Climate warming could increase recruitment success in glacier foreland plants

Background and Aims Glacier foreland plants are highly threatened by global warming. Regeneration from seeds on deglaciated terrain will be crucial for successful migration and survival of these species, and hence a better understanding of the impacts of climate change on seedling recruitment is urgently needed to predict future plant persistence in these environments. This study presents the first field evidence of the impact of climate change on recruitment success of glacier foreland plants.Methods Seeds of eight foreland species were sown on a foreland site at 2500 m a.s.l., and at a site 400 m lower in altitude to simulate a 2·7 °C increase in mean annual temperature. Soil from the site of origin was used to reproduce the natural germination substrate. Recruitment success, temperature and water potential were monitored for 2 years. The response of seed germination to warming was further investigated in the laboratory.Key Results At the glacier foreland site, seedling emergence was low (0 to approx. 40 %) and occurred in summer in all species after seeds had experienced autumn and winter seasons. However, at the warmer site there was a shift from summer to autumn emergence in two species and a significant increase of summer emergence (13–35 % higher) in all species except two. Survival and establishment was possible for 60–75 % of autumn-emerged seedlings and was generally greater under warmer conditions. Early snowmelt in spring caused the main ecological factors enhancing the recruitment success.Conclusions The results suggest that warming will influence the recruitment of glacier foreland species primarily via the extension of the snow-free period in spring, which increases seedling establishment and results in a greater resistance to summer drought and winter extremes. The changes in recruitment success observed here imply that range shifts or changes in abundance are possible in a future warmer climate, but overall success may be dependent on interactions with shifts in other components of the plant community.     

Soil warming increases plant species richness but decreases germination from the alpine soil seed bank

Global warming is occurring more rapidly above the treeline than at lower elevations and alpine areas are predicted to experience above average warming in the future. Temperature is a primary factor in stimulating seed germination and regulating changes in seed dormancy status. Thus, plant regeneration from seed will be crucial to the persistence, migration and post disturbance recruitment of alpine plants in future climates. Here, we present the first assessment of the impact of soil warming on germination from the persistent alpine soil seed bank. Contrary to expectations, soil warming lead to reduced overall germination from the soil seed bank. However, germination response to soil temperature was species specific such that total species richness actually increased by nine with soil warming. We further explored the system by assessing the prevalence of seed dormancy and germination response to soil disturbance, the frequency of which is predicted to increase under climate change. Seeds of a significant proportion of species demonstrated physiological dormancy mechanisms and germination of several species appeared to be intrinsically linked to soil disturbance. In addition, we found no evidence of subalpine species and little evidence of exotic weed species in the soil, suggesting that the soil seed bank will not facilitate their invasion of the alpine zone. In conclusion, changes in recruitment via the alpine soil seed bank can be expected under climate change, as a result of altered dormancy alleviation and germination cues. Furthermore, the alpine soil seed bank, and the species richness therein, has the potential to help maintain local species diversity, support species range shift and moderate species dominance. Implications for alpine management and areas for further study are also discussed.     

Seeds of alpine plants are short lived: implications for long-term conservation

Background and Aims

Alpine plants are considered one of the groups of species most sensitive to the direct and indirect threats to ecosystems caused by land use and climate change. Collecting and banking seeds of plant species is recognized as an effective tool for providing propagating material to re-establish wild plant populations and for habitat repair. However, seeds from cold wet environments have been shown to be relatively short lived in storage, and therefore successful long-term seed conservation for alpine plants may be difficult. Here, the life spans of 69 seed lots representing 63 related species from alpine and lowland locations from northern Italy are compared.

Methods

Seeds were placed into experimental storage at 45 °C and 60 % relative humidity (RH) and regularly sampled for germination. The time taken in storage for viability to fall to 50 % (p₅₀) was determined using probit analysis and used as a measure of relative seed longevity between seed lots.

Key Results

Across species, p₅₀ at 45 °C and 60 % RH varied from 4·7 to 95·5 d. Seed lots from alpine populations/species had significantly lower p₅₀ values compared with those from lowland populations/species; the lowland seed lots showed a slower rate of loss of germinability, higher initial seed viability, or both. Seeds were progressively longer lived with increased temperature and decreased rainfall at the collecting site.

Conclusions

Seeds of alpine plants are short lived in storage compared with those from lowland populations/related taxa. The lower resistance to ageing in seeds of alpine plants may arise from low selection pressure for seed resistance to ageing and/or damage incurred during seed development due to the cool wet conditions of the alpine climate. Long-term seed conservation of several alpine species using conventional seed banking methods will be problematic.     

高寒草甸15种植物种子发芽的比较研究

对高寒草甸 15种植物种子的发芽进行了比较实验研究。结果显示 ,冷湿层化、温度变幅及光照条件能够提高或者降低多数高寒草甸植物种子发芽率。其中 ,13种植物对层化、11种对光照条件、14种对温度变幅处理有显著性响应。 15种植物中 ,有14种对单一因子或因子组合有反应 ,仅藏嵩草种子发芽对设定的因子或因子组合没有响应。根据不同植物种子对不同处理及其组合的发芽反应可将植物种子划分为不同的反应类型 ,通过对种子进行冷湿层化处理 ,可以部分或者全部地替代某些植物种子发芽对光、温需求。探明植物种子在特定环境因子组合条件下的发芽表现 ,对通过种子恢复退化草甸是至关重要的。     

The effect of light and seed mass on seed germination of common herbaceous species from the eastern Qinghai‐Tibet Plateau

Smaller seeds might encounter more severe selective pressure than larger ones because they have fewer food reserves and are more easily buried; thus, seed mass can be considered to be directly related to the effect of light on germination. To investigate the effect of light on seed germination and associated seed mass variation within a whole plant community, we compiled germination data for common herbaceous species from an alpine meadow on the eastern Qinghai‐Tibet plateau. The results showed the following. (i) Light had a general positive effect on seed germination. Under light, the proportion of species with lower germinability was decreased, mean germination percentage was increased by 20% and the speed of germination was doubled. (ii) Irrespective of light environment, species with medium‐sized seeds (seed mass ranging from 0.11 to 0.5 mg) had higher germination percentage and speed when compared with species within the largest seed mass group. (iii) The germination of smaller‐seeded species was more dependent on light stimulation than larger‐seeded ones. In darkness, the species within the smallest seed mass group had the lowest percentage and speed of germination; however, under light, the species within the largest seed mass group had the lowest percentage and speed of germination. Our results suggested that the germination characteristics and especially seeds’ response to light among species in the alpine meadow might be an adaptation to natural selective pressure.     

长白山高山冻原种子植物的调查

通过多次对长白山高山冻原的实地考察,统计得到冻原种子植物共计34科、94属、146种,有6种属的分布区类型(包括3个变型),北温带分布类型最多,占总属数的68.09%。在整个冻原上,草本有125种,占总数的85.62%,其中多年生草本124种。高山冻原植物中具有多种生态,生理适应方式,低矮平卧状植株、极矮小草本、密集丛生是植物的重要适应方式,细长密集须根是冻原上主要的适应方式,占植物总数的54.94%。果实中干果共计137种,其中蒴果56种。由于高山冻原上生态环境十分残酷,极易受人为因素的影响。     

Climate change and plant regeneration from seed

At the core of plant regeneration, temperature and water supply are critical drivers for seed dormancy (initiation, break) and germination. Hence, global climate change is altering these environmental cues and will preclude, delay, or enhance regeneration from seeds, as already documented in some cases. Along with compromised seedling emergence and vigour, shifts in germination phenology will influence population dynamics, and thus, species composition and diversity of communities. Altered seed maturation (including consequences for dispersal) and seed mass will have ramifications on life history traits of plants. Predicted changes in temperature and precipitation, and thus in soil moisture, will affect many components of seed persistence in soil, e.g. seed longevity, dormancy release and germination, and soil pathogen activity. More/less equitable climate will alter geographic distribution for species, but restricted migratory capacity in some will greatly limit their response. Seed traits for weedy species could evolve relatively quickly to keep pace with climate change enhancing their negative environmental and economic impact. Thus, increased research in understudied ecosystems, on key issues related to seed ecology, and on evolution of seed traits in nonweedy species is needed to more fully comprehend and plan for plant responses to global warming.     

Forecasting changes in population genetic structure of alpine plants in response to global warming

Species range shifts in response to climate and land use change are commonly forecasted with species distribution models based on species occurrence or abundance data. Although appealing, these models ignore the genetic structure of species, and the fact that different populations might respond in different ways because of adaptation to their environment. Here, we introduced ancestry distribution models, that is, statistical models of the spatial distribution of ancestry proportions, for forecasting intra-specific changes based on genetic admixture instead of species occurrence data. Using multi-locus genotypes and extensive geographic coverage of distribution data across the European Alps, we applied this approach to 20 alpine plant species considering a global increase in temperature from 0.25 to 4 °C. We forecasted the magnitudes of displacement of contact zones between plant populations potentially adapted to warmer environments and other populations. While a global trend of movement in a north-east direction was predicted, the magnitude of displacement was species-specific. For a temperature increase of 2 °C, contact zones were predicted to move by 92 km on average (minimum of 5 km, maximum of 212 km) and by 188 km for an increase of 4 °C (minimum of 11 km, maximum of 393 km). Intra-specific turnover-measuring the extent of change in global population genetic structure-was generally found to be moderate for 2 °C of temperature warming. For 4 °C of warming, however, the models indicated substantial intra-specific turnover for ten species. These results illustrate that, in spite of unavoidable simplifications, ancestry distribution models open new perspectives to forecast population genetic changes within species and complement more traditional distribution-based approaches.     

Comparisons of germination traits of alpine plants between fellfield and snowbed habitats

We examined the seed-germination responses of 27 alpine species with reference to habitat type (fellfield and snowbed), temperature (five regimes), and light requirement. About 70% of species showed >40% germination at warm temperatures without cold stratification. However, a moist-chilling treatment markedly improved the germination percentages in most species, especially under cool conditions. Thus, cold stratification effectively reduced the temperature requirement for germination. Patterns of germination response within species were not consistent between the fellfield and snowbed habitats for species inhabiting both habitats. For interspecific comparisons, there were no significant differences in germination responses to the temperature regimes and the cold stratification between the fellfield and snowbed species. Also, germination speed and the length of germinating period did not differ between fellfield and snowbed species. Most species (86%) showed a requirement for light for germination without cold stratification. Although the extent of the light requirement was reduced after cold stratification in some species, the light requirement of most small-seeded species remained. The combination of cold stratification and the light requirement is a major factor determining the seedling emergence and formation of seed banks in alpine plants. However, habitat-specific patterns of germination traits were less clear, suggesting similar germination traits in fellfield and snowbed plants, at least under controlled conditions in the laboratory.     

生物土壤结皮对荒漠土壤种子库和种子萌发的影响

研究了腾格里沙漠东南缘在不同自然条件（风、温度、水分）下,人工固沙植被区（24龄、41龄、50龄）和相邻天然植被区的两种生物土壤结皮对荒漠土壤种子库和种子萌发的影响。结果表明,荒漠土壤种子库在苔藓结皮上的储量显著高于藻类结皮。随着生物土壤结皮的发育,种子萌发量在苔藓结皮上增加,在藻类结皮上减少。生物土壤结皮层的含水量对种子萌发有显著的影响（p〈0.05）,植物种子在湿润处理的生物土壤结皮上的萌发量高于干燥处理的生物土壤结皮上的种子萌发量。生物土壤结皮表层温度和亚表层温度对荒漠植物种子萌发无显著影响（p〉0.05）,但总体而言,对于苔藓结皮,植物种子在较高温度下的萌发量略高于在较低温度下的萌发量,而对于藻类结皮,植物种子在较低温度下的萌发量略高。     

Effect of yak rumen content treatments on seed germination of 11 alpine meadow species on the Qinghai-Tibetan Plateau

The Qinghai-Tibetan Plateau is located in the ‘Third Pole’ of the world, characterized by a harsh environment. Despite this, the alpine meadow ecosystem have developed over a wide area but serious grassland degradation is threatening the ecological environment on the Plateau. Recruitment of new plants to the population, via germination and establishment, is vital to plant community survival. Previous work on the seeds in this area has mainly focused on community-wide germination strategies, seed germination characteristics and their correlations with seed size and seed mass. However, there have been no studies on the effects of soaking in rumen contents on the plant seed germination characteristics of alpine meadow species. The present study had two main objectives: (i) to determine the effect of fresh rumen content from yaks on seed germination characteristics and seedling growth of species common to the eastern Tibetan Plateau alpine meadow, and (ii) to develop an effective method to enhance seed germination. Seeds of 11 common species were collected together with fresh rumen content from three yaks that grazed there. Seed germination tests were conducted after they had been soaked in rumen content for one of six soaking periods (12, 24, 36, 48, 60 or 72 h). The seeds were incubated under natural light conditions of 8 h light at 25 °C and 16 h darkness at 15 °C, for the germination period of 34 days. The results showed that seed germination and seedling growth were affected by soaking time, seed coat completeness and seed type. After soaking in rumen content, the germination percentages of scarified (peeled or with the seed coat cut through) seeds of some species (true seeds Oxytropis ochrocephala and Medicago ruthenia var inschanica, nutlet Carex enervis, achenes Anemone rivularis and Polygonum sibiricum) and complete seeds of C. enervis, and A. rivularis were improved but the duration of soaking was also important. Seed germination of caryopsis Achnatherum inebrians (a toxic grass) was significantly inhibited by any exposure to rumen fluids. Scarified seeds generally had higher germination percentages than complete ones after treatment, but with the increase in soaking time, germination percentages declined and scarified seeds were more sensitive to the treatment than the complete seeds. After soaking in yak rumen content, the germination indices of scarified M. ruthenia at 12 h treatment, O. ochrocephala and achene Rumex acetosa at 12–24 h treatment, nutlet Kobresia humilis at 24 h treatment, P. sibiricum at 24–48 h treatment, C. enervis at 12–48 h treatment and A. rivularis at 12–60 h treatment were significantly higher than the control (P < 0.05), while the germination indices of complete C. enervis seeds at 12 h and 36 h treatment, and A. rivularis at 12–60 h treatment were significantly higher compared with the control. The germination indices of other species gradually decreased with the increase in soaking time. We concluded that yak rumen digestion could enhance, inhibit or not affect seed germination and seedling growth of the alpine meadow species, which might influence seedling recruitment, interspecific competition, and the plant community structure of the eastern Tibetan Plateau alpine meadow. Overall, yak digestion has a positive effect on alpine meadow seed germination and seed dispersal.     

Seed germinating characteristics of 54 gramineous species in the alpine meadow on the eastern Qinghai-Tibet plateau

The germination experiment was started on March 3,2004,and seeds were collected from July to October in 2003.We analyzed the percentage of germination,days to first germination,germination period and days to 50% germination.Among the 54 examined species,26 species exceeded 80% germination,11 species exceeded 60%-80% germination,8 exceeded 40%-0%,5 exceeded20%-40%,and 4 showed less than 20%.A principalcomponent analysis revealed that the species were distributed along two statistically independent axes,the first primarily represented the germination rate and the second represented the time of germination process.Based on scores of germination characteristics,duster analysis of the 54 gramineous species could be divided into 4 distinct groups:rapid,slow,intermediate germinating (germination percentage＞ 50%),and low germinating (germination percentage＜ 50%).The meaning of different groups to the vegetation regeneration was discussed.     

Ethylene in seed dormancy and germination

The role of ethylene in the release of primary and secondary dormancy and the germination of non-dormant seeds under normal and stressed conditions is considered. In many species, exogenous ethylene, or ethephon – an ethylene-releasing compound - stimulates seed germination that may be inhibited because of embryo or coat dormancy, adverse environmental conditions or inhibitors (e.g. abscisic acid, jasmonate). Ethylene can either act alone, or synergistically or additively with other factors. The immediate precursor of ethylene biosynthesis, 1-aminocyclopropane-1-carboxylic acid (ACC), may also improve seed germination, but usually less effectively. Dormant or non-dormant inhibited seeds have a lower ethylene production ability, and ACC and ACC oxidase activity than non-dormant, uninhibited seeds. Aminoethoxyvinyl-glycine (AVG) partially or markedly inhibits ethylene biosynthesis in dormant or non-dormant seeds, but does not affect seed germination. Ethylene binding is required in seeds of many species for dormancy release or germination under optimal or adverse conditions. There are examples where induction of seed germination by some stimulators requires ethylene action. However, the mechanism of ethylene action is almost unknown.
The evidence presented here shows that ethylene performs a relatively vital role in dormancy release and seed germination of most plant species studied.     

Seed germinating characteristics of 54 gramineous species in the alpine meadow on the eastern Qinghai-Tibet plateau

The germination experiment was started on March 3, 2004, and seeds were collected from July to October in 2003. We analyzed the percentage of germination, days to first germination, germination period and days to 50% germination. Among the 54 examined species, 26 species exceeded 80% germination, 11 species exceeded 60%–80% germination, 8 exceeded 40%–0%, 5 exceeded 20%–40%, and 4 showed less than 20%. A principal-component analysis revealed that the species were distributed along two statistically independent axes, the first primarily represented the germination rate and the second represented the time of germination process. Based on scores of germination characteristics, cluster analysis of the 54 gramineous species could be divided into 4 distinct groups: rapid, slow, intermediate germinating (germination percentage > 50%), and low germinating (germination percentage < 50%). The meaning of different groups to the vegetation regeneration was discussed. __________ Translated from Journal of Plant Ecology, 2006, 30(4): 624–632 [译自: 植物生态学报]     

植物化感物质对种子萌发的影响

所有的化感物质都对一些植物的种子萌发产生影响.本文介绍了植物化感作用和化感物质的定义,化感物质的释放方式和种类,然后重点综述了化感物质影响种子萌发的作用机理、内外因素和生态学意义.化感物质通过影响细胞膜透性、细胞分裂生长和分化、呼吸作用、蛋白质合成、基因表达、激素合成和平衡,最终影响种子萌发.化感物质对种子萌发的影响与化感物质的种类、浓度、受体植物种类和环境条件等有关.     

Effects of aqueous extract of rice plants (Oryza sativa L.) on seed germination and radicle elongation of Monochoria vaginalis var. plantaginea

Laboratory experiments were conducted to examine the allelopathic potentials of rice plants (Oryza sativa L.) on seed germination and radicle elongation of Monochoria vaginalis (Burm. f.) Presl var. plantaginea (Roxb.) Solms-Laubat. To compare the relative allelopathic potentials of rice plants at different growth stages, aqueous extracts of dried tissues were obtained from the seeds, husks, and seedlings harvested 10, 20, 40 and 120 days after seeding. When M. vaginalis seeds were incubated in solutions containing aqueous extracts, significant increases in the germination rate were observed for all the aqueous extracts except for the extract of 10 d-old shoots at higher dosages. When partitioned with ethyl acetate, the germination-promoter(s) in the aqueous extracts remained in the aqueous phase while some inhibitors were extracted with ethyl acetate. In contrast, aqueous shoot extracts added to the incubation media at the same dosage for promotion of seed germination inhibited radicle elongation of M. vaginalis, indicating that the sensitivity of the weed varies between these two growth stages.