3.1 Plasticity of life history traits in response to
elevated temperature and its correspondence with plasmotype diversity
We wished to examine the effects of plasmotype diversity on barley
fitness including growth and productivity while growing under ambient
vs. high temperatures and to examine the possible relationship between
photosynthetic rhythm and growth plasticity. Previously, we described
the generation and clock analysis of the ASHER doubled haploid
population divided between carriers of the B1K-09-07 and B1K-50-04
plasmotypes. For the current study, we also developed a set of crosses
between 11 wild barley accessions to achieve reciprocal hybrids lines
(RHL) with few genotypes missing to achieve full half-diallel (see
Methods).
In ASHER, under both HT and AT, carriers of the Hermon plasmotype
flowered significantly earlier than the Ashkelon types. However, in both
subpopulations, this manifested in the same thermal acceleration of
flowering by more than two days (Figure 1a ; TableS2a ). The reproductive traits were higher under AT vs. HT
conditions (avg spike dry weight (ASDW) =0.89 ±0.13 vs. 0.7 ±0.12 gr and
Spikes dry weight (SpDW) =7.8 ±1.9 vs. 6.24 ±1.7 gr, respectively).
Plant height (PH) at harvest was also higher under AT (124.9 ±8.5 cm)
than under HT (108.1 ±7.8 cm), although vegetative dry weight (VDW) was
lower under AT, i.e., 13.1 ±3.5 gr vs. 14.4 ±4.7 gr in HT (FigureS4a ). For SL, there was no significant difference between
sub-populations (Figure 1b ). However, for the SLCV, Hermon
plasmotype was linked to lower stability (Fridman 2015), i.e., higher CV
under HT (14.45% under HT vs. 8.8% under AT) as compared to Ashkelon
(12.33% under HT vs. 9.32% under AT) (Fig. 1c ). One
interesting comparison is between the total vegetative and reproductive
outputs. The carriers of the Ashkelon plasmotype are, on average, very
plastic for the plant biomass and the derived total dry matter (Figure1d, e ). In contrast, the Hermon plasmotype carriers are
relatively stable for the biomass yet respond significantly to the heat
with significant reduction of the SpDW (Figure 1e, f ). This is
in comparison to the relative stable SpDW of the Ashkelon types (Figure1f ).
Unlike in the ASHER’s case, in the RHL, DTF was almost identical between
HT and AT (DTF=-109.9 ±5.6 and 111.73 ±4.97 days, respectively) (FigureS4b ). Similarly, unlike the significant effects of the thermal
environment on the vegetative traits, the reproductive traits were less
affected; ASDW is significantly yet mildly lower under AT (0.93 ±0.24
gr) than under HT (1.03 ±0.27 gr). For SpDW, there was not a significant
difference between environments (7.13 ±2.2 and 7.35 ±3.16 gr,
respectively). PH was also not significantly different between
environments (104.06 ±10.17 cm in AT and 104.04 ±12.05 cm in HT), as
compared to VDW and TDM that were significantly lower under AT (11.29 ±4
and 18.5 ±5.5 gr) than HT (16.38 ±6.8 and 24.13 ±9.08 gr). SL and SLCV
are significantly lower under AT condition (Figure S4b ; TableS2b ). The reciprocal nature of the hybrids allowed us to group
the F1 genotypes into different plasmotype subpopulations and different
male parent subpopulations (representing the nucleotype). One-way ANOVA
for each of these two divisions of the hybrids indicated a larger
percentage variation explained (PVE) by the nucleotype (male donors) in
comparison to differences between plasmotype (female donors) for a few
traits (Table 1 ). For example, for the ASDW under HT the
nucleotype factor explained 41% of trait variation (PVE=41%) vs.
PVE=27% by the plasmotype. For most life history traits, however, we
found higher variation explained by the plasmotype than by the
nucleotype under both temperatures (AT and HT): for PH, PVE=39% vs.
30% and 33% vs. 21% under AT and HT, respectively. Higher variation
explained by the plasmotype than nucleotype was true also for
reproductive output, e.g., SpDW, which showed higher variance between
plasmotypes under AT (PVE=35% vs. 21%) and to a lesser extent under HT
(PVE=23% vs. 19% between plasmotype and nucleotype contributions).
To summarize, plants in both field experiments of the two populations
accumulated more VDW on average at higher temperatures and showed lower
stability between spikes, i.e., higher VDW and SLCV. The nature of the
ASHER population allowed us to relate the positive correlation between
increased biomass plasticity and stabilizing of the reproductive output
with plasmotype diversity.