Litter of the hemiparasite Bartsia alpina enhances plant growth: evidence for a functional role in nutrient cycling

Abstract

Hemiparasitic angiosperms concentrate nutrients in their leaves and also produce high quality litter, which can decompose faster and release more nutrients than that of surrounding species. The impact of these litters on plant growth may be particularly important in nutrient-poor communities where hemiparisites can be abundant, such as the sub-Arctic. We tested the hypothesis that plant growth is enhanced by the litter of the hemiparasite Bartsia alpina, in comparison with litter of co-occurring dwarf shrub species, using a pot based bioassay approach. Growth of Betula nana and Poa alpina was up to 51% and 41% greater, respectively, in the presence of Bartsia alpina litter than when grown with dwarf shrub litter (Vaccinium uliginosum, Betula nana and Empetrum nigrum subsp. hermaphroditum). The nutrient concentrations of Betula nana plants grown with Bartsia alpina litter were almost double those of plants grown with dwarf shrub litter, and a significantly greater proportion of biomass was allocated to shoots rather than roots, strongly suggesting that nutrient availability was higher where Bartsia alpina litter was present. The presence of litter from dwarf shrubs, or the moss Hylocomium splendens, did not reduce the positive effect of Bartsia alpina litter on plant growth. E. nigrum litter did not appear to affect plant growth substantially differently from litter of other dwarf shrub species, despite earlier reports of its allelopathic action. The enhanced nutrient uptake and growth of plants in the presence of Bartsia alpina (and potentially other hemiparasitic species) litter could have important implications for communities in which it occurs, including enhanced survival of seedlings of co-occurring species and increased resource patchiness.

Resource limitation and the role of a hemiparasite on a restored prairie

“…Through the parasitism pathway strong parasites reduce host growth, which in turn alters diversity and reduces community productivity. However, hemiparasites tend to concentrate nutrients in leaves, which increases litter decomposition and nutrient release (Quested et al 2002(Quested et al , 2003Watson 2009). Through the alternative litter pathway, hemiparasites increase nutrient availability in the community, leading to little change in diversity and increased community productivity.…”

Interactions between hemiparasitic plants and their hosts

“…34,38,44 However, nutrient-rich litter of hemiparasitic plants decomposes quickly, which may in some cases act in an opposite way enhancing nutrient cycling in communities. 45 Little is known on the effect of light competition on stem parasites due to methodical difficulties of studying ecological interactions of epiphytes. It is however likely that negative effects of light competition are less pronounced given the position that mistletoes occupy in the host canopy and rather high heterotrophic carbon acquisition (Fig.…”

Does infection tilt the scales? Disease effects on the mass balance of an invertebrate nutrient recycler

“…Their epidemics can reduce the population size of their hosts which alters foodwebs and ecosystems (Kohler and Wiley 1997;Wilmers et al 2006). Even without reducing host density, parasites can affect the nature of consumer-primary producer interactions (Wood et al 2007;Bernot and Lamberti 2008) and modify the trophic transfer of nutrients and energy (Quested et al 2003;Johnson et al 2010;Grami et al 2011). While efforts to incorporate entire parasite communities into ecosystem paradigms are proving fruitful (Lafferty et al 2006;Amundsen et al 2009), we still lack a basic framework for predicting how parasites affect ecosystem function through changes in host metabolism.…”