Leaf litterfall decomposition of pedunculate (Quercus robur L.) and sessile (Q-petraea [Matt.] Liebl.) oaks and their hybrids and its impact on soil microbiota

Trakas Forest is the only natural habitat of sessile oak in Lithuania. Sessile oak stand here is growing about 60-70 km from the nearest natural sessile oak stands in Poland. The purpose of this study was to determine whether autumn leaf litterfall of pedunculate and sessile oaks and their hybrids have different biochemical composition and decomposition rate and, consequently, different impacts on microbial condition of rhizosphere. For this purpose in autumn leaf litterfall C, N, P, K, Ca, Mg, lignin, ash, fat, crude fibre and water-soluble carbohydrates contents and stocks, lignin/N, lignin/P, C/N, C/P, N/P ratios, the decomposition rate and CO2 emissions were determined. In rhizosphere of studied oak species N, C concentration, pHH(2)O, C/N ratio, and dehydrogenase, urease, phosphatase, bacteria and micromycetes amount were estimated as well. The litterfall of pedunculate oak was distinguished by a higher content of lignin, higher lignin/N ratio, lower decay rate and lower carbon release, which determines decreased activity of micromycetes in the rhizosphere. Metabolic activity of microorganisms differed insignificantly among tree species rhizospheres. However, the potential for the use of carbon compound substrates and biodiversity index have a tendency to be higher in the soil under sessile oak. Lower decomposition rate of leaf litterfall and organic compounds in the rhizosphere under pedunculate oak allowed to suppose that the conditions for natural regeneration were more suitable in stands where sessile and hybrid oaks dominate.