Changes in yield attributes and K allocation in wheat as affected by K deficiency and elevated CO2

Abstract

Elevated carbon dioxide enhances biomass production and final crop yield of C3 species as a consequence of increased photosynthesis, water use efficiency and RuBisCO saturation. However, this enhancement is limited by environmental conditions such as nutrient deficiencies. This study evaluates the interactive effects of K supply (deficient or adequate) and atmospheric CO2 (ambient or elevated) on grain yield and yield related attributes along with allocation of K in different shoot parts (i.e. grains, leaves, stem and peduncle) in bread wheat. Bread wheat (T. aestivum cv. Tahirova) was cultivated in soil fertilized with adequate or deficient K in pots under ambient (420 μmol mol−1) or elevated (700 μmol mol−1) atmospheric CO2 conditions in dedicated plant growth chambers. At full maturity, plants were harvested and grain yield and yield attributes along with K status of grains, peduncle, leaves and stem parts were determined. While K deficiency severely reduced grain yield and yield attributes under both ambient (a-CO2) and elevated (e-CO2) CO2 conditions, e-CO2 significantly enhanced grain yield even in K-deficient plants through maintaining a greater harvest index, spikes per plant and grain weight and thus increased overall K use efficiency. Deficient-K treatment significantly increased grain K concentration as a consequence of “concentration effect”. On the contrary, K concentration in leaf, stem and peduncle was severely decreased whereas e-CO2 had an additive effect on the decrease in K concentrations. Consequently, in deficient-K plants K content (total K accumulated/taken up) in all shoot parts including grains was reduced to only a fraction of adequate-K plants. Moreover, deficient-K plants tended to allocate a greater portion of K in grains as compared to other shoot parts. Elevated CO2 also enhanced K allocation into grains particularly in deficient-K plants. Potassium deficiency severely reduces grain yield and biomass production in bread wheat in both a-CO2 and e-CO2 environments, however e-CO2 partly alleviates the detrimental effect of K deficiency on grain yield, but not straw yield. Plants under K deficiency stress allocated a greater portion of K in the grains and e-CO2 augmented this effect. In wheat, any one of peduncle, leaf or stem K concentration is a better measure of overall plant K nutritional status as compared to grain K, which may be severely biased due to “concentration effect” in K-deficient plants.