SummarySpecies diversity and abundance in weed seedbanks were measured at the beginning, and after 3 and 6 yr of the TALISMAN experiment at ADAS Boxworth, Drayton and High Mowthorpe. Fifty species were distinguished in the seedbanks of treatments comprising winter and spring rotations and full and reduced herbicide input. After 6 yr, the number of seedbank species in the main treatments ranged from 11 in the most intense to 26 in the least intense management. Principal co‐ordinate analysis showed that the seedbank community diverged over time between sites and additionally between the two rotation treatments at Boxworth. Only four species were common to all sites but community‐scale descriptors indicated that the change in seedbanks following reduced inputs had common features at the three sites. First, species‐area relations showed a greater relative increase in number of taxa at a plot scale than in the site as a whole, indicating lower inputs encouraged the common weeds more than rare species. Second, both the mean and the standard deviation of the species‐abundance distribution at 6 yr increased in response to reduced inputs. As a result, the number of species slightly more than doubled as herbicide units were reduced from four to one while the total number of seeds increased by two orders of magnitude. Some causes of seedbank change were identified: spring‐germinating species tended to increase when spring cultivation was common in the rotation, while some competitive weeds had a relatively low abundance when they were targeted by herbicide. The results are discussed in relation to optimising the various functions of the seedbank.

No abstract

We investigated the influence of root border cells on the colonisation of seedling Zea mays roots by Pseudomonas fluorescens SBW25 in sandy loam soil packed at two dry bulk densities. Numbers of colony forming units (CFU) were counted on sequential sections of root for intact and decapped inoculated roots grown in loose (1.0 mg m(-3)) and compacted (1.3 mg m(-3)) soil. After two days of root growth, the numbers of P. fluorescens (CFU cm(-1)) were highest on the section of root just below the seed with progressively fewer bacteria near the tip, irrespective of density. The decapped roots had significantly more colonies of P. fluorescens at the tip compared with the intact roots: approximately 100-fold more in the loose and 30-fold more in the compact soil. In addition, confocal images of the root tips grown in agar showed that P. fluorescens could only be detected on the tips of the decapped roots. These results indicated that border cells, and their associated mucilage, prevented complete colonization of the root tip by the biocontrol agent P. fluorescens, possibly by acting as a disposable surface or sheath around the cap.

Soil organisms in direct and indirect interaction with plant roots affect aboveground herbivores, likely by inducing different plant responses. We investigated the combined effects of the root-knot nematode Meloidogyne incognita (in direct interaction with roots) and the endogeic earthworm Octolasion tyrtaeum (in indirect interaction with roots) on the performance of Brassica oleracea. Both earthworms and nematodes increased N uptake and shoot biomass of B. oleracea. Earthworm activity mobilized more soil N than litter N, and herbivory by nematodes tended to increase the microbial biomass in soil. Only the structural class of sulphur containing glucosinolates was affected by the soil organisms. Earthworms decreased glucoiberin concentrations in B. oleracea shoots. Glucoraphanin was affected by an interaction between earthworms and nematodes.

The root-knot nematode Meloidogyne incognita is a major pathogen of a range of important crops. Currently, control is typically achieved by the use of nematicides. However, recent work suggests that manipulating the ability of roots to slough off border cells, which then act as a decoy to the nematode, can significantly decrease damage to the roots. We investigated the attractiveness of border cells to M. incognita and the response of the nematode to border cells in close proximity. We found very limited attraction, in that nematodes did not preferentially alter direction to move toward the border cells, but a large and significant increase in nematode speed was observed once they were in the immediate vicinity of border cells. We discuss the results in the context of physical and biological mechanisms in relation to the control of pathogenic nematodes.