Biogeochemistry is a key but relatively neglected part of the abiotic template that underlies ecology. The template has a geography, one that is increasingly being rearranged in this era of global ...change. Justus von Liebig’s law of the minimum has played a useful role in focusing attention on biogeochemical regulation of populations, but given that ∼25+ elements are required to build organisms and that these organisms use and deplete nutrients in aggregates of communities and ecosystems, we make the case that it is time to move on. We review available models that suggest the many different mechanisms that give rise to multiple elements, or colimitation. We then review recent empirical data that show that rates of decomposition and primary productivity may be limited by multiple elements. In that light, given the tropics’ high species diversity and generally more weathered soils, we predict that colimitation at community and ecosystem scales is more prevalent closer to the equator. We conclude with suggestions for how to move forward with experimental studies of colimitation.
In the United States, chronic ulcers--including decubitus, vascular, inflammatory, and rheumatologic subtypes--affect >6 million people, with increasing numbers anticipated in our growing elderly and ...diabetic populations. These wounds cause significant morbidity and mortality and lead to significant medical costs. Preventative and treatment measures include disease-specific approaches and the use of moisture retentive dressings and adjunctive topical therapies to promote healing. In this article, we discuss recent advances in wound care technology and current management guidelines for the treatment of wounds and ulcers.
Hanging by a thread? Forests and drought Brodribb, Timothy J; Powers, Jennifer; Cochard, Hervé ...
Science (American Association for the Advancement of Science),
04/2020, Letnik:
368, Številka:
6488
Journal Article
Recenzirano
Trees are the living foundations on which most terrestrial biodiversity is built. Central to the success of trees are their woody bodies, which connect their elevated photosynthetic canopies with the ...essential belowground activities of water and nutrient acquisition. The slow construction of these carbon-dense, woody skeletons leads to a slow generation time, leaving trees and forests highly susceptible to rapid changes in climate. Other long-lived, sessile organisms such as corals appear to be poorly equipped to survive rapid changes, which raises questions about the vulnerability of contemporary forests to future climate change. The emerging view that, similar to corals, tree species have rather inflexible damage thresholds, particularly in terms of water stress, is especially concerning. This Review examines recent progress in our understanding of how the future looks for forests growing in a hotter and drier atmosphere.
The carbon use efficiency (CUE) of microbial communities partitions the flow of C from primary producers to the atmosphere, decomposer food webs, and soil C stores. CUE, usually defined as the ratio ...of growth to assimilation, is a critical parameter in ecosystem models, but is seldom measured directly in soils because of the methodological difficulty of measuring in situ rates of microbial growth and respiration. Alternatively, CUE can be estimated indirectly from the elemental stoichiometry of organic matter and microbial biomass, and the ratios of C to nutrient-acquiring ecoenzymatic activities. We used this approach to estimate and compare microbial CUE in >2000 soils from a broad range of ecosystems. Mean CUE based on C:N stoichiometry was 0.269 ± 0.110 (mean ± SD). A parallel calculation based on C:P stoichiometry yielded a mean CUE estimate of 0.252 ± 0.125. The mean values and frequency distributions were similar to those from aquatic ecosystems, also calculated from stoichiometric models, and to those calculated from direct measurements of bacterial and fungal growth and respiration. CUE was directly related to microbial biomass C with a scaling exponent of 0.304 (95% CI 0.237–0.371) and inversely related to microbial biomass P with a scaling exponent of –0.234 (95% CI –0.289 to –0.179). Relative to CUE, biomass specific turnover time increased with a scaling exponent of 0.509 (95% CI 0.467–0.551). CUE increased weakly with mean annual temperature. CUE declined with increasing soil pH reaching a minimum at pH 7.0, then increased again as soil pH approached 9.0, a pattern consistent with pH trends in the ratio of fungal:bacteria abundance and growth. Structural equation models that related geographic variables to CUE component variables showed the strongest connections for paths linking latitude and pH to β-glucosidase activity and soil C:N:P ratios. The integration of stoichiometric and metabolic models provides a quantitative description of the functional organization of soil microbial communities that can improve the representation of CUE in microbial process and ecosystem simulation models.
We assessed whether diversity in plant hydraulic traits can explain the observed diversity in plant responses to water stress in seasonally dry tropical forests (SDTFs).
The Ecosystem Demography ...model 2 (ED2) was updated with a trait-driven mechanistic plant hydraulic module, as well as novel drought-phenology and plant water stress schemes. Four plant functional types were parameterized on the basis of meta-analysis of plant hydraulic traits. Simulations from both the original and the updated ED2 were evaluated against 5 yr of field data from a Costa Rican SDTF site and remote-sensing data over Central America.
The updated model generated realistic plant hydraulic dynamics, such as leaf water potential and stem sap flow. Compared with the original ED2, predictions from our novel traitdriven model matched better with observed growth, phenology and their variations among functional groups. Most notably, the original ED2 produced unrealistically small leaf area index (LAI) and underestimated cumulative leaf litter. Both of these biases were corrected by the updated model. The updated model was also better able to simulate spatial patterns of LAI dynamics in Central America.
Plant hydraulic traits are intercorrelated in SDTFs. Mechanistic incorporation of plant hydraulic traits is necessary for the simulation of spatiotemporal patterns of vegetation dynamics in SDTFs in vegetation models.
The distribution of tropical forest biomass across the landscape is poorly understood, particularly in increasingly common secondary tropical forests. We studied the landscape-scale distribution of ...edaphic properties, plant community characteristics, and aboveground biomass (AGB) in secondary tropical dry forests in northwest Costa Rica. We used structural equation modeling to examine conceptual models of relationships among these factors, with data from 84 0.1 ha plots. Stand age and soils explained 33%â60% of the variation in community-weighted mean values of foliar traits including specific leaf area, foliar nitrogen, phosphorus, and δ¹³C. Aboveground biomass ranged from 1.7 to 409 Mg·haâ»Â¹ among plots between 5 and >100 years old. Stand age alone explained 46% of the variation in AGB among plots, while a model including age, soil pH, traits, and forest type explained 58%. Stand age was the most important variable explaining the distribution of AGB and community characteristics in secondary forests. We speculate that plot size, landscape heterogeneity, disturbance history, and stand dynamics contribute to the unexplained variation in AGB across the landscape.
Celotno besedilo
Dostopno za:
BF, DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Occupational sun exposure is a well-studied risk factor for skin cancer development, but more work is needed to assess melanoma and nonmelanoma skin cancer risk among US military personnel to improve ...education and screening efforts in this population.
To conduct an extensive review of skin cancer risks for US military personnel to inform preventive education, diagnosis, and treatment efforts to better protect these individuals from future skin cancer development.
A systematic review of published studies on the subject of melanoma and nonmelanoma skin cancer in military personnel was conducted.
A total of 9 studies describing skin cancer incidence in the US military were identified, with 4 studies specific to melanoma. The study findings reveal an increased risk for melanoma associated with service in the military or prisoner of war status. Service in tropical environments was associated with an increased incidence of both melanoma and nonmelanoma skin cancer among World War II soldiers. Two studies found that increased melanoma risk was also branch dependent, with the highest rates among the United States Air Force. Several of the reviewed studies implicated increased sun exposure during military service and lack of sufficient sun protection as the causes of higher rates of skin cancer among US military and veteran populations as compared with among the nonmilitary population in the United States.
The reviewed articles have variable results; a prospective randomized controlled trial would be helpful to develop interventions that mitigate skin cancer risk in the US military.
This review identifies an abundance of evidence for an increased risk for skin cancer development among US active duty and veteran populations.
Secondary tropical forests that are in a state of regeneration following clearing for agriculture are now more abundant than primary forests. Yet, despite their large spatial extent and important ...role in the global carbon (C) cycle, secondary tropical forests are understudied, which challenges our ability to predict how tropical landscapes will respond to future disturbance and global change. We summarize research advances on alterations to C and nutrient dynamics during reforestation and how these are influenced by ecosystem state factors. During forest succession, aboveground biomass stocks and litter fluxes increase in a predictable way, but patterns in soil C dynamics are highly variable. The heterogeneous response of nutrients to reforestation is influenced by multiple factors, including losses incurred during prior land use and management. In contrast to primary tropical forests, where productivity is often limited by rock-derived nutrients, secondary forest growth may be more limited by nutrients from the atmosphere. Future research should identify which nutrients constrain forest regrowth.
PDF
