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|Author||Topic:Carbon Assimilation||1353 Views|
27 May 2011 at 12:53pm Last edited: 27 May 2011 1:18pm
Relation between P and T is curvilinear, therefore it may not be accurate to estimate P at higher T values. Ex: when there is plenty of water in the soil and g is at max, VPD can further increae T but may have little impact on P or biomass accumulation. Can you comment?
Have you measured FI on fruit trees like citrus or mango and what do you recommend to do it right?
Do you think it could be possibe to genettically manipulate RUBISCO to fix more CO2?
Based on your experience and knowledge which would be the most practical way to Model Carbon Assimilation across different plant species?
2 June 2011 at 10:24am
I am going to let Colin comment on the model part of your question but I cannot resist throwing in 2 cents on the rubisco question. Rubisco is HIGHLY evolutionarily conserved. In relation to other enzymes common to life rubisco has not changed very much no matter where you find it. Rubisco is pretty much the same even in the tube worms that grow in the high sulfur content thermal vents in the ocean. If you talk to any biochemist they will go on about how horrible and inefficient an enzyme it is, but the problem is not actually with rubisco. If you give it the right conditions it will stack a CO2 molecule on Rubp all day long. The problem is that terrestrial (or aquatic plants for that matter) very seldom get ideal conditions. Water limitations cause stomata to close and that causes CO2 limitations which are good conditions for photorespiration. If you are not doing photosynthesis in the middle of the day because water is limiting, your sensitive light harvesting complexes are getting bombarded with solar radiation and that causes all sorts of problems with oxy-radicals and your electron transport chain.
Even if you can genetically improve rubisco, and I think work has/is being done to eliminate or decrease photorespiration (not sure, I've been out of that literature for a couple of years now) you are not solving the real problems that the plant is experiencing.
29 June 2011 at 9:44am
As with all of the topics we discussed in the seminar, the principles we discussed were a starting point to model the carbon assimilation, not the finished product. As I showed with the RUE graphs for the rice, there was a point where the intercepted PAR continued to increase, but carbon assimilation reached a maximum. Although we didn't see a similar relationship when we considered carbon assimilation vs. evapotranspiration, it may have been overshadowed by the flooded conditions of the rice. You may be correct that high vapor deficit conditions lead to increased transpiration without an increase in photosynthesis, but some of this may be accounted for in that model (P = kT/D) as T and D will balance. If this relationship does not fit at high T values, adding empirical factors to account for the deviation will be necessary.
I have never measured FI on fruit trees. However, I have had some experience measuring in tree canopies. My recommendation is to first set up transects and make measurements in reasonably short intervals (1 m spacing?). Take these data and use geostatistics to develop a variogram to determine the distance between measurements that will be statistically different. Use this distance to sample the canopy. Other tips are available on the support tab in the LP80 area.
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