Higher quantity and lower frequency of N addition and mowing improved
gross N turnover in a temperate steppe of Northern China
Abstract
1. 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. 2. 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. 3. 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.