Contrasting Responses of Arbuscular Mycorrhizal Fungal Families to Simulated Climate Warming and Drying in a Semiarid Shrubland

The impact of multifactorial stress combination on plants, crops, and ecosystems: how should we prepare for what comes next?

The complexity of environmental conditions encountered by plants in the field, or in nature, is gradually increasing due to anthropogenic activities that promote global warming, climate change, and increased levels of pollutants. While in the past it seemed sufficient to study how plants acclimate to one or even two different stresses affecting them simultaneously, the complex conditions developing on our planet necessitate a new approach of studying stress in plants: Acclimation to multiple stress conditions occurring concurrently or consecutively (termed, multifactorial stress combination [MFSC]). In an initial study of the plant response to MFSC, conducted with Arabidopsis thaliana seedlings subjected to an MFSC of six different abiotic stresses, it was found that with the increase in the number and complexity of different stresses simultaneously impacting a plant, plant growth and survival declined, even if the effects of each stress involved in such MFSC on the plant was minimal or insignificant. In three recent studies, conducted with different crop plants, MFSC was found to have similar effects on a commercial rice cultivar, a maize hybrid, tomato, and soybean, causing significant reductions in growth, biomass, physiological parameters, and/or yield traits. As the environmental conditions on our planet are gradually worsening, as well as becoming more complex, addressing MFSC and its effects on agriculture and ecosystems worldwide becomes a high priority. In this review, we address the effects of MFSC on plants, crops, agriculture, and different ecosystems worldwide, and highlight potential avenues to enhance the resilience of crops to MFSC.

Elevated CO2 and temperature increase arbuscular mycorrhizal fungal diversity, but decrease root colonization, in maize and wheat

Anthropogenic climate change threatens ecosystem multifunctionality. Arbuscular mycorrhizal (AM) fungi are important symbionts that participate in mediating many ecosystem processes, and thus being potentially essential link in the chain of responses to climate change. Yet, how climate change affect the abundance and community structure of AM fungi associated with different crops remains elusive. Here, we investigated the changes in rhizosphere AM fungal communities and growth performance of maize and wheat grown in Mollisols under experimentally elevated CO2 (eCO2, +300 ppm), temperature (eT, +2 °C) and both in-combination (eCT) with open-top chambers, representing a scenario likely to occur by this century's end. The results showed that eCT significantly shifted AM fungal communities in both rhizospheres compared with control, but with no remarkable variation of the overall communities in maize rhizosphere, suggesting their greater resistance to climate change. Both eCO2 and eT increased rhizosphere AM fungal diversity, and conversely they reduced mycorrhizal colonization of both crops, probably since AM fungi had distinct adaptive strategies to climate change in rhizospheres (i.e., r-strategy) and roots (K-strategy), while the colonization intensity positively correlated with a decreased phosphorus (P)-uptake in two crops. Furthermore, co-occurrence network analysis showed that eCO2 strongly decreased the modularity and betweenness centrality of network structure than that of eT and eCT in both rhizospheres, along with the reduced network robustness, implied their destabilized communities under eCO2, while root stoichiometry (C:N and C:P ratio) was the most important factor associating with taxa in networks regardless of climate change. Overall, those findings suggest that rhizosphere AM fungal communities in wheat appear to be more sensitive to climate change than that in maize, further highlighting the importance of effective monitoring and managing AM fungi, which may allow crops to maintain critical levels of mineral nutrients (at least P) under future global change.

Soil microbial communities shift along an urban gradient in Berlin, Germany

The microbial communities inhabiting urban soils determine the functioning of these soils, in regards to their ability to cycle nutrients and support plant communities. In an increasingly urbanized world these properties are of the utmost importance, and the microbial communities responsible are worthy of exploration. We used 53 grassland sites spread across Berlin to describe and explain the impacts of urbanity and other environmental parameters upon the diversity and community composition of four microbial groups. These groups were (i) the Fungi, with a separate dataset for (ii) the Glomeromycota, (iii) the Bacteria, and (iv) the protist phylum Cercozoa. We found that urbanity had distinct impacts on fungal richness, which tended to increase. Geographic distance between sites and soil chemistry, in addition to urbanity, drove microbial community composition, with site connectivity being important for Glomeromycotan communities, potentially due to plant host communities. Our findings suggest that many microbial species are well adapted to urban soils, as supported by an increase in diversity being a far more common result of urbanity than the reverse. However, we also found distinctly separate distributions of operational taxonomic unit (OTU)s from the same species, shedding doubt of the reliability of indicator species, and the use of taxonomy to draw conclusion on functionality. Our observational study employed an extensive set of sites across an urbanity gradient, in the region of the German capital, to produce a rich microbial dataset; as such it can serve as a blueprint for other such investigations.