Diversifying crop rotations with temporary grasslands - Université de ...
Diversifying crop rotations with temporary grasslands - Université de ...
Diversifying crop rotations with temporary grasslands - Université de ...
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C.II.4.3 Un<strong>de</strong>rlying mechanisms<br />
Decreasing weed population dynamics in PFCs may be quite astonishing, given the complete<br />
absence of herbici<strong>de</strong>s and soil tillage and the sowing of 17 weed species at the beginning of<br />
the experiment. Other mechanisms must thus be responsible for these reductions.<br />
Annual and perennial <strong>crop</strong>s differ in several aspects that may affect the growth of weeds (cf.<br />
Table 4 in the general introduction). Thanks to the rather complex study <strong>de</strong>sign comparing<br />
nine <strong>crop</strong> treatments and the high temporal resolution of weed <strong>de</strong>nsity and biomass<br />
observations, this experimental study allows to learn more about several of the mechanisms<br />
potentially un<strong>de</strong>rlying the impacts of PFCs on weeds. This has, to our knowledge, rarely been<br />
investigated previously. In the following three paragraphs (C.II.4.3.1-3), I will discuss three<br />
main factors governing the impacts of PFCs on arable weeds: the absence of soil tillage (A),<br />
the strong and temporally exten<strong>de</strong>d competition (B), and the frequent hay cuttings (C). Table<br />
12 gives an overview how these factors varied <strong>with</strong> the experimental treatments. Our results<br />
suggest that these three factors affected several important parts of the weed life cycle (Fig.<br />
20). These impacts are also summarized in Table 13.<br />
†<br />
(3)<br />
vegetative<br />
growth<br />
Seedlings<br />
Emergence<br />
(2)<br />
†<br />
(1)<br />
Initial<br />
growth<br />
Germination<br />
Seed aging, <strong>de</strong>cay<br />
Post-dispersal seed predation<br />
†<br />
Survival of<br />
perennials<br />
(7)<br />
†<br />
Vegetative<br />
plants<br />
(7)<br />
(4)<br />
Survival in<br />
the seed bank<br />
Seeds<br />
Fig. 20: Life cycle of annual and perennial weeds.<br />
Grey boxes, four stages; arrows, transitions between stages; †, mortality. The thickness of the arrows corresponds<br />
to approximate <strong>de</strong>nsities of individuals (varies between species and populations). The survival of established<br />
plants (4) will be more important for perennial species, seed rain and the survival of seeds in the seed bank will<br />
be more important for annual species. The numbers (1-6) corresponds to the weed life stages in Table 13 showing<br />
the possible impacts of PFCs.<br />
99<br />
(4)<br />
Flowering<br />
Immigration<br />
Emigration<br />
(5)<br />
Pollen<br />
Reproducing<br />
plants<br />
Seed<br />
rain<br />
(6)<br />
†<br />
†<br />
Pre-dispersal<br />
seed predation<br />
(4)