Controlling audibility with noise for online experiments using sound.

Online auditory experiments use the sound delivery equipment of each participant, with no practical way to calibrate sound level or frequency response. Here, a method is proposed to control sensation level across frequencies: embedding stimuli in threshold-equalizing noise. In a cohort of 100 online participants, noise could equate detection thresholds from 125 to 4000 Hz. Equalization was successful even for participants with atypical thresholds in quiet, due either to poor quality equipment or unreported hearing loss. Moreover, audibility in quiet was highly variable, as overall level was uncalibrated, but variability was much reduced with noise. Use cases are discussed.

The mechanism of sugar export from long conifer needles.

The green leaves of plants are optimised for carbon fixation and the production of sugars, which are used as central units of carbon and energy throughout the plant. However, there are physical limits to this optimisation that remain insufficiently understood. Here, quantitative anatomical analysis combined with mathematical modelling and sugar transport rate measurements were used to determine how effectively sugars are exported from the needle-shaped leaves of conifers in relation to leaf length. Mathematical modelling indicated that phloem anatomy constrains sugar export in long needles. However, we identified two mechanisms by which this constraint is overcome, even in needles longer than 20 cm: (1) the grouping of transport conduits, and (2) a shift in the diurnal rhythm of sugar metabolism and export in needle tips. The efficiency of sugar transport in the phloem can have a significant influence on leaf function. The constraints on sugar export described here for conifer needles are likely to also be relevant in other groups of plants, such as grasses and angiosperm trees.