Heatherington extra reading Flashcards
sharp et al 1988
grew Maize seedlings at different water potentials and measured spatial distribution of growth at various water potentials by marking growth of roots on plexiglass.
shoot growth inhibited but roots insensitive to low water pot. insensitive at root apex, sens increases away from apex. Roots thinner and less radial growth.
Beardsell and Cohen 1975
Drought recovery cycles of maize and sorghum
Initially for 1-2h no change in ABA levels and then rise, and stomata close.
Differences in recovery, Sorghum only 24h to return to normal ABA levels, whereas maize took 72h. Lag before rise in ABA suggestion that ABA nor directly affecting stomatal closure.
Pantin et al 2013
stomata of the youngest leaves are insensitive to ABA and wide open, high RH
Stomatal density and aperture of older leaves is reduced by ABA with an increasing effect as the leaf develops. Lower RH.
test using exogeneous ABA spray, ontogenetic ABA sensitivity restored in ABA biosynthesis mutants.
Tested using mutants - no sig effect of cuticular waxes (cer-1 mutant and cerOE) on transpiration rate, or trichomes (Col-5 mutant)
Tardeiu 2016
must be any components in root to shoot communication eg Strigalactone might be important.
ABA too short half life. Grafts of aba deficient scions on WT roottstock show ABA insufficient as chemical message.
however: Christmann et al – signal is exclusively hydraulic
Long et al 2006
FACE exp show 50% less yield increase than in lab studies.
C4 - rubisco already sat so no further incresase in rising CO2
Chamber grown pots in lab not representative as: 75% full sunlight, warmer, water vapour pressure deficit 0.8 kPa higher. Altered air flow and intercept rainfall. Pests and disease restricted
mini FACE prelim trials, 1m diameter.
found plant production stops increasing at 800-2000ppm.
no increase yield for grasses seen.
Myers et al 2014
• Metaanalysis of 143 comparisons of the edible portions of crops grown at ambient and elevated [CO2] from seven different FACE experimental locations in Japan, Australia and the United States involving six food crops.
2 billion people suffer Fe and Zn deficiency, usually rely on grains. grains and legumes lower nutrient conc at high CO2.
selective breeding could help.
found higher concs of Fe and Zn in lab but not in FACE.
plant phytate - inhibits absorption of zinc in gut. decreased at elevated CO2 only in wheat. however, phytate decrease is less than half zinc decrease so not useful.
Zinc concs differ from other mineral changes so not dilution occurring alone.
McGrath and Lobell 2013
Meta-analysis to disprove fertilization effect.
lower protein and mineral conc at elevated CO2.
• Due to dilution by enhanced production of carbohydrates, 1) reduced canopy transpiration reduces mass flow of nutrients to roots, evidence: Nutrients acquired through mass flow sig reduced more than those acquired through diffusion through roots
2) changes in enzyme concs caused by physiological changes, alter requirements for minerals, shifting allocation btw tissues and altering uptake. evidence: Mg large conc decline in leaves and wheat stems, smaller decrease in other tissues.
Why dont legumes show same decrease in nutrients as other crops?
• Legumes don’t show same decrease in nutrients at high CO2 levels. Non-legumes N content decreases 10-14%, and Soybean only 1.5%.
Gray et al 2016
8 year study to disprove fert effect
stimulation of soybean yield due to increasing CO2 diminished to 0 as drought intensified.
rainfall exclusion experiments. Reduced or control rain, and Elevated or control CO2.
interaction with weather (greater canopy temp) and indirect effects of elevated CO2 on plant water use results in lower soil water during hot and dry years. Caused greater stom closure due to dry soil, and eliminated uptake of C required for greater carbon assimilation
Licausi et al
N end rule pathway RAP2.12
first mechanism for oxygen sensing mechanism described in plants.
RAP2.12 is ERF with conserved N terminal AA sequence.
Oxygen dep sequence of post translational modifications eventually degrades RAP2.12 in aerobic cond.
Hypoxia - accumulates in nucleus, activated gene expression for hypoxia response.
Experimentally manipulated N terminal with HA tag and by deleting 13 AA- reduced plant growth in air and in submergence.
35S::RAP2.12- Hypoxia marker genes strongly increased in flooding and slightly increased in aerobic conditions, this shows additional reg mechanism needed to sense low O2 conc for hypoxic gene exp.
Both upregulation of the hypoxia response genes during flooding AND down regulation during recovery are very important.
RAP2.12 localisation using RAP2.12::GFP - aerobic - localised around membrane, hypoxia - in nucleus.
Corlett et al - forest drought
forest fragmentation sig increases dry season dessication of canopies.
Deforestation = hotter drier regional climates due to reduced evapotranspiration.
large long lived trees at most risk - these have big ecological impact.
sub lethal drought - often shed leaves, reduced diameter growth rates
Throughfall experiments - divert 30-70% rainfall
Deciduousness common adaptation to drought, more common in canopy tha sub canopy - difficulty in maintaining water supply up high.
Coniferous trees keep leaves but close stom - risk depleting carb supply.
Stom remail open - greater risk of embolisms and reduce water connectivity.
Hydraulic segmentation in severe drought.
How have Corlett et al suggested to minimise impact of drought?
early detection of developing droughts, continuous monitoring of impacts as they develop. Integrate a variety of passive and active satellite sensors in real time, combined with enforcement and fire-fighting, and penalties for starting fires in droughts.
Once a drought has started, priority is preventing spread of fires.
Better logging management to retain large forest blocks rather than fragmentation.
