Plant-soil feedbacks have recently received considerable attention for their potential role in influencing community structure and dynamics. However, most empirical studies are performed as greenhouse pot experiments under very controlled conditions and measure only individual plant growth responses. Thus it is unclear whether the feedbacks measured in these experiments operate and drive population and community dynamics in the field, in which many other processes undoubtedly occur. In this study, we test net plant-soil feedback in the field, which incorporates feedback via soil nutrients, moisture, light, soil pathogens, and mycorrhizae and integrates effects through nontrophic as well as resource-uptake (competition) mechanisms. We test the two components of feedback, species effects on the environment and species responses to the environment, in a xeric perennial grassland using environmental measurements and a two year transplant experiment in natural field monocultures. For species effects, we focus on abiotic soil characteristics (nutrients and moisture) because these are the most limiting in this dry, nutrient poor system. For species responses, we measure both population (ramet production) and individual growth. We hypothesize that plants in this system produce negative feedbacks, because previous work suggests intraspecific interactions are more negative than interspecific.
Results/Conclusions
The four dominant plant species in this community are associated with different suites of environmental characteristics, which are also distinct from plots with no plants (bare) or with reindeer lichen (another dominant in the system). Specifically, species differ in soil characteristics such as soil moisture, ammonium and nitrate levels, and nitrogen mineralization and nitrification rates, and also in aboveground environmental characteristics like litter biomass, litter height, and light levels. Species exhibit some differential responses to these environments both at the population and individual plant level. Overall, species responses suggest weak negative feedbacks occur but are not pervasive in this system. At the population level, Danthonia transplants produced fewer stems (ramets) in conspecific plots, but none of the other three species’ populations were affected by plot identity. At the individual level, Hieracium plants had fewer leaves in conspecific environments, and Carex and Hieracium grew taller in one of the heterospecific environments. Thus, similar to many greenhouse experiments that test only nontrophic feedbacks, this study shows that net feedbacks combining nontrophic plus competitive mechanisms are also negative to neutral. The negative feedbacks found here can contribute to the coexistence of the dominant species in this system.
