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Increased warming in spring and prolonged summer drought may alter soil microbial denitrification. We measured potential denitrification activity and denitrifier marker gene abundances (nirK, nirS, nosZ) in grasslands soils in three geographic regions characterized by site-specific land-use indices (LUI) after warming in spring, at an intermediate sampling and after summer drought. Potential denitrification was significantly increased by warming, but did not persist over the intermediate sampling. At the intermediate sampling, the relevance of grassland land-use intensity was reflected by increased potential N2O production at sites with higher LUI. Abundances of total bacteria did not respond to experimental warming or drought treatments, displaying resilience to minor and short-term effects of climate change. In contrast, nirS- and nirK-type denitrifiers were more influenced by drought in combination with LUI and pH, while the nosZ abundance responded to the summer drought manipulation. Land-use was a strong driver for potential denitrification as grasslands with higher LUI also had greater potentials for N2O emissions. We conclude that both warming and drought affected the denitrifying communities and the potential denitrification in grassland soils. However, these effects are overruled by regional and site-specific differences in soil chemical and physical properties which are also related to grassland land-use intensity., (© FEMS 2015. All rights reserved. For permissions, please e-mail: journals.permissions@oup.com.)

Changes in frequency and intensity of drought events are anticipated in many areas of the world. In pasture, drought effects on soil nitrogen (N) cycling are spatially and temporally heterogeneous due to N redistribution by grazers. We studied soil N cycling responses to simulated summer drought and N deposition by grazers in a 3-year field experiment replicated in two grasslands differing in climate and management. Cattle urine and NH4NO3 application increased soil NH4(+) and NO3(-) concentrations, and more so under drought due to reduced plant uptake and reduced nitrification and denitrification. Drought effects were, however, reflected to a minor extent only in potential nitrification, denitrifying enzyme activity (DEA), and the abundance of functional genes characteristic of nitrifying (bacterial and archaeal amoA) and denitrifying (narG, nirS, nirK, nosZ) micro-organisms. N2O emissions, however, were much reduced under drought, suggesting that this effect was driven by environmental limitations rather than by changes in the activity potential or the size of the respective microbial communities. Cattle urine stimulated nitrification and, to a lesser extent, also DEA, but more so in the absence of drought. In contrast, NH4NO3 reduced the activity of nitrifiers and denitrifiers due to top-soil acidification. In summary, our data demonstrate that complex interactions between drought, mineral N availability, soil acidification, and plant nutrient uptake control soil N cycling and associated N2O emissions. These interactive effects differed between processes of the soil N cycle, suggesting that the spatial heterogeneity in pastures needs to be taken into account when predicting changes in N cycling and associated N2O emissions in a changing climate.

Lacking comparability among rainfall manipulation studies is still a major limiting factor for generalizations in ecological climate change impact research. A common framework for studying ecological drought effects is urgently needed to foster advances in ecological understanding the effects of drought. In this study, we argue, that the soil–plant–atmosphere‐continuum (SPAC), describing the flow of water from the soil through the plant to the atmosphere, can serve as a holistic concept of drought in rainfall manipulation experiments which allows for the reconciliation experimental drought ecology. Using experimental data, we show that investigations of leaf water potential in combination with edaphic and atmospheric drought – as the three main components of the SPAC – are key to understand the effect of drought on plants. Based on a systematic literature survey, we show that especially plant and atmospheric based drought quantifications are strongly underrepresented and integrative assessments of all three components are almost absent in current experimental literature. Based on our observations we argue, that studying dynamics of plant water status in the framework of the SPAC can foster comparability of different studies conducted in different ecosystems and with different plant species and can facilitate extrapolation to other systems, species or future climates. [ABSTRACT FROM AUTHOR]

Crop productivity and plant physiology are affected by rising temperatures and altered precipitation patterns due to climate change. We studied the impacts of an increase in soil temperature of 2.5 °C, a decrease in summer precipitation amount of 25%, a reduction in summer precipitation frequency of 50%, and their interactions on photosynthesis, biomass production, and yield of spring barley (Hordeum vulgare L. cv. RGT Planet) in a temperate agricultural ecosystem near Stuttgart (Germany). Leaf gas exchange of barley appeared to be affected mainly by drought in the form of reduced precipitation frequency or by a combination of changes in soil temperature and precipitation patterns. In contrast, biomass production and yield parameters were more affected under soil warming alone. In addition, biomass of roots increased under soil warming at stem elongation. Stable grain yield was observed under reduced precipitation amount and also under increased evaporation through soil warming. These fndings provide additional evidence that barley is relatively drought tolerant, which should be taken into consideration in the context of appropriate crop selection under climate change. [ABSTRACT FROM AUTHOR]

Abstract: Rising atmospheric CO2 concentrations are expected to increase nitrous oxide (N2O) emissions from soils via changes in microbial nitrogen (N) transformations. Several studies have shown that N2O emission increases under elevated atmospheric CO2 (eCO2), but the underlying processes are not yet fully understood. Here, we present results showing changes in soil N transformation dynamics from the Giessen Free Air CO2 Enrichment (GiFACE): a permanent grassland that has been exposed to eCO2, +20% relative to ambient concentrations (aCO2), for 15 years. We applied in the field an ammonium‐nitrate fertilizer solution, in which either ammonium ( NH 4 +) or nitrate ( NO 3 −) was labelled with 15N. The simultaneous gross N transformation rates were analysed with a 15N tracing model and a solver method. The results confirmed that after 15 years of eCO2 the N2O emissions under eCO2 were still more than twofold higher than under aCO2. The tracing model results indicated that plant uptake of NH 4 + did not differ between treatments, but uptake of NO 3 − was significantly reduced under eCO2. However, the NH 4 + and NO 3 − availability increased slightly under eCO2. The N2O isotopic signature indicated that under eCO2 the sources of the additional emissions, 8,407 μg N2O–N/m2 during the first 58 days after labelling, were associated with NO 3 − reduction (+2.0%), NH 4 + oxidation (+11.1%) and organic N oxidation (+86.9%). We presume that increased plant growth and root exudation under eCO2 provided an additional source of bioavailable supply of energy that triggered as a priming effect the stimulation of microbial soil organic matter (SOM) mineralization and fostered the activity of the bacterial nitrite reductase. The resulting increase in incomplete denitrification and therefore an increased N2O:N2 emission ratio, explains the doubling of N2O emissions. If this occurs over a wide area of grasslands in the future, this positive feedback reaction may significantly accelerate climate change. [ABSTRACT FROM AUTHOR]

Global warming will likely enhance greenhouse gas ( GHG) emissions from soils. Due to its slow decomposability, biochar is widely recognized as effective in long-term soil carbon (C) sequestration and in mitigation of soil GHG emissions. In a long-term soil warming experiment (+2.5 °C, since July 2008) we studied the effect of applying high-temperature Miscanthus biochar (0, 30 t/ha, since August 2013) on GHG emissions and their global warming potential ( GWP) during 2 years in a temperate agroecosystem. Crop growth, physical and chemical soil properties, temperature sensitivity of soil respiration ( R s), and metabolic quotient ( qCO2) were investigated to yield further information about single effects of soil warming and biochar as well as on their interactions. Soil warming increased total CO2 emissions by 28% over 2 years. The effect of warming on soil respiration did not level off as has often been observed in less intensively managed ecosystems. However, the temperature sensitivity of soil respiration was not affected by warming. Overall, biochar had no effect on most of the measured parameters, suggesting its high degradation stability and its low influence on microbial C cycling even under elevated soil temperatures. In contrast, biochar × warming interactions led to higher total N2O emissions, possibly due to accelerated N-cycling at elevated soil temperature and to biochar-induced changes in soil properties and environmental conditions. Methane uptake was not affected by soil warming or biochar. The incorporation of biochar-C into soil was estimated to offset warming-induced elevated GHG emissions for 25 years. Our results highlight the suitability of biochar for C sequestration in cultivated temperate agricultural soil under a future elevated temperature. However, the increased N2O emissions under warming limit the GHG mitigation potential of biochar. [ABSTRACT FROM AUTHOR]

Climate change is affecting agricultural crop production, but there is little information to date from climate change experiments on agricultural ecosystems over the long-term. Data from a ten-year experimental arable field using several climate change factors and their interactions were analyzed with respect to their impacts on crop biomass and harvestable yield production. From a crop rotation of wheat, barley, and oilseed rape was exposed to increased soil temperature (+2.5 °C), reduced summer precipitation amount (−25%), and frequency (−50%) in a multifactorial design. Depending on the growing period, aboveground biomass and crop yield of spring wheat, winter wheat, and spring barley were either increased or unaffected under soil warming. In moist years with high cumulative ambient precipitation, cereal productivity was enhanced due to soil warming, whereas no effect was visible in dry years. Experimental reductions in summer precipitation amount had only minor effects on aboveground biomass and yield of wheat, barley, or oilseed rape, possibly due to an increase in those crops' water use efficiency under water scarcity. However, a reduction in summer precipitation frequency had no effects on aboveground biomass and yield of the selected crops. The results illustrate that effects of climate change on plant development and yield also depend on the immediate weather conditions during the growing period. This underscores the need for long-term climate change experiments under field conditions where, in addition to manipulated experimental treatments, annual variations in precipitation and temperature can be studied. • Year-to-year weather variations studied in ten-year climate change field experiment. • Inter-annual variations in precipitation explained soil warming effects on cereals. • Soil warming enhanced cereal (wheat, barley) biomass and yield in moist years. • Whereas in dry years soil warming showed no effects on biomass and yield of cereals. [ABSTRACT FROM AUTHOR]

Wetlands represent sources or sinks of the greenhouse gas nitrous oxide (N2O). The acidic fen Schlöppnerbrunnen emits denitrification derived N2O and is also capable of N2O consumption. Global warming is predicted to cause more extreme weather events in future years, including prolonged drought periods as well as heavy rainfall events, which may result in flooding. Thus, the effects of prolonged drought and flooding events on the abundance, community composition, and activity of fen denitrifiers were investigated in manipulation experiments. The water table in the fen was experimentally lowered for 8 weeks in 2008 and raised for 5.5 months in 2009 on three treatment plots, while three plots were left untreated and served as controls. In situ N2O fluxes were rather unaffected by the drought treatment and were marginally increased by the flooding treatment. Samples were taken before and after treatment in both years. The structural gene markers narG and nosZ were used to assess possible changes in the nitrate reducer and denitrifier community in response to water table manipulations. Detected copy numbers of narG and nosZ were essentially unaffected by the experimental drought and flooding. Terminal restriction fragment length polymorphism (TRFLP) patterns of narG and nosZ were similar before and after experimental drought or experimental flooding, indicating a stable nitrate reducer and denitrifier community in the fen. However, certain TRFs of narG and nosZ transcripts responded to experimental drought or flooding. Nitrate-dependent Michaelis-Menten kinetics were assessed in anoxic microcosms with peat samples taken before and 6 months after the onset of experimental flooding. Maximal reaction velocities vmax were higher after than before flooding in samples from treament but not in those from control plots taken at the same time. The ratio of N2O to N2O + N2 was lower in soil from treatment plots after flooding than in soil from control plots, suggesting mitigation of N2O emissions by increased N2O-reduction rates after flooding. N2O was consumed to subatmospheric levels in all microcosms after flooding. The collective data indicate that water table manipulations had only minor effects on in situ N2O fluxes, denitrifier abundance, and denitrifier community composition of the acidic fen, while active subpopulations of denitrifiers changed suggesting functionally redundant subpopulations occupying distinct ecological niches in the fen. [ABSTRACT FROM AUTHOR]

The future nicrease of soil temperatures will affect the activity of decomposer organisms, potentially enhancing element cycling and greenhouse gas (i.e. CO 2 and N 2 O) emissions. In a three-factorial microcosm experiment, we investigated the effects of the incorporation of N-rich green manure litter ( Phacelia tanacetifolia Benth.) into an arable soil, of the presence of endogeic earthworms and of elevated soil temperatures (+3.5 °C) on C and N cycling over a period of 42 days. Effects of litter addition were most pronounced. Litter strongly increased amounts of mineral and organic N in the leachate, soil extractable mineral and organic N and organic C, denitrification activity, CO 2 and N 2 O emissions as well as earthworm biomass. Elevated soil temperatures also increased CO 2 emissions, but this effect was more pronounced in treatments without litter. Furthermore, elevated soil temperature reduced the amounts of extractable organic C and NH 4 + , but increased amounts of NO 3 − , indicating enhanced nitrification activity in warmed soils. Earthworm presence increased NO 3 − leaching and this was more pronounced under elevated soil temperatures. N 2 O emissions were strongly increased by 70–90% by earthworm activity, with the highest emissions in the treatment with litter incorporation under elevated temperatures. This treatment also had the largest amount of NO 3 − leaching and the highest denitrification activities. Our results indicate an increasing risk for N losses in the form of nitrate leaching and/or N 2 O emissions from earthworm populated arable soils with a warmer climate in the future. [ABSTRACT FROM AUTHOR]

Abstract: Modifications in temperature and precipitation due to climate change will likely affect carbon cycling and soil respiration in terrestrial ecosystems. Despite the important feedback mechanism of ecosystems to climate change, there is still a lack of experimental observation in agricultural ecosystems. In July 2008, we established the Hohenheim Climate Change (HoCC) experiment to investigate effects of elevated temperature and altered precipitation on soil respiration in an arable soil (mean annual temperature and precipitation 8.7°C and 679mm, respectively). We elevated soil temperature to 4cm depth by 2.5°C, reduced the amount of summer precipitation by 25%, and extended dry intervals between precipitation events. For two years, CO2 fluxes were measured weekly and aboveground plant biomass and soil microbial biomass was determined. The results of the two-year study underline the importance of soil moisture as a driving factor in ecosystem response to climate change. Soil warming did not increase soil respiration in the first year; in the second year, a 27% increase was measured. The differential response of soil respiration to warming was most likely driven by soil moisture. In summer 2009, water limitation reduced microbial biomass in the heated plots thereby suppressing the stimulatory effect of elevated temperature on soil microorganisms. In summer 2010, the reduction in soil moisture was less pronounced and microbial biomass and respiration were not affected by water limitation. Temperature elevation significantly reduced Q 10 values of soil respiration by 0.7–0.8. Altered precipitation showed only minor effects during the first two years of the experiment. We conclude from our study that the moisture regime of soils under elevation of temperature will largely determine whether different soils will serve either as carbon sources or as carbon sinks. [Copyright &y& Elsevier]

Increasing air and soil temperatures and changes in precipitation patterns as consequences of climate change will affect crop production in agricultural ecosystems. The combined effects of soil warming and altered precipitation on the productivity and product quality of oil crops are not yet well studied. Winter oilseed rape (OSR) (Brassica napus L., cv. Mercedes) was field-grown under elevated soil temperature (+2.5 °C), reduced precipitation amount (−25%), reduced precipitation frequency (−50%) both separately and in combination in order to investigate effects on crop development, seed yield, and seed quality. Soil warming accelerated crop development during early plant growth and during spring. At maturity, however, plants in all treatments were similar in quantitative (aboveground biomass, seed yield) and qualitative (protein and oil content, amino acids, fatty acids) parameters. We observed the long-term effects of the precipitation manipulation on leaf size, leaf senescence and biomass allocation. Seed yield was not affected by the altered climatic factors, perhaps due to adaptation of soil microorganisms to permanent soil warming and to relatively wet conditions during the seed-filling period. Overall, OSR performed well under moderate changes in soil temperature and precipitation patterns; thus, we observed stable seed yield without negative impacts on nutritive seed quality. [ABSTRACT FROM AUTHOR]

Abstract: Spring barley was grown in a field experiment under moderately elevated soil temperature and changed summer precipitation (amount and frequency). Elevated temperature affected the performance and grain quality characteristics more significant than changes in rainfall. Except for the decrease in thousand grain weight, warming had no impacts on aboveground biomass and grain yield traits. In grains, several proteinogenic amino acids concentrations were increased, whereas their composition was only slightly altered. Concentration and yield of total protein remained unaffected under warming. The concentrations of total non-structural carbohydrates, starch, fructose and raffinose were lower in plants grown at high temperatures, whereas maltose was higher. Crude fibre remained unaffected by warming, whereas concentrations of lipids and aluminium were reduced. Manipulation of precipitation only marginally affected barley grains: amount reduction increased the concentrations of several minerals (sodium, copper) and amino acids (leucine). The projected climate changes may most likely affect grain quality traits of interest for different markets and utilisation requirements. [Copyright &y& Elsevier]

Global environmental change is causing increases in soil temperatures and alternations in precipitation patterns, which are affecting soil biota in natural and managed systems. Arable soils, generally disturbed due to management practice, are particularly sensitive to a changing environment. However, little is known how warming interacts with precipitation pattern to affect soil fauna and thereby ecosystem functions. In an arable system, we investigated the interactions of soil warming and altered precipitation amount and frequency on soil conditions and health using nematodes as bioindicators. Our findings showed that the nematode population density was significantly increased by warming and decreased by reduced precipitation frequency. Warming mainly fostered the density of fungal feeders and obligatory plant parasites, with the latter suggesting higher crop damage. Root-associated plant feeders were further affected by changes in precipitation pattern; their density declined with reduced precipitation frequency and increased with the alternated precipitation amount. The nematode abundance was generally low in the arable ecosystem and remained stable under the simulated environmental change. In response to warming, the major soil decomposition channel via bacteria was reduced, and the fungal mediated pathway fostered, implying more fungal dominated depleted and degraded soil conditions. Soil decomposition pathways were not affected by altered precipitation pattern, neither by amount nor by frequency. Overall, warming and precipitation independently altered the soil nematode fauna and the functioning of belowground food webs. Therefore, our study highlights the need for more research considering the interactions of environmental variables to see if this lack is a general pattern and to develop strategies for agroecosystem's management under climate change. • Impacts of warming and precipitation on nematodes were generally not linked. • Population density increased with warming but decreased with low rain frequency. • Warming fostered the density of obligatory plant parasites. • Root-associated plant feeders responded positively to summer drought. • Warming shifted the decomposition channels towards the fungal mediated pathway. [ABSTRACT FROM AUTHOR]