The third poem may be the song of the nightingale at the end of poem 2. Poem 3 may be the song that was announced at the end of song 2. The love for nature has vanished, because his love is nature as a whole. Is there any irony in this song? In itself, you don't recognize it, but the tears at song 2 suggest that it the cheerfulness as a dark undertone. He is singing about his love, but maybe, love is not reciprocal and it is only a dream.
In contrast with the first two poems, this poem has only one strophe of six lines. The use of "eine" in lines three and four is very characteristic. The rhyme is two by two lines. The repetition of the nature aspects mentioned in the first line in the last line creates a more or less circular structure in the poem.
The rose, the lily, the dove and the sun all have metaphorical associations that may become apparent already at the start of the poem. In the second half of the poem the metaphors are on a higher level, integrated in his love.
If you look at the start of the song, the singer continuous with the last soprano tone of the piano and uses it as the dominant of D. Till m. 8 nothing happens. But then the harmony modules towards A, with the Gis suggesting something like E7 in measure 8, as does the Gises later and the E by the singer. Half way m. 10 the D-C in the bass in combination with the D-G chords create a G major tonality. With respect to melody, recognize the similarity between the bass line from C downwards with the bass line at the start of song 2. Is this the irony in the music?
In measure 13 the melody seems to be clear in e, while the harmony of the second half of the measure may suggest Cis, especially because it goes towards Fis in m. 14. But in m. 14 the melody suggests A. So, minor and major at the same time? In m. 15 we see E7-A, followed by E7-A7-D at the end of the song. The piano postlude is clearly in D, with I-IV repeatedly till a IV-I-V-I at the end.
The melody has a lot of resemblance with song 2. See the line D-Cis-B-A. But in m. 4 and 8 the melody continuous till E. The pressure is created by the bass line, the repetition and the tempo. The highest tones of the melody are at the moments when is expressed that his love is all beautiful of nature in one.
The end is a little bit of a surprise. The lowest note of the singer suggests a fall. The deep bass line that is rising suggests an attempt to go back. The static nature of the postlude suggests not much success in this, as does the fading out at the end. But then we have the surprise of the V-I chords at the end, in mezzo forte. To me it suggests the end of the dream. It is like it is.