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Paribok et al. 1989

nitrogen level may increase and the phosphorus level may decrease (FIEDLER and Höhne 1987).

Nutrient levels in plant organs depend on many factors, including seasonal variation (WYTTENBACH and TOBLER1988). Seasonal dynamics of spruce needle growth and nitrogen accumulation is more clearly reflected in the absolute nitrogen content of individual needles than in nitrogen concentration. within the first 6 weeks of needle development, a rapid increase in the absolute nitrogen content is observed, while nitrogen concentration decreases. In summer the dry mass of individual needles and the absolute nitrogen content are increasing continuously, reaching maximum values in autumn, while nitrogen concentration remains constant (BAUER et al. 1997). Concentrations of elements may change in successive years. In 1-year-old needles of 25-year-old Norway spruce trees, maximum differences in concentrations among seven successive years (1987-1993) approached 60% for potassium and manganese, 40-50% for calcium, magnesium, and sulphur, 35% for phosphorus, and 9% for nitrogen (LINDER 1995). Nutrient concentrations in needles may be affected by the accumulation of starch in spring and the subsequent decrease in starch concentration. According to LINDER (1995), the starch concentration in Norway spruce needles varies during the growing season from 0 to 30% of dry mass.

Concentrations of nutrients in needles are not the same in all parts of the tree crown. One-year-old needles have higher concentrations of nitrogen, phosphorus, potassium, magnesium, and lower concentrations of calcium, manganese or sulphur, compared to older needles (HÖHNE 1963; FOBER 1976; NEBE1991; RANGER et al. 1992; RACHWALD 1996; DOHRENBUSCH and Jaehne 1998; Hahn and MARSCHNER 1998; INGERSLEV 1999; ROBERNTZ and LINDER 1999). In late June in the current-year needles of older Norway spruce trees, concentrations of nitrogen, phosphorus, and potassium are higher in inner and lower portions of the crown, whereas calcium levels increase towards the top and outer crown positions (FOBER 1976).

In addition to environmental factors, the concentration and content of elements in various organs and tissues is affected by genetic factors. There is a great potential for intraspecific selection within Norway spruce (provenances, families, clones) with respect to nutrient metabolism and use (FOBER and GlERTYCH 1971; KLEINSCHMIT 1982; FOBER 1986; SCHMIDT-VOGT 1991; Sabor etal. 1994).

7.2.5. Nutrition and growth

7.2.5.1. Nitrogen

Nitrogen has the largest impact on tree growth, and nitrogen fertilization usually increases the size and dry mass of the plant. Positive results of nitrogen application are readily observed in experiments with young Norway spruce seedlings (INGESTAD 1959; FOBER and GlERTYCH 1968; SWAN 1972). A

greater nitrogen supply enhances shoot growth often at the expense of root growth, resulting in a declining ratio of root to shoot dry mass (Clemensson-Lindell and ASP 1995; Seith et al. 1996; HATTENSCHWILER and KORNER1998; GEORGE et al. 1999).

Positive effects of nitrogen fertilization may be observed both in nurseries and in young and old forest stands. in the literature, there are many examples of increased tree height (GUSSONE and ZÖTTL 1975; KUKKOLA1978; ORLOV et al. 1987; NILSSON and WIKLUND 1992; BERDEN et al. 1997), basal area (Fiedler et al. 1977; Kreutzer 1981; Mead and Tamm 1988, Nilsson and WIKLUND 1992), and volume (BAULE and FRICKER1973; FIEDLER et al. 1973; Nebe 1974; Fiedler et al. 1977; Saramaki and VALTANEN1981; WESTMAN et al. 1985; HOLSTENER-J0RGENSEN and Holmsgaard 1993). In an experiment conducted by MEAD and TAMM (1988), a significant increase in basal area was associated with a higher tree taper following nitrogen treatment. According to NEBE (1970), among 64 selected experiments concerned with nitrogen fertilization of spruce stands, 40 gave positive results. On the basis of numerous experiments carried out in Germany and Scandinavia, he calculated that the mean increase in volume per hectare after application of 100 kg N/ha amounted to 1-3 m3 per year. Under favourable climatic conditions, the influence of fertilization may approach 20 m3 (FIEDLER et al. 1973).

7.2.5.2. Phosphorus

The response of spruce seedlings to phosphorus fertilization is reflected in increased height and dry mass (INGESTAD 1959; SWAN 1972). Fertilization with superphosphate is highly effective in forest nurseries (BAULE and FRICKER 1973). There are also examples of a positive influence of phosphorus fertilization in spruce stands. In an experiment conducted in the state forests of Baden-Württemberg, stem volume was 14% higher in a fertilized plot than in the control. In the United Kingdom, on more fertile peaty soils and on strongly podzolized soils of moors, new shoots of spruce trees were 50% longer in the first few years after fertilization. Phosphorus treatment provides positive results if the soil contains sufficient amounts of other nutrients (BAULE and FRICKER 1973). Long-term intensive fertilization of a spruce stand in central Sweden with ammonium nitrate and superphosphate resulted in a three-fold increase in stem volume in comparison with the control (ERIKSSON etal. 1996).

7.2.5.5. Potassium

FORNES et al. (1970) report that in a 19-year-old spruce plantation, spruce trees fertilized with potassium were on average 19.2% taller than in the control. Similarly, potassium treatment had a significant impact on the growth rate of 4-year-old spruce seedlings planted in a sandy soil (HOLSTE-NER-J0RGENSEN and GREEN 1971; Tamm 1968; NEBE 1974; MELZER 1980).

Optimum potassium supply enhanced root growth and reduced the symptoms of stress in spruce trees exposed to environmental pollution with nitrogen (SETZER and MOHR 1998). Stem volume also increases in response to potassium fertilization (Tamm 1968; NEBE 1974; MELZER 1980). Potassium plays an important role in multi-component fertilizers with nitrogen, phosphorus and sometimes other elements, which significantly improves tree growth (MANGALIS 1969; Glatzel 1971; HOLSTENER-J0RGENSEN and GREEN 1971; Gussone and Zottl 1975; PURO 1977; Haveraaen 1978; Nys 1981; Sheedy 1982; Hunger 1985; Sture 1986; Sarnacki 1988; Hogberg et al. 1992; NILSSON and WIKLUND 1992; HOLSTENER-JO0RGENSEN and HOLMS-GAARD 1993; Sundstrom 1998; INGERSLEV and HALLBACKEN 1999).

Mayer-Krapoll (1968) found that in response to liming, the rate of tree height growth increased by 26%. EVERS (1963) recorded a substantial improvement in the growth rate of slow-growing spruce trees after application of calcium sulfate. In a seedling pot experiment with peat, calcium treatment improved seedling growth, although in some treatment combinations calcium reduced the positive effect of other fertilizers (Haveraaen 1978). Kramer and ULRICH (1985) observed increased biomass production by 3-year-old spruce seedlings after application of 4 t or 6 t CaO/ha. In a spruce stand over 30-years-old in Limousin, France, liming resulted in a significant increase in stem diameter and basal area (Nys 1981).

A positive effect of calcium on plant growth is sometimes observed only upon combining fertilizers with nitrogen (HOLSTENER-J0RGENSEN and Bryndum 1970, NYS 1981), phosphorus (MELZER and LUCKE1984; HUNGER 1986), magnesium (BOSCH et al. 1986), or other nutrients (Mayer-Krapoll 1968; BUSHS et al. 1970; HAUSSER 1971; Nys 1981; HUNGER 1985, 1986; HOLSTENER-J0RGENSEN and Holmsgaard 1993). It must be noted that liming often improves soil properties, enhances the positive effect of other fertilizers, and reduces injury from environmental pollution (FEHLEN and PICARD 1994). Nevertheless, in the literature there are many examples of no effects or even negative effects of calcium on spruce growth, both in seedlings and in young or old forest stands.

7.2.5.4. Magnesium

There are some reports of a positive effect of magnesium on spruce seedlings (Ingestad 1963; Jandl 1996) and forest stands (Baule and FRICKER1973). Magnesium may be effective in multi-component fertilizers (KOMLENOVIC et al. 1969; GUSSONE and ZOTTL 1975; BOSCH et al. 1986). Magnesium treatment or its presence in multi-component fertilizers improves the health of weakened forest stands exposed to environmental pollution, especially to acid rain. It slows down the decline of trees and improves their nutritional status. More over, magnesium may have positive impacts on soil properties by increasing the buffering capacity and consequently improving nutrient supply (HEINSDORF etal. 1988,1990; KATZENSTEINER etal. 1992;SCHAAFandZECH1993).

7.2.5.5. Micronutrients

In forestry research, fertilizers with micronutrients are rarely applied, although these elements are essential for the balanced nutrition of trees. BR^KKE (1979, 1983) observed a positive effect of borax treatment on the growth of spruce stands on peatlands in Norway. An application of 0.12 kg B/ha in combination with P and K fertilization increased the rate of tree height growth by 18-49% compared to an unfertilized control.

7.2.6. Conclusions

Mineral fertilization enhances net photosynthetic carbon gain in spruce (SOIKKELI and KARENLAMPI 1984a, b; MAREK and LOMSKY1987; HAAG et al. 1992; NILSEN 1995), and thus tree growth and development. Moreover, various nutrients have strong indirect effects on root system development, especially on the growth of fine roots (ROST-SIEBERT 1983; ABRAZHKO 1985; Murach and SCHUNEMANN 1985; ASP et al. 1988; VOGELEI and ROTHE 1988). The nutritional requirements of individual elements are closely related to plant developmental processes and phenology throughout the growing season, such as tree crown growth in spring, trunk growth in summer, root growth in autumn, and dormancy in winter (SATO and Muto 1953).

INGESTAD (1979) determined the optimum concentrations of nutrients in culture media for Norway spruce seedlings. He reports that the mass proportions of nutrients should be: 100 N, 50 K, 16 P, 5 Ca, and 5 Mg, and the absolute N content for maximum growth rate of seedlings should be between 60-80 mg/l of medium. The preferred form of nitrogen is ammonium or a mixture of ammonium and nitrate, as it reduces the risk of negative effects of other cations. EVERS (1967c) reports that in spruce stands with optimum growth, the C/N ratio in the surface layer of the soil is 20.3, while C/P, C/K, and C/Ca ratios are respectively 112, 92, and 54. Obviously, there is a wide range of tolerance, so maximum values are: 24-26 for C/N, 350-450 for C/P, and 400-500 for C/K (EVERS 1967b, c).

In addition to nutrient ratios, the pH of the culture medium or the soil solution is important for Norway spruce growth. Optimum values vary from 4.5 to 5.0 (INGESTAD 1967), although sufficient growth is possible even atpH ranging from 3.6 to 4.2 (FIEDLER 1975). In an experiment described by SCHONNAM-SGRUBER (1958), two-year-old spruce seedlings in hydroponic culture absorbed the largest amounts of mineral salts at a pH of 5.5.

It is noteworthy that interactions between genotype and mineral nutrition are observed for many traits of spruce trees, reflected in differing responses of provenances, breeding lines, or clones to nutritional conditions. In one-year-old spruce seedlings, the interaction between phosphorus concentration in culture media and breeding lines within provenances was significant for major traits of growth and development (FOBER 1990). Similar findings, although for fewer traits, were obtained with varying nitrogen and calcium nutrition (FOBER 2004). The significance of the genotype-environment interaction component of variance indicates that possibilities exist for the selection of genotypes suitable for specific site conditions, as well as for genotypes that remain stable over many nutrient levels. Preferred genotypes could include those that efficiently absorb nutrients from the soil or have low nutrient requirements.

Henryk Fober, Polish Academy of Sciences, Institute of Dendrology, Kornik.

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