Evolutsioonilised seosed taimede konkureerimiskäitumise ning naabrite identiteedi ja esinemissageduse vahel parasvöötme niidukooslustes

Väitekirja elektrooniline versioon ei sisalda publikatsiooneTaimed on paikse eluviisiga ning võivad reageerida välistingimustele morfoloogilise plastilisuse abil. Plastilised reaktsioonid ilmnevad mitte ainult eluta loodusele, vaid ka naabertaimede identiteedile (liigikaaslastele või teiste liikide esindajatele, sugulastele või mittesugulastele). Koosluses toimuvad evolutsioonilised protsessid võivad vormida taimeliigi plastilisust juhul kui paljude põlvkondade jooksul ümbritsevad taimeliiki teatud identiteediga naabrid. Minu doktoritöö aluseks oli meeskonnatöö, milles uuriti seitset Eesti poollooduslikku niitu ja viidi läbi suur potikatse. Töörühma liikmena leidsin, et uuritaval taimeliigil on suurim plastilisus kui kaks naabritüüpi (liigikaaslased ja teise liigi esindajad, sugulased ja mittesugulased) on koosluses tavalised ja ümbritsevad liiki sarnase sagedusega. Samuti leidsin, et taimed võivad hoiduda konkurentsist lähisugulastega ja olla mittesugulaste suhtes agressiivsemad. Siiski rohumaa liikide seas pole sugulaste äratundmist lihtne tuvastada. Selle ilmnemine sõltub paljudest tegurites, sealhulgas naabrite kasvutihedusest. Katsest selgus, et taimede konkurentne käitumine teisest liigist naabrite suhtes oli seotud liigi paljunemis- ja levimisstrateegiaga. Seemnetega paljunevad ja kaugele levivad liigid (näiteks liblikõielised) omasid tugevamat konkurentsivõimet. Samas vegetatiivselt paljunevad liigid, mis paigutavad tütarvõsusid lähestikku ja enamasti puutuvad kokku sama liigi esindajatega, olid teiste liikide suhtes nõrgad konkurendid. Kokkuvõtvalt võib öelda, et taimeliigid kasvasid kõige paremini nende naabritega, kellega nad sageli kohtusid oma kodukoosluses. Igal kooslusel on oma kujunemislugu ja evolutsioonilised mehhanismid, mis mõjutavad taimede ruumilist paigutust, konkurentsi ning püsisuhteid naabritega. Taimede võime ära tunda oma naabreid ja reageerida neile rohkem või vähem agressiivsel moel sõltuvalt liigi paljunemisstrateegiast avardab meie arusaamist nende keerukast käitumisest.Plants are sessile organisms and can react to surrounding environment by morphological plasticity. They respond plastically not only to the abiotic environment, but also to the identity of neighbours (individuals of the same or other species, relatives or non-relatives). Plant responses to neighbours are shaped by evolutionary processes as plant species are exposed to the neighbours of a certain identity during many generations. The findings of this thesis are based on the field study of seven semi-natural grasslands in Estonia and pot experiments conducted in a common garden. We found that plants were able to discriminate between different types of neighbours (the same or another species, kin or nonkin) only when these neighbours were common in the plants’ home environment. We also found that plants could avoid competition with kin and show more aggressive behaviour towards nonkin. However, kin recognition is not easy to detect among grassland species, because it may depend on different factors, including the density of neighbours, and can elicit species-specific responses that vary in magnitude and direction. We discovered that plant ability to compete with other species varied with species reproductive strategy and dispersal. Species that reproduce by seed have a low degree of conspecific aggregation in the field (e.g., legumes) and were on average stronger competitors than species that reproduce clonally and form clumps of the same species. As a rule, plants grew better with the neighbour type that they encountered most frequently in nature. Each plant community has its own formation history and is subject to evolutionary processes that shape the patterns of species spatial distribution, neighbour recognition and species co-existence. Plants’ ability to recognize their neighbours and interact with them in a more or less aggressive manner depending on species reproductive strategy expand our understanding of the complexity of plant behaviour

Functional trait data for 27 temperate grassland species

Traits were measured on plants grown in a common garden in Tartu, Estonia (58°22´N, 26°41´E) using seeds collected from seven grasslands that differed in species richness and composition, soil fertility, pH, and management history (seed origin coordinates supplied). Individual plants of each focal species were subjected to treatments that manipulated a) neighbour identity (surrounded by either conspecifics or heterospecifics), and b) neighbour density (0, 1, 2, 3, 4, 6 or 8 neighbours). Each neighbour identity by density combination was replicated twice. In the heterospecific treatment, each focal species was grown together with a species that it frequently encountered in the field as its nearest neighbour. Five aboveground traits and total aboveground dry mass of focal and neighbour plants were recorded. The maximum vegetative height of the focal plants was measured as the highest point reached by stem leaves (or rosette leaves in the absence of a leafed stem). Leaf water content was calculated by dividing the difference between fresh and dry mass by the fresh mass of two newly produced but fully expanded leaf blades (four leaves for Carex ornithopoda, Juncus gerardii, Veronica chamaedrys; five leaves for Antennaria dioica; ten leaves for Lotus corniculatus; 25 leaves for Galium verum). Specific leaf area (SLA), was calculated as the ratio of leaf area and leaf dry mass of leaves used for water content measurements. The dry mass of the supportive structures was found by summing the dry mass of stems (including stolons), leaf petioles and leaf sheaths (in the case of graminoids). All above-ground parts of each focal plant and its neighbours were oven-dried at 70C for 48 h and weighed separately as necessary for calculations

Data from: Plasticity in plant functional traits is shaped by variability in neighbourhood species composition

Plant functional traits can vary widely as a result of phenotypic plasticity to abiotic conditions. Trait variation may also reflect responses to the identity of neighbours, although not all species are equally responsive to their biotic surroundings. We hypothesized that responses to neighbours are shaped by spatial community patterns and resulting variability in neighbour composition. More precisely, we tested the theoretical prediction that plasticity is most likely to evolve if alternative environments (in this case, different neighbour species) are common and encountered at similar frequencies. We estimated the frequencies of encountering different neighbour species in the field for 27 grassland species and measured the aboveground morphological responses of each species to conspecific vs heterospecific neighbours in a common garden. Responses to neighbour identity were dependent on how frequently the experimental neighbours were encountered by the focal species in their home community, with the greatest plasticity observed in species that encountered both neighbours (conspecific and heterospecific) with high and even frequency. Biotic interactions with neighbouring species can impose selection on plasticity in functional traits, which may feed back through trait divergence and niche differentiation to influence species coexistence and community structure

Data from: Plasticity in plant functional traits is shaped by variability in neighbourhood species composition

Plant functional traits can vary widely as a result of phenotypic plasticity to abiotic conditions. Trait variation may also reflect responses to the identity of neighbours, although not all species are equally responsive to their biotic surroundings. We hypothesized that responses to neighbours are shaped by spatial community patterns and resulting variability in neighbour composition. More precisely, we tested the theoretical prediction that plasticity is most likely to evolve if alternative environments (in this case, different neighbour species) are common and encountered at similar frequencies. We estimated the frequencies of encountering different neighbour species in the field for 27 grassland species and measured the aboveground morphological responses of each species to conspecific vs heterospecific neighbours in a common garden. Responses to neighbour identity were dependent on how frequently the experimental neighbours were encountered by the focal species in their home community, with the greatest plasticity observed in species that encountered both neighbours (conspecific and heterospecific) with high and even frequency. Biotic interactions with neighbouring species can impose selection on plasticity in functional traits, which may feed back through trait divergence and niche differentiation to influence species coexistence and community structure