Soil Respiration Dynamics In Two Typical Forest Communities In The Semiarid Loess Plateau Region, China

Soil respiration is one of the important topics in the field of global carbon cycle and receives increasing attention in recent years. Soil respiration in forest land in arid and semiarid regions has been less investigated than in other regions. In this research, soil respiration was investigated in two typical forest stands at Mt. Gonglushan of Yan'an city of the semiarid forest–grassland transition zone, an exotic black locust (Robinia pseudoacacia) plantation and an indigenous oak (Quercus liaotungensis) forest. Total soil respiration was measured with the LI-8100 automated soil CO₂ flux system and the corresponding environmental factors were measured with several automatic meteorological instruments. Variations of soil respiration in the two typical forests in different time scales were studies to reveal relation of soil respiration and its components in the two typical forests to bio/abio factor changes. And the response of soil respiration in the two typical forests to precipitation was analyzed. Moreover, the temperature sensitivity of soil respiration and its components in the two typical forests was discussed. The Q10 function was assessed with analysis of multiple factors. The main conclusions are as follows:(1) The diurnal course of soil respiration of the two forests is single-peak curve. The lowest value appears at 6:00, but the peak value is not identical along the daytime. In the growing season, the fluctuation of soil respiration is large, and in the dormant season that is small at diurnal scale. The soil respiration rate of oak forest is higher than black locust plantation. The relationship between soil respiration and soil temperature & solar radiation is significant.(2) The seasonal pattern of soil respiration in the two forests is same basically. The mean annual RT, RA and RH were 3.68, 1.06 and 3.26μmol m^–2 s^–1 in oak forest and 2.76, 0.87 and 2.23μmol m^–2 s^–1 in black locust plantation. The seasonal pattern of autotrophic and heterotrophic respiration is also same but the fluctuation is smaller than that of total soil respiration. In seasonal scale, the soil respiration in oak forest is higher than black locust plantation.(3) In both ecosystems, precipitation significantly increased soil moisture, decreased soil temperature, and accelerated soil respiration. The peak values of soil respiration were 4.8 and 4.4μmol CO₂ m^–2 s^–1 in the oak plot and the black locust plot, respectively. In the dry period after rainfall, the soil moisture and respiration rate gradually decreased and the soil temperature increased. Soil respiration rate in black locust stand was consistently less than that in oak stand, However, autotrophic respiration per unit fine root mass and heterotrophic respiration per unit the amount of soil organic matter were higher in black locust stand than in oak stand. Autotrophic respiration in black locust stand was the dominant component resulting in total respiration changes, whereas respiration by roots and soil microbes contributed equally in oak stand. Soil respiration in the black locust plantation showed higher sensitivity to precipitation than that in the oak forest.(4) The Q10 of autotrophic respiration in oak forest and black locust plantation was higher than those heterotrophic in seasonal and diurnal scale. The Q10 of autotrophic respiration of black locust is higher than oak during growing season and that is lower during dormant season. Applying multiple regressions, we found photosynthesis is important parameters in soil CO₂ studies in diurnal scale and multiple factors model is more suitable than Q10 function in growing season.