Aboveground Biomass Invariance Masks Significant Belowground Productivity Changes in Response to Salinization and Nitrogen Loading in Reed Marshes

Abstract

The surface waters of Tianjin municipality exhibit severe nitrogen loading and salinization; however, the extent to which the current levels of nitrogen enrichment and salinization have impacted belowground biomass and root morphology in reed marshes is poorly documented. This study was conducted at typical saline reed marshes (Dahuangpu, Qilihai, and Beidagang) in the Tianjin municipality. The relationships between belowground biomass, belowground-aboveground biomass (B-A) ratio, root morphology and the varying sediment nitrogen and salinity levels were investigated. Results showed: 1) Higher salinity levels related to a substantial decrease in the belowground biomass, B-A ratio, and root length density; 2) Higher nitrogen stress levels related to decreased belowground biomass, specific root length and root length density, and B-A ratio at Qilihai site with the highest nitrogen loading; 3) specific root length, root length density, and B-A ratio were significantly correlated to the aboveground plant nitrogen concentration; and 4) neither salinity nor nitrogen stress significantly altered aboveground biomass. The results show that aboveground biomass invariance masks significant belowground productivity changes in response to salinization and nitrogen loading in Reed Marshes. Impact of salinization and nitrogen loading on belowground productivity in wetlands should be considered to fine-tune critical carbon-dependent components of global change models.

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