CAPÍTULO 3 METODOLOGÍA EXPERIMENTAL
3.3 SÍNTESIS DE LOS COMPOSITES POLIPROPILENO/GRAFENO
Plantain and chicory generally displayed similar rates of photosynthesis and
evapotranspiration per unit of leaf area under Optimum and Very-Dry conditions, with
photosynthesis and evapotranspiration rates of both species being lower under Very-Dry
conditions. However, experiments one and two showed plantain consistently had a
greater number of live leaves per plant and a lighter mass per leaf than chicory. This
difference demonstrates that chicory and plantain have different growth strategies with
plantain investing its energy in many smaller leaves while chicory supports fewer larger
leaves. Thus, it could be speculated that plantain may have had a greater leaf area than
chicory and therefore had a higher total rate of photosynthesis per plant. A greater leaf
area could explain its ability to continue to sustain its higher absolute shoot mass and
relative shoot growth rate under both optimal and water stress conditions, when
compared to chicory. Therefore, plantains ability to yield more than chicory under water
stress conditions in the glasshouse could be as a result of morphological factors such as
total leaf area rather than physiological differences between the two species. However,
further research is required to confirm this. Furthermore, plantain tended to have a
greater stomatal conductance than chicory under all conditions. While stomatal
conductance tended to be reduced under Very-Dry conditions for both species compared
to Optimum conditions. Plantain’s greater stomatal conductance would allow it to sustain greater photosynthetic rates when compared to chicory under both optimal and
water stress conditions. However, stomatal closure has been found to reduce water use
per unit foliage cover by 20-30% (Johns 1978), and therefore chicory’s drought strategy may be more sustainable in the long term than that of plantain. Moreover, in chicory,
132 water stress that impacts on photosynthesis, may be more closely linked to non-stomatal
effects, as found by Monti et al. (2005) in witloof chicory.
In experiment two, chicory had a greater leaf water potential than plantain under Very-
Dry conditions on days three and four. In comparison to white clover, Alemseged
(2000) found the leaf water potential of chicory decreased during summer as soil
moisture declined, to a lesser degree, with a low of -1.0 MPa compared to -4.6 MPa.
Osmotic adjustment can be defined as the lowering of osmotic potential due to net
solute accumulation in response to water stress. It is considered to be a beneficial
drought tolerance mechanism in some crop species as it enables the plant to maintain
the physiological plant processes (Turner 1986; Thomas 1987) and delay plant
dehydration (Kramer and Boyer 1995). In experiment two, osmotic adjustment was
observed on Days 4 and 5 in chicory, while in plantain it was only observed on Day 5.
This suggests that plantain and chicory have different growth strategies in response to
moisture stress with chicory responding quicker to the moisture stress, while plantain
maintained its high leaf osmotic potential for longer. The maintenance of a high leaf
osmotic potential has been proposed as vital for short-term plant productivity (Passioura
1982). Therefore, plantain appears to display resistance to moderate drought, by
attempting to maintain yield stability. Conversely, chicory appears to display resistance
to severe drought, by partial avoidance of the stress period through summer quiescence,
resulting in lower herbage yields during water stress periods (Knight 1973). In support
of this, Vandoorne et al. (2012) concluded that witloof chicory displays a good level of
133 a valuable plant adaptation during part of the plant cycle which may enhance long term
persistence and productivity under increasing drought (Lelièvre et al. 2011). A further
adaptive advantage of chicory in the field is its deeper roots, which allow it to access
sub-soil moisture and therefore potentially adjust better than plantain to water deficits in
the soil surface, reducing the rate of decline in relative water content with leaf water
potentials.
4.6 Conclusions
In conclusion, experiment one indicates that plantain performs better than chicory under
simulated drought conditions in the glasshouse. Neither chicory nor plantain respond
well to weekly defoliation (displaying poor shoot and root production) and performed
better under three-weekly defoliation. Experiment two showed that relatively small
differences in leaf water potential and osmotic potential exist between chicory and
plantain, helping to explain why plantain outperforms chicory under drought conditions
in the glasshouse. Experiment three shows in the field chicory has roots deeper in the
soil profile than plantain, which likely explains anecdotal evidence suggesting chicory
outperforms plantain under drought conditions. However, species with different root
systems may be complementary by exploiting different layers of soil. Combined, these
experiments indicate that both chicory and plantain are relatively tolerant of moisture
stress and thus when sown in a Herb and Legume Mix, the sward is likely to perform
well and persist under both a moderate and severe drought. Further experiments need to
assess the performance and sustainability of the Herb and Legume Mix under grazing in
135