Carbon Storage, Fixation And Distribution In Mao Bamboo(Phyllostachys Pubescens) Stands Ecosystem

Forest ecosystems have been increasingly paid more and more attentions due to the roles in sequestration and storage of carbon with an increase in green house gas concentration in the atmosphere for the last decades. For forest ecosystems, the carbon storage and the cycling of carbon are common indicators to assess the CO₂ -fixation capacity. In southern China, mao bamboo (Phyllostachy pubescens) is an important forest resource, which can be widely utilized as materials, energy etc., and forms one of essential income sources for local farms. Mao bamboo is a fast-growing plant and grows in uneven stands which can be harvested every two years in a repeating manner. The bamboo has a higher potential in fixing CO₂ from the atmosphere. The objectives of this dissertation are to study, (1) the storage of carbon in the bamboo forests at both a stand and regional (Zhejiang Province) scales, (2) C accumulation dynamics in the one-year old stands and the older stands under different silvicultural systems, and (3) the dynamics of soil C pool in intensively managed bamboo stands and the difference in soil C pool as the result of different ways of management. .The following is a summary of these studies.1. The results from the investigation of C density, total C storage of mao bamboo ecosystems and proportions in different organs have shown that C density ranged from 468 to 521 g · kg^-1 in different organs of mao bamboo in the following order: C storage in roots > stems > underground trunk >branches > underground stems> leaves. C stored in trunksaccounted for 50.97%, roots for 19.79% and 4.87% was stored in leaves. The total C storage in mao bamboo ecosystems was 106.362 t ? hm². The above-ground green vegetation C storage amounted to 34.231 t ? hm'2 accounting for 32.18% and the first 60 cm layer, along with litter on the ground, accounting for 67.82%. The bamboo layer can annually fix C 5.097 t ? hm"2. It is estimated that total C storage of mao bamboo ecosystems is reduced by 8.133 t ? hm"2 after stands have been intensively managed for 10 years than extensively managed, despite an annual average increase of 0.5891 C ? hm"2 in the bamboo layer.2. Carbon storage of mao bamboo in Zhejiang Province was estimated by improved methods presently available. It was found that: the Levenberg—Marquart technique used to fit nonlinear models had some problems, i.e., linearization of the nonlinear model evaluated parametric and convergence values of the iteration process;a nonlinear regression principlewas used to mitigate these problems and two improved indices were proposed: fiT <\, fiN <1.It was judged that these two indices improved the estimation of the fitted parameters and usefulness over the convergence of iteration process.Forest resource data banks in Zhejiang Province were consulted, typical sample plots investigated by field observations and distribution models of age and breast height diameter of mao bamboo developed for a corresponding single biomass model. Total biomass of bamboo in the province was estimated to be 15.2 million t. By applying a transformation index, total C storage in bamboo forests was estimated as 7.7 million t. The study made used of a new method of scaling firstly which can directly get an estimation of the biomass carbon of various sized stands from a single tree biomass carbon storage. This scaling method takes full advantage of all the information available from sample plots, resulting in a credible estimate..3. In order to discover the regularity of C accumulation of individual mao bamboo trees, from the emergence of shoots to the end of the fast growth period during the first stage, which usually lasts one and half month, bamboo samples were collected every 3 days. Bamboo grows relative rapidly in the middle of the first month and comparative slowly during the first and last ten days. The biomass of individual bamboo trees was positively related to the diameter of bamboo near the ground. Carbon density of individual bamboo trees increasedwith their growth and ranged from 440 g C to 460 g C per kg dry weight biomass. The average C storage of individual bamboo changed from 0.04 kg at the beginning to 1.823 kg at the end of the fast growth period, 45.5 times greater. C storage(A/) is a function of ground diameter(Z)), height(/f) and the time for emergence of bamboo(/) and is represented by the, s,0-0.021/ , ,q^0.019/ following model: M = 0.002DJ-:>-38e Hi-Me4. It was found in a comparison of intensive management (IM) with extensive management (EM) in mao bamboo stands, that the capacity for C accumulation, deduced from the accumulated bamboo biomass, was 12.740 6 t ? hm"2 ? a"1 in IM bamboo system. One-year-old new bamboo accumulated 11.389 0 t ? hm'2 ? a"1, which accounted for 89.4% of the total accumulation and three or five years old bamboo accumulated 0.648 1 t ? hm"2 ? a"1. The corresponding data for EM bamboo system are respective 8.184 3, 6.056 3 (accounting for 74.36% ) and 0.461 1 t ? hm"2 ? a"1. The C accumulation in the understory vegetation and litter in IM bamboo system are: respective 0 and 1.172 5 t *hm"2 *a"' and the corresponding data for EM bamboo system are respective 0.545 9 and 2.155 8 t ? hm"2 ? a"1. C loss in the form of litter decomposition is 0.4690 t *hm"2 ? a"1 in the IM bamboo system and 1.034 8 t 'hm'2 ? a"1 in the EM system. The net carbon sequestration in IM bamboo above-ground was 1.56 times greater than in the EM system.5. The yearly dynamics of soil organic carbon under intensive management and extensive management of mao bamboo stands have been studied. The total organic soil carbon (TOC) in both EM and IM systems was at a minimum level in June and reached a maximum in the following month of January. Soil microbial biomass carbon (MBC) increased from May, reached a maximum in September, after which it decreased and reached a minimum in January. As far as soil water soluble organic carbon (WSOC) is concerned, two peaks were measured in May and November. The low point was observed in January. Intensive management of bamboo resulted in a decline in each of the following carbon fractions: TOC, MBC and WSOC of soil in the 0-20 cm layer decreased by 12.1%, 26.08% and 29.29% respectively, indicating that intensive management in bamboo plantations depletes the soil C pool. The vertical distribution of each C pool, however, was not altered by IM.6. Soils under IM for 5, 10, 20 and 40 years were collected and several fractions ofcarbon were analyzed and compared with the soil under extensive management. The result showed: soil TOC, MBC, WSOC and mineralized carbon (MC) decreased considerably (P<0.05) after 5-year IM;soil TOC continued to decrease until year 20;however, WSOC and MC remained constant from year 5 until year 40. The percentage of labile TOC did not decrease very much except between 0-5 years for MC and 10-20 years for MBC. Soil TOC and MBC decreased by 34.70% and 49.35% respectively during the 20-year IM. The vertical distribution of different fractions of organic carbon was not changed by intensive practice. The amount of organic carbon generally decreased with the depth at a similar gradient. It can be concluded that IM of bamboo has induced a big loss of soil carbon storage and degradation of biological soil properties.