A spatialized assessment of ecosystem service relationships in a multifunctional agroforestry landscape of Senegal

Agroforestry systems are an integral part of Sub-Saharan agricultural landscapes. Studies conducted at tree or plot scales on the supply of ecosystem services (ES) suggest that agroforestry practices are a promising way to build multifunctional agricultural landscapes. However, the current characterization and understanding of how multiple ES are associated across such heterogeneous agricultural landscapes are still limited. This study provides the first characterization of the multiple ESs supplied by a Sahelian Faidherbia albida agroforestry parkland and their relationships. Relying on field data for 11 ES indicators, recent advances in remote sensing-derived information, and blending different ES mapping approaches, we first assessed the spatial heterogeneity of the supply of each ES. We found that the majority of ES indicators remained below ES potential values over the study area by 25 % to 50 %, revealing that there is a considerable scope for increasing the ES supply in the F. albida parkland. Then, using a scoring approach, we analyzed the supply of multiple ESs. We observed a large number of hotspots and a clear effect of the proximity of F. albida trees fostering the supply of multiple ESs in their vicinity. Finally, we mapped and analyzed the dominant relationships - trade-offs, synergies or losses - between ESs from a cooccurrence spatial approach. We showed that significant trade-offs and losses (58 % of the area) between ESs can exist in the F. albida parkland. Interestingly, we also showed that synergies occurred mainly up to 10 m from the F. albida trees, suggesting that synergies need to be increased beyond this threshold. By adopting an original ES valuation framework, we provided basic insights into ESs and their relationships. The different maps and information generated can support public debates and target new policies fostering the multifunctionality of F. albida parklands as well as in various other parklands of West Africa.

First Episode Psychosis and intensity of care after discharge : difference at two years between lost and maintained follow-up patients

Introduction

Disengagement from care in early psychosis is frequent. In outpatient general psychiatric services rates range from 17 % to 60 %. In early intervention programs, rates range from 14 % to 33 % at two years. In Europe, a study reported an initial drop out rate at 48 %.

Objectives

Measure intensity of care during two years after first hospitalization in a schizophrenia spectrum disorder population. Search for a difference between lost and maintained follow-up patients.

Methods

A monocentric retrospective study was conducted. All patients aged 16 to 30 with at least one hospitalization for schizophrenia spectrum disorder from January 2013 to December 2018 in CHAC were included. First hospitalization medical charts and all (social, nurse, psychologist, psychiatrist) outpatient appointments were assessed. A monthly mean of all appointments (MMA) was calculated for each patient. Lost or maintained groups at two years were compared with a Mann-Whitney test.

Results

Among 48 patients, 52,1 % (N=25) disengaged from initial follow up within 2 years. The MMA for (N=46) patients was 1,45 (SD 1,35), 0,5 (SD 0,33) for psychiatrists. For lost patients, the MMA was 1,35 (SD 1,40) compared to 1,55 (SD 1,32) for maintained. No significant difference was found : U=229,50 p=0,45.

Conclusions

At two years, care appears more intensive for maintained patients than for lost ones, but no significant difference was found.

Disclosure

No significant relationships.

A glycopyrronium bromide 1% cream for topical treatment of primary axillary hyperhidrosis: efficacy and safety results from a phase IIIa randomized controlled trial

BACKGROUND

Effective topical treatment options for patients with primary axillary hyperhidrosis (PAHH) are limited. A phase I trial showed promising results regarding the efficacy and safety of a topical cream containing glycopyrronium bromide (GPB).

OBJECTIVES

To assess the efficacy, safety and tolerability of a 4-week topical treatment of GPB 1% cream in patients with PAHH vs. placebo.

METHODS

In total, 171 patients (84 receiving placebo; 87 receiving GPB 1%) with PAHH were included in the 4-week, multicentre, randomized, double-blind, placebo-controlled phase IIIa part of the pivotal study. Sweat production was measured by gravimetry. Patients rated the impact of disease with the Hyperhidrosis Disease Severity Scale (HDSS) and Hyperhidrosis Quality of Life Index (HidroQoL© ).

RESULTS

Absolute change in sweat production from baseline to day 29 in logarithmic values was significantly larger in the GPB 1% group compared with the placebo group (P = 0·004). The improvement in HidroQoL exceeded the minimal clinically important difference of 4. The proportion of responders was twofold higher for sweat reduction (-197·08 mg GPB 1% vs. -83·49 mg placebo), HDSS (23% GPB 1% vs. 12% placebo) and HidroQoL (60% GPB 1% vs. 26% placebo). Treatment was safe: most treatment-emergent adverse effects were mild or moderate, and transient. Local tolerability was very good, with 9% of patients having only mild or moderate application-site reactions. The most reported adverse drug reaction was dry mouth (16%), an expected anticholinergic effect of the treatment.

CONCLUSIONS

GPB 1% cream may provide an effective new treatment option exhibiting a good safety profile for patients with PAHH. The long-term open-label part (phase IIIb) is ongoing.

Implication of substance use in suicidal or violent behaviours in a first episode psychosis spectrum disorder population : A 45 patients retrospective study

Introduction

In First Episode Psychosis (FEP), Suicidal Behaviours (SB), Violent Behaviours (VB) and substance use are frequent respectively 10% to 30%, 34.5% and 50% (Pompili et al., 2011), (Tournier et al., 2013). The role of substance use in facilitating SB and VB is described (Large et al., 2011).

Objectives

We aim to evaluate the impact of substance use in FEP patients. Our hypothesis is that substance use is associated with more SB or VB before first admission.

Methods

First admission files of 45 patients diagnosed ICD10 F20 to F29 during the 2013-2018 period were retrospectively studied. SB, VB and substance use (Cannabis, alcohol and opiate/cocaine) before admission were collected. Correlation between SB and VB were tested with cannabis, alcohol, opiate/cocaine use with chi2 Pearson independance test.

Results

The frequencies of suicidal behaviours and violent behaviours were 25 % and 22.7 %. The frequencies of cannabis use, alcohol use, opiate/cocaine use were 56.1 %, 10 % and 16.3 %. A strong significant correlation was found between opiate/cocaine use and violent behaviour, p = 0.011 Chi2 was 6.471 DF 1. No other significant correlations were found.

Conclusions

Suicidal behaviours and violent behaviours are known to be more frequent in psychotic patients with addictive comorbidity. Our french rural hospital retrospective study confirms that violent behaviours in first admission psychotic patients are strongly associated with opiate/cocaine substance use comorbidity.

Hyperhidrosis Quality of Life Index (HidroQoL©): further validation and clinical application in patients with axillary hyperhidrosis using data from a phase III randomized controlled trial

BACKGROUND

The Hyperhidrosis Quality of Life Index (HidroQoL©) is a validated patient-reported outcome measure capturing the quality of life of people affected by hyperhidrosis.

OBJECTIVES

We aimed to extend the validity evidence to physician-confirmed diagnosis of primary axillary hyperhidrosis.

METHODS

Data from a phase III randomized placebo-controlled clinical trial were used (n = 171). Confirmatory factor analysis was carried out to confirm the a priori two-factor structure of the HidroQoL. Internal consistency was assessed using Cronbach's α. Intraclass correlation coefficients (ICCs) were calculated to evaluate test-retest reliability after days -7 to -4. Convergent validity was assessed using correlations with the Dermatology Life Quality Index (DLQI), the Hyperhidrosis Disease Severity Scale (HDSS) and gravimetric sweat production. Known groups were analysed to evaluate discriminative validity. Responsiveness after 29 days was assessed and minimal important difference (MID) values were calculated using both anchor- and distribution-based approaches. All analyses were carried out for total HidroQoL and its two domains.

RESULTS

The two-factor structure of the HidroQoL was confirmed. Internal consistency and test-retest reliability were strong (Cronbach's α 0·81-0·90; ICCs 0·89-0·93). Correlations with other outcome measures were in line with a priori hypotheses. The HidroQoL discriminated between different severity groups (P ≤ 0·001) and showed sensitivity to change towards improvement (P < 0·001). An MID value of 4 is proposed for the total scale.

CONCLUSIONS

This study supports excellent measurement properties including clinical applicability of the HidroQoL in primary axillary hyperhidrosis and suggests a MID of 4 be applied to clinical trial data.

The Mi-2 nucleosome remodeler and the Rpd3 histone deacetylase are involved in piRNA-guided heterochromatin formation

In eukaryotes, trimethylation of lysine 9 on histone H3 (H3K9) is associated with transcriptional silencing of transposable elements (TEs). In drosophila ovaries, this heterochromatic repressive mark is thought to be deposited by SetDB1 on TE genomic loci after the initial recognition of nascent transcripts by PIWI-interacting RNAs (piRNAs) loaded on the Piwi protein. Here, we show that the nucleosome remodeler Mi-2, in complex with its partner MEP-1, forms a subunit that is transiently associated, in a MEP-1 C-terminus-dependent manner, with known Piwi interactors, including a recently reported SUMO ligase, Su(var)2-10. Together with the histone deacetylase Rpd3, this module is involved in the piRNA-dependent TE silencing, correlated with H3K9 deacetylation and trimethylation. Therefore, drosophila piRNA-mediated transcriptional silencing involves three epigenetic effectors, a remodeler, Mi-2, an eraser, Rpd3 and a writer, SetDB1, in addition to the Su(var)2-10 SUMO ligase.

How deep can ectomycorrhizas go? A case study on Pisolithus down to 4 meters in a Brazilian eucalypt plantation

Despite the strong ecological importance of ectomycorrhizal (ECM) fungi, their vertical distribution remains poorly understood. To our knowledge, ECM structures associated with trees have never been reported in depths below 2 meters. In this study, fine roots and ECM root tips were sampled down to 4-m depth during the digging of two independent pits differing by their water availability. A meta-barcoding approach based on Illumina sequencing of internal transcribed spacers (ITS1 and ITS2) was carried out on DNA extracted from root samples (fine roots and ECM root tips separately). ECM fungi dominated the root-associated fungal community, with more than 90% of sequences assigned to the genus Pisolithus. The morphological and barcoding results demonstrated, for the first time, the presence of ECM symbiosis down to 4-m. The molecular diversity of Pisolithus spp. was strongly dependent on depth, with soil pH and soil water content as primary drivers of the Pisolithus spp. structure. Altogether, our results highlight the importance to consider the ECM symbiosis in deep soil layers to improve our understanding of fine roots functioning in tropical soils.

Anthropic impacts on Sub-Saharan urban water resources through their pharmaceutical contamination (Yaoundé, Center Region, Cameroon)

Sub-Saharan urban centers have to tackle high population growth, lack of sanitation infrastructures and the need for good quality water resources. To characterize the impacts of anthropization on the water resources of the capital of Cameroon (Yaoundé), a multi-disciplinary approach was used in ten sub-watersheds (peri-urban and urban) of the Méfou watershed. Pharmaceutical residues were used as tracers of surface and groundwater contamination caused by the release of domestic wastewater from pit latrines and landfills. A water use survey was conducted in the vicinity of the sampling sites to better assess water use, treatment and management. Available land use and hydro-geomorphological data completed characterization of the sub-watersheds. The combined data showed that natural features (elevation, slope, and hydrography) and human activities (land use) favor rainfall-runoff events and hence surface water contamination. Pharmaceutical monitoring revealed contamination of both surface and groundwater especially in the urban sub-watersheds. Analgesics/anti-inflammatory drugs and anti-epileptic carbamazepine were the most frequently found compounds (in up to 91% of water samples) with concentrations of acetaminophen reaching 5660 ng/L. In urban sub-watersheds, 50% of the groundwater sites used for drinking water were contaminated by diclofenac (476-518 ng/L), carbamazepine (263-335 ng/L), ibuprofen (141-276 ng/L), sulfamethoxazole (<2-1285 ng/L) and acetaminophen (110-111 ng/L), emphasizing the need for a deeper understanding of the interactions between surface and groundwater. The use of groundwater as drinking water by 68% of the total population surveyed raises concerns about population exposure and potential health risks. This case study highlights the need for strategies to limit contamination of the water resource given the predicted future expansion of Sub-Saharan urban centers.

Improvement of BDNF signalling by P42 peptide in Huntington's disease

Huntington's disease (HD) is caused by a mutation in the Huntingtin (HTT) protein. We previously reported that the 23aa peptide of HTT protein, P42, is preventing HD pathological phenotypes, such as aggregation, reduction of motor performances and neurodegeneration. A systemic treatment with P42 during the pre-symptomatic phase of the disease showed therapeutic potential in R6/2 mice. We here tested P42 effects when administered during the post-symptomatic phase. The P42 treatment alleviated deficits in motor performances, even when symptoms have already started. Because changes in the level and activity of brain-derived neurotrophic factor (BDNF) have been shown to play a central role in HD, we analysed the influence of P42 on BDNF deficit and associated phenotypes. Our data suggest that P42 is involved in the spatio-temporal control of bdnf and trkB mRNA and their protein levels. Related to this enhancement of BDNF-TrkB signalling, R6/2 mice treated with P42, exhibit reduced anxiety, better learning and memory performances, and better long-term potentiation (LTP) response. Finally we identified a direct influence of P42 peptide on neuronal plasticity and activity. These results suggest that P42 offers an efficient therapeutic potential not only by preventing aggregation of mutant HTT at early stages of the disease, but also by favouring some physiological functions of normal HTT, as P42 is naturally part of it, at the different stages of the disease. This makes P42 peptide potentially suitable not only to prevent, but also to treat HD.

Tree root dynamics in montane and sub-alpine mixed forest patches

BACKGROUND AND AIMS

The structure of heterogeneous forests has consequences for their biophysical environment. Variations in the local climate significantly affect tree physiological processes. We hypothesize that forest structure also alters tree root elongation and longevity through temporal and spatial variations in soil temperature and water potential.

METHODS

We installed rhizotrons in paired vegetation communities of closed forest (tree islands) and open patches (canopy gaps), along a soil temperature gradient (elevations of 1400, 1700 and 2000 m) in a heterogeneous mixed forest. We measured the number of growing tree roots, elongation and mortality every month over 4 years.

KEY RESULTS

The results showed that the mean daily root elongation rate (RER) was not correlated with soil water potential but was significantly and positively correlated with soil temperature between 0 and 8 °C only. The RER peaked in spring, and a smaller peak was usually observed in the autumn. Root longevity was dependent on altitude and the season in which roots were initiated, and root diameter was a significant factor explaining much of the variability observed. The finest roots usually grew faster and had a higher risk of mortality in gaps than in closed forest. At 2000 m, the finest roots had a higher risk of mortality compared with the lower altitudes.

CONCLUSIONS

The RER was largely driven by soil temperature and was lower in cold soils. At the treeline, ephemeral fine roots were more numerous, probably in order to compensate for the shorter growing season. Differences in soil climate and root dynamics between gaps and closed forest were marked at 1400 and 1700 m, but not at 2000 m, where canopy cover was more sparse. Therefore, heterogeneous forest structure and situation play a significant role in determining root demography in temperate, montane forests, mostly through impacts on soil temperature.

DigR: a generic model and its open source simulation software to mimic three-dimensional root-system architecture diversity

Background and Aims

Many studies exist in the literature dealing with mathematical representations of root systems, categorized, for example, as pure structure description, partial derivative equations or functional-structural plant models. However, in these studies, root architecture modelling has seldom been carried out at the organ level with the inclusion of environmental influences that can be integrated into a whole plant characterization.

Methods

We have conducted a multidisciplinary study on root systems including field observations, architectural analysis, and formal and mathematical modelling. This integrative and coherent approach leads to a generic model (DigR) and its software simulator. Architecture analysis applied to root systems helps at root type classification and architectural unit design for each species. Roots belonging to a particular type share dynamic and morphological characteristics which consist of topological and geometric features. The DigR simulator is integrated into the Xplo environment, with a user interface to input parameter values and make output ready for dynamic 3-D visualization, statistical analysis and saving to standard formats. DigR is simulated in a quasi-parallel computing algorithm and may be used either as a standalone tool or integrated into other simulation platforms. The software is open-source and free to download at http://amapstudio.cirad.fr/soft/xplo/download.

Key Results

DigR is based on three key points: (1) a root-system architectural analysis, (2) root type classification and modelling and (3) a restricted set of 23 root type parameters with flexible values indexed in terms of root position. Genericity and botanical accuracy of the model is demonstrated for growth, branching, mortality and reiteration processes, and for different root architectures. Plugin examples demonstrate the model's versatility at simulating plastic responses to environmental constraints. Outputs of the model include diverse root system structures such as tap-root, fasciculate, tuberous, nodulated and clustered root systems.

Conclusions

DigR is based on plant architecture analysis which leads to specific root type classification and organization that are directly linked to field measurements. The open source simulator of the model has been included within a friendly user environment. DigR accuracy and versatility are demonstrated for growth simulations of complex root systems for both annual and perennial plants.

Results and complications of superficialis-to-profundus tendon transfer in brain-damaged patients, a series of 26 patients

INTRODUCTION

In hemiplegic patients with a spastic clenched fist deformity, one of the goals of surgery is to address the hygiene, nursing and appearance problems. Transfer of the flexor digitorum superficialis (FDS) to the flexor digitorum profundus (FDP), initially described by Braun and colleagues, opens the non-functional hand in these patients. The primary objective of our study was to confirm the effectiveness of this technique for correcting these deformities. The secondary objectives were to demonstrate potential functional gains and to identify potential complications.

MATERIAL AND METHODS

A Braun procedure was performed in 26 patients (9 women, 17 men, ranging in age from 36 to 79 years). The overall appearance of the hand was graded using the Keenan classification system. Complications related to the surgery were documented. The hand's function was evaluated with the House score.

RESULTS

The average follow-up was 47 months. Preoperatively, all patients had a class V hand: severe clenched-fist deformity with zero pulp-to-palm distance. Postoperatively, 10 patients had a type I hand (open hand, with less than 20° spontaneous extension deficit of the metacarpophalangeal (MCP) and proximal interphalangeal (PIP) joints) and 12 patients had a type II hand (20° to 40° spontaneous extension deficit of the MCP and PIP joints). The mean House score for all patients went from 0 to 0.88, and seven patients had functional improvements. Four patients had a forearm supination posture, 10 had intrinsic deformity with spontaneous MCP flexion and 6 had a swan-neck deformity.

CONCLUSION

Superficialis-to-profundus tendon transfer (STP) provides satisfactory outcomes in terms of hand opening, with some patients also experiencing improved hand function. However, the complications cannot be ignored.

LEVEL OF EVIDENCE

IV-retrospective or historical series.

Control of nerve cord formation by Engrailed and Gooseberry-Neuro: A multi-step, coordinated process

One way to better understand the molecular mechanisms involved in the construction of a nervous system is to identify the downstream effectors of major regulatory proteins. We previously showed that Engrailed (EN) and Gooseberry-Neuro (GsbN) transcription factors act in partnership to drive the formation of posterior commissures in the central nervous system of Drosophila. In this report, we identified genes regulated by both EN and GsbN through chromatin immunoprecipitation ("ChIP on chip") and transcriptome experiments, combined to a genetic screen relied to the gene dose titration method. The genomic-scale approaches allowed us to define 175 potential targets of EN-GsbN regulation. We chose a subset of these genes to examine ventral nerve cord (VNC) defects and found that half of the mutated targets show clear VNC phenotypes when doubly heterozygous with en or gsbn mutations, or when homozygous. This strategy revealed new groups of genes never described for their implication in the construction of the nerve cord. Their identification suggests that, to construct the nerve cord, EN-GsbN may act at three levels, in: (i) sequential control of the attractive-repulsive signaling that ensures contralateral projection of the commissural axons, (ii) temporal control of the translation of some mRNAs, (iii) regulation of the capability of glial cells to act as commissural guideposts for developing axons. These results illustrate how an early, coordinated transcriptional control may orchestrate the various mechanisms involved in the formation of stereotyped neuronal networks. They also validate the overall strategy to identify genes that play crucial role in axonal pathfinding.

Increased light-use efficiency sustains net primary productivity of shaded coffee plants in agroforestry system

In agroforestry systems, shade trees strongly affect the physiology of the undergrown crop. However, a major paradigm is that the reduction in absorbed photosynthetically active radiation is, to a certain extent, compensated by an increase in light-use efficiency, thereby reducing the difference in net primary productivity between shaded and non-shaded plants. Due to the large spatial heterogeneity in agroforestry systems and the lack of appropriate tools, the combined effects of such variables have seldom been analysed, even though they may help understand physiological processes underlying yield dynamics. In this study, we monitored net primary productivity, during two years, on scales ranging from individual coffee plants to the entire plot. Absorbed radiation was mapped with a 3D model (MAESPA). Light-use efficiency and net assimilation rate were derived for each coffee plant individually. We found that although irradiance was reduced by 60% below crowns of shade trees, coffee light-use efficiency increased by 50%, leaving net primary productivity fairly stable across all shade levels. Variability of aboveground net primary productivity of coffee plants was caused primarily by the age of the plants and by intraspecific competition among them (drivers usually overlooked in the agroforestry literature) rather than by the presence of shade trees.

History of traumatic brain injury in prison populations: A systematic review

Traumatic brain injury (TBI) can lead to cognitive, behavioural and social impairments. The relationship between criminality and a history of TBI has been addressed on several occasions.

OBJECTIVE

The objective of this review was to present an update on current knowledge concerning the existence of a history of TBI in prison populations.

METHODS

PubMed and PsycINFO databases were searched for relevant papers, using the PRISMA guidelines. We selected papers describing TBI prevalence among incarcerated individuals and some that also discussed the validity of such studies.

RESULTS

Thirty-three papers were selected. The majority of the papers were on prison populations in Australia (3/33), Europe (5/33) and the USA (22/33). The selected studies found prevalence rates of the history of TBI ranging from 9.7% and 100%, with an average of 46% (calculated on a total population of 9342). However, the level of evidence provided by the literature was poor according to the French national health authority scale. The majority of the prisoners were males with an average age of 37. In most of the papers (25/33), prevalence was evaluated using a questionnaire. The influence of TBI severity on criminality could not be analysed because of a lack of data in the majority of papers. Twelve papers mentioned that several comorbidities (mental health problems, use of alcohol…) were frequently found among prisoners with a history of TBI. Two papers established the validity of the use of questionnaires to screen for a history of TBI.

CONCLUSION

These results confirmed the high prevalence of a history of TBI in prison populations. However, they do not allow conclusions to be drawn about a possible link between criminality and TBI. Specific surveys need to be performed to study this issue. The authors suggest ways of improving the screening and healthcare made available to these patients.

Root biomass, turnover and net primary productivity of a coffee agroforestry system in Costa Rica: effects of soil depth, shade trees, distance to row and coffee age

Background and Aims In Costa Rica, coffee (Coffea arabica) plants are often grown in agroforests. However, it is not known if shade-inducing trees reduce coffee plant biomass through root competition, and hence alter overall net primary productivity (NPP). We estimated biomass and NPP at the stand level, taking into account deep roots and the position of plants with regard to trees. Methods Stem growth and root biomass, turnover and decomposition were measured in mixed coffee/tree (Erythrina poeppigiana) plantations. Growth ring width and number at the stem base were estimated along with stem basal area on a range of plant sizes. Root biomass and fine root density were measured in trenches to a depth of 4 m. To take into account the below-ground heterogeneity of the agroforestry system, fine root turnover was measured by sequential soil coring (to a depth of 30 cm) over 1 year and at different locations (in full sun or under trees and in rows/inter-rows). Allometric relationships were used to calculate NPP of perennial components, which was then scaled up to the stand level. Key Results Annual ring width at the stem base increased up to 2·5 mm yr-1 with plant age (over a 44-year period). Nearly all (92 %) coffee root biomass was located in the top 1·5 m, and only 8 % from 1·5 m to a depth of 4 m. Perennial woody root biomass was 16 t ha-1 and NPP of perennial roots was 1·3 t ha-1 yr-1. Fine root biomass (0-30 cm) was two-fold higher in the row compared with between rows. Fine root biomass was 2·29 t ha-1 (12 % of total root biomass) and NPP of fine roots was 2·96 t ha-1 yr-1 (69 % of total root NPP). Fine root turnover was 1·3 yr-1 and lifespan was 0·8 years. Conclusions Coffee root systems comprised 49 % of the total plant biomass; such a high ratio is possibly a consequence of shoot pruning. There was no significant effect of trees on coffee fine root biomass, suggesting that coffee root systems are very competitive in the topsoil.

Measured and modeled interactive effects of potassium deficiency and water deficit on gross primary productivity and light-use efficiency in Eucalyptus grandis plantations

Global climate change is expected to increase the length of drought periods in many tropical regions. Although large amounts of potassium (K) are applied in tropical crops and planted forests, little is known about the interaction between K nutrition and water deficit on the physiological mechanisms governing plant growth. A process-based model (MAESPA) parameterized in a split-plot experiment in Brazil was used to gain insight into the combined effects of K deficiency and water deficit on absorbed radiation (aPAR), gross primary productivity (GPP), and light-use efficiency for carbon assimilation and stem biomass production (LUEC and LUEs ) in Eucalyptus grandis plantations. The main-plot factor was the water supply (undisturbed rainfall vs. 37% of throughfall excluded) and the subplot factor was the K supply (with or without 0.45 mol K m(-2 ) K addition). Mean GPP was 28% lower without K addition over the first 3 years after planting whether throughfall was partly excluded or not. K deficiency reduced aPAR by 20% and LUEC by 10% over the whole period of growth. With K addition, throughfall exclusion decreased GPP by 25%, resulting from a 21% decrease in LUEC at the end of the study period. The effect of the combination of K deficiency and water deficit was less severe than the sum of the effects of K deficiency and water deficit individually, leading to a reduction in stem biomass production, gross primary productivity and LUE similar to K deficiency on its own. The modeling approach showed that K nutrition and water deficit influenced absorbed radiation essentially through changes in leaf area index and tree height. The changes in gross primary productivity and light-use efficiency were, however, driven by a more complex set of tree parameters, especially those controlling water uptake by roots and leaf photosynthetic capacities.

Impact of tapping and soil water status on fine root dynamics in a rubber tree plantation in Thailand

Fine roots (FR) play a major role in the water and nutrient uptake of plants and contribute significantly to the carbon and nutrient cycles of ecosystems through their annual production and turnover. FR growth dynamics were studied to understand the endogenous and exogenous factors driving these processes in a 14-year-old plantation of rubber trees located in eastern Thailand. FR dynamics were observed using field rhizotrons from October 2007 to October 2009. This period covered two complete dry seasons (November to March) and two complete rainy seasons (April to October), allowing us to study the effect of rainfall seasonality on FR dynamics. Rainfall and its distribution during the two successive years showed strong differences with 1500 and 950 mm in 2008 and 2009, respectively. FR production (FRP) completely stopped during the dry seasons and resumed quickly after the first rains. During the rainy seasons, FRP and the daily root elongation rate (RER) were highly variable and exhibited strong annual variations with a total FRP of 139.8 and 40.4 mm(-) (2) and an average RER of 0.16 and 0.12 cm day(-) (1) in 2008 and 2009, respectively. The significant positive correlations found between FRP, RER, the appearance of new roots, and rainfall at monthly intervals revealed the impact of rainfall seasonality on FR dynamics. However, the rainfall patterns failed to explain the weekly variations of FR dynamics observed particularly during the rainy seasons. At this time step, FRP, RER, and the appearance of new FR were negatively correlated to the average soil matric potential measured at a depth of between 30 and 60 cm. In addition, our study revealed a significant negative correlation between FR dynamics and the monthly production of dry rubber. Consequently, latex harvesting might disturb carbon dynamics in the whole tree, far beyond the trunk where the tapping was performed. These results exhibit the impact of climatic conditions and tapping system in the carbon budget of rubber plantations.