Plant-soil feedbacks in a temporally and spatially variable environment

Background/Question/Methods

Plant effects on soil biotic components can result in feedbacks affecting plant performance, thereby driving temporal and potentially spatial plant community and ecosystem dynamics. Plant-soil feedbacks are inherently time-dependent: first, A affects B, then B feeds back to A. Hence, feedback effects depend directly on the response rates of its components. Over longer time scales, the strength and direction of plant-soil feedbacks depend on temporal shifts in environmental conditions. Moreover, plant-soil feedbacks are dependent on spatial variation in environmental conditions. How do plant-soil feedbacks operate across spatio-temporal scales, and how and to what extent are plant-soil feedbacks influenced by environmental context? Here, we synthesize current knowledge on spatio-temporal aspects of plant-soil feedback and propose a conceptual framework to better understand the effects of PSF on community and ecosystem properties across temporal and spatial scales.

Results/Conclusions

Our framework considers natural and human-induced disturbances, showing how the strength and direction of biotic plant-soil feedbacks can change over time and space. At the short-term and small spatial scale, spatio-temporal feedback dynamics are best explained in terms of ‘internal’ feedback interactions, i.e., dynamics resulting from interactions between plants, soil organisms, and locally available resources. Such interactions may include the temporal build-up of pathogens in a plant’s rhizosphere, the establishment of mycorrhizal networks, as well as facilitative and competitive interactions. Importantly, such ‘internal’ feedback interactions do not occur in a spatio-temporally stable environment, but instead depend on longer-term and larger-scale ecosystem dynamics. These would be considered as ‘external dynamics’, and include pedogenic processes such as weathering and leaching of nutrients, but also human-induced changes, such as N deposition and shifts in precipitation patterns.

Our model suggests that the shape of the spatio-temporal scaling relationships depends on environmental context such as the temporal and spatial variation in soil physicochemical conditions. We explore the scaling relationships for contrasting feedback mechanisms (such as positive feedbacks with mycorrhizal fungi and negative feedbacks with soil pathogens), and for plants with contrasting nutrient acquisition strategies (e.g., N₂-fixation, mycorrhizal-dependence, and production of non-symbiotic roots). We further explain how the importance of biotic versus abiotic soil drivers in explaining plant community dynamics shifts with increasing spatio-temporal scale (from local neighbourhood interactions to landscape scale dynamics). We conclude that understanding and predicting the importance of plant-soil feedbacks in regulating community and ecosystem dynamics, requires explicit consideration of the spatio-temporal context under which plant-soil feedback occurs.