Reproductive allocation of Carex flava reacts differently to competition and resources in a designed plant mixture of five species

Abstract

In natural plant communities, reproductive allocation can be affected by complex interactions among abiotic resources, species competition and plant size. This topic was addressed using a variety of designed mixed stands of five species (Carex elata, Carex flava, Lycopus europaeus, Lysimachia vulgaris and Mentha aquatica) under four abiotic conditions to investigate how competition and abiotic resources influence the reproductive allocation of one of the five species, C. flava. The plant mixtures varied systematically in both the relative abundance of the five species and the absolute density, and were each established with two levels of water and nutrients. In total, 176 mixtures were maintained for two growing seasons in large pots in an experimental garden. Reproductive allocation of C. flava increased from 6.8% to 9.7% under high nutrient application; however, for both nutrient levels, reproductive allocation was independent of shoot mass (sizeindependent allocation). Under low competition, reproductive allocation of C. flava decreased as its shoot mass increased, indicating a relatively high investment in vegetative structures under higher light availability. However, under strong competition, the allocation pattern changed and a constant reproductive allocation for different plant sizes was observed. Different water levels did not influence the shoot mass, seed mass or reproductive allocation of C. flava, indicating that the species was not stressed under dryer conditions. When under competitive pressure, however, the species responded with reduced shoot and seed production under more favourable water conditions. This behaviour indicates a trade-off between the ability to tolerate stress and the competitive and reproductive response of C. flava. In conclusion, C. flava was adversely affected by competition with some of the species, and competition, mediated by plant size, indirectly affected reproductive allocation. C. flava was able to modify its allocation pattern depending on the available resources and retained its reproductive allocation even under unfavourable conditions for varying plant sizes, which is interpreted as an advantageous reaction to greater competition pressure.

Asteraceae invaders have limited impacts on the pollination of common native annual species in SW Western Australia’s open woodland wildflower communities

“…In spite of the often shared biogeographic and evolutionary histories of native insect-pollinated plants and their pollinators, pollinator interactions are more often opportunistic than oligolectic in nature and pollinator infidelity is common (Kearns et al 1998). Even where exotic and native species do not share pollinators, exotic species may indirectly impact native plant pollination by reducing native species densities and thus floral density (through direct competition) (Karron et al 1995;Kirchner et al 2005;SteffanDewenter et al 2001) or by driving a reduction in flowering effort per individual (driving a reallocation of resources away from flower production, Suter 2009;Wang et al 2014). The mechanisms and impacts of pollinator-mediated interactions between native and exotic species are clearly variable, and the introduction of an exotic species into a native plant community can produce contrasting effects on different native species (Waters et al 2014).…”