THE DIURNAL DYNAMIC PATTERNS OF SOIL RESPIRATION FOR DIFFERENT PLANT COMMUNITIES IN THE AGRO-PASTORAL ECOTONE WITH REFERENCE TO DIFFERENT MEASURING METHODS

Abstract

Soil respiration is one of the key components in the carbon cycle of terrestrial ecosystems. Many studies on methodologies for measuring soil respiration have been conducted. However, soil respiration is difficult to measure accurately due to the uncertainty associated with the various methods, and the large spatial and temporal variability that is inherent in soil respiration due to many biotic and abiotic factors. In this study, we used the closed-chamber IRGA method to determine the diurnal (24 h) dynamic pattern of soil respiration at the maximum biomass period, and daily soil respiration rates calculated by this method were compared to those measured by the alkali absorption (AA) method for ten different plant communities in the agro-pastoral ecotone. For the IRGA method, we used the LI-6400 system (LI-COR, Lincoln, NE, USA) and for the AA method, we used NaOH solution for absorption of CO 2. The major results were as follows: 1) The diurnal fluctuations in soil respiration rate for the ten communities were remarkable, all of them showed a single-peaked curve that was driven primarily by soil temperature. The combined influence of other meteorological factors such as temporary rainfall (thus soil moisture), wind speed and clouds were non-negligible. Therefore, the diurnal patterns for the ten communities differed; 2) The daily soil respiration rate for these communities varied from 394 to 894 mg C·m -2·d -1 as estimated by the alkali absorption method, and from 313 to 2 043 mg C·m -2·d -1 by the closed-chamber method, with the AA method averaging 67.5% of that measured by the closed chamber method; (is this what is meant? It wasn't clear from the previous wording) 3) The results measured by the alkali absorption method compared well with those measured by the closed-chamber IRGA method, and the correlation between them was highly significant (R 2=0.873 9). Of particular note was that when soil respiration rates were low, the measured values by the two methods were similar, whereas when soil respiration rates were high, the values measured by the closed-chamber method were significantly higher than that by the alkali absorption method. In general, the variation in measured values by the two methods was regular and systematic providing a reliable basis for correcting our past measurements by the alkali absorption method in the region.