The thesis involves computer simulation and theoretical studies of dynamics of water under confinement and structural transformation in different complex systems. Based on the systems and phenomena of interest, the work has been classified in to three major parts: I. Dynamics of water under confinement II. Dynamics of water in presence of amphiphilic solutes III. Structural transformation in complex systems The three parts have further been divided into nine chapters. Brief chapter wise outline of the thesis is discussed below. Part I deals with the dynamics of water in confined systems. In Chapter I.1, we provide a brief introduction of water dynamics inc on fined systems. We also give a brief outline of relevant experimental and theoretical techniques used to study the water dynamics under confinement. Chapter I.2 describes a model based analytical study of dynamical correlation in confined systems. Here, we introduce a novel one dimensional Ising model to investigate the propagation and annihilation of dynamical correlations in confined systems and to understand the intriguing shortening of the orientational relaxation time that has been reported for small sized reverse micelles (RMs).In our model, the two spins located at the two end cells are oriented in the opposite directions to mimic the surface effects present in the real systems. These produce opposing polarizations which propagate from the surface to the center, thus producing bulk like condition at the center. This model can be solved analytically for short chains. For long chains, we solve the model numerically with Glauber spin flip dynamics (and also with Metropolis single-spin flip Monte Carlo algorithm).We show that the model satisfactorily reproduces many of the features observed in experiments. Due to the destructive interference among correlations that propagate from the surface to the core, one of the rotational relaxation time components decays faster than the bulk. In general, the relaxation of spins is non-exponential due to the interplay between various interactions. In the limit of strong coupling between the spins or in the limit of low temperature, the nature of the relaxation of spins undergoes a change with the emergence of homogeneous dynamics, where the decay is predominantly exponential. In Chapter I.3, layer-wise distance dependent orientation relaxation of water confined in reverse micelle s(RM)is studied using theoretical and computational tools. We use both a newly constructed spins on a ring (SOR) Ising-type model with modified Shore-Zwanzig rotational dynamics and atomistic simulations with explicit water. Our study explores the size effect of RMs and the role of intermolecular correlations, compromised by the presence of a highly polar surface, on the distance (from the surface) dependence of water relaxation. The SOR model can capture some aspects of distance dependent orientation relaxation, such as acceleration of orientation relaxation at intermediate layers. In atomistic simulations, layer-wise decomposition of hydrogen bond (H-bond) formation pattern clearly reveal that the H-bond arrangement of water at a certain distance away from the surface can remain frustrated due to interaction with the polar surface head groups. We show that this layer-wise analysis also reveals the presence of a non-monotonic, slow relaxation component which can be attributed to the frustration effect and is accentuated in small to intermediate size RMs. For larger RMs, the long-time component decreases monotonically from the interface to the interior of the RMs with slowest relaxation observed at the interface. In ChapterI.4, we present theoretical two dimensional infrared spectroscopic (2D-IR) studies of water confined within RMs of various sizes. Here we focus again mainly on the altered dynamics of confined water by performing a layer-wise decomposition of water. We aim to quantify the relative contributions to the calculated 2D-IR spectra by water molecules located in different layers. The spectra of 0-1 transition clearly show substantial elongation along the diagonal, due to in homogeneous broadening and incomplete spectral diffusion, in the surface water layer of different size of RMs studied in this work. Our study reveals that the motion of the surface water molecules is sub-diffusive, establishing the constrained nature of their dynamics. This is further supported by the two peak nature of the angular analogue of the van Hove correlation function. With increasing system size the motion of water molecules becomes more diffusive in nature and the structural diffusion is observed to be almost completed in the central layer of larger RMs. Comparisons between experiment and simulation help establishing the correspondence between the spectral decomposition available in experimental 2D-IR with the spatial decomposition of simulated 2D-IR. Simulations also allow a quantitative exploration of the relative role of water, sodium ions and sulfonate head groups in irrational dephasing. Interestingly, the negative cross correlation between forces on oxygen and hydrogen of O-H bond in bulk water significantly decreases in the surface layer of different RMs. This negative cross correlation gradually increases in the central layer with increasing size of the RMs and this is found to be partly responsible for the faster relaxation rate of water in the central layer. Part II consists of two chapters and focuses on the dynamics of water in presence of amphiphilic solutes. In Chapter II.1, we present a brief introduction of water – DMSO binary mixture and various anomalous properties of the same. In Chapter II.2, we present theoretical IR study of water dynamics in water–DMSO binary mixtures of different compositions. We show that with increasing DMSO concentration, the IR absorption peak maxima show the presence of structural transformation in similar concentration range, observed in earlier studies. Analysis of H-bonded network near hydrophilic and hydrophobic part of DMSO also suggests that average number of hydrogen bonds near the hydrophobic parts possess maxima at the same concentration range. We also show that with increasing DMSO concentration water dynamics becomes very slow. This has been supported by the diagonal elongation of the 2D-IR spectra and also the slow decay of frequency fluctuation correlation n function (FFCF) and the orientation time correlation function (OTCF). The decoupling of the OTCF establishes that water-DMSOH-bond is much stronger than that of water-water. The last part (Part III) consists of three chapters that deal with structural transformation in various complex systems. In Chapter III.1, we introduce polydisperse systems and present existing theoretical, computer simulation and experimental studies. It also contains the importance and diversity of polydisperse system in nature. In Chapter III.2, we present computer simulation study of melting of polydisperse Lennard-Jones (LJ) system with Gaussian polydispersity in size. The phase diagram reproduces the existence of an early temperature in variant terminal polydispersity (δt0.11), with no signature of re-entrant melting. The absence of re-entrant melting can be attributed to the influence of attractive part of the potential on melting. We find that at terminal polydispersity the fractional density change approaches zero that seems to arise from vanishingly small compressibility of the disordered phase. At constant temperature and volume fraction system undergoes a sharp transition from crystalline solid to disordered state with increasing polydispersity. This has been quantified by second and third order rotational invariant bond orientational orders as well as by the average inherent structure energy. The translational order parameter also indicates similar structural change The free energy calculation further supports the nature of the transition. The third order bond orientational order shows that with increasing polydispersity, local cluster favors more icosahedral-like arrangements and thus the system loses its crystalline symmetry. In Chapter III.3, we present study of phase transition and effect of confinement on it in SOR model. This system is similar to our SOR model discussed in Chapter I.3. The spins execute continuous rotation under a modified XY Hamiltonian. In order to understand the nature of phase transition in such confined spin systems we have performed extensive Monte Carlo simulations. The system size dependence of Binders cumulant, specific heat, order parameter and finite size scaling of order parameter universally suggest the existence of a phase transition. The absence of hysteresis and Scaling of Binders energy cumulant minimum confirm the continuous nature of the transition. The finite size scaling analyses give rise to the mean field nature of the transition. Plausible applications of the proposed model in modeling dipolar liquids in confined systems are also discussed. In Appendix A, we discuss a preliminary study of front propagation in a non-equilibrium system. The model system analogous to the super cooled liquid shows non-Avrami domain growth during rejuvenation. The origin of the non-Avrami nature of the domain growth and the presence of cross over are also discussed. In Appendix B, we discuss umbrella a sampling technique and WHAM analysis which is used in ChapterIII.2 to get the free energy of polydisperse LJ system.

Biochemische Prozesse treten in wässriger Umgebung auf und Wechselwirkungen der Wasserhülle mit Biomolekülen spielt eine Schlüsselrolle für deren Struktur und Funktion. In dieser Arbeit wird die Strukturdynamik der Wassermoleküle und Gegenionen in der umgebenden Wasserhülle der DNA mit der Methode der zweidimensionalen Infrarotspektroskopie (2D IR) sowie Anrege-Abfrage-Spektroskopie untersucht. Die Ergebnisse der vorliegenden Arbeit zeigt das starke Potenzial von Schwingungsmoden an Grenzflächen für die Abbildung und das Verständnis von Wechselwirkungen zwischen Biomolekülen und ihrer Wasserhülle. In Zukunft soll dieses Konzept auch auf andere Biomoleküle angewendet werden. / Biochemical processes occur in an aqueous environment and interactions of the water shell with biomolecules play a key role for their structure and function. In this thesis, the structural dynamics of water molecules and counterions in the hydration shell of DNA is investigated by two-dimensional infrared (2D IR) spectroscopy and pump-probe transient spectroscopy. 2D IR spectroscopy is a powerful technique that can track molecular couplings between different vibrational modes and structural fluctuations of the chemical environment on a femto- to picosecond time scale. In the present study, vibrational modes of the DNA backbone serve as probes located at the DNA-water interface. The results of this thesis demonstrate the strong potential of interfacial vibrational modes for mapping and understanding interactions between biomolecules and their water shell. In future, this concept will be applied to other biomolecular systems.

In dieser Arbeit wurde die Methode der breitbandigen fs-zeitaufgelösten Fluoreszenzaufkonversionsspektroskopie (FLUPS) weiterentwickelt und vollständig theoretisch beschrieben, was anhand des Vergleichs von vorhergesagten und experimentell bestimmten photometrischen Korrekturfunktionen gezeigt werden konnte. Die Methode wurde verwendet, um lokale Fluoreszenzspektren von solvatochromen Sonden in der Nähe bestimmter Matrizes in wässrigen Lösungen zu messen. Aus der Dynamik der Stokes-Verschiebung konnte die Solvatations- bzw. Umgebungsdynamik bestimmt werden. Es wurden mittlere Solvatationszeiten τsolv von 0.57±0.06 für reines Wasser, 2.8±0.2 ps für DNA, 480±30 ps für Phospholipid-Kopfgruppen, 0.71±0.03 ps für ein Peptid (α-Helix) und 0.76±0.03 ps für eine t-Butyl-Gruppe erhalten. Hervorzuheben sind dabei die überraschend schnelle Relaxation nahe des Peptids und die sehr langsame Dynamik nahe der Lipid-Kopfgruppen, welche über 5 Größenordnungen der Zeit beobachtet wurde. Um den Einfluss einer hydrophoben Gruppe auf die Solvatationsdynamik erstmals zu aufzuzeigen, wurden präzise Messungen bei verschiedenen Temperaturen vor-genommen. Zuordnungen dieser Dynamiken zu molekularen Prozessen konnten durch Vergleiche zu MD-Simulationen durchgeführt werden. / The method of broadband fs time-resolved fluorescence upconversion spectroscopy (FLUPS) was further developed and completely theoretically described in this work. This was shown by comparing predicted and measured photometric correction functions. This method was used to obtain local fluorescence spectra of solvatochromic dyes near certain matrices in aqueous solution. From the dynamics of the Stokes-Shift the solvation or environmental dynamics respectively were obtained. Average solvation times τsolv of 0.57±0.06 for bulk water, 2.8±0.2 ps for DNA, 480±30 ps for phospholipid head groups, 0.71±0.03 ps for a peptide (α-helix) and 0.76±0.03 ps for a t-butyl group were obtained. Emphasized are the surprisingly fast dynamics near the peptide and the slow dynamics of the lipid head group region. The latter was observed over 5 orders of magnitude in time. To distinguish the influence a hydrophobic group for the first time, precise measurements at different temperatures were performed. Molecular processes were assigned to the obtained dynamics by comparisons to MD studies.

This thesis is a contribution to the work of the Texas Environmental Observatory (TEO), which provides environmental information from the Greenbelt Corridor (GBC) of the Elm Fork of the Trinity River. The motivation of this research is to analyze the short-term water dynamic of soil in response to the substantial rainfall events that occurred in North Texas in 2007. Data collected during that year by a TEO soil and weather station located at the GBC includes precipitation, and soil moisture levels at various depths. In addition to these field measurements there is soil texture data obtained from lab experiments. By comparing existing water dynamic models, water balance equations were selected for the study as they reflect the water movement of the soil without complicated interrelation between parameters. Estimations of water flow between soil layers, infiltration rate, runoff, evapotranspiration, water potential, hydraulic conductivity, and field capacity are all obtained by direct and indirect methods. The response of the soil at field scale to rainfall event is interpreted in form of flow and change of soil moisture at each layer. Additionally, the analysis demonstrates that the accuracy of soil characteristic measurement is the main factor that effect physical description. Suggestions for model improvement are proposed. With the implementation of similar measurements over a watershed area, this study would help the understanding of basin-scale rainfall-runoff modeling.

Agricultural system models integrate many different processes that cannot all be measured in field experiments and help quantify soil water dynamics, crop evapotranspiration, and crop growth with high temporal resolution. Understanding soil water dynamics and crop evapotranspiration is essential to improve agricultural management of field crops. For example, the interaction between nitrogen application rate and water dynamics is not sufficiently understood. In most cases, model simulations deviate from field measurements, especially when model input parameters are indirectly and unspecifically derived. The extent to which measured soil hydraulic property inputs decrease the discrepancy between measured and simulated soil water status is not well understood. Consequently, this study: (i) investigated thr use of measured soil hydraulic properties as Root Zone Water Quality Model (RZWQM2) inputs compared to indirectly derived inputs; (ii) explored the capability of calibrating measured soil hydraulic property input parameters for one crop and using them for other crops without further calibration; (iii) studied the effect of the nitrogen application rate on the behavior of soil water dynamics and crop evapotranspiration using RZWQM2 under different rainfall amounts. To evaluate the model in different field management conditions, a field experiment with soybean, corn, wheat, and fallow soil was conducted from 2015 – 2017 to collect field data to calibrate and validate the RZWQM2 model. The model presented a satisfactory response to using measured soil hydraulic property inputs and a satisfactory capability to quantify the effect of nitrogen rates on daily crop evapotranspiration, soil water dynamics, and crop growth. With sufficient measurements of soil hydraulic parameters, it was possible to build a RZWQM2 model that produced reasonable results even without calibration.

Post-pelagic juvenile and subadult Kemp's ridley sea turtles (Lepidochelys kempii) (20-40 cm straight carapace length) utilize nearshore waters of the northwestern Gulf of Mexico as nursery or developmental feeding grounds. This study utilizes 10 years of entanglement netting data to characterize long-term abundance and distribution of Kemp's ridley sea turtles at index habitats in this region. Netting surveys were conducted during April-October 1993-2002, primarily at Sabine Pass, Texas and Calcasieu Pass, Louisiana. Additionally, this study takes an ecosystem-based approach to understanding factors influencing Kemp's ridley in-water abundance and distribution via the development of a conceptual model incorporating data on nesting dynamics, environmental conditions, prey availability, and predation pressure. Overall monthly mean ridley catch-per-unit-effort (CPUE) peaked in the beginning of summer (April-June), probably in response to rising water temperatures and seasonal occurrence of blue crab prey. Annual mean ridley CPUE across all study areas peaked in 1994, 1997, 1999 and 2002, suggesting a 2-3 year cycle in abundance that may be related to patterns in clutch size or hatch success at the Rancho Nuevo, Mexico nesting beach. However, ridley CPUE in nearshore waters remained relatively constant or decreased slightly even as number of hatchlings released from Rancho Nuevo increased exponentially. Annual declines in Texas strandings since 1994 and subsequent increases in Florida counterparts since 1995 suggest a shift in ridley distribution from the western to eastern Gulf in recent years. Significant declines in ridley CPUE at Sabine Pass since 1997 coincided with a concurrent reduction in blue crab size, but a similar trend was not detected at Calcasieu Pass. Kemp's ridley occurrence at study sites was not significantly related to shrimping activity/by-catch. There also were no biologically significant relationships between Kemp's ridley CPUE and abiotic factors, nor were ridleys deterred from utilizing areas frequented by bull sharks. Overall, nesting dynamics and prey availability were conceptual model components appearing to have the greatest influence on nearshore ridley occurrence.

Made available in DSpace on 2016-12-23T14:37:34Z (GMT). No. of bitstreams: 1 ANGELO ANTONIO CAMPOS.pdf: 660395 bytes, checksum: 449c13f957ade5ea58be1aee63b345e2 (MD5) Previous issue date: 2007-03-30 / The interest in studying problems of underground drainage and solutos transport not in soils saturated it has been increasing significantly in the last years, mainly because of the growing concern with the quality of the soil and of the environment in general. Applied fertilizers in agricultural lands move below the zone radicular of the plants and they can contaminate underground water tables and aqüíferos. One of the most significant challenges of the current agriculture is the increase of the competitiveness associated to the preservation of the environment, allowing maintainable benefits in the agricultural explorations. The impact of pollutants in the quality of the underground water has been research object and of public health, especially in areas where she is to main source of drinking water. The mathematical models appear as useful tool in the prediction of as and when she should proceed the irrigation and the behavior of the solutos in solo.Devido to the complexity involved in these physical phenomena, it is used now beside the experimental work, the numeric simulation as forecast tool. The numeric simulation of the problem of infiltration of water and solutos in soil not saturated it is of great importance, because the growth of the agricultural production demands transformations with technological innovations that allow the improvement of the productivity of the cultures. To simulate the transport transiente of fertilizers, defensive, herbicidas and pollutant in an agricultural soil not saturated it is necessary the solution of two equations you not differentiate lineal. One of them is the equation of Richards, that governs the movement of water in the soil and, after your solution for a certain time, the results obtained for humidity, they are used for the solution of the other equation that treats of the transport of a certain soluto in matter. This work had for objective, to solve the proposed model of infiltration of water and soluto in the soil for the method of finite volumes, being used programming FORTRAN 90, to treat the case of the non linearidade of the movement of the water and a certain soluto not in soils saturated. Among the analyzed solutos, we used samples of abrasive mud coming of the sawmills and politrizes of the companies of marbles and granites of the municipal district of Cachoeiro of Itapemirim, where several rehearsals and analyses were accomplished, to feed the program and to evaluate the material in subject it is a pollutant in potential of the soil. The proposed method was shown appropriate to solve problems of infiltration of water and solutos transport not in soils saturated. / O interesse em estudar problemas de escoamento subterrâneo e transporte de solutos em solos não saturados tem aumentado significativamente nos últimos anos, principalmente por causa da preocupação crescente com a qualidade do solo e do meio ambiente em geral. Fertilizantes aplicados em terras agrícolas movem-se abaixo da zona radicular das plantas e podem contaminar lençóis de água subterrâneos e aqüíferos. Um dos desafios mais significativos da agricultura atual é o aumento da competitividade associada à preservação do meio ambiente, permitindo benefícios sustentáveis nas explorações agrícolas. O impacto de contaminantes na qualidade da água subterrânea tem sido objeto de pesquisa e de saúde pública, especialmente em regiões onde ela é a principal fonte de água potável. Os modelos matemáticos surgem como ferramenta útil na predição de quanto e quando se deve proceder a irrigação e o comportamento dos solutos no solo.Devido à complexidade envolvida nestes fenômenos físicos, utiliza-se atualmente ao lado do trabalho experimental, a simulação numérica como ferramenta de previsão. A simulação numérica do problema de infiltração de água e solutos em solo não saturado é de grande importância, pois o crescimento da produção agrícola exige transformações com inovações tecnológicas que permitam a melhoria da produtividade das culturas. Para simular o transporte transiente de fertilizantes, defensivos, herbicidas e poluentes num solo agrícola não saturado é necessária a solução de duas equações diferenciais não lineares. Uma delas é a equação de Richards, que governa o movimento de água no solo e, após a sua solução para um determinado tempo, os resultados obtidos para umidade, são empregados para a solução da outra equação que trata do transporte de um determinado soluto em particular. Este trabalho teve por objetivo, resolver o modelo proposto de infiltração de água e soluto no solo pelo método de volumes finitos, utilizando-se programação FORTRAN 90, para tratar o caso da não inearidade da movimentação da água e um determinado soluto em solos não saturados. Dentre os solutos analisados, utilizamos amostras de lama abrasiva provenientes das serrarias e politrizes das empresas de mármores e granitos do município de Cachoeiro de Itapemirim, onde foram realizados vários ensaios e análises, para alimentar o x programa e avaliar se o material em questão é um contaminante em potencial do solo. O método proposto mostrou-se adequado para resolver problemas de infiltração de água e transporte de solutos em solos não saturados.

Tropical forests are storehouses of more thanhalf of the world‘s biodiversity and play a key role in global carbon, water and energy cycles. However, as a consequence of rapid anthropogenic climate change, biodiversity and climate functions of these forests are under a threat. Climate is changing not only in mean state but its variability is increasing, with extreme events such as droughts, heat waves and storms also rising. Water is fundamental to plants‘ existence, and in the tropics, is a key determinant of plant species‘richness, composition, growth and survival. There is thus an increasing interest in understanding how changing rainfall may cause functional changes in forests or change their species composition. Therefore, the overarching goal of thisdissertation was to understand the impact of water variability on tropical forest tree growth and vulnerability to drought.Forest tree growth along spatial and temporal rainfall gradientsObservational studies that measure whole forest tree growth along spatial or temporal gradients of rainfall are the most common way of formulating forest growth response curves to water availability, when manipulative experiments are cost-prohibitive or impractical (fire or large mammal disturbance). In the tropics, since very few species show anatomically distinct tree rings, estimating tree growth from trunk diameter is the standard practice to obtain growth patterns across species. However, this method—of equating woody growth to diameter change--is susceptible to bias from water-induced stem flexing. In the absence of bias correction, temporal variability in growth is likely to be overestimated and incorrectly attributed to fluctuations in resource availability, especially in forests with high seasonal and inter-annual variability in water. This problem has been largely ignored in the absence of any corrective measure and due to under-appreciation of the magnitude of error. While diameter re-censuses in permanent sampling plots (PSPs) have been most commonly done at 3-5 year scale (using a graduate tape), increasingly they are done at seasonal and annual scales (using band dendrometers) to closely match variation in rainfall, the scales at which hydrostatic bias may be greater in magnitude relative to woody growth. Besides, along a spatial rainfall gradient, inter-annual variability in water may vary, causing systematic differences in the hydrostatic bias for forests along the gradient. Therefore, one broad objective of this thesis was to evaluate the problem of hydrostatic bias in whole forest growth-rainfall relationship at annual and supra-annual scales, for temporal as well as spatial rainfall gradients and propose and test a novel corrective solution.Further, it also examines if growth-diameter relationship vary along the spatial gradient, which it may arise due to differences in light environments and/or disturbance history and species composition. The missing link of Eco-hydrology Differential responses of tree species in terms of growth and survival to variation in water that they can access, the proximate cause is likely shaped through their life-history strategies, the ultimate cause. However, we neither know the depths at which the diverse tree species in a forest draw water from and its dynamics, nor variation in water at those depths vis-à-vis rainfall patterns—for lack of appropriate methods. This has been a key missing link in understanding how water shapes trees‘ life-history strategies, their demographic trade-offs and co-existence, and also our predictive ability to determine species-specific responses to changing rainfall patterns, especially droughts. Since droughts are highly stochastic events and trees‘ responses to their drought ―experiences‖ may be revealed at decadal scales, long-term evaluations are key. Therefore, the second broad objective of this thesis was to develop a framework to determine trees’ water uptake depths, variation in water availability at those depths and trees’ demographic responses over multiple decades. From this, to understand how belowground hydrology shapes drought-vulnerability, demographic trade-offs and coexistence of forest tree species. This thesis titled—Eco-Hydrology of a Seasonally Dry Tropical Forest: Tree Growth, Belowground Water Dynamics and Drought-Vulnerability—is organized as follows: Chapter 1 lays down an introduction to the thesis, followed by a description of the study site and datasets used in the thesis in Chapter 2. This thesis uses a variety of methods and multiple datasets, all of which are from the protected Seasonally Dry Tropical Forests of the Western Ghats in southern India in the Mudumalai and Bandipur National Parks. It is then followed by three data chapters: Chapter 3 describes the seasonal fluctuations in a five year long (1980-1985) tree diameter time series (using dendrometers) of a Seasonally Dry Tropical Forest in Bandipur National Park to illustrate the issue of hydrostatic stem-flexing. It investigates the possibility that band dendrometers may themselves underestimate stem shrinkage at diurnal or seasonal scale. It also evaluates if there could be a best season and time of the day for undertaking forest diameter censuses that can minimize hydrostatic bias. Chapter 4(published in Forest Ecology and Management)measures the hydrostatic bias in a sample of trees in a 50 ha PSP of a Seasonally Dry Tropical Forest in Mudumalai National Park, and proposes a novel way to correct this bias at the whole community level in the 20 year long 4-year interval growth time series. Chapter 5 (in review with Environmental Research Letters) investigates and presents two new confounding factors in growth-rainfall relationships along a spatial rainfall gradient: hydrostatic bias and size-dependency in growth rates. For this it evaluates forest tree growth estimates in seven 1-ha PSPs (~800 trees, 3-year annual time series 9using dendrometers) along a 1000 mm rainfall gradient spanning a mesic savanna-moist forest transition in Mudumalai National Park. Using the period for which seasonal diameter time series was available (2 yrs), it evaluates if the extent of seasonal fluctuations systematically vary along the gradient—most likely due to hydrostatic stem flexing. It also describes the presence of an anomalous size-diameter relationship in the mesic savanna from a large plots (50 ha PSP, diameter records using graduated tape). These observations are then used to draw insights for ―space for time‖ substitution modeling. Chapter 6 (in prep for Nature Plants) analyses belowground water environments of trees over two decades (1992-2012), a period that includes a prolonged and intense drought, in the 50 ha PSP of a Seasonally Dry Tropical Forest in Mudumalai. It uses a locally parametarised dynamic hydrological model in which site rainfall is also a forcing variable. It then develops a novel dynamic growth model and inversely estimates water uptake depths for adult trees of all common species (include ~9000 trees) in the PSP from their above-ground growth patterns over two decades vis-à-vis belowground water availability at multiple depths. It then examines if species‘ water uptake depth obtained thus is a predictor of their drought-driven mortality. Finally, this is used to evaluate the hydrological niche partitioning tree species operate under and how that drives their water uptake strategies, demographic trade-offs, and drought-vulnerability. Summarizes the thesis and suggests future directions

Les systèmes de culture en Protection Intégrée de Cultures contre les adventices (systèmes PIC-adventices) sont d’un grand intérêt pour réduire significativement l’utilisation des herbicides en les substituant par une combinaison complexe de différentes techniques culturales. L’objectif principal de notre travail a été de contribuer au volet environnemental de l’évaluation multicritère des systèmes PIC-adventices mis en place depuis 2000 sur le domaine expérimental de l’INRA à Bretenière (21). La variabilité des propriétés physiques et hydrodynamiques qui interviennent dans le transfert de l’eau dans le sol a été étudiée dans les 5 systèmes de culture présents sur le site (1 système de référence et 4 systèmes PIC-adventices). Le premier volet du travail a consisté à étudier la rétention de l’eau dans la couche du sol travaillée dans les 5 systèmes de culture. La rétention de l’eau a été comparée dans des échantillons de sol dont la structure a été soit « conservée », soit « remaniée » afin d’identifier la part de la variabilité liée aux caractéristiques physiques intrinsèques du sol de celle induite par les pratiques culturales. Les résultats ont montré que le sol du système de culture avec suppression totale des herbicides, associant une teneur élevée en argile, une teneur moyenne en C organique et un travail superficiel intensif, présentait les valeurs les plus élevées de rétention de l’eau dans la couche de sol travaillée. Le second volet a porté sur l’étude de la variabilité de la conductivité hydraulique proche de la saturation, K(h), aux échelles de l’année culturale et du profil du sol. Pour cette étude, 3 systèmes PIC-adventices (système de culture en semis direct et systèmes de culture avec travail du sol modéré à intensif) ont été caractérisés pendant 2 ou 3 années culturales consécutives, en considérant 3 profondeurs de sol incluant la couche du sol travaillée et l’horizon sous-jacent. Les résultats n’ont montré aucune variabilité de K(h) à l’échelle verticale. Par contre, ils ont mis en évidence les effets à long terme des systèmes PIC-adventices sur les valeurs de K(h). Enfin, le dernier volet a étudié la dynamique de l’eau dans le sol de 2 systèmes PIC-adventices contrastés (système avec conduite du sol en semis direct et système sans herbicide avec travail du sol intensif) en suivant une approche d’hydraulique agricole et par le biais de la caractérisation in situ du potentiel matriciel de l’eau dans le sol et de la mesure des quantités d’eau collectée au moyen de lysimètres à mèche. L’approche utilisée a permis la description de la dynamique de l’eau du sol pendant la période de drainage, la validation du fonctionnement des lysimètres à mèche et le calcul de la surface de sol équivalente qui contribuait au transfert de l’eau dans ces dispositifs. Ces premiers résultats prometteurs nécessiteront néanmoins d’être validés au cours de prochaines campagnes de mesure. L’ensemble des résultats recueillis constituent une première évaluation du fonctionnement physique et hydrodynamique du sol des systèmes PIC-adventices présents sur le dispositif expérimental. La base de données constituée permettra ultérieurement la poursuite du travail engagé en modélisant le transfert de l’eau, de solutés, de pesticides ou d’autres polluants dans le sol de ces systèmes PIC-adventices. / Integrated weed management (IWM)-based cropping systems are of great interest due to their significant reduction of herbicide inputs by using a complex combination of agricultural techniques. The main objective of our work was to contribute to the environmental dimension of the multi-criteria evaluation of IWM-based cropping systems which were set up since 2000 on the experimental domain of the National Institute for Agronomical Research (INRA) to Bretenière (France). The variability of physical and hydrodynamic soil properties involved in the transfer of water through the vadose zone was studied for the 5 cropping systems present on the experimental site (1 reference cropping system and 4 IWM-based cropping systems). The first section of our study consisted in studying the water retention of the tilled soil layers for the 5 cropping systems. Water retention values were compared between undisturbed and repacked soil samples in order to distinguish the part of the variability due to the intrinsic soil properties from the one induced by the agricultural practices. Our results show that the soil from cropping system without any herbicides, associating high clay content, average organic C content and intensive superficial tillage, may increase soil water retention in the tilled soil layer. The second section carried on the study of the annual and vertical variability of the near-saturated hydraulic conductivity, K(h). For this study, 3 IWM-based cropping systems (no-tilled cropping system and moderate to intensive tilled cropping systems) were characterized during 2 or 3 consecutive years and considering 3 depths including the soil tilled layer and the underlying no-tilled layer. The results showed no vertical variability of K(h). However, they highlighted the long-term effect of IWM-based cropping systems on K(h). Finally, the third section studied the soil water dynamics of 2 contrasted IWM-based cropping systems (no-tilled and zero herbicide cropping systems with intensive tillage) by using ,a hydraulic agricultural approach and by the means of the in situ characterization of soil matric potential and the measure of the amounts of water collected with wick lysimeters. This approach allowed the description of the water dynamics during the drainage season, the validation of the wick lysimeters functioning and the calculation of the surface contributing to water flows collected by the wick lysimeters. These promising results will need to be validated during forthcoming campaigns of measurement. All data collected provided constitute a first evaluation of the soil physical and hydraulic functioning of IWM-based cropping systems present on the experimental site. The established database will allow later the pursuit of work by modeling the water transfer and the transport of solutes, pesticides or other pollutants through the vadose zone of these IWM-based cropping systems.