Relationships between the root system size and its hydraulic properties in white spruce seedlings

Seedlings grown under different N supply were examined for relationships between root system size attributes and its hydraulic properties. These relationships were also studied on seedlings of different stock types (grown in different container types). Measurements with root pressure probes were taken at various times after germination, under applied hydrostatic pressure and non-limiting soil moisture. Different N-treatments and stock types were used solely to produce seedling of different sizes, especially root system sizes. Specific root hydraulic conductivity (Lp_r) typically declined with an increasing root system size and correlations between Lp_r and the root system size attributes were often negative. The flow of water through the root system correlated well with root system size attributes only in young (3–4 month old) seedlings but the correlations were inconsistent among different N treatments and stock types. Neither the root system surface area nor dry weight reliably reflected its ability to absorb and conduct water. Generally, the amount of water delivered through the root system and available for transpiration per unit or leaf surface area or unit of leaf dry weight correlated poorly or negatively with the root system size. Practical and scientific implications of the findings are discussed. *Paper presented at Forest Seedling Root Development Conference: From the Nursery to the Field, Eugene, Oregon, May 12–13, 2004.