144 J.E. FAUST, J.M. DOLE, AND R.G. LOPEZ
but rooting could be improved if the stock plants were grown with
1200 ppm CO 2 prior to harvest.
Endogenous carbohydrate levels can be affected by the time of day
when the cuttings are harvested. Lantana cuttings harvested in the
morning (0800 HR) had the lowest amounts of starch and sugars (glu-
cose, fructose, and sucrose) (Rapaka et al. 2007b). Sugar levels increased
greatly at noon (1200 HR), but by the late afternoon (1600 HR) levels
decreased almost to the same levels as in the morning. Starch levels
increased at noon and again in the afternoon. Starch levels in portu-
laca cuttings followed a similar pattern as for lantana; however, sugars
levels in the leaves increased with later harvests or stayed relatively the
same in the stem (Rapaka et al. 2007a). The higher carbohydrate levels of
afternoon-harvested lantana and portulaca cuttings greatly decreased in
leaf abscission after dark storage of cuttings. For portulaca and lantana,
leaf abscission was negatively correlated with total non-structural car-
bohydrates (starch and sugars), but not with ethylene levels. In another
experiment with geranium, Rapaka et al. (2008) lengthened the pre-
harvest dark period by covering stock plants with black cloth for the
entire day before harvest, resulting in reduced starch and sugar levels in
the cuttings, decreased rooting, and greatly increased leaf senescence.
Leaf senescence was negatively correlated with sucrose, total sugars,
starch, and total non-structural carbohydrates. The connection between
rooting and carbohydrate levels, however, is dependent on total lev-
els within the cuttings, as correlations were evident during the winter
under low-light levels (82μmol⋅m−^2 ⋅s−^1 ), but not evident during the
spring or summer under high light (300 or 359μmol⋅m−^2 ⋅s−^1 ), and sub-
sequently, higher carbohydrate levels (Rapaka et al. 2005).
It should be noted that carbohydrate levels in cuttings can also be
affected, at least in geranium and chrysanthemum, by nitrogen concen-
tration and form delivered to the stock plants in the fertilizer solution
(Roeber and Reuther 1982; Druege et al. 2000, 2004). Increasing nitro-
gen supply generally resulted in substantially lower starch levels, but
higher sucrose concentrations in leaves of cuttings at the time of har-
vest for poinsettia and geranium (Druege et al. 2000, 2004; Zerche and
Druege 2009). High nitrogen levels in the cuttings also reduced carbohy-
drate levels in chrysanthemum and poinsettia. Low carbohydrate lev-
els in cutting tissue limit root development in geranium, but less so in
chrysanthemum and poinsettia, both of which are more responsive to
high nitrogen level in the cuttings. Interestingly, in one study rooting
was positively correlated with cutting total nitrogen concentration and
negatively correlated with total and individual soluble carbohydrates in
mum cuttings (Druege et al. 1998). The authors attributed the disparity