| In this paper, rates of soil heterotrophic respiration(Rh)and root respiration(Rr)of a 40-year-old Robinia pseudoacacia Plantation and a 35-year-old Platycladus orientalis Plantation in the Lithoid Hilly Area of North China were analyzed. The experiments were conducted in Jiyuan city of Henan province during a period of Mar. 2010 to Dec. 2010. Root respiration was separated from soil heterotrophic respiration by stem girdling method and was measured by Li-8100 automatic monitoring system. The results were shown as follows:(1) The diurnal variation of Rh and Rr were all apparent in these two types of plantations, and it was a single peak curve. Rh and Rr of R. pseudoacacia and P.orientalis were increased with increasing soil temperature in the morning, reached a peak at noon and decreased with decreasing soil temperature in the night. The highest Rh and Rr of R. pseudoacacia observed at 14pm, varying consistently with soil temperature. The highest Rr of P.orientalis occurred at 17pm, observing a hysteresis of 1-2.5 hour, the highest Rh observed consistently with the highest soil temperature. In minor growing season, the diurnal variation of Rh and Rr was not apparent and had a gentle trend.(2) Rh and Rr of R. pseudoacacia and P.orientalis had apparent seasonal dynamic, which changed significantly during different seasons(P<0.01). Rr of R. pseudoacacia and P.orientalis had same regulation of a single peak curve. The peak presented to late summer-early fall and the lowest in winter. The highest root respiration rate of R. pseudoacacia in the whole year observed in September nearly to rainfall, 2.38μmol·m-2·s-1, and the averaged root respiration rate was 1.26μmol·m-2·s-1. The highest root respiration rate of P.orientalis observed in August when the vegetation grew vigorously, was 2.47μmol·m-2·s-1, and the averaged root respiration rate was 1.32μmol·m-2·s-1. In minor growing season, the lowest root respiration rate were 0.14μmol·m-2·s-1, 0.24μmol·m-2·s-1separately. The highest root respiration rate and the averaged in P.orientalis were both lager than in R. pseudoacacia. Rh of R. pseudoacacia and P.orientalis had same regulation of a single peak curve.The peak presented in July. Rh of R. pseudoacacia changed from 0.226-2.226μmol·m-2·s-1,Rh of P.orientalis changed from0.324-3.836μmol·m-2·s-1. Rh of P.orientalis was larger than Rh of R. pseudoacacia.(3) Rh and Rr of R. pseudoacacia and P.orientalis increased exponentially with soil temperature at 5cm depth (p<0.01). Soil temperature could explain 72.22%,84.02%,78.57% and 81.98% of variation to Rh and Rr separately. The Q10 of R. pseudoacacia was 2.703 and 2.61, P. orientalis was 3.371 and 2.46, indicating that soil microbal and roots was easily affected by soil temperature change. Apparently Rh and Rr of P.orientalis was more sensitive to temperature than R. pseudoacacia.(4) The relationship between Rh and Rr of R. pseudoacacia and soil moisture (SW) at 5cm depth was poor. It was significant quadratic curtives(p<0.05) in R. pseudoacacia.More soil water in a certain range would improve it, but excessive water in soil would restrain.(5) Factor models were built, which was superior to single factor model. Rh and Rr was significantly related to Ts and soil moisture at 5cm depth(p<0.01). Ts and SW together accounted for 63.9%,88.5%,85.3% and 84.4% of variations of Rh and Rr in R. pseudoacacia and P.orientalis sites. Ts was the most important soil physical parameter that affected on Rh and Rr through comparing the partial coefficient of Ts and SW at the 5cm depth.(6) Contribution of Rr to soil respiration had apparent seasonal dynamic in all of the two R. pseudoacacia and P. orientalis plantation. It was a single peak curve in the year and the higher contribution observed in trees growing season. Contribution of Rh was larger than Rr. Contribution of root respiration to soil respiration in R. pseudoacacia plantation changed from 37.54% to 59.82% and the average was 49.00%, the highest contribution rate observed in September and lowest rate in December. Contribution of root respiration to soil respiration in P. orientalis plantation changed largely, which varied from 33.66% to 52.11%. The averaged contribution rate was 42.98%, the highest was in October and the lowest in December. It was concluded that contribution of root respiration to soil respiration in R. pseudoacacia plantation was larger than in P.orientalis plantation.
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