Relationship between severity of trunk decay of Pinus koraiensis and soil properties around roots

The decay rate of standing Korean pine(Pinus koraiensis)in natural forests can be as high as 50%and is likely infl uenced by the soil properties and nutrient and water status of the site.To clarify the relationship between the severity of tree decay and soil properties in order to prevent decay in a natural mixed forest in the Xiaoxing'an Mountains,wood strength of standing trees was nondestructively assessed,and the severity of decay of extracted wood cores was quantified based on differences in mass between two decayed increment cores extracted at breast height and an intact increment core near the decayed ones.Soil samples from the critical root zone(non-rhizosphere)of each tree were analyzed for chemical properties and microbial composition.The abundance of chemical elements(especially total N and K)and the species richness of soil microbes increased as decay severity increased.Fungal number(FN)and actinomycetes number(AN)were related to decay severity(R^(2)=0.504).Bacterial number(BN)was higher than FN or AN,but had a minor effect on tree decay.Path analysis showed BN might indirectly inhibit decay by affecting FN.Decay severity was not significantly correlated with either soil fungal or bacterial diversity.These results suggest that forest managers need to monitor levels of fungi and total N and total K levels to reduce the decay of Korean pine.

Effect of soil physical–chemical properties on the decay of standing Pinus koraiensis in Xiaoxing'an Mountains,northeast China

We selected 18 rotten and nine healthy post- mature live standing Korean pine （Pinus koraiensis） to study the correlation between the degree of tree decay and soil physical-chemical properties in the Dialing Forest District of the Xiaoxing＇an Mountains, China. One trans- verse section of each sample tree at 40-50 cm height above the ground was tested by Resistograph to determine the inner decay status. We collected soil samples around the root zones （6-20 cm depth） of each sample tree to test the soil physical-chemical indicators including moisture con- tent, bulk density, total porosity, pH, organic matter con- tent, total and hydrolyzed N contents, total and available P contents, total and available K contents, and C/N ratio. The degree of decay of postmature Korean pine live standing trees was significantly and positively correlated with the C/N ratio （R = 0.838, P 〈 0.05）, organic matter （R = 0.615, P = 0.007） and moisture content （R = 0.543, P = 0.020） of soil around the rodt. The contents of total N, hydrolyzed N and available P sample trees were significantly in the soil under healthy greater than those underdecayed sample trees, and larger N and P contents might inhibit the decay fungi breeding in soils of pH 4.4-6.29. The optimum multiple regression equation for degree of tree decay on soil physical-chemical indicators showed that the linear correlations between the degree of decay and soil C/N ratio and pH were significant （P 〈 0.01） and the correlation was high （R2 = 0.778）. Enhancement soil C/N ratio and pH could promote the decay of tree trunks.