Fourteen months of seed rain in three Australian semi‐arid communities

The abundance and composition of seed rain was measured over 14 months (February 2004 to March 2005) in Currawinya National Park, western Queensland. The experimental design included four measurement periods, three vegetation communities and two grazing regimes. A total of 12 586 seeds from 104 species were captured. There were significantly more seeds and species captured during the measurement period with the least rainfall, although no significant correlation was found between the amount of rainfall and the number of seeds or species captured. More seeds and species were captured where native and feral grazing pressure was removed, but this was only significant for the number of species. The above‐ground vegetation showed no significant difference between grazing treatments over the study period and exhibited far fewer species than the seed rain. However, the majority of species found in the above‐ground vegetation were represented in the seed rain. Hypotheses are explored as an attempt to understand the apparent lack of a relationship between seed rain and rainfall. The effects of grazing and seed movement and storage are also discussed.     

Similarities in the impact of three large invasive plant species on soil seed bank communities

Invasions by alien plant species may substantially alter soil seed bank communities. While decreases in seed bank species richness, diversity, and composition as a consequence of plant invasions have been reported, the characteristics of seed banks associated with different invasive species have not been compared in any detail. Here, we describe changes in the characteristics of soil seed banks invaded by three large herbaceous invasive plants, Fallopia japonica, Gunnera tinctoria, and Heracleum mantegazzianum. The study was carried out at the spatial scales of site and plot, to reduce variability in seed bank data. Information on seed bank persistence was inferred from seed depth (0–5, 5–10, and 10–15 cm) and from time of sampling (May and October). Despite differences in the reproductive strategy and geographic distribution of these invaders, as well as in the standing vegetation and habitat types examined, the seed banks of invaded areas were similar in composition and in the relative abundance of different species. Invaded seed banks were dominated by seeds of a few agricultural weed species and/or rushes, suggesting that common features of the invaders, including a large standing biomass, extensive litter production, and the formation of mono-species stands may result in comparable selection pressures that favors traits that are largely genera or species-specific. These findings have a direct relevance for the development of strategies aimed at restoring previously-invaded sites while also improving our understanding of the long-term implications of plant invasions.     

Aggregated seed arrival alters plant diversity in grassland communities

Aims Species aggregation is commonly seen in plant communities and may increase diversity by causing intraspecific competition to exceed interspecific competition. One potential source of this spatial aggregation is seed dispersal but it is unclear to what extent aggregated seed distributions affect plant diversity in real communities. Using a field experiment, I tested whether uniform or aggregated seed arrival alters community structure and whether these effects vary with sowing density.Methods The experiment consisted of two spatial seeding treatments (uniform and aggregated) that were fully crossed with three seed density treatments. Sixty, 3 × 4-m plots were arrayed in a low-diversity grassland located in Kansas, USA. Each plot was divided into forty-eight, 0.5 × 0.5-m patches. For aggregated seeding treatments, each of the 15 species was sown into three randomly selected patches within the plot (3×15 = 45). To create a uniform species arrival but control for the seed addition method, all 15 species were sown into 45 individual patches (with three patches remaining unsown) within each plot. Seed mass for each species was held constant at the plot scale between uniform or aggregated treatments within a given level of the sowing density treatment. After two growing seasons, plant density was quantified for all sown species in 15 randomly selected patches from each plot.Important findings I found evidence for shifts in community structure in response to the different spatial seeding patterns. The evenness of added species was higher under aggregated than uniform sowing patterns. There was no detectable effect of aggregated seed sowing on species richness at 3.75 m 2 scale. However, when species richness was extrapolated to larger scales (11.25 m 2), aggregated sowing was predicted to have greater richness than uniform sowing. Effects of seed aggregation on community structure were apparent only at moderate to high sowing rates, yet the latter are within the range of measured seed dispersal in similar grasslands. Additionally, as sowing density increased, seed mass became an increasingly effective predictor of relative abundances for added species, but only under uniform sowing patterns supporting the idea that aggregated dispersal may buffer weaker (smaller seeded) species from competition during colonization. This is the first experiment to show that aggregated seed dispersal patterns can increase at least some components of plant diversity in undisturbed grasslands and suggests that previous seed dispersal experiments, which utilize uniform seed sowing, may underestimate the potential effect of dispersal on plant community structure.     

Cryopreservation of seed of Western Australian native species

The ability of seed of native Western Australian species to be stored using cryopreservation methods was investigated by subjecting seed of 90 native species representing 84 genera and 33 families to storage in liquid nitrogen. Seed of 68 native Western Australian species were germinated after storage in liquid nitrogen for two weeks following treatments which involved direct plunging into liquid nitrogen or slow cooling at 0.4°C min^–1 in 15% dimethyl sulphoxide (DMSO) or slow cooling at 0.4°C min^–1 in 35% DMSO. The largest number of species (37) responded positively to direct plunging without pretreatments, with only 10 species responding to slow cooling in 15% DMSO. Thirty one species had enhanced germination and 10 species depressed germination after any of the liquid nitrogen treatments. There were no trends in a species ability to survive liquid nitrogen storage and freezing regime, moisture content, seed size or taxonomic relatedness. However, hard seeded species belonging to the families Caesalpinaceae and Papilionaceae showed a consistently high degree of tolerance to liquid nitrogen storage. Significant physical damage to seed and cotyledons only occurred in Templetonia retusa (Papilionaecae) and this was alleviated by nicking the seed coat. This study indicates that seed of a large proportion of native Western Australian species may be amenable to storage in liquid nitrogen and that at least 40% of the listed rare and endangered species of Western Australia could be maintained in this way.     

Nectar dispersion patterns in three Australian plant species

Standing crops of floral nectar were measured from three species of plants: Dampiera stricta, Goodenia bellidifolia and Aotus ericoides. The amount of nectar in nearest neighbour blossoms in nine of the 10 samples were significantly correlated with one another suggesting that patches of high and low reward quality exist in these species. The patterns further suggest that the pollinators of these species employ arearestricted searching behaviour. The range of variability in standing crops for all three species was quite high. The nature of that variability suggests that A. ericoides is less variable in its rate of nectar production than are the other two species and, therefore, that it has the potential to be more tightly co-evolved with its pollinators.     

Environmental associations of abundance-weighted functional traits in Australian plant communities

Predictions of how vegetation responds to spatial and temporal differences in climate rely on established links with plant functional traits and vegetation types that can be encoded into Dynamic Global Vegetation Models. Individual traits have been linked to climate at species level and at community level within regions. However, a recent global assessment of aggregated community level traits found unexpectedly weak links with macroclimate, bringing into question broadscale trait–climate associations and implicating local-scale environmental differences in the filtering of communities. To further evaluate patterns in light of these somewhat contradictory results, we quantified the power of macro-environmental variables to explain aggregated plant community traits, taking advantage of new trait data for leaf area, plant height and seed mass combined with a national survey that records cover-abundance using consistent methods for a large number of plots across Australia. In contrast to the global study, we found that abundance-weighted community mean and variance of leaf area and maximum height were correlated with macroclimate. Height and leaf area were highest in wet (especially warm, wet) environments, with actual evapotranspiration explaining 30% of variation in leaf area and 26% in maximum height. Seed mass was weakly related to environment, with no variable explaining more than 5% of variance. Considering all three traits together in a redundancy analysis, the complete set of environmental variables explained 43% of variation in site-mean traits and 29% of within-site trait variance. While significant trait variation remains unexplained, the trait–environment relationships reported here suggest climatically-driven filtering plays a strong role in assembling these vegetation communities. Regional assessments using standardised species abundances can therefore be used to predict aspects of vegetation function. Our quantification of plant community trait patterns along macroclimatic gradients at continental scale thereby contributes a much-needed functional basis for Australian vegetation.     

Effect of disturbance and nutrient addition on native and introduced annuals in plant communities in the Western Australian wheatbelt

To investigate factors affecting the ability of introduced species to invade natural communities in the Western Australian wheatbelt, five communities were examined within a nature reserve near Kellerberrin. Transect studies indicated that introduced annuals were more abundant in woodland than in shrub communities, despite an input of introduced seed into all communities. The response of native and introduced annuals to soil disturbance and fertilizer addition was examined. Small areas were disturbed and/or provided with fertilizer prior to addition of seed of introduced annuals. In most communities, the introduced species used (Avena fatua and Ursinia anthemoides) established well only where the soil had been disturbed, but their growth was increased greatly when fertilizer was also added. Establishment and growth of other introduced species also increased where nutrient addition and soil disturbance were combined. Growth of several native annuals increased greatly with fertilizer addition, but showed little response to disturbance. Fertilizer addition also significantly increased the number of native species present in most communities. This indicates that growth of both native and introduced species is limited by nutrient availability in these communities, but also that introduced species respond more to a combination of nutrient addition and soil disturbance.     

Species richness and canopy productivity of Australian plant communities

The species richness (number of vascular plants per hectare) of Australian plant communities (containing a mosaic of gap, regeneration, maturation and senescent phases) is correlated with the annual biomass productivity of the overstorey canopy.The annual production of leaves and stem in the canopy of the plant community is shown to be limited by the requirements of photosynthesis (particularly light and the availability of water) and the length of the growing season.The species richness of Australian plant communities is the product of the blance between the dominance of the overstorey and the response of the understorey to the shading of the overstorey. For all climatic regions and zones the species richness of the overstorey of the plant community is shown to be exponentially related to the annual shoot growth of the overstorey canopy, until the latitudinal or altitudinal tree line is reached. With latitudinal increase outside the tropics, overstorey canopies of forest communities absorb increasingly more of the incident solar radiation. markedly reducing the species richness of the understorey strata. In contrast, in these latitudes the overstorey of plant communities with widely spaced trees or tall shrubs will absorb far less solar radiation, thus enabling the species richness of the understorey to be maintained.     

Characterizing soil seed banks and relationships to plant communities

Estimates of soil seed banks are important to many ecological investigations and plant conservation, yet seed banks are among the most difficult plant community attributes to accurately quantify. To compare extraction and emergence seed bank characterization methods, we collected 0- to 5-cm soil seed bank samples and measured plant community composition in six microsite types (below different perennial plant species and interspaces) at 10 field sites in the Mojave Desert, USA. Extraction detected five times more species sample^?1 and orders of magnitude greater seed density than emergence, though evaluating viability of extracted seed was not straightforward. Only 13 % of 847 tested seeds from extraction emerged in follow-up assays. Considering all sites, species detection was more similar between methods: 21 taxa for emergence and 28 for extraction. Results suggest that: (i) capturing microsite variation is critical for efficiently estimating site-level desert seed banks; (ii) method comparisons hinged on the scale of analysis for species richness, as differences in species detection between methods diminished when increasing resolution from the sample to the regional scale; (iii) combining data from all seed bank methods provided the strongest correlation with vegetation; and (iv) improving knowledge of seed germinability is important for advancing both seed bank methods, including for extraction to evaluate the proportion of extracted seeds that are viable. Multifactor approaches that balance several effectiveness measures (e.g., both seed density and species detection at multiple scales) and procedural challenges are most likely to accurately represent complexity in tradeoffs for choosing methods to quantify soil seed banks.     

Effect of altered snow conditions on decomposition in three subalpine plant communities

Snow cover and its spatio-temporal changes play a crucial role in the ecological functioning of mountains. Some human activities affecting snow properties may cause shifts in the biotic components of ecosystems, including decomposition. However, these activities remain poorly understood in subalpine environments. We explored the effect of human-modified snow conditions on cellulose decomposition in three vegetation types. Snow density, soil temperature, and the decomposition of cellulose were studied in Athyrium, Calamagrostis, and Vaccinium vegetation types, comparing stands intersected by groomed ski slope and natural (outside the ski slope) stands. Increased snow density caused the deterioration of snow insulation and decreased the soil temperature inside the ski slope only slightly in comparison with that outside the ski slope in all vegetation types studied. The decomposition was apparently lower in Athyrium vegetation relative to the other vegetation types and strongly (Athyrium vegetation) to weakly lower (other vegetation types) in groomed than in ungroomed stands. Wintertime, including the melting period, was decisive for overall decomposition. Our results suggest that differences in decomposition are influenced by ski slope operations and vegetation type. Alterations in snow conditions appeared to be subtle and long-term but with important consequences for conservation management.     

Decomposition of roots of three plant communities in a Dutch salt marsh

Results of the first published study on root decomposition in a West European salt marsh are presented. In situ decomposition of roots of Spartinetum, Puccinellietum and Halimionetum communities were investigated using litter bags. Both the temporal pattern of decomposition and decomposition rate of belowground tissues of the three communities differed during 30 weeks in the marsh; Puccinellietum root litter lost 30–45% ash-free dry weight, Halimionetum root litter 17–26% and Spartinetum root litter 7–17%. Compared to aboveground decomposition in salt marshes these rates are low, however they are in the range of results reported for American and Australian salt marshes. Decomposition rates of root material buried at depths of 10 and 20 cm differed and there was a community × depth interaction. Initial content of structural components was highest in Halimionetum root litter and lowest in Puccinellietum root litter. Integrated soil temperature was highest in the Puccinellietum habitat, while flooding frequency was lowest in the Halimionetum habitat. Results indicate that environmental conditions can cause irregular fluctuations in belowground decomposition rates.     

松嫩草原三种主要植物群落枯落物层生态水文功能

分析了松嫩草原主要植物群落羊草群落、虎尾草群落、碱茅群落枯落物层的蓄积量及持水能力、枯落物层对降水的截留以及枯落物层抑制土壤水分蒸发的效应.结果表明,羊草群落枯落物蓄积量最大为4.7t·hm-2,最大持水量为9.6t·hm-2,最大持水率为208.4%;虎尾草群落枯落物层蓄积量、最大持水量和最大持水率分别为3.0t·hm-2、7.4t·hm-2和262.8%;碱茅群落分别为2.6t·hm-2、5.0t·hm-2和202.2%;3种群落枯落物层对降水的截留量分别为6.57、5.79和5.26t·hm-2,随着降雨量的增加,截留量增加,截留率减小;0.5~2mm枯落物覆盖下不同含水量的土壤水分蒸发比无覆盖的土壤减少7.95%~56.79%,枯落物层减少土壤水分蒸发的效应随枯落物层厚度和土壤含水量的增大而增加.     

The role of seed traits in determining the phylogenetic structure of temperate plant communities

Background and Aims

Phylogenetic clustering of species within plant communities can be expected to result from environmental filtering acting on an evolutionary-conserved plant trait. One such a candidate trait is the embryo to seed-size ratio (E:S). A high E:S may allow faster germination immediately after imbibition, and is therefore assumed to be advantageous in dry habitats. In this study the hypothesis was tested that habitat filtering driven by soil moisture conditions and acting on seed germination and seedling establishment is an important ecological mechanism in structuring temperate plant communities.

Methods

Vegetation samplings were performed in three habitats located within 200 km of each other in western Europe: Ellenberg indicator values showed that the habitats selected differed substantially in terms of soil moisture and light availability. E.S ratio and seed mass data for all genera were obtained from literature. Data were analysed using recently developed phylogenetic methods.

Key Results

Genera with a similar E:S tend to co-occur, as low and high E:S genera dominate in moist and dry habitats, respectively. A phylogenetically clustered pattern of community structure was evident, and dispersion of E:S was positively related to phylogenetic dispersion.

Conclusions

The phenotypically and phylogenetically clustered pattern indicates that E:S-mediated habitat filtering is an important assembly process structuring the plant community of the temperate climate habitats studied.     

Post-dispersal seed predation of three grassland species in a plant diversity experiment

Aims Post-dispersal seed predation is an important ecosystem process because it can influence the seed's fate after the initial dispersal from the mother plant and subsequently transform communities. Even at small scales, post-dispersal seed predation can vary greatly depending on seed identity, granivorous taxa or microhabitat structure. However, little is known about the role of plant species richness and functional group richness in post-dispersal seed predation. The overall aim of this study was to test whether increasing plant species richness or plant functional group richness affects the rate and variability of post-dispersal seed predation. We additionally investigated the influence of vegetation structure and seed species identity on the rate and variability of post-dispersal seed predation and whether the influence of different granivorous taxa changed with increasing plant species richness.Methods We conducted seed removal experiments along a long-term experimental plant diversity gradient, comprising plots with monocultures to 60 species mixtures of common grassland species in Jena, Germany, in August 2011. We studied seeds of Onobrychis viciifolia, Pastinaca sativa and Trifolium pratense in exclusion experiments (seed cafeterias), an experimental setup that allowed access either for arthropods or slugs or for all granivorous taxa. Traditionally, seeds removed from seed cafeterias were classified as consumed but we used traceable fluorescent-coloured seeds to obtain more accurate predation rates by subtracting recovered seeds from overall removed seeds. The effect of multiple vegetation variables on mean and variability of seed predation rates was analysed using generalized mixed-effect models and linear regressions, respectively.Important findings Rates of recovered seeds were low but contributed to significant differences between seed predation rates and removal rates of seeds in some treatments. Seed predation rates were not directly correlated with increasing plant species richness or plant functional group richness but were influenced byseed species identity and granivorous taxa. Vegetation variables such as vegetation height and cover were significantly associated with seed predation rates. Depending on the seed species and/or the granivorous taxa, different vegetation variables correlated with seed predation rates. Our results indicate that effects of plant functional group richness and multiple vegetation variables on the magnitude of post-dispersal seed predation varied with seed identity and seed predator taxa. A direct effect of plant species and plant functional group richness could be shown on the variability of post-dispersal seed predation for some seed species and their respective predators. Thus, the changes in magnitude of post-dispersal seed predation with increasing plant species richness could potentially impact the fitness of some plant species and thereby influence plant community structure.     

科尔沁沙地植被恢复演替进程中群落土壤种子库研究

研究了科尔沁沙地植被恢复演替进程中各群落土壤种子库种类组成、密度以及物种多样性等特征。主要结论是:①科尔沁沙地植被退化后的恢复演替是一种次生的中途恢复演替。演替各阶段土壤种子库密度为流动沙丘<半流动沙丘<固定沙丘,从流动到半流动沙丘阶段,土壤种子库密度平均增加了709%;从半流动到固定沙丘阶段,土壤种子库密度平均增加了393%。从流动到半流动沙丘阶段是土壤种子库密度的快速增长期。②植被恢复演替过程中,土壤种子库组成均以1年生草本植物为主(优势度为60.40%~91.83%),到演替中后期阶段,多年生草本植物的种类有所增加,但其所占比例仍很小。③演替各阶段群落种子库物种多样性指数分别为0.6616、0.7736、0.7281、1.0939、1.0648和0.9682,可见种子库物种多样性最高的群落并非是演替历史最大的群落。④恢复演替系列各阶段土壤种子库间的相似性系数都较大,在0.368~1.000范围之内,任一群落总是与其下一阶段最邻近的群落具有最高的相似性系数。     

Associations between leaf structure, orientation, and sunlight exposure in five Western Australian communities

Five plant communities in Western Australia, as well as selected desert and Rocky Mountain species of the western USA, were surveyed to evaluate associations among leaf structure, orientational properties, and the sunlight exposure and precipitation characteristic of each community. Selected leaf structural features have been associated previously with photosynthetic function and included shape, thickness, the ratio of thickness to width, stomatal distribution, leaf surface coloration, and the number and distribution of palisade cell layers. Decreases in annual precipitation (<4 to over 15 cm/yr) and increases in total daily sunlight (4.2 to 29.2 mol photons/m1) corresponded strongly to an increase in the percentage of species in a given community with more inclined (more inclined than +/- 45 degrees from horizontal) or thicker leaf mesophyll (>0.4 mm) leaves. Also, the percentage of species with a leaf thickness to width ratio >0.1, which were amphistomatous, or which had palisade cell layers beneath both leaf surfaces, increased from >20% in the highest rainfall and lowest sunlight community to >80% in the community with least rainfall but greatest sunlight exposure. Over 70% of the species in the most mesic, shaded community had lighter abaxial than adaxial leaf surfaces (leaf bicoloration). All of the above structural features were positively associated with a more inclined leaf orientation (r1 = 0.79), except for leaf bicoloration, which was negatively associated (r1 = 0.75). The ratio of adaxial to abaxial light was more strongly associated with leaf bicoloration (r1 = 0.83) and the presence of multiple adaxial and isobilateral palisade cell layers(r1 = 0.80) than with total incident sunlight on just the adaxial leaf surface (r1 = 0.69 and 0.73, respectively). These results provide field evidence that leaf orientation and structure may have evolved in concert to produce a photosynthetic symmetry in leaf structure in response to the amount of sunlight and other limiting factors of the community. This structural symmetry may serve fundamentally to regulate the distribution of both light and CO2 levels inside the leaf and, thus, increase photosynthetic CO2 uptake per unit leaf biomass.     

A comparison between reclamation stockpile and boreal forest seed banks and plant communities

Soil stockpiles are essential to the reclamation of large‐ and small‐scale mining and other industrial sites. However, stockpiling soils can lead to the degradation of seed banks. This study examines the diversity, composition, depth of seed storage, and relationships between the aboveground and seed bank plant communities in stockpiles and compares them to the nearby boreal forest. The seed bank and aboveground vegetation sampled at eight stockpiles and six mature forest sites were near Fort McMurray (57.337°N, 111.755°W) and Cold Lake (54.695°N, 110.730°W), Alberta, Canada. Seed bank samples were taken from the forest floor (LFH) and depths of 0–5, 5–10, 10–20, 20–30, >50 cm. Aboveground vegetation cover was also estimated at these locations. The seed bank composition was determined using the seedling emergence method in a greenhouse. Stockpile seed banks had higher seedling abundance and species richness than nearby forested sites but were dominated by grasses and non‐native forbs. Most seeds germinated from the surface layer, with 92% of seeds germinating from the LFH layers in the forested sites, and 68% from the 0 to 5 cm layer in the stockpiles. Mature forest sites had more similar aboveground and seed bank communities than the stockpiles. Overall, integrating information on seed bank and aboveground plant communities would improve reclamation decisions, rather than relying on aboveground vegetation alone.