Diversity of leaf traits related to productivity in 31 Populus deltoides x Populus nigra clones

To test if some leaf parameters are predictors of productivity in a range of Populus deltoides (Bartr.) Marsh. x P. nigra L. clones, we assessed leaf traits and productivity in 2-month-old rooted cuttings from 31 clones growing in 4-l pots in a greenhouse, under conditions of controlled temperature and optimal irrigation. We evaluated four groups of variables describing (1) productivity (total biomass), (2) leaf growth (total leaf number increment and total leaf area increment rate), (3) leaf structure (specific leaf area and nitrogen and carbon contents) and (4) carbon isotope discrimination (delta), which is negatively correlated with time-integrated water-use efficiency. High-yielding clones did not necessarily display high leaf growth rates, but they displayed a larger total leaf area, lower specific leaf area and lower leaf nitrogen concentration than clones with low productivity. Total leaf area was mainly controlled by maximal individual leaf area and total leaf area increment rate (r = 0.51 and 0.56, respectively). Carbon isotope discrimination did not correlate with total biomass, but it was associated with total number of leaves and total leaf area increment rate (r = 0.39 and 0.45, respectively). Therefore, leaf area and specific leaf area were better indicators of productivity than leaf growth traits. The observed independence of delta from biomass production provides opportunities for selecting poplar clones combining high productivity and high water-use efficiency.     

Effects of crown development on leaf irradiance,leaf morphology and photosynthetic capacity in a peach tree

The three-dimensional (3-D) architecture of a peach tree (Prunus persica L. Batsch) growing in an orchard near Avignon, France, was digitized in April 1999 and again four weeks later in May 1999 to quantify increases in leaf area and crown volume as shoots developed. A 3-D model of radiation transfer was used to determine effects of changes in leaf area density and canopy volume on the spatial distribution of absorbed quantum irradiance (PAR(a)). Effects of changes in PAR(a) on leaf morphological and physiological properties were determined. Leaf mass per unit area (M(a)) and leaf nitrogen concentration per unit leaf area (N(a)) were both nonlinearly related to PAR(a), and there was a weak linear relationship between leaf nitrogen concentration per unit leaf mass (N(m)) and PAR(a). Photosynthetic capacity, defined as maximal rates of ribulose-1,5-bisphosphate carboxylase (Rubisco) carboxylation (V(cmax)) and electron transport (J(max)), was measured on leaf samples representing sunlit and shaded micro-environments at the same time that the tree crown was digitized. Both V(cmax) and J(max) were linearly related to N(a) during May, but not in April when the range of N(a) was low. Photosynthetic capacity per unit N(a) appeared to decline between April and May. Variability in leaf nitrogen partitioning between Rubisco carboxylation and electron transport was small, and the partitioning coefficients were unrelated to N(a). Spatial variability in photosynthetic capacity resulted from acclimation to varying PAR(a) as the crown developed, and acclimation was driven principally by changes in M(a) rather than the amount or partitioning of leaf nitrogen.     

Modelling diameter class distribution with a second-order matrix model

Matrix models of forest dynamics rely on four hypotheses: independence hypothesis, Markov’s hypothesis, Usher’s hypothesis, and temporal homogeneity hypothesis. We investigate the consequences of relaxing Markov’s hypothesis, allowing the state of the tree at time t to depend on its states at time t−1 and t−2. The methodology for building and testing the relevance of second-order matrix model is thus proposed. The derivation of second-order transition probabilities turns to be sensitive to the width of the diameter classes. A strategy for choosing diameter classes is proposed. A second-order matrix model is then built for a tropical rain-forest in French Guiana. A different behaviour is detected between small (dbh ≤30 cm) and large trees, the smaller trees being more sensitive to their past history: small trees that have well grown have a tendency to grow well again, and small trees that have not grown tend to have a higher probability to die. The widths of the diameter classes that are selected are much less than the widths usually retained, that favour first-order selection.     

Size class distribution and spatial pattern of Vitellaria paradoxa in relation to farmers' practices in Mali

The impact of human activities on size class distribution and spatial distribution of Vitellaria paradoxa (karité or shea butter tree) in the parklands of sub-Saharan Africa has not been reported in the literature. Two sites (Koumantou and Mperesso) in southern Mali and three treatments (cultivated field, fallow and forest) per site were involved in the present study. Results of a statistical test for random distribution showed that the spatial pattern of Vitellaria paradoxa became progressively aggregated from cultivated field to fallow and then to forest. A permanent aggregated pattern found at Koumantou was not found at Mperesso. A test of the independence of larger and smaller tree locations shows that size classes clump together at Koumantou but not at Mperesso. Results of the third test showed that in the cultivated field, auto-correlation was only observed at large scale. In the fallow the trend was towards negative correlation for both sites. In the forest, negative correlation was observed up to 20 m at Koumantou whereas at Mperesso, positive correlation was observed around 35 m and above 50 m. Site differences may be explained by the intensity of fruit production and recruitment, bound to rainfall and land use pressure. Greater regularity of the spatial pattern in cultivated field, then fallow, may be the result of human intervention.This revised version was published online in November 2005 with corrections to the Cover Date.     

Relationship of isopentenyl diphosphate (IDP) isomerase activity to isoprene emission of oak leaves

Oaks emit large amounts of isoprene, a compound that plays an important role in tropospheric chemistry. Isopentenyl diphosphate isomerase (IDI, E.C. 5.3.3.2) catalyzes the isomerization of isopentenyl diphosphate (IDP) to dimethylallyl diphosphate (DMADP), and in isoprene-emitting plants, isoprene synthase (IS) converts the DMADP to isoprene. To study the role of IDI in isoprene biosynthesis of oak leaves, we compared IDI and IS activities in pedunculate oak (Quercus robur L.) and pubescent oak (Quercus pubescens Willd.) with the isoprene emission rates of these species. We developed a non-radioactive enzyme assay to detect IDI activity in crude leaf extracts of Q. robur. The substrate dependency of IDI activity showed biphasic kinetics with Michaelis constants (K(m)(IDP)) of 0.7 +/- 0.2 micro M for a high-affinity phase and 39.5 +/- 6.9 micro M for a low-affinity phase, potentially attributable to different IDI isoforms. Under standard assay conditions, the temperature optimum for IDI activity was about 42 degrees C, but IDI activity was detectable up to 60 degrees C. A sharp pH optimum appeared around pH 7, with 20 mM Mg(2+) also required for IDI activity. Neither IDI activity nor IS activity showed diurnal variation in Q. robur leaves. The sum of IDI activities showed a significant linear correlation with IS activity in both Q. robur and Q. pubescens leaves, and both enzyme activities showed a linear relationship to isoprene emission factors in leaves of these oak species, indicating the possible involvement of IDI in isoprene biosynthesis by oak leaves.     

Classical swine fever virus replicon particles lacking the Erns gene: a potential marker vaccine for intradermal application

Classical swine fever virus replicon particles (CSF-VRP) deficient for E(rns) were evaluated as a non-transmissible marker vaccine. A cDNA clone of CSFV strain Alfort/187 was used to obtain a replication-competent mutant genome (replicon) lacking the sequence encoding the 227 amino acids of the glycoprotein E(rns) (A187delE(rns)). For packaging of A187delE(rns) into virus particles, porcine kidney cell lines constitutively expressing E(rns) of CSFV were established. The rescued VRP were infectious in cell culture but did not yield infectious progeny virus. Single intradermal vaccination of two pigs with 10(7) TCID(50) of VRP A187delE(rns) elicited neutralizing antibodies, anti-E2 antibodies, and cellular immune responses determined by an increase of IFN-gamma producing cells. No anti-E(rns) antibodies were detected in the vaccinees confirming that this vaccine represents a negative marker vaccine allowing differentiation between infected and vaccinated animals. The two pigs were protected against lethal challenge with the highly virulent CSFV strain Eystrup. In contrast, oral immunization resulted in only partial protection, and neither CSFV-specific antibodies nor stimulated T-cells were found before challenge. These data represent a good basis for more extended vaccination/challenge trials including larger numbers of animals as well as more thorough analysis of virus shedding using sentinel animals to monitor horizontal spread of the challenge virus.     

Plasticity of growth and sylleptic branchiness in two poplar families grown at three sites across Europe

Two hybrid poplar maternal half-sib families, resulting from controlled crosses of the female parent Populus deltoides 'S9-2' with P. nigra 'Ghoy' and P. trichocarpa 'V24', were grown at three sites: northern Italy, central France and southern England. Juvenile stem growth traits (height, circumference and volume) and sylleptic branchiness (number of branches, density of branches per unit of stem height, percentage of the stem carrying branches and distance of the highest sylleptic branch to the top of the stem) were measured on 1-year-old shoots. Our general objectives were to determine the degree to which the expression of stem growth and syllepsis and the relationships between them are affected by environmental conditions and to evaluate the efficiency of indirect selection for stem growth using branching traits as secondary criteria. The performance of both families differed significantly within and between sites. Pronounced heterosis was observed and highly significant genotype x environment interactions were found for all traits across the sites. Syllepsis showed more marked genetic variation and plasticity than stem growth traits. Relationships between sylleptic branchiness and stem growth depended on environmental conditions. Heritability values at the individual level ranged between 0.09 and 0.59, but genetic gain in stem volume was not significantly improved when selection was based on sylleptic branch characteristics. However, despite strong phenotypic plasticity among sites, genotypic ranking among the sites was relatively stable.