Relationships among the Contents of Total Phenolics, Soluble Carbohydrate, and Free Amino Acids of 15 Aquatic Macrophytes

Abstract

In order to examine how carbon and nitrogen status of a macrophyte may affect its total phenolics (TP) production, the contents of free amino acids (FAA), soluble carbohydrate (SC) and TP were examined in leaves of seven submersed, four floating-leaved, and four emergent macrophytes. The floating-leaved and emergent macrophytes had much higher contents of SC and TP than the submersed macrophytes. The contents of FAA were not significantly different among the submersed, floating-leaved, and emergent macrophytes. Correlations among the contents of FAA, SC, and TP indicated that the production of TP was more dependent on the SC content than on the FAA content.

Nitrogen/carbon metabolism in response to NH4+ pulse for two submersed macrophytes

“…Visible chlorosis in leaves was observed for M. spicatum, but not for C. demersum in the treatments with NH 4 + pulse, illustrating that M. spicatum is more sensitive to a NH 4 + pulse, which is consistent with the results of Zhong et al (2013) that the toxic threshold of NH 4 + concentration was lower in M. spicatum (2 mg L −1 NH 4 N) than in C. demersum (8 mg L −1 NH 4 N) based on leaf chlorosis of the plants. The result that M. spicatum accumulated much more FAA than C. demersum in the NH 4 + pulse was in line with previous findings based on field investigations in 31 lakes along the middle-lower reaches of Yangtze River (Cao et al, 2008) and experiments with NH 4 + enrichments (0.1-0.25 mg L −1 NH 4 N; (Cao et al, 2011)). Although the effects of NH 4 + pulse on FAA accumulation were quite different between M. spicatum and C. demersum, the NH 4 + pulse affected NH 4 N contents of the two plants similarly, supporting the idea that leaves of submersed macrophytes lack a feedback mechanism for downregulating NH 4 + absorption (van Katwijk et al, 1997;Cao et al, 2011), and thus, the NH 4 N contents in the plant leaves are largely dependent on their surrounding available NH 4 + levels.…”

“…In seagrass Zostera noltii Hornem, underwater PAR-dependent photosynthetic C supply also played an importance role in affecting the plant response to external NH 4 + pulse (Brun et al, 2002). Field observations have demonstrated a higher C reserve in M. spicatum than in many submersed macrophytes, e.g., V. natans, C. demersum, Hydrylla verticilata, P. crisp and Vallisneria americana (Titus and Adams 1979;Cao et al, 2008). Interestingly, the contents of SC and starch were positively correlated with the contents of NH 4 N and FAA in M. spicatum, while negative relationships among these metabolites were observed in C. demersum in our study and reported for seagrass Gracilaria gracilis (Smit et al, 1996), indicating species-specific strategies in CN metabolism of the plants in response to external NH 4 + pulse.…”

Ammonium, microcystins, and hypoxia of blooms in eutrophic water cause oxidative stress and C–N imbalance in submersed and floating-leaved aquatic plants in Lake Taihu, China

“…In this study, the FAA/SC ratios in the plants belonging to both life forms are much higher than those recorded in another study (Cao et al, 2008), especially during the period of high NH þ 4 concentration. An imbalance in the C-N reserves of aquatic plants were found, which is attributed to high NH þ 4 in the water (Smolders et al, 1996;Cao et al, 2004Cao et al, , 2007Zhang et al, 2010).…”

“…The FAA of the plants in this study are even higher especially during the period ''before the blooms'' when MCs in the water column are low and NH þ 4 is high, indicating that the increase in FAA is due mainly to NH þ 4 stress in the lake, but not to the occurrence or decay of the blooms. Although the FAA contents of the submersed macrophytes are considerably reduced in periods during and after the blooms, the FAA contents in the macrophytes are still higher than the levels reported in another study (Cao et al, 2008), indicating that in hyper-eutrophic Lake Taihu, the NH þ 4 concentration of the water column is also significantly reduced by the effective utilization of phytoplankton during the occurrence of heavy blooms. However, the concentration of NH þ 4 in the water at the time is still high enough to affect the metabolism of macrophytes.…”

“…In this study, NH þ 4 -N concentration in the water column is higher than 0.3 mg L À1 most of the year, and the FAA contents of these five aquatic plants (7.01 ± 2.08, 8.56 ± 5.08, 4.14 ± 0.85, 5.01 ± 3.10, and 6.06 ± 2.68 mg g À1 DW on annual average for M. spicatum, P. malaianus, V. natans, T. bispinosa and N. peltata, respectively) are much higher than those reported by Cao et al (2008) (FAA: 4.11 ± 3.33, 3.69 ± 2.21, 2.33 ± 1.42, 1.74 ± 0.68, and 3.05 ± 2.05 mg g À1 DW, respectively) for the plants growing in the lakes of this area. The FAA of the plants in this study are even higher especially during the period ''before the blooms'' when MCs in the water column are low and NH þ 4 is high, indicating that the increase in FAA is due mainly to NH þ 4 stress in the lake, but not to the occurrence or decay of the blooms.…”