Arbuscular Mycorrhizas Of Betula Alnoides Plantations In Tropical And Sub-tropical Regions Of Yunnan

As a multipurpose indigenous species, Betula alnoides was widely planted as a promising tree species to produce timber and regenerate degraded areas in tropical and south sub-tropical mountainous regions of Yunnan province. Selected B. alnoides plantations of five ages in Puwen tropical experimental farm of Xishuangbanna, two different aged plantations in Ruili of Dehong prefecture, and the natural forests adjacent to the plantations as study sites, this thesis aimed to assess the disturbance of the plantation establishment on the abundance and diversity of arbuscular mycorrhizal fungi (AMF), a key and integral component in the ecology and physiology of terrestrial ecosystem, which played important roles in the vigour of plant communities and the restoration of disturbed ecosystem. Based on the theories and principles of ecology and mycorrhizology, by using the methods and techniques of morphology and molecular biology, the following aspects were carried out:1) Impact of B. alnoides plantation establishment on AMF;2) With the increasing of the plantation age, the AMF succession pattern in B. alnoides plantations reflected by both root AMF colonization and AMF community composition in rhizosphere soils, and the effects of soil characteristics on AMF of B. alnoides;3) Molecular diversity of AMF within the roots of B. alnoides. Adopting different indexes, the adaptability of B. alnoides plantation development in tropical and sub-tropical region of Yunnan province was evaluated from different perspectives. Results are as follows:1) Arbuscular mycorrhizal fungi colonization was detected in all the root samples collected at Puwen experimental forest farm of Xishuangbanna and Ruili of Dehong prefecture, despite the source of root samples, natural growing or planting trees, trees of different ages, and abundant and diversified AMF spores were found in the rhizosphere soil of B. alnoides, which revealed that AMF was an important ecological component in both B. alnoides plantations and forests with B. alnoides naturally regenerated.2) At the study sites of Puwen experimental forest farm of Xishuangbanna, choosing two B. alnoides plantations of19and8years old, tropical montane rain forest adjacent to the plantations as the sample plots, using the microscopy technique, the percent of AMF colonization in roots of the main plant species in various forests, the AMF spores in the rhizosphere soils were studied. No significant differences were found between the hyphal colonization percent of the major plants from8years old plantation and tropical montane rain forest, the same result went to the percent of vesicular colonization. However the hypha and vesicule percent of8years old plantation and tropical montane rain forest were significantly higher than that of19years old plantation. The AMF spore density in the rhizosphere soil of8years old plantation was the highest among the three studied plots, and that of the tropical montane rain forest was the lowest; by contrast, the Shannon’s diversity index of AMF community in tropical montane rain forest was remarkably higher than the two plantations. Glomus was found to be the dominant genus in all the three forests, however different stands had different AMF species composition, and the compositions of AMF communities of two plantations were similar.3) Choosing five B. alnoides plantations in Puwen experimental forest farm of Xishuangbanna that have been established for2,8,11,19and21years, two B. alnoides plantations in Ruili of Dehong prefecture that have been established for3and5years, and the natural forests in two study areas as sample plots, the AMF colonization in roots of B. alnoides and AMF spores in the rhizosphere were investigated. Within the roots of B. alnoides, no regular changes of AMF colonization in response to the succession of plantation age were found. Namely, during different development stage, the AMF colonization extends in roots of B. alnoides did not showed the tendency of either increase or decrease with the age of host plant. The AMF colonization rates in the natural forests were always lower than those of B. alnoides in the plantations. However, the AMF spore density showed the tendency of decrease as the age of plantation increase. Soil available phosphorus, total nitrogen and organic matter were the major factors affecting the AM status of B. alnoides, these three factors were negatively correlated with root colonization of hypha and vesicule, and the AMF spore density in the rhizosphere soil.4) The LSU rDNA library of AMF from root samples of B. alnoides growing in tropical montane rain forest of Puwen experimental forest farm of Xishuangbanna was constructed based on cloning sequencing. A total of425AMF sequences, which were grouped into40operational taxonomic units (OTUs), were obtained, and27OTUs were novel. Based on sequence analysis, it was found that the majority of sequences detected in the roots of B. alnoides, belonged to the genus Glomus, which was in accordance with study results based on morphology. Comparative analysis on the molecular diversity of AMF in roots of B. alnoides growing in tropical montane rain forest and in plantation showed that there were9of42OTUs in common between the natural growing and planting B. alnoides, the number of unique OTUs from B. alnoides in natural forest was27, whereas there was only6unique OTUs obtained from B. alnoides in the plantation. The AMF diversity of the natural growing B. alnoides was remarkably higher than that of B. alnoides in the plantation. This evidence supports the importance of conservation of natural forests. Even though there was only9OTUs common to B. alnoides in natural vegetation and plantation,339sequences were included in these9OTUs, accounted for65%of the total number of sequences (522sequences); this was an interesting point deserved attention since it indicating that there was a preference between B. alnoides, namely the host plant and some AMF. Additionally, it was found that the number of OTUs of AMF increased with increasing plantation age, still the OTUs number of B. alnoides in the tropical montane rain forest was significantly higher than those of the plantations by analyzing the molecular diversity of AMF in the roots of B. alnoides from the plantations that have been established for2,8,21years. Similar results were obtained in AMF community study base on the AMF spores in the rhizosphere soils identified by microscopy technique.The major conclusions of the thesis includes:1) Despite the source of natural vegetation and plantation, AMF generally colonized the roots of B. alnoides, and play a particular important role in the tropical forest ecosystem. Glomus was the predominant genus, and a kind of preference between host plant B. alnoides and AMF existed.2) Establishment of B. alnoides plantation did not reduce the abundance of AMF spore in soils, however, it decreased the diversity of AMF to some extend and built different dominant AMF species. Still, with the increase of plantation age, gradually entering of other indigenous plant species into the plantation, combining with the preference between B. alnoides and AMF, some AMF species of natural forest were also maintained in the B. alnoides plantations, the AMF diversity of plantation was recovered to some extent.3) The contents of available phosphorus, total nitrogen and organic matter in soil were three important factors influencing the arbuscular mycorrhiza of B. alnoides.Taken as a whole, estimated from the community biodiversity and distribution of AMF, satisfy the prerequisite of effective conservation of current natural vegetation, moderate development of B. alnoides plantations was feasible, and it was an advisable selection for vegetation restoration in degraded tropical and sub-tropical mountainous areas in Yunnan, southwestern China.