The change of accumulation of heavy metal drive interspecific facilitation under copper and cold stress

Plant diversity has important functions in ecosystem productivity overyielding and community stability. Little is known about the mechanism causing productivity overyielding and stability under harsh conditions. This study investigated the photosynthetic response and subcellular distribution of uni- and co-cultured duckweeds (Lemna aequinoctialis and Spirodela polyrhiza) under excess copper (1.0 mg/L) and low temperature (5 degrees C) conditions. The results showed that the growth of uni-cultured L. aequinoctialis was not different from that of uni-cultured S. polyrhiza across copper treatments at control temperature (25 degrees C). The growth rate of L. aequinoctialis increased by 55.5 % under excess copper concentration when it coexisted with S. polyrhiza, compared with uni-culture. Subcellular distributions of copper were predominantly distributed in cell walls. S. polyrhiza accumulated more copper in cell walls than L. aequinoctialis under uni-cultured condintion at excess copper concentration. Cocultured S. polyrhiza increased copper accumulation in cell walls of co-cultured L. aequinoctialis to decrease toxicity at excess copper concentration, compared with L. aequinoctialis. Low temperature increased copper toxicity, with duckweeds having lower growth rate and photosynthetic activities (Fv/Fm). The L. aequinoctialis growth rate in co-culture was higher than in uni-culture under excess copper concentration and low temperature conditions, indicating that S. polyrhiza decreased the copper toxicity for L. aequinoctialis. The photosynthetic activity (Fv/Fm) of co-cultured L. aequinoctialis was higher than that of uni-cultured L. aequinoctialis exposed to excess copper concentration at low temperature. The community that formed by co-culturing S. polyrhiza and L. aequinoctialis produced more biomass by avoiding the toxicity of excess copper through heavy metal compartmentalization and photosynthetic activities.