Plant strategies include mechanisms and responses plants use to reproduce, defend, survive, and compete on the landscape. The term “plant strategy” has existed in the literature since at least 1965, however multiple definitions exist. Strategies have been classified as adaptive strategies (through a change in the genotype), reproductive strategies, resource allocation strategies, ecological strategies, and functional trait based strategies, to name a few. While numerous strategies exist, one underlying theme is constant: plants must make

trade-off A trade-off (or tradeoff) is a situational decision that involves diminishing or losing one quality, quantity, or property of a set or design in return for gains in other aspects. In simple terms, a tradeoff is where one thing increases, and anot ...

s when responding to their

environment Environment most often refers to: __NOTOC__ * Natural environment, all living and non-living things occurring naturally * Biophysical environment, the physical and biological factors along with their chemical interactions that affect an organism or ...

. These trade-offs and responses lay the groundwork for classifying the strategies that emerge.

Background

The concept of plant strategies started gaining attention in the 1960s and 1970s. At this time, strategies were often associated with

genotypic The genotype of an organism is its complete set of genetic material. Genotype can also be used to refer to the alleles or variants an individual carries in a particular gene or genetic location. The number of alleles an individual can have in a ...

changes, such that plants could respond to their environment by changing their “genotypic programme” (i.e., strategy). Around this same time, the

r/K selection theory In ecology, ''r''/''K'' selection theory relates to the selection of combinations of traits in an organism that trade off between quantity and quality of offspring. The focus on either an increased quantity of offspring at the expense of individ ...

was introduced, which classifies plants by life history strategies, particularly reproductive strategies. In general, plants alter their reproductive strategies (i.e., number of

offspring In biology, offspring are the young creation of living organisms, produced either by a single organism or, in the case of sexual reproduction, two organisms. Collective offspring may be known as a brood or progeny in a more general way. This ca ...

) and their growth rate to respond to their

ecological niche In ecology, a niche is the match of a species to a specific environmental condition. Three variants of ecological niche are described by It describes how an organism or population responds to the distribution of resources and competitors (for ...

. The theory is still popular in the 21st century and frequently taught in science curricula. However, plant strategies really gained notoriety in 1977 with the introduction of

Grime Grime may refer to: * Dirt, in the form of black, ingrained dust * Grime (music genre), a genre of music * ''Grime'' (album), a 2001 album by Iniquity * ''Grime'' (video game), a 2021 Metroidvania video game * "Grime", a 2022 song by Dallas Woo ...

’s C-S-R Triangle, which categorizes plants according to how they respond under varying levels of

stress Stress may refer to: Science and medicine * Stress (biology), an organism's response to a stressor such as an environmental condition * Stress (linguistics), relative emphasis or prominence given to a syllable in a word, or to a word in a phrase ...

and

competition Competition is a rivalry where two or more parties strive for a common goal which cannot be shared: where one's gain is the other's loss (an example of which is a zero-sum game). Competition can arise between entities such as organisms, indiv ...

. According to

, plants develop strategies that demonstrate resource trade-offs between growth, reproduction, and maintenance. The association between genotypic change and strategies was also still present in Grime’s theories, as he noted that the “genotypes of the majority of plants appear to represent compromises between the conflicting selection pressures” that generally classify plants into three strategy types. The C-S-R Triangle remained the dominant plant strategy for several decades. However, in the early 1980s David Tilman introduced the R* theory, which focused on resource partitioning as strategies to deal with competition. More recently, additional strategies have been introduced. In 1998, the L-H-S strategy scheme was introduced as an alternative to Grime's C-S-R scheme. The L-H-S strategy focuses on

leaf A leaf ( : leaves) is any of the principal appendages of a vascular plant stem, usually borne laterally aboveground and specialized for photosynthesis. Leaves are collectively called foliage, as in "autumn foliage", while the leaves, ste ...

and seed mass traits to classify plant strategies, noting that these traits can be measured and compared between species, which cannot easily be done with Grime's abstract categories. The goal of the L-H-S scheme was to develop an international network that could provide quantifiable comparisons between plant strategies. This started a movement towards incorporating functional traits in plant strategies, and understanding how plant functional traits and

environmental factor An environmental factor, ecological factor or eco factor is any factor, abiotic or biotic, that influences living organisms. Abiotic factors include ambient temperature, amount of sunlight, and pH of the water soil in which an organism lives. Bi ...

s are related. While Grime's C-S-R Triangle is still frequently referenced in

plant ecology Plant ecology is a subdiscipline of ecology which studies the distribution and abundance of plants, the effects of environmental factors upon the abundance of plants, and the interactions among and between plants and other organisms. Examples ...

, new strategies are being introduced and gaining momentum in the 21st century.

Grime's C-S-R Triangle / Universal Adaptive Strategy Theory (UAST)

J. P. Grime identified two factor gradients, broadly categorized as disturbance and

, which limit plant biomass. Stresses include factors such as the availability of water, nutrients, and light, along with growth-inhibiting influences like temperature and toxins. Conversely, disturbance encompasses

herbivory A herbivore is an animal anatomically and physiologically adapted to eating plant material, for example foliage or marine algae, for the main component of its diet. As a result of their plant diet, herbivorous animals typically have mouthpart ...

pathogen In biology, a pathogen ( el, πάθος, "suffering", "passion" and , "producer of") in the oldest and broadest sense, is any organism or agent that can produce disease. A pathogen may also be referred to as an infectious agent, or simply a germ ...

s, anthropogenic interactions,

fire Fire is the rapid oxidation of a material (the fuel) in the exothermic chemical process of combustion, releasing heat, light, and various reaction products. At a certain point in the combustion reaction, called the ignition point, flames a ...

wind Wind is the natural movement of air or other gases relative to a planet's surface. Winds occur on a range of scales, from thunderstorm flows lasting tens of minutes, to local breezes generated by heating of land surfaces and lasting a few ho ...

, etc. Emerging from high and low combinations of stress and disturbance are three life strategies commonly used to categorize plants based on environment: (1) C-competitors, (2) S-stress tolerators, and (3) R- ruderals. There is no viable strategy for plants in high stress and high disturbance environments, therefore categorization for this habitat type is absent. Each life strategy varies in trade-offs of resource allocation to seed production,

leaf morphology The following is a list of terms which are used to describe leaf morphology in the description and taxonomy of plants. Leaves may be simple (a single leaf blade or lamina) or compound (with several leaflets). The edge of the leaf may be regular o ...

, leaf longevity,

relative growth rate Relative growth rate (RGR) is growth rate relative to size - that is, a rate of growth per unit time, as a proportion of its size at that moment in time. It is also called the exponential growth rate, or the continuous growth rate. Rationale RGR ...

, and other factors, which can be summarized as allocation to (1) growth, (2) reproduction, and (3) maintenance. Competitors are primarily composed of species with high relative growth rate, short leaf-life, relatively low seed production, and high allocation to leaf construction. They persist in high nutrient, low disturbance environments, and “rapidly monopolize resource capture by the spatially-dynamic foraging of roots and shoots.” Stress-tolerators, found in high stress, low disturbance habitats, allocate resources to maintenance and defenses, such as anti-herbivory. Species are often

evergreen In botany, an evergreen is a plant which has foliage that remains green and functional through more than one growing season. This also pertains to plants that retain their foliage only in warm climates, and contrasts with deciduous plants, whic ...

with small, long-lived leaves or needles, slow resource turnover, and low plasticity and relative growth rate. Due to high stress conditions, vegetative growth and reproduction are reduced. Ruderals, inhabiting low stress, high disturbance regimes, allocate resources mainly to seed reproduction and are often annuals or short-lived

perennials A perennial plant or simply perennial is a plant that lives more than two years. The term ('' per-'' + '' -ennial'', "through the years") is often used to differentiate a plant from shorter-lived annuals and biennials. The term is also widel ...

. Common characteristics of ruderal species include high relative growth rate, short-lived leaves, and short statured plants with minimal lateral expansion.

Tilman’s R* Rule

G. David Tilman developed the R* rule in support of resource competition theory. Theoretically, a plant species growing in

monoculture In agriculture, monoculture is the practice of growing one crop species in a field at a time. Monoculture is widely used in intensive farming and in organic farming: both a 1,000-hectare/acre cornfield and a 10-ha/acre field of organic kale are ...

, and utilizing a single limiting resource, will deplete the resource until reaching an equilibrium level where growth and losses are balanced. The concentration of the resource at the equilibrium level is termed R*; this is the minimum concentration at which the plant is able to persist in the environment. Population growth is indicated by values greater than the R*. Conversely, population decline is associated with values lower than the R*. If two species are competing for the same limiting

resource Resource refers to all the materials available in our environment which are technologically accessible, economically feasible and culturally sustainable and help us to satisfy our needs and wants. Resources can broadly be classified upon their ...

, the superior competitor will have the lowest R* value for that resource. This will eventually lead to the displacement of the inferior competitor, regardless of initial plant densities. Displacement rate depends on the magnitude of the difference in R*. Greater differences lead to a faster exclusion. Every plant species differs in R* values due to differences in plant morphology and

physiology Physiology (; ) is the scientific study of functions and mechanisms in a living system. As a sub-discipline of biology, physiology focuses on how organisms, organ systems, individual organs, cells, and biomolecules carry out the chemical ...

. The realized R* level is dependent on physical factors that vary by habitat, such as temperature, pH, and

humidity Humidity is the concentration of water vapor present in the air. Water vapor, the gaseous state of water, is generally invisible to the human eye. Humidity indicates the likelihood for precipitation, dew, or fog to be present. Humidity dep ...

Westoby’s L-H-S Strategy

In 1998, Mark Westoby proposed a plant ecology strategy scheme (PESS) to explain species distributions based on traits. The dynamic model incorporated a three axes trade-off among

specific leaf area Specific leaf area (SLA) is the ratio of leaf area to leaf dry mass. The inverse of SLA is Leaf Mass per Area (LMA). Rationale Specific leaf area is a ratio indicating how much leaf area a plant builds with a given amount of leaf biomass: SLA \ = ...

(SLA),

canopy Canopy may refer to: Plants * Canopy (biology), aboveground portion of plant community or crop (including forests) * Canopy (grape), aboveground portion of grapes Religion and ceremonies * Baldachin or canopy of state, typically placed over an ...

height at maturity, and seed mass. SLA is defined as the area per unit dry mass of mature leaves, developed in the fullest natural light of the species. These traits were selected for incorporation because of their trade-off functionality. Resource allocation to one trait is only possible by diverting resources from the others. Similarly to Grime's C-S-R triangle, each gradient represents different strategic responses to the environment; variation in disturbance adaptation is represented by canopy height and seed mass (Grime's R-axis), whereas SLA reflects variation in growth in response to stress (Grime's C-S axis). The L-H-S strategy avoids the assumption that high disturbance, high stress environments lack viable plant strategies, unlike Grime's model. However, Westoby's model is at a disadvantage when predicting potential variation in plant strategies since the axes only include single variables, compared to Grime's multivariable axes.

r/K Selection

This linear model, first introduced by MacArthur and Wilson (1967), has been commonly applied to both plants and animals to describe reproductive strategies. Representing opposing extremes of a continuum, r-species commit all energy into maximizing seed production with minimal input to individual propagules, whereas K-species allocate energy into a few, highly fit individuals; this is a spectrum of quantity versus quality. The model assumes that perfect r-species function under competitive-free environments with no density effects and K-species under maximum competitive and density saturation. Most species are categorized as intermediates between both extremes.

Summary

The term “plant strategies” has many definitions, and includes several different mechanisms for responding to one's environment. While different strategies focus on different plant characteristics, all strategies have an overarching theme: ''plants must make trade-offs between where and how to allocate resources''. Whether that's allocation to growth, reproduction, or maintenance, plants are responding to their environment by employing strategies that allow them to persist, survive, and reproduce. Plants may have multiple strategies to survive at different life-stages and therefore be subject to multiple trade-off throughout their life-cycle.

References

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