Identifying appropriate methodology to diagnose aeration limitations with large peat and bark particles in growing media

Large-sized particles (coarse peat, bark or sawdust) are often added to growing media to improve substrate aeration properties (gas storage and exchange). Recent studies have shown that large fragments mixed with fines may create barriers that restrict gas diffusion or create competition for oxygen even if they improve air storage. An experiment was carried out to compare the growth performances of growing media containing large fragments and to assess their aeration status using different methods. Different mixes were made of a fine sphagnum peat (average size 2.4 mm) and a coarse (1-2, 2-4, 4-6, 6-10, and 10-20 mm particles) sphagnum peat or bark (2-4 and 10-20 mm). These substrates had different aeration properties and were used to grow Poinsettia and Impatiens ‘New Guinea’ in a greenhouse, resulting in differences in plant growth. The results show that air-filled porosity remained relatively unaffected by fragment size. Gas relative diffusivity differed significantly between treatments and was highest in the mix with the 2-4 mm particles and diminished rapidly as fragment size increased from 4 to 20 mm or decreased to 1-2 mm. Diffusivity was clearly lower in the bark/peat mixes but showed the same trend with coarse fragments. Root and shoot growth parameters were significantly and positively correlated to gas relative diffusivity. Moreover, the growth reduction observed in the bark/peat mixes relative to pure peat was most likely linked to limited gas exchange. Air-filled porosity assessments performed in situ (in the pot itself) or prior to potting, in cylinders, gave inconsistent results or were not significantly correlated to plant growth, indicating that aeration limitations are better diagnosed with gas diffusivity in growing media

Blue light effects on rose photosynthesis and photomorphogenesis

Through its impact on photosynthesis and morphogenesis, light is the environmental factor that most affects plant architecture. Using light rather than chemicals to manage plant architecture could reduce the impact on the environment. However, the understanding of how light modulates plant architecture is still poor and further research is needed. To address this question, we examined the development of two rose cultivars, Rosa hybrida‘Radrazz’ and Rosa chinensis‘Old Blush’, cultivated under two light qualities. Plants were grown from one-node cuttings for 6 weeks under white or blue light at equal photosynthetic efficiencies. While plant development was totally inhibited in darkness, blue light could sustain full development from bud burst until flowering. Blue light reduced the net CO2 assimilation rate of fully expanded leaves in both cultivars, despite increasing stomatal conductance and intercellular CO2 concentrations. In ‘Radrazz’, the reduction in CO2 assimilation under blue light was related to a decrease in photosynthetic pigment content, while in both cultivars, the chl a/b ratio increased. Surprisingly, blue light could induce the same organogenetic activity of the shoot apical meristem, growth of the metamers and flower development as white light. The normal development of rose plants under blue light reveals the strong adaptive properties of rose plants to their light environment. It also indicates that photomorphogenetic processes can all be triggered by blue wavelengths and that despite a lower assimilation rate, blue light can provide sufficient energy via photosynthesis to sustain normal growth and development in roses

Idealized digital models for conical reed instruments, with focus on the internal pressure waveform

International audienceTwo models for the generation of self-oscillations of reed conical woodwinds are presented. They use the fewest parameters (of either the resonator or the ex-citer), whose influence can be quickly explored. The formulation extends iterated maps obtained for loss-less cylindrical pipes without reed dynamics. It uses spherical wave variables in idealized resonators, with one parameter more than for cylinders: the missing length of the cone. The mouthpiece volume equals that of the missing part of the cone, and is implemented as either a cylindrical pipe (first model) or a lumped element (second model). Only the first model adds a length parameter for the mouthpiece and leads to the solving of an implicit equation. For the second model, any shape of nonlinear characteristic can be directly considered. The complex characteristics impedance for spherical waves requires sampling times smaller than a round trip in the resonator. The convergence of the two models is shown when the length of the cylindrical mouthpiece tends to zero. The waveform is in semi-quantitative agreement with experiment. It is concluded that the oscillations of the positive episode of the mouthpiece pressure are related to the length of the missing part, not to the reed dynamics