Soil Microbial and Organic Carbon Legacies of Pre-Existing Plants Drive Pioneer Tree Growth during Subalpine Forest Succession

Abstract

Fast-growing pioneer tree species play a crucial role in triggering late successional development in forests. Experimental evidence of the soil legacy effects of pre-existing plants on pioneer tree performance is lacking. We explored the legacy effects of soils conditioned by early successional herbs (Poa poophagorum Bor and Potentilla fragarioides L.) and mid-successional shrubs (Rhododendron fortunei Lindl. and Enkianthus quinqueflorus Lour.) on late-successional ectomycorrhizal (ECM) pioneer tree (Betula platyphylla Sukaczev) seedling growth. The soils were analyzed for soil nutrient status and fungal and bacterial compositions using ITS and 16S rRNA gene sequencing. B. platyphylla seedlings produced higher biomass in soils conditioned by shrubs. Soil organic carbon (SOC) and bacterial and fungal legacies most impacted pioneer tree seedling growth. Additionally, the partial least squares path model revealed that soil nutrients, especially SOC, indirectly affected seedling biomass by their direct effects on the bacterial and fungal communities. The changes in bacterial community composition had a stronger effect on seedling biomass than those of fungi because bacteria with shorter turnover times are generally considered to be more efficient than fungi in enhancing nutrient availability. Our study integrates soil microbial and nutrient legacies to explain the potential mechanisms of pioneer tree regeneration.

Trophic facilitation in forest restoration: Can Nothofagus trees use ectomycorrhizal fungi of the pioneer shrub Leptospermum?

“…Additionally, it is likely that other soil properties altered by Leptospermum species such as soil nutrients or bacterial communities could have strong effects on Nothofagus seedlings in the field, similar to those observed in Betula forests by Liang et al. ( 2022 ). We aimed to only manipulate ectomycorrhizal communities in our study (with the underlying soil mix kept constant between treatments) in order to examine the direct effects of fungal communities on plant performance.…”

“…Long-term studies tracking changes in fungal community composition to determine the rate or extent to which communities might transition toward those present in mature forests are lacking, and so it is unclear whether Nothofagus seedlings establishing in Leptospermum shrublands in the field might experience symbiont-related limitations at some point. Additionally, it is likely that other soil properties altered by Leptospermum species such as soil nutrients or bacterial communities could have strong effects on Nothofagus seedlings in the field, similar to those observed in Betula forests by Liang et al (2022). We aimed to only manipulate ectomycorrhizal communities in our study (with the underlying soil mix kept constant between treatments) in order to examine the direct effects of fungal communities on plant performance.…”