Morphological and physiological adjustment to N and P fertilization in nutrient-limited Metrosideros polymorpha canopy trees in Hawaii

Leaf-level studies of Metrosideros polymorpha Gaud. (Myrtaceae) canopy trees at both ends of a substrate age gradient in the Hawaiian Islands pointed to differential patterns of adjustment to both nutrient limitation and removal of this limitation by long-term (8-14 years) nitrogen (N), phosphorus (P) and N + P fertilizations. The two study sites were located at the same elevation, had similar annual precipitation, and supported forests dominated by M. polymorpha, but differed in the age of the underlying volcanic substrate, and in soil nutrient availability, with relatively low N at the young site (300 years, Thurston, Hawaii) and relatively low P at the oldest site (4,100,000 years, Kokee, Kauai). Within each site, responses to N and P fertilization were similar, regardless of the difference in soil N and P availability between sites. At the young substrate site, nutrient addition led to a larger mean leaf size (about 7.4 versus 4.8 cm2), resulting in a larger canopy leaf surface area. Differences in foliar N and P content, chlorophyll concentrations and carboxylation capacity between the fertilized and control plots were small. At the old substrate site, nutrient addition led to an increase in photosynthetic rate per unit leaf surface area from 4.5 to 7.6 micromol m(-2) s(-1), without a concomitant change in leaf size. At this site, leaves had substantially greater nutrient concentrations, chlorophyll content and carboxylation capacity in the fertilized plots than in the control plots. These contrasting acclimation responses to fertilization at the young and old sites led to significant increases in total carbon gain of M. polymorpha canopy trees at both sites. At the young substrate site, acclimation to fertilization was morphological, resulting in larger leaves, whereas at the old substrate site, physiological acclimation resulted in higher leaf carboxylation capacity and chlorophyll content.     

Effects of timing of nitrogen fertilization on shoot development in peach (Prunus persica) trees

Shoot development was studied for two consecutive years in peach trees fertilized with N either in the previous fall or in the middle of the growing season. During the first year, two additional treatments were studied: no N supply and nitrate supplied in the irrigation water throughout the growing season. The number of shoots that developed depended on nitrogen availability in the period following bud break. During shoot development, leaf emergence occurred in one, two, or three stages, which ended at about 500 to 600 degree days, 1,000 to 1,200 degree days, and 1,500 to 2,000 degree days after bloom, respectively. The proportion of shoots exhibiting a second or third developmental stage depended on nitrogen availability at the beginning of that stage. Increasing nitrogen availability during a developmental stage prolonged the stage and increased the number of leaves produced.     

Establishment and dissemination of hypovirulent strains of Cryphonectria parasitica in Greece

Chestnut blight caused by Cryphonectria parasitica has been one of the major reasons for the decline of chestnut cultivation in Greece over the last 50 years. A previous detailed study of the vc types of the fungus has revealed only four vc types in the entire country, those of EU‐1, EU‐2 and EU‐10 with the dominant being EU‐12 counting for 88% of the isolates. As the loss in orchard trees reached in some chestnut producing prefectures over 35% of the trees, the decision was taken to apply biological control on a nationwide scale. The project was implemented in 17 prefectures during the period 2007–2009. Hypovirulent (hv) strains of C. parasitica which were infected by the CHV‐1 subtype I (Italian subtype) viruses which occur naturally in Greece were used. The necessary hypovirulent inoculum was prepared at the Forest Research Institute during the period 2007–2009 on a large scale, however, with laboratory care. Three million inoculations were made around accessible developing cankers over three consecutive years by trained personnel. An extensive evaluation conducted in 2011 in the 12 of the 17 treated prefectures, where no natural hypovirulence had been found before, demonstrated not only the successful establishment of hypovirulence but also profound dissemination and healing of non‐inoculated cankers. The extent of dissemination varied significantly among sampling plots and among prefectures. The conclusion is drawn that CHV‐1 subtype I has successfully established and spread into chestnut orchards and coppice forests resulting in a gradual decline of chestnut blight.     

Nitrogen loading of Eucalyptus globulus seedlings: nutritional dynamics and influence on morphology and root growth potential

New Forests - Achieving successful outplanting of trees on increasingly harsher sites is a global concern. In Chile, for example, new Eucalyptus globulus plantations are being targeted to poorer,...     

When the ground cover brings guests: is <Emphasis Type="Italic">Anaphothrips obscurus</Emphasis> a friend or a foe for the biological control of <Emphasis Type="Italic">Tetranychus urticae</Emphasis> in clementines?

Biological control of Tetranychus urticae Koch (Acari: Tetranychidae), a key pest of clementines, can be improved in this crop with the establishment of a ground cover of Festuca arundinacea Schreber (Poaceae). This cover houses an abundant and diverse community of predatory Phytoseiidae mites including Euseius stipulatus (Athias-Henriot), Neoseiulus barkeri Hughes, Neoseiulus californicus (McGregor) and Phytoseiulus persimilis Athias-Henriot and a dense population of the grass thrips Anaphothrips obscurus Müller (Thysanoptera: Thripidae) throughout the year. The aim of this study was to determine whether the presence of this thrips species could be related to the improvement in the biological control of T. urticae. Therefore, the capacity of the abovementioned phytoseiids to feed and reproduce on A. obscurus and their feeding preferences when T. urticae and A. obscurus were simultaneously offered, were analyzed. The results show that E. stipulatus, N. barkeri and N. californicus have a type II functional response when offered A. obscurus nymphs, whereas P. persimilis barely feeds on this thrips species. Furthermore, N. barkeri and N. californicus can reproduce feeding only on thrips. Regarding prey preference, the Tetranychus spp.-specialist P. persimilis preferably preyed on T. urticae, the generalists N. barkeri and E. stipulatus preferred A. obscurus, and the selective predator of tetranychid mites N. californicus showed no preference. Therefore, we hypothesize that the enhanced biological control of T. urticae observed could be related to A. obscurus becoming an alternative prey for non-specialist phytoseiids, without altering the control exerted by the T. urticae-specialist P. persimilis and likely reducing intraguild predation.     

Male multiple matings and reproductive success in commodity-adapted strains of <Emphasis Type="Italic">Sitophilus oryzae</Emphasis>

Multiple matings occur in many species of stored-grain insect pests, such as the rice weevil Sitophilus oryzae (L.), with both female and male mating more than once and with more than one partner. Multiple female mating in S. oryzae increased lifetime fecundity by extending the period of time progeny were produced, but consequences of multiple male mating in S. oryzae were not yet studied although it is likely to increase male fitness by increasing offspring production. Here, the effects of polygynous mating on male mating behavior, success, and fitness were assessed in two strains of S. oryzae, one adapted to barley and another to wheat. Two insect strains were considered because they may differ in response depending on the host grain, which present distinct nutritional value to the insects. Mating by pairs formed between the two strains did not impact mating success, but wheat-adapted females exhibited longer mating duration, which was positively correlated with progeny production. Wheat-adapted males exhibited higher fertility than barley-adapted males. When male multiple matings were considered in successive polygynous matings, late matings led to lower non-cumulative values of progeny production, but higher cumulative performance, and wheat-adapted S. oryzae always performed better. Thus, male fitness and grain losses in wheat are higher than in barley, even when S. oryzae was adapted to the latter.     

Importance of soil extractable phosphorus distribution for mature Norway spruce nutrition and productivity

Phosphorus is an essential nutrient for forest growth. In this study, we assessed the impact of soil extractable phosphorus using two simple extraction methods on nutrition and productivity of Norway spruce in sixteen mature forest stands on different bedrocks and soils in Bavaria, Southern Germany. Representative trees were sampled for needles, twigs, branches, stem bark, and stem wood. Total phosphorus content in the tree parts and soil phosphorus stock extractable with citric acid and sodium bicarbonate up to a soil depth of 80 cm were determined. We found that easily soil extractable phosphorus is a suitable indicator for estimating phosphorus uptake and stand productivity in Norway spruce. In contrast, organic layer phosphorus showed no significant correlation with aboveground biomass phosphorus contents. In the biomass, the highest phosphorus contents were measured in young needles and twigs, but the highest correlation with soil phosphorus was detected for phosphorus contents in needles and bark. The stock of phosphorus extracted by citric acid down to 40 cm soil depth revealed the best correlation with phosphorus in needles and bark. Therefore, as a supplemental or alternative method to needle analysis, our study suggests the use of phosphorus contents in stem bark to evaluate tree phosphorus nutrition. These results highlight the suitability of the citric acid soil extraction method to characterize plant available phosphorus in Norway spruce ecosystems.