Long-term and realistic global change manipulations had low impact on diversity of soil biota in temperate heathland

Abstract

In a dry heathland ecosystem we manipulated temperature (warming), precipitation (drought) and atmospheric concentration of CO2 in a full-factorial experiment in order to investigate changes in below-ground biodiversity as a result of future climate change. We investigated the responses in community diversity of nematodes, enchytraeids, collembolans and oribatid mites at two and eight years of manipulations. We used a structural equation modelling (SEM) approach analyzing the three manipulations, soil moisture and temperature, and seven soil biological and chemical variables. The analysis revealed a persistent and positive effect of elevated CO2 on litter C:N ratio. After two years of treatment, the fungi to bacteria ratio was increased by warming, and the diversities within oribatid mites, collembolans and nematode groups were all affected by elevated CO2 mediated through increased litter C:N ratio. After eight years of treatment, however, the CO2-increased litter C:N ratio did not influence the diversity in any of the four fauna groups. The number of significant correlations between treatments, food source quality, and soil biota diversities was reduced from six to three after two and eight years, respectively. These results suggest a remarkable resilience within the soil biota against global climate change treatments in the long term.

On the problems of using linear models in ecological manipulation experiments: lessons learned from a climate experiment

“…Although the reduction of soil moisture in warmed plots was small, it was consistent and statistically significant (Holmstrup et al. ). For some biological responses, even such minor changes in soil moisture may be important and therefore must be accounted for when trying to unravel the mechanistic interactions between organisms and the environment.…”

“…However, a number of interactions are inherent, such as the passive nighttime warming technique causing simultaneous reduction in soil moisture due to increased evaporation related to increased temperature, but likely also related to reduced dew formation during nighttime due to the coverage by the reflective curtains used for nighttime passive warming. Although the reduction of soil moisture in warmed plots was small, it was consistent and statistically significant (Holmstrup et al 2017). For some biological responses, even such minor changes in soil moisture may be important and therefore must be accounted for when trying to unravel the mechanistic interactions between organisms and the environment.…”

“…A wide range of biological response variables have been investigated in the Climaite experiment, and the results have been reported in >100 peerreviewed scientific papers. The findings range from measurements of responses in plant processes, such as photosynthesis (Albert et al 2011), the aboveground plant community (Kongstad et al 2012), and belowground root production (Arndal et al 2018), to responses in the soil, such as soil respiration (Selsted et al 2012), nitrogen cycling (Larsen et al 2011), soil fauna diversity (Holmstrup et al 2017), and aboveground herbivore fauna (Scherber et al 2013). The observed effects include significant responses to individual factors or combinations of treatment factors as well as interactions among them or no effects at all.…”

“…More importantly, SEM does not assume orthogonality of the manipulations, and since the underlying variation of the manipulated ecosystem is measured directly, the assumption of unit-treatment additivity is met. For example, in a recent study SEM was used to model the effect of soil physical conditions (temperature and moisture) on the biodiversity of soil fauna (Holmstrup et al 2017). By using a traditional statistical ANOVA model including all treatments and their interactions, the authors did not find significant effects of any of the three treatments (temperature, drought, or CO 2 ) on biodiversity, which was a counterintuitive result because soil moisture is a critical environmental factor for abundance and function of many soil invertebrate taxa (Rapoport and Tschapek 1967).…”

Fast attrition of springtail communities by experimental drought and richness–decomposition relationships across Europe

“…Likely, the intensity of the warming applied was moderate not only for collembolans (although see Petersen, 2011, for a further discussion on the modest warming effects found in some of the sites) but also for plant communities and ecosystem functions like net primary productivity and respiration, which were also rather insensitive to the warming treatment (Kröel-Dulay et al, 2015;Reinsch et al, 2017). Recent findings have nonetheless revealed that springtails, and in general soil fauna, may be quite resistant to increases in temperature (Alatalo et al, 2015;Holmstrup et al, 2017Holmstrup et al, , 2018. Recent findings have nonetheless revealed that springtails, and in general soil fauna, may be quite resistant to increases in temperature (Alatalo et al, 2015;Holmstrup et al, 2017Holmstrup et al, , 2018.…”