| In recent years, biochar application played an important role in improving soil fertility, increasing soil carbon storage and reducing greenhouse gas emissions, however, such majority of researches generally focused on agricultural soil, its effects in forest soils still remains unclear. Intensive management in economic forest in Zhejiang Province was very popular, which has significantly decreased soil quality. Therefore, assessment the effects of bamboo biochar addition on soil fertility and greenhouse gas emission will be essential to restore and improve soil quality in forest. As an important driver of soil functioning, soil microorganisms are also considered as an indicator of soil fertility. This study focused on soil microbial diversity and abundance of functional genes to reveal the effect of bamboo biochar application on plant growth, soil fertility, greenhouse gases emissions by conducting a pot experiment with clover planting and an incubation study with biochar amendment. Two amendment rates (3%and9%, w/w) and three particle sizes (diameter size<0.05mm (fine),0.05-1.0mm (intermediate) and1.0-2.0mm (coarse)) of bamboo biochar were used in two soils (sand and clay), resulting a total of seven treatments in each soil as follows:a null check (CK) received no charcoal addition; treatments1,2and3receiving3%biochar but with fine, intermediate and coarse particle size, respectively; and treatments4,5and6receiving9%biochar but with fine, intermediate and coarse particle size, respectively. The main results obtained were as follows:(1)The pot experiment revealed that bamboo biochar addition clearly promoted clover growth, particularly in the initial periods, both in sand and clay soils. The effect of biochar addition on plant growth had a better performance in clay soil than in sand soil. Both biochar addition rates and particle size had little impact on plant growth in sand soil, however this impact varied in clay soil with fine particle size showing a better effect on plant growth than addition rates.(2)The pot experiment showed that application of bamboo charcoal increased pH and electrical conductivity but decreased alkali-hydrolyzed nitrogen contents in soil. The available P was increased in sand soil, however, no differences were observed in clay soil. Bamboo charcoal significantly increased available K both in sand and clay soils, and the degree of increases was positively correlated with application rates. Both N2O and CH4. gases emissions were not detected during the pot experiment except the CO2The cumulative CO2emissions under bamboo charcoal amendment were higher than the control, which was mainly attributed to the increased respiration of plant due to its promotion of plant growth, while no differences were found between the application rates of charcoal. Bamboo charcoal amendment significantly increased soil carbon storage. In the sand soils, the average contents of soil organic carbon under3%and9%charcoal amendments were20.66g·kg-1and39.76g·kg-1. In the clay soils, the average contents of soil organic carbon under3%and9%charcoal amendments were23.90g·kg-1and43.40g·kg-1.So we know that3%charcoal amendment promoted plant growth and soil fertility, while9%charcoal amendment played a better role in increasing soil carbon storage, fertility and plant growth than the3%amendment treatments.(3)The pot experiment proved that bamboo charcoal could promote microbial activity. DGGE analysis of bacterial and fungal community structure showed that bamboo charcoal primarily increased the brightness of the species (characteristics as abundance of individual species) and Shannon diversity index of bacterial species, while increased the number of species and the individual number of species. The effects of diameter of charcoal particles on bacterial abundance were higher than that of the application rates in the sand soils, with the abundance of bacterial in fine particle of charcoal higher than the middle one. However, the application rates had more influence on bacterial abundance than the diameter in the clay soils. To the fungal community, the application rates contributed more impacts than the particle diameter in sand and clay soils. Ammonia-oxidizing bacteria (AOB) and ammonia-oxidizing archaea (AOA) proved that comparing with the control, charcoal amendment decreased amoA gene copies of AOA in the two soils, and the9%treatments showing more decreases than the3%treatment. And, the amoA gene copies in the fine particle with9%charcoal amendment were lowest among all the treatments. We concluded that:Soil bacteria, fungi and AOB were higher than that of the control to add bamboo charcoal expect AOA, and the fine particle other than the coarse particle of charcoal had a better effect on promoting these microorganisms.(4)In80days of incubation process, both the CO2and N.2O emissions rates decreased with the increasing time. Bamboo charcoal addition reduced emissions of the two gases, and the reduction degree was raised with the application rates. Bamboo charcoal addition on the first day showed an inhibition of CO2emission but a priming effect on the second day. Particle size had no effect on the two gases emissions, but the gases emissions were negatively related with the application rates. The control of soil bacterial and fungal abundance were lower or significantly lower than the bamboo treatment, but no differences were found on the80th day. The two incubation time control soil AOB were lower than those of bamboo charcoal treatment, while the control soil AOA slightly less (3th day) or approximately (80th day) of bamboo charcoal treatment. In summary, both pot and incubation experiments showed that the bamboo charcoal amendment could promote the growth of soil bacteria, fungi and ammonia oxidizing bacteria, changing their community structures, increasing their numbers of species. Furthermore, the fine particle size bamboo charcoal had a better effect on promoting growth of microorganisms. But inhibit the ammonia oxidizing archaea. |
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