Early performance of planted hybrid larch: effects of mechanical site preparation and planting depth

Some site preparation is generally recommended to enhance the growth and survival of planted and naturally regenerated seedlings, but it must be justified both economically and environmentally. More severe preparation is thought to be necessary for intensive plantation silviculture, e.g., using fast-growing, ameliorated stocks, especially in boreal ecosystems. Although not justified scientifically, deep-planting of seedlings is often discouraged and may even be financially penalized in eastern Canada. We thus evaluated early seedling growth and survival of hybrid larch (Larix 9 marschlinsii Coaz) in an experiment including mechanical site preparation and planting depth treatments. Our results suggest that satisfactory early hybrid larch establishment and growth could be met using low environmental impact or low cost treatments (such as soil inversion using an excavator or single-pass disk trenching), and that deeper planting has no negative effect. Structural equation modelling (SEM) was used to explore causal relationships between factors influencing seedling performance at the local scale (planting microsites), including soil moisture, soil temperature, surrounding vegetation, and seedling nutrition. SEM analysis supported the absence of overall differences among treatments, while also highlighting the negative impact of increased soil water content where drainage was suboptimal, as well as the unexpected positive impact of increased competition on growth mostly through seedling nutrition, among others. These early observations will need to be confirmed over a longer period, as well as with a more comprehensive assessment of site environmental conditions and competition intensity

Thermotolerance of Fungal Conidia

Conidia of entomopathogenic fungi (EF) are the propagules most frequently used in arthropod biocontrol programs. This anamorphic form is essential for the infection process, including spore germination, penetration, vegetative growth, conidiogenesis and dissemination. Most EF are mesophilic and can develop between 10 and 40 °C, but optimal growth is between 25 and 35 °C. Abiotic factors, especially temperature (high or low) can determine their viability, virulence and success or failure of infection process. Temperature has the highest impact on conidial stress inhibiting metabolic processes, such as decreased morphogenesis during germination, protein denaturation and membrane disorganization. Several studies show that some strains of Beauveria spp., Metarhizium spp., and Isaria spp. exhibit conidial survival even when grown at high temperatures, indicating a relationship between conidial thermotolerance and their geographical isolation origin. Moreover, the high variability in fungal thermotolerance is also dependent of the culture media composition and growth condition. EF that grow at high temperatures do not grow at low temperatures and vice versa. Moreover, when growth conditions are not set at optimal temperatures, EF development is affected and their effectiveness in biological control programs of arthropods is reduced. Thermal stress directly impacts on fungal strains ability to target arthropods and their environmental activity performance. The screening for fungal strains with a higher thermotolerance and the improvement on conidial formulations may aid in optimizing the conditions for biocontrol agent application.Fil: Paixão, Flávia R. S.. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Investigaciones Bioquímicas de La Plata "Prof. Dr. Rodolfo R. Brenner". Universidad Nacional de la Plata. Facultad de Ciencias Médicas. Instituto de Investigaciones Bioquímicas de La Plata "Prof. Dr. Rodolfo R. Brenner"; ArgentinaFil: Fernandes, Éverton. Universidade Federal de Goiás; BrasilFil: Pedrini, Nicolás. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Investigaciones Bioquímicas de La Plata "Prof. Dr. Rodolfo R. Brenner". Universidad Nacional de la Plata. Facultad de Ciencias Médicas. Instituto de Investigaciones Bioquímicas de La Plata "Prof. Dr. Rodolfo R. Brenner"; Argentin