Temporal variation and its drivers in the elemental traits of four boreal plant species

4种北方植物元素性状的时间变化及其驱动因素 植物种内性状的变异对个体适合度和草食动物的觅食有重要影响。对于植物来说,在空间维度上的性状变异已经得到了很好的证明。然而,对性状变异的时间维度仍知之甚少,但其可能受生长度日、温度和降水季节差异的影响。本研究的目的是量化4种常见的北方植物物种性状的种内时间变异及其变异的驱动因素。我们对4种常见树种的叶片进行了为期两年的元素和化学计量性状采样(%C, %N, %P, C:N, C:P, N:P)。本研究分两个步骤进行,首先将广义线性模型(GzLM, n = 24)与我们研究的物种的元素和化学计量性状拟合,以测试它们是否随年份而变化。当我们获得时间变异性的证据时,我们拟合第二组GzLMs (n = 8),将温度、生产力和湿度作为解释变量。研究结果显示,除了两个例外,4种北方植物的大部分元素和化学计量性状都没有时间变异性。年份是所有4种植物的碳百分比(R² = 0.47–0.67)以及香脂冷杉(Abies balsamea)中多种元素和化学计量性状(5/8, R² = 0.29–0.67)的重要预测因子。因此,碳百分比的变化与年际差异有关,而与限制北方森林养分的氮和磷关系更大。这些研究结果还表明,由于生活史的差异,针叶树的化学计量比落叶植物的化学计量的年际差异更大。生长度日是第二轮模型中最频繁出现的变量(8/8 次,R² = 0.21–0.41),表明温度是这些性状时间变异的重要驱动因素。     

Flow regulation affects temporal patterns of riverine plant seed dispersal: potential implications for plant recruitment

1. Changes to the natural flow regime of a river caused by flow regulation may affect waterborne seed dispersal (hydrochory), and this may be an important mechanism by which regulation affects riverine plant communities. We assessed the effect of altered timing of seasonal flow peaks on hydrochory and considered the potential implications for plant recruitment. 2. We sampled hydrochory within five lowland rivers of temperate Australia, three of which are regulated by large dams. These dams are operated to store winter and spring rains and release water in summer and autumn for agriculture. At three sites on each river, hydrochory was sampled monthly for 12 months using passive drift nets. The contents of the drift samples were determined using the seedling‐emergence method. 3. More than 33 000 seedlings from 142 taxa germinated from the samples. In general, more seeds and taxa were observed in the drift at higher flows. By altering the period of peak flows from winter–spring to summer–autumn, flow regulation similarly affected the period of peak seed dispersal. The effect of regulation on seed dispersal varied between taxa depending on their timing of seed release and whether or not they maintain a persistent soil seed bank. 4. Hydrochory in rivers is a product of flow regime and the life history of plants. By altering natural flow regimes and thus hydrochorous dispersal patterns, flow regulation is likely to affect adversely the recruitment of native plant species with dispersal phenologies adapted to natural flow regimes (such as many riparian trees and shrubs) and encourage the spread of non‐native (exotic) species. 5. Changes to hydrochorous dispersal patterns are an important mechanism by which altered flow timing affects riverine plant communities. Natural seasonal flow peaks (in this case spring) are likely to be important for the recruitment of many native riparian woody taxa.     

How seed traits predict floating times: a biophysical process model for hydrochorous seed transport behaviour in fluvial systems

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Midsummer spatial variation in methane efflux from stands of littoral vegetation in a boreal meso-eutrophic lake

1. Spatial variation of methane (CH₄) efflux from the littoral zone of a meso‐eutrophic boreal lake was studied with a closed‐chamber technique for three summer days in 22 vegetation stands, consisting of three emergent and three floating‐leaved species. 2. Between‐species differences in CH₄ emission were significant. The highest emissions were measured from the emergent Phragmites australis stands (0.5–1.7 mmol m^?2 h^?1), followed by Schoenoplectus lacustris > Equisetum fluviatile > Nuphar lutea > Sparganium gramineum > Potamogeton natans. Within‐species differences between stands were not significant. 3. In P. australis stands, the stand‐specific mean CH₄ emission was significantly correlated with solar radiation, probably indicating the role of effective pressurised ventilation on CH₄ fluxes. The proportion of net primary production emitted as CH₄ was significantly higher in P. australis stands (7.4%) than in stands of S. lacustris and E. fluviatile (both 0.5%). 4. In N. lutea stands, CH₄ efflux was negatively correlated with the mean fetch and positively with the percentage cover of leaves on the water surface. There were no differences in CH₄ efflux between intact N. lutea leaves and those grazed by coleopteran Galerucella nymphaeae. In S. graminaeum and P. natans stands, CH₄ effluxes were not related to any of the measured environmental variables. 5. For all vegetation stands, the biomass above water level explained about 60% of the observed spatial variation in CH₄ emission, indicating the important role of plants as gas conduits and producers of substrates for methanogens in the anoxic sediment.     

Distribution and hydraulic significance of large woody debris in a lowland Australian river

The line-intersect technique was used to measure the loading of large woody debris in a 1.8 km reach of the Thomson River, Victoria (catchment area of 3540 km²). A debris census (measuring every item present) was done over 0.775 km of this reach. The transect technique over-estimated the actual loading revealed by the census. The loading of debris 0.01 m in diameter for the total 1.8 km reach was 0.0172 m³ m^–2, which is higher than that measured in many headwater streams in other parts of the world. The volume loading of debris measured from low level aerial photographs was only 4.8% of the value estimated by the line-intersect technique. The line-intersect estimates were biased due to non-random orientation of debris in the stream (causing estimated errors of +8% for volume loading and +16% for surface area loading). It is recommended that to avoid this problem, when using the line-intersect transect technique in lowland rivers, each line should comprise at least two obliquely-angled transects across the channel. The mean item of debris (0.1 m in diameter) had a trunk basal diameter of 0.45 m, a length of 7.4 m, and volume of 0.7 m³. The riparian trees and the in-channel debris were of similar dimensions. The debris tended to be close to the bed and banks and was oriented downstream by the flow at a median angle of 27°. Because of this orientation, most debris had a small projected cross-sectional area, with the median value being only 1 m². Thus, the blockage ratio (proportion of projected area of debris to channel cross-sectional area) was also low, ranging from 0.0002 to 0.1, with a median value of 0.004. The average item of debris, which occupied only 0.4% of the cross-section, would have minimal influence on banktop flow hydraulics, but the largest items, which occupied around 10%, could be significant. Judicious re-introduction of debris into previously cleared rivers is unlikely to result in a large loss of conveyance, or a detectable increase in flooding frequency.     

新疆郁金香一居群个体性别7年的动态变化

在雌雄同株植物中, 花性别被认为是两性资源分配对环境条件的响应, 了解个体性别随时间的变化对探讨植物性系统的变异有重要意义。早春短命植物新疆郁金香(Tulipa sinkiangensis)多为两性花居群, 前期调查显示一些居群由雄花和两性花构成。为了探讨新疆郁金香雄花的发生与变化, 我们连续7年对一个居群的花性别及其变化动态进行了跟踪。结果显示: (1)该居群主要是由一朵花植株和两朵花植株构成, 分别占居群植株总数的74.5%和23.0%。两种性别的花随机分布在不同类型的单株上, 形成了以两性花植株为主, 含有雄株、雄花与两性花同株(andromonoecy)的居群结构。(2)雄花相对较小, 子房退化, 无胚珠发育, 在植株或居群中花期较晚出现。与相同大小的两性花相比, 雄花在单花花粉量、花粉败育率、花粉粒大小及形态、雄性功能等方面没有差异。(3) 7年间, 雄花在居群中的比例经历了2011-2014年间的显著下降(23.4-3.1%)和2015-2017年间相对稳定的零星分布(1.5-1.0%)两个阶段。居群中一朵花植株数量和两朵花植株数量在年份间呈波动性变化。(4)雄花的出现可能是植株受自身资源状况及环境条件等因素的影响在花性别选择上作出的可塑性反应。     

Gene flow and genetic structure of the aquatic macrophyte Sparganium emersum in a linear unidirectional river

1. River systems offer special environments for the dispersal of aquatic plants because of the unidirectional (downstream) flow and linear arrangement of suitable habitats.
2. To examine the effect of this flow on microevolutionary processes in the unbranched bur-reed ( Sparganium emersum ) we studied the genetic variation within and among nine (sub)populations along a 103 km stretch of the Niers River (Germany–The Netherlands), using amplified fragment length polymorphisms.
3. Genetic diversity in S. emersum populations increased significantly downstream, suggesting an effect of flow on the pattern of intrapopulation genetic diversity.
4. Gene flow in the Niers River is asymmetrically bidirectional, with gene flow being approximately 3.5 times higher in a downstream direction. The observed asymmetry is probably caused by frequent hydrochoric dispersal towards downstream locations on the one hand, and sporadic zoochoric dispersal in an upstream direction on the other. The spread of vegetative propagules (leaf and stem fragments) is probably not an important mode of dispersal for S. emersum , suggesting that gene flow is mainly via seed dispersal. Realized dispersal distances exceeded 60 km, revealing a potential for long-distance dispersal in S. emersum .
5. There was no correlation between geographical and genetic distances among the nine S. emersum populations (i.e. no isolation by distance), which may be due to the occurrence of long-distance dispersal and/or colonization and extinction dynamics in the Niers River.
6. Overall, the genetic population structure and regional dispersal patterns of S. emersum in the Niers River are best explained by a linear metapopulation model. Our study shows that flow can exert a strong influence on population genetic processes of plants inhabiting stream systems.     

四川间作地区作物高度、覆盖度和叶面积指数的动态变化

为研究间作系统的作物参数,于2005年在四川间作地区进行了作物高度、覆盖度和叶面积指数的时间变化研究.结果表明:作物的高度、覆盖度和叶面积指数随时间变化很大;玉米的最大高度是177 cm,最大覆盖度(86%)出现在花期,最大叶面积指数是1.96;红苕的最大和最小株高分别为22和12 cm,最大覆盖度(73%)出现在薯块膨大期,最大叶面积指数为1.79.与玉米间作时,红苕所有作物参数均受玉米影响.在玉米-红苕间作系统中,最危险的侵蚀期是玉米收获后至红苕覆盖度最大期.     

The influence of leaf litter on zooplankton in floodplain wetlands: changes resulting from river regulation

1. The loss of input of leaf litter through clearing of riparian vegetation may result in significant changes to aquatic ecosystems. River red gums (Eucalyptus camaldulensis) surrounding floodplain wetlands in the Murray–Darling Basin, Australia, contribute large quantities of leaf litter, but the quality of this resource may change depending on the timing of inundation. 2. We used experimental mesocosms to test the hypotheses that zooplankton would have a greater abundance with an input of leaf litter and that fewer zooplankton would emerge from egg banks in cleared than forested wetlands. The experiment was carried out in summer/autumn and in spring to test a third hypothesis that zooplankton would respond to changes in the timing of wetland inundation as a result of river regulation. 3. In summer/autumn, leaf litter reduced zooplankton abundance by 89% at the beginning of the experiment through its influence on water quality. Only a few taxa (Polyarthra spp., Colurella spp. and the cladoceran Family Moinidae) responded positively to leaf litter when water quality improved later in the experiment, indicating a switch in the role of leaf litter from a non‐trophic to a trophic pathway. 4. In spring, microcrustaceans emerged in smaller numbers from sediment sourced from cleared compared to forested wetlands, reflecting different communities in these two wetland types and/or disturbances to the sediment that interfere with emergence. 5. Although leaf litter appears not to be an important resource for zooplankton in floodplain wetlands, riparian clearing may have lasting effects on future emerging zooplankton communities. Additionally, river regulation may have considerable impacts on the influence of leaf litter on zooplankton, which has implications for the management of floodplain river systems.     

Genetic diversity and dispersal of Phragmites australis in a small river system

Even though the reed, Phragmites australis, is an extensively studied wetland species, little is known about reproduction and dispersal modes within and among reed populations at the scale of small river systems. Using microsatellite analysis of 189 individuals from three adjacent river catchments in the Czech Republic, we elucidated the role of the river corridors in the dispersal of P. australis. Using Bayesian clustering of individuals, we found that 19% of clusters were distributed only along one river, which implied dispersal by water (or by wind) along river corridors, whereas 38% of clusters were widely distributed and were likely the product of wind long-distance dispersal among rivers. Intensive exchange of propagules among river systems is further demonstrated by only 6% of total variance being attributed to the variance among rivers in the AMOVA-analysis. Spatial autocorrelation analysis revealed a decreasing pattern up to 5–10 km and no clear pattern over longer distances. This gives an evidence for pollen and seed dispersal at short distances (up to 1 km), whereas most likely only seed dispersal at longer distances up to 10 km. We found five multilocus genotypes distributed in two different populations. The distances between populations with the same genotype ranged from 0.5 to 10.8 km. This can be interpreted as long-distance vegetative dispersal.     

Small scale application and assessment of a Index of Biotic Integrity for a large boreal river

Modifications and use of Karr’s Index of Biotic Integrity (IBI) for assessing the effects of anthropogenic impacts to aquatic ecosystems have typically occurred using data collected at the macro scale. However, some non-point sources of habitat degradation occur at small scales. One possible source of perturbation to fish habitat in boreal rivers is the application of rip rap shoreline armouring in human use areas. In this study we assess the use of IBI in a small scale setting and discuss the potential impact of rip rap shoreline armouring. We captured small and juvenile fishes weekly during 2002–2003 from 12 sample sites within the littoral zone of a human use area using a modified beach seine. Principal component analysis (PCA) was performed on the data to examine the relationship between species composition and IBI scores. We also performed PCA on the IBI metrics to assess our modifications. The IBI method produced higher scores for armoured sites than for unarmoured sites. We found a strong rank order correlation (Spearman’s ρ > 0.93; p < 0.001) between the modified IBI scores and the first principal component, suggesting that Karr’s original empirically-based IBI is strongly linked to species composition. We found a high degree of redundancy between the metrics of the IBI that validate our modifications. These results suggest that IBI can be a suitable method for assessing non-point impacts from within a small study area. Our results also indicate that fish habitat from rip rap armoured sites within the test area had consistently higher IBI scores that unarmoured sites.     

Temporal variation in the genetic structure of host-associated populations of the small ermine moth Yponomeuta padellus (Lepidoptera, Yponomeutidae)

Temporal changes in allele frequencies were studied in host-associated populations of the small ermine moth Yponomeuta padellus. At one site, populations from three host plants (Sorbus aucuparia, Amelanchier larnarckii , and Crataegus spp.) were sampled annually during a four-year-period and analysed with 20 polymorphic allozyme markers. At two other sites, allele frequencies at 5- 6 enzyme loci of Y. padellus populations from two different host plants were also tested for consistency over a 13-year-pcriod. Significant allele frequency changes occurred in the short-term analysis, whereas allele frequencies remained relatively stable through time in the long-term analyses. Furthermore, allele frequencies of Y. padellus populations from Crataegus spp. were relatively stable compared to the other host populations. The role of the agents responsible for the observed patterns is discussed.     

Greater variation in boreal plant community composition and community-level traits at local- than regional-scale

Questions

Rapid climate change in northern latitudes is expected to influence plant functional traits of the whole community (community-level traits) through species compositional changes and/or trait plasticity, limiting our ability to anticipate climate warming impacts on northern plant communities. We explored differences in plant community composition and community-level traits within and among four boreal peatland sites and determined whether intra- or interspecific variation drives community-level traits.

Location

Boreal biome of western North America.

Methods

We collected plant community composition and functional trait data along dominant topoedaphic and/or hydrologic gradients at four peatland sites spanning the latitudinal extent of the boreal biome of western North America. We characterized variability in community composition and community-level traits of understorey vascular and moss species both within (local-scale) and among sites (regional-scale).

Results

Against expectations, community-level traits of vascular plant and moss species were generally consistent among sites. Furthermore, interspecific variation was more important in explaining community-level trait variation than intraspecific variation. Within-site variation in both community-level traits and community composition was greater than among-site variation, suggesting that local environmental gradients (canopy density, organic layer thickness, etc.) may be more influential in determining plant community processes than regional-scale gradients.

Conclusions

Given the importance of interspecific variation to within-site shifts in community-level traits and greater variation of community composition within than among sites, we conclude that climate-induced shifts in understorey community composition may not have a strong influence on community-level traits in boreal peatlands unless local-scale environmental gradients are substantially altered.     

泉州湾蟳埔潮间带大型底栖动物群落的时空分布

为了比较泉州湾蟳埔潮间带沙滩、互花米草滩和牡蛎石泥滩3种生境(3个潮层)的大型底栖动物群落,2011年4月至2012年1月对3种生境的大型底栖动物进行了季度定量取样。在3种生境共获得85种大型底栖动物,其中环节动物39种,软体动物20种,节肢动物21种,刺胞动物、扁形动物、纽虫动物、星虫动物和脊索动物各1种。多维标度排序(MDS)分析表明,春季和冬季泉州湾蟳埔潮间带3种生境的大型底栖动物群落相似性较低;夏季和秋季互花米草滩与牡蛎石泥滩的大型底栖动物群落相似性较高,而与沙滩的大型底栖动物群落相似性较低。沙滩大型底栖动物群落的季节变化较明显,其次是牡蛎石泥滩,而互花米草滩大型底栖动物群落的季节变化较不明显。大型底栖动物栖息密度和生物量随着潮层降低而增加。单变量双因素方差分析(Two-way ANOVA)表明,不同生境之间的大型底栖动物物种数、栖息密度、多样性指数、均匀度指数和丰度指数有显著差异,但生物量无显著差异,这是因为沙滩的物种数较少,栖息密度较低,但优势种弧边招潮蟹(Uca arcuata)个体较大,互花米草滩和牡蛎石泥滩的优势种为加州中蚓虫(Mediomastus californiensis),个体相对弧边招潮蟹小。不同季节之间大型底栖动物物种数、栖息密度、生物量和丰度指数有显著差异,但多样性指数和均匀度指数元显著差异,这是因为沙滩物种数少,但个体分布比较均匀,而互花米草滩和牡蛎石泥滩物种数较多,个体分布较不均匀。以上结果表明,潮汐、沉积物粒径和生境是影响潮间带大型底栖动物群落的主要因素。潮汐导致潮间带的空间异质性,空间异质性导致大型底栖动物群落的差异。