Question

1. Beyond plants and soil microbes, in what other biological systems could inter-generational microbial feedbacks be important? Give a detailed explanation of why you would predict such feedbacks. (at 5 sentences)

2. Compare and contrast plant-soil microbe feedbacks in wild and agricultural communities. Be specific (at 5 sentences)

Answer 1

1. Interactions between plant and soil communities are known to play an integral role in shaping ecosystems. Plants influence the composition of soil communities and soil communities in turn influence plant performance. Such a plant–soil feedback may incur selection pressure on plants and the associating soil community. However, the evolutionary consequences of these above-belowground feedback interactions remain largely speculative. Here we assess whether plant–soil feedback effects differ between intraspecific plant populations and between generations within the same plant population. We used two populations of Trifolium pratense and assessed their performance when grown in association with their home versus away soil biota. Both populations were colonized by distinct microbial communities and performed better with their own home soil communities than with the soil community from the other intraspecific population, demonstrating intraspecific positive feedback effects of home soil. In one of the two populations, we found that plant performance and the root associated microbiota community differed between parental and progeny plants when inoculated with their own home soil. Differences in root associated community characteristics could explain more than 80% of the variation in performance among the progeny and parental plants. Our results highlight that intraspecific differences in both plant and associated soil communities shape plant–soil feedback effects, and consequently indicate that plant–soil feedback can influence the direction of selection between intraspecific plant populations.

2. Plant–soil feedback affects performance and competitive ability of individual plants. However, the importance of plant–soil feedback in historical contingency processes and plant community dynamics is largely unknown. In microcosms, we tested how six early‐successional plant species of secondary succession on ex‐arable land induced plant‐specific changes in soil community composition. Following one growth cycle of conditioning the soil community, soil feedback effects were assessed as plant performance in soil of their own as compared to soil from a mixture of the other five early‐successional species. Performance was tested in monocultures and in mixed communities with heterospecific competition from mid‐successional species. The role of soil microorganisms was determined by isolating the microbial component from the soil community, re‐inoculating microorganisms into sterilized substrate, and analyzing plant biomass responses of the early‐ and mid‐successional species.

Plant–soil feedback responses of the early‐successional species were negative and significantly increased when the plants were grown in a competitive environment with heterospecifics. In monocultures, three early‐successional species experienced negative feedback in soil with a history of conspecifics, while all early‐successional species experienced negative feedback when grown with interspecific competition. Interestingly, the nonnative forb Conyza canadensis showed the weakest soil feedback effect. Biomass production of the early‐successional plant species was profoundly reduced by the microbial inocula, most strongly when exposed to inocula of conspecific origin. Molecular characterization of the fungal and bacterial rhizosphere communities revealed a relationship between plant biomass production and the composition of the dominant fungal species. Furthermore, our results show that, in early secondary succession, the early‐successional plant species induce changes in the soil microbial community composition that cause historical contingency effects in dominance patterns of mid‐succession plant communities.

We conclude that feedback between early‐successional plant species and soil microorganisms can play a crucial role in breaking dominance of early‐successional plant communities. Moreover the influences on soil microorganism community composition influenced plant community dynamics in the mid‐successional plant communities. These results shed new light on how feedback effects between plants and soil organisms in one successional stage result in a biotic legacy effect, which influences plant community processes in subsequent successional stages.

PSF has been extensively studied in both agricultural and natural systems, with increased activity in recent years, but a framework for integrating the concepts and principles developed in these systems is lacking.

Interactions between soil biota and plant leaf and root traits have become an important tool in understanding PSF in wild plants, but this understanding has not yet been utilized in agricultural crop rotations.

Soil inoculations with microbial strains are increasingly being used for steering the soil microbiome in agriculture but might also offer a promising method of restoration of degraded systems, and for controlling the spread of invasive species.

Increasing evidence shows that PSF can play important roles in mediating ecosystem responses to forecasted climate change and extreme weather events.

In agricultural and natural systems researchers have demonstrated large effects of plant–soil feedback (PSF) on plant growth. However, the concepts and approaches used in these two types of systems have developed, for the most part, independently. Here, we present a conceptual framework that integrates knowledge and approaches from these two contrasting systems. We use this integrated framework to demonstrate (i) how knowledge from complex natural systems can be used to increase agricultural resource-use efficiency and productivity and (ii) how research in agricultural systems can be used to test hypotheses and approaches developed in natural systems. Using this framework, we discuss avenues for new research toward an ecologically sustainable and climate-smart future.