Compare Rossini's “Kyrie” from Petite Messe Solennelle with Gershwin's An American In Paris”(b. 1-209) in terms of use of dynamics

Being the two pieces from very different contexts in terms of genre, orchestration, historical period and geographical location, I expect them to have some noticeable divergences that will find justification in these differences.Kyrie is the opening piece of Gioachino Rossini's “Petite Messe Solennelle”, a sacred piece for SATB choir and soloists, two pianos, and harmonium. Being written in the latest period of his life, it is obviously belonging to the Romantic period and genre. Kyrie is characterised by the extremely soft dynamics, with a range between p and pppp, which is rarely seen in a score. The layering of instrumentation and soloists (or choir) makes the overall actual result of dynamics louder than that, but the individual performers have to keep following that written p. The overall theme of silence is again highlighted by the annotation for the singer's performance “sotto voce” which literally means “whispering” in Italian. There are, however, some moments of crescendos that go up to fortissimo (e.g. bar 29), to decrease immediately with a diminuendo to pp.The middle part of the piece, Christe eleison, is different from the rest for it being a cappella, which means only sung by the voices without accompaniment. This makes sure that the interpretation given by the singers in this “solo” part is still kept quiet, as well as expressive, while the pianos and the harmonium are not contributing to the overall resulting dynamics. The third part, a repetition of Kyrie, still keeps the “sotto voce” and the extreme dynamics (pppp) with occasionals ff for contrast which suddenly decrease to a pp again.On the other hand, Gershwin's dynamics in the first part of An American in Paris are much more varied, as the author himself uses the piece to explore instrumentation and timbre and this results in many contrasts and variations.The range of dynamics doesn't generally go below piano, being it an orchestral piece for a concert hall, but some instruments use sordina or muted effect (e.g. bar 91, trumpet), and go up to ff and even some sfz-p contrasts (b. 83, trombone). Overall, there is a contrast between very loud sections and soft ones, also presenting a varied orchestration to permit the dynamic contrast, and there are ofter episodes of fermata (e.g. bar 72).