Effects of diversity of tree species on nutrient cycling and soil-related processes

The long-term consequences of changing beech abundance by admixture of valuable broad-leaved species and its effects on nutrient cycling and soil-related processes are not sufficiently investigated. Four different forest types [i.e., beech-hornbeam-maple-alder (Fagus orientalis-Carpinus betulus-Acer velutinum-Alnus glutinosa), beech hornbeam-maple (Fagus orientalis-Carpinus betulus-Acer velutinum), beech-hornbeam (Fagus orientalis-Carpinus betulus), and pure beech (Fagus orientalic)] in northern Iran were evaluated. Litter samples were collected via litter traps, and topsoil samples were taken and analyzed for selected properties. It was found that litter quality and turnover time improved with decreasing beech abundance. Soil pH, total N, nutrient pools (i.e., P, K, Ca, and Mg), C and N stock, fine root biomass, earthworm and nematode activities, respiration, microbial biomass N, C and N mineralization, and dissolved organic N were significantly higher under mixed beech stands. However, water content, C/N ratio, and dissolved organic C were found to be significantly higher under pure beech forest type. Greater amount of soil organic C was found under beech and beech-hornbeam-maple-alder, but the microbial biomass C was not significantly different among different forest types. The stands with higher tree diversity enhanced the level of soil qCO(2) and particulate organic N. A higher value of microbial entropy was recorded under beech-hornbeam stands, whereas soil particulate organic C increased under beech and beech-hornbeam forest types. Based on the result, the abundance of beech influenced nutrient cycling via litter quality and turnover time. This led to an increase in soil fertility through the admixture of broadleaf species into beech forests.