Ph.D Thesis

• Principal investigator of the tropical sub-project and leading the subproject after the death of the leader (Dr Elias Chacko) in 1997. Wrote annual and final reports. My contribution has been highly praised by the International review team. I quote, ‘His expertise in sap flow measurement was seen as an opportunity to take a novel approach to the understanding of the role of water stress in mango flowering and cropping behaviour. We were impressed by the quality and quantity of data assembled on this topic… This is novel science of a high international standard.’ (ACIAR PN9012 Review report)

• Demonstrated for the first time pre-flowering water stress promotes early and more intense mango flowering in low latitude tropics where temperatures remain too high for induction of flowering by cool nights (Lu & Chacko, 2000).

• Demonstrated environmental x genotype variation in photosynthetic performance, water relations and bearing behaviour among 6 mango cultivars (ACIAR Project Reports). Low stomatal conductance caused by high vapour pressure deficit and partially dried root system was identified as major physiological limitation to mango productivity in northern Australia. These physiological traits are now important for the assessment of progeny in the mango breeding/selection program.

• Tested, selected and standardized a low cost and reliable sap flow measuring system (Granier system) for water use studies in mango. I have also adapted this method for other tropical crops (cashew, mangosteen, banana and macadamia) (Lu, 1997; Lu & Chacko, 1997; Lu & Chacko, 1998; Blaikie et al, 2001). This is important because until now there had been no accurate estimate of true tree water use under the Northern Territory conditions.

• Established the pattern of sap flow in mango and cashew and demonstrated high spatial variation of sap flow in sapwood of mature trees. A model was developed for taking account of the radial variation (Lu et al, 2000)

• Developed a direct method for monitoring the average sap flux densities at several measuring points, which greatly improves the quality of sap flow measurement in orchards with minimum need for expensive data loggers (Lu, 1997). This method has been adopted by eco-hydrologists in Canada.

• Designed an ‘ambient temperature gradient auto-compensating system’ for improving quality of sap flow measurements in young tropical fruit trees under orchard conditions (ACIAR Project Reports).

• Established daily and seasonal water use patterns of mango trees of different cultivars and ages. Provided the baseline to the industry for improving irrigation scheduling and water use efficiency (Lu, 2001).

• Provided expert assistance in planning, design, measurement and data interpretation and publication. Applied the principles developed in previous studies with mango to describe the spatial variation in sap flow in cashew. (Blaikie et al, 2001, Lu, 2001). This work will help provide benchmarks for irrigation planning and implementation.

• Established microdendrometric measurements (shrinking and swelling of stem) as a reliable and sensitive indicator of plant water status in mango trees. This is important because traditional pressure chamber methods are not applicable owing to the destructive nature of the measurement and latex exudation in leaves of most mango cultivars. Threshold values of stem microdendrometry for quantifying the critical level of stress and automated irrigation scheduling were determined. Results from a two-year field trial using such threshold values to control irrigation showed a substantial improvement in irrigation efficiency (77%, compared to 31% for the control) (Lu, 2002). This has resulted in the involved farm adopting the revised irrigation schedule which saves 3.3 ML water per season compared with current industry practice.

• Co-investigator: in charge of measurements of whole-plant water use and weather conditions.

• Established for the first time diurnal and seasonal patterns of whole-tree transpiration of field-grown macadamia plantation and their relationship with environmental factors (HRDC Project Reports). This will assist in irrigation scheduling and provide a sound base for future improvements in irrigation efficiency and manipulation of canopy structure through irrigation management.

• Co-investigator: in charge of the part of the project in NT on a mango farm. This project provides the land managers with a simple device (FullStop wetting front detector) to evaluate and improve their performance in managing water, salt and nutrients in irrigated horticulture.

• For the first time in the world sap flow has been successfully measured in banana plants. Transpiration was accurately estimated by sap flow measurement in the central cylinder in the corm and confirmed by gravimetric techniques. Established close correlation between sap flow and changes in soil water status and micrometeorological variables. This knowledge will greatly improve our understanding of the whole plant physiology of bananas and their irrigation requirement, especially in the field conditions. Another significant outcomes of this work is for the first time we explained what caused a ‘reversed sap flow pattern’ which puzzled many researchers for years (Lu et al, 2002, J. Exp. Bot).

FUTURE DIRECTIONS

• Initiating and developing a conceptual framework for the modelling and maximising carbon assimilation and water use efficiency at the whole-orchard scale by optimising canopy structure and orchard design (obtained a CSIRO McMaster Fellowship for Year 2002 to bring a world expert to assist us with this project)
• Investigating and discussing with industry/peers to develop a project on using bamboo as windbreak to improve the crop productivity (quantity, quality and diversity) and water use efficiency at orchard level.
• Developing expertise in the measurement of canopy structure and developing simulation models for tropical fruit trees and setting a solid scientific foundation for MangoLOGIC, an expert software package being developed for mango.