• TOPIC: CONCEPTS OF SOURCE AND SINK –TRANSLOCATION OF PHOTOSYNTHATES AND FACTORS INFLUENCING TRANSPORT OF SUCROSE AND CONCEPTS OF CROP GROWTH MODELING- DIFFERENT MODELS – ADVANTAGES AND DISADVANTAGES OF CROP GROWTH MODELS- MODELS FOR TESTING YIELD PREDICTION.

PRESENTED BY : ZUBY GOHAR ANSARI TAM/2014/026

CONCEPTS OF SOURCE AND SINK –TRANSLOCATION OF PHOTOSYNTHATES AND FACTORS INFLUENCING TRANSPORT

OF SUCROSE

• Introduction: Source is an organ which synthesis the food material. In general we consider a mature leaf as source. An organ which stores the photosynthesis is called a sink. In plant 92.94% dry matter comes from photosynthesis and 6 to 8% comes from mineral matter. Photosynthates generally moves in the form of sucrose from source to sink. This source is used for growth and development . Photosynthates stored as starch or sent for growth purpose in the shape of sucrose, depends upon the source – sink relationship.

HOW TO DIFFERENTIATE SOURCE AND SINK

• There are 3 criteria to differentiate source from sink• 1. Morphology : Seeds, fruits, roots, tubers, are generally

considered as sinks. Mature leaf is considered as source.• 2.Direction of transport: Source is a plant part which

exports the photosynthates sink imports the assimilates.• Contrast: Leaf at young stage is a sink till it gets 75% of its

total expansion it will not become source. A fully expanded mature leaf is a source. A senescing leaf is also treated as a source because the stored food material from it will be exported back to growing points.

• Seed: A germinating seed is generally considered as source as it supplies food material for radical elongation.

• However, a growing seed on a ear head is treated as a sink.

• 3. Metabolism: Source is an organ which capable of synthesizing photosynthates to satisfy its demand as well as to supply the extra food material to other growing points.

• Sink is an organism which utilizes these photo assimilates for growth or stage.

TYPES OF SINK• 1.Primary sink: Economically useful parts• Seeds- rice , timber- forest crops, fruits-

mango , leaves-green, stem-sugarcane• Primary sinks are those which are of prime

importance to man.• 2.Secondary sink: Rhizomes, tubers, corns.• In a plant tubers are produced as storage organs. This

plant might also produce seeds. These storage organs are produced much earlier to the reproductive organs(seeds ultimately) development.

• Sec. sinks are also useful for vegetative reproduction.

• 3.Alternate sinks: Fiber, lint or stem in perennial plants are called as alternate sinks.

• Eg. Sun hemp, flax-fiber• Cotton-lint• Dry weight of these alternate sinks develops after the

reproductive growth.• In cotton lint is formed after the seed development.• 4.Additional sinks: Rhizobium nodules, galls, parasitic

weeds, symbiosis or parasitism.• 5.Metabolic sinks: Stem tips, root tips where

photosynthesis are used for active growth and development.• Finally the classification of source or sink is highly dynamic in

nature in nature which changes with time, plant age, organ age etc.

• Some organs act as both source & sink• Green pods of beans, okra etc., which are capable of

photosynthesizing and also draws resources as sink (to a greater extent they are sinks).

• Measures of sink• Sinks are measured in terms of carbohydrates, oils,

and proteins etc. largely based on the biological energy units they produce. In general sinks are measured in terms of number(coconut), (in this case weight is not important but number is important), volume(timber), weight(agricultural crops).

• Weight is the most dependable measure of sink size is expressed as

• SINK SIZE=SINK CAPACITY*SINK ACTIVITY• Sink capacity: It is the max. space available for the

accumulation of photosynthetic products.• In grain crops it is expressed as number and size of

grains.• Eg: no. of panicles/plant *avg. no. of spikelets per

panicle*specific grain weight• Sink Activity: It is the inherent capacity of sink to

create a translocation gradient for photosynthates assimilated at source.

• Always the photosynthates translocated in the form of sucrose from leaves to grains where it gets converted to starch. The rate of conversion influences the rate of translocation.

• If rate of conversion of sucrose to starch is more • ↓• Translocation gradient will be more.• ↓• Higher will be the rate of translocation• Measures of source: source is generally measured

in the terms of Cm square/ plant i.e. on area basis eg: LAI

• SOURCE STRENGTH=SOURCE SIZE * SOURCE ACTIVITY

• =Leaf area/plant*Average photosynthetic rate per unit area

• Eg: LAI*NAR

• The source size and activity is highly dynamic or sensitive to cultural, nutritional and climatic factors.

• Source: Region which export the assimilates • Eg. Expanded green leaves• Two types of assimilates are:• 1.Current assimilates: They are translocated and

linked to photosynthesis Eg. Sugars produced through carbon fixation- these assimilate contribute for maximum phytomass. These are carried out by expanded leaves.

• 2.Accumulated assimilate: Mainly as stored food material to serve as some for seedling growths. These accumulated assimilates are from plant parts.

• Eg. Endosperm of germinating seeds, cotyledons, Sugarcane sets.

• SINK: Region which imports the assimilates Eg. Growing points of roots, shoots, storage organs( pods, rhizomes, tubers, seeds and fruits)

• There is a relationship between source & sink• A. In cereals reproductive organs initially serve as sink

and later when seeds formed serve as source for accumulated assimilates.

• B. This relationship was given by Mason and Mask well (1928 working as cucurbitacae fruit serve as sink while leaf serves as source.

• C. In Maize husk contributes enormously for grain filling.

• D. Flag leaf will serve as source in cereals to about 50% for grain development. Rest of the organs like glumes and other organs serve for the rest 50%.

• Metabolic sink: The utilization of assimilates during respirations give rise to energy to plants and in turn produce the growth.

• Carbohydrates metabolism: Utilized in respiration- in turn give rise to energy-and finally growth of the plants.

• Beevers (1969) done extensive work on metabolic sinks.

• Warren and Wilson(1967) mentioned that

• Source strength (capacity) formed by 2 components

• =source size* source activity• The size means how much assimilates are

available for export. Activity means rate of photosynthesis source size Eg. Expanded area i.e. leaf area and no. of leaves

• Source activity : P.S. rate mg CO2 dm per square per hour or NAR (ULR)

• Sink strength (capacity):Sink Size*Sink Activity

SINK SIZE SINK ACTIVITIESNo. of Rep. structures No. of growing pointsWt. of flowersGrowing leafShoot and root tips

Growth rate of sink i.e. RGR of Growing points viz Shoot apex,Root apex or Rep. structuresLike flower buds and flowers

• This relationship can be used for single plant or for a crop depending upon the objective of study.

• Yield constraints or limitations may be due to source limitation or sink limitation or both.

• Source size limitation: Suppose source size is limiting due to defoliation(decrease in LAI) caused by certain environmental factors or due to diseases or sucking insects i.e. any factor that limits the leaf area development affects the source size.

• Similarly source activity refers to NAR which is limited due to

• 1. Certain environmental factors like light intensity. If light intensity is not sufficient then source activity in decreased.

• 2. Mutual shading of leaves with in the crop.• 3. Intercropping due to different crops. Above three

considerably affects the source activity.• Sink Limitation: It is due to• A. Floret sterility ( cereals)• B. Insect damage• C. Flower drop due to many factors• Possible reasons for flower drops:• 1. Limitation of P.synthesis.• 2. Limitation of N availability.• 3.Reduced light intensity in plant canopies.• 4. Canopy temperature

• 5. Hormonal factors• 6. Gas exchange in canopies• 7. Humidity in canopies• 8. Soil & water factors• 9. Water logging• 10. Shading and salinity• Sink activity is limited due to unfavorable environmental

conditions ( High temperature in wheat, low temperature in monsoon season)

• Source Size Manipulation: These can be experimentally accounted for source limitation . If it occurs during rep. stage it will be crucial and affect yield. one can know its effect by reducing source size by way of defoliation ( 25%, 50%, 75%, 100% & 0%)at reproductive stage (50% flowering ) as was done in sorghum.

• In Maize by cutting the leaf size to 25%, 50%, 75% of leaf to adjust source size and see the effect on yields components in cereals and in legumes( G.nut).

• Instances where hormonal treatment prevent flower drop and increase in yield one may explain in such genotypes that the extra source was utilized by the increased sink size.

• The source activity can be manipulated by reducing light intensity (shading of crops)with muslin cloth with different layers to have different degree of shading. The light intensity can be measured under different degree of shades. Light intensity without shade is taken as full light (Zero shade, 75% shade, 50% shade, & 25% shade).

• Sink manipulation: Major sink is reproductive parts. It does not mean that it is the only sink but the vegetative meristems (apical shoots) and root meristems etc., whose sink is stronger in requirement of , assimilates.

• Size of reproductive sink: Size of inflorescence (cereals), No. of pods & capsules (dicots), weight of tubers (potato) form the sink size. If the inflorescence is reduced by half or one fourth or any %, the sink size can be manipulated. In case of number, reduced the number by removing flowers by 25%or any %. Then study the export of Photosynthates to the sink, since the sink size is reduced, the photosynthates may be diverted to other plant parts.

• Seed size in cut ear head is big as compared to in normal ear head. Sometimes the assimilates accumulates in source itself causing leaf wt. to increase. Once the process of accumulation of assimilates takes place in leaves, starch content increases and finally the P.S. rate goes down.

• Sink Activity : RGR of sink should have the capacity to store materials transported to it under natural conditions.

• Temp stress-At extreme the RGR is less. • Light- It is important for reproductive structures.• Sink capacity can be manipulated by growth retardants.

Sink act as source. Reproductive structures can be covered (shading) and light intensity is reduced to reduce sink activity

• The translocation of assimilates mainly sucrose transported through phloem sieve tubes to the sink.

• Excess Source →Translocations →Sink (Increase in sink size).

• If excess assimilates does not increase the sink size the reasons may be

• 1. Physical construction in the phloem vessel.• 2.The phloem loading may be more at source side

due to fewer diameters at the delivery and receiving point, less photosynthate reaches to sink.

• 3.Chemical nature of metabolites itself.

MODELS OF SOURCE- SINK RELATIONSHIP

• For easy demonstrations. Source is of 2 kinds• A. Fixed Source (Accumulated assimilates )-

seed and tuber at the time of germination.• B. Producing (Current assimilates) and

exporting the assimilation.• We can study the source in seed, the rate &

amount of translocation to the root & shoot (can be studied) in germinating seedlings which is a simple growth model.

• Rooting of leaves: If leaves are cut and pit in water, develops callus from petioles & produce the roots. EX. Cowpea, Tapioca & groundnut.

• A mature leaf along with petioles taken & provide light to leaves, these will produce photosynthesis and translocate to petioles (units)sink. After certain time sink is not in a position to take assimilates and these assimilates are stored in source itself. When this is put in humid condition (in a beaker of water) the petiole at its base produces a white callus tissue and then callus will give rise to roots. This is the simple model to study source and sink relationship.

DYNAMICS OF SOURCE AND SINK• Relationship b/w sink activity & source activity• A. Sink activity dictates the source activity.• Case 1: In detached rooted leaves of dwarf bean the

photosynthetic rate is related to the activity of the root system.

• In this system the photosynthetic rate will be very less initially however when it starts developing the root system rate of photosynthesis also starts picking up.

• Increase root demand for photosynthates → source activity ↑

• Other argument: Development of roots → ↑ cytokinin concentration → ↑ source activity.

• More the demand higher the photosynthetic activity.• Case 2: Nature of root stocks control the net

assimilation rate in spinach, sugar beet.• Where sugar beet is used as root stock it improved

the rate of photosynthesis on spinach scion.• Case 3: The assimilation rate of potato is controlled

by tuber activity at least during bulking.• Conclusion: Assimilation in these plants is linked

with size & activity of their sinks.

• Case 4: In Rice, • Genotypes with High sink & source ratio.( High H.I.)• High photosynthetic rate per unit leaf area was

observed.• Very low amount of carbohydrates are accumulate in

vegetative & structural organs.• Genotypes with Low sink & source ratio.(Low H.I.)• Low photosynthetic rate per unit leaf area was

recorded.• Vegetative & structural organs accumulate more

amounts of photosynthesis• Case 5: In Wheat, Flag leaf gives more contribution• Assimilation rate ↓ immediately after the removal of

head.

When the lower leaf are shaded

• Case 6 : In tomato a compound leaf opposite to trees ( Inflorescence) provides photosynthates for the development for the development of fruits on a trees. If that trees is removed, leaf translocated assimilates to another trees which increases the yield 10-15% , but the total yield decreases.

• B. Increasing source capacity increases grain yield

• Additional nitrogen supply during flowering & pod filling stage increases pod yield.(This is to increase the source activity but not the source size)

• CO2 fertilization: Maintaining plant under 600 ppm CO2 from flowering to harvesting increasing the yield, pod set, pod no., seed no., seed set also increases.

• Low temp. during grain filling pd. Increases seed wt. & yield ( because of reduction in the dark respiration).

• Source – Conclusions: Source size may not be a limiting factor, but source activity limits the yield.

• Increased availability of photosynthates from source increases the yield.

• Source development & distribution in the canopy must be improved.

• Characters associated with high source sink ratio: • In such varieties leaves remain green even at harvest.• Seed No. & seed wt. per pod remain almost constant to

the first formed pod to last formed.• Large No. of biomass is partitioned into vegetative parts

( stems, leaves etc.)• Very low H.I.• In pulses & oilseeds most of the varieties are of

determinate type both vegetative & reproductive growth continues simultaneously.

• Low source to high sink ratio:• Leaves show very early senescence forced

maturity of the plant is seen. • Pod wt., pod No., seed wt./pod decreases

from the first formed pod to last formed pod.• Very low amount of biomass is partitioned to

vegetative growth.• H.I. is very high.• Most of the varieties of this type are of

determinate,

PULSES• Traditional varieties in several crop plants

possess greater source than sink (they are leafy).

• During crop development leafy ness is reduced and sinks size gradually increased.

• What happens if greater source capacity is there?

• It results in poor crop performance as fertilization & any other cultural practices results in a greater foliage & poor productivity.

• Sink No. though increased flower drop occurred:

• In few crop plants like vegetables (cucurbits, beans, tomato) pulses (determinate cowpea, soybean) & oilseeds ( bunchy type g.nut, sunflower) though the sink in terms of more number is initiated they drop prematurely due to lack of adequate supply of photosynthates proper time.

• General recommendations: In crops growing assured water supply and available nutrients.

• Large No. of flowers must be produced synchronously in one week to 10 days. This is to avoid the competition among sinks.

• Photosynthates should not be wasted in such structures like peduncle & thalamus more than a certain ratio.

• Increase in duration of grain filling.• Determinate growth of inflorescence terminal & few

auxiliary inflorescences are needed.• Translocation of photosynthates to sink is important.

It is generally influenced by the sink characters such as

• 1. Rate of utilization of carbohydrates by sink or rate of conversion should be more.

• 2. No. of competing sinks with in a plant (more No. of sinks more competition).

• 3. No. of competing sinks with in on inflorescence.

• 4. Distance of sink from the source.• 5. Endogenous hormones concentration ( like

Auxin, GA3 & cytokinins).• More the hormone production more will be

the translocation.

INTRODUCTION(GROWTH MODELING)• One of the ways for increasing food production is

either genotype may be modified to suit the prevailing environment or environment could be modified and made conducive to the existing genotype.

• What is environment and what are the climatic factors that limits yield.

• BILLINGS(1952) defined environment of a plant as a external forces and substances affecting growth, structure and reproductions.

• Envt. is dynamic, constantly changing from season to season, day to day and hour to hour.

• The primary factors that determine the productivity of crop plants are water, temp., soil physical, and chemical factors. The interaction of pests with envt. is a major factor is crop production.

• For increasing production from present cultivated land by reduction of climatic stress conditions.

• For thorough understanding of crop, micro climate interactions and interactions among soil, crop, insects, weed and weather- a new methodology called crop modeling was introduced – a new technique to crop scientists.

CROP GROWTH MODEL (MONTEITH, 1993)

• It is defined as “ quantitative scheme to predict the growth, development and yield of a crop under specific set of genetic and environmental factors”.

• Reynolds and Acock (1985) divided crop stimulation models into 2 groups.

• 1.Empirical model: in these models one or several independent variables representing weather or soil characteristics are related to dependent variable representing crop response such as growth or yield .

• These models do not explain cause and effects of relationship but provide most practical approach for the assessment and prediction of yield and are largely

used many countries like India. This growth model indicates the relationship

b/w variables without reffering underlying physical or biological

structures that exists b/w variables.• Y=qo-q1(trend)+

• 2. Mechanistic Models: These models explain not only the relationship b/w the weather and yield but also the mechanism of these models. Explain relationship of influencing dependent variable.

• In these models, processes like photosynthesis, respiration, ET, nutrient balance involved are calculated numerous equations and integrated. Many models contain a mixture of above two.

• NORMAN (1979) further divided the models into 3 arbitrary categories.

1. Statistical Models : These models express the relationship b/w the yield and yield components and the weather parameters. In these types relationships are measured in a system using statistical techniques. They do not require detailed information about the plant involved, but depends mainly on statistical techniques such as correlations or regressions of plant and environmental variable. Example: crop yield weather models.

• 2. Para materialization or crop weather analysis models: this model proposed by Bair (1973). In these model, it was assumed that the crop yields depend basically on 3 agro meteorological variables solar energy temp., and soil moisture or evapotranspiration. These 3 variables modify each other during the life cycle of a crop and produce positive or negative effect on final yield.

3.Analog- physical Models: use for detailed plants- envt. formulations. Among them, Dynamic stimulation models are prominent. It predicts the change in crop status with time as a function of environmental parameters.

Ex: Soil water content of oat at certain depths through out the season.

Changing number of bolls on a cotton plants with advancement of season.

ADVANTAGES OF CROP GROWTH MODELS

• 1.To reduce site specific long term field experiments.• 2. To interpret climatological records in terms of

production potential and limitations.• 3.To evaluate risk associated with management

practices.• 4.To communicate research results b/w locations.• 5.To conceptualize multi disciplinary activities.• 6.These models give pre-season and in-season

management discussions on cultural practices like fertilization, irrigation and pesticides.

• 7.It is easy way for avoiding experimentation.• 8. These models can assist policy makers by

predicting soil erosion, leaching of agricultural chemicals, effects of climatic changes and large yields forecasts.

• 9.Modeling relates to plant growth and development from seedling to maturity.

• 10.The variability of growth and development is understood by basic concepts explained on mathematical basis.

• 11.The response of plants to their macro and micro environment are actually quantified.

• 12.It also helps in knowing missing data to have a complete picture of processes.

• 13.It will give new ideas leading to experimental approaches.

• 14.Models will indicate priorities for applied research.

• 15.It will help the manager in making suitable decisions.

• 16.It evaluates expected returns of soil and crop management practices.

• 17.It enhances understanding of biological and physical system and their interactions.

• The information required for production of growth model:-

• A. Aerial environment: • 1.Mean day/night temperature• 2.Total amount of visible radiation in each photoperiod.• 3.Total net radiation in each photo and dark period.• 4.Length of photoperiod.• 5.Profile of visible radiation through crop land.• 6.Profile of visible temperature through crop land.• 7.Profile of visible water vapor content through crop land.• 8.Profile of net radiation through land crop.• 9.Daily wind velocity.• 10.Rainfall.

• B.Soil environment:• 1.Amount of water in soil layers at the start of

simulation.• 2.Soil water content at wilting point and field capacity.• 3.Amount of available N and Pin each soil layer.• 4.Temperature profile through soil.• 5.Rate of fixation and release of N and P in soil.

• C.Crop characteristics:• 1.Light perception-PAR.• 2.CO2 fixation.• 3.Carbon partitioning.• 4.Tissue expansion.

EXAMPLES OF GROWTH MODELS• 1.Sorghum: SORGF model-used to evaluate crop-

weather interactions.• Simulates timing of development of plant, dry matter

partitioning and partitioning of dry matter into different plant parts based upon the stage of development as influenced by environmental conditions. Huda et al, ICRISAT, 1984

• 2.Pearlmillet: SORGF with slight modifications. Based on dry matter accumulation, dry matter partitioning and evapo transpiration models simulates final grain yield. Both simulated and observed grain yield and TDM are in close agreement.

• 3. Maize: Weaich et al(1996) at Australia for simulating maize emergence using soil and climate data-PGS model.

• 4. Cotton: Staggren boog et al(1994)-GOSS Y M model- to assess Water use in cotton and also as a tool for scheduling irrigations in SAR.

• 5. Soybean: GLYCIM simulation model-Acock et al (1985).

• 6. Groundnut: PNUT GRO-model, Singh et al 1992. to predict pod yield in different environment as determined by season, short days and moisture regimes.

• 7.Wheat: CERES Model- Havi et al 1993 climate change and wheat yields in Punjab.

• Input data required for SORGF- a sorghum simulation model

PLANT DATA

Leaf number Total no. of leaves produced

Leaf area Max. area of each individual leaf

Planting data Sowing data, Plant population, Row width, Row directions, Depth of sowing

Climatic data Max. temperature, Min. temperature, Solar radiation, Rainfall (Daily from planting to Maturity)

Soil data Soil water holding capacity, Initial available water content, location data, latitude.