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生物碳系列性质之五:激发效应

发布时间:06-08 23:01 来源: 作者: 阅读:4789 网友评论0

介绍了生物碳与生物群落的关系

          Soil quality can be considered to be relatively high for supporting plant production and provision of ecosystem services if it contains carbon in the form of complex and dynamic substances such as humus and SOM. There has been some evidence to suggest that biochar addition to soil may lead to accelerate decomposition of SOM via a priming effect in the short term. The fact that Terra Pretas contain SOM as well as char seems to demonstrate that the priming effect either does not exist in all situations or if it does, perhaps it only lasts a few seasons and it appear not to be sufficient to drive the loss of all native SOM from the soil. Disturbance of added biochar to the soil which is sufficient to break up soil aggregates and expose previously protected soil organic matter to microbial decomposition and mineralisation itself has a strong priming effect on SOC. There is some evidence that the availability of N in a soil is the main factor affecting the priming effect, with more available N leading to a reduced priming effect. This suggests that the priming effect could perhaps be reduced or eliminated through the co-addition of N fertiliser along with biochar.
Much of the data currently reported in the literature shows a slight, but significant positive effect on the soil biota, with increased microbial biomass and respiration efficiency per unit carbon, with associated increases in above ground biomass production reported in the majority of cases. The soil biota plays the vital role in regulating numerous ecosystem services and soil functions. After its initial application to soil, biochar can function to stimulate the edaphic microflora and fauna due to various substrates, such as sugars, which can be present on the biochar's surface. Once these are metabolised, biochar functions more as a mineral component of the soil rather than an organic component, as evidenced by its high levels of recalcitrance meaning that it is not used as a carbon source for respiration. Rather, the biochar functions as a highly porous network the edaphic biota can colonise. Due to the large inherent porosity, biochar particles in soil can provide refugia for microorganisms whereby they may often be protected from grazing by other soil organisms which may be too large to enter the pores. This is likely to be one of the main mechanisms by which biochar-amended soils are able to harbour a larger microbial biomass when compared to non-biochar amended soils. Biochar may also include compounds which have bactericidal and fungicidal properties such as formaldehyde and cresols. However, residence times of these substrates has been shown to be in the range of one to two seasons and, therefore, long term effects of these chemicals on the soil biota are unlikely.

           A very suitable method for probing priming effect, nutrient transfer and interactions with contaminants would be the use of Stable Isotope Probing (SIP), which can be used with other molecular techniques to trace the flow of carbon from particular sources through the soil system. Pyrolysing biomass labeled with a stable isotope and measuring its emission from the soil will allow accurate measures of its recalcitrance over time. Conducting controlled atmosphere experiments with stable isotope-labelled CO2 will enable assessing the observed increased microbial respiration and investigation of whether this increase is due to a more efficient use of plant provided substrates (in case the label is detected in soil respiration), or if a priming effect has occurred leading to increased metabolisation of the SOM (in case the label is not detected).

           While soil microorganisms were not dependant on BC as an energy source, the extracellular enzymes also decomposed the BC, in the range of 0.5% per year. The mean residence time of black carbon in soil is likely to be in the range of about 2000 years.

           Biochar increases the level of C in soils. If this is C in the form of a highly recalcitrant substance, then ecosystem functioning of soils may well be compromised, because it is not the presence of C within the soil which is important for functioning, but rather it is the decomposition of SOC which drives the soil biota and leads to the provision of ecosystem services.

           Microorganisms within these micropores are likely to be restriced in growth rate due to relying on diffusion to bring necessary nutrients and gases, but as this occurs in micropores within the soil, this demonstrates that microorganisms utilising these refugia almost certainly would not be reliant of decomposition of the biochar for an energy source. There is a strong positive effect on mycorrhizal abundance associated with biochar in soil.
It is the interaction between the biochar and the soil biota which leads to positive effects on yield, and not just the biochar itself. More culturable bacterial populations and a greater culturable diversity were found in all of the Anthrosols. The addition of organic fertiliser amendments along with biochar lead to further increases in microbial biomass.
Woody charcoal at lower pyrolysis temperatures retains an interior layer of bio-oil which is equal to glucose in its effect on microbial growth. When pyrolysed at higher temperatures, this internal layer of bio-oil is lost and so it is likely that the biochar will have less impact with regard to promoting soil fertility.  
     
           Earthworm was the organisms most responsible for the incorporation of charcoal into the topsoil in the form of silt size particles which aids the formation of stable humus in Terra Pretas. If the increase in microbial biomass occurs within biochar particles, then the microorganisms may not be available as a food source for soil invertebrates.

          However, if the stimulated growth in microbial biomass also occurs outside of biochar particles within the soil, then it is possible that an increase in the soil invertebrate community may also occur. Earthworms ingest biochar, it is probable that moles will in turn ingest charcoal particles when they ingest worms. It is still currently unclear what quantity of heavy metals will be able to pass from the biochar into the tissues of other organisms which requires further work to ensure safety of heavy metal containing biochars in soils.
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