Short-lived Plant Species Research Articles

Germination strategies of annual and short-lived perennial species in the Arabian Desert

Germination timing is highly regulated in short-lived plant species since it strongly influences recruitment success of vegetation. In deserts, the spatiotemporal distribution of plant-available water is highly episodic and unpredictable, making winter months more favorable for seed germination when other abiotic conditions co-occur. We hypothesized that changes in photoperiod and thermoperiod would impact germination more in seeds that had undergone in situ storage. We assessed 21 annual and short-lived perennial species in the Arabian Desert to find (1) if seeds were dormant at maturity, (2) if in situ seed storage increased germination percentage compared with no storage, (3) if photoperiod and thermoperiod germination requirements were influenced by in situ storage, and (4) if a phylogenetic association in seed germination could be observed. Seeds of each species collected in early 2017 were divided into two batches. One was tested for germination within one week (fresh seeds). The other was stored in situ at the maternal location (stored seeds) until October 2017 and tested for seed germination in the first week of November. Seed germination was conducted in incubators at two thermoperiods (15°C/20°C and 20°C/30°C; 12 h/12 h), and two photoperiods (12 and 0 h light per day). Results indicated that seed germination percentages of 13 species were significantly enhanced by in situ storage. A thermoperiod response was exhibited by stored, but not fresh seeds. Light exposure increased germination of fresh seeds but had only a minimal effect on stored seeds. Germination traits exhibited no phylogenetic correlation. This result indicated that selection pressure for germination strategy was stronger than that for taxonomic traits of these desert species.

Fast–slow continuum and reproductive strategies structure plant life-history variation worldwide

The identification of patterns in life-history strategies across the tree of life is essential to our prediction of population persistence, extinction, and diversification. Plants exhibit a wide range of patterns of longevity, growth, and reproduction, but the general determinants of this enormous variation in life history are poorly understood. We use demographic data from 418 plant species in the wild, from annual herbs to supercentennial trees, to examine how growth form, habitat, and phylogenetic relationships structure plant life histories and to develop a framework to predict population performance. We show that 55% of the variation in plant life-history strategies is adequately characterized using two independent axes: the fast-slow continuum, including fast-growing, short-lived plant species at one end and slow-growing, long-lived species at the other, and a reproductive strategy axis, with highly reproductive, iteroparous species at one extreme and poorly reproductive, semelparous plants with frequent shrinkage at the other. Our findings remain consistent across major habitats and are minimally affected by plant growth form and phylogenetic ancestry, suggesting that the relative independence of the fast-slow and reproduction strategy axes is general in the plant kingdom. Our findings have similarities with how life-history strategies are structured in mammals, birds, and reptiles. The position of plant species populations in the 2D space produced by both axes predicts their rate of recovery from disturbances and population growth rate. This life-history framework may complement trait-based frameworks on leaf and wood economics; together these frameworks may allow prediction of responses of plants to anthropogenic disturbances and changing environments.

Investigating the likelihood of a reservoir offset in the radiocarbon record for ancient Egypt

Some radiocarbon dates for ancient Egypt have been significantly offset from the established historical chronology (see Bonani et al., 2001). In this paper, short-lived plant species collected in Egypt between 1700 and 1900 AD were used to investigate the possibility that the radiocarbon record had been influenced by reservoir effects. AMS radiocarbon measurements were made on 66 known-age samples, resulting in an average offset from expected values of 19 years. The implications of this minor discrepancy on the likelihood of a reservoir process are discussed, and the agreement of the data with recent models of radiocarbon seasonality is also considered.

Plant responses to agricultural intensification

Summary 1. A large proportion of the world's land surface is extensively managed for livestock production. In areas where livestock systems are becoming more intensive, a major challenge is to predict those plant species likely to decline, persist or increase as a result of agricultural intensification. 2. Most analyses develop inferences for frequent or abundant species, or rely on intensive studies of single species. A promising approach is to identify plant traits related to disturbance to enable inference to be made about changes in plant community composition. We used a Bayesian hierarchical model to analyse the response to agricultural intensification of 494 plant species of pastures and woodlands in southern Australia, and to identify how simple species' traits (life form, growth form and species origin) influence those responses. 3. The probability of occurrence of most species declined along the two intensification gradients, grazing intensity and soil phosphorous concentration, although the occurrence of a greater proportion of species was negatively correlated with soil phosphorous. Responses could be broadly predicted from both plant origin and plant traits, in particular growth form. 4. Native perennial geophytes, ferns and shrubs were most negatively affected by both gradients, while exotic annual grasses and forbs were more tolerant. Along the phosphorous gradient, 24 of the 30 most negatively affected plant species were native geophytes. Mean within-group responses masked considerable within- and between-species variation, particularly for the exotic species group which included species that responded both negatively and positively to intensification. 5. Synthesis and applications. The hierarchical model described here provides a powerful method for estimating individual plant responses and identifying how species' traits influence those responses. Plant species native to southern Australia are sensitive to grazing and phosphorous apparently due to a shared evolutionary history of low grazing intensity and low phosphorous soils. Invading exotic plants have faced strongly contrasting ecological filters, leading to a greater diversity of responses. Where grazing systems have been most intense, a small suite of exotics dominate. Maintaining native and functional plant diversity will necessitate limits being placed on intensive livestock management systems.

Effects of fragment size and isolation on the occurrence of four short-lived plants in semi-natural grasslands

Habitat fragmentation is predicted to lead to an area-related reduction in population size and a decreasing colonisation rate due to isolation. A reduction in grassland size may promote a “run-away-decline process” leading to reduced individual fitness and viability of the populations originally inhabiting the grassland. To circumvent the problems of time-lags associated with the slow response of long-lived plants to semi-natural grassland fragmentation, four short-lived grassland species were studied. During three years, data on population sizes were gathered for Carum carvi, Rhinanthus minor, Trifolium arvense and Viola tricolor in Swedish semi-natural grasslands varying in size and degree of isolation. A seed-sowing experiment was conducted to assess dispersal and seed limitation at a local and regional scale, respectively. Overall, the presence/absence of species was not related to fragment size and isolation (connectivity). However, for the fragments where the species were present, positive relationships between grassland size and population size were detected for three species. No significant relationships between isolation and population size were detected for any species. This study thus demonstrates that short-lived plant species, confined to semi-natural grasslands, respond to decreases in fragment size by forming smaller populations. Seed sowing indicated that the species are both dispersal and seed limited in the study area, and that disturbances are important for establishment. In order to maintain characteristic grassland species in fragmented (isolated) semi-natural grasslands, it may therefore be of interest to preserve large intact fragments instead of several small ones.

Herbaceous vegetation of seasonally wet habitats on inselbergs and lateritic crusts in West and Central Africa

Inselbergs, mountain ridges and lateritic crusts are characteristic landscape elements in many tropical regions. They are of great interest from a botanical point of view. Their vegetation is relatively uniform and differs from the surrounding vegetation. The first synopsis of herbaceous vegetation of seasonally wet or inundated habitats on rocks, inselbergs, mountain ridges and lateritic crusts in several bioclimatic zones of tropical West Africa and Atlantic Central Africa is presented. A classification of 43 partial data sets, based on 378 releves, resulted in four associations and several rankless communities, grouped into four different classes (Drosero-Xyridetea, Afrotrilepidetea pilosae, Lycopodietea cernui andMicrochloetea indicae). Plant communities from Atlantic Central Africa and West Africa are very distinct from a floristic point of view; in an ordination, they are clearly separated. TheDrosero indicae-Utricularietalia subulatae (Drosero-Xyridetea) comprises ephemeral vegetation in rock pools and depressions over lateritic crusts. It contains theEriocaulo pumili-Ophioglossion gomezianum, which combines communities with short-lived plant species in small pools on rock outcrops and in shallow depressions over laterite, and theGenliseo africanae-Sporobolion pauciflori, which colonizes similar habitats but is geographically restricted to few mountains in Guinea, Sierra Leone and Liberia. Mats of monocytyledonous plants (Afrotrilepidetea pilosae, Afrotrilepidetalia pilosae) are very widespread in humid parts of tropical West Africa. They colonize gentle slopes and are often close to communities of theDrosero-Utricularietalia subulatae. Three alliances can be distinguished: West African alliancesCyanotido lanatae-Afrotrilepidion pilosae andSpermacoco hepperanae-Afrotrilepidion pilosae, and an Atlantic Central AfricanOreonesiono testui-Afrotrilepidion pilosae. Small-sacle alterations of the ecological situation often result in a mosaic-like pattern of the plant communities. Especially small inselberg and rock outcrop habitats are often affected by heavy fluctuations of their environmental and climatic conditions. Besides regular short-term dynamics, there are also long-term vegetation dynamics with cycles spanning several years.

Temporal changes affect plant chemistry and tritrophic interactions

In nature, individuals of short-lived plant species (e.g. annuals, biennials) may grow at different times during the growing season. These plants are therefore exposed to different season-related conditions such as light and temperature, which in turn may have consequences for primary and secondary chemistry of the plant. Despite this, many studies examining plant–consumer interactions are performed in single replicates, which may thus ignore temporal variation in the expression of phenotypic plant traits that affect multitrophic interactions. In the present study, we demonstrated that even under strictly controlled conditions in a greenhouse, secondary plant chemistry changes dramatically in plants growing at different times in a single year, i.e. July, August and November. Glucosinolate (GS) contents in herbivore-damaged leaves of two different crucifer species, Brassica oleracea and Sinapis alba were higher in the August and November replicates than in the July replicate and GS concentrations were 10–25 times higher in S. alba than in B. oleracea. The development of a specialist herbivore, Plutella xylostella, also varied significantly over the three replicates. Larvae of P. xylostella that had fed upon either S. alba or B. oleracea, attained the largest biomass and had the fastest development rate in the November replicate. Female P. xylostella moths grew larger on S. alba than on B. oleracea, whereas male biomass was not significantly affected by host-plant species. Plant species, but not season also affected performance of the endoparasitoid, Diadegma semiclausum. Similar to the performance of host females, parasitoid males developed faster and attained the highest biomass when attacking P. xylostella larvae feeding on S. alba. Most importantly, the performance of the herbivore and its parasitoid only appeared to partially conform to levels of GS in damaged leaves, indicating that there is a complex of factors involved in determining the effects of plant quality on higher trophic levels.

Disturbance, life history, and optimal management for biodiversity.

Both frequency and intensity of disturbances in many ecosystems have been greatly enhanced by increasing human activities. As a consequence, the short-lived plant species including many exotics might have been dramatically increased in terms of both richness and abundance on our planet, while many long-lived species might have been lost. Such conclusions can be drawn from broadly observed successional cycles in both theoretical and empirical studies. This article discusses 2 major issues that have been largely overlooked in current ecosystem management policies and conservation efforts: i) life history constraints; and ii) future global warming trends. It also addresses the importance of these 2 factors in balancing disturbance frequency and intensity for optimal biodiversity maintenance and ecosystem management.

Nutrient requirements of ephemeral plant species from wet, mesotrophic soils

Abstract. Nanocyperion plant communities occur on wet, more or less nutrient‐poor and sparsely vegetated soils in temperate climates and are characterized by tiny, very shortlived plant species. Most of these have become locally extinct. It is generally assumed that drainage and eutrophication were the most important reasons for this decrease. However, chemical analysis of soil pore water from plots on growth sites of these ephemerals showed that phosphorus availability was relatively high.In a greenhouse experiment, the growth of ephemeral species was strongly limited by the amount of available phosphorus, whereas there was little or no limitation to the growth of other plant species from this habitat. At low phosphorus concentrations, the ephemeral species reached their reproductive phase within the same period, but showed a strong reduction in the amount of flowers that were produced. We concluded that ephemeral species in particular require a minimum amount of phosphorus for reproduction. Other species on nutrient‐poor, wet soils have a longer life span and can postpone flowering in nutrient‐poor soils.In contrast to other short‐lived plant species from the same habitat, the growth of ephemeral species was barely stimulated by enhanced nitrogen availability. Apparently, the ephemerals are adapted to low nitrogen concentrations. The occurrence on nitrogen‐poor and relatively phosphorus‐rich soils suggests that this community may be very sensitive to nitrogen deposition. Reduced phosphorus availability below the minimum requirements of ephemerals, for example after acidification or the exclusion of human activities, has possibly contributed to the decrease of ephemeral plant species.

RESPONSES OF SUBALPINE MEADOW VEGETATION TO FOUR YEARS OF EXPERIMENTAL WARMING

Ecosystems at high elevations may be especially sensitive to global warming, because productivity is limited to a snow-free growing season, and warming is expected to cause earlier snowmelt. Here we report on vegetation responses to experimental warming in a subalpine meadow in the Colorado Rocky Mountains. We found no evidence that the plant community changed during four years of warming. Species composition in warmed plots did not change more through time than in control plots, nor did warmed plots diverge from adjacent control plots through time. Contrary to an earlier report, we found no evidence that warming facilitated adults or seedlings of sagebrush, a shrub characteristic of lower elevation ecosystems; nor did it facilitate short-lived plant species as a group. Total vegetation cover, as well as cover of graminoids, forbs, and shrubs, did not differ between control and warmed plots, nor did species richness or species' distributions along a small elevational gradient within each plot. Shrub cover tended to increase more, and forb cover to decrease more, in warmed than in control plots during one summer season, but not significantly so. This lack of detectable plant community response contrasts with pronounced responses to warming in some arctic and alpine ecosystems over similar time spans. Warming in these ecosystems is thought to act indirectly via increased mobilization of soil nutrients. One possible reason for the lack of response in our system is that drying of soil limits microbial activity, photosynthesis, and plant growth sooner in the season in warmed plots, canceling out effects of earlier snowmelt. If this is correct, and if summer precipitation patterns are unchanged under global warming, then vegetation in arid high-elevation ecosystems may change only slowly.

On the ecology of short-lived forbs in chalk grasslands: micro-site tolerances in relation to vegetation structure

Some aspects of vegetation structure in two chalk grasslands were studied throughout the year in relation to the occurrence of some short-lived plant species per life-cycle stage. Whereas the main growth period is in May–June, there is another relatively important growth period in less productive stands in August. When the species are arranged in the order of their tolerance for less to more productive micro-sites during the adult life phase the following sequence emerges considering a generally weak significance in the results. Carlina vulgaris, Euphrasia officinalis, Gentianella germanica, and Scabiosa columbaria, Linum catharticum, Anthyllis vulneraria, and Daucus carota. In some species this preference was found to shift from seedling to vegetative and reproductove phase. Each life phase usually has its special abundance with regard to vegetation density.

Do Grazers Maximize Individual Plant Fitness?

The hypothesis of Owen and Wiegert stating that grazers may increase individual plant fitness has been found plausible from a theoretical point of view by analyzing two mathematical models. The technique adapted is to search for evolutionarily stable strategies (or ESS) in a system where the plant's palatability is the only evolutionary variable considered. It is concluded that the fitness of particularly shortlived plant species is enhanced when grazed by animals wasting extensive amounts of clipped vegetation and/or defecating close to the eaten plant. Based on this, several generalizations are stated: The hypothesized form of mutualism is (1) more likely to apply for plants which are r-strategists than K-strategists; (2) more likely to apply in early successional stages than close to climax; and (3) more likely in terrestrial than in aquatic systems. Furthermore (4), a gradient with respect to herbivore defense features as a function of plant life histories is likely to exist only in systems with extensive grazing pressure. From these discussions it is concluded that theories for herbivore population regulation relying on mechanisms such as toxic substances in plants are mainly likely to apply for herbivores feeding on long lived plant species. Lastly it is concluded that further theoretical studies on herbivory might prove rewarding by supplementing such studies on predator-prey interactions.