Prevalence of interspecific competition in a mixed poplar/black locust plantation under adverse climate conditions

Key message

In a mixed poplar/black locust plantation in central France, adverse conditions have led to a prevalence of interspecific competition, resulting in a poorer performance than monocultures.

Context

In mixed tree plantations, the presence of woody N₂-fixing species is thought to reduce N needs by fertilization. However, benefits associated to soil nitrogen enrichment have to outweigh the negative effects of interspecific competition. To do so, co-occurring tree species have to be chosen carefully to promote niche sharing between species and reduce competition. Black locust and poplar mixtures therefore seem promising since both species are fast growing and have potentially complementary crown shapes.

Aims

Our objective was to evaluate the impact of the poplar/black locust mixture on the growth, above- and belowground biomass production, and nitrogen allocation of the two species, as compared to their respective monocultures.

Methods

An experimental plantation mixing poplar and black locust was set up in central France. For five growing seasons, growth, nitrogen allocation, and carbon allocation were monitored for the two species growing either in mixture or in monoculture.

Results

After a couple of promising growing seasons, black locust growth and survival slowly declined, mainly in the mixture. At the stand level, biomass production in the mixed plots was nearly 50% below the most productive monoculture (poplar) by age 5 years.

Conclusion

Under adverse conditions, interspecific competition in the mixture was the preponderant interaction, resulting in higher mortality and lower biomass production than the two monocultures.

     

When warmer means weaker: high temperatures reduce behavioural and immune defences of the larvae of a major grapevine pest

Phytophagous insects evolving in agroecosystems express numerous defences when faced with myriads of natural enemies. Such defensive traits might impair the effectiveness of biological control relying on these natural enemies, mostly parasitoids. In the case of parasitoid threat, these defences consist of the avoidance of the parasitoid (reduced exposure to antagonists through shortening of developmental time), hindrance of oviposition (evasive behaviours and morphological protection) or destruction of the parasitoid eggs (encapsulation and melanisation by means of the immune system). Previous works focused on one defensive trait only when investigating the effects of temperature on host resistance. By doing so, they assumed that all defensive traits would respond uniformly to a change occurring in thermal environment, which remains an undocumented fact. To test this assumption in the context of global warming, we adopted a global overview of host resistance by examining the effects of rising temperatures on multiple defensive traits used by the grape pest, Lobesia botrana, against its larval parasitoids. Although warmer conditions led to reduced exposure to parasitoids by accelerating larval development, warmer conditions also elicited extensive weakening of behavioural and immune defences. These results confirm that temperatures might differently modulate the levels of expression of several defensive traits. An increase in growth rate and pupal mass also occurred, especially for females, which may contribute to greater pest fecundity in the future. However, the decline of L. botrana resistance might enhance the efficiency of the biological control naturally exerted by parasitoids in vineyards, thereby limiting the damage to crops.     

Comparison of lidocaine and lidocaine–epinephrine for the paravertebral brachial plexus block in dogs

Objective

To compare the motor and sensory block efficacy and duration of a modified paravertebral brachial plexus block (PBPB) after administration of lidocaine alone (LI) or combined with epinephrine (LE).

A common pesticide decreases foraging success and survival in honey bees

Nonlethal exposure of honey bees to thiamethoxam (neonicotinoid systemic pesticide) causes high mortality due to homing failure at levels that could put a colony at risk of collapse. Simulated exposure events on free-ranging foragers labeled with a radio-frequency identification tag suggest that homing is impaired by thiamethoxam intoxication. These experiments offer new insights into the consequences of common neonicotinoid pesticides used worldwide.     

Influence of Sodium Chloride on Color Development of Cereal Model Systems Through Changes in Glass Transition Temperature and Water Retention

Research efforts aim to enhance fundamental understanding about the role of salt in cereal products. Such knowledge may open new strategies for salt reduction in respective product categories. A model system, containing pregelatinized starch, glucose, and amino acids heated at 230°C for up to 10 min demonstrated that NaCl leads to darker products compared with the same model heated without NaCl (P < 0.05). The same trend was observed in wheat breakfast cereal flakes toasted at 230°C. The present study investigated two hypotheses how salt may influence color formation through Maillard Reaction: 1) hygroscopic behavior of salt may change the retention of water during heating and encourage Maillard reactions by improving mobility of reactants; 2) salt has a plasticizing effect and the presence of salt might keep the product in a rubbery state longer while heating, hence improving mobility and Maillard reactions of reactants. The same models (pregelatinized starch, glucose, and amino acids) mixed with several types of plasticizers (NaCl, KCl, or trehalose) and a blank without plasticizer were made and heat‐treated under controlled conditions. The presence of plasticizers always led to darker products but no correlation was found between color formation, the hygroscopic behavior of the system, and its glass transition temperature as measured by phase transition analyzer.     

Effects of oral administration of meloxicam,carprofen, and a nutraceutical on thyroid function in dogs with osteoarthritis

The purpose of this study was to evaluate the effect of the administration of meloxicam; carprofen; and a slow-acting disease modifying osteoarthritis agent, that contains chondroitin sulfate, purified glucosamine, and manganese ascorbate (CS-G-M), on thyroid function in dogs. Forty-six healthy (except for osteoarthritis) euthyroid dogs were blindly assigned to 3 treatment groups: meloxicam, carprofen, and CS-G-M. Each group received the recommended dose of the drug for 60 days. Sixteen other osteoarthritic euthyroid dogs, which received a placebo, were used as a control group to validate the study. For all groups, blood samples were collected on days 0, 30, and 60 to evaluate the serum total and free thyroxine, and endogenous thyrotropin concentrations. There were no significant differences among the treatment groups at each time or within each group over a 60-day period for all parameters. Moreover, none of these values were within the hypothyroid range. Based on the results of this study, the administration of meloxicam, carprofen, and CS-G-M did not affect canine thyroid function evaluation.     

Superiority of the gastroduodenal safety profile of licofelone over rofecoxib, a COX-2 selective inhibitor, in dogs

This study assessed the gastroduodenal safety profile of licofelone, a new nonsteroidal anti-inflammatory drug with dual inhibitory activity against 5-lipoxygenase and cyclo-oxygenase (COX), by using endoscopic evaluations and by comparing licofelone to rofecoxib, a selective COX-2 inhibitor. Twenty-one dogs underwent blinded gastroduodenoscopies, during which the mucosa of the gastroduodenal tract was assessed and scored. Blood analyses were monitored on days 0 (baseline), 14, 28, 42, and 56. Examinations to detect fecal occult blood were performed daily. Dogs were randomly assigned to three groups that received either a placebo, licofelone at a dose of 2.5 mg/kg twice daily, or rofecoxib at a dose of 0.5 mg/kg daily, respectively. Significant differences between the groups in gastric (P = 0.003), duodenal (P = 0.009), and gastroduodenal (P = 0.002) endoscopic lesion scores were observed at day 56. Rofecoxib-treated dogs had more lesions in all areas when compared with placebo-treated dogs, more duodenal lesions when compared with licofelone-treated dogs and more lesions than they had at baseline. In contrast to licofelone, rofecoxib was found to induce significant gastric and gastroduodenal lesions in dogs that lacked pre-existing lesions at baseline. Blood analyses and fecal examinations did not reveal abnormalities in any of the experimental groups. Treatment with licofelone was well tolerated and was shown to be safer than rofecoxib in terms of upper gastrointestinal damage. In this way, this study demonstrates the gastroduodenal safety profile of licofelone for chronic treatment.     

Effects of pesticides on mite predators (Acari: Phytoseiidae) and colonization of apple trees byTetranychus urticae

A 2-year survey of mite populations and pesticide use was carried out in Nova Scotia, Canada, in apple orchards where the two-spotted spider mite (Tetranychus urticae Koch) was the dominant phytophagous mite. Fungicides were the only class of pesticides that affected cumulative number ofT. urticae-days per leaf in tree canopies and colonization success — the ratio ofT. urticae-days to number of immigratingT. urticae caught in sticky bands on tree trunks. In 2000, increased numbers ofT. urticae-days in the tree canopy were associated with more frequent applications of ethylene bis-dithiocarbamate (EBDC) fungicides and with higher fungicide toxicity scores, which indicate cumulative level of suppression of the phytoseiid predatorTyphlodromus pyri Scheuten by all fungicide applications. Higher rates of colonization success were also associated with higher toxicity scores. EBDC’s applied in 2000 promotedT. urticae immigration as indicated by their counts on sticky bands. In 2000 and 2001, number ofT. pyri-days in the tree canopies was decreased by more frequent EBDC applications and by higher fungicide toxicity scores. Promotion ofT. urticae in tree canopies by EBDC’s was attributed to their toxicity toT. pyri. BothT. pyri and another phytoseiid,Amblyseius fallacis (Garman), were found in ground cover vegetation. Hence, increased immigration from the ground cover attributed to the toxicity of EBDC’s toT. pyri and, especially, toA. fallacis, which is a specialist predator of spider mites and an effective natural enemy ofT. urticae. http//www.phytoparasitica.org posting Sept. 13, 2006. Formerly, Atlantic Food and Horticulture Research Centre, now retired.