Alterations to biological soil crusts with alpine meadow retrogressive succession affect seeds germination of three plant species

Biological soil crusts(BSCs) are the important components of alpine meadow ecosystems.The extent and morphology of BSCs vary greatly with alpine meadow retrogressive succession due to grazing pressure.There is significant interest in impacts of crust composition on plant seed germination,especial l y in(semi-) arid environments.However,little is known about the influences of BSCs,and their associations with alpine meadow succession,on germination of typical alpine meadow vascular plant species.In a full factorial common-gardenexperiment,we studied effects of:(1) crust type,(2) seed position,and(3) surface texture on seed germination.We chose three typical alpine meadow plant species(i.e.Poa pratensis,Tibetia himalaica and Potentillen nivea),which belonged to different functional groups(graminoids,legumes,and forbs) and play important roles in all alpine meadow succession stages.Crust type and seed position influenced seed germination,and the inhibitory effects of BSCs depended on the crust type and seed species tested.The major factors influencing seed germination were BSC type,seed position,soil texture,and the interactions between BSC type and seed position; species and seed position; species andsurface texture; and species,crust type,and surface texture.Cyanobacteria crust significantly inhibited germination of all seeds.Seed position also had a significant effect on seed germination(p < 0.001).Fewer seedlings germinated on the surface than below the surface,this was especially true for P.nivea.seeds within cyanobacteria and lichen crusts.Only germination rates of T.himalaica on the soil surface were significantly correlated with plant occurrence frequency within the alpine meadow community.The poor correlation for the other two species is possibly that they are perennials.Our results clearly demonstrated that BSCs can be biological filters during seed germination,depending on the BSC succession stage.Through their influences on seed germination,BSCs can strongly influence community assemblages throughout alpine meadow retrogressive succession.

Effects of plant density on cotton yield components and quality

Yield and ifber quality of cotton even varies within locules in a bol, but it is not clear how yield components and quality parameters are altered across seed positions of a locule （SPL）. A ifeld experiment was arranged in a split plot design with transgenic insect resistant Bt （Bacilus thuringiensis） cotton hybrid cultivar CRI75 and conventional cultivar SCRC28 as the main plots, and three plant densities （15000, 51000 and 87000 plants ha–1） as the subplots in 2012 and 2013 at Anyang, Henan Province, China. Cotton was hand harvested by node and fruiting position, and then seeds of the ifrst fruiting posi-tion bols from nodes 6–10 were separated by SPL. The effects of plant density on lint yield, ifber quality, especialy across SPL were determined. It was showed that plant densities of 51000 and 87000 plants ha–1 increased lint yield by 61.3 and 65.3% in 2012 and 17.8 and 15.5% in 2013 relative to low plant density （15000 plants ha–1）, however, no signiifcant differ-ence was observed between 51000 and 87000 plants ha–1. The number of bols （bol density） increased while bol weight decreased as plant density raised, and no signiifcant changes occured in lint percentage in 2013 but increased with plant density in 2012. The number of bols in upper nodes and distal fruiting positions, the number of seeds per bol, seed area （SA） and seed vigor index increased with decreasing plant density. Seed area was found to be greater from the base to the middle compared to the apex of a locule. Mote frequency （MF） increased as plant density increased, and ifber quality was the best at the middle of the locule regardless of plant density. As the number of ifbers per seed area is geneticaly determined, adjusting plant density to produce more seeds and greater seed area can be a potentialy promising alternative to improve lint yield in cotton. These ifndings might be of great importantance to cotton breeding and ifled management.

Relative position of seeds driven the seedling growth are mediated by root-leaf traits

Variations in plant traits are indicative of plant adaptations to forest environments,and studying their relationships with tree growth provides valuable insights into forest regeneration.The spatial arrangement of plant seeds within the forest litter or soil critically infuences the variations of root-leaf traits,thereby affecting the adaptive strategies of emerging seedlings.However,our current understanding of the impacts of individual root-leaf traits on seedling growth in different relative position,and whether these traits together affect growth,remains limited.This study focuses on the dominant tree species,Castanopsis kawakamii,within the Sanming C.kawakamii Nature Reserve of China.The present experiment aimed to examine the variations in root-leaf traits of seedling,focus on the relative positions of seeds within different layers:beneath or above the litter layer,or within the bare soil layer(without litter).Our fndings provided evidence supporting a coordinated relationship between root and leaf traits,wherein leaf traits varied in conjunction with root traits in the relative positions of seeds.Specifcally,we observed that seedlings exhibited higher values for specifc leaf area and average root diameter,while displaying lower root tissue density.The mixed model explained 86.1%of the variation in root-leaf traits,surpassing the variation explained by the relative positions.Furthermore,soil nitrogen acted as a mediator,regulating the relationship between seedling growth and root-leaf traits,specifcally leaf dry matter content and root tissue density.Therefore,future studies should consider artifcially manipulating tree species diversity based on root-leaf traits characteristics to promote forest recovery.