Microbial Phosphatase Activity Research Articles

Impacts of Invasive Australian Acacias on Soil Bacterial Community Composition, Microbial Enzymatic Activities, and Nutrient Availability in Fynbos Soils.

Invasive plants often impact soil conditions, notably through changes in soil chemistry and microbial community composition, potentially leading to altered soil functionality. We determine the impacts of invasive nitrogen-fixing Australian Acacia trees on soil chemistry and function (carbon, nitrogen, and phosphorus cycling) in South Africa's Core Cape Subregion, and whether any differences in soil function are linked to differences in soil chemical properties and bacterial community composition between neighbouring acacia-invaded and uninvaded sites. We do so by using Illumina MiSeq sequencing data together with soil chemistry and soil enzyme activity profiles. Acacias significantly increased levels of soil nitrogen (NO3-, NH4+, and total N), C, and pH. Although we did not find evidence that acacias affected soil bacterial community diversity, we did find them to alter bacterial community composition. Acacias also significantly elevated microbial phosphatase activity, but not β-glucosidase, whilst having contrasting effects on urease. Changes in soil chemical properties under acacia invasion were found to correlate with changes in enzyme activities for urease and phosphatase. Similarly, changes in soil bacterial community composition were correlated to changes in phosphatase enzymatic activity levels under acacia invasion. Whilst we found evidence for acacias altering soil function by changing soil chemical properties and bacterial community composition, these impacts appear to be specific to local site conditions.

Influence of Uranium Concentration and pH on U-Phosphate Biomineralization by Caulobacter OR37

Uranium contamination of soils and groundwater in the United States represents a significant health risk and will require multiple remediation approaches. Microbial phosphatase activity coupled to the addition of an organic P source has recently been studied as a remediation strategy that provides an extended release of inorganic P (Pi) into U-contaminated sites, resulting in the precipitation of meta-autunite minerals. Previous laboratory- and field-based biomineralization studies have investigated environments with relatively high U concentrations (>20 μM). However, most contaminated sites have much lower U concentrations (<2 μM). The Environmental Protection Agency (EPA) limit for U in drinking water is 0.126 μM. Reaching this regulatory limit becomes challenging as U concentrations approach autunite solubility. We studied the precipitation of U(VI)-phosphate minerals by an environmental isolate of Caulobacter sp. (strain OR37) from an Oak Ridge, Tennessee, U-contaminated site. Abiotic U(VI) solubility experiments reveal that U(VI)-phosphate minerals do not form in the presence of excess Pi (500 μM) when U(VI) concentrations are <1 μM and pH is <5. When OR37 cells are reacted under the same conditions with Pi or glycerol-2-phosphate, U(VI)-phosphate mineral formation was observed, along with the formation of intracellular polyphosphate granules. These results show that bacteria provide supersaturated microenvironments needed for U(VI)-phosphate mineralization while hydrolyzing organic P sources. This provides a pathway to lower U concentrations to below EPA limits for drinking water.

Leaf-litter stoichiometry and microbial phosphatase activity, respiration, and decomposition as phosphorus enrichment endpoints: A laboratory experiment

AbstractDeciduous-forested streams are often fueled by terrestrial litter detritus and have some of the lowest scores for biological condition in the United States (US). Detrital endpoints may be m...

The Effect of Trails on Soil in the Oak Openings of Northwest Ohio

Trails are a form of recreational disturbance affecting natural areas. Trail disturbances can cause soil degradation such as compaction, which facilitates soil erosion and overland water flow. This study analyzed the effects of four different types of trails—paved, gravel, equestrian, and hiking—on soils in the Oak Openings of Northwest Ohio, a globally rare ecosystem that harbors more than a third of Ohio's rare plant species. Bulk density and soil moisture content were measured in order to determine physical impacts of trails. Soil pH, ammonium, nitrate, phosphate, and dissolved organic C and N concentrations were measured to determine effects on soil chemistry. Finally, soil microbial biomass and exoenzyme activities were measured to determine biological responses to trail disturbances. Soils from the gravel trail were the most affected by the trail, with significant effects on chemical (PO43-concentration) and biological (phosphatase and NAG activity, and MB-N) properties. The soils near the paved trail were the second most affected after the gravel trail, with a trend toward a pH change and a significant biological (microbial peptidase activity) effect of this trail. The soils of the horse and natural trails were generally not significantly different from the soils in the surrounding ecosystem. The only significant disturbance in the horse trail was increased bulk density in the trail, while the natural hiking trail had no statistically significant differences, but trends lean toward increased bulk density and reduced microbial phosphatase activity. These results suggest that the natural and horse trails have the least impact on the Oak Openings ecosystem.Jared Hawkins and Michael N. Weintraub. 2011. “The Effect of Trails on Soil in the Oak Openings of Northwest Ohio.” Natural Areas Journal 31(4):391-399.

Can we reduce phosphorus runoff from agricultural fields by stimulating soil biota?

When fertilizer phosphorus (P) is applied to soils, the P can run off fields and cause harmful algal blooms. Due to its chemistry, much of the added P that does not run off can bind to soil particles and become inaccessible to plants. In natural systems, microbial and faunal decomposers can increase soil P accessibility to plants. We tested the hypothesis that this may also be true in agricultural systems, which could increase P application efficiency and reduce runoff potential. We stimulated soil fauna with sodium (Na+ ) and microbes with carbon (C) by adding corn (Zea mays L.) stover and Na+ solution to plots in conventionally managed corn fields in northwestern Ohio. Stover addition increased microbial biomass by 65 ± 12% and respiration by 400-700%. Application of stover with Na+ increased soil detritivore fauna abundance by 51 ± 20% and likely did not affect the other invertebrate guilds. However, soil biological activity was low compared with natural systems in all treatments and was not correlated with instantaneous measures of P accessibility, though cumulative P accessibility over the course of the growing season was correlated with microbial phosphatase activity (slope=1.01, p<.01) and respiration (slope=0.42, p=.02). Therefore, in agricultural systems, treatments to stimulate decomposers already in those systems may be ineffective at increasing soil P accessibility in the short term, but in the long term, higher microbial activities can be associated with higher soil P accessibility.

Decoupled above‐ and belowground responses to multi‐decadal nitrogen and phosphorus amendments in two tundra ecosystems

AbstractGlobal change in the Arctic promotes deeper soil thaw and enhanced soil microbial activity, increasing nitrogen (N) and phosphorus (P) availability to plants and microbes in strongly nutrient‐limited ecosystems. This critical, positive climate feedback has been examined through fertilization experiments that describe short‐term (&lt;10 yr) above‐ or belowground responses to combined NP additions, with evidence of enhanced shrub growth, nutrient availability, and soil organic matter decomposition. There has been less opportunity for long‐term comparisons of both above‐ and belowground responses with factorial N and P additions in different systems, despite broad awareness that ecosystem response can shift with time, and the potential for decoupled above‐ vs. belowground or N vs. P responses, currently and with further predicted global change. We examined the response of the plants, soil microbes, and soil nutrients, to factorial N and P additions in the moist acidic tundra (MAT; 26 yr of nutrient additions) and moist non‐acidic tundra (MNT; 16 yr). Aboveground, the MAT plant community continues to change as predicted by earlier studies: Functional groups responded independently to N and P, but NDVI‐biomass, especially of Betula nana, only increased with N addition. Unlike shorter‐term MNT studies, the MNT vegetation, which does not include B. nana, shows few new fertilization responses. Belowground responses were not predicted by aboveground responses in either MAT or MNT. In contrast to the N response aboveground, MAT microbial biomass responded positively and microbial phosphatase activity negatively to P additions, implying possible release from microbial P limitation. Critically, earlier published results of declines in soil total carbon (C) with combined NP addition in the MAT are not present in the long term. We make two conclusions: (1) Arctic ecosystems are not universally N‐limited but also exhibit complex responses to P alone or in combination with N; and (2) the presence or absence of key vegetation species can cascade from aboveground to belowground and restrict the extrapolation of responses of nutrient addition in a single arctic ecosystem to other arctic ecosystems, the short‐term to the long term, or aboveground to belowground.

In Vitro and in Silico Evidence of Phosphatase Diversity in the Biomineralizing Bacterium Ramlibacter tataouinensis.

Microbial phosphatase activity can trigger the precipitation of metal-phosphate minerals, a process called phosphatogenesis with global geochemical and environmental implications. An increasing diversity of phosphatases expressed by diverse microorganisms has been evidenced in various environments. However, it is challenging to link the functional properties of genomic repertoires of phosphatases with the phosphatogenesis capabilities of microorganisms. Here, we studied the betaproteobacterium Ramlibacter tataouinensis (Rta), known to biomineralize Ca-phosphates in the environment and the laboratory. We investigated the functional repertoire of this biomineralization process at the cell, genome and molecular level. Based on a mineralization assay, Rta is shown to hydrolyse the phosphoester bonds of a wide range of organic P molecules. Accordingly, its genome has an unusually high diversity of phosphatases: five genes belonging to two non-homologous families, phoD and phoX, were detected. These genes showed diverse predicted cis-regulatory elements. Moreover, they encoded proteins with diverse structural properties according to molecular models. Heterologously expressed PhoD and PhoX in Escherichia coli had different profiles of substrate hydrolysis. As evidenced for Rta cells, recombinant E. coli cells induced the precipitation of Ca-phosphate mineral phases, identified as poorly crystalline hydroxyapatite. The phosphatase genomic repertoire of Rta (containing phosphatases of both the PhoD and PhoX families) was previously evidenced as prevalent in marine oligotrophic environments. Interestingly, the Tataouine sand from which Rta was isolated showed similar P-depleted, but Ca-rich conditions. Overall, the diversity of phosphatases in Rta allows the hydrolysis of a broad range of organic P substrates and therefore the release of orthophosphates (inorganic phosphate) under diverse trophic conditions. Since the release of orthophosphates is key to the achievement of high saturation levels with respect to hydroxyapatite and the induction of phosphatogenesis, Rta appears as a particularly efficient driver of this process as shown experimentally.

Effects of phosphorus-mobilizing bacteria on tomato growth and soil microbial activity

AimsThe aim of our study was to clarify whether inoculating a soil with Pseudomonas sp. RU47 (RU47) bacteria would stimulate the enzymatic cleavage of organic P compounds in the rhizosphere and bulk soil, promoting plant growth. Adding either viable or heat treated RU47 cells made it possible to separate direct from indirect effects of the inoculum on P cycling in soil and plants.MethodsWe performed a rhizobox experiment in the greenhouse with tomato plants (Solanum lycopersicum) under low P soil conditions. Three inoculation treatments were conducted, using unselectively grown soil bacteria (bacterial mix), heat treated (HT-RU47) and viable RU47 (RU47) cells, and one not inoculated, optimally P-fertilized treatment. We verified plant growth, nutrient availability, enzyme activities and microbial community structure in soil.ResultsA plant growth promotion effect with improved P uptake was observed in both RU47 treatments. Inoculations of RU47 cells increased microbial phosphatase activity (PA) in the rhizosphere.ConclusionsPlant growth promotion by RU47 cells is primarily associated with increased microbial PA in soil, while promotion of indigenous Pseudomonads as well as phytohormonal effects appear to be the dominant mechanisms when adding HT-RU47 cells. Thus, using RU47 offers a promising approach for more efficient P fertilization in agriculture.

Effect of Malathion on Microbial Population, Acid and Alkaline Phosphatase Activity of Soil

Effect of Malathion on Microbial Population, Acid and Alkaline Phosphatase Activity of Soil

Distribution of phosphatase activity and various bacterial phyla in the rhizosphere of Hordeum vulgare L. depending on P availability

Despite the importance of the rhizosphere for nutrient turnover, little is known about the spatial patterns of organic phosphorus mineralization by plants and by microorganisms in the rhizosphere. Therefore, the distribution of acid and alkaline phosphatase activity and the abundance of bacteria belonging to various bacterial phyla were investigated in the rhizosphere of barley (Hordeum vulgare L.) as dependent on the availability of inorganic P. For this purpose, we conducted a greenhouse experiment with barley growing in inclined boxes that can be opened to the bottom side (rhizoboxes), and applied soil zymography and fluorescence-in situ-hybridization (FISH). Acid phosphatase activity was strongly associated with the root and was highest at the root tips. Due to P fertilization, acid phosphatase activity decreased in the bulk soil, and less strongly in the rhizosphere. Alkaline phosphatase activity, i.e., microbial phosphatase activity was high throughout the soil in the control treatment and was reduced due to inorganic P fertilization especially in the rhizosphere and less strongly in the bulk soil. P-fertilization slightly increased the total number of bacteria in the rhizosphere. Moreover, P-fertilization decreased the abundance of Firmicutes and increased the abundances of Beta- and Gamma-Proteobacteria. The total number of bacterial cells was significantly higher at the root surface than at the root tip and at a distance of 30 μm from the root surface. Our results show that alkaline phosphatase activity decreased more strongly in the rhizosphere than in the bulk soil due to P fertilization, which might be because of greater C deficiency in the bulk soil compared to the rhizosphere. Furthermore, the results indicate a spatial separation between hotspots of acid phosphatase activity and hotspots of bacteria in the rhizosphere of H. vulgare. Taken together, our study shows that bacteria and phosphatase activity were very heterogeneously distributed in soil, and that the effects of P fertilization on phosphatase activity differed strongly between bulk soil and rhizosphere as well as between various zones of the rhizosphere.

Effects of oats and grazing vetch cover crops and fertilisation on microbial biomass and activity after five years of rotation with maize

Degraded soil quality could be improved by cover crops. This study determined effects of maize–oats and maize– vetch rotations with or without fertilisation on soil microbial biomass and activity. Winter treatments were oats, vetch and weedy fallow, in rotation with summer maize. Fertilisation strategies were: fertilised cover crop and maize (F1), fertilised cover crops only (F2), fertilised maize only (F3) and no fertiliser (F4). The 2×4 factorial (plus control) was laid out in a randomised complete block design with three replications. After five years, soils were sampled from the 0–5 and 5–20 cm depths and analysed for microbial biomass carbon (MBC), dehydrogenase, β-glucosidase, urease and phosphatase activities. Cover crops resulted in higher MBC and enzyme activities than the weedy fallow. Fertilisation of cover crop (F2) and maize (F3) resulted in similar MBC. The F4 in cover crops and F3 under weedy fallow had similar dehydrogenase activities, whereas F4 under vetch was similar to F3 under oats. The F4 for vetch had similar β-glucosidase activity to F1, and urease activity to F1, F2 and F3, of oats. Phosphatase activities in F1 and F2 were similar. The use of vetch and fertilisation of cover crops stimulated soil biological activity compared with the control.

Chromophoric Dissolved Organic Matter Fluctuation Assessment in an Urban River

AbstractTo investigate the compositions and spatio‐temporal changes of chromophoric dissolved organic matter (CDOM) in a typical urban river in Taihu Basin, China, that has been treated with series of water quality mitigation measures, 180 water samples were collected from November 2011 to October 2012 and analyzed with fluorescence excitation–emission matrices combined with parallel factor analysis (EEMs–PARAFAC). Three humic‐like components (C1, C2, and C4) and two protein‐like components (C3 and C5) were identified. Fluorescent intensity showed more apparent temporal changes than spatial changes, and humic‐like substances were dominant. The C3, C4, and C5 components decreased from November 2011 to October 2012, indicating effective CDOM removal by the water quality mitigation measures. Significant positive correlations were found between fluorescent components (C3 and C5) and nutritional factors including TN, NH4+‐N, and NO3−‐N. Furthermore, changes of fluorescent components (C2) were found to be related to microbial phosphatase activities. The application of EEMs–PARAFAC presents a promising approach to track the compositions and spatio‐temporal changes of CDOM in urban rivers.

Changes in Biological Properties in Soil Amended with Rock Phosphate and Waste Mica Enriched Compost using Biological Amendments and Chemical Fertilizers Under Wheat-Soybean Rotation

The main aim of this research work is to prepare an enriched compost using rice straw mixed with rock phosphate, waste mica and Aspergillus awamori and to study their effect on changes in microbial properties in soils with and without chemical fertilizers under wheat-soybean rotation. Data revealed that significant increase in microbial biomass carbon (MBC), dehydrogenase activity, phosphatase activities, and microbial biomass phosphorus (MBP) in soil were maintained in enriched compost than ordinary compost after both the crops. Significant increase in MBC, dehydrogenase activity, phosphatase activities, and MBP were found in surface soil. The maximum microbial activities were observed in the treatment receiving 50% recommended dose of fertilizer (RDF) + enriched compost at 5 t ha−1 indicating that integrated use of chemical fertilizers and enriched compost significantly improved the biological properties of soil under wheat–soybean rotation thereby enhanced soil fertility and crop production.

Peri-Urban Vertisol Properties as Influenced by Sewage and Bore Well Water Irrigation to Wheat (Triticum aestivum L.)

Field experiment was conducted in farmer’s field near Agricultural Research Station, Dharwad, Karnataka State, India which was on the bank domestic sewage course in split plot design with three replications. Main plots included two types of lands (land irrigated with sewage water since 1970 and land irrigated with bore well water since 1992). Sub plots allotted with sources of irrigation consisted of sewage alone, bore well water alone (good water) and alternate sewage and bore well water. Analysis of sewage water for major and minor plant nutrients content revealed its potential as source of nutrients and water for crop growth. The soil physical properties especially bulk density and moisture holding capacity was improved significantly in sewage land over bore well irrigated land. Yield of wheat crop was positively correlated with these soil properties. There was reduction in soil pH in sewage land (7.24) over bore well irrigated land (7.65). The sewage irrigated land recorded significantly more bacterial and fungal colonies, dehydrogenase and alkaline phosphatase enzymes activities in soil. Sources of irrigation also differed significantly producing the highest microbial colonies, phosphatase and dehydrogenase enzymes activity in sewage water irrigation treatment followed by alternate irrigation as sewage water is good source of organic phosphorus (11.9–17.3 ppm). Irrigation with sewage water improved the performance of wheat crop as evidenced by higher grain yield (4100 kg ha-1), protein content in grains (12.8%), and dry gluten (8.9%) compared to bore well water irrigation. Characterization of domestic sewage effluent showed that it can be used as source of irrigation water and top dressing nutrients.

Effect of Imidacloprid and Triadimefon on microbial phosphatase, protease and urease enzyme activities in tomato (Lycopersicon esculentum sp.) cultivated soil

The laboratory studies were conducted to resolute the effects of Imidacloprid (insecticide) and Triadimefon (fungicide) singly and in combination on enzymatic activities of soil microorganisms in tomato cultivated soils at different concentrations of 0.2, 0.5 and 0.7 kg per hectare. It was observed that phosphatase, protease and urease activities were elevated noteworthy at 0.5kg per hectare after 10 days of incubation. At lower concentration the activities of these enzymes showed no significant difference from that of control. The combination of the two pesticides led to a pronounced decline of phosphatase and protease enzyme activities at higher concentration. Triadimefon had no effect on urease activity at low concentrations whereas at 0.5 and 0.7 concentrations there was a significant increase when compared to control.

Response of Soil Microbial Biomass and Enzyme Activity to Soil Fertilization in an Eroded Farmland of Chinese Mollisols

The aims of this study were to examine interrelationships between microbial biomass and enzyme activities of soil quality and to determine their suitability for differentiating areas. The study included five simulated erosion soil depths (0, 5, 10, 20, and 30 cm), which had received contrasting fertilizer treatments over a 5-year period in an eroded black soil of northeastern China. Our results indicated that soil microbial carbon, nitrogen, urease, phosphatase, and invertase activities declined as the erosion depth increased. On the five erosion depths, soil microbial carbon, phosphatase, and invertase variation ranged as follows: 35.4–53.3, 39.8–45.2, and 55.9–67.1%, respectively. In the fertilizer + manure treatment, soil microbial carbon, nitrogen, urease, phosphatase, and invertase activities were significantly greater (P < 0.05) than those of fertilizer treatment in all five different erosion depths. Overall, this study may be considered as the foundation for soil quality evaluation and fertility restoration in northeastern China and similar regions.

Impact of long-term organic and inorganic nutrient managements on the biological properties and eubacterial community diversity of the Indian semi-arid Alfisol

Intensive cropping with limited nutrient management options in low fertile semi-arid tropical soils will have agricultural sustainability problems in future. A better understanding of soil variables as influenced by long-term nutrient amendments could lead to the identification of more precise indicators to monitor soil fertility that would promote sustainability. Long-term nutrient experiment in semi-arid Alfisol at Coimbatore, India was investigated in two successive years, 2009 and 2010 to assess the enduring effects of organic (OM) and inorganic (IC) nutrient managements on soil variables. The organic amendments induced higher microbial population and enzyme activity compared to IC and control soils. The principal component analysis of observed variables revealed that soil organic carbon, microbial biomass carbon (MBC), dehydrogenase and alkaline phosphatase activity and diazotrophs population could be the possible indicators for predicting soil fertility resulting from long-term nutrient managements. The eubacterial community profile assessed by 16S rRNA gene sequence polymorphism revealed that the abundance and relative ratio of phyla belonging to Proteobacteria, Actinobacteria, Acidobacteria and Firmicutes were considerably affected due to either organic manures or inorganic fertilizers, and organic nutrient management favours bacterial community diversity. These results emphasize the importance of organic nutrient management to maintain soil biological properties in semi-arid Alfisol.

Effect of elevated CO2 on degradation of azoxystrobin and soil microbial activity in rice soil

An experiment was conducted in open-top chambers (OTC) to study the effect of elevated CO2 (580 ± 20μmolmol(-1)) on azoxystrobin degradation and soil microbial activities. Results indicated that elevated CO2 did not have any significant effect on the persistence of azoxystrobin in rice-planted soil. The half-life values for the azoxystrobin in rice soils were 20.3days in control (rice grown at ambient CO2 outdoors), 19.3days in rice grown under ambient CO2 atmosphere in OTC, and 17.5days in rice grown under elevated CO2 atmosphere in OTC. Azoxystrobin acid was recovered as the only metabolite of azoxystrobin, but it did not accumulate in the soil/water and was further metabolized. Elevated CO2 enhanced soil microbial biomass (MBC) and alkaline phosphatase activity of soil. Compared with rice grown at ambient CO2 (both outdoors and in OTC), the soil MBC at elevated CO2 increased by twofold. Elevated CO2 did not affect dehydrogenase, fluorescein diacetate, and acid phosphatase activity. Azoxystrobin application to soils, both ambient and elevated CO2, inhibited alkaline phosphates activity, while no effect was observed on other enzymes. Slight increase (1.8-2 °C) in temperature inside OTC did not affect microbial parameters, as similar activities were recorded in rice grown outdoors and in OTC at ambient CO2. Higher MBC in soil at elevated CO2 could be attributed to increased carbon availability in the rhizosphere via plant metabolism and root secretion; however, it did not significantly increase azoxystrobin degradation, suggesting that pesticide degradation was not the result of soil MBC alone. Study suggested that increased CO2 levels following global warming might not adversely affect azoxystrobin degradation. However, global warming is a continuous and cumulative process, therefore, long-term studies are necessary to get more realistic assessment of global warming on fate of pesticide.

Microbial enzyme stoichiometry and nutrient limitation in US streams and rivers

We analyzed water and sediment chemistry, catchment land cover, and microbial dehydrogenase (DHA) and extracellular enzymes activities (EEA) related to microbial C, N, P, and S acquisition in more than 2100 1st–10th order streams. The streams and their catchments represented gradients in water and sediment chemistry (C, N, P, S) and land cover (% forest, % wetland, % row crop agriculture) against which to compare biofilm and sediment DHA and EEA, and to estimate the extent of nutrient limitation in US streams and rivers. Water chemistry was significantly correlated with catchment land cover. Biofilm and sediment DHA and EEA were inversely correlated with water and sediment chemistry, and positively correlated with % forest. Canonical correlation analysis described two environmental gradients to which biofilm and sediment DHA and EEA were significantly correlated. Structural equation modeling (SEM) revealed a significant causal relationship between catchment land cover, chemistry, and biofilm and sediment EEA and DHA. Biofilm and sediment EEA was dominated by phenol oxidase and peroxidase, enzymes related to the degradation of recalcitrant C. However, the hydrolytic enzymes (those which hydrolyze glycoside, peptide, and ester bonds to release C, N, P, S) were better correlated with the chemical variables. This was reflected in the relative apportionment of enzyme activity toward C, N, P, and S acquisition. We compared molar stoichiometry of C, N, and P in water and sediment with biofilm and sediment ratios of GLYC:PEPT:PHOS to gauge how each measure of nutrient limitation compares with the others. Overall, water chemistry suggested many biofilms were P-limited and this was corroborated by allocation of microbial phosphatase activity. Sediments were found to be predominantly C and N-limited, and this was reflected in sediment EEA. We used these measures of nutrient limitation to assess the extent of N or P-limitation in streams and rivers of the conterminous United States and for nine ecoregions of interest to the US EPA's National Rivers and Streams Assessment (NRSA). Enzymatic stoichiometry provides a biological perspective on the influence of catchment scale anthropogenic disturbances resulting in an imbalance of nutrients being transported from those catchments. Enzyme activities represent the interface between microbial demands for, and environmental supplies of, C, N, and P, effectively linking ecological stoichiometric theory with the concept of threshold elemental ratios. The relative activities of the functional classes of extracellular enzymes provide both a measure of nutrient availability and ecosystem metabolism that may be used to assess large-scale phenomena such as regional impacts of climate change or anthropogenic disturbances.

The Effect of Trails on Soil in the Oak Openings of Northwest Ohio

Trails are a form of recreational disturbance affecting natural areas. Trail disturbances can cause soil degradation such as compaction, which facilitates soil erosion and overland water flow. This study analyzed the effects of four different types of trails—paved, gravel, equestrian, and hiking—on soils in the Oak Openings of Northwest Ohio, a globally rare ecosystem that harbors more than a third of Ohio's rare plant species. Bulk density and soil moisture content were measured in order to determine physical impacts of trails. Soil pH, ammonium, nitrate, phosphate, and dissolved organic C and N concentrations were measured to determine effects on soil chemistry. Finally, soil microbial biomass and exoenzyme activities were measured to determine biological responses to trail disturbances. Soils from the gravel trail were the most affected by the trail, with significant effects on chemical (PO43-concentration) and biological (phosphatase and NAG activity, and MB-N) properties. The soils near the paved trail were the second most affected after the gravel trail, with a trend toward a pH change and a significant biological (microbial peptidase activity) effect of this trail. The soils of the horse and natural trails were generally not significantly different from the soils in the surrounding ecosystem. The only significant disturbance in the horse trail was increased bulk density in the trail, while the natural hiking trail had no statistically significant differences, but trends lean toward increased bulk density and reduced microbial phosphatase activity. These results suggest that the natural and horse trails have the least impact on the Oak Openings ecosystem.