Soil Respiration In Typical Forest Plantations In Lithoid Hilly Areas Of North-China

The lithoid hilly areas of north-China are an ecological barrier to North China Plain, are also the key areas of the forest ecological project of returning farmland to forest. Soil respiration of 3 typical forest plantations (Robinia pseudoacacia, Platycladus orientalis and Quercus variabilis) in this areas were analyzed by Li-8100 soil CO2 flux automated analyzer and AR5 soil temperature and water content automated monitoring system to get the time change regulation, to study the relationship between the soil respiration and the main environmental factors. It will help us to take an evaluation on ecological benefits to the ecological development of this region, to enrich the middle latitude data of the global carbon flux observation, to offer a reference to the forecasting of global climate change, to play an important reference role in evaluating on soil respiration in similar climatic areas or in hilly areas. Conclusions of this study are as following:(1) Soil respiration rates (SRR) and root respiration rates (Rroot) of all 3 typical forest plantations (Robinia pseudoacacia, Platycladus orientalis and Quercus variabilis) in main growing season were much higher than in minus growing season. In minus growing season, the diurnal variation had no remarkable change. In main growing season, the diurnal variation had remarkable change, displayed single peak curve volatility characters. Daily variation of all 3 typical forest plantations SRR and Rroot had remarkable change. Mainly, SRR attained the lowest value in February, rose quickly in March, and reached a peak during about July, then fell down gradually. Rroot attained the lowest value in minus growing season, rose quickly in March, and reached a peak during about June and July, then fell down gradually.The annual average SRR of Robinia pseudoacacia was 2.52μmol?m-2s-1, the Platycladus orientalis was 2.08μmol?m-2s-1 and the Quercus variabilis was 1.45μmol?m-2s-1. The proportions of Rroot in SRR (RS/SS) of all 3 typical forest plantations in main growing season were all higher than those in minus growing season. RS/SS attained the lowest value in minus growing season, rose quickly in March, and reached a peak during about June, then fell down gradually. The annual average Rroot of Robinia pseudoacacia was 1.16μmol?m-2s-1, the RS/SS was 46.09%, the Platycladus orientalis was 0.98μmol?m-2s-1, 47.11%, the Quercus variabilis was 0.77μmol?m-2s-1, 52.88% separately.(2) Significant relationship were found between the 3 typical forest plantations SRR and soil temperatures at different depths (the surface, 5 cm depth, 10 cm depth, 15 cm depth and 20 cm dept, p<0.01), which could be best described by exponential equations, and the best was at 20cm for Robinia pseudoacacia, at 10cm for Platycladus orientalis, at 15cm for Quercus variabilis. The Q10 of Robinia pseudoacacia from soil surface (0cm) to soil 20cm depth were 2.20, 2.28, 2.34, 2.40 and 2.48; the Platycladus orientalis were 2.19, 2.47, 2.61, 2.89 and 2.99; and the Quercus variabilis were 2.51, 2.59, 2.72, 2.80 and 2.94 respectively. Q10 increased with the deepening of soil layer.The degree of correlation between soil surface (0-20cm) water content and SRR, and Rroot were not uniform with each other. In condition of lower water content (such as Robinia pseudoacacia), SRR and Rroot had significant relationship with both soil temperate and soil water content. As to the higher water content (such as Platycladus orientalis, Quercus variabilis), SRR and Rroot had significant relationship with soil temperate only.(3) Significant relationship were found between the 3 typical forest plantations Rroot and 5 cm soil temperatures (p<0.01), which could be best described by exponential equations. The Rroot's Q10 of Robinia pseudoacacia was 2.38, the Platycladus orientalis was 2.71, and the Quercus variabilis was 3.05. All 3 typical forest plantations Rroot's Q10 were higher than SRR's Q10 in 5cm.