Doctor of Philosophy / Department of Biology / David C. Hartnett / In perennial grasslands, the belowground population of meristems (the bud bank) plays a fundamental role in local plant population structure and dynamics. I tested the “meristem limitation hypothesis” prediction that bud banks increase along an increasing precipitation/productivity gradient in North American grasslands. I sampled bud populations quarterly at six sites across a 1,100 km gradient in central North America. Bud banks increased with average annual precipitation, which explained 80% of variability in bud banks among sites. Seasonal changes in grass bud banks were surprisingly similar across a 2.5-fold range in precipitation and a 4-fold range of aboveground net primary productivity (ANPP). Secondly, I tested the hypothesis that tallgrass prairie plants respond to increases in a limiting resource (nitrogen) through demographic effects on the bud bank. I parameterized matrix models for individual genets, considering each genet as a population of plant parts (buds and stems). Nitrogen addition significantly impacted bud bank demography of both Sporobolus heterolepis and Koeleria macrantha. In 2005, emergence from the bud bank and growth rates (λ) of the tiller population were significantly higher in S. heterolepis genets that received nitrogen. In contrast, nitrogen addition decreased λ in K. macrantha. Both prospective and retrospective analyses indicated that bud bank dynamics are the key demographic processes driving genet responses to nutrient availability. Lastly, I tested the hypothesis that the effects of fire and grazing on plant species composition and ANPP are mediated principally through demographic effects on bud banks. I found that plants respond to fire and grazing with altered rates of belowground bud natality, bud emergence, and both short-term (fire cycle) and long-term changes in bud density. The size of the bud bank is an excellent predictor of long-term ANPP, supporting my hypothesis that ANPP is strongly regulated by belowground demographic processes. Meristem limitation due to water or nutrient availability or management practices such as fire and grazing may constrain grassland responses to inter-annual changes in resource availability. An important consequence is that grasslands with a large bud bank may be the most responsive to future climatic change or other phenomena such as nutrient enrichment, and may be most resistant to exotic species invasions.

Doctor of Philosophy / Department of Biology / David C. Hartnett / Grazing and drought are instrumental in the development and maintenance of perennial grasslands. In this research I tested the belowground bud bank contribution to tallgrass prairie resistance and resilience when perturbed by grazing and drought. First, I tested the bud bank role in vegetation response to and recovery from severe drought (Chapter 2). I compared above- and belowground responses of experimentally droughted plots to ambient controls and irrigated plots during two years of severe drought and two years of recovery. I found that although aboveground net primary productivity declined 30-60% during drought, bud bank density and demography were insensitive to drought. These results suggest that grassland resistance and resilience when perturbed by drought may be mediated by stability of belowground bud banks. Second, I investigated vegetation and soil nutrient legacies following release from long-term grazing (Chapter 3). I documented a relatively rapid shift in aboveground vegetation within four years of grazer exclusion, with productivity, stem density, and diversity becoming relatively more similar to ungrazed than grazed prairie. The density and composition of the belowground bud bank and soil seed bank shifted more slowly, remaining more similar to grazed than ungrazed prairie. Responses of soil nutrients to removal of grazers varied, and in some cases was affected by recent fire history. These results demonstrate the contribution of belowground propagules to the maintenance of a diverse plant community both during grazing and after grazers are removed. Finally, I examined short-term vegetation responses to both drought and grazing (Chapter 4). Despite extreme drought and simulated grazing that reduced productivity and increased mortality of individual stems, the dominant C4 grasses maintained a stable bud bank. Aboveground net primary productivity and bud bank density of sedges and forbs, however, were reduced by both drought and grazing. This differential response of species to extreme drought and grazing led to shifts in community composition and species diversity over one growing season. Across drought and grazing treatments, live rhizome biomass was highly correlated with bud bank density and may be a useful, more easily measured index of bud bank density.

A área de Cerrado escolhida para o estudo está em regeneração na Estação Ecológica de Santa Bárbara, localizada no município de Águas de Santa Bárbara, SP. Nesta área o Pinus, que estava sob cultivo desde os anos 70, foi retirado em 2012 e, em 2014, foi realizada uma queimada. As espécies Eugenia dysenterica (Mart.) DC. e E. punicifolia (Kunth) DC. foram escolhidas devido ao elevado número de indivíduos que rebrotaram na área. O objetivo geral do projeto foi conduzir análises morfoanatômicas e químicas das estruturas relacionadas ao potencial de rebrotamento. Foram realizadas: a contagem das gemas subterrâneas nos primeiros 10 centímetros abaixo do nível do solo, as análises químicas das raízes e análises anatômicas na região terminal de ramos aéreos e no sistema subterrâneo. Nas duas espécies, além da gema apical dos ramos aéreos, nas três regiões nodais subsequentes, acima da gema axilar ocorre uma gema acessória. Em todas as gemas, observam-se estruturas de proteção, pois junto ao meristema apical caulinar (MAC) ocorrem coléteres e cristais. Além disso, o MAC é protegido por primórdios foliares com cavidades de óleo, muitos cristais e tricomas unicelulares não glandulares que possuem espessamento parietal em celulose e podem acumular compostos fenólicos. Nos sistemas subterrâneos, o número de gemas, localizadas preferencialmente nos primeiros cinco centímetros do solo, variou entre os três indivíduos da mesma espécie: E. dysenterica 162, 17 e 253, E. punicifolia 24, 40 e 109. Esta variação deveu-se ao grau de desenvolvimento das estruturas subterrâneas as quais certamente formaram-se antes do período da retirada do Pinus. O sistema subterrâneo das espécies é formado por um eixo lenhoso cuja porção superior é caulinar e emite vários ramos aéreos enquanto a porção inferior é constituída por uma raiz axial espessada que pode atingir até um metro de profundidade em E. dysenterica. Em E. punicifolia o sistema subterrâneo ocupa uma região mais superficial do solo e, assim como o caule, as raízes axial e adventícias são distribuídas num plano mais horizontal. O tecido de revestimento nas raízes de E. punicifolia e no caule e raízes de E. dysenterica, apresenta camadas alternadas de células de paredes suberizadas e de células com espessamentos parietais em pectina; no caule de E. punicifolia há esclereides que se alternam com as células suberizadas. Em E. punicifolia o espessamento resulta de divisões anticlinais e expansão tangencial das células do parênquima floemático. Há floema interno e parênquima medular nos caules subterrâneos de ambas as espécies. Compostos fenólicos e grãos de amido estão presentes nas células parenquimáticas de regiões mais espessadas dos caules e raízes. Os teores de carboidratos totais, hemicelulose, celulose e lignina não diferem significativamente nas duas espécies. No entanto, as concentrações de flavonoides totais e de compostos fenólicos totais foram superiores nas raízes de E. punicifolia. O grau de proteção das gemas aéreas, o elevado número de gemas e o acúmulo de compostos de reserva (amido) e de proteção (fenóis, flavonoides, lignina) nas estruturas subterrâneas podem ter favorecido o seu rebrotamento após a retirada do Pinus e a sua permanência das espécies na área. / The Cerrado area studied is under regeneration at the Estação Ecológica de Santa Bárbara, located in Águas de Santa Bárbara (São Paulo, Brazil). In this area, the Pinus, cultivated since the 1970s, was removed in 2012 and then, in 2014, the area was burnt. The species Eugenia dysenterica (Mart.) DC. and E. punicifolia (Kunth) DC. were studied due to their high resprouting after the burnt event. The aim was to carry out morphoanatomical and chemical analyses of the structures related to the resprouting capacity. The number of belowground buds was counted in the first 10 cm below the soil surface. The chemical analyses of the roots and anatomical analyses of the end portion of the aerial branches and the underground system were performed. Besides the apical bud, both species showed an accessory bud above the axillary one at the three subsequent nodal regions. In all studied buds, protection structures were observed, as colleters and crystals occur close to the shoot apical meristem (SAM). Moreover, SAM is protected by leaf primordia with oil cavities, many crystals and non-glandular unicellular trichomes. These trichomes present parietal cellulose thickening and are able to accumulate phenolic compounds. In underground systems, the number of buds, mostly in the first five centimeters below the soil surface, varied between individuals per species: E. dysenterica 162, 17 and 253; E. punicifolia 24, 40 and 109. This variation was caused by the development degree of the underground system, whose structures were certainly developed before Pinus removal. The underground system of the species display a woody axis, whose upper portion is a stem structure and produces several aerial branches. Its lower part is formed by an axial thickened root that can reach one metre deep in E. dysenterica. In E. punicifolia, the subterranean system occupies a more superficial region of the soil and, similar to the stem, the axial and adventitious roots are distributed in a more horizontal plane. The covering tissue of underground systems in E. punicifolia and E. dysenterica displays alternate layers of cells with suberized walls and pectin-thickened walls. In E. punicifolia stem, the covering tissue exhibits sclereids alternate with cells of suberized walls. The thickening in E. punicifolia is a result of anticlinal divisions and tangential expansion of phloematic parenchyma cells. Both species show internal phloem and medullary parenchyma in underground stems. Phenolic compounds and starch grains are present in parenchyma cells of thickened regions in stems and roots. The contents of total carbohydrates, hemicellulose, cellulose and lignin do not differ significantly in the two species. However, concentrations of total flavonoids and total phenolic compounds are higher in roots of E. punicifolia. The protection level of aerial buds, large number of underground buds, and accumulation of storage (starch) and protection (phenols, flavonoids, lignin) compounds in the underground structures may have favoured resprouting of the species after Pinus removal and their maintenance in the area.

A área de Cerrado escolhida para o estudo está em regeneração na Estação Ecológica de Santa Bárbara, localizada no município de Águas de Santa Bárbara, SP. Nesta área o Pinus, que estava sob cultivo desde os anos 70, foi retirado em 2012 e, em 2014, foi realizada uma queimada. As espécies Eugenia dysenterica (Mart.) DC. e E. punicifolia (Kunth) DC. foram escolhidas devido ao elevado número de indivíduos que rebrotaram na área. O objetivo geral do projeto foi conduzir análises morfoanatômicas e químicas das estruturas relacionadas ao potencial de rebrotamento. Foram realizadas: a contagem das gemas subterrâneas nos primeiros 10 centímetros abaixo do nível do solo, as análises químicas das raízes e análises anatômicas na região terminal de ramos aéreos e no sistema subterrâneo. Nas duas espécies, além da gema apical dos ramos aéreos, nas três regiões nodais subsequentes, acima da gema axilar ocorre uma gema acessória. Em todas as gemas, observam-se estruturas de proteção, pois junto ao meristema apical caulinar (MAC) ocorrem coléteres e cristais. Além disso, o MAC é protegido por primórdios foliares com cavidades de óleo, muitos cristais e tricomas unicelulares não glandulares que possuem espessamento parietal em celulose e podem acumular compostos fenólicos. Nos sistemas subterrâneos, o número de gemas, localizadas preferencialmente nos primeiros cinco centímetros do solo, variou entre os três indivíduos da mesma espécie: E. dysenterica 162, 17 e 253, E. punicifolia 24, 40 e 109. Esta variação deveu-se ao grau de desenvolvimento das estruturas subterrâneas as quais certamente formaram-se antes do período da retirada do Pinus. O sistema subterrâneo das espécies é formado por um eixo lenhoso cuja porção superior é caulinar e emite vários ramos aéreos enquanto a porção inferior é constituída por uma raiz axial espessada que pode atingir até um metro de profundidade em E. dysenterica. Em E. punicifolia o sistema subterrâneo ocupa uma região mais superficial do solo e, assim como o caule, as raízes axial e adventícias são distribuídas num plano mais horizontal. O tecido de revestimento nas raízes de E. punicifolia e no caule e raízes de E. dysenterica, apresenta camadas alternadas de células de paredes suberizadas e de células com espessamentos parietais em pectina; no caule de E. punicifolia há esclereides que se alternam com as células suberizadas. Em E. punicifolia o espessamento resulta de divisões anticlinais e expansão tangencial das células do parênquima floemático. Há floema interno e parênquima medular nos caules subterrâneos de ambas as espécies. Compostos fenólicos e grãos de amido estão presentes nas células parenquimáticas de regiões mais espessadas dos caules e raízes. Os teores de carboidratos totais, hemicelulose, celulose e lignina não diferem significativamente nas duas espécies. No entanto, as concentrações de flavonoides totais e de compostos fenólicos totais foram superiores nas raízes de E. punicifolia. O grau de proteção das gemas aéreas, o elevado número de gemas e o acúmulo de compostos de reserva (amido) e de proteção (fenóis, flavonoides, lignina) nas estruturas subterrâneas podem ter favorecido o seu rebrotamento após a retirada do Pinus e a sua permanência das espécies na área. / The Cerrado area studied is under regeneration at the Estação Ecológica de Santa Bárbara, located in Águas de Santa Bárbara (São Paulo, Brazil). In this area, the Pinus, cultivated since the 1970s, was removed in 2012 and then, in 2014, the area was burnt. The species Eugenia dysenterica (Mart.) DC. and E. punicifolia (Kunth) DC. were studied due to their high resprouting after the burnt event. The aim was to carry out morphoanatomical and chemical analyses of the structures related to the resprouting capacity. The number of belowground buds was counted in the first 10 cm below the soil surface. The chemical analyses of the roots and anatomical analyses of the end portion of the aerial branches and the underground system were performed. Besides the apical bud, both species showed an accessory bud above the axillary one at the three subsequent nodal regions. In all studied buds, protection structures were observed, as colleters and crystals occur close to the shoot apical meristem (SAM). Moreover, SAM is protected by leaf primordia with oil cavities, many crystals and non-glandular unicellular trichomes. These trichomes present parietal cellulose thickening and are able to accumulate phenolic compounds. In underground systems, the number of buds, mostly in the first five centimeters below the soil surface, varied between individuals per species: E. dysenterica 162, 17 and 253; E. punicifolia 24, 40 and 109. This variation was caused by the development degree of the underground system, whose structures were certainly developed before Pinus removal. The underground system of the species display a woody axis, whose upper portion is a stem structure and produces several aerial branches. Its lower part is formed by an axial thickened root that can reach one metre deep in E. dysenterica. In E. punicifolia, the subterranean system occupies a more superficial region of the soil and, similar to the stem, the axial and adventitious roots are distributed in a more horizontal plane. The covering tissue of underground systems in E. punicifolia and E. dysenterica displays alternate layers of cells with suberized walls and pectin-thickened walls. In E. punicifolia stem, the covering tissue exhibits sclereids alternate with cells of suberized walls. The thickening in E. punicifolia is a result of anticlinal divisions and tangential expansion of phloematic parenchyma cells. Both species show internal phloem and medullary parenchyma in underground stems. Phenolic compounds and starch grains are present in parenchyma cells of thickened regions in stems and roots. The contents of total carbohydrates, hemicellulose, cellulose and lignin do not differ significantly in the two species. However, concentrations of total flavonoids and total phenolic compounds are higher in roots of E. punicifolia. The protection level of aerial buds, large number of underground buds, and accumulation of storage (starch) and protection (phenols, flavonoids, lignin) compounds in the underground structures may have favoured resprouting of the species after Pinus removal and their maintenance in the area.

Master of Science / Department of Biology / David C. Hartnett / Perennial grasses on tallgrass prairie primarily reproduce vegetatively via the belowground bud bank, yet the production, dynamics, and morphology of belowground buds is largely unexplored. Since the two main photosynthetic pathway guilds (C3 and C4) on tallgrass prairie vary in their aboveground phenology, their belowground phenology would also be expected to vary. Differences in bud production, development, and spatial arrangement result in different growth forms. Therefore, an extensive biweekly examination of a dominant tallgrass prairie C4 rhizomatous grass Andropogon gerardii and C3 caespitose grass Dichanthelium oligosanthes was conducted over an entire year. Andropogon gerardii and D. oligosanthes have multiple distinctive bud developmental stages. Andropogon gerardii was synchronous in its bud development and its bud bank was composed of multiple annual cohorts. The bud bank of D. oligosanthes was developmentally asynchronous and was comprised of a single bud cohort since its bud bank underwent a complete turnover in early summer. The different roles of buds in the life history of each species reflected their differences in bud longevity, quality, and dormancy. In D. oligosanthes, belowground buds enabled plant survival over the C3 summer dormant period whereas juvenile tillers overwintered during the longer winter dormant period. In contrast, A. gerardii survived its single, winter dormant period as dormant buds. The higher-order bud production observed in D. oligosanthes multiplied its tiller production potential and, along with its shortened internodes, contributed to its caespitose growth form. The rhizomatous growth form of A. gerardii resulted from its lack of higher-order bud production and its elongated internodes. Differences in production of buds per vegetative and flowering tiller were quantified in A. gerardii. Flowering tillers of A. gerardii produced larger numbers of buds per tiller and transitioned a larger proportion of their buds to tillers than did vegetative tillers. Therefore, no tradeoff between sexual and vegetative reproduction was evident. Developmental constraints likely prevented such a tradeoff. Bud bank dynamics offer insight into the control of grass population dynamics, production, and ultimately aboveground net primary production (ANPP) and will be useful in understanding the underlying mechanisms by which management practices and environmental change can alter perennial grasslands.

Doctor of Philosophy / Department of Biology / David C. Hartnett / Perennial grass populations propagate vegetatively via the belowground bud bank. Climate, photosynthetic pathway, and growth form impact bud production, longevity, and dormancy; leading to alterations in bud bank and tiller dynamics. Previous research in mesic C₄-dominated tallgrass prairie revealed that a C₄ grass had greater bud longevity and differing bud bank dynamics than a C₃ species. This study examined the bud bank dynamics of rhizomatous and caespitose grasses in a more arid C₃ dominated prairie to gain insights into how bud banks differ among grass species, growth forms, and environments, and the relationship between bud bank characteristics and grass architecture and growth patterns. The bud bank and tiller dynamics of four perennial grasses in the C₃-dominated northern mixed grass prairie were examined over 15 months. The C₃ caespitose and rhizomatous grasses produced similar numbers of buds per tiller and their bud longevity was [greater than or equal to] 2 years. Tiller longevity drove the turnover within the bud bank of the dominant C₃ caespitose grasses Hesperostipa comata and Nassella viridula. Their polycyclic tillers (tillers that lived for more than one year) created multi-aged bud banks. The rhizomatous C₃ grass Pascopyrum smithii also had a multi-aged bud bank because buds were able to live longer than its annual tillers. Differences between caespitose and rhizomatous C₃ grass bud banks were driven by differences in tiller and rhizome production and spatial distribution. Responses to water availability fluctuations are likely buffered by the maintenance of polycyclic tillers in the caespitose grasses and flexible timing of annual tiller recruitment in the rhizomatous grass. The C₄ rhizomatous grass Andropogon gerardii had similar phenology to populations in its tallgrass prairie range center. Despite declines in bud production per tiller and lowered flowering probability in mixed-grass prairie, A. gerardii maintained a multi-aged bud bank and a positive population growth rate via vegetative reproduction at both the center and edge of its range. Bud bank dynamics of different growth forms and photosynthetic pathways, as they offer insight into the control of grass population dynamics and production, will enhance understanding of the mechanisms by which management practices and environmental change can alter perennial grasslands.

Wetland plant species rely largely on vegetative reproduction. Although all types of clonal growth organs are found in wetlands, special adaptations, e.g., turions, fragmentation and budding, are more frequent in true aquatic communities. However, root-sprouting is underrepresented, although it can be beneficial under disturbed conditions. This thesis focuses on ecological constrains potentially hindering root-sprouting in wetlands. This ability was studied in a wetland herb Rorippa palustris in relation to life history, injury timing and carbon economy of a plant. In addition, plant regeneration following submergence and severe disturbance was assessed.

Disturbance is one of most important selective factor causing removal of plant biomass. Man-made habitats are characterized by strong and unpredictable disturbances, providing bare soil surface colonized by plants with short life cycle. Populations of the short-lived plants are, however, vulnerable to the strong disturbance removing all stem parts with reserve axillary meristems in the case it occurs before plant flowering and fruiting. Nevertheless, 2 % of annual and 14 % of biennial plants are able to overcome meristem limitation by adventititous sprouting from hypocotyle or/and roots. This thesis is composed of four original studies describing the occurrence of adventitious sprouting in natural populations of 22 monocarpic weeds of Central Europe and one species in Indonesia. The studied phenomenon was analyzed in relation to various environmental factors and plant traits in the field and in experimental conditions.