Soil water availability varies spatially, affecting the growth and survival of terrestrial plants, particularly those with large root systems. Effective response to drought conditions relies upon mechanisms that improve or maintain water accessibility and uptake. Although boreal ecosystems are generally not considered water limiting, susceptibility to drought, a consequence of climate change, poses potential concerns for tree survival. This research aims to explore (i) the capability of aspen, a common tree species native to the boreal forest, to spatially homogenize soil water through hydraulic redistribution, and (ii) the allocation of structural and non-structural carbon to the root system in response to localized drought to enhance water uptake and maintain root function. In a split-pot experiment, the root systems of aspen seedlings were subjected to different soil moisture conditions, which were spatially separated. In order to assess hydraulic redistribution, soil water availability was monitored using soil water potential sensors and isotopic water was applied to track potential water movement through the root system between the pots. Biomass, nonstructural carbohydrate reserves, and 13C were measured in the divided root systems to assess carbon allocation and dynamics in response to the drought treatments.
Results/Conclusions
Isotopic water moved between wet and dry areas of the split-pot via the root system; this observation was supported by clear diurnal patterns in soil water potential changes in the dry side of the pots, indicative of hydraulic redistribution. The observed increases in nonstructural carbohydrate concentrations in the part of the root system that was subjected to drought, suggest that a spatial partitioning of carbon reserves occurred in the root system. These increases may be related to slowed root growth and/or a need for osmotic adjustment that enhances water uptake in dry sections of the root system. Compared to fully droughted aspen, the volume and mass of the root system was maintained on both sides of the localized droughted seedlings, suggesting that hydraulic redistribution is an important factor in overall root system maintenance and survival. This is particularly important for plants with extensive root systems, such as trees, which can, with access to local areas of higher soil water, maintain larger root systems through extended periods of drought stress.