Showing papers by "Richard D. Bardgett published in 2001"

Accounting for variability in soil microbial communities of temperate upland grassland ecosystems

Abstract: This study aimed to determine the factors which regulate soil microbial community organisation and function in temperate upland grassland ecosystems Soil microbial biomass (Cmic), activity (respiration and potential carbon utilisation) and community structure (phospholipid fatty acid (PLFA) analysis, culturing and community level physiological profiles (CLPP) (Biolog®)) were measured across a gradient of three upland grassland types; Festuca–Agrostis–Galium grassland (unimproved grassland, National Vegetation Classification (NVC) — U4a); Festuca–Agrostis–Galium grassland, Holcus–Trifolium sub-community (semi-improved grassland, NVC — U4b); Lolium–Cynosurus grassland (improved grassland, NVC — MG6) at three sites in different biogeographic areas of the UK over a period of 1 year Variation in Cmic was mainly due to grassland type and site (accounting for 55% variance, v, in the data) Cmic was significantly (P

Soil microbial community patterns related to the history and intensity of grazing in sub montane ecosystems.

Abstract: Long-term variations in the frequency and intensity of sheep (Ovis aries) grazing have led to the development of ubiquitous plant successional transitions in sub-montane regions of the UK. In this study, we measured a range of soil microbial properties across these successional transitions in three biogeographic regions of the UK, to establish how gradients of grazing-influence (in terms of the history and intensity of sheep grazing) alter the biomass, activity, and structure of soil microbial communities. We also measured soil physicochemical variables to relate changes in soil microbial community arrangement along these grazing-related successional transitions to key soil properties. Our results from three locations show that microbial communities of soils display some consistent and ‘broad-scale’ trends along successional transitions that are related to the history and intensity of grazing. We show that microbial biomass of soil is maximal at low-to-intermediate levels of grazing influence and that the phenotypic evenness (a component of diversity) of the microbial community declines as the intensity of grazing increases. We also provide evidence that soil microbial communities of heavily grazed sites are dominated by bacterial-based energy channels of decomposition, whereas in systems that are less intensively grazed, or completely unmanaged, fungi have a proportionally greater role. Further studies are needed to establish the significance of these changes in relation to soil-level ecosystem processes of decomposition and nutrient cycling. The data show that human disturbances can have profound effects on the biomass and structure of the soil communities that regulate soil processes in these ecosystems and that these effects are consistent across sites.

How changes in soil faunal diversity and composition within a trophic group influence decomposition processes

Abstract: There are few experimental data on the consequence of varying the composition and diversity of soil animals communities, or soil food-webs, on ecosystem properties. Here, we tested the hypothesis that varying the diversity and composition of soil animals within a trophic group, the microbial-feeders, affects litter decomposition and nutrient flux in grassland. Microcosms containing grassland plant litter were inoculated with individual species of Collembola Folsomia candida, Pseudosinella alba, and Protaphorura armata,and all possible two and three species combinations of these species. Our data show that towards the end of the experiment individual species of Collembola, and especially F. candida, had markedly different, but positive, effects on measures of litter mass loss, microbial activity (CO2 respiration) and the leaching of dissolved organic carbon (DOC) and nitrate-N. Two and three species combinations of Collembola revealed that effects of fauna on ecosystem processes were due to differences in the composition of the collembolan community, rather than the number of species present. In comparison to a treatment that had no fauna, significantly higher rates of litter mass loss, microbial activity, and DOC and nitrate release were detected only in microcosms that contained F. candida. There was no evidence of effects of F. candida in combination with other species, relative to effects of F. candida alone, on the above properties. These findings support the notion that changes in the diversity of microbivorous fauna may not have a predictable effect on decomposition processes rates and that the functioning of the microbial-feeding trophic group is influenced mainly by the physiological attributes of the dominant animal species present, in this case F. candida.

Site and management effects on soil microbial properties of subalpine meadows: a study of land abandonment along a north–south gradient in the European Alps

Abstract: We studied the factors which regulate microbial community organization in soils of managed ecosystems. Soil microbial biomass C and N (SMBC, SMBN), EC/ENIN ratio, ergosterol, and phospholipid fatty acids (PLFA) were determined in organically fertilised meadows and grasslands with abandoned management at three sites (Stubai Valley, Passeier Valley, and Monte Bondone) to study the relative importance of the factors site and management in governing the variability of soil microbial biomass and community structure in subalpine grasslands of the European Alps. Our data provide evidence that management abandonment has important effects on the structure of the soil microbial biomass, namely an increase in the fungal biomass. SMBC, SMBN, EC/ENIN ratio and ergosterol contents differed significantly between sites. SMBC was similar in abandoned and managed grasslands, whereas SMBN was lower and ergosterol contents were higher in abandoned grasslands as compared to managed meadows. We concluded that the impact of management abandonment on soil microbial biomass was of relatively less importance than effects of site and sampling time, and the effect of abandonment may be better detected at the community scale of resolution.

The influence of soil biodiversity on hydrological pathways and the transfer of materials between terrestrial and aquatic ecosystems

Abstract: The boundaries between terrestrial and aquatic ecosystems, known as critical transition zones (CTZ), are dynamic interfaces for fluxes of water, sediment, solutes, and gases. Moreover, they often support unique or diverse biotas. Soils, especially those of riparian zones, have not been recognized as CTZ even though they play a critical role in regulating the hydrologic pathways of infiltration and leaching, or runoff and erosion, which can cumulatively affect biogeochemical processes and human livelihoods at landscape scales. In this review, we show how the processes that regulate hydrologic fluxes across and through soil CTZ are influenced by the activities of soil biota. Our message is fourfold. First, there are a variety of ways in which soil biodiversity, in terms of richness and dominance, can influence hydrological pathways in soil and thus the transfer of materials from terrestrial to aquatic ecosystems. Second, the influence of soil organisms on these hydrological pathways is very much interlinked with other environmental, soil biophysical, and vegetation factors that operate at different spatial and temporal scales. Third, we propose that the influence of soil biodiversity on hydrological pathways is most apparent (or identifiable), relative to other factors, in situations that lead to the dominance of certain organisms, such as larger fauna. Fourth, soils are buffered against environmental change by biophysical properties that have developed over long periods of time. Therefore, the effects of changes in soil biodiversity on hydrological processes at the ecosystem scale might be delayed and become most apparent in the long term.

Accounting for variability in soil microbial communities of temperate upland grasslands.

Abstract: This study aimed to determine the factors which regulate soil microbial community organisation and function in temperate upland grassland ecosystems Soil microbial biomass (Cmic), activity (respiration and potential carbon utilisation) and community structure (phospholipid fatty acid (PLFA) analysis, culturing and community level physiological profiles (CLPP) (Biolog®)) were measured across a gradient of three upland grassland types; Festuca–Agrostis–Galium grassland (unimproved grassland, National Vegetation Classification (NVC) — U4a); Festuca–Agrostis–Galium grassland, Holcus–Trifolium sub-community (semi-improved grassland, NVC — U4b); Lolium–Cynosurus grassland (improved grassland, NVC — MG6) at three sites in different biogeographic areas of the UK over a period of 1 year Variation in Cmic was mainly due to grassland type and site (accounting for 55% variance, v, in the data) Cmic was significantly (P<0001) high in the unimproved grassland at Torridon (2374 g C m−2 cf 812 g C m−2 in semi- and 638 g C m−2 in improved grasslands) and Sourhope (1146 g C m−2 cf in 448 g C m−2 semi- and 683 g C m−2 in improved grasslands) and semi-improved grassland at Abergwyngregyn (760 g C m−2 cf 417 g C m−2 in un- and 583 g C m−2 in improved grasslands) Cmic showed little temporal variation (v=37%) Soil microbial activity, measured as basal respiration was also mainly affected by grassland type and site (n=32%) In contrast to Cmic, respiration was significantly (P<0001) high in the improved grassland at Sourhope (2634 l h−1m−2 cf 796 l h−1m−2 in semi- and 2039 l h−1m−2 unimproved grasslands) and Abergwyngregyn (1988 l h−1m−2 cf 1737 l h−1m−2 in semi- and 882 l h−1m−2 unimproved grasslands) Microbial activity, measured as potential carbon utilisation, agreed with the respiration measurements and was significantly (P<0001) high in the improved grassland at all three sites (A590 014 cf 009 in semi- and 007 in unimproved grassland) However, date of sampling also had a significant (P<0001) impact on C utilisation potential (v=247%) with samples from April 1997 having highest activity at all three sites Variation in microbial community structure was due, predominantly, to grassland type (average v=236% for bacterial and fungal numbers and PLFA) and date of sampling (average v=397% for bacterial and fungal numbers and PLFA) Numbers of culturable bacteria and bacterial PLFA were significantly (P<0001) high in the improved grassland at all three sites Fungal populations were significantly (P<001) high in the unimproved grassland at Sourhope and Abergwyngregyn The results demonstrate a shift in soil microbial community structure from one favouring fungi to one favouring bacteria as grassland improvement increased Numbers of bacteria and fungi were also significantly (P<0001) higher in August than any other sampling date Canonical variate analysis (CVA) of the carbon utilisation data significantly (P<005) differentiated microbial communities from the three grassland types, mainly due to greater utilisation of sugars and citric acid in the improved grasslands compared to greater utilisation of carboxylic acids, phenolics and neutral amino acids in the unimproved grasslands, possibly reflecting substrate availability in these grasslands Differences in Cmic, activity and community structure between grassland types were robust over time In addition, broad scale measures of microbial growth and activity (Cmic and respiration) showed little temporal variation compared to measures of soil microbial community structure, which varied quantitatively with respect to environmental variables (temperature, moisture) and plant productivity, hence substrate supply

How changes in animal diversity within a soil trophic group influence ecosystem processes.

Abstract: There are few experimental data on the consequence of varying the composition and diversity of soil animals communities, or soil food-webs, on ecosystem properties. Here, we tested the hypothesis that varying the diversity and composition of soil animals within a trophic group, the microbial-feeders, affects litter decomposition and nutrient flux in grassland. Microcosms containing grassland plant litter were inoculated with individual species of Collembola Folsomia candida, Pseudosinella alba, and Protaphorura armata,and all possible two and three species combinations of these species. Our data show that towards the end of the experiment individual species of Collembola, and especially F. candida, had markedly different, but positive, effects on measures of litter mass loss, microbial activity (CO2 respiration) and the leaching of dissolved organic carbon (DOC) and nitrate-N. Two and three species combinations of Collembola revealed that effects of fauna on ecosystem processes were due to differences in the composition of the collembolan community, rather than the number of species present. In comparison to a treatment that had no fauna, significantly higher rates of litter mass loss, microbial activity, and DOC and nitrate release were detected only in microcosms that contained F. candida. There was no evidence of effects of F. candida in combination with other species, relative to effects of F. candida alone, on the above properties. These findings support the notion that changes in the diversity of microbivorous fauna may not have a predictable effect on decomposition processes rates and that the functioning of the microbial-feeding trophic group is influenced mainly by the physiological attributes of the dominant animal species present, in this case F. candida.

Biological interactions in grassland soils and productivity

Abstract: Cook, R., Bardgett, R. D., Eason, W. R., Skot, L., Webb, K. Judith (2001). Biological interactions in grassland soils and productivity. Pages 167-168 in: Gomide, J.A., Mattos, W.R.S., Carneiro da Silva, S. (Eds). Grassland Ecosystems: An Outlook into the 21st Century. Proceedings of the 19th International Grassland Congress, Sao Paulo, Brazil, 10-21 February 2001. Fundacao Estudos Agrarios Luiz Queiroz (Fealq), Piracicaba, ISBN:8571330107. Gomide, J. A.; Mattos, W. R. S.; Carneiro da Silva, S. (eds.)