Dynamics and Vertical Distribution of Roots in European Beech Forests and Douglas Fir Plantations in Bulgaria

Identifying patterns in roots spatial distribution and dynamics, and quantifying the root stocks, annual production and turnover rates at species level is essential for understanding plant ecological responses to local environmental factors and climate change. We studied selected root traits in four different stands, two European beech (Fagus sylvatica L.) forests and two Douglas fir (Pseudotsuga menziezii Mirb. Franco) plantations. Root system vertical distribution and dynamics were studied using sequential coring method and characterised into three root diameter size classes (0–2, 2–5 and 5–10 mm) sampled at three different soil depths (0–15, 15–30, 30–45 cm). Root annual production and turnover rates were analysed and quantified using Decision Matrix and Maximum-Minimum estimation approaches. The overall root mass (<10 mm diameter up to 0–45 cm soil depth) was higher in the beech forests than in the Douglas fir plantations. Some root traits, e.g., the overall root mass, the fine (0–2 mm) and small (2–5 mm) roots mass, differed significantly between the sampling plots rather than between the forest types. The root system revealed a tree species specific vertical distribution pattern. More than half of the fine and small roots biomass of the Douglas fir stands were allocated in the uppermost soil layer and decreased significantly with depths, while in the beech forests the biomass was more uniformly distributed and decreased gradually with increasing soil depth. Although both tree species belong to two different plant functional types and the stands were situated in two distantly located regions with different climatic and soil characteristics, we revealed similar trends in the root biomass and necromass dynamics, and close values for the annual production and turnover rates. The mean turnover rates for all studied stands obtained by sequential coring and Decision Matrix were 1.11 yr−1 and 0.76 yr−1 based on mean and maximum biomass data, respectively. They were similar to the averaged values suggested for Central and Northern European forests but higher compared to those reported from Southern Europe.

The use of laboratory measurements to predict nitrogen mineralization and nitrification in Pinus radiata plantations after harvesting

We tested whether laboratory estimates of net N mineralization and nitrification (subsequently termed N mineralization and nitrification) could be used to predict these processes in the field after harvesting nine Pinus radiata D. Don. plantations. Laboratory rates of N mineralization and nitrification were measured by aerobic incubation (20°C) of intact cores. Annual rates of these processes in the field were measured using a sequential coring procedure. Rates of N mineralization in the laboratory were 1.1-6.6 and 0.019-0.525mg·kg-1·day-1 for forest floor and mineral soil, respectively (nitrification accounted for 6-71 and 8-93% of N mineralization). Annual N mineralization by forest floor in the field was 5.2-23.9kg·ha-1·year-1and was not correlated with N mineralized in the laboratory. Annual N mineralization in mineral soil in the field was 16-74kg·ha-1·year-1and was highly correlated (r2 = 0.97) with N mineralized in the laboratory. Annual nitrification in forest floor in the field ranged from 3 to 45% of annual N mineralization, and in mineral soil from 4 to 27%, both were correlated with relative nitrification measured in the laboratory.