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, 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]
The evolutionary and ecological drivers of the annual life cycle
editTraditionally, 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
editAnnual 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 more 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
editIn 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
edit- Biennial plant – Flowering plant that takes two years to complete its biological life cycle
- Perennial plant – Plant that lives for more than two years
- Monocarpic plant – Plants that flower and set seeds only once - Plant that flowers & sets seeds once, then dies.
- Ephemeral plant
References
edit- ^ a b c d e Poppenwimer, Tyler; Mayrose, Itay; DeMalach, Niv (8 November 2023). "Revising the global biogeography of annual and perennial plants". Nature. 624 (7990): 109–114. arXiv:2304.13101. doi:10.1038/s41586-023-06644-x. ISSN 1476-4687. PMC 10830411. PMID 37938778. S2CID 260332117.
- ^ Friedman, Jannice (2 November 2020). "The Evolution of Annual and Perennial Plant Life Histories: Ecological Correlates and Genetic Mechanisms". Annual Review of Ecology, Evolution, and Systematics. 51 (1): 461–481. doi:10.1146/annurev-ecolsys-110218-024638. ISSN 1543-592X. S2CID 225237602.
- ^ a b Hjertaas, Ane C.; Preston, Jill C.; Kainulainen, Kent; Humphreys, Aelys M.; Fjellheim, Siri (2023). "Convergent evolution of the annual life history syndrome from perennial ancestors". Frontiers in Plant Science. 13. doi:10.3389/fpls.2022.1048656. ISSN 1664-462X. PMC 9846227. PMID 36684797.
- ^ a b c Boyko, James D.; Hagen, Eric R.; Beaulieu, Jeremy M.; Vasconcelos, Thais (November 2023). "The evolutionary responses of life-history strategies to climatic variability in flowering plants". New Phytologist. 240 (4): 1587–1600. doi:10.1111/nph.18971. ISSN 0028-646X. PMID 37194450.
- ^ Charnov, Eric L.; Schaffer, William M. (November 1973). "Life-History Consequences of Natural Selection: Cole's Result Revisited". The American Naturalist. 107 (958): 791–793. doi:10.1086/282877. ISSN 0003-0147. S2CID 264255777.
- ^ Taylor, Amanda; Weigelt, Patrick; Denelle, Pierre; Cai, Lirong; Kreft, Holger (November 2023). "The contribution of plant life and growth forms to global gradients of vascular plant diversity". New Phytologist. 240 (4): 1548–1560. doi:10.1111/nph.19011. ISSN 0028-646X. PMID 37264995.
- ^ Díaz, Sandra; Lavorel, Sandra; McIntyre, Sue; Falczuk, Valeria; Casanoves, Fernando; Milchunas, Daniel G.; Skarpe, Christina; Rusch, Graciela; Sternberg, Marcelo; Noy-Meir, Imanuel; Landsberg, Jill; Zhang, Wei; Clark, Harry; Campbell, Bruce D. (February 2007). "Plant trait responses to grazing – a global synthesis". Global Change Biology. 13 (2): 313–341. Bibcode:2007GCBio..13..313D. doi:10.1111/j.1365-2486.2006.01288.x. hdl:11336/42236. ISSN 1354-1013. S2CID 84886127.
- ^ Clark, Adam Thomas; Knops, Johannes M. H.; Tilman, Dave (March 2019). Bardgett, Richard (ed.). "Contingent factors explain average divergence in functional composition over 88 years of old field succession". Journal of Ecology. 107 (2): 545–558. Bibcode:2019JEcol.107..545C. doi:10.1111/1365-2745.13070. ISSN 0022-0477.
- ^ Uricchio, Lawrence H.; Daws, S. Caroline; Spear, Erin R.; Mordecai, Erin A. (February 2019). "Priority Effects and Nonhierarchical Competition Shape Species Composition in a Complex Grassland Community". The American Naturalist. 193 (2): 213–226. doi:10.1086/701434. ISSN 0003-0147. PMC 8518031. PMID 30720356.
- ^ DeMalach, Niv; Shnerb, Nadav; Fukami, Tadashi (1 August 2021). "Alternative States in Plant Communities Driven by a Life-History Trade-Off and Demographic Stochasticity". The American Naturalist. 198 (2): E27–E36. arXiv:1812.03971. doi:10.1086/714418. ISSN 0003-0147. PMID 34260874. S2CID 226191832.
- ^ Vico, Giulia; Manzoni, Stefano; Nkurunziza, Libère; Murphy, Kevin; Weih, Martin (January 2016). "Trade-offs between seed output and life span – a quantitative comparison of traits between annual and perennial congeneric species". New Phytologist. 209 (1): 104–114. doi:10.1111/nph.13574. ISSN 0028-646X. PMID 26214792.
- ^ DeMalach, Niv; Kigel, Jaime; Sternberg, Marcelo (1 March 2023). "Contrasting dynamics of seed banks and standing vegetation of annuals and perennials along a rainfall gradient". Perspectives in Plant Ecology, Evolution and Systematics. 58: 125718. arXiv:2301.12696. doi:10.1016/j.ppees.2023.125718. ISSN 1433-8319. S2CID 256389403.
- ^ Glover, Jerry D.; Reganold, John P.; Cox, Cindy M. (September 2012). "Plant perennials to save Africa's soils". Nature. 489 (7416): 359–361. doi:10.1038/489359a. ISSN 1476-4687. PMID 22996532.
- ^ Foley, Jonathan A.; DeFries, Ruth; Asner, Gregory P.; Barford, Carol; Bonan, Gordon; Carpenter, Stephen R.; Chapin, F. Stuart; Coe, Michael T.; Daily, Gretchen C.; Gibbs, Holly K.; Helkowski, Joseph H.; Holloway, Tracey; Howard, Erica A.; Kucharik, Christopher J.; Monfreda, Chad (22 July 2005). "Global Consequences of Land Use". Science. 309 (5734): 570–574. Bibcode:2005Sci...309..570F. doi:10.1126/science.1111772. ISSN 0036-8075. PMID 16040698. S2CID 5711915.
- ^ Pimentel, David; Cerasale, David; Stanley, Rose C.; Perlman, Rachel; Newman, Elise M.; Brent, Lincoln C.; Mullan, Amanda; Chang, Debbie Tai-I (15 October 2012). "Annual vs. perennial grain production". Agriculture, Ecosystems & Environment. 161: 1–9. doi:10.1016/j.agee.2012.05.025. ISSN 0167-8809.
- ^ Melzer, S; Lens, F; Gennen, J; Vanneste, S; Rohde, A; Beeckman, T (2008). "Flowering-time genes modulate meristem determinacy and growth form in Arabidopsis thaliana". Nature Genetics. 40 (12): 1489–92. doi:10.1038/ng.253. PMID 18997783. S2CID 13225884.
External links
edit