种子传播提高生物多样性的机制

种子是保存物种遗传信息的载体,保护种子资源是植物保护和生物多样性保护的重要内容。种子传播不仅对保护植物自身的繁殖和生存至关重要,而且对群落稳定甚至生态系统功能具有重要意义。该文综述了种子传播的方式、干扰因素以及种子传播通过提高生物多样性来促进植物保护的机制,即丰富的生物多样性降低了病虫害对植物的危害。种子传播易受人为活动和气候变化等因素干扰传播媒介和破坏生境;需要采取构建廊道等措施来降低因生境破碎化引起的负面影响。种子传播提高生物多样性的机制主要通过增加基因交流来提高遗传多样性,通过增加种子扩散效率和存活率等来提高物种多样性、稳定群落结构和通过连通生境斑块来提高生态系统多样性。因此,构建基于生态系统的种子传播网络对保护生物多样性具有重要意义。     

Impact of the pathogen Pyrenophora semeniperda on Bromus tectorum seedbank dynamics in North American cold deserts

Bromus tectorum is a dominant winter annual weed in cold deserts of western North America. We followed patterns of seed carry-over and abundance of the pathogen Pyrenophora semeniperda over 5 years at B. tectorum -dominated shadscale ( Atriplex confertifolia ) and sagebrush ( Artemisia tridentata ) sites in southern Idaho. We hypothesised that more seeds could potentially carry over at the drier shadscale site because of minimal autumn precipitation, but that P. semeniperda , a pathogen that primarily kills dormant seeds, would have more impact at the drier site, where a higher density of dormant seeds would likely be present in the early spring seedbank. Successful first-year seed carry-over was higher in years with below-average autumn precipitation. It was lower at the shadscale site than at the sagebrush site (9% vs.16%). The number of seeds killed during incubation by P. semeniperda averaged three times higher at the drier site and the number of field-killed seeds averaged almost five times higher. This suggests that pathogen-related mortality caused the greater decrease in seed carry-over at the drier site. Mortality risk increased dramatically with seed age. This climate–pathogen interaction apparently limits B. tectorum seedbank carry-over in cold deserts to 3 years or less. Pyrenophora semeniperda shows potential as a biocontrol agent for B. tectorum in these habitats.     

Effects of human-mediated processes on weed species composition in internationally traded grain commodities

International trade is a major route by which non‐indigenous organisms are introduced into new habitats. Various kinds of weed seeds have been introduced through grain trade. The objectives of this study were to understand the factors that affect the initial assemblage of plant species introduced by the international grain trade and to extract their general attributes. We surveyed weed seed contamination of spring wheat imported from Canada to Japan and analysed the effects of the field abundance of each weed and of harvesting and cleaning on the quantity of weed seed included in the imported wheat. The field abundance was positively correlated with the weed seed quantity. Seeds of short weeds and seeds with a pappus were eliminated from the wheat by the harvesting or cleaning process. Many other crop plants contaminated the wheat. Because various transportation vehicles, temporary storage sites and port elevators are used commonly with all exported crops and it is difficult to remove all residues from them, other crops might be carried over into the wheat commodity. These relationships also apply to other grains.     

Potential of weed seedbanks for managing weeds: a review of recent New Zealand research

Weed seedbanks are the primary source of weeds in cultivated soils. Some knowledge of the weed seedbank may therefore be appropriate for integrated weed management programs. It would also be very useful in planning herbicide programs and reducing the total herbicide use. However, a number of problems are inherent in the estimation of the seedbank size for arable weeds that usually have annual life cycles. In a long-term research project we have investigated the dynamics of weed seedbanks in corn fields for the past 8 years. Specific studies have included (i) developing cheap and efficient methods for estimating the weed seedbank; (ii) developing guidelines for efficient soil sampling (including the number and size of samples); (iii) influence of cultivation methods on weed seed distribution; (iv) mapping the spatial variability of the seedbank; (v) estimating the rate of seedbank decline for certain weed species; and (vi) assessing the potential of using the weed seed content in the soil to predict future weed problems. This paper reviews and summarizes the results of our research on the above aspects. The strong correlation between seedlings emerged in the greenhouse and seeds extracted in the laboratory for the most abundant weed species has demonstrated the potential for using the weed seed content of the soil to predict future weed infestations. The next step is to establish correlations with field emergence under commercial conditions using the sampling guidelines developed in our studies. Subsequently, we aim to offer the weed seedbank estimation as a commercial service to farmers for planning the most appropriate weed management options.     

Seed rain and soil seed bank compensatory roles on Nassella tenuis (Phil.) Barkworth seedling recruitment in ungrazed and grazed sites

In semi-arid lands, vegetation is distributed in shrub patches immersed in a less vegetated interpatch matrix. Grazing affects perennial grass seed bank through a decrease in seed rain and an increase in seed predation and soil compaction. Nevertheless, some species with anchorage mechanisms in their seeds might overcome this, such as Nassella tenuis (Phil.) Barkworth. This is an important species in grazing paddocks because it has an intermediate palatability and its relatively tolerant to grazing. These characteristics allow N. tenuis to increase its abundance in grazed sites. Our objective was to assess how grazing affects the key palatable species from seeds to seedlings: i.e., seed rain, soil seed bank, and seedling recruitment in different microsites along a windward-leeward transect across shrub canopy. We hypothesized that: (1) the negative effects of grazing on N. tenuis fructification are reflected in its seed rain, soil seed bank, and seedling recruitment, especially in interpatches; (2) Nassella tenuis seed rain reduction, soil compaction by cattle in grazed sites, and removal of seeds by wind decrease its soil seed bank, especially in microsites exposed to the predominant wind; and (3) the decrease in N. tenuis soil seed bank and cover increase in annual species in grazed sites have negative effects on its seedling recruitment, especially in microsites exposed to predominant wind. We placed seed traps, collected soil samples, and monitored seedling recruitment in different locations around shrub canopy to address our hypotheses. Also, we established a manipulative experiment in which we sow N. tenuis seeds and followed its recruitment in different microsites. We compared the seed rain, soil seed bank, natural seedling recruitment, and sown seeds recruitment of N. tenuis between grazed and ungrazed sites. We analyzed differences between microsites along a windward-leeward transect across shrubs patches. Seed rain and soil seed bank had the same density in patches and interpatches both in ungrazed and grazed sites. But seed rain was higher, and soil seed bank was lower in ungrazed sites than in grazed sites. Almost all under-canopy microsites showed greater soil seed bank abundance and natural seedling recruitment in ungrazed sites. Sown seeds recruitment was the same between grazed and ungrazed sites, but it showed protective effects of shrubs in leeward microsites under grazed sites. As a conclusion, seed rain and soil seed bank are complementary under grazed sites.     

毛乌素沙地天然臭柏群落种子产量、种子库及幼苗更新

采用样方调查法,研究了毛乌素沙地臭柏(Sabinavulgaris)群落的种子产量、种子库及幼苗更新。结果表明:毛乌素沙地天然臭柏群落的球果丰富,约为3093. 83粒/m2,种子产量为9118. 5粒/m2,优良种子达2954. 4粒/m2。5种立地条件间的土壤种子库差异大、质量低,种子优良度最高的也仅为3. 7%。土壤种子集中分布于0 ~5cm土层内,并随着土壤深度增加,优良种子数由0~5cm的30. 52粒/m2减少到5~10cm的1. 3粒/m2。5 种立地中当年幼苗数的平均值仅为7. 98株/m2,最高的(A类立地)为14. 7株/m2,仅占表土优良种的30%左右,最低的(D类立地)已经丧失了更新能力。臭柏群落内种子更新苗少,而且种子更新集中在少数滩地小生境中。种子库小、质量差、更新环境的丧失是限制臭柏群落天然更新与拓展的主要因子。     

古尔班通古特沙漠羽毛针禾（Stipagrostis pennata）种群种子雨特征

通过布设种子收集器收集种子,对收集的种子以时空差异进行分组分析,探讨羽毛针禾[WTBX]（Stipagrostis pennata）[WTBZ]种子散布规律以及古尔班通古特沙漠种群的种子雨特征。结果表明：① 羽毛针禾种子雨的积累密度平均达到3 766.30粒·株-1,其中饱满种子占19.56%;② 种子散布的高峰集中在6月25到7月15日,其落种量占整个种子雨的61.96%,其后种子雨密度随时间逐渐减小;③ 种子雨密度与生境之间均不存在显著性差异;④ 种子雨总量与其年龄之间存在显著性差异;⑤ 种子雨的前扩散过程中种子集中降落在背风方向4 m范围和株丛周围1 m内。古尔班通古特沙漠南缘种子雨虽质量不高,但密度大,对种群的自然更新具有一定的意义。     

土壤种子库的研究方法综述

主要从取样方法、取样时间和种类鉴定等方面对土壤种子库研究方法进行综述,重点介绍了种子萌发法,并且提出了要采取长期定位观测的方法对土壤种子库的长期完整动态进行较系统的研究,而且最好在种子库长期的定位研究中搞清楚研究区内植物种的物种特性并且建立一个幼苗标本库,以增加土壤种子库研究的准确性。     

Ecophysiological study on weed seed banks and weeds in Cambodian paddy fields with contrasting water availability

Weed infestations are a major cause of yield reduction in rice (Oryza sativa) cultivation, particularly with direct‐seeding methods, but the relationship between weed dynamics and water availability in Cambodian paddy fields has not been documented previously. We surveyed the weed abundance and weed seed banks in the soil of paddy fields with inferred differences in their water regime in 22 farm fields in three provinces of Cambodia in the 2005 and 2006 rainy seasons. We studied rain‐fed lowland fields in upslope and downslope topographic positions and fields at different distances from the irrigation water source inside an irrigation rehabilitation area. The weed seed banks were estimated by seedling emergence in small containers and weed abundance and vigor were estimated by a simple scoring system. The estimated weed seed bank in the top 5 cm of soil ranged from 52.1 to 167 × 10³ seeds m^?2 (overall mean of 8.5 × 10³ seeds m^?2) and contained a high proportion (86%) of sedge species, such as Fimbristylis miliacea L. and Cyperus difformis. Several fields had particularly large seed banks, including one near the reservoir. No clear difference was found in the weed seed banks between the irrigated fields that were located close to (upstream) and distant from (downstream) the water source or between the irrigated and rain‐fed lowland fields, but the weed scores were larger in the rain‐fed fields and the downstream fields within the irrigated area. A water shortage during the late growing season in 2005 led to a proliferation of weeds in some fields and an associated increase in weed seedbank size in 2006. However, the weed scores in 2006 were more strongly associated with that year's water conditions than with the weed seedbank size.     

Effects of the seed weight and burial depth on the seed behavior of common ragweed (Ambrosia artemisiifolia)

Common ragweed (Ambrosia artemisiifolia L.) is one of the annual plants that were described recently as invasive weeds in Europe. This species is described as an invasive plant that produces seeds that are highly variable. Its production of variably sized seeds is regarded as promoting its spread in different environments. Experiments were carried out to determine the influence of the seed weight and temperature on germination and the influence of the seed weight and burial depth on seedling emergence. The seeds were divided into a number of classes of weight and the seed weight effect on germination was evaluated by Petri dish assays. In another experiment, the seeds were buried at different depths in a clay soil/sand mix to estimate the burial effect on germination and seedling emergence. The germination level of A. artemisiifolia was high overall, between 76.8% and 94.2%. The seed germination was modified by temperature but it was not influenced by the seed weight. The amounts of germination and seedling emergence were greater for the seeds on the soil surface and decreased with an increasing burial depth, from 2 to 8 cm. No germination or emergence was observed for the seeds that were buried at 10 and 12 cm. The lightest seeds were more sensitive to burial. A greater level of seedling emergence for those seeds that were placed near the soil surface could explain the success of this species in open habitats, where the probability of deeper burial is low. After high seed production, the management of A. artemisiifolia in fields could be partly achieved through soil tillage, burying seeds below 10 cm, and not carrying out deep soil tillage the following year.     

Precision of soil seedbank sampling: how many soil cores?

A prerequisite for a precise estimate of the abundance of weed seeds in sou is prior knowledge of sampling variability, Based on an analysis of EWRS working group trials, it is shown that the sampling variance (s²) of seed counts increases with the sampling mean (S²) and can be predicted with the logarithmic form of Taylor's power law: log₁₀(s^z)=a+b log₁₀(x?). This relationship is constant over time for means greater than 0.1 seeds per core within each of the five different sites studied (temporal variability) but differs slightly among sites (geographical variability). An attempt is made to use a general s² : x? relationship to predict the number of samples as a function of precision and density.     

Assessment of the sample size to estimate the weed seedbank in soil

It was found that, in order to estimate the number of weed seeds in soil with a desirable degree of accuracy and confidence level. the sample size depends to large extent on the spatial distribution pattern of the seeds in the soil. The seeds of most weeds found in cultivated soils are distributed according to one of two statistical distributions: Poisson or Negative Binomial. For an acceptable degree of accuracy in estimating the number of seeds in the soil, the sample size must be large, Taking this into account, in this study a practical solution based on a theoretical approach is proposed for the problem of establishing the sample size for a species distributed according to either statistical pattern. In addition, given the sample size, it was possible to determine the estimation error to be expected. This theoretical approach is compared with that proposed in previous studies. Two abaci, based on simple expressions, are provided to determine the sample size, according to the Poisson or the Negative Binormal distribution of the weed species. For Poisson distribution, the sample size is determined (given the desired maximum relative error estimation and the confidence level) as a function of only one parameter: the expected number of seeds per sampling unit m (estimaied by the sample mean). For Negative Binomial distribution, the sample size is determined as a function of two parameters: m and p (estimated according to the relationship between the sample mean and the sample variance). A sample size n nol very different from those given in previous studies is obtained, but the lower limit found for the n -values is lower than that found in these studies.     

Maternal salinity environment affects salt tolerance during germination in Anabasis setifera: A facultative desert halophyte

The effects of maternal salinity and light incubation on the salinity tolerance of the facultative halophyte Anabasis setifera during their germination stages were assessed. Seeds were collected from non-saline habitats in Egypt and saline habitats in the United Arab Emirates(UAE). The seeds of the two populations were germinated in 0, 100, 200, 400, 600 and 800 m M Na Cl, and incubated at 25°C/15°C in both 12-h light and 12-h darkness regimes and continuous darkness. Significantly more seeds germinated in the Egyptian population than in the UAE population. Salinity tolerance was significantly greater with the Egyptian population than with the UAE population, especially under the conditions of higher salinities. The difference in salinity tolerance between the seeds of two populations was attributed to their seed mass. In addition, germination was significantly faster for the Egyptian population than for the UAE population. Most of the saline treated seeds were able to recover their germination when transferred to distilled water, but this depended on their maternal salinity and light incubation. Recovery from higher salinities was significantly better for the seeds under darkness than for those under light in the UAE population, but the reverse was true for the seeds in the Egyptian population. The higher salinity tolerance for the A. setifera seeds from the non-saline Egyptian population and the lower salinity tolerance for the seeds from the saline UAE population cannot explain their natural distribution. Further studies about other possible roles, such as levels of different promoting and inhibiting phytohormones, are needed to understand the importance of salinity as an environmentally induced maternal effect.     

How much of seed dormancy in weeds can be related to seed traits?

Seed dormancy contributes to species persistence in unpredictable environments and is a key process to be taken into account in weed dynamics models. As the level of seed dormancy, photosensitivity and the dates of dormancy induction and release are difficult to measure, our objective was to relate weed seed dormancy with morphological, chemical or physiological seed traits and with expert knowledge. Dormancy of four species was studied experimentally during a 2‐year seed burial experiment. Experiments were supplemented with data from the literature to increase the number of species analysed, resulting in a data set of 29 species. Proportions of non–dormant seeds were higher for elongated than spherical seeds, even when accounting for phylogenetic relatedness between species. Elongated seeds, which tend to remain on the soil surface in undisturbed habitats, may have been selected for lack of dormancy and immediate germination to limit mortality due to predation. Dormancy increased with seed coat thickness, which can act as a chemical and physical barrier to germination, while no relation was found with seed lipid or protein content. No correlation was found between photosensitivity parameters and any of the species traits analysed. Variations in dormancy dates (induction and release) were highly correlated with average field emergence season estimated from expert knowledge. The observed correlations suggest that the level of dormancy results both from direct and from indirect effects of traits being involved in trade‐offs together with seed mortality.     

Factors impacting the detection of weed seed contaminants in seed lots

BACKGROUND

The setting and following of phytosanitary standards for weed seeds can lessen the impacts of weeds on agriculture. Standards adopted by seed companies, laboratories and regulators ensure the contamination rates do not exceed some thresholds. Globally sample size standards are set based on the amount needed to obtain a contaminant in a random sample of the seed lot, not detectability. New Zealand requires a 95% confidence that the maximum pest limit of 0.01% of quarantine weed seed contamination is not exceeded in an imported seed lot. We examined 24 samples each containing approximately 150 000 seeds of either perennial ryegrass (12 samples) or white clover seeds (12 samples) that were then spiked with seeds (contaminants) from 12 non-crop species (3–8 seeds of each). We considered factors that may impact detection rates: shape, color, size, and texture relative to the crop, and technician (including a commercial seed laboratory).

RESULTS

A linear mixed model fitted to the data indicated significant observer, crop, and seed color, shape, and size effects on detection. Detectability increased by 20% ± 7.7 (± standard error) when seeds had a distinct shape or color (28% ± 8.1), or were larger (23% ± 8.7) rather than smaller, relative to the crop. Commercial laboratory identifications were usually correct at the level of genus, and species for common weeds, but some misidentifications occurred.

CONCLUSION

Sample sizes for border inspections should be based on detectability of regulated weed seeds in the crop in combination with weed risk for the crop and location. © 2022 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.     

Relative contribution of genotype, seed size and environment to secondary seed dormancy potential in Canadian spring oilseed rape (Brassica napus)

Secondary seed dormancy has been linked to seedbank persistence of volunteer oilseed rape (Brassica napus) in western Canada. It has been suggested that there is a genetic component to secondary seed dormancy expression in oilseed rape, but little is known of its importance in relation to non‐genetic factors. In a series of experiments we investigated the relative importance of genotype, seed size, time of windrowing and pre‐ and post‐harvest environment on the expression of secondary seed dormancy. We found that genotype contributed between 44 and 82% to the total variation in secondary seed dormancy. A broad range in secondary seed dormancy expression was observed among 16 genotypes examined. Nevertheless, three‐quarters of the genotypes investigated exhibited relatively high potential for the expression of secondary seed dormancy (back‐transformed mean 71% dormant seeds). Seed size contributed 21% to the total variation, while the influence of seed maturity (harvest regime) on secondary seed dormancy expression was negligible. Despite diverging environmental conditions during the four growing seasons spanning these experiments, the influence of pre‐harvest environment on seed dormancy expression was relatively small and ranged from 0.1% to 4.5%. Secondary seed dormancy potential decreased over time during seed storage. This decrease was greatest when seeds were stored at ambient temperatures and least when seeds were stored at ?70°C.     

Determination of fatty acids content,global antioxidant activity and energy value of weed seeds from agricultural fields in France

The ecological consequences of seed size variation have been studied extensively in plants. Curiously, little attention has been paid to the qualitative and quantitative variation of the seed‐stored molecules and on their ecological significance. Here, we analysed the oil content and oil composition of ca. 200 weed seed species from agricultural fields in France based on single seed accessions, concentrating on interspecies differences and ignoring within‐species variation. The relationships between seed weight, oil %, fatty acids (FAs) and the energetic value of the seed and its antioxidant properties were also investigated. The antioxidant activity could contribute to protect the oily seed reserves from alteration over time. Among the species analysed, we found a considerable quantitative (oil%) and qualitative variation of FAs stored in the seeds. Such variation was largely related to the plant family of the different species, but intrafamily variation was also found. Heavier seeds contained less oil on a per gram basis than lighter seeds, suggesting a trade‐off between seed weight and oil ratio in the seed and that oil storage strategy depends on seed size. Moreover, oily seeds contained more polyunsaturated FAs. However, contrary to our hypothesis, we did not found a higher antioxidant capability in oily seed extracts than in non‐oily seeds, nor to the quantitative or to the qualitative variation of FAs in the seeds. Considering the role of these important trait variations on weed ecological strategies, such as germination period, seed predation rate and competition–colonisation trade‐off, could improve the sustainable management of weed communities.     

Reproduction of Hedysarum scoparium (Fabaceae) in patched habitat is pollen limited, but not just pollinator limited

Pollen limitation of plant reproduction occurs across Angiosperms,particularly those in patched habitats.We investigated the relationship between pollen limitation and patch variables (patch size,visitation frequency) in the desert plant Hedysarum scoparium (Fabaceae),which is an important xerophyte in the arid and semi-arid regions of Northwest China and can grow well as a pioneer plant in shifting sand dunes.We observed insect visitation to H.scoparium over two flowering seasons and estimated pollen limitation using fruit set and seed production.Our results indicate that fruit set and seed production increased significantly with pollen supplementation compared with open pollination.Hedysarum scoparium was pollinated by over 8 species of bees,with 88.4% of visits made by introduced honeybees (Apis mellifera).Bee visitation varied significantly among the patches of habitats,but not associated with patch size of habitat.In general,pollen limitation occurred more strongly during fruit set than during seed production.The patches that received higher rates of pollinator visits were less pollen limited for fruit set.Pollen limitation for seed production,however,was not associated with pollinator visitation frequency.We conclude that pollen limitation in H.scoparium was caused by more than one reason,not just pollinator visits.     

The effect of crop,cultivation and seed addition for birds on surface weed seed densities in arable crops during winter

Weed seeds present an agronomic threat, but are also an important food resource for wildlife in winter. Weed seed densities on the soil surface in winter were examined from 1999 to 2002 in 105 fields on three different farms in UK. The effect of the preceding crop, cultivation, position within the field and the application of seed for birds (bird seed) on surface seed abundance and species composition was tested. Six or fewer species comprised c. 80% of the weed seeds. By January of each study year, the densities of seeds important for farmland birds (key seeds) were 73% or 87% lower compared with early winter on two of the farms, but were stable on the third where seeds were incorporated through cultivation. At the edge and mid‐field, seed densities only exceeded 400 m^?2 in 17%, 10% and 12% of fields for total, key and dicotyledonous seeds respectively. The preceding crop only affected seed densities at one site; stubbles of winter barley had fewer seeds compared with winter wheat or spring barley. Seed densities varied between the edge and mid‐field, but trends were inconsistent between sites. The density of the larger seeds (Atriplex patula, Viola arvensis, Polygonum aviculare and Chenopodium album) were reduced in fields receiving bird seed. The objectives of weed control and conservation may not be mutually exclusive because seed return was most reduced where the ground remained uncultivated through the winter, yet this also provided the best foraging opportunities for surface feeding seed predators.     

Weed seed predation rate in cereals as a function of seed density and patch size,under high predation pressure by rodents

Weed seed predation is an ecosystem service, influencing weed population dynamics. The impact of weed seed predation on weed population dynamics depends on how predators respond to seed patches at the field scale. Seed predation will be most effective if the proportion of seeds predated increases with increasing size and seed density of patches. Density‐dependent rodent seed predation was measured by varying seed density and patch size in four irrigated conventionally managed cereal fields in north eastern Spain. Artificial weed seed patches were created by applying a range of Lolium multiflorum seed densities from 0 to 7500 seeds m^?2 in 225 m² patches (2008) or in patches that varied in size from 1 to 9 m² (2009). Seed predation was estimated using seed cards and seed frames. The granivorous rodents Mus spretus and Apodemus sylvaticus caused high seed predation rates (92%) in three fields, whereas in a fourth field, it was lower (47%). Rodents responded in an inversely density‐dependent manner, but this had little biological meaning as even in patches seeded with the highest density, the input to the soil seedbank was reduced by 88%. For the period of time this experiment lasted, hardly any new seeds would have entered the seedbank.