Effect of irrigation on the soil respiration of constructed grasslands in Inner Mongolia, China

Abstract

We tested the responses of soil respiration to irrigation, at different proportions of field capacity, in constructed grasslands in the Inner Mongolia Autonomous Region of northern China, and tried to identify the underlying physiological mechanisms. The experiment included a legume (Medicago sativa) and a forage grass (Elymus nutans) in sole-crops and a mixed sowing, with four water treatments: a control and three levels of irrigation (low, medium, and high) at three application times: during the regreening, elongation, and heading stages. The soil respiration rate (R s) responded strongly to water addition. Irrigation increased the cumulative growing season R s, which ranged from 257 g C m−2 years−1 to 500 g C m−2 years−1 for M. sativa, from 299 to 391 g C m−2 years−1 for E. nutans + M. sativa, and from 209 to 296 g C m−2 years−1 for E. nutans. Irrigation increased the cumulative R s by 7 to 49 %. R s of the grass–legume mixture was 1.2 to 1.4 times the corresponding values in the E. nutans plots. In addition to the effects of soil temperature and moisture content, R s was explained by differences in the net photosynthetic rate and in microbial biomass. Water addition increased Q 10, which was strongly and positively correlated with the total C, C/N ratio, and cellulose content of the plants. R s responded strongly to irrigation, although the response differed between the two species. The grass–legume mixtures showed increased R s compared to values in the grass sole-crop. R s appears to be determined by moisture and temperature, but also by the net photosynthetic rate and by microbial properties such as microbial biomass.