Diversifying crop rotations with temporary grasslands - Université de ...

the leaves (needed for photosynthesis) and buds (needed for regrowth) were destroyed for
species belonging to the latter groups. Moreover, results of the greenhouse experiments
showed that the residual green surface remaining after cutting is correlated to the plants’
regrowth speed (Article 4) and that broadleaved weed species have a higher probability to
survive if the terminal buds are not destroyed (unpublished results).
2) In the greenhouse experiments, post-cutting regrowth was also better for perennial species
compared to annual species. Besides their longer life span, perennial species might also
have more belowground reserves of carbohydrates that may be remobilized for regrowth
after cutting. Differences between these species functional types observed in the largescale
studies (Article 2) are thus probably also caused by the impact of cuttings (and not
only due to the absence of soil tillage).
Results of the greenhouse experiments in 2007 and 2008 also suggested that the regrowth of
weed plants a) increased with plant biomass before cutting (for plants of the same age), b)
decreased with plant age, c) increased with cutting height for broadleaved species, and d)
decreased with the number of previous cuttings (see Articles 4 & 5 and two master thesis of
Henriot (2007) and Bonnot (2008) co-supervised by the present author. The impacts of plant
age and cutting height roughly corresponded to previous studies (El-Shatnawi et al., 1999;
Andreasen et al., 2002), while the two other factors have rarely been investigated (Mager et
al., 2006; Wilson et al., 2007). These observations on the interspecific variation of the
regrowth ability may also be explained by the hypothesis postulating that the plant growth
ability depends on the amount of carbohydrate resources remobilizable from roots and
stubbles to replace the deficit caused by the absence of photosynthesis. An additional
greenhouse experiment (presented in the co-supervised Master-I thesis (Bonnot, 2008) but not
yet published in a journal), comparing the regrowth speed of cut plants with the initial growth
speed of young uncut plants with the same (small) leaf area supported this hypothesis (Wilson
et al., 2007). The observed higher growth speed of cut plants was probably caused by
remobilisation of belowground resources. Moreover, cut plants may also profit from the
bigger rooting system compared to younger uncut plants. Such additional knowledge about the
effects of cuttings as a function of the plants’ regrowth ability may be useful for explaining
and predicting the impacts of hay cuttings on arable weeds (see chapter D.III.2 for more
details).
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