Long-lasting effects of land use history on soil fungal communities in second-growth tropical rain forests

Our understanding of the long-lasting effects of human land use on soil fungal communities in tropical forests is limited. Yet, over 70% of all remaining tropical forests are growing in former agricultural or logged areas. We investigated the relationship among land use history, biotic and abiotic factors, and soil fungal community composition and diversity in a second-growth tropical forest in Puerto Rico. We coupled high-throughput DNA sequencing with tree community and environmental data to determine whether land use history had an effect on soil fungal community descriptors. We also investigated the biotic and abiotic factors that underlie such differences and asked whether the relative importance of biotic (tree diversity, basal tree area, and litterfall biomass) and abiotic (soil type, pH, iron, and total carbon, water flow, and canopy openness) factors in structuring soil fungal communities differed according to land use history. We demonstrated long-lasting effects of land use history on soil fungal communities. At our research site, most of the explained variation in soil fungal composition (R2 = 18.6%), richness (R2 = 11.4%), and evenness (R2 = 10%) was associated with edaphic factors. Areas previously subject to both logging and farming had a soil fungal community with lower beta diversity and greater evenness of fungal operational taxonomic units (OTUs) than areas subject to light logging. Yet, fungal richness was similar between the two areas of historical land use. Together, these results suggest that fungal communities in disturbed areas are more homogeneous and diverse than in areas subject to light logging. Edaphic factors were the most strongly correlated with soil fungal composition, especially in areas subject to light logging, where soils are more heterogenous. High functional tree diversity in areas subject to both logging and farming led to stronger correlations between biotic factors and fungal composition than in areas subject to light logging. In contrast, fungal richness and evenness were more strongly correlated with biotic factors in areas of light logging, suggesting that these metrics might reflect long-term associations in old-growth forests. The large amount of unexplained variance in fungal composition suggests that these communities are structured by both stochastic and niche assemblage processes

Age does not predict need for reintervention in patients with critical limb ischemia

ObjectiveConventional wisdom holds that patients with a need for intervention for femoropopliteal occlusive disease at a younger age have more aggressive disease, although there is a paucity of support in the literature. The purpose of this study was to evaluate this assumption.MethodsA retrospective cohort of patients undergoing endovascular or open revascularization for femoropopliteal occlusive disease for critical limb ischemia during a 4-year period was assembled. Demographic information, comorbidities, disease characteristics, and time to last follow-up, repeat intervention, amputation, or death was recorded. The patients were stratified by age into a young (≤55 years) group, middle (56-77 years) group, and elderly (≥78 years) group. Univariate and multivariate statistical methods were used to evaluate the primary outcome.ResultsThe study included 124 patients with a mean age of 64.4 ± 0.8 years. Progression to reintervention or amputation occurred in 50% of the patients during the follow-up period, with 18% dying before having an outcome. Kaplan-Meier analysis showed a trend toward significance (P = .06) in time to reintervention, amputation, or death among the three groups, with time to event of 253, 1083, and 504 days for the young, middle, and elderly groups, respectively. However, differences based on age were not significant (P = .57) in Cox regression analysis.ConclusionsThere does not appear to be an association between time to reintervention and patient age