Humic Acid Degradation Characteristics Under Typical Vegetation Restoration Measures Of The Loess Plateau

Humic acid(HA) in0~10cm depth from an arable soil, four forest soils(Chinese pine,black locust, Sea-buckthorn and mixed forest) in typical Land Conversion Projects area wasextracted respectively and was the sole energy constitute in HA medium. Severalmicroorganisms, from soils of these vegetation types and capable of utilizing HA as carbonand nitrogen source, were trained and isolated in that medium.This research was consisted oftwo proportions. The first part was aimed at conducting the isolation and identity of HAdecomposing bacteria and their degradation features under different vegetation types. Then,three HA decomposing bacteria Bacillus licheniformis、 Microbacterium resistens、Stenotrophomonas maltophilia(marked1,2and3) were selected based on the former processto study the response of carbon degradation rate and structural characteristics of arable HA tothe influence of these strains and their combinations. The three bacteria strains subjected toseven treatments T1, T2, T3, T12, T13, T23and T123, cultured in the medium that arable HAserved as sole C and N sources. Results:1. Decomposing Characteristics of Soil Humic Acid Under Different Vegetation Types.(1)The HA extracted from the four forest soils had higher content of C, and lowercontent of N than that from the arable land.(2)Four bacteria strains and one strain actinomycetes were isolated by HA substrate, theywere Bacillus licheniformis (99.65%), Rhizobium nepotum (99.78%),Microbacteriumresistens(98.71%), Stenotrophomonas maltophilia(99.23%) and Streptomyces azureus(99.78%)based on the16s rDNA sequence analysis. Bacillus licheniformis was dominating species inHA substrate of arable land, Chinese pine, black locust and mixed forest, and Streptomycesazureus was dominant species in Sea-buckthorn. Rhizobium nepotum was not found in blacklocust HA substrate, and Stenotrophomonas maltophilia was not found in that substrate ofSea-buckthorn and mixed forest. Colony forming unit(CFU) of decomposing bacteria in HAmedium was in the decreasing order Sea-buckthorn>arable land>black locus>Chinesepine>Mixed forest, CFU in Mixed forest was only66.34%of Sea-buckthorn.(3)The microbial respiration carbon(RC) of Mixed forest, Chinese pine, Sea-buckthornand Black locust increased by25.35%,11.28%,10.36%and7.11%than that of arable land, respectively, and the difference between the mixed forest and arable land wassignificant(P<0.05). The microbial biomass carbon(MBC) in Sea-buckthorn, Black locust,arable land, and Chinese pine increased by131.91%,68.48%,64.98%and54.47%than thatof Mixed forest, respectively. MBC of Black locust, arable land and Chinese pine tended to beno significant differences, but the differences among the three, Sea-buckthorn and Mixedforest were significant(P<0.05). The total degradation rate of Sea-buckthorn soil HA wassignificantly higher than that in arable land and Mixed forest(P<0.05). The correlationanalysis showed CFU was correlated positively with MBC and with RC negatively(P<0.01).That indicated the change of vegetation types had some influence on the community ofHA decomposing bacteria and their decomposing characteristics to some extent.2. Degradation features of arable soil humic acid decomposing bacteria strains and theircombination.(1) CFU of all treatments decreased in the order T13>T3>T123>T23>T1>T2>T12. Themost active growth of the three strains was exhibited by Stenotrophomonas maltophilia whichCFU accounted for86.92%、83.23%、82.52%in T13, T23and T123, T1and T2were53.95%and26.98%of T3only, which revealed Stenotrophomonas maltophilia was more adoptive inHA medium than Bacillus licheniformis and Microbacterium resistens.(2) Carbon of HA in T23and T13were degraded to a greater extent of59.87%and56.71%than were other treatments in14days(P<0.05), and in T123, T12, T3and T1between42.68%~50.91%were degraded, while T2was the lowest21.73%.(3)Compared infrared spectrum of CK with all treatments after degrading processindicated an increasing proportion of carbohydrate C contents which susceptible todegradation, while aromatic C had no significant change, thus acting as a carbon constituentappear unavailable by HA degradation bacteria.