Evaluating the growth perfromance of Centaurea stoebe ssp. micranthos (Asteraceae) in different substrates

Background/Question/Methods

Centaurea stoebe ssp. micranthosis increasingly recognized as an aggressive invasive species in eastern North America as well as out west. The purpose of this experiment was to observe and test the growing patterns of Centaurea stoebe when placed in different substrates. C. stoebe is commonly found in dry sandy soils that have lower nutrient levels. One characteristic of invasive species is that they are often capable of surviving harsh conditions.  Seedling and young Centaurea have been seen to quickly establish relatively long taproots, which may be a general trait of good invaders in dry, nutrient poor habitats. Field census data and greenhouse experiments were carried out to investigate the invasive potential of C. stoebe across a range of soil substrate types in a recently restored habitat in central Virginia. Field observations and census data indicated C. stoebe grew more frequently in dry, sandier soils. Greenhouse experiments were set up to reflect the range growing conditions found in the field: three sold types of increasingly sandy composition were tested for early seedling establishment. Accessions were made from field sites of invasive plants which were transferred initially to growth chambers and to 3 treatments of increasingly sandy-soil pots in the greenhouse.

Results/Conclusions

At the end of the growing period, the plants were dried and weighed. Sandy soil plants had roots that were 63% larger than the medium sand treatment and 79% larger than the low sand. Conversely, above ground growth was lower in the sandy soil, possibly more constrained by nutrient availability. Sandy soil produced plants with 59% to 61% less above ground growth than the less sandy treatments. Statistical significance was high to very high for pairwise comparisons of the sandy soil to other treatments. Plants in sandier soil may use more of their nutrients and energy to grow larger root systems. Notably, mortality rates were lowest in the sandiest soil, below 3%. In the least sandy soil there was 18% mortality and in the medium treatment mortality was above 65%. It appeared that some sort of fungus or mold infected the half and half mixture. Although the plants were not karyotyped, previous studies in the west suggest that the plants are tetraploid. Previous work has established the greater root growth of the tetraploid cytolyses in comparison to diploid plants. Greater root growth is linked to more successful establishment, especially in dry soils, and is a likely characteristic associated with invasiveness.