The decomposition of salt marsh plants is affected by the variation of physiochemical factors caused by the
change of tide level. In the present study, plant tissues of Spartina alterniflora fromcontrolled metal exposure experimentswere
subjected to a field decomposition trial at different tidal levels in a tidal flat of Chongming Island,
Shanghai. The contents of the metals and Pb stable isotope ratios of the plant litter and the adjacent sediment
were followed. The mass loss rate of the root and leaf litters of S. alterniflora decreasedwith the increase of burial
time. Leaf had the highest decomposition rate (0.009 day−1 to 0.020 day−1) compared to that of the roots
(0.004 day−1 to 0.005 day−1) and stems (0.002 day−1 to 0.006 day−1). Leaf had the highest decomposition
rate possibly due to the significantly lower C/N ratio (16.0–44.6) compared to that of the roots (32.8–88.9)
and stems (43.7–120.9). The mass loss rate of the roots and leaves of S. alterniflora was higher in the high tidal
marsh than that in the low tidal marsh, especially at the late stages of decomposition. The concentrations of
metals in leaf litter of S. alterniflora increased, whereas the pools of metals in most of the plant litters decreased
significantly with the increasing of the decomposition time. The ratios of 207Pb/206Pb and 208Pb/206Pb in the root
litters decreased significantly in the first 290 days of decomposition and then increased significantly at Day 350,
while the Pb isotope ratios in adjacent sediment showed no significant changes. Fast mass loss of plant litters induced
the significant decrease in metals' pools at early stages of decomposition, and release of the plant tissue Pb
was greatly inhibited due to the slowed mass loss at the late stages of decomposition.