Water depth affects reproductive allocation and reproductive allometry in the submerged macrophyte Vallisneria natans

Abstract

In freshwater ecosystems, shifts in hydrological regimes have profound effects on reproductive output (R), along with vegetative biomass (V) and survival of plants. Because reproductive allocation (RA) is allometric, it remains unclear whether the observed variation of RA in response to water level variability is due to fixed patterns of development or plasticity in the developmental trajectories. Here, we investigated shifts in RA of a submerged macrophyte Vallisneria natans in response to water depth to test the hypothesis that allometric trajectories of RA are highly plastic. Plants were grown at three water depths (50, 100 and 150 cm) and measured after 26 weeks of growth. The relationships between R and V among treatments were compared. Deep water affected both biomass and number of fruits produced per plant, leading to less sexual reproduction. Plants in deep water started flowering at a smaller size and despite their small mature size, had a relatively high RA. Furthermore, these plants had a much lower log R–log V relationship than shallow- or intermediate-water plants. In conclusion, reproduction of V. natans is highly variable across water depth treatments, and variations in reproductive allometry represent different strategies under an important stress gradient for these freshwater angiosperms.

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

“…This general pattern probably occurred because shallow water subjects these submerged aquatic plants to high light conditions that may interfere with photosynthesis, whereas our deep‐water treatment decreased light availability, photosynthesis, and energy‐use efficiency. Similar nonlinear responses to these three water depth treatments in growth have also been reported in semelparous V. natans (Li et al., ). Our range of water depth treatments therefore probably encompassed both stressful and less stressful conditions for growth.…”

“…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.…”

Plasticity in Sexual Dimorphism Enhances Adaptation of Dioecious Vallisneria natans Plants to Water Depth Change

“…Submerged macrophytes normally adapt to low light availability in water column by one of two distinct strategies – elongating shoot toward water surface to alleviate low light stress or enhancing low light tolerance through photosynthetic adjustments (Riis et al, 2012; Chen et al, 2016). Yet relatively fewer studies exist dealing with the variation in plant reproductive traits (Li et al, 2017, 2018), and even fewer studies have been conducted to further understand patterns of sexual dimorphism in dioecious macrophytes compared to their terrestrial relatives (Dorken and Barrett, 2004; Li et al, 2019b). Reproductive strategies influence the response of populations to environmental variation (Dorken and Barrett, 2004).…”

Species-Specific Responses of Submerged Macrophytes to Simulated Extreme Precipitation: A Mesocosm Study

“…The responses of flowering also depend on growth form; thus, the rosette-type macrophyte V. denseserrulata produces female flowers at the bottom of the plant, while the canopy-forming P. lucens flowers at the growing tips after the tips reach the water surface [30]. Thus, P. lucens elongated to the surface even in the extreme treatment and tended to exhibit advanced florescence with more flowers, while V. denseserrulata likely faced a higher cost of producing female flowers in deeper water [47].…”