Are gas exchange responses to resource limitation and defoliation linked to source:sink relationships?

• Published in: Plant, cell and environment cell and environment, 2011-10, Vol.34 (10), p.1652-1665
• Main Authors: PINKARD, E. A, EYLES, A, O'GRADY, A. P
• Format: Article
• Language: English
• Subjects: acclimation; Acclimatization; Biological and medical sciences; Biological Transport - physiology; Biological Transport - radiation effects; carbohydrate; Carbohydrates; carbon; Carbon Dioxide - metabolism; Carbon Dioxide - radiation effects; Cell Respiration - physiology; Defoliation; Dehydration; Eucalyptus - enzymology; Eucalyptus - growth & development; Eucalyptus - physiology; Eucalyptus - radiation effects; Eucalyptus globulus; Fundamental and applied biological sciences. Psychology; gas exchange; Growth rate; leaves; Light; Nitrogen; Nitrogen - metabolism; nutrients; Photosynthesis; Photosynthesis - physiology; Photosynthesis - radiation effects; Plant Leaves - growth & development; Plant Leaves - physiology; Plant Leaves - radiation effects; Plant Stems - growth & development; Plant Stems - physiology; Plant Stems - radiation effects; Plant Transpiration - physiology; Plant Transpiration - radiation effects; resource availability; Respiration; Ribulose-Bisphosphate Carboxylase - metabolism; saplings; Seedlings - metabolism; Soil - analysis; Stress, Physiological; Trees; Up-Regulation - physiology; Water - metabolism; water resources; water stress
• ISSN: 0140-7791; 1365-3040
• DOI: 10.1111/j.1365-3040.2011.02361.x

Productivity of trees can be affected by limitations in resources such as water and nutrients, and herbivory. However, there is little understanding of their interactive effects on carbon uptake and growth. We hypothesized that: (1) in the absence of defoliation, photosynthetic rate and leaf respiration would be governed by limiting resource(s) and their impact on sink limitation; (2) photosynthetic responses to defoliation would be a consequence of changing source:sink relationships and increased availability of limiting resources; and (3) photosynthesis and leaf respiration would be adjusted in response to limiting resources and defoliation so that growth could be maintained. We tested these hypotheses by examining how leaf photosynthetic processes, respiration, carbohydrate concentrations and growth rates of Eucalyptus globulus were influenced by high or low water and nitrogen (N) availability, and/or defoliation. Photosynthesis of saplings grown with low water was primarily sink limited, whereas photosynthetic responses of saplings grown with low N were suggestive of source limitation. Defoliation resulted in source limitation. Net photosynthetic responses to defoliation were linked to the degree of resource availability, with the largest responses measured in treatments where saplings were ultimately source rather than sink limited. There was good evidence of acclimation to stress, enabling higher rates of C uptake than might otherwise have occurred.