Integrating ecology and physiology of root‐hemiparasitic interaction: interactive effects of abiotic resources shape the interplay between parasitism and autotrophy

Abstract

SummaryRoot hemiparasites are green photosynthetic plants, which parasitically acquire resources from host xylem. Mineral nutrients and water, two principal below-ground abiotic resources, were assumed to affect the interaction between hemiparasites and their hosts. The shape of these effects and the underlying physiological mechanisms have, however, remained unclear.We conducted a glasshouse experiment with root-hemiparasitic Rhinanthus alectorolophus, in which we manipulated the availability of mineral nutrients and water. Biomass production and Chl fluorescence of the hemiparasites and hosts were recorded, together with proportion of host-derived carbon in hemiparasite biomass.The abiotic resources had profound interactive effects on the performance of both the hemiparasite and the hosts, as well as the balance of above-ground biomass between them. These effects were mainly based on an increase of growth and photosynthetic efficiency under high nutrient concentrations, on the hemiparasite's ability to induce strong water stress on the hosts if water is limiting, and on release of the host from parasitism by simultaneous abundance of both resources.Hemiparasitism is a highly variable interaction, in which environmental conditions affect both the parasitic and autotrophic (and thus competitive) components. A hemiparasite's own photosynthesis plays a crucial role in the assimilation of parasitized mineral resources and their transformation into growth and fitness.

Suppressing competitive dominants and community restoration with native parasitic plants using the hemiparasitic Rhinanthus alectorolophus and the dominant grass Calamagrostis epigejos

“…This limitation due to competition for light from fast‐growing dominants can be expected to be strongest at sites that are simultaneously moist and nutrient‐rich where the relative advantages provided by hemiparasitism decrease as does the suppressive effect on the host (Těšitel et al . ).…”

Root hemiparasitic plants are associated with high diversity in temperate grasslands

“…Hemiparasites perform poorly under either of these extremes (Těšitel et al. ) and consequently rarely occur in such conditions (Těšitel et al. ).…”

Root hemiparasites in productive communities should attack competitive host, and harm them to make regeneration gaps

“…Although the uptake of organic carbon can be very helpful in overcoming critical life stages or stressful conditions, the fitness of hemiparasites generally depends on their own photosynthesis, the efficiency of which is greatly increased by mineral nutrients (Těšitel et al. ). This makes their relationship with their host unique – whereas below‐ground it is a parasitic interaction, above‐ground it is pure competition for light.…”

“…Competition for light has been identified as the factor strongly limiting hemiparasite seedling establishment in highly and moderately productive environments (Těšitel et al. , ; Mudrák et al. ).…”

“…Moreover, hemiparasites tend to suppress the growth of host shoots more than roots, decreasing the host's above‐ground competitive ability while keeping functional root systems that provide them with nutrients (Těšitel et al. ). The host resource depletion is also prevented by at least partial regeneration after the dieback of short‐lived annual or biennial hemiparasites, which might be supported via fertilization by good‐quality hemiparasite litter (Spasojevic & Suding ; Demey et al.…”