Cloning and characterization of the genes involved in cambial growth in response to elevated [CO2]

Aspen (Populus tremuloides) trees growing under elevated [CO2] at a free-air CO2 enrichment (FACE) site have produced significantly more biomass compared to control trees. The molecular mechanisms underlying the observed increase in biomass productivity was investigated by producing transcriptomic profiles of the vascular cambium zone (VCZ) and leaves, followed by a comparative study to identify genes and pathways that showed significant changes following long-term exposure to elevated [CO2]. This study is mainly to verify if genetic modification of a few selected candidate genes including CAP1, CKX6, and ASML2 that are expressed in vascular cambium in response to elevated [CO2] can cause the changes in plant growth and development. To this end, these three genes were cloned into both sense and antisense constructs. Then antisense and sense transgenic lines of above-mentioned genes were developed. 15 events were generated for 5 constructs, which were confirmed with regular PCR and RT-PCR. Confirmed plants were planted in greenhouse for growth and phenotypic characterization. The expression of CAP1, CKX6 and ASML2 in antisense plants was measured by real-time RT-PCR, and the changes caused by gene interference in cambial growth were studies by analyzing the microscopic sections made from the antisense transgenic plants. It has been found that 1) CAP1 is mainly expressed in xylem and root. 2) RNAi suppression of CAP1 significantly affected height and diameter. 3) CAP1, ASML2 and CKX6 affected xylem and phloem cell proliferation and elongation. Due to the delay in regenerating sense transgenic plants, the characterization of sense transgenic plants is limited to growth only.

Regulation of woody plant development by auxin and polar auxin transport

Auxin is a key regulator in plant growth and development. This dissertation examines the role of auxin and polar auxin transport in woody growth and development. Strategies of promoter reporter system, microarray expression analysis, transgenic modification, physiological assays, anatomical analysis, and histochemical/biochemical assays were employed to improve our understanding of auxin study in Populus. The results demonstrate various aspects of auxin regulation on shoot growth, root development, wood formation, and gravitropism in woody tissues. We describe the behavior of the DR5 reporter system for measuring auxin concentrations and response in stably transformed Populus trees. Our study shows that DR5 reporter system can be efficiently used in Populus to study auxin biology at a cellular resolution. We investigated the global gene expression in responding to auxin in Populus root. The results revealed groups of IBA up- and down- regulated genes involved in various biological processes including cell wall modification, root growth and lateral root formation, transporter activity and hormone crosstalk. We also verify two of the identified genes' function by transgenic modification in Populus, which encode auxin efflux carrier PtPIN9 and transcription factor PtERF72. We investigated the role of PtPIN9 in woody growth and development, especially in wood formation and gravitropic response in woody stem. We found that overexpressing PtPIN9 enhanced several growth parameters while suppression of PtPIN9 has inhibited tension wood formation. Our results show that PIN9 and other members from PIN family could be possible useful tools for increasing biomass productivity, wood quality, or in modifying plant form.

Tracing the origin of Arctic driftwood

Arctic environments, where surface temperatures increase and sea ice cover and permafrost depth decrease, are very sensitive to even slight climatic variations. Placing recent environmental change of the high-northern latitudes in a long-term context is, however, complicated by too short meteorological observations and too few proxy records. Driftwood may represent a unique cross-disciplinary archive at the interface of marine and terrestrial processes. Here, we introduce 1445 driftwood remains from coastal East Greenland and Svalbard. Macroscopy and microscopy were applied for wood anatomical classification; a multi-species subset was used for detecting fungi; and information on boreal vegetation patterns, circumpolar river systems, and ocean current dynamics was reviewed and evaluated. Four conifer (Pinus, Larix, Picea, and Abies) and three deciduous (Populus, Salix, and Betula) genera were differentiated. Species-specific identification also separated Pinus sylvestris and Pinus sibirica, which account for ~40% of all driftwood and predominantly originate from western and central Siberia. Larch and spruce from Siberia or North America represents ~26% and ~18% of all materials, respectively. Fungal colonization caused different levels of driftwood staining and/or decay. Our results demonstrate the importance of combining wood anatomical knowledge with insight on boreal forest composition for successfully tracing the origin of Arctic driftwood. To ultimately reconstruct spatiotemporal variations in ocean currents, and to better quantify postglacial uplift rates, we recommend consideration of dendrochronologically dated material from many more circumpolar sites.

Vegetation responses to rapid warming and to minor climatic fluctuations during the Late-Glacial Interstadial (GI-1) at Gerzensee (Switzerland)

High-resolution pollen analyses made on the same samples on which the ratios of oxygen isotopes were measured that provided the time scale and a temperature proxy after correlation to NorthGRIP. (1) A primary succession: The vegetation responded to the rapid rise of temperatures around 14,685 yr BP, with a primary succession on a decadal to centennial time scale. The succession between ca 15,600 and 13,000 yr BP included: (1.1.) The replacement of shrub-tundra by woodland of Juniperus and tree birch (around 14,665 yr BP) (1.2.) The response of Juniperus pollen to the shift in oxygen isotopes in less than 20 yr, (1.3.) A sequence of population increases of Hippophaë rhamnoides (ca 14,600 yr BP), Salix spp. (ca 14,600 yr BP), Betula trees (ca.14,480 yr BP), Populus cf. tremula (ca. 14,300 yr BP), and Pinus cf. sylvestris (ca. 13,830 yr BP). (2) Biological processes: Plants responded to the rapid increase of summer temperatures on all organisational levels: (2.1) Individuals may have produced more pollen (e.g. Juniperus); (2.2) Populations increased or decreased (e.g. Juniperus, Betula, later Pinus), and (2.3) Populations changed their biogeographical range and may show migrational lags. (2.4) Plant communities changed in their composition because the species pools changed through immigration and (local) extinction. Some plant communities may have been without modern analogue.These mechanisms require increasing amounts of time. (2.5) Processes on the level of ecosystems, with species interactions, may involve various time scales. Besides competition and facilitation, nitrogen fixation is discussed. (3) The minor fluctuations of temperature during the Late-Glacial Interstadial, which are recorded in δ18O, resulted in only very minor changes in pollen during the Aegelsee Oscillation (Older Dryas biozone, GI-1d) and the Gerzensee Oscillation (GI-1b). (4) Biodiversity: The afforestation at the onset of Bølling coincided with a gradual increase of taxonomic diversity up to the time of the major Pinus expansion.

Pollen and macroremains from sediment core Aschenhütte

The Upper Pleistocene sediments of the Aschenhütte sink-hole (west of Herzberg am Harz, Lower Saxony) enable one to make interesting correlations between palynological and geological results. The sequence is composed of limnic-telmatic deposits (Eemain to Lower Weichselian) and loess with paleosoils (Weichselian). Sedimentation started during the hornbeam-dominated phase of the Eemian interglacial period and continued throughout the Eemian, the Weichselian Brörup interstadial (sensu Andersen) and parts of the preceding and the following stadial phases, the Herning and the Rederstall stadials. As opposed to most of the known Eemian sites spruce was a major tree species during the hornbeam-dominated phase of the Eemian. The vegetational development during the interstadial phase does not show a period of climatic deterioration as is the case for the Brörup interstadial when considering regions with a more demanding vegetation or regions close to the natural boundaries of the tree species concerned. Pollen or seeds of Bruckenthalia and Picea omoricoides have not been found in the Aschenhütte cores. The limnic-telmatic sediments interlock with loess-paleosoils (Eemian soil and Lower Weichselian bleaching soils) at the lake shore. They are overlaid by loess paleosoils of the Stillfried-B interstadial (Hattorf soil and Lohne soil). Lake level fluctuations were determined by means of the facies distribution and isochrones as defined by pollen analysis. A relatively high stand of the lake level existed after the end of the Eemian interglacial and during the Brörup interstadial periods. In the course of the Herning stadial period the water level dropped, whereas during the Rederstall stadial phase the lake basin was covered by sediments and therefore dried up.

Requerimiento hídrico en álamos de 6 años : Rivadavia, Mendoza (Argentina)

Durante tres años consecutivos se desarrolló el ensayo de riego en álamos de 6 años (Populus euramericana I-214), en el Departamento de Rivadavia, Mendoza, Argentina. El suelo es de textura franco-arenosa. El ensayo se estableció en cuatro bloques completos aleatorizados. El área unitaria fue de 192 m2, con un total de 20 árboles por parcela. Los Intervalos de Riego (IR) fueron 7,14 y 21 días. El número de riegos anuales fue de 21 y la evapotranspiración diaria del cultivo fue de 14.6 mm/día. Los resultados muestran que para el IR = 7 días la Evapotranspiración real (Etc) fue de 2.097 mm; para IR = 14 días fue de 1 467 mm y para IR = 21 días fue de 1 051 mm. El Coeficiente Kc de cultivo se obtuvo al relacionar la Etc con la Evapotranspiración potencial obtenida por la fórmula de Blaney y Criddle y del tanque de evaporación estándar tipo A. Los esultados fueron respectivamente: Kc = 2.95 y 2.06 para IR = 7 días; Kc = 2.07 y 1.45 para IR = 14 días y Kc = 1.47 y 1.05 para IR = 21 días. Del análisis estadístico del volumen de madera producido se concluye que el IR de 7 días fue el mejor para álamos de seis años.