Photosynthetic Efficiency and Carbon Allocation Under Elevated Temperature in Nigerian Crop Varieties: Implications for Climate Change Adaptation Agronomy

This study investigates photosynthetic efficiency and carbon allocation patterns in Nigerian crop varieties under elevated temperature conditions, developing original quantitative understanding of the photosynthetic basis of heat stress yield losses and identifying physiological traits for climate change adaptation agronomy. Rising temperatures associated with climate change are projected to significantly reduce photosynthetic efficiency and grain filling in Nigerian crop systems, but the specific mechanisms vary substantially among crop species and varieties in ways that are poorly characterised for Nigerian germplasm. This study subjects contrasting varieties of maize, sorghum, rice, and cowpea to temperature treatments from 25 to 44 degrees Celsius in precisely controlled growth chambers at University of Ibadan and ABU Zaria, measuring gas exchange parameters including net photosynthesis, stomatal conductance, transpiration, and water use efficiency using LI-COR photosynthesis systems. Photosystem II efficiency is assessed by chlorophyll fluorescence. Carbon allocation to grain versus vegetative pools is traced using C-13 labelling. Rubisco activity and heat stability are measured enzymatically. Findings reveal species-specific thermal optima for photosynthesis ranging from 30 to 35 degrees Celsius, with sorghum showing the highest heat stability of photosynthetic enzymes. The depression of photosynthetic carbon assimilation per degree above optimum is steepest in rice at 8 percent per degree Celsius. Carbon allocation to grain decreases most severely in maize under heat stress due to disrupted phloem loading. The study contributes original photosynthetic efficiency data across Nigerian crop varieties and recommends chlorophyll fluorescence screening as a high-throughput tool for heat tolerance variety selection.

Keywords: photosynthetic efficiency, carbon allocation, heat stress, climate change adaptation, Nigeria.