Soil legacies of tree species richness in a young plantation do not modulate tree seedling response to watering regime

Trees have a strong and species-specific influence on biotic and abiotic properties of the soil. Even after the vegetation is removed, the effect can persist to form so-called soil legacies. We investigated the effects of soil legacies of tree species richness on the emergence and growth of tree seedlings, and how these legacy effects modulate the seedling responses to irrigation frequency.We used a 9-year-old tree plantation on former agricultural land in Belgium, which is part of a biodiversity-ecosystem functioning experiment (FORBIO). Soil originating from monocultures and four-species plots, with different species combinations, was translocated to a greenhouse. Five tree species (Betula pendula, Fagus sylvatica, Pinus sylvestris, Quercus robur, and Tilia cordata) were sown and grown for one growing season in these soils. We performed a watering treatment (low and high irrigation frequency) to measure any potential interaction effects between the soil legacies and irrigation frequency.There was no evidence for soil legacy effects of species richness on plant performance or their response to the irrigation frequency. However, the effect of irrigation frequency was dependent on species identity of the tree seedlings. Despite the lack of clear legacy effects, performance measures did show correlated responses that are likely due to species composition effects.We ascribe these patterns to the young age of the forest and the agricultural past land use. At this early stage in forest development, the land-use history likely has a more important role in shaping soil characteristics that affect plant growth and their response to drought, than species diversity. Forest soils originating from experimental stands differing in species richness did not provoke legacy effects on the seedlings' response to irrigation in a pot experiment.image

Automated summary

Trees have a strong influence on soil properties, even after they are removed. This study investigated the effects of soil legacies of tree species richness on tree seedling growth and how these legacies interact with irrigation frequency. The results showed that species richness did not have a significant effect on plant performance or response to irrigation frequency. However, the effect of irrigation frequency varied depending on the species identity of the seedlings. These patterns can be attributed to the young age of the forest and the previous agricultural land use, which have a greater impact on soil characteristics and plant response to drought than species diversity.