Your browser doesn't support javascript.
loading
Mostrar: 20 | 50 | 100
Resultados 1 - 12 de 12
Filtrar
Mais filtros

Bases de dados
Tipo de documento
Intervalo de ano de publicação
1.
Schizophr Bull ; 50(2): 238-265, 2024 Mar 07.
Artigo em Inglês | MEDLINE | ID: mdl-37606276

RESUMO

BACKGROUND: Ecological momentary assessment (EMA) involves completing multiple surveys over time in daily life, capturing in-the-moment experiences in real-world contexts. EMA use in psychosis studies has surged over several decades. To critically examine EMA use in psychosis research and assist future researchers in designing new EMA studies, this systematic review aimed to summarize the methodological approaches used for positive symptoms in psychosis populations and evaluate feasibility with a focus on completion rates. METHODS: A systematic review of PubMed, PsycINFO, MEDLINE, Web of Science, EBSCOhost, and Embase databases using search terms related to EMA and psychosis was conducted. Excluding duplicate samples, a meta-analysis was conducted of EMA survey completion rates and meta-regression to examine predictors of completion. RESULTS: Sixty-eight studies were included in the review. Characteristics and reporting of EMA methodologies were variable across studies. The meta-mean EMA survey completion computed from the 39 unique studies that reported a mean completion rate was 67.15% (95% CI = 62.3, 71.9), with an average of 86.25% of the sample meeting a one-third EMA completion criterion. No significant predictors of completion were found in the meta-regression. A variety of EMA items were used to measure psychotic experiences, of which few were validated. CONCLUSIONS: EMA methods have been widely applied in psychosis studies using a range of protocols. Completion rates are high, providing clear evidence of feasibility in psychosis populations. Recommendations for reporting in future studies are provided.


Assuntos
Avaliação Momentânea Ecológica , Transtornos Psicóticos , Humanos , Estudos de Viabilidade , Inquéritos e Questionários , Projetos de Pesquisa
2.
Front Psychiatry ; 14: 1192655, 2023.
Artigo em Inglês | MEDLINE | ID: mdl-37559917

RESUMO

Aim: There is growing interest in tailoring psychological interventions for distressing voices and a need for reliable tools to assess phenomenological features which might influence treatment response. This study examines the reliability and internal consistency of the Voice Characterisation Checklist (VoCC), a novel 10-item tool which assesses degree of voice characterisation, identified as relevant to a new wave of relational approaches. Methods: The sample comprised participants experiencing distressing voices, recruited at baseline on the AVATAR2 trial between January 2021 and July 2022 (n = 170). Inter-rater reliability (IRR) and internal consistency analyses (Cronbach's alpha) were conducted. Results: The majority of participants reported some degree of voice personification (94%) with high endorsement of voices as distinct auditory experiences (87%) with basic attributes of gender and age (82%). While most identified a voice intention (75%) and personality (76%), attribution of mental states (35%) to the voice ('What are they thinking?') and a known historical relationship (36%) were less common. The internal consistency of the VoCC was acceptable (10 items, α = 0.71). IRR analysis indicated acceptable to excellent reliability at the item-level for 9/10 items and moderate agreement between raters' global (binary) classification of more vs. less highly characterised voices, κ = 0.549 (95% CI, 0.240-0.859), p < 0.05. Conclusion: The VoCC is a reliable and internally consistent tool for assessing voice characterisation and will be used to test whether voice characterisation moderates treatment outcome to AVATAR therapy. There is potential wider utility within clinical trials of other relational therapies as well as routine clinical practice.

3.
Health Technol Assess ; 26(27): 1-174, 2022 05.
Artigo em Inglês | MEDLINE | ID: mdl-35639493

RESUMO

BACKGROUND: Relapse is a major determinant of outcome for people with a diagnosis of schizophrenia. Early warning signs frequently precede relapse. A recent Cochrane Review found low-quality evidence to suggest a positive effect of early warning signs interventions on hospitalisation and relapse. OBJECTIVE: How feasible is a study to investigate the clinical effectiveness and cost-effectiveness of a digital intervention to recognise and promptly manage early warning signs of relapse in schizophrenia with the aim of preventing relapse? DESIGN: A multicentre, two-arm, parallel-group cluster randomised controlled trial involving eight community mental health services, with 12-month follow-up. SETTINGS: Glasgow, UK, and Melbourne, Australia. PARTICIPANTS: Service users were aged > 16 years and had a schizophrenia spectrum disorder with evidence of a relapse within the previous 2 years. Carers were eligible for inclusion if they were nominated by an eligible service user. INTERVENTIONS: The Early signs Monitoring to Prevent relapse in psychosis and prOmote Wellbeing, Engagement, and Recovery (EMPOWER) intervention was designed to enable participants to monitor changes in their well-being daily using a mobile phone, blended with peer support. Clinical triage of changes in well-being that were suggestive of early signs of relapse was enabled through an algorithm that triggered a check-in prompt that informed a relapse prevention pathway, if warranted. MAIN OUTCOME MEASURES: The main outcomes were feasibility of the trial and feasibility, acceptability and usability of the intervention, as well as safety and performance. Candidate co-primary outcomes were relapse and fear of relapse. RESULTS: We recruited 86 service users, of whom 73 were randomised (42 to EMPOWER and 31 to treatment as usual). Primary outcome data were collected for 84% of participants at 12 months. Feasibility data for people using the smartphone application (app) suggested that the app was easy to use and had a positive impact on motivations and intentions in relation to mental health. Actual app usage was high, with 91% of users who completed the baseline period meeting our a priori criterion of acceptable engagement (> 33%). The median time to discontinuation of > 33% app usage was 32 weeks (95% confidence interval 14 weeks to ∞). There were 8 out of 33 (24%) relapses in the EMPOWER arm and 13 out of 28 (46%) in the treatment-as-usual arm. Fewer participants in the EMPOWER arm had a relapse (relative risk 0.50, 95% confidence interval 0.26 to 0.98), and time to first relapse (hazard ratio 0.32, 95% confidence interval 0.14 to 0.74) was longer in the EMPOWER arm than in the treatment-as-usual group. At 12 months, EMPOWER participants were less fearful of having a relapse than those in the treatment-as-usual arm (mean difference -4.29, 95% confidence interval -7.29 to -1.28). EMPOWER was more costly and more effective, resulting in an incremental cost-effectiveness ratio of £3041. This incremental cost-effectiveness ratio would be considered cost-effective when using the National Institute for Health and Care Excellence threshold of £20,000 per quality-adjusted life-year gained. LIMITATIONS: This was a feasibility study and the outcomes detected cannot be taken as evidence of efficacy or effectiveness. CONCLUSIONS: A trial of digital technology to monitor early warning signs that blended with peer support and clinical triage to detect and prevent relapse is feasible. FUTURE WORK: A main trial with a sample size of 500 (assuming 90% power and 20% dropout) would detect a clinically meaningful reduction in relapse (relative risk 0.7) and improvement in other variables (effect sizes 0.3-0.4). TRIAL REGISTRATION: This trial is registered as ISRCTN99559262. FUNDING: This project was funded by the National Institute for Health and Care Research (NIHR) Health Technology Assessment programme and will be published in full in Health Technology Assessment; Vol. 26, No. 27. See the NIHR Journals Library website for further project information. Funding in Australia was provided by the National Health and Medical Research Council (APP1095879).


WHAT WAS THE PROBLEM?: Relapse is a considerable problem for people with a diagnosis of schizophrenia. Relapse can be predicted by early warning signs that are unique to the person. They include withdrawal, fear and paranoia. WHAT WAS THE QUESTION?: Is it possible to investigate the effectiveness of an intervention to recognise and promptly manage early warning signs of relapse in schizophrenia with the aim of preventing relapse? WHAT DID WE DO?: We spoke with 88 mental health staff, 40 carers and 21 service users before we designed a system that used a mobile phone to help people monitor early warning signs. We included peer support to help people using the system reflect on their experiences. We hoped the overall system, called EMPOWER, would help people to be more in charge of their mental health. After consenting 86 people to the study, we were able to randomly assign 73 people either to use the EMPOWER system (42 people) or to receive their normal treatment alone (31 people). We used research measures over 1 year to help us better understand people's experiences. We also involved carers (for example family or friends) and mental health service providers in the research. WHAT DID WE FIND?: We found that it was possible to recruit people to the study and to gather research data. We also found that people used the EMPOWER system and found it acceptable. We found that those who used EMPOWER had a lower rate of relapse over 12 months than people who did not. They were also less likely to be fearful of relapse. We found that EMPOWER was likely to be cost-effective. WHAT DOES THIS MEAN?: This means that a study to investigate the effectiveness of a system to recognise and respond to early warning signs of relapse in schizophrenia is possible.


Assuntos
Transtornos Psicóticos , Esquizofrenia , Doença Crônica , Estudos de Viabilidade , Humanos , Transtornos Psicóticos/diagnóstico , Transtornos Psicóticos/prevenção & controle , Recidiva , Esquizofrenia/diagnóstico , Esquizofrenia/prevenção & controle , Smartphone
4.
Lancet Psychiatry ; 9(6): 477-486, 2022 06.
Artigo em Inglês | MEDLINE | ID: mdl-35569503

RESUMO

BACKGROUND: Early warning signs monitoring by service users with schizophrenia has shown promise in preventing relapse but the quality of evidence is low. We aimed to establish the feasibility of undertaking a definitive randomised controlled trial to determine the effectiveness of a blended digital intervention for relapse prevention in schizophrenia. METHODS: This multicentre, feasibility, cluster randomised controlled trial aimed to compare Early signs Monitoring to Prevent relapse in psychosis and prOmote Well-being, Engagement, and Recovery (EMPOWER) with treatment as usual in community mental health services (CMHS) in Glasgow and Melbourne. CMHS were the unit of randomisation, selected on the basis of those that probably had five or more care coordinators willing to participate. Participants were eligible if they were older than 16 years, had a schizophrenia or related diagnosis confirmed via case records, were able to provide informed consent, had contact with CMHS, and had had a relapse within the previous 2 years. Participants were randomised within stratified clusters to EMPOWER or to continue their usual approach to care. EMPOWER blended a smartphone for active monitoring of early warning signs with peer support to promote self-management and clinical triage to promote access to relapse prevention. Main outcomes were feasibility, acceptability, usability, and safety, which was assessed through face-to-face interviews. App usage was assessed via the smartphone and self-report. Primary end point was 12 months. Participants, research assistants and other team members involved in delivering the intervention were not masked to treatment conditions. Assessment of relapse was done by an independent adjudication panel masked to randomisation group. The study is registered at ISRCTN (99559262). FINDINGS: We identified and randomised eight CMHS (six in Glasgow and two in Melbourne) comprising 47 care coordinators. We recruited 86 service users between Jan 19 and Aug 8, 2018; 73 were randomised (42 [58%] to EMPOWER and 31 [42%] to treatment as usual). There were 37 (51%) men and 36 (49%) women. At 12 months, main outcomes were collected for 32 (76%) of service users in the EMPOWER group and 30 (97%) of service users in the treatment as usual group. Of those randomised to EMPOWER, 30 (71%) met our a priori criterion of more than 33% adherence to daily monitoring that assumed feasibility. Median time to discontinuation of these participants was 31·5 weeks (SD 14·5). There were 29 adverse events in the EMPOWER group and 25 adverse events in the treatment as usual group. There were 13 app-related adverse events, affecting 11 people, one of which was serious. Fear of relapse was lower in the EMPOWER group than in the treatment as usual group at 12 months (mean difference -7·53 (95% CI -14·45 to 0·60; Cohen's d -0·53). INTERPRETATION: A trial of digital technology to monitor early warning signs blended with peer support and clinical triage to detect and prevent relapse appears to be feasible, safe, and acceptable. A further main trial is merited. FUNDING: UK National Institute for Health Research Health Technology Assessment programme and the Australian National Health and Medical Research Council.


Assuntos
Esquizofrenia , Austrália , Análise Custo-Benefício , Estudos de Viabilidade , Feminino , Humanos , Masculino , Recidiva , Esquizofrenia/prevenção & controle , Escócia , Prevenção Secundária
5.
BMC Psychiatry ; 22(1): 82, 2022 02 03.
Artigo em Inglês | MEDLINE | ID: mdl-35114980

RESUMO

BACKGROUND: There is good evidence that psychological interventions improve patient well-being and independent living, but patients on acute mental health wards often do not have access to evidence-based psychological therapies which are strongly advised by NICE guidance for severe mental health problems. The overall aim of this programme of work is to increase patient access to psychological therapies on acute mental health inpatient wards. Stage one of the programme (which is complete) aimed to identify barriers and facilitators to delivering therapy in these settings through a large qualitative study. The key output of stage one was an intervention protocol that is designed to be delivered on acute wards to increase patient access to psychologically-informed care and therapy. Stage two of the programme aims to test the effects of the intervention on patient wellbeing and serious incidents on the ward (primary outcomes), patient social functioning and symptoms, staff burnout, ward atmosphere from staff and patient perspectives and cost effectiveness of the intervention (secondary outcomes). METHODS: The study is a single blind, pragmatic, cluster randomised controlled trial and will recruit thirty-four wards across England that will be randomised to receive the new intervention plus treatment as usual, or treatment as usual only. Primary and secondary outcomes will be assessed at baseline and 6-month and 9-month follow-ups, with serious incidents on the ward collected at an additional 3-month follow-up. DISCUSSION: The key output will be a potentially effective and cost-effective ward-based psychological intervention that increases patient access to psychological therapy in inpatient settings, is feasible to deliver in inpatient settings and is acceptable to patients. TRIAL REGISTRATION NUMBER: ClinicalTrials.gov Identifier: NCT03950388. Registered 15th May 2019. https://clinicaltrials.gov/ct2/show/NCT03950388.


Assuntos
Esgotamento Profissional , Pessoas Mentalmente Doentes , Análise Custo-Benefício , Humanos , Saúde Mental , Método Simples-Cego
6.
IEEE J Biomed Health Inform ; 25(5): 1770-1780, 2021 05.
Artigo em Inglês | MEDLINE | ID: mdl-33055042

RESUMO

Wearable and mobile technology provides new opportunities to manage health conditions remotely and unobtrusively. For example, healthcare providers can repeatedly sample a person's condition to monitor progression of symptoms and intervene if necessary. There is usually a utility-tolerability trade-off between collecting information at sufficient frequencies and quantities to be useful, and over-burdening the user or the underlying technology, particularly when active input is required from the user. Selecting the next sampling time adaptively using previous responses, so that people are only sampled at high frequency when necessary, can help to manage this trade-off. We present a novel approach to adaptive sampling using clustered continuous-time hidden Markov models. The model predicts, at any given sampling time, the probability of moving to an 'alert' state, and the next sample time is scheduled when this probability has exceeded a given threshold. The clusters, each representing a distinct sub-model, allow heterogeneity in states and state transitions. The work is illustrated using longitudinal mental-health symptom data in 49 people collected using ClinTouch, a mobile app designed to monitor people with a diagnosis of schizophrenia. Using these data, we show how the adaptive sampling scheme behaves under different model parameters and risk thresholds, and how the average sampling can be substantially reduced whilst maintaining a high sampling frequency during high-risk periods.


Assuntos
Aplicativos Móveis , Esquizofrenia , Avaliação Momentânea Ecológica , Humanos , Saúde Mental , Monitorização Fisiológica
7.
Early Interv Psychiatry ; 14(1): 37-43, 2020 02.
Artigo em Inglês | MEDLINE | ID: mdl-30908854

RESUMO

AIMS: Co-design implies genuine partnership in the generation of knowledge between service users and researchers. Service user involvement in research has been encouraged in government policy, but it is rarely achieved, especially at trial initial stages. Co-designed with service users, we adapted existing manualised social cognition intervention for people with a first episode of psychosis to a virtual world environment. METHODS: We invited a group of young people who have used mental health services to co-design a virtual environment to deliver an accessible social cognition intervention to a hard to engage service user group. We used an iterative process with young service users and the design team that included developing initial ideas, creating a prototype and testing the virtual world. RESULTS: Twenty young service users of local mental healthcare services provided feedback on the design and delivery of the intervention. Reflecting the demographic of the sample, young people felt the virtual environment should be familiar, urban spaces, akin to therapy rooms or classrooms they have used in real-life situations rather than non-traditional therapy spaces that were initially proposed. CONCLUSION: The co-design process led to the development of a specific design, approach and protocol to be tested in a proof-of-concept trial. Young service users were integral to an agile and iterative design. Technological innovations should be routinely co-designed and co-produced if they are to realise their potential to deliver acceptable and affordable mental health interventions.


Assuntos
Terapia Cognitivo-Comportamental/organização & administração , Participação da Comunidade , Atenção à Saúde/organização & administração , Comunicação Interdisciplinar , Colaboração Intersetorial , Serviços de Saúde Mental/organização & administração , Transtornos Psicóticos/terapia , Cognição Social , Terapia de Exposição à Realidade Virtual/organização & administração , Adolescente , Fatores Etários , Aconselhamento/organização & administração , Retroalimentação , Humanos , Transtornos Psicóticos/psicologia , Reino Unido , Adulto Jovem
8.
Psychol Psychother ; 92(2): 277-297, 2019 06.
Artigo em Inglês | MEDLINE | ID: mdl-30924316

RESUMO

The digital revolution is evolving at an unstoppable pace. Alongside the unprecedented explosion of digital technology facilities and systems, mental health care is under greater pressure than ever before. With its emphasis on big data, computing power, mobile technology, and network information, digital technology is set to transform health care delivery. This article reviews the field of digital health technology assessment and intervention primarily in secondary service mental health care, including the barriers and facilitators to adopting and implementing digitally mediated interventions in service delivery. We consider the impact of digitally mediated communication on human interaction and its potential impact on various mental states such as those linked to mood, anxiety but also well-being. These developments point to a need for both theory- and data-driven approaches to digital health care. We argue that, as developments in digital technology are outpacing the evaluation of rigorous digital health interventions, more advanced methodologies are needed to keep up with the pace of digital technology development. The need for co-production of digital tools with and for people with chronic and mental health difficulties, and implications of digital technology for psychotherapy practice, will be central to this development. PRACTITIONER POINTS: Mental health problems are one of the main causes of global and societal burden and are a growing public health. People with mental health problems around the world have limited, if any, chance of accessing psychological help at all. Technological innovations and solutions are being considered in an attempt to address the size and scale of the mental health crisis worldwide. Digital platforms allow people to self-monitor and self-manage in a way that face-to-face/paper-based methods of assessment have up until now not allowed. We provide examples of digital tools that are being developed and used in the secondary setting and identify a number of challenges in the digital health field that require careful consideration.


Assuntos
Saúde Mental/tendências , Psicoterapia/métodos , Telemedicina/tendências , Necessidades e Demandas de Serviços de Saúde , Humanos , Aplicativos Móveis
9.
Tree Physiol ; 37(9): 1251-1262, 2017 09 01.
Artigo em Inglês | MEDLINE | ID: mdl-28633378

RESUMO

Stems and leaves of Olea europaea L. (olive) avoid freezing damage by substantial supercooling during the winter season. Physiological changes during acclimation to low temperatures were studied in five olive cultivars. Water relations and hydraulic traits, ice nucleation temperature (INT) and temperatures resulting in 50% damage (LT50) were determined. All cultivars showed a gradual decrease in INT and LT50 from the dry and warm summer to the wet and cold winter in Patagonia, Argentina. During acclimation to low temperatures there was an increase in leaf cell wall rigidity and stomatal conductance (gs), as well as a decrease in leaf apoplastic water content, leaf water potential (Ψ), sap flow and stem hydraulic conductivity (ks). More negative Ψ as a consequence of high gs and detrimental effects of low temperatures on root activity resulted in a substantial loss of ks due to embolism formation. Seasonal stem INT decrease from summer to winter was directly related to the xylem resistance to cavitation, determined by the loss of ks across cultivars. Thus the loss of freezable water in xylem vessels by embolisms increased stem supercooling capacity and delayed ice propagation from stems to the leaves. For the first time, a trade-off between xylem resistance to cavitation and stem and leaf supercooling capacity was observed in plants that avoid extracellular freezing by permanent supercooling. The substantial loss of hydraulic function in olive cultivar stems by embolism formation with their high repair costs are compensated by avoiding plant damage at very low subzero temperatures.


Assuntos
Congelamento , Caules de Planta/fisiologia , Madeira/fisiologia , Xilema/fisiologia , Argentina , Folhas de Planta , Estações do Ano , Água
10.
Schizophr Bull ; 42(2): 448-55, 2016 Mar.
Artigo em Inglês | MEDLINE | ID: mdl-26400871

RESUMO

There is currently growing interest in using mobile phones to support the treatment of psychotic disorders, such as schizophrenia. However, the widespread implementation of these interventions will ultimately depend upon patients' access to mobile devices and their willingness to engage with mobile health ("mHealth"). Thus, we conducted a systematic review and meta-analysis to assess mobile phone ownership and interest in mHealth among patients with psychosis. An electronic search of Ovid MEDLINE, Embase, PsycINFO, CENTRAL, AMED, Health Technology Assessment Database, and Health Management Information Consortium Database was conducted, using search terms synonymous with mobile phones and psychotic disorders. The initial literature search yielded 2572 results. Fifteen studies matched eligibility criteria, reporting data from 12 independent samples of psychiatric patients (n = 3227). Data pertaining to mobile phone ownership, usage, and opinions on mHealth among patients with psychotic disorders were extracted from these studies, and meta-analytic techniques were applied. The overall mobile phone ownership rate was 66.4% (95% CI = 54.1%-77.6%). However, we found strong statistical evidence that mobile phone ownership has been significantly increasing since 2007, and the rate among patients surveyed in the last 2 years was 81.4% (n = 454). Furthermore, in surveys of mHealth acceptability, the majority of patients responded in favor of using mobile phones to enhance contact with services and support self-management. Considering the increasing availability of mobile phones and the broad acceptability of mHealth among patients, there is now a need to develop and evaluate mHealth interventions to enhance healthcare services for people with psychosis.


Assuntos
Telefone Celular/estatística & dados numéricos , Aceitação pelo Paciente de Cuidados de Saúde/estatística & dados numéricos , Transtornos Psicóticos , Telemedicina , Humanos
11.
Tree Physiol ; 33(12): 1308-18, 2013 Dec.
Artigo em Inglês | MEDLINE | ID: mdl-24284866

RESUMO

Leaves can be both a hydraulic bottleneck and a safety valve against hydraulic catastrophic dysfunctions, and thus changes in traits related to water movement in leaves and associated costs may be critical for the success of plant growth. A 4-year fertilization experiment with nitrogen (N) and phosphorus (P) addition was done in a semideciduous Atlantic forest in northeastern Argentina. Saplings of five dominant canopy species were grown in similar gaps inside the forests (five control and five N + P addition plots). Leaf lifespan (LL), leaf mass per unit area (LMA), leaf and stem vulnerability to cavitation, leaf hydraulic conductance (K(leaf_area) and K(leaf_mass)) and leaf turgor loss point (TLP) were measured in the five species and in both treatments. Leaf lifespan tended to decrease with the addition of fertilizers, and LMA was significantly higher in plants with nutrient addition compared with individuals in control plots. The vulnerability to cavitation of leaves (P50(leaf)) either increased or decreased with the nutrient treatment depending on the species, but the average P50(leaf) did not change with nutrient addition. The P50(leaf) decreased linearly with increasing LMA and LL across species and treatments. These trade-offs have an important functional significance because more expensive (higher LMA) and less vulnerable leaves (lower P50(leaf)) are retained for a longer period of time. Osmotic potentials at TLP and at full turgor became more negative with decreasing P50(leaf) regardless of nutrient treatment. The K(leaf) on a mass basis was negatively correlated with LMA and LL, indicating that there is a carbon cost associated with increased water transport that is compensated by a longer LL. The vulnerability to cavitation of stems and leaves were similar, particularly in fertilized plants. Leaves in the species studied may not function as safety valves at low water potentials to protect the hydraulic pathway from water stress-induced cavitation. The lack of rainfall seasonality in the subtropical forest studied probably does not act as a selective pressure to enhance hydraulic segmentation between leaves and stems.


Assuntos
Magnoliopsida/fisiologia , Transpiração Vegetal/fisiologia , Argentina , Biomassa , Carbono/farmacologia , Fertilizantes , Magnoliopsida/efeitos dos fármacos , Magnoliopsida/crescimento & desenvolvimento , Nitrogênio/farmacologia , Fenótipo , Fósforo/farmacologia , Folhas de Planta/fisiologia , Caules de Planta/fisiologia , Transpiração Vegetal/efeitos dos fármacos , Árvores , Água/fisiologia
12.
Tree Physiol ; 28(3): 395-404, 2008 Mar.
Artigo em Inglês | MEDLINE | ID: mdl-18171663

RESUMO

Biologists have long been puzzled by the striking morphological and anatomical characteristics of Neotropical savanna trees which have large scleromorphic leaves, allocate more than half of their total biomass to belowground structures and produce new leaves during the peak of the dry season. Based on results of ongoing interdisciplinary projects in the savannas of central Brazil (cerrado), we reassessed the validity of six paradigms to account for the water economy of savanna vegetation. (1) All savanna woody species are similar in their ability to take up water from deep soil layers where its availability is relatively constant throughout the year. (2) There is no substantial competition between grasses and trees for water resources during the dry season because grasses exclusively explore upper soil layers, whereas trees access water in deeper soil layers. (3) Tree species have access to abundant groundwater, their stomatal control is weak and they tend to transpire freely. (4) Savanna trees experience increased water deficits during the dry season despite their access to deep soil water. (5) Stomatal conductance of savanna species is low at night to prevent nocturnal transpiration, particularly during the dry season. (6) Savanna tree species can be classified into functional groups according to leaf phenology. We evaluated each paradigm and found differences in the patterns of water uptake between deciduous and evergreen tree species, as well as among evergreen tree species, that have implications for regulation of tree water balance. The absence of resource interactions between herbaceous and woody plants is refuted by our observation that herbaceous plants use water from deep soil layers that is released by deep-rooted trees into the upper soil layer. We obtained evidence of strong stomatal control of transpiration and show that most species exhibit homeostasis in maximum water deficit, with midday water potentials being almost identical in the wet and dry seasons. Although stomatal control is strong during the day, nocturnal transpiration is high during the dry season. Our comparative studies showed that the grouping of species into functional categories is somewhat arbitrary and that ranking species along continuous functional axes better represents the ecological complexity of adaptations of cerrado woody species to their seasonal environment.


Assuntos
Raízes de Plantas/fisiologia , Estômatos de Plantas/fisiologia , Transpiração Vegetal/fisiologia , Árvores/metabolismo , Água/metabolismo , Brasil , Ritmo Circadiano/fisiologia , Ecossistema , Raízes de Plantas/anatomia & histologia , Poaceae/fisiologia , Estações do Ano , Solo , Árvores/anatomia & histologia , Árvores/classificação , Clima Tropical
SELEÇÃO DE REFERÊNCIAS
DETALHE DA PESQUISA