Understory vegetation plays a key role in sustaining soil microbial biomass and extracellular enzyme activities

Abstract

Abstract. It is desirable to learn more how understory vegetation affects soil microbial biomass and extracellular enzyme activities in a subtropical Chinese fir (Cunninghamia lanceolata) forests. The aim of this study was to determine the role of understory vegetation in controlling soil properties, through an examination of the effects of understory vegetation on soil environmental factors, microbial biomass, and extracellular enzyme activities. One paired treatment, which comprised understory vegetation removal (None) and understory vegetation left intact (Understory) in the context of litter removal, was established in a subtropical Chinese fir plantation. We mainly evaluated the effects of understory vegetation on soil environmental factors, the biomass of bacteria, fungi and actinomycetes, and the activities of five hydrolases, i.e., α-1,4-glucosidase, β-1,4-glucosidase (βG), β-1,4-N-acetylglucosaminidase (NAG), β-1,4-xylosidase and acid phosphatase (AP), and two oxidase, i.e., phenol oxidase (PPO) and peroxidase (PER). The soil moisture content (SMC), and the concentrations of soil dissolved organic carbon (DOC), particulate organic carbon (POC), soil organic carbon (SOC), ammonia nitrogen (NH4+-N), and total nitrogen, and the POC / SOC ratio declined by 4 % to 34 %, and the biomass of soil bacteria and fungi, total PLFA contents, and the activities of βG, NAG, PPO, and PER were between 13 % and 27 % lower, when understory vegetation was removed. The highest activity of AP among all the measured enzymes may reflect the P was limited in this area, while NAG was positive with the concentration of NO3−-N, reflected that P- and N-degrading enzyme affected by different mechanism. The positive relationship between DOC and AP implied that microorganisms absorb carbon to meet their needs for phosphorus. The concentrations of NO3−-N and NH4+-N were positively correlated with and αG and βG suggested the increased availability of N promoted the decomposition of carbon. Understory vegetation removal inhibited the propagation of microorganisms and restricted their enzyme activities, by reducing soil energy and above-ground nutrient inputs and altering the soil micro-environment. We therefore propose that, to sustain soil quality in subtropical Chinese fir plantations, understory vegetation should be maintained.