The role of heterotrophic carbon acquisition by the hemiparasitic plant Rhinanthus alectorolophus in seedling establishment in natural communities: a physiological perspective

Abstract

Summary Heterotrophic acquisition of substantial amounts of organic carbon by hemiparasitic plants was clearly demonstrated by numerous studies. Many hemiparasites are, however, also limited by competition for light preventing the establishment of their populations on highly productive sites. In a growth‐chamber experiment, we investigated the effects of competition for light, simulated by shading, on growth and heterotrophic carbon acquisition by the hemiparasite Rhinanthus alectorolophus attached to C3 and C4 hosts using analyses of biomass production and stable isotopes of carbon. Shading had a detrimental effect on biomass production and vertical growth of the hemiparasites shaded from when they were seedlings, while shading imposed later caused only a moderate decrease of biomass production and had no effect on the height. Moreover, shading increased the proportion of host‐derived carbon in hemiparasite biomass (up to 50% in shaded seedlings). These results demonstrate that host‐derived carbon can play a crucial role in carbon budget of hemiparasites, especially if they grow in a productive environment with intense competition for light. The heterotrophic carbon acquisition can allow hemiparasite establishment in communities of moderate productivity, helping well‐attached hemiparasites to escape from the critical seedling stage.

SEED GERMINATION AND PLANT DEVELOPMENT IN Escobedia grandiflora (OROBANCHACEAE): EVIDENCE OF OBLIGATE HEMIPARASITISM?

“…Escobedia grandiflora seeds do not require the presence of the host in order to germinate, which is typical of facultative parasitic plants (Těšitel et al, 2011). Although no studies on Escobedia seed germination are known, studies on seeds of related obligately parasitic genera, Alectra and Aeginetia L., recorded a lower percentage of germination than that of those found here (French and Sherman, 1976;Bennett and Mathews, 2006).…”

“…Seedlings even with the host, were few in number and showed slow growth afterwards. It is possible that, as in other hemiparasitic species of the family, the state of the seedling is critical (Těšitel et al, 2011) although it initially seems to depend on the food reserve of the seeds, and on their own photosynthetic activity. Germinated seeds need to quickly parasitize a host in order to obtain nutrition.…”

“…In order to evaluate the reproductive phase, the application of this study over longer periods of time is recommended. Hemiparasitic plants have an ambiguous relation with their host since they take nutrients from it but also compete with it for light thus affecting photosynthetic activity (Těšitel et al, 2011). In this experiment, the leaves of the host were pruned to favor the photosynthetic activity of the E. grandiflora.…”

Growth, survival and generative reproduction in a population of a widespread annual hemiparasite Melampyrum pratense

“…On the other hand, the reproductive output appears fairly high if the heavy weight (Melampyrum seeds are the heaviest among related genera; Matthies 1991;Těšitel et al 2011) of the seeds is considered. Seed production is closely linked to the size of the vegetative part of plant individuals depending closely on the dry mass during the late summer fruiting season.…”

“…This suggests that the total reproductive output and hence also fitness is dependent on vegetative growth across the whole lifespan. In this respect, it is quite likely that differential rate of early development are underpinned by quality of attachment to the host (Cameron & Seel 2007) since otherwise all individuals occur on the same site and the intensity of competition for light potentially affecting the seedlings in the spring period (Těšitel et al 2011) is minimal due to the very open forest understory.…”