Multi-Element Regulation of the Tropical Forest Carbon Cycle

Tropical ecosystems dominate the exchange of carbon dioxide between the atmosphere and terrestrial biosphere, yet our understanding of how nutrients control the tropical carbon (C) cycle remains far from complete. In part, this knowledge gap arises from the marked complexity of the tropical forest biome, in which nitrogen, phosphorus, and perhaps several other elements may play roles in determining rates of C gain and loss. As studies from other ecosystems show, failing to account for nutrient–C interactions can lead to substantial errors in predicting how ecosystems will respond to climate and other environmental changes. Thus, although resolving the complex nature of tropical forest nutrient limitation – and then incorporating such knowledge into predictive models – will be difficult, it is a challenge that the global change community must address

The soil and plant biogeochemistry sampling design for The National Ecological Observatory Network

Human impacts on biogeochemical cycles are evident around the world, from changes to forest structure and function due to atmospheric deposition, to eutrophication of surface waters from agricultural effluent, and increasing concentrations of carbon dioxide (CO2) in the atmosphere. The National Ecological Observatory Network (NEON) will contribute to understanding human effects on biogeochemical cycles from local to continental scales. The broad NEON biogeochemistry measurement design focuses on measuring atmospheric deposition of reactive mineral compounds and CO2 fluxes, ecosystem carbon (C) and nutrient stocks, and surface water chemistry across 20 eco‐climatic domains within the United States for 30 yr. Herein, we present the rationale and plan for the ground‐based measurements of C and nutrients in soils and plants based on overarching or “high‐level” requirements agreed upon by the National Science Foundation and NEON. The resulting design incorporates early recommendations by expert review teams, as well as recent input from the larger natural sciences community that went into the formation and interpretation of the requirements, respectively. NEON\u27s efforts will focus on a suite of data streams that will enable end‐users to study and predict changes to biogeochemical cycling and transfers within and across air, land, and water systems at regional to continental scales. At each NEON site, there will be an initial, one‐time effort to survey soil properties to 1 m (including soil texture, bulk density, pH, baseline chemistry) and vegetation community structure and diversity. A sampling program will follow, focused on capturing long‐term trends in soil C, nitrogen (N), and sulfur stocks, isotopic composition (of C and N), soil N transformation rates, phosphorus pools, and plant tissue chemistry and isotopic composition (of C and N). To this end, NEON will conduct extensive measurements of soils and plants within stratified random plots distributed across each site. The resulting data will be a new resource for members of the scientific community interested in addressing questions about long‐term changes in continental‐scale biogeochemical cycles, and is predicted to inspire further process‐based research

Omni-conducting and omni-insulating molecules

The source and sink potential model is used to predict the existence of omni-conductors (and omni-insulators): molecular conjugated π systems that respectively support ballistic conduction or show insulation at the Fermi level, irrespective of the centres chosen as connections. Distinct, ipso, and strong omni-conductors/omni-insulators show Fermi-level conduction/insulation for all distinct pairs of connections, for all connections via a single centre, and for both, respectively. The class of conduction behaviour depends critically on the number of non-bonding orbitals (NBO) of the molecular system (corresponding to the nullity of the graph). Distinct omni-conductors have at most one NBO; distinct omni-insulators have at least two NBO; strong omni-insulators do not exist for any number of NBO. Distinct omni-conductors with a single NBO are all also strong and correspond exactly to the class of graphs known as nut graphs. Families of conjugated hydrocarbons corresponding to chemical graphs with predicted omni-conducting/insulating behaviour are identified. For example, most fullerenes are predicted to be strong omni-conductors

Prognostic model to predict postoperative acute kidney injury in patients undergoing major gastrointestinal surgery based on a national prospective observational cohort study.

Background: Acute illness, existing co-morbidities and surgical stress response can all contribute to postoperative acute kidney injury (AKI) in patients undergoing major gastrointestinal surgery. The aim of this study was prospectively to develop a pragmatic prognostic model to stratify patients according to risk of developing AKI after major gastrointestinal surgery. Methods: This prospective multicentre cohort study included consecutive adults undergoing elective or emergency gastrointestinal resection, liver resection or stoma reversal in 2-week blocks over a continuous 3-month period. The primary outcome was the rate of AKI within 7 days of surgery. Bootstrap stability was used to select clinically plausible risk factors into the model. Internal model validation was carried out by bootstrap validation. Results: A total of 4544 patients were included across 173 centres in the UK and Ireland. The overall rate of AKI was 14·2 per cent (646 of 4544) and the 30-day mortality rate was 1·8 per cent (84 of 4544). Stage 1 AKI was significantly associated with 30-day mortality (unadjusted odds ratio 7·61, 95 per cent c.i. 4·49 to 12·90; P < 0·001), with increasing odds of death with each AKI stage. Six variables were selected for inclusion in the prognostic model: age, sex, ASA grade, preoperative estimated glomerular filtration rate, planned open surgery and preoperative use of either an angiotensin-converting enzyme inhibitor or an angiotensin receptor blocker. Internal validation demonstrated good model discrimination (c-statistic 0·65). Discussion: Following major gastrointestinal surgery, AKI occurred in one in seven patients. This preoperative prognostic model identified patients at high risk of postoperative AKI. Validation in an independent data set is required to ensure generalizability

A new synthesis for terrestrial nitrogen inputs

Nitrogen (N) inputs sustain many different aspects of local soil processes, their services, and their interactions with the broader Earth system. We present a new synthesis for terrestrial N inputs that explicitly considers both rock and atmospheric sources of N. We review evidence for state-factor regulation over biological fixation, deposition, and rock-weathering inputs from local to global scales and in transient vs. steady-state landscapes. Our investigation highlights strong organism and topographic (relief) controls over all three N input pathways, with the anthropogenic factor clearly important in rising N deposition rates. In addition, the climate, parent material, and time factors are shown to influence patterns of fixation and rock-weathering inputs of N in diverse soil systems. Data reanalysis suggests that weathering of N-rich parent material could resolve several known cases of "missing N inputs" in ecosystems, and demonstrates how the inclusion of rock N sources into modern concepts can lead to a richer understanding of spatial and temporal patterns of ecosystem N availability. For example, explicit consideration of rock N inputs into classic pedogenic models (e.g., the Walker and Syers model) yields a fundamentally different expectation from the standard case: weathering of N-rich parent material could enhance N availability and facilitate terrestrial succession in developmentally young sites even in the absence of N-fixing organisms. We conclude that a state-factor framework for N complements our growing understanding multiple-source controls on phosphorus and cation availability in Earth's soil, but with significant exceptions given the lack of an N fixation analogue in all other biogeochemical cycles. Rather, non-symmetrical feedbacks among input pathways in which high N inputs via deposition or rock-weathering sources have the potential to reduce biological fixation rates mark N as fundamentally different from other nutrients. The new synthesis for terrestrial N inputs provides a novel set of research issues and opportunities in the multidisciplinary Earth system sciences, with implications for patterns of N limitation, tectonic controls over biogeochemical cycling, and carbon–nutrient–climate interactions

Nutrient Limitations of Carbon Uptake: From Leaves to Landscapes in a California Rangeland Ecosystem

Nutrient controls of ecosystem pattern and process have been widely studied at the Jasper Ridge Biological Preserve, a well-studied California rangeland ecosystem. Here we review these studies, from leaf to landscape scales, with the intention of developing a deeper understanding of carbon (C)-nutrient interactions in such an ecosystem. At the leaf scale, several studies conducted on diverse plant species have revealed a strong positive relationship between leaf nitrogen (N) concentrations and maximal rates of photosynthesis. This relationship, which has subsequently been observed globally, can be explained by the nutritional requirements of photosynthetic machinery. Consistent with this local physiological constraint, N availability has been shown to limit carbon uptake of California rangeland ecosystems. In some cases phosphorus (P; and N plus P) limits productivity, too—particularly in serpentine soils, pointing to the importance of parent material in regulating CO2 uptake at landscape scales. Nutrient dynamics are also affected by herbivory, which seems to accelerate N and P cycles over the short term (years), but may lead to nutrient limitation of plant production over the longer term (decades). Simulated global change experiments at Jasper Ridge have also provided insight into C-nutrient interactions in grasslands. In particular, several field- based experiments have shown that CO2 doubling does not necessarily simulate productivity of California grasslands; rather, the strength and sign of net primary productivity (NPP) responses to CO2 doubling varies across years and conditions. Although simulated N deposition stimulates NPP, N plus CO2 combinations do not necessarily increase productivity beyond N treatments singly. Poorly understood feedbacks between plants, microbes, and P availability may underlie variation in the response of California grasslands to increasing atmospheric CO2 concentrations. We conclude that interactions between C, N, and P appear especially vital in shaping plant productivity patterns in California rangelands and the capacity of this ecosystem to store additional C in the future. The Rangeland Ecology & Management archives are made available by the Society for Range Management and the University of Arizona Libraries. Contact [email protected] for further information.Migrated from OJS platform August 202

Isotopic identification of nitrogen hotspots across natural terrestrial ecosystems

Nitrogen (N) influences local biological processes, ecosystem productivity, the composition of the atmospheric-climate system, and the human endeavour as a whole. Here we use natural variations in N isotopes, coupled with two models, to trace global pathways of N loss from the land to the water and atmosphere. We show that denitrification accounts for approximately 35 % of total N losses from the natural soil, with NO, N&lt;sub&gt;2&lt;/sub&gt;O, and N&lt;sub&gt;2&lt;/sub&gt; fluxes equal to 15.7 &amp;plusmn; 4.7 Tg N yr&lt;sup&gt;−1&lt;/sup&gt;, 10.2 &amp;plusmn; 3.0 Tg N yr&lt;sup&gt;−1&lt;/sup&gt;, and 21.0 &amp;plusmn; 6.1 Tg N yr&lt;sup&gt;−1&lt;/sup&gt;, respectively. Our analysis points to tropical regions as the major "hotspot" of nitrogen export from the terrestrial biosphere, accounting for 71 % of global N losses from the natural land surface. The poorly studied Congo Basin is further identified as one of the major natural sources of atmospheric N&lt;sub&gt;2&lt;/sub&gt;O. Extra-tropical areas, by contrast, lose a greater fraction of N via leaching pathways (~77 % of total N losses) than do tropical biomes, likely contributing to N limitations of CO&lt;sub&gt;2&lt;/sub&gt; uptake at higher latitudes. Our results provide an independent constraint on global models of the N cycle among different regions of the unfertilized biosphere

Imprint of denitrifying bacteria on the global terrestrial biosphere

Loss of nitrogen (N) from land limits the uptake and storage of atmospheric CO2 by the biosphere, influencing Earth's climate system and myriads of the global ecological functions and services on which humans rely. Nitrogen can be lost in both dissolved and gaseous phases; however, the partitioning of these vectors remains controversial. Particularly uncertain is whether the bacterial conversion of plant available N to gaseous forms (denitrification) plays a major role in structuring global N supplies in the nonagrarian centers of Earth. Here, we use the isotope composition of N (15N/14N) to constrain the transfer of this nutrient from the land to the water and atmosphere. We report that the integrated 15N/14N of the natural terrestrial biosphere is elevated with respect to that of atmospheric N inputs. This cannot be explained by preferential loss of 14N to waterways; rather, it reflects a history of low 15N/14N gaseous N emissions to the atmosphere owing to denitrifying bacteria in the soil. Parameterizing a simple model with global N isotope data, we estimate that soil denitrification (including N2) accounts for ≈1/3 of the total N lost from the unmanaged terrestrial biosphere. Applying this fraction to estimates of N inputs, N2O and NOx fluxes, we calculate that ≈28 Tg of N are lost annually via N2 efflux from the natural soil. These results place isotopic constraints on the widely held belief that denitrifying bacteria account for a significant fraction of the missing N in the global N cycle

Isotopic evidence for large gaseous nitrogen losses from tropical rainforests

The nitrogen isotopic composition ((15)N/(14)N) of forested ecosystems varies systematically worldwide. In tropical forests, which are elevated in (15)N relative to temperate biomes, a decrease in ecosystem (15)N/(14)N with increasing rainfall has been reported. This trend is seen in a set of well characterized Hawaiian rainforests, across which we have measured the (15)N/(14)N of inputs and hydrologic losses. We report that the two most widely purported mechanisms, an isotopic shift in N inputs or isotopic discrimination by leaching, fail to explain this climate-dependent trend in (15)N/(14)N. Rather, isotopic discrimination by microbial denitrification appears to be the major determinant of N isotopic variations across differences in rainfall. In the driest climates, the (15)N/(14)N of total dissolved outputs is higher than that of inputs, which can only be explained by a (14)N-rich gas loss. In contrast, in the wettest climates, denitrification completely consumes nitrate in local soil environments, thus preventing the expression of its isotope effect at the ecosystem scale. Under these conditions, the (15)N/(14)N of bulk soils and stream outputs decrease to converge on the low (15)N/(14)N of N inputs. N isotope budgets that account for such local isotopic underexpression suggest that denitrification is responsible for a large fraction (24–53%) of total ecosystem N loss across the sampled range in rainfall