Effect of grazing on carbon stocks and assimilate partitioning in a Tibetan montane pasture revealed by 13CO2 pulse labeling

Since the late 1950s, governmental rangeland policies have changed the grazing management on the Tibetan Plateau (TP). Increasing grazing pressure and, since the 1980s, the privatization and fencing of pastures near villages has led to land degradation, whereas remote pastures have recovered from stronger overgrazing. To clarify the effect of moderate grazing on the carbon (C) cycle of the TP, we investigated differences in below‐ground C stocks and C allocation using in situ ¹³CO₂ pulse labeling of (i) a montane Kobresia winter pasture of yaks, with moderate grazing regime and (ii) a 7‐year‐old grazing exclosure plot, both in 3440 m asl. Twenty‐seven days after the labeling, ¹³C incorporated into shoots did not differ between the grazed (43% of recovered ¹³C) and ungrazed (38%) plots. In the grazed plots, however, less C was lost by shoot respiration (17% vs. 42%), and more was translocated below‐ground (40% vs. 20%). Within the below‐ground pools, <2% of ¹³C was incorporated into living root tissue of both land use types. In the grazed plots about twice the amount of ¹³C remained in soil (18%) and was mineralized to CO₂ (20%) as compared to the ungrazed plots (soil 10%; CO₂ 9%). Despite the higher contribution of root‐derived C to CO₂ efflux, total CO₂ efflux did not differ between the two land use types. C stocks in the soil layers 0–5 and 5–15 cm under grazed grassland were significantly larger than in the ungrazed grassland. However, C stocks below 15 cm were not affected after 7 years without grazing. We conclude that the larger below‐ground C allocation of plants, the larger amount of recently assimilated C remaining in the soil, and less soil organic matter‐derived CO₂ efflux create a positive effect of moderate grazing on soil C input and C sequestration.     

Effect of Bovine Manure on Cryptosporidium parvum Oocyst Attachment to Soil

The objective of this work was to assess the effect of dilute bovine manure (1.0% and 0.1%) versus that of no manure on attachment and subsequent detachment of Cryptosporidium parvum oocysts to soil. Manure enhanced the attachment of oocysts to soil particles; the maximum attachment was observed with 0.1% manure. Oocyst attachment was partially reversible; maximum detachment was observed with dilute manure. These results indicate that oocyst attachment to soil is substantially affected by bovine manure in a complex manner and should have implications for how oocysts may be transported through or over soils.     

Modular biodegradable biomaterials from surfactant and polyelectrolyte mixtures

Polymeric assemblies are used in many biomaterials applications, ranging from drug-bearing nanoparticles to macroscopic scaffolds. Control over their biodegradation rates is usually achieved through synthetic modification of their molecular structure. As a simpler alternative, we exploit the associative phase separation in mixtures of bioderived surfactants and polyelectrolytes. The gel fiber scaffolds are formed via phase inversion, using a homologous series of fatty acid salts-sodium caprate (NaC10), laurate (NaC12), and myristate (NaC14), and a water-soluble chitosan derivative, N-[(2-hydroxy-3-trimethylammonium)propyl] chitosan chloride (HTCC). Their dissolution times are modulated through the selection of the fatty acid molecule and vary in a predictable manner from minutes (for NaC10-HTCC), to hours (for NaC12-HTCC), to days (for NaC14-HTCC). These variations are linked to differences in surfactant-polyelectrolyte binding strength and scale with the equilibrium binding constants of their mixtures. These fibers were found to be both cytocompatible and cell-adhesive using neural stem/progenitor cells, suggesting their potential for utility in biomedical applications.     

The Rhodobacter capsulatus genome

The genome of Rhodobacter capsulatus has been completely sequenced. It consists of a single chromosome containing 3.5 Mb and a circular plasmid of 134 kb. This effort, started in 1992, began with a fine-structure restriction map of an overlapping set of cosmids that covered the genome. Cosmid sequencing led to a gapped genome that was filled by primer walking on the chromosome and by using lambda clones. Methods had to be developed to handle strong stops in the high GC (68%) inserts. Annotation was done with the ERGO system at Integrated Genomics, as was the reconstruction of the cell's metabolism. It was possible to recognize 3709 orfs of which functional assignments could be made with high confidence to 2392 (65%). Unusual features include the presence of numerous cryptic phage genomes embedded in the chromosome. This revised version was published online in June 2006 with corrections to the Cover Date.     

Human Gene-Centric Databases at the Weizmann Institute of Science: GeneCards,UDB, CroW 21 and HORDE

Recent enhancements and current research in the GeneCards (GC) (http://bioinfo.weizmann.ac.il/cards/) project are described, including the addition of gene expression profiles and integrated gene locations. Also highlighted are the contributions of specialized associated human gene-centric databases developed at the Weizmann Institute. These include the Unified Database (UDB) (http://bioinfo.weizmann.ac.il/udb) for human genome mapping, the human Chromosome 21 database at the Weizmann Insti-tute (CroW 21) (http://bioinfo.weizmann.ac.il/crow21), and the Human Olfactory Receptor Data Explora-torium (HORDE) (http://bioinfo.weizmann.ac.il/HORDE). The synergistic relationships amongst these efforts have positively impacted the quality, quantity and usefulness of the GeneCards gene compendium.     

Carbon and nitrogen availability in paddy soil affects rice photosynthate allocation,microbial community composition,and priming: combining continuous 13C labeling with PLFA analysis

Plant and Soil - Soil alkalization imposes severe ion toxicity, osmotic stress, and high pH stress to plants, inhibiting their growth and productivity. NaHCO3 is a main component of alkaline soil....     

Root exudate components change litter decomposition in a simulated rhizosphere depending on temperature

The release of root exudates into the rhizosphere is known to enhance soil biological activity and alter microbial community structure. To assess whether root exudates also stimulated litter decomposition, in a rhizosphere model system we continuously injected solutions of glucose, malate or glutamate through porous Rhizon^® soil solution samplers into the soil at rhizosphere concentrations. The effect of these substances on the decomposition of ¹⁴C-labelled Lolium perenne shoot residues present in the soil was evaluated by monitoring ¹⁴CO₂ evolution at either 15°C or 25°C. The incorporation of the ¹⁴C into the microbial biomass and appearance in the dissolved organic matter (DOM) pool was estimated after 32 d incubation. The presence of malate and glutamate increased the mineralization of L. perenne residues by approximately 20% relative to the soil without their addition at 15°C, however, no significant effects on residue decomposition were observed at 25°C. The incorporation of the ¹⁴C-label into the microbial biomass and DOM pool was not affected by the addition of either glucose, malate or glutamate. Although nearly the same amount of L. perenne residues were mineralized at either temperature after 32 d, less ¹⁴C was recovered in the microbial biomass and DOM pools at 25°C compared to 15°C. Alongside other results, this suggests that the rate of microbial turnover is greater at 25°C compared to 15°C. We conclude that the addition of labile root exudate components to the rhizosphere induced a small but significant increase on litter decomposition but that the magnitude of this effect was regulated by temperature.