Wainhouse D, Staley J T, Jinks R, Morgan G
Forest Research, Alice Holt Lodge, Wrecclesham, Farnham, Surrey, GU10 4LH, UK.
Oecologia. 2009 Jan;158(4):641-50. doi: 10.1007/s00442-008-1173-0. Epub 2008 Oct 31.
Defence in young trees has been much less studied than defence in older ones. In conifers, resin within ducts in bark is an important quantitative defence, but its expression in young trees may be influenced by developmental or physical constraints on the absolute size of the resin ducts as well as by differential allocation of resources to growth and resin synthesis. To examine these relationships, we used nitrogen fertilisation of 1- and 2-year-old pine and spruce to produce trees of different sizes and measured the effect on the number and size of resin ducts and the amount of resin they contained. All of these variables tended to increase with stem diameter, indicating a positive relationship between resin-based defence and growth of 1- and 2-year-old trees. In pine, however, the mass of resin flowing from severed ducts was much lower relative to duct area in 1- than in 2-year-old trees, suggesting that the older trees allocated a higher proportion of the carbon budget to resin synthesis. Resin-based defence in 1-year-old pines appears to be both positively related to growth and resource limited. In spruce, resin production was generally lower, and age-related differences were not observed, suggesting that resin-based defence is less important in this species. Bio-assays of 2-year-old trees with the pine weevil, Hylobius abietis, emphasised the importance of resin as a defence against this bark feeding insect. Nitrogen fertilisation had a limited influence on resistance expression. One-year-old trees remained susceptible because of their small size, low resin production and limited response to fertilisation. The strong growth response of 2-year-old trees to fertilisation increased resin-based defence, but most spruce trees remained susceptible, while most pines were resistant at all levels of fertilisation.
对幼树防御的研究比对老树防御的研究少得多。在针叶树中，树皮导管内的树脂是一种重要的定量防御物质，但其在幼树中的表达可能受到树脂导管绝对大小的发育或物理限制，以及生长和树脂合成资源分配差异的影响。为了研究这些关系，我们对1年生和2年生的松树和云杉进行了氮肥处理，以培育出不同大小的树木，并测量了其对树脂导管数量和大小以及所含树脂量的影响。所有这些变量都倾向于随茎直径增加，表明基于树脂的防御与1年生和2年生树木的生长之间存在正相关关系。然而，在松树中，1年生树木切断导管流出的树脂质量相对于导管面积比2年生树木低得多，这表明老树将更高比例的碳预算分配给了树脂合成。1年生松树中基于树脂的防御似乎既与生长呈正相关，又受到资源限制。在云杉中，树脂产量通常较低，未观察到与年龄相关的差异，这表明基于树脂的防御在该物种中不太重要。用松树象鼻虫（Hylobius abietis）对2年生树木进行的生物测定强调了树脂作为抵御这种取食树皮昆虫的防御物质的重要性。氮肥对抗性表达的影响有限。1年生树木由于体型小、树脂产量低以及对施肥反应有限，仍然易感。2年生树木对施肥的强烈生长反应增加了基于树脂的防御，但大多数云杉树仍然易感，而大多数松树在所有施肥水平下都具有抗性。
