantly with age and no major differences were observed between the
two sampling dates. Higher carbon and nitrate availability in the late succession
probably enhanced the anaerobe respiration of nitrate to nitrite.
In summary, we observed sensitive responses of the nitrate reductase activity to
elevated atmospheric CO2 and to successional age. The most significant effect proved
to be Corg and NO3-. In contrast, the community structure of the nitrate-reducing
microorganisms was quite stable under elevated atmospheric CO2 and changed only
slightly across the glacier foreland mainly due to pH. These results document that
different mechanisms are responsible for the regulation of community structure and
the corresponding enzyme activity.
Etienne Yergeau, G.A. Kowalchuk (Netherlands Institute of Ecology (NIOOKNAW), Heteren)
Global warming effects on the size, diversity and function of soil-borne microbial
communities in Antarctic ecosystems
Many factors are unfavorable for terrestrial life in harsh Antarctic regions, including
low thermal capacity of the substratum, frequent freeze-thaw and wet-dry cycles, low
and transient precipitation, low humidity, rapid drainage, and limited organic
nutrients. However, several studies have reported that certain microorganisms can
thrive even in these kinds of environments, and microbial processes are the key
drivers of soil-borne nutrient cycles in Antarctic environments. In order to describe
such microbial communities, we sampled vegetated and bare sites along a south polar
latitudinal gradient ranging from the Falkland Islands (51°S) to the base of the
Antarctic peninsula (72°S). We coupled molecular (DGGE, real-time PCR) and
traditional microbiological (CFU counts using a range of incubation temperatures and
media) methods with soil analyses. We report data concerning community structure
and abundance of nematodes, bacteria and fungi, and analyze these data with respect
to different environmental parameters. Bacterial populations were closely linked to
the presence of plant cover and to temperature parameters, probably caused by the
sheltering effect of plants. Fungal populations were influenced by the species
composition of the overlying plant community and were less connected to
temperature, showing a possible dependence on the type of organic input available.
Nematode community structure was affected by both the presence of plant cover and
by the sampling location, although nematode abundance did not show any significant
trends. Results are discussed with respect to possible effects of global warming on
soil-borne microbial community structure and function in Antarctic environments.
Jo Staley (The University of Reading, UK)
Impacts of climate change on plant-mediated interactions between foliar and
root-feeding insects
Summer rainfall in south-east UK is predicted to decrease by 20 to 50% by 2080, and
the occurrence of severe droughts is likely to increase, under current climate change
scenarios. Drought can affect the performance and abundance of plants and their
associated invertebrates, yet research into climate change impacts has focussed
mainly on changes in temperature and carbon dioxide concentration. Here, impacts of
summer drought on the abundance of root and foliar phytophages, and the interactions
between them, were investigated.
One group of foliar phytophages (leaf miners) was found to be variable in their
response to drought, though the abundance of the dominant species (Stephensia
brunnichella) was reduced by 54% under a summer drought treatment, while its rate
of parasitism was increased by 58%. Larvae of the most common root chewing
species, Agriotes lineatus, were also less abundant under drought. Agriotes larvae
reduced the abundance, pupal weight and parasitism of S. brunnichella larvae feeding
on a mutual host plant. This interaction was disrupted by a severe drought treatment,
though not by moderate drought. In contrast, Agriotes larvae increased the pupal
weight of a second leaf miner species (Chromatomyia syngenesiae), and the
interaction was stronger under drought.
Root feeders can either increase foliar phytophage performance (potentially through
an increase in plant nutritional quality), or reduce it (possibly due to an induced
defence response in the foliage). This study provides examples of each, and it is
proposed that the effect of drought on these indirect interactions may depend on the
mechanisms by which these two phytophagous groups are interacting. Climate
change may therefore have idiosyncratic effects of plant mediated interactions
between insect herbivores. A clear understanding of the plant traits that determine the
frequency with which these different mechanisms occur may aid the prediction of
climate change impacts.
Lisa Cole (Centre for Ecology and Hydrology, Banchory, Kincardine, Scotland)
Global change impacts on enchytraeid worms
Enchytraeids (Oligochaeta) are a keystone group of soil invertebrates found in
ecosystems that represent important stores of terrestrial carbon, notably moorland,
boreal forest and tundra. They are not a diverse group, communities are often
dominated by a single species, Cognettia sphagnetorum, and therefore, they are
expected to be less resistant and resilient to global change impacts such as warming,
atmospheric N deposition and elevated concentrations of atmospheric carbon dioxide.
Soil warming studies in UK moorland have shown that the response of enchytraeids
to warming is species specific, with communities dominated by enchytraeids of the
genus Cognettia increasing in size with soil temperature, so long as soil moisture does
not become limiting. In contrast, after 4 years of warming arctic tundra soil by 1ºC
(Svalbard, Norway), communities dominated by enchytraeids of the genus Henlea
showed no change in their abundance. Further, there was an increase in the abundance
of enchytraeids, albeit non-significantly, under enhanced atmospheric N deposition in
montane moss heath (Grampian Mountains, UK) after 7 years. Conversely,
enchytraeid populations in a raised bog (Cumbria, UK) declined markedly after two
years exposure to an almost doubled concentration of atmospheric carbon dioxide.
Whilst these findings were found to correlate with changes in plant litter quality or
biomass, they were also found to be strongly influenced by corresponding changes in
other biotic (competition from macrofauna such as earthworms and tipulid larvae) and
abiotic factors (soil moisture). Clearly, enchytraeids can be sensitive to global change
phenomena and it is known that changes in the size of enchytraeid communities can
impact strongly upon C cycling in these systems through their influence on the release
of dissolved organic carbon in the soil solution. Therefore, the response of this group
of soil biota to global change might result in a significant biotic feedback to climate
change.
Thomas Bolger (Dept of Zoology, University College Dublin, Belfield, Dublin 4,
Ireland)
Relationship between earthworm diversity and ecosystem function – Need for
studies and experimental design.
The need to examine the relationships between ecosystem function and species
richness specifically for soil fauna is discussed using data from field studies of
invasive species and relationships between above and below ground richness. A series
of studies are described which overcome the problems with the designs used
commonly in those studies. Soil fauna and microflora are an ideal model system for
such studies because they are critical in the decomposition process, and the number of
species present in most soils appears to be far greater than the number of functions
which they serve, i.e. functional redundancy is expected to be widespread. The
experiments described show a lack of redundancy among the functional groups of
earthworms occurring in temperate grassland soils. They illustrate the advantages of
the Simplex experimental design and emphasise the requirement that studies be
carried out under a variety of environmental conditions in order to address the issues
of insurance value among apparently redundant groups.
Sebastien Barot (Laboratoire d'Écologie des Sols Tropicaux, Bondy, France)
Earthworm effects on plant communities: insights from field studies, microcosm
experiments and modelling
Recycling of mineral nutrients incorporated in plant biomass is a key ecosystem
process. Soil ecosystem engineers are known to accelerate mineralization of soil
organic matter and are often supposed to be beneficial for plant growth. This has been
shown in short-term microcosm experiments. It is legitimate to ask whether these
increases in plant growth are due to sudden and brief pulses of mineralization or
whether these increases are long-lasting and still apply to ecosystems at equilibrium.
This issue was tackled using a system of differential equations involving trophic
effects on nutrient cycling due to the assimilation of nutrients by the considered
decomposers, and indirect effects through their ecosystem engineering activities. It
was shown that both these effects are positive for plant primary production if and only
if they recycle nutrients efficiently, i.e. allowing a small fraction of the recycled
nutrients to be leached out of the ecosystem. Together with former results on
herbivory our results suggest that: (i) At equilibrium, the effect of any actor of an
ecosystem on primary production depends on its recycling efficiency not on its
capacity to recycle nutrients quickly. (ii) This applies either when this actor recycles
nutrients feeding on a compartment of the ecosystem or when this actor is involved in
nutrient cycling through its ecosystem engineering activities. (iii) The efficiency of a
recycling pathway influences all compartments of the ecosystem. This shows that a
decomposer can increase its own biomass by ecosystem engineering activities leading
to the mineralization of nutrients it cannot assimilate if the created recycling loop is
efficient. This also suggests an explanation for the evolution in earthworms of
particular ecosystem engineering activities leading for example to the control of
parasite nematodes or the production of plant growth hormones. Increasing plant
growth would be a way for earthworms to increase indirectly their own biomass
through a better conservation of nutrients inside the ecosystem.
Klaus Birkhofer (Technische Universität Darmstadt, Germany. Animal Ecology
Group, Prof. S. Scheu)
Organic Farming: Consequences for Generalist Predator Communities
Since 1985 the agricultural area under organic management practices increased
steadily to approximately 6.3 million hectare in Europe (2003, 1). Avoidance of
pesticides and management techniques such as no-till and mechanical weed control
influence the plant and animal community. The DOC trial (Therwil, Switzerland)
carried out by the Research Institute of Organic Agriculture and the Swiss Federal
Research Station for Agroecology & Agriculture compares different farming systems
since 1978. The wheat plots studied in this survey were under organic, respectively
conventional management for 27 years and truly reflect long-term effects of different
farming systems. Organic and conventional plots had four replicates, which were
sampled in May 2005 using fenced pitfalls (1.8 m²) and D-Vac suction sampling (0.7
m²). Ground beetles, cursorial and web building spiders were significantly more
abundant in organic plots. The number of species was also higher for ground dwelling
spiders and carabids in these plots. Cursorial spiders such as Pardosa and Pachygnatha
species preferred the organic fields, whereas some web builders (Meioneta rurestris,
Lepthyphantes tenuis) were more characteristic for conventional plots. Three carabid
species showed distinctive preferences for the conventional plots (Clivinia fossor,
Demtrias atricapilus and Brachinus explodens), whereas the collembola-feeding
species Loricera pillicornis and omnivorous species (Amara sp.) were more abundant
in organic fields. These findings show the beneficial long-term effect of organic
farming on functional diversity, promoting the role of generalist predators as
biocontrol agents.
Kerstin Endlweber (Technische Universität Darmstadt, Germany Animal Ecology
Group, Prof. S. Scheu)
Getting rid of mycorrhiza – how to establish experiments on mycorrhiza –
decomposer interactions
Many studies focus on the interdependency between plant nutrition and mycorrhiza –
decomposer interaction. To investigate this interaction, mycorrhiza free treatments are
often compared to re-inoculated treatments. But common methods to achieve
mycorrhiza free soil affect nutrient availability and microbial activity in soil. Thus,
the interaction between plants and mycorrhiza and plant nutrition might be influenced
by mycorrhizal elimination. We investigated the applicability of soil heating (60, 80,
100 and 120°C), autoclaving and chloroform fumigation on elimination of
mycorrhiza. Furthermore we determined the impact of the tested methods on
mobilisation of ammonium, nitrate and phosphorus as well as on microbial activity.
Heating at 60°C and chloroform fumigation reduced mycorrhizal inoculation rate to
less than 1%, whereas all other treatments decreased the inoculation rate to less than
0.2%. All six methods affected plant growth and nutrient content. This was in part due
to a high mobilisation of ammonium and nitrate in particular in autoclaved soil and
soil heated at 100 and 120°C. But the observed changes in plant growth and nutrition
might also depend on changes in microbial activity by the soil treatments. Although
heating soil at 60°C increased plant growth and shoot nutrient content, it caused the
least side effects on nutrient mobilisation and microbial activity compared to control.
Questions raised by policy makers and end users
Soils and the biodiversity they support are threatened by climate change and other
drivers such as land use change. In addition to the direct effects of climate change on
the soil, below-ground processes also provide feedback linkages to drivers of climate
change. Such feedback interactions make the predictions of climate change impacts
difficult. Consequently, knowledge of the responses of soil biodiversity to changing
climate, and the likely implications for carbon sequestration and greenhouse gas
emissions is essential.
The importance of soil biodiversity is acknowledged in international treaties (UNCBD, UNFCCC, UNCCD), by international organisations (OECD, FAO, UNEP,
CGIAR) and by national governments. It has been recommended (OECD meeting
Zürich 2001; FAO conference Rome 2003; ARF workshop Rothamsted 2005) that
Agri-Biodiversity Indicators should be developed to allow monitoring of soil
biodiversity, the functions it performs, and their resistance and resilience in response
to environmental change. The workshop discussed the findings of an integrated
national survey of soils and their biota carried out in Great Britain.
Helaina Black (Centre for Ecology and Hydrology, The Lancaster Environment
Centre, UK)
Assessing soil biodiversity on a national scale
An assessment of the biodiversity of soils across Great Britain was described. This
was the first integrated survey of soil biota and chemical properties at a national scale.
A total of 1052 soil samples were collected across Great Britain and analysed for a
range of soil microbial and invertebrate characteristics resulting in the production of a
series of robust datasets. A principal objective was to use these datasets to investigate
relationships between soil biota and environmental factors such as geographical
location, vegetation. land use, land cover, soil type and pollutant levels as first stages
in characterising the inherent biodiversity of British soils and investigating the
potential of soil biodiversity as indicators of soil health at a regional or national scale.
Preliminary results for culturable heterotrophic, invertebrate taxa, Acari, Collembola
and Oribatid mites were presented to illustrate the nature of the data collected and the
patterns of soil biodiversity in relation to large-scale regional, vegetation and soil
characteristics across the British countryside (see J. Env. Man. 67: 255-266).