Climate change goes underground: effects of elevated atmospheric CO2 on microbial community structure and activities in the rhizosphere.

General concern about climate change has led to growing interest in the responses of terrestrial ecosystems to elevated concentrations of CO2 in the atmosphere. Experimentation during the last two to three decades using a large variety of approaches has provided sufficient information to conclude that enrichment of atmospheric CO2 may have severe impact on terrestrial ecosystems. This impact is mainly due to the changes in the organic C dynamics as a result of the effects of elevated CO2 on the primary source of organic C in soil, i.e., plant photosynthesis. As the majority of life in soil is heterotrophic and dependent on the input of plant-derived organic C, the activity and functioning of soil organisms will greatly be influenced by changes in the atmospheric CO2 concentration. In this review, we examine the current state of the art with respect to effects of elevated atmospheric CO2 on soil microbial communities, with a focus on microbial community structure. On the basis of the existing information, we conclude that the main effects of elevated atmospheric CO2 on soil microbiota occur via plant metabolism and root secretion, especially in C3 plants, thereby directly affecting the mycorrhizal, bacterial, and fungal communities in the close vicinity of the root. There is little or no direct effect on the microbial community of the bulk soil. In particular, we have explored the impact of these changes on rhizosphere interactions and ecosystem processes, including food web interactions

Local Soft Tissue Compression Enhances Fracture Healing in a Rabbit Fibula

Local soft tissue compression of fractures enhances fracture healing. The mechanism remains uncertain. Past studies have focused on intermittent soft tissue compression. We report a preliminary study assessing the relationship between constant soft tissue compression and enhanced fracture healing in an osteotomy model designed to minimize confounding variables. Fibulae of nine New Zealand white rabbits were bilaterally osteotomized, openly stabilized, and fitted with spandex stockinets. Soft tissue at the osteotomy site was unilaterally compressed using a deforming element (load = 26 mmHg). The contralateral side was saved as the control and was not compressed. Osteotomies were monitored with weekly radiographs. All fibulae in both groups were healed 6 weeks postoperatively. Micro-CT analysis of bone mineral density (BMD) and bone volume (BV) was then performed on both the experimental and control sides. Radiographic measurement of transverse callus-to-shaft ratios (TCSR) was compared. BMD of the experimental callus was greater than the noncompressed controls. BV and TCSR were not different between controls and experimental osteotomies. Constant local soft tissue compression produced significant increases in BMD, but not in BV or transverse callus size, indicating significant measurable increases in callus composition without significant change in gross dimensions. Our experimental design minimizes confounding factors, such as micromotion, immobilization, and altered venous flow, suggesting that these are not the primary mechanisms for fracture healing enhancement. Further studies with more animals and study groups are necessary to confirm efficacy and identify optimal compression pressures and schedules