No abstract

Propagules dispersal and colonization ability are major issues of macrophyte regeneration. For submerged macrophyte Potamogeton crispus L., turion dispersal along water flow can favor the long‐distance expansion of its population; therefore, it is crucial to investigate factors that affect turion dispersal. For this purpose, we studied effects of buoyancy and season on dispersal P. crispus turions by collecting field samples from Taihu Lake, over a three‐months period (turion‐formatting season, from May to July). Germination experiments (30 days in each sampling month) revealed that the floating turions germinated earlier and faster than the sinking ones across the three sampling months. After germination, the floating turions showed higher seedling height; whereas the sinking turions accumulated more sprouts biomass. The soluble sugar, total nitrogen (TN), and total phosphorus (TP) concentrations were found higher in the floating turions. The starch concentrations remained high without buoyancy or season effects. These results indicate that both internal (e.g., buoyancy, soluble sugar, TN, and TP concentrations) and external environmental factors (e.g., light condition and temperature) may contribute to germinability and plant growth of P. crispus turions. This study offers new insights into the dispersal of asexual propagules of submerged macrophytes.

Potamogeton crispus is widely used in submerged macrophyte restoration in China. Turions are an important means of reproduction in this species. To compare the regeneration abilities of P. crispus turions in macrophyte- and phytoplankton-dominated lakes, we collected P. crispus turions from a macrophyte-dominated lake (Liangzi Lake) and a phytoplankton-dominated lake (Taihu Lake). Both lakes are important lakes in the middle and lower reaches of the Yangtze River in China. Our field survey revealed that the turions from the phytoplankton-dominated lake had smaller sizes and higher concentrations of total nitrogen (TN) and total phosphorus (TP) than did those from the macrophyte-dominated lake. Rapid sprouting of the turions from the phytoplankton-dominated lake in 32 days was observed under experimental conditions, although the sprout sizes (heights and biomass) were smaller than those from the macrophyte-dominated lake. Compared with sprouted turions from macrophyte-dominated lake, the sprouted turions from the phytoplankton-dominated lake accumulated higher soluble sugar (SS) but lower starch and free amino acid (FAA) concentrations. A 12-day interval sprout removal treatment significantly stimulated the re-sprouting of turions from both lakes, but scale-leaf-removal treatments had no effect. This study provides evidence that the regeneration strategies of P. crispus turions differ in macrophyte- and phytoplankton-dominated lakes.

We investigated carbon (C) fluxes from Spartina alterniflora community comparing with native C 3 -plant (Suaeda salsa and Phragmites australis) communities as well as mudflat in a coastal marsh in eastern China by determining the net ecosystem exchange (NEE), ecosystem respiration (R ECO ) and soil respiration (R SOIL ) monthly with static chambers over one year. Plant biological traits and soil organic carbon (SOC) were measured at the end of the growing season. Gross primary production (GPP) was calculated as the sum of R ECO and NEE, while the respiration of aboveground plant (R AG ) was assessed by the difference between R ECO and R SOIL . The invasion of S. alterniflora significantly increased R ECO , GPP, and R AG in salt marsh. The NEE in the S. alterniflora community was significantly lower than in mudflat and S. salsa community (p < 0.05), but was comparable to that in P. australis community (p > 0.05). R SOIL among sites with different communities did not show significant variations (p > 0.05). Surface water inhibited R SOIL and made it insensitive to changes in environmental factors across communities. Relative to other communities, the lower shoot-root ratio of S. alterniflora community together with its higher R ECO and R AG determined a higher proportion of C allocated in belowground, which ultimately resulted in increment of SOC as well as increased GPP. The invasion of S. alterniflora potentially induces a negative feedback to the global climate change by regulating the C sequestration in salt marsh ecosystems.