Impact of temperature and defoliation (simulated grazing) on soil respiration of pasture (Cenchrus ciliaris L.) in a controlled experiment

A controlled experiment was conducted on Cenchrus ciliaris L. grass (exotic to Australia) commonly grownQueensland pastures to investigate the impact of defoliation (simulated grazing), temperature andmoisture on total soil respiration, and to isolate different components of total soil respiration i.e. the root, free soil and rhizosphere respiration. The six types of treatments i.e. control (soil only without grass (control with grass but no defoliation (C2) grown for 9 months, non-defoliated treatments with grass grownmonths (D0), and three defoliation treatments (grass defoliated once, D1; twice, D2; and thrice, D3 during growth) were maintained over 9 months. Our results suggested that defoliation had no effect on totalrespiration. However, soil temperature accounted for significant changes in total soil respiration across alldefoliation and C2 treatments but not in D0, and the greatest change in soil respiration in responsetemperature was noted at the third stage of defoliation, suggesting that defoliation increased the sensitivitysoil respiration to temperature. Root respiration was significantly (P <0.05) related to root biomass and greater root biomass contributed mainly to increased rate of total soil respiration. The greater sensitivity of totalrespiration to temperature in D1, D2, D3 and C2 treatments and the greater contribution of root respirationtotal soil respiration suggests that the root respiration, rather than the total soil respiration, is likely to be more sensitive to change in temperature. With rising ambient temperature and consequently soil temperature,CO2 emissions may increase in a pasture with greater root biomass than that with lesser root biomass.