Research On Soil Respiration Of Different Plantations In A Coastal Sandy Plain Area

This research was carried out in Dahe Forest Farm in Changle City, Fujian Province. Five locations in the coastal sandy land adjacent to each other with the similar topography, soil texture and land use history were selected, and the current plantation types are:Pinus elliottii, Casuarina equisetifolia, Eucalyptus urophylla×Eucalyptus grandis, Acacia aulacocarpa, and Acacia cunninghamii. This field experiment was established to:(1) monitor the monthly dynamics of soil respiration in the 5 plantations; Additionally, in order to know the relative contribution of forest root systems and litterfall to soil respiration, root cutting and litterfall removing experiments were set in the plantations of E. urophylla×E. grandis, P. elliottii, A. aulacocarpa, C. equisetifolia, also to determine different components of soil respiration:autotrophic respiration and heterotrophic respiration. We further conducted a fire treatment (burning on ground cover) in the E. urophylla X E. grandis and C. equisetifolia forest to study the effects of forest fire on soil respiration. In addition, in the P. elliottii plantations, ringing girdling experiment was also set to explored changes in soil respiration after blocking nutrients produced by photosynthesis from canopy to roots. (2) Tree height, diameter at breast height, stand density, monthly dynamics of litterfall were monitored, and soil samples were collected to determine its bio-physicochemical properties including soil pH, total carbon, total nitrogen, soil soluble carbon and nitrogen, and soil microbial biomass carbon, which may systematically affect soil respiration. Such key environmental and biotic factors affecting the soil respiration have also been linked to different sources of variations for soil respiration among different stands. The main purpose of this study is to quantitatively monitor the soil carbon emissions in different plantations on a coastal sandy soil in subtropical China, and to clarify the key processes of soil carbon cycling and its influencing factors in this region, providing a scientific basis for selecting tree species that have higher capacity of soil carbon sequestration and higher potential for mitigating climate change.The main findings are as follows:(1) Soil respiration rate in 5 plantations all showed strong variations in different seasons and different months, which peaked in summer and was lower in winter (P<0.0001). Average soil respiration rates in the 5 plantations differed significantly (P=0.0024).(2) Annual flux of soil respiration in the control plots were 1148.80±173.72 gc·m-2·a-1, 1148.80±173.72 gc·m-2·a-1,727.19±89.74 gc·m-2·a-1,1087.13±156.08 gc·m-2·a-1,1055.73±163.18 gc·m-2·a-1,870.25±124.79 gc·m-2·a-1 for E. urophylla×E. grandis, P. elliottii, A. aulacocarpa, C. equisetifolia, A.cunninghamii, respectively. In E. urophylla×E. grandis, C. equisetifolia, A. aulacocarpa plantations, respectively. The annual flux of soil respiration was decreased after litter removal and root cutting, and the soil respirations in different plantations were more affected by litter removal rather than root cutting (except the P. elliottii plantation).(3) After burning the vegetation, soil respiration rate in C. equisetifolia and E. urophylla x E. grandis was reduced in each species compared to control plots. Similarly, after girdling, soil respiration rate in P. elliottii was also reduced compared to control plots, mainly due to declines in substrates input.(4) In this study, Regression analysis showed that soil respiration and annual litterfall of eucalyptus trees exhibited significant positive correlation (P=0.0037), however, positive correlations between soil respiration and annual litterfall in A. aulacocarpa, P. elliottii and A. cunninghamii were not statistically significant.(5) One-way ANOVA revealed that pH (P=0.000), dissolved organic carbon (DOC: P=0.034), dissolved organic nitrogen (DON:P=0.000), microbial biomass nitrogen (P=0.002), NO3--N (P=0.000), NH4+-N (P=0.044), soil total nitrogen (P=0.004) in 0-10 cm depth in E. urophylla x E. grandis, P. elliottii, A. aulacocarpa, C. equisetifolia, A. cunninghamii were significantly different. But tree specie had no significant effect on the microbial biomass carbon (MBC:P=0.436).(6) Soil respiration rate were significantly correlated (P<0.05) with DOC rather than other factors.(7) There are no significant exponential relationships between soil respiration rate and soil temperature among these five tree species, nor did linear correlation between respiration rate and soil moisture. However, when including both of soil temperature and moisture, the model R=aebTWc explained 52.8%,53.6%,65.8%,51.9%,24.6% of the variations in soil respiration rates of E. urophylla×E. grandis, P. elliottii, A. aulacocarpa, C. equisetifolia and A. cunninghamii, respectively. In addition, the temperature sensitivity value (Q10) was 1.44,1.51,1.71,1.27,1.28 for E. urophylla×E. grandis, P. elliottii, A. aulacocarpa, C. equisetifolia, A. cunninghamii, respectively.