Various source and sink related traits participate in the
response to elevated CO2
Observed trait means and analysis of variance (ANOVA) are presented in
Table S2 (supplemental materials). Figure 3 presents correlation
heatmaps for the observed traits under ambient (A) and elevated (B)
CO2 levels, whereby the CO2 effect onA max and grain yield (trait variation) was
included in both matrices. The A max and grain
yield variation between the two environments were positively correlated
(P<0.01) with each other, and both were negatively correlated
with LSSR as also shown in Fig. 2. They were similarly correlated with
two other calculated, potential, proxy traits for source-sink ratio: the
LSSR(sink) that uses the product of panicle spikelet number and the
genotypic filled-grain weight (instead of just the spikelet number) as
an estimate of the sink; and [LSSR(sink) * SPAD] which factors the
area leaf chlorophyll content into the equation to strengthen the source
term (Table S1). In fact, A max and the electron
transport rate ETR were positively correlated with SPAD
(P<0.01) under ambient but not under elevated
CO2 levels (Fig. 3). The ETR was negatively correlated
with SLA (P<0.05) in both environments. Leaf sucrose
concentration was weakly, positively correlated (P<0.05) with
the tentative proxy traits LSSR, LSSR(sink) and LSSR(sink)*SPAD under
elevated CO2, but not ambient CO2 level.
The spikelet number per panicle was positively correlated with flag leaf
ETR (P<0.05). The SPAD chlorophyll content was generally
negatively correlated with SLA but positively with most of the other
morphological traits such as leaf dimensions, panicle size traits and
total shoot dry matter.