Chapter 8 - 6 Nutrient Relations : Deficiency

Figure 1. Dicranum spadiceum in an alpine habitat where nutrients are typically deficient. Photo by Michael Lüth. Tracheophytes have well-known adaptations to low nutrients. Among the herbaceous seed plants adapted for low nutrient habitats, a small growth form with narrow leaves or basal rosettes seems to predominate (Grime 1977). Evergreenness is common in both dry and wet habitats (bogs and fens), presumably affording the plant the opportunity of using their leaves for several years without having to provide the nutrients to grow a new supply. Like the shade plants, these plants possess an inherently slow growth rate. Bryophytes in general seem to grow best in low-nutrient habitats (Figure 1). It is interesting that their productivity is no greater in extreme rich fens than in bogs and poor fens (Vitt 1990). Furthermore, the addition of nutrients to bryophytes in intermediate fens does not result in an increase in productivity. If we compare the bryophytes to the low-nutrient-adapted plants described by Grime (1977), the bryophytes are likewise small, have narrow leaves, and are mostly evergreen (but not leathery). As discussed earlier, they are able to move soluble nutrients from older tissues to growing apices. Furthermore, bryophytes are able to survive in low-nutrient habitats despite their small size and slow growth rate. In nutrient-rich habitats, they have no chance of competing with the fast-growing tracheophytes. In bogs and fens, Sphagnum seems to have its own way of "competing" for the limited supply of nutrients. In experiments where both Sphagnum fuscum and Drosera rotundifolia (sundew, Figure 2) were fertilized with N, the Sphagnum was able to advance its growth (Svensson 1995), seemingly ready to outcompete the tiny Drosera plants for light. However, the Drosera tapped into the nutrients at a different depth in the system, elongated its vertical stem that connected two successive years of growth, and hence