Modelling of carbon cycle in grassland ecosystems of diverse water availability using Biome-BGCMuSo.

Grassland ecosystems have an important role in agriculture, and at the same time, are highlysensitive to changes in land use and climate change. Simulation of the biogeochemical cycles ofmanaged grasslands may help in identifying and quantifying the main processes contributing tochanges in their productivity. In our work we used the latest version of Biome-BGCMuSo model,the modified version of the widely used biogeochemical Biome-BGC model, with structuralimprovements to simulate herbaceous ecosystem carbon and water cycles more faithfully.Our sampling areas were in diverse grasslands in the Kiskunság, Hungary. Different soil textureand changing water table level, consequently highly different water conditions are characteristicin these ecosystems, influencing the development and productivity of vegetation, and also thepotential for animal husbandry. Hence, for the meadows and the marshland ecosystems weincluded mowing management in the simulations. In order to compare the ecosystems and studytheir functions we simulated ecosystem variables, such as ecosystem respiration, standing andharvested aboveground biomass etc.We found that ecosystems with higher water availability are more sensitive to changes in waterconditions, and their productivity is more variable between years. By calibration processes usingleaf area and aboveground biomass we aim to further specify our findings.Biome-BGCMuSo is available as a standalone model, but also through virtual laboratoryenvironment and Biome-BGC Projects database (http://ecos.okologia.mta.hu/bbgcdb)developed within the BioVeL project (http://www.biovel.eu). Scientific workflow management,web service and desktop grid technology can support model optimization in the so-called"calibrated runs" within MACSUR

Reduction in primary production followed by rapid recovery of plant biomass in response to repeated mid-season droughts in a semiarid shrubland

The frequency and severity of extreme weather events, including droughts, are expected to increase due to the climate change. Climate manipulation field experiments are widely used tools to study the response of key parameters like primary production to the treatments. Our study aimed to detect the effect of drought on the aboveground biomass and primary production both during the treatments as well as during the whole growing seasons in semiarid vegetation. We estimated aboveground green biomass of vascular plants in a Pannonian sand forest-steppe ecosystem in Hungary. We applied non-destructive field remote sensing method in control and drought treatments. Drought treatment was carried out by precipitation exclusion in May and June, and was repeated in each year from 2002. We measured NDVI before the drought treatment, right after the treatment, and at the end of the summer in 2011 and 2013. We found that the yearly biomass peaks, measured in control plots after the treatment periods, were decreased or absent in drought treatment plots, and consequently, the aboveground net primary production was smaller than in the control plots. At the same time, we did not find general drought effects on all biomass data. The studied ecosystem proved resilient, as the biomass in the drought-treated plots recovered by the next drought treatment. We conclude that the effect of drought treatment can be overestimated with only one measurement at the time of the peak biomass, while multiple within-year measurements better describe the response of biomass

Few multiyear precipitation-reduction experiments find a shift in the productivity-precipitation relationship

Well-defined productivity–precipitation relationships of ecosystems are needed as benchmarks for the validation of land models used for future projections. The productivity–precipitation relationship may be studied in two ways: the spatial approach relates differences in productivity to those in precipitation among sites along a precipitation gradient (the spatial fit, with a steeper slope); the temporal approach relates interannual productivity changes to variation in precipitation within sites (the temporal fits, with flatter slopes). Precipitation–reduction experiments in natural ecosystems represent a complement to the fits, because they can reduce precipitation below the natural range and are thus well suited to study potential effects of climate drying. Here, we analyse the effects of dry treatments in eleven multiyear precipitation–manipulation experiments, focusing on changes in the temporal fit. We expected that structural changes in the dry treatments would occur in some experiments, thereby reducing the intercept of the temporal fit and displacing the productivity–precipitation relationship downward the spatial fit. The majority of experiments (72%) showed that dry treatments did not alter the temporal fit. This implies that current temporal fits are to be preferred over the spatial fit to benchmark land-model projections of productivity under future climate within the precipitation ranges covered by the experiments. Moreover, in two experiments, the intercept of the temporal fit unexpectedly increased due to mechanisms that reduced either water loss or nutrient loss. The expected decrease of the intercept was observed in only one experiment, and only when distinguishing between the late and the early phases of the experiment. This implies that we currently do not know at which precipitation–reduction level or at which experimental duration structural changes will start to alter ecosystem productivity. Our study highlights the need for experiments with multiple, including more extreme, dry treatments, to identify the precipitation boundaries within which the current temporal fits remain valid

Permanent grasslands in Europe : Land use change and intensification decrease their multifunctionality

Acknowledgments We acknowledge the financial support of this work by European Union Horizon 2020 research and innovation programme, under grant agreement 774124, project SUPER-G (Developing Sustainable Permanent Grassland Systems and Policies).Peer reviewedPublisher PD

Experimental warming does not enhance soil respiration in a semiarid temperate forest-steppe ecosystem

The influence of simulated climate change on soil respiration was studied in a field experiment on 4 m × 5 m plots in the semiarid temperate Pannonian sand forest-steppe. This ecosystem type has low productivity and soil organic matter content, and covers large areas, yet data on soil carbon fluxes are still limited. Soil respiration rate — measured monthly between April and November from 2003 to 2006 — remained very low (0.09 — 1.53 μmol CO2 m-2 s-1 ) in accordance with the moderate biological activity and low humus content of the nutrient poor, coarse sandy soil. Specific soil respiration rate (calculated for unit soil organic matter content), however, was relatively high (0.36–7.92 μmol CO2 g-1 Corg h-1 ) suggesting substrate limitation for soil biological activity. During the day, soil respiration rate was significantly lower at dawn than at midday, while seasonally clear temperature limitation in winter and water limitation in summer were detected. Between years, annual precipitation appeared to be important in determining soil carbon efflux intensity. Nocturnal warming increased soil temperature in 1 cm depth at dawn by 1.6°C on the average, and decreased topsoil (0–11 cm) moisture content by 0.45 vol%. Drought treatment decreased soil moisture content by an average of 0.81 vol%. Soil respiration rate tended to decrease by 7–15% and 13–15% in response to heat and drought treatment, respectively, although the changes were not statistically significant. Nocturnal warming usually prevented dew formation, and that probably also influenced soil respiration. Based on these results, we expect a reduction in the volume and rate of organic matter turnover in this ecosystem in response to the anticipated climate change in the region

Leaf gas exchange and isoprene emission in poplar in response to long-term experimental night-time warming and summer drought in a forest-steppe ecosystem

Climate change projections forecast an average warming in mean temperature and an associated change in the distribution and intensity of rainfalls. At the manipulation experiment in Kiskunság, Hungary, we aimed to study the effect of the soil drought and night-time warming conditions projected for the coming decades on leaf gas exchange, including photosynthetic rates and isoprene emission rates and on isoprene synthase expression levels of Populus alba sprouts (root suckers). During the years 2010 and 2011, warming treatment increased the air temperature 0.35 °C on average whereas drought treatment reduced the soil moisture by 13% on average in relation to control plots. The results highlighted important seasonal differences. Photosynthesis was limited by stomatal closure in summer and also isoprene emission and isoprene synthase expression levels were lower in summer than in autumn for all treatments. As a consequence, a negative relationship was found between temperature, ranging from 25 °C to 35 °C, and isoprene emission throughout all the study period and treatments. Results also showed significant treatments effects on isoprene parameters but only in July 2011. Isoprene emission decreased with drought, and isoprene synthase expression levels decreased with night-time warming. A positive relationship was found between isoprene emission and leaf internal carbon in drought treated poplar plants, which contrasted with our findings for control and warming treated plants. These results indicated either a change in the regulation of pyruvate distribution between isoprene synthesis and respiration under drought or a utilization of alternative carbon sources for isoprene emission. © 2018 Elsevier B.V

Leaf gas exchange and isoprene emission in poplar in response to long-term experimental night-time warming and summer drought in a forest-steppe ecosystem

Climate change projections forecast an average warming in mean temperature and an associated change in the distribution and intensity of rainfalls. At the manipulation experiment in Kiskunság, Hungary, we aimed to study the effect of the soil drought and night-time warming conditions projected for the coming decades on leaf gas exchange, including photosynthetic rates and isoprene emission rates and on isoprene synthase expression levels of Populus alba sprouts (root suckers). During the years 2010 and 2011, warming treatment increased the air temperature 0.35 °C on average whereas drought treatment reduced the soil moisture by 13% on average in relation to control plots. The results highlighted important seasonal differences. Photosynthesis was limited by stomatal closure in summer and also isoprene emission and isoprene synthase expression levels were lower in summer than in autumn for all treatments. As a consequence, a negative relationship was found between temperature, ranging from 25 °C to 35 °C, and isoprene emission throughout all the study period and treatments. Results also showed significant treatments effects on isoprene parameters but only in July 2011. Isoprene emission decreased with drought, and isoprene synthase expression levels decreased with night-time warming. A positive relationship was found between isoprene emission and leaf internal carbon in drought treated poplar plants, which contrasted with our findings for control and warming treated plants. These results indicated either a change in the regulation of pyruvate distribution between isoprene synthesis and respiration under drought or a utilization of alternative carbon sources for isoprene emission. © 2018 Elsevier B.V