An increasing interest has emerged with respect to the importance of microbial diversity in soil habitats The extent of the diversity of microorganisms in soil is seen to be critical to the maintenance of soil health and quality, as a wide range of microorganisms is involved in important soil functions This review focuses on recent data relating how plant type, soil type, and soil management regime affect the microbial diversity of soil and the implication for the soil's disease suppressiveness The two main drivers of soil microbial community structure, ie, plant type and soil type, are thought to exert their function in a complex manner We propose that the fact that in some situations the soil and in others the plant type is the key factor determining soil microbial diversity is related to the complexity of the microbial interactions in soil, including interactions between microorganisms and soil and microorganisms and plants A conceptual framework, based on the relative strengths of the shaping forces exerted by plant and soil versus the ecological behavior of microorganisms, is proposed

Microbial diversity in soil: Selection of microbial populations by plant and soil type and implications for disease suppressiveness

Salt marshes are among the most abundant, fertile, and accessible coastal habitats on earth, and they provide more ecosystem services to coastal populations than any other environment. Since the Middle Ages, humans have manipulated salt marshes at a grand scale, altering species composition, distribution, and ecosystem function. Here, we review historic and contemporary human activities in marsh ecosystems—exploitation of plant products; conversion to farmland, salt works, and urban land; introduction of non-native species; alteration of coastal hydrology; and metal and nutrient pollution. Unexpectedly, diverse types of impacts can have a similar consequence, turning salt marsh food webs upside down, dramatically increasing top down control. Of the various impacts, invasive species, runaway consumer effects, and sea level rise represent the greatest threats to salt marsh ecosystems. We conclude that the best way to protect salt marshes and the services they provide is through the integrated approach of ecosystem-based management.

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Centuries of Human-Driven Change in Salt Marsh Ecosystems

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Treatment Wetlands, Second Edition

Denitrification, the anaerobic reduction of nitrogen oxides to nitrogenous gases, is an extremely challenging process to measure and model. Much of this challenge arises from the fact that small areas (hotspots) and brief periods (hot moments) frequently account for a high percentage of the denitrification activity that occurs in both terrestrial and aquatic ecosystems. In this paper, we describe the prospects for incorporating hotspot and hot moment phenomena into denitrification models in terrestrial soils, the interface between terrestrial and aquatic ecosystems, and in aquatic ecosystems. Our analysis suggests that while our data needs are strongest for hot moments, the greatest modeling challenges are for hotspots. Given the increasing availability of high temporal frequency climate data, models are promising tools for evaluating the importance of hot moments such as freeze-thaw cycles and drying/rewetting events. Spatial hotspots are less tractable due to our inability to get high resolution spatial approximations of denitrification drivers such as carbon substrate. Investigators need to consider the types of hotspots and hot moments that might be occurring at small, medium, and large spatial scales in the particular ecosystem type they are working in before starting a study or developing a new model. New experimental design and heterogeneity quantification tools can then be applied from the outset and will result in better quantification and more robust and widely applicable denitrification models.

Challenges to incorporating spatially and temporally explicit phenomena (hotspots and hot moments) in denitrification models

Effects of site and plant species on rhizosphere community structure as revealed by molecular analysis of microbial guilds

Functional evaluation of wetlands in nutrient cycling, water quality maintenance, and wetland construction and restoration contexts requires knowledge of differences in microbial processes between different wetland types and understanding of the nature and extent of variation in these processes within a given wetland type. In this study, we measured a suite of microbial variables (microbial biomass C and N content, denitrification enzyme activity, potential net N mineralization and nitrification, and soil respiration) that are indices of wetland nutrient cycling and water quality maintenance functions in four different wetland types (calcareous fens, red maple swamps, woodland pools, and wet clay meadows) in eastern New York state. Total soil C and N content, water content, pH, water-table levels, and groundwater NH 4 + , NO 3 - and electrical conductivity were also measured. The clay meadow wetlands were drier and had lower levels of organic matter and most microbial variables than the other wetland types. Site-to-site variation within the fens was very high and was not strongly controlled by water-table levels. Organic matter content and N status appear to be strong regulators of microbial biomass and activity in fens. Red maple swamps and woodland pools had similar levels of most microbial variables. Variation within these wetland types was controlled by hydrology and organic matter quality. The suite of microbial variables that we measured identified potential functional differences between wetland types and should be useful for comparisons of the water quality maintenance value of different wetlands and for functional evaluation of altered or restored sites.

Variation in Microbial Biomass and Activity in Four Different Wetland Types

The muskrat (Ondatra zibethicus) is a wetland mammal whose disturbance activities include grazing, burrowing and lodge construction. We evaluated the effects of these disturbances on plant biomass, species richness and diversity, stem density and potential net nitrogen mineralization and nitrification rates in a freshwater tidal marsh on the Hudson River in New York. We hypothesized that muskrats increase floristic richness and diversity by decreasing the biomass of narrowleaf cattail (Typha angustifolia) and that muskrats increase potential net nitrogen mineralization and nitrification rates through aeration and reduced plant uptake because of herbivory. Because muskrats commonly build lodges on or close to creek banks, we separated the disturbance effects of muskrats from the disturbance effects of the creek bank by sampling quadrats along transects placed perpendicular to creek banks at lodge sites. Muskrats decreased biomass, particularly of cattail, but had no measurable effect on stem count...

Muskrat (Ondatra zibethicus) Disturbance to Vegetation and Potential Net Nitrogen Mineralization and Nitrification Rates in a Freshwater Tidal Marsh

Phragmites use by Native North Americans

Calcareous wetlands are of great interest in conservation biology. Previous research has suggested that there are significant differences in soil microbial N cycle processes between calcareous wetlands developed on organic vs. mineral soils. In the study presented here, we measured potential net N mineralization and nitrification, denitrification enzyme activity and soil inorganic N levels at 25 calcareous wetland sites with variable substrate types. We also evaluated the response of N cycling to livestock grazing by sampling at two sites with heavy grazing activity. All N cycle variables were significantly higher in organic soils than mineral soils on a weight basis; however, there were very few differences when results were expressed on an areal (volume) basis because of the low bulk density of the organic soils. The areal results suggest that organic and mineral soil calcareous wetland sites have similar N water quality maintenance values, that is, the ability to absorb N from upland land areas. Heavily grazed sites had significantly decreased pH and increased NO 3 - levels relative to undisturbed sites, but the differences were small. The lack of strong differences in N cycle variables between mineral and organic soil sites raises questions about the need to make a classification distinction between calcareous peatlands (fens) and calcareous mineral soil wetlands in nutrient cycling and water quality maintenance contexts.

Soil Nitrogen Dynamics in Organic and Mineral Soil Calcareous Wetlands in Eastern New York

The literature is reviewed and analysis made of references to more than 60 vertebrates that use lodges or bank burrows built by the muskrat,Ondatra zibethicus L. Muskrat homes are important to turtles, waterfowl, terns, carnivores, rodents, and other species for shelter, nesting, getting above the water, or seeking food. No use is obligate but the availability of muskrat homes may limit some species. Effects on vertebrate associates should be considered when muskrat populations are manipulated.

Erik Kiviat

Papers

Variation in Microbial Biomass and Activity in Four Different Wetland Types

Muskrat (Ondatra zibethicus) Disturbance to Vegetation and Potential Net Nitrogen Mineralization and Nitrification Rates in a Freshwater Tidal Marsh

Phragmites use by Native North Americans

Soil Nitrogen Dynamics in Organic and Mineral Soil Calcareous Wetlands in Eastern New York

Vertebrate use of muskrat lodges and burrows