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.     

Vegetative and reproductive phenology of the mangrove Bruguiera gymnorrhiza (L.) Lam. on Okinawa Island, Japan

Vegetative and reproductive phenology of the subtropical mangrove Bruguiera gymnorrhiza was investigated at Manko Wetland, Okinawa Island, Japan. Phenology was assessed using litterfall data over 4 years. Leaf and stipule litterfall occurred throughout the year, with distinct seasonal patterns. Kendall’s coefficient of concordance, W, revealed that the monthly changes in leaf and stipule litterfall were strongly and significantly concordant among years. Leaf litterfall was linked to monthly day length and maximum wind speed, and stipule litterfall was linked to monthly mean air temperature, monthly rainfall, and maximum wind speed. Branch litterfall showed no clear monthly pattern, but tended to vary with monthly maximum wind speed. Mean leaf longevity was 19 months. Mean total litterfall was 10.1 Mg ha^?1 year^?1, with the largest component being vegetative organs (58 %). Flower and propagule litterfall were highest in autumn and summer, respectively, and lowest in winter. The W values revealed that, of the reproductive organs, only flower litterfall had a significant monthly trend. Flower litterfall was correlated with monthly mean air temperature and relative humidity. The average development periods from flower buds to flowers and from flowers to mature propagules were approximately 1 and 8 months, respectively. It took 9 months to produce mature propagules from flower buds. Except for branches, all vegetative and reproductive components of litterfall had clear annual cycles.     

青藏高原东缘高寒草甸植物群落的开花物候

利用2008年整个生长季的地面花期物候观测数据,初步研究了青藏高原东缘高寒草甸植物群落开花物候的动态、格局、参数间的联系及其与物种共存的关系.结果表明:植物群落的花期从5月初开始,8月上旬进入开花数目的高峰期,到10月初结束,遍及整个生长季节;不同物种进入花期的时间、峰值期及持续时间不同,各物种花期物候生态位相分离,但群落中大部分物种开花峰值期主要集中在7-8月;不同物种的开花峰值期时间与花期持续时间有负相关关系:开花越早的植物其花期持续时间越长;物种间的开花物候差异主要是由植物本身的特性和环境条件共同决定的,而群落水平上的开花物候格局主要受非生物因素的控制.

Abstract：

Based on the observation on the flowering phenology in the whole growth season of 2008, the dynamics, patterns, and relationships among various parameters of flowering phenology of alpine meadow plant community in eastern Qinghai-Tibetan Plateau were studied, and the potential effects of above-mentioned factors on the species coexistence of the plant community were approached. The flowering period of the plant community started from early May, came into peak period in the first ten days of August, and ended in early October, extending all over whole growth period. Different species had their different first flowering date, peak flowering period, and flowering duration, and their flowering phenologieal niches differentiated obviously. Most species had their peak flowering period centralized in July-August. There was a negative rela-tionship between peak flowering period and flowering duration: the earlier the flowering, the lon-ger the flowering duration. The differences in flowering phonology among the species were mainly determined by species per se characteristics and environmental conditions, but the flowering phe-nological pattern on community level was primarily controlled by abiotic factors.     

Phylogenetic conservatism and climate factors shape flowering phenology in alpine meadows

The study of phylogenetic conservatism in alpine plant phenology is critical for predicting climate change impacts; currently we have a poor understanding of how phylogeny and climate factors interactively influence plant phenology. Therefore, we explored the influence of phylogeny and climate factors on flowering phenology in alpine meadows. For two different types of alpine plant communities, we recorded phenological data, including flowering peak, first flower budding, first flowering, first fruiting and the flowering end for 62 species over the course of 5 years (2008–2012). From sequences in two plastid regions, we constructed phylogenetic trees. We used Blomberg’s K and Pagel’s lambda to assess the phylogenetic signal in phenological traits and species’ phenological responses to climate factors. We found a significant phylogenetic signal in the date of all reproductive phenological events and in species’ phenological responses to weekly day length and temperature. The number of species in flower was strongly associated with the weekly day lengths and followed by the weekly temperature prior to phenological activity. Based on phylogenetic eigenvector regression (PVR) analysis, we found a highly shared influence of phylogeny and climate factors on alpine species flowering phenology. Our results suggest the phylogenetic conservatism in both flowering and fruiting phenology may depend on the similarity of responses to external environmental cues among close relatives.     

Performance and phenology of alpine herbs along a snow-melting gradient

Responses of plants to the length of the growing season were studied in an alpine snow-bed by setting five plots along a snow-melting gradient. Performance and phenology were compared between the plots for five herbaceous species (Peucedanum multivittatum, Primula cuneifolia, Veronica stelleri var.longistyla, Solidago virga-aurea var.leiocarpa andPotentilla matsumurae). Performance characteristics measured were flower height, leaf height, leaf number, flower number and fruit number. In the late exposed plots with short snow-free periods, fruit-set was reduced in many species due to the decrease in flower number and/or the short growing season for fruit development.Veronica stelleri var.longistyla andSolidago virga-aurea var.leiocarpa, which decreased in flower and leaf numbers due to the short snow-free period, were sensitive to the short growing season.Peucedanum multivittatum was vigorous in the late exposed plots, but its slow flowering and fruiting prevented the fruit-set from developing in the last exposed plot.Primula cumeifolia andPotentilla matsumurae, quick flowering species that maintained their flower number throught the snow-melting gradient, were considered the most successful species in late exposed habitats.     

Calcium isotope fractionation in alpine plants

In order to develop Ca isotopes as a tracer for biogeochemical Ca cycling in terrestrial environments and for Ca utilisation in plants, stable calcium isotope ratios were measured in various species of alpine plants, including woody species, grasses and herbs. Analysis of plant parts (root, stem, leaf and flower samples) provided information on Ca isotope fractionation within plants and seasonal sampling of leaves revealed temporal variation in leaf Ca isotopic composition. There was significant Ca isotope fractionation between soil and root tissue $\Updelta^{44/42}\hbox{Ca}_{\rm root-soil} \approx -0.40\,\permille$ in all investigated species, whereas Ca isotope fractionation between roots and leaves was species dependent. Samples of leaf tissue collected throughout the growing season also highlighted species differences: Ca isotope ratios increased with leaf age in woody species but remained constant in herbs and grasses. The Ca isotope fractionation between roots and soils can be explained by a preferential binding of light Ca isotopes to root adsorption sites. The observed differences in whole plant Ca isotopic compositions both within and between species may be attributed to several potential factors including root cation exchange capacity, the presence of a woody stem, the presence of Ca oxalate, and the levels of mycorrhizal infection. Thus, the impact of plants on the Ca biogeochemical cycle in soils, and ultimately the Ca isotope signature of the weathering flux from terrestrial environments, will depend on the species present and the stage of vegetation succession.     

Leaf dynamics and shoot phenology of eleven warm-temperate evergreen broad-leaved trees near their northern limit in central Japan

Dynamic features of shoot phenology including leaf emergence and leaf fall, and leaf life span for eleven evergreen broad-leaved tree species were investigated in a warm-temperate rain forest in Mount Kiyosumi, central Japan. All species had periodic leaf emergence or flushing pattern, and were classified into two types; single and multiple flush and only one species, Eurya japonica, represented the latter type and the rest had single flush in spring. The single flush type can further be subdivided into two groups according to their duration of shoot growth; short and long flush. Seasonal patterns of leaf fall were categorized into four; unimodal, bimodal, broad unimodal, and multimodal type though they were not fixed pattern. The leaf emergence and leaf fall patterns were correlated for the eleven species, and five phenological types were categorized. Four of them were the single flush types, i.e., short flush of leaf emergence with unimodal leaffall (SSU) type of Castanopsis sieboldii and Quercus salicina, short flush with bimodal leaf fall (SSB) type of Quercus acuta, Machilus thunbergii, Neolitsea sericea, and Cinnamomum japonicum, long flush with bimodal leaffall (SLB) type of Myrsine seguinii, and long flush with broad unimodal leaffall (SLR) type of Symplocos prunifolia, Cleyera japonica, and Illicium anisatum. The multiple flush type is only one species, Eurya japonica, and it had multimodal leaffall pattern (MM type). The phenological pattern varied in relation to leaf life span, leaf size, and tree habit. Leaf life span ranged from 1.1 to 5.8 yr. The short flush species or SSU and SSB types were all canopy or subcanopy trees, and the former had short and the latter had long leaf life spans. The long flush species were all microphyllous small trees, and SLB type had a relatively long leaf life span in understory, SLR type had a long leaf life span in understory or in open habitat and/or forest gap as a pioneer tree. MM type had a long leaf life span and colonizing species in open habitat but they can survive in understory as well. The phenological attributes of evergreen trees were well corresponded to the ecological guild of the tree in both forest structure and successional stage, and were also constrained by phylogenetic groups.     

Nitrogen and carbon storage in alpine plants

Alpine plants offer unique opportunities to study the processesand economics of nutrient storage. The short alpine growingseason forces rapid completion of plant growth cycles, whichin turn causes competition between vegetative and reproductivegrowth sinks during the early part of the growing season. Mobilizationof stored nitrogen and carbon reserves facilitates competingsinks and permits successful completion of reproduction beforethe onset of winter stress. We discuss the theoretical frameworkfor assessing the costs and benefits of nutrient storage inalpine plants in order to lay the foundation for interpretationof observations. A principal point that has emerged from pasttheoretical treatments is the distinction between reserve storage,defined as storage that occurs with a cost to growth, and resourceaccumulation, defined as storage that occurs when resource supplyexceeds demand, and thus when there is no cost to growth. Wethen discuss two case studies, one already published and onenot yet published, pertaining to the storage and utilizationof nitrogen and carbon compounds in alpine plants from NiwotRidge, Colorado. In the first case, we tested the hypothesisthat the seasonal accumulation of amino acids in the rhizomeof N-fertilized plants of Bistorta bistortoides provides anadvantage to the plant by not imposing a cost to growth at thetime of accumulation, but providing a benefit to growth whenthe accumulated N is remobilized. We show that, as predicted,there is no cost during N accumulation but, not as predicted,there is no benefit to future growth. In the presence of N accumulation,reliance on stored N for growth increases, but reliance on current-season,soil-derived N decreases; thus the utilization of availableN in this species is a ‘zero sum’ process. Inherentmeristematic constraints to growth cause negative feedback thatlimits the utilization of accumulated N and precludes long-termadvantages to this form of storage. In the second case study,we discuss new results showing high concentrations of cyclicpolyol (cyclitol) compounds in the leaves of many alpine speciesdominant in the dry fellfield habitat. In Artemisia scopulorum,cyclitols were induced as the growing season progressed, andreached highest concentrations during the dry, late-summer months.Leaf cyclitol concentrations were high in all four species ofthe Caryophyllaceae that we examined and appeared to be constitutivecomponents of the leaf carbohydrate pool as concentrations werehigh through the entire growing season. We observed correlationsamong seedling abundance, seeding survivorship and the presenceof high leaf cyclitol concentrations. We propose that the primaryfunction of cyclitols in the leaves of alpine, fellfield herbsis to promote drought tolerance through osmotic protection,and enhance fitness by improving seedling survival. We consideredthe possibility that cyclitols also function as carbon storagecompounds that are remobilized at the end of the growing seasonand used to support growth the following year. Our observationsdo not support this hypothesis in the Caryophyllaceae becausethe requirement for high constitutive concentrations year-after-yearprevents long-term advantages of storage and remobilization.However, in A. scopulorum, remobilization of cyclitols followingthe end of the growing season may provide storage substratesthat can be used for growth the following season. From our analysiswe conclude that it is difficult to use current theory thatis embedded in the economic concept of costs and benefits tointerpret observed dynamics in nitrogen and carbon allocation.Future theoretical developments that move away from an abstractfoundation embedded in cost-benefit tradeoffs and toward phenotypicintegration of source-sink relationships will improve our abilityto merge observations and theory.     

Optimal phenology of annual plants under grazing pressure

Plants show phenological responses to herbivory. Some enclosure experiments have demonstrated that the onset of the peak flowering season is dependent on grazing pressure. We constructed a mathematical model using Pontryargin's maximum principle to investigate changes in flowering time by examining shifts in resource allocation from vegetative to reproductive plant components. We represented a primary production of a plant individual by two types of function of vegetative part size, a linear function and a convex non-linear function. The results of a linear production model indicate that optimal phenology follows a schedule that switches from the production of vegetative parts to that of reproductive parts at a given time ('bang-bang' control). However, in a non-linear model, a singular control, wherein the plant invests in both productive and reproductive parts, may be included between obligate production and reproduction periods. We assumed that the peak of the flowering season occurs immediately following the exclusive investment in reproduction. In a linear production model, differential herbivory rates on the vegetative and reproductive parts of a plant resulted in shifts in the peak flowering time. A higher herbivory rate on the vegetative components advanced the peak, whereas it was delayed when grazing pressure focused on reproductive components of the plant. In the non-linear production model, increased grazing pressure tended to postpone the flowering peak. These results corresponded well with results of enclosure experiments, thus suggesting adaptive control of flowering time in plants.     

Leaf anatomy and photosynthetic characteristics of succulent alpine plants growing at high elevations

Sempervivum monlanum and Saxifraga particulate are succulent alpine plants, with flat leaves, growing at up to 3300 m; Sedum atraium , with cylindrical leaves, is only present at the highest elevations. We have made a preliminary study of the photosynthetic mechanism (C, or CAM) of these species in relation to morphological and ultrastructural differences. The following physiological parameters were determined in plants collected at 3000 m: δ¹³C, night/day variations of titratable acidity and kinetic properties (Vmax, Km, S_0.5, n) of phosphoenolpyruvate carboxylase (EC 4.1.1.31). The results suggest that, even at the highest elevations, the photosynthetic system can be obligate CAM ( Sempervivum monlanum ), facultative C₃-CAM ( Sedum atratum ) or obligate C, ( Saxifraga paniculata ). Other parameters such as chlorophyll a/b ratio, succulence and succulence of mesophyll were measured and the results were consistent with the above mechanisms. Morphological analyses were performed by using LM, SEM and TEM. Sempervivum monlanum (CAM) leaves were found to differ from those of Saxifraga paniculata (C,) in having fewer thyreoids per granum, more plastoglobules per chloroplast, a higher plastoglobule relative density and a lower stomatal density. In Sedum atratum (facultative C₃-CAM) corresponding values were intermediate.     

Seedling establishment and life history trade-offs in alpine plants

Seedling establishment is central to population maintenance for nonclonal plant species. Plants with low recruitment rates are expected to have high survival rates, and life history theory indicates there should be a single curve for the trade-off between recruitment and mortality that applies to most or all plant species. Alpine perennials are thought to have extraordinarily low recruitment rates because of the harsh environment, but the importance of recruitment in the life history of these plants is unknown. Two alpine cushion plant species, Minuartia obtusiloba and Paronychia pulvinata, were used to (1) determine the role of recruitment in population maintenance and (2) determine whether the fecundity/mortality trade-off for these alpine plants falls on or off of the curve for other perennial plant species. Using size-based population projection matrices, we determined that the life history of Minuartia and Paronychia emphasizes recruitment less than that of any other nonclonal species in a literature survey. Estimated maximum life spans of these two species are 200 and 324 yr, respectively, and a regression with other perennial species from the literature indicated that the relationship between fecundity and mortality in these alpine species is consistent with the predicted trade-off curve for perennial species from other environments.     

Some views on plants in polar and alpine regions

Many plants growing in polar and alpine regions clearly solve serious problems of life under extreme climatic conditions, as low temperatures, strong winds, unstable soils and in the North partly 24-h of light.     

Asynchronicity in root and shoot phenology in grasses and woody plants

Phenology is central to understanding vegetation response to climate change, as well as vegetation effects on plant resources, but most temporal production data is based on shoots, especially those of trees. In contrast, most production in temperate and colder regions is belowground, and is frequently dominated by grasses. We report root and shoot phenology in 7‐year old monocultures of 10 dominant species (five woody species, five grasses) in southern Canada. Woody shoot production was greatest about 8 weeks before the peak of root production, whereas grass shoot maxima preceded root maxima by 2–4 weeks. Over the growing season, woody root, and grass root and shoot production increased significantly with soil temperature. In contrast, the timing of woody shoot production was not related to soil temperature (r=0.01). The duration of root production was significantly greater than that of shoot production (grasses: 22%, woody species: 54%). Woody species produced cooler and moister soils than grasses, but growth forms did not affect seasonal patterns of soil conditions. Although woody shoots are the current benchmark for phenology studies, the other three components examined here (woody plant roots, grass shoots and roots) differed greatly in peak production time, as well as production duration. These results highlight that shoot and root phenology is not coincident, and further, that major plant growth forms differ in their timing of above‐ and belowground production. Thus, considering total plant phenology instead of only tree shoot phenology should provide a better understanding of ecosystem response to climate change.     

Flowering phenology of a palm community in a central Amazon forest

The flowering phenology of 27 taxa of palms in a lowland moist forest in the central Amazon was recorded over a 40 month period. Phenological data were transformed into measures, of synchrony, regularity, and duration. Flowering was observed at all times of year and there was no correlation with rainfall either for the current month or for any monthly lag interval. The 27 taxa were divided into three pollination groups—weevil, bee/fly, or beetle—based on their behavior at anthesis. Phenology was significantly correlated with pollination groups. Weevilpollinated palms had higher synchrony and shorter duration of flowering than other groups. Bee/fly-pollinated palms had lower synchrony and longer duration of flowering. The beetle-pollinated palms were intermediate between the two other groups. Seasonal regularity of flowering was similar in all three groups. We suggest that, at least inBactris, taxa exhibit staggered flowering.