Photosynthesis and assimilate distribution in relation to yield of cassava grown in controlled environments

Abstract

Cassava (Manihot esculenta Crantz) plants were grown for 52 weeks in controlled-environment growth rooms with day/night (14/10 h) temperatures of 29/24 °C and 24/19 °C. Plants were sampled for growth analysis at monthly intervals for 36 weeks and at 52 weeks. At intervals the photosynthetic CO₂ uptake by leaf parts and the respiration were measured in situ by using infrared CO₂ analysis.The growth rate at both temperatures was directly related to the product of leaf photosynthesis and total leaf area, and the decreasing net assimilation rate of the high-temperature plants was reflected in the declining mean photosynthetic rates of the leaf tissue. The rate of photosynthetic CO₂ uptake was between 9 and 18 mg dm⁻² h⁻¹, depending on leaf position.During the early stages of growth, the relationship between root weight and total weight was unaffected by temperature. As the plants increased in size, the proportion of dry matter in the roots increased in low-temperature plants but remained constant in high-temperature plants. The estimated plant respiration averaged 45% of the total assimilation. In high-temperature plants the root respiration was equivalent to 0.7% of the root dry weight per day and after 36 weeks the total root respiration exceeded the root growth.