Why Photosynthesis? Growth Respiration, and Maintenance Growth - PDF document

6/13/2008 Estimating Carbon Use Efficiency, Estimating Carbon Use Efficiency, Why Photosynthesis? Growth Respiration, and Maintenance Growth Respiration, and Maintenance Respiration from Crop Gas Exchange Respiration from Crop Gas Exchange • Plants contain approximately: Measurements Measurements – 40% C Marc van Iersel – 45% O 45% O – 6% H The University of Georgia • Leaf photosynthesis and plant growth or yield are poorly correlated 2008 Meeting on controlled environment agriculture Plexiglas Whole Crop Photosynthesis and Growth Whole Crop Photosynthesis and Growth chambers • Direct measure of C incorporated into the plant • With continuous measurements, net carbon gain can be determined can be determined • Daily net carbon gain closely related to growth rate • Cumulative carbon gain closely related to dry mass Alan Lakso Cornell Fred Davies Texas A&M Corelli-Grappadelli and Magnanini, 1993, HortScience 1

6/13/2008 S oil- P lant- A tmosphere- R esearch chambers (SPAR) Diurnal CER USDA Beltsville dark light dark e rate CO 2 exchange P net 0 R dark 0 24 Time (hours) Daily Carbon Gain (DCG) Cumulative Carbon Gain (area 1 - area 2) 10 respiration dark light dark dark light dark mol.m -2 ) photosynthesis 8 e rate 6 CCG (m CO 2 exchange 1 P net 4 0 2 2 R dark 2 0 0 24 0 24 0 2 4 6 8 10 12 14 Time (hours) Time (hours) Time (days) Whole Plant Photosynthesis and Growth Case Study 45 DW = 5.55 + 25.8 x CCG 40 r = 0.99 • Marigold grown at 20 or 30 o C 35 ght (g) 30 • CO 2 exchange measured for 60 days 25 25 Dry wei 20 15 10 5 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 Cumulative carbon gain (mol) 2

6/13/2008 30 o C nmol/plant/s) mol/plant/s) 80 30 30 o C 20 o C 60 20 40 P net (nm R dark (n 20 o C 20 o C 10 20 van Iersel, 2005 Physiol. Plant. 0 0 0 10 20 30 40 50 60 0 10 20 30 40 50 60 Time (days after seeding) Time (days after seeding) Carbon Use Efficiency Data Interpretation (area 1 - area 2)/(area 1 + area 3) dark light dark dark light dark • Carbon-use efficiency = e rate Net amount of carbon incorporated into the plant CO 2 exchange Gross amount of photosynthates produced G t f h t th t d d 1 P net P gross 0 R dark 2 3 2 0 24 0 24 Time (hours) Time (hours) Growth and maintenance 0.7 fficiency (mol.mol-1) respiration 0.6 Photosynthates Growth Biomass (70%) 20 o C 0.5 30 o C 0 4 0.4 Carbon use ef Growth Maintenance Respiration (30%) 0.3 respiration 0.2 Maintenance 0 10 20 30 40 50 60 Growth Dry weight Time after seeding (days) respiration respiration Growth coefficient (r g ) coefficient (r m ) 3

6/13/2008 Growth and maintenance respiration Calculations • Growth rate and plant dry weight were • R = R m + R g = r m x weight + r g x growth calculated from CO 2 exchange measurements and carbon content of the plants plants • R / weight = r m + r g x growth/weight R / i h h/ i h • RGR (growth rate / dry weight) and = r m + r g x RGR specific respiration rate (R dark / dry weight) IF r m and r g are constants, they can be were calculated from these data estimated from linear regression Relative growth rate Growth and maintenance respiration ration (mg.g -1 .d -1 ) 30 o C 30 o C 120 0.20 100 20 o C 80 (d -1 ) 20 o C 0.15 60 RGR Specific respi 40 0.10 20 0 0.05 20 30 40 50 60 Time (days after seeding) 0.00 0 10 20 30 40 50 60 70 Time (days after seeding) Growth and maintenance respiration Growth and maintenance respiration ation (mg.g -1 .d -1 ) 140 120 30 o C m r (mg g -1 d -1 ) Temperature g r (g g -1 ) 100 20 o C 8.4 ± 0.6 0.56 ± 0.01 80 r r g Specific respira 60 30 o C 11.9 ± 0.5 0.50 ± 0.01 r m 40 20 o C 20 R spec = r m + r g x RGR Q 10 1.42 0.89 0 90 0.00 0.05 0.10 0.15 0.20 0.25 1.10 Relative growth rate (g.g -1 .d -1 ) Q 10 Maintenance respiration = m r × dry mass Growth respiration = g r × growth rate 4

6/13/2008 ance respiration (mg . d -1 ) ance respiration (mg . d -1 ) 60 60 30 o C 30 o C 50 50 growth growth 40 40 30 20 o C 30 20 o C 20 C 20 C Growth and maintena Growth and maintena 20 20 maintenance 20 o C 10 10 30 o C 0 0 20 30 40 50 60 20 30 40 50 60 Time (days) Time (days) Conclusions • Continuous whole plant CER gives: – Direct measure of growth – Physiological components of growth • Carbon use efficiency • growth respiration • maintenance respiration Thank you 5