Competition between Free-Floating Plants Is Strongly Driven by Previously Experienced Phosphorus Concentrations in the Water Column

Abstract

Nutrients can determine the outcome of the competition between different floating plant species. The response of floating plants to current phosphorus levels may be affected by previously experienced phosphorus concentrations because some species have the ability to store excess phosphorus for later use. This might have an impact on their competition. Here, we investigate the effect of previous and actual phosphorus concentrations on the growth rate of free-floating plant species (Azolla filiculoides, Lemna minor/gibba and Ricciocarpus natans)and the effect of phosphorus history on the competition between L. minor/gibba and A. filiculoides and between L. minor/gibba and R. natans. As expected, plant growth was lower when previously kept at low instead of high phosphorus concentrations. Growth of L. minor/gibba and A. filiculoides with a phosphorus rich history was comparable for low and high actual phosphorus concentrations, however, internal phosphorus concentrations were significantly lower with low actual phosphorus concentration. This indicates that both species perform luxury phosphorus uptake. Furthermore, internal P concentration in Azolla and Lemna increased within two weeks after a period of P deficit without a strong increase in growth. A. filiculoides in a mixture with L. minor/gibba grew faster than its monoculture. Morphological differences may explain why A. filiculoides outcompeted L. minor/gibba and these differences may be induced by phosphorus concentrations in the past. Growth of L. minor/gibba was only reduced by the presence of A. filiculoides with a high phosphorus history. Growth of L. minor/gibba and R. natans in mixtures was positively affected only when they had a high phosphorus history themselves and their competitor a low phosphorus history. These observations clearly indicate that phosphorus history of competing plants is important for understanding the outcome of the competition. Therefore, actual and previously experienced phosphorus concentrations should be taken into account in future studies dealing with competition between plants.

Competition Between Lemna minuta, Lemna minor, and Azolla filiculoides. Growing Fast or Being Steadfast?

“…In general, distribution of a species depends on the match of an array of physico-chemical parameters with the specific environmental requirements of the species (Santamaría, 2002 ). For example, a study by Peeters et al ( 2016 ) revealed the relative importance of phosphorus for growth and competitiveness of free-floating macrophytes, and the presence of many species of aquatic macrophytes is associated with eutrophic conditions (Carbiener et al, 1990 ). The study presented here revealed a substantial gradient of light and nutrients across the 24 natural ponds in the study area.…”

Species interactions in three Lemnaceae species growing along a gradient of zinc pollution

“…Additionally, there is a lack of research concerning the influence of species interaction on duckweed resistance to metal pollution. Previous studies suggest that species interactions in duckweeds can influence growth rates (Clatworthy & Harper, 1962;Gopal & Goel, 1993;Peeters et al, 2016). Here, we hypothesized that the presence of a second species in a mixed setting could increase heavy metal tolerance because of facilitation.…”

Azolla along a phosphorus gradient: biphasic growth response linked to diazotroph traits and phosphorus-induced iron chlorosis

“…The general composition of the solution was similar to the quality of natural surface waters where Azolla is abundant (Supplementary Table S1 ). After sufficient Azolla biomass had been produced in the greenhouse for 30 days 37 , the plants were pretreated for 10 days in larger basins without harvesting to minimize P history effects 13 . Nutrient solutions were replaced 3 times a week.…”

“…Nutrient solutions were replaced 3 times a week. After this period 13 , 7.5 g (surface cover of 90%) of carefully dry-blotted A. filiculoides was transferred to a 1 l glass aquarium (10 cm × 10 cm × 12 cm; L × W × H; 750 g FW m −2 ), which was continuously fed by the same nutrient solution (pH = 7.3) as during the acclimatization period, at a rate of 1 l d −1 using peristaltic pumps (Masterflex L/S; Cole-Palmer, Chicago, IL, USA). Nutrient concentrations were checked biweekly.…”

“…Given its high potential P uptake rates, luxury accumulation of P 12 , 13 and high growth rates, Azolla may well be used for phytoremediation with respect to P 4 , 12 , 14 – 17 . The cultivation of Azolla spp.…”