Thinning Effect of C Sequestration along an Elevation Gradient of Mediterranean Pinus spp. Plantations

Forests are key elements in mitigating the effects of climate change due to the fact of their carbon sequestration capacity. Forest management can be oriented to optimise the carbon sequestration capacity of forest stands, in line with other productive objectives and the generation of ecosystem services. This research aimed to determine whether thinning treatments have a positive influence on the growth patterns of some of the main Mediterranean pine species and, therefore, on their Carbon (C) fixation capacity, both in terms of living biomass and soil organic carbon. The results obtained show that C sequestration capacity (biomass and SOC) increased at higher thinning intensities due to the induced alterations in tree growth patterns. We observed almost a 1.5-fold increase in P. nigra and P. sylvestris, respectively, and over a two-fold increase in P. pinaster under heavy thinning treatments; SOC stocks were affected by the intensity of the thinning treatments. These results can contribute to improving silvicultural practices aimed at C sequestration in forest plantations located in dry areas of the Mediterranean.

Evaluation of phosphorous fixation capacity on river alluvium, beach ridge and coastal plain sand of Akwa ibom state, Nigeria

Phosphorous fixation capacities of selected parent materials in Akwa Ibom State were assessed. The soils used were those derived from river alluvium, beach ridge sand and coastal plain sand. These soils were incubated with four rates of P ranging from 0, 20, 40, 80 mgl-l prepared from KH2PO4 and incubated for 1, 7, 30, 60 and 90 days. The design was 3 x 4 factorial experiment (3 soil types and 4 rates of P) fitted into Completely Randomized Design (CRD) with three replications. At a set day, the exchangeable and water-soluble (available) P were extracted with Bray P – I extractant and P not extracted by this extractant was considered fixed in the soils, using fractional recovery of P to obtained. The results showed that the available P in the soils decrease with days of incubation. Beach ridge sand had the highest fractional recovery of P while river alluvium had the least. The trend were beach ridge sand (5.04 gkg-1) > coastal plain sand (2.34 gkg-1) > river alluvium (1.07 gkg-1). The recovery of P increase with increasing P addition. The fixing capacity of the soils increased in this order: river alluvium (97%) > coastal plain sand (92%) > beach ridge sand (84%). The result also revealed that the amount of P fixed increases with increasing rates of P addition.

Multi-omics Analysis of the Symbiotic Green Algae, Chlorella Variabilis, Revealing the Genetic Basis of the Obligate Endosymbiotic Lifestyle

Background: Photosynthetic eukaryotes have evolved through the acquisition of plastids by secondary endosymbiosis, a process that requires several steps. Immediately before plastid acquisition, the genome of the symbiont is known to be dramatically reduced, but few studies have focused on the genomic changes in the symbiont at the early stages of secondary endosymbiosis. Methods: To investigate the genetic basis of the transition from facultative to obligate endosymbiosis, we compared the genomes of Chlorella variabilis, a representative symbiotic alga, with that of Paramecium bursaria, to compare closely related free-living species and transcriptomes between organisms in symbiotic and non-symbiotic conditions. Results: We found that the non-reduced genome of C. variabilis and its genes play a crucial role in endosymbiosis, being involved in cell wall biogenesis and degradation, and metabolic exchanges with the host. Our results suggest that the genetic mechanism underlying the enhancement of photosynthesis under symbiosis is the increasing light absorption efficiency and carbon fixation capacity of the endosymbiont, resulting in an increase in the supply of maltose to P. bursaria.

Differential responses of the sunn4 and rdn1-1 super-nodulation mutants of Medicago truncatula to elevated atmospheric CO2

Background and Aims Nitrogen fixation in legumes requires tight control of carbon and nitrogen balance. Thus, legumes control nodule numbers via an autoregulation mechanism. ‘Autoregulation of nodulation’ mutants super-nodulate and are thought to be carbon-limited due to the high carbon-sink strength of excessive nodules. This study aimed to examine the effect of increasing carbon supply on the performance of super-nodulation mutants. Methods We compared the responses of Medicago truncatula super-nodulation mutants (sunn-4 and rdn1-1) and wild type to five CO2 levels (300-850 μmol mol -1). Nodule formation and N2 fixation were assessed in soil-grown plants at 18 and 42 days after sowing. Key results Shoot and root biomass, nodule number and biomass, nitrogenase activity and fixed-N per plant of all genotypes increased with increasing CO2 concentration and reached the maximum around 700 μmol mol -1. While the sunn-4 mutant showed strong growth-retardation compared to wild-type plants, elevated CO2 increased shoot biomass and total N content of rdn1-1 mutant up to two-fold. This was accompanied by a four-fold increase in nitrogen fixation capacity in the rdn1-1 mutant. Conclusions These results suggest that the super-nodulation phenotype per se did not limit growth. The additional nitrogen fixation capacity of the rdn1-1 mutant may enhance the benefit of elevated CO2 on plant growth and N2 fixation.

Molecular Components of Nitrogen Fixation Gene Cluster and Associated Enzymatic Activities of Non-Heterocystous Thermophilic Cyanobacterium Thermoleptolyngbya sp.

Thermoleptolyngbya is a genus of non-heterocystous cyanobacteria that are typical inhabitants of hot spring microbial mats. These filamentous cyanobacteria are capable of nitrogen fixation. In this study, we examined the genome sequences of five publicly available Thermoleptolyngbya strains to explore their nitrogen fixation gene cluster. Analysis of the nitrogen-fixation clusters in these extremophilic strains revealed that the cluster is located in a single locus in Thermoleptolyngbyace. The average nucleotide and amino acid identities of the nitrogen-fixation cluster combined with phylogenetic reconstructions support that nitrogen fixation genes in Thermoleptolyngbyaceae are closely related to one another but also heterogeneous within the genus. The strains from Asia, and China more specifically, generate a separate clade within the genus. Among these strains Thermoleptolyngbya sp. PKUAC-SCTB121 has been selected for experimental validation of clade’s nitrogen fixation capacity. The acetylene reduction experiments of that strain shown that the strain can reduce acetylene to ethylene, indicating a fully functional nitrogenase. The activity of nitrogenase has been tested using different gas compositions across 72 h and exhibited a two-phase trend, high nitrogenase activity at the beginning of the assay that slowed down in the second phase of the analysis.

Characterizing the impact of MnO2 addition on the efficiency of Fe0/H2O systems

The role of manganese dioxide (MnO2) in the process of water treatment using metallic iron (Fe0/H2O) was investigated in quiescent batch experiments for t ≤ 60 d. MnO2 was used as an agent to control the availability of solid iron corrosion products (FeCPs) while methylene blue (MB) was an indicator of reactivity. The investigated systems were: (1) Fe0, (2) MnO2, (3) sand, (4) Fe0/sand, (5) Fe0/MnO2, and (6) Fe0/sand/MnO2. The experiments were performed in test tubes each containing 22.0 mL of MB (10 mg L−1) and the solid aggregates. The initial pH value was 8.2. Each system was characterized for the final concentration of H+, Fe, and MB. Results show no detectable level of dissolved iron after 47 days. Final pH values varied from 7.4 to 9.8. The MB discoloration efficiency varies from 40 to 80% as the MnO2 loading increases from 2.3 to 45 g L−1. MB discoloration is only quantitative when the operational fixation capacity of MnO2 for Fe2+ was exhausted. This corresponds to the event where adsorption and co-precipitation with FeCPs is intensive. Adsorption and co-precipitation are thus the fundamental mechanisms of decontamination in Fe0/H2O systems. Hybrid Fe0/MnO2 systems are potential candidates for the design of more sustainable Fe0 filters.

Micorrizas arbusculares e absorção de fósforo em função da capacidade de fixação de fósforo do solo e da competição com a microbiota

Fungos micorrízicos arbusculares (FMA) se associam às raízes das plantas e incrementam a absorção de fósforo (P), macronutriente com baixa mobilidade no solo. A capacidade de fixação de P do solo e a competição com a biota heterotrófica afetam sua disponibilidade para plantas. Visando avaliar a contribuição dos FMA na absorção de P em solos com capacidade crescente de fixação ou em situação de competição com a biota foram realizados experimentos em vasos compartimentalizados cultivados com braquiária associada a FMA, contendo substrato marcado com 32P. Foram quantificadas a massa seca das plantas, o conteúdo e a atividade específica do P. No experimento 1 avaliou-se a absorção de P por raízes e hifas de FMA ou somente por hifas em solos com alta, média e baixa capacidade fixação de P. No experimento 2 avaliou-se a absorção de P por raízes e hifas de FMA ou somente por hifas em solos com alta e baixa capacidade fixação de P em situação de competição com a biota do solo ativada por fontes de carbono. O aumento da capacidade de fixação de P pelo solo resultou em diminuição de massa seca, conteúdo de P e atividade específica nas plantas. No solo com alta fixação de P, plantas com absorção exclusiva por hifas de FMA tiveram aumento da massa seca e conteúdo de P. Em situação de competição, houve diminuição na massa seca e no conteúdo de P nas plantas. Plantas com absorção por raízes e hifas de FMA tiveram maior atividade específica de P. Arbuscular mycorrhizae and phosphorus uptake in soils as a function of adsorption capacity and competition with microbiota A B S T R A C TArbuscular mycorrhizal fungi (AMF) are associated with plant roots and increase the absorption of phosphorus (P), macronutrient with low soil mobility. Soil P fixation capacity and competition with heterotrophic biota affect its availability. To evaluate the contribution of AMF to P uptake in soils with increasing fixation capacity or in competition with biota, experiments were carried out in compartmentalized pots cultivated with AMF-associated Brachiaria decumbens containing 32P-labeled substrate. Plant dry mass, content and specific activity of P. were quantified. In experiment 1, the absorption of P by roots and hyphae of AMF or only by hyphae in soils with high, medium and low P. fixation capacity was evaluated. In experiment 2, the absorption of P by roots and hyphae of AMF or only by hyphae in soils with high and low P fixation capacity in competition with carbon-activated soil biota was evaluated. Increasing P fixation capacity by soil resulted in decreased dry matter, P content and specific activity in plants. In soil with high P fixation, plants with exclusive absorption by FMA hyphae had increased dry matter and P content. In a competition situation, there was a decrease in dry matter and P content in plants. Plants absorbed by roots and hyphae of AMF had higher P-specific activity.Keywords: 32P, P-soil fixing, AMF, extraradical mycelium, hyphal absorption