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Leaf Nitrogen (leaf + nitrogen)
Terms modified by Leaf Nitrogen Selected AbstractsEffects of variable phytochemistry and budbreak phenology on defoliation of aspen during a forest tent caterpillar outbreakAGRICULTURAL AND FOREST ENTOMOLOGY, Issue 4 2008Jack R. Donaldson Abstract 1,The present study assessed the relationship between clonally variable rates of defoliation in trembling aspen (Populus tremuloides Michx.) and two potential resistance traits: defensive chemistry and leaf phenology. 2,In 2001, coincident with a major outbreak of the forest tent caterpillar (Malacosoma disstria Hubner) in the northcentral U.S.A., we monitored defoliation rates, phytochemical composition, and foliar development in 30 clones of trembling aspen. Leaf chemistry was also assessed in re-flushed leaves and 2 years post-outbreak. 3,Early in the season, differences in defoliation among clones were substantial but, by mid-June, all clones were completely defoliated. Leaf nitrogen, condensed tannins, and phenolic glycosides varied among clones but did not relate to defoliation levels. Budbreak phenology differed by 3 weeks among clones and clones that broke bud early or late relative to forest tent caterpillar eclosion experienced reduced rates of defoliation. 4,Defoliation led to increased tannins and slight decreases in phenolic glycoside concentrations in damaged leaf remnants, but to moderately decreased tannins and a six-fold increase in phenolic glycosides in reflushed leaves. This shift in chemical composition may significantly affect late season herbivores. 5,These results suggest that aspen chemical resistance mechanisms are ineffective during intense episodic eruptions of outbreak folivores such as the forest tent caterpillar. Variable budbreak phenology may lead to differential susceptibility during less intense outbreak years and, at peak forest tent caterpillar population densities, mechanisms affording tolerance are probably more important than chemical defences. [source] Effects of growth and measurement light intensities on temperature dependence of CO2 assimilation rate in tobacco leavesPLANT CELL & ENVIRONMENT, Issue 3 2010WATARU YAMORI ABSTRACT Effects of growth light intensity on the temperature dependence of CO2 assimilation rate were studied in tobacco (Nicotiana tabacum) because growth light intensity alters nitrogen allocation between photosynthetic components. Leaf nitrogen, ribulose 1·5-bisphosphate carboxylase/oxygenase (Rubisco) and cytochrome f (cyt f) contents increased with increasing growth light intensity, but the cyt f/Rubisco ratio was unaltered. Mesophyll conductance to CO2 diffusion (gm) measured with carbon isotope discrimination increased with growth light intensity but not with measuring light intensity. The responses of CO2 assimilation rate to chloroplast CO2 concentration (Cc) at different light intensities and temperatures were used to estimate the maximum carboxylation rate of Rubisco (Vcmax) and the chloroplast electron transport rate (J). Maximum electron transport rates were linearly related to cyt f content at any given temperature (e.g. 115 and 179 µmol electrons mol,1 cyt f s,1 at 25 and 40 °C, respectively). The chloroplast CO2 concentration (Ctrans) at which the transition from RuBP carboxylation to RuBP regeneration limitation occurred increased with leaf temperature and was independent of growth light intensity, consistent with the constant ratio of cyt f/Rubisco. In tobacco, CO2 assimilation rate at 380 µmol mol,1 CO2 concentration and high light was limited by RuBP carboxylation above 32 °C and by RuBP regeneration below 32 °C. [source] CONTRASTING PLANT PHYSIOLOGICAL ADAPTATION TO CLIMATE IN THE NATIVE AND INTRODUCED RANGE OF HYPERICUM PERFORATUMEVOLUTION, Issue 8 2007John L. Maron How introduced plants, which may be locally adapted to specific climatic conditions in their native range, cope with the new abiotic conditions that they encounter as exotics is not well understood. In particular, it is unclear what role plasticity versus adaptive evolution plays in enabling exotics to persist under new environmental circumstances in the introduced range. We determined the extent to which native and introduced populations of St. John's Wort (Hypericum perforatum) are genetically differentiated with respect to leaf-level morphological and physiological traits that allow plants to tolerate different climatic conditions. In common gardens in Washington and Spain, and in a greenhouse, we examined clinal variation in percent leaf nitrogen and carbon, leaf ,13C values (as an integrative measure of water use efficiency), specific leaf area (SLA), root and shoot biomass, root/shoot ratio, total leaf area, and leaf area ratio (LAR). As well, we determined whether native European H. perforatum experienced directional selection on leaf-level traits in the introduced range and we compared, across gardens, levels of plasticity in these traits. In field gardens in both Washington and Spain, native populations formed latitudinal clines in percent leaf N. In the greenhouse, native populations formed latitudinal clines in root and shoot biomass and total leaf area, and in the Washington garden only, native populations also exhibited latitudinal clines in percent leaf C and leaf ,13C. Traits that failed to show consistent latitudinal clines instead exhibited significant phenotypic plasticity. Introduced St. John's Wort populations also formed significant or marginally significant latitudinal clines in percent leaf N in Washington and Spain, percent leaf C in Washington, and in root biomass and total leaf area in the greenhouse. In the Washington common garden, there was strong directional selection among European populations for higher percent leaf N and leaf ,13C, but no selection on any other measured trait. The presence of convergent, genetically based latitudinal clines between native and introduced H. perforatum, together with previously published molecular data, suggest that native and exotic genotypes have independently adapted to a broad-scale variation in climate that varies with latitude. [source] Plant functional type classifications in tropical dry forests in Costa Rica: leaf habit versus taxonomic approachesFUNCTIONAL ECOLOGY, Issue 4 2010Jennifer S. Powers Summary 1.,One way to simplify the high taxonomic diversity of plant species in vegetation models is to place species into groups based on shared, dominant traits. Many studies have suggested that morphological and physiological traits of tropical dry forest tree species vary with leaf habit (i.e. leaves from evergreen, deciduous or semi-deciduous species) and thus this characteristic may serve as a useful way to distinguish ecologically meaningful functional types. 2.,In this study we examine whether 10 plant traits vary with leaf habit in replicated leaves and individual trees of 87 species from a tropical dry forest in Costa Rica. We also looked for evidence of phylogenetic conservatism, i.e. closely related species sharing similar trait values compared to more distantly related taxa. 3.,While some of the traits varied within and among individual trees of the same species, interspecific variation accounted for 57,83% of the variance among samples. Four traits in addition to leaf habit showed evidence of phylogenetic conservatism, but these results were strongly dependent on the inclusion of the 18 species of legumes (Fabaceae) in our dataset. Contrary to our predictions, none of the traits we measured differed among leaf habits. However, five traits (wood density, leaf C, leaf N, N/P and C/N) varied significantly between legumes and other functional types. Furthermore, when all high-nitrogen non-legume taxa were compared to the high-nitrogen legumes, six traits excluding leaf N differed significantly, indicating that legumes are functionally different from other tree species beyond high N concentrations. Similarly, the 18 legume taxa (which all have compound leaves) also differed from other compound-leaved species for six traits, thus leaf type does not explain these patterns. 4.,Our main conclusions are that (i) a plant functional type classification based on leaf habit alone has little utility in the tropical dry forest we studied, and (ii) legumes have a different suite of traits including high leaf carbon and wood density in addition to high leaf nitrogen. Whether this result generalizes to other tropical forests is unknown, but merits future research due to the consequences of these traits for carbon storage and ecosystem processes. [source] Strategy shifts in leaf physiology, structure and nutrient content between species of high- and low-rainfall and high- and low-nutrient habitatsFUNCTIONAL ECOLOGY, Issue 4 2001I. J. Wright Summary 1,Relationships were examined among photosynthetic capacity (Amass and Aarea), foliar dark respiration rate (Rd-mass and Rd-area), stomatal conductance to water (Gs), specific leaf area (SLA), and leaf nitrogen (N) and phosphorus (P) across 79 perennial species occurring at four sites with contrasting rainfall levels and soil nutrients in eastern Australia. We hypothesized that the slope of log,log ,scaling' relationships between these traits would be positive and would not differ between sites, although slope elevations might shift between habitat types. 2,Amass, Rd-mass, SLA, Nmass and Pmass were positively associated in common slopes fitted across sites or rainfall zones, although rather weakly within individual sites in some cases. The relationships between Amass (and Rd-mass) with each of Nmass and SLA were partially independent of each other, with Amass (or Rd-mass) increasing with SLA at a given Nmass, or with Nmass at a given SLA (only weakly in the case of Amass). These results improve the quantification and extend the generalization of reported patterns to floras largely unlike those studied previously, with the additional contribution of including phosphorus data. 3,Species from drier sites differed in several important respects. They had (i) higher leaf N and P (per dry mass or area); (ii) lower photosynthetic capacity at a given leaf N or P; (iii) higher Rd-mass at a given SLA or Amass; and (iv) lower Gs at a given Aarea (implying lower internal CO2 concentration). 4,These trends can be interpreted as part of a previously undocumented water conservation strategy in species from dry habitats. By investing heavily in photosynthetic enzymes, a larger drawdown of internal CO2 concentration is achieved, and a given photosynthetic rate is possible at a lower stomatal conductance. Transpirational water use is similar, however, due to the lower-humidity air in dry sites. The benefit of the strategy is that dry-site species reduce water loss at a given Aarea, down to levels similar to wet-site species, despite occurring in lower-humidity environments. The cost of high leaf N is reflected in higher dark respiration rates and, presumably, additional costs incurred by N acquisition and increased herbivory risk. [source] Physiological responses of two contrasting desert plant species to precipitation variability are differentially regulated by soil moisture and nitrogen dynamicsGLOBAL CHANGE BIOLOGY, Issue 5 2009LISA D. PATRICK Abstract Alterations in global and regional precipitation patterns are expected to affect plant and ecosystem productivity, especially in water-limited ecosystems. This study examined the effects of natural and supplemental (25% increase) seasonal precipitation on a sotol grassland ecosystem in Big Bend National Park in the Chihuahuan Desert. Physiological responses , leaf photosynthesis at saturating light (Asat), stomatal conductance (gs), and leaf nitrogen [N] , of two species differing in their life form and physiological strategies (Dasylirion leiophyllum, a C3 shrub; Bouteloua curtipendula, a C4 grass) were measured over 3 years (2004,2006) that differed greatly in their annual and seasonal precipitation patterns (2004: wet, 2005: average, 2006: dry). Precipitation inputs are likely to affect leaf-level physiology through the direct effects of altered soil water and soil nitrogen. Thus, the effects of precipitation, watering treatment, soil moisture, and nitrogen were quantified via multivariate hierarchical Bayesian models that explicitly linked the leaf and soil responses. The two species differed in their physiological responses to precipitation and were differentially controlled by soil water vs. soil nitrogen. In the relatively deeply rooted C3 shrub, D. leiophyllum, Asat was highest in moist periods and was primarily regulated by deep (16,30 cm) soil water. In the shallow-rooted C4 grass, B. curtipendula, Asat was only coupled to leaf [N], both of which increased in dry periods when soil [N] was highest. Supplemental watering during the wet year generally decreased Asat and leaf [N] in D. leiophyllum, perhaps due to nutrient limitation, and physiological responses in this species were influenced by the cumulative effects of 5 years of supplemental watering. Both species are common in this ecosystem and responded strongly, yet differently, to soil moisture and nitrogen, suggesting that changes in the timing and magnitude of precipitation may have consequences for plant carbon gain, with the potential to alter community composition. [source] Interactive effects of elevated CO2 and soil fertility on isoprene emissions from Quercus roburGLOBAL CHANGE BIOLOGY, Issue 11 2004Malcolm Possell Abstract The effects of global change on the emission rates of isoprene from plants are not clear. A factor that can influence the response of isoprene emission to elevated CO2 concentrations is the availability of nutrients. Isoprene emission rate under standard conditions (leaf temperature: 30°C, photosynthetically active radiation (PAR): 1000 ,mol photons m,2 s,1), photosynthesis, photosynthetic capacity, and leaf nitrogen (N) content were measured in Quercus robur grown in well-ventilated greenhouses at ambient and elevated CO2 (ambient plus 300 ppm) and two different soil fertilities. The results show that elevated CO2 enhanced photosynthesis but leaf respiration rates were not affected by either the CO2 or nutrient treatments. Isoprene emission rates and photosynthetic capacity were found to decrease with elevated CO2, but an increase in nutrient availability had the converse effect. Leaf N content was significantly greater with increased nutrient availability, but unaffected by CO2. Isoprene emission rates measured under these conditions were strongly correlated with photosynthetic capacity across the range of different treatments. This suggests that the effects of CO2 and nutrient levels on allocation of carbon to isoprene production and emission under near-saturating light largely depend on the effects on photosynthetic electron transport capacity. [source] Acclimation of photosynthesis and respiration to elevated atmospheric CO2 in two Scrub OaksGLOBAL CHANGE BIOLOGY, Issue 4 2002Graham J. Hymus Abstract For two species of oak, we determined whether increasing atmospheric CO2 concentration (Ca) would decrease leaf mitochondrial respiration (R) directly, or indirectly owing to their growth in elevated Ca, or both. In particular, we tested whether acclimatory decreases in leaf-Rubisco content in elevated Ca would decrease R associated with its maintenance. This hypothesis was tested in summer 2000 on sun and shade leaves of Quercus myrtifolia Willd. and Quercus geminata Small. We also measured R on five occasions between summer 1999 and 2000 on leaves of Q. myrtifolia. The oaks were grown in the field for 4 years, in either current ambient or elevated (current ambient + 350 µmol mol,1) Ca, in open-top chambers (OTCs). For Q. myrtifolia, an increase in Ca from 360 to 710 µmol mol,1 had no direct effect on R at any time during the year. In April 1999, R in young Q. myrtifolia leaves was significantly higher in elevated Ca,the only evidence for an indirect effect of growth in elevated Ca. Leaf R was significantly correlated with leaf nitrogen (N) concentration for the sun and shade leaves of both the species of oak. Acclimation of photosynthesis in elevated Ca significantly reduced maximum RuBP-saturated carboxylation capacity (Vc max) for both the sun and shade leaves of only Q. geminata. However, we estimated that only 11,12% of total leaf N was invested in Rubisco; consequently, acclimation in this plant resulted in a small effect on N and an insignificant effect on R. In this study measurements of respiration and photosynthesis were made on material removed from the field; this procedure had no effect on gas exchange properties. The findings of this study were applicable to R expressed either per unit leaf area or unit dry weight, and did not support the hypothesis that elevated Ca decreases R directly, or indirectly owing to acclimatory decreases in Rubisco content. [source] Photon flux partitioning among species along a productivity gradient of an herbaceous plant communityJOURNAL OF ECOLOGY, Issue 6 2006ANNE AAN Summary 1We studied light partitioning among species along the natural productivity gradient of herbaceous vegetation with an above-ground dry mass of 150,490 g m,2. The aim was to investigate how the light capturing ability per above-ground biomass and leaf nitrogen changes in an entire community and to reveal whether different species respond similarly to changes in soil conditions and competition. 2Species becoming dominant at high soil resources have intrinsically low leaf area ratios (LAR) and lower tissue nitrogen concentration, and hence relatively high nitrogen use efficiency. These traits lead to dominance when soil resources allow rapid growth so that benefits arising from the ability to locate leaves above neighbours and thereby increasing asymmetry of competition, become more crucial. 3In contrast to our expectations, above-ground efficiency of nitrogen use on the community level (aNUE) increased along the productivity gradient. Species level nitrogen use efficiency was unaffected by variation in site productivity; the increase in community aNUE was solely as a consequence of changes in species composition. 4Light absorption per unit of above-ground mass, ,M, declined significantly at the community level and also in most species, indicating that light use efficiency increased with increased site productivity and LAI. 5Light absorption per unit of leaf nitrogen, ,N, as an indicator of the ratio NUE/LUE showed no clear pattern on the community level because both NUE and LUE tend to increase with increased productivity. At the species level, ,N tends to decrease because NUE did not change with stand productivity. 6Some subordinate species responded by enlarging their LAR to increased competition. Additionally, these species were the most responsive in their leaf chlorophyll/nitrogen ratio to changes in light conditions, which shows that physiological plasticity is important for species that are unable to compete for light with the ability to position their leaves above those of other species. 7This study shows how plasticity in above-ground growth pattern and nitrogen allocation differs between species with respect to increased soil fertility and competition, leading to distinctive strategies of survival. Light partitioning analysis reveals that increased competition for light, resulting in changes in species composition, is the key factor that leads to decoupling of species and community level acclimation. [source] Winter browsing on Alaska feltleaf willow twigs improves leaf nutritional value for snowshoe hares in summerOIKOS, Issue 1 2003John P. Bryant In boreal forests, browsing by mammals on winter-dormant twigs increases leaf nitrogen, leaf greenness, and leaf size. This suggests browsing reduces competition among meristems for mineral nutrients, and in particular, competition for nitrogen. Winter browsing also reduces the shoot carbohydrate reserves used by leaves to produce condensed tannin. These effects of winter browsing are predicted to improve the nutritional value of leaves for mammals because they increase the mass of digestible nitrogen in leaves. This hypothesis was tested using Alaska feltleaf willow and the snowshoe hare as the experimental system. Six in vivo indicators of leaf nutritional quality were used to compare leaves from winter-browsed plants with leaves from unbrowsed plants. The indicators used were dry matter intake, nitrogen intake, condensed tannin intake, dry matter digestibility, apparent digestibility of nitrogen and nitrogen retention. The results obtained were in agreement with the above hypothesis. In early summer, at the time snowshoe hares and other northern herbivores reproduce, hares fed leaves from browsed plants consumed more nitrogen, digested more of the nitrogen they consumed, and retained more of the nitrogen they digested than did hares fed leaves from unbrowsed plants. The high nitrogen content and low tannin content of leaves from browsed plants may explain this browsing caused increase in leaf nutritional value. How these positive effects of winter browsing on snowshoe hare nutrition at the time of reproduction might affect hare population dynamics are briefly discussed. [source] Leaves of Lianas and Self-Supporting Plants Differ in Mass per Unit Area and in Nitrogen ContentPLANT BIOLOGY, Issue 3 2000M. Kazda Abstract: The aim of this study was to test the hypothesis that the reduction in supporting tissues in climbers compared to self-supporting plants is also true for their leaves, and that climbers generally require higher leaf nitrogen than self-supporting plants to accomplish fast growth. This hypothesis was tested using paired samples of both growth forms with assessment of leaf area index above the sampled plants (LAIa) in a tropical rain forest in Gabon. The sampling protocol ensured that within a highly fluctuating low canopy environment, the growth conditions were identical for each pair sampled. The results confirmed the hypothesis. Lianas had significantly lower leaf mass per unit leaf area (LMA) than their supporters. Liana leaves also contained significantly more nitrogen than host tree leaves. The differences in nitrogen concentration between liana and tree leaves reversed for the most shaded sites, when nitrogen was expressed on a leaf area base (Narea). Significant regression between leaf nitrogen and LAIa was found for the climbers on the shaded sites but not for their supporters. This indicated better acclimation of climbers to prevailing light conditions. Better nitrogen allocation at low LMA, together with lower carbon costs for building supporting tissues, makes lianas highly competitive, especially where high nitrogen availability is assured. [source] Adjustment of leaf photosynthesis to shade in a natural canopy: rate parametersPLANT CELL & ENVIRONMENT, Issue 3 2005A. LAISK ABSTRACT The present study was performed to investigate the adjustment of the rate parameters of the light and dark reactions of photosynthesis to the natural growth light in leaves of an overstorey species, Betula pendula Roth, a subcanopy species, Tilia cordata P. Mill., and a herb, Solidago virgaurea L., growing in a natural plant community in Järvselja, Estonia. Shoots were collected from the site and individual leaves were measured in a laboratory applying a standardized routine of kinetic gas exchange, Chl fluorescence and 820 nm transmittance measurements. These measurements enabled the calculations of the quantum yield of photosynthesis and rate constants of excitation capture by photochemical and non-photochemical quenchers, rate constant for P700+ reduction via the cytochrome b6f complex with and without photosynthetic control, actual maximum and potential (uncoupled) electron transport rate, stomatal and mesophyll resistances for CO2 transport, Km(CO2) and Vm of ribulose-bisphosphate carboxylase-oxygenase (Rubisco) in vivo. In parallel, N, Chl and Rubisco contents were measured from the same leaves. No adjustment toward higher quantum yield in shade compared with sun leaves was observed, although relatively more N was partitioned to the light-harvesting machinery in shade leaves (H. Eichelmann et al., 2004). The electron transport rate through the Cyt b6f complex was strongly down-regulated under saturating light compared with darkness, and this was observed under atmospheric, as well as saturating CO2 concentration. In vivo Vm measurements of Rubisco were lower than corresponding reported measurements in vitro, and the kcat per reaction site varied widely between leaves and growth sites. The correlation between Rubisco Vm and the photosystem I density was stronger than between Vm and the density of Rubisco active sites. The results showed that the capacity of the photosynthetic machinery decreases in shade-adjusted leaves, but it still remains in excess of the actual photosynthetic rate. The photosynthetic control systems that are targeted to adjust the photosynthetic rate to meet the plant's needs and to balance the partial reactions of photosynthesis, down-regulate partial processes of photosynthesis: excess harvested light is quenched non-photochemically; excess electron transport capacity of Cyt b6f is down-regulated by ,pH-dependent photosynthetic control; Rubisco is synthesized in excess, and the number of activated Rubisco molecules is controlled by photosystem I-related processes. Consequently, the nitrogen contained in the components of the photosynthetic machinery is not used at full efficiency. The strong correlation between leaf nitrogen and photosynthetic performance is not due to the nitrogen requirements of the photosynthetic apparatus, but because a certain amount of energy must be captured through photosynthesis to maintain this nitrogen within a leaf. [source] Photosynthetic acclimation of plants to growth irradiance: the relative importance of specific leaf area and nitrogen partitioning in maximizing carbon gainPLANT CELL & ENVIRONMENT, Issue 8 2001J. R. Evans Abstract Changes in specific leaf area (SLA, projected leaf area per unit leaf dry mass) and nitrogen partitioning between proteins within leaves occur during the acclimation of plants to their growth irradiance. In this paper, the relative importance of both of these changes in maximizing carbon gain is quantified. Photosynthesis, SLA and nitrogen partitioning within leaves was determined from 10 dicotyledonous C3 species grown in photon irradiances of 200 and 1000 µmol m,2 s,1. Photosynthetic rate per unit leaf area measured under the growth irradiance was, on average, three times higher for high-light-grown plants than for those grown under low light, and two times higher when measured near light saturation. However, light-saturated photosynthetic rate per unit leaf dry mass was unaltered by growth irradiance because low-light plants had double the SLA. Nitrogen concentrations per unit leaf mass were constant between the two light treatments, but plants grown in low light partitioned a larger fraction of leaf nitrogen into light harvesting. Leaf absorptance was curvilinearly related to chlorophyll content and independent of SLA. Daily photosynthesis per unit leaf dry mass under low-light conditions was much more responsive to changes in SLA than to nitrogen partitioning. Under high light, sensitivity to nitrogen partitioning increased, but changes in SLA were still more important. [source] Changes in leaf photosynthetic parameters with leaf position and nitrogen content within a rose plant canopy (Rosa hybrida)PLANT CELL & ENVIRONMENT, Issue 4 2000M. M. Gonzalez-Real ABSTRACT This paper deals with changes in leaf photosynthetic capacity with depth in a rose (Rosa hybrida cv. Sonia) plant canopy. Measurements of leaf net CO2 assimilation (Al) and total nitrogen content (Nl) were performed in autumn under greenhouse conditions on mature leaves located at different layers within the plant canopy, including the flower stems and the main shoots. These leaves were subjected (i) to contrasting levels of CO2 partial pressure (pa) at saturating photosynthetic photon flux density (I about 1000 ,mol m,2 s,1) and (ii) to saturating CO2 partial pressure (pa about 100 Pa) and varying I, while conditions of temperature were those prevailing in the greenhouse (20,38 °C). A biochemical model of leaf photosynthesis relating Al to intercellular CO2 partial pressure (pi) was parameterized for each layer of leaves, supplying corresponding values of the photosynthetic Rubisco capacity (Vlm) and the maximum rate of electron transport (Jm). The results indicated that rose leaves growing at the top of the canopy had higher values of Jm and Vlm, which resulted from a higher allocation of nitrogen to the uppermost leaves. Mean values of total leaf nitrogen, Nl, decreased about 35% from the uppermost leaves of flower stem to leaves growing at the bottom of the plant. The derived values of non-photosynthetic nitrogen, Nb, varied from 76 mmolN m,2leaf (layer 1) to 60 mmolN m,2leaf (layer 4), representing a large fraction of Nl (50 and 60% in layer 1 and 4, respectively). Comparison of leaf photosynthetic nitrogen (Np=Nl,Nb) and I profiles supports the hypothesis that rose leaves acclimate to the time-integrated absorbed I. The relationships between I and Np, obtained during autumn, spring and summer, indicate that rose leaves seem also to acclimate their photosynthetic capacity seasonally, by allocating more photosynthetic nitrogen to leaves in autumn and spring than in summer. [source] The effect of incorporating straw or manure into the soil on the natural microflora of winter wheatPLANT PATHOLOGY, Issue 5 2001B. S. Rodgers-Gray Over 3 years, five crops of winter wheat with different fertilization or pesticide treatments were grown in replicated plots in which straw, cattle manure or nothing was incorporated into the soil. It was previously shown that severities of several foliar diseases were reduced by the treatment with straw. Treatments with straw slightly increased leaf microbial numbers at growth stage (GS) 10, and significantly but slightly decreased numbers at GS 60 and 70, when averaged over all crops. There was no evidence of differences in potential for biological control between plots, because no differences were demonstrated between treatments in the proportion of phylloplane residents able to produce chitinase, siderophores or antibiotics. There was no link between soil and leaf nitrogen and microbial populations or soil amendment. The two youngest leaves of straw-treated plants remained green longer than leaves from untreated or manure-treated plants. Microbial numbers differed between crops, but within crops were more stable on leaves and ears than in soil. Soil populations were larger before the crops were sown. Bacteria predominated over fungi in all habitats throughout the growing season. The ratio of Gram-negative to Gram-positive bacteria recovered was similar on leaves and in soil, but not on ears. Soil and leaf microbes utilized similar carbon sources. More leaf epiphytes than soil microbes produced siderophores. The majority of identified organisms belonged to only a few species. Chromogenic organisms were more abundant on aerial surfaces. A fungicide, chlorothalonil, was applied in one crop; it reduced the microbial population but did not alter its composition (without affecting the reduction in disease due to straw). It is postulated that straw acts in the field by altering plant physiology and thus altering both microbial colonization and disease. [source] | ||||||||||||||||||||||