Grassland ecosystem plays a great role in improving regional environment
condition and maintaining soil and water． With the nitrogen deposition increasing， vegetation
characteristics and soil properties of grassland ecosystem would be changed，which in turn influence their
effects on reducing soil erosion． Bothriochloa ischaemum community is considered as typical vegetation on
the Loess Plateau． Besides，the nitrogen content of soil in this region is relatively low． Hence，
researching nitrogen addition effect on the characteristics of B． ischaemum community has a great
significance in vegetation construction and soil and water conservation． ［Methods］B． ischaemum was
seeded in the soil bin (2 m in length and 1m in width; soil bulk density was 1. 2 g/cm 3 ) with 20 cm row spacing for each plant． Totally，50 plants of B． ischaemum were seeded for each soil bin． Watered
regularly during the first year and added nitrogen in the next year． Ammonium nitrate was used as
nitrogen source with four nitrogen levels (0，2. 5，5 and 10 g N/(m 2 ·a))，which was added to the soil
once every two weeks from June to August (six times in total)． Moreover，the bare loess soil was selected
as control． For each treatment，there were three repetitions and 15 soil bins totally． Inflorescence number
and plant height of B． ischaemum were measured before each nitrogen addition，also the soil was sampled
(0 －5，5 －10，10 －20，and 20 －30 cm) at the same time to determine the soil organic matter，total
nitrogen and phosphorus，available nitrogen and phosphorus，pH and particle size distribution． At the
end of growth stage，vegetation coverage，biomass of aboveground and roots (65 ℃，48 h) were
measured． In addition to this，root characteristics such as total surface area were measured with
WinＲHIZO software． The differences of vegetation characteristics and soil properties between all
treatments were analyzed by multiple comparison method． ［Ｒesults］1) The height and inflorescence
number of B． ischaemum reached the maximum at the nitrogen addition level of 2. 5 g N/(m 2 ·a)，then
decreased with the enhancement of nitrogen addition． 2) The aboveground biomass increased significantly
with the growing nitrogen addition level (P ＜0. 05) and the root biomass density of B． ischaemum got its
maximum at 5 g N/(m 2 ·a) nitrogen addition level． However，with nitrogen addition increased，root
biomass density showed a decreasing trend． 3) With the nitrogen addition up，the soil organic matter and
nitrate nitrogen content increased，while available phosphorus content decreased，whereas，there was no
significant relationship between nitrogen levels and total nitrogen or ammonium nitrogen．［Conclusions］
This study indicated that nitrogen deposition had a significant effect on grassland ecosystem． The B．
ischaemum grew well with the certain nitrogen addition level，while lower or higher nitrogen addition level
may limit its growth． This study may make a better understanding of potential impact of nitrogen
deposition on the characteristics of vegetation and soil properties，and would provide fundamental
scientific basis for regional vegetation construction under the background of global atmospheric nitrogen
deposition．
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