Distribution of persistent organic pollutants in aggregate fractions of a temperate forest and semi-rural soil

The fate of persistent organic pollutants (POPs) and their interactions with aggregates of forest soils are not completely understood. Our objectives here were to quantify the distribution of different POPs in water-stable aggregate fractions and to study their influence on soil organic carbon (Corg) content. Soil samples were taken from a forest-site, Gogerddan (G) and a semi-rural site, Hazelrigg (H) in Great Britain, from 0-2 and 2-5 cm and 0-4 and 8-12 cm soil depth, respectively. POPs analyzed were PAHs, PCBs, total DDT, PBDEs and HCB. The bulk soil analysis showed that the concentration of POPs was significantly higher (p ≤ 0.05) in forest site G than in semi-rural site H, particularly at the surface soil levels compared to the subsurface soil depths in both sites. Total concentrations of PCBs and PAHs of both sites were positively correlated with Corg contents. POPs concentrations and Corg, Nt contents of forest site G were significantly higher (p ≤ 0.05) in water-stable macro aggregates (>0.25, >1, >2 mm) than the micro aggregates (>0.053 mm). The POP concentrations of all aggregate fractions after normalizing to their respective Corg content were increased due higher contamination and strong sorption by Corg. These results showed a strong effect of Corg on the partitioning of organic pollutants to soil aggregate size fractions. The present study affirms the ecological significance of forest soils act as a potential sink of POPs. In summary, our results suggest that aggregate fractions may promote soil C storage and act as a potential POP sink in surface soil without increasing their concentration in the aggregate fraction of subsoil.

Changes in plant community and soil ecological indicators in response to Prosopis juliflora and Acacia mearnsii invasion and removal in two biodiversity hotspots in Southern India

Invasion of alien plant species can alter local plant diversity and ecosystem processes closely linked to soil organic carbon(SOC)and nutrient dynamics.Soil ecosystem processes such as microbial respiration and enzyme activity have been poorly explored under alien plant invasion and especially following invasive plant species removal.We studied the impact of Prosopis juliflora and Acacia mearnsii invasion and subsequent removal on local plant community composition and diversity and on soil microbial respiration and enzyme activity in two biodiversity hotspots in Southern India.Removal of Prosopis promoted recolonisation of local vegetation as indicated by a 38% and 28% increase in species richness and ground vegetation cover,respectively,compared to an unremoved site.Prosopis and Acacia removal led to a significant reduction in soil microbial biomass C(MBC),respiration,dehydrogenase and urease activity due to increased microbial respiration and N mineralisation rate.Higher metabolic quotients qCO_(2) in soil at Prosopis and Acacia removed sites indicate that MBC pools declined at a faster rate than SOC,resulting decreased MBC/SOC ratios compared to their respective removed sites.Natural and undisturbed ecosystems maintain more SOC through increased belowground and aboveground C input in the soil,resulting in a higher MBC content per unit SOC.Our results indicate that the interaction between above-and below-ground communities is a critical factor determining the structure and dynamics of local plant communities,especially in ecosystems affected by plant invasions.

Land rehabilitation improves edaphic conditions and increases soil microbial biomass and abundance

Rehabilitation of farmland improves the local eco-environmental conditions.But to what extent this transformation influences soil microbial properties is less known.In our study we compared variations in soil microbial attributes following changes in land-use types to understand the influence of altered soil properties on microbial biomass and their community structure using chloroform fumigation extraction method and phospholipid fatty acid(PLFA)analysis.For this purpose,3 agricultural(AL)(farmland,apple orchard and 2 years abandoned land)and 4 rehabilitated lands(RL)of various vegetations grassland,shrubland,mixed forest(Amorpha fruticosa and Pinus tabuliformis Carr.)and forest(Robinia pseudoacacia)were selected.Our results showed higher soil organic carbon(SOC)contents in RL soils(forest>mixed forest>grassland>shrub land)than that in AL soils.In RL soils,soil microbial biomass and abundance of group specific PLFA were significantly higher than those in AL soils.Under different land-use types,microbial community was bacteria dominated over fungi.The microbial physiological indices(G^(+)/G^(-),cyc/prec and S/M)indicated decreased environmental stress in RL soils in comparison with AL soils.In loess soils,SOC and total N correlated positively(p<0.05)with microbial biomass C,N and P and also with fungal and bacterial PLFA,indicating a positive microbial mediation in improving soil fertility.Taking together,our findings suggest that land rehabilitation,especially Robinia pseudoacacia planation,improves overall edaphic conditions and accelerates soil microbial biomass accumulation in local regions.