The effects of nitrogen addition on the soil microbial biomass and fine root biomass in Cinnamomum camphora plantation

It is estimated that the nitrogen deposition to forests has been doubled in the past century, which has the potential to cause a series of changes therein, including increasing productivity, carbon allocation and soil... [ view full abstract ]

It is estimated that the nitrogen deposition to forests has been doubled in the past century, which has the potential to cause a series of changes therein, including increasing productivity, carbon allocation and soil respiration, etc. As the nitrogen input accumulates, some would become “nitrogen saturated”. Here we simulated nitrogen input by spray nitrogen fertilizer (NH4NO3) at low level (LN, 50 kg N·hm-2·yr-1), medium level (MN, 150 kg N·hm-2·yr-1), high level (HN, 300 kg N·hm-2 ·yr-1) and control level (CK, no nitrogen fertilization) in subtropical Cinnamomum camphora plantation. Soil microbial carbon (Cmic) and microbial nitrogen (Nmic) was determined using the chloroform fumigation extraction method to assess the effects of Nitrogen deposition on soil microbial biomass and fine root biomass. The results showed that Cmic and Nmic exhibited different patterns as the concentrations of Cmic were somehow lower in treatments with nitrogen fertilizer, whereas Nmic showed higher value instead, suggesting the nitrogen input would have altered the nitrogen content in microbial organisms. The fine root biomass decreased as the elevated nitrogen input and the control treatment showed highest fine root biomass. The nitrogen concentration, however, were significantly higher in fine roots in treatments with nitrogen fertilizer, and the carbon concentration in fine root showed the opposite. Our results suggested the elevated nitrogen input to forests has impacts not only on the amounts of microbial organisms and fine root biomass, but also the activities of them.