Effects of pollination and pollen source on the seed set ofPedicularis palustris |
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Authors: | Sophie Karrenberg Kai Jensen |
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Institution: | (1) Graduate School of Environmental Science, Hokkaido University, Sapporo 060–0810, Japan |
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Abstract: | Habitat alteration can deteriorate plant-pollinator interactions and thereby increase the risk of population extinction. As
part of a larger study on the effects of changes in land use on fen grassland vegetation, factors influencing the seed set
of a short-lived, endangered wetland plant,Pedicularis palustris, were studied. We conducted field pollination experiments in one large and one small population. To investigate the effect
of pollen source on seed set, individual flowers of caged plants were left unpollinated or were pollinated with pollen from
the same flower, the same population or another population. To study pollen limitation and flower display, whole plants were
subjected to pollinator exclosure, hand pollination or natural pollination. Self-compatibility was high, but differed between
populations (61% and 97% of seed set after cross-pollination within populations). Cross-pollination between populations did
not significantly alter seed number per capsule. Pollinator exclosure resulted in a very low seed set (<15% of natural seed
set), despite high self-compatibility. The most likely explanations for high self-compatibility in combination with low autofertility
are geitonogamy as reproductive assurance, selective neutrality of self-compatibility and phylogenetic constraints. Because
of low autofertility, the seed set inP. palustris depends on pollinators. In the study populations, natural pollination was clearly sufficient for maximum seed production
per plant, but seed set per capsule was significantly pollen-limited in the smaller population. Plants in this population
also had a higher maximum percentage of simultaneously open flowers than those of the large population (31% vs. 13%), while
flower longevity was generally extended without pollination. It is concluded thatP. palustris may influence pollinator behaviour and therefore the risk of pollen limitation by flower display.P. palustris showed a flexible reaction to differing pollination regimes without losses in overall seed set in the study populations. |
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