Higher quantity and lower frequency of N addition and mowing improved
gross N turnover in a temperate steppe of Northern China
Anthropogenic effects, such as nitrogen (N) enrichment and mowing, are
constantly changing the function and structure of grassland ecosystems.
In order to test whether the magnitude and frequency of N addition, as
well as occurrence of mowing, affects gross N turnover. We designed a
long-term field experiment which included 5 levels of N addition (0, 2,
10, 20, and 50 g N m-2 yr-1) and mowing in a typical grassland of
northern China. To test the effects of N addition frequency, the amount
of N applied was separated evenly by two times (twice a year, low
frequency) or twelve times (monthly, high frequency) that results were
compared against a control site where none of the treatments were
applied. Mowing effects were also considered at each N treatment levels.
Our results showed that the N level, the frequency of N addition, and
mowing significantly influenced gross ammonification (GA) and
nitrification (GN) rates. Specifically, the effect of N addition
frequency was significantly different under the highest N addition level
(50 g N m-2 yr-1), lower frequency (twice a year) significantly
increased N turnover rates. Mowing significantly increased the GA rate,
while decreased GN rate both under the highest N addition level (50 g N
m-2 yr-1) and lower N addition frequency. Further long-term study of the
effects of the interactions between N addition and mowing on N turnover
will be needed for understanding the mechanisms by which nutrient
cycling in typical grassland ecosystems may change in the future.