Study On Temporal And Spatial Variation Of Soil Organic Carbon Storage In Phyllostachys Praecox Stands With Intensive Cultivation Management

Phyllostachys praecox forest intensive management is charcterized with over fertilizing,heavy winter mulching of bio-mass and careful field management to promote earlier producing and higher yield of bamboo shoot with higher economic value to bamboo farmers.With our research,we found that intensive managed Phyllostachys praecox forest ecosystem was even a large carbon pool which included the great quantity of organic matters produced aboveground and the large amount of soil organic matter accumulated underground.With the planting years passing by,the quantity of CO₂ sequestrated by Phyllostachys praecox forest--soil ecosystem will be a worldbeater in the future.Up today,there was only little information related to the temporal and spatial variation of soil organic carbon storaged in Phyllostachys Praecox Stands and even less on chemical structure of soil organic carbon with ¹³ C-NMR analysis.From March 2006 to March 2008,about 240 soil profiles from Phyllostaehys praecox forest of 0a,1a,5a,10a and 15a（each with 4 replications） in three different towns（Sankou,Xitianmu and Hengfan） and plus some from Zaoxi town of Lin’an county Zhejiang province were taken as research objects.We studied the spatial and temporal variation of soil TOC、WSOC、ROC、MBC、HA、FA、E₄ and E₆ with these samples in different planting years,profile depth, geography and social economic conditions.At meantime,the chemical structure of soil organic carbon with ¹³ C-NMR technology was also used.The results obtained are summarized as follows:1.Temporal and spatial variation of soil organic carbon:Via our research to 720 soil samplings in Sankou,Hengfan and Xitianmu,we found that with planting years increase,TOC was higher.The average TOC of the 10a’s increased to 1.119 times,compared to paddy field soil,the 15a’s increased to 2.086 times.The highest soil TOC samples from 15a in Sankou town even reached to 78.31 g.kg^-1.All these significant increase of TOC were tracked back to the intensive management of over fertilization, heavy winter mulching of bio-mass for Phyllostachys praecox forest.In spatial variation,within 15 years planting,soil TOC content of the surface layer changed and upgraded mostly,sub-surface layers second and the bottom layers less affected.As different geography and social economic condition of three towns concerned,during 15 years planting,soil TOC content increased mostly in Sankou,second in Xitianmu.These two towns located at mountain and hill areas with higher altitude however lower altitude in Hengfan which located relatively in lower altitude plain or valley.In addition,it was also according to how much input and how fine management of bamboo farmers had adoptted in different town..Significant correlationship between soil organic matter and total nitrogen of surface layer in Phyllostachys Praecox Stands had been identified.A suitable C/N was very important to soil fertility. Accumulating rate of TOC was much faster than TN with planting years increase.It was not good for soil fertility but beneficial to soil carbon sequestration of Phyllostachys praecox forest.2.Temporal and spatial variation of WSOC,ROC and MBC:It was found that with planting years increase,WSOC content was gradual higher,and with the profile depth deeper,WSOC content gradual decreased,which were also tracked back to the intensive management of over fertilization,heavy winter mulching of bio-mass for Phyllostachys praecox forest.As spatial variation of WSOC content concerned,it was higher in Xitianmu than in Hengfan,again it was due to different geography and social economic condition of two towns same as TOC described above.With planting years increase, the ratio of WSOC/TOC gradual decreased which showed the soil organic carbon became more stable. Significant correlation-ship between WSOC and TOC especially in surface layer,also between WSOC and TN、RAP、HN had been identified.Within 15 years of planting,ROC content of Phyllostachys praecox forest soil in Zaoxi town （close to Xitianmu town） reached the highest despite it was the lowest at beginning and higher than Sankou and Hengfan at last.MBC and MBC/TOC decreased with planting years increase.MBC content dropped with different track in Hengfan and Xitianmu,but the trends were both the same.3.Temporal and spatial variation of HA,FA and E₄,E₆:With planting years increase,HA content was gradual higher and HA/（HA+FA）dropped first and upgraded later,changing trends was similar to TOC’s.Due to the soil condition changing from wetland paddy field to dryland,HA dropped at first 5 years and upgraded later on.The changing trend of FA was just opposite of HA.The ratio of HA/FA were all above 1.0 and increased with planting years prolong which indicated that HA was inactive and accumulated faster than FA.As the spatial variration concerned,content of HA,FA and HA+FA were all highest in surface layers,second in sub-surface layers and lowest in bottom layers.With planting years increase,E_4（HA）,E_6（HA） content and E₄/E_6（HA+FA）were gradual higher which indicated that HA molecule structure became more complicated,higher aromaticity and more stable characteristic.With soil depth deeper,E_4（HA） content decreased too which indicated that SOC in suface layers had highest degree of aromaticity and most stable characteristic.4.Chemical structure of soil organic carbon with ¹³ C-NMR:¹³C NMR analysis data revealed that basic chemical structure of Phyllostachys Praecox forest SOC from of 1a’s to 15a’s were all similar.It could be divided into four clear nuclear magnetic resonance areas.15 years was such a short time to the molecular structural variation of SOC and there showed a few differences in structure.As spatial variation of chemical structure of SOC,with soil depth deeper,SOC in sub-surface layers had most stable structure in 15a Phyllostachys Praecox forest soil for its higest ratio of A/O-A.With variation by sampling areas,SOC in Congkeng villiage had lower aromatic degree compared to Sankou town,so that Phyllostachys Praecox forest soil in Sankou town had more strong potential to sequestrate carbon due to higher aromatic degree of SOC there.With planting years increase,the ratio of A/O-A decreased and the aromatic degree had a little bit increased within 15 years and it was beneficial to soil carbon sequestration.However,to such a huge soil carbon pool and long variation process,15 years was only a very short time and it could not have a big increase of aromatic degree of SOC.With sustainable extension of intensive management of Phyllostachys Praecox forest soil,it will make great contribution to minimize greenhouse effect and remediate to global warming.