The carbon balance of plants: economics, optimization, and trait spectra in a historical perspective.

Over fifty years have passed since the publication of Harold Mooney's formative paper, "The Carbon Balance of Plants" on pages 315-346 of Volume 3 (1972) of Annual Review of Ecology and Systematics. Arguably, the conceptual framework presented in that paper, and the work by Mooney and his students leading up to the paper, provided the foundational principles from which core disciplines emerged in plant economic theory, functional trait theory and, more generally, plant physiological ecology. Here, we revisit the primary impacts of those early discoveries to understand how researchers constructed major concepts in our understanding of plant adaptations, and where those concepts are likely to take us in the near future.

Examination of amino acid hydrogen isotope measurements of scalp hair for region-of-origin studies.

Rationale: Hydrogen isotope (δ H) analysis of keratinaceous bulk tissues has been used in forensic science to reconstruct an individual's travel history or determine their region-of-origin. Here, we use a compound-specific approach to examine patterns of individual amino acid δ H values in relation to those of local tap water, bulk scalp hair tissues, and region-of-origin.

Methods: We measured δ H values of amino acids in anonymously collected scalp hair (n = 67) and tap water from 28 locations in the United States.

Intrinsic water-use efficiency influences establishment in Encelia farinosa.

We describe establishment of Encelia farinosa, a drought-deciduous shrub common to the Mojave and Sonoran Deserts, based on annual observations of two populations between 1980 and 2020. Only 11 establishment events of 50 + yearlings (0.02-0.

A multi-city urban atmospheric greenhouse gas measurement data synthesis.

Urban regions emit a large fraction of anthropogenic emissions of greenhouse gases (GHG) such as carbon dioxide (CO) and methane (CH) that contribute to modern-day climate change. As such, a growing number of urban policymakers and stakeholders are adopting emission reduction targets and implementing policies to reach those targets. Over the past two decades research teams have established urban GHG monitoring networks to determine how much, where, and why a particular city emits GHGs, and to track changes in emissions over time.

Breath Stable Isotope Analysis Serves as a Non-invasive Analytical Tool to Demonstrate Dietary Changes in Adolescent Students Over Time.

Concern about adolescent diets, obesity, and the associated health risks have been growing in the United States. This inspired former First Lady Michelle Obama to spearhead the Healthy Hunger-Free Kids Act (HHFKA), which made changes to the national school lunch program by increasing servings of whole grains, fruits, and vegetables. Our study examined the variability of student carbohydrate sources throughout the day and before and after the implementation of HHFKA using a stable isotope dietary biomarker.

Heterogeneous isotope effects decouple conifer leaf and branch sugar δO and δC.

Isotope ratios of tree-ring cellulose are a prominent tool to reconstruct paleoclimate and plant responses to environmental variation. Current models for cellulose isotope ratios assume a transfer of the environmental signals recorded in bulk leaf water to carbohydrates and ultimately into stem cellulose. However, the isotopic signal of carbohydrates exported from leaf to branch may deviate from mean leaf values if spatial heterogeneity in isotope ratios exists in the leaf.

Rapid increases in shrubland and forest intrinsic water-use efficiency during an ongoing megadrought.

Globally, intrinsic water-use efficiency (iWUE) has risen dramatically over the past century in concert with increases in atmospheric CO concentration. This increase could be further accelerated by long-term drought events, such as the ongoing multidecadal "megadrought" in the American Southwest. However, direct measurements of iWUE in this region are rare and largely constrained to trees, which may bias estimates of iWUE trends toward more mesic, high elevation areas and neglect the responses of other key plant functional types such as shrubs that are dominant across much of the region.

Variations in human body water isotope composition across the United States.

Accurate human provenancing using stable isotopes depends directly on solid understandings of the geographic and individual factors affecting isotope variability and incorporation into human tissues. Transfer of isotopic, and therefore spatial, information between environmental water and biological tissues is mediated by the isotopic composition of body water. Thus, there is a need to study body water isotope ratios at a population level and over a large isotopic and geographic range.

Long-term nitrogen isotope dynamics in Encelia farinosa reflect plant demographics and climate.

While plant δ N values have been applied to understand nitrogen (N) dynamics, uncertainties regarding intraspecific and temporal variability currently limit their application. We used a 28 yr record of δ N values from two Mojave Desert populations of Encelia farinosa to clarify sources of population-level variability. We leveraged > 3500 foliar δ N observations collected alongside structural, physiological, and climatic data to identify plant and environmental contributors to δ N values.

Interactions among intrinsic water-use efficiency and climate influence growth and flowering in a common desert shrub.

Plants make leaf-level trade-offs between photosynthetic carbon assimilation and water loss, and the optimal balance between the two is dependent, in part, on water availability. "Conservative" water-use strategies, in which minimizing water loss is prioritized over assimilating carbon, tend to be favored in arid environments, while "aggressive" water-use strategies, in which carbon assimilation is prioritized over water conservation, are often favored in mesic environments. When derived from foliar carbon isotope ratios, intrinsic water-use efficiency (iWUE) serves as a seasonally integrated indicator of the balance of carbon assimilation to water loss at the leaf level.

Seasonal and diurnal trends in progressive isotope enrichment along needles in two pine species.

The Craig-Gordon type (C-G) leaf water isotope enrichment models assume a homogeneous distribution of enriched water across the leaf surface, despite observations that Δ O can become increasingly enriched from leaf base to tip. Datasets of this 'progressive isotope enrichment' are limited, precluding a comprehensive understanding of (a) the magnitude and variability of progressive isotope enrichment, and (b) how progressive enrichment impacts the accuracy of C-G leaf water model predictions. Here, we present observations of progressive enrichment in two conifer species that capture seasonal and diurnal variability in environmental conditions.

Stable isotopes in hair reveal dietary protein sources with links to socioeconomic status and health.

Carbon and nitrogen isotope ratios in hair sampled from 65 communities across the central and intermountain regions of the United States and more intensively throughout 29 ZIP codes in the Salt Lake Valley, Utah, revealed a dietary divergence related to socioeconomic status as measured by cost of living, household income, and adjusted gross income. Corn-fed, animal-derived proteins were more common in the diets of lower socioeconomic status populations than were plant-derived proteins, with individual estimates of animal-derived protein diets as high as 75%; United States towns and cities averaged 57%. Similar patterns were seen across the socioeconomic status spectrum in the Salt Lake Valley.

Multidecadal records of intrinsic water-use efficiency in the desert shrub reveal strong responses to climate change.

While tree rings have enabled interannual examination of the influence of climate on trees, this is not possible for most shrubs. Here, we leverage a multidecadal record of annual foliar carbon isotope ratio collections coupled with 39 y of survey data from two populations of the drought-deciduous desert shrub to provide insight into water-use dynamics and climate. This carbon isotope record provides a unique opportunity to examine the response of desert shrubs to increasing temperature and water stress in a region where climate is changing rapidly.

Increased in carbon isotope ratios of Brazilian fingernails are correlated with increased in socioeconomic status.

High C in human tissues in Brazil indicate high consumption of C-based sources due to the consumption of highly processed food and animal protein. The significant positive correlation between the human developed index (HDI) developed by the United Nations Development Program, and fingernail C at the county level proved to be useful as a new proxy in tracking human nutrition. Regions with higher HDI are those with higher consumption of highly processed food.

Distinguishing the region-of-origin of roasted coffee beans with trace element ratios.

Determining coffee region-of-origin is most appropriately addressed through analyses of the product available to the consumer. We analyzed the concentrations of 44 trace elements in 53 samples of roasted Arabica coffee beans (Coffea arabica) from 21 different countries. Variations in absolute elemental concentrations of coffee beans arise through varying degrees of roasting (from green through dark roasts).

Recent increases in drought frequency cause observed multi-year drought legacies in the tree rings of semi-arid forests.

Recent analyses on the length of drought recovery in forests have shown multi-year legacies, particularly in semi-arid, coniferous ecosystems. Such legacies are usually attributed to ecophysiological memory, although drought frequency itself, and its effect on overlapping recovery times, could also contribute. Here, we describe a multi-decadal study of drought legacies using tree-ring carbon-isotope ratios (δC) and ring-width index (RWI) in Pinus ponderosa at 13 montane sites traversing a winter-summer precipitation gradient in the Southwestern U.

A predictive spatial model for roasted coffee using oxygen isotopes of α-cellulose.

Rationale: Fraudulent region-of-origin labeling is a concern for high-value, globally traded commodities such as coffee. The oxygen isotope ratio of cellulose is a useful geographic tracer, as it integrates climate and source water signals. A predictive spatial model ("isoscape") of the δ O values of coffee bean cellulose is generated to evaluate coffee region-of-origin claims.

Climate and lawn management interact to control C plant distribution in residential lawns across seven U.S. cities.

In natural grasslands, C plant dominance increases with growing season temperatures and reflects distinct differences in plant growth rates and water use efficiencies of C vs. C photosynthetic pathways. However, in lawns, management decisions influence interactions between planted turfgrass and weed species, leading to some uncertainty about the degree of human vs.

Strontium isotope ratios of human hair from the United States: Patterns and aberrations.

Rationale: Strontium isotope ratios ( Sr/ Sr) of hair may be a valuable tool to estimate human provenance. However, the systematics and mechanisms controlling spatial variation in Sr/ Sr of modern human hair remain unclear. Here, we measure Sr/ Sr of hair specimens from across the USA to assess the presence of geospatial relationships.

Strontium isotope ratios ( Sr/ Sr) of human fingernail clippings reveal multiple location signals.

Rationale: Strontium isotope ratios ( Sr/ Sr) in human fingernail keratin tissues have been underexplored for region of origin and travel history reconstruction studies. Here we investigated Sr/ Sr ratios in fingernail keratin to establish baseline measurements in a resident group and to examine how Sr/ Sr ratios changed with relocation.

Methods: Fingernail clippings were collected from resident (n = 10) and non-resident/traveler groups (n = 4 and n = 4) that were part of a larger study in Salt Lake City (UT, USA) from 2015 to 2016.

Disentangling seasonal and interannual legacies from inferred patterns of forest water and carbon cycling using tree-ring stable isotopes.

Tree-ring carbon and oxygen isotope ratios have been used to understand past dynamics in forest carbon and water cycling. Recently, this has been possible for different parts of single growing seasons by isolating anatomical sections within individual annual rings. Uncertainties in this approach are associated with correlated climate legacies that can occur at a higher frequency, such as across successive seasons, or a lower frequency, such as across years.

Resident and Nonresident Fingernail Isotopes Reveal Diet and Travel Patterns,

Global travel has increased, and having a diagnostic tool to distinguish residents from visitors would be valuable. This study examined stable isotope biomarkers of fingernail tissues of resident (n = 26) and nonresident (n = 22) participants in Salt Lake City (SLC), UT, from 2015 to 2016. The purpose of this research was to determine whether fingernail isotopes could be used for reconstructing geolocation movements and to examine the convergence in nonresident fingernail isotopes to that of the resident signal following their arrival to SLC.

A tale of ENSO, PDO, and increasing aridity impacts on drought-deciduous shrubs in the Death Valley region.

Germination, establishment, phenology, and death among three drought-deciduous shrubs were influenced by ENSO/PDO and precipitation, based on 37 years of annual surveys. Encelia farinosa forms near monospecific stands on slopes, whereas E. frutescens and Ambrosia salsola dominate wash habitats.

Ecophysiological plasticity of Amazonian trees to long-term drought.

Episodic multi-year droughts fundamentally alter the dynamics, functioning, and structure of Amazonian forests. However, the capacity of individual plant species to withstand intense drought regimes remains unclear. Here, we evaluated ecophysiological responses from a forest community where we sampled 83 woody plant species during 5 years of experimental drought (throughfall exclusion) in an eastern Amazonian terra firme forest.

Some like it hot: the physiological ecology of C plant evolution.

The evolution of C photosynthesis requires an intermediate phase where photorespiratory glycine produced in the mesophyll cells must flow to the vascular sheath cells for metabolism by glycine decarboxylase. This glycine flux concentrates photorespired CO within the sheath cells, allowing it to be efficiently refixed by sheath Rubisco. A modest C biochemical cycle is then upregulated, possibly to support the refixation of photorespired ammonia in sheath cells, with subsequent increases in C metabolism providing incremental benefits until an optimized C pathway is established.