Coated diammonium phosphate combined with Paecilomyces variotii extracts improves root architecture, enhances spring low temperature tolerance, and increases wheat yield

The growth, development, and grain yield of winter wheat (Triticum aestivum L.) was seriously limited by the low use efficiency of phosphorus (P) fertilizers and the spring low-temperature events. Diammonium phosphate is one of the most important sources of P fertilizers worldwide. Controlled release diammonium phosphate (CRDAP) synchronizes fertilizers P release and crop growth demand is positive to improve P use efficiency (PUE) and reduce P loss, whereas biostimulants such as Paecilomyces variotii extracts (ZNC) have ultrahigh activity in promoting crop growth and abiotic stress resistance. However, little information is available on synergistic effects of CRDAP and ZNC on winter wheat growth. A three-year field experiment from October 2017 to June 2020 was conducted with five treatments: DAP (application of conventional diammonium phosphate); CDAP (CRDAP application); DAPZ (application of diammonium phosphate-ZNC composite); CDAPZ (application of CRDAP-ZNC composite); Control (no P fertilizer or ZNC). Plant growth (root, shoot, and photosynthesis), hormone (auxin content from roots and leaves, and ABA content from leaves), ROS scavenging system (H2O2, superoxide dismutase (SOD), peroxidase (POD), catalase (CAT), and glutathione reductase (GR)), and soil available P were measured along with yield and PUE. The results showed that the yield and PUE of CDAPZ were significantly more (by 6.0% and 9.3 percentage points, respectively) than for CDAP. The interactive effects between CRDAP and ZNC were evidenced by the CDAPZ enhanced soil available-P supply and increased average available-P content (22.0% more than CDAP in the 0-40 cm soil layer) and improved root growth with 29.9% increase in total root length by CDAPZ than CDAP at the jointing stage. Moreover, the IAA content of roots from CDAPZ was higher than any other treatments, and the effect of ZNC on IAA content was verified by a laboratory incubation experiment. Similarly, the highest photosynthetic rate was found in CDAPZ, which was 11.0-17.0% higher than that in CDAP. The application of CRDAP combined with ZNC decreased H2O2 content by 8.6%, and increased the activities of SOD, POD, CAT, and GR, thereby enhancing the cold tolerance of wheat. Hence, CRDAP-ZNC composite may serve as an emerging green fertilizer technology and play a crucial role in improving crops response to climate change, and increasing crop yield and PUE.