• Energy Research

Many scientific disciplines currently are experiencing a “reproducibility crisis” because numerous scientific findings cannot be repeated consistently. A novel but controversial hypothesis postulates that stringent levels of environmental and biotic standardization in experimental studies reduces reproducibility by amplifying impacts of lab-specific environmental factors not accounted for in study designs. A corollary to this hypothesis is that the deliberate introduction of controlled systematic variability (CSV) in experimental designs can increase reproducibility. We tested this hypothesis using a multi-laboratory microcosm study in which the same ecological experiment was repeated in 14 laboratories across Europe. Each laboratory introduced environmental and genotypic CSV within and among replicated microcosms established in either growth chambers (with stringent control of environmental conditions) or glasshouses (with more variable environmental conditions). The introduction of genotypic CSV led to lower among-laboratory variability in growth chambers, indicating increased reproducibility, but had no significant effect in glasshouses where reproducibility also was lower. Environmental CSV had little effect on reproducibility. Although there are multiple causes for the “reproducibility crisis”, deliberately including genetic variation may be a simple solution for increasing the reproducibility of ecological studies performed in controlled environments.

AbstractDrought duration and intensity are expected to increase with global climate change. How changes in water availability and temperature affect the combined plant–soil–microorganism response remains uncertain. We excavated soil monoliths from a beech (Fagus sylvatica L.) forest, thus keeping the understory plant–microbe communities intact, imposed an extreme climate event, consisting of drought and/or a single heat‐pulse event, and followed microbial community dynamics over a time period of 28 days. During the treatment, we labeled the canopy with 13CO2 with the goal of (i) determining the strength of plant–microbe carbon linkages under control, drought, heat and heat–drought treatments and (ii) characterizing microbial groups that are tightly linked to the plant–soil carbon continuum based on 13C‐labeled PLFAs. Additionally, we used 16S rRNA sequencing of bacteria from the Ah horizon to determine the short‐term changes in the active microbial community. The treatments did not sever within‐plant transport over the experiment, and carbon sinks belowground were still active. Based on the relative distribution of labeled carbon to roots and microbial PLFAs, we determined that soil microbes appear to have a stronger carbon sink strength during environmental stress. High‐throughput sequencing of the 16S rRNA revealed multiple trajectories in microbial community shifts within the different treatments. Heat in combination with drought had a clear negative effect on microbial diversity and resulted in a distinct shift in the microbial community structure that also corresponded to the lowest level of label found in the PLFAs. Hence, the strongest changes in microbial abundances occurred in the heat–drought treatment where plants were most severely affected. Our study suggests that many of the shifts in the microbial communities that we might expect from extreme environmental stress will result from the plant–soil–microbial dynamics rather than from direct effects of drought and heat on soil microbes alone.

Abstract Key message Understory plant communities are essential for the recruitment of trees making up future forests. Independent of plant diversity, the understory across different forest ecosystems shows considerable physiological acclimation and structural stability towards drought events, which are expected to occur more frequently in future. Context Understory plant communities are essential for the recruitment of trees making up the future forest. It is so far poorly understood how climate change will affect understory in beech and conifer forests managed at different intensity levels. Aims We hypothesized that drought would affect transpiration and carbon isotope discrimination but not species richness and diversity. Moreover, we assumed that forest management intensity will modify the responses to drought of the understory community. Methods We set up roofs in forests with a gradient of management intensities (unmanaged beech—managed beech—intensively managed conifer forests) in three regions across Germany. A drought event close to the 2003 drought was imposed in two consecutive years. Results After 2 years, the realized precipitation reduction was between 27% and 34%. The averaged water content in the top 20 cm of the soil under the roof was reduced by 2% to 8% compared with the control. In the 1st year, leaf level transpiration was reduced for different functional groups, which scaled to community transpiration modified by additional effects of drought on functional group leaf area. Acclimation effects in most functional groups were observed in the 2nd year. Conclusion Forest understory shows high plasticity at the leaf and community level, and high structural stability to changing climate conditions with drought events.

In the future, periods of strongly increased temperature in concert with drought (heat waves) will have potentially detrimental effects on trees and forests in Central Europe. Norway spruce might be at risk in the future climate of Central Europe. However, Douglas-fir is often discussed as an alternative for the drought and heat sensitive Norway spruce, because some provenances are considered to be well adapted to drier and warmer conditions. In this study, we identified the physiological and growth responses of seedlings from two different Douglas-fir provenances to increased temperature and atmospheric drought during a period of 92 days. We analysed (i) plant biomass, (ii) carbon stable isotope composition as an indicator for time integrated intrinsic water use efficiency, (iii) apparent respiratory carbon isotope fractionation as well as (iv) the profile of polar low molecular metabolites. Plant biomass was only slightly affected by increased temperatures and atmospheric drought but the more negative apparent respiratory fractionation indicated a temperature-dependent decrease in the commitment of substrate to the tricarboxylic acid cycle. The metabolite profile revealed that the simulated heat wave induced a switch in stress protecting compounds from proline to polyols. We conclude that metabolic acclimation successfully contributes to maintain functioning and physiological activity in seedlings of both Douglas-fir provenances under conditions that are expected during heat waves (i.e. elevated temperatures and atmospheric drought). Douglas-fir might be a potentially important tree species for forestry in Central Europe under changing climatic conditions. PLoS ONE, 9 (12) ISSN:1932-6203

AbstractIn trees, the interplay between reduced carbon assimilation and the inability to transport carbohydrates to the sites of demand under drought might be one of the mechanisms leading to carbon starvation. However, we largely lack knowledge on how drought effects on new assimilate allocation differ between species with different drought sensitivities and how these effects are modified by interspecific competition. We assessed the fate of 13C labelled assimilates in above‐ and belowground plant organs and in root/rhizosphere respired CO2 in saplings of drought‐tolerant Norway maple (Acer platanoides) and drought‐sensitive European beech (Fagus sylvatica) exposed to moderate drought, either in mono‐ or mixed culture. While drought reduced stomatal conductance and photosynthesis rates in both species, both maintained assimilate transport belowground. Beech even allocated more new assimilate to the roots under moderate drought compared to non‐limited water supply conditions, and this pattern was even more pronounced under interspecific competition. Even though maple was a superior competitor compared to beech under non‐limited soil water conditions, as indicated by the changes in above‐ and belowground biomass of both species in the interspecific competition treatments, we can state that beech was still able to efficiently allocate new assimilate belowground under combined drought and interspecific competition. This might be seen as a strategy to maintain root osmotic potential and to prioritise root functioning. Our results thus show that beech tolerates moderate drought stress plus competition without losing its ability to supply belowground tissues. It remains to be explored in future work if this strategy is also valid during long‐term drought exposure.

Although microcosm experiments are a frequent tool used to address fundamental ecological questions, there has been no quantitative assessment of the reproducibility of any microcosm experiment. This dataset contains the response variables measured in a multi-laboratory microcosm study in which the same microcosm experiment was repeated in 14 laboratories across Europe. All laboratories simultaneously run a simple microcosm experiment using grass (Brachypodium distachyon L.) monocultures and grass and legume (Medicago truncatula Gaertn.) mixtures. All twelve variables were then used to calculate the effect of the presence of nitrogen-fixing legume on the grass-legume mixtures (i.e. the net legume effect).The project tested a controversial hypotheses postulating that stringent levels of environmental and biotic standardization in experimental studies reduces reproducibility by amplifying impacts of lab-specific environmental factors not accounted for in the experimental design. This implies that the deliberate introduction of controlled systematic variability (CSV) in experimental designs can increase reproducibility. To test this hypothesis, each laboratory followed the same experimental protocol and introduced environmental and genotypic controlled systematic variability (CSV) within and among replicated microcosms established in either growth chambers (with stringent control of environmental conditions) or glasshouses (with more variable environmental conditions). Data were used to test the extent to which the effect size of the net legume effect varied with the CSV treatment and to estimate the number of laboratories that produced results that can be considered reproducible. Supplement to: Milcu, Alexandru; Puga-Freitas, Ruben; Ellison, Aaron M; Blouin, Manuel; Scheu, Stefan; Girin, Thomas; Freschet, Grégoire T; Rose, Laura; Scherer-Lorenzen, Michael; Barot, Sebastien; Lata, Jean-Christophe; Cesarz, Simone; Eisenhauer, Nico; Gigon, Agnès; Weigelt, Alexandra; Hansart, Amandine; Greiner, Anna; Pando, Anne; Gessler, Arthur; Grignani, Carlo; Assandri, Davide; Gleixner, Gerd; LeGalliard, Jean-Francois; Urban-Mead, Katherine; Zavattaro, Laura; Müller, Marina E H; Lange, Markus; Lukac, Martin; Bonkowski, Michael; Mannerheim, Neringa; Buchmann, Nina; Butenschoen, Olaf; Rotter, Paula; Seyhun, Rahme; Devidal, Sébastien; Kayler, Zachary; Roy, Jacques (2018): Genotypic variability enhances the reproducibility of an ecological study. Nature Ecology & Evolution, 2, 279-287