Phonological Alternations

Morphophonology

Sereer has salient alternations in the initial consonants of noun and verb stems. These alternations appear to be morphologically conditioned in a lexically specified manner, since they occur in several different segmental contexts whose only common element is being within a morphologically derived environment (e.g. plurality in both nouns and verbs; addition of apparent nominalizing suffixes to verbs).

Nouns

(discussion on sg./pl. alternations here)

Deverbal nouns: A noun can be formed from (any?) verb by affixing a prefix a- to the verb root, and altering the initial consonant of the root.

verb	meaning	noun	meaning
ret	go	atet	a trip, "going"
ɗing	fence (in)	aƭing	fence
tos	gather manure	atos	pile of manure
piis	draw a line	apiis	line
weʄ	swim	abeʄ	a swim, swimming

Further alternations remain to be seen, but it appears that the same sorts of alternations seen elsewhere in the language are present here (r,d > t ; voiced implosive > voiceless implosives, etc.)

There are some less straightforward alternations involving not only the initial consonant:

rain (v): deb
rain (n): ateƥ

slap (v): faɗ
slap (n): ombaƭ

Verbs

The initial consonant of verb roots can vary based on whether the subject is singular or plural. Non-implosives alternate with prenasalized stops, and implosives alternate with their voiceless counterparts. So far, these alternations appear to be completely predictable.

sg.~pl.
f~mb
b~mb
w~mb
ɉ~ɲɉ
χ~ɴɢ
ɗ~ƭ
ɓ~ƥ
ʄ~ƈ
r~nd
d~nd
g~ng

Invariant:
j~j
l~l
m~m
n~n
ŋ~ŋ
ɲ~ɲ
p~p
t~t
k~k
c~c
s~s

We still need to get the sg vs. pl. forms of verbs starting with:
q
ʔ, or vowel initial

It seems that verb roots (as seen with singular subjects) cannot start with voiceless implosives or prenasalized stops.