Responses of Pinus sylvestris branches to simulated herbivory are modified by tree sink/source dynamics and by external resources

• Published in: Functional Ecology
• Main Authors: Honkanen, T., Haukioja, E., Kitunen, V.
• Format: Article in Journal/Newspaper
• Language: English
• Published: Wiley 1999
• Subjects: Northern Finland
• Online Access: http://dx.doi.org/10.1046/j.1365-2435.1999.00296.x; https://api.wiley.com/onlinelibrary/tdm/v1/articles/10.1046%2Fj.1365-2435.1999.00296.x; https://besjournals.onlinelibrary.wiley.com/doi/pdf/10.1046/j.1365-2435.1999.00296.x

1. It is claimed that the quality of foliage following defoliation depends on carbon/nutrient balance of the tree. To study the importance of sink/source regulation for the quality of foliage, as well as for its quantity, Pinus sylvestris trees were defoliated and fertilized both in southern Finland and at the tree line in northern Finland. 2. The pattern of defoliation in a shoot was more decisive for quantitative changes in new foliage than its extent: removal of similar amounts of foliage from different branch parts led to different outcomes. 3. Defoliation of 50% spread evenly within a shoot, or applied to the basal part of a shoot only, did not alter production of new foliage, whereas defoliation applied to the apical part of a shoot decreased the mass and length of needles in the new shoot. Defoliation of apically located 1‐year‐old needles of the branch leader shoot, but not of 2‐year‐old ones, significantly reduced the mass and length of needles in new shoots. 4. These results are consistent with the explanation that damage alters the ability of shoots and branches to form strong meristematic sinks and that sink strength determines the ability of these meristems to draw resources from the common pool of the tree. 5. Defoliation of the main photosynthate source lowered concentrations of the fructose and glucose, indicating shortage of carbon. However, whole‐tree defoliation did not affect the concentrations of individual foliar sugars. 6. Traits describing pine shoot growth correlated negatively with foliar phenolic concentrations but not with concentrations of other secondary compounds. Concentrations of foliage phenolics consistently increased after defoliation, while terpenoids, putatively the main class of defensive compounds in Scots Pine, did not respond to defoliation. Defoliation of a branch or a whole tree had only slight effects on the concentrations of fibre, mono‐ and sesquiterpenes, resin acids or nitrogen. 7. Likewise, fertilization significantly increased the concentration of some ...