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Eastern gamagrass [Tripsacum dactyloides (L.) L] (EG) is reported to exhibit acid tolerance and root penetration through clay-pans. To study its root growth in these conditions, a greenhouse column study was conducted under simulated soil stress conditions, using EG and sordan [Sorghum x drummondii (Steud.) Millsp. & Chase] as a comparison species. Treatments consisted of incomplete factorial combinations of plant species (EG and sordan), soil water potential (-10 and -300 kPa), lime (pH 3.5 and 4.8), and soil bulk density ([D.sub.b]) (1.3 and 1.7 g [cm.sup.-3]). The treatments were arranged as a randomized complete block design (RCBD). For some of the response variables that were analyzed at different depths, depth was considered as a subplot factor. Treatments were applied to Al-toxic Tatum Bt horizon material (clayey, fine, mixed, semiactive, thermic Typic Hapludults) used in the middle 30-cm section of 15 by 60-cm polyvinyl Cl (PVC) columns. Soil strength was determined at harvest by cone penetrometer resistance. Results indicated that EG tolerated acid, Al-toxic conditions, while sordan roots were sensitive to the low pH conditions. Eastern gamagrass roots penetrated high soil strength layers that inhibited sordan root growth. The characteristics of acid, Al tolerance, and penetration of high soil strength make EG valuable in establishing grassed buffers, vegetative conservation barriers, and pastures in extremely acid or dense soils.

Natural and anthropogenic changes (e.g., land use change, pollution) will alter many environmental factors in the coming years, including the amount of solar radiation reaching the earth’s surface. Alterations in solar radiation exposure is likely to impact the ecologies of many living organisms, including invertebrates that inhabit aquatic habitats. In this study, we assessed the effect of UV-B radiation on the metabolic rates and fitness (survival, development time, body size) of Aedes albopictus and Culex pipiens mosquitoes and the activity of their microbial food resources in experimental aquatic microcosms. We exposed single-species cohorts of newly hatched Ae. albopictus and Cx. pipiens larvae and a control treatment with no larvae to three UV-B conditions that mimicked those in full-sun and shade in the field and to a control condition with no UV-B radiation. Our results indicated that UV-B radiation affected the metabolic rates of both Ae. albopictus and Cx. pipiens larvae, with significantly higher rates found in full-sun compared to shade and no-UV conditions, 8 and 15 days after exposure began. Ae. albopictus and Cx. pipiens survival was also affected by UV-B radiation condition, with significantly lower survival in full-sun compared to shade and no UV-B conditions. Microbial metabolic rates were consistently significantly lower in full-sun compared to shade and no-UV conditions, especially at 8 days of exposure. These results show that UV-B radiation at levels found in open spaces showed strong and important impacts on the metabolic rates and survival of Ae. albopictus and Cx. pipiens larvae. Decreased survival of Ae. albopictus and Cx. pipiens with higher UV-B radiation levels may be caused by both direct exposure to radiation as well as the indirect effects of reduced microbial food, resulting in greater metabolic demands and stress. Negative impacts of UV-B radiation on the survival of Ae. albopictus and Cx. pipiens are likely to have important implications for the distribution and abundance of these mosquitoes, and the transmission of pathogens that these two broadly distributed mosquitoes vector. [ABSTRACT FROM AUTHOR]

Drought poses serious threats to the valuable coastal marsh ecosystems, especially considering that the frequency, intensity, and acuteness of drought may increase with prospective climate change. We study the drought-associated phenological changes of Louisiana coastal marshes through combining remote sensing-derived phenological record (i.e., Landsat-derived Normalized Difference Vegetation Index, or NDVI) and field-based environmental data during the past 30 yr. We find that drought condition in southeast Louisiana is characterized by decreased discharge of the Mississippi River and reduced precipitation, which correlate with the continental weather patterns over the conterminous United States influenced by La Niña. The peak NDVI day of saline marshes delays for two months (P < 0.01), from mid-July to mid-September, and their growth duration consequently shortens for two months (P < 0.01) in drought years. Such phenological changes might result from the inhibition of the growth of Spartina alterniflora, a dominant species in saline marshes whose biomass peaks earlier than the coexisting species, perhaps due to reduced freshwater input and increased water deficit. Drought might also cause Spartina dieback via similar mechanisms. Our results underline the correlation between drought in southeast Louisiana and La Niña and highlight the sensitivity of saline marshes to drought, thereby providing valuable information for coastal marsh management and conservation facing climate change. [ABSTRACT FROM AUTHOR]