Bruce L. Vasilas

Evaluation of the N2-fixation capacity of four soybean genotypes by several methods

Abstract Plant-N derived from N 2 -fixation (N 2 -fixed) and the percentage of plant-N derived from N 2 -fixation (% Ndff) were determined for four field-grown soybean lines by several techniques. The objective was to determined which technique would distinguish between the lines on the basis of their N 2 -fixing abilities. Variables in the techniques included method (total N or 15 N isotope dilution), plant sample (seed, shoot at physiological maturity and whole plant) and placement of control (non-nodulating soybean) plots. Estimates of N 2 -fixed generated by isotope dilution were. on average, higher than those generated by the difference method (total N). Greater distinction between the genotypes was possible using the difference method than with isotope dilution. Separation of genotypes on the basis of N 2 -fixed as estimated by isotope dilution was not affected by the tissue sample used (seed, shoot or whole plant).

Effect of Tide Level and Time of Day on Detection Rate and Abundance of Clapper Rails (Rallus longirostris) in a Mid-Atlantic Tidal Marsh System

Abstract. Obligate marsh bird detection rates during surveys are affected by the time of day and the tide level, but previous research on both factors has produced conflicting results and no research has been conducted in east coast tidal marshes. Relative abundance and detection rate of Clapper Rails (Rallus longirostris) were compared between morning and evening surveys at high, medium, and low tide levels in Worcester County, Maryland, during 2006. The detection rate of Clapper Rails was greatest in the morning at the medium tide level ( = 0.69, SE = 0.14, F5,40 = 5.87, P = 0.001). Morning surveys ( = 1.2, SE = 0.14) resulted in a greater relative abundance of Clapper Rail detections compared to evening surveys ( = 0.8, SE = 0.12, F1,195 = 5.31, P = 0.022), and surveys done at medium tide level ( = 1.3, SE = 0.17) resulted in greater relative abundance than those conducted at low ( = 0.8, SE = 0.15) or high levels ( = 0.7, SE = 0.15, F2,195 = 6.56, P = 0.002). The results suggest that surveys should be conducted in the morning at medium tide to maximize detection rate of Clapper Rails. The detection rate of obligate marsh birds during surveys is affected by time and tide level so additional research is necessary to determine how these variables affect the detection rate of marsh birds other than Clapper Rails.

ECTOMYCORRHIZAL MANTLES AS INDICATORS OF HYDROLOGY FOR JURISDICTIONAL WETLAND DETERMINATIONS

Ectomycorrhizae are symbiotic relationships between soil fungi and higher plants. Evidence of the symbiosis is the presence of a ‘mantle,’ a hyphal layer that covers root tips, and a change in root morphology. The potential use of ectomycorrhizal mantles as hydrology indicators for wetland determinations was evaluated on the Delmarva Coastal Plain (Delaware and eastern shores of Maryland and Virginia, USA) over three seasons. In theory, the distribution of mantles with soil depth should vary from uplands to wetlands in most years, as mantle development is considered to be impeded by anaerobic conditions. At four forested locations, plots were set up in seasonally-saturated wetlands and adjacent uplands and drained wetlands (twelve sub-sites). Plots were evaluated according to the Corps of Engineers Wetlands Delineation Manual for soils, plant community, and hydrology to identify a jurisdictional classification. Hydrology was further addressed using automated monitoring wells (twice daily readings), and anaerobic conditions were confirmed via platinum electrodes. Plant roots (Pinus taeda was targeted) were sampled via spade slices in March and August each year and separated by depth: O horizon, 0–5 cm, 5–10 cm, 10–15 cm, and 15–20 cm. Roots were evaluated for the presence of mantles. A threshold depth of 5 cm was identified. From a total of 892 roots with mantles in uplands (including effectively-drained wetland sub-sites), 253 (28%) were found below the threshold depth. For wetlands (including one ineffectively-drained wetland), seven of 331 roots with mantles (2%) were found below the threshold depth. Temporal and spatial variability in mantle data was common; however, mantles consistently occurred at greater depths where seasonally high water tables were lower. We concluded that mantle depth has potential as a hydrology indicator.

Wetland Biogeochemistry Techniques

Biogeochemistry is the scientific discipline that addresses the biological, chemical, physical, and geological processes that govern the composition of the natural environment, with particular emphasis placed on the cycles of chemical elements critical to biological activity. Biogeochemical assays may measure a specific elemental pool, determine the rate of a pathway, or address a surrogate of a biogeochemical process or an elemental pool. In this chapter, we have attempted to emphasize field techniques; however, some of the techniques have relatively standard laboratory components that are beyond the scope of this chapter. This chapter is not meant to be all inclusive. We have chosen to emphasize the cycling of carbon, nitrogen, phosphorous, sulfur, manganese, and iron. Some of these techniques are not appropriate for all types of wetlands, or may be appropriate for a seasonally saturated wetland only during part of the season. Some of the techniques are simple and rely on equipment available to most wetlands practitioners. Others, which utilize isotopic methodologies, require expensive sophisticated equipment. Some techniques, such as soil organic matter determination by loss on ignition, have been accepted as standard methods for decades. Others, such as the determination of dissolved organic matter represent recent advances in a rapidly evolving field of ultra-violet and fluorescence technology. Some techniques rely solely on direct field measurements; others rely on the incorporation of published data with field data. Apparent strengths and weaknesses of the various approaches, and wetland scenarios that would preclude the use or compromise the accuracy of a given technique are addressed.

Environmental Impact of Long Piers on Tidal Marshes in Maryland-Vegetation, Soil, and Marsh Surface Effects

Piers may impact the health of coastal wetlands by altering vegetation, soil organic matter accretion, and sediment deposition or erosion. Permit requests for piers have recently increased in the U.S. leading to concern by environmental regulatory agencies on potential impacts. In response, a project was conducted in Maryland to assess the impacts of long piers on plant communities, soils, and marsh surface characteristics. Twenty sites with piers and 20 control sites were assessed. Control sites and pier sites were similar with respect to soil types, marsh surface characteristics, and plant community composition. Shading consistently reduced vegetation density directly beneath piers and occasionally reduced vegetation density adjacent to piers. Shading favored Spartina alterniflora over Distichlis spicata, and Distichlis spicata over Spartina patens. Distribution of marsh surface components (high marsh, low marsh, mudflats, open water) was unaffected by proximity to piers. Direct evidence of pier effects on erosion or deposition was limited to the immediate vicinity of a few piers. In general, thickness of the organic horizons or that of the root mats was unaffected by proximity to a pier. We concluded that any effects of piers on vegetation or erosion were restricted to the close proximity of the piers.

Effects of Long Piers on Birds in Tidal Wetlands

Abstract As human development continues in coastal areas, shoreline properties adjacent to expansive tidal marsh habitat are increasingly used for access to coastal waterways via long piers (>30 m) over marsh habitat. These tidal wetlands provide breeding and foraging habitat for many marsh birds, which may be affected by the human disturbance associated with long piers. Our objectives were to determine the effect of long piers over vegetated tidal marshes on the relative abundance and species richness of marsh birds. We completed combined passive and callback surveys in tidal marsh habitat at 22 sites with long piers and 24 sites without long piers, May–July 2005–2006 in Worcester County, Maryland, USA. Pier sites had lower relative abundance and species richness of obligate marsh birds than nonpier sites. Pier sites had a greater relative abundance of gulls, terns, herons, and egrets than nonpier sites. Pier sites had fewer species of herons and egrets than at nonpier sites. The presence of long piers had no affect on facultative marsh birds. Long pier density was negatively related to obligate marsh bird relative abundance and species richness, and facultative marsh bird species richness, whereas it was positively related to the relative abundance and species richness of gulls and terns. Herons and egrets relative abundance and species richness were not related to long pier density. Obligate marsh birds were negatively affected by long piers, whereas herons, egrets, gulls, and terns appeared to benefit from perching opportunities. Based on the negative effects of long piers on obligate marsh birds, management should focus on reducing the presence and density of long piers in tidal marshes by requiring the removal of existing long piers, or reducing or eliminating permits for construction of new long piers.

Field response of the Glycine-bradyrhizobium symbiosis to modified early-nodule occupancy

Abstract A 2 yr field study was conducted to monitor the response of the Glycine-Bradyrhizobium symbiosis to high initial levels of nodulation by selected strains of B. japonicum when grown in soil containing indigenous soybean bradyrhizobia. Nodulated soybean seedlings were prepared under greenhouse conditions and transplanted to 15 N-amended field microplots when ca 23 days old. The population of indigenous bradyrhizobia at the study site was ca 7 × 10 5 g −1 soil. Inoculation treatments included strains USDA 122 (a superior N 2 fixer), USDA 94 (a strong rhizobitoxine producer), and a soil suspension containing a mixture of strains indigenous to the study site. Occupancy of root nodules was monitored serologically with an ELISA and morphologically by colony type on yeast extract-mannitol agar. The frequencies of serogroups 122 and 94 in early-formed (tap root) nodules of plants receiving USDA 122 and 94 as inocula dropped from 99.5 and 94.5% during vegetative growth to 55.0 and 28.5% during seedfill, respectively. The incidence of B. japonicum DNA homology Group II increased during host development for those plants initially treated with the soil suspension. Relative to the soil control treatment, inoculation with USDA 122 significantly increased soybean seed yield by 32%, N 2 fixation by 29% and total shoot N content by 30%. Conversely, USDA 94 decreased the magnitude of these variables by 39, 44 and 42%, respectively. These results demonstrate that the successful introduction of contrasting strains of B. japonicum into early-formed nodules can modify soybean productivity despite subsequent nodulation by indigenous soybean bradyrhizobia.

Hydric Soil Identification Techniques

Conceptually, hydric soils are soils that formed under hydrologic conditions associated with wetlands. Identification of soils as “hydric” is critical to the identification and protection of wetlands. Conditions of saturation and anaerobiosis associated with wetland hydrology create morphological characteristics in soils that can be used to distinguish them from non-hydric (upland) soils. These distinctive morphological characteristics have been used to develop “indicators” to facilitate the rapid identification of hydric soils in the field without relying on chemical assays or long term monitoring. An understanding of how soils form and the soil properties related to hydric soil morphologies such as soil color and texture are needed to field identify indicators of hydric soils. This chapter emphasizes the proper application of field indicators of hydric soils, the process of describing soil morphology inherent to the use of hydric soil indicators, and approaches to address soils suspected to be hydric but do not meet a field indicator.

The Hydrogeomorphic Approach to Functional Assessment for Piedmont Slope Wetlands

Wetland functions are the characteristic activities (biological, chemical, and physical processes) that occur in these ecosystems. Functional assessment models are used to quantify the functional capacity of individual wetlands. The Hydrogeomorphic (HGM) Approach to functional assessment of wetlands classifies wetlands to the regional subclass level and then creates a model for an individual subclass in a given geographic area. An HGM model is essentially a functional profile that describes the physical, chemical, and biological characteristics of wetlands in the regional subclass, identifies those functions that are most likely to be performed on a sustained basis, and addresses landscape and ecosystem attributes that can be expected to influence each targeted function. The HGM Approach does not assign absolute values to functional capacity. Instead it rates functional capacity for a given wetland relative to reference standards-the highest level of functional capacity exhibited by wetlands in the regional subclass. Reference standards are established by assessment of wetlands that exhibit those attributes consistent with maximum sustained functional capacity. The HGM Approach is presently being applied to Piedmont slope wetlands in the Mid-Atlantic Region.