Nitrogen addition stimulates forest litter decomposition and disrupts species interactions in Patagonia,Argentina

Nitrogen (N) deposition and biodiversity loss are important drivers of global change, with uncertain consequences for carbon (C) and nutrient turnover in terrestrial ecosystems. We evaluated the simultaneous effects of N deposition and plant diversity on litter decomposition within a temperate forest in Patagonia. We identified ‘tree triangles’ created by the intersection of three tree‐canopies that directly controlled micro‐environmental conditions on the forest floor, and combined it with an N addition treatment. Triangles were composed of one or three Nothofagus species (N. dombeyi, N. obliqua or N. nervosa). We placed litterbags containing litter of each of the Nothofagus species and litterbags containing a mixture of the three species within all triangles and assessed mass loss over 2 years. We used a standard litter type in all triangles to independently evaluate triangle effects on decomposition. N addition had strong and positive effects on decomposition with an average 46% increase in the decomposition constant. Litter species significantly differed in their response to N addition; litter with higher lignin content and lower labile C content had larger increase in decomposition due to fertilization. Also, N addition disrupted two types of species interactions that control decomposition. The affinity relation between litter and decomposers, that enhanced decomposition of home litter (‘home‐field advantage’) that was demonstrated to be significant for all three Nothofagus species, disappeared with N addition. Second, N addition modified litter species interactions, transforming neutral effects of litter mixtures to positive, nonadditive effects on mass loss. Finally, N addition stimulated N release from decomposing litter which was modulated by plant species effects. Together, these results suggest that N addition to unpolluted forests increases C loss, contrary to what has been observed for temperate forests in industrialized areas of the world, and that alterations in nutrient pools have effects on species interactions, including the elimination of affinity effects for decomposition.     

Long‐term dynamics of submerged macrophytes and algae in a small and shallow,eutrophic lake: implications for the stability of macrophyte‐dominance

1. Submerged macrophyte and phytoplankton components of eutrophic, shallow lakes have frequently undergone dynamic changes in composition and abundance with important consequences for lake functioning and stability. However, because of a paucity of long‐term survey data, we know little regarding the nature, direction and sequencing of such changes over decadal–centennial or longer timescales. 2. To circumvent this problem, we analysed multiple (n = 5) chronologically correlated sediment cores for plant macro‐remains and a single core for pollen and diatoms from one small, shallow, English lake (Felbrigg Hall Lake, Norfolk, U.K.), documenting 250 years of change to macrophyte and algal communities. 3. All five cores showed broadly similar stratigraphic changes in macrophyte remains with three distinct phases of macrophyte development: Myriophyllum–Chara–Potamogeton (c. pre‐1900), to Ceratophyllum–Chara–Potamogeton (c. 1900–1960) and finally to Zannichellia–Potamogeton (c. post‐1960). Macrophyte species richness declined from at least 10 species pre‐1900 to just four species at the present day. Additionally, in the final Zannichellia–Potamogeton phase, a directional shift between epi‐benthic and phytoplankton‐based primary production was indicated by the diatom data. 4. Based on macrophyte–seasonality relationships established for the region, concomitant with the final shift to Zannichellia–Potamogeton, we infer a reduction in the seasonal duration of plant dominance (plant‐covered period). Furthermore, we hypothesise that this change in species composition resulted in a situation whereby macrophyte populations were seasonally ‘sandwiched’ between two phytoplankton peaks in spring and late summer as observed in the contemporary lake. 5. We suggest that eutrophication‐induced reductions in macrophyte species richness, especially if the number of plant‐seasonal strategies is reduced, may constrict the plant growing season. In turn, this may render a shallow lake increasingly vulnerable to seasonal invasions of phytoplankton resulting in further species losses in the plant community. Thus, as part of a slow (over perhaps 10–100s of years) and self‐perpetuating process, macrophytes may be gradually pushed out by phytoplankton without the need for a perturbation as required in the alternative stable states model of plant loss.     

Within-Stand Selection of Canada Lynx Natal Dens in Northwest Maine,USA

Abstract Canada lynx (Lynx canadensis) were listed as threatened in the contiguous United States under the Endangered Species Act in March 2000. Little information on lynx ecology at the southern extent of their range was available at the time of listing, and no ecological studies had been conducted in the eastern USA. Between 1999 and 2004, we investigated habitat selection at natal dens in northern Maine to address questions on the importance of forest conditions to denning requirements. We compared within-stand characteristics of 26 den sites to general characteristics of the stands containing dens. We used logistic regression to identify components within stands that distinguished natal dens from the residual stand and used the information-theoretic approach to select models that best explained lynx den-site selection. The top-ranked model had 2 variables: tip-up mounds of blown-down trees and visual obscurity at 5 m from the den (w_i = 0.92). Within-stand structure was useful for predicting lynx den-site selection in managed forests in Maine and suitable denning habitat did not appear to be limiting.     

Long‐term effects of exclusion of grazing stock on degraded herbaceous plant communities in a riparian Eucalyptus camaldulensis forest in south‐eastern Australia

Abstract Stock grazing has degraded many riparian ecosystems around the world. However, the potential for ecosystem recovery following the removal of grazing stock is poorly known. We developed a conceptual model to predict the responses of native and exotic herbaceous plants to grazing exclusion, based on site productivity and the degree of initial vegetation degradation. The effects of excluding grazing stock on richness, cover and composition of herbaceous plants were examined over 12 years in the degraded understorey of a riparian forest in Gulpa Island State Forest in south‐eastern Australia. We predicted that grazing exclusion would lead to limited changes in vegetation cover, richness and composition, owing to presumed low site productivity and the high degree of understorey degradation. Results showed that the cover, richness and composition of native and exotic species varied significantly among years. Over all plots, regions and years, total cover was slightly but significantly lower in grazed than in ungrazed plots (43.4% vs. 50.8%). While the cover of native plants increased over time in both treatments, the rate of increase was slightly greater in ungrazed plots. Grazing exclusion had no effect on the richness of native or exotic species, but had a significant but minor impact on plant composition, with different common species (mostly exotics) being promoted or diminished in ungrazed plots. The composition of grazed and ungrazed areas did not become more different over time. Overall, the effects that could be attributed to grazing exclusion were relatively minor and transient. Results are consistent with predictions based on site productivity and initial degradation, and should not be extrapolated to other more productive, or less degraded, riparian systems.     

The tobacco Cel7 gene promoter is auxin-responsive and locally induced in nematode feeding sites of heterologous plants

Emerging evidence suggests that plant cell-wall-modifying enzymes induced by root-parasitic nematodes play important roles in feeding cell formation. We previously identified a tobacco endo-β-1,4-glucanase (cellulase) gene, NtCel7 , that was strongly induced in both root-knot and cyst nematode feeding cells. To characterize further the developmental and nematode-responsive regulation of NtCel7 , we isolated the NtCel7 promoter and analysed its expression over a time course of nematode infection and in response to auxin, gibberellin, ethylene and sucrose in soybean and tomato hairy roots and in Arabidopsis containing the NtCel7 promoter fused to the β-glucuronidase (GUS) reporter gene. Histochemical analyses of transgenic plant materials revealed that the NtCel7 promoter exhibited a unique organ-specific expression pattern during plant development suggestive of important roles for NtCel7 in both vegetative and reproductive growth. In all plant species tested, strong GUS expression was observed in root tips and lateral root primordia of uninfected roots with weaker expression in the root vasculature. Further analyses of transgenic Arabidopsis plants revealed expression in shoot and root meristems and the vasculature of most organs during plant development. We also determined that the NtCel7 promoter was induced by auxin, but not gibberellin, ethylene or sucrose. Moreover, strong GUS activity was observed in both cyst and root-knot nematode-induced feeding sites in transgenic roots of soybean, tomato and Arabidopsis. The conserved developmental and nematode-responsive expression of the NtCel7 promoter in heterologous plants indicates that motifs of this regulatory element play a fundamental role in regulating NtCel7 gene expression within nematode feeding sites and that this regulation may be mediated by auxin.     

Cytological aspects of uterine cervical adenocarcinoma, adenosquamous carcinoma and combined adenocarcinoma-squamous carcinoma: appraisal of diagnostic criteria for in situ versus invasive lesions

Cytological aspects of uterine cervical adenocarcinoma, adenosquamous carcinoma and combined adenocarcinoma-squamous carcinoma: appraisal of diagnostic criteria for in situ versus invasive lesions
This paper reports the cytological findings based on air-dried smears in a retrospective series of 143 cases of endocervical adenocarcinoma, combined adenocarcinoma-squamous carcinoma and adenosquamous carcinoma drawn from the files of the BC Cancer Registry. Cervical cytology smears were available before biopsy in 131 patients, but in 18 cases the cytology showed no abnormality. Malignant changes or high-grade atypia of glandular and/or squamous cells (defined as moderate or severe dyskaryosis) were detected in 103 cases. In 46 cases, only a high-grade squamous abnormality was detected. Low-grade glandular and/or squamous lesions were detected in nine cases and one showed atypical endometrial-type glands. The cervical smears of 64 cases were reviewed in detail to determine the important cytomorphological criteria of in situ and invasive adenocarcinoma in air-dried smears, the technique used for preparing PAP smears in British Columbia. Endocervical cells were absent in four cases. Numerous (>10) groups of glandular cells were present in 51 cases. Important clues to the diagnosis of adenocarcinoma included crowding of nuclei, stratification of nuclei, loss of polarity, syncytial balls and papillary groups of glandular cells, nuclear enlargement, nuclear pleomorphism, and the presence of free-lying atypical glandular cells. Nuclear hyperchromatism, chromatin pattern, nuclear borders, nuclear membranes, and numbers and morphology of nucleoli were not helpful criteria in our material. Criteria enabling reliable distinction between in situ and invasive adenocarcinoma and/or mixed adenocarcinoma-squamous carcinoma could not be established.     

Acquisition of foraging skills by Heron Island Silvereyes Zosterops later alis chlorocephala

Age-related differences in foraging efficiency and behaviour were investigated in a population of colour-ringed Silvereyes Zosterops lateralis . First-year birds were less efficient foragers than older birds with second-year birds being intermediate. First- and second-year birds had lower success rates than older birds overall, and for most capture techniques and substrates. First-year birds never attempted breeding while about half of the second-year birds and all of the older birds did. Both learning and selection effects may have been involved in causing the age-related differences in foraging behaviour. Foraging skills appear to improve during the first 2 years of life and selection could remove the least efficient foragers from the population in winter when food is short. That second-year birds, some of which had already attempted breeding, were not significantly more efficient foragers than first-year birds suggests that reproduction is not delayed until adult levels of foraging efficiency have been attained.     

FLAVOR THRESHOLD AS AFFECTED BY INTERACTION AMONG THREE DAIRY‐RELATED FLAVOR COMPOUNDS*

The hypothesis of the present study was that the presence of one or more flavor compounds in a matrix would alter the perception (either enhance or suppress) of individual compounds as compared to a single flavor compound in a matrix. Thresholds were established for the flavor compounds (diacetyl, hexanal and δ‐decalactone) within each matrix; for each compound in the presence of a second compound; and for each compound in the presence of the remaining two compounds. An ascending order 2‐alternative forced choice test with 12 panelists was used for the evaluations. Results showed that diacetyl in water was suppressed by the presence of hexanal, but the presence of δ‐decalactone with hexanal reversed the trend. In the binary skim milk solutions diacetyl perception was enhanced, while being suppressed in the ternary solution. The perception of hexanal was enhanced in water (binary and ternary solutions). Hexanal and δ‐decalactone were suppressed in skim milk (binary and ternary solutions). δ‐Decalactone showed similar trends as hexanal in water, except that it was suppressed in the presence of diacetyl.