Annual plant

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Peas are an annual plant. Doperwt rijserwt peulen Pisum sativum.jpg
Peas are an annual plant.

An annual plant is a plant that completes its life cycle, from germination to the production of seeds, within one growing season, and then dies. Globally, only 6% of all plant species and 15% of herbaceous plants (excluding trees and shrubs) are annuals. [1] The annual life cycle has independently emerged in over 120 different plant families throughout the entire angiosperm phylogeny. [2]

Contents

The evolutionary and ecological drivers of the annual life cycle

Traditionally, there has been a prevailing assumption that annuals have evolved from perennial ancestors. However, recent research challenges this notion, revealing instances where perennials have evolved from annual ancestors. [3] Intriguingly, models propose that transition rates from an annual to a perennial life cycle are twice as fast as the reverse transition. [4]

The life-history theory posits that annual plants are favored when adult mortality is higher than seedling (or seed) mortality, [5] i.e., annuals will dominate environments with disturbances or high temporal variability, reducing adult survival. This hypothesis finds support in observations of increased prevalence of annuals in regions with hot-dry summers, [1] [4] [6] with elevated adult mortality and high seed persistence. Furthermore, the evolution of the annual life cycle under hot-dry summer in different families makes it one of the best examples of convergent evolution. [1] [4] [3] Additionally, annual prevalence is also positively affected by year-to-year variability. [1]

Globally, the prevalence of annual plants shows an upward trend with an increasing human footprint. [1] Moreover, domestic grazing has been identified as contributing to the heightened abundance of annuals in grasslands. [7] Disturbances linked to activities like grazing and agriculture, particularly following European settlement, have facilitated the invasion of annual species from Europe and Asia into the New World.

In various ecosystems, the dominance of annual plants is often a temporary phase during secondary succession, particularly in the aftermath of disturbances. For instance, after fields are abandoned, annuals may initially colonize them but are eventually replaced by long-lived species. [8] However, in certain Mediterranean systems, a unique scenario unfolds: when annuals establish dominance, perennials do not necessarily supplant them. [9] This peculiarity is attributed to alternative stable states in the system—both annual dominance and perennial states prove stable, with the ultimate system state dependent on the initial conditions. [10]

Traits of annuals and their implication for agriculture

Annual plants commonly exhibit a higher growth rate, allocate more resources to seeds, and allocate fewer resources to roots than perennials. [11] In contrast to perennials, which feature long-lived plants and short-lived seeds, annual plants compensate for their lower longevity by maintaining a higher persistence of soil seed banks. [12] These differences in life history strategies profoundly affect ecosystem functioning and services. For instance, annuals, by allocating less resources belowground, play a minor role in reducing erosion, storing organic carbon, and achieving lower nutrient- and water-use efficiencies than perennials. [13]

The distinctions between annual and perennial plants are notably evident in agricultural contexts. Despite constituting a minor part of global biomass, annual species stand out as the primary food source for humankind, likely owing to their greater allocation of resources to seed production, thereby enhancing agricultural productivity. In the Anthropocene epoch, marked by human impact on the environment, there has been a substantial increase in the global cover of annuals. [14] This shift is primarily attributed to the conversion of natural systems, often dominated by perennials, into annual cropland. Currently, annual plants cover approximately 70% of croplands and contribute to around 80% of worldwide food consumption. [15]

Molecular genetics

In 2008, it was discovered that the inactivation of only two genes in one species of annual plant leads to its conversion into a perennial plant. [16] Researchers deactivated the SOC1 and FUL genes (which control flowering time) of Arabidopsis thaliana . This switch established phenotypes common in perennial plants, such as wood formation.

See also

Related Research Articles

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Flowering plants are plants that bear flowers and fruits, and form the clade Angiospermae, commonly called angiosperms. They include all forbs, grasses and grass-like plants, a vast majority of broad-leaved trees, shrubs and vines, and most aquatic plants. The term "angiosperm" is derived from the Greek words ἀγγεῖον / angeion and σπέρμα / sperma ('seed'), meaning that the seeds are enclosed within a fruit. They are by far the most diverse group of land plants with 64 orders, 416 families, approximately 13,000 known genera and 300,000 known species. Angiosperms were formerly called Magnoliophyta.

<span class="mw-page-title-main">Convergent evolution</span> Independent evolution of similar features

Convergent evolution is the independent evolution of similar features in species of different periods or epochs in time. Convergent evolution creates analogous structures that have similar form or function but were not present in the last common ancestor of those groups. The cladistic term for the same phenomenon is homoplasy. The recurrent evolution of flight is a classic example, as flying insects, birds, pterosaurs, and bats have independently evolved the useful capacity of flight. Functionally similar features that have arisen through convergent evolution are analogous, whereas homologous structures or traits have a common origin but can have dissimilar functions. Bird, bat, and pterosaur wings are analogous structures, but their forelimbs are homologous, sharing an ancestral state despite serving different functions.

<span class="mw-page-title-main">Embryophyte</span> Subclade of green plants, also known as land plants

The embryophytes are a clade of plants, also known as Embryophyta or land plants. They are the most familiar group of photoautotrophs that make up the vegetation on Earth's dry lands and wetlands. Embryophytes have a common ancestor with green algae, having emerged within the Phragmoplastophyta clade of freshwater charophyte green algae as a sister taxon of Charophyceae, Coleochaetophyceae and Zygnematophyceae. Embryophytes consist of the bryophytes and the polysporangiophytes. Living embryophytes include hornworts, liverworts, mosses, lycophytes, ferns, gymnosperms and angiosperms. Embryophytes have diplobiontic life cycles.

<span class="mw-page-title-main">Zamiaceae</span> Family of cycads

The Zamiaceae are a family of cycads that are superficially palm or fern-like. They are divided into two subfamilies with eight genera and about 150 species in the tropical and subtropical regions of Africa, Australia and North and South America.

<i>Hibiscus trionum</i> Species of flowering plant

Hibiscus trionum, commonly called flower-of-an-hour, bladder hibiscus, bladder ketmia, bladder weed, puarangi and venice mallow, is an annual plant native to the Old World tropics and subtropics. It has spread throughout southern Europe both as a weed and cultivated as a garden plant. It has been introduced to the United States as an ornamental where it has become naturalized as a weed of cropland and vacant land, particularly on disturbed ground.

The soil seed bank is the natural storage of seeds, often dormant, within the soil of most ecosystems. The study of soil seed banks started in 1859 when Charles Darwin observed the emergence of seedlings using soil samples from the bottom of a lake. The first scientific paper on the subject was published in 1882 and reported on the occurrence of seeds at different soil depths. Weed seed banks have been studied intensely in agricultural science because of their important economic impacts; other fields interested in soil seed banks include forest regeneration and restoration ecology.

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<span class="mw-page-title-main">Plant evolution</span> Subset of evolutionary phenomena that concern plants

Plant evolution is the subset of evolutionary phenomena that concern plants. Evolutionary phenomena are characteristics of populations that are described by averages, medians, distributions, and other statistical methods. This distinguishes plant evolution from plant development, a branch of developmental biology which concerns the changes that individuals go through in their lives. The study of plant evolution attempts to explain how the present diversity of plants arose over geologic time. It includes the study of genetic change and the consequent variation that often results in speciation, one of the most important types of radiation into taxonomic groups called clades. A description of radiation is called a phylogeny and is often represented by type of diagram called a phylogenetic tree.

<span class="mw-page-title-main">Hartig net</span> Network of inward-growing hyphae

The Hartig net is the network of inward-growing hyphae, that extends into the plant host root, penetrating between plant cells in the root epidermis and cortex in ectomycorrhizal symbiosis. This network is the internal component of fungal morphology in ectomycorrhizal symbiotic structures formed with host plant roots, in addition to a hyphal mantle or sheath on the root surface, and extramatrical mycelium extending from the mantle into the surrounding soil. The Hartig net is the site of mutualistic resource exchange between the fungus and the host plant. Essential nutrients for plant growth are acquired from the soil by exploration and foraging of the extramatrical mycelium, then transported through the hyphal network across the mantle and into the Hartig net, where they are released by the fungi into the root apoplastic space for uptake by the plant. The hyphae in the Hartig net acquire sugars from the plant root, which are transported to the external mycelium to provide a carbon source to sustain fungal growth.

Malcolm Colin Press is a British ecologist, professor and Vice-Chancellor of Manchester Metropolitan University (MMU), in the United Kingdom.

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<span class="mw-page-title-main">Annual vs. perennial plant evolution</span>

Annuality and perenniality represent major life history strategies within plant lineages. These traits can shift from one to another over both macroevolutionary and microevolutionary timescales. While perenniality and annuality are often described as discrete either-or traits, they often occur in a continuous spectrum. The complex history of switches between annual and perennial habit involve both natural and artificial causes, and studies of this fluctuation have importance to sustainable agriculture.

<span class="mw-page-title-main">Glacial survival hypothesis</span>

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<span class="mw-page-title-main">Mixed mating systems</span> Plants which reproduce in multiple ways

A mixed mating system, also known as “variable inbreeding” a characteristic of many hermaphroditic seed plants, where more than one means of mating is used. Mixed mating usually refers to the production of a mixture of self-fertilized (selfed) and outbred (outcrossed) seeds. Plant mating systems influence the distribution of genetic variation within and among populations, by affecting the propensity of individuals to self-fertilize or cross-fertilize . Mixed mating systems are generally characterized by the frequency of selfing vs. outcrossing, but may include the production of asexual seeds through agamospermy. The trade offs for each strategy depend on ecological conditions, pollinator abundance and herbivory and parasite load. Mating systems are not permanent within species; they can vary with environmental factors, and through domestication when plants are bred for commercial agriculture.

<span class="mw-page-title-main">Distyly</span>

Distyly is a type of heterostyly in which a plant demonstrates reciprocal herkogamy. This breeding system is characterized by two separate flower morphs, where individual plants produce flowers that either have long styles and short stamens, or that have short styles and long stamens. However, distyly can refer to any plant that shows some degree of self-incompatibility and has two morphs if at least one of the following characteristics is true; there is a difference in style length, filament length, pollen size or shape, or the surface of the stigma. Specifically these plants exhibit intra-morph self-incompatibility, flowers of the same style morph are incompatible. Distylous species that do not exhibit true self-incompatibility generally show a bias towards inter-morph crosses - meaning they exhibit higher success rates when reproducing with an individual of the opposite morph.

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