**4. Characteristics of wild plasticity: examples in trees and weeds**

Phenotypic plasticity, especially within wild plant populations, is a mechanism that enhances plant invasion and survival [12]. The invasiveness of a plant species is influenced by many phenotypic characteristics and responses [12]. The three major phenotypic characteristics that impact plasticity in wild plant populations are plant development, plant morphology, and plant physiology (**Figure 2**) [36]. Phenotypic responses associated with each characteristic occur at every stage of plant development, influencing the overall plasticity from generation to generation (**Figure 2**). Common phenotypic responses known to be associated with plant development, plant morphology, and plant physiology include: (1) rapid seedling growth allowing maximum capture of light, water, and nutrients [37–41], (2) a short vegetative phase allowing life cycle completion in various growing seasons and conditions [42–47], (3) deep root systems allowing plants to survive through drought conditions [47, 48], (4) high seed output ensuring spatial and temporal dispersal, (5) discontinuous or extensive seed dormancy ensuring germination only in favorable conditions [49–51], (6) efficient

### **Figure 2.**

*The key characteristics and responses of wild plant plasticity including plant development (green), plant morphology (yellow), and plant physiology (blue) [1, 13, 36–53].*

**43**

adapted species [14].

*Phenological Plasticity of Wild and Cultivated Plants DOI: http://dx.doi.org/10.5772/intechopen.85070*

abiotic environmental factors [1, 13].

cellular machinery for scavenging reactive oxygen species (ROS) [52, 53], and (7) environmental plasticity, or the ability to respond to changing biotic or

environment [58]. However, if a given climatic event exceeds the limit of

adaptive capacity, the same population of trees may also be replaced by a new, more

Plasticity in weeds, as with trees, is governed by adaptive responses that impact physiology, morphology, and anatomy [36]. However, unlike trees, many weed species have relatively short life spans and must make rapid and frequent adjustments to environmental changes to ensure survival [16]. In addition to the wild characteristics for plasticity listed above, other characteristics in weeds that demonstrate enhanced phenotypic plasticity include: discontinuous or extensive seed dormancy ensuring germination only in favorable conditions, indeterminant or simultaneous flowering and vegetative growth, self-compatibility allowing genetic divergence from previous generations without requiring special pollinators to ensure seed viability, long-distance seed dispersal by air or water; competition with crop plants resulting in reduced crop yield, sexual and asexual reproduction strategies; and allelopathy, or the ability to produce chemicals that retard or kill other plants (**Figure 2**) [16, 36, 61]. Adaptive responses in weeds occur throughout development [16, 36]. Sometimes adaptive responses are more apparent in plant architecture than in signaling responses, are more pronounced at certain developmental stages or in specific populations, or involve the same tissue types during different developmental phases [1, 16, 36, 61]. The invasiveness of weeds is thought to be associated with several phenotypic plasticity traits including plant height, flower development, flowering, and light quality, [62, 63]. A direct correlation between plant height and invasiveness remains unclear. However, there may be an association between tall plant phenotypes, increased phenotypic diversity,

Phenotypic plasticity was first described for non-cultivated plants species including trees and weeds [1, 4, 12, 17–20, 54]. Trees are excellent models for studying phenotypic plasticity due to their longevity [12]. Trees have developed a diverse set of plasticity mechanisms that are specific for both short and long development programs occurring in different developmental tissues at the same time [12]. Simultaneous root and leaf canopy development are an example of parallel programing [12, 54]. Phenotypic plasticity in trees occurs through a diverse collection of physiological, anatomical, and morphological responses [12, 54]. Many studies exploring global warming have investigated the possibility of using physiological or morphological indicators of beneficial adaptive responses as predictors of species survival [1]. Adaptive mechanisms in trees, as well as other plants, are important for mitigating the stress that is associated with fluctuations in native environments or, after new colonization, for rapid adaptation to novel environments [54–57]. Studies investigating drought stress in trees have shown that by reducing the leaf canopy and increasing root proliferation, trees become more drought tolerant because both phenotypic responses limit water loss [58]. The occurrence of phenotypic responses occurring in parallel suggests that there may be a coordinated regulation of these traits [59, 60]. Other traits indicative of drought responses and plasticity in trees include leaf area, leaf dry mass, leaf mass per area (LMA), leaf tissue density, net photosynthesis, stomatal conductance, leaf respiration, water use efficiency, leaf water potential at midday, total chlorophyll content, relative water content, gross photosynthesis, leaf transpiration, and the ratio between leaf respiration and net photosynthesis [58]. Drought avoidance may also be viewed as a strategy for drought tolerance by altering the timing of growth and reproduction [14]. By maximizing the adaptive response of traits related to drought response, the overall fitness of an existing population of trees has the potential to adapt to a new

*Plant Communities and Their Environment*

selection [13, 33, 34].

Not all adaptive strategies are beneficial for plants and often result in decreased

All phenotypic responses, neutral, positive, and negative, may occur simultaneously within an individual or across a population (**Figure 1f**) [13]. Changes in plasticity may be measured by examining the relationship between a specific genotype (G) in a specific environment (E) [13]. A genotype-by-environment (GXE) study tracks genetic plasticity and is a powerful tool for targeted genotypic

**4. Characteristics of wild plasticity: examples in trees and weeds**

Phenotypic plasticity, especially within wild plant populations, is a mechanism that enhances plant invasion and survival [12]. The invasiveness of a plant species is influenced by many phenotypic characteristics and responses [12]. The three major phenotypic characteristics that impact plasticity in wild plant populations are plant development, plant morphology, and plant physiology (**Figure 2**) [36]. Phenotypic responses associated with each characteristic occur at every stage of plant development, influencing the overall plasticity from generation to generation (**Figure 2**). Common phenotypic responses known to be associated with plant development, plant morphology, and plant physiology include: (1) rapid seedling growth allowing maximum capture of light, water, and nutrients [37–41], (2) a short vegetative phase allowing life cycle completion in various growing seasons and conditions [42–47], (3) deep root systems allowing plants to survive through drought conditions [47, 48], (4) high seed output ensuring spatial and temporal dispersal, (5) discontinuous or extensive seed dormancy ensuring germination only in favorable conditions [49–51], (6) efficient

*The key characteristics and responses of wild plant plasticity including plant development (green), plant* 

*morphology (yellow), and plant physiology (blue) [1, 13, 36–53].*

fitness or yield [35]. A maladaptive response describes a phenomenon which reflects the absence of plasticity (**Figure 1e**) [34]. Maladaptive responses are not easy to distinguish from neutral responses because the average response of the population may mask any decline in response by individuals within the population over a long period of time [35]. Maladaptive responses are often misinterpreted as

adaptive responses and difficult to study genetically [34, 35].

**42**

**Figure 2.**

cellular machinery for scavenging reactive oxygen species (ROS) [52, 53], and (7) environmental plasticity, or the ability to respond to changing biotic or abiotic environmental factors [1, 13].

Phenotypic plasticity was first described for non-cultivated plants species including trees and weeds [1, 4, 12, 17–20, 54]. Trees are excellent models for studying phenotypic plasticity due to their longevity [12]. Trees have developed a diverse set of plasticity mechanisms that are specific for both short and long development programs occurring in different developmental tissues at the same time [12]. Simultaneous root and leaf canopy development are an example of parallel programing [12, 54]. Phenotypic plasticity in trees occurs through a diverse collection of physiological, anatomical, and morphological responses [12, 54]. Many studies exploring global warming have investigated the possibility of using physiological or morphological indicators of beneficial adaptive responses as predictors of species survival [1]. Adaptive mechanisms in trees, as well as other plants, are important for mitigating the stress that is associated with fluctuations in native environments or, after new colonization, for rapid adaptation to novel environments [54–57]. Studies investigating drought stress in trees have shown that by reducing the leaf canopy and increasing root proliferation, trees become more drought tolerant because both phenotypic responses limit water loss [58]. The occurrence of phenotypic responses occurring in parallel suggests that there may be a coordinated regulation of these traits [59, 60]. Other traits indicative of drought responses and plasticity in trees include leaf area, leaf dry mass, leaf mass per area (LMA), leaf tissue density, net photosynthesis, stomatal conductance, leaf respiration, water use efficiency, leaf water potential at midday, total chlorophyll content, relative water content, gross photosynthesis, leaf transpiration, and the ratio between leaf respiration and net photosynthesis [58]. Drought avoidance may also be viewed as a strategy for drought tolerance by altering the timing of growth and reproduction [14]. By maximizing the adaptive response of traits related to drought response, the overall fitness of an existing population of trees has the potential to adapt to a new environment [58]. However, if a given climatic event exceeds the limit of adaptive capacity, the same population of trees may also be replaced by a new, more adapted species [14].

Plasticity in weeds, as with trees, is governed by adaptive responses that impact physiology, morphology, and anatomy [36]. However, unlike trees, many weed species have relatively short life spans and must make rapid and frequent adjustments to environmental changes to ensure survival [16]. In addition to the wild characteristics for plasticity listed above, other characteristics in weeds that demonstrate enhanced phenotypic plasticity include: discontinuous or extensive seed dormancy ensuring germination only in favorable conditions, indeterminant or simultaneous flowering and vegetative growth, self-compatibility allowing genetic divergence from previous generations without requiring special pollinators to ensure seed viability, long-distance seed dispersal by air or water; competition with crop plants resulting in reduced crop yield, sexual and asexual reproduction strategies; and allelopathy, or the ability to produce chemicals that retard or kill other plants (**Figure 2**) [16, 36, 61]. Adaptive responses in weeds occur throughout development [16, 36]. Sometimes adaptive responses are more apparent in plant architecture than in signaling responses, are more pronounced at certain developmental stages or in specific populations, or involve the same tissue types during different developmental phases [1, 16, 36, 61]. The invasiveness of weeds is thought to be associated with several phenotypic plasticity traits including plant height, flower development, flowering, and light quality, [62, 63]. A direct correlation between plant height and invasiveness remains unclear. However, there may be an association between tall plant phenotypes, increased phenotypic diversity,

and higher plant abundance in unfavorable environments [63]. Associations have not been observed with flowering phenology among native and non-native plant populations, but this may be because flowering time is dependent on the environment [62–64]. Flower development and invasiveness in Purple loosestrife (*Lythrum salicaria*) demonstrate that both anther and stigma respond to changes in soil moisture during either of vegetative and reproductive development [65]. Tufted knotweed (*Polygonum cespitosum*) has been enhanced through adaptive responses to drought and high temperature without any observable decrease in fitness when grown in the shade [66]. Narrow-leaf plantain (Plantago lanceolata) is very sensitive to changes in light quality and modulates seed germination and leaf size as a mechanism for shade avoidance [67]. It is also the case in this weed species that leaf size and germination patterns share common physiological mechanisms where the short leaf phenotype is more plastic than the long leaf phenotype in shady conditions [20]. This discovery illustrates that wild plasticity is a dynamic network of processes that work synergistically to enhance the likelihood of survival [20]. Both trees and weeds demonstrate how, through the process of natural selection, non-cultivated plants have adopted very different and dynamic strategies that ensure reproduction and survival [1, 4, 12, 16–21, 24].
