GRAZING TOLERANCE OF BIENNIAL MEADOW PLANTS IN RELATION TO RESOURCE AVAILABILITY, ACTA UNIVERSITATIS OULUENSIS A Sci e n t i a e Rerum Nat u r a l i u m 557

In this thesis I studied responses of three biennial, monocarpic plants Erysimum strictum,\nGentianella amarella, and G. campestris, to various aspects in resource availability (i.e.\ncompetition, mineral nutrition, neighbor removal) and environmental stress (early frost) at adult\nor rosette stages and how these effects are related to grazing tolerance. I also studied how\nmanipulations in resource availability affected arbuscular mycorrhizal colonization of the roots.\nAll three species were relatively tolerant to simulated grazing and in most cases plants were\nable to compensate quite well for minor biomass losses. According to the compensatory\ncontinuum hypothesis, tolerance is most pronounced in resource-rich conditions, but this was not\nalways the case in the present experiments. Erysimum strictum compensated for defoliation at the\nrosette stage but the reproductive output of adult plants was reduced markedly in the next year.\nThis reduction was strongest among fertilized plants. Moreover, apex removal at the adult stage\nresulted in overcompensation (i.e. clipped plants were more productive) but only in the absence of\nfertilization and in the presence of competition, which is against the compensatory continuum\nhypothesis. In E. strictum a potential cost of compensation appeared as delayed flowering and fruit\nmaturation among clipped plants. However, in spite of early frost treatment clipped plants were\nstill able to overcompensate. In Gentianella amarella and G. campestris, apex removal reduced\ngrowth and reproductive performance in most cases. Effects on root fungal parameters were\npositive or neutral. This pattern suggests that simulated above-ground herbivory tends to increase\ncarbon limitation, and therefore regrowing shoots and the fungal symbionts may appear as\nalternative, competing sinks for the limited carbon reserves of the host plant.\nBoth shoot architecture and resource availability modify the responses of the study plants to\napical damage at both rosette and adult stages. In addition, different environmental stress factors\naffect success in compensatory growth.

ISBN-10:
978-951-42-6210-4
Kieli:
eng.
Sivumäärä:
134 s.
Tekijät:
Piippo Sari
Tuotekoodi 013980
20,00 €