Unravelling knotweed clonal control of soil microbial activities related to the nitrogen cycle through plant growth phases and ramet positions within the patch

Abstract

Background and aims

Knotweeds are known to influence microbial processes. This study aimed to unravel the clonal control of microbial nitrogen cycle activities by established knotweed patches, as function of plant growth phases and ramet positions within the patch, all according to six different soils.

Methods

At six sites, we measured N-microbial activities (free-living nitrogen fixation, nitrification, and denitrification, substrate-induced respiration), soil N mineral forms, moisture and pH across five plant growth phases and at two ramet positions within the patch (centre and front). The sites were categorized as having High, Medium or Low soil functioning based on (a)biotic parameters (nitrification, denitrification, soil moisture, and pH).

Results

The influence of the patch centre on N-microbial activities varied with soil functioning during the plant growth phases. Nitrification and N fixation increased in Low functioning soils but decreased or remained unchanged in High functioning soils. Denitrification remained constant in Low functioning soils but decreased in High functioning soils. In Medium functioning soil, denitrification and N fixation were reduced, whereas nitrification remained unchanged. Significant differences in N cycle control were found between the patch centre and front, depending on the growth phase and soil functioning.

Conclusion

During the growth period (N demand), the patch centre influences N-microbial activities differently, depending on soil functioning, leading to improved N acquisition in soils with strong competition for mineral N (High and Medium functioning soils). Ramets at the patch centre and front control the N cycle differently, with the centre likely facilitating N acquisition and the front promoting colonization.