| A trenching method and an open-flow gas exchange system with an infrared gas analyzer (IRGA) were used to investigate the differences between tropical seasonal rain forest (RF for short below) and rubber plantation (RP for short below) in the contribution of root respiration (RR for short below) and heterotrophic respiration (HR for short below) to soil respiration (SR for short below), and the factors influencing soil respiration and its components as well, in Xishuangbanna, Yunnan, SW China from January 2008 to February 2009. In addition, a one-year litterbag experiment was designed to research the decomposition of different-size roots in these two forests simultaneously. And the fine root growth was studied by scanning regularly in both forests.The main results were as follows.a) The contribution of RR to SR in RF was much less than that in RP with 29% in RF and 42% in RP (p<0.01), but the contribution of HR to SR was on the contrary,71% in RF and 58% in RP (p< 0.01). The contribution of RR to SR in both forests showed strong seasonal variation. Over the sampling period, the contribution of RR to SR in RF ranged from 6% to 51%, in RP from 21% to 77%.b) Environmental and biological factors significantly affected the contribution of RR to SR in both forests. Linear regression analyzing demonstrated strong correlation between the contribution of RR to SR and soil temperature, soil moisture or air temperature.c) On an annual average, SR, RR and HR rates in RF were 2.66,0.71,1.95μmolCO2m 2·s-1, respectively, and 2.06,0.84,1.22μmolCO2m-2·s-1 in RP, respectively. And SR and HR rates in RF were significantly higher than those in RP except for RR rate. SR and HR rates in both forests fluctuated seasonally, with a rank of rainy season> dry-hot season> foggy season, while RR rate in RF with a rank of rainy season> foggy season> dry-hot season, and RR rate in RP with foggy season> rainy season> dry-hot season.d) Soil temperature and moisture were the main key factors of SR, RR and HR. In the model of soil temperature at 5cm depth (T5), Q10 of SR, HR and RR was 2.948,3.900 and 1.455 in RF, respectively, and 1.493,2.328,～in RP, respectively, except that the correlation between T5 and RR in RF was not significant.e) The root decomposition rate in RF was significantly lower than that in RP. And in each forest, the decomposition rates of fine and small roots were significantly higher than those of medium and coarse roots.f) After one-year's decomposition, the mass-loss rates of fine, small, medium and coarse roots in RF were 30%,56%,25%,30%, respectively, and 63%, 52%,41%,51% in RP, respectively. And the daily decomposition coefficients of fine, small, medium and coarse roots in RF were 0.0010, 0.0025,0.0007,0.0007, respectively, and 0.0030,0.0019,0.0013,0.0017 in RP, respectively.g) There was strong correlation between root decomposition rate and contribution of RR to SR.h) The fine root growth rate was much higher in RF than that in RP. Furthermore, the fine root growth rate in both forests varied seasonally, and the rate in dry season was much lower than that in rainy season. |
PDF Full Text Request