Effects of Mowing Heights on N&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt;O Emission from Temperate Grasslands in Inner Mongolia, Northern China

Lihua Zhang,Longyu Hou,Qibing Wang,Dufa Guo,Hendrikus J Laanbroek

doi:10.4236/ajcc.2015.45032

Abstract

Grazing and mowing are two common practices for grassland management. Mowing is now recommended as an alternative to the traditional grazing for grassland conservation in Inner Mongolia, northern China. Many studies have revealed that mowing may alter ecosystem properties in various ways. However, little attention has been paid to the effect of mowing on trace gas emissions, especially on N2O flux. We conducted an experiment to investigate the effects of mowing on N2O fluxes from the semiarid grassland in Inner Mongolia. The mowing experiment, which started in 2003, comprised four mowing intensity treatments, i.e. mowing heights at 2 cm, 5 cm, 10 cm and 15 cm above the soil surface, respectively, and a control (non-mowing), with five replicates. Gas fluxes were measured through a closed static chamber technique during the growing seasons (usually from May to September, depending on local climate at the time) of 2008 and 2009, respectively. Our results showed that mowing decreased N2O emissions, above-ground biomass and total litter production. N2O emissions were greater in May and June than in other sampling periods, regardless of treatments (P < 0.05). A co-relationship analysis suggested that variations in seasonal N2O fluxes were mainly driven by variations in soil moisture, except in July and August. In July and August, above-ground plant biomass and soil total nitrogen became the major drivers of N2O fluxes under the soil temperatures between 16 ° C and 18 ° C. Though there were some uncertainties due to the low frequency of N2O flux measurement, our study mainly indicated that 5 cm mowing height might decrease N2O emissions in grasslands during the growing season, and soil properties affected the magnitude of the reduction.

Highlights

The temperate steppe in northern China is a typical vegetation type on the Eurasian continent and is sensitive to anthropogenic disturbances and climate change [1] [2]
Soil moisture peaked in July and had similar temporal fluctuation patterns over the two growing seasons, the amount of rainfall was substantially different during the same period
Our observations are in line with the results of another similar investigation conducted in a grazed grassland in Inner Mongolia [21], but opposite to the findings in a heavily grazed alpine grassland by Gao [22]

Summary

Introduction

The temperate steppe in northern China is a typical vegetation type on the Eurasian continent and is sensitive to anthropogenic disturbances and climate change [1] [2]. Mowing is one of the prevailing management practices in these areas [3]. Mowing is highly recommended for sustainable grassland management in a national project called Grain for Green, which aims to restore the degraded ecosystems in western China [4]. The removal of a part of plant shoot tissue, has negative effects on overall plant growth and carbon allocation [5], which can influence root carbon exudation and rhizosphere organisms that rely on the carbon and nitrogen released from the plant roots [6]. The removal of some plants by mowing inevitably leads to the adjustment of the size of the root system and causes the death and decay of the roots and nodules, followed by decomposition, mineralization of nitrogen, nitrification and denitrification. Mowing reduces the input of above-ground litter to the soil [7], and decreases the amount of coarse organic matter in the soil [8] and related gas emissions from soil, including nitrous oxide (N2O) [9]

Methods

Results

Conclusion