Speaker
Description
Background and objectives
Tree fine roots are a major pathway of carbon (C) transfer to the soil and play a central role in nutrient uptake and C allocation. In boreal regions, climate change is expected to increase temperatures, precipitation, and the frequency of extreme rainfall events. In peatland forests, this may increase the occurrence of short-term soil waterlogging (WL), exposing roots to oxygen deficiency altering root survival, turnover, and root-derived C input to the soil. However, the effects of intermittent WL on fine root longevity and their implications for belowground C cycling remain insufficiently understood. This study assessed how short-term waterlogging affects the survival of tree fine roots and explored the implications of altered root longevity and mortality for C input to soil in boreal forest ecosystems.
Methods
This study used results from four previous experiments conducted in the Joensuu Root Laboratory, a facility for studying environmental effects on plant growth, performance and survival. The experiments differed in duration and tree species, but all included a common WL treatment applied at different seasonal phases and for varying durations, together with a control treatment. Fine root dynamics were monitored using minirhizotron imaging, and survival analyses were used to compare treatment effects across experiments.
Results
The effects of WL on fine root survival depended strongly on season: WL during the dormant season did not have clear effects, whereas WL during the growing season reduced root survival. This negative effect became stronger with a longer treatment, indicating that cumulative hypoxic stress is an important factor for root survival. In addition, birch showed shorter fine root longevity than pine, suggesting faster turnover and potentially greater root-derived C inputs to the soil. In pine, increased mortality due to WL may likewise increase necromass input to the soil.
Conclusions
Our results show that short-term WL during the growing season can substantially decrease fine root survival in boreal trees, with important implications for belowground C cycling, and that hydrological stress may influence both the timing and magnitude of root-derived soil C input. These findings highlight the importance of considering fine root responses to hydrological stress in assessments of climate change impacts, ecosystem C sequestration and the sustainable management of boreal peatland forests.
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