Effects of Experimental Canopy Manipulation on Amphibian Egg Deposition

ABSTRACT Although effects of forest management on amphibians are relatively well studied, few studies have examined how these practices affect egg deposition by adults, which can impact population recruitment. We quantified the effects of 4 canopy tree-retention treatments on amphibian oviposition patterns in clusters of 60-L aquatic mesocosms located in each treatment. We also related aquatic and terrestrial biophysical parameters in treatment plots to oviposition patterns. Cope's gray treefrogs (Hyla chrysoscelis) deposited more egg masses in clear-cut and 25–50% tree-retention treatments than in controls. In contrast, mountain chorus frogs (Pseudacris brachyp***hona) deposited more egg masses in unharvested control and 75% retention treatments than in clear-cut or 25–50% retention treatments. Spotted salamanders (Ambystoma maculatum) only deposited eggs in 75% retention treatments and controls. The number of egg masses deposited by mountain chorus frogs was positively related to canopy cover and negatively related to water temperature, pH, and dissolved oxygen, whereas we noted the opposite relationships for Cope's gray treefrogs. We did not detect a relationship between the number of egg masses deposited by any species and the distance of mesocosms to either the nearest mature closed-canopy forest or to the nearest natural amphibian breeding pool. The impacts of the silvicultural treatments we studied were species-specific and depended on the amount of trees removed. In areas where protection of spotted salamander and mountain chorus frog breeding habitat is a priority, we recommend harvests retain at least 75% of the canopy. Our results also suggest that retention of 25–50% of canopy trees surrounding amphibian breeding pools has little conservation benefit.     

Nodule Function in Symbiotic Bambara Groundnut (Vigna subterraneaL.) and Kersting's Bean (Macrotyloma geocarpumL.) is Tolerant of Nitrate in the Root Medium

Nitrogen-fixing activity in two nodulated African legumes, Bambaragroundnut (Vigna subterraneaL.) and Kersting's bean (MacrotylomageocarpumL.), was assessed in the presence of nitrate (NO₃^-)ions in the rooting medium. Nitrogenase activity was unimpairedby the supply of 5 mol m^-3NO₃to both species. Also, large concentrationsof ureides dominated the transpiration stream of NO₃-fed plants.Compared to other symbiotic legumes cultured with similar NO₃concentrations,nodule functioning in the tested landraces of Bambara groundnutand Kersting's bean is tolerant of NO₃ions in the rhizosphere.The potential benefits of such naturally occurring NO₃-tolerantsymbioses are substantial, as they would permit inorganic Nfertilizer application in intercropping systems without inhibitingN₂fixation in the associated legumes.Copyright 1998 Annals ofBotany Company NO₃tolerance, Bambara groundnut, Kersting's bean, nitrogenase activity, xylem ureides.     

Raised water temperature lowers diversity of hyporheic aquatic hyphomycetes

1. The hyporheic zone of a permanent first‐order stream was divided into a treatment and a control section using a 1 m deep sheet‐metal barrier. During a 4‐month pre‐treatment period, water temperatures in two transects of the two sections were not different. Upon heating, the water temperature in the treatment transect increased by an average of 4.3 °C over values in the control transect. 2. Eleven bimonthly core samples were taken from a treatment and a control transect, and recovered CPOM was classified as twigs, wood, grass, roots, cedar and deciduous leaves. 3. In both transects, twigs were the most common and deciduous leaves the least common substrates. The number of leaf fragments declined significantly in the heat‐treated transect. 4. Diversity and frequencies of occurrence of aquatic hyphomycetes were highest on leaves and lowest on grass and wood. On leaves, their frequency of occurrence was higher in control than in treatment samples. 5. Preliminary results with amplified and cloned 18S DNA sequences revealed many fungal taxa with high affinities to Basidiomycota, particularly to Limnoperdon incarnatum. 6. By itself, higher water temperature due to global warming is likely to lower the availability of substrates for, and therefore the occurrence of, aquatic hyphomycetes.