Fiction. Poetry. Romance. HTML:John Updike�??s fifth collection of poetry faces nature on a number of levels.  An opening section of sonnets touches upon death, aging, and, in a sequence of describing a week in Spain, insomnia and dread.  The poems that follow consider nature in the form of seasons, of planting trees and being buried, of shadow and rain, of pain and accumulation, and of such human diversions as art and travel.  The last poem here, and the longest in the book, undertakes a walking tour of each of Jupiter�??s four major moons, a scientific excursion that leads into the extravagant precisions of the �??Seven Odes to Seven Natural Processes,�?� a lyrical yet literal-minded celebration of some of the earthly forces that uphold and surround us.  Finally, a dozen examples of light verse toy with such natural phenomena as presbyopia, the energy crunch, food, and sex.  Like the best of the metaphysical poets, Mr. Updike embraces the world in all its forms and creates conceits out of the casual as well as