Potassium ions enhances photosynthetic tolerance to salt stress. We hypothesized that potassium ions, by minimizing the trans-thylakoid proton diffusion potential difference, can alleviate an over-reduced photosynthetic electron transport chain and maintain the integrity of the photosynthetic apparatus. This study investigated the effects of exogenous potassium on the transcription level and activity of proteins related to the photosynthetic electron-transport chain of tobacco seedlings under salt stress. Salt stress retarded the growth of seedlings, and caused potassium ion outflow from the chloroplast. It also lowered qP (indicator of the oxidation state of Q A), Y PSII (average photochemical yield of PSII) while increasing Y NO+NF (non-regulatory energy dissipation), accompanied by reduced expression of most light-harvesting, energy-conversion, and electron-transport genes. Interestingly, Lincomycin (a D1 protein-synthesis inhibitor) significantly diminished the alleviation effect of exogenous potassium on salt stress. We attribute the comprehensive NaCl-induced down-regulation of transcription and photosynthetic activities to ROS-induced retrograde signalling. There probably exists at least two types of ROS-induced retrograde signalling, distinguished by their sensitivity to Lincomycin. Exogenous potassium appears to exert its primary effect by ameliorating the trans-thylakoid proton diffusion potential difference caused by salt stress, thereby alleviating over-reduction of the photosynthetic electron transport chain, and maintaining the integrity of photosynthetic proteins.

In natural forests, it is increasingly suggested that stand factors are far more important for community biomass and productivity than biodiversity, but the relative importance of stand factors vs. diversity on ecosystem stability, and how their relative roles change with grain size, still remain unclear. Using inventory data from tropical forest plots in southwestern China from 2004 to 2010, we found that stand factors were clearly more stronger drivers than diversity for forest biomass and productivity (at each grain size from 400 m2 to 0.25 ha), while diversity was predominate for temporal stability of biomass and productivity. The effect of diversity on biomass and productivity increased with increasing grain size, but did not change clearly for ecosystem stability. Functional diversity was more important for ecosystem functions and stability than taxonomic and phylogenetic diversity, and richness was more important than the other two diversity components (evenness and divergence). Our results reconcile the recent debate on the relative importance of diversity vs. stand factors on ecosystem properties, and suggest that forest management to adjust stand structure is an effective way to increase forest carbon storage rapidly, but biodiversity conservation may be crucial for long-term ecosystem stability under climate change.