Communication

===Plants, fungi, and bacteria===
[[Plant communication]] refers to plant processes involving the sending and receiving of information.<ref>{{harvnb|Karban|2015|pp=4–5}}</ref> The field studying plant communication is called [[phytosemiotics]].<ref>{{harvnb|Sebeok|1991|p=[https://books.google.com/books?id=Moc8XzWbT-QC&pg=PA111 111]}}</ref> This field poses additional difficulties for researchers since plants are different from humans and other animals in that they lack a [[central nervous system]] and have [[Cell wall#Plant cell walls|rigid cell walls]].<ref>{{multiref | {{harvnb|Karban|2015|pp=1–4}} | {{harvnb|Schenk|Seabloom|2010|pp=2, 7}} | {{harvnb|Blatrix|Mayer|2010|p=128}} }}</ref> These walls restrict movement and usually prevent plants from sending and receiving signals that depend on rapid movement.<ref>{{harvnb|Schenk|Seabloom|2010|p=6}}</ref> However, there are some similarities since plants face many of the same challenges as animals. For example, they need to find resources, avoid predators and [[pathogen]]s, find mates, and ensure that their offspring survive.<ref>{{harvnb|Karban|2015|pp=1–2}}</ref> Many of the evolutionary responses to these challenges are analogous to those in animals but are implemented using different means.<ref>{{harvnb|Karban|2015|p=2}}</ref> One crucial difference is that [[chemical communication]] is much more prominent in the plant kingdom in contrast to the importance of visual and auditory communication for animals.<ref>{{multiref | {{harvnb|Schenk|Seabloom|2010|p=7}} | {{harvnb|Blatrix|Mayer|2010|p=128}} }}</ref>

[[File:Stages of plant communication.svg|thumb|upright=1.5|alt=Diagram of the steps of plant communication: a cue is first emitted and later received, leading to a response|Steps of plant communication]]
In plants, the term ''behavior'' is usually not defined in terms of physical movement, as is the case for animals, but as a biochemical response to a [[Stimulus (physiology)|stimulus]]. This response has to be short relative to the plant's lifespan. Communication is a special form of behavior that involves conveying information from a sender to a receiver. It is distinguished from other types of behavior, like defensive reactions and mere sensing.<ref>{{harvnb|Karban|2015|pp=2–4}}</ref> Like in the field of animal communication, plant communication researchers often require as additional criteria that there is some form of response in the receiver and that the communicative behavior is beneficial to sender and receiver.<ref>{{multiref | {{harvnb|Karban|2015|p=5}} | {{harvnb|Schenk|Seabloom|2010|p=1}} | {{harvnb|Blatrix|Mayer|2010|p=128}} }}</ref> Biologist Richard Karban distinguishes three steps of plant communication: the emission of a cue by a sender, the perception of the cue by a receiver, and the receiver's response.<ref>{{harvnb|Karban|2015|p=7}}</ref> For plant communication, it is not relevant to what extent the emission of a cue is intentional. However, it should be possible for the receiver to ignore the signal. This criterion can be used to distinguish a response to a signal from a defense mechanism against an unwanted change like intense heat.<ref>{{harvnb|Karban|2015|p=45}}</ref>

Plant communication happens in various forms. It includes communication within plants, i.e. within [[plant cells]] and between plant cells, between plants of the same or related species, and between plants and non-plant organisms, especially in the [[rhizosphere|root zone]].<ref>{{harvnb|Baluska|Volkmann|Hlavacka|Mancuso|2006|loc=[https://books.google.com/books?id=IH9N4SKWTokC&pg=PA19 2. Neurobiological View of Plants and Their Body Plan]}}</ref> A prominent form of communication is airborne and happens through [[volatile organic compound]]s (VOCs). For example, [[maple]] trees release VOCs when they are attacked by a [[herbivore]] to warn neighboring plants, which then react accordingly by adjusting their defenses.<ref>{{multiref | {{harvnb|Arimura|Pearse|2017|pp=4–5}} | {{harvnb|Schenk|Seabloom|2010|p=1}} | {{harvnb|Baldwin|Schultz|1983|pp=277–279}} }}</ref> Another form of plant-to-plant communication happens through [[mycorrhizal fungi]]. These fungi form underground networks, colloquially referred to as the [[Wood-Wide Web]], and connect the roots of different plants. The plants use the network to send messages to each other, specifically to warn other plants of a pest attack and to help prepare their defenses.<ref>{{harvnb|Gilbert|Johnson|2017|pp=84, 94}}</ref>

Communication can also be observed for fungi and bacteria. Some fungal species communicate by releasing [[pheromone]]s into the external environment. For instance, they are used to promote sexual interaction in several aquatic fungal species.<ref>{{multiref | {{harvnb|O'Day|2012|pp=[https://books.google.com/books?id=kNB4u65WK6MC 8–9]|loc=1. Modes of cellular communication and sexual interactions in eukaryotic microbes}} | {{harvnb|Davey|1992|pp=951–960}} | {{harvnb|Akada|Minomi|Kai|Yamashita|1989|pp=3491–3498}} }}</ref> One form of communication between bacteria is called [[quorum sensing]]. It happens by releasing [[hormone]]-like molecules, which other bacteria detect and respond to. This process is used to monitor the environment for other bacteria and to coordinate population-wide responses, for example, by sensing the density of bacteria and regulating [[gene expression]] accordingly. Other possible responses include the induction of [[bioluminescence]] and the formation of [[biofilm]]s.<ref>{{multiref | {{harvnb|Waters|Bassler|2005|pp=319–320}} | {{harvnb|Demuth|Lamont|2006|p=xiii}} | {{harvnb|Berea|2017|p=59}} }}</ref>