Dataset Information

Rapid Leaf Deployment Strategies in a Deciduous Savanna.

ABSTRACT: Deciduous plants avoid the costs of maintaining leaves in the unfavourable season, but carry the costs of constructing new leaves every year. Deciduousness is therefore expected in ecological situations with pronounced seasonality and low costs of leaf construction. In our study system, a seasonally dry tropical savanna, many trees are deciduous, suggesting that leaf construction costs must be low. Previous studies have, however, shown that nitrogen is limiting in this system, suggesting that leaf construction costs are high. Here we examine this conundrum using a time series of soil moisture availability, leaf phenology and nitrogen distribution in the tree canopy to illustrate how trees resorb nitrogen before leaf abscission and use stored reserves of nitrogen and carbon to construct new leaves at the onset of the growing season. Our results show that trees deployed leaves shortly before and in anticipation of the first rains with its associated pulse of nitrogen mineralisation. Our results also show that trees rapidly constructed a full canopy of leaves within two weeks of the first rains. We detected an increase in leaf nitrogen content that corresponded with the first rains and with the movement of nitrogen to more distal branches, suggesting that stored nitrogen reserves are used to construct leaves. Furthermore the stable carbon isotope ratios (?13C) of these leaves suggest the use of stored carbon for leaf construction. Our findings suggest that the early deployment of leaves using stored nitrogen and carbon reserves is a strategy that is integrally linked with the onset of the first rains. This strategy may confer a competitive advantage over species that deploy leaves at or after the onset of the rains.

SUBMITTER: February EC

PROVIDER: S-EPMC4911110 | biostudies-literature | 2016

REPOSITORIES: biostudies-literature

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Rapid Leaf Deployment Strategies in a Deciduous Savanna.

February Edmund Carl EC Higgins Steven Ian SI

PloS one 20160616 6

Deciduous plants avoid the costs of maintaining leaves in the unfavourable season, but carry the costs of constructing new leaves every year. Deciduousness is therefore expected in ecological situations with pronounced seasonality and low costs of leaf construction. In our study system, a seasonally dry tropical savanna, many trees are deciduous, suggesting that leaf construction costs must be low. Previous studies have, however, shown that nitrogen is limiting in this system, suggesting that le ...[more]

PMID: 27310398

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Project description:BACKGROUND AND AIMS: Plant relative growth rate (RGR) depends on biomass allocation to leaves (leaf mass fraction, LMF), efficient construction of leaf surface area (specific leaf area, SLA) and biomass growth per unit leaf area (net assimilation rate, NAR). Functional groups of species may differ in any of these traits, potentially resulting in (1) differences in mean RGR of groups, and (2) differences in the traits driving RGR variation within each group. We tested these predictions by comparing deciduous and evergreen savanna trees. METHODS: RGR, changes to biomass allocation and leaf morphology, and root non-structural carbohydrate reserves were evaluated for juveniles of 51 savanna species (34 deciduous, 17 evergreen) grown in a common garden experiment. It was anticipated that drivers of RGR would differ between leaf habit groups because deciduous species have to allocate carbohydrates to storage in roots to be able to flush leaves again, which directly compromises their LMF, whereas evergreen species are not subject to this constraint. KEY RESULTS: Evergreen species had greater LMF and RGR than deciduous species. Among deciduous species LMF explained 27 % of RGR variation (SLA 34 % and NAR 29 %), whereas among evergreen species LMF explained between 2 and 17 % of RGR variation (SLA 32-35 % and NAR 38-62 %). RGR and LMF were (negatively) related to carbohydrate storage only among deciduous species. CONCLUSIONS: Trade-offs between investment in carbohydrate reserves and growth occurred only among deciduous species, leading to differences in relative contribution made by the underlying components of RGR between the leaf habit groups. The results suggest that differences in drivers of RGR occur among savanna species because these have different selected strategies for coping with fire disturbance in savannas. It is expected that variation in the drivers of RGR will be found in other functional types that respond differently to particular disturbances.

Project description:ObjectivesSutureless and rapid-deployment valves were recently introduced into clinical practice. The Edwards INTUITY valve system is a combination of the Edwards Magna pericardial valve and a subvalvular stent-frame to enable rapid deployment. We performed a parallel cohort study for comparison of the two valve types.MethodsAll patients receiving either an Edwards Magna Ease valve or an Edwards INTUITY valve system due to aortic stenosis from May 2010 until July 2014 were included. Patients undergoing bypass surgery, an additional valve procedure, atrial ablation surgery or replacement of the ascending aorta were excluded. Preoperative characteristics, operative specifications, survival, valve-related adverse events and transvalvulvar gradients were compared.ResultsOne hundred sixteen patients underwent rapid-deployment aortic valve replacement [mean age 75 years (SD: 8); 62% female] and 132 patients underwent conventional aortic valve replacement [70 years (SD: 9); 31% female; P < 0.001]. Conventional valve patients were taller and heavier. The mean EuroSCORE II was 3.1% (SD: 2.7) and 4.4% (SD: 6.0) for rapid-deployment and conventional valve patients, respectively (P = 0.085). The mean implanted valve size was higher in the conventional group [23.2 mm (SD: 2.0) vs 22.5 mm (SD: 2.2); P = 0.007], but postoperative transvalvular mean gradients were comparable [15 mmHg (SD: 6) vs 14 mmHg (SD: 5); P = 0.457]. A subgroup analysis of the most common valve sizes (21 and 23 mm; implanted in 63% of patients) revealed significantly reduced mean postoperative transvalvular gradients in the rapid-deployment group [14 mmHg (SD: 4) vs 16 mmHg (SD: 5); P = 0.025]. A significantly higher percentage received minimally invasive procedures in the rapid-deployment group (59 vs 39%; P < 0.001). The 1- and 3-year survival rate was 96 and 90% in the rapid-deployment group and 95 and 89% in the conventional group (P = 0.521), respectively. Valve-related pacemaker implantations were more common in the rapid-deployment group (9 vs 2%; P = 0.014) and postoperative stroke was more common in the conventional group (1.6 vs 0% per patient year; P = 0.044).ConclusionsWe conclude that this rapid-deployment valve probably facilitates minimally invasive surgery. Furthermore, a subgroup analysis showed reduced transvalvular gradients in smaller valve sizes compared with the conventionally implanted valve of the same type. The favourable haemodynamic profile and the potentially different spectrum of valve-related adverse events should be addressed in further clinical trials.

Project description:Amazonian savannas are isolated patches of open habitats found within the extensive matrix of Amazonian tropical forests. There remains limited evidence on how Amazonian plants from savannas differ in the traits related to drought resistance and water loss control. Previous studies have reported several xeromorphic characteristics of Amazonian savanna plants at the leaf and branch levels that are linked to soil, solar radiation, rainfall and seasonality. How anatomical features relate to plant hydraulic functioning in this ecosystem is less known and instrumental if we want to accurately model transitions in trait states between alternative vegetation in Amazonia. In this context, we combined studies of anatomical and hydraulic traits to understand the structure-function relationships of leaf and wood xylem in plants of Amazonian savannas. We measured 22 leaf, wood and hydraulic traits, including embolism resistance (as P50), Hydraulic Safety Margin (HSM) and isotope-based water use efficiency (WUE), for the seven woody species that account for 75% of the biomass of a typical Amazonian savanna on rocky outcrops in the state of Mato Grosso, Brazil. Few anatomical traits are related to hydraulic traits. Our findings showed wide variation exists among the seven species studied here in resistance to embolism, water use efficiency and structural anatomy, suggesting no unique dominant functional plant strategy to occupy an Amazonian savanna. We found wide variation in resistance to embolism (-1.6 ± 0.1 MPa and -5.0 ± 0.5 MPa) with species that are less efficient in water use (e.g. Kielmeyera rubriflora, Macairea radula, Simarouba versicolor, Parkia cachimboensis and Maprounea guianensis) showing higher stomatal conductance potential, supporting xylem functioning with leaf succulence and/or safer wood anatomical structures and that species that are more efficient in water use (e.g. Norantea guianensis and Alchornea discolor) can exhibit riskier hydraulic strategies. Our results provide a deeper understanding of how branch and leaf structural traits combine to allow for different hydraulic strategies among coexisting plants. In Amazonian savannas, this may mean investing in buffering water loss (e.g. succulence) at leaf level or safer structures (e.g. thicker pit membranes) and architectures (e.g. vessel grouping) in their branch xylem.

Dataset Information

Rapid Leaf Deployment Strategies in a Deciduous Savanna.

Publications

Rapid Leaf Deployment Strategies in a Deciduous Savanna.

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