Population dynamics and nitrogen allocation of Sonchus arvensis L. in relation to initial root size.

To develop better mechanical management strategies, more information on the impact of root partitioning on changes in the population dynamics ofSonchus arvensisis needed. Therefore, the effects of root fragmentation ofS. arvensison shoot height frequency distributions, biomass production and nitrogen allocation were studied in an outdoor experiment in Sweden in 2008. Three artificial populations ofS. arvensisof different initial root lengths but with the same total root length per area were planted. Shoot heights were measured at the onset of flowering and dry weight and nitrogen content of leaves, stems, buds and roots were quantified twice during the season. Height frequency distributions of the populations were bimodal, indicating the existence of two generations distinctly different in height growth pattern. Shorter root fragments produced shoots with a lower mean height compared to longer fragments. Plants originating from longer root fragments had higher dry weight and more nitrogen compared to plants from shorter root fragments. Dry matter production per square meter did not differ between the populations. The proportion of dry matter and nitrogen allocated to the different plant components (leaves, stems, buds and roots) at harvest did not differ between the populations. Over time, nitrogen was reallocated from leaves and stems to roots. Our results show that initial root length ofS. arvensisper square meter, rather than the number of root fragments per square meter, is a good predictor of biomass at harvest, and that the degree of root fragmentation does not affect nitrogen allocation patterns. Root fragmentation, however, leads to a lower average canopy height forS. arvensis, and thus may be an effective weed control measure in combination with a crop which is competitive for light. [ABSTRACT FROM AUTHOR]