Seasonal Effects of Extreme Weather Events on Potential Extracellular Enzyme Activities in a Temperate Grassland Soil

Verena B. Hammerl,Karin Pritsch,Silvia Gschwendtner,Michael Schloter,Kerstin Grant,Anke Jentsch,Carl Beierkuhnlein

doi:10.3389/fenvs.2018.00157

Abstract

Magnitude and timing of precipitation events within the growing season might be decisive for alterations in potential extracellular enzyme activity (PEEA), with consequences for nutrient cycle and carbon storage in grassland ecosystems. Pattern of PEEA catalyzing major steps of the carbon cycle (β-glucosidase (β-gls), cellobiohydrolase (cel), glucuronidase (glr) and xylosidase (xyl)), soil respiration rates and extractable organic carbon were analyzed in response to increased intra-annual precipitation variability in a European, mesic temperate grassland. The field experiment was carried out in three subsequent years by simulating recurrent drought events combined with heavy rainfall either early or late in the growing season (spring or summer) by rainout shelters and irrigation systems. Our data indicated comparable effects of the drought settings independent from the timing of the drought. Both for the simulated spring- and summer drought a decrease of enzymatic activities was observed compared to the control plots, with s-gls activity after the summer drought being the only exception. However, response pattern towards rewetting differed depending on the seasonal timing of the drought being introduced. After spring drought, a fast recovery to control level was observed for PEEA of s-gls and xyl, whereas cel and glr activity remained constantly lower. Rewetting after summer drought induced an increase of all enzymatic activities to values even higher compared to the controls. Overall, our data indicate a high resilience of PEEA towards drought and rewetting events in grassland soils, which is modulated by the seasonal timing of the extreme weather events.

Highlights

Extreme weather events such as heavy rainfall or extreme drought are predicted to increase in frequency and magnitude as a consequence of climate change (O’Gorman and Schneider, 2009; IPCC, 2014)
In 2009 and 2010 soil moisture did not drop below permanent wilting point (PWP) during the spring drought (D1) but during the summer drought (D2)
Our results indicate that drought/rewetting itself and the seasonal timing of the extreme event remarkably affected exoenzymatic activity: while reduced potential extracellular enzyme activities (PEEAs) recovered after summer drought rewetting, the negative effect of spring drought was much more pronounced, resulting in irreversible lower cel and glr activity despite rewetting

Summary

Introduction

Extreme weather events such as heavy rainfall or extreme drought are predicted to increase in frequency and magnitude as a consequence of climate change (O’Gorman and Schneider, 2009; IPCC, 2014). Results from several studies have suggested that the consequences of extreme events on ecosystem functioning will be much stronger than the effects of changes in mean values. In contrast to drought, enhanced precipitation increases microbial activity (Barnard et al, 2015), resulting in increase of enzyme activity and decrease of EOC (Fierer and Schimel, 2003). Not much is known about to which extent the seasonal timing of the extreme event affects the response of microbial and enzymatic activity, this might be an important factor. Chou et al (2008) observed that changes in the seasonal timing of rainfall significantly affected soil respiration, suggesting that C cycling in annual grasslands will be more affected by altered seasonal timing of precipitation than by changes in rainfall quantity

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