Effects of climate change and simulated herbivory on growth responses and leaf characteristics of silver birch (Betula pendula) seedlings

The main objective of this thesis was to examine the effects of climate change and simulated herbivory (artificial foliage damage) on growth responses and leaf characteristics (chemical and morphological structure and consequent palatability) of silver birch (Betula pendula) seedlings. In order to achieve this target, seedlings were grown in climate controlled closed-top chambers under ambient and elevated levels of temperature and CO2 with different nutrient regimens. Four degrees (0, 25, 50 or 75%) of defoliation was conducted on the seedlings. Additionally, the effects of climate change and nutrient availability on chemical composition and subsequent decay process of the abscised leaves were studied by leaving litter in bags in the field to decompose. The results showed that height and biomass growth were stimulated in the same season of tissue loss especially in the fertilized seedlings defoliated to 25% and subjected to elevated temperature and CO2. In comparison, the growth was slowed down in the seedlings defoliated to 50%. In the following season, compared to the intact controls, the corresponding growth was less in the seedlings defoliated to 25%, but higher in the seedlings defoliated to 50% and 75%. This phenomenon was evident particularly under elevated temperature. In the same season of tissue loss, the concentrations of different phenolic compounds were lower and the leaves were smaller in defoliated seedlings than those in intact controls. Fertilization also lowered phenolic compounds, but increased leaf sizes. Leaves developed under elevated temperature were less palatable for blue alder leaf beetles (Agelastica alni). Similarly, the decay process of leaf litter produced under elevated temperature was slowed down. To summarize, climate change and increased nutrient availability may intensify the growth of defoliated seedlings, but also alter the quality of leaves or leaf litter so that they may repel herbivores and slow down the activity of soil microorganisms.