Unpopular opinion: A vs ci curves have become a religion, with consequent unearned faith and unquestioning allegiance. Amax (A at saturating light and CO2) is often preferable.

1/n

Amax is a direct measurement, whereas Vcmax and Jmax are inferred from a fitted model with at least 7 parameters (Vm, Jm, K', gamma*, Rd, theta, phi) and many typically tacit and questionable assumptions (Rd=Rlight; T responses same across spp; gm=infinite, constant or ~gs).

2/n

Amax can be measured much more quickly than Vcmax and Jmax can be inferred, enabling vastly greater throughput and hence real biological/ecological insight. Rapid A vs ci curves are dubious without rematching.

3/n

Amax is literally the "photosynthetic capacity" of a real leaf. It's the highest net assimilation rate achievable when stomatal limitations are eliminated (using saturating CO2) and light is maximal. Whereas Vcmax and Jmax are theoretical parameters in a model.

4/n

Amax and Jmax are uniquely related given the assumptions typically used to infer Jmax from A vs ci curves (namely that we know theta, phi, gamma*, & Rlight, and all their T responses). So all the A vs ci curve adds is Vcmax, which is extremely well correlated w/ Jmax.

5/n

A vs ci curves have methodological issues. (1) chamber leaks bias ci. (2) ci is the poster child of a theory-laden operational measurement, sensitive to error in A, E, T, gb, & ca. The industrial approach to A vs ci generally precludes careful assessment of these issues.

6/n

Unless (1) the research question specifically requires comparing PS parameters, or (2) the objective is to inform highly detailed modeling using FvCB (combined with an equally precise gs model, which, BTW, doesn't exist), A vs ci curves may *subtract* net value vs Amax.

7/n

So ask yourself honestly whether your study requires A vs ci curves per se. As a reviewer, ask yourself whether the paper/proposal you're reviewing really benefits from having N highly theory-laden Vcmax and Jmax estimates rather than 5N or 10N direct measurements of Amax.

8/8