Surface Of Leaf Litter Research Articles

Effects of root growth on dynamics of microbes and enzyme activities during litter decomposition.

To understand the influence of roots of understory plant entering litter layer on litter decomposition in forest ecosystems, we examined the effects of different treatments of Lolium multiflorum root biomass on microorganisms and enzyme activities during leaf litter decomposition of Symplocos setchuensis, a dominant species in a mid-subtropical evergreen broad-leaved forest, through a litter bag simulation experiment. Results showed that diversity index of bacterial and fungal communities of leaf litter surface under three treatments, i.e. no root (N), less roots (L), more roots (M), in a 240-day decomposition process showed the following pattern: M > L > N. The effects of these different root biomass treatments on the composition and quantity of fungal community were more significant than those on bacterial community. The biomass of living roots growing in the litter bag gradually decreased at the end of the growing season of L. multiflorum. The impacts of root growth on the composition of the fungal community gradually decreased during decomposition. At the same decomposition stage, the activities of acid phosphatase, β-glucosidase, polyphenol oxidase, and peroxidase on the litter surface were higher in the treatments with roots than that without roots. These results indicated that root growth could change the composition and quantity of microbial communities and increase the extracellular enzyme activities of microbes, and thus stimulating litter decomposition.

Environmental Factors Affecting Survival of Immature Ixodes scapularis and Implications for Geographical Distribution of Lyme Disease: The Climate/Behavior Hypothesis.

Recent reports suggest that host-seeking nymphs in southern populations of Ixodes scapularis remain below the leaf litter surface, while northern nymphs seek hosts on leaves and twigs above the litter surface. This behavioral difference potentially results in decreased tick contact with humans in the south, and fewer cases of Lyme disease. We studied whether north-south differences in tick survival patterns might contribute to this phenomenon. Four month old larvae resulting from a cross between Wisconsin males and South Carolina females died faster under southern than under northern conditions in the lab, as has previously been reported for ticks from both northern and southern populations. However, newly-emerged larvae from Rhode Island parents did not differ consistently in mortality under northern and southern conditions, possibly because of their younger age. Survival is lower, and so the north-south survival difference might be greater in older ticks. Larval survival was positively related to larval size (as measured by scutal area), while survival was positively related to larval fat content in some, but not all, trials. The difference in larval survival under northern vs. southern conditions might simply result from faster metabolism under warmer southern conditions leading to shorter life spans. However, ticks consistently died faster under southern than under northern conditions in the laboratory when relative humidity was low (75%), but not under moderate (85%) or high (95%) RH. Therefore, mortality due to desiccation stress is greater under southern than under northern conditions. We hypothesize that mortality resulting from the greater desiccation stress under southern conditions acts as a selective pressure resulting in the evolution of host-seeking behavior in which immatures remain below the leaf litter surface in southern I. scapularis populations, so as to avoid the desiccating conditions at the surface. If this hypothesis is correct, it has implications for the effect of climate change on the future distribution of Lyme disease.

Bleaching of leaf litter and associated microfungi in subboreal and subalpine forests.

Fungal decomposition of lignin leads to the whitening, or bleaching, of leaf litter, especially in temperate and tropical forests, but less is known about such bleaching in forests of cooler regions, such as boreal and subalpine forests. The purposes of the present study were to examine the extent of bleached area on the surface of leaf litter and its variation with environmental conditions in subboreal and subalpine forests in Japan and to examine the microfungi associated with the bleaching of leaf litter by isolating fungi from the bleached portions of the litter. Bleached area accounted for 21.7%-32.7% and 2.0%-10.0% of total leaf area of Quercus crispula and Betula ermanii, respectively, in subboreal forests, and for 6.3% and 18.6% of total leaf area of B. ermanii and Picea jezoensis var. hondoensis, respectively, in a subalpine forest. In subboreal forests, elevation, C/N ratio and pH of the FH layer, and slope aspect were selected as predictor variables for the bleached leaf area. Leaf mass per area and lignin content were consistently lower in the bleached area than in the nonbleached area of the same leaves, indicating that the selective decomposition of acid unhydrolyzable residue (recalcitrant compounds such as lignin, tannins, and cutins) enhanced the mass loss of leaf tissues in the bleached portions. Isolates of a total of 11 fungal species (6 species of Ascomycota and 5 of Basidiomycota) exhibited leaf-litter-bleaching activity under pure culture conditions. Two fungal species (Coccomyces sp. and Mycena sp.) occurred in both subboreal and subalpine forests, which were separated from each other by approximately 1100 km.

Habitat structure alters top-down control in litter communities

The question whether top-down or bottom-up forces dominate trophic relationships, energy flow, and abundances within food webs has fuelled much ecological research with particular focus on soil litter ecosystems. Because litter simultaneously provides habitat structure and a basal resource, disentangling direct trophic and indirect non-trophic effects on different trophic levels remains challenging. Here, we focussed on short-term per capita interaction strengths of generalist predators (centipedes) on their microbi-detritivore prey (springtails) and addressed how the habitat structuring effects of the leaf litter modifies this interaction. We performed a series of laboratory functional response experiments where four levels of habitat structure were constructed by adding different amounts of leaf litter to the experimental arenas. We found that increased leaf litter reduced the consumption rate of the predator. We interpreted this as a dilution effect of the augmented habitat size provided by the increasing leaf litter surface available to the species. Dilution of the prey population decreased encounter rates, whereas the capture success was not affected. Interestingly, our results imply that top-down control by centipedes decreased with increasing resource supply for the microbi-detritivore prey (i.e. the leaf litter that simultaneously provides habitat structure). Therefore, effective top-down control of predators on microbi-detritvore populations seems unlikely in litter-rich ecosystems due to the non-trophic, habitat-structuring effect of the basal litter resource.Electronic supplementary materialThe online version of this article (doi:10.1007/s00442-012-2530-6) contains supplementary material, which is available to authorized users.

Acorn viability following prescribed fire in upland hardwood forests

Restoration of structure and function of mixed-oak (Quercus spp.) forests is a focal issue of forest land managers in the eastern United States due to widespread regeneration failure and poor overstory recruitment of oaks, particularly on productive sites. Prescribed fire is increasingly used as a tool in oak ecosystem restoration, with the goal of reducing competition, and creating light and seedbed conditions conducive to germination and growth of oak seedlings. Yet, oak seedling establishment is dependent on the presence of viable acorns, which may be vulnerable to prescribed fire. We assessed the effect of prescribed burning and fire temperature on the viability of white oak and northern red oak acorns placed on the leaf litter surface, in the duff, or in the mineral soil during five winter prescribed burns in southern Appalachian upland hardwood forests. Fire temperatures varied among acorn plots, ranging from <79 to <371°C. After the burns, acorns were planted in trays with water-saturated vermiculite, exposed to 14 continuous hours of light daily, and maintained at 27°C on germination beds in a greenhouse. After three weeks we recorded the proportion of acorns germinating and the proportion of germinants with shoots. Our study indicated that patchy, low-intensity dormant season prescribed fire in upland hardwood forests reduced viability of white oak and northern red oak acorns located on the leaf litter surface, but did not generally affect acorns in the duff or mineral soil. Germination rates of both northern red oak and white oak acorns on the leaf litter surface decreased with increasing fire temperature. Shoot production by northern red oak germinants from acorns on the leaf litter surface (and less so in the duff), also decreased with increasing fire temperature. Acorns of both species on the leaf litter surface burned at temperatures ⩾204°C showed high mortality levels, with mortality virtually 100% at temperatures ⩾260°C. Fall burns, especially after a heavy acorn crop, could result in high acorn mortality, potentially impacting oak regeneration from seedlings for many years given erratic acorn production patterns among years and species. Frequent burning that reduces litter and duff depth could compromise availability of ‘safe sites’ where acorns are insulated from high fire temperatures. When oak ecosystem restoration is a goal, land managers should consider the timing and size of acorn crops, as well as the forest floor condition when determining the timing and frequency of prescribed burning.

Survival, Dispersal, and Potential Soil-Mediated Suppression of Phytophthora ramorum in a California Redwood-Tanoak Forest

Because the role of soil inoculum of Phytophthora ramorum in the sudden oak death disease cycle is not well understood, this work addresses survival, chlamydospore production, pathogen suppression, and splash dispersal of the pathogen in infested forest soils. Colonized rhododendron and bay laurel leaf disks were placed in mesh sachets before transfer to the field in January 2005 and 2006. Sachets were placed under tanoak, bay laurel, and redwood at three vertical locations: leaf litter surface, litter-soil interface, and below the soil surface. Sachets were retrieved after 4, 8, 20, and 49 weeks. Pathogen survival was higher in rhododendron leaf tissue than in bay tissue, with >80% survival observed in rhododendron tissue after 49 weeks in the field. Chlamydospore production was determined by clearing infected tissue in KOH. Moist redwood-associated soils suppressed chlamydospore production. Rain events splashed inoculum as high as 30 cm from the soil surface, inciting aerial infection of bay laurel and tanoak. Leaf litter may provide an incomplete barrier to splash dispersal. This 2-year study illustrates annual P. ramorum survival in soil and the suppressive nature of redwood-associated soils to chlamydospore production. Infested soil may serve as primary inoculum for foliar infections by splash dispersal during rain events.

Behavioral and Ecological Adaptations to Water Economy in Two Plethodontid Salamanders, Ensatina eschscholtzii and Batrachoseps attenuatus

Amphibians in general, and plethodontid salamanders in particular, are highly susceptible to cutaneous water loss. We compared behavior, habitat use, and physiology of Batrachoseps attenuatus (Eschscholtz) and Ensatina eschscholtzii (Gray) in Humboldt County, California, to identify adaptations of water economy. Both species lost more body water in a dry environment than in a wet one. In the field, sites with salamanders had higher relative humidity than sites without salamanders. In behavioral experiments, both species used water-conserving postures; they positioned themselves deep in leaf litter in dry environments while remaining on the surface of leaf litter in wet environments. The slender morphology of B. attenuatus may aid in habitat partitioning by plethodontid salamanders; in the field we found B. attenuatus closer to the surface of the leaf litter than E. eschscholtzii. The evolution of a slender body shape appears to be unconstrained by microclimates typically encountered by this species.

BODY CONDITION OF SWAINSON'S WARBLERS WINTERING IN JAMAICA AND THE CONSERVATION VALUE OF CARIBBEAN DRY FORESTS

Abstract Despite conservation concern for the Swainson's Warbler (Limnothlypis swainsonii), little is known about its nonbreeding ecology. Because body condition can provide an indication of habitat quality, we examined Swainson's Warbler body condition indices in dry limestone forest and second growth scrub habitats in Jamaica, where this species was relatively common. In dry limestone forests, Swainson's Warblers showed no seasonal change in body mass corrected for structural size, furcular fat score, or age ratio. This contrasts with results from studies of other species of Neotropical migrant warblers that showed significant seasonal declines in body mass in similar xeric habitats. Dry limestone forest sites also supported a greater and less spatially variable biomass of prey commonly consumed by Swainson's Warblers than second growth scrub and shade coffee. Because Swainson's Warblers consume prey concealed beneath the leaf litter surface, they apparently are less susceptible to the extreme dry seaso...

Air temperature and relative humidity effects on behavioral activity of blacklegged tick (Acari: Ixodidae) nymphs in New Jersey.

Air-temperature and relative humidity data were used to explain variation in behavioral activity of Ixodes scapularis Say nymphs. We estimated behavioral activity as the residual variation in drag-sample data after seasonal changes in population density were removed by regression. The seasonal decline in drag samples between June and August 1995 on field plots at Morristown National Historical Park, NJ, can be described by a simple negative exponential function. Residuals around a fitted exponential were significantly correlated with temperature and with relative humidity measured at the leaf-litter surface, and explained 34 and 44% of the variance, respectively. Multiple regression on temperature and relative humidity explained 51% of the variance. These regressions estimated the explanatory power of microclimate, independent of seasonal correlations, and might provide a basis for day-to-day prediction of human exposure to Lyme disease.

Effect of leaf litter and density on fitness and population performance of the hole mosquito Aedes triseriatus

Abstract. We tested the effects of food, in the form of leaf litter, and density on population growth and fitness correlates of the tree hole mosquito Aedes triseriatus. Our field experiment used a 2 x 2 randomized block design, with three holes as blocks. In cages within three holes, we manipulated densities of Aedes triseriatus larvae, and presence of leaf litter. Our laboratory experiment used a 2 x 3 factorial design in which we also manipulated densities of larvae and availability of leaf litter within similar cages (inside, outside, or absent). For both experiments we determined effects on survival, days to and mass at eclosion of both sexes, and a composite index of population performance λ′, that estimates finite rate of increase. In the field experiment, we found significant and large effects of leaf litter and of density on the performance of A. triseriatus. The effect of density did not depend on leaf litter availability. We documented significant variation among tree holes for most correlates of fitness. Often, the effects of treatments varied significantly depending on the tree hole tested. In the laboratory experiment we found significant effects of density and litter, and that direct browsing on leaf litter is necessary for the effect of litter on performance of A. triseriatus. In the laboratory, the negative effect of increased density was dependent on leaf litter availability. Our results demonstrate that leaf litter has important effects on population performance of tree hole mosquitoes in natural tree holes. Direct browsing on the surface of leaf litter is the most likely mechanism by which litter enhances population growth. The impact of litter on populations varies among tree holes.

Ecology of the Ant Pogonomyrmex mayri: Foraging and Competition

Aspects of recruitment and behavior of Pogonomyrmex mayri (Myrmicinae: Formicidae) are described. Foragers leave and return to the nest in all directions, but each worker tends to forage only in one sector of the territory. When food is discovered, nestmates are recruited by a trail pheromone, but even with a persistent food source, a single file of foragers never develops. Foragers rarely cooperate to transport prey. Foraging is strictly diurnal with the amount of activity controlled by temperature, which in turn is affected by season, time of day, and nest location. Strong territorial defense by neighboring colonies and competition from other ant species often severely restrict direction and distance. VIRTUALLY NOTHING IS KNOWN OF THE SOUTH AMERICAN species of the genus Pogonomyrmex. The North American Pogonomyrmex of the subgenus Pogonomyrmex are well known for living in open habitats and collecting and storing large quantities of seeds in underground granaries, and for stinging fiercely when disturbed (Wheeler 1910). It is not known to what degree the subgenera Ephebomyrmex and Forelomyrmex, which dwell primarily in South America, share those characteristics. Pogonomyrmex (Forelomyrmex) mayri s a large, velvety black ant whose entire known distribution lies at the foot of the Sierra Nevada de Santa Marta in northeastern Colombia. Kugler (1978) and Kugler and Hincapie (1983) have shown that this species differs morphologically and ecologically from its better-known relatives. Instead of forming large colonies in open desert or grassland, it forms rather small colonies usually at the bases of trees and shrubs in dry forest. It scavenges dry arthropod remains and miscellaneous plant parts by on the soil or leaf litter surface. It does not sting or store seeds. This report makes further comparisons of diurnal activity, territoriality, and recruitment. MATERIALS AND METHODS Most observations come from a study area 33 x 40 m in the forest behind Gairaca Bay of Tayrona National Park, 8 km east of Santa Marta, Colombia. A description of the study site and the means used to locate, mark, and map nests are found in Kugler and Hincapie (1983). To record the temporal patterns of activity in wet and dry seasons and in the presence and absence of competing ants, I used what will be referred to henceforth as foraging plots. These plots were 1 x 2 m rectangles outlined by string held several centimeters off the ground by small wire stakes at the corners. They were placed within a meter of a P. mayri nest entrance, and each hour the numbers of P. mayri and its most likely competitors, Odontomachus bauri and Ectatomma ruidum, were recorded using the following procedure. First, I placed two mercury thermometers on the ground near the plot, one in shade and one in full sun, and stood immobile at the edge of the plot for five minutes, during which time I estimated the percentage of the plot in direct sun. Then, each species was counted in a separate inspection of the plot, and the thermometer temperatures were recorded. Those temperatures are of course only approximations of the temperatures of the ants. A record of activity throughout the day was obtained by repeating this procedure ach hour beginning and ending in darkness. I accumulated 21 such records of diurnal activity using 10 nests in a variety of microhabitats and spanning both wet and dry seasons (November and March, respectively). Intraspecific competition in was inferred from three types of evidence: (1) mapping the limits of the territories by offering peanut chips to foragers and following them to their nests, (2) luring marked foragers from one colony to the territory ofanother colony and observing the resulting interactions, and (3) measuring territorial expansion after excavation of a neighboring nest. Mapping was accurate to within 50 cm (Kugler and Hincapie 1983). Interspecific competition was also studied by removal experiments. Twice I tested whether P. mayri limits the of E. ruidum. In each experiment, I recorded hourly the numbers of both ants in a plot located 1 m from a P. mayri entrance. Then the foragers of that colony were removed by entrapment in the nest or by excavation, and the hourly activity of E. ruidum alone was recorded. In a third experiment, I tested whether E. ruidum restricts the of P. mayri. The territory ofa P. mayri nest was mapped and the positions of all E. ruidum entrances in and around that territory were marked with small flags. The normal levels of forI Received 26 July 1983, revised 6 December 1983, accepted 13 December 1983. BIOTROPICA 16(3): 227-234 1984 227 This content downloaded by the authorized user from 192.168.52.67 on Tue, 20 Nov 2012 12:43:37 PM All use subject to JSTOR Terms and Conditions Ants 35c o 2 sq. m. I 20~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ 0 0 0 ~~~~~251