Durland L. Shumway

Winter wheat cover cropping, VA mycorrhizal fungi and maize growth and yield

The relationships among winter cover cropping, inoculum potential of vesicular-arbuscular mycorrhizal (VAM) fungi, and the growth and yield of a subsequent maize crop were investigated. In the first experiment, an autumn-sown winter wheat cover crop increased VAM fungal inoculum potential of a field soil as measured by an in situ maize bioassay during the following growing season. Infective extra-radical hyphal densities were significantly increased by cover cropping as interpreted from the effect of soil disturbance on infection of the maize bioassay plants. In a second experiment the following year, the winter wheat cover crop again increased VAM fungal inoculum potential as assessed by an in situ maize bioassay during the following growing season. Moreover, the degree of mycorrhizal infection of maize was correlated with maize growth and yield. This study suggests that the management of mycorrhizal fungi by cover cropping may be a useful practice in sustainable agriculture.

Mycorrhizal symbiosis increases growth, reproduction and recruitment of Abutilon theophrasti Medic. in the field

We examined in the field the effect of the vesicular-arbuscular (VA) mycorhizal symbiosis on the reproductive success of Abutilon theophrasti Medic., an early successional annual member of the Malvaceae. Mycorrhizal infection greatly enhanced vegetative growth, and flower, fruit and seed production, resulting in significantly greater recruitment the following year. In addition, the seeds produced by mycorrhizal plants were significantly larger and contained significantly more phosphorus than seeds from non-mycorrhizal plants, an effect which may improve offspring vigor. Infection by mycorrhizal fungi may thus contribute to the overall fitness of a host plant and strongly influence long-term plant population dynamics.

Timing of Cover-Crop Management Effects on Weed Suppression in No-Till Planted Soybean using a Roller-Crimper

Abstract Integrated weed management tactics are necessary to develop cropping systems that enhance soil quality using conservation tillage and reduced herbicide or organic weed management. In this study, we varied planting and termination date of two cereal rye cultivars (‘Aroostook’ and ‘Wheeler’) and a rye/hairy vetch mixture to evaluate cover-crop biomass production and subsequent weed suppression in no-till planted soybean. Cover crops were killed with a burn-down herbicide and roller-crimper and the weed-suppressive effects of the remaining mulch were studied. Cover-crop biomass increased approximately 2,000 kg ha−1 from latest to earliest fall planting dates (August 25–October 15) and for each 10-d incremental delay in spring termination date (May 1–June 1). Biomass accumulation for cereal rye was best estimated using a thermal-based model that separated the effects of fall and spring heat units. Cultivars differed in their total biomass accumulation; however, once established, their growth rates were similar, suggesting the difference was mainly due to the earlier emergence of Aroostook rye. The earlier emergence of Aroostook rye may have explained its greater weed suppression than Wheeler, whereas the rye/hairy vetch mixture was intermediate between the two rye cultivars. Delaying cover-crop termination reduced weed density, especially for early- and late-emerging summer annual weeds in 2006. Yellow nutsedge was not influenced by cover-crop type or the timing of cover-crop management. We found that the degree of synchrony between weed species emergence and accumulated cover-crop biomass played an important role in defining the extent of weed suppression. Nomenclature: Cereal rye, Secale cereale L.; hairy vetch, Vicia villosa Roth; yellow nutsedge, Cyperus esculentus L.

Seed preferences of Lumbricus terrestris L.

Abstract We performed an experiment to determine factors affecting preference in the selection of seeds by Lumbricus terrestris L. Earthworms were given a menu consisting of seeds of nine plant species that were sorted into three size classes and sand particles that were sorted into the same three size classes. The experiment was conducted over a period of 84 days in worm beds under laboratory conditions. Seed and sand particles from the small (0.5–1.0 mm) size class were chosen four to one over seeds and sand in the intermediate (1.0–2.0 mm) size class. Seeds and sand particles in the intermediate size class were chosen 14 to one over seeds and sand particles in the large (2.0–2.5 mm) size class. Seeds were chosen two to one over sand in the small size class, six to one in the intermediate size class, and 15 to one in the large size class. Seeds with smooth surfaces were generally preferred over seeds with rough surfaces. Excavation of the bedding material at the conclusion of the experiment revealed that germination of seeds was occurring beneath the surface in chambers created by the earthworms, and that these seedlings were being grazed by L. terrestris.

Wildlife herbivory and rare plants : the effects of white-tailed deer, rodents, and insects on growth and survival of Turk's cap lily

Abstract Current land-use changes in eastern deciduous forests, such as fragmentation, may affect population sizes of native wildlife that may exacerbate declines in rare and endangered wildflower populations in the eastern deciduous forests. In this study, we examined the influence of herbivory by rodents (Peromyscus leucopus, Sciurus sp., and Tamias striatus) and white-tailed deer (Odocoileus virginianus) on the growth and survival of Turks cap lily (Lilium superbum) planted in Virginia. Bulbs were planted in pairs and in patches. One plant per pair was protected from deer damage with a wire cage, and patches consisted of two, 10 and 25 bulbs planted within 0.04 ha. Rodents dug up and consumed 9% of all the bulbs planted, and fatal rodent damage was 3 times greater in successional than in upland hardwood and creek bottom habitats. White-tailed deer consumed the apical meristem of 28% of the unprotected lilies that emerged, reducing mean plant height and stopping growth and reproduction for that season. Deer and insects, but not rodents, damaged a greater proportion of plants emerging in small patches (1–2 plants/0.04 ha) than on larger patches (3–20 plants/0.04 ha). Therefore, when protecting remaining populations or restoring new populations of rare perennial wildflowers in the eastern deciduous forest, methods for protecting plants from herbivory by rodents and white-tailed deer should be considered.

Relations between Physical Habitat and American Eel Abundance in Five River Basins in Maryland

Abstract Although the American eel Anguilla rostrata occurs in a variety of habitats over large geographic areas, little is known regarding the specific habitat relations that regulate eel distribution and abundance in freshwater streams. We evaluated the importance of 17 physical habitat, chemical, and biological variables in predicting eel density in five major river basins in Maryland. Because artificial structures impede eel migration in all five basins, only sites determined to be on unblocked streams or downstream of structures that significantly restrict eel passage were used in the analysis. Stepwise regression identified a model consisting of four variables—velocity–depth diversity, the log-transformed distance (km) to the Chesapeake Bay, the log-transformed density of noneel fishes, and the distance to a semipassable or impassable structure—as the best predictor of eel densities. When applied to a random subset of data not used for model development, the model correctly predicted 44.4% of eel de...

THE EFFECTS OF BEAVER-CREATED WETLANDS ON THE BENTHIC MACROINVERTEBRATE ASSEMBLAGES OF TWO APPALACHIAN STREAMS

We examined the effects of beaver impoundments on the benthic macroinvertebrate assemblages of two small Appalachian streams, Mountain Run (Somerset County, Pennsylvania) and a tributary to Herrington Creek (Garrett County, Maryland). Benthic macroinvertebrate assemblages above the impoundments were compared with assemblages within the impoundments and 1 m, 10 m, and 100 m below the impoundments. The results of our study indicate that beaver affect both within-impoundment and downstream benthic macroinvertebrate assemblages. Taxonomic and functional changes in benthic macroinvertebrate assemblages of the beaver-altered streams were a result of direct (impoundment) and indirect (changes in temperature, water chemistry, plant growth) alterations of the stream environment.

Community-Level Interactions Between Plants and Vesicular-Arbuscular Mycorrhizal Fungi

In this contribution we discuss several interactions between mycorrhizal fungi and their host plants. In particular we illustrate how plant communities may be affected by mycorrhizal fungi, and how mycorrhizal fungal communities may be affected by plants and plant cultural practices. The justification for the study of the mycorrhizal symbiosis at the level of the community is rooted in the fact that organisms in nature are usually assembled into interactive communities and do not exist as solitary entities. The function of the symbiosis must therefore be viewed in the context of communities. Although we draw extensively from the ecological literature, the concepts discussed herein are also relevant to horticulture, agronomy, forestry, and land reclamation. We believe that successful use of mycorrhizal fungi in these fields requires an essentially ecological perspective. This chapter deals primarily with the vesicular-arbuscular (VA) mycorrhizal symbiosis. We call to the reader’s attention other recent reviews on related ecological treatments of the mycorrhizal symbiosis including those by St. John and Coleman (1983), Hetrick (1984), Loree and Williams (1984), Fitter (1990), Allen (1991), Brundrett (1991), Marx (1991), Read (1991a,b), Soderstrom (1991) and Fahey (1992), among others.

On variation in forest floor thickness across four red pine plantations in Pennsylvania, USA

We studied variation in forest floor thickness in four plantations of red pine (Pinus resinosa Ait.) which were similar in age, soil type and associated vegetation. The plantations were located (west to east) in the Clear Creek, Moshannon, Sproul and Tiadaghton State Forests of Pennsylvania, USA. A gradient in forest floor thickness exists across these plantations; the forest floor is thickest in the west and it becomes progressively thinner toward the east. Decomposition of imported litter increased from west to east, suggesting that the variation in forest floor thickness is related to variation in the rate of decomposition. Decomposition rates were related to saprotroph abundance. Variation in forest floor N and phenolic concentrations, in overall mycorrhiza density and in the relative proportions of three common mycorrhiza morphotypes could not explain the variation in decomposition rate. The P concentrations and pH of the forest floor were significantly lower at Clear Creek and Moshannon, where decomposition rates were lowest, compared to Sproul and Tiadaghton, where decomposition rates were most rapid. This suggests that P concentration and pH may have exerted some control on decomposition.

Diversity and Structure in Natural Communities: The Role of the Mycorrhizal Symbiosis

In this contribution we discuss several interactions between mycorrhizal fungi and their host plants. In particular we illustrate how plant communities may be affected by mycorrhizal fungi, and how mycorrhizal fungal communities may be affected by plants and plant cultural practices. The justification for the study of the mycorrhizal symbiosis at the level of the community is rooted in the fact that organisms in nature are usually assembled into interactive communities and do not exist as solitary entities. The function of the symbiosis must, therefore, be viewed in the context of communities. An important focus in ecological research in recent years has been to understand which factors regulate the structure and diversity of natural populations and communities. It has long been hypothesized that diversity may be crucial for maintaining productivity the and also the stability of ecosystems and recent experimental investigations support these ideas. Therefore, in this chapter we also discuss the role of diversity in arbuscular mycorrhizal (AM) fungal communities and the effect this may have on diversity of plant populations and communities. Although we draw extensively from the ecological literature, the concepts discussed herein are also relevant to horticulture, agronomy, forestry, and land reclamation. We believe that successful use of mycorrhizal fungi in these fields requires an essentially ecological perspective. This chapter deals primarily with the arbuscular mycorrhizal (AM) symbiosis. We call to the reader’s attention other recent reviews on related ecological treatments of the mycorrhizal symbiosis including those by St. John and Coleman (1983), Hetrick (1984), Loree and Williams (1984), Fitter (1990), Allen (1991), Brundrett (1991), Marx (1991), Read (1991a,b), Soderstrom (1991), Fahey (1992), Newsham et al. (1995), among others.