The deleterious effects of salinity stress on leafminers and their freshwater host

Abstract.  1. Salinity is an important cause of abiotic stress in wetland communities yet little is known about its consequences for freshwater plants and their insect herbivores. The goal of this study was to test the effect of salinity on a leafmining insect, Cerodontha iridiphora , and its herbaceous host plant, Iris hexagona .
2. Leafminer performance was evaluated on irises grown in control and saline treatments, and the effects of salinity and herbivory on leaf quality and mortality was measured.
3. Leafminer density and size were significantly lower on irises grown in saline water compared with freshwater.
4. Both salinity and herbivory accelerated leaf senescence and mortality, and their combined effects increased tissue loss by an order of magnitude compared with controls.
5. Leafminers acted as nutrient sinks. The undamaged regions of mined leaves contained 40% less nitrogen than unmined leaves, providing a mechanism for the premature leaf mortality.
6. Salinity was detrimental to the performance and survival of both the iris leafminer and its host plant. We propose that glycophytic host plants and their insect herbivores will suffer more than halophytic communities from environmental salinity because they lack the adaptive mechanisms to tolerate this potent physiological stress.     

SAMPLE/RINSE TEMPERATURE EFFECTS ON DISCRIMINATION OF SWEET AND SALTY DIFFERENCES IN A FOOD SYSTEM

The ability of panelists to distinguish between samples of apple juice with two levels of added sucrose (0.1 and 0.9 g/100 mL) or NaCl (0.05 and 0.14 g/100 mL) was determined using a modified signal detection technique. Samples at various temperatures (6, 24, or 50C) were presented with various rinse conditions. Sometimes a water rinse (6, 24, or 50C) was presented between samples and somtimes not. R-index values were calculated to predict the ability of panelists to distinguish between samples. No temperature effect was found for sweetness difference tests; however, R-indices showed that salty differences in apple juice were more distinguishable at a sample temperature of 24C than at 6 or 50C. Samples temperature had a greater effect than rinse condition (temperature or no rinse) on discrimination between samples differing in NaCl concentration.     

Lamium mild mosaic virus: a virus distantly related to broad bean wilt

Lamium mild mosaic virus (LMMV) was compared with some strains of broad bean wilt virus (BBWV). It differed somewhat in host range from BBWV; serologically, it was only distantly related to four strains of BBWV, all belonging to serotype I, but no reaction was detected with serotype II. BBWV and LMMV were not serologically related to six comoviruses. Like BBWV, LMMV sedimented in three components and the two viruses were morphologically indistinguishable, but LMMV had more slowly migrating RNAs and coat proteins. No distinctive pathological changes were seen in LMMV infected cells. It is proposed that LMMV be considered a distinct virus from BBWV but included with it in a new group of plant viruses.     

Stream inflow and predation risk affect littoral habitat selection by benthic fish

1. We examined small, fishless headwater streams to determine whether transport of macroinvertebrates into the littoral zone of an oligotrophic lake augmented food availability for Cottus asper, an abundant predatory fish in our study system. We sampled fish and macroinvertebrates during the recruitment and growth season of 2 years, either monthly (2004) or bi‐monthly (2005), to observe whether stream inputs increased prey availability and whether variation in total macroinvertebrate biomass was tracked by fish. 2. Observations from eight headwater streams indicated that streams did not increase the total macroinvertebrate biomass in the shallow littoral zone at stream inflows, relative to adjacent plots without stream inputs (controls). The taxonomic composition of stream macroinvertebrates drifting toward the lake differed from that in the littoral lake benthos itself, although there was no evidence of any species change in the composition of the littoral benthos brought about by stream inputs. 3. Although streams made no measurable contribution to the biomass or taxonomic composition of the littoral macroinvertebrate benthos, there was substantial temporal variation in biomass among the eight sites for each of the (n = 7) sample periods during which observations were made. Variation in total biomass was primarily a function of bottom slope and benthic substrata in the lake habitats. Dominant taxonomic groups were Baetidae, Ephemerellidae (two genera), Leptophlebiidae, Chironomidae (three subfamilies) and Perlodidae, although we did not determine the specific substratum affinities of each taxon. 4. Mixed effects linear models identified a significant interaction between macroinvertebrate biomass and plot type (stream inflow vs. control) associated with fish abundance. Across the observed range of macroinvertebrate biomass, fish showed a significant preference for stream inflows, but more closely tracked food availability in the controls. For young‐of‐the‐year (YOY), a negative effect of temperature was also included in the model, and we observed lower temperatures at stream inflows. However, abundance of predatory adults affected habitat selection for YOY. Lake‐bottom slope also accounted for variation in abundance in both fish models. 5. Our results suggest that the effect of fishless headwater streams on downstream fish may not always be through direct delivery of food. In this study system, fish preferred stream inflow plots, but this preference interacted with macroinvertebrate biomass in a manner that was difficult to explain. For YOY, predation risk was related to the preference for stream inflows, although the specific factor that mitigates predation risk remains poorly understood.     

Negative fire feedback in a transitional forest of southeastern Amazonia

Anthropogenic understory fires affect large areas of tropical forest, particularly during severe droughts. Yet, the mechanisms that control tropical forests' susceptibility to fire remain ambiguous. We tested the widely accepted hypothesis that Amazon forest fires increase susceptibility to further burning by conducting a 150 ha fire experiment in a closed-canopy forest near the southeastern Amazon forest–savanna boundary. Forest flammability and its possible determinants were measured in adjacent 50 ha forest plots that were burned annually for 3 consecutive years (B3), once (B1), and not at all (B0). Contrary to expectation, an annual burning regime led to a decline in forest flammability during the third burn. Microclimate conditions were more favorable compared with the first burn (i.e. vapor pressure deficit increased and litter moisture decreased), yet flame heights declined and burned area halved. A slight decline in fine fuels after the second burn appears to have limited fire spread and intensity. Supporting this conclusion, fire spread rates doubled and burned area increased fivefold in B3 subplots that received fine fuel additions. Slow replacement of surface fine fuels in this forest may be explained by (i) low leaf litter production (4.3 Mg ha⁻¹ yr⁻¹), half that of other Amazon forests; and (ii) low fire-induced tree and liana mortality (5.5±0.5% yr⁻¹, SE, in B3), the lowest measured in closed-canopy Amazonian forests. In this transitional forest, where severe seasonal drought removed moisture constraints on fire propagation, a lack of fine fuels inhibited the intensity and spread of recurrent fire in a negative feedback. This reduction in flammability, however, may be short-lived if delayed tree mortality or treefall increases surface fuels in future years. This study highlights that understanding fuel input rate and timing relative to fire frequency is fundamental to predicting transitional forest flammability – which has important implications for carbon emissions and potential replacement by scrub vegetation.     

Microsatellite DNA markers for population genetic studies in the dinoflagellate Karenia brevis

Nine nuclear‐encoded microsatellites from an enriched genomic DNA library of the HAB (harmful algal bloom) dinoflagellate Karenia brevis were isolated and characterized. The microsatellites include five perfect (three dinucleotide and two trinucleotide) and four imperfect (two dinucleotide and two trinucleotide) repeat motifs. Gene (haplotype) diversity ranged from 0.153 to 0.750 among a sample of 13 isolates; the number of alleles among the isolates ranged from two to six and pairwise tests of genotypic disequilibria were nonsignificant. The microsatellites developed in this study will provide insight into the genetic diversity of this HAB species and tools that may prove useful in predicting source populations and physiological parameters of individual K. brevis blooms.     

Nitrogen deposition interacts with climate in affecting production and decomposition rates in Sphagnum mosses

Increasing rates of atmospheric nitrogen (N) deposition may reduce growth and accelerate decomposition of Sphagnum mosses in bogs. Sphagnum growth and rates of Sphagnum litter decomposition may also vary because of climate change as both processes are controlled by climatic factors. The initial purpose of this study was to assess if growth and litter decomposition of hummock and lawn Sphagnum species varied with increasing N input in a factorial mid‐term (2002–2005) experiment of N and phosphorus (P) addition, in a bog on the southern Alps of Italy. However, as the experimental period was characterized by an exceptional heat wave in summer 2003, we also explored the interacting effects of fertilization and strongly varying climate on growth and decomposition rates of Sphagnum. The heat wave implied strong dehydration of the upper Sphagnum layer even if precipitation in summer 2003 did not differ appreciably from the overall mean. Sphagnum production was somewhat depressed by high levels (3 g m⁻² yr⁻¹) of N addition without concomitant addition of P presumably because of nutrient imbalance in the tissues, but production rates were much lower than the overall means in 2003, when no effect of nutrient addition could be observed. Adding N at high level also increased the potential decay of Sphagnum litter. Higher CO₂ emission from N‐fertilized litter was due to amelioration of litter chemistry showing lower C/N quotients in the N‐fertilized treatments. Rates of CO₂ emission from incubated litter also were more strongly affected by water content than by nutrient status, with practically no CO₂ emission detected when litter was dry. We conclude that higher rates of atmospheric N availability input may depress Sphagnum growth because of P, and presumably potassium, (co‐)limitation. Higher N availability is also expected to promote potential decay of Sphagnum litter by ameliorating litter chemistry. However, both effects are less pronounced if the growing Sphagnum apex and the underlying senescing tissues dry out.     

Gopher Tortoise Response to Habitat Management by Prescribed Burning

ABSTRACT As quality of forested habitat declines from altered fire regimes, gopher tortoises (Gopherus polyphemus) often move into ruderal areas to the detriment of the animal and land manager. We evaluated effects of a dormant-and-growing-season prescribed fire on habitat and gopher tortoise use of degraded longleaf pine (Pinus palustris) forests surrounding military training areas. We burned 4 of 8 sites in winter 2001–2002 and again in April 2003. Changes in vegetation measured during 2001–2004 indicated that burn treatments did not increase herbaceous vegetation. Similarly, movement patterns, burrow usage, and home range of tortoises radiotracked from 2002–2004 did not differ between treatments. Woody cover initially was reduced in the forests postburn, and we found more new burrows in burned forest sites. Once shrub cover was reduced, tortoises started using forested habitat that had become overgrown. However, shrub reduction may be temporary, as woody stem densities increased postburn. Thus, the one-time use of fire to manage tortoise habitat may not rapidly restore the open canopy, sparse woody midstory, and abundant herbaceous vegetation that this species requires. Repeated prescribed fires or additional management techniques may be needed for complete restoration.