Prairie Soils Research Articles

Seven years of enhanced water availability influences the physiological, structural, and functional attributes of a soil microbial community

Water availability is known to influence many aspects of microbial growth and physiology, but less is known about how complex soil microbial communities respond to changing water status. To understand how long-term enhancement of soil water availability (without flooding) influences microbial communities, we measured the seasonal dynamics of several community-level traits following >7 years of irrigation in a drought-prone tallgrass prairie soil. From late May to mid-September, water was supplied to the irrigated treatments based on calculated plant water demand. Phospholipid fatty acids (PLFA) were used to assess changes in microbial community structure and physiology. To assess the community-level physiological profile, microbial utilization of BIOLOG substrates was determined. After incubation for 2 days, the distribution of added 13C-glucose in microbial and respired pools was used as an index of substrate utilization efficiency. We also measured the relative contribution of fungi and bacteria to soil microbial biomass via substrate-induced respiration (SIR). Multivariate analysis of mol% PLFA and BIOLOG substrate utilization indicated that both water availability and sampling time influenced both the physiological and structural characteristics of the soil microbial community. Specific change in biomarker PLFA revealed a decreased ratio of cyclopropyl to ω7-precursors due to water addition, suggesting community-level stresses were reduced. Over the growing season, continuously greater water availability resulted in a 53% greater ratio of fungal to bacterial biomass using SIR, and a 65% increase in fungal PLFA. The number of substrates utilized by the cultivable microbial community tended to be greater in continuously wetted soil, especially during periods of low rainfall. While water dynamics appeared to be associated with some of the shifts in microbial community activity, structural and functional changes in the community appeared to be more closely linked to the cumulative effects of water regime on ecosystem properties. Seasonality strongly influenced microbial communities. The environmental factors associated with seasonal change need to be more closely probed to better understand the drivers of community structure and function.

Woody encroachment effects on the calcareous prairie soils of Louisiana

The calcareous prairies of Louisiana have been threatened by the encroachment of woody plants, primarily eastern red cedar (Juniperus virginiana). The knowledge of whether eastern red cedar encroachment has altered the soil chemical characteristics is of interest in light of the restoration and management of these rare plant communities. The objectives of this study were to investigate differences in soil nutrient levels among prairie, transition and forest soils and to determine which soil properties could be used to differentiate prairie soils from soils impacted by woody vegetation. We collected soil samples along transects traversing prairie, transition, and forest from three remnant calcareous prairies in Louisiana. We also measured relative elevation (RE) at the points where soil samples were taken. The transition was the area heavily encroached by red cedar. The soil samples were analyzed for pH, electrical conductivity (EC), and Mehlich III extractable nutrients. Factor analysis and stepwise discriminant analysis were used to determine differences in these soil properties among the vegetation types and to identify the soil properties that could be used to discriminate the soil types (prairie soil, transition soil and forest soil). The prairie soil was distinctly different from the forest soil in nutrient levels while the transition soil shared the properties of both the forest soil and the prairie soil but with a change toward the forest soil, indicating that eastern red cedar impacted the prairie soil. The discriminating soil and topographical attributes were pH, nutrients (Ca, Mg, Fe, and Mn) and RE. The discriminant functions derived from these attributes reasonably predicted the soil types and may be used as a predictive and classification tool in the effort to delineate similar prairie‐forest associations encroached upon by eastern red cedar. In addition, these findings provide land managers of natural areas, especially of humid regions, a better perspective on eastern red cedar impact on prairie soil nutrient levels.

Using landscape and depth gradients to decouple the impact of correlated environmental variables on soil microbial community composition

Simultaneously assessing shifts in microbial community composition along landscape and depth gradients allows us to decouple correlations among environmental variables, thus revealing underlying controls on microbial community composition. We examined how soil microbial community composition changed with depth and along a successional gradient of native prairie restoration. We predicted that carbon would be the primary control on both microbial biomass and community composition, and that deeper, low-carbon soils would be more similar to low-carbon agricultural soils than to high carbon remnant prairie soils. Soil microbial community composition was characterized using phospholipid fatty acid (PLFA) analysis, and explicitly linked to environmental data using structural equations modeling (SEM). We found that total microbial biomass declined strongly with depth, and increased with restoration age, and that changes in microbial biomass were largely attributable to changes in soil C and/or N concentrations, together with both direct and indirect impacts of root biomass and magnesium. Community composition also shifted with depth and age: the relative abundance of sulfate-reducing bacteria increased with both depth and restoration age, while gram-negative bacteria declined with depth and age. In contrast to prediction, deeper, low-C soils were more similar to high-C remnant prairie soils than to low-C agricultural soils, suggesting that carbon is not the primary control on soil microbial community composition. Instead, the effects of depth and restoration age on microbial community composition were mediated via changes in available phosphorus, exchangeable calcium, and soil water, together with a large undetermined effect of depth. Only by examining soil microbial community composition shifts across sites and down the soil column simultaneously were we able to tease apart the impact of these correlates environmental variables.

A review of copper fertilizer management for optimum yield and quality of crops in the Canadian Prairie provinces

Deficiency of copper (Cu) in Canadian prairie soils is not widespread, but whenever it occurs it can cause a drastic reduction in seed yield and quality of most cereals, especially wheat. Field experiments conducted in western Canada indicated that broadcast-incorporation of granular Cu fertilizers prior to seeding at 3-5.6 kg Cu ha-1 was usually sufficient to prevent Cu deficiency in wheat, and improve seed yield and quality. At lower rates (< 2.0 kg Cu ha-1), broadcast-incorporation of granular Cu fertilizers was not effective, while surface spray-broadcast followed by incorporation of liquid Cu fertilizers was much more effective in increasing seed yield of wheat in the first year of application. Surface broadcast without incorporation and seedrow-placed granular Cu fertilizers were much less effective in improving seed yield of wheat than their foliar or soil-incorporated applications. In the growing season, foliar applications of Cu at 0.20 to 0.28 kg Cu ha-1 to wheat at the Feekes 6 (first node of stem visible at base of shoot or stem elongation), Feekes 10 (sheath of last leaf completely grown or flag-leaf) and early boot growth stages were very effective in restoring seed yield, while Cu applications at the Feekes 2 (four-leaf) or Feekes 10.5 (complete heading) growth stage did not have a consistent effect to correct damage caused by Cu deficiency. Some Cu fertilizers (e.g., Cu oxide) were less effective than others in preventing/correcting Cu deficiency. Soil application at relatively high rates produced residual benefits in increasing seed yield for a number of years. The sensitivity of crops to Cu deficiency is usually in the order (wheat, flax, canary seed) > (barley, alfalfa) > (timothy seed, oats, corn) > (peas, clovers) > (canola, rye, forage grasses). Stem melanosis in wheat was associated with deficiency of Cu in soil, and the disease was reduced substantially with Cu application. A high level of available P in soil was observed to induce/increase severity of Cu deficiency in wheat. Soil analysis for diethylene triamine pentacetic acid- (DTPA) extractable Cu in soil can be used as a good diagnostic tool to predict Cu deficiency, but there was a poor relationship between total Cu concentration in shoots and the degree of Cu deficiency in crops. Application of Cu fertilizers to wheat on Cu-deficient soils also generally improved seed quality. Key words: Application time, Cu source, foliar application, granular Cu, growth stage, placement method, rate of Cu, seedrow-placed Cu, soil incorporation, wheat

English

This study was conducted to determine the long-term influence (>11 years) of a number of reclamation management practices on the concentration microbial biomass carbon (MBC) and the concentration and mass of soil organic carbon (SOC) in reclaimed soils from a number of surface coal mines located in Wyoming. We compared a number of commonly used reclamation management practices (grazed vs. ungrazed; stockpiled topsoil vs. direct hauled topsoil; hay-crimp mulch vs. stubble mulch; grass seed mixture vs. shrub seed mixture) at five surface coal-mines. In addition, a native, undisturbed prairie soil was also sampled at each of the five coal-mines native sites. Reclamation management practices compared in this study, with the exception of stubble mulching, did not have significantly different long-term effects on SOC concentrations. Microbial biomass C was more influenced than SOC by the compared practices in the soils examined. In more than half of the sites analyzed, reclaimed soils had SOC concentrations similar to undisturbed soil reflecting the potential to accumulate C in reclaimed coal-mine soils.

Short‐term Versus Continuous Chisel and No‐till Effects on Soil Carbon and Nitrogen

For various reasons, North American crop farmers are more likely to practice limited‐duration no‐till than continuous no‐till (NT). Little is known about effects of short‐term no‐till (ST‐NT) on organic C and total N relative to NT and conventional‐till systems. A field experiment was initiated in 1980 to study the effects of NT, chisel plow (CP), and moldboard plow in continuous corn (CC; Zeamays L.) and soybean (Glycinemax L.)–corn (SC) rotations on dark prairie soil. In 1996, the moldboard treatments were split into a ST‐NT subplot and an intermittently chisel‐plowed (STI‐CP) subplot that was chiseled only before corn. In 2003, soil samples were taken incrementally to the 1.0‐m depth from NT, CP, ST‐NT, and STI‐CP plots. Soil C and N accumulation was unaffected by rotation system at any depth interval. Tillage treatments significantly affected soil C and N concentrations only in the upper 50 cm. On an equivalent soil mass basis, C storage to 1.0 m after 24 yr totaled 151 Mg ha−1 in continuous NT, but just 108 Mg ha−1 in continuous CP. Short‐term no‐till and STI‐CP systems resulted in 26 and 21 Mg ha−1, respectively, more soil C than CP. Total N storage was similar for NT and ST‐NT systems, but was significantly lower (4 Mg ha−1 less) with CP. Our results suggest that the combination of moldboard plowing (17 yr) followed by short‐term (6–7 yr) no‐till or intermittent chisel was generally superior to continuous chisel plowing (24 yr) in soil C and N contents.

Effluxed CO 2- 13C from sterilized and unsterilized treatments of a calcareous soil

Soil inorganic carbon (C) represents a substantial C pool in arid ecosystems, yet little data exist on the contribution of this pool to ecosystem C fluxes. A closed jar incubation study was carried out to test the hypothesis that CO 2- 13C production and response to sterilization would differ in a calcareous (Mojave Desert) soil and a non-calcareous (Oklahoma Prairie) soil due to contributions of carbonate-derived CO 2. In addition to non-sterilized controls, soils were subjected to sterilization treatments (unbuffered HgCl 2 addition for Oklahoma soil and unbuffered HgCl 2 addition, buffered HgCl 2 addition, and autoclaving for Mojave Desert soil) to decrease biotic respiration and more readily measure abiotic CO 2 flux. Temperature and moisture treatments were also included with sterilization treatments in a factorial design. The rate of CO 2 production in both soils was significantly decreased (36–87%) by sterilization, but sterilization treatments differed in effectiveness. Sterilization had no significant effect on effluxed CO 2- 13C values in the non-calcareous Oklahoma Prairie soil and autoclaved Mojave Desert soil as compared to their respective non-sterilized controls. However, sterilization significantly altered CO 2- 13C values in Mojave Desert soil HgCl 2 sterilization treatments (both buffered and non-buffered). Plots of 1/CO 2 versus CO 2-δ 13C (similar to Keeling plots) indicated that the source CO 2-δ 13C value of the Oklahoma Prairie soil treatments was similar to the δ 13C value of soil organic matter [(SOM); −17.76‰ VPDB] whereas the source for the (acidic) unbuffered-HgCl 2 sterilized Mojave Desert soil was similar to the δ 13C value of carbonates (−0.93‰ VPDB). The source CO 2-δ 13C value of non-sterilized and autoclaved (−18.4‰ VPDB) Mojave Desert soil treatments was intermediate between SOM (−21.43‰ VPDB) and carbonates and indicates up to 13% of total C efflux may be from abiotic sources in calcareous soils.

Spatial Variability of Soil Chemical Properties of a Prairie–Forest Transition in Louisiana

Woody plant expansion, particularly eastern red cedar (Juniperus virginiana L.), has been a major threat to Louisiana calcareous prairies. Previous studies have shown that woody plant expansion into grasslands is associated with an increase in soil heterogeneity. We studied the within site spatial variability and among site differences of surface (0–15 cm depth) soil pH, electrical conductivity (EC), and Mehlich III extractable Ca, Mg, K, Fe and Mn from three remnant prairie-forest associations in Winn Parish, Louisiana. The prairie soil was consistently basic (pH > 7.0) and the forest soil was acidic (pH < 7.0) while the transition soil was neutral (pH = 7.0). A nonparametric statistical test for the equality of medians among sites showed the median values of the soil attributes differed (α = 0.05) except for soil Ca and Fe. The similarity in Ca concentration among sites was attributed to the calcareous parent material common to the three sites. Geostatistical analysis showed that spatial dependence was expressed over a range of 20–30 m for most of the soil attributes considered. Semivariogram shapes were similar among sites, suggesting the greater control of soil parent material on the observed spatial soil pattern. Shorter range of variation emerged only for soil pH when soil data from the forest and transition were deleted, indicating the scaling characteristics of soil pH and its susceptibility to plant induced changes. It is concluded that soil pH can be used as an index to determine prairie-forest boundary, and to access the impact of eastern red cedar on these and similar sites derived from calcareous parent material. Further, results from this study can be used for designing future ecological studies within the prairie by taking the soil spatial variability into account.

Amycolatopsis minnesotensis sp. nov., isolated from a prairie soil

Two actinomycete strains, 32U-2T and 32U-4, were isolated from a prairie soil in Minnesota and subjected to characterization by means of polyphasic taxonomy. The 16S rRNA gene sequences were determined following PCR amplification and cloning. A phylogenetic analysis, based on comparative analysis of 16S rRNA gene sequences, indicated that the organisms consistently formed a well-separated, distinct sub-branch within the radiation of the genus Amycolatopsis of the family Pseudonocardiaceae. The levels of 16S rRNA sequence similarity between the isolates and the type strains of recognized Amycolatopsis species ranged from 94.1 to 97.9 %. The highest levels of sequence similarity were found between the isolates and Amycolatopsis coloradensis (97.6-97.9 %), Amycolatopsis alba and Amycolatopsis orientalis (97.3-97.6 %) and Amycolatopsis lurida (97.2-97.5 %). Chemotaxonomic characteristics supported the phylogenetic relationships between the organisms and members of the genus Amycolatopsis. However, a broad range of phenotypic and genetic data revealed that the isolates should be classified as novel species of the genus Amycolatopsis, for which the name Amycolatopsis minnesotensis sp. nov. is proposed. The type strain is 32U-2T (=KCCM 42246T = NRRL B-24435T).

Effects of invasive scotch broom on soil properties in a Pacific coastal prairie soil

Scotch broom ( Cytisus scoparius) is a leguminous shrub, native to Europe that has invaded significant areas of the Pacific Northwest and rigorously competes with native vegetation. Mineral soils under scotch broom colonies and adjacent coastal prairie on the Mendocino Coast of Northern California were sampled to determine how soil properties and microbial processes have been affected. Soils under scotch broom were significantly more acidic and had greater organic matter content than prairie soils. The activities of two soil enzymes responsible for processing major detrital carbon and phosphorus pools were significantly higher under scotch broom. Organic matter accumulation with no change in C:N, a greater increase in phosphatase activity (123%) than in β-glucosidase (84%) under scotch broom, and a significant difference between soil C:P under scotch broom (619) and prairie vegetation (470) all suggest that the coupling of nutrient cycles has changed.

Relationships Between Soil Characteristics, Distribution and Restoration Potential of The Federal Threatened Eastern Prairie Fringed Orchid, Platanthera leucophaea (Nutt.) Lindl

The Federal threatened eastern prairie fringed orchid (Platanthera leucophaea) occupies prairies, sedge meadows, bogs and fens, primarily north of the Wisconsinan glacial boundary. In the Midwest, where restoration is a recovery objective, its southern distribution is thought to be limited by the transition from nutrient-rich Wisconsinan-aged soils to more acidic nutrient poor soils of Illinoian-aged glacial drift. To better understand edaphic factors affecting its distribution and potential for establishment of new populations, we analyzed soil characteristics across the range of habitats occupied by this species, as well as from unoccupied habitats on the Illinoian Till Plain. We found that P. leucophaea occupies a complex edaphic gradient in variation of % organic matter, base content and soil texture. On Wisconsinan-aged substrates, it occurs in circum-neutral base-rich organic prairie soils in Illinois and Wisconsin and in less calcareous soils with slightly higher pH and lower organic matter content in Michigan lake plain prairies. Eastern sand prairie and sedge meadow habitats on Wisconsinan-aged drift and on unglaciated soils are moderately acid and nutrient poor, while bog and fen habitats are more strongly acidic and highly organic, with no evidence for an underlying calcareous substrate. In comparison, unoccupied prairie soils on the Illinoian till plain have lower pH, % organic matter and base concentrations. These soils also have relatively high % silt content which results in comparatively low available soil moisture holding capacity. This combination of soil conditions may exceed the tolerance limits of P. leucophaea and prevent this species from occurring south of the Wisconsin glacial boundary in the Midwest. On the other extreme, calcareous fens have high pH levels as well as extremely high calcium concentrations, which may exceed the tolerance limits of this species. These findings have implications for guiding efforts to establish P. leucophaea into habitats that should be suitable for this species.

Changes in Soil Microbial Community Structure in a Tallgrass Prairie Chronosequence

Increasing the abundance of fungi relative to bacteria should favor C accrual, because fungi use C more efficiently, and are composed of more recalcitrant C compounds. We examined changes in soil microbial community structure following cessation of tillage‐based agriculture and through subsequent succession in a C‐accruing tallgrass prairie restoration chronosequence. We predicted that the relative abundance of fungi would increase following conversion from tillage‐based agriculture. Soil microbial community structure was assessed as relative abundances of phospholipid fatty acids (PLFAs). Cessation of tillage‐based agriculture did initially lead to an increase in the abundance of fungi, particularly arbuscular mycorrhizal fungi (AMF), relative to bacteria. We suggest this is primarily due to reduced disturbance when tilling ceases. Vegetation characteristics also appear to be important, with high cyclopropyl/precursor PLFA ratios indicating bacterial communities under stress in agricultural soils, probably due to low C, and possibly to low C relative to N inputs. A secondary gradient in soil microbial community structure was related to successional time, and tied to soil characteristics, particularly bulk density (Db), pH, and soil organic C and N. However, while the fungi/bacteria (F/B) ratio was high in early succession plots, it declined later in succession. In addition, although the F/B ratio increased with SOC in the agricultural soils, it decreased with SOC in prairie soils. We conclude that increased community metabolic efficiency due to higher relative abundances of fungi is not the primary mechanism leading to enhanced C storage in these soils.

Natural 15N abundances in a tallgrass prairie ecosystem exposed to 8-y of elevated atmospheric CO 2

After 8-y of elevated CO 2, we previously detected greater amounts of total soil nitrogen, suggesting that rates of ecosystem N flux into or out of tallgrass prairie had been altered. Denitrification and associative N fixation rates are the two primary biological processes that are known to control N loss and accumulation in tallgrass prairie soil. Therefore, our objective was to assess the natural abundance of plant and soil 15N isotopes as a cumulative index of potential change in efflux or influx of N into and out of the tallgrass prairie after 8-y of exposure to elevated CO 2. Aboveground plant delta 15N values of Andropogon gerardii were close to zero and more positive as a result of elevated CO 2, but whole-soil values at the 5–30 cm depth were significantly reduced (6.8 vs 7.3; P<0.05) under elevated CO 2-chamber (EC) relative to ambient CO 2- chamber (AC). Total, aboveground plant biomass, root-in-growth, extractable N, microbial biomass N, and soil pools collectively exhibited a range of delta 15N values from −2.8 to 7.3. Measurements of surface soil 15N indicate that a change in N inputs and outputs has occurred as a result of elevated atmospheric CO 2. In addition to possible changes in denitrification and N 2 fixation, other sources of N such as the re-translocation of N to the surface from deeper soil layers are needed to explain how soil N accrues in surface soils as a consequence of elevated CO 2. Our results support the notion that C accrual may promote N accrual, possibly driven by high plant and microbial N demand amplified by soil N limitation.

Diminishing effects of ant mounds on soil heterogeneity across a chronosequence of prairie restoration sites

It is well recognized that mound-building ants affect soil and vegetation heterogeneity, yet little is known about the extent to which such changes are propagated through time. We compared soil properties from ant mounds (built by Formica montana and Acanthamyops claviger ) and from adjacent prairie soils at three tallgrass prairie restoration sites in the Midwestern United States, ranging in age from 8 to 26 years post-restoration of native species on former row-crop agriculture plots. We were particularly interested in N -dynamics on and off the mounds. All of the soil variables measured showed the greatest difference between mound and prairie soils at the 8-year old site. At that site, we found that ant mounds had significantly higher concentrations of total N, dissolved organic N, and NH 4 + compared to prairie soil. Differences in concentrations of these nitrogen pools between mound and prairie soils were, however, lost with increasing time since restoration. The lack of N-enrichment at the older sites suggests that nutrient enrichment of ant mounds may be a transient phenomenon in certain ecosystems. To our knowledge, this is the first report that illustrates a critical, but a temporally dynamic role of ant mounds in creating resource heterogeneity in a restoration project.

Long-term cultivation effects on the quantity and quality of organic matter in selected Canadian prairie soils

Sixteen Orthic Chernozemic surface soil samples, one half from virgin prairie and one half from adjacent cultivated prairie (cultivated for 31 to 94 years), were collected from eight sites throughout Southern Saskatchewan, Canada. Samples were analyzed for total organic C and a number of other chemical and physical properties. The virgin and cultivated soils at site No. 4 were selected for more detailed analysis by CP-MAS 13C NMR, Curie-point-pyrolysis-gas chromatography/mass spectrometry (Cp-Py-GC/MS), and by pyrolysis-field ionization mass spectrometry (Py-FIMS). Long-term cultivation resulted in large significant decreases in total SOM (soil organic matter), as represented by total soil organic C. There were significant increases in aromaticity of the SOM as a result of long-term cultivation as indicated by CP-MAS 13C NMR spectroscopy. This was mainly attributable to the result of cultivation-enhanced degradation of aliphatic C relative to aromatic C. Organic compounds identified in the Cp-Py-GC/MS spectra of the virgin and cultivated soils at site No. 4 consisted of n-alkanes (ranging from C 11 to C 22) and alkenes (ranging from C 7:1 to C 21:1), with the virgin soil being richer in alkenes than the cultivated soil. Other components identified were cyclic aromatics, carbocyclics, N-containing aromatics, N-heterocyclics, benzene and substituted benzenes, phenols and substituted phenols and substituted furans. The compounds identified appeared to originate from long-chain aliphatics, lignins, polyphenols, aromatics, polysaccharides, and N-containing compounds in the two soils. While qualitatively similar compounds were identified by Py-FIMS in the two soils, the total ion intensity (TII) of the virgin soil was almost 2.5 times as high as that of the cultivated soil. This suggests that cultivation made the organic matter less volatile, either by favouring the formation of higher molecular weight organic matter or by promoting the formation of non-volatile metal-organic matter complexes. The Py-FIMS spectra showed that the virgin soil contained relatively more lignin dimers, lipids, sterols, and n-C 16 to n-C 34 fatty acids than the cultivated soil. Thus, conversely, the cultivated soil was richer in carbohydrates, phenols and lignin monomers, alkyl aromatics and N-containing compounds, including peptides, than the virgin soil.

The abundance and efficacy of Rhizobium leguminosarum bv. viciae in cultivated soils of the eastern Canadian prairie

For optimum production, the use of commercial rhizobial inoculant on pea ( Pisum sativum L.) at seeding is necessary in the absence of compatible rhizobial strains or when rhizobial soil populations are low or symbiotically ineffective. Multiple site experiments were conducted to characterize the abundance and effectiveness of resident populations of Rhizobium leguminosarum bv. viciae ( Rlv) in eastern Canadian prairie soils. A survey of 20 sites across a broad geographical range of southern Manitoba was carried out in 1998 and was followed by more intensive study of five of the sites in 1999 and 2000. Appreciable nodulation of uninoculated pea was observed at all sites which had previously grown inoculated pea. However, uninoculated pea grown at two sites, which had not previously grown pea, had negligible nodulation. Likewise, wild Lathyrus sp. and Vicia sp. plants collected from uncultivated areas adjacent to agricultural sites were poorly nodulated. In the more intensively studied sites, there was a tendency towards higher nodulation in pea plants receiving commercial inoculant containing Rlv strain PBC108 across all site-years (e.g., 4.7% in nodulation and 22% in nodule mass), but the effect was significant at only 2 of 10 site-years. Despite a relatively high range of soil pH (6–8), regression analysis indicated that decreasing soil pH resulted in lower nodulation rates. Likewise, electrical conductivity (EC) was correlated to nodulation levels, however the effect of EC was likely more indicative of the influence of soil texture and organic matter than salinity. As with nodulation, commercial inoculation tended to increase above-ground dry matter (DM) and fixed-N (estimated by the difference method) at the early pod-filling stage, but again the effects were significant at only 2 of 10 site-years. Specifically, above-ground DM and fixed-N levels were up to 29 and 51% greater, respectively, in inoculated compared to non-inoculated treatments at these sites. Addition of N-fertilizer at a rate of 100 kg N ha −1 decreased nodulation at almost all site-years (by as much as 70% at one site), but rarely resulted in increases in above-ground DM compared to inoculated plots. The study indicates for the first time that populations of infective, and generally effective strains of Rlv occur broadly in agricultural soils across the eastern Canadian prairie, but that there is a tendency for increased symbiotic efficiency with the use of commercial inoculant.

Measurement of actinide, fission and daughter product contamination in prairie soil

In 1951, 6.7 liter of an aqueous solution of actinides, fission and daughter products leaked from an underground storage tank into prairie soil. In 2001, soil samples were collected from the site to determine the degree and extent of the contamination. This paper reports on the continuation of complementary analytical techniques used to determine the concentrations of the contaminants in the soil samples, including gamma-ray spectroscopy, neutron activation analysis (NAA) and liquid scintillation counting (LSC). Gamma-ray spectroscopy was able to identify and quantify the presence of 137 Cs, while the activities of the actinides and remaining fission and daughter products were too low to be measured. Concentrations of 137 Cs as low as 0.15 Bq/g and as high as 341 Bq/g were measured. NAA was successful in detecting 238 U. Only preliminary LSC analysis has been conducted, resulting in gross beta-counts for the soil samples. Finally, correlations were developed between borehole gamma logging values and corresponding concentrations of 137 Cs determined by gamma-spectroscopy and gross beta-counts from LSC analysis.

Measuring tree root respiration using 13C natural abundance: rooting medium matters

Tree root respiration utilizes a major portion of the primary production in forests and is an important process in the global carbon cycle. Because of the lack of ecologically relevant methods, tree root respiration in situ is much less studied compared with above-ground processes such as photosynthesis and leaf respiration. This study introduces a new (13)C natural tracer method for measuring tree root respiration in situ. The method partitions tree root respiration from soil respiration in buried root chambers. Rooting media substantially influenced root respiration rates. Measured in three media, the fine root respiration rates of longleaf pine were 0.78, 0.27 and 0.18 mg CO(2) carbon mg(-1) root nitrogen d(-1) at 25 degrees C in the native soil, tallgrass prairie soil, and sand-vermiculite mixture, respectively. Compared with the root excision method, the root respiration rate of longleaf pine measured by the field chamber method was 18% higher when using the native soil as rooting medium, was similar in the prairie soil, but was 42% lower if in the sand-vermiculite medium. This natural tracer method allows the use of an appropriate rooting medium and is capable of measuring root respiration nondestructively in natural forest conditions.

Response of soil δ15N and nutrients to eastern red cedar (Juniperus virginiana) encroachment into a relict calcareous prairie

The calcareous prairies of Louisiana have been threatened by the encroachment of woody plants, primarily eastern red cedar (Juniperus virginiana). The restoration and management of these rare plant communities require a thorough understanding of the soils supporting them. The knowledge of whether eastern red cedar encroachment has altered these soils is also of interest. We studied the depth distribution, at contrasting vegetation types (prairie, transition, forest) and landscape positions, of δ15N, total N, organic C, C/N ratio, Ca, Mg, K and pH of three relict prairie-forest associations in north central Louisiana, USA. The effect of vegetation type was significant for soil δ15N and Ca. Plant leaf samples from prairie, transition, and forest showed similar δ15N signals, and mean values ranged between −1.6‰ and −1.1‰. The order of soil 15N enrichment of the 0–10 cm depth relative to corresponding leaves was forest soil > transition soil > prairie soil. The forest soil was significantly enriched with 15N compared with the prairie soil and transition soil. Except for C/N ratio, all the soil properties significantly decreased with depth while δ15N increased with depth. Significant differences in C/N ratio, Ca and Mg were associated with landscape position. The change in soil pH due to woody encroachment was restricted to the 0–10 cm depth. The results suggest that the prairie soil was distinctly different from the forest soil and that the vegetation at transition (encroaching woody plants) was altering the surface soil pH towards ‘forest-like’ conditions.

Microbial community PLFA and PHB responses to ecosystem restoration in tallgrass prairie soils

Native North American prairie grasslands are renowned for the richness of their soils, having excellent soil structure and very high organic content and microbial biomass. In this study, surface soils from three prairie restorations of varying ages and plant community compositions were compared with a nearby undisturbed native prairie remnant and a cropped agricultural field in terms of soil physical, chemical and microbial properties. Soil moisture, organic matter, total carbon, total nitrogen, total sulfur, C:N, water-holding capacity and microbial biomass (total PLFA) were significantly greater ( p<0.05) in the virgin prairie remnant as well as the two long-term (21 and 24 year) prairie restorations, compared with the agricultural field and the restoration that was begun more recently (7 years prior to sampling). Soil bulk density was significantly greater ( p<0.05) in the agricultural and recently restored sites. In most cases, the soil quality indicators and microbial community structures in the restoration sites were intermediate between those of the virgin prairie and the agricultural sites. Levels of poly-β-hydroxybutyrate (PHB) and PLFA indicators of nutritional stress were significantly greater ( p<0.05) in the agricultural and recent restoration sites than in the long-term restorations or the native prairie. Samples could be assigned to the correct site by discriminant analysis of the PLFA data, with the exception that the two long-term restoration sites overlapped. Redundancy analysis showed that prairie age ( p<0.005) was the most important environmental factor in determining the PLFA microbial community composition, with C:N ( p<0.015) also being significant. These findings demonstrate that prairie restorations can lead to improved quality of surface soils. We predict that the conversion of farmland into prairie will shift the soil quality, microbial community biomass and microbial community composition in the direction of native prairies, but with the restoration methods tested it may take many decades to approach the levels found in a virgin prairie throughout the soil profile.