Tracheid buckling buys time, foliar water uptake pays it back: Coordination of leaf structure and function in tall redwood trees.

Tracheid buckling may protect leaves in the dynamic environments of forest canopies, where rapid intensifications of evaporative demand, such as those brought on by changes in light availability, can result in sudden increases in transpiration rate. While treetop leaves function in reliably direct light, leaves below the upper crown must tolerate rapid, thermally driven increases in evaporative demand. Using synchrotron-based X-ray microtomography, we visualized impacts of experimentally induced water stress and subsequent fogging on living cells in redwood leaves, adding ecological and functional context through crown-wide explorations of variation in leaf physiology and microclimate. Under drought, leaf transfusion tracheids buckle, releasing water that supplies sufficient temporal reserves for leaves to reduce stomatal conductance safely while stopping the further rise of tension. Tracheid buckling fraction decreases with height and is closely coordinated with transfusion tissue capacity and stomatal conductance to provide temporal reserves optimized for local variation in microclimate. Foliar water uptake fully restores collapsed and air-filled transfusion tracheids in leaves on excised shoots, suggesting that trees may use aerial water sources for recovery. In the intensely variable deep-crown environment, foliar water uptake can allow for repetitive cycles of tracheid buckling and unbuckling, protecting the tree from damaging levels of hydraulic tension and supporting leaf survival.

Safe spaces for beneficiaries of a combination HIV prevention intervention for adolescent girls and young women in South Africa: access, feasibility, and acceptability.

BACKGROUND: Safe Spaces are a feature of combination HIV prevention interventions for adolescent girls and young women (AGYW) in South Africa. We investigated whether AGYW at risk for adverse sexual and reproductive health (SRH) outcomes accessed Safe Spaces that were part of an intervention, as well as their feasibility and acceptability. METHODS: In December 2020 to February 2021, as part of a process evaluation of a combination HIV prevention intervention, we randomly sampled 2160 AGYW intervention beneficiaries aged 15-24 years from 6 of the 12 intervention districts. We invited them to participate in a phone survey, with questions about their vulnerability to adverse SRH outcomes, and participation in intervention components including Safe Spaces. We examined factors associated with use of Safe Spaces using bivariate analyses and Pearson's chi squared tests. We also conducted in-depth interviews with 50 AGYW beneficiaries, 27 intervention implementers, 4 health workers, 7 social workers, and 12 community stakeholders, to explore perceptions and experiences of the intervention. Thematic analysis of the qualitative data was performed. RESULTS: At least 30 Safe Spaces were established across 6 districts. Five hundred fifteen of two thousand one hundred sixty sampled AGYW participated in the survey of whom 22.6% visited a Safe Space, accessing HIV testing (52.2%), mobile health services (21.2%) and counselling for distress (24.8%) while there. Beneficiaries of lower socioeconomic status (SES) were less likely to have visited a Safe Space, compared with those of higher SES (13.6% versus 25.3%; p < 0.01). Implementers described political, structural and financial challenges in identifying and setting up Safe Spaces that were safe, accessible and adequately-resourced, and challenges with AGYW not utilising them as expected. AGYW shared positive views of Safe Spaces, describing benefits such as access to computers and the internet, support with homework and job and education applications, and a space in which to connect with peers. CONCLUSION: AGYW are attracted to Safe Spaces by educational and employment promoting interventions and recreational activities, and many will take up the offer of SRH services while there. The poorest AGYW are more likely to be excluded, therefore, an understanding of the obstacles to, and enablers of their inclusion should inform Safe Space intervention design.

Adaptation and Resilience: Lessons Learned From Implementing a Combination Health and Education Intervention for Adolescent Girls and Young Women in South Africa During the COVID-19 Pandemic.

The COVID-19 pandemic has been associated with reduced access to health services and worsening health outcomes for HIV and sexual and reproductive health (SRH). Through the analysis of data from an evaluation study of a combination intervention for adolescent girls and young women (AGYW) in South Africa, we sought to examine the way in which implementation and service provision were impacted by the COVID-19 pandemic and related restrictions, describing the adaptation implementers made to respond to this context. The intervention was implemented from 2019 in South African districts identified as high priority, given the high rates of HIV and teenage pregnancy amongst AGYW. The South African government introduced the first COVID-19 lockdown in March 2020. We conducted in-depth interviews with 38 intervention implementers in the period from November 2020 to March 2021. Respondents described various ways in which the COVID-19 pandemic and related restrictions had limited their ability to implement the intervention and provide services as planned. As a result, AGYW intervention beneficiary access to SRH and psychosocial services was disrupted. Implementers described several ways in which they attempted to adapt to the pandemic context, such as offering services remotely or door-to-door. Despite attempts to respond to the context and adapt services, overall COVID-19 negatively affected implementation and service provision, and heightened issues around community acceptability of the programs. Our findings can help to inform efforts to reduce health service disruption, increase health system resilience, and ensure continuous SRH service provision to AGYW in times of pandemics and other crises.

The dynamics of stem water storage in the tops of Earth's largest trees-Sequoiadendron giganteum.

Water stored in tree stems (i.e., trunks and branches) is an important contributor to transpiration that can improve photosynthetic carbon gain and reduce the probability of cavitation. However, in tall trees, the capacity to store water may decline with height because of chronically low water potentials associated with the gravitational potential gradient. We quantified the importance of elastic stem water storage in the top 5-6 m of large (4.2-5.0 m diameter at breast height, 82.1-86.3 m tall) Sequoiadendron giganteum (Lindley) J. Buchholz (giant sequoia) trees using a combination of architectural measurements and automated sensors that monitored summertime diel rhythms in sap flow, stem diameter and water potential. Stem water storage contributed 1.5-1.8% of water transpired at the tree tops, and hydraulic capacitance ranged from 2.6 to 4.1 l MPa-1 m-3. These values, which are considerably smaller than reported for shorter trees, may be associated with persistently low water potentials imposed by gravity and could indicate a trend of decreasing water storage dynamics with height in tree. Branch diameter contraction and expansion consistently and substantially lagged behind fluxes in water potential and sap flow, which occurred in sync. This lag suggests that the inner bark, which consists mostly of live secondary phloem tissue, was an important hydraulic capacitor, and that hydraulic resistance between xylem and phloem retards water transfer between these tissues. We also measured tree-base sap flux, which lagged behind that measured in trunks near the tree tops, indicating additional storage in the large trunks between these measurement positions. Whole-tree sap flow ranged from 2227 to 3752 l day-1, corroborating previous records for similar-sized giant sequoia and representing the largest yet reported for any individual tree. Despite such extraordinarily high daily water use, we estimate that water stored in tree-top stems contributes minimally to transpiration on typical summer days.

Hydraulic constraints modify optimal photosynthetic profiles in giant sequoia trees.

Optimality theory states that whole-tree carbon gain is maximized when leaf N and photosynthetic capacity profiles are distributed along vertical light gradients such that the marginal gain of nitrogen investment is identical among leaves. However, observed photosynthetic N gradients in trees do not follow this prediction, and the causes for this apparent discrepancy remain uncertain. Our objective was to evaluate how hydraulic limitations potentially modify crown-level optimization in Sequoiadendron giganteum (giant sequoia) trees up to 90 m tall. Leaf water potential (Ψ l ) and branch sap flow closely followed diurnal patterns of solar radiation throughout each tree crown. Minimum leaf water potential correlated negatively with height above ground, while leaf mass per area (LMA), shoot mass per area (SMA), leaf nitrogen content (%N), and bulk leaf stable carbon isotope ratios (δ(13)C) correlated positively with height. We found no significant vertical trends in maximum leaf photosynthesis (A), stomatal conductance (g s), and intrinsic water-use efficiency (A/g s), nor in branch-averaged transpiration (E L), stomatal conductance (G S), and hydraulic conductance (K L). Adjustments in hydraulic architecture appear to partially compensate for increasing hydraulic limitations with height in giant sequoia, allowing them to sustain global maximum summer water use rates exceeding 2000 kg day(-1). However, we found that leaf N and photosynthetic capacity do not follow the vertical light gradient, supporting the hypothesis that increasing limitations on water transport capacity with height modify photosynthetic optimization in tall trees.

Vanished Twins and Misdiagnosed Sex: A Case Report with Implications in Prenatal Counseling Using Noninvasive Cell-Free DNA Screening.

Cell-free DNA testing is a recently introduced method for screening pregnant women for fetal trisomy, which is associated with some common significant genetic diseases, as well as the sex of the fetus. The case described here demonstrates the connection between the ultrasound "vanishing twin" phenomenon and the misdiagnosis of prenatal sex using cell-free DNA testing.

Contrasting drought-response strategies in California redwoods.

We compared the physiology and growth of seedlings originating from different Sequoia sempervirens (D. Don.) Endl. (coast redwood) and Sequoiadendron giganteum (Lindl.) Buchh. (giant sequoia) populations subjected to progressive drought followed by a recovery period in a controlled greenhouse experiment. Our objective was to examine how multiple plant traits interact to influence the response of seedlings of each species and seed population to a single drought and recovery cycle. We measured soil and plant water status, leaf gas exchange, stem embolism and growth of control (well-watered) and drought-stressed (water withheld) seedlings from each population at the beginning, middle and end of a 6-week drought period and again 2 weeks after re-watering. The drought had a significant effect on many aspects of seedling performance, but water-stressed seedlings regained most physiological functioning by the end of the recovery period. Sequoiadendron seedlings exhibited a greater degree of isohydry (water status regulation), lower levels of stem embolism, higher biomass allocation to roots and lower sensitivity of growth to drought compared with Sequoia. Only minor intra-specific differences were observed among populations. Our results show that seedlings of the two redwood species exhibit contrasting drought-response strategies that align with the environmental conditions these trees experience in their native habitats, and demonstrate trade-offs and coordination among traits affecting plant water use, carbon gain and growth under drought.

Cloud shading and fog drip influence the metabolism of a coastal pine ecosystem.

Assessing the ecological importance of clouds has substantial implications for our basic understanding of ecosystems and for predicting how they will respond to a changing climate. This study was conducted in a coastal Bishop pine forest ecosystem that experiences regular cycles of stratus cloud cover and inundation in summer. Our objective was to understand how these clouds impact ecosystem metabolism by contrasting two sites along a gradient of summer stratus cover. The site that was under cloud cover ~15% more of the summer daytime hours had lower air temperatures and evaporation rates, higher soil moisture content, and received more frequent fog drip inputs than the site with less cloud cover. These cloud-driven differences in environmental conditions translated into large differences in plant and microbial activity. Pine trees at the site with greater cloud cover exhibited less water stress in summer, larger basal area growth, and greater rates of sap velocity. The difference in basal area growth between the two sites was largely due to summer growth. Microbial metabolism was highly responsive to fog drip, illustrated by an observed ~3-fold increase in microbial biomass C with increasing summer fog drip. In addition, the site with more cloud cover had greater total soil respiration and a larger fractional contribution from heterotrophic sources. We conclude that clouds are important to the ecological functioning of these coastal forests, providing summer shading and cooling that relieve pine and microbial drought stress as well as regular moisture inputs that elevate plant and microbial metabolism. These findings are important for understanding how these and other seasonally dry coastal ecosystems will respond to predicted changes in stratus cover, rainfall, and temperature.

Management of gestational hypertension - the impact of HYPITATa.

AIMS: The objective of this study was to examine the impact of one trial (the HYPITAT trial) on management of gestational hypertension. STUDY DESIGN: This is a retrospective cohort study of 5077 patients delivered at our institution from 7/1/2008 to 6/15/2011. "Pre-HYPITAT" was defined as 7/1/2008-9/30/2009 and "Post-HYPITAT" as 10/1/2009-6/15/2011. The primary outcome is the rate of delivery intervention for gestational hypertension. Secondary maternal and neonatal outcomes were analyzed in patients with gestational hypertension only. Statistical analyses included the χ2-test, Fisher's exact test, and the two-sample t-test. RESULTS: The rate of delivery intervention Pre-HYPITAT was 1.9%, compared to 4% Post-HYPITAT (P<0.001). There was no significant change in secondary outcomes. CONCLUSION: There was a statistically significant increase in delivery intervention for gestational hypertension at our institution after the publication of the HYPITAT trial. There was no significant change in immediate maternal or neonatal outcomes for patients with gestational hypertension.

Seasonal and episodic moisture controls on plant and microbial contributions to soil respiration.

Moisture inputs drive soil respiration (SR) dynamics in semi-arid and arid ecosystems. However, determining the contributions of root and microbial respiration to SR, and their separate temporal responses to periodic drought and water pulses, remains poorly understood. This study was conducted in a pine forest ecosystem with a Mediterranean-type climate that receives seasonally varying precipitation inputs from both rainfall (in the winter) and fog-drip (primarily in the summer). We used automated SR measurements, radiocarbon SR source partitioning, and a water addition experiment to understand how SR, and its separate root and microbial sources, respond to seasonal and episodic changes in moisture. Seasonal changes in SR were driven by surface soil water content and large changes in root respiration contributions. Superimposed on these seasonal patterns were episodic pulses of precipitation that determined the short-term SR patterns. Warm season precipitation pulses derived from fog-drip, and rainfall following extended dry periods, stimulated the largest SR responses. Microbial respiration dominated these SR responses, increasing within hours, whereas root respiration responded more slowly over days. We conclude that root and microbial respiration sources respond differently in timing and magnitude to both seasonal and episodic moisture inputs. These findings have important implications for the mechanistic representation of SR in models and the response of dry ecosystems to changes in precipitation patterns.

Effects of height on treetop transpiration and stomatal conductance in coast redwood (Sequoia sempervirens).

Treetops become increasingly constrained by gravity-induced water stress as they approach maximum height. Here we examine the effects of height on seasonal and diurnal sap flow dynamics at the tops of 12 unsuppressed Sequoia sempervirens (D. Don) Endl. (coast redwood) trees 68-113 m tall during one growing season. Average treetop sap velocity (V(S)), transpiration per unit leaf area (E(L)) and stomatal conductance per unit leaf area (G(S)) significantly decreased with increasing height. These differences in sap flow were associated with an unexpected decrease in treetop sapwood area-to-leaf area ratios (A(S):A(L)) in the tallest trees. Both E(L) and G(S) declined as soil moisture decreased and vapor pressure deficit (D) increased throughout the growing season with a greater decline in shorter trees. Under high soil moisture and light conditions, reference G(S) (G(Sref); G(S) at D = 1 kPa) and sensitivity of G(S) to D (-δ; dG(S)/dlnD) significantly decreased with increasing height. The close relationship we observed between G(Sref) and -δ is consistent with the role of stomata in regulating E(L) and leaf water potential (Ψ(L)). Our results confirm that increasing tree height reduces gas exchange of treetop foliage and thereby contributes to lower carbon assimilation and height growth rates as S. sempervirens approaches maximum height.

Effects of tree height on branch hydraulics, leaf structure and gas exchange in California redwoods.

We examined changes in branch hydraulic, leaf structure and gas exchange properties in coast redwood (Sequoia sempervirens) and giant sequoia (Sequoiadendron giganteum) trees of different sizes. Leaf-specific hydraulic conductivity (k(L)) increased with height in S. sempervirens but not in S. giganteum, while xylem cavitation resistance increased with height in both species. Despite hydraulic adjustments, leaf mass per unit area (LMA) and leaf carbon isotope ratios (delta(13)C) increased, and maximum mass-based stomatal conductance (g(mass)) and photosynthesis (A(mass)) decreased with height in both species. As a result, both A(mass) and g(mass) were negatively correlated with branch hydraulic properties in S. sempervirens and uncorrelated in S. giganteum. In addition, A(mass) and g(mass) were negatively correlated with LMA in both species, which we attributed to the effects of decreasing leaf internal CO(2) conductance (g(i)). Species-level differences in wood density, LMA and area-based gas exchange capacity constrained other structural and physiological properties, with S. sempervirens exhibiting increased branch water transport efficiency and S. giganteum exhibiting increased leaf-level water-use efficiency with increasing height. Our results reveal different adaptive strategies for the two redwoods that help them compensate for constraints associated with growing taller, and reflect contrasting environmental conditions each species faces in its native habitat.

Successful use of argatroban during the third trimester of pregnancy: case report and review of the literature.

Direct thrombin inhibitors are commonly used anticoagulants in patients with known or suspected heparin-induced thrombocytopenia (HIT). All three direct thrombin inhibitors available in the United States-argatroban, bivalirudin, and lepirudin-are pregnancy category B drugs based on animal studies, but little data are available on the safety of these agents during human pregnancy. Whereas several case reports support the safe use of lepirudin, only one case report has been published with argatroban and none with bivalirudin. We describe a 26-year-old pregnant woman with portal vein thrombosis and thrombocytopenia treated with argatroban for possible HIT during her last trimester. An argatroban infusion was started at 2 microg/kg/minute during her 33rd week of pregnancy, with the dosage titrated based on the activated partial thromboplastin time; infusion rates ranged from 2-8 microg/kg/minute. Treatment continued until her 39th week of pregnancy, when labor was induced. Argatroban therapy was discontinued 7 hours before epidural anesthesia. The patient successfully delivered a healthy male newborn, devoid of any known adverse effects from argatroban. The infant was found to have a small ventricular septal defect and patent foramen ovale at birth, but it is unlikely that these were caused by argatroban since organogenesis occurs in the first trimester. Even though the cause of this patient's thrombocytopenia was later determined to be idiopathic thrombocytopenic purpura, this is an important case that adds to the literature on use of argatroban during pregnancy.

Nighttime transpiration in woody plants from contrasting ecosystems.

It is commonly assumed that transpiration does not occur at night because leaf stomata are closed in the dark. We tested this assumption across a diversity of ecosystems and woody plant species by various methods to explore the circumstances when this assumption is false. Our primary goals were: (1) to evaluate the nature and magnitude of nighttime transpiration, E(n), or stomatal conductance, g(n); and (2) to seek potential generalizations about where and when it occurs. Sap-flow, porometry and stable isotope tracer measurements were made on 18 tree and eight shrub species from seven ecosystem types. Coupled with environmental data, our findings revealed that most of these species transpired at night. For some species and circumstances, nighttime leaf water loss constituted a significant fraction of total daily water use. Our evidence shows that E(n) or g(n) can occur in all but one shrub species across the systems we investigated. However, under conditions of high nighttime evaporative demand or low soil water availability, stomata were closed and E(n) or g(n) approached zero in eleven tree and seven shrub species. When soil water was available, E(n) or g(n) was measurable in these same species demonstrating plasticity for E(n) or g(n). We detected E(n) or g(n) in both trees and shrubs, and values were highest in plants from sites with higher soil water contents and in plants from ecosystems that were less prone to atmospheric or soil water deficits. Irrespective of plant or ecosystem type, many species showed E(n) or g(n) when soil water deficits were slight or non-existent, or immediately after rainfall events that followed a period of soil water deficit. The strongest relationship was between E(n) or g(n) and warm, low humidity and (or) windy (> 0.8 m s(-1)) nights when the vapor pressure deficit remained high (> 0.2 kPa in wet sites, > 0.7 kPa in dry sites). Why E(n) or g(n) occurs likely varies with species and ecosystem type; however, our data support four plausible explanations: (1) it may facilitate carbon fixation earlier in the day because stomata are already open; (2) it may enhance nutrient supply to distal parts of the crown when these nutrients are most available (in wet soils) and transport is rapid; (3) it may allow for the delivery of dissolved O(2) via the parenchyma to woody tissue sinks; or (4) it may occur simply because of leaky cuticles in older leaves or when stomata cannot close fully because of obstructions from stomatal (waxy) plugs, leaf endophytes or asymmetrical guard cells (all non-adaptive reasons). We discuss the methodological, ecophysiological, and theoretical implications of the occurrence of E(n) or g(n) for investigations at a variety of scales.