Review Article

Interactions Among the Plants with Different Neighbor Identities and Plant Communication (A Review)

Syed Wajahat Husain Jaafry1* and Amber Fatima2

1School of Ecological and Environmental Sciences, East China Normal University, Shanghai, 200241, China; 2Department of Environmental Sciences, Kinnaird College for Women University, Jail Road Lahore, Pakistan.

Received | August 22, 2019; Accepted | January 15, 2022; Published | July 28, 2022

*Correspondence | Syed Wajahat Husain Jaafry, School of Ecological and Environmental Sciences, East China Normal University, Shanghai, 200241, China; Email: wajahatjaafry@yahoo.com

Citation | Jaafry, S.W.H. and A. Fatima. 2022. Interactions among the plants with different neighbor identities and plant communication (A Review). Sarhad Journal of Agriculture, 38(3): 1017-1025.

DOI | https://dx.doi.org/10.17582/journal.sja/2022/38.3.1017.1025

Keywords | Plant interaction, Conspecific, Heterospecific, Plant communication, Plant competition, Plant facilitation

Copyright: 2022 by the authors. Licensee ResearchersLinks Ltd, England, UK.

This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https://creativecommons.org/licenses/by/4.0/).

Introduction

Plants and animals compete for resources, resulting in two sorts of transformative processes: those that improve competitive capabilities and those that diminish competing interactions. (Schmitt et al., 1995; 1999; Nardini et al., 1999). Plant growth is greatly influenced by the existence or absence of neighboring competitors within close proximity. Biologists have recognized that various animal species have transformed to distinguish and collaborate with other members of the same community, especially from the kin members of that community for survival In recent, studies it has been well established that numerous microbes/pathogens, some of the simplest creatures, are also capable of distinguishing their kin (Jaafry et al., 2019; Jaafry and Fatima, 2021). So, it is not surprising that plants may also communicate and recognize the presence of neighboring plants within close proximity. Interaction among plants is one of the key processes which can amend the composition, structure, diversity, and mechanism of plant populations (Schmitt et al., 1995). Plants are immovable organisms; they are not mobile and free to move like animals so that communication between plants most likely takes place within the nearest neighbors (Milbau et al., 2007). Increasing studies of plant-plant collaboration indicate that intraspecific genetic assortment may have extensive ecological consequences for interspecies interactions (Genung et al., 2012) and that difference between genotypes maybe even more significant than the disparity among the different species in understanding species cohabitation (Husain Jaafry et al., 2020).

 

 

Contrary to kin recognition in plants, classical ecological theory entails that competition is anticipated to be tougher as individuals become more alike in their resource concerns (Figure 1). In this study, a systematic review was conducted to collect evidence if plant interaction and species recognition. This study has focused on explaining different factors that may influence plant interaction and species recognition (Figure 2).

According to recent studies on plant species recognition and competition, plants may identify neighboring plants within a close vicinity on the basis of relatedness and species identity (conspecific or heterospecific). Until now, inconsistencies and contradictory conclusions have plagued the subject of plant species recognition, with some studies supporting the kin recognition phenomenon. (Crepy and Casal, 2016), other established contrasting results (Cheplick and Kane, 2004; Lepik et al., 2012; Mercer and Eppley, 2014), and some studies concluded insignificant change between sibling conspecific and non-sibling conspecific groups (Puustinen et al., 2004; Husain Jaafry et al., 2020). This is why the understanding of kinship and species recognition phenomenon is still ambiguous. Progress regarding molecular proofs and protein-protein interaction is not sufficiently provided for root secretions, and, to date, lesser molecular information to determine the kin recognition has been established, leaving many queries in the field unrequited. In this text review, we attempt to provide a comprehensive background to this innovative topic to inspire young researchers to do further studies to understand kin, species identification, and plant interaction mechanism in a better way.

Many studies of animal kin or species recognition have been published; however, plant kin and species recognition, as well as their reactions, has only lately piqued ecologists’ interest, and many ecologists remain unconvinced that plants might have such a differentiating feature. Plants, like animals, have evolved over millions of years and are emerging under similar circumstances, such as competition for above- and below-ground resources, as well as reproduction. As a result, they have developed a lot of intricate survival and survival procedures, which we will go over in more detail later.

Species interaction and recognition in plants

Intraspecific competition may affect the overall fitness of plants through modification in above and below-ground growth patterns (Bisseling and Scheres, 2014). Previous research on different species mainly focused on interspecific competition as compared with intraspecific interaction in different ecosystems (Padilla et al., 2013), and competitive indices used to estimate interspecific competition have been reported explicitly, but it has been well established that intraspecific competition is more severe than interspecific interaction (Husain Jaafry et al., 2020). However, little evidence is presented on the evaluation of the intraspecific competition in crops, clonal, and non-clonal plants. Intraspecific competition is the main factor that can influence the plant growth pattern to increase root density for capturing the below-ground resources (e.g., water and nutrients), above-ground resources (e.g., light), or both.

Before consideration of siblings or kin, specific studies, self-recognition, and non-self roots, discrimination in plants was studied. Mahall and Callaway studied the feedback of Ambrosia dumosa (a desert shrub). They split the roots and observed the root morphology of the exposure with self roots and compared with exposure to other plant roots belong to the same population (conspecifics). They depicted that the root growth of A. dumosa was quenched when it exposed to different individual’s roots as compared with self roots (Mahall and Callaway 1991; 1992; 1996; Maina et al., 2002). Additionally in their research, it was established that the desert shrub (A. dumosa) did not sense the neighboring roots from strangers (different population or heterospecific neighbors) hence, they concluded that self, a non-self distinction may only develop among siblings or genetically related plants (Callaway RM 1992; Mahall and Callaway 1996).

In the study of Dudley and File (2007), they examined the structure of the roots of sea rocket (Cakile edentula). When C. edentula has placed with strangers, it allocated more biomass in roots as compared when it has grown with the close relatives (i.e. same mother plants). Based on this rearch, Biedrzycki et al. (2010) investigated kin recognition in Arabidopsis thaliana. They grew A. thaliana plants in individual either exposing to kin and strangers conspecific roots secretions. (Biedrzycki and Bais, 2010). Their findings were similar to those of Dudley and File (2007). Plants treated with stranger secretions produced more slanted roots than those planted with kin root excretion (Biedrzycki et al., 2014). This change in the root allocation pattern in response to neighbor relatedness supports the idea that, in any case, some plants are capable of sensing and categorizing their relatedness-related neighbors in the same population.

Another study regarding species recognition and facilitation shown Centaurea stoebe an exotic herb may transform its defensive approach in response to different neighboring plants, either conspecific or heterospecific (Broz et al., 2010). While grown with conspecific (same species) neighbor, C. stoebe, a grown-up with other C. stoebe, plants changed their defense response in comparison to the interaction with heterospecific (different species) neighbors. These findings implied that an individual C. stoebe plant might alter its defensive mechanism based on the identity of different neighboring individuals. This approach is likely to have significant value for individual and community success. The recent studies stimulated the ecologists to figure out the defensive characteristics among the plants, which indicated that the plant species grown in a conspecific population might be more tolerant to pathogen/aphid attacks as compared to those grown in a heterospecific environment. Despite the conspecific population of C. stoebe were not taken as related conspecifics (siblings), it would be interesting to establish if the defense and biochemical mechanism of plants may change in kin versus conspecific environment. All of the previous results implied that invasive plants have evolved strategies to cope with its neighbors and utilized the territory and available resources (above/below-ground) more efficiently compared with normal plants (Broz et al., 2010).

In the study of Murphy and Dudley (2009), they observed kin acknowledgement and competition response in Impatiens pallida. Inconsistent to the prior studies, which indicated that neighboring roots responded to kin or strangers by changing the growth pattern, this experiment showed that below ground kin or stranger acquaintances could also modify the above-ground growth pattern. I. pallida augmented allocation in the above-ground rather than to below ground by increasing stem height and number of branches when exposed with strangers versus being grown with kin (Murphy and Dudley, 2009).

Glycine max and Sorghum vulgare either grown with a sibling or a stranger, both did not show any differences in above-ground biomass. G. max did not differ among siblings and stranger groups in below-ground biomass, but S. vulgare grown with siblings showed lower below-ground biomass compared with strangers group (Zhang et al., 2016). Conversely, G. max took up more nitrogen in the sibling group as compared to strangers without changing root allocation. It implies that resource uptake capacity and root competition

 

Table 1: Plant interaction brief summary.

Plant-plant communication	Outcome	Reference
Plant VOCs released differently when spider mite introduced to damaged lima beans and normal leaves	Spider mite behavior changed under different VOCs exposure from damaged and normal leaves	(Dicke, 1986)
Plant VOCs signaling, which also leads to ‘snoop’ on surrounding plants	Willow (Salix sitchensis), induced natural resistance against herbivory to their immediate neighbours	(Baldwin and Schultz, 1983)
VOCs triggered predatory insect attraction against herbivory	Herbivore-mediated VOCs stimulate a defensive response in undamaged neighbor plants of lima beans (Phaseolus lunatus) against herbivory damage	(Heil and Silva Bueno, 2007)
Pollinator attraction due to VOCs	Native tobacco (Nicotiana attenuata) attracted pollinators due to plant VOCs	(Halitschke et al., 2008)
Attraction to predator insects induced by VOCs	Nicotiana attenuata showed resistance to three herbivore insects, by attracting predators	(Kessler, 2001)
Change in diurnal and nocturnal VOCs release due to herbivory	Tobacco plants (Nicotiana tabacum), numerous chemical airborne cues excreted extensively at night found highly obnoxious to female moths (Heliothis virescens).	(De Moraes et al., 2011)
GLVs and terpenoids released to attract predators after leaf damage	Transgenic Nicotiana attenuata attracted predators with volatile signals, to reduce the load of herbivore	(Halitschke et al., 2008)
Predatory attraction due to VOCs against insect damage	Salicylic acid and protein kinase stimulated by Manduca sexta attack and mediated damage induced caution in Nicotiana attenuata.	(Steppuhn et al., 2004; Meldau et al., 2009)
Herbivore specific VOCs	VOCs released from damaged plants specifically depend upon the nature of leaf wounding and its age, abundance of neighboring plants	(Clavijo McCormick et al., 2012)

 

are two different factors that may vary according to the species. This inconsistency in competitive behavior and how species endorse erratically to kin and strangers according to the given conditions may not be specified. Wild soya bean Glycine soja and commercial soya bean Glycine max changed their leaf pattern when grown with closely related conspecifics as compared to unrelated neighbors (Murphy et al., 2017).

Furthermore, according to another study, plants have the aptitude to gather evidence about their surroundings as well as nutrients. According to Cahill et al., (2010), an annual plant, Abutilon theophrasti, displayed a distinct strategy in response to the presence of a competitor and uneven resource distributions. Rooting was reduced in plants that sensed and responded to their neighbors and were cultivated in soil with uniform nutrients. Contrary, plants with competitors and heterogeneous resource distributions abridged their belowground growth only moderately (Cahill et al., 2010). While these findings are inconsistent with the data from Broz et al. (2010), which specified those plant responses towards its neighbors may greatly be controlled by the soil resource availability. From the previous examples of plant-plant interactions, it is obvious that plants actively contribute to the shaping of their communities. These interactions may be harmful to one or favorable to both plants and, given the variety of these communications, it is more complex and challenging to establish that plants may always be interacting explicitly with their kin. For example, pea (Pisum sativum L.) did not recognize their kin. It showed lower competition with the interspecific neighbor as compared to intraspecific kin (Jacob et al., 2017).

So far, identity and kin recognition has not yet become the attraction for crop breeders (Chen et al., 2012); not solid pieces of evidence could be found for kinship mechanism in crop species. Fang et al. (2013) revealed that the root behavior pattern of seedlings of rice from the same genotype grown in close space tented to overlap more and grow closer to each other than seedlings from strangers (Fang et al., 2013). Likewise, results of Fang et al. (2011) showed when intercropping with the same genotype, roots of maize or soybean overlapped to each other, in contrast, maize GZ1 intercropped with soybean HX3, roots pattern was reversed and tended to avoid each other (Fang et al., 2011). Investigating critically, both studies targeted on the interface between the same or different genotypes, comparatively kin or non-kin, and how to root morphology affected by competition in plants and fitness consequences were also not examined (Table 1).

Evidence of VOC and molecular communication in plants

Plants are rooted and stationary, unlike mammals. Plants are unable to move around in search of food or reproduction, or to protect themselves against predators, despite the fact that their development is oriented toward the sun and may bend due to gravity. To ensure their survival in the nature, plants have created intricate tactics. Internal chemical transmission is used by both plants and animals to govern the shape and mechanism of different portions of the same individual, according to numerous research. (Henriksson, 2001). Plant chemical communication, i.e., VOCs emission, plays an essential part in the rhizosphere and greater ecological perspectives. Plants have evolved extremely sophisticated and intricate sensing processes that enable them to persist in their ever-changing environments, as has been well documented (Pierik and De Wit, 2014). Undeniably, plants may sense and retort to variations in their surroundings, by collecting and evaluating disparate information and then modify their physiological, morphological and characteristics accordingly (Gundel et al., 2014; Kessler, 2015).

Plants communicate with countless organisms surrounding them, i.e., insects/aphids and animals that help them to pollinate and disperse their seeds for sexual reproduction, call for predator and parasitic insects that exterminate the attacking herbivorous insects, and microorganisms that support the nutrient procurement or induce resistance to disease and herbivores (Jaafry and Fatima, 2021). Due to these capabilities, plants are allowed to broaden and protect their territory. Furthermore, plants can distinguish themselves and communicate with one another, by warning them through above and below ground release of chemical signals neighboring conspecific or heterospecific plants (Farmer, 2001; Heil and Karban, 2010). Normally this form of plant communication occurs volatile chemicals transmission through the air (Karban et al., 2011) or via soluble compounds excreted by roots and mycelial networks (root exudates) in the rhizosphere (Johnson and Gilbert, 2015), although in some cases possibly alternative routes, for example, through sound (Husain Jaafry et al., 2020; Jaafry and Fatima, 2021).

Plants also make changes at molecular level and release different kinds of proteins after stressful conditions and herbivore attack (Meents and Mithöfer, 2020; Jaafry and Fatima, 2021). Despite of molecular variations chemical response of the plants during stressful periods has been studied enormously due to active of VOCs release in the plants. Though primarily discouraged critically, the phenomenon of plant-plant collaboration via airborne signaling is now extensively acknowledged and has been tested in agriculture to improve agricultural practices to enhance the crops protection against pests (Blande et al., 2014; Pierik et al., 2014). Plant communication or plant–plant signaling also triggered more effectively after herbivore damage and caused plants to emit volatile cues that neighboring plants (Karban et al., 2014).

Future Directions

Regardless of criticism, the method of kin selection and the effect of neighbor’s identity between plant species is one of the key aspects that ecologists can use to better understand plant interactions. (Klemens, 2008). Soil microorganisms may play an important role in the outcome of competitive interactions among related conspecifics, non-kin members, and communication with neighboring plants. Negative interaction (allelopathy) and positive interaction (volatile communication) between the plants may be better understood by investigating the chemical traits of the plants.

One of the most important examples of the chemical effects among the plants is garlic mustard (Alliaria petiolata), an invasive herbaceous flower in North American forests. Garlic mustard discharges benzyl isothiocyanate in the soil, which prevents the growth of mycorrhizal fungi that benefit tree diversity (Wolfe et al., 2008). Research also proposed that exotic plants, such as Canada goldenrod (Solidago canadensis), Centaurea stoebe, and narrow-leaf cattail (Typha angustifolia), may secrete allelochemicals in the soil that precisely suppress the growth of native plants. By these examples, it can be assumed that the variation in plant growth of specific genotypes may be due to the influence of the identity of their neighbors and community composition of soil microorganisms.

In the rhizosphere, numerous reactions occur and may influence plant-plant communication with changing the surrounding environment. For better results interacting siblings versus non-siblings conspecifics and heterospecific must belong to a similar environment and size symmetry. There are several environmental aspects concerning kin and species recognition, and plant communication has not been fully considered. Furthermore, comparative research should be conducted in the field and controlled condition as well, to figure out the main differences among plant response in species recognition and volatile communications. Crop species with the capability to distinguish kin related stronger and beneficial chemical communication may somehow protect the species for further herbivore attack.

More research into the processes and signaling components included in kin identification, such as root excretions and volatile cue emanations and protein interaction will be required, with implications for multitrophic plant relationships. Plants’ reactions to adjacent related conspecifics are just as important, and the differential in reactivity between related and unrelated conspecifics is one of the most significant aspects of plant-plant communication. Upcoming research should focus on interactions between plants from the same and other genera, as this could bring new insights into the field of plant interaction and species reactions to a variety of neighbors. To assist make this expanding field of study more visible and understandable, further research and investigations focused on kin and species relationships are needed.

Acknowledgments

This study was supported by Professor Li Dezhi and the East China Normal University online library for downloading relevant research articles.

Novelty Statement

The review article provides evidence regarding plant interaction and species recognition which would be beneficial for new researchers to understand the mechanism of species recognition.

Author’s Contribution

Syed Wajahat Husain Jaafry: Manuscript preparation, core concept and relevant articles selection.

Amber Fatima: Manuscript editing, proofreading and reference management.

Conflict of interest

The authors have declared no conflict of interest.

References

Baldwin, I.T. and Schultz, J.C. 1983. Rapid Changes in Tree Leaf Chemistry Induced by Damage: Evidence for Communication Between Plants. Science, 221:277–279. https://doi.org/10.1126/science.221.4607.277

Biedrzycki, M.L. and Bais, H.P. 2010. Kin recognition in plants: A mysterious behaviour unsolved. J. Exp. Bot., 61:4123–4128. https://doi.org/10.1093/jxb/erq250

Bisseling, T. and Scheres, B. 2014. Nutrient computation for root architecture. Science, 346:300–301. https://doi.org/10.1126/science.1260942

Blande, J.D., Holopainen, J.K. and Niinemets, Ü. 2014. Plant volatiles in polluted atmospheres: Stress responses and signal degradation. Plant Cell Environ., 37:1892–1904. https://doi.org/10.1111/pce.12352

Broz, A.K., Broeckling, C.D., De-la-Peña,, C., Lewis M.R., Greene, E., Callaway, R.M., Sumner, L.W. and Vivanco, J.M. 2010. Plant neighbor identity influences plant biochemistry and physiology related to defense. BMC Plant Biol., 10:115. https://doi.org/10.1186/1471-2229-10-115

Cahill, J.F., McNickle, G.G., Haag, J.J., Lamb, E.G., Nyanumba, S.M. and St Clair, C.C. 2010. Plants integrate information about nutrients and neighbors. Science, 328:1657. https://doi.org/10.1126/science.1189736

Callaway, R.M.M.B. 1992. Family Roots. Nature,

Chen, B.J.W., During, H.J. and Anten, N.P.R. 2012. Detect thy neighbor: Identity recognition at the root level in plants. Plant Sci., 195:157–167. https://doi.org/10.1016/j.plantsci.2012.07.006

Cheplick, G.P. and Kane, K.H. 2004. Genetic Relatedness and Competition in Triplasis purpurea (Poaceae): Resource Partitioning or Kin Selection? Int. J. Plant Sci., 165:623–630. https://doi.org/10.1086/386556

Clavijo McCormick, A., Unsicker, S.B. and Gershenzon, J. 2012. The specificity of herbivore-induced plant volatiles in attracting herbivore enemies. Trends Plant Sci., 17:303–310. https://doi.org/10.1016/j.tplants.2012.03.012

Crepy, M.A. and Casal, J.J. 2016. Kin recognition by self-referent phenotype matching in plants. New Phytol., 209:15–16. https://doi.org/10.1111/nph.13638

Dicke, M. 1986. Volatile spider???mite pheromone and host???plant kairomone, involved in spaced???out gregariousness in the spider mite Tetranychus urticae. Physiol. Entomol., 11:251–262. https://doi.org/10.1111/j.1365-3032.1986.tb00412.x

Dudley, S.A. and A.L. File. 2007. Kin recognition in an annual plant. Biol. Lett. 3: 435–8. https://doi.org/10.1098/rsbl.2007.0232

Fang, S., Clark, R.T., Zheng, Y., Iyer-Pascuzzi, A.S., Weitz, J.S., Kochian, L. V., Edelsbrunner, H., Liao, H. and Benfey, P.N. 2013. Genotypic recognition and spatial responses by rice roots. Proceed. National Acad. Sci., 110:2670–2675. https://doi.org/10.1073/pnas.1222821110

Fang, S., Gao, X., Deng, Y., Chen, X. and Liao, H. 2011. Crop root behavior coordinates phosphorus status and neighbors: from field studies to three-dimensional in situ reconstruction of root system architecture. Plant Physiol., 155:1277–1285. https://doi.org/10.1104/pp.110.167304

Farmer, E.E. 2001. Surface-to-air signals. Nature, 411:854–856. https://doi.org/10.1038/35081189

Genung, M.A., Bailey, J.K. and Schweitzer, J.A. 2012. Welcome to the neighbourhood: Interspecific genotype by genotype interactions in Solidago influence above- and belowground biomass and associated communities. Ecol. Lett., 15:65–73. https://doi.org/10.1111/j.1461-0248.2011.01710.x

Gundel, P.E., Pierik, R., Mommer, L., Ballar, C.L. 2014. Competing neighbors: Light perception and root function. Oecologia, 176:1–10. https://doi.org/10.1007/s00442-014-2983-x

Halitschke, R., Stenberg, J.A., Kessler, D., Kessler, A. and Baldwin, I.T. 2008. Shared signals - “Alarm calls” from plants increase apparency to herbivores and their enemies in nature. Ecol. Lett., 11:24–34. https://doi.org/10.1111/j.1461-0248.2007.01123.x

Heil, M. and Karban, R. 2010. Explaining evolution of plant communication by airborne signals. Trends Ecol. Evolut., 25:137–144. https://doi.org/10.1016/j.tree.2009.09.010

Heil, M. and Silva, Bueno J.C. 2007. Within-plant signaling by volatiles leads to induction and priming of an indirect plant defense in nature. Proceed. National Acad. Sci. United States Am., 104:5467–5472. https://doi.org/10.1073/pnas.0610266104

Henriksson, J. 2001. Differential shading of branches or whole trees: Survival, growth, and reproduction. Oecologia, 126:482–486. https://doi.org/10.1007/s004420000547

Husain Jaafry, S.W., Li, D., Ouyang, Y., Liu, L., Li, L., Yang, T., Wei, X., Zhu, Y., Sun, Y., Ren, Z. and Kong, R. 2020. Interactions among individuals of Setaria Italica at different levels of genetic relatedness under different nutrient and planting density conditions. Acta Oecologica, 105:103549. https://doi.org/10.1016/j.actao.2020.103549

Jaafry, S.W.H. and Fatima, A. 2021. Do Plants Really Communicate With Their Neighbor? A short communication. J. Nat. Appl. Sci. Pak., 3:703–709. http://jnasp.kinnaird.edu.pk/wp-content/uploads/2021/12/2.-S.-W.-Husain-JNASP-703-709-MI-0222.pdf

Jaafry, S.W.H., Li, D., Fan, Z., Liu, L., Wei, X., Yang, T., Sun, Y., Zhu, Y., Li, L., Ren, Z. and Kong, R. 2019. Effect of soil nutrient, neighbor identities and root separation types on the intra- and interspecific interaction among the three clonal plant species. Nordic J. Bot., 37. https://doi.org/10.1111/njb.02070

Jacob, C.E., Tozzi, E., Willenborg, C.J., Swanton, C., Swanton, C. and Ghersa, C. 2017. Neighbour presence, not identity, influences root and shoot allocation in pea. Plos One 12:e0173758. http://dx.plos.org/10.1371/journ al.,pone.0173758 https://doi.org/10.1371/journal.pone.0173758

Johnson, D. and Gilbert, L. 2015. Interplant signalling through hyphal networks. New Phytol., 205:1448–1453. https://doi.org/10.1111/nph.13115

Karban, R., Shiojiri, K. and Ishizaki, S. 2011. Plant communication – why should plants emit volatile cues? J. Plant Interactions, 6:81–84. https://doi.org/10.1080/17429145.2010.536589

Karban, R., Yang, L.H. and Edwards, K.F. 2014. Volatile communication between plants that affects herbivory: A meta-analysis. Ecol. Lett., 17:44–52. https://doi.org/10.1111/ele.12205

Kessler, A. 2015. The information landscape of plant constitutive and induced secondary metabolite production. Curr. Opin. Insect Sci., 8:47–53. https://doi.org/10.1016/j.cois.2015.02.002

Kessler, B.T.A. 2001. Defensive function of Herbivore- induced plant volatile emission in nature. Science, 291:2141–2144. https://doi.org/10.1126/science.291.5511.2141

Klemens, J.A. 2008. Kin recognition in plants? Biol. Lett., 4:S243–S245. https://doi.org/10.1098/rsbl.2007.0518

Lepik, A., Abakumova, M., Zobel, K. and Semchenko, M. 2012. Kin recognition is density-dependent and uncommon among temperate grassland plants. Functional Ecol., 26:1214–1220. https://doi.org/10.1111/j.1365-2435.2012.02037.x

Mahall, B.E. and Callaway, R.M. 1991. Root communication among desert shrubs. Proceedings of the National Academy of Sciences of the United States of America 88:874–876. https://doi.org/10.1073/pnas.88.3.874

Mahall, B.E. and Callaway, R.M. 1992. Root communication mechanisms and intracommunity distributions of two Mojave Desert shrubs. Ecology, 73:2145–2151. https://doi.org/10.2307/1941462

Mahall, B.E. and Callaway, R.M. 1996. Effects of regional origin and genotype on intraspecific root communication in the desert shrub Ambrosia dumosa (Asteraceae). Am. J. Bot. 83:93–98. https://doi.org/10.1002/j.1537-2197.1996.tb13879.x

Maina, G.G., Brown, J.S. and Gersani, M. 2002. Intra-plant versus inter-plant root competition in beans: Avoidance, resource matching or tragedy of the commons. Plant Ecol., 160:235–247. https://doi.org/10.1023/A:1015822003011

Meents, A.K. and Mithöfer, A. 2020. Plant–Plant Communication: Is There a Role for Volatile Damage-Associated Molecular Patterns? Front. Plant Sci., 11. https://doi.org/10.3389/fpls.2020.583275

Meldau, S., Wu, J. and Baldwin, I.T. 2009. Silencing two herbivory-activated MAP kinases, SIPK and WIPK, does not increase Nicotiana attenuata’s susceptibility to herbivores in the glasshouse and in nature. New Phytol., 181:161–173. https://doi.org/10.1111/j.1469-8137.2008.02645.x

Mercer, C.A. and Eppley, S.M. 2014. Kin and sex recognition in a dioecious grass. Plant Ecol., 215:845–852. https://doi.org/10.1007/s11258-014-0336-9

Milbau, A., Reheul, D., De Cauwer, B. and Nijs, I. 2007. Factors determining plant-neighbour interactions on different spatial scales in young species-rich grassland communities. Ecol. Res., 22:242–247. https://doi.org/10.1007/s11284-006-0018-8

De Moraes, C.M., Mescheer, M.C. and Tumlinson, J.H. 2011. Caterpillar induced nocturnal plant volatiles repel nonspecific females. Nature, 410:577– 580. https://doi.org/10.1038/35069058

Murphy, G.P., Acker, R. Van, Rajcan, I. and Swanton, C.J. 2017. Identity recognition in response to different levels of genetic relatedness in commercial soya bean. Royal Society Open Science https://doi.org/10.1098/rsos.160879

Murphy, G.P. and Dudley, S.A. 2009. Kin recognition: Competition and cooperation in Impatiens (Balsaminaceae). Am. J. Bot., 96:1990–1996. https://doi.org/10.3732/ajb.0900006

Nardini, A., Lo Gullo, M.A. and Salleo, S. 1999. Competitive strategies for water availability in two Mediterranean Quercus species. Plant, Cell Environ., 22:109–116. https://doi.org/10.1046/j.1365-3040.1999.00382.x

Padilla, F.M., Mommer, L., de Caluwe, H., Smit-Tiekstra, A.E., Wagemaker, C.A.M., Ouborg, N.J. and de Kroon, H. 2013. Early Root Overproduction Not Triggered by Nutrients Decisive for Competitive Success Belowground. PLoS ONE 8 https://doi.org/10.1371/journal.pone.0055805

Pierik, R., Ballaré, C.L. and Dicke, M. 2014. Ecology of plant volatiles : taking a plant community perspective. Plant, Cell Environ., 37:1845–1853. https://doi.org/10.1111/pce.12330

Pierik, R. and De Wit, M. 2014. Shade avoidance: Phytochrome signalling and other aboveground neighbour detection cues. J. Exp. Bot., 65:2815–2824. https://doi.org/10.1093/jxb/ert389

Puustinen, S., Koskela, T. and Mutikainen, P. 2004. Relatedness affects competitive performance of a parasitic plant (Cuscuta europaea) in multiple infections. J. Evolut. Biol., 17:897–903. https://doi.org/10.1111/j.1420-9101.2004.00728.x

Schmitt, J., Dudley, S.A. and Pigliucci, M. 1999. Manipulative Approaches to Testing Adaptive Plasticity: Phytochrome-Mediated Shade-Avoidance Responses in Plants. Am. Naturalist, 154:S43–S54. https://doi.org/10.1086/303282

Schmitt, J., McCormac, A.C. and Smith, H. 1995. A test of the adaptive plasticity hypothesis using transgenic and mutant plants disabled in phytochrome-mediated elongation responses to neighbors. Am. Naturalist, 146:937. https://doi.org/10.1086/285832

Steppuhn, A., Gase, K., Krock, B., Halitschke, R. and Baldwin, I.T. 2004. Nicotine’s defensive function in nature. PLoS Biol., 2. https://doi.org/10.1371/journal.pbio.0020217

Wolfe, B.E., Rodgers, V.L., Stinson, K.A. and Pringle, A. 2008. The invasive plant Alliaria petiolata (garlic mustard) inhibits ectomycorrhizal fungi in its introduced range. J. Ecol., 96:777–783. https://doi.org/10.1111/j.1365-2745.2008.01389.x

Zhang, L., Liu, Q., Tian, Y., Xu, X. and Ouyang, H. 2016. Kin selection or resource partitioning for growing with siblings: implications from measurements of nitrogen uptake. Plant Soil, 398:79–86. https://doi.org/10.1007/s11104-015-2641-z