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Leaves Only (leaf + only)
Selected AbstractsFreezing induced leaf movements and their potential implications to early spring carbon gain: Rhododendron maximum as exemplarFUNCTIONAL ECOLOGY, Issue 3 2009Raymond B. Russell Summary 1Thermonastic leaf movements (TLM) are induced by freezing and are correlated with freezing tolerance, and our goal was to determine the significance of TLM to photosynthesis during the winter and early spring. 2We performed field experiments in which we prevented TLM of Rhododendron maximum leaves and determined the consequences of that prevention to photoinhibition (measured by chlorophyll fluorescence) from fall to spring, photosynthesis (measured by gas exchange) in the winter, and recovery of photosynthesis in the spring. 3TLM significantly reduced photoinhibition in the winter for leaves on branches in the outer canopy of R. maximum plants, but not for leaves on inner canopy branches. 4During warm periods in the winter, TLM were associated with significantly lower photoinhibition, but TLM did not have a significant effect on photosynthesis during these times. 5In early spring, leaves with TLM recovered from photoinhibition more quickly than for leaves prevented from TLM. 6Photosynthesis in the early spring was higher at any stomatal conductance for leaves with TLM than for leaves prevented from TLM for outer canopy leaves only. 7Our results demonstrate that TLM during the winter prevent excessive photoinhibition and promote rapid recovery of photosynthesis in the early spring. [source] Photosynthetic Responses of a Temperate Liana to Xylella fastidiosa Infection and Water StressJOURNAL OF PHYTOPATHOLOGY, Issue 1 2004A. J. McElrone Abstract Xylella fastidiosa is a xylem-limited bacterial plant pathogen that causes bacterial leaf scorch in its hosts. Our previous work showed that water stress enhances leaf scorch symptom severity and progression along the stem of a liana, Parthenocissus quinquefolia, infected by X. fastidiosa. This paper explores the photosynthetic gas exchange responses of P. quinquefolia, with the aim to elucidate mechanisms behind disease expression and its interaction with water stress. We used a 2 × 2-complete factorial design, repeated over two growing seasons, with high and low soil moisture levels and infected and non-infected plants. In both years, low soil moisture levels reduced leaf water potentials, net photosynthesis and stomatal conductance at all leaf positions, while X. fastidiosa -infection reduced these parameters at basally located leaves only. Intercellular CO2 concentrations were reduced in apical leaves, but increased at the most basal leaf location, implicating a non-stomatal reduction of photosynthesis in leaves showing the greatest disease development. This result was supported by measured reductions in photosynthetic rates of basal leaves at high CO2 concentrations, where stomatal limitation was eliminated. Repeated measurements over the summer of 2000 showed that the effects of water stress and infection were progressive over time, reaching their greatest extent in September. By reducing stomatal conductances at moderate levels of water stress, P. quinquefolia maintained relatively high leaf water potentials and delayed the onset of photosynthetic damage due to pathogen and drought-induced water stress. In addition, chlorophyll fluorescence measurements showed that P. quinquefolia has an efficient means of dissipating excess light energy that protects the photosynthetic machinery of leaves from irreversible photoinhibitory damage that may occur during stress-induced stomatal limitation of photosynthesis. However, severe stress induced by disease and drought eventually led to non-stomatal decreases in photosynthesis associated with leaf senescence. [source] Microlensing by cosmic stringsMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 1 2008Konrad Kuijken ABSTRACT We consider the signature and detectability of gravitational microlensing of distant quasars by cosmic strings. Because of the simple image configuration such events will have a characteristic lightcurve, in which a source would appear to brighten by exactly a factor of 2, before reverting to its original apparent brightness. We calculate the optical depth and event rate, and conclude that current predictions and limits on the total length of strings on the sky imply optical depths of , 10,8 and event rates of fewer than one event per 109 sources per year. Disregarding those predictions but replacing them with limits on the density of cosmic strings from the cosmic microwave background fluctuation spectrum, leaves only a small region of parameter space (in which the sky contains about 3 × 105 strings with deficit angle of the order of 0.3 milli-seconds) for which a microlensing survey of exposure 107 source years, spanning a 20,40-year period, might reveal the presence of cosmic strings. [source] Interactions between above- and belowground insect herbivores as mediated by the plant defense systemOIKOS, Issue 3 2003T. M. Bezemer Plants are frequently attacked by both above- and belowground arthropod herbivores. Nevertheless, studies rarely consider root and shoot herbivory in conjunction. Here we provide evidence that the root-feeding insect Agriotes lineatus reduces the performance of the foliage feeding insect Spodoptera exigua on cotton plants. In a bioassay, S. exigua larvae were allowed to feed on either undamaged plants, or on plants that had previously been exposed to root herbivory, foliar herbivory, or a combination of both. Previous root herbivory reduced the relative growth rates as well as the food consumption of S. exigua by more than 50% in comparison to larvae feeding on the undamaged controls. We found no effects in the opposite direction, as aboveground herbivory by S. exigua did not affect the relative growth rates of root-feeding A. lineatus. Remarkably, neither did the treatment with foliar herbivory affect the food consumption and relative growth rate of S. exigua in the bioassay. However, this treatment did result in a significant change in the distribution of S. exigua feeding. Plants that had been pre-exposed to foliar herbivory suffered significantly less damage on their young terminal leaves. While plant growth and foliar nitrogen levels were not affected by any of the treatments, we did find significant differences between treatments with respect to the level and distribution of plant defensive chemicals (terpenoids). Exposure to root herbivores resulted in an increase in terpenoid levels in both roots as well as in mature and immature foliage. Foliar damage, on the other hand, resulted in high terpenoid levels in young, terminal leaves only. Our results show that root-feeding herbivores may change the level and distribution of plant defenses aboveground. Our data suggest that the reported interactions between below- and aboveground insect herbivores are mediated by induced changes in plant secondary chemistry. [source] Measurement of xylem sap amino acid concentrations in conjunction with whole tree transpiration estimates spring N remobilization by cherry (Prunus avium L.) treesPLANT CELL & ENVIRONMENT, Issue 12 2002G. GRASSI Abstract Prunus avium trees were grown in sand culture for one vegetative season with contrasting N supplies, in order to precondition their N storage capacities. During the spring of the second year a constant amount of 15N was supplied to all the trees, and the recovery of unlabelled N in the new biomass production was used as a direct measure of N remobilization. Destructive harvests were taken during spring to determine the pattern of N remobilization and uptake. Measurements of both xylem sap amino acid profiles and whole tree transpiration rates were taken, to determine whether specific amino acids are translocated as a consequence of N remobilization and if remobilization can be quantified by calculating the flux of these amino acids in the xylem. Whereas remobilization started immediately after bud burst, N derived from uptake by root appeared in the leaves only 3 weeks later. The tree internal N status affected both the amount of N remobilization and its dynamics. The concentration of xylem sap amino acids peaked shortly after bud burst, concurrently with the period of fastest remobilization. Few amino acids and amides (Gln, Asn and Asp) were responsible for most of N translocated through the xylem; however, their relative concentration varied over spring, demonstrating that the transport of remobilized N occurred mainly with Gln whereas transport of N taken up from roots occurred mainly with Asn. Coupling measurements of amino acid N in the xylem sap with transpiration values was well correlated with the recovery of unlabelled N in the new biomass production. These results are discussed in relation to the possibility of measuring the spring remobilization of N in field-grown trees by calculating the flux of N translocation in the xylem. [source] Nocturnally retained zeaxanthin does not remain engaged in a state primed for energy dissipation during the summer in two Yucca species growing in the Mojave DesertPLANT CELL & ENVIRONMENT, Issue 1 2002D. H. Barker Abstract Differently oriented leaves of Yucca schidigera and Yucca brevifolia were characterized in the Mojave Desert with respect to photosystem II and xanthophyll cycle activity during three different seasons, including the hot and dry summer, the relatively cold winter, and the mild spring season. Photosynthetic utilization of a high percentage of the light absorbed in PSII was observed in all leaves only during the spring, whereas very high levels of photoprotective, thermal energy dissipation were employed both in the summer and the winter season in all exposed leaves of both species. Both during the summer and the winter season, when energy dissipation levels were high diurnally, xanthophyll cycle pools (relative to either Chl or other carotenoids) were higher relative to the spring, and a nocturnal retention of high levels of zeaxanthin and antheraxanthin (Z + A) occurred in all exposed leaves of both species. Although this nocturnal retention of Z + A was associated with nocturnal maintenance of a low PSII efficiency (Fv/Fm) on a cold winter night, pre-dawn Fv/Fm was high in (Z + A)-retaining leaves following a warm summer night. This indicates nocturnal engagement of Z + A in a state primed for energy dissipation throughout the cold winter night , while high levels of retained Z + A were not engaged for energy dissipation prior to sunrise on a warm summer morning. Possible mechanisms for a lack of sustained engagement of retained Z + A for energy dissipation at elevated temperatures are discussed. [source] Diet selection in the green ringtail possum (Pseudochirops archeri): A specialist folivore in a diverse forestAUSTRAL ECOLOGY, Issue 7 2006KATHERINE M. W. JONES Abstract This study investigated the feeding ecology of the green ringtail possum, Pseudochirops archeri (Pseudocheiridae) in a tropical rainforest with 94 plant species in the canopy. Over 50% of tree use was from only four tree species, Aleurites rockinghamensis, Ficus fraseri, Arytera divaricata and Ficus copiosa. These species were used significantly more frequently than would be expected if tree species were selected randomly in proportion to their relative abundance in the forest. Conversely, 88 other tree species present were used less frequently than expected. Possums also favoured particular individual trees within some of the preferred tree species. In 91% of feeding observations, possums consumed mature leaves only. The availability of young leaves, flowers and fruit varied throughout the year, with a peak in availability of these resources during the early wet season. By primarily selecting mature leaves, green ringtail possums reduce their dependence on seasonally variable resources. We suggest that green ringtail possums should be considered as specialist folivores, focusing on only a few of the tree species available, possibly due to advantages associated with limiting the number of plant secondary metabolites in their diet. Furthermore, they favour certain individual trees within species, perhaps due to intraspecific variation in plant secondary metabolites or nutrient content, behaviour that has been well established in eucalypt folivores. We conclude that green ringtail possums are highly specialized in their feeding ecology, limiting their diet to a small number of continuously available food items. [source] | ||||||||||