The Simulated Study On The Short-term Effects Of Nitrogen Deposition On The Larix Principis-rupprechtii Natural Secondary Forest

In order to determine the effect of nitrogen deposition on Larix principis-rupprechtii forest, the study was conducted in a natural secondary forest of Larix principis-rupprechtii (-50years old). During the growing season, we conducted the experiment of simulated nitrogen deposition. The levels of nitrogen treatment were0,8and15g m-2a-1for control (CK), low and high nitrogen, respectively. Measured the the soil respiration, the soil nutrient contents of0-20cm horizon including ammonium nitrogen(NH4+-N), nitrate nitrogen (NO3--N), total organic carbon(TOC), total nitrogen (TN), the fine root characteristic of0-20cm horizon that including total root length, root superficial area, root density, root biomass, root nitrogen concentration and root carbon concentration, etc. And collected the current year needle from the mature plant, then measured the needle nutrient contents including needle length(L), needle width(W), needle projected area(PA), specific leaf area(SLA), needle nitrogen content(LN) and carbon content(LN), etc. The result showed:the short-term nitrogen treatment significantly increased concentrations of NH4+-N, NO3--N, TOC at0-20cm horizon, and the increasing of the soil nutrient contents at0-10cm horizon were relatively obvious. The short-term nitrogen treatment significantly increased concentrations of NH4+-N, NO3--N, TOC at0-20cm horizon, and the increasing of the soil nutrient contents at0-10cm horizon were relatively obvious. The low nitrogen treatment increased the root total length, root superficial area, root density, root biomass, root nitrogen concentration at0-20cm horizon, and the responsing at0-10cm horizon were relatively obvious. The low nitrogen treatment increased the needle L, SLA, LN; thus the high nitrogen reduced the needle W and SLA, and had no effect on LN. In addition, the nitrogen deposition observably enhanced the soil respiration. Fine root biomass at10-20cm horizon was significant positively correlated with the TOC at0-10cm horizon, NH4+-N and TN at10-20cm horizon; and fine root biomass at0-10cm horizon also was significant positively correlated with NH4+-N at10-20cm horizon. LN was significant positively correlated with TN at0-20cm and10-20cm horizon, as well as NH4+-N at10-20cm horizon; while LC was significant positively related to TOC at10-20cm horizon and TN at0-10cm horizon. Results suggested that the Larix natural secondary forest is N-limited, the slight short-term nitrogen input may improve the soil fertility and be beneficial to the absorption and utilization of plants; but the excess nitrogen input may play a inhibitory effect.