Light Availability and Patterns of Allocation to Reproductive and Vegetative Biomass in the Sexes of the Dioecious Macrophyte Vallisneria spinulosa

Abstract

Environmental changes, e.g., eutrophication, in aquatic ecosystems can greatly alter light available to submerged macrophytes. In dioecious plants, given potential for sex-specific differences in resource requirements (i.e., high-carbon for seeds vs. high-nitrogen for pollen), females and males are expected to divergently adjust allocations toward resource acquisition structures when resources are limited during growth. Here, Vallisneria spinulosa was used as a representative dioecious submerged macrophyte to detect sex-specific responses to light limitation and assess whether sexual dimorphism varied with resource availability. Plants were grown under varying levels of light availability in nine outdoor mesocosms for 14 weeks. Late in the reproductive season, allocations to vegetative and reproductive traits for both sexes were determined and relative allocation to reproduction vs. vegetative growth was analyzed. Female and male reproductive plants differed in adjustments of resource allocation in response to light availability. Under low light, females showed a smaller reduction in allocation of resources to vegetative tissues and greater leaf area than males, suggesting female plasticity to increase carbon capture. Under low light, males showed a smaller reduction in reproductive allocation than females (flowers and inflorescences in males vs. fruits in females), suggesting that carbon limitation has greater impacts on sexual reproduction by females than males. Our study provides evidence of differences in reproductive costs and currencies for female vs. male reproduction in aquatic macrophytes, as V. spinulosa responded plastically to reduced light, with sexually dimorphic allocation strategies. Sex-related resource currencies are potentially important drivers for sex-specific variations in allocation patterns, with females safeguarding their vegetative carbon-rich biomass to satisfy future fruit and seed production.

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).…”

Response of Growth-Related Traits of Submerged Macrophytes to Light Reduction: A Meta-Analysis

“…Experimental factors (e.g., plant type, leaf shape, treatment method, experiment duration and percentage, and experimental end season) have been shown to affect the growth responses of plants to light reduction [3,30,74,75]. We found that the lnRRs of RGR were significantly negative for plants grown from shoots and seedlings but nonsignificantly positive for those grown from mature plants at the beginning of the experiment (Figure 1b), which might be related to more carbon storage in mature plants leading to greater adaptability.…”

“…For instance, submerged macrophytes could ease low light stress via growth-related and physiological trait adjustments (e.g., shoot length, biomass allocation, and leaf photosynthesis parameters) to optimize light utilization and increase survival probability [27][28][29]. Thus, functional traits are considered vital drivers in regulating the growth strategies of submerged macrophytes [26,30].…”

Carbon, Nitrogen, and Phosphorus Allocation Strategy Among Organs in Submerged Macrophytes Is Altered by Eutrophication

“…Eutrophication arising from N and P enrichments is supposed to reduce light availability by promoting the growth of phytoplankton and periphyton, thereby resulting in a shading effect upon submerged macrophytes (Roberts et al, 2003;Sayer et al, 2010;Olsen et al, 2015). Furthermore, the allocation of limiting resources, as an important adaptive strategy for how plants respond to different and changeable environments, reflects the influences of evolutionary history, environmental stresses and trade-offs of functional traits (Xie et al, 2005;Kerkhoff et al, 2006;Dulger et al, 2017;Scartazza et al, 2017;Li et al, 2019). To maximize their multiple functions, namely growth, reproduction, and nutrient storage of plants, plants need to rebalance the allocation of elements across organs under various environmental stresses (Schreeg et al, 2014;Yang et al, 2014).…”

“…Nutrient allocation strategies among organs may reflect the interplay between plants and their ambient environments, because plants can coordinate different organs to satisfy the nutritional requirements of various functions with respect to the allocation of limited nutrients and adaptation to a changing environment (Liu et al, 2010). According to previous studies, plant species as well as the availability of light resources and nutrient can significantly influence the nutrient concentrations of a single organ (Xing et al, 2013;Grasset et al, 2015;Su et al, 2016;Dulger et al, 2017;Li et al, 2017Li et al, , 2019Velthuis et al, 2017). Accordingly, we hypothesize that nutrient allocation among organs differs not only among growth forms but also changes with key environmental factors.…”