Mineral Nutrition

7.2.1. Methods in evaluating mineral requirements

The nutritional status of trees is most frequently assessed on the basis of the elemental analysis of leaves (MATERNA 1960; KRAL 1963; FIEDLER et al. 1965; Lavrichenko 1968; Tamm 1968; Zech 1968; Swan 1972; Linder 1995 and others). In spruce, needles sampled for this purpose should be collected be tween mid-August and mid-September (Touzet et al. 1970), preferably from the same sector of the tree crown (JUNG and RIEHLE1966), and separately for each needle age class cohort or from the youngest age class (LINDER 1995). Roots, wood, or bark are also sampled for chemical analyses (INGESTAD 1959; OVINGTON 1959; FORNES et al. 1970; FEGER et al. 1991) as well as whole plants, especially small seedlings (Kral 1961; FOBER and GIERTYCH 1968, 1970a; FOBER 1974).

The nutrient requirements of trees may also be based on soil analyses. EVERS (1967a, b, 1972) suggests that soil nutrient status depends on the ratios among elements in the soil. FIEDLER and NEBE (1963) as well as HUNGER and FIEDLER (1965) observed a negative correlation between tree height and the C:N ratio in the humus horizon. Nevertheless, HORN et al. (1987) found that needle analysis frequently provides more information on the nutritional status of trees than does routine soil analyses.

Employing multiple methods at the same time should increase the accuracy of the assessment of the nutritional needs of trees. These methods include visual evaluation of plants, chemical analysis of the soil, needles, and whole seedlings, as well as growth (HUNGER and NEBE 1964; LEAF 1970; WITT 1987). Other reported methods for evaluating the response of spruce trees to fertilization include: needle color assessment on the youngest shoots (LUUKKANEN et al. 1971), measurement of organic acid concentrations in needles (CLEMENT 1977), chlorophyll fluorescence (BAILLON etal. 1988), and the measurement of electrical resistance in the cambium zone (Huttl et al. 1990).

7.2.2. Symptoms of deficiency and toxicity

7.2.2.1. Deficiency symptoms

Spruce seedlings growing under conditions of nitrogen deficiency exhibit poor development and slower growth (FOBER and GIERTYCH 1968; Swan 1972; FIEDLER etal. 1973). The young needles, especially the tips appear light yellow (INGESTAD 1959). Mature needles may appear small and yellowish-green in color (Baule and FRICKER1973; FIEDLER et al. 1973). Chlorosis arising from nitrogen deficiency is typically observed throughout the tree crown in all needle age classes and often appears evenly distributed over the entire forest stand (Hartmann et al. 1988). The shoots are short and poorly branched. Summer shoots do not develop and the growth period is often shortened (Baule and Fricker 1973; Fiedler et al. 1973). Root growth is comparatively more vigorous; however, the roots may grow long and thin (INGESTAD 1959; Baule and FRICKER 1973). Clear symptoms of nitrogen deficiency are observed when its concentration on a needle dry mass basis falls below 1% (Fiedler etal. 1973; Hartmann etal. 1988).

Young needles of seedlings growing under conditions of phosphorus deficiency are short and yellow, especially at tips (INGESTAD 1959). Old needles are dark green, often with a purplish hue. In older trees, needles are grey or bluish-grey, and later they turn purple, purplish-brown, or even red (BAULE and FRICKER1973). Older needles change color more quickly and to a greater degree than younger needles. Later on they slowly senesce but are not shed, thus contrasting with the remaining younger, healthy needles (BAULE and FRICKER 1973). The roots of spruce seedlings lacking phosphorus are long and thin (INGESTAD 1959). Symptoms of phosphorus deficiency are observed when concentrations on a needle dry mass basis are below 0.08-0.1% (SWAN 1972; Hartmann etal. 1988).

In coniferous trees, potassium deficiency results in an initial yellowish-green and later yellow discoloration of needle tips (BAULE and FRICKER 1973). When the deficiency is severe, the needle tips turn reddish-brown, brown, or purplish-brown, and eventually senesce. Young needles are especially discolored, although their bases often remain green, and the transition between colors is gradual (INGESTAD 1959; MAYER-KRAPOLL 1964). According to ZECH (1968), there are two types of symptoms of potassium deficiency. When P supply is sufficient and K is lacking, mainly the young needles in the outer parts of the tree crown turn yellow or red at their tips, while older needles in the inner parts of the crown remain green. If both P and K are deficient, older needles are discolored first, and appear yellow at the tips or greyish with green spots. Discoloration is most severe in autumn and winter, and occasionally early spring (MAYER-KRAPOLL 1964; ZECH 1968; BAULE and FRICKER 1973). The symptoms are often exacerbated by high light intensities (ZECH 1968). Tree growth slows (ZECH 1968; FORNES et al. 1970; BAULE and FRICKER 1973) and roots appear short, thin, and poorly branched (INGESTAD 1959). Lignification of young shoots is often incomplete, so the tree is prone to frost damage, drought, and pathogens (BAULE and FRICKER 1973). Symptoms of potassium deficiency are observed when its concentration on a needle mass basis is below ca 0.4% (HARTMANN et al. 1988).

A lack of magnesium causes yellowing of needles (LIU and TrUby 1989; Roberts et al. 1989; FINK1991; SCHAAF and ZECH 1993) and symptoms occur at concentrations below ca 0.03% needle dry mass (HARTMANN et al. 1988) and below 2 yueq/g of soil (LIU and TrUby 1989). The needle tips turn yellow, while their bases remain green (INGESTAD 1959; BAULE and FRICKER 1973) and the transition between colors is sharp (MAYER-KRAPOLL 1964). Chlorosis progresses from older to younger needles (HARTMANN et al. 1988). Needle discoloration is the most conspicuous in autumn. When magnesium deficiency is severe, the needle tips first turn orange-yellow, then brown, and finally they senesce (BAULE and FRICKER 1973). In seedlings, roots are often poorly branched (INGESTAD 1959). The changes in spruce needle morphology that result from shortages of potassium and especially magnesium are due to the modification of chloroplast structure, partial accumulation of starch in mesophyll cells, premature necroses, and sunken tracheids in vascular bundles (Fink 1991).

Calcium deficiency is rarely observed in conifers, even if its uptake is limited by soil acidification. In hydroponics, the visual symptoms of calcium deficiency include browning of twig tips, followed by their senescence (BAULE and Fricker 1973). In spruce seedlings, INGESTAD (1959) observed yellowing of young needles, whereas all needles had yellow or brown tips and postponed development of apical buds. Root growth was also poor; they were short and densely branched. Calcium deficiency reduces plant height, but the response of Norway spruce is less than that of other coniferous trees.

In case of iron deficit in Norway spruce, young needles are completely yellow, while older needles are light green or green (ZECH 1968). In INGESTAD'S (1959) experiments, spruce seedlings grown in hydroponic cultures lacking iron had light-yellow young needles, thick and long roots, and a lack of bud development.

Symptoms of manganese deficiency are observed when its concentration in needles is below 20 ppm (ZECH 1968; FIEDLER et al. 1973; HARTMANN et al. 1988). Developing needles turn yellow. The discoloration is most apparent in autumn and winter in lower and inner portions of the tree crown.

When the copper concentration in spruce needles is below 2-3 ppm, the tips of apical shoots die in autumn and winter (MATERNA1962; FIEDLER et al. 1973). Likewise, the critical level of boron in current-year needles appears to be ca 3 ppm (BREKKE 1979, 1983). Drought reduces the uptake of boron. Symptoms of boron deficiency include shoot death and disruption of apical dominance. Sensitivity in terms of visible injury varies among populations.

7.2.2.2. Toxicity symptoms

Excessive rates of nitrogen fertilization often accelerate tree height growth, but trees may exhibit poor root growth and limited mycorrhizal development (FIEDLER et al. 1973). Lignification may be compromised to the extent that the trees become prone to frost damage. Particularly harmful is the excessive nitrogen fertilization of planted seedlings in competition with weeds. In contrast, high phosphorus availability may result in a slight decrease in seedling growth, but no other unfavourable symptoms are observed (FIEDLER et al. 1973).

ZECH (1968,1970) describes the chloroses observed on spruce trees grown on calcareous soils. On young spruce trees, current-year needles are whitish-yellow, especially at tips. According to ZECH, this discoloration is often due to a deficiency of iron in needles and reduction in manganese. In other cases, young needles started to turn yellow in July and the discoloration proceeded from the lowermost to the uppermost branches. Such symptoms are usually observed in young forest stands or in older trees and are probably caused by shortages of physiologically active iron.

An excess of trace elements may also be a stress factor for plants. In a polluted environment, the dominant factors in acid soils are toxic concentrations of polyvalent cations and low concentrations of nutrients. High aluminium levels in hydroponic cultures of spruce seedlings, ranging from 350 to 1200 umol AlCWl of medium, greatly limit root growth (GODBOLD et al. 1988). The treatment of five-year-old spruce seedlings with aluminium under acid stress, causes swelling of root tips and increases their fragility (VOGELEI and ROTHE 1988). Under conditions of poor mineral nutrition, an excess of aluminium or manganese in hydroponic cultures of spruce seedlings causes a so-called golden chlorosis of needle tips, as in the case of magnesium deficiency (Hecht-Buchholz etal. 1987).

GLATZEL (1985) reports negative effects of lead, zinc, copper, and nickel, reflected in slower tree growth and a reduction in needle and root length, when the total concentration of those elements was higher than 2 g/1 kg humus. In laboratory experiments, heavy metal compounds limited the germination and growth of spruce seedlings, causing chloroses and necroses, and consequently the death of whole seedlings at high concentrations (FOBER 1978,1979). High levels of the heavy metals lead, cadmium, arsenic, zinc, and copper in the substrate injured the roots of spruce seedlings (GODBOLD et al. 1985a, b; ZOTTL 1990).

In the case of heavy pollution with SO2, needles on the youngest shoots turn yellow-brown or red-brown from the tip towards the base of the needle (HARTMANN et al. 1988). Necrotic spots or bands occur in the central part of the needle. Other pollutant effects such as chloride toxicity may appear on spruce trees growing along roadways. Visible symptoms occur when the concentration of chloride in needles reaches 0.25-0.35% on a dry mass basis (HARTMANN et al. 1988). In early stages, pale greenish-yellow areas without well-defined borders can be seen on younger needles, and less intensively on older needles. As a result of the long-term effects of chloride, needles of the previous-year's shoots appear dark copper-brown in the spring, and are shed in early summer. Buds are also dead, or if they develop, the new shoots have needles of only one or two age classes. In addition, ozone pollution may cause a chlorotic mottle in needles of spruce trees, appearing as well-defined pale yellow to yellow-brown spots (HARTMANN et al. 1988). Visible injury arising as symptoms of a disease are often the result of a complex of factors. It is important to make detailed observations of early stages, which tend to be more diagnostic and easier to distinguish.

7.2.3. Uptake of mineral elements

The uptake of individual elements and their concentration in plants depends mainly on their concentration in the substrate, and generally increases with increasing concentration in the culture medium. Nitrogen is taken up as ammo nium and nitrate ions. Norway spruce seedlings prefer nitrate, which is accumulated more readily and in larger amounts (GEORGE et al. 1999). In hy-droponic cultures, Norway spruce seedlings grow best on a medium where the NO3/NH4 ratio is 55/45, and a total N concentration of 3.7 mmol/l (SANCHEZet al. 2000). Likewise, field experiments indicate that fertilization has a significant positive effect on the uptake and concentration of individual elements in plants (Br^KKE 1979, 1983; Matzner 1985; MURACH and SCHUNEMANN 1985; NILSSON and WIKLUND 1992; DREYER et al. 1994; NILSSON et al. 1995; MOILANEN et al. 1996; INGERSLEV and HALLBACKEN 1999).

Interactions among individual nutrients can be observed. A higher nitrogen supply reduces the concentrations of phosphorus and potassium in needles of 3-year-old spruce seedlings, clearly increasing the N/P and N/K ratios (SEITH et al. 1996). Potted spruce seedlings treated with ammonium sulphate have lower concentrations of magnesium in needles and higher concentrations of aluminium and iron (WILSON and SKEFFINGTON 1994). Application of nitrate significantly reduces plant phosphorus concentration. In spruce stands growing on the dry bogs of northern Finland, nitrogen fertilization decreased the concentrations of calcium, zinc, and boron in needles (MOILANEN et al. 1996). Application of nitrogen and phosphorus in a young spruce stand resulted in a sharp reduction in boron concentration, which is most often explained as a dilution effect (ARONSSON 1983; NILSSON et al. 1995). Intensive potassium fertilization of Norway spruce plantations increases nitrogen and magnesium uptake (FORNES et al. 1970). Glatzel (1970) reports a significant reduction in calcium content in needles of 2-year-old spruce seedlings treated with potassium or with nitrogen, phosphorus, and potassium simultaneously.

Application of magnesium fertilizers may result in a critical dilution of potassium in needles of spruce seedlings (JANDL1996). Liming with magnesium limestone increased the concentration of magnesium and calcium in needles of 15-25-year-old spruce trees in the western part of the Czech Republic (Materna 1989), but significantly decreased concentrations of potassium, calcium, manganese, and aluminium in 10-year-old trees in the Vosges Mts in France (DREYER et al. 1994). Matzner (1985) and MURACH and SCHUNEMANN (1985) observed increased uptake of magnesium following liming of a 100-year-old spruce stand. However, intensive liming caused a reduction in the boron content of needles of the youngest four age classes. If liming is accompanied by boron fertilization, then the manganese content of needles may decline (LEHTO and MALKONEN 1994). In another study, a greater supply of boron resulted in increased rates of magnesium uptake from the soil (B^KKE 1979).

In hydroponic cultures, ions are taken up from the medium very quickly. One-year-old spruce seedlings, treated with labelled phosphorus absorbed a large amount of this element within a 24-h period, and over the next six days their phosphorus content increased only by 30% (FOBER and GIERTYCH

1970b). Following maximum absorption of potassium and sodium by pine and spruce seedlings, these elements were exuded by the roots (GLADUNOV1966). Drought reduces the uptake of nutrients (BECKER and LEVY 1983; BR^KKE 1983; HUNGER and MARSCHNER1987; GRABAROVAand MARTINKOVA2001). The availability and uptake of elements is also very strongly affected by soil pH (LEHTO and MALKONEN 1994), especially the pH of the rhizosphere, and by the surface area of roots (MARSCHNER et al. 1991).

In general, fertilization with an element, especially on poor sites, causes an increase in its concentration in plants. If the nutrient had earlier limited plant growth, then the increase in biomass caused by fertilization results in a decrease in concentrations of other elements because of a dilution effect. Application of an element, especially in amounts exceeding growth requirements, may enhance the uptake of other elements. There are antagonisms between some elements, so the presence of certain ions in the substrate may limit the uptake of others. Calcium is mainly stored in older organs, whereas phosphorus and potassium are transported to developing organs. The uptake of nutrients by plants is affected by various factors including light intensity, the concentration and form of nutrients in the substrate, soil water relations, the physico-chemical properties of the substrate, and the developmental stage of the plant.

7.2.4. Concentration of elements in organs

The concentrations of elements in leaves reflect the nutrient status of the individual plant and may provide valuable information on potential deficiencies before visual symptoms are observed. Foliar concentrations also form the basis for fertilizer recommendations. In addition, high concentrations of some elements may serve as indicators of industrial pollution in the environment. Thus, it is important to assess range of nutrient concentrations in needles, characteristic of various levels of mineral nutrition, ranging from severe deficiency to luxury consumption, or toxicity. Numerous publications report the values of individual elements in various organs of seedlings and older trees (e.g. Fober and Giertych 1971; Fober 1977; Abrazhko 1985; Ogner and BJOR 1988; STIENEN and BAUCH 1988; FINER 1989; Feger et al. 1991; Ranger et al. 1992; Nilsson and WIKLUND 1994; BORATYNSKI and BUGALA 1998). Table 1 shows concentrations of various elements measured in trees of various ages. Within the ranges of deficient concentrations of individual elements in needles, a significant growth response to fertilization is expected if other factors do not limit plant growth. Within the optimum ranges, and especially within ranges of luxury consumption, fertilization is generally ineffective. In addition, the proportional relationships between individual nutrients are important for proper nutrition. In one-year-old needles of optimally growing spruce trees, the N:P:K ratio was 67:8:25, but with increasing tree age, the

Table 1. Ranges of element contents in one-year-old needles of Norway spruce (% or ppm on a dry mass basis)

Severe deficiency

Intermediate Suboptimal deficiency range

Optimum range

Luxurious content

Reported by

Tree age

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