Nitrogen leaching is enhanced after a winter warm spell but mainly controlled by vegetation composition in temperate zone mesocosms

Abstract

Background and aims Leaching of nitrogen (N) from natural ecosystems poses serious environmental problems. Extreme events such as winter warm spells could exacerbate N leaching by disrupting biogeochemical cycles and will become more frequent with the projected climate change.Methods We used lysimeters to investigate N leaching in response to a 12-day winter warm spell at two field sites with contrasting winter climate and in seven different vegetation covers in 140 well established mesocosms. Results Mean rates of N leaching reached 3.4 ± 0.4 mg N m −2 d −1 over the 49 days of observations in late winter/ early spring. The winter warm spell resulted in an 82 % increase of N leaching after the warm spell (up to 18 mg N l −1 ). Stronger leaching occurred at the colder site which can be explained by plants becoming photosynthetically active with subsequent frost damaging their above-ground tissue due to missing insulation by snow and/or dehardening, resulting in reduced N uptake. N leaching differed by >600 % among contrasting vegetation composition with almost no leaching from grassland types and strongest leaching from shrubland types that even surpassed leaching from bare ground controls. Conclusions Winter warm spells can affect the biogeochemistry of temperate ecosystems with plant performance and vegetation composition controlling the amount of N leaching.

Winter warming is ecologically more relevant than summer warming in a cool-temperate grassland

“…More productive (taller) species may benefit more from a longer growing season and thereby become more dominant by outcompeting smaller, light demanding species by shading. Changes in plant-community composition induce lasting changes in ecosystem functioning, relevant not only for aboveground biomass production, but also for decomposition and nutrient cycling 12 or N leaching 30 and potentially leading to hysteresis and regime shifts in plant-community composition and ecosystem functions 31 . Changes in plant-community composition are therefore more relevant than short-term physiological effects, which may simply be due to phenotypic plasticity 32 , are generally reversible and may be transient.…”

“…A reduction in snow cover and the loss of its insulating effect followed by subsequent frost can increase frost damage 30,34,35 . Frost tolerance differs among grass species 36 and can therefore be expected to act as a selective driver that can contribute to changes in community composition.…”

Biotic responses to climate extremes in terrestrial ecosystems

“…These two traits enable plants to resist drought ( Van Der Knaap et al., 2014 ). However, some grasses, e.g., the common native European grass Holcus lanatus, can benefit when higher temperatures enhance soil nutrient mineralization ( Kreyling et al., 2015 ). Common or dominant plant species may also be the ones to respond the most to climate extremes ( Gitlin et al., 2006 ).…”