Rubber plantation ageing controls soil biodiversity after land conversion from cassava

The rapid expansion of perennial crops is a major threat to biodiversity in Southeast Asia. The biodiversity losses related to the conversion of forest lands to oil palm or rubber plantations (RP) are well documented by recent studies. However, the impact of the conversion from intensively managed annual crops to perennial crops on soil biodiversity has not yet been addressed. This study aims at assessing the impact on soil biodiversity of a) the shortterm effect of land use conversion from cassava crop to RP, and b) the long-term effect of RP ageing. Soil biodiversity (bacterial, fungal and macrofaunal), microbial activities and pedoclimatic characteristics were measured over a chronosequence of 1–25 years old of RP compared to cassava fields, the former crop, in Thailand. The conversion from cassava to young RP (1–3 yr) had a significant effect on microbial biomass and activities and fungal composition, but did not impact the bacterial and macrofaunal diversity. This effect of land use conversion could be explained by the change in land management due to the cultivation of pineapple in the inter-row of the young RP. Canopy closure appeared to be the main driver of soil biota shifts, as most of the biotic parameters, composition, abundance and activities were significantly modified after 7 years of RP. The changes of composition in older rubber plantations originated from the dominance of Trichoderma (fungi), Firmicutes (bacteria), and earthworms. Old rubber plantations (23–25 yr) harboured the highest microbial and macrofaunal biomass; however, they were also characterised by a significant decrease in bacterial richness. The change in pedoclimatic conditions across the rubber chronosequence, i.e. increase in soil moisture, litter and organic carbon content, was a stronger driver of soil biota evolution than land use conversion. The macrofaunal composition was more resistant to land use conversion than the bacterial composition, whereas the microbial biomass was sensitive to land use conversion, but showed resilience after 20 years. However, bacterial, fungal and macrofaunal diversity, macrofaunal and microbial biomass and microbial activities were all sensitive to RP ageing

Novel psbA1 Gene from a Naturally Occurring Atrazine-Resistant Cyanobacterial Isolate

A naturally occurring atrazine-resistant cyanobacterial isolate, strain SG2, was isolated from an atrazine-containing wastewater treatment system at the Syngenta atrazine production facility in St. Gabriel, La. Strain SG2 was resistant to 1,000 μg of atrazine per ml but showed relatively low resistance to diuron [3-(3,4-dichlorophenyl)-1,1-dimethyl urea]. Analyses of 16S ribosomal DNA indicated that strain SG2 falls into the Synechocystis/Pleurocapsa/Microcystis group. Photosynthetically driven oxygen evolution in strain SG2 was only slightly inhibited (about 10%) by 2,000 μg of atrazine per ml, whereas in the control strain Synechocystis 6803, oxygen evolution was inhibited 90% by 1,000 μg of atrazine per ml. No atrazine accretion, mineralization, or metabolites were detected when strain SG2 was grown with [(14)C]atrazine. Strain SG2 contained three copies of the psbA gene, which encodes the D(1) protein of the photosystem II reaction center. Nucleotide sequence analyses indicated that the psbA2 and psbA3 genes encoded predicted proteins with the same amino acid sequence. However, the psbA1 gene product contained five extra amino acids, which were not found in PsbA proteins from five other cyanobacteria. Moreover, the PsbA1 protein from strain SG2 had an additional 13 amino acid changes compared to the PsbA2/PsbA3 proteins and contained 10 amino acid alterations compared to conserved residues found in other cyanobacteria. Reverse transcriptase PCR analysis indicated that the psbA1 gene and the psbA2/psbA3 gene(s) were expressed in photosynthetically grown cells in the presence of atrazine. These results suggest that strong selection pressure conferred by the continual input of atrazine has contributed to the evolution of a herbicide-resistant, yet photosynthetically efficient, psbA gene in a cyanobacterium

Relationships between physico-chemical, biological and functional approaches for soil quality assessment. A case study along a gradient of disturbance

International audienceThe assessment of the impacts of land management on soil quality is crucial in the current environmental context. Among the many approaches available to assess soil quality, most of studies or monitoring programs consist in the measurement of stocks using an additive approach of physical, chemical and biological, parameters. More recently, functional methods have been developed to provide tools which better account the abioticbiotic interactions. The objective of our study was to evaluate and compare the capacity of physico-chemical, biological and functional parameters to assess the effect of land management on soil quality over a gradient of disturbance based on rubber tree plantations in Chachoengsao province, Thailand. Three sets of indicators were applied based on i. soil physico-chemical analyses, ii. biological analyses, based on soil free-living nematode indices iii. functional analyses, with Biofunctool (R) indicators linked to three main soil functions (carbon transformation, nutrient cycling, soil structure maintenance). A soil quality index resulting from the aggregation of each set of indicators into a single score showed that functional assessment was the most sensitive to the gradient of disturbance. Co-inertia analysis between sets revealed a significant relationship between functional analysis and both physico-chemical and biological sets of indicators, whereas the two latter were not related. Our results validated the ability of the functional method to better reflect the complexity of the abiotic-biotic interactions of the soil system.Highlights:• Three sets of soil quality indicators were compared.• Functional indicators were the most sensitive to the gradient of disturbance.• Functional set of indicators was significantly linked to physico-chemical and biological sets.• The functional method Biofunctool® integrate both soil biotic and abiotic components