Changes in leaf nitrogen and phosphorus content, photosynthesis, respiration, growth, and resource use efficiency of a rapeseed cultivar as affected by drought and high temperatures

A comprehensive understanding of the impacts of the environmental stresses on both vegetative and reproductive stages of crop growth is required to assess the impacts of climate change and climate variability on crop production. However, little is known about the effects of drought and high temperature stress and their combination on leaf nitrogen (N) and phosphorus (P), the key physiological processes such as photosynthesis and respiration and resource-use efficiency (i.e., water and nitrogen use efficiency) in crop plants.

Rapeseed (Brassica napus) is a major oilseed crop over 28 countries and also a promising biofuel crop in arid, semi-arid and temperate regions. Despite the fact that prediction of future climate change with high temporal and spatial variability, there has been little attention paid to the impacts of drought and/or high temperature on the vegetative development of rapeseed crop plants. The limitation of photosynthesis and growth by environmental stresses such as drought and high temperature might be associated with an alteration in N and P levels in plants as carbon and nitrogen assimilation in plants are coupled in plant metabolism. However, the interactions of climate variability, particularly drought and heat stress with plant nutrients have received far less attention. Therefore, we designed a controlled growth chamber study to test the hypothesis that drought, high temperature and their combination would differentially alter N and P levels in leaves, key physiological processes, growth and resource use efficiency in plants.

We found that drought reduced N concentrations by 22% and P concentrations by 23% relative to control plants, and therefore the total content of N and P in leaves was found to be decreased as much as by 43% and 44%, respectively under drought. The results obtained in concentration and total content of N and P in rapeseed under moderate drought are consistent with the notion that plant shoots are metabolically deactivated during short term drought to reduce the consumption of water and nutrients, whereas roots are metabolically activated to increase consumption resources in order to buffer the effects of drought. Our results also indicate that drought could reduce high temperature-caused increased soil mineralization, plant nutrient availability and nutrient uptake under combined drought and high temperature treatment. These changes in N and P levels and associated plant growth are important in determining plant nutrient requirements or fertilizer recommendations when the likelihood of plants experiencing drought and high temperature stresses.