Orientador: Valdemir Antônio Rodrigues / Coorientador: Silvio Fronsini de Barros Ferraz / Banca: Alexandre Vicente Ferraz / Banca: Deivid Lopes Machado / Resumo: A presença de espécies exóticas em ambientes ripários pode influenciar na quantidade e qualidade de folhas que são realocadas no sistema ecológico. Desse modo, o objetivo deste trabalho foi determinar a influência do Eucalyptus saligna Sm. na dinâmica de produção e decomposição de folhas em três zonas ripárias, cujas hipóteses visam verificar se o estresse hídrico, a densidade e área basal do eucalipto afetam a produção de folhedo, e também constatar se a decomposição de folhas senescentes de eucalipto, em meio aquático e terrestre, ocorre mais lentamente do que das folhas nativas. A pesquisa foi realizada em três microbacias denominadas Forquilha, Monjolinho e Tinga, situadas na Estação Experimental de Itatinga, SP. Apresentam respectivamente 0,4%, 1,2% e 11,9% do total de indivíduos de eucalipto. A avaliação transcorreu durante um ano, e as folhas coletadas foram triadas em eucaliptos e nativas. Avaliou-se a entrada de folhedo por meio de coletores terrestres e verticais, distribuídos sistematicamente por ambas as margens dos rios e também sobre o curso d'água. Para maior caracterização do local, o levantamento dos parâmetros da vegetação foi realizado por meio de parcelas 5x10m e mensuradas as espécies com altura > 1,30 m e DAP ≥ 3,5 cm. Para o estudo de decomposição aquática e terrestre, avaliaram-se um mix de folhas de eucalipto, nativas e eucalipto/nativas (1:1) introduzidas em litter bags. A decomposição em meio aquático foi avaliada ao longo de 112 dias, enquanto que... / Abstract: The presence of exotic species in riparian environments can influence in the quantity and quality of leaves that are relocated in the ecological system. Thus, the aim of this work was to determine the influence of the eucalyptus in the dynamics of production and decomposition of leaves in three riparian zones. The research was done in three micro watersheds named Forquilha, Monjolinho and Tinga located in Estação Experimental de Itatinga in São Paulo. They present respectively 0.4%, 1.2% and 11.9% of the total of eucalyptus individuals. The data collection occurred in a year, and the collected leaves were sorted in eucalyptus and native. The leaf-litter were collected through terrestrial and vertical collectors, systematically distributed on both banks and on the watercourse. For greater characterization of the site, the vegetation parameters were surveyed through 5x10m parcels. For decomposition study, it was evaluated the decomposition of eucalyptus, native and eucalyptus/native (1:1) introduced in litter bags. The decomposition in aquatic environment was evaluated for 112 days, and terrestrial decomposition in 3, 6, 9 and 12 months. The vegetal reminiscent of Tinga watershed showed a higher density (individuals number/ha) and basal area (m²/ha) of eucalyptus. The Forquilha vegetation showed the highest H (Shannon) and J (Pielou) values. In general, leaf-litter decomposition was higher in the end of the dry period. Except for the Monjolinho watershed in the aquatic environment, the eucalyptus leaves had a lower decomposition rate. The eucalyptus leaves, mainly in Tinga and Forquilha watersheds, showed higher quantities of lignin, cellulose, high ratio C/N, low concentration of N and Ca. The forestry fragment of the three watersheds showed significant differences in eucalyptus and native leaves production, where Tinga micro watershed outstanded with the higher eucalyptus deposition. It can ... / Mestre

Abstract In northernmost Fennoscandia, grazing by reindeer (Rangifer tarandus L.) has a substantial impact on the vegetation of boreal forests and arctic-alpine tundra heaths, which are reflected in below-ground processes, such as nutrient mineralization and soil organic matter decomposition. In the present thesis, the effects of reindeer grazing on soil nutrient cycling were studied by comparing grazed situation with an ungrazed control area in ten boreal forests and six arctic-alpine tundra heaths. In boreal forests, reindeer grazing reduced microbial respiration in both the oligotrophic and mesotrophic study areas, indicating a deficiency of labile substrates for the soil microbes due to reindeer grazing. Simultaneously, there was heterogeneity in the impact on nitrogen mineralization rates as at some sites, mineralization was enhanced by grazing. The fertilization effect of urine and faeces can therefore be strong enough a factor to outweigh a reduction in quality of soil organic matter. In the oligotrophic forests, low soil moisture content in the grazed areas could sometimes limit the mineralization rates even when the potential for mineralization was enhanced by grazing. In the tundra ecosystems, there was spatial variation in the impact of grazing on microbial respiration and nitrogen mineralization. Low grazing intensity occurring outside the growing season had a retarding impact on nutrient cycling in both unfertilized, nutrient-poor and fertilized, nutrient-rich conditions. In contrast, a relatively high grazing intensity enhanced the mineralization rates in two nutrient-poor and two nutrient-rich tundra heaths. When three different grazing intensities were compared in one oceanic, nutrient-rich and one continental, nutrient-poor tundra heath, the strongest positive effect of grazing on soil nutrient cycling occurred in the heavily grazed areas. The data do not support the assumption that soil nutrient availability regulates whether herbivores enhance or retard nutrient cycling in the soil. Instead, the net effect of grazing is determined by the balance between the underlying mechanisms that may work at opposite directions. The most important of these mechanisms are the grazer-mediated impact on the decomposability of the dominant vegetation and fertilization by urine and faeces. The duration, intensity and seasonal timing of the grazing seem to be important factors that regulate whether reindeer grazing enhances or retards soil nutrient cycling in each specific area. Due to the high spatial and temporal variation in the effects of grazing observed in this study, it is not possible to generalize the overall impact of grazing. Further study is required in order to determine the exact conditions under which grazing enhances or it retards soil nutrient cycling.

Ce travail de recherche a été mené dans l’équipe MODGEN du département GenPhySE, 1388 UMR de l’INRA. Il avait pour perspectives de modéliser les variabilités de la taille de portée des ovins pour une meilleure évaluation génétique et de proposer des modèles d’analyse adoptés à ce type de caractère.Les objectifs de l’étude étaient d'identifier, et d'analyser les facteurs environnementaux et génétiques des variabilités des tailles de portée des brebis et de proposer une méthode adaptée pour canaliser les caractères discrets qui prenne en compte conjointement des objectifs sur la moyenne et sur la variabilité du caractère. La thèse s’appuyait sur des données issues de la chaîne nationale de contrôle de performances en relation avec des organismes de sélection ovin qui sont particulièrement intéressés par les résultats de ces recherches (CORAM). Choix des races. Nous avons considéré trois races dont les fréquences de la taille de portée sont plus ou moins élevées. La race Romane connue par sa forte prolificité ainsi des effectifs contrôlés importants a permis des analyses précises. Les deux autres races choisies sont la race Suffolk et la race Rouge de l’Ouest qui ont servi à tester les modèles sur des populations comportant de moins en moins de portées multiples. La taille de portée des ovins considérée comme une variable continue. Au cours de l’étude, nous avons identifié et hiérarchisé les facteurs de variation environnementaux du niveau de prolificité et de de sa variance pour trois races ovines (Suffolk, Rouge de l’Ouest et Romane). Si les facteurs de variation environnementaux du niveau de prolificité étaient déjà bien connus, peu de données concernaient les facteurs de variation environnementaux de la variance. Nous avons également estimé les paramètres génétiques du niveau de prolificité et de sa variance, ils sont cohérents entre eux. Les héritabilités estimées sur la moyenne sont faibles, en cohérences entre les trois races et avec des études antérieures. La non homogénéité des corrélations estimées par le modèle à deux étapes peut s’expliquer par la relation structurelle entre la moyenne et la variance sur l’échelle observée qui n'est pas prise en compte dans ce type d'analyse. A l'échelle d'une race, cette relation dépend de l’écart spécifique entre les seuils; elle est différente de la relation moyenne – variance observée pour l’ensemble des races et qui est calculée sur des données brutes. La taille de portée des ovins considérée comme une variable discrète Nous avons montré l’existence d’une variabilité d’origine génétique dans les trois races étudiées et nous avons montré que le modèle à seuils homothétique [HTM] s’ajustait mieux aux données et qu'il permettait de calculer conjointement l’effet génétique sur la moyenne et sur la variance. Nous avons aussi montré les limites de ce modèle et nous avons proposé une solution afin de donner un cadre plus général à son utilisation et l’utiliser dans les évaluations génétiques. Nous avons également identifié un critère de sélection pertinent qui permet de sélectionner les individus de même moyenne ayant des variances différentes. Nous avons proposé le modèle à seuils indépendants [ITM] ou le modèle multi caractères avec contrainte, ce modèle considère que chaque réalisation est un caractère. Nous avons montré la faisabilité de ce modèle sur les trois races. Ceci nous a permis de mettre en évidence les problèmes liés à la convergence du programme utilisé, et nous avons proposé d’implémenter ce modèle en modifiant le programme TM. / This research work was conducted in the MODGEN team of GenPhySE department, 1388 UMR of INRA. The aim of the study was to model the range size variability of sheep for a better genetic evaluation and to propose models of analysis adopted for this type of character. The objectives of the study were to identify, and analyze the environmental and genetic factors of ewe range size variability and to propose a suitable method for channeling discrete traits that takes into account both mean and character variability objectives. The thesis was based on data from the national chain of performance control in relation to sheep breeding organizations that are particularly interested in the results of this research (CORAM). Choice of breeds We have considered three breeds whose litter size frequencies are higher or lower. The Romance breed known for its high prolificity and important controlled numbers allowed precise analyzes. The other two breeds selected are the Suffolk breed and the Western Red breed, which were used to test the models on populations with fewer and fewer litters. Sheep litter size considered a continuous variable During the study, we identified and prioritized the environmental variation factors of the level of prolificacy and its variance for three sheep breeds (Suffolk, Western Red, and Romane). ). While the environmental variation factors of the level of prolificacy were already well known, there was little data on the environmental variance factors of the variance. We have also estimated the genetic parameters of the level of prolificacy and its variance, they are coherent with each other. Heritabilities estimated on the mean are low, consistent between the three races and with previous studies. The non-homogeneity of the correlations estimated by the two-stage model can be explained by the structural relationship between the mean and the variance on the observed scale that is not taken into account in this type of analysis. At the scale of a race, this relation depends on the specific difference between the thresholds; it is different from the mean - variance relationship observed for all breeds and calculated on raw data. Sheep litter size considered a discrete variable We have shown the existence of genetic variability in the three races studied and we have shown that the homothetic threshold model [HTM] fits better with the data and that it allowed to calculate jointly the genetic effect on the mean and on the variance. We have also shown the limitations of this model and have proposed a solution to provide a more general framework for its use and use it in genetic evaluations. We have also identified a relevant selection criterion that makes it possible to select individuals of the same average with different variances. We proposed the model with independent thresholds [ITM] or the multi-character model with constraint, this model considers that each realization is a character. We have shown the feasibility of this model on the three races. This enabled us to highlight the problems related to the convergence of the program used, and we proposed to implement this model by modifying the TM program.

The present study was undertaken to examine the litter decay fungi of red cedar (Thuja piicata Donn). The fungi involved in conifer litter decay have not been examined intensively and there has been no study of red cedar litter decay. Since Thuja is often found in wet, poorly drained areas, it provided an opportunity to observe occurrence of litter decay fungi relative to slight differences in distance from a stream margin. This was determined by observing changes in the frequency of the fungi at various distances from the margin of a stream and also by observing seasonal changes in fungal populations. An ordination of the data was performed to determine if there were species associations which would characterize the relatively minor horizontal and vertical spatial changes in the sites. The sites were divided into subsites (high, middle and low with respect to the stream) and samples were taken at each subsite. Red cedar branchlets from the L and F litter layers were washed and plated on a selective medium or placed in moist chambers; all observed species were isolated and identified. Most of these were members of the Fungi Imperfecti. The frequency of occurrence of the more commonly isolated species was utilized in a Principal Components Analysis (PCA) to determine associations of subsites, layers or species. There was little distinction between the three subsites, but there was a general separation of the high subsite from the low subsite, the middle subsite showing affinities to both. The L and F layers represented a division of the litter layer which formed more distinct clusters in the ordination, especially in the Site B data. Seasonal distinction among the samples seemed to reflect the extremes of the seasons. The spring and summer samples generally grouped together, as did the fall and winter samples. Species associations reflected various combinations of the above groupings, depending on the species groups involved. Again the most distinct groups represented extremes, e.g., species prominent in dry samples, especially in the high subsite, or species prominent in moist conditions, especially in the low subsite. No single variable provided clear distinction among the various subsites, layers, seasons or species. However, the combination of all of these gave general indications as to probable fungal associations. / Science, Faculty of / Botany, Department of / Graduate

Plastic pollution has become of public concern recently and only in the last decades the need of quantifying loads of plastic in the marine environment and identifying their ultimate destination has been urged as a mean to point at where interventions should concentrate. The Arabian seas (Red Sea and Arabian Gulf) have oceanographic features that candidate them as accumulation zones for marine plastics, but, especially the Red Sea, are largely unexplored. The dissertation here presented provides significant advances in the understanding of the marine plastic distribution in the two basins. Despite the initial hypothesis, the Red Sea was found to hold a remarkably low abundance of plastic particles in its surface waters. Similarly, previous assessments have reported the same in the Arabian Gulf. In line with the global estimates, only a small portion of the plastic that is discarded yearly in the marine environment is found in its surface waters, implying the presence of removal processes. However, the unexpectedly low loads of floating plastics in the Arabian seas indicate that sinks are likely more significant here than elsewhere. In the Red Sea, an extensive survey of macroplastic stranded on shores, globally considered a major sink of marine plastic, has indicated that Avicennia marina mangrove forests, through the mesh created by their pneumatophores, contribute significantly more than unvegetated shores in retaining plastics. Loads of plastic in the Arabian Gulf mangrove stands, more impacted by coastal development than stands in the Red Sea, are even larger. The role of mangroves as significant sinks of plastics is further corroborated by the finding that the burial rates of plastic in their sediments follow an exponential increase in line with the global plastic production increase, ultimately demonstrating that plastic is likely sequestered there permanently. Mangrove forests alone are, however, not enough to justify the mismatch between plastic inputs and loads in surface waters. The experimental finding showed here that coral structures can passively trap substantial loads of microplastics and the large extension of reefs, especially in the Red Sea, suggest that reefs might constitute a missing sink of marine plastic in the basin worth exploring.

Soil quality and health indicators are necessary to monitor and improve the agricultural sustainability. This experiment was conducted at Mississippi State, MS between 2015 and 2016. Soil samples were taken to determine bulk density, enzymatic activity, and total C and N. Results indicated greater bulk density, total C and N, and enzymatic activity for inter-row position than for within the corn row which was disturbed by strip-tillage. Soil bulk density tended to increase with soil depth; however, total C and N and total microbial activity decreased with depth both years. Total soil C and N increased from 2015 to 2016. Enzymatic activity was greatest at corn planting and decreased up thru four weeks apparently due to total C and N decomposition. Total C and N were related to bulk density and enzymatic activity because increase in soil C and N decreased the bulk density and increased the enzymatic activity values.

Considerable concern has developed over the possible pollution from poultry litter storage methods. This study was conducted to evaluate three different storage scenarios; covered stockpiles, uncovered stockpiles, and litter sheds. The stockpiles were monitored over two rainfall simulation events, in both the Ridge and Valley and the Piedmont physiographic provinces, with both surface and subsurface flows analyzed. An observational study, where subsurface water was sampled for a nine-month period was conducted using six litter sheds, three in each of the above provinces. Samples were analyzed for nutrients, fecal coliforms, and solids. Concentrations of NHx, TKN, OP, TP, VSS, and FC in surface runoff from uncovered litter piles were all statistically higher than that from covered piles, with NO3 being the exception. However, increased runoff volumes originating from the covered litter piles caused mass loadings from both covered and uncovered piles to be similar enough that statistical significance was not obtained, except in the case of FC. Soil water samples from litter stockpiles did not show a statistically significant treatment effect for concentration data, but uncovered piles did exhibit higher nitrogen concentration estimates than the covered piles. Sample collection frequency showed a statistically significant increase in the number of samples that could be obtained from the edge lysimeter under uncovered litter piles from the Piedmont experimental site. This result indicates uncovered piles are releasing the precipitation absorbed during the rainfall simulation into the sub-surface environment. In the storage shed study, a greater number of samples were collected per attempt at the Piedmont sheds compared to those at the Ridge and Valley site. While both areas were undergoing a significant drought, Piedmont porous-cup lysimeters yielded samples 63% of the time, compared to 10% for Ridge and Valley lysimeters. Lysimeters located near the edge of the shed were also more likely to yield a sample than those in the center or a background location. Unknown interferences within the litter shed samples prevented three laboratories from obtaining valid nutrient concentrations. / Master of Science

In north Mississippi, I evaluated fuel loads in the late dormant season and after leaf fall in unburned areas and after a dormant season burn. Fuel loads beneath winged elm (Ulmus alata) were assessed to determine if this shade-tolerant species impacts fine fuel loads in the area immediately near its bole. I found leaf litter fuel loads are higher after leaf fall suggesting that burns conducted closer to leaf fall may have increased burn intensity. Burning reduced leaf litter fuels and exposed mineral soil which returned to pre-burn levels following leaf fall. Declines in duff layer fuels were not evident until after leaf fall. Leaf litter fuels underneath winged elms had higher mass and percentage of winged elm litter beneath them compared to areas away from them. These results will help determine appropriate time for restoring prescribed fire and the implications of encroachment by non-oak species into upland oak forests.

Soil microorganisms are important for the stabilization and preservation of a good soil structure. Management practices can affect the diversity and population of microorganisms, which could beneficially change soil properties and promote a more sustainable dryland system. This study was established near Pontotoc, MS on Atwood silt loam to evaluate the impacts of cover crops and fertilizer sources on selected biologically related soil properties in a no-tillage, dryland soybean system. Soil analyses included total carbon and nitrogen, permanganate oxidizable carbon (POXC), easily extractable glomalin-related soil protein (EE-GRSP), water stable aggregate (WSA) and soil pH. Cover crop biomass and percent groundcover, soybean leaf area index (LAI), plant height, and yield were also determined. Results indicated that fertilizer source did have an impact on total nitrogen, EE-GRSP and soybean yield. A positive impact on soil properties is expected with the use of cover crops if studied for a longer period of time.

Previous research documented that white-tailed deer body mass and antler size varied across physiographic regions of Mississippi. Deer from regions with greater soil fertility had greater body mass and antler size; however, this information is known only for individuals 6 months of age and older. I monitored birth mass and skeletal size of fawns produced by bred, adult, female white-tailed deer transplanted from the Delta, Thin Loess (Loess), and Lower Coastal Plain (LCP) soil regions to fawn in the Mississippi State University Rusty Dawkins Memorial Deer Unit. I evaluated the effect of soil region of origin, litter size, and fawn gender on mass and size of fawns at birth. Birth mass was not as variable as mass of older animals, but LCP fawns were lighter and shorter than loess and/or delta fawns. Twins were lighter and shorter than singletons. Males were heavier than females. Differences between regional birth dates within the pens and estimated regional birth dates based on a fetal growth curve raises questions about the wide-spread application of this method of estimating deer breeding and fawning dates.