Changes of soil microbial communities during decomposition of straw residues under different land uses

Monitoring soil microbial communities can lead to better understanding of the transformation processes of organic carbon in soil. The present study investigated the changes of soil microbial communities during straw decomposition in three fields, i.e., cropland, peach orchard and vineyard. Straw decomposition was monitored for 360 d using a mesh-bag method. Soil microbial metabolic activity and functional diversity were measured using the Biolog-Eco system. In all three fields, dried straws with a smaller size decomposed faster than their fresh counterparts that had a larger size. Dried corn straw decomposed slower than dried soybean straw in the early and middle stages, while the reverse trend was found in the late stage. The cropland showed the highest increase in microbial metabolic activity during the straw decomposition, whereas the peach orchard showed the lowest. There was no significant change in the species dominance or evenness of soil microbial communities during the straw decomposition. However, the species richness fluctuated significantly, with the peach orchard showing the highest richness and the cropland the lowest. With different carbon sources, the peach orchard utilised carbon the most, followed by the cropland and the vineyard. In all three fields, carbon was utilized in following decreasing order： saccharides〉amino acids〉polymers〉polyamines〉carboxylic acids〉aromatic compounds. In terms of carbon-source utilization, soil microbial communities in the peach orchard were less stable than those in the cropland. The metabolic activity and species dominance of soil microbial communities were negatively correlated with the straw residual percentage. Refractory components were primarily accumulated in the late stages, thus slowing down the straw decomposition. The results showed that dried and crushed corn straw was better for application in long-term fields. The diversity of soil microbial communities was more stable in cropland than in orchards during the straw decomposition.

Microbial production of CO_2 in red soil in Stone Forest National Park

Lunan stone forest is a kind of typical karst in China, which is mainly developed under red soil. In the winter of 1999, three study sites were chosen in stone forest national park according to vegetation cover, geomorphologic location and soil types. CO 2 concentration was measured with Gastec pump at different depths of soil (20, 40, 60 cm) and at the same time soil samples were gathered and soil properties such as soil moisture, pH, soil organic content were analyzed and the total number of viable microbes were counted in laboratory. In the study, dependent variable was chosen as the mean soil log (PCO 2 ), and soil properties were chosen as the independent variables. Multiple stepwise regression analysis showed that the total amount of microbes and soil moisture are the best indicators of the CO 2 production, with the equation LOG(PCO 2 ) = - 0.039(TNM) - 0.056(Mo) + 1.215 accounting for 86% of the variation of the soil CO 2 concentration, where TNM is the total number of microbes in the soil and Mo is the moisture of soil sample.

Changes in particulate and mineral-associated organic carbon with land use in contrasting soils

Soil organic carbon(SOC)is the largest terrestrial carbon(C)stock,and the capacity of soils to preserve organic C(OC)varies with many factors,including land use,soil type,and soil depth.We investigated the effect of land use change on soil particulate organic matter(POM)and mineral-associated organic matter(MOM).Surface(0–10 cm)and subsurface(60–70 cm)samples were collected from paired sites(native and cropped)of four contrasting soils.Bulk soils were separated into POM and MOM fractions,which were analyzed for mineralogy,OC,nitrogen,isotopic signatures,and14C.The POM fractions of surface soils were relatively unaffected by land use change,possibly because of the continuous input of crop residues,whereas the POM fractions in corresponding subsurface soils lost more OC.In surface soils,MOM fractions dominated by the oxides of iron and aluminum(oxide-OM)lost more OC than those dominated by phyllosilicates and quartz,which was attributed to diverse organic matter(OM)input and the extent of OC saturation limit of soils.In contrast,oxide-OM fractions were less affected than the other two MOM fractions in the subsurface soils,possibly due to OC protection via organo-mineral associations.The deviations in isotopic signature(linked with vegetation)across the fractions suggested that fresh crop residues constituted the bulk of OM in surface soils(supported by greater14C).Increased isotopic signatures and lower14C in subsurface MOM fractions suggested the association of more microbially processed,aged OC with oxide-OM fractions than with the other MOM fractions.The results reveal that the quantity and quality of OC after land use change is influenced by the nature of C input in surface soils and by mineral-organic association in subsurface soils.

Long-term(42 years)effect of thinning on soil CO_(2)emission in a mixed broadleaved-Korean pine(Pinus koraiensis)forest in Northeast China

Thinning is an important forest management practice that has great potential to influence regional soil carbon storage and dynamics.The present study measured soil respiration(RS,the efflux of CO2 emitted)and its two components(heterotrophic(RH)and autotrophic(RA)respiration)from soil 42 years after thinning in comparison to un-thinning(control).Autotrophic respiration was significantly greater in the thinning plot,approximately 44%higher compared to the control,while both RSand RHwere slightly,but not significantly,higher in the thinning plot.Higher fine root biomass might have contributed to the higher RAin the thinning plot.Both RSand RHshowed clear soil temperature-dependent seasonal patterns,whereas RAwas less responsive to changes in temperature,especially within one specific season.The annual and season-specific temperature sensitivities of RSand RHwere lower in the thinning plot,specifically during the mid-growing season.Furthermore,variations in the season-specific temperature sensitivity of RSand RHwere less intense in the thinning plot.We conclude that forest thinning can reduce the temperature sensitivity of RSand RHduring the mid-growing season and increase soil CO2 emission in the long term.