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At least 1,045 records · Page 58
All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

The effects of different types of mulch on soil properties and tea production and quality

Abstract BACKGROUND Tea is an important economic crop in China. Mulching, a modern agricultural practice, can modify the soil microenvironment and maintain the crop yield. RESULTS To investigate the effect of different mulching modes on tea plant growth, filed experiments were conducted in a Shizipu tea plantation located in Langxi Country (Xuanchen City, Anhui Province, China). Five treatments were carried out in a randomized complete block arrangement: (i) clean tillage (control); (ii) black plastic film; (iii) weed barrier fabric; (iv) rice straw mulch; and (v) intercropping with Vulpia myuros . The effects of different mulch modes on soil temperature, water moisture, soil compactness, root activity, soil enzyme activity and nutrition status on tea yield, quality and economic benefits were compared at the harvest stage. In the present study, compared with other mulch treatments, intercropping with V. myuros significantly reduced the topsoil temperature (to an optimum temperature) and soil compactness, and increased the water holding capacity in the deep soil layer, which contributed to increased tea root activity and respiration. Furthermore, intercropping with V. myuros significantly increased soil enzymes activity, soil organic matter, and the available nitrogen and phosphorus concentrations in the main root zone. Therefore, the stronger tea root activity accelerated nutrition uptake and increased the tea yield and quality‐related components of the tea, thus resulting in a larger average net income. CONCLUSION Intercropping with V. myuros could serve as a profitable agricultural method for tea production. © 2020 Society of Chemical Industry

Xianchen, Zhang↗
DOE OSTI2019

Time‐series metatranscriptomes reveal conserved patterns between phototrophic and heterotrophic microbes in diverse freshwater systems

Abstract Microbial communities form the base of food webs in freshwater ecosystems, yet the interactions within these diverse assemblages are poorly understood. Based on evidence showing that primary production and respiration follow diurnal trends in lakes, we hypothesized that gene expression in freshwater microbes would have similar diel cycles. We used three 2‐d time series of metatranscriptomes to test this hypothesis in a eutrophic lake, an oligotrophic lake, and a humic lake. We identified prominent diel cycles in all three lakes, particularly in genes related to photosynthesis, sugar transport, and carbon fixation. The maximal time of expression for sugar transport genes tended to trail that of photosynthesis genes by several hours, indicating possible metabolic exchange between co‐occurring microbial lineages. These results provide an initial step in understanding sophisticated multispecies transcriptional organization within freshwater microbial communities.

Linz, Alexandra M.↗
DOE OSTI2020

Differential effects of press vs. pulse seawater intrusion on microbial communities of a tidal freshwater marsh

Abstract Tidal freshwater marshes (TFMs) are threatened by seawater intrusion, which can affect microbial communities and alter biogeochemical processes. Here, we report on a long‐term, large‐scale manipulative field experiment that investigated continuous (press) and episodic (pulse, 2 months/yr) inputs of brackish water on microbial communities in a TFM. After 2.5 yr, microbial diversity was lower in press treatments than in control (untreated) plots whereas diversity in pulse plots was unaffected by brackish water additions. Sulfate reducer abundance increased in response to both press and pulse treatments whereas methanogens did not differ among treatments. Our results, along with other lab and field measurements that show reduced soil respiration and extracellular enzyme activity suggest that continuous seawater intrusion will decrease macrophyte C inputs that reduce bacterial diversity in ways that also diminish ecosystem carbon cycling.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2021

Nodal root diameter and node number in maize ( Zea mays L.) interact to influence plant growth under nitrogen stress

Under nitrogen limitation, plants increase resource allocation to root growth relative to shoot growth. The utility of various root architectural and anatomical phenotypes for nitrogen acquisition are not well understood. Nodal root number and root cross-sectional area were evaluated in maize in field and greenhouse environments. Nodal root number and root cross-sectional area were inversely correlated under both high and low nitrogen conditions. Attenuated emergence of root nodes, as opposed to differences in the number of axial roots per node, was associated with substantially reduced root number. Greater root cross-sectional area was associated with a greater stele area and number of cortical cell files. Genotypes that produced few, thick nodal roots rather than many, thin nodal roots had deeper rooting and better shoot growth in low nitrogen environments. Fewer nodal roots offset the respiratory and nitrogen costs of thicker diameter roots, since total nodal root respiration and nitrogen content was similar for genotypes with many, thin and few, thick nodal roots. We propose that few, thick nodal roots may enable greater capture of deep soil nitrogen and improve plant performance under nitrogen stress. Synergistic interactions between an architectural and anatomical trait may be an important strategy for nitrogen acquisition. Understanding trait interactions among different root nodes has important implications in for improving crop nutrient uptake and stress tolerance.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2018

Plant Cell Vacuoles: Staining and Fluorescent Probes

In plant cells, vacuoles are extremely important for growth and development, and influence important cellular functions as photosynthesis, respiration, and transpiration. Plant cells contain lytic and storage vacuoles, whose size can be different depending on cell type and tissue developmental stage. One of the main roles of vacuoles is to regulate the cell turgor in response to different stimuli. Thus studying the morphology, dynamics and physiology of vacuole is fundamentally important to advance knowledge in plant cell biology at large. The availability of fluorescent probes allows marking vacuoles in multiple ways. These may be fast, when using commercially available chemical dyes, or relatively slow, in the case of specific genetically-encoded markers based on proteins directed either to the membrane of the vacuole (tonoplast) or to the vacuole lumen. Any of these approaches provides useful information about the morphology and physiology of the vacuole.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2020

Dynamic changes in dissolved organic matter composition in a Mountain Lake under ice cover and relationships to changes in nutrient cycling and phytoplankton community composition

We studied Bear Lake, a sub-alpine oligotrophic lake in Rocky Mountain National Park, Colorado U.S.A, during the winter ice cover period of 2018. Our goal was to understand relationships between biogeochemical processes and the chemical quality of the dissolved organic matter, a major pool of organic carbon in all lakes. The lake exhibited a highly stratified environment with limited light availability, a consistent oxycline at 7 meters, and dilute hydrochemistry. Nutrient concentrations were low and depletion of nitrogen, particularly for NH4 to a lesser extent NO3, were related to increasing phytoplankton abundance. The deep chlorophyll maxima that developed above the oxycline was dominated by a potentially mixotrophic dinoflagellate. DOM chemical quality as measured through high-resolution mass spectrometry was related to these shifts in aquatic ecosystem structure. However, CDOM spectroscopy of the whole water was a poor indicator of biogeochemical changes in the DOM pool. The spectrometry data highlighted an evolving and contrasting reservoir of phosphorus, nitrogen, and sulfur-containing organic compounds sensitive to nutrient cycling and redox conditions. We also observed reduced chemodiversity between the surface and bottom water DOM molecular formulas over time. Homogeneity increased in the surface and more unique compounds were produced in the bottom waters, where an overall increase occurred in the favorability of carbon to support microbial respiration. Our results show dynamic chemical changes in the DOM pool reflect dynamic nutrient cycling under ice cover, potentially driven by mixotrophic growth of the dinoflagellate Gymnodinium sp.

Rue, Garrett↗
DOE OSTI2022

Evaluation of changes in the microbial community structure in the sediments of a constructed wetland over the years

This study presents the results of the long term (2007–2014) monitoring of the microbial community structure in the surface sediments of the H-02 constructed wetland system, which was built on the Savannah River Site in Aiken, SC, USA, to treat the waste water generated at the Tritium facility. Microbial community structure provides valuable information about the functioning of constructed wetlands and helps understand the biogeochemical cycling of nutrients and contaminants. Phospholipids fatty acid (PLFA) analysis and qPCR were used to identify major bacterial phyla in the sediments. The physiochemical properties of the sediments were also used to deduce potential effects on the microbial community structure over the years. Sulfate-reducing bacteria (SRB) were the most dominant bacterial groups, and their prevalence was progressively increasing throughout the years most likely on the account of methane producers. Concentrations of trace metals (copper and zinc) were negatively associated with methane producers and oxidizer while positively correlated with SRB. Overall, the H-02 wetland system was efficient in immobilizing copper and zinc through the anaerobic respiration of sulfate by SRB and minimizing methane emission through the progressive elimination of methane producers by SRB and Geobacter. Furthermore, the aim of this study was to monitor the changes in the microbial community structure in the surface sediments of a constructed wetland during the first 7 years of operation.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2014

Hydrogenase Activity of Mineral-Associated and Suspended Populations of Desulfovibrio desulfuricans Essex 6

The interactions between sulfate-reducing microorganisms and iron oxides influence a number of important redox-sensitive biogeochemical processes including the formation of iron sulfides. Enzymes, such as hydrogenase which catalyze the reversible oxidation of molecular hydrogen, are known to mediate electron transfer to metals and may contribute to the formation and speciation of ferrous sulfides formed at the cell–mineral interface. In the present study, we compared the whole cell hydrogenase activity of Desulfovibrio desulfuricans strain Essex 6 growing as biofilms on hematite (hematite-associated) or as suspended populations using different metabolic pathways. Hematite-associated cells exhibited significantly greater hydrogenase activity than suspended populations during sulfate respiration but not during pyruvate fermentation. The enhanced activity of the hematite-associated, sulfate-grown cells appears to be dependent on iron availability rather than a general response to surface attachment since the activity of glass-associated cells did not differ from that of suspended populations. Hydrogenase activity of pyruvate-fermenting cells was stimulated by addition of iron as soluble Fe(II)Cl2 and, in the absence of added iron, both sulfate-reducing and pyruvate-fermenting cells displayed similar rates of hydrogenase activity. These data suggest that iron exerts a stronger influence on whole cell hydrogenase activity than either metabolic pathway or mode of growth. The location of hydrogenase to the cell envelope and the enhanced activity at the hematite surface in sulfate-reducing cells may influence the redox conditions that control the species of iron sulfides on the mineral surface.

58 GEOSCIENCES↗
DOE OSTI2024

Omics-driven onboarding of the carotenoid producing red yeast Xanthophyllomyces dendrorhous CBS 6938

Transcriptomics is a powerful approach for functional genomics and systems biology, yet it can also be used for genetic part discovery. Here, we derive constitutive and light-regulated promoters directly from transcriptomics data of the basidiomycete red yeast Xanthophyllomyces dendrorhous CBS 6938 (anamorph Phaffia rhodozyma) and use these promoters with other genetic elements to create a modular synthetic biology parts collection for this organism. X. dendrorhous is currently the sole biotechnologically relevant yeast in the Tremellomycete class-it produces large amounts of astaxanthin, especially under oxidative stress and exposure to light. Thus, we performed transcriptomics on X. dendrorhous under different wavelengths of light (red, green, blue, and ultraviolet) and oxidative stress. Differential gene expression analysis (DGE) revealed that terpenoid biosynthesis was primarily upregulated by light through crtI, while oxidative stress upregulated several genes in the pathway. Further gene ontology (GO) analysis revealed a complex survival response to ultraviolet (UV) where X. dendrorhous upregulates aromatic amino acid and tetraterpenoid biosynthesis and downregulates central carbon metabolism and respiration. The DGE data was also used to identify 26 constitutive and regulated genes, and then, putative promoters for each of the 26 genes were derived from the genome. Simultaneously, a modular cloning system for X. dendrorhous was developed, including integration sites, terminators, selection markers, and reporters. Each of the 26 putative promoters were integrated into the genome and characterized by luciferase assay in the dark and under UV light. The putative constitutive promoters were constitutive in the synthetic genetic context, but so were many of the putative regulated promoters. Notably, one putative promoter, derived from a hypothetical gene, showed ninefold activation upon UV exposure. Thus, this study reveals metabolic pathway regulation and develops a genetic parts collection for X. dendrorhous from transcriptomic data. Therefore, this study demonstrates that combining systems biology and synthetic biology into an omics-to-parts workflow can simultaneously provide useful biological insight and genetic tools for nonconventional microbes, particularly those without a related model organism. This approach can enhance current efforts to engineer diverse microbes.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2016

Percutaneous Treatment of Splenic Cystic Echinococcosis: Results of 12 Cases

PurposeCystic echinococcosis (CE) in the spleen is a rare disease even in endemic regions. The aim of this study was to examine the efficacy of percutaneous treatment for splenic CE.Materials and MethodsTwelve patients (four men, eight women) with splenic CE were included in this study. For percutaneous treatment, CE1 and CE3A splenic hydatid cysts were treated with either the PAIR (puncture, aspiration, injection, respiration) technique or the catheterization technique.ResultsEight of the hydatid cysts were treated with the PAIR technique and four were treated with catheterization. The volume of all cysts decreased significantly during the follow-up period. No complication occurred in seven of 12 patients. Abscess developed in four patients. Two patients underwent splenectomy due to cavity infection developed after percutaneous treatment, while the spleen was preserved in 10 of 12 patients. Total hospital stay was between 1 and 18 days. Hospital stay was longer and the rate of infection was higher in the catheterization group. Follow-up period was 5–117 months (mean, 44.8 months), with no recurrence observed.ConclusionThe advantages of the percutaneous treatment are its minimal invasive nature, short hospitalization duration, and its ability to preserve splenic tissue and function. As the catheterization technique is associated with higher abscess risk, we suggest that the PAIR procedure should be the first percutaneous treatment option for splenic CE.

62 RADIOLOGY AND NUCLEAR MEDICINE↗
DOE OSTI2022

Compartment-specific energy requirements of photosynthetic carbon metabolism in Camelina sativa leaves

Abstract Main conclusion The oxidative pentose phosphate pathway provides cytosolic NADPH yet reduces carbon and energy use efficiency. Repressing this pathway and introducing cytosolic NADPH-dependent malate dehydrogenase may increase crop yields by ≈5%. Abstract Detailed knowledge about plant energy metabolism may aid crop improvements. Using published estimates of flux through central carbon metabolism, we phenotype energy metabolism in illuminated Camelina sativa leaves (grown at 22 °C, 500 µmol photons m −2 s −1 ) and report several findings. First, the oxidative pentose phosphate pathway (OPPP) transfers 3.3% of the NADPH consumed in the Calvin–Benson cycle to the cytosol. NADPH supply proceeds at about 10% of the rate of net carbon assimilation. However, concomitantly respired CO 2 accounts for 4.8% of total rubisco activity. Hence, 4.8% of the flux through the Calvin–Benson cycle and photorespiration is spent on supplying cytosolic NADPH, a significant investment. Associated energy requirements exceed the energy output of the OPPP. Thus, autotrophic carbon metabolism is not simply optimised for flux into carbon sinks but sacrifices carbon and energy use efficiency to support cytosolic energy metabolism. To reduce these costs, we suggest bioengineering plants with a repressed cytosolic OPPP, and an inserted cytosolic NADPH-dependent malate dehydrogenase tuned to compensate for the loss in OPPP activity (if required). Second, sucrose cycling is a minor investment in overall leaf energy metabolism but a significant investment in cytosolic energy metabolism. Third, leaf energy balancing strictly requires oxidative phosphorylation, cofactor export from chloroplasts, and peroxisomal NADH import. Fourth, mitochondria are energetically self-sufficient. Fifth, carbon metabolism has an ATP/NADPH demand ratio of 1.52 which is met if ≤ 21.7% of whole electron flux is cyclic. Sixth, electron transport has a photon use efficiency of ≥ 62%. Last, we discuss interactions between the OPPP and the cytosolic oxidation–reduction cycle in supplying leaf cytosolic NADPH.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2018

Removal of Woody Riparian Vegetation Substantially Altered a Stream Ecosystem in an Otherwise Undisturbed Grassland Watershed

Riparian zones are key interfaces between stream and terrestrial ecosystems. Yet, we know of no whole-watershed experiments that cut only woody vegetation in the riparian zone in an otherwise intact watershed to isolate the role of riparian zones on stream ecology. We removed all of the woody riparian vegetation (from 10- and 30-m-wide buffers in headwaters and main channels, respectively) for 5 km of stream in a single watershed while leaving the remainder of the grassland watershed un-impacted. We assessed water chemistry changes 3 years before and 3 years after riparian wood removal and in two neighboring control watersheds with a before–after, control-impact design and analysis. Riparian woody removal caused 10–100-fold increases in mean stream water nitrate concentrations and pulses of high nitrate for 3 years thereafter. Other nutrients and total suspended solids increased 2–25 times for the 3 years of post-removal. In-stream rates of gross primary production, ecosystem respiration, and net ecosystem production had large treatment effect sizes but also high variance among samples. Past studies of whole-watershed deforestations showed similar water quality responses to our riparian deforestation. Riparian zones of grassland streams are sensitive to disturbance and likely impart relatively greater influence on stream structure and function than the upslope of the watershed. Finally, our results further emphasize the role of riparian zones in biogeochemically linking aquatic and terrestrial habitats.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2019

The Shifting Role of mRUE for Regulating Ecosystem Production

To design a comprehensive view of ecosystem resource use, in this work we integrated parallel resource use efficiency observations into a multiple-resource use efficiency (mRUE) framework using a dynamic factor analysis model. Results from 56 site-years of eddy covariance data and mRUE factors for a site in the US Midwest show temporal dynamics and coherence (using Pearson’s R) among resources are associated with interannual variation in precipitation. Loading factors are derived from mRUE observations and quantify how strongly data are connected to the underlying ecosystem state. Water and light resource use loading factors are coherent at annual timescales (Pearson’s R of 0.86), whereas declining patterns of carbon use efficiency loading factors highlight the ecosystem’s trade-off between carbon uptake and respiration during the growing season. At annual and monthly timescales, influence decreases from ~85 to ~65% for loading factors for carbon use, while influence of light use loading factors peaks to ~60% at growing season timescales. Quantifying variation in ecosystem function provides novel insights into the temporal dynamics of changing significance of multiple resources to ecosystem function.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2021

Response of Stream Metabolism to Coarse Woody Debris Additions Along a Catchment Disturbance Gradient

We evaluated the ecological effectiveness of an in-stream restoration project involving coarse woody debris (CWD) additions to streams along an upland soil and vegetation disturbance gradient at the Fort Benning Military Installation near Columbus, GA. We examined short-term (immediate effectiveness) and longer-term (sustainability) responses to CWD additions by measuring ecosystem metabolism rates in 8 streams quarterly over a 6-year period, including 3 years before (2001–2003) and 3 years after (2004–2006) CWD additions that were made to half of the streams. Ecosystem respiration (ER) rates in most CWD addition streams increased relative to control streams from spring 2004 through autumn 2005, suggesting heterotrophic bacteria were the initial responders to CWD additions. Gross primary production (GPP) rates remained low (typically < 0.3 g O 2 m -2 d -1 ) but increased in some CWD addition streams relative to control streams in spring 2004 and 2005. The magnitude of ER increases in CWD addition streams during the first two years post-addition increased with catchment disturbance intensity, indicating that more heavily disturbed streams responded most strongly to restorations—an important consideration when targeting future restoration locations. Because restorations did not address actual upland disturbance, continued high erosion rates resulted in 32–77% of the added CWD being buried by year two and a corresponding return of GPP and ER rates to pre-CWD addition levels by year three. If restoration projects do not adequately address the source of catchment disturbances, CWD additions will provide only short-term increases in streambed structure and stability, hydrodynamic complexity, and nutrient and organic matter processing and retention.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2020

Extracellular electron uptake by autotrophic microbes: physiological, ecological, and evolutionary implications

Abstract Microbes exchange electrons with their extracellular environment via direct or indirect means. This exchange is bidirectional and supports essential microbial oxidation–reduction processes, such as respiration and photosynthesis. The microbial capacity to use electrons from insoluble electron donors, such as redox-active minerals, poised electrodes, or even other microbial cells is called extracellular electron uptake (EEU). Autotrophs with this capability can thrive in nutrient and soluble electron donor-deficient environments. As primary producers, autotrophic microbes capable of EEU greatly impact microbial ecology and play important roles in matter and energy flow in the biosphere. In this review, we discuss EEU-driven autotrophic metabolisms, their mechanism and physiology, and highlight their ecological, evolutionary, and biotechnological implications.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2015

Reducing conditions, reactive metals, and their interactions can explain spatial patterns of surface soil carbon in a humid tropical forest

Humid tropical forests support large stocks of surface soil carbon (C) that exhibit high spatial variability over scales of meters to landscapes (km). Reactive minerals and organo-metal complexes are known to contribute to C accumulation in these ecosystems, although potential interactions with environmental factors such as oxygen (O 2 ) availability have received much less attention. Reducing conditions can potentially contribute to C accumulation, yet anaerobic metabolic processes such as iron (Fe) reduction can also drive substantial C losses. We tested whether these factors could explain variation in soil C (0–10 and 10–20 cm depths) over multiple spatial scales in the Luquillo Experimental Forest, Puerto Rico, using reduced iron (Fe(II)) concentrations as an index of reducing conditions across sites differing in vegetation, topographic position, and/or climate. Fine root biomass and Fe(II) were the best overall correlates of site (n = 6) mean C concentrations and stocks from 0 to 20 cm depth (r = 0.99 and 0.98, respectively). Litterfall decreased as reducing conditions, total and dead fine root biomass, and soil C increased among sites, suggesting that decomposition rates rather than C inputs regulated soil C content at the landscape scale. Strong relationships between Fe(II) and dead fine root biomass suggest that reducing conditions suppressed particulate organic matter decomposition. The optimal mixed-effects regression model for individual soil samples (n = 149) showed that aluminum (Al) and Fe in citrate/ascorbate and oxalate extractions, Fe(II), fine root biomass, and interactions between Fe(II) and Al explained most of the variation in C concentrations (pseudo R 2 = 0.82). The optimal model of C stocks was similar but did not include fine root biomass (pseudo R 2 = 0.62). In these models, soil C concentrations and stocks increased with citrate/ascorbate-extractable Al and oxalate-extractable Fe. However, soil C decreased with citrate/ascorbate-extractable Fe, an index of Fe susceptible to anaerobic microbial reduction. At the site scale (n = 6), ratios of citrate/ascorbate to oxalate-extractable Fe consistently decreased across a landscape O 2 gradient as C increased. Finally, we suggest that the impact of reducing conditions on organic matter decomposition and the presence of organo-metal complexes and C sorption by short-range order Fe and Al contribute to C accumulation, whereas the availability of an Fe pool to sustain anaerobic respiration in soil microsites partially attenuates soil C accumulation in these ecosystems.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2016

Chamber measurements of high CO 2 emissions from a rainforest stream receiving old C-rich regional groundwater

Carbon emissions from fluvial systems are a key component of local and regional carbon cycles. We used floating chambers to investigate the CO 2 flux from stream water to air (f CO 2 ) in the Arboleda, a stream in the lowland rainforest of Costa Rica, fed partly by old regional groundwater high in dissolved inorganic carbon (DIC). Drifting and static chambers showed f CO 2 averaging 35.5 and 72.7 μmol C m –2 s –1 , respectively, bracketing the previously-published f CO 2 value of 56 μmol C m –2 s –1 obtained using tracer methods in this stream. These values are much higher than most f CO 2 data in the literature and reflect a large flux of deep crustal (non-biogenic) CO 2 out of the Arboleda, a flux that does not represent a component of ecosystem respiration. Static chambers appeared to overestimate f CO 2 by creating artificial turbulence, while drifting chambers may have underestimated f CO 2 by under-sampling areas of potentially high gas exchange (e.g., riffles around coarse woody debris obstructions). Both static and drifting chambers revealed high spatial heterogeneity in f CO 2 at the scale of 5–30 m reaches. Some observed temporal trends were localized, e.g., among three reaches with repeated measurements through the wet and dry seasons, (1) only the reach located between the other two showed significantly lower f CO 2 during the dry season, and (2) the highest and lowest f CO 2 were consistently observed in the reaches farthest upstream and downstream, respectively. As a result, streams like the Arboleda receiving significant inputs of high-DIC regional groundwater merit additional study as hotspots for C emissions from terrestrial ecosystems.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2016

CLMcrop yields and water requirements: avoided impacts by choosing RCP 4.5 over 8.5

Here, we perform CLMcrop simulations of the 20th and 21st centuries to assess potential avoided impacts in (a) crop yield losses and (b) water demand increases if humanity were to choose the representative concentration pathway (RCP) 4.5 instead of 8.5. RCP 8.5 imposes more extreme climatic changes on CLMcrop, while simultaneously exposing the crops to higher CO2 fertilization than RCP 4.5. As a result CLMcrop simulates global to regional scale changes in yield and water requirements for RCP 8.5 that exceed and sometimes more than double the RCP 4.5 changes relative to today. Under RCP 4.5 then, human societies may confront easier adaptation to changes in crop yields and water requirements. Under both RCPs, CLMcrop projects declining global yields for C3 crops (e.g., wheat, soybean, rice) without CO 2 fertilization and C4 crops (corn, sugarcane) without irrigation. Yield declines of 3 t ha -1 stand out in parts of tropical and subtropical Africa and South America (presently areas of rapid agricultural expansion) and are due to increasing plant respiration and decreasing soil moisture, both due to rising temperatures. Irrigation and CO 2 fertilization mitigate yield losses and in some cases lead to gains, so irrigation may help maintain or increase current yields through the 21st century. However, simulated global irrigation requirements increase: as much as 23 % for C4 crops without CO 2 fertilization under RCP 8.5 and as little as 3 % for C4 crops with CO 2 fertilization under RCP4.5. Nitrogen fertilized crops display greater vulnerability to climate and environmental change than unfertilized crops in our simulations; still relative to unfertilized crops, they deliver significantly higher yields and remain indispensable in supporting a more populous and affluent humanity. These CLMcrop results broadly agree with previously published outcomes for the 21st century. We describe in this article a new version of CLMcrop that represents prognostic crop behavior not only in the mid-latitudes but also the tropics.

54 ENVIRONMENTAL SCIENCES↗