N uptake, assimilation and isotopic fractioning control δ 15N dynamics in plant DNA: A heavy labelling experiment on Brassica napus L

Natural 15N abundance as an indicator of nitrogen utilization efficiency in rice under alternate wetting and drying irrigation in soils with high clay contents

The ¹⁵N natural abundance is an effective indicator of nitrogen dynamics in plants. The impact of different irrigation regimes as a function of varied soil clay contents on stable nitrogen isotope abundance (δ¹⁵N) in rice remains unknown. Therefore, the response of δ¹⁵N and nitrogen utilization efficiency (NUE) of rice to different combinations of alternate wetting and drying irrigation (AWD) and clay contents were investigated. The study included three AWD regimes, viz. I100, (100 % saturation, 30 mm flooded), I90 (90 % saturation, 30 mm flooded) and I70 (70 % saturation, 30 mm flooded), and three soil clay content treatments, viz. 40 % (S40), 50 % (S50), and 60 % (S60) clay content. Compared with I100, I90 and I70 with high clay content (S60) significantly increased the crack volumes and N leaching losses and reduced the total N accumulation and different forms of NUE of rice plants. The values of δ¹⁵N in above-ground organs and soil were greatly increased by I90 and I70 irrigation regimes compared to I100. An increasing trend of organs δ¹⁵N from root to shoot was found for all three irrigation regimes. Significant negative relationships were found between (i) N partial factor productivity (PFP) and grain ¹⁵N, (ii) PFP and leaf ¹⁵N, and (iii) N harvest index (NHI) and leaf ¹⁵N. These significant negative relationships might contribute to the increased N losses and changed N allocation under AWD with high clay contents. Hence, it is suggested that cracks should be taken into consideration in rice cultivation. Moreover, δ¹⁵N may serve as an effective indicator of NUE in rice grown under AWD irrigation with high clay contents as well as an indirect indicator for assessing the N loss in agro-ecosystems.

Comparative Performances of Beneficial Microorganisms on the Induction of Durum Wheat Tolerance to Fusarium Head Blight

Durum wheat production is seriously threatened by Fusarium head blight (FHB) attacks in Tunisia, and the seed coating by bio-agents is a great alternative for chemical disease control. This study focuses on evaluating, under field conditions, the effect of seed coating with Trichoderma harzianum, Meyerozyma guilliermondii and their combination on (i) FHB severity, durum wheat grain yield and TKW in three crop seasons, and (ii) on physiological parameters and the carbon and nitrogen content and isotope composition in leaves and grains of durum wheat. The results indicated that the treatments were effective in reducing FHB severity by 30 to 70% and increasing grain yield with an increased rate ranging from 25 to 68%, compared to the inoculated control. The impact of treatments on grain yield improvement was associated with higher NDVI and chlorophyll content and lower canopy temperature. Furthermore, the treatments mitigated the FHB adverse effects on N and C metabolism by resulting in a higher δ¹³Cgrain (¹³C/¹²Cgrain) and δ¹⁵Ngrain (¹⁵N/¹⁴Ngrain). Overall, the combination outperformed the other seed treatments by producing the highest grain yield and TKW. The high potency of seed coating with the combination suggests that the two microorganisms have synergetic or complementary impacts on wheat.