Nitrogen and Light Responses of Cotton Photosynthesis and Implications for Crop Growth

Abstract

Leaf nitrogen content and light intensity affect leaf photosynthesis. Responses of cotton (Gossypium hirsutum L.) leaf photosynthesis to nitrogen and light were developed and used in a framework that scales from leaf photosynthesis to canopy radiation use efficiency (RUE). This was then used to explore the impact of nitrogen and light dynamics on RUE of cotton canopies. Photosynthetic rate and nitrogen concentration of leaves (specific leaf nitrogen, SLN) were measured from two field experiments in which the rate of nitrogen application was varied. The overall shape of the relationship between photosynthesis and SLN of individual leaves was consistent with that for other species, being described by an exponential rise to a maximum of 32.49 ± 1.08 μmol CO2 m−2 s−1 Incorporating the influence of age improved the relationship, showing an impact of leaf age independent of SLN. The photosynthesis relationship developed should be appropriate for use in simulating cotton crops. The approach used to scale from leaf photosynthesis to canopy RUE was effective in capturing the variation in the RUE of cotton as observed in three field experiments. There appeared to be little impact of the ontogenetic changes in light extinction coefficient and vertical gradients of SLN within the canopy on the variation in RUE. For crop simulation purposes, this simplifies the process of modulating RUE in growth models.