Abstract: A field investigation was made to understand the seedlings root nodula
tion, biomass accumulation, root length, and fine root percentage of Sophora d
avidii, Indigofera lenticellata and Campylotropis polyantha along an alt
itudinal gradient on two contrasting sloped hills (north Zongqu and south Jingzh
oushan) in the dry valley of  Minjiang River. In the meantime, a greenhouse
 experiment was conducted to study the adaptation responses of 2 month-old
S. davidii and C. polyantha seedlings root nodulation  to different soil moisture regimes (80%, 60%, 40%, and 20% WHC). For the thr
ee test shrub species, fewer nodules were observed at lower altitude (1600〖KG-*
2〗-〖KG-*7〗1950 m) areas, the nodule number per plant of S. davidii, I. lent
icellata, and C. polyantha being 01±01, 09±05, and 57±19, a
nd the non-nodulation plant accounting for 651%, 123% and 176%, respectiv
ely. The nodule number of the three species increased with increasing altitude,
and correlated positively with root length and fine root percentage. However, th
ere were no significant differences in the plant growth and biomass at different
 altitudes. When the soil moisture content was lower than
 60% WHC, the nodule number and the  fresh and dry mass of both S. davidi
i and C. polyantha decreased markedly, and at 20% WHC, no nodule and only
98±36 nodules were observed for S. davidii and C. polyantha, respec
tively, indicating that in this dry valley, the root nodulation capability of en
demic leguminous shrubs was very low. Comparing with S. davidii, C. polyan
tha had higher root nodulation capability and drought-resistance. Prior
 to introducing these shrub species in forestation practices, to keep the soil m
oisture content higher than 40% WHC was recommended for relatively efficient bio
logical nitrogen fixation.

Key words: environmental factor, dry valley, altitudinal gradient, biological nitrogen fixation, water stress, biological invasion., sympatry, mosquitofish, ecomorphology, Oryzias species