The Ups and Downs of Life on the Edge: The Influence of Water Level Fluctuations on Biomass Allocation in two Contrasting Aquatic Plants

Abstract

Plant communities at wetland edges typically exhibit strong zonation along water depth gradients, although community structure is not as simple as this common observation may suggest. Water levels fluctuate at many temporal scales and in varied patterns. Understanding of how water regime controls plant community structure requires information on how individual species are affected by water regime. The allocation of biomass to roots, tillers, stolons and inflorescences was measured over 16 weeks in two species of aquatic plants with contrasting life histories. Juncus articulatus L. produces large numbers of small seeds while Glyceria australis C. E. Hubb produces small numbers of large seeds. Both species also reproduce vegetatively. Changes in biomass allocation were measured in response to duration, frequency and amplitude of water level fluctuations. The fluctuations in water level were achieved by suspending plants in pots from chains and raising and lowering the pots in and out of water in replicate tanks. There were complex responses to water regime components. As is common to many emergents, both species increased allocation to above ground vegetative structures in response to increasing water depth. Differences between the species in overall patterns of allocation reflected differences in life history. Juncus articulatus showed greater overall biomass production and greater proportional resource allocation to inflorescences than Glyceria australis. There were other differences in response to components of water regime that distinguished the species, mainly in allocation to reproduction in response to the range of depths (amplitude) and extended dry periods. These different functional responses to aspects of water level fluctuations indicate it may be possible to manipulate species composition if water levels are controllable. The most important characteristics of water regime were threshold events such as extremes of depth and dry periods. These may not be captured in measures of water regime such as average water levels.

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“…Wetland hydrologic regime can be described by two descriptors, namely, mean depth of standing water (the average aboveground water depth) and hydro-period (the percentage of time with the presence of standing water)-their combined use is found to be crucial to the study of plant response (Geoff et al, 2007). The two regimes used in the analysis below have 1 , which results in a wetter regime having mean standing water depth of 25 cm and being flooded 99% of the time.…”

Estimation of ecological water requirements based on habitat response to water level in Huanghe River Delta, China

“…In wetlands, water depth directly influences the distribution, growth and suitability of specific species (Jackson and Colmer, 2005;Smith and Brock, 2007;Laitinen et al, 2008). Our study results showed that the biodiversity and coverage of macrophyte communities dominated by Phragmites australis reach their peaks at the water depths of -0.30 m and 0 m, respectively, and decrease either above or below that depth.…”

Laboratory study of subtropical wetland plant Lepironia articulata’s water use and sensitivity to groundwater availability

“…0, 30 and 60cm at a high drawdown rate of 8cm/day. Studies of lower groundwater drawdown amplitudes (at 32cm) had demonstrated some degree of impact on wetland vegetation growth, in terms of root shoot ratio (Smith & Brock, 2007). In this experiment, drawdown was extended to 60cm below the initial water level and more rigorous measurements were applied.…”

“…A number of studies have investigated how wetland vegetation growth responds to controlled water level fluctuations, such as rate, frequency and depth of controlled flooding and drought conditions (Deegan et al, 2007;Smith & Brock, 2007;Wei et al, 2014). Deegan et al (2007) studied the impact of ±0cm, ±15cm, ±30cm and ±45cm…”

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