Water brownification may increase the invasibility of a submerged non-native macrophyte

Abstract

Environmental conditions and human activities play a significant role in structuring novel assemblages of native and non-native species. Ongoing and future climatic change may alter the performance of native and non-native species and their biotic interactions. In the northern hemisphere, expected climate changes include warmer temperatures and higher precipitation, the latter of which may increase dissolved organic carbon (humic) concentrations, resulting in browner water in aquatic ecosystems (brownification). We tested the effects of elevated temperature (3°C) and brownification on native and non-native aquatic plant production in mesocosms over 56 days. Elodea canadensis, an aquatic invasive plant, had higher relative growth rate in terms of both length and weight, as well as higher weight to length ratio when grown in brown versus clear water; E. canadensis did not respond to temperature treatments. Different functional groups of native producers (phytoplankton, periphyton, macrophytes) showed different relationships to temperature and brownification treatments, with the macrophyte response being most notable because it was opposite to that of E. canadensis. Native macrophytes decreased in biomass in browner water, where they represented about 40 % of total biomass compared to 85 % in clear water. In regression analyses, E. canadensis length RGR was best predicted only by water color treatment, but biomass RGR and biomass per length were inversely correlated with native macrophyte biomass, which is consistent with competition. Our results unexpectedly showed water brownification to have more influence on lake invasion than climate warming at this temperature regime. Two pathways emerged for climate to interact with biological invasions in structuring novel communities: directly, if non-native species respond positively to climate change, and indirectly through species interactions, for instance, because water brownification impairs growth of native macrophytes and reduces biotic resistance to invasion.

Ecological mechanisms of invasion success in aquatic macrophytes

“…Mormul et al (2012) observed that although temperature did not seem to have an effect, water ''brownification'' (increased organic carbon concentrations, resulting in browner water) owing to changing climatic conditions resulted in increased growth of invasive E. canadensis and decreased growth of native species. They suggest that this brownification gives E. canadensis a competitive advantage, facilitating increasing future spread.…”

Insect herbivory on native and exotic aquatic plants: phosphorus and nitrogen drive insect growth and nutrient release

“…Furthermore, they can indirectly affect vegetation composition by releasing nutrients and organic compounds through excretion following the consumption of large amounts of macrophytes (Newman, 1991;Vanni, 2002). The microbial degradation of dissolved organic compounds into humic acids can then cause brownification of the water (Roulet & Moore, 2006;Graneli, 2012), which affects light availability and vegetation composition (Mormul et al, 2012).…”

Mesocosm Experiments as a Tool for Ecological Climate-Change Research

“…Mesocosm Experiments as a Tool for Ecological Climate-Change Research consequences of climate change, such as increases in run-off Vinebrooke, 2009), salinisation (Herbst andBlinn, 1998;Jeppesen et al, 2007), and browning by increasing concentrations of humic substances in the water column (Mormul et al, 2012;. Some of the ultimate consequences of climate change, such as cycling of nitrogen (Veraart et al, 2011) and carbon (Atwood et al, 2013;Flanagan and McCauley, 2010;Moss, 2010;Yvon-Durocher et al, 2010a,b, 2011a, benthic-pelagic or terrestrial-aquatic coupling (Boros et al, 2011;, or the implications of biodiversity change for ecosystem stability (Thompson and Shurin, 2011) have only recently been addressed using pond mesocosms.…”