Soil Labile Organic Carbon And Nitrogen Pools And Associated Microbial Process Under Three Forest Types In Australia

Soil soluble organic matter was components which should not be ignored in carbon and nitrogen cycles of terrestrial ecosystems, and the soil microbes were the decomposers of ecosystems. They were involved in soil bio-geochemical processes, and played an important role in maintenance of soil ecological equilibrium. There had been main distribution of forest and typical subtropical geographical unit in southeast Queensland, Australia. It was very sensitive to climate change in Australia and global climate, and played an important role, and its unique natural environment and ecosystems occupied a special place in the world, but our knowledge about this versatile microbial community was very limited. In this paper, soil samples under the slash (Pinus elliottii Engelm. var. elliotttii), hoop pine(Araucaria cunninghamii) and kauri pine(Agathis australis) populations for 90 years test plots were collected to investigate the effects of forest types on soil soluble organic matter, microbial biomass C (MBC) and nitrogen (MBN), enzyme activities, soil respiration as well as microbial community structural and functional diversity by bio-chemical and molecular biological methods. We discuss soil available carbon and nitrogen pools and related microbial process under different forest types. Furthermore, some suggestions are important theoretical significance for further study of the soil ecosystem structure and function. The main results were described as follows:(1) The 11 main soil metal elements were analyzed that the difference of soil Al, Cu, Fe, K, Mg and Mn contents were significantly. The soil SOC and SON contents were different by different extraction methods. SONHW and SOCHW were higher than that of 2 mol L-1KCl extract. The SONHW contents of soil in slash pine, hoop pine and kauri pine were 26.7 mg kg-1,46.2 mg kg-1 and 39.2 mg kg-1, respectively. The differences between forest types and soil SONHW, SONHW/TSNHW were significant (P<0.01). The NH4+-NHW contents were more than 21.4 mg kg-1, and NO3--NHW content was no less than 8.02 mg kg-1. The NH4+-NHW content was not consistent with that of SOCHW with SONHW, while the organic carbon and nitrogen ratio (C:NHW) was consistent with SOCHW, and the difference of C: NHW were significant among different forest types (P<0.05). The SOCHW content was 552-1154 mg kg-1 in different forest types, and the order of SOCHW content was slash pine> hoop pine> kauri pine, but the difference was not significant. The order of SONHW content was hoop pine> kauri pine> slash pine, and the soil SONHW in hoop pine was significantly (P<0.05) higher than that of slash pine. The SONKCl contents were lower than that of SONHW, the mean was 9.93 mg kg-1, and the SONKCl content accounting for TSN was 24.6-33.5%, and accounting for TN was 0.14-0.25%. The SONKCl content was 29.3-32.1% and the highest accounting for TSNKCl in the slash pine, but was the lowest to account for TN and 0.14-0.16%. The results suggested that the TSN content of slash pine was low. The soil SOCKCl content of hoop pine forest was the highest, and lowest that of slash pine SOCKCl-The NH4+-NKCl was mainly from inorganic nitrogen pools, and the changes of its content was similar to that of hot water extract. The differences of soil NH4+-NKCl content were significant among different forest types (P<0.05). The NO3--NKCl content was lower than 7.7 mg kg-1 in the forest types. The change of SOCKCl was similar to C:NKCl and the differences of SONKCl and SOCKCl were not significant among different forest types.(2) The soil MBC content was 188.2 mg-kg-1 and highest in kauri pine, following in slash pine was 112.8 mg kg-1. Its in hoop pine forest MBC was the lowest, and their content was 77.1 mg kg-1, MBC content were significantly different among forest types (P<0.05). MBC /TC ranged from 0.48% to 1.55% under three forest soil, and MBC/TC was significantly different among three forest types. MBN average content was 18.0 mg kg-1, and MBN content was similar to MBC under three forest types. The differences of MBC were significant. The?13C content ranged from-28.5‰to -27.5‰. The?13C in hoop pine was high, and mean was -27.8‰. The differences of?13C content in slash pine were significant with hoop pine and kauri pine. The?15N contents ranged from-2.1‰to 3.4‰, and the?15N content in kauri pine was the highest, accounting for 2.33‰. There was no significant difference of 815N among three forest types. The change of PMN was similar to PMN/TN under three forest types. The PMN in hoop pine was highest 77.19mg kg-1, and PMN/TN was 0.138%. The following PMN and PMN/TN in Kauri pine were 71.87 mg kg-1 and 0.14%, respectively. The PMN and PMN/TN in slash Pine were the lowest 43.55 mg kg-1 and 0.082%, respectively. The analysis of variance showed that there were significant difference of PMN and PMN/TN between in slash pine and other two forest types.(3) The soil respiration for 63 days lab incubation in kauri pine was strongest, was 680.28 g CO2-C kg-1, which was significantly stronger than that of slash pine, was 277.73 g CO2-C kg-1 (P<0.05). We obtained the maximum potential carbon emissions (Co) in kauri pine which was 1117.8 g CO2-C kg-1 by simulated soil respiration, and following was 1082.1 g CO2-C kg-1 in hoop pine, and 783.0 g CO2-C kg-1 in slash pine, the lowest. The difference of Co was significant between slash pine and other two forest types, and the correlation coefficients were above 0.99. This indicated that Co was simulated to a good fitting effect. The changes for soil CO2 production by respiration were similar by adding substrate. Adding Glucose substrate on the amount of soil respiration of CO2 compared with the control (CK) were significantly increased (P= 0.000). Adding Glucose and Na2HPO4 with Glucose, NH4NO3 and Na2HPO4 interaction could increase soil CO2 production compared with the control. But soil CO2 production was reduced in the substrate H4NO3 or Na2HPO4 and Na2HPO4 interaction, especially Na2HPO4 inhibited soil respiration to some extent. The change of soil CO2 production under added substrate was consistent with the control (P 0.001), and the pattern of soil respiration rate curves was similar and showed a single peak under three forest types. Substrate addition on microbial biomass carbon and nitrogen is not uniform to different forest types, and its impact was similar to soil respiration by adding substrate.(4) Microbial activity increased with incubation time increased. After incubating 24h, microbial utilization substrate was increasing rapidly. The order of different soil microorganism utilize carbon source during 96h incubation was hoop pine> kauri pine> slash pine. The metabolism of microbial communities in hoop pine was the strongest, and the difference of utilization carbon sources was significant between slash pine and the others (P<0.05). Shannon index in hoop pine was 4.391, evenness was 0.046, Simpson index was 67.9, Mclntosh index was 14.07, and evenness was 0.979, which were higher than that of the other forest types, and that of slash pine was lowest, and the difference of diversity and evenness was significant to hoop pine and Kauri pine (P<0.05). The difference of carbon source utilization under the same forest type was significant. The microorganism prefers to utilization carbohydrate and polymer during the Biolog Microplate incubation.(5) The order of soil chitinase and LAP activity in different forest types was slash pine> hoop pine>kauri pine. The order of soil acid phosphatase and (3-glucosidase activity as follows:slash pine> kauri> hoop pine, and alkaline phosphatase as follows:kauri pine> slash pine> hoop pine. The difference of relationship was significant between soil chitinase and TC, pH and chitinase, LAP and (3-gluocosidase, TC and alkaline phosphatase (P<0.01). Redundancy analysis showed that the relationship between alkaline phosphatase and hoop pine, LAP and?-gluocosidase and kauri pine, microbial biomass and slash pine were closer. There was negatively related between Chitinase and acid phosphatase to slash pine.(6) There were 45 PLFAs in slash pine soil, and 39 and 35 PLFAs, respectively, in the hoop pine and kauri pine. The number of PLFAs in slash Pine was higher than that of hoop pine and kauri pine. PCR-DGGE analysis showed that the number of bands ranged from 17 to 28, and the average number of bands under slash pine, hoop pine and kauri pine were 25.5,17 and 23, respectively. The results indicated that abundance of soil bacterial in slash pine was the highest, and was similar to the results by PLFA.