SOIL RESPIRATION IN RESPONSE TO SHORT-TERM NITROGEN ADDITION IN AN ALPINE STEPPE IN NORTHERN TIBET

Northern Tibet has a vital role in global ecological security. This study determined the effect of environmental factors on the soil respiration of an alpine steppe. Short-term nitrogen addition (2 g N m(-2) yr(-1)) was performed in an alpine steppe in Northern Tibet in June, 2011. Soil respiration was observed during the growing season of 2011 using LI-8100. The results were as follows. First, soil respiration had clear seasonal patterns, and significant differences existed between the control (CK) and nitrogen addition (ND) treatments (P = 0.004). Second, soil respiration was more sensitive to soil temperature (R-2 = 0.988, ND; R-2 = 0.05, CK) than soil moisture (R-2 = 0.0003, ND; R-2 = 0.038, CK), and the relationship between soil temperature and soil respiration in ND treatment was more significant than that in CK. Third, the relationships between soil chemical properties and root biomass in CK were greater than that in ND plots, especially the relationship of root biomass with the available nitrogen and nitrate nitrogen. These results indicated that differences among geographical conditions resulted in different phenomena of gas emissions, immature soil, and extremely short plant growing time, which may all be remarkably influenced in an alpine steppe.