Leaf photosynthesis was lowest in cool climate leaves , and after one week of acclimation in warmer climate photosynthetic rates partially increased with an apparent upward shift in optimum temperature, particularly in the cool-humid habitat cv M Col 2059. Rates of leaves developed in warm climate were the highest, showing also an apparent upward shift in optimum temperature. Rates in all sets of leaves were greater in the hot-humid cultivar from Brazil, M Bra 12. These findings attest to the adaptability of cassava to warmer climate, and hence to its predicted suitability to future climate changes as shown in Figure 2. The adaptation of cassava photosynthetic capacity to warmer temperature is also illustrated by the lack of light saturation in warmclimate leaves, compared to responses observed in cool-climate leaves and in cool-climate leaves acclimated for one week in warm climate.

Under field conditions at the university of Illinois, Urbana, US, using the sophisticated “Free Air Carbon Dioxide Enrichment ” method, increasing to 585 ppm within canopy for 30 days enhanced cassava leaf photosynthesis, as measured at elevated , for both plants growing at ambient and elevated , with the former showing greater response . However, when leaf photosynthesis was measured at greater than 600 ppm, plants grown at elevated CO2 showed, over the tested external CO2 range, consistent and slightly higher rates than plants grown at ambient CO2. Such data indicate that acclimation of photosynthesis , if it occurs due to long exposure to higher than ambient CO2, may not result in reduction in cassava growth and productivity. Similar findings were reported from Venezuela using opentop chambers where cassava photosynthesis, growth and root yield of field-grown plants exposed during its entire growth period to double-ambient CO2 concentrations, were significantly greater than those in ambient CO2- grown plants . Also, greenhouse-grown cassava under elevated CO2 at USDA-ARS labs in Maryland, US, had greeter photosynthesis, biomass and yield, compared to ambient CO2 level-grown cassava .

These findings contradict reports from Australia on potted indoor-grown cassava, where leaf photosynthesis, plant growth and storage roots were reduced in plants grown in elevated CO2, compared to plants grown under ambient CO2 . Cassava is a shrub that requires large volume of soils for storage root development and filling, and therefore, in the Australian experiments there were apparently feedback inhibition of leaf photosynthesis due to restricted root-sinks. Moreover, cassava plant is resilient in nature with plasticity in its growth habits forming several branches on main stems associated with reproductive organs in most cultivars, thus, providing alternative sinks for extra photo-assimilates . This type of growth and phenology behavior with multiple and larger sink demands for photo-assimilates should enhance leaf photosynthesis under elevated CO2 and, hence, could lead to greater total biomass and yield . Using the EPIC crop model to assess the impact of climate change on cassava adaptability and productivity in marginal lands of northeastern Thailand, Sangpenchan reported that cassava grown in water-limited areas would benefit from the so-called “CO2 fertilization” contribution when combined with improved production technologies. Moreover, the crop would likely respond to rising CO2 by decreasing its evapotranspiration rate because of its tight stomatal control mechanism and, hence, increasing the efficiency with which it used limited water supply predicted with climate changes. When cassava leaves were exposed to dry air under laboratory conditions, their stomata closed in both well-watered and stressed plants without changes in leaf water potential. Transpiration initially increased with rising leaf-to-air vapor pressure deficit up to 2 kPa and then declined with further increases. Such response contrasts with transpiration in maize leaves where transpiration increased with rising VPD.

At canopy level in wet soils, raising air humidity via fine misting enhanced PN that led to increases in storage roots . The striking response to humidity is a “stress avoidance mechanism” that underlies cassava conservative water use, particularly under soil water deficits, an advantage as compared to less sensitive species such as maize. Two-year field trials were conducted under prolonged early water stress ; mid-season stress , and terminal stress . Table 3 presents data on root yield, shoot and total biomass at 12 months, and nutrient use efficiency in terms of root production. On one hand, water stress reduced shoot biomass in all stages but reduction was significant only in early stress. On the other hand, final root yield across clones was not significantly reduced at any water shortage treatment.