Abstract: With the sediment applied with 0, 024%, and 048% NH4Cl (treatme
nts CK, SN1, and SN2) as the substrate, a greenhouse experiment was conducte
d to study the physiological responses of Myriophyllum spicatum to ammonium nitr
ogen. The NH4+-N concentration in the sediment, pore-water, and overlying
-water ranged in 1235〖KG-*2〗-〖KG-*7〗87032 mg·kg-1, 109〖KG-*2
〗-〖KG-*7〗103605 mg·L-1, and 010〖KG-*2〗-〖KG-*7〗2430 mg·L-1
, respectively. Comparing with those in CK, the plant height, root length, and
 fresh biomass of M. spicatum in treatments SN1 and SN2 decreased by 15
66% and 5552%, 4572% and 6765%, and 1969% and 8116%, respectively. T
he SOD activity in M. spicatum leaves and roots was SN1<SN2<CK, but the
peroxidase (POD) and catalase (CAT) activities in the leaves were SN2<SN1<CK， while those in the roots were significant higher in SN1 and SN2 than in CK.
 The malondialdehyde (MDA) contents of leaves and roots in SN1 and SN2 were
increased by 4630% and 8275%, and 1966% and 5519%, respectively. It was
suggested that NH4+-N had toxic effects on M. spicatum, and the higher
the NH4+-N concentration in sediment, the more obvious the physiological re
sponses of M. spicatum exhibited.

Key words: ammonium nitrogen, Myriophyllum spicatum, physiological response,  antioxidant enzymes, evapotranspiration, eddy covariance method, alpine shrubland meadow, Qinghai-Tibet Plateau, seasonal variation, interannual dynamics, ChinaFLUX.