Allocation to clonal and sexual reproduction and its plasticity in Vallisneria spinulosa along a water‐depth gradient

Abstract

Citation: Li, L., Z. Lan, J. Chen, and Z. Song. 2018. Allocation to clonal and sexual reproduction and its plasticity in Vallisneria spinulosa along a water-depth gradient. Ecosphere 9(1):e02070. 10.1002/ecs2.2070 Abstract. Variations in water level profoundly affect functional stability of freshwater ecosystems, as well as macrophyte growth and reproduction. Although the trade-off between allocation to clonal and sexual reproduction in clonal plants can be influenced by a variety of environmental factors, whether variations of reproductive allocation (RA) in response to different environments are driven only by a sizedependent effect (apparent plasticity) or whether RA can also change independently of plant size (true plasticity) is uncertain. We conducted an experiment in nine outdoor mesocosms (6400 L) to investigate the response of clonal and sexual reproduction and vegetative growth of a perennial submerged macrophyte Vallisneria spinulosa at water depths of 50, 100, or 150 cm. We evaluated size-dependent and sizeindependent effects of water depth on sexual and clonal RA. Deep water reduced vegetative size and sexual output (mass of fruits produced), but increased tuber production of V. spinulosa. There was an apparent trade-off between reproductive modes in terms of biomass investment; plants in deep water allocated more resources into clonal propagation and reduced investment in sexual reproduction compared to plants in shallow or intermediate water. Slopes of allometric relationships (sexual vs. vegetative biomass and clonal vs. vegetative biomass) were significantly affected by water depth. Shifts in sexual RA in response to varying water depths were largely size-dependent, but there were also size-independent effects. In contrast, size-independent effects were more important than effects of size changes in determining clonal RA. We concluded that V. spinulosa adapted to a water-depth gradient by plastic trade-offs between clonal propagation and sexual reproduction. Furthermore, a size-independent effect on RA suggests a flexible reproductive strategy that could be critical for plant performance in changing aquatic environments.

Morphological and physiological response strategies ofVallisneria natansat different water depths and light conditions

“…We found that V. natans faced a trade-off between biomass increase and clonal expansion. In the light control experiment, the population growth increased with light, which agrees with the trade-off theory (Thompson and Eckert, 2004; Reusch, 2006; Van Drunen and Dorken, 2012; Li et al, 2018). V. natans clonal growth and regeneration depend strongly on water depth and light availability (Ferreiro et al, 2013; Søndergaard et al, 2013; Dong et al, 2014; Fu et al, 2014; Wei et al, 2018).…”

“…V. natans clonal growth and regeneration depend strongly on water depth and light availability (Ferreiro et al, 2013; Søndergaard et al, 2013; Dong et al, 2014; Fu et al, 2014; Wei et al, 2018). When light resources are sufficient, V. natans allocates more energy to reproduction and population growth as a more abundant populations can share or prevent the likelihood of extinction, while under low light conditions, V. natans allocated most of its biomass to growth of light resource acquisition organs and the least to reproduction (Li et al, 2018). Darkness therefore increases the likelihood of population extinction (Xiao et al, 2007).…”

“…Phenotypic plasticity is ubiquitous in all types of organisms (Sultan, 1987; Sultan, 1995; Tollrian, 2002) and is an important ecological strategy for plants adapt to heterogeneous habitats (Sultan, 1995; Orr, 1999; Huey et al, 2000; Debat and David, 2001; Mai and Lovett-Doust, 2005; Bradshaw, 2006). As emphasized in life history theory, shifts in phenotypic plasticity can be instrumental for maintaining plant fitness in a changing environment (Li et al, 2018). Phenotypic plasticity increases resistance and adaptability and allows species to have a wider ecological niche, to better tolerate stressful environmental conditions, and to expand their potential range of available diet resources (Sultan and Bazzaz, 1993; Cao et al, 2016).…”

“…Water depth and underwater light intensity are crucial to the survival and growth of submerged macrophytes. Light availability is severely attenuated by water depth, which may be the main factor restricting the growth of submerged macrophytes as photosynthesis can be constrained in deep water (Li et al, 2018). Along with the increasing water depth, the underwater light intensity decreases dramatically, submerged macrophytes usually show adaptations through a variety of adjustments of plant morphology, biomass reallocation, photosynthesis pigment content, and root traits (Maberly, 1993; Strand, 2001; Hussner et al, 2009).…”

Sex‐specific plasticity of reproductive allocation in response to water depth in a clonal, dioecious macrophyte

“…The effect of water depth on growth and reproduction in submerged macrophytes has been widely studied (e.g., Strand and Weisner, ; Zhou et al., ; reviewed by Sculthorpe, ), including in several Vallisneria species (Lovett Doust and Laporte, ; Li et al., , ). However, earlier studies of Vallisneria did not consider whether variation in water depth may lead to plasticity in sexual dimorphism.…”