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

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 ß-gls activity after the summer drought being the only exception. However, response pattern toward 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 ß-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 toward drought and rewetting events in grassland soils, which is modulated by the seasonal timing of the extreme weather events

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

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 processe

Shallow non-inversion tillage in organic farming maintains crop yields and increases soil C stocks: a meta-analysis

Reduced tillage is increasingly promoted to improve sustainability and productivity of agricultural systems. Nonetheless, adoption of reduced tillage by organic farmers has been slow due to concerns about nutrient supply, soil structure, and weeds that may limit yields. Here, we compiled the results from both published and unpublished research comparing deep or shallow inversion tillage, with various categories of reduced tillage under organic management. Shallow refers to less than 25 cm. We found that (1) division of reduced tillage practices into different classes with varying degrees of intensity allowed us to assess the trade-offs between reductions in tillage intensity, crop yields, weed incidence, and soil C stocks. (2) Reducing tillage intensity in organic systems reduced crop yields by an average of 7.6 % relative to deep inversion tillage with no significant reduction in yield relative to shallow inversion tillage. (3) Among the different classes of reduced tillage practice, shallow non-inversion tillage resulted in non-significant reductions in yield relative to deep inversion; whereas deep non-inversion tillage resulted in the largest yield reduction, of 11.6 %. (4) Using inversion tillage to only a shallow depth resulted in minimal reductions in yield, of 5.5 %, but significantly higher soil C stocks and better weed control. This finding suggests that this is a good option for organic farmers wanting to improve soil quality while minimizing impacts on yields. (5) Weeds were consistently higher, by about 50 %, when tillage intensity was reduced, although this did not always result in reduced yields

Influence of rewetting on microbial communities involved in nitrification and denitrification in a grassland soil after a prolonged drought period

Abstract The frequency of extreme drought and heavy rain events during the vegetation period will increase in Central Europe according to future climate change scenarios, which will affect the functioning of terrestrial ecosystems in multiple ways. In this study, we simulated an extreme drought event (40 days) at two different vegetation periods (spring and summer) to investigate season-related effects of drought and subsequent rewetting on nitrifiers and denitrifiers in a grassland soil. Abundance of the microbial groups of interest was assessed by quantification of functional genes (amoA, nirS/nirK and nosZ) via quantitative real-time PCR. Additionally, the diversity of ammonia-oxidizing archaea was determined based on fingerprinting of the archaeal amoA gene. Overall, the different time points of simulated drought and rewetting strongly influenced the obtained response pattern of microbial communities involved in N turnover as well as soil ammonium and nitrate dynamics. In spring, gene abundance of nirS was irreversible reduced after drought whereas nirK and nosZ remained unaffected. Furthermore, community composition of ammonia-oxidizing archaea was altered by subsequent rewetting although amoA gene abundance remained constant. In contrast, no drought/rewetting effects on functional gene abundance or diversity pattern of nitrifying archaea were observed in summer. Our results showed (I) high seasonal dependency of microbial community responses to extreme events, indicating a strong influence of plant-derived factors like vegetation stage and plant community composition and consequently close plant-microbe interactions and (II) remarkable resistance and/or resilience of functional microbial groups involved in nitrogen cycling to extreme weather events what might indicate that microbes in a silty soil are better adapted to stress situations as expected

Soil quality changes in field trials comparing organic reduced tillage to plough systems across Europe (TILMAN-ORG Session)

Field trials on reduced soil tillage under organic farming conditions across Europe were used to compare the soil quality changes over time. Soil organic carbon fractions, soil carbon stocks and microbial community structure were analysed. Most severe differences between plough and reduced tillage were found in the top ten cm of the soil profile. Differences became less or not significant in deeper layers. Analyses are still ongoing and will only be ready to be presented at the conference

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

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 processe