Growth, photosynthesis, and extracellular organic release in colonized and axenic Myriophyllum spicatum

Abstract

Growth and photosynthesis of axenic and colonized Myriophyllum were compared to test the validity of using axenic plants as controls in the quantification of extracellular organic carbon (EOC) release. Axenic plants were characterized by lower growth rates that could be attributed to the unavailability of some major nutrients other than N, P, or C and (or) micronutrients in the culture medium. Vmax, the maximum rate of bicarbonate uptake, and Pmax, the maximum light-saturated rate of photosynthesis, of nonaxenic Myriophyllum were significantly higher than those of axenic plants. These differences could be attributed to epiphytic algal photosynthesis. At subsaturating dissolved inorganic carbon concentrations (below 15 mg C ∙ L−1), both plants achieved similar rates of photosynthesis but differed in the kinetics of EOC release. In short-term incubation (2–6 h), 14C-EOC accounted for 0.2–0.4% of photosynthesis, and total EOC amounted to 1.3–3.8%. 14C-EOC consisted primarily (≥ 60%) of low molecular weight products (≤ 1500). No differences were apparent in size distribution patterns of 14C-EOC from axenic and nonaxenic Myriophyllum and at different dissolved inorganic carbon concentrations. Axenic plants generally showed lower rates of EOC release (in absolute values). On colonized Myriophyllum, the contribution of the epiphytes to the EOC release pool was found to be low (≤ 20% of 14C-EOC) and could partly explain the greater EOC release rates of nonaxenic plants. However, our results are not totally conclusive because the lower growth rate of axenic plants could also be responsible for the lower photosynthetic and EOC release rates of these plants.

Epiphytic bacterial community composition on two common submerged macrophytes in brackish water and freshwater

“…Based on our data and the meagre knowledge about planctomycetes ecology, we propose that either nutrient content or plant age (senescence) might account for differences in the abundance of planctomycetes because of the strong negative correlations with carbon, nitrogen, chlorophyll, and total phenolic content. This is supported by a study of marine planctomycetes, which were affected by organic compounds [ 41 ], and the observation that M. spicatum excretes substantial amounts of organic compounds [ 42 ]. Planctomycetes occur in many different habitats, yet their ecology is unexplored since only a few species have been cultivated [ 43 ].…”

The accumulation of amino-acids and humic substances in media conditioned by axenic and non-axenic duckweed (Lemna minor L.) and their possible ecological significance

“…In contrast, Godmaire & Nalewajko (1989) found the opposite trend, as their axenic Myriophyllum released significantly less DOC than non-axenic plants on a weight specific basis. However, in this latter case the comparison was invalidated by the fact that the non-axenic and axenic plants were not in the same growth phase, as the non-axenic plants were growing significantly faster.…”

Allelopathy in Benthic and Littoral Areas: Case Studies on Allelochemicals from Benthic Cyanobacteria and Submersed Macrophytes

“…Observations on freshwater (WetzeI, 1983) and marine macrophytes (Harlin, 1973) indicate that they rely in part on organic compounds obtained from accompanying microorganisms and algae. Some macrophytes may no longer be capable of a sufficient synthesis of certain vitamins, phytohormones, or enzymes (Godmaire and Nalewajko, 1989) and, therefore, obtain those, perhaps in exchange for extracellular organic compounds (EOq, from bacteria or microalgae. A couple of studies with axenic cultures of macrophytes and algae provide further evidence for stimulatory biochemical interactions.…”