Change Characteristics Of Soil Microbal Diversity And Its Ecological Function In Pinus Tabulaeformis And Larix Kaempferi Plantation In West Qinling Mountains

The soil microbial organisms play an important role in keeping the ecosystems health and the soil fertility of forest, for they are the main promoters and regulator of the nutrient recycling and energy flow. The study was conducted at Shaba Forest Experimental Station of West Qinling Mountain located in Xiaolong Mountain. The objective of the study was to compare the differences in soil microbial community structure between P.tabulaeformis and L.kaempferi plantation stand at different development stages. We determined parameters that indicate the microbial microbial biomass C,N,I (MBC, MBN, MBP) under two types of plantations stand with different development stages, and parameters that indicate the general activity (resipiration) and specific activity (urease and dehydrogenase, respectively). The structure and function of the microbial community was studied by analysing phospholipid fatty acid methyl ester (FAMEs) and Biolog-Eco. plate respectively. The main findings were summarized below:1. Soil pH under two types of plantations stand was acid and slight neutral. The pH was between 6.43 and 6.67 in P.tabulaeformis stands with different development stages, among which the highest one was juvenile plantation-Ⅰ, and lowest one was medium plantation. In L.kaempferi stands the pH was between 5.27 and 6.20 and decreased with the ages increasing of plantation. Compared with which of native P.tabulaeformis stands, in L.kaempferi stands the soil pH decreased significantly, the organic matter and the total nitrogen also presented the trend decreased (-21.66% and-22.04% respectively), while the available nitrogen and available phosphorus increased by 19.45% and 28.81% respectively. And the total phosphorus changed a little.2. The MBC, MBN, MBP were determined by the fumigation-extraction method. In P.tabulaeformis stands change of microbial biomass presented a decrease first and then increase from juvenile to medium plantation, then to mature plantation while in L.kaempferi stands that increased first and then decreased. The mean of the microbial biomass was lower in L.kaempferi stands than in P.tabulaeformis stands, but the MBC/MBN was becoming higher.3. The microbial functional diversity was measures by Biolog method. The result showed that the AWCD decreased with the ages of P.tabulaeformis stands, while that of L.kaempferi increased, and there were a significantly differences (p<0.05) between juvenile and medium plantation of P.tabulaeformis and among all L.kaempferi stands respectively. The species richness index(S) and the Shannon-Weaver diversity index (H) which were significantly different (P<0.05) with ages of stand were both lowest in mature plantation (22.33±1.15 and 3.05±0.02 respectively), and highest in juvenile plantation-Ⅰ(29.33±1.53 and 3.28±0.04 respectively) among the four P.tabulaeformis stands. The two indexes both increased from juvenile to mature plantation of L.kaempferi, and the differences were significant (P<0.05). Also, the result showed there was a significant different in the evenness index (E) between mature plantation of L.kaempferi (P<0.05) and the other stands, which indicated that L.kaempferi introduced changed the proportion of different functional groups in local soil microbial community considerably after a long-term colonization.4. By (FAMEs) analysis showed that two types of forest at different developmental stages microflora changes had taken place to some extent, especially change of bacteria and fungi content was the main factors that caused the differences of microbial community structure in forest soil. Variation trends of each group in the two forest types is not uniform, in P.tabulaeformis stands bacteria and fungi biomass fluctuated with extending of ages, actinomycetes first increased and then decreased, mycorrhizal fungi into a decreasing trend; in L.kaempferi stands the microbial biomass of bacteria decreased with extending of ages, fungi and arbuscular mycorrhizal fungi (AMF) first increased and then decreased, fluctuated in actinomycetes. But in the two types of forest, the fungi and bacteria biomass ratio were both is first increased and then decreased, the peak appear in the middle-age forest. Paired samples t test (sig.=0.049<0.05) result showed that L.kaempferi, the exotic species, had changed the microflora of the native soil microbial community by reduced the amount of fungi and bacteria biomass ratio significantly.5. Result of soil microbial respiration showed that total microbial activity in the both two forest types presented an increase first and then decreased from juvenile to medium plantation, among which the differences were significantly (P<0.05). And the highest respiration appeared in the medium plantation among P.tabulaeformis stands, while that was highest in juvenile plantation-Ⅱamong L.kaempferi stands. At different developmental stages of the two forest types, Urease and dehydrogenase also had changed at some degre, but was not significant. In P.tabulaeformis stands, urease and dehydrogenase activity was in the range of 0.49～0.61 mg NH3-N/g d.w. Soil and 145.83～321.73 ug TPF/g d.w. soil, respectively. In L.kaempferi stands that was 0.52～0.67 mg NH3-N/g d.w. soil and 166.06～341.61 ug TPF/g d.w. Soil, respectively. Correlation analysis showed that soil respiration was significantly correlated with pH (P= 0.05), and paired samples t test showed that the introduction of L.kaempferi significantly affect the total microbial activity (respiration) and bacterial activity (dehydrogenase) (sig.=0.024 and sig.=0.018 respectively). Moreover, in L.kaempferi stands, soil respiration was significantly correlated with dehydrogenase activity.6. According to principal component analysis (PCA) and clustering, the soil microbial communities changed a lot along the developmental stages of P.tabulaeformis, while that changed a little among L.kaempferi stands. But in the mature forest of L.kaempferi, the microbial community structure and functional diversity had changed; soil microbial biomass and activity are significantly reduced. Comparison of the cluster analysis showed that the same developmental stages in different forest types were in ifferent groups except the two medium plantations. According to PCA, the component 1 and 2 accounted for 32.18% and 23.02% of the variability among all the stands. And the component 1 reflected the total microbial biomass and the special microbial biomass related to bacteria, fungi and AMF, while component 2 reflected the microbial functional diversity and microbial activity.The results suggested that changes of the soil microbial community and soil physicochemical properties were influnced by the development stage of tree, and which depended on the plant species. Introduced species L.kaempferi had affected the structure and function of the local soil microbial community to some degree, involving in the microbial biomass, community structure and function diversity and microbial activity. And the properties of soil chemical and biochemical had altered by L.kaempferi. But whether these effects may shift the local soil ecosystem, or the mechanism of the possibility for this change, was still unknown and need to be studied further more.