黄土丘陵区小流域次生灌丛群落生物量研究

生物量是整个生态系统运行的能量基础和营养物质来源。用直接收获法,对延安康家屹崂沟小流域5个次生灌丛群落类型和2个人工灌丛样地地上部生物量的研究结果表明:地上部生物量黄刺玫>杂灌>虎榛子>柠条(阴坡)>沙棘>狼牙刺>柠条(阳坡);灌木树种组成复杂的、群落盖度较大的类型生物量较大;各类型灌丛生物量在小流域空间分布上阴坡>阳坡,阴坡坡下>坡中>坡上;阳坡灌丛中的草本植物生物量比阴坡高,而灌木生物量较低。所调查的5个次生灌丛群落类型地上部生物量和生产力呈线性相关关系,回归方程Y=3.1995+0.1939X,净生产力随生物量的增加而提高。     

Interval estimation of the kappa coefficient with binary classification and an equal marginal probability model

We derive a likelihood score method for interval estimation of the intraclass version of the kappa coefficient of agreement with binary classification using a general theory of Bartlett (1953, Biometrika 40, 306-317). By exact evaluation, we investigate statistical properties of the score method, the chi-square goodness-of-fit procedure (Donner and Eliasziw, 1992, Statistics in Medicine 11, 1511-1519; Hale and Fleiss, 1993, Biometrics 49, 523-534), and a crude confidence interval for small and medium sample sizes. Actual coverage percentages of the score and chi-square methods are satisfactorily close to the nominal confidence coefficient, while that of the crude method is quite unsatisfactory. The expected length of the score method is shorter than that of the chi-square procedure when the response rate is very small or very large.     

Shrub range expansion alters diversity and distribution of soil fungal communities across an alpine elevation gradient

Global climate and land use change are altering plant and soil microbial communities worldwide, particularly in arctic and alpine biomes where warming is accelerated. The widespread expansion of woody shrubs into historically herbaceous alpine plant zones is likely to interact with climate to affect soil microbial community structure and function; however, our understanding of alpine soil ecology remains limited. This study aimed to (i) determine whether the diversity and community composition of soil fungi vary across elevation gradients and to (ii) assess the impact of woody shrub expansion on these patterns. In the White Mountains of California, sagebrush (Artemisia rothrockii) shrubs have been expanding upwards into alpine areas since 1960. In this study, we combined observational field data with a manipulative shrub removal experiment along an elevation transect of alpine shrub expansion. We utilized next‐generation sequencing of the ITS1 region for fungi and joint distribution modelling to tease apart effects of the environment and intracommunity interactions on soil fungi. We found that soil fungal diversity declines and community composition changes with increasing elevation. Both abiotic factors (primarily soil moisture and soil organic C) and woody sagebrush range expansion had significant effects on these patterns. However, fungal diversity and relative abundance had high spatial variation, overwhelming the predictive power of vegetation type, elevation and abiotic soil conditions at the landscape scale. Finally, we observed positive and negative associations among fungal taxa which may be important in structuring community responses to global change.     

Short‐term efficacy and nontarget effects of aerial glyphosate applications for controlling Lonicera maackii (Amur honeysuckle) in oak‐hickory forests of Eastern Missouri,U.S.A.

Lonicera maackii (Amur honeysuckle) is a non‐native species that has invaded forest stands throughout the eastern United States. This research examined using aerially applied glyphosate in autumn 2013 to control L. maackii in oak‐hickory forest stands in Missouri, U.S.A. We targeted the spraying time period when L. maackii was still green and most native plants were dormant. Across treatment units, the mean difference in L. maackii stem density significantly declined (p = 0.004) by 5.4 stems per plot from spring 2013 to summer 2014 when compared to control units which increased by 1.8 stems per plot. Treated units with a high initial infestation level of L. maackii (>50% cover) had a significant (p = 0.004) decline in the mean difference in L. maackii cover of ?50.0% per plot between spring 2013 and summer 2014 compared to an average increase of 9.2% in the controls. Similar results were found for treated units with a low initial infestation level of L. maackii (10–50% cover). Mortality of native overstory and understory trees post‐treatment was negligible. In the ground layer of forest stands with a low initial L. maackii infestation level, native non‐spray‐sensitive forb cover per plot significantly increased (p = 0.023) relative to controls between summer 2013 and summer 2014 while native spray‐sensitive species cover significantly decreased (p = 0.021) during the same period. These results suggest that an aerial application of glyphosate can provide an L. maackii control option, but with trade‐offs in compositional shifts in the native ground‐layer vegetation.     

Sexual and temporal variations in floral scent in the subdioecious shrub Eurya japonica Thunb

In many flowering plants, floral scents are a significant trait for visitors, playing an important role in attracting pollinators and/or detracting herbivores. The evolution of flowering plants from hermaphroditism to dioecy is often accompanied by sexual dimorphism in floral scent. In this study, floral scents emitted by different sexual morphs of the subdioecious shrub Eurya japonica Thunb. were collected using a dynamic headspace method, and sexual and temporal variations were evaluated by gas chromatography–mass spectrometry (GC–MS). Two volatiles, α‐pinene and linalool, were identified as the major components of floral scents in females, hermaphrodites, and males. The males emit higher amounts of floral scents, particularly α‐pinene, compared to females or hermaphrodites. Floral scents emitted by males generally decrease as flowers enter senescence, whereas those from females or hermaphrodites do not significantly differ. Intraspecific variations in floral scents of subdioecious species provided by this study would contribute to better understanding of sexual dimorphism in floral scent.     

Direct effects of warming increase woody plant abundance in a subarctic wetland

Both the direct effects of warming on a species’ vital rates and indirect effects of warming caused by interactions with neighboring species can influence plant populations. Furthermore, herbivory mediates the effects of warming on plant community composition in many systems. Thus, determining the importance of direct and indirect effects of warming, while considering the role of herbivory, can help predict long‐term plant community dynamics. We conducted a field experiment in the coastal wetlands of western Alaska to investigate how warming and herbivory influence the interactions and abundances of two common plant species, a sedge, Carex ramenskii, and a dwarf shrub, Salix ovalifolia. We used results from the experiment to model the equilibrium abundances of the species under different warming and grazing scenarios and to determine the contribution of direct and indirect effects to predict population changes. Consistent with the current composition of the landscape, model predictions suggest that Carex is more abundant than Salix under ambient temperatures with grazing (53% and 27% cover, respectively). However, with warming and grazing, Salix becomes more abundant than Carex (57% and 41% cover, respectively), reflecting both a negative response of Carex and a positive response of Salix to warming. While grazing reduced the cover of both species, herbivory did not prevent a shift in dominance from sedges to the dwarf shrub. Direct effects of climate change explained about 97% of the total predicted change in species cover, whereas indirect effects explained only 3% of the predicted change. Thus, indirect effects, mediated by interactions between Carex and Salix, were negligible, likely due to use of different niches and weak interspecific interactions. Results suggest that a 2°C increase could cause a shift in dominance from sedges to woody plants on the coast of western Alaska over decadal timescales, and this shift was largely a result of the direct effects of warming. Models predict this shift with or without goose herbivory. Our results are consistent with other studies showing an increase in woody plant abundance in the Arctic and suggest that shifts in plant–plant interactions are not driving this change.     

Complex effects of mammalian grazing on extramatrical mycelial biomass in the Scandes forest‐tundra ecotone

Mycorrhizal associations are widespread in high‐latitude ecosystems and are potentially of great importance for global carbon dynamics. Although large herbivores play a key part in shaping subarctic plant communities, their impact on mycorrhizal dynamics is largely unknown. We measured extramatrical mycelial (EMM) biomass during one growing season in 16‐year‐old herbivore exclosures and unenclosed control plots (ambient), at three mountain birch forests and two shrub heath sites, in the Scandes forest‐tundra ecotone. We also used high‐throughput amplicon sequencing for taxonomic identification to investigate differences in fungal species composition. At the birch forest sites, EMM biomass was significantly higher in exclosures (1.36 ± 0.43 g C/m²) than in ambient conditions (0.66 ± 0.17 g C/m²) and was positively influenced by soil thawing degree‐days. At the shrub heath sites, there was no significant effect on EMM biomass (exclosures: 0.72 ± 0.09 g C/m²; ambient plots: 1.43 ± 0.94). However, EMM biomass was negatively related to Betula nana abundance, which was greater in exclosures, suggesting that grazing affected EMM biomass positively. We found no significant treatment effects on fungal diversity but the most abundant ectomycorrhizal lineage/cortinarius, showed a near‐significant positive effect of herbivore exclusion (p = .08), indicating that herbivory also affects fungal community composition. These results suggest that herbivory can influence fungal biomass in highly context‐dependent ways in subarctic ecosystems. Considering the importance of root‐associated fungi for ecosystem carbon balance, these findings could have far‐reaching implications.     

Long‐term deepened snow promotes tundra evergreen shrub growth and summertime ecosystem net CO2 gain but reduces soil carbon and nutrient pools

Arctic climate warming will be primarily during winter, resulting in increased snowfall in many regions. Previous tundra research on the impacts of deepened snow has generally been of short duration. Here, we report relatively long‐term (7–9 years) effects of experimentally deepened snow on plant community structure, net ecosystem CO₂ exchange (NEE), and soil biogeochemistry in Canadian Low Arctic mesic shrub tundra. The snowfence treatment enhanced snow depth from 0.3 to ~1 m, increasing winter soil temperatures by ~3°C, but with no effect on summer soil temperature, moisture, or thaw depth. Nevertheless, shoot biomass of the evergreen shrub Rhododendron subarcticum was near‐doubled by the snowfences, leading to a 52% increase in aboveground vascular plant biomass. Additionally, summertime NEE rates, measured in collars containing similar plant biomass across treatments, were consistently reduced ~30% in the snowfenced plots due to decreased ecosystem respiration rather than increased gross photosynthesis. Phosphate in the organic soil layer (0–10 cm depth) and nitrate in the mineral soil layer (15–25 cm depth) were substantially reduced within the snowfences (47–70 and 43%–73% reductions, respectively, across sampling times). Finally, the snowfences tended (p = .08) to reduce mineral soil layer C% by 40%, but with considerable within‐ and among plot variation due to cryoturbation across the landscape. These results indicate that enhanced snow accumulation is likely to further increase dominance of R. subarcticum in its favored locations, and reduce summertime respiration and soil biogeochemical pools. Since evergreens are relatively slow growing and of low stature, their increased dominance may constrain vegetation‐related feedbacks to climate change. We found no evidence that deepened snow promoted deciduous shrub growth in mesic tundra, and conclude that the relatively strong R. subarcticum response to snow accumulation may explain the extensive spatial variability in observed circumpolar patterns of evergreen and deciduous shrub growth over the past 30 years.     

Species composition and structure characteristics of the major montane shrub communities in the west slope of Helan Mountains,Nei Mongol,China

灌丛是贺兰山最主要的植被组分, 但关于该地区灌丛群落的专门研究并不多见。为了解该地区灌丛资源的分布及生长状况, 该研究对内蒙古贺兰山国家级自然保护区内主要的山地灌丛群落进行样方调查, 通过分析样方数据, 量化描述了各群落的基本特征。结果表明: 贺兰山自然保护区沿海拔梯度主要有准噶尔栒子群系(Form. Cotoneaster soongoricus)、紫丁香群系(Form. Syringa oblata)、小叶金露梅群系(Form. Potentilla parvifolia)、虎榛子群系(Form. Ostryopsis davidiana)、小叶忍冬群系(Form. Lonicera microphylla)、银露梅群系(Form. Potentilla glabra)、山生柳群系(Form. Salix oritrepha)和鬼箭锦鸡儿群系(Form. Caragana jubata) 8种主要的山地灌丛群系。