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Silicon (Si) is known to have beneficial effects on the growth and stress tolerance of some plants, especially rice. However, Si uptake varies very much between plant species, and it is not well known how widely spread the beneficial effects are. In particular, peat soils are likely to have very low Si levels, consequently low Si may be an issue in the boreal region, where these soils are common. We studied the effects of Si in a deciduous forest tree, silver birch (Betula pendula). One-year-old birch seedlings in peat plugs were planted in larger pots in unfertilized, unlimed peat. They were fed with a nutrient solution with or without Si for 7 weeks. Tests were done on leaf drying and leaf palatability to an insect herbivore, Epirrita autumnata. Plant parts were weighed after final harvest. There was a 6% increase on leaf growth in the Si fed plants. No effect on herbivory was observed. However, the leaves with no Si dried significantly faster after excision, which may have affected herbivory more than the Si as such. Further studies particularly in the water relations of silver birch would be of interest.

Abstract: Reflection by waxy or resinous surface structures and hairs, repair reactions of biomolecules and induction of different sheltering components provide the means of plant protection from harmful solar UV-B radiation. Secondary products, especially flavonoids and phenolic acids as defense components are also important in plant tolerance to UV-B, fulfilling the dual role as screens that reduce UV-B penetration in plant tissues, and as antioxidants protecting from damage by reactive oxidant species. Plants are sensitive to UV-B radiation, and this sensitivity can be even more clone-specific than species-specific. The results available in the literature for deciduous trees and shrubs indicate that UV-B radiation may affect several directions in the interaction of woody species with biotic (herbivores) and abiotic (CO2 and nutrition) factors depending on the specific interaction in question. These multilevel interactions should have moderate ecological significance via the overall changed performance of woody species and shrubs. [Copyright &y& Elsevier]

The response of Fuchsia magellanica Lam. -- a shade-tolerant perennial -- to white light photon flux density and end-of-day red and far-red light irradiation was studied to evaluate the role that different morphological and functional alterations play in whole-plant acclimation to shade. The estimated relative growth rate of plants growing under a photon flux density of 30 μmol m-2 s-1 was 71% of that of those growing under 450 μmol m-2 s-1. The proportion of total dry weight allocated to shoots was higher in low light plants, but the proportion of shoot dry weight allocated to leaf blades was not affected by any of the treatments. The estimated relative growth rate, specific leaf area and leaf conductance were not affected by end-of-day irradiation. In low light plants the specific leaf area was higher, and at saturating photon flux density photosynthesis was lower on a leaf area basis, but was not on a leaf dry weight basis. Dark respiration was higher in high light plants when expressed on an area basis, but not when expressed on a dry weight basis. During the normal photoperiod, leaf conductance measured in darkness was higher in high light plants than in low light ones, which is consistent with the higher stomatal density observed in these plants. The cross-sectional area of the petioles was slightly reduced in low light in spite of a large increase in the area of individual leaves. Low irradiance affected the display of leaves, decreased leaf thickness and increased chlorophyll content per unit dry weight. End-of-day far-red resulted in plants with more erect branches. Both low photon flux density and far-red enhanced internode elongation. The effect of end-of-day irradiations was bigger in low light than in high light, which is the opposite to what is observed in shade-avoiders. The relatively small difference in mean growth rate can be explained by changes in specific leaf area, shoot : root dry weight partition ratio, and by the shape of the photosynthetic light response curve. However when comparing photosynthetic rates on a dry weight basis low light plants do not seem to be at a disadvantage under high light. [ABSTRACT FROM AUTHOR]