Pflanzenreaktionen auf Wurzelherbivoren — Variationen, Ursachen und Mechanismen: Experimente an Zweijährigen Kompositen

Abstract

Response mechanisms of plants to below-ground herbivory. — The impact of two root herbivores, the moth Agapeta zoegana (Lep.: Cochylidae) and the weevil Cyphocleonus achates (Col.: Curculionidae), on the survival and performance of Centaurea maculosa (Asteracea), was studied under various levels of intra- and interspecific plant competition and nutrient availability, both in field plots and with potted plants. Competition with the grass Festuca pratensis (Poaceae) was by far the most important single stress factor, strongly reducing survival, growth and reproduction of Centaurea maculosa. Nitrogen shortage, applied as a single stress factor, had no effect on these plant traits. The reaction of C. maculosa to root herbivory was highly plastic, and supports the view of a continuum of compensatory responses to herbivory depending on the conditions influencing the plant’s physiological status, rather than of a fixed, species-specific response. The ability to compensate for root herbivory decreased as stress increased; stress in these experiments was represented by increase in herbivory, increase in competition with neighbours, and decrease in nutrient availability. Plants responded to root herbivory by increasing the allocation of nitrogen and biomass to the roots to adjust the carbon/nutrient balance, causing reduced allocation to reproduction in infested plants. Competition, however, mainly affected plant size, leaving reproductive allocation unchanged. The factors permitting the observed compensatory growth in C. maculosa are the presence of taproots with their stored reserves and the presence of dormant buds, which allow an increase in shoot number when the apical meristem has been damaged by herbivores.