Simultaneously Improving Soil AMF Community and Phosphorus Uptake by Cotton Plants by Continuous Straw Incorporation and Optimizing Phosphorus Management

Abstract

Phosphorus (P) fertilization and straw incorporation are essential agricultural practices, both of which have an influence on the abundance and diversity of the indigenous arbuscular mycorrhizal fungal (AMF) community. However, there are still research gaps on the interactive effects of P fertilizer application and straw incorporation on indigenous AMF in coastal saline–alkali land. Thus, this study aimed to assess several mycorrhizal features, the abundance, and the community composition of soil AMF in a field after a 4-year barley–cotton rotation. We also explored the roles of AMF play in enhancing cotton P uptake. The field was treated with five triple superphosphate levels (0, 22, 44, 66, and 88 kg ha⁻¹) and subjected to either straw incorporation or removal. The total P content of cotton increased with straw incorporation and increasing P application rates; however, the percentage of P partitioned to bolls, the boll capacity of the root system (BCR), and the boll loading of the root system (BLR) exhibited a trend of initially increasing followed by a decrease. The highest value was achieved when straw incorporation was combined with 44 kg P ha⁻¹. Besides, the root colonization by AMF, soil AMF abundance, and spore density were highest at 22 kg P ha⁻¹ without straw and 44 kg P ha⁻¹ in the straw incorporation treatment. Redundancy analysis (RDA) revealed that the observed community shift was primarily driven by the enhancement of rhizosphere soil pH and organic matter following straw incorporation. Overall, these findings showed that straw incorporation coupled with moderate P fertilizer created a favorable rhizosphere soil environment, which, in turn, enhanced rhizosphere soil AMF diversity and abundance, thereby improving cotton root production capacity and facilitating P distribution to reproductive organs. Our results suggested that the threshold of P fertilizer input can provide a basis for saving P fertilizer and effectively maintain agricultural ecosystems' AMF diversity and abundance in coastal saline–alkali land.