Differential invasion of a wetland grass explained by tests of nutrients and light availability on establishment and clonal growth.

Abstract

Phalaris arundinacea (Poaceae) is aggressively invading wetlands across North America. We tested the hypotheses that open canopies and increased nutrients facilitate vegetative establishment in the field, using a phytometer (6 rhizome fragments/plot, 24 plots/wetland). In each of three wetlands, phytometers received three levels of an NPK fertilizer or served as controls. Emergence and survival differed among sites (P=0.0005), but not due to NPK addition. P. arundinacea survival was highest in a wet prairie with a late-developing canopy, but limited by prolonged flooding in one sedge meadow and by an early-growing, dense plant canopy in a second. These patterns were explained in greenhouse experiments, where both flooding (P<0.0001) and heavy shade (P=0.0002) decreased P. arundinacea aboveground biomass by up to 73% and 97%, respectively. Rhizome fragment survival was reduced by 30% under flooded conditions and 25% under heavy shade. We then tested the hypothesis that a clonal subsidy facilitates vegetative expansion into heavy shade. Established clones were allowed access to bare soil under four levels of shade and two levels of NPK fertilizer in a two-factor greenhouse experiment. Young ramets attached to parent clones readily grew into heavy shade, and the high nutrient treatment increased aboveground growth (P<0.0001) and distance of ramet spread (P=0.0051) by nearly 50%. Under low nutrient conditions, root biomass increased by 30% (P<0.0001). P. arundinacea's rapid expansion into a variety of wetland types is likely a function of clonal subsidy, morphological plasticity, and nutrient availability: young ramets that emerge under shaded conditions are supported by parental subsidies; where nutrients are plentiful, P. arundinacea can maximize aboveground growth to capture more light; and where nutrients are scarce, it can increase belowground foraging.

Impact of water depth and sediment type on root morphology of the submerged plantVallisneria natans

“…However, plants may focus on growing leaves for photosynthesis at the cost of limiting root growth. In the present study, root/leaf mass ratio decreased with increasing water depth overall, indicating that the biomass allocation favors leaf growth rather than root growth, which is thought to be an efficient strategy for plants to adapt to poor light conditions in deep water (Chambers & Kalff 1985;Strand & Weisner 2001;Maurer & Zedler 2002). Meanwhile, photosynthesis of submerged plants is constrained in deep water and there is not enough photosynthate for roots, which, in turn, limits root growth.…”

“…However, it does not work alone. Water depth works in conjunction with sediment type and other environmental factors such as light, air temperature, wave and flow velocity among others (Sand-Jensen & Søndergaard 1979;Barko et al 1986;Maurer & Zedler 2002). Research indicates that, for many submerged plants, the achievement of maximum summer biomass is impacted by both water depth and sediment composition (Chambers & Kalff 1987).…”

Invasive alien plants in China: role of clonality and geographical origin

“…For example, Pysˇek et al (2003) found that novel hybrid invasive genotypes may be produced by rare sexual reproduction, fixed by clonal growth, and presents a previously unknown threat to native vegetation. Maurer and Zedler (2002) suggested that both the resource subsidy from parent clones and resource foraging plasticity contribute to invader's ability to spread rapidly into native vegetation. Reichard and Hamilton (1997) studied the invasive plants of America and also found that clonality may enhance invasion.…”

“…Clonality, an important trait enhancing plants' exploitation of ubiquitous environmental heterogeneity, may aid plants to invade new habitats (Maurer and Zedler 2002). Also, clonality can contribute to spatial occupation at a local scale and risk spreading of the clonal plants (Dong 1996b).…”

Invasion Age and Invader Removal Alter Species Cover and Composition at the Suisun Tidal Marsh, California, USA

“…Seed germination and early life stages are typically suppressed by higher water salinities and by daily inundation, and only those able to tolerate these harsh physical conditions can become established as seedlings. The clonal life-history strategy for reinvasion of gaps has been important in other systems (e.g., [61][62][63]). We observed that clonal species from the surrounding habitat dominated our newly-opened patches created by pepperweed elimination.…”