Seed consumption by millipedes

Seed predation is a key mortality factor for plants that reproduce by seeds. We investigated seed consumption by Cylindroiulus caeruleocinctus (Wood, 1864), an abundant representative of an unrecognised group of seed predators – the millipedes (Diplopoda: Julidae). The consumption of small seed species by millipedes was measured in the absence (41 species) and in the presence (11 species) of alternative food sources (dead leaves). We examined whether millipedes would consume seeds at all and if so whether there were any seed size constraints that determined millipede seed acceptance (i.e., the proportion of millipedes that ate seeds) and seed consumption (i.e., the mass of the seeds eaten). Our results indicated that C. caeruleocinctus readily accepted seeds with 75% of seed species accepted in a no-choice experiment and 100% of seed species in a choice experiment. Seed acceptance decreased with increasing seed mass but increased with increasing millipede mass. Seed consumption increased with the size of the offered seed species but was found to be independent of millipede mass. After the millipedes were given dead leaves to consume, the acceptance slightly decreased, and the consumption of the more preferred seed species decreased. Seeds form a small part of the millipede diet but are consumed regularly. Because of millipedes’ foraging preferences and their patchy distribution they may notably contribute to the local mortality of some seed species in their natural environment.     

The role of imbibition on seed selection by Harpalus pensylvanicus

Invertebrate weed seed predation is an important component of weed seed loss in agricultural fields. This study investigated the role of seed imbibition on the selection and consumption of the seeds of seven common agricultural weed species by Harpalus pensylvanicus De Geer, a granivorous carabid beetle (Coleoptera: Carabidae) that is found throughout North America. The volatile organic compounds released by ambient dry and imbibed weed seeds were quantified, and Y-tube bioassays were conducted to determine if H. pensylvanicus individuals responded to volatile compounds released from weed seeds. H. pensylvanicus individuals were found to consume higher masses of seeds for each weed species examined in imbibed versus ambient dry trials (P < 0.05). Larger seeded species had the greatest increase in mass consumption between dry seed and imbibed seed trials. The seeds from the seven weed species examined released carbon dioxide and ethylene when ambient dry and imbibed, but H. pensylvanicus adults were only able to detect weed seeds through olfaction when volatile release was highest as a result of imbibition. These results demonstrate that seed imbibition is important in determining seed detection and consumption by invertebrates and may affect seed banks in agricultural fields.     

Litter N-content influences soil millipede abundance,species richness and feeding preferences in a semi-evergreen dry forest of Guadeloupe (Lesser Antilles)

Despite the impact of soil millipedes on litter fragmentation in tropical forests, there have been few studies dealing with factors determining their habitat preference in these ecosystems. In a natural secondary dry forest of Guadeloupe on Leptosol, two complementary studies were carried out in order to test the hypothesis that litter N-content strongly influences millipede distribution. Millipede abundance and species richness were described in the field under two tree species, Bursera simaruba and Pisonia subcordata, and were related to the chemical characteristics of their foliage. In addition, a laboratory experiment was done in order to assess millipede feeding preferences regarding the chemical characteristics of leaves from various species. Millipede abundance and species richness were significantly higher under P. subcordata than under B. simaruba, probably due to the higher N content of P. subcordata leaves. Moreover, millipedes fed preferentially on N-rich leaves. The present study confirms that there was a close correlation between the preferred food, its chemical composition and the local distribution of millipede populations.     

风沙土中荒漠植物出苗和生长的比较研究

选择了5种荒漠植物红砂（Reaumuria soongorica）、泡泡刺（Nitraria sphaerocarpo）、花棒（Hedysarum scoparium）、白刺（Nitraria tangutorum）和沙拐枣（Calligonum mongolicum），设计了沙埋和幼苗生长两个控制实验，来研究它们的萌发出苗和生长定植能力。结果表明：5种植物的高出苗率、快出苗现象集中在0～3cm的沙埋深度；红砂、泡泡刺、花棒、白刺、沙拐枣的最佳沙埋深度分别为1cm、2cm、2．5cm、2cm和5cm。出苗率与沙埋深度方程的斜率显著相关于种子重量。种子重量与幼苗的绝对生长率、相对生长率正相关。相对生长率与单位叶速率和叶面积干重比显著正相关，但和叶面积比率和叶干重比率显著负相关。种子重量与根绝对伸长速率无关，但与根长比率和根长叶面积比率显著负相关。种子重量和单位叶速率是出苗和生长的较好的指示者，但仅仅种子重量和幼苗相对生长率并不能预示植物成活能力。     

Millipedes (Diplopoda) in birds nests

Nests of birds represent an unusual microhabitat for diverse groups of soil and epigeic invertebrates including millipedes. The millipede faunas of 301 birds nests from 63 localities throughout Slovakia were obtained by heat extraction of the nest substrates. In total 18 species of millipedes were found in 7 different types of nests of 40 bird species. The most frequent millipede species were Polyxenus lagurus and Proteroiulus fuscus. The similarities in the millipede nidifauna depending on the type of nests, ecological characteristics and geographical distribution of millipede species are discussed.     

Distribution and species grouping of millipedes (Myriapoda, Diplopoda) in dry biotopes in Saxony-Anhalt/Eastern Germany

Within an extensive study on endangered biotopes in the State of Saxony-Anhalt/Eastern Germany, the millipede fauna of 50 dry habitats, belonging to 5 types of biotopes was studied from 1995 to 1998 using pitfall traps. The most abundant species were Glomeris marginata and Cylindroiulus caeruleocinctus. By applying a combination of the criteria repraesentanz, constancy and dominance a new criterion, the “common-habitat-relation”, has been introduced to establish biotope-characteristic species and communities of millipedes. The results show that by using these criteria together, distinct groups can be formed consisting of “characteristic” and “companion species”. Eleven out of 34 species that occurred on the sites fitted into this grouping. Characteristic species groups were determined for mesoxeric meadows (C. caeruleocinctus, G. marginata and Glomeris hexasticha) and “succession” sites (Allaiulus nitidus and Polydesmus angustus). The sandy dry meadows were characterized by companion species only (Megaphyllum unilineatum and Ommatoiulus sabulosus), the heavy-metal grassland by the characteristic species Craspedosoma rawlinsii without companion species. For dwarf-shrub heaths no typical species groups could be found.     

The influence of seed size and shape on their removal by water erosion

Under semiarid environments where surface runoff takes place, the role of water erosion in the removal of seeds and then in the plant establishment and distribution is unknown. Within the scientific literature, data about the size and shape of seeds exist, but little information can be found about the susceptibility of seeds to be removed by water erosion processes. These data are important not only from an eco-geomorphological point of view, but also for afforestation strategies in order to improve the selection of species to develop the recovery of vegetation on degraded environments. Eighty-three seed species were selected from Southeastern Spain. Variables related to size, such as weight (M), length (L), width (W) and height (H) of these seeds, were measured. From this information, other variables such as the surface (S), volume (V), density (D) and the ratio S/M were calculated. Seed shape was characterised by the Flatness Index (F.I.=L+W/2H) and the Eccentricity Index (E.I.=L/W). Laboratory rainfall simulation experiments at 55 mm h⁻¹ during 25 min on 26×26 cm plots with slope angle equal to 11° were performed with five lots of 50 seeds of each species. Results demonstrated that size is the main factor explaining seed removal, whereas the shape becomes important only when the seeds are larger than 50 mg. Seeds for vegetation recovery planning should have a mass between 10 and 50 mg to avoid removal by water erosion.     

Husking stations provide evidence of seed predation by introduced rodents in Tongan rain forests

The islands of Tonga, in Western Polynesia, lacked rodents prior to human colonization. During the past 3000 years, people have introduced three species of rats (Rattus). Seed predation by rodents structures plant communities in many parts of the world. Therefore, there is the potential for rats to have a significant impact on the regeneration of plant communities in Tonga. We found 53 husking stations—sheltered sites used by rats to strip inedible protective structures (husks) from the seeds they eat—on eight islands in Tonga. The stations contained 13,555 empty husks from at least 18 plant species, but only 165 viable seeds and seedlings. These husking stations provide evidence of seed predation by rats. Determining the extent to which seed predation threatens plant regeneration will be important for conservation of native forest remnants.     

Seed longevity in terrestrial orchids - Potential for persistent in situ seed banks

Terrestrial orchids typically produce numerous small seeds that contain very small nutrient reserves. The seeds are structurally adapted for wind dispersal but little is known about their fate after dispersal. Some studies of seed viability in situ indicate survival for up to two years in temperate orchid species. Seeds stored in the laboratory may last much longer. We investigated seed viability of seven North American orchid species with seed packets buried in a range of soil and wood substrates within their natural habitats. In Goodyera pubescens most seeds germinated within one year. Four other species continued to germinate sparsely during the observation period, but after almost seven years many seeds were still viable. In one species, Liparis liliifolia, seeds that had been in situ for four years had germination rates as high as 68% when sown in vitro with a compatible fungus. The remaining two species did not germinate during the observation period but the seeds were judged to be intact and tested positively for viability after four years in the ground. These observations are interpreted as different species-specific strategies for in situ germination and their seed bank potential is discussed.     

The biochemical transformation of oak (Quercus robur) leaf litter consumed by the pill millipede (Glomeris marginata)

Soil macrofauna play an essential role in the initial comminution and degradation of organic matter entering the soil environment and yet the chemical effects of digestion on leaf litter are poorly understood at the molecular level. This study was undertaken to assess the selective chemical transformations that saprophagous soil invertebrates mediate in consumed leaf litter. A number of pill millipedes (Glomeris marginata) were fed oak leaves (Quercus robur) after which the biomolecular compositions (lipids and macromolecular components) of the leaves and millipede faeces were compared using a series of wet chemical techniques and subsequent analysis by gas chromatography (GC) and gas chromatography-mass spectrometry (GC/MS). It was found that the concentrations of short chain (<C₂₀) n-alkanoic acids, sterols and triacylglycerols reduced dramatically in the millipede faeces relative to the leaf litter. Hydrolysable carbohydrates and proteins both decreased in concentration in the faeces, whereas similar yields of phenolic components were observed for the cupric oxidation products of lignin, although the oxygenated functionalities were affected by passage through the millipede gut, yielding a more highly condensed state for lignin. This shows that the chemical composition of fresh organic matter entering the soil is directly controlled by invertebrates feeding upon the leaf litter and as such that they are key contributors to the early stages of diagenesis in terrestrial soils.     

An investigation into the role of the Mauritian flying fox, Pteropus niger, in forest regeneration

This study was conducted over a 7-month period in the south-west of Mauritius and investigates the diet of the endemic flying fox Pteropus niger and its potential role as pollinator and seed disperser. The identification of food plants and seed dispersal events were made by direct observations of bats or indirectly by the analysis of ejecta found on the ground. P. niger was observed to visit 22 plant species for food of which 20 were visited for fruit, two for floral resources, and one for foliage (one species was visited for both fruit and floral resources). Two thousand thirty-two P. niger fruit ejecta from 16 species were collected containing 2460 seeds. Ejecta from eight of these species (including five endemic to Mauritius) contained seeds, all of which were mature and intact (with one possible exception) and some were germinating. Forty-seven observations were made of the dispersal of seeds in fruit, ejecta and faeces, including seeds from three endemic and one native plant species. All seeds in dispersed ejecta were found to be mature and undamaged by bats. Pollen smears from the lips of six dead and 12 captured bats showed that these animals carried a minimum of 18 pollen species. Each smear had an average of 2.2 pollen species and a pollen load of 17.7 grains. Our results suggest that P. niger plays an important role in maintaining plant diversity in the heavily fragmented landscape of Mauritius.     

Effects of yeast on the growth and reproduction of the saprophagous millipedePolydesmus angustus (Diplopoda, Polydesmidae)

The millipedePolydesmus angustus was reared in the laboratory from hatching to maturity, reproduction and death. Two food types were used: dead leaves alone or dead leaves supplemented monthly with dry food yeast (Saccharomyces cerevisiae) at a rate not exceeding 5% of leaf dry weight. Growth, survival, adult live weight and fertility were compared between females reared on the two diets. Although the species was able to complete its life cycle on dead leaves alone, several parameters were strongly affected by the addition of yeast: growth was significantly faster, adult females became significantly larger and there was a 4.3-fold increase in fertility. Only survival was unaltered by the addition of yeast. The comparison between these laboratory results and field data on female fertility and live weight suggests that the natural diet of millipedes includes foods of higher quality than dead leaves. Possible sources of high-quality food in natural conditions are discussed.     

Fat but slim: Criteria of seed attractiveness for earthworms

Earthworms were shown to significantly affect seeds and seedlings survival via their ingestion and digestion for nutritive purposes. Such selective feeding of earthworms on plant seeds is likely to favour certain plant species and to affect seed bank composition, plant recruitment and plant community structure. Relationships between earthworms and seeds, particularly seed traits that determine attractiveness of seeds for earthworms, are yet to be determined. In this study, the influence of six seed traits was tested on the ingestion, digestion and germination of seeds by two earthworm species (Lumbricus terrestris, anecic and Satchellius mammalis, epigeic). The seed traits tested were their length, width, weight, shape, oil content and the presence of trichomes on their surface. Each earthworm species was introduced into a microcosm with eleven seed species from a chalk grassland that represented those different traits. Ingested, digested and germinated seeds were counted after voiding the guts of the earthworms. Univariate and multivariate analyses showed that seed length, width, weight and seed oil content could significantly affect the ingestion of seeds for both earthworm species. Seed width and seed oil content were the two traits that influenced the digestion of seeds the most, but only for L. terrestris. We also found that seed ingestion was earthworm species-specific but we found no correlation between earthworm traits and number of ingested or digested seeds. Few seeds germinated from L. terrestris casts and no seeds germinated from S. mammalis casts. Implications in terms of plant evolution strategies are further discussed.     

Effect of forest fragmentation on fruit and seed predation of the tropical dry forest tree Ceiba aesculifolia

Forests fragmentation reduces the density of natural plant populations forming patches of the remaining individuals. One of the biotic interactions that can be affected by forest fragmentation and is poorly studied is seed predation. We determined the effects of forest fragmentation on seed and fruit predation in Ceiba aesculifolia by comparing trees in continuous forest with trees in fragmented forest. We compared the following variables: (a) frequency of fruit predation by Collie’s squirrel (Sciurus colliaei) in each habitat; (b) frequency of the cotton-staining bug seed predator (Dysdercus, Orden Hemiptera) in each habitat; (c) the effect of seed predation on germination frequency and time; and (d) the effect of different life stages of Dysdercus on seed viability. In continuous habitat, 100% of the trees presented fruits with squirrel predation while only 34% of trees in fragmented habitats presented fruit predation. In continuous forest 27% of the trees contained fruits with the seed predator Dysdercus, while only 2% of the trees in fragmented forest presented Dysdercus. The initial weight of damaged seeds was greater than seeds that were not damaged indicating that seed predators select heavier seeds to feed upon. Frequency of seed germination was affected by different life stages; pre-adults decreased germination significantly more than nymphs and adults. Seed predation significantly increased the time it took for germination to occur. Our study shows that forest fragmentation significantly affects predation patterns of squirrels and cotton-staining bugs. Reduction of natural seed predators in forest fragments may have long-term consequences on forest structure and diversity.     

Faunal stage-dependent altering of soil nitrogen availability in a temperate forest

Functional traits of organisms often depend on their developmental stages during growth. However, whether the ecological functions of organisms change at different developmental stages remains poorly understood, especially for soil animals. The train millipede, Parafontaria laminata, which has a synchronised life cycle, often dominates in soil invertebrate communities in central Japan. Because adults of this species are litter-feeders and larvae are soil-feeders, we hypothesised that the train millipede assumes a different role in of the cycling of nitrogen (N) depending on its developmental stage. To determine the effects of P. laminata on N retention or loss in temperate forest soil, millipede density was manipulated in two mesocosm experiments using adult and larval millipedes. We found strong evidence that the effects of P. laminata on N dynamics differ between millipede developmental stages. Larvae enhanced N leaching, which was significantly higher in the high-density treatment than in treatments without millipedes (control). In contrast, adults did not affect N leaching, although high and intermediate adult density significantly increased soil N content compared to control and low-density treatments. Our results suggest that soil-feeding larvae promote soil N mineralisation, whereas litter-feeding adults inhibit N mineralisation, potentially sustaining N levels in the soil for at least the duration of our experimental period. Because natural populations of P. laminata exhibit high abundance and a synchronised life cycle at the landscape level, the soil-to-litter feeding shift that depends on P. laminata's developmental stage-of may cause large temporal variation in N dynamics in forest ecosystems compared to macrofauna-free systems.     

Determinants of reproductive success: A comparative study of five endangered river corridor plants in fragmented habitats

River corridor plants in Central Europe have in recent decades become increasingly rare, caused mainly by habitat destruction and change. The aim of this study was to examine the impact of soil quality, but especially of habitat fragmentation in terms of population size and isolation, on seed production and germination of five selected species, all of which being endangered, perennial herbs: Euphorbia palustris, Lathyrus palustris, Pseudolysimachion longifolium, Sanguisorba officinalis, and Senecio paludosus. We sampled totally 58 populations in flood plains in the surroundings of Bremen, North-western Germany.

In all five species, there were positive correlations between the number of seeds (total seed mass) and plant height, as well as between germination and seed mass. Seed traits values and/or germination were negatively affected by small population size, in Euphorbia, Lathyrus and Pseudolysimachion additionally by high population isolation. There were also significant effects of soil quality, but these were less consistent across species. The contribution of population size and isolation, compared to soil quality, to the variance explained in the reproductive components was especially high in Euphorbia and Lathyrus, the only two species depending on insect pollination.

The results indicate that the five species are likely to decline as a consequence of decreased plant fitness in small and/or isolated populations, probably caused by pollen limitation. The studied species may be representative for the group of river corridor plants as a whole that are often restricted to isolated remnants of near-natural flood plain vegetation in a matrix of heavily used agricultural land.     

Weed seed bank affected by tillage intensity for barley in Alaska

The weed seed bank of a long-term tillage study in subarctic Alaska was studied at the end of 10 years of continuous spring barley (Hordeum vulgare L.). Tillage treatments were: no-till, disked once (spring), disked twice (spring and fall), and chisel plow (fall). Soil cores were obtained from each tillage treatment and seeds were manually separated from soil after washing through sieves. Tillage treatment had a significant effect on seed density of shepherds purse (Capsella bursa-pastoris (L.) Medic.), cinquefoil (Potentilla norvegica L.), foxtail barley (Hordeum jubatum L.), and on total seed density. Seed density was higher for these species and total seed density was greater under no-till than under other tillage treatments. Seed density was higher near the soil surface under no-till and chisel plow treatments than under disked treatments, which helps explain the greater difficulty of controlling weeds under reduced tillage.     

The ant Lasius flavus alters the viable seed bank in pastures

The creation of small-scale vegetation mosaics by mound building is an important aspect of ant activity in grasslands. The consequences of this process for the composition of the viable soil seed bank are poorly understood. In this study we quantified the impact of the yellow ant Lasius flavus on both aboveground vegetation and seed bank of a low-intensity pasture located in the Vogelsberg area (Hesse, Germany). A few species of the mound vegetation (mainly therophytes) were restricted to the mounds, but most species also occurred in the surrounding area. The seed bank of ant mounds differed from that of the pasture soil between the mounds, with the abundance of germinating seeds being twice as high in the mounds. This was mainly due to the very large number of seeds originating from winter annuals and Thymus pulegioides. Seed abundance of most other species was lower in the mounds. Our results showed that this is partly due to dispersule weight limiting dispersal of seeds from the surrounding vegetation onto the mounds.     

苦豆子和披针叶黄华种子萌发和幼苗生长对干旱胁迫的响应

以采集于河西走廊中部荒漠边缘的苦豆子(Sophora alopecuroides L.)和披针叶黄华(Thermopsis lanceolate L.)种子为试验材料, 以不同渗透势PEG-6000 溶液模拟干旱条件, 研究了2 种植物种子萌发和幼苗生长对干旱胁迫的响应特征。研究结果显示, 随着干旱胁迫程度的加剧, 2 种植物种子吸胀速率、萌发率、萌发指数、活力指数、苗高、根长和组织饱和含水量等指标均表现出明显降低趋势, 而幼苗干重、根干重和根冠比均呈先升后降趋势。2 种植物种子萌发对干旱胁迫均较为敏感, 苦豆子和披针叶黄华种子能够萌发的最低渗透势阈值分别为-0.65 MPa 和-0.42 MPa。2 种植物因干旱胁迫未能萌发的种子复水后萌发率均较高。分析认为, 2 种植物种子萌发和幼苗生长对干旱胁迫的响应特征对幼苗的成功定植和种群的自然更新具有重要生态学意义, 但在人工栽培时保证土壤墒情应是保障建植成功的关键措施。     

种子引发对小麦抗盐及抗旱特性影响综述

小麦是我国北方重要粮食作物,在农业生产中经常受到干旱和盐分胁迫影响,造成减产。种子引发是在种子萌发前用天然或人工合成试剂对种子进行处理,从而提高植物抗逆性的一种简单而有效的方法。在干旱或高盐条件下,利用引发剂对小麦种子引发后,种子萌发提前,幼苗生长发育代谢增强,抗逆境相关生理指标提升,作物抗旱耐盐能力增强,最终产量及质量得到提高。本文阐述了水、有机物、植物激素、生物活性物质、生物、氧化物、无机信号物质等不同种类引发剂对小麦种子引发的作用机理和效果。并总结了种子引发的主要作用机制,如:减少植株对Na~+的吸收,增加对K~+、Ca~(2+)的吸收,减少盐分对生长造成的阻碍;促进可溶性蛋白和可溶性糖等渗透调节物质的合成和积累,细胞内维持高渗透压,有利于根系吸水;诱使胁迫条件下细胞内超氧化物歧化酶、过氧化物酶、过氧化氢酶、抗坏血酸过氧化物酶等抗氧化酶的合成增多、活性增强,有效清除活性氧,维持细胞内氧平衡;调节植物内源激素合成与运输从而使激素水平处于更加适应胁迫条件的平衡状态等。并讨论了引发剂与植物逆境生理研究之间相互补充、相互促进的关系,展望了种子引发在农业方面的发展及应用前景。