Possible effects of climate Possible effects of climate change on crop-weed change on crop-weed

interactionsinteractions

Professor Andreas J. KaramanosProfessor Andreas J. Karamanos

Faculty of Crop ScienceFaculty of Crop Science

Agricultural University of AthensAgricultural University of Athens

Definition of climate changeDefinition of climate change

the long-term change in the average the long-term change in the average weather conditions prevailingweather conditions prevailing in a regionin a region

they are expressed as changes:they are expressed as changes:

-- in the average air temperaturein the average air temperature

- in precipitation- in precipitation

- in winds etc.- in winds etc.

CausesCauses

External External (( changes in solar or cosmic changes in solar or cosmic radiationradiation, , earth’s orbit etc.earth’s orbit etc.))

Human activitiesHuman activities ( (greenhousegreenhouse gases gases))

Greenhouse effectGreenhouse effect

Global warming:Global warming:

- - increase in average air temperature fromincrease in average air temperature from 1 1..5 – 5 – 55..55οοCC between the yearsbetween the years1990-20101990-2010

Parallel impacts:Parallel impacts:

--distortion in the movement of barometric distortion in the movement of barometric systemssystems

- - distortion indistortion in the hydrologic cyclethe hydrologic cycle

- - ice meltingice melting

- - increase in the frequency of extreme incidentsincrease in the frequency of extreme incidents

Climate change aspects affecting Climate change aspects affecting agricultureagriculture

Increase in air temperatureIncrease in air temperature Increase in COIncrease in CO22-concentration-concentration Change in the amount and distributionChange in the amount and distribution of of

precipitationprecipitation Change in evapotranspirationChange in evapotranspiration Increase in the frequency of extreme Increase in the frequency of extreme

weather incidents (droughts, floods etc.)weather incidents (droughts, floods etc.)

Precipitation/evapotranspiration Precipitation/evapotranspiration forecasts in the Mediterraneanforecasts in the Mediterranean

Time-series of rainfall intensity in Time-series of rainfall intensity in AthensAthens

Increase inIncrease in [CO[CO22] and ] and plant physiologyplant physiology

Positive effects on photosynthesisPositive effects on photosynthesis

Increase in [COIncrease in [CO22] and plant physiology] and plant physiology

Decrease in photorespirationDecrease in photorespiration ( (only inonly in CC33-plants-plants))

Increase in net photosynthesisIncrease in net photosynthesis

Namely, increase in overall carbon balanceNamely, increase in overall carbon balance

Increase inIncrease in [CO[CO22] and plant physiology] and plant physiology

Decrease in transpiration byDecrease in transpiration by 25-50% ( 25-50% (partial partial stomatal closurestomatal closure))

Increase inIncrease in water use efficiency (WUE, g of dry water use efficiency (WUE, g of dry matter / g of transpired water)matter / g of transpired water)

ElevatedElevated [CO[CO22] and] and WUEWUE

Increase in temperature and plant Increase in temperature and plant physiologyphysiology

Acceleration of most physiological processesAcceleration of most physiological processes

Increase in temperature and plant Increase in temperature and plant physiologyphysiology

Increase in respiratory dry matter consumptionIncrease in respiratory dry matter consumption

Increase in temperature and plant traitsIncrease in temperature and plant traits

Decrease in average grain weightDecrease in average grain weight of temperate of temperate cropscrops

Increase in temperature and plant traitsIncrease in temperature and plant traits

Increase in growth rateIncrease in growth rate

Effects of temperature on phenologyEffects of temperature on phenology

Increase in temperature and plant traitsIncrease in temperature and plant traits

Vernalization in temperate cropsVernalization in temperate crops

Combined temperature and [COCombined temperature and [CO22]-effects on ]-effects on

photosynthesisphotosynthesis

Combined temperature andCombined temperature and [CO[CO22] - effects] - effects

Water shortage effectsWater shortage effects

Less intense under higher [COLess intense under higher [CO22] ]

Evident on all physiological processesEvident on all physiological processes Different degrees of sensitivity among Different degrees of sensitivity among

physiological processesphysiological processes Plant differentiation according to their Plant differentiation according to their

adaptability to droughtadaptability to drought

Reasons for change in the weed / crop Reasons for change in the weed / crop competition patternscompetition patterns

Differential effects of [CODifferential effects of [CO22] on C] on C3 3 and Cand C4 4

plants:plants: more beneficial to Cmore beneficial to C3 3 plantsplants

- - 14 of the 18 “worlds worst weeds” are C14 of the 18 “worlds worst weeds” are C4 4 plantsplants

- - 12 of the 15 major crops are C12 of the 15 major crops are C33 plants plants

perennial weeds more difficult to control perennial weeds more difficult to control due to the stimulation of growth of rhizomes due to the stimulation of growth of rhizomes and storage organsand storage organs

Ranges of increase in biomass of CRanges of increase in biomass of C3 3 and Cand C4 4

weeds and crops grown under weeds and crops grown under doubled [COdoubled [CO22] (Patterson, 1995)] (Patterson, 1995)

C-assimilationpathway

Weeds Crops

CC33 95 – 272 % 107 – 494 %

CC44 56 – 161 % 98 – 182 %

Reasons for change in the weed / crop Reasons for change in the weed / crop competition patternscompetition patterns

Differential effects of temperature increase Differential effects of temperature increase (2 to 5(2 to 5ooC) on weeds and crops:C) on weeds and crops:

- expansion of warm season weeds to higher - expansion of warm season weeds to higher latitudes and cooler areas (e.g. latitudes and cooler areas (e.g. Cassia, Cassia, Amaranthus, Sesbania, Crotalaria, Rottboellia, Amaranthus, Sesbania, Crotalaria, Rottboellia, Imperata, Panicum, Striga, etc.Imperata, Panicum, Striga, etc.))

- - competitive advantage (higher growth rates) competitive advantage (higher growth rates) of warm season weedsof warm season weeds against temperate crops against temperate crops

Reasons for change in the weed / crop Reasons for change in the weed / crop competition patternscompetition patterns

Differential effects of water availability to Differential effects of water availability to crops and weeds:crops and weeds:

- less severe water stress-effects in raised - less severe water stress-effects in raised [CO[CO22] levels (reduction in transpiration, ] levels (reduction in transpiration,

development of osmotic adjustment, higher root / development of osmotic adjustment, higher root / shoot ratio)shoot ratio)

- they depend on the drought resistance - they depend on the drought resistance mechanisms to be developed by crops and mechanisms to be developed by crops and weedsweeds

Interventions on weed control Interventions on weed control

Choice of the appropriate crop species/cultivarChoice of the appropriate crop species/cultivar Adjustment of planting time/seasonAdjustment of planting time/season Possible effects of the elevated [COPossible effects of the elevated [CO22], ],

temperature, and water availability on chemical temperature, and water availability on chemical efficacyefficacy

Adjustment of the irrigation/fertilization schemesAdjustment of the irrigation/fertilization schemes

ConclusionsConclusions

The increase in [COThe increase in [CO22] and temperature will affect the ] and temperature will affect the

weed-crop competitive interactions. Water availability weed-crop competitive interactions. Water availability might be a less decisive factor.might be a less decisive factor.

The effects on crop production will depend on:The effects on crop production will depend on:

- the local weed flora- the local weed flora

- the C-assimilation pathway and the temperature - the C-assimilation pathway and the temperature requirements of the crop and weed speciesrequirements of the crop and weed species

The interacting effects of many factors influence The interacting effects of many factors influence weed/crop competition in a complex way and make an weed/crop competition in a complex way and make an overall prediction on the consequences on crop overall prediction on the consequences on crop production risky.production risky.

Thank you for your attentionThank you for your attention