{"id":1457,"date":"2022-10-19T12:47:27","date_gmt":"2022-10-19T11:47:27","guid":{"rendered":"https:\/\/research.reading.ac.uk\/lemontree\/?p=1457"},"modified":"2022-10-25T10:53:09","modified_gmt":"2022-10-25T09:53:09","slug":"the-a-ci-curve-updates-from-the-lemontree-experimental-team","status":"publish","type":"post","link":"https:\/\/research.reading.ac.uk\/lemontree\/the-a-ci-curve-updates-from-the-lemontree-experimental-team\/","title":{"rendered":"The A\/Ci Curve. Updates from the LEMONTREE experimental team\u00a0"},"content":{"rendered":"

Whilst there are decades of global, remotely sensed data on vegetation cover, biomass and photosynthetic activity, reliable and more accurate models will not emerge from data analysis alone. Most data on plant responses to climate change scenarios have come from large facilities such as Free Air Carbon Enrichment (FACE) experiments, which have been instrumental in model development. But to test new theories, like EEO (Eco Evolutionary Optimality), we need new data from targeted experiments.<\/span>\u00a0<\/span><\/p>\n

We have a team of\u00a0experimental scientists working on developing more data to quantify plant carbon allocation and trait responses to CO<\/span>2<\/span><\/sub>, water, N and P. They are also developing experiments to assess the relationship between nitrogen and phosphorus supply and demand for different nutrient acquisition strategies (mycorrhizal types and nitrogen-fixers). This work is done in both laboratories\u00a0and in the field.<\/span>\u00a0<\/span><\/p>\n

In our LEMONTREE October science meeting, we heard from members of the experimental team about their recent research on the A\/C<\/span>i<\/span><\/sub> curve. The A\/C<\/span>i <\/span><\/sub>curve is the relationship between the photosynthetic CO2<\/sub><\/span> assimilated into the plant structure (A)\u00a0versus the\u00a0CO2<\/sub><\/span>\u00a0<\/span>inside the plant (C<\/span>i<\/span><\/sub>). From these curves, we can obtain the maximum rates of carboxylation (V<\/span>cmax<\/sub>)<\/span> and electron transport (J<\/span>max<\/span><\/sub>). <\/span>\u00a0<\/span><\/p>\n

 <\/p>\n

Introduction to measurements. <\/span>\u00a0<\/span><\/h2>\n

Hugo de Boer (Utrecht University)<\/span>\u00a0<\/span><\/h2>\n

The A\/Ci<\/sub> Curve. <\/span><\/b>This is<\/span> the photosynthetic response to changes in the leaf interior CO<\/span>2<\/sub><\/span> concentrations which can be used to derive parameters of V<\/span>cmax<\/span><\/sub> and J<\/span>max<\/span><\/sub>. It is based on the Farquhar, von Caemmerer & Berry (FvCB) model of photosynthesis for the relationship between net photosynthesis (A) and leaf-interior CO<\/span>2<\/sub><\/span> concentration (C<\/span>i<\/span><\/sub>) and limitations due to maximum rates of carboxylation (V<\/span>cmax<\/span><\/sub>) and electron transport (J<\/span>max<\/span><\/sub>).\u00a0However, Ci<\/sub> cannot be (easily) measured directly as it is occurring inside the leaf. <\/span>\u00a0<\/span><\/p>\n

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Figure 1. Using the LI6400XT to develop the A\/Ci curves. \u00a9Hugo de Boer.<\/figcaption><\/figure>\n

To conduct these experiments and\u00a0develop the curves, we use LI-COR readers, either LI6400XT or the newer LI6800. These are portable photosynthesis measurement devices which provide<\/span> measurements based on leaf gas exchange on single leaves in a closed cuvette. This allows us to change environmental conditions, e.g.,\u00a0light, temperature, humidity, and CO<\/span>2<\/sub><\/span> to measure the changes in gas exchange. Concentrations of water vapour and CO<\/span>2<\/sub><\/span> are measured by IRGAs (infrared gas analysers) in two air streams: Reference (unaffected by the leaf) and Sample (with CO<\/span>2<\/sub><\/span> and water vapour altered by the leaf). Using the difference between the sample and reference concentrations and the known leaf area, we can calculate the photosynthesis and respiration rates. The measurement of C<\/span>i<\/span><\/sub> is based on measurements of both water vapour and CO<\/span>2<\/sub><\/span> fluxes and T<\/span>leaf<\/span><\/sub>.<\/span>\u00a0<\/span><\/p>\n

Protocol <\/span><\/b>\u00a0<\/span><\/p>\n