HOS 6545 - ADVANCED CITRICULTURE I, REGULATION OF VEGETATIVE GROWTH PHOTOSYNTHESIS L. G. ALBRIGO
Kriedemann, P.E. 1968. Some photosynthetic characteristics of citrus leaves. Aust. J. Biol. Sci. 21:895-905 INTRODUCTION In 1968 little known about Pn activity of citrus Primary factors affecting Pn were studied light intensity, CO 2, T, RH
Materials and Methods Potted trees from rooted cuttings of Washington Navel orange, Valencia orange and Eureka lemon. Expanding to fully expanded, but unhardened leaves often used, but data suggests not always. Pn and respiration measured with IR gas analyzer using attached leaves. No statistics mentioned
Results Light Carbon dioxide Temperature Relative Humidity
Figure 1. Net Pn as a function of light intensity. A. orange and B. lemon leaves of different ages up to 6 months old.
Figure 2. Effect of CO 2 concentration in air on Pn of orange and lemon leaves at saturated light Didn t occur to him to look above 300 ppm
Figure 3. Effect of temperature on orange (a) and lemon (b) leaf Pn with humid (o) or dry (x) air at saturating light.
Table 1. Effect of leaf temperature, humidity and soil moisture
Cyclic oscillations of orange leaves at 20 o C in dry air followed by moist air.
Oscillations of Pn of orange leaves at 35 o C in dry air followed by moist air.
Assimilation rate low Discussion 1.9 to 3.6 mg CO 2 /mg chlorophyll/hr sunflower & corn, 14 and 11.6 grape and apple, 6.8 and 6.4 Light saturation at 25 % full sunlight CO 2 compensation point 30-65 ppm Broad temperature optimum (15-20 or 20-30 o C, low versus high humidity) Low RH at high T results in low Pn Pn cyclic oscillations can occur
Conclusions M & M mixed in with Results Poor or little use of statistics Limited leaf ages studied considering long lived Citrus leaves low Pn, but Pn occurs 12 months Climate varies this, total leaf area large Deep canopy allows all light to be captured Shade plant CO 2 not limiting & compensation point low T limiting if <15 or > 30 o C Broader if high humidity, cyclic oscillations if T high and RH low, stomatal control
Khairi, M.A. and A.E. Hall. 1976. Temperature and humidity effects on net photosynthesis and transpiration of citrus. Physiol. Plant. 36:29-34 Broader look at humidity (vapor pressure deficit) and temperature on Pn. Partitioning of conductance, stomatal versus mesophyll, to CO 2.
Materials and Methods Budded trees of Parent Navel, Campbell Valencia and Frost Marsh grapefruit on Troyer citrange. Potted, greenhouse, but tree age not given. Leaves 6 to 8 weeks old, expanded but not hardened. IR gas analyzer, open flow with controlled CO 2 and humidity.
Results Increasing vapor pressure deficit decreased Pn, but effect less after acclimation
Figure 1. Effect of VPD on Pn and leaf conductance at 26 o C on the first day (open symbols) and 5 th day (closed symbols) of treatment
Table 1. Effect of T and VPD on Pn and leaf conductance of grapefruit and orange leaves after 1, 2 or 3 days of the specified conditions. Temperature 20 % effect, high T plus high VPD = large reductions Pn, g
Major effect of VPD not T until Temp. exceeded 30 o C
Effect of low and high irradiance at 26 o C on Pn and conductance of orange leaves at different VPD on the 1st through 3rd day of treatment. Again Pn not reduced much by 3 fold increase in VPD, but g was reduced.
Results Table 1. Pn and leaf conductance to water vapor decrease with increasing temperature and VPD. Some adjustment occurs in both Pn and g t within 3 days Table 2. Mesophyll conductance decreases primarily as a function of decreasing VPD Table 4. At moderate temperature (26 o C), high light increased Pn and g t (slightly), but increasing VPD from 7 to 21 mbar had little effect.
Discussion Pn higher than previously reported High leaf T, large VPD, low irradiance pre-treatments substantially reduce Pn. Pn optimum for citrus is not higher than 22 o C (Why is optimum growth nearer 30 o C?) Pn at saturation much higher for high light leaves.
Conclusions Citrus still low Pn crop, under-story plant Citrus adjusts gas exchange and Pn to adverse conditions Adverse conditions (high T, high VPD, low light) still reduce Pn Reason citrus can grow in many climates Why difference in optimum T for Pn and g?
Khairi, M.M.A. and A.E. Hall. 1976. Comparative studies of net photosynthesis and transpiration of some citrus species and relatives. Physiol. Plant. 36:35-39. Compare several citrus with different leaf types and climatic adaptation M & M as in previous paper.
Table 1. Pn and leaf conductance of Citropsis gabunensis and Citrus sinensis at different temperatures and VPD after 1 to 3 days of treatment. Although Citropsis is of humid subtropical origin, Pn was ½ of C. sinensis
Table 2. Pn of Eromolemon and Frost Lisbon lemon at different temperatures and VPD after 1 to 3 days of treatment. Eremolemon drought tolerant with higher Pn, additional improvement after 3 days of stress, already high at 34 & 38 o, C. lemon also improved with time under stress
Discussion & Conclusions All species behaved in a similar manner to temperature and VPD Drought tolerant Eremolemon had improved water use efficiency primarily at moderate temperatures, not at high VPD & 30 o C or above. Any practical use of differences in breeding are still questionable.
Vu, J.C. V. and G. Yelenosky. 1987. Photosynthetic characteristics in leaves of Valencia orange (Citrus sinensis (L.) Osbeck) grown under high and low temp. regimes. Environ. And Expt. Bot. 27:279-287. Measurement of Pn and related functions after one month under different environmental conditions. Extended look at adaptation to moderate conditions versus lower than ideal?
Materials and Methods Valencia orange leaves on 1 year old trees budded on rough lemon. Fully developed top leaves measured after 30 days of conditions. 15.6/4.4 (cool) temperatures compared to 32.2/21.1 (higher) under saturated light
Results After 30 days, leaves had higher Pn functions when grown at higher T conditions.
Table 1. CO 2 exchange, stomatal conductance, transpiration and water potential of orange leaves after 30 days at high temperature (32/21) or low temperature (15.6/4.4). Transpiration nearly 4 times higher, but conductance & Pn only double. Doubling of Pn for 32/21 conditions = to conductance.
Table. 2. CO 2 exchange, stomatal conductance, and transpiration of orange leaves after reversal of high or low temperature regimes for 4, 24 or 96 hours. Reversal of gas exchange rates for high and low temp. regimes within 4 days.
Fig. 1. PEPCase activity as a function of HCO 3 - concentration in extracts of orange leaves grown for 30 days under high or low temperatures. Enzyme related to Pn higher, not lower at low temperature.
Discussion & Conclusions Increased gas exchange (Pn) at higher temperature related to conductance, not PEP carboxylate activity. Much of regulation of Pn and water relations (?) by stomatal or mesophyll conductance?
Brakke, M. and L.H. Allen, Jr. 1995. Gas exchange of Citrus seedlings at different temperatures, vapor-pressure deficits, and soil water contents. J. Amer. Soc. Hort. Sci. 120: 497-504. Examined gas exchange of rootstock seedlings Purpose to identify water relations that contribute to mid-day reduction in assimilation of CO 2
Materials and Methods Two year old seedlings in 2 liter pots, flooded for irrigation and weighed for soil water content. Controlled environments in cycling growth chambers. Usual gas exchange measurements. A at specified PPFD, T, VPD and soil available water conditions (AWS as % of total.
Results A and or water use efficiency reported.
Fig. 1. Net canopy CO 2 assimilation (A), PPFD, T and VPD for low and high temperature for high and low available soil moisture levels. Normal CO 2 level of 330 ppm. A followed PPFD, T & VPD. Large effect of ASW at high T even though VPD not too different
Fig. 2. Water use efficiency of Swingle and Carrizo seedlings at low and high temperatures and high or low soil moisture. Water use efficiency low at high temperature and midday for low ASW, particularly at high T
Fig. 3. Net assimilation rate (A) and ET of Swingle seedlings at PPFD, T and VPD as indicated for a daily cycle. Large reduction in A for Swingle at high T and VPD mid-day.
Fig. 4. Net assimilation rate (A), PPFD, T and VPD at low and high temperature for 2 soil moisture conditions. Elevated CO 2 at 840 ppm At elevated CO 2, A remained high even at low ASW.
Fig. 5. Hourly max and min A for low and high T and different PPFD levels for various available soil water levels at normal CO 2. Severe drop-off of max A below 40 % available soil moisture, a general difference of 20 % less due to high T.
Fig. 6. A for different T and soil water availability at high CO 2 At high CO 2, A remained relatively high even at low ASW levels. A slightly higher at low T.
Discussion & Conclusions Why treat rootstock seedlings? Not typical leaf of scion cultivar. In this study LT was 29 o C while HT was 37 o C, therefore higher A at LT. Good ASW levels at mid-day negated much of HT, high VPD effect on reducing A. Higher CO 2 would also compensate for some of the reduced conductance that occurs under stress
Syvertsen, J.P. 1984. Light acclimation in citrus leaves. II. CO 2 assimilation and light, water, and nitrogen use efficiency. J. Amer. Soc. Hort. Sci. 109:812-817 Natural consequence of hedging and topping is to change shade leaves to sun leaves. Question of how they adapt is addressed in relation to A and water relations
Materials and Methods Seedlings of orange and grapefruit grown for 9 months under high PPFD (2300 umol s -1 m -2 ) or 50 or 90 % shade. Some seedlings where switched from low or intermediate to high light after initial measurements and then leaves measured for A, WUE, etc. at different intervals.
Results High light = high A, able to use more PPFD After shock, low light leaves adjusted to become high light leaves. Took about 6 weeks for this adjustment.
Fig. 1. Light response for A for grapefruit and orange leaves grown for 5 months under low ( ) and high (O) PPFD.
Fig. 2. A, E and WUE of grapefruit leaves grown for 5 months under low (solid bars), medium (shaded bars) or high light (open bars) PPFD and also 2, 4, and 6 weeks after transfer to high or medium light. Moderate and high light leaves did not change much in 6 weeks, but low light leaves did in A, E and WUE
Fig. 3. A, E and WUE of orange leaves grown for 5 months under low (solid bars), medium (shaded bars) or high light (open bars) PPFD and also 2, 4, and 6 weeks after transfer to high or medium light. Orange leaves showed slightly more adjustment to changes within moderate and high light leaves than grapefruit did.
Fig. 4. A, E and WUE for orange and grapefruit leaves grown for 5 months under low PPFD (solid symbols) and then transferred to high PPFD (open symbols). Changes in orange just starting in 4 th week.
Discussion & Conclusions Leaves from shade to light did adjust, earlier paper showed thickness change. Most of adjustment in conductance. Little improvement in WUE
Photosynthetic acclimation of young sweet orange trees to elevated growth CO2 and temperature J. C. V. Vu, Y. C. Newman, L. H. Allen, Jr., M. Gallo- Meagher, M-Q. Zhang. J. Plant Physiol. 159. 147 157 (2002) The objectives: Characterize the physiology and biochemistry of citrus photosynthesis in response to both elevated [CO2] and temperature Test if the photosynthetic capacity of sweet orange, in terms of rubisco activity and protein concentration, was down-regulated under long-term elevated growth [CO2].
Background Assuming global warming continues, what will be impact on citrus Pn and presumably productivity Elevated CO2 and temperature often initially increase Pn but then various levels of regulation diminish the response (C3 plants) Wanted long-term controlled climate experiment
Materials and Methods Ambersweet/Swingle grown for 29 months Temperature gradient greenhouse with 1.5 and 6 o C above ambient, avg ambient 24 o C CO 2 of 360 μmol & 720 μmol mol 1 evaluated Leaf gas exchange, Pn enzymes and carbohydrates measured.
Figure 1. Treatment layout in a temperature-gradient greenhouse (TGG). Unidirectional arrows indicate the direction of air flow. TA, outdoor ambient temperature; TA + 1.5 C, average temperature of the TGG segment 1; TA + 3.0 C, average temperature of the TGG segment 2; TA + 4.5 C, average temperature of the TGG segment 3; TA + 6.0 C, average temperature of the TGG segment 4.
Results Both mature (old) and expanding (new) leaves of trees grown under elevated CO 2 had higher photosynthetic rates, lower transpiration and conductance, & higher water-use efficiency (WUE) compared to those grown under ambient CO 2. Although leaf WUE was reduced by high temperature, elevated CO 2 compensated for adverse effect of high temperature on leaf WUE.
Figure 2. Monthly averages for the year 1996 (A) mean daily temperature in the 360 μmol CO2 mol 1 temperature-gradient greenhouse (TGG), (B) mean daily temperature in the 720 μmol CO2 mol 1 TGG (C) mean daily photosynthetic photon flux density. TA, outdoor ambient temperature A & B similar, good control
Figure 3. Diurnal changes in starch concentrations of fully-developed leaves of the mature flushes (Old) and most-expanding leaves of the recent flushes (New) of Ambersweet orange grown in temperature gradient greenhouses under 360 and 720 μmol CO2 mol 1 and at average temperatures of 1.5 and 6.0 C above outdoor ambient temperature (TA).
Conclusions Activities of sucrose-p synthase and adenosine 5 - diphosphoglucose pyrophosphorylase were reduced at elevated [CO2] in the old leaves, but not in the new leaves. The photosynthetic acclimation of Ambersweet orange leaves at elevated [CO2] allowed an optimization of nitrogen use by reallocation/redistribution of the nitrogen resources away from rubisco.
Conclusions Soluble sugars and starch, which were higher under elevated CO 2, were generally not affected by high temperature. Within each CO 2 -temperature treatment and leaf type, total soluble sugars remained relatively unchanged throughout the day, as did the starch content of early morning and midday samples, and only a moderate increase in starch for the old leaves at late afternoon sampling was observed. In contrast, starch content in the new leaves increased substantially in late afternoon. In the absence of other environmental stresses, citrus photosynthesis would perform well under rising atmospheric CO 2 and temperature as predicted for this century.
Pluses and Limitations? Careful setup and relatively long term study over more than a year with both temp and CO 2 levels + Used Ambersweet on Swingle rootstock - Not a true sweet orange A limited performance rootstock? Other studies found that citrus trees, after initial higher Pn, adjusted and did not continue to have higher Pn with elevated CO 2
Jahn, O.L. 1979. Penetration of photosynthetically active radiation as a measurement of canopy density of citrus trees. J. Amer. Soc. Hort. Sci. 104:557-560 Due to various causes of leaf loss, canopy leaf density can decline. A loss of 10 to 20 % of older leaves did not reduce yields. Attempt to quantify light capture changes.
Materials and Methods Used different aged trees Measured penetrated light before and after different levels of leaf removal. Used different concepts of leaf area index (LAI)
Light interception as a function of LAI. LAI is leaf area divided by ground area covered by canopy of tree. LAI of 7 required to reduce penetrated light to 20 % of incident.
Discussion & Conclusions LAI per tree is not as useful as a LAI per acre (ground area as done for agronomics). Doubling LAI, nearly doubles captured light (ok in useable range). Simple LAI of about 7 needed to reduce incident light below saturation point of inside leaves. Per area this is about 2/3rds or 4.6 LAI (= hallow tree centers?)
Some aspects of citrus ecophysiology in subtropical climates: re-visiting photosynthesis under natural conditions R. V. Ribeiro* and E. C. Machado. Braz. J. Plant Physiol., 19(4):393-411, 2007 A review based heavily on authors experiences and studies in Brazil Physiological aspects of field-grown plants is probably highly complex due to the interaction of citrus trees with their environment, ranging from soil temperature and root metabolism to the variation in light exposure of leaves
Background Citrus trees subjected to large seasonal variation of environmental conditions throughout the annual cycle Emphasize two periods: (a) the autumn-winter season with low soil water availability and low temperatures; and (b) the spring-summer season with abundant rainfall, high temperatures and high radiation
Materials and Methods Use data from standard methods of Pn gas exchange measured in several studies Refer to many studies done by others, but most data for their SP, Brazil studies, all work reported had 5 to 10 replications Still this is primarily a review of previous work Allows more freedom to extrapolate from the existing data.
Results
Figure 1. Diurnal variations of photosynthetic photon flux density (PPFD, A,C), potential quantum efficiency of photosystem II (Fv/Fm, left axis in B,D), and relative photoinhibition (right axis in B,D) in sun-exposed leaves of sweet orange trees grown under natural conditions in Cordeirópolis (A,B) and Bebedouro (C,D), southeastern Brazil.
Figure 2. The effective quantum efficiency of photosystem II (Fq /Fm, A) and the apparent electron transport rate (ETR, B) as affected by the photosynthetic photon flux density (PPFD) in sun-exposed leaves of field grown sweet orange trees in Cordeirópolis, southeastern Brazil. Evaluations were performed between September 2004 and August 2005, under natural conditions.
Figure 3. The stomatal conductance as a function of the photosynthetic photon flux density (PPFD) in sun-exposed leaves of irrigated sweet orange trees in Cordeirópolis, southeastern Brazil. Measurements were taken during the winter (September, open symbols) and spring (November, closed symbols) seasons, when minimum/maximum air temperatures were: 11.1/24.1 o C (winter) vs. 16.5/27.2 o C (spring).
Figure 4. Seasonal variation of rainfall (A), soil volumetric water content (B) and stem water potential (C) in exposed canopy positions of field-grown sweet orange trees sampled at predawn (closed circles) and 1400 h (open circles) in Cordeirópolis, southeastern Brazil. The soil volumetric water content refers to the mean value of readings taken at 0.3, 0.6 and 0.9 m of soil depth. 160-280 days
Figure 5. Diurnal-integrated leaf transpiration as function of the stem water potential measured at 1400 h during the spring-summer seasons (A) or at pre-dawn during the autumn-winter seasons (B) in sun-exposed leaves of sweet orange trees under natural conditions in Cordeirópolis, southeastern Brazil.
Figure 6. Diurnal variation of the stomatal conductance as a function of the leaf-toair vapor pressure difference in sun-exposed leaves of irrigated young sweet orange trees during the winter (July) and summer (February) seasons in Piracicaba, southeastern Brazil. Arrows indicate the direction from the morning to the evening.
Table 1. Seasonal variation of environmental elements, the maximum diurnal stomatal conductance (gmax) and predawn stem water potential (Ψpd) in exposed leaves of irrigated Valencia orange trees grown in Cordeirópolis, southeastern Brazil. Measurements made in winter (Aug.) and spring (Nov.).
Figure 7. Seasonal variation of the daily mean air temperature (T air, A), the global solar radiation (Q G, A), maximum leaf CO 2 assimilation (A max, B) and diurnalintegrated leaf CO 2 assimilation (A I, B) in sun-exposed leaves of field-grown sweet orange trees in Cordeirópolis, southeastern Brazil.
Table 2. Seasonal variation of diurnal-integrated CO 2 assimilation (mmol m-2 d-1) in exposed leaves of Valencia orange trees as affected by irrigation and canopy position, in Cordeirópolis, southeastern Brazil. Measurements were made in winter (July) and summer (December).
Table 3. Seasonal variation of maximum CO 2 assimilation (Amax), maximum rate of Rubisco carboxylation (Vc,max), maximum rate of electron transport driving RuBP regeneration (Jmax) and Vc,max:Jmax ratio in exposed leaves of young irrigated Valencia orange trees during the morning under natural conditions, in Piracicaba, southeastern Brazil. Measurements were made in winter (July) and spring (February). Environmental conditions were 35.0 ± 0.2 o C leaf temp. and 1.65 ± 0.03 kpa VPDL (February), and 21.6 ± 0.3 o C leaf temperature and 0.78 ± 0.04 kpa VPDL (July). PPFD was fixed at 1200 μmol m-2 s-1 in both months
Table 4. Seasonal variation of the diurnal-integrated CO 2 assimilation (mmol m-2 d-1) in exposed leaves of sweet orange trees as affected by irrigation and two regions of southeastern Brazil. Accumulated water deficiency until the evaluation time was ~40 and ~230 mm in Cordeirópolis and Bebedouro, respectively. Summer and winter refer to measurements taken in December and July, respectively. Irrigation was 100% of ET. Wet Dry Wet Very Dry
Figure 8. The total (soluble + starch) carbohydrate content as a function of the diurnal-integrated CO 2 assimilation in sun-exposed leaves of field-grown sweet orange trees in Cordeirópolis, southeastern Brazil. Samples for carbohydrate evaluations were collected around 1500 h, when the maximum leaf carbohydrate content is to be expected.
Table 5. Seasonal variation of diurnal-integrated CO2 assimilation (AI), total leaf carbohydrate concentration (TCC), nocturnal leaf starch consumption (NSC), daily exportation of photoassimilates (DEP), and total leaf area (LA) in young Valencia orange irrigated trees under natural conditions, in Piracicaba, southeastern Brazil. AI, NSC and DEP refer to sun-exposed leaves. Summer and winter refer to measurements taken in February and July, respectively. Carbohydrates were assessed at 1400 h.
Conclusions Even with irrigation, CO 2 assimilation was much less in winter and much less in Bebeduoro than Piricicaba or Cordieropolis Photoinhibition occurred in warmer, high light, period (Citrus an understory plant and developed under low light conditions)
Sao Paulo Maximum Temperatures Bebeduoro Southern area
Pluses and Limitations? Probably did not compare most stressful, nonirrigated conditions in Northern Sao Paulo State I expect there are conditions under which Pn is reduced much more than study indicates Identity of Winter, Spring and Summer was questionable as months varied perhaps outside of normal range Interesting, well designed experiments providing useful information for drought stresses trees, but didn t characterize drought as well as should have
Syvertsen, J.P. and J.L. Lloyd. 1994. Citrus Chapt. 4 In Handbook of Environmental Physiology of Fruit Crops Vol. II: Sub-tropical and Tropical Crops. ; pp.65-99 Review article of many principles applied to citrus Deals with many issues of growth as related to Pn and water use. Some of data not available elsewhere. Some interesting synthesis of information for Pn productivity potential.
Materials and Methods Mostly a review of data already reported, but a significant interpretation of this information
Fig. 2. Stomatal conductance in response to PPFD Stomatal conductance increases with PPFD, but stomatal conductance in the leaf decreases only slightly in relation to ambient CO 2. Stomatal response to PPFD is greater than Pn response.
Fig. 4. Changes in stomatal conductance to partial pressure of CO 2 in the stomatal cavity Stomatal conductance decreases as CO 2 increases, g ^ not needed.
Fig. 9. Assimilation (A) under low and high light at different T and partial pressures of CO 2.
Fig. 10. Carbon isotopic compensation and leaf nitrogen concentration relationship for grapefruit leaves on two rootstocks.
Simulated A and stomatal conductance for PPFD for 3 areas
Annual Carbon Gain Annual carbon gain (mol C m -2 ) Site Annual T @ 35 Pa, N @ 70 Pa, D @ 35 Pa, N @ 70 Pa, D Valencia 16.5 71 89 129 145 Yuma 22.3 58 99 110 132 Lake Alfred 22.4 76 103 140 161 350 ppm = 35 Pa, N = normal response to VPD, D = no response, Yuma and Lake Alfred have = avg. T, but distribution and VPD are quite different. Lake Alfred best soluble solids producer for processing oranges.
Discussion & Conclusions Stomatal conductance more important than enzyme limits Good water and high light give best Pn Need maximum canopy to get max. Pn Rootstocks and irrigation management to optimize Pn or are other factors as important?