Nitrogen Nutrition Improves the Potential of Wheat (Triticum aestivum L.) to Alleviate the Effects of Drought Stress during Vegetative Growth Periods.

Muhammad Abid,Dong Jiang,Syed Tahir Ata-Ul-Karim,Yakun Cui,Zhongwei Tian,Tingbo Dai,Yang Liu,Rizwan Zahoor

doi:10.3389/fpls.2016.00981

Abstract

Efficient nitrogen (N) nutrition has the potential to alleviate drought stress in crops by maintaining metabolic activities even at low tissue water potential. This study was aimed to understand the potential of N to minimize the effects of drought stress applied/occur during tillering (Feekes stage 2) and jointing (Feekes stage 6) growth stages of wheat by observing the regulations and limitations of physiological activities, crop growth rate during drought periods as well as final grain yields at maturity. In present study, pot cultured plants of a wheat cultivar Yangmai-16 were exposed to three water levels [severe stress at 35–40% field capacity (FC), moderate stress at 55–60% FC and well-watered at 75–80% FC] under two N rates (0.24 g and 0.16 g/kg soil). The results showed that the plants under severe drought stress accompanied by low N exhibited highly downregulated photosynthesis, and chlorophyll (Chl) fluorescence during the drought stress periods, and showed an accelerated grain filling rate with shortened grain filling duration (GFD) at post-anthesis, and reduced grain yields. Severe drought-stressed plants especially at jointing, exhibited lower Chl and Rubisco contents, lower efficiency of photosystem II and greater grain yield reductions. In contrast, drought-stressed plants under higher N showed tolerance to drought stress by maintaining higher leaf water potential, Chl and Rubisco content; lower lipid peroxidation associated with higher superoxide dismutase and ascorbate peroxidase activities during drought periods. The plants under higher N showed delayed senescence, increased GFD and lower grain yield reductions. The results of the study suggested that higher N nutrition contributed to drought tolerance in wheat by maintaining higher photosynthetic activities and antioxidative defense system during vegetative growth periods.

Highlights

Plants match their growth rate according to the availability of resources such as light, water, and nitrogen (N) by a number of acclimation mechanisms
There was a progressive decline in the w and membrane stability index (MSI) during the drought stress (Figure 1)
There was no significant difference in w and MSI between the two N levels under WW conditions, but there was a significant difference between treatments on these parameters under drought stress conditions. w and MSI declined more under low N application and greater decline was observed at jointing stage as comapred to the tillering stage under drought stress

Summary

Introduction

Plants match their growth rate according to the availability of resources such as light, water, and nitrogen (N) by a number of acclimation mechanisms. Photosynthetic rate and chlorophyll (Chl) fluorescence, and their fluctuation around their normal values are the significant indicators of both plant fitness and extent of environmental stress (Maxwell and Johnson, 2000). A change in Chl and Rubisco contents under unfavorable conditions may reflect the extent of damage to the light-harvesting complexes of the leaf. Moderate drought stress decreases the photosynthesis mainly due to the stomatal limitations; other interrelated photosynthetic processes are not significantly damaged. In contrast under extreme drought stress when stomatal opening is less than 0.1 mol H2O m−2s−1 stomatal resistance, poor performance of photosystem II (Fv/Fm) and downregulated activities of CO2 assimilating enzymes such as Rubisco become the dominant limitations to reduced photosynthesis (Grassi and Magnani, 2005)

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