Photosynthesis and Transpiration of Pinus Radiata D. Don Under Plantation Conditions in Southern Australia. I. Response to Irrigation With Waste Water.

Abstract

A plantation of P. radiata growing on sandy soil responded by greatly increased growth to applications of waste water over 3 years. Foliar concentrations of phosphorus and potassium increased following imgation but, although the waste water contained sodium up to 200 mg l-¹, the concentration of sodium in the foliage remained low. Maximum rates of photosynthesis of branches within the canopy were 1 .8 ¼mol m-² s-¹ (imgated trees) and 0.7 ¼mol m-² s-¹ (unimgated trees). Needle conductance (g,) in imgated trees was 20-50 mmol m-² s-¹ and, in unimgated trees, less than 10 mmol m-2 s-¹. Greater rates of photosynthesis in imgated trees might be explained by greater values of g*l; variations in the rate of photosynthesis during the course of a day did not, however, always follow variations in g*l particularly in irrigated trees. Needle water potential (¨*p) of imgated trees reached a minimum of -2.0 MPa during the day, indicating a large internal resistance to the transport of water through the tree. Minimum ¨*p of unirrigated trees was -2.6 MPa; substantial rainfall during the measurement period did not reduce the difference in ¨*p between imgated and unimgated trees.