Effects of simulated climate change on phenology and life history traits in Carex bigelowii

Climate change may have large effects on plants, especially in the Arctic. At two different sites, we studied the effects of enhanced temperature by using open-top chambers (OTCs) on the clonal sedge Carex bigelowii , a common plant in arctic and alpine tundra. At the subarctic-alpine site Latnjajaure, northern Sweden, overall flowering phenology was accelerated by open-top chambers (OTCs) during the five years of treatment. For this protogynous population, male flower phenology accelerated more than female flower phenology, which resulted in an increased gender phase overlap. Sexual reproductive effort at the ramet-level increased, both in male and female functions. Smut fungus incidence was not different among treatments, but a Dipteran seed predator attacked more ramets in the OTCs in one of five years. However, neither the fungus nor the seed predators affected plant growth or seed set measurably. Ramet-level growth increased in the OTCs at Latnjajaure, but decreased in the OTCs at the maritime subarctic site Thingvellir, Iceland after three years of treatment. At Latnjajaure, the initial ramet- level responses were still evident after five years, while responses at the ramet population level disappeared: there was no difference in flowering frequency of ramets in the fifth year of the warming treatment. This is interpreted as either meristem limitation or internal resource depletion. At Thingvellir flowering frequency was unaffected by warming treatment, while ramet production decreased. Ramet production was unaffected by the treatment at Latnjajaure. These site differences in responses could be the consequences of differences in climate or site specific conditions. The trade-off (negative correlation) between the number and size of vegetative offspring at Latnjajaure disappeared under enhanced temperatures (within the OTCs). This trade-off was not apparent under the warmer conditions at Thingvellir.     

Effects of temperature on performance and phenotypic selection on plant traits in alpine Ranunculus acris

Discovering temperature effects on the performance of tundra plants is important in the light of expected climate change. In this 4-year study on alpine Ranunculus acris, I test the hypothesis that temperature influences flowering phenology, reproductive success, growth, population dynamics, and phenotypic selection on quantitative traits, by experimental warming using open-top chambers (OTCs). Warming significantly advanced flowering phenology in only one season. Seed number and weight were significantly increased by warming during the first three seasons, but not in the fourth. Plants inside OTCs produced bigger leaves than control plants in the fourth season, but leaf number was unaffected by the OTC treatment. Despite increased seed number and weight, the density of flowering plants decreased inside OTCs compared to control plots, possibly because of a higher graminoid cover inside OTCs. Phenotypic-selection regression showed a significant selection differential and gradient in the direction of larger leaf sizes in control plants, whereas no selection on leaf size was detected on warmed plants. The direction and strength of selection on flowering time, flower number, and leaf number did not differ between control and warmed plants. The results suggest that increased reproductive output of R. acris may not be sufficient to maintain current population density under a denser vegetation cover. Received: 1 December 1998 / Accepted: 14 April 1999     

Response to simulated climatic change in an alpine and subarctic pollen-risk strategist, Silene acaulis

The aim of this study was to test if early flowering species respond with increased seed production to climate warming as is predicted for late-flowering seed-risk strategists. Experimental climate warming of about 3°C was applied to two populations of the cushion-forming plant Silene acaulis (L.) Jacq. The experiment was run at one subarctic site and one alpine site for 2 years and 1 year, respectively, using open-top chambers (OTC).
The 2-year temperature enhancement at the subarctic site had a marked effect on the flowering phenology. Cushions inside the OTC started flowering substantially earlier than control cushions. Both the male and female phases developed faster in the OTCs, and maturation of capsules occurred earlier. The cushions also responded positively in reproductive terms and produced more mature seeds and had a higher seed/ovule ratio. After 1 year temperature enhancement at the alpine site there was a weak trend for earlier flowering, but there was no significant difference in seed production or seed/ovule ratio.     

Effects of experimental warming on plant reproductive phenology in Xizang alpine meadow北大核心CSCD

Aims: Climate warming strongly influences reproductive phenology of plants in alpine and arctic ecosystems. Here we focus on phenological shifts caused by warming in a typical alpine meadow on the Qinghai-Xizang Plateau. Our objective was to explore phenological responses of alpine plant species to experimental warming. Methods: Passive warming was achieved using open-top chambers (OTCs). The treatments included control (C), and four levels of warming (T1, T2, T3, T4). We selected Kobresia pygmaea, Potentilla saundersiana, Potentilla cuneata, Stipa purpurea, Festuca coelestis and Youngia simulatrix as the focal species. Plant phenology was scored every 3-5 days in the growing season. The reproductive phenology phases of each species were estimated through fitting the phenological scores to the Richards function. Important findings: Under soil water stress caused by warming, most plants in the alpine meadow advanced or delayed their reproductive events. As a result, warming significantly delayed phenological development of K. pygmaea. Warming significantly advanced reproductive phenology of P. saundersiana, S. purpurea and F. coelestis, but not of P. cuneata and Y. simulatrix. In addition, warming significantly shortened the average flowering duration of alpine plant species. The potentially warmer and drier growing seasons under climate change may shift the reproductive phenology of the alpine systems in similar pattern.     

实验增温对藏北高寒草甸植物繁殖物候的影响

全球气候变暖对高寒和极地地区的植物物候产生强烈的影响。该研究主要关注增温条件下藏北高寒草甸不同功能型植物繁殖时间(生殖物候)的改变。实验采用开顶箱式增温方法, 对3个主要功能群浅根-早花、浅根-中花和深根-晚花植物的现蕾、开花、结实时间进行观测。研究结果表明: (1)增温导致了土壤水分胁迫, 显著推迟了浅根-早花植物高山嵩草(Kobresia pygmaea)的繁殖时间; (2)增温显著提前了浅根-中花植物钉柱委陵菜(Potentilla saundersiana)和深根晚花植物紫花针茅(Stipa purpurea)和矮羊茅(Festuca coelestis)的繁殖时间; (3)增温没有显著影响浅根-中花植物楔叶委陵菜(Potentilla cuneata)和深根-晚花植物无茎黄鹌菜(Youngia simulatrix)的繁殖时间; (4)增温缩短了3种类型植物的开花持续时间。这些结果显示增温改变了藏北高寒草甸群落中多数物种的繁殖时间, 这预示着在未来更热更干的生长季, 青藏高原高寒草甸系统的植物物候格局可能会被重塑。     

Effects of experimental warming on plant reproductive phenology in Xizang alpine meadow

Aims Climate warming strongly influences reproductive phenology of plants in alpine and arctic ecosystems. Here we focus on phenological shifts caused by warming in a typical alpine meadow on the Qinghai-Xizang Plateau. Our objective was to explore phenological responses of alpine plant species to experimental warming. Methods Passive warming was achieved using open-top chambers (OTCs). The treatments included control (C), and four levels of warming (T1, T2, T3, T4). We selected Kobresia pygmaea, Potentilla saundersiana, Potentilla cuneata, Stipa purpurea, Festuca coelestis and Youngia simulatrix as the focal species. Plant phenology was scored every 3-5 days in the growing season. The reproductive phenology phases of each species were estimated through fitting the phenological scores to the Richards function. Important findings Under soil water stress caused by warming, most plants in the alpine meadow advanced or delayed their reproductive events. As a result, warming significantly delayed phenological development of K. pygmaea. Warming significantly advanced reproductive phenology of P. saundersiana, S. purpurea and F. coelestis, but not of P. cuneata and Y. simulatrix. In addition, warming significantly shortened the average flowering duration of alpine plant species. The potentially warmer and drier growing seasons under climate change may shift the reproductive phenology of the alpine systems in similar pattern.     

Short-term effects of simulated environmental change on phenology, leaf traits, and shoot growth of alpine plants on a temperate mountain, northern Japan

In order to assess the responses of circumpolar and semicircumpolar plants growing around their southern distribution margins to artificial warming, we set up 11 open-top chambers (OTCs) on a fell-field (1680 m a.s.l.) in the Taisetsu Mountains, northern Japan. The OTCs increased mean air temperature by 1.3°C through the growing season (June–September) and extended the length of the growing season. We examined phenology and leaf traits of plants in the OTCs and control plots during the first season under artificial warming treatment using two deciduous and three evergreen species. Ledum palustre (evergreen shrub), Vaccinium uliginosum , and Arctous alpinus (deciduous shrubs) showed earlier leaf emergence and/or flowering in the OTCs. Deciduous shrubs had longer individual leaf longevity and an extended foliage period in the OTCs than in the control plots. There were no significant differences in specific leaf area and leaf size for many species between the OTCs and the control plots. Vaccinium vitis-idaea (evergreen shrub), L. palustre, A. alpinus , and Empetrum nigrum (evergreen shrub) had lower leaf nitrogen concentration in the OTCs than in the control plots, whereas it was higher in V. uliginosum . Only E. nigrum showed larger annual shoot growth in the OTCs. No clear differences in response to the warming effect were detected between evergreen and deciduous species in the first season. Circumpolar plants growing in temperate alpine regions may be more affected by season length rather than temperature itself.     

Sexual reproductive ecology of Carex bigelowii an arctic-alpine sedge

Carex bigelowii an arctic-alpine sedge that shows an extensive clonal growth, and in many years also has a high degree of flowering. To see which factors are most important in determining the sexual reproductive success, the effects of self- and cross-pollination, pollen donor distance, amount of pollen, temperature, and time of flowering were studied. The study was conducted at Latnjajaure Field Station, northern Sweden and Thingvellir National Park, Iceland during three field seasons. Experimentally increased air temperature raised the fruit set and the fruit weight, in two of the three seasons. Pollen donor distance did not influence either fruit set or fruit weight, and there was no difference in fruit weight between selfing and cross-pollination. An increased amount of pollen raised the fruit set. but did not affect fruit weight. The time of flowering was also important; there was a negative relationship between flowering time and fruit set and fruit weight, i.e. late flowering ramets had a lower fruit set and fruit weight. The results suggest that Carex bigelowii is an outcrossed species where the reproductive success is mainly determined by the weather, and that there are differences between the two study sites.     

FLOWERING PHENOLOGY AT BIG RUN BOG,WEST VIRGINIA

In each of four major plant communities at Big Run Bog, a 15-ha Sphagnum-dominated wetland in the Appalachian Mountains of West Virginia, the flowering phenology of 21 species was measured by counting the number of flowering stems at frequent intervals throughout the growing season. The four plant communities exhibited no consistent differences with regard to the patterns of flowering phenology. Mean flowering duration was 30 days for all species, and was 32 and 31 days for wind- and insect-pollinated species, respectively. Peak flowering times for the 21 species were randomly distributed throughout the growing season. Results from Big Run Bog are not markedly different from those reported for other bogs in North America.     

Synchrony in the phenology of a culturally iconic spring flower

We examine the flowering phenology of the cultural iconic Spring Snowflake Leucojum vernum, a considerable tourist attraction, recorded from two sites in western Poland. Flowering dates at the two sites were closely correlated but about 6 days later at the more natural area. The end of flowering was associated with the start of canopy leafing. Early flowering was related to a longer flowering season which may benefit ecotourism under future climate warming.     

Litterfall seasonality and adaptive strategies of tropical and subtropical evergreen forests in China

中国热带和亚热带常绿林凋落物季节特征及适应策略 本研究收集了来自中国热带/亚热带常绿林共85个站点的凋落物量季节性变化数据,并采用线性回归、结构方程模型构建以及相位差分析等方法,综合探究中国热带/亚热带地区常绿阔叶林和针叶林叶片脱落对土壤水分、饱和水气压差和辐射强度等气候因子的响应机制。研究结果显示,在雨热同期和雨热异期两种热带/亚热带气候类型中,呈现出两种典型凋落物的物候类型(单峰季节型/双峰季节型)。在雨热同期气候条件下,光照强度和降水呈现季节性正相关,单峰的凋落物峰值和双峰的第一个峰值约出现在3–4月,不断增加的光照能促进新叶的萌发,老叶被代谢更强的新叶所替代,该类型属于一种最大程度利用光照来实现树木生长的自适应策略。双峰的第二个峰值出现在雨季末期,约在8–10月,是由不断增强的水分亏缺所导致的(常绿阔叶林：大气水分亏缺;常绿针叶林：土壤水分亏缺),这种类型是一种凋落老叶减少水分丢失来应对水分胁迫的自适应策略。在雨热异期气候条件下,光照强度和降水呈现季节性负相关,饱和水气压差与光照强度表现出一致的季节性动态变化,诱导了常绿阔叶林单峰和双峰物候的第一个凋落峰(约在3–4月),是一种权衡大气干旱胁迫和最大程度利用光照进行生长的综合自适应策略。在雨季初期,显著的土壤水分亏缺加速叶片凋落,诱导了常绿阔叶林双峰物候的第二个凋落峰(约在11月),属于凋落老叶应对土壤水分胁迫的自适应策略。这些研究结果可以为地球系统模式中热带物候的精确模拟提供重要参考。     

Effects of Warming on Chlorophyll Degradation and Carbohydrate Accumulation of Alpine Herbaceous Species during Plant Senescence on the Tibetan Plateau

Plant senescence is a critical life history process accompanied by chlorophyll degradation and has large implications for nutrient resorption and carbohydrate storage. Although photoperiod governs much of seasonal leaf senescence in many plant species, temperature has also been shown to modulate this process. Therefore, we hypothesized that climate warming would significantly impact the length of the plant growing season and ultimate productivity. To test this assumption, we measured the effects of simulated autumn climate warming paradigms on four native herbaceous species that represent distinct life forms of alpine meadow plants on the Tibetan Plateau. Conditions were simulated in open-top chambers (OTCs) and the effects on the degradation of chlorophyll, nitrogen (N) concentration in leaves and culms, total non-structural carbohydrate (TNC) in roots, growth and phenology were assessed during one year following treatment. The results showed that climate warming in autumn changed the senescence process only for perennials by slowing chlorophyll degradation at the beginning of senescence and accelerating it in the following phases. Warming also increased root TNC storage as a result of higher N concentrations retained in leaves; however, this effect was species dependent and did not alter the growing and flowering phenology in the following seasons. Our results indicated that autumn warming increases carbohydrate accumulation, not only by enhancing activities of photosynthetic enzymes (a mechanism proposed in previous studies), but also by affecting chlorophyll degradation and preferential allocation of resources to different plant compartments. The different responses to warming can be explained by inherently different growth and phenology patterns observed among the studied species. The results implied that warming leads to changes in the competitive balance among life forms, an effect that can subsequently shift vegetation distribution and species composition in communities.     

Male-biased sex allocation in late-blooming flowers driven by resource limitation in the clonal perennial Aconitum kusnezoffii (Ranunculaceae)

Flowering phenology and clonal growth are known to affect resource and pollen availability, and therefore select for adaptive or constrained sex allocation strategies to some degree. However, the consequences of temporal sex allocation patterns for reproductive fitness across the flower, inflorescence, and genet levels have rarely been examined. Moreover, experimental tests of the underlying regulatory mechanisms are scarce. We examined the association of flowering phenology and inflorescence position with temporal sex allocation and reproductive success in the protandrous perennial clonal herb, Aconitum kusnezoffii, over four consecutive growing seasons by examining more than 39 000 flowers. We also conducted controlled experiments to test the effects of resource and pollen limitation on the female reproductive success of lateral inflorescences. We found that some male functions were positively correlated with flowering phenology, whereas female reproductive success was negatively correlated with flowering phenology and inflorescence position. Lateral inflorescences invested more in male function than terminal inflorescences and therefore yielded fewer and smaller seeds. Resource limitation may serve as the key mechanism underlying this differentiated pattern. Decreased female reproductive success was consistently observed at the flower and inflorescence levels as flowering occurred later in the growth season. Late-blooming lateral inflorescences specialized in the male function, and their female reproductive success was constrained by early-blooming terminal inflorescences. This might be the first attempt to systematically demonstrate sex allocation strategy differentiation in a protandrous plant species at the inflorescence level. In addition, our study provides empirical evidence of dichogamy selecting for specialized sex allocation strategies among inflorescences.     

Responses of alpine shrubs to simulated environmental change during three years in the mid-latitude mountain, northern Japan

Effects of artificial warming on phenology, individual leaf traits, vegetative growth, and reproduction of five alpine species (two deciduous and three evergreen shrubs) were investigated during three years in the mid-latitude alpine, northern Japan. Eleven open-top chambers (OTCs) were set up on a fellfield (1680 m a. s. l.) in the Taisetsu Mountains by which air temperature at plant height was increased by ca 2°C. Vaccinium uliginosum (deciduous shrub) showed earlier leaf emergence in every season and earlier flowering only in the first season in the OTCs. By contrast, acceleration of leaf emergence in the OTCs was not clear for other species, i.e. Arctous alpinus (deciduous shrub). Ledum palustre. V. vitis-idaea , and Empetrum nigrum (evergreen shrub). Both deciduous species showed longer leaf life-span in the OTCs every season. All evergreen species had higher leaf survival rates in the OTCs. indicating extension of leaf life-span. Leaf nitrogen concentration and leaf mass per unit leaf area (mg cm ⁻²) generally tended to decrease in the OTCs. Relationships between the individual leaf traits and cumulative air temperature during the leaf developing period were not clear. Total leaf production during the three seasons increased in the OTCs in A. alpinus. L. palustre. V. vitis-idaea , and E. nigrum. All evergreen shrubs showed larger shoot growth in the OTCs but both deciduous shrubs did not show significant changes. In contrast to the vegetative growth, deciduous shrubs produced more flowers in the OTCs. Fruit production was not influenced by the OTCs for all species. The extension of photosynthetic period in the OTCs may contribute to the larger vegetative growth or flower production.     

Spiny east Mediterranean plant species flower later and in a drier season than non-spiny species

We compared the flowering phenology of spiny and non-spiny native species belonging to three families (Asteraceae, Fabaceae and Lamiaceae), which include the highest number of spiny species in the flora of Israel. We found that the peak of flowering (when the highest number of species flowered) was 4–8 weeks later for spiny species than for non-spiny species. The flowering peak of non-spiny species was in late March, while that of spiny species was at the beginning of May. The seasonal shift in flowering time from the main season, when most Mediterranean plants bloom, to the end of the flowering season, when fewer species bloom, might be the evolutionary result of a change in phenology reducing the competition for pollinators. Our results clearly indicate that spinescence of plants in the semi-arid east Mediterranean region is associated with a delayed flowering season at the beginning of the dry summer when most of the herbaceous vegetation is already dry. During this season, mammalian grazers consume any edible herbaceous vegetation, selecting for late flowering species that allocate more resources for anti-herbivore defenses than early flowering species. There is a well-known global geographical trend where the occurrence of spiny plants is higher in arid regions than in humid ones. In parallel to the global trend, we show a seasonal one, that non-spiny plants grow and flower in the spring, which is the main flowering season in the Mediterranean basin, while spiny plants flower later, in the hot and dry summer. Under the current trend of global warming, there are prospects of future increase in the dominance of spiny species in the Mediterranean region.     

Growth responses to ozone in plant species from wetlands

Ten wet grassland species were fumigated with four concentrations of ozone (charcoal-filtered air, non-filtered air and non-filtered air plus 25 or 50 nl l(-1) ozone) in open-top chambers during one growing season to investigate the long-term effect of this air pollutant on various growth variables. Only Eupatorium cannabinum showed ozone-related foliar injury, while five species reacted with significantly ozone-enhanced senescence. Premature senescence was paralleled by a significant ozone-induced reduction of green leaf area in Achillea ptarmica, E. cannabinum and Plantago lanceolata. At the intermediate harvest performed after 28 days shoot weights were significantly decreased by ozone in A. ptarmica and increased in Molinia caerulea. At the final harvest performed at the end of the growing season two other species, Cirsium dissectum and E. cannabinum had a significantly reduced shoot weight due to ozone. Root biomass was determined only at the intermediate harvest. The root:shoot ratio (RSR) was significantly reduced in C. dissectum, while it increased in M. caerulea. Seven of the species developed flowers during the experiment. While no significant ozone effects on flowering date and flower numbers were detected, flower weights were significantly reduced in E. cannabinum and P. lanceolata.     

Life-history QTLS and natural selection on flowering time in Boechera stricta, a perennial relative of Arabidopsis

Plants must precisely time flowering to capitalize on favorable conditions. Although we know a great deal about the genetic basis of flowering phenology in model species under controlled conditions, the genetic architecture of this ecologically important trait is poorly understood in nonmodel organisms. Here, we evaluated the transition from vegetative growth to flowering in Boechera stricta, a perennial relative of Arabidopsis thaliana. We examined flowering time QTLs using 7920 recombinant inbred individuals, across seven laboratory and field environments differing in vernalization, temperature, and photoperiod. Genetic and environmental factors strongly influenced the transition to reproduction. We found directional selection for earlier flowering in the field. In the growth chamber experiment, longer winters accelerated flowering, whereas elevated ambient temperatures delayed flowering. Our analyses identified one large effect QTL (nFT), which influenced flowering time in the laboratory and the probability of flowering in the field. In Montana, homozygotes for the native allele at nFT showed a selective advantage of 6.6%. Nevertheless, we found relatively low correlations between flowering times in the field and the growth chambers. Additionally, we detected flowering-related QTLs in the field that were absent across the full range of laboratory conditions, thus emphasizing the need to conduct experiments in natural environments.     

Do the phenology and functional stem attributes of woody species allow for the identification of functional groups in the semiarid region of Brazil?

The phenology of tree species in environments that are subject to strong climatic seasonality is mainly determined by water availability, which may vary as a function of wood density. The relationship among phenology, water potential, wood density and the capacity of water storage in the stem were determined for woody species of caatinga vegetation (dry forest) in the semiarid region of NE Brazil. Leaf flush and fall, flowering and fruiting events were recorded over a 31-month period, and the water potential was measured over a two-year period. These data were related to precipitation, water availability in the soil and photoperiod. Seven deciduous species exhibited low wood density (DLWD,?<0.5?g?cm^?3), high capacity of water storage in the stem (until 250?% of the dry weight) and high water potential during the year, as opposed to 15 deciduous species that showed high wood density (DHWD,?≥0.5?g?cm^?3). Leaf flush, flowering and the fruiting of DHWD species were related to precipitation, whereas these phenological events occurred at the end of the dry season and/or the beginning of the rainy season for DLWD species and were related to the photoperiod. The two evergreen species showed variations of water potential that were intermediate between those of DHWD and DLWD deciduous species, leaf flush during the dry season and flowering at the end of dry season. These results suggest the existence of three functional groups: evergreen species, DHWD deciduous species and DLWD deciduous species.     

Reproductive phenology of a wet forest understorey in the Western Ghats, South India

The reproductive phenology of 60 understorey species was monitored at monthly intervals for 20 months in a medium elevation wet evergreen forest in the Southern Western Ghats. The life forms monitored were herbs (including terrestrial orchids), shrubs and small trees. Flowering and fruiting were non‐uniform with a dry season flowering peak and wet season fruiting peak. Flowering in the understorey correlated negatively with rainfall. No significant correlation was detected for fruiting. Life forms had flowering and fruiting peaks at different times of the year.     

Vegetation disturbance by fire affects plant reproductive phenology in a shrubland community in northwestern Patagonia, Argentina

Reproductive phenology is likely to vary spatially with environmental conditions that alter microclimate, in particular temperature. We hypothesized that within the same plant community type, environmental changes produced by recent burning would alter plant phenological patterns and temporal structure of the plant community. Specifically, we predicted accelerated flowering and fruiting dates in the burned, open environment compared with the unburned, intact community. We tested this hypothesis in a post-fire tall shrubland (matorral) in northwestern Patagonia, Argentina. During the reproductive season, phenological stages of seven vascular plant species were monitored weekly. Temperature, humidity, soil nutrients and photosynthetically-active radiation were also recorded. At the burned site, flowering began earlier in all species and the success rate of fruiting was higher. These patterns correlated with significant environmental differences, including higher mean temperatures at the burned site.