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Suboptimal boron availability, fine root growth and drought resistance in Norway spruce. Suboptimal boron (B) availability ( below 8 mg kg-1 in needles) is common in Finland, and nitrogen deposition may increase occurrence of boron deficiency in the future through a dilution effect. Low boron availability limits growth of roots, and deficiency affects mycorrhizal symbiosis more than fine roots alone. Most of the diverse symptoms of boron deficiency probably follow from the role of boron in the stability of the cell wall and in the interface of the cell wall and membranes.
In a future, (possibly) warmer climate, more frequent droughts are probable due to increased evapotranspiration. If Norway spruce already has difficulties in keeping up enough roots and mycorrhizas because of low B availability, and droughts further exacerbate the situation by causing damage to fine roots and mycorrhizas, Norway spruce trees may not be able to take up enough water and nutrients to keep up their growth rates, and damage may follow. Furthermore, suboptimal boron in the plant may also reduce nutrient and water uptake per unit root or mycorrhiza because of the effects of boron on cell walls and membranes, without any effects on the amounts of roots. Both possibilities will be explored.
Objectives: (1) To confirm earlier findings on the effects of low B levels on amounts of fine roots and mycorrhizas in Norway spruce, and to study the effect of B on the turnover of fine roots and mycorrhizas. (2) To study the water relations and nutrient uptake of spruce with different internal B concentrations in well watered and drought conditions to establish whether inadequate B can cause enough damage to roots to prevent efficient nutrient and water uptake. (3) To separate two possible kinds of effects of low B on water and nutrient uptake of spruce: caused through the smaller amount of fine roots and mycorrhizas, and those caused through reduced ability of a unit of fine root or mycorrhiza to take up nutrients and water.
Experiments: Long term field experiments (plots with and without B fertilizer) will be used as well as short term pot experiments (treatments usually factorial combinations of different B availability and water availability) in growth rooms or greenhouse.
Methods: In the field experiments, growth and longevity of fine roots and mycorrhizas will be monitored using minirhizotrons, and the past water relations of trees with and without B fertilizer will be studied using 13C analysis. In pot experiments, a method based on growth analysis will be used to study nutrient uptake, alongside with 15N uptake. Water potential of shoot, root hydraulic conductivity and gas exchange will be measured. Short root counting and ergosterol analysis will be used to assess mycorrhiza formation. Damage will also be studied from sections of needles and mycorrhizas. To separate effects of B on amount of root and cellular structure (objective 3), measurements of water relations and 15N uptake will be done before and after restoring the B status of deficient seedlings.
Lehto T, Kallio E, Aphalo P J. (2000) Boron mobility in two coniferous species. Annals of Botany, 86, 547-550.
Möttönen M, Aphalo P J, Lehto T. (2001) The role of boron in drought resistance of Norway spruce (Picea abies) seedlings. Tree Physiology, 21, 673-681.
Möttönen M, Lehto T, Aphalo P J. (2001) Growth dynamics and mycorrhizas of Norway spruce (Picea abies) seedlings in relation to boron availability. Trees ? structure and function, 15, 319?326, DOI 10.007/s004680100106.
Aphalo P J, Schoettle A W, Lehto T (2002) Leaf life span and the mobility of ?non-mobile? mineral nutrients - the case of boron in conifers. Silva Fennica, 36, 671?680.
Möttönen M, Lehto T M, Aphalo P J, Kukkola M, Mälkönen E (2003) Response of mature stands of Norway spruce (Picea abies) to boron fertilization. Forest Ecology and Management, 180, 401?412.
Author: Pedro J. Aphalo.