A prospective cause of death classification system for maternal deaths in low and middle-income countries: results from the Global Network Maternal Newborn Health Registry

OBJECTIVE

To describe the causes of maternal death in a population-based cohort in six low- and middle-income countries using a standardised, hierarchical, algorithmic cause of death (COD) methodology.

DESIGN

A population-based, prospective observational study.

SETTING

Seven sites in six low- to middle-income countries including the Democratic Republic of the Congo (DRC), Guatemala, India (two sites), Kenya, Pakistan and Zambia.

POPULATION

All deaths among pregnant women resident in the study sites from 2014 to December 2016.

METHODS

For women who died, we used a standardised questionnaire to collect clinical data regarding maternal conditions present during pregnancy and delivery. These data were analysed using a computer-based algorithm to assign cause of maternal death based on the International Classification of Disease-Maternal Mortality system (trauma, termination of pregnancy-related, eclampsia, haemorrhage, pregnancy-related infection and medical conditions). We also compared the COD results to healthcare-provider-assigned maternal COD.

MAIN OUTCOME MEASURES

Assigned causes of maternal mortality.

RESULTS

Among 158 205 women, there were 221 maternal deaths. The most common algorithm-assigned maternal COD were obstetric haemorrhage (38.6%), pregnancy-related infection (26.4%) and pre-eclampsia/eclampsia (18.2%). Agreement between algorithm-assigned COD and COD assigned by healthcare providers ranged from 75% for haemorrhage to 25% for medical causes coincident to pregnancy.

CONCLUSIONS

The major maternal COD in the Global Network sites were haemorrhage, pregnancy-related infection and pre-eclampsia/eclampsia. This system could allow public health programmes in low- and middle-income countries to generate transparent and comparable data for maternal COD across time or regions.

TWEETABLE ABSTRACT

An algorithmic system for determining maternal cause of death in low-resource settings is described.

OSIRIS-REx Contamination Control Strategy and Implementation

OSIRIS-REx will return pristine samples of carbonaceous asteroid Bennu. This article describes how pristine was defined based on expectations of Bennu and on a realistic understanding of what is achievable with a constrained schedule and budget, and how that definition flowed to requirements and implementation. To return a pristine sample, the OSIRIS-REx spacecraft sampling hardware was maintained at level 100 A/2 and <180 ng/cm² of amino acids and hydrazine on the sampler head through precision cleaning, control of materials, and vigilance. Contamination is further characterized via witness material exposed to the spacecraft assembly and testing environment as well as in space. This characterization provided knowledge of the expected background and will be used in conjunction with archived spacecraft components for comparison with the samples when they are delivered to Earth for analysis. Most of all, the cleanliness of the OSIRIS-REx spacecraft was achieved through communication among scientists, engineers, managers, and technicians.

Development, Implementation, and Use of a Process to Promote Knowledge Translation in Rehabilitation

OBJECTIVE

To examine the use and effect of the Battery of Rehabilitation Assessments and Interventions on evidence-based practice (EBP) over 6 years.

DESIGN

Successive independent samples study.

SETTING

Large rehabilitation system.

PARTICIPANTS

Successive samples of allied health clinicians (N=372) in 2009 (n=136), 2012 (n=115), and 2015 (n=121).

INTERVENTIONS

The Battery of Rehabilitation Assessments and Interventions includes 2 components: (1) a process to synthesize, adapt, and make recommendations about the application of evidence; and (2) a process to implement the recommended practices in 3 levels of care.

MAIN OUTCOME MEASURES

To assess the effect of the project, surveys on EBP perspectives, use, and barriers were conducted before Battery of Rehabilitation Assessments and Interventions implementation and 3 and 6 years after implementation. Questions about effect of the project on clinical practice were included 3 and 6 years postimplementation.

RESULTS

Survey data indicate the Battery of Rehabilitation Assessments and Interventions resulted in a significant increase in use of EBPs to make clinical decisions and justify care. As a result of the project, survey participants reported a substantial increase in use of outcome measures in 2012 (74%) and 2015 (91%) and evidence-based interventions in 2012 (62%) and 2015 (82%). In 2012, significant differences (P≤.01) in effect of the Battery of Rehabilitation Assessments and Interventions on practice were identified between therapists who were directly involved in the project and Interventions compared with uninvolved therapists. In 2015, no significant differences existed between involved and uninvolved therapists.

CONCLUSIONS

After 6 years of sustained implementation efforts, the Battery of Rehabilitation Assessments and Interventions expedited the adoption of EBPs throughout a large system of care in rehabilitation.

Global Network for Women's and Children's Health Research: probable causes of stillbirth in low- and middle-income countries using a prospectively defined classification system

OBJECTIVE

We sought to classify causes of stillbirth for six low-middle-income countries using a prospectively defined algorithm.

DESIGN

Prospective, observational study.

SETTING

Communities in India, Pakistan, Guatemala, Democratic Republic of Congo, Zambia and Kenya.

POPULATION

Pregnant women residing in defined study regions.

METHODS

Basic data regarding conditions present during pregnancy and delivery were collected. Using these data, a computer-based hierarchal algorithm assigned cause of stillbirth. Causes included birth trauma, congenital anomaly, infection, asphyxia, and preterm birth, based on existing cause of death classifications and included contributing maternal conditions.

MAIN OUTCOME MEASURES

Primary cause of stillbirth.

RESULTS

Of 109 911 women who were enrolled and delivered (99% of those screened in pregnancy), 2847 had a stillbirth (a rate of 27.2 per 1000 births). Asphyxia was the cause of 46.6% of the stillbirths, followed by infection (20.8%), congenital anomalies (8.4%) and prematurity (6.6%). Among those caused by asphyxia, 38% had prolonged or obstructed labour, 19% antepartum haemorrhage and 18% pre-eclampsia/eclampsia. About two-thirds (67.4%) of the stillbirths did not have signs of maceration.

CONCLUSIONS

Our algorithm determined cause of stillbirth from basic data obtained from lay-health providers. The major cause of stillbirth was fetal asphyxia associated with prolonged or obstructed labour, pre-eclampsia and antepartum haemorrhage. In the African sites, infection also was an important contributor to stillbirth. Using this algorithm, we documented cause of stillbirth and its trends to inform public health programs, using consistency, transparency, and comparability across time or regions with minimal burden on the healthcare system.

TWEETABLE ABSTRACT

Major causes of stillbirth are asphyxia, pre-eclampsia and haemorrhage. Infections are important in Africa.

Changes in Upper-Extremity Functional Capacity and Daily Performance During Outpatient Occupational Therapy for People With Stroke

OBJECTIVE

This study explored how upper-extremity (UE) functional capacity and daily performance change during the course of outpatient rehabilitation in people with stroke.

METHOD

Fifteen participants receiving outpatient occupational therapy services for UE paresis poststroke were enrolled. UE motor capacity was measured with the Action Research Arm Test (ARAT), and UE performance was measured using bilateral, wrist-worn accelerometers. Measurements were taken at or near the start of therapy, at every 10th visit or every 30 days throughout the duration of services, and at discharge.

RESULTS

Three patterns were observed: (1) increase in ARAT scores and more normalized accelerometry profiles, (2) increase in ARAT scores but no change in accelerometry profiles, and (3) no change in ARAT scores or in accelerometry profiles.

CONCLUSION

UE performance in daily life was highly variable, with inconsistencies between change in UE capacity and change in UE performance. UE capacity and performance are important constructs to assess separately during rehabilitation.

Local Pharmacy Partnership to Prevent Pediatric Asthma Reutilization in a Satellite Hospital

OBJECTIVES

In our previous work, providing medications in-hand at discharge was a key strategy to reduce asthma reutilization (readmissions and emergency revisits) among children in a large, urban county. We sought to spread this work to our satellite hospital in an adjacent county. A key initial barrier was the lack of an outpatient pharmacy on site, so we sought to determine if a partnership with community pharmacies could improve the percentage of patients with medications in-hand at discharge, thus decreasing reutilization.

METHODS

A multidisciplinary team partnered with community pharmacies. Using rapid-cycle improvement methods, the team aimed to reduce asthma reutilization by providing medications in-hand at discharge. Run charts were used to display the proportion of patients with asthma discharged with medications in-hand and to track 90-day reutilization rates.

RESULTS

During the intervention period, the median percentage of patients with asthma who received medications in-hand increased from 0% to 82%. A key intervention was the expansion of the medication in-hand program to all patients. Additional changes included expanding team to evening stakeholders, narrowing the number of community partners, and building electronic tools to support key processes. The mean percentage of patients with asthma discharged from the satellite who had a readmission or emergency department revisit within 90 days of their index admission decreased from 18% to 11%.

CONCLUSIONS

Impacting population-level asthma outcomes requires partnerships between community resources and health providers. When hospital resources are limited, community pharmacies are a potential partner, and providing access to medications in-hand at hospital discharge can reduce asthma reutilization.

Feasibility of high-repetition, task-specific training for individuals with upper-extremity paresis

OBJECTIVE. We investigated the feasibility of delivering an individualized, progressive, high-repetition upper-extremity (UE) task-specific training protocol for people with stroke in the inpatient rehabilitation setting. METHOD. Fifteen patients with UE paresis participated in this study. Task-specific UE training was scheduled for 60 min/day, 4 days/wk, during occupational therapy for the duration of a participant's inpatient stay. During each session, participants were challenged to complete ≥300 repetitions of various tasks. RESULTS. Participants averaged 289 repetitions/session, spending 47 of 60 min in active training. Participants improved on impairment and activity level outcome measures. CONCLUSION. People with stroke in an inpatient setting can achieve hundreds of repetitions of task-specific training in 1-hr sessions. As expected, all participants improved on functional outcome measures. Future studies are needed to determine whether this high-repetition training program results in better outcomes than current UE interventions.

Feasibility of Focused Stepping Practice During Inpatient Rehabilitation Poststroke and Potential Contributions to Mobility Outcomes

BACKGROUND

Optimal physical therapy strategies to maximize locomotor function in patients early poststroke are not well established. Emerging data indicate that substantial amounts of task-specific stepping practice may improve locomotor function, although stepping practice provided during inpatient rehabilitation is limited (<300 steps/session).

OBJECTIVE

The purpose of this investigation was to determine the feasibility of providing focused stepping training to patients early poststroke and its potential association with walking and other mobility outcomes.

METHODS

Daily stepping was recorded on 201 patients <6 months poststroke (80% < 1 month) during inpatient rehabilitation following implementation of a focused training program to maximize stepping practice during clinical physical therapy sessions. Primary outcomes included distance and physical assistance required during a 6-minute walk test (6MWT) and balance using the Berg Balance Scale (BBS). Retrospective data analysis included multiple regression techniques to evaluate the contributions of demographics, training activities, and baseline motor function to primary outcomes at discharge.

RESULTS

Median stepping activity recorded from patients was 1516 steps/d, which is 5 to 6 times greater than that typically observed. The number of steps per day was positively correlated with both discharge 6MWT and BBS and improvements from baseline (changes; r = 0.40-0.87), independently contributing 10% to 31% of the total variance. Stepping activity also predicted level of assistance at discharge and discharge location (home vs other facility).

CONCLUSION

Providing focused, repeated stepping training was feasible early poststroke during inpatient rehabilitation and was related to mobility outcomes. Further research is required to evaluate the effectiveness of these training strategies on short- or long-term mobility outcomes as compared with conventional interventions.

Outbreak of pyrazinamide-monoresistant tuberculosis identified using genotype cluster and social media analysis

SETTING

Monoresistance to pyrazinamide (PZA) has infrequently been associated with Mycobacterium tuberculosis.

OBJECTIVE

To report an outbreak of PZA-monoresistant M. tuberculosis in Virginia involving two genotype clusters from December 2004 to August 2010.

RESULTS

Thirty cases were identified involving a predominantly young, US-born population with histories of substance use and incarceration and a large proportion of children aged <15 years (n= 6, 20%); of these, 23 cases (77%) were culture-confirmed as M. tuberculosis complex. DNA fingerprinting and molecular analysis of the PZA resistance gene, pncA, demonstrated a clonal strain that was not M. bovis. Genotypic data provided the initial link between seemingly unrelated cases, and helped reveal a historic genotype cluster of cases from 2004. Further genotype cluster and contact investigation procedures, including the novel use of the social networking website Facebook.com, revealed additional links between the 2004 and 2009 genotype clusters and described an ongoing, extensive outbreak necessitating an enhanced screening and treatment protocol for contacts.

CONCLUSIONS

This outbreak demonstrates how tuberculosis can spread through a young, vulnerable population. The use of genotypic data and the novel incorporation of social media investigations were critical to understanding the settings and context of infectivity.

The effectiveness of physical therapist-administered group-based exercise on fall prevention: a systematic review of randomized controlled trials

BACKGROUND

Falls are a verified cause of morbidity and mortality in adults older than 65 years. Exercise under the direction of a physical therapist has been shown to reduce the risk of falls in older adults; however, it is not clear whether physical therapist-directed group-based exercise could produce similar results.

PURPOSE

The purpose of this systematic review was to summarize the evidence on the effectiveness of physical therapist-administered group-based exercise when compared with various controls for falls prevention and improvement of quality of life.

METHODS

A computerized search of PubMed and CINAHL was performed. An exhaustive hand search was also performed of the references of all full-text articles. Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines were followed for this review. Studies were included if they met the following criteria: (1) comparison of group-based exercise led by a physical therapist to a control group; (2) ambulatory elderly men or women, aged 65 years or older; (3) subjects in the community or institutional setting; (4) the use of 1 or more outcome measures related to functional balance and/or quality of life; (5) randomized controlled or clinical trials; and (6) published in English, between December 1, 2001, and June 7, 2012. The PEDro scale was used to assess the quality of each study included in this review.

RESULTS

The computerized search strategy and hand search revealed 213 potential articles, 10 of which met the inclusion criteria. After assessment with the PEDro scale, 8 of these were considered high-quality studies (score > 6/10). Seven studies compared group-based exercise to a nonexercise control group, while 3 studies compared group-based exercise with a physical therapist-prescribed home exercise program. Outcomes measured include fall rate, balance, physical performance, health-related quality of life, and fear of falling.

DISCUSSION

When group-based exercise was compared with no intervention, group-based exercise was found to be more effective in decreasing fall frequency, increase balance, and improve quality of life. When compared with a physical therapist-prescribed home exercise program, the group-based exercise results were not statistically different but showed improvements in some quality of life and physical functioning measures. There is also some evidence to suggest that group-based exercise promotes greater patient satisfaction and exercise adherence.

CONCLUSION

There is preliminary evidence to suggest that the group-based exercise is effective for falls prevention, quality-of-life enhancement, and balance improvements in the older adults comparable with traditional home exercise programs.

Development and use of a knowledge translation tool: the rehabilitation measures database

Clinical translation of research evidence is a challenge for rehabilitation clinicians. Publicly accessible and free, online educational resources that summarize research evidence can support implementation of research evidence into practice. Several online resources have been developed recently to overcome common knowledge translation barriers. The Rehabilitation Measures Database (RMD) is a free, web-based searchable database of standardized instruments that was designed to support knowledge translation. It helps clinicians select valid and sensitive instruments for screening patients, monitoring progress, and assessing rehabilitation outcomes. The RMD was developed using feedback from focus groups and beta-test participants. Since its launch in 2011, RMD use has grown to an average of 1851 hits per day from 168 countries. As of September 2013, 202 instrument summaries are viewable in the RMD. Most summaries are linked to copies of the instrument or to purchase instructions. A challenge in updating and expanding the RMD is securing the resources to ensure its future. Collaborative relationships with professional associations and graduate programs in the health sciences are critical in sustaining this resource.

Carbene catalysts

The use of N-heterocyclic carbenes as catalysts for organic transformations has received increased attention in the past 10 years. A discussion of catalyst development and nucleophilic characteristics precedes a description of recent advancements and new reactions using N-heterocyclic carbenes in catalysis.

Mechanistic investigation of the enantioselective intramolecular stetter reaction: proton transfer is the first irreversible step

A study on the mechanism of the asymmetric intramolecular Stetter reaction is reported. This investigation includes the determination of the rate law, kinetic isotope effects, and competition experiments. The reaction was found to be first order in aldehyde and azolium catalyst or free carbene. A primary kinetic isotope effect was found for the proton of the aldehyde. Taken together with a series of competition experiments, these results suggest that proton transfer from the tetrahedral intermediate formed upon nucleophilic attack of the carbene onto the aldehyde is the first irreversible step.

Pursuing the panderer: an analysis of United States v. Williams

In May 2008, the Supreme Court addressed whether the government can regulate the ownership and distribution of virtual child pornography. U.S. v. Williams marked the first time the Court directly addressed the concept of pandering virtual child pornography. This article examines the Court's decision in U.S. v. Williams and the relative importance of its holding. In U.S. v. Williams, the Supreme Court upheld an act of Congress targeting the business people behind the child pornography market. Restricting the sale of both real and virtual child pornography is essential to combat the various problems surrounding its existence, which include policing its creation and distribution on the Internet as well as the connection between child pornography and subsequent sexual offenses against children.

Locomotor Training Improves Daily Stepping Activity and Gait Efficiency in Individuals Poststroke Who Have Reached a “Plateau” in Recovery

Background and Purpose— Individuals with chronic stroke often demonstrate a “plateau,” or deceleration of motor recovery, which may lead to discharge from physical therapy (PT). However, numerous studies report improvements in motor function when individuals are provided intensive practice of motor tasks. We suggest that reduced task-specific walking practice during clinical PT contributes to limited gains in ambulatory function in those with a perceived plateau poststroke, and suggest that further gains can be realized if intensive stepping, or locomotor training (LT) is provided after discharge.

Methods— Twenty subjects with chronic stroke completed a repeated baseline measures, randomized crossover trial in which walking performance was assessed during the last 4 weeks of clinical PT before discharge secondary to reaching a plateau, followed by 4 weeks of intensive LT and 4 weeks of no intervention. Outcome measures included clinical and physiological (metabolic) measures of walking overground and on a treadmill, and measures of daily stepping activity in the home and community, including during clinical PT and subsequent LT sessions.

Results— Stepping practice was more than 4-fold higher during LT versus clinical PT sessions, with significant improvements in daily stepping and gait efficiency only after LT. Changes in daily stepping after clinical PT and intensive LT were correlated ( P <0.001) with the amount of stepping practice received during these interventions.

Conclusions— Intensive LT results in improved daily stepping in individuals poststroke who have been discharged from PT because of a perceived plateau in motor function. These improvements may be related to the amount and intensity of stepping practice.

A longitudinal study of indoor nitrogen dioxide levels and respiratory symptoms in inner-city children with asthma

BACKGROUND

The effect of indoor nitrogen dioxide concentrations on asthma morbidity among inner-city preschool children is uncertain.

OBJECTIVES

Our goal was to estimate the effect of indoor NO2 concentrations on asthma morbidity in an inner-city population while adjusting for other indoor pollutants.

METHODS

We recruited 150 children (2-6 years of age) with physician-diagnosed asthma from inner-city Baltimore, Maryland. Indoor air was monitored over a 72-hr period in the children's bedrooms at baseline and 3 and 6 months. At each visit, the child's caregiver completed a questionnaire assessing asthma symptoms over the previous 2 weeks and recent health care utilization.

RESULTS

Children were 58% male, 91% African American, and 42% from households with annual income < $25,000; 63% had persistent asthma symptoms. The mean (+/- SD) in-home NO2 concentration was 30.0 +/- 33.7 (range, 2.9-394.0) ppb. The presence of a gas stove and the use of a space heater or oven/stove for heat were independently associated with higher NO2 concentrations. Each 20-ppb increase in NO2 exposure was associated significantly with an increase in the number of days with limited speech [incidence rate ratio (IRR) = 1.15; 95% confidence interval (CI), 1.05-1.25], cough (IRR = 1.10; 95% CI, 1.02-1.18), and nocturnal symptoms (IRR = 1.09; 95% CI, 1.02-1.16), after adjustment for potential confounders. NO2 concentrations were not associated with increased health care utilization.

CONCLUSIONS

Higher indoor NO2 concentrations were associated with increased asthma symptoms in preschool inner-city children. Interventions aimed at lowering NO2 concentrations in inner-city homes may reduce asthma morbidity in this vulnerable population.

Enhanced gait-related improvements after therapist- versus robotic-assisted locomotor training in subjects with chronic stroke: a randomized controlled study

BACKGROUND AND PURPOSE

Locomotor training (LT) using a treadmill can improve walking ability over conventional rehabilitation in individuals with hemiparesis, although the personnel requirements often necessary to provide LT may limit its application. Robotic devices that provide consistent symmetrical assistance have been developed to facilitate LT, although their effectiveness in improving locomotor ability has not been well established.

METHODS

Forty-eight ambulatory chronic stroke survivors stratified by severity of locomotor deficits completed a randomized controlled study on the effects of robotic- versus therapist-assisted LT. Both groups received 12 LT sessions for 30 minutes at similar speeds, with guided symmetrical locomotor assistance using a robotic orthosis versus manual facilitation from a single therapist using an assist-as-needed paradigm. Outcome measures included gait speed and symmetry, and clinical measures of activity and participation.

RESULTS

Greater improvements in speed and single limb stance time on the impaired leg were observed in subjects who received therapist-assisted LT, with larger speed improvements in those with less severe gait deficits. Perceived rating of the effects of physical limitations on quality of life improved only in subjects with severe gait deficits who received therapist-assisted LT.

CONCLUSIONS

Therapist-assisted LT facilitates greater improvements in walking ability in ambulatory stroke survivors as compared to a similar dosage of robotic-assisted LT.

Scope of the asymmetric intramolecular stetter reaction catalyzed by chiral nucleophilic triazolinylidene carbenes

A highly enantioselective intramolecular Stetter reaction of aromatic and aliphatic aldehydes tethered to different Michael acceptors has been developed. Two triazolium scaffolds have been identified that catalyze the intramolecular Stetter reaction with good reactivity and enantioselectivity. The substrate scope has been examined and found to be broad; both electron-rich and -poor aromatic aldehydes undergo cyclization in high yield and enantioselectivity. The tether can include oxygen, sulfur, nitrogen, and carbon linkers with no detrimental effects. In addition, the incorporation of various tethered Michael acceptors includes amides, esters, thioesters, ketones, aldehydes, and nitriles. The catalyst loading may be reduced to 3 mol % without significantly affecting the reactivity or selectivity of the reaction.

Cardiovascular effects of cadence and workload

Increases in cadence may augment SV during submaximal cycling (> 65 % VO2max) via effects of increased muscle pump activity on preload. At lower workloads (45 - 65 % VO2max), SV tends to plateau, suggesting that effects of increases in cadence on pump activity have little influence on SV. We hypothesized that cadence-induced increases in CO at submaximal workloads, where SV tends to plateau, are due to elevations in HR and/or O2 extraction. SV, CO, HR, VO2, and delta a - vO2 were assessed at 80 and 100 rpm during workloads of 50 % (LO) or 65 % (HI) of VO2max in 11 male cyclists. No changes in SV were seen. CO was higher at 100 rpm in 10 of 11 subjects at LO (18.1 +/- 2.7 vs. 17.2 +/- 2.6 L/min). VO2 at both workloads was greater at 100 than 80 rpm as was HR (LO: 129 +/- 11 vs. 121 +/- 10 beats/min; HI: 146 +/- 13 vs. 139 +/- 14 beats/min) (p < 0.05). delta a - vO2 was greater at HI compared to LO at 80 (15.1 +/- 1.6 vs. 13.6 +/- 1.3 ml) and 100 rpm (16.0 +/- 1.7 vs. 15.1 +/- 1.6 ml) (p < 0.05). Results suggest that increases in O2 demand during low submaximal cycling (50 % VO2max) at high cadences are met by HR-induced increases in CO. At higher workloads (65 % VO2max), inability of higher cadences to increase CO and O2 delivery is offset by greater O2 extraction.

Comparing contributions of soil versus root colonization to variations in stomatal behavior and soil drying in mycorrhizal Sorghum bicolor and Cucurbita pepo

In prior studies we learned that colonization of soil can be as important as colonization of roots in determining mycorrhizal influence on the water relations of host plants. Here we use a path analysis modeling approach to test (a) whether quantity of hyphae in soil contributes to variations in stomatal behavior and soil drying, and (b) whether soil colonization or root colonization has a stronger influence on these stomatal and soil drying responses. Experiments were performed on Sorghum bicolor and Cucurbita pepo, with soils and roots colonized by a mixture of Glomus intraradices and Gigaspora margarita. Soil colonization generally made more significant contributions to stomatal conductance than did root colonization. Soil colonization did not make significant direct contributions to soil water potential measures (soil water potential at stomatal closure or soil drying rate), whereas root colonization did contribute a potentially important path to each. The findings further support a role for mycorrhization of the soil itself in contributing to the regulation of stomatal behavior of host plants.

Mycorrhizal symbiosis and response of sorghum plants to combined drought and salinity stresses

Arbuscular mycorrhizal (AM) symbiosis can confer increased host resistance to drought stress, although the effect is unpredictable. Since AM symbiosis also frequently increases host resistance to salinity stress, and since drought and salinity stress are often linked in drying soils, we speculated that the AM influence on plant drought response may be partially the result of AM influence on salinity stress. We tested the hypothesis that AM-induced effects on drought responses would be more pronounced when plants of comparable size are exposed to drought in salinized soils. In two greenhouse experiments, several water relations characteristics were measured in sorghum plants colonized by Glomus intraradices (Gi), Gigaspora margarita (Gm) or a mixture of AM species, during a sustained drought following exposure to salinity treatments (NaCl stress, osmotic stress via concentrated macronutrients, or soil leaching). The presence of excess salt in soils widened the difference in drought responses between AM and nonAM plants in just two instances. Days required for plants to reach stomatal closure were similar for Gi and nonAM plants exposed to drought alone, but with exposure to combined NaCl and drought stress, stomates of Gi plants remained open 17-22% longer than in nonAM plants. Promotion of stomatal conductance by Gm occurred with exposure to NaCl/drought stress but not with drought alone or with soil leaching before drought. In other instances, however, the addition of salt tended to nullify an AM-induced change in drought response. Our findings confirm that AM fungi can alter host response to drought but do not lend much support to the idea that AM-induced salt resistance might help explain why AM plants can be more resilient to drought stress than their nonAM counterparts.