| Litterfall is an important medium for the nutrient cycling process of forest ecosystems.Litterfall biomass,litterfall dynamics,and its nutrient release during the decomposition process directly reflect the productivity and dynamic equilibrium of forest ecosystems.The mass loss and nutrient release rate during the litterfall decomposition process are caused by the interaction of soil animals and microorganisms.A large number of scholars have focused much more on the annual litterfall dynamics,nutrient release,and litterfall decomposition rate,but less on the effect of slope and seasonal changes on litterfall dynamics and the relationship between litterfall decomposition and soil microbial community.The types of microhabitats in the karst area are diverse,and the soil is shallow and discontinuous.Environmental changes have important effects on the litterfall dynamics and decomposition dynamics of vegetation litter.Based on these,a combination of space and time series methods was conducted to apply to the field survey sampling and laboratory analysis of litterfall and soil of different vegetation restoration types within the karst forest ecosystem in Maolan,Guizhou.The study of litter biomass,main nutrient element content,litter decomposition nutrient release,soil physicochemical properties,soil microbial properties,and the relationship between litter decomposition and soil microbes was aim to elucidate the impacts of aspect and seasonal variation to litter and the relationship between litter and soil microbes,which provided basic theories for monitoring nutrient cycling and dynamic equilibrium in forest ecosystems in karst areas.The main conclusions were as follows:?1?The seasonal dynamic changes of litterfall on different slopes were explored though soil sampling analysis adret slope,ubac slope and semi-shady slope under karst forest ecosystem by collect litter and soil samplings in summer,autumn,winter and spring,respectively.The results showed that the litterfall biomass of the ubac slope(6.35 t·hm-2)was significantly higher than those of the semi-shade slope(5.75 t·hm-2)and the adret slope(4.89 t·hm-2).The annual litterfall(4.07 t·hm-2)and branch biomass(1.25 t·hm-2)accounted for 67.8%and 20.8%of the total,respectively,of which litterfall was 1.93t·hm-2 and litterfall was 2.14 t·hm-2.The seasonal dynamics of broad-leaved trees showed a single-peak pattern,and all three slopes had the maximum litterfall biomass in spring?March-May?,and small peaks of litterfall in autumn?September-November?.On all three slopes,the maximum branch biomass was reached in spring.?2?The contents of main nutrient elements in leaf litter and branches of different slope in karst primary forests of Maolan were as follows:TC>Ca>TK>Mg>TN>TP.Litter contents were higher in carbon and calcium,lower in nitrogen,phosphorus and potassium.The carbon content of the branches was higher than that of the leaf litter,but their nitrogen content was lower than that of the leaf litter.The annual average C/N ratio?27.5?of their litter branches was higher than that of the leaf litter?21.4?,making the leaf litter to decompose more easily than the branches.Phosphorus content in branches and leaves was the highest in summer,and the content of phosphorus in leaf litter was higher than that in branches.The phosphorus content in litter of the three slopes showed no significant difference.There was no significant correlation between evergreen leaves litter and deciduous litter and their own nutrient content,but it was found that there was a significantly negative correlation between the biomass of evergreen leaf litter and leaf litter magnesium content.?3?The residual mass of the litter in the decomposition bag during the360-day decomposition period was 4.11 on adret slope,and 4.47 g on ubac slope,respectively,and the mass loss rate was about 73.3%-70.2%.The initial contents of carbon,nitrogen and phosphorus in the adret and the ubac were as in the order of TC>TN>TP.The total carbon content and C/N ratio of litter on the adret were significantly higher than those of the ubac,while the total phosphorus content of the adret slope was significantly lower than that of the ubac slope.During the litter decomposition process,the total carbon content was released,and the total nitrogen content of the litter showed a tendency of enrichment,which accouted for 0.52%.The total phosphorus content was gradually released,and the C/N ratio showed a trend of gradual decrease.?4?The contents of total phospholipid fatty acid?PLFA?in the adret and ubac during litter decomposition were the highest in autumn and spring,which were 559.2 and 513.6 nmol·g-1,respectively.The content of soil microbial community showed Bacteria(149.8 nmol·g-1)>Actinomycetes(63.9 nmol·g-1)>Fungi(31.3 nmol·g-1).The bacterial content on the adret showed a trend of increasing first,then decreasing and finally increasing again,and the bacterial content on the ubac reached the maximum in autumn(186.2 nmol·g-1),and the fungal and bacterial proved to be relatively consistent;microbial community structure on the adret slpoe had a strong correlation with the release rates of carbon,nitrogen,and phosphorus in the litter,and the rate of litter mass loss and bacteria on the ubac slope.The litter mass loess rate with bacteria and fungal community on the ubac showed a significantly negative correlation?P<0.05?,while there was a significantly positive correlation between litter mas loss rate and fungal communities on adret?P<0.01?.?5?Using high-throughput sequencing technology to examine the soils of varying interference degrees,the Chao1 index of soil fungi and the observed species were analyzed,and the effect of interference on the fungal community structure was studied.The results showed that there were a total of 361 species of soil fungi detected in the soil of the karst region.The abundance and total species of fungal communities in the soils with less disturbance were relatively high,while in farmland soil with more disturbance were relatively low.PCoA and LEfSe analyses between the three types of soil fungal communities found that the influence of disturbance on the composition of soil fungal communities was significant.The differential flora of undisturbed soils in the virgin forest were mainly Sordariomycetes,Sordariales,Chaetomiaceae,Chaetomaceae,Penicillium and Nectriaceae,and in less-disturbed thin-leaf forests were Leotiomycetes,Helotiales and Xylariales,and in most disturbed farmland soil were Hypocreales and Clavicipitaceae.?6?Different types of vegetation restorations were used as research objects to compare and analyze changes of soil physical and chemical properties,microbial biomass and microbial community structure in 0-10 cm and 10-20 cm soils.The results showed that the total content of PLFA in the soil was the highest in the two soil layers of the virgin forest,and the abundance of the bacterial and fungal communities was significantly affected by the type of vegetation restoration and soil depth.The relative abundance of Gram-positive bacteria was highest in the two soil layers?19.1%and 20.1%?in unused grassland.Spearman correlation analysis showed that the Gram-positive bacteria?GP?was negatively correlated with soil physiochemical properties?P<0.01?in the 0-10 cm soil layer.The abundance of fungal phospholipid fatty acids 18:1?9c and arbuscular mycorrhizal fungi?AMF?were negatively correlated with the soil total nitrogen and total carbon contents.The soil total nitrogen content of soil layer was positively correlated with the total PLFA content,GP abundance,and 18:1?9c and AMF in 10-20cm.Therefore,the soil microbial community could be used as a sensitive index to reflect the stability of the karst forest ecosystem. |
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