Planted saltbush (Atriplex nummularia) and its value for birds in farming landscapes of the South Australian Murray Mallee

Summary In the fragmented agricultural landscapes of temperate southern Australia, broad‐scale revegetation is underway to address multiple natural resource management issues. In particular, commercially‐driven fodder shrub plantings are increasingly being established on non‐saline land to fill the summer‐autumn feed gap in grazing systems. Little is known of the contribution that these and other planted woody perennial systems make to biodiversity conservation in multifunctional landscapes. In order to address this knowledge gap, a study was conducted in the southern Murray Mallee region of South Australia. Selected ecological indicators, including plant and bird communities, were sampled in spring 2008 and autumn 2009 in five planted saltbush sites and nearby areas of remnant vegetation and improved pasture. In general, remnant vegetation sites had higher biodiversity values than saltbush and pasture sites. Saltbush sites contained a diverse range of plants and birds, including a number of threatened bird species not found in adjacent pasture sites. Plant and bird communities showed significant variation across saltbush, pasture and remnant treatments and significant differences between seasons. This study demonstrates that saltbush plantings can provide at least partial habitat for some native biota within a highly modified agricultural landscape. Further research is being conducted on the way in which biota, such as birds, use available resources in these dynamic ecosystems. An examination of the effects of grazing on biodiversity in saltbush would improve the ability of landholders and regional natural resource management agencies in making informed land management decisions.     

铬对中国林蛙蝌蚪生长发育的毒性效应

为评价水域环境中铬元素对两栖动物幼体的急性毒性,将中国林蛙(Rana chensinensis)28～29期蝌蚪分别暴露于30～35 mg·L-1Cr(Ⅲ)6个不同浓度和10 ～ 45mg·L-1Cr(Ⅵ)6个不同浓度的水体中,分别在24、48、72和96 h统计蝌蚪的死亡率及半致死浓度(LC50).结果表明:暴露24、48、72和96 h,Cr(Ⅲ)对蝌蚪的LC50分别为34.09±1.06、33.47±0.65、32.58±0.11和(32.05±0.20) mg·L-1,安全浓度(SC)为(3.21±0.02)mg·L-1;Cr(Ⅵ)对蝌蚪的LC50分别为91.97±5.32、51.19±4.62、35.79±1.40和(28.81±1.87) mg·L-1,安全浓度(SC)为(2.88±0.19) rng·L-1.观察表明:Cr(Ⅲ)的急性毒性是通过与蝌蚪皮肤表面的分泌物结合后粘附在鳃部,导致呼吸障碍致死;而Cr(Ⅵ)的强氧化性可导致蝌蚪的表皮溃变,鳃部萎缩致死;另外,将28～29期蝌蚪暴露于安全浓度(SC)以下的含铬水体进行慢性实验,通过检测蝌蚪的体长、体重和完全变态时间显示,低浓度的Cr(Ⅲ)和Cr(Ⅵ)对蝌蚪的生长发育仍具有一定的抑制作用,并可导致畸型发生,其作用强度呈现剂量效应,但时间累积效应不规律.     

Phylogeny and the patterns of leaf phenolics in gap-and forest-adapted Piper and Miconia understory shrubs

Summary The types and quantities of defense compounds found in plants occupying ecologically distinct habitats have received much theoretical and little empirical attention. Here we characterize the leaf phenolic chemistry of eight species in two genera of tropical rainforest shrubs; four species in each genus are typical of disturbed sites, and four are typical of mature forest understory. Two Miconia species growing in light gaps had significantly higher leaf tannin and total phenolic contents than congenors growing in the primary forest; this pattern was not found among the gap- and forest-adapted Piper species. Tannin patterns were not mirrored by leaf cinnamic acids. These results indicate that plant phylogeny must be considered when predicting plant defense investment.     

Latitudinal patterns of range size and species richness of New World woody plants

Aim  Relationships between range size and species richness are contentious, yet they are key to testing the various hypotheses that attempt to explain latitudinal diversity gradients. Our goal is to utilize the largest data set yet compiled for New World woody plant biogeography to describe and assess these relationships between species richness and range size.
Location  North and South America.
Methods  We estimated the latitudinal extent of 12,980 species of woody plants (trees, shrubs, lianas). From these estimates we quantified latitudinal patterns of species richness and range size. We compared our observations with expectations derived from two null models.
Results   Peak richness and the smallest- and largest-ranged species are generally found close to the equator. In contrast to prominent diversity hypotheses: (1) mean latitudinal extent of tropical species is greater than expected; (2) latitudinal extent appears to be decoupled from species richness across New World latitudes, with abrupt transitions across subtropical latitudes; and (3) mean latitudinal extents show equatorial and north temperate peaks and subtropical minima. Our results suggest that patterns of range size and richness appear to be influenced by three broadly overlapping biotic domains (biotic provinces) for New World woody plants.
Main conclusions  Hypotheses that assume a direct relationship between range size and species richness may explain richness patterns within these domains, but cannot explain gradients in richness across the New World.     

Vascular plants promote ancient peatland carbon loss with climate warming

Northern peatlands have accumulated one third of the Earth's soil carbon stock since the last Ice Age. Rapid warming across northern biomes threatens to accelerate rates of peatland ecosystem respiration. Despite compensatory increases in net primary production, greater ecosystem respiration could signal the release of ancient, century‐ to millennia‐old carbon from the peatland organic matter stock. Warming has already been shown to promote ancient peatland carbon release, but, despite the key role of vegetation in carbon dynamics, little is known about how plants influence the source of peatland ecosystem respiration. Here, we address this issue using in situ ¹⁴C measurements of ecosystem respiration on an established peatland warming and vegetation manipulation experiment. Results show that warming of approximately 1 °C promotes respiration of ancient peatland carbon (up to 2100 years old) when dwarf‐shrubs or graminoids are present, an effect not observed when only bryophytes are present. We demonstrate that warming likely promotes ancient peatland carbon release via its control over organic inputs from vascular plants. Our findings suggest that dwarf‐shrubs and graminoids prime microbial decomposition of previously ‘locked‐up’ organic matter from potentially deep in the peat profile, facilitating liberation of ancient carbon as CO₂. Furthermore, such plant‐induced peat respiration could contribute up to 40% of ecosystem CO₂ emissions. If consistent across other subarctic and arctic ecosystems, this represents a considerable fraction of ecosystem respiration that is currently not acknowledged by global carbon cycle models. Ultimately, greater contribution of ancient carbon to ecosystem respiration may signal the loss of a previously stable peatland carbon pool, creating potential feedbacks to future climate change.     

Seedling growth response to added nutrients depends on seed size in three woody genera

1 We tested whether seedlings of small‐seeded species were more reliant on soil nutrients than large‐seeded ones by growing 21 species from three woody genera ( Eucalyptus, Hakea and Banksia ) along a gradient of nutrient availability.
2 At very low nutrient availability, larger seeds produced larger seedlings. This was seen especially among the eucalypts, but the difference was eliminated at optimal soil nutrient levels. Hakea species with large seed mass, and all Banksia species, appeared unable to exploit additional soil nutrients for growth, whatever the level supplied.
3 Larger seeds tended to have proportionately higher contents of N, P and K and, under nutrient‐poor conditions, supplied more of these to their seedlings, although at a diminishing rate.
4 We suggest that large‐seededness could be an adaptation to the high‐light, nutrient‐impoverished habitats in which these species occur by providing the seedling with the mineral nutrients, rather than carbon‐based metabolites, needed for maximizing initial root growth. Reaching reliable moisture before summer (drought avoidance) is an alternative strategy to physiological tolerance of drought.     

Genomics in a changing arctic: critical questions await the molecular ecologist

Molecular ecology is poised to tackle a host of interesting questions in the coming years. The Arctic provides a unique and rapidly changing environment with a suite of emerging research needs that can be addressed through genetics and genomics. Here we highlight recent research on boreal and tundra ecosystems and put forth a series of questions related to plant and microbial responses to climate change that can benefit from technologies and analytical approaches contained within the molecular ecologist's toolbox. These questions include understanding (i) the mechanisms of plant acquisition and uptake of N in cold soils, (ii) how these processes are mediated by root traits, (iii) the role played by the plant microbiome in cycling C and nutrients within high‐latitude ecosystems and (iv) plant adaptation to extreme Arctic climates. We highlight how contributions can be made in these areas through studies that target model and nonmodel organisms and emphasize that the sequencing of the Populus and Salix genomes provides a valuable resource for scientific discoveries related to the plant microbiome and plant adaptation in the Arctic. Moreover, there exists an exciting role to play in model development, including incorporating genetic and evolutionary knowledge into ecosystem and Earth System Models. In this regard, the molecular ecologist provides a valuable perspective on plant genetics as a driver for community biodiversity, and how ecological and evolutionary forces govern community dynamics in a rapidly changing climate.     

鄂尔多斯高原西部几种荒漠灌丛群落种间联结关系的研究

采用ＰＣ、ＰＣＣ、ＡＣ、Ｘ２和ｒ等公式对鄂尔多斯高原西部５种典型荒漠灌丛群落种间联结系数的求算,通过这些种间的相互关系,阐述了这些物种对生境要求的差异和分布特点,本文的研究结果对与建立在种群关系基础上的荒漠植被的研究具有重要的意义。     

Responses of riparian trees and shrubs to flow regulation along a boreal stream in northern Sweden

1. Flow dynamics is a major determinant of riparian plant communities. Therefore, flow regulation may heavily affect riparian ecosystems. Despite the large number of dams worldwide, little specific information is available on the longitudinal impacts of dams on vegetation, for example how far downstream and at what degree of regulation a dam on a river can influence riparian woodlands. 2. We quantified the long‐term responses of riparian trees and shrubs to flow regulation by identifying their lateral distribution and habitat conditions along a boreal river in northern Sweden that has been regulated by a single dam since 1948. The regulation has reduced annual flow fluctuations, this effect being largest at the dam, downstream from which it progressively decreases following the entrance of free‐flowing tributaries. 3. We related changes in the distribution patterns, composition, abundance and richness of tree and shrub species to the degree of regulation along the river downstream from the dam. Regulation has triggered establishment of trees and shrubs closer to the channel, making it possible to measure ecological impacts of flow regulation as differences in vegetation attributes relative to the positions of tree and shrub communities established before and after regulation. 4. Trees and shrubs had migrated towards the mid‐channel along the entire study reach, but the changes were largest immediately downstream of the dam. Shrubs were most impacted by flow regulation in terms of lateral movement, but the effect on trees extended furthest downstream. 5. The species composition of trees progressively returned to its pre‐regulation state with distance downstream, but entrance of free‐flowing tributaries and variation in channel morphology and substratum caused local deviations. Species richness after regulation increased for trees but decreased for shrubs. The changes in species composition and richness of trees and shrubs showed no clear downstream patterns, suggesting that other factors than the degree of regulation were more important in governing life form.     

Shrubline but not treeline advance matches climate velocity in montane ecosystems of south‐central Alaska

Tall shrubs and trees are advancing into many tundra and wetland ecosystems but at a rate that often falls short of that predicted due to climate change. For forest, tall shrub, and tundra ecosystems in two pristine mountain ranges of Alaska, we apply a Bayesian, error‐propagated calculation of expected elevational rise (climate velocity), observed rise (biotic velocity), and their difference (biotic inertia). We show a sensitive dependence of climate velocity on lapse rate and derive biotic velocity as a rigid elevational shift. Ecosystem presence identified from recent and historic orthophotos ~50 years apart was regressed on elevation. Biotic velocity was estimated as the difference between critical point elevations of recent and historic logistic fits divided by time between imagery. For both mountain ranges, the 95% highest posterior density of climate velocity enclosed the posterior distributions of all biotic velocities. In the Kenai Mountains, mean tall shrub and climate velocities were both 2.8 m y^?1. In the better sampled Chugach Mountains, mean tundra retreat was 1.2 m y^?1 and climate velocity 1.3 m y^?1. In each mountain range, the posterior mode of tall woody vegetation velocity (the complement of tundra) matched climate velocity better than either forest or tall shrub alone, suggesting competitive compensation can be important. Forest velocity was consistently low at 0.1–1.1 m y^?1, indicating treeline is advancing slowly. We hypothesize that the high biotic inertia of forest ecosystems in south‐central Alaska may be due to competition with tall shrubs and/or more complex climate controls on the elevational limits of trees than tall shrubs. Among tall shrubs, those that disperse farthest had lowest inertia. Finally, the rapid upward advance of woody vegetation may be contributing to regional declines in Dall's sheep (Ovis dalli), a poorly dispersing alpine specialist herbivore with substantial biotic inertia due to dispersal reluctance.