Number Of Bacterial-feeding Nematodes Research Articles

Correlation between soil development and native plant growth in forest restoration after surface mining

Recovery of soil conditions in ecosystems that have been modified by human activities can happen in time, but empirical data indicating how soil development influences plant growth are limited. Here, we studied the changes in 23 properties of jarrah-forest soils restored after bauxite mining (1.5, 7, 22 years post-restoration) and their correlative effects on the growth of bossiaea, a plant that grows in the jarrah-forest of Western Australia. We found that physico-chemical and biological properties of restored soils were different compared with properties of unmined soils, and were correlated with time post-restoration. In turn, biomass produced by bossiaea seedlings was correlated with time post-restoration. Differential correlative effects of restored soils properties translated into higher biomass produced by bossiaea in soils aged 22 years compared with biomass produced in younger soils and in unmined soils. Biomass variation of bossiaea seedlings grown in restored soils was matched to the physico-chemical and biological properties of the soils to detect correlative effects of individual soil properties on plant growth. We found that biomass produced by bossiaea seedlings was positively correlated with the number of bacterial-feeding nematodes in soils, a likely consequence of increased microbial biomass, and with the rate of CO2 produced by microbial respiration of phenolic compounds. Our data suggest recovery of physico-chemical and key biological properties of soil through restoration after bauxite mining, but overall, at 22 years soils were not recovered to reference conditions. Our study has implications for restoration projects aiming to promote soil development in addition to plant growth.

Effects of six grassland plant species on soil nematodes: A glasshouse experiment

The effects of six individual plant species on the abundance and composition of nematode communities were studied in a glasshouse experiment during 16 weeks. The effect of the presence of plants, the correlation between nematode abundance and plant biomass, the response of plant-feeding nematodes and other nematode groups to different plant species was examined and also whether the effect differed between plant species within a plant functional group. The total number of nematodes increased during the study period in all treatments, although in some treatments, the increase levelled off after 8 or 12 weeks. The identity of the plant species affected both the total abundance of nematodes and the nematode community composition. The number of bacterial-feeding nematodes was greatest under grasses and legumes and was positively correlated with shoot biomass and negatively with root biomass. The response of the plant-feeding nematodes, which differed in abundance under both the investigated legume and the forb species, suggests that the identity of the plant species is more important than the plant functional group. A possible explanation could be related to differences in plant secondary metabolites. Despite some differences in the nematode species pool, the effects of plant species appear quite consistent between the present glasshouse study and previous field experiments.

Effects of climate change on soil factors and metazoan microfauna (nematodes, tardigrades and rotifers) in a Swedish tundra soil – a soil transplantation experiment

In order to study the effects of climate changes on soil organisms and processes, a transplantation experiment was undertaken. Eighteen soil blocks from an ombrotrophic mire (Stordalenmyren) at Abisko in northern Sweden were transplanted to nine sites in Sweden, from Umeå in the north to Alnarp in the south. The study was part of the EC-project DEGREE (Diversity effects in grassland ecosystems of Europe). The development of populations of nematodes, tardigrades and rotifers was followed in a monthly sampling programme. Microbial biomass and inorganic nitrogen were determined by other partners in the project. Some effects could be related to climatic conditions at the transplantation sites and the most clear influence was found at open sites with great fluctuations in temperature and moisture. The parameters most clearly influenced were amount of mineralized nitrogen, numbers of bacterial feeding nematodes belonging to the Rhabditida, and numbers of tardigrades. These components had a fairly large coefficient of variation (CV = 0.9–1.2). Microbial biomass as indicated by the CFE and Ergosterol methods varied less (CV = 0.3). The Shannon index, Evenness and Maturity index varied very little (CV = 0.1). In most changing parameters the effect was most clearly seen during the autumn. The fluctuations of microorganisms, nematodes, tardigrades and inorganic nitrogen could indicate a food web interaction.

Grazing in a porous environment. 2. Nematode community structure

The influence of soil matric potential on nematode community composition and grazing associations were examined. Undisturbed cores (5 cm diameter, 10 cm depth) were collected in an old field dominated by perennial grasses on a Hinckley sandy loam at Peckham Farm near Kingston, Rhode Island. Ten pairs of cores were incubated at −3, −10, −20 and −50 kPa matric potential after saturation for 21–28 or 42–58 days. Nematodes were extracted using Cobb's decanting and sieving method followed by sucrose centrifugal-flotation and identified to family or genus. Collembola and enchytraeids present were also enumerated because they are grazers that reside in air-filled spaces. Direct counts of bacteria and fungi were made to estimate biovolume using fluorescein isothiocyanate and fluorescein diacetate stains, respectively. Trophic diversity and maturity indices were calculated for nematode communities. Three patterns of matric potential effect were observed for nematode taxa. One, there was a consistent effect of matric potential for all seasons for Alaimus, Monhysteridae, Prismatolaimus, Paraxonchium and Dorylaimoides. Two, some effects of matric potential were consistent among seasons and other effects were inconsistent for Aphelenchoides, Aphelenchus, Cephalobidae, Coomansus, Eudorylaimus, Huntaphelenchoides, Panagrolaimidae, Paraphelenchus, Sectonema, and Tripyla. Third, effects of matric potential were always inconsistent among seasons for Aphanolaimus, Aporcelaimellus, Bunonema, Rhabditidae, and Tylencholaimus. As predicted, fungal and bacterial biomass responded oppositely to matric potential. Total bacterial biomass was greater at −3 kPa than −10, −20 and −50 kPa (P=0.0095). Total fungal biomass was greater at −50, −20 and −10 kPa than −3 kPa (P=0.0095). Neither bacterial-feeding, fungal-feeding nor predacious nematodes correlated significantly with bacterial or fungal biomass. Omnivorous and predacious nematodes correlated positively with number of bacterial-feeding nematodes; predacious nematodes also correlated positively with fungal-feeding nematodes. Numbers of Collembola and enchytraeids were more often correlated positively with microbial-grazing nematode numbers in drier than moist soils. From this study, we propose two mechanisms that may explain nematode community structure changes with matric potential: differential anhydrobiosis and/or enclosure hypotheses. The later suggests that drying of soil generates pockets of moisture in aggregates that become isolated from one another enclosing nematodes and their food in relatively high concentrations creating patches of activity separated by larger areas of inactivity.

Effects of Klebsiella planticola SDF20 on soil biota and wheat growth in sandy soil

The potential for ecological effects to occur after the release of genetically engineered microorganisms is a global concern and the release of biotechnology products must be assessed on a case-by-case basis. In this research, a genetically engineered strain of Klebsiella planticola (SDF20) bacteria was added to microcosms containing sandy soil and wheat plants to assess the potential for effects on soil biota and plant growth. One half of the soil treatments in this study contained wheat plants to compare some effects on growing rhizosphere communities in the experimental system. When SDF20 was added to soil with plants, the numbers of bacterial and fungal feeding nematodes increased significantly, coinciding with death of the plants. In contrast, when the parental strain, SDF15 was added to soil with plants, only the number of bacterial feeding nematodes increased, but the plants did not die. The introduction of either SDF15 or SDF20 strains to soil without plants did not alter the nematode community. No effects were observed on the activity of native bacterial and fungal communities by either SDF15 or SDF20. This study is evidence that SDF20 can persist under conditions found in some soil ecosystems and for long enough periods of time to stimulate change in soil biota that could affect nutrient cycling processes. Further investigation is needed to determine the extent these observations may occur in situ but this study using soil microcosms was the first step in assessing potential for the release of genetically engineered microorganisms to result in ecological effects.

Bacterial numbers in a pine forest soil in relation to environmental factors

Numbers of soil bacteria stained with acridine orange (AO) or fluorescein diacetate (FDA) were studied for 3 and 2 yr respectively. Three pine forest sites were used and both organic and mineral soil layers were included. Different patterns of fluctuation in bacterial numbers were found each year. Significant correlations were demonstrated between AO-stained bacterial numbers and soil moisture content and between FDA-stained bacteria and the accumulated precipitation during a week before the sampling date. In multiple regression analyses 60–80% of the variation in numbers of AO-stained bacteria could be accounted for by soil moisture and numbers of bacterial-feeding nematodes at the sampling dates, and 30–45% of the variation in numbers of FDA-stained bacteria was accounted for by precipitation.

Biological Aspects of Nitrogen Mineralization in Humus from a Pine Forest Podsol Incubated under Different Moisture and Temperature Conditions

Abstract in Undetermined Fluctuations of soil organism abundance, soil respiration and inorganic nitrogen were studied in a laboratory experiment on material taken from the humus layer of a Scots pine forest and incubated under different moisture and temperature regimes. The experiment was run for 28 wk with samplings every 7 wk. At 28 wk, increases in total movable (inorganic N + biomass N) were observed in samples incubated at high temperature and/or high moisture content. Most of the N was found in biomass except in incubations at the highest temperatures and moistures. Under those conditions, high abundance of nematodes occurred together with drastically increased amounts of inorganic N. Low values of inorganic N were recorded under conditions common in the field. No obvious relations could be detected between standing crops of bacteria and temperature, moisture or respiration. The number of bacterial-feeding nematodes seemed to be a possible measure of previous bacterial production contributing more information than the standing crop measurements of the bacteria, which varied little despite the direct evidence of substantial bacterial production in some incubation conditions. (Less)