1,210 publications from this institution
Our studies are part of a programme of research into possible harmful effects of heavy metal‐contaminated sewage sludge being applied to soils supporting growth of trees. We have shown that ectomycorrhizal fungi vary in their growth response to heavy metals incorporated into agar plates. Lacearia laccata proved sensitive to Cu and Al when the concentration reached only 10 ppm but was tolerant of Zn at 10 ppm. Thelephora terrestris proved highly tolerant of Cu at 100 and 500 ppm in agar plates and Zn even at 1000 ppm. Mycelial growth in liquid media was inhibited between 200 and 400 ppm Cu. Growth of T. terrestris was reduced by 100 ppm Al. Suillus variegatus proved to be the most tolerant of Al on agar plates with growth increasing at least up to 100 ppm. It was sensitive to Cu at 100 ppm (but not consistently) and Zn at 1000 ppm. Abnormal morphological changes were observed in Scots pine mycorrhizas (T. terrestris) subjected to continuous application of Zn and Cu (as sulphates) in pots in the greenhouse. X‐ray micro‐analysis of the mycorrhizas in a scanning electron microscope revealed accumulation of Zn in the mycobiont‐hyphae. The studies indicate problems that might result from addition of excessive amounts of metals to soils with developing trees.
Soil microorganisms play a key role in regulating soil organic carbon (SOC) accrual. Organic amendments with distinct stoichiometry may lead to imbalanced supply of carbon (C), nitrogen (N), and phosphorus (P) to the microbiome, causing changes in microbial community composition and their life strategies, as well as enzyme production. However, the response of soil microorganisms to these imbalances and whether their adaptive strategies are related to the fate of SOC pools remain largely unknown in low-fertility paddy soil. To address this uncertainty, soils were sampled from a 12-year experimental fertilisation trial under integrated application of mineral fertilizers and three types of organic materials (green manure, rice straw, and cattle manure). Stoichiometric imbalances between soil microbes and their available resources, enzyme activities, and microbial community composition, and their linkages with soil particulate (POC) and mineral-associated (MAOC) organic C were investigated. The results showed that despite equal C input, strongest increase in MAOC occurred with organic amendments causing the smallest microbial C:N imbalance and C:P imbalance, suggesting that alleviation in N and P limitation was inductive to the accrual of soil stable organic C fraction. Additional organic amendments with lower C: nutrient ratios shifted the microbial community towards the prevalence of r-strategists, with cattle manure addition supporting copiotrophic bacteria and green manure addition favouring copiotrophic fungi. Importantly, the relative abundances of Proteobacteria, Gemmatimonadetes, and Actinobacteria belonging to copiotrophs were negatively related to microbial C:N imbalance and C:P imbalance, but positively related to POC and MAOC, while Chloroflexi, Basidiomycota and Glomeromycota belonging to oligotrophs exhibited reversed relationships. In addition, greater MAOC accrual was associated with an increase in microbial biomass and a decrease in biomass-specific P-acquiring enzyme activity. Random forest analysis and partial least squares path model revealed that microbial C:N imbalance and C:P imbalance played an important but indirect role in shaping MAOC by concurrently regulating soil microbial biomass, community composition and enzyme production, whereas the POC pool was predominantly and directly controlled by the proportion of macroaggregates. These results provide empirical evidence for the stoichiometric control of microbial communities and their feedback to SOC pools, highlighting the role of low C:nutrient ratio organic amendments for long-term storage and the persistence of C in intensively managed paddy soils.
