Research On Soil Respiration Dynamics And Poplar Fine Root For Four Hybrid Poplar (Populus×Euramericana Cv.) Plantation Patterns In The Northern Areas Of Jiangsu Province

With the emergence of the word"global change"in 1970's, people have realized that greenhouse effect cause global climate warmer than before which have brought us many problems. Global carbon cycle study, which is an across subjects, all-around and larger-scale research, coming of 1980's, is becoming the focus of international cooperating study projects. Finding missing carbon sink and how to decrease carbon releasing are the mainly research aim all the while. Soil respiration, which is a mainly source of CO₂, have been more and more attented by reaearchers. Lots of studies on soil respiration in forest ecosystems have been developed in many countries. Research on soil respiration in China is started lately, and many studies are about forest, grassland and agriculture ecosystems, but there is almost no research on agroforestry ecosystem carbon cycle by far. In addition, forest fine root is a mainly part of soil carbon pool and has an important effect on carbon cycle. Fine root biomass accouts for a little proportion of total forest biomass, but it's turnover is rapid, so fine root production is very large and becoming mainly source of soil carbon pool.Poplar is one of the most important fast growing trees in china. Following the developing of poplar plantation patterns in the northern area of Jiangsu province China, popar planting is promoting the development of forest industry, increasing income of farmers, improving environment quality, and bring us great benefit. A large assimilated carbon by poplar growth annually has a much important impact on Agro-forest compound carbon cycling ecosystem in the northern area of Jiangsu province, however, carbon sequestration capacity of poplar plantations is still not known by us by far, and carbon source-sink trend of which is also not found out. It is not reported studying on soil respiration for all kinds of poplar plantation patterns in the northern area of Jiangsu province. Basing on our above discussion, soil respiration and poplar fine root were studied for four popular poplar plantation patterns and agriculture ecosystem in the northern area of Jiangsu province in this study. A comprehensive model about soil temperature and soil moisture was established to count annual total soil respiration. Annual fine root production and turnover rate were assessed, the results are as follow:1. The seasonal change of soil respiration in all patterns was summer>spring>autumn>winter and only one peak was found in a year. Soil respiration rate in poplar growing seasons (July-Augest) was at the peak from 153.00mg CO₂·m^-2·h^-1 to 253.62 mgCO₂·m^-2·h^-1, and that of poplar dormancy seasons (December-Juanary) was at the vale from 46.75mgCO₂·m^-2·h^-1 to 54.48mgCO₂·m^-2·h^-1, for four poplar plantation patterns and agriculture ecosystem.2. Based on annual soil respiration data, soil temperature had a significantly exponential relationship with soil respiration rate, and explained 64.6%～80.7% of soil respiration variation for four poplar plantation patterns and agriculture ecosystem. Regression equations are as follows: R=51.711e^0.0628T for M1a (M1a is the measurement plot with root for M1), R=49.553e^0.0542T for M1b (M1b is the measurement plot without root for M1), R=51.013e0.0584T for M2a, R=47.898e^0.0536T for M2b, R=50.559e^0.0572T for M3a, R=48.603e^0.056T for M4a, R=50.511e0.0569T for N.2. Based on annual soil respiration data, soil moisture hadn't a significant relationship with soil respiration. Linear regression equations with soil moisture for four poplar plantation patterns and agriculture ecosystem are as follows: R=109.04W+136.88 for M1a, R=474.83W+58.193 for M1b, R=181.27W+122.82 for M2a, R=421.86W+61.314 for M2b, R=118.43W+124.9 for M3a, R=^-223W+167.25 for M4a, R=313.46W+90.341 for N.4. Based on annual soil respiration data, the two parameters soil respiration model equations about soil temperature and soil moisture were established, which had an improvement of R² campared to the one parameter soil respiration model equations with soil temperature or soil moisture, and which showed that soil respiration rate variation were drived by both soil temperature and soil moisture. The model equations for four poplar plantation patterns and agriculture ecosystem are as follows: R = 37.677e^0.064Te^{((1.897W-1.453W2))} for M1a, R = 30.714e^0.054Te^{((3.904Q-6.446W2))} for M1b, R = 59.49e^0.056Te^{(3.192W-12.925W2)} for M2a, R = 33.217e^0.053Te^{(2.67W-3.643W2)} for M2b, R = 30.194e^0.062Te^{(2.028W-4.485W2)} for M3a, R = 11.376e^0.069Te^{(15.053W-39.254W2)} for M4a, R = 37.677e^0.064Te^{(1.897W-1.453W₂)} for N.5. The annual total CO₂ flux for four poplar plantation patterns and agriculture ecosystem are as follow: 1492gCO₂·m^-2·a^-1 for M2a, 1484gCO₂·m^-2·a^-1 for M3a, 1395gCO₂·m^-2·a^-1 for M1a, 1361gCO₂·m^-2·a^-1 for N, 1200gCO₂·m^-2·a^-1 for M2b, 1135gCO₂·m^-2·a^-1 for M1b, 1088gCO₂·m^-2·a^-1 for M4a. Annual total CO₂ flux in agriculture ecosystem was marginally significantly lower than that of measurement plots with roots in M1 and M2 patterns, and significantly higher than that of measurement plots without roots in M1 and M2 patterns. Annual total CO₂ flux in M4 pattern was significantly lower than that in agriculture ecosystem, but not significantly campared to annual total CO₂ flux of measurement plots without roots in M1 and M2 patterns.6. Annual total root respiration rate in M1 and M2 patterns were 260gCO₂·m^-2·a^-1and 292gCO₂·m^-2·a^-1, accounting for 18.7% and 19.6% of annual total CO₂ flux in M1 and M2 patterns, respectively.7. Diurnal dynamics of soil respiration rate in growing seasons (on August 5-6) was measured to be well correlated with soil temperature. 5cm and 15cm soil temperature could explain 10%～80% and 10%～92% of the diurnal variability in soil respiration rates, respectively.8. Comparing AA method to IRGA method in growing seasons (on August 5-6), diurnal soil respiration rate measured by AA method is larger than that measured by IRGA method, and the result by AA method accounted for 27%～44% of that by IRGA method, and 33.8% on average. The linear relationship between soil respiration rates measured by two methods is IRGA=3.8231×AA^-1118(p<0.059).9. The temporal and spatial distribution pattern of poplar fine roots showed that: poplar fine roots biomass were mainly allocated at 1m^-1.5m distance from tree bole; poplar fine roots biomass at 0^-10cm depth accouted for 62.8%, 60.8%, 43.4% and 27.2% of total fine roots biomass in M1, M2, M3 and M4 patterns, respectively. A larger number of fine root biomass distributed at 20-40cm depth in M4 pattern was in favor of water absorption by poplar growing.10. The annual fine root (0-5mm) biomass in average for M3 and M4 patterns were 1.86 t·ha^-1 and 1.26 t·ha^-1. The fine root biomass at 0^-1mm diameter class accounted for 58.4% and 59.4% of that at 0-5mm diameter class in M3 and M4 patterns, respectively. Life fine root biomass at diameter level accounted for 68.6%～91.1% of total fine root biomass.11. The monthly varibility in fine root biomass show two peaks for both M3 and M4 patterns. Annunal net productions for 0^-2mm diameter class fine root were 1.40 t·ha^-1·a^-1 and 1.06t·ha^-1·a^-1, and accouted for 89.7% and 90.6% of that for 0-5mm diameter class in M3 and M4 patterns, respectively. Annual turnover rates of fine root (0^-2mm) were 1.11time·a^-1 and 1.18time·a^-1, and that of fine root 2-5mm diameter class, which is slowly decomposed relatively after death, were 0.52time·a^-1 and 0.57time·a^-1 in M3 and M4 patterns, respectively.