Microbial carbon use efficiency: accounting for population, community, and ecosystem-scale controls over the fate of metabolized organic matter

Microbial carbon use efficiency (CUE) is a critical regulator of soil organic matter dynamics and terrestrial carbon fluxes, with strong implications for soil biogeochemistry models. While ecologists increasingly appreciate the importance of CUE, its core concepts remain ambiguous: terminology is inconsistent and confusing, methods capture variable temporal and spatial scales, and the significance of many fundamental drivers remains inconclusive. Here we outline the processes underlying microbial efficiency and propose a conceptual framework that structures the definition of CUE according to increasingly broad temporal and spatial drivers where (1) CUEP reflects population-scale carbon use efficiency of microbes governed by species-specific metabolic and thermodynamic constraints, (2) CUEC defines community-scale microbial efficiency as gross biomass production per unit substrate taken up over short time scales, largely excluding recycling of microbial necromass and exudates, and (3) CUEE reflects the ecosystem-scale efficiency of net microbial biomass production (growth) per unit substrate taken up as iterative breakdown and recycling of microbial products occurs. CUEE integrates all internal and extracellular constraints on CUE and hence embodies an ecosystem perspective that fully captures all drivers of microbial biomass synthesis and decay. These three definitions are distinct yet complementary, capturing the capacity for carbon storage in microbial biomass across different ecological scales. By unifying the existing concepts and terminology underlying microbial efficiency, our framework enhances data interpretation and theoretical advances

A click chemistry-based, free radical-initiated delivery system for the capture and release of payloads

AbstractClick chemistries are efficient and selective reactions that have been leveraged for multi-stage drug delivery. A multi-stage system allows independent delivery of targeting molecules and drug payloads, but targeting first-phase materials specifically to disease sites remains a challenge. Stimuli-responsive systems are an emerging strategy where common pathophysiological triggers are used to target payloads. Oxidative stress is widely implicated in disease, and we have previously demonstrated that reactive oxygen species (ROS) can crosslink and immobilize polyethylene glycol diacrylate (PEGDA) in tissue mimics. To build on these promising results, we present a two-step, catch-and-release system using azide-DBCO click chemistry and demonstrate the capture and eventual release of a fluorescent payload at defined times after the formation of a PEGDA capturing net. The azide component is included with radical-sensitive PEGDA, and the payload is conjugated to the DBCO group. In cell-free and cell-based tissue mimic models, azides were incorporated at 0–30% in the first-phase polymer net, and DBCO was delivered at 2.5–10 µM in the second phase to control payload delivery. The payload could be captured at multiple timepoints after initial net formation, yielding a flexible and versatile targeting system. Matrix metalloproteinase (MMP)-degradable peptides were incorporated into the polymer backbone to engineer fluorescent payload release by MMPs, which are broadly upregulated in diseases, through degradation of the capture net and directly from the DBCO. Taken together, this research demonstrates proof-of-principle for a responsive and clickable biomaterial to serve as a multi-potent agent for the treatment of diseases compounded by high free radicals

The conversion of even-aged stands to uneven-aged structure in southern New England

Partial cutting is common in mature even-aged stands in southern New England because the level of disturbance associated with even-aged regeneration methods is unacceptable to many private owners of small forest properties. This cutting often consists of high-grading, but foresters seeking an alternative generally turn to the selection method to begin the conversion of these stands to uneven-aged structure. However, the single-tree or small-group selection methods used may produce long-term results that are similar to high-grading in shifting stand composition toward shade tolerant species (many of which have low timber value). A review was made of the extensive research on the use of the selection method in northern New England and central Appalachian forest types, as well as of the limited research in the southern New England transition hardwood-white pine (Pinus strobus)-hemlock (Tsuga canadensis) type. Recent management experience in a Massachusetts public watershed forest was also reviewed. These provide general guidelines for using selection cutting in the region to regenerate species of a wide range in shade tolerance: (a) use patch selection (rather than single-tree or group selection) with a minimum patch size of 0.3 ac, and with understory as well as overstory trees removed in the patches; (b) use area control (proportion of stand to be harvested) rather than a target diameter distribution (q-value or other method) to regulate the stand cutting level. This approach is likely to be effective in meeting regeneration goals and in being logistically feasible, given the intensity of management possible on most of these properties

Massachusetts: Managing a watershed protection forest

The Quabbin forest of central Massachusetts is the first barrier to contamination at the source of Boston\u27s water supply. An interdisciplinary team is implementing an uneven-aged management strategy to create a watershed protection forest that both ensures water quality and enhances site productivity, biological diversity, and cultural resources. Adapting to changing conditions and learning from experience define this approach to interdisciplinary forestry. Recent green certification by SmartWood provided external review of the public forest\u27s sustainability. Quabbin managers hope to lead local private landowners by their example