Both a resource for those professionally engaged in work with
sexual and gender minorities and a comprehensive text for use in
courses on working with vulnerable youth populations, Growing
into ...Resilience is a timely and transdisciplinary book.
Row-crop agriculture is a major source of nitrous oxide (N₂O) globally, and results from recent field experiments suggest that significant decreases in N₂O emissions may be possible by decreasing ...nitrogen (N) fertilizer inputs without affecting economic return from grain yield. We tested this hypothesis on five commercially farmed fields in Michigan, USA planted with corn in 2007 and 2008. Six rates of N fertilizer (0-225 kg N ha⁻¹) were broadcast and incorporated before planting, as per local practice. Across all sites and years, increases in N₂O flux were best described by a nonlinear, exponentially increasing response to increasing N rate. N₂O emission factors per unit of N applied ranged from 0.6% to 1.5% and increased with increasing N application across all sites and years, especially at N rates above those required for maximum crop yield. At the two N fertilizer rates above those recommended for maximum economic return (135 kg N ha⁻¹), average N₂O fluxes were 43% (18 g N₂O-N ha⁻¹ day⁻¹) and 115% (26 g N₂O-N ha⁻¹ day⁻¹) higher than were fluxes at the recommended rate, respectively. The maximum return to nitrogen rate of 154 kg N ha⁻¹ yielded an average 8.3 Mg grain ha⁻¹. Our study shows the potential to lower agricultural N₂O fluxes within a range of N fertilization that does not affect economic return from grain yield.
Leaves are arguably the most complex and important physicobiological systems in the ecosphere. Yet, water transport outside the leaf xylem remains poorly understood, despite its impacts on stomatal ...function and photosynthesis. We applied anatomical measurements from 14 diverse species to a novel model of water flow in an areole (the smallest region bounded by minor veins) to predict the impact of anatomical variation across species on outside-xylem hydraulic conductance (Kox). Several predictions verified previous correlational studies: (1) vein length per unit area is the strongest anatomical determinant of Kox, due to effects on hydraulic pathlength and bundle sheath (BS) surface area; (2) palisade mesophyll remains well hydrated in hypostomatous species, which may benefit photosynthesis, (3) BS extensions enhance Kox; and (4) the upper and lower epidermis are hydraulically sequestered from one another despite their proximity. Our findings also provided novel insights: (5) the BS contributes a minority of outside-xylem resistance; (6) vapor transport contributes up to two-thirds of Kox; (7) Koxis strongly enhanced by the proximity of veins to lower epidermis; and (8) Koxis strongly influenced by spongy mesophyll anatomy, decreasing with protoplast size and increasing with airspace fraction and cell wall thickness. Correlations between anatomy and Koxacross species sometimes diverged from predicted causal effects, demonstrating the need for integrative models to resolve causation. For example, (9) Koxwas enhanced far more in heterobaric species than predicted by their having BS extensions. Our approach provides detailed insights into the role of anatomical variation in leaf function.
Given increasing water deficits across numerous ecosystems world-wide, it is urgent to understand the sequence of failure of leaf function during dehydration.
We assessed dehydration-induced losses ...of rehydration capacity and maximum quantum yield of the photosystem II (F
v/F
m) in the leaves of 10 diverse angiosperm species, and tested when these occurred relative to turgor loss, declines of stomatal conductance g
s, and hydraulic conductance K
leaf, including xylem and outside xylem pathways for the same study plants. We resolved the sequences of relative water content and leaf water potential Ψleaf thresholds of functional impairment.
On average, losses of leaf rehydration capacity occurred at dehydration beyond 50% declines of g
s, K
leaf and turgor loss point. Losses of F
v/F
m occurred after much stronger dehydration and were not recovered with leaf rehydration. Across species, tissue dehydration thresholds were intercorrelated, suggesting trait co-selection. Thresholds for each type of functional decline were much less variable across species in terms of relative water content than Ψleaf.
The stomatal and leaf hydraulic systems show early functional declines before cell integrity is lost. Substantial damage to the photochemical apparatus occurs at extreme dehydration, after complete stomatal closure, and seems to be irreversible.
This study aimed to examine differences in muscle activity between young people with and without neck-shoulder pain (n = 20 in each group), when they performed texting on a smartphone. Texting was ...compared between using both hands ('bilateral texting') and with only one hand ('unilateral texting'). Texting tasks were also compared with computer typing. Surface electromyography from three proximal postural muscles and four distal hand/thumb muscles on the right side was recorded. Compared with healthy controls, young people with neck-shoulder pain showed altered motor control consisting of higher muscle activity in the cervical erector spinae and upper trapezius when performing texting and typing tasks. Generally, unilateral texting was associated with higher muscle loading compared with bilateral texting especially in the forearm muscles. Compared with computer typing, smartphone texting was associated with higher activity in neck extensor and thumb muscles but lower activity in upper and lower trapezius as well as wrist extensors.
Practitioner Summary: This study demonstrated that symptomatic individuals had increased muscle activity in the neck-shoulder region when texting on a smartphone. Contemporary ergonomic guidelines should include advice on how to interact with handheld electronic devices to achieve a relaxed posture and reduced muscle load in order to reduce the risk of musculoskeletal disorders.
Leaf dry mass per unit leaf area (LMA) is a central trait in ecology, but its anatomical and compositional basis has been unclear. An explicit mathematical and physical framework for quantifying the ...cell and tissue determinants of LMA will enable tests of their influence on species, communities and ecosystems. We present an approach to explaining LMA from the numbers, dimensions and mass densities of leaf cells and tissues, which provided unprecedented explanatory power for 11 broadleaved woody angiosperm species diverse in LMA (33–262 g m−2; R2 = 0.94; P < 0.001). Across these diverse species, and in a larger comparison of evergreen vs. deciduous angiosperms, high LMA resulted principally from larger cell sizes, greater major vein allocation, greater numbers of mesophyll cell layers and higher cell mass densities. This explicit approach enables relating leaf anatomy and composition to a wide range of processes in physiological, evolutionary, community and macroecology.
Stomata, the microvalves on leaf surfaces, exert major influences across scales, from plant growth and productivity to global carbon and water cycling. Stomatal opening enables leaf photosynthesis, ...and plant growth and water use, whereas plant survival of drought depends on stomatal closure. Here we report that stomatal function is constrained by a safety-efficiency trade-off, such that species with greater stomatal conductance under high water availability (g
) show greater sensitivity to closure during leaf dehydration, i.e., a higher leaf water potential at which stomatal conductance is reduced by 50% (Ψ
). The g
- Ψ
trade-off and its mechanistic basis is supported by experiments on leaves of California woody species, and in analyses of previous studies of the responses of diverse flowering plant species around the world. Linking the two fundamental key roles of stomata-the enabling of gas exchange, and the first defense against drought-this trade-off constrains the rates of water use and the drought sensitivity of leaves, with potential impacts on ecosystems.
Clarifying the mechanisms of leaf and whole plant drought responses is critical to predict the impacts of ongoing climate change. The loss of rehydration capacity has been used for decades as a ...metric of leaf dehydration tolerance but has not been compared with other aspects of drought tolerance. We refined methods for quantifying the percent loss of rehydration capacity (PLRC), and for 18 Southern California woody species, we determined the relative water content and leaf water potential at PLRC of 10%, 25%, and 50%, and, additionally, the PLRC at important stages of dehydration including stomatal closure and turgor loss. On average, PLRC of 10% occurred below turgor loss point and at similar water status to 80% decline of stomatal conductance. As hypothesized, the sensitivity to loss of leaf rehydration capacity varied across species, leaf habits, and ecosystems and correlated with other drought tolerance traits, including the turgor loss point and structural traits including leaf mass per area. A new database of PLRC for 89 species from the global literature indicated greater leaf rehydration capacity in ecosystems with lower growing season moisture availability, indicating an adaptive role of leaf cell dehydration tolerance within the complex of drought tolerance traits.
The capacity for leaves to rehydrate after dehydration has long been used as a metric of tissue desiccation tolerance. We refined a classical method for quantifying the percent loss of rehydration capacity (PLRC) for 18 Southern California woody species, compared this metric with other indices of drought tolerance, and placed the irreversible loss of rehydration capacity in the known sequence of leaf responses to drought. On average, across species, PLRC of 10% occurred below turgor loss point and at a similar water status as 80% stomatal closure. A compilation of PLRC data from the published literature showed strong variation across ecosystems, with ecosystems experiencing greater aridity in the growing season showing greater capacity for leaf rehydration. Our findings highlight leaf tissue desiccation tolerance as an adaptive trait and the importance of research establishing the mechanisms for leaf damage and resilience during and after drought.
The Sites of Evaporation within Leaves Buckley, Thomas N.; John, Grace P.; Scoffoni, Christine ...
Plant physiology (Bethesda),
03/2017, Letnik:
173, Številka:
3
Journal Article
Recenzirano
Odprti dostop
The sites of evaporation within leaves are unknown, but they have drawn attention for decades due to their perceived implications for many factors, including patterns of leaf isotopic enrichment, the ...maintenance of mesophyll water status, stomatal regulation, and the interpretation of measured stomatal and leaf hydraulic conductances. We used a spatially explicit model of coupled water and heat transport outside the xylem, MOFLO 2.0, to map the distribution of net evaporation across leaf tissues in relation to anatomy and environmental parameters. Our results corroborate earlier predictions that most evaporation occurs from the epidermis at low light and moderate humidity but that the mesophyll contributes substantially when the leaf center is warmed by light absorption, and more so under high humidity. We also found that the bundle sheath provides a significant minority of evaporation (15% in darkness and 18% in high light), that the vertical center of amphistomatous leaves supports net condensation, and that vertical temperature gradients caused by light absorption vary over 10-fold across species, reaching 0.3°C. We show that several hypotheses that depend on the evaporating sites require revision in light of our findings, including that experimental measurements of stomatal and hydraulic conductances should be affected directly by changes in the location of the evaporating sites. We propose a new conceptual model that accounts for mixed-phase water transport outside the xylem. These conclusions have far-reaching implications for inferences in leaf hydraulics, gas exchange, water use, and isotope physiology.
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•Baseline vulnerabilities and climate change impacts intersect in complex ways.•Climate Vulnerability Index (CVI) combines indicators to identify risk drivers.•Climate change risks ...are broadly and heterogeneously distributed across the U.S.•Existing disparities in the U.S. are often further exacerbated by climate change.•CVI is a basis for future research and prioritizing resources and interventions.
Climate change will cause a range of related risks, including increases in infectious and chronic disease, intensified social and economic stresses, and more frequent extreme weather events. Vulnerable groups will be disproportionately affected due to greater exposure to climate risks and lower ability to prepare, adapt, and recover from their effects. Better understanding of the intersection of vulnerability and climate change risks is required to identify the most important drivers of future climate risks and effectively build resilience and deploy targeted adaptation efforts. Incorporating community stakeholder input, we identified and integrated available public health, social, economic, environmental, and climate data in the United States (U.S.), comprising 184 indicators, to develop a Climate Vulnerability Index (CVI) composed of four baseline vulnerabilities (health, social/economic, infrastructure, and environment) and three climate change risks (health, social/economic, extreme events). We find that the vulnerability to and risks from climate change are highly heterogeneous across the U.S. at the census tract scale, and geospatially cluster into complementary areas with similar climate risks but differing baseline vulnerabilities. Our results therefore demonstrate that not only are climate change risks both broadly and variably distributed across the U.S., but also that existing disparities are often further exacerbated by climate change. The CVI thus lays a data-driven, scientific foundation for future research on the intersection of climate change risks with health and other inequalities, while also identifying health impacts of climate change as the greatest research gap. Moreover, given U.S. government initiatives surrounding climate and equity, the CVI can be instrumental in empowering communities and policymakers to better prioritize resources and target interventions, providing a template for addressing local-scale climate and environmental justice globally.
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