Measuring nutrient depletion by roots of mature trees in the field

The kinetics of ion uptake by roots is of fundamental importance to the study of the mineral nutrition of plants and the definition of an effective root system. Our understanding of ion uptake by roots comes from studies of transport phenomena using new, white roots of young plants. Much less is known about nutrient absorption by older roots of perennial plants, where these root may encompass >90% of the fine root system. However, studies of nutrient uptake in situ are complicated because of plant size, age, and access to the root system. This is also true when considering roots of mature trees. The objectives of this study were to: (i) present the design and construction of a system suitable for measuring nutrient uptake by lateral root systems of mature trees in the field, and (ii) test the system under laboratory and field conditions. We developed a system for root regeneration that allows easy access to roots while minimizing disturbance. The design includes: (i) a system for gas supply; (ii) a root chamber; and (iii) a Mariotte flask system. The system was tested under laboratory and field conditions. Laboratory results showed that all components of the nutrient uptake system were inert to P and K. Under field conditions when the chambers were aerated, P and K were absorbed from the nutrient solutions. In comparison, when roots were gassed with N 2 (hypoxic conditions), P was still absorbed but K absorption was inhibited.