Assessing the performance of woody plants in uptake and utilisation of carbon, water and nutrients - Implications for designing agricultural mimic systems

This article introduces a series of innovative experimental approaches for monitoring current and past performances of woody plant species in utilisat ion of key resources within ecosystems. We demonstrate how such information might be useful for monitoring the progress of any novel agricultural syst em which attempts to mimic such natural systems. The experimental data pres ented principally involve the use of stable isotope techniques coupled to c ollection and analysis of substances transported in the sap of xylem and ph loem. Study species examined are sugar maple (Acer saccharum), tagasaste (C hamaecytisus proliferus), blue gum (Eucalyptus globulus), and acorn banksia (Banksia prionotes). Topics covered include investigations of (a) seasonal changes in water source utilisation using hydrogen stable isotope analyses , (b) water loss from tree roots to the surrounding soil (termed hydraulic lift) using hydrogen stable isotope analyses, (c) relationships between car bon isotope discrimination of plant dry matter and whole-plant water-use ef ficiency, (d) phloem sap analysis as a means for assessing aspects of a pla nt's water and nutrient status, (e) carbon isotope ratios of foliage and an nual growth rings as they relate to seasonal changes in carbon isotope rati os of phloem translocate, and (f) the composition of simultaneously collect ed samples of xylem and phloem sap as a means of monitoring current plant p erformance in uptake and mobilisation of key mineral resources. The chapter concludes with discussion of prospective uses of the above- mentioned tech niques in study of managed ecosystems in which woody species play pivotal r oles in maintenance of functional stability.