Trees adjust nutrient acquisition strategies across tropical forest secondary succession.

Nutrient limitation may constrain the ability of recovering and mature tropical forests to serve as a carbon sink. However, it is unclear to what extent trees can utilize nutrient acquisition strategies - especially root phosphatase enzymes and mycorrhizal symbioses - to overcome low nutrient availability across secondary succession. Using a large-scale, full factorial nitrogen and phosphorus fertilization experiment of 76 plots along a secondary successional gradient in lowland wet tropical forests of Panama, we tested the extent to which root phosphatase enzyme activity and mycorrhizal colonization are flexible, and if investment shifts over succession, reflective of changing nutrient limitation.

Leaf N:P ratio does not predict productivity trends across natural terrestrial ecosystems.

Nitrogen (N) and phosphorus (P) are crucial nutrients for regulating plant growth. The classic growth rate hypothesis (GRH) proposes that fast-growing organisms have lower N:P ratios, and it is promising to predict net primary productivity (NPP) using the leaf N:P ratio at the community level (N:P ). However, whether leaf N:P ratio can predict NPP in natural ecosystems on a large scale remains nebulous.

Dysbiosis of the Salivary Microbiome is Associated with Hypertension and Correlated with Metabolic Syndrome Biomarkers.

Background: Hypertension (HT) is an idiopathic disease with severe complications and a high incidence of global mortality. Although the disease shares characteristic features with diabetes and obesity, the complex interplay of endogenous and environmental factors is not well characterized. The oral microbiome has recently been studied to better understand the role of commensal microorganisms in metabolic disorders, including HT, although its role in disease etiology is unclear.

Legume-microbiome interactions unlock mineral nutrients in regrowing tropical forests.

Legume trees form an abundant and functionally important component of tropical forests worldwide with N-fixing symbioses linked to enhanced growth and recruitment in early secondary succession. However, it remains unclear how N-fixers meet the high demands for inorganic nutrients imposed by rapid biomass accumulation on nutrient-poor tropical soils. Here, we show that N-fixing trees in secondary Neotropical forests triggered twofold higher in situ weathering of fresh primary silicates compared to non-N-fixing trees and induced locally enhanced nutrient cycling by the soil microbiome community.

Publisher Correction: Global plant-symbiont organization and emergence of biogeochemical cycles resolved by evolution-based trait modelling.

An amendment to this paper has been published and can be accessed via a link at the top of the paper.

Tropical carbon sink accelerated by symbiotic dinitrogen fixation.

A major uncertainty in the land carbon cycle is whether symbiotic nitrogen fixation acts to enhance the tropical forest carbon sink. Nitrogen-fixing trees can supply vital quantities of the growth-limiting nutrient nitrogen, but the extent to which the resulting carbon-nitrogen feedback safeguards ecosystem carbon sequestration remains unclear. We combine (i) field observations from 112 plots spanning 300 years of succession in Panamanian tropical forests, and (ii) a new model that resolves nitrogen and light competition at the scale of individual trees.

Rapid nitrogen fixation by canopy microbiome in tropical forest determined by both phosphorus and molybdenum.

Biological nitrogen fixation is critical for the nitrogen cycle of tropical forests, yet we know little about the factors that control the microbial nitrogen fixers that colonize the microbiome of leaves and branches that make up a forest canopy. Forest canopies are especially prone to nutrient limitation because they are (1) disconnected from soil nutrient pools and (2) often subject to leaching. Earlier studies have suggested a role of phosphorus and molybdenum in controlling biological N-fixation rates, but experimental confirmation has hitherto been unavailable.

Author Correction: Evolutionary history resolves global organization of root functional traits.

We thank reader Joseph Craine for pointing out three inadvertent errors in this Letter. First, 4 of the 71 divergence dates extracted from ref. of this Amendment and used in Fig.

Nitrogen fixation does not balance fire-induced nitrogen losses in longleaf pine savannas.

Fire is a critical force in structuring ecosystems, but it also removes substantial amounts of nitrogen (N), which can limit plant growth. Biological N fixation (BNF) may alleviate fire-induced N deficiencies that inhibit ecosystem recovery, yet if and how BNF achieves this under frequent fire is unclear. This problem is further complicated in the context of modern human influences (such as land-use history and atmospheric N deposition), which may confound the relationship between fire and fixation.

Global plant-symbiont organization and emergence of biogeochemical cycles resolved by evolution-based trait modelling.

One of the most distinct but unresolved global patterns is the apparent variation in plant-symbiont nutrient strategies across biomes. This pattern is central to our understanding of plant-soil-nutrient feedbacks in the land biosphere, which, in turn, are essential for our ability to predict the future dynamics of the Earth system. Here, we present an evolution-based trait-modelling approach for resolving (1) the organization of plant-symbiont relationships across biomes worldwide and (2) the emergent consequences for plant community composition and land biogeochemical cycles.

Phosphatase activity and nitrogen fixation reflect species differences, not nutrient trading or nutrient balance, across tropical rainforest trees.

A fundamental biogeochemical paradox is that nitrogen-rich tropical forests contain abundant nitrogen-fixing trees, which support a globally significant tropical carbon sink. One explanation for this pattern holds that nitrogen-fixing trees can overcome phosphorus limitation in tropical forests by synthesizing phosphatase enzymes to acquire soil organic phosphorus, but empirical evidence remains scarce. We evaluated whether nitrogen fixation and phosphatase activity are linked across 97 trees from seven species, and tested two hypotheses for explaining investment in nutrient strategies: trading nitrogen-for-phosphorus or balancing nutrient demand.

Erratum: Evolutionary history resolves global organization of root functional traits.

This corrects the article DOI: 10.1038/nature25783.

Phosphorus and species regulate N fixation by herbaceous legumes in longleaf pine savannas.

Longleaf pine savannas house a diverse community of herbaceous N-fixing legume species that have the potential to replenish nitrogen (N) losses from fire. Whether legumes fill this role depends on the factors that regulate symbiotic fixation, including soil nutrients such as phosphorus (P) and molybdenum (Mo) and the growth and fixation strategies of different species. In greenhouse experiments, we determined how these factors influence fixation for seven species of legumes grown in pure field soil from two different regions of the southeastern US longleaf pine ecosystem.

Evolutionary history resolves global organization of root functional traits.

Plant roots have greatly diversified in form and function since the emergence of the first land plants, but the global organization of functional traits in roots remains poorly understood. Here we analyse a global dataset of 10 functionally important root traits in metabolically active first-order roots, collected from 369 species distributed across the natural plant communities of 7 biomes. Our results identify a high degree of organization of root traits across species and biomes, and reveal a pattern that differs from expectations based on previous studies of leaf traits.

Soils and fire jointly determine vegetation structure in an African savanna.

Savanna vegetation is variable, and predicting how water, nutrients, and chronic disturbances interact to determine vegetation structure in savannas represents a challenge. Here, we examined in situ interactions among rainfall, soils, grasses, fire, and elephants that determine tree layer responses to resource gradients in Kruger National Park in South Africa, using 363 long-term monitoring sites throughout the park. Grass biomass increased with rainfall and on nutrient-rich clay soils.

N-fixing tropical legume evolution: a contributor to enhanced weathering through the Cenozoic?

Fossil and phylogenetic evidence indicates legume-rich modern tropical forests replaced Late Cretaceous palm-dominated tropical forests across four continents during the early Cenozoic (58-42 Ma). Tropical legume trees can transform ecosystems via their ability to fix dinitrogen (N) and higher leaf N compared with non-legumes (35-65%), but it is unclear how their evolutionary rise contributed to silicate weathering, the long-term sink for atmospheric carbon dioxide (CO). Here we hypothesize that the increasing abundance of N-fixing legumes in tropical forests amplified silicate weathering rates by increased input of fixed nitrogen (N) to terrestrial ecosystems via interrelated mechanisms including increasing microbial respiration and soil acidification, and stimulating forest net primary productivity.

Aridity, not fire, favors nitrogen-fixing plants across tropical savanna and forest biomes.

Tropical savannas are hypothesized to be hot spots of nitrogen-fixer diversity and activity because of the high disturbance and low nitrogen characteristic of savanna landscapes. Here we compare the abundances of nitrogen-fixing and non-fixing trees in both tropical savannas and tropical forests under climatically equivalent conditions, using plant inventory studies across 566 plots in South America and Africa. A single factor, aridity, explained 19-54% of the variance in fixer abundance, and unexpectedly was more important than fire frequency, biome, and continent.

Bendamustine, etoposide and dexamethasone to mobilize peripheral blood hematopoietic stem cells for autologous transplantation in patients with multiple myeloma.

Chemotherapeutic agents without cross-resistance to prior therapies may enhance PBSC collection and improve patient outcomes by exacting a more potent direct antitumor effect before autologous stem cell transplant. Bendamustine has broad clinical activity in transplantable lymphoid malignancies, but concern remains over the potential adverse impact of this combined alkylator-nucleoside analog on stem cell mobilization. We performed a prospective, nonrandomized phase II study including 34 patients with multiple myeloma (MM) (n=34; International Staging System (ISS) stages I (35%), II (29%) and III (24%); not scored (13%)) to evaluate bendamustine's efficacy and safety as a stem cell mobilizing agent.

Taxonomic identity determines N2 fixation by canopy trees across lowland tropical forests.

Legumes capable of fixing atmospheric N2 are abundant and diverse in many tropical forests, but the factors determining ecological patterns in fixation are unresolved. A long-standing idea is that fixation depends on soil nutrients (N, P or Mo), but recent evidence shows that fixation may also differ among N2-fixing species. We sampled canopy-height trees across five species and one species group of N2-fixers along a landscape P gradient, and manipulated P and Mo to seedlings in a shadehouse.

Microbiota and the control of blood-tissue barriers.

The gastro-intestinal tract is an ecosystem containing trillions of commensal bacteria living in symbiosis with the host. These microbiota modulate a variety of our physiological processes, including production of vitamins, absorption of nutrients and development of the immune system. One of their major functions is to fortify the intestinal barrier, thereby helping to prevent pathogens and harmful substances from crossing into the general circulation.

Fire alters ecosystem carbon and nutrients but not plant nutrient stoichiometry or composition in tropical savanna.

Fire and nutrients interact to influence the global distribution and dynamics of the savanna biome, but the results of these interactions are both complex and poorly known. A critical but unresolved question is whether short-term losses of carbon and nutrients caused by fire can trigger long-term and potentially compensatory responses in the nutrient stoichiometry of plants, or in the abundance of dinitrogen-fixing trees. There is disagreement in the literature about the potential role of fire on savanna nutrients, and, in turn, on plant stoichiometry and composition.