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Biomass, tiller numbers, flowering, and genet survival were accessed for the rhizomatous Elymus lanceolatus ssp. lanceolatus and caespitose E. l. ssp. wawawaiensis growing in mixtures with a range of densities of each taxon. Models of aboveground biomass of each taxon as a function of mixed densities were used to calculate competition indices. Tiller numbers and biomass of ssp. lanceolatus were higher than those of the caespitose taxon in the first year, but declined in the second year, while biomass and tiller numbers of ssp. wawawaiensis changed little. All tillers of ssp. wawawaiensis emerged in autumn; tillers of ssp. lanceolatus emerged from autumn through late spring. The rhizomatous taxon better exploited open resources in the first year; ssp. wawawaiensishad slower growth, but its production of many tillers early in the season may allow it to quickly exploit seasonally variable conditions of semiarid environments. Decline in flowering at higher densities and in the second year was more pronounced than that of biomass and tiller numbers. Genet survival was high and similar for both taxa. Substitution rates indicated ssp. lanceolatus was the better competitor in both years. In the second year, the two taxa differed somewhat less in substitution rates. A greater overlap in resources used by the two taxa was indicated. Subspecies lanceolatus experienced greater intensity of competition. Substitution rates and relative efficiency index indicated ssp. lanceolatus was the greater competitor between early and late spring, when overlap in resource use was greater. Another experiment addressed advantages of clonal foraging of ssp. lanceolatus in exploiting soil nutrient patches. A foraging response was found in the rhizomatous taxon, with greater numbers of closely spaced tillers in high-nutrient patches adjacent to the main clone, but root biomass in these patches, and aboveground biomass of the clones, indicated that both taxa accessed nutrients in the patches, but ssp. wawawaiens is used only root growth. The taxa were similar in their tolerance of low levels of soil nutrients. No difference among genets in degree of foraging response, and no relationship between degree of foraging response and fitness when nutrients are patchy were found. Subspecies lanceolatus did not show such a foraging response to high neighbor densities in mixed-density plots. Instead, rhizome lengths were reduced by higher neighbor densities and in the second year, by reduced resources overall.

The impact of carp on a rhizomatous macrophyte was examined in two consecutive years using three outdoor aquaculture ponds with naturally established beds of Potamogeton tricarinatus. Each pond was divided with wire fencing to form a carp (500 kg ha-1) and control treatment. After 6 weeks, plant biomass had declined to the same extent in the carp and control treatments, indicating that direct physical disturbance by carp was not reducing the biomass of P. tricarinatus. In a second experiment, carp were added to two of the same ponds when plants were regenerating after a 9-11 month drying period. After 8 weeks, P. tricarinatus biomass in the carp treatments was between one half and one tenth of the biomass in the control treatments and one control treatment supported more Najas tenuifolia than the paired carp treatment. The lower biomass of Potamogeton in the carp treatments was a result of fewer shoots and less growth per shoot. Rhizomes had been undermined in the carp treatment with less than 1% of plants growing from rhizome compared to 36% in the control treatment. Accumulation of sediment into traps was significantly higher in the carp treatments (2.5 to 77.5 times more than the control). On average, carp resuspended 662 kg dry sediment ha-1 for each 100 kg ha-1 of carp or 6.6 times their wet weight biomass in dry sediments each day. Some implications of high sediment resuspension are discussed. The research demonstrates that well anchored macrophyte species can show tolerance to the physical disturbance associated with carp benthic feeding, however, these same species are vulnerable during regenerating and recruitment stages. It is suggested that anchorage is the most important factor for determining plant tolerance to carp. The implications for aquatic plant and riverine management are discussed, including the importance of excluding carp from newly flooded wetlands and the role of carp in determining alternative stable states.

Master of Science / Department of Biology / David C. Hartnett / Herbivory is one of the major biotic interactions shaping the structure and dynamics of grassland plant populations and community structure. The two major grass growth forms, rhizomatous and caespitose species, may show different grazing tolerance and short-term overcompensation may offset long-term reductions in plant performance and fitness. The objectives of this study were to assess 1) the effects of long-term ungulate grazing on plant architecture, population structure, and life history traits of the caespitose perennial grass, Schizachyrium scoparium (little bluestem), and the rhizomatous Bouteloua curtipendula (sideoats grama) in tallgrass prairie, and 2) the effects of grazing intensity (frequency of defoliation) on growth responses of little bluestem. Long-term bison grazing decreased the cover, frequency, tiller height, and proportion of tillers producing seed in little bluestem, but caused no changes in tiller density and total genet size. Grazed little bluestem plants maintained a significantly larger below ground bud bank. Bison grazing had no long-term effect on the abundance, bud bank densities, or rhizome growth of the rhizomatous side-oats grama grass. Biomass, tiller density, relative growth rates, and proportion of tillers flowering in little bluestem all decreased with increasing frequency of defoliation. However, even an intense grazing regime (9 defoliations over a 12 month period) caused no plant mortality and no changes in new tiller emergence rates, or bud bank densities. Increasing defoliation frequency did result in shifts in plant architecture, as an increasing proportion of extravaginal tillers led to a more lateral, decumbent growth form. These results show that the rhizomatous side-oats grama grass has a significantly higher grazing tolerance than does little bluestem, and/or that bison selectively graze little bluestem. Results from responses to the experimental defoliation regimes suggest that little bluestem shows lower tolerance to high frequency of defoliation, and its maintenance of a reserve below ground bud bank may be its primary tolerance mechanism, allowing tiller populations to recover following severe defoliation.

L'obiettivo della ricerca è stato quello di identificare la coltura bioenergetica con il maggior potenziale di sequestro del carbonio (C); sono state considerate tre colture perenni arboree (pioppo, robinia e salice) e tre colture erbacee perenni (canna comune , miscanto e panico ) al sesto anno dal loro impianto e coltivate nello stesso ambiente. In primo luogo sono state misurate le variazioni dei tassi del C organico del suolo (COS) per il primo 1 m, mentre per i primi 30 cm di suolo è stato stimato il grado di stabilita del COS valutando sette frazioni di COS che presentano differenti gradi di stabilizzazione; in secondo luogo, sono stati caratterizzati gli apparati radicali delle sei specie per la stessa profondità di suolo, per valutare dove le specie accumulano la biomassa radicale lungo il profilo di suolo. I risultati confermano che l’impianto di colture bioenergetiche perenni su superfici precedentemente dedite a colture annuali gestite convenzionalmente rappresenta una opzione valida per sequestrare C nel soulo. Tuttavia, è stata osservata una diversa capacità di sequestro di C tra specie arboree ed erbacee: le specie arboree hanno dimostrato aumentre il contenuto di COS nel primo strato di suolo ( 0-10 cm di suolo), ma la loro capacità di allocare biomassa radicale negli strati profondi del suolo è limitata; mentre, la specie erbacee allocano un’alta quantità di biomassa radicale negli strati profondi del suolo, ma solo il panico ed il miscanto hanno aumentato il contenuto di C nel primo strato di suolo. / The objective of the present research was to identify the bioenergy crop with the greatest carbon sequestration potential among three perennial woody crops (poplar, black locust and willow) and three perennial herbaceous crops (giant reed, miscanthus and switchgrass) at the sixth year from plantation and in the same location. First of all the SOC stock variations for the first 1 m soil depth and the quantification of seven soil C fractions related to SOC stabilization level of the first 30 cm of soil were assessed; secondly, a characterization of the root system and the traits which affect the carbon allocation in soil were considered. The results confirm that the establishment of perennial bioenergy crops in previous arable fields can be a suitable option to sequester carbon (C) belowground. However, a different C sequestration capacity was observed between woody and herbaceous crops: woody species showed the greatest SOC sequestration potential in the first soil layer (0-10 cm of soil) but their ability to allocate root biomass in the deeper soil layers was limited; while, the herbaceous species allocated a high amount of root biomass in the deeper soil layers, but only switchgrass and miscanthus sequester C in the first soil layer.