GROWTH RESPONSE AND PHOTOSYNTHETIC ACCLIMATION TO CO₂: COMPARATIVE BEHAVIOUR IN TWO C₃ CROP SPECIES

Growth response to supplementary carbon-dioxide (1350 versus 330-350 μbar CO₂) was followed on Cucumis sativus and Brassica pekinensis under natural illumination over 40–50 days of continuous treatment.
Photosynthetic characteristics were derived from gas exchange measurements on partially enclosed attached organs under closely controlled laboratory conditions.

Greater final biomass in treated plants resulted in part from higher net assimilation rate but more especially from faster leaf expansion during early exponential growth phases.
This response diminished with age, and relative leaf growth rate fell to even lower values on CO₂-enriched plants of ambient controls in some cases.

Photosynthetic acclimation to elevated CO₂ occurred in Cucumis sativus and was associated with some loss of carboxylating efficacy.
Initial slopes of curves relating assimilation (A) to intercellular CO₂ (p_i) responded within 2 days of transfer from ambient levels, with an associated reduction of in vitro RUBISCO and Hill activities.
By contrast, Brassica pekinensis showed no loss of carboxylating efficacy despite continuous enrichment over 33 days.
Both initial slope of A/P_i curves and in vitro activity of RUBISCO remained unchanged.

Implications for crop response to CO₂ enrichment under greenhouse conditions are discussed.

Symposium on CO2 Enrichment

P.E. Kriedemann, S.C. Wong

https://doi.org/10.17660/ActaHortic.1984.162.10