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

Abstract

Responses of Pinus sylvestris branches to simulated herbivory are modified by tree sink/source dynamics and by external resources T. HONKANEN,* E. HAUKIOJA* and V. KITUNEN † *Laboratory of Ecological Zoology, Department of Biology, University of Turku, FIN-20014 Turku and †Finnish Forest Research Institute, P. O. Box 18, FIN-01301, Vantaa, Finland Summary 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 sesquiterpenes only in pine foliage. Whole-branch defoliation and fertilization together had no effect on the concentration of fibre or nitrogen in pine foliage. 8. Altogether, the amount of foliar biomass removed, nutrients or carbon did not explain in any consistent way the qualitative changes in the pine foliage. Instead, results were consistent with simple physiological dependence of foliar traits on sink strength. Production of terpenoids reflected increased sink strength, but the production of phenolics was negatively correlated with sink strength. 9. The difference between shoot growth characteristics and foliage concentrations of phenolics and, on the...

Do artificial and natural defoliation have similar effects on physiology of Eucalyptus globulus Labill. seedlings?

“…II). Based on the source-sink hypothesis (Honkanen et al, 1999), damage by herbivory modifies the strength of either pre-existing sink or newly formed sinks. In the present study, insect defoliation altered the ability of new shoots to draw resources to maintain stem growth, although it increased sink strength of directly damaged leaves.…”

Seagrass–pathogen interactions: ‘pseudo-induction’ of turtlegrass phenolics near wasting disease lesions

“…lesions damage vascular tissues in seagrass blades, disrupting the flow of carbohydrates within seagrass blades and resulting in accumulations of phenolics wherever carbohydrates are in overabundance, as predicted by Jones & Hartley (1999). Such responses are known from terrestrial plants, including birch, pine and poplar, and are predicted by the sink/source model of plant defense (Haukioja 1990, Tuomi et al 1991, Honkanen et al 1999, Arnold et al 2004). This model predicts that 'induced' responses arise when the allocation of carbon resources among tissues acting as carbohydrate sources and sinks is altered, e.g.…”

Growth response of young Scots pines to needle loss assessed from productive foliage

“…In the artificial defoliation experiments the effect of the removal of needles had varied according to the age of the removed needles and to the season of this violent action (Linzon, 1958;O'Neil, 1962;Ericsson et al, 1980;Honkanen et al, 1999). The growth reduction in conifers, achieved by the artificial removal of green needles or caused by herbivory (Ericsson et al, 1980;Honkanen et al, 1999;Armour et al, 2003;Piene et al, 2003;Williams et al, 2003;Kurkela et al, 2005;Straw et al, 2005) can not be correctly compared with the growth reduction in trees caused by abiotic stress situations (like drought) or by fungal needle pathogens (like Lophodermium needle cast).…”

“…The growth reduction in conifers, achieved by the artificial removal of green needles or caused by herbivory (Ericsson et al, 1980;Honkanen et al, 1999;Armour et al, 2003;Piene et al, 2003;Williams et al, 2003;Kurkela et al, 2005;Straw et al, 2005) can not be correctly compared with the growth reduction in trees caused by abiotic stress situations (like drought) or by fungal needle pathogens (like Lophodermium needle cast). The reason is that the first type of needle removal is accompanied by the additional energy-consuming traumatic effects (resin flow etc.…”