Heterobasidion annosum root rot of Norway spruce in agricultural soils | Heterobasidion annosum izraisītā egļu sakņu trupe lauksaimniecības zemēs

Root rot which is caused by Heterobasidion spp. is notably more common in forests on former agricultural soils. In these areas antagonistic microflora of Heterobasidion annosum is not so widely spread; as well as there are practically no mycorrhiza forming fungi. The aim of our work was to analyze soil microflora, morphological parameters and mycorrhization of fine roots in forest and agricultural soils. Material was collected in 26 spruce stands - 19 were located on agricultural soils and 7 on forest soils. Soil microflora was analyzed also in grasslands which were located beside agricultural lands. Dilution method was used to estimate the plate counts of bacteria and microscopic fungi in soil. Morphological parameters of roots were analyzed by computer program Win RHIZO 2002 C (Regent instrument). Obtained results show that morphological parameters of spruces fine roots (lengthy surface area and volume of roots) in forest soils have significantly higher values (a=0.05) in comparison with agricultural lands. Mean number of root tips from single sample in agricultural soils is 1180±60, but in forest soils - 1948±73. At confidence limit of 95% differences are significant (P is less than 0.0001). In agricultural lands mycorrhizal fungus Cortinarius sp. is common on 6% of analyzed root samples, but in forest lands - on 37% of analyzed root samples. Cenococcum geophilum was found on 54% root samples from forest soils and on 18% samples from agricultural lands. On roots of 11-year old spruce cultures dominated mycorrhizal fungus Amphinema byssoides, however mycorrhizas were convoluted, damaged and irregularly thickened. Number of bacteria in samples, which were taken from 5-10 cm depth, in agricultural lands is significantly higher in comparison with forest soils (P is less than 0.05). The number of bacteria in samples, which were taken from 15-20 cm depth, does not differ materially in agricultural and forest lands. Number of microscopic fungi in samples, taken from both depths, does not materially differ in agricultural and forest lands. In agricultural soils amount of calcium is 2-3 times higher than in forest soils. Forest soils have lower pH value. At depth of 5-10 cm pH in forest soils was 3.7±0.1, in agricultural lands - 4.2±0.3. At depth of 20-25 cm pH in forest and agricultural soils was accordingly 3.9±0.1 and 4.5±0.2.