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

Verena Hammerl,Juergen Kreyling,Josep Peñuelas,Anke Jentsch,Michael Schloter,Carl Beierkuhnlein,Jan Schuerings,Mohammed A S Arfin-Khan,Andrey V Malyshev,Kerstin Grant,Karin Pritsch,Jordi Sardans

doi:10.1038/s41598-019-51221-w

Abstract

Climate change affects all seasons, but warming is more pronounced in winter than summer at mid- and high latitudes. Winter warming can have profound ecological effects, which are rarely compared to the effects of summer warming, and causal explanations are not well established. We compared mild aboveground infrared warming in winter to warming in summer in a semi-natural, cool-temperate grassland in Germany for four years. Aboveground plant biomass increased following winter warming (+18%) and was unaffected by summer warming. Winter warming affected the composition of the plant community more than summer warming, favoring productive species. Winter warming increased soil respiration more than summer warming. Prolonged growing seasons and changes in plant-community composition accounted for the increased aboveground biomass production. Winter warming stimulated ecological processes, despite causing frost damage to plant roots and microorganisms during an extremely cold period when warming reduced the thermal insulation provided by snow. Future warming beyond such intermittent frosts may therefore further increase the accelerating effects of winter warming on ecological processes.

Highlights

Summer warming can increase aboveground plant biomass production, but this effect is often limited by water, light, and nutrient availability[3]
Plants in areas characterized by seasonal frost are directly limited by temperature in winter[6], and winter warming increases the spring[7] or annual[8] aboveground plant biomass production in temperate grasslands, if warming leads to the absence of soil frost[9]
Aboveground net primary production (ANPP, i.e. the biomass produced over one year) was on average 18% higher and differed significantly from control in all four study years, with increasing effect sizes over time, in the winter-warming treatment compared to reference conditions (Fig. 1a)

Summary

Introduction

Summer warming can increase aboveground plant biomass production, but this effect is often limited by water, light, and nutrient availability[3]. This earlier start of the growing season due to warming, can lead to pre-mature de-hardening, with an increased risk of subsequent frost damage[16]. Snow is an excellent insulator, and reduced snow cover and depth can lead to “colder soils in a warmer world”[20] because of the reduced insulation of the soil during atmospheric frost The effect of this insulation complicates predictions of soil biotic responses to winter warming. In order to explain the observed net effects of winter warming (annual aboveground biomass production, plant community composition, soil respiration), plant performance (greenness, root growth, leaf C:N ratio) and soil biotic processes (microbial biomass, potential extracellular enzyme activity, N-availability, soil respiration) were quantified during winter

Methods

Results

Conclusion