Continuous Planting Reshapes Root Endophytic Microbes and Drives Growth Decline in Casuarina equisetifolia.

UNLABELLED: Continuous planting barrier limits the growth of Casuarina equisetifolia (C. equisetifolia), an ecological and economic tree species, yet its microbial mechanism remains unclear. This study revealed microbial-driven barriers by examining the impact of continuous planting on root endophyte communities in C. equisetifolia. The results showed that continuous planting significantly reduced the antioxidant enzyme activities, root activity, and nutrient accumulation in the root system of C. equisetifolia, and inhibited root length and plant height growth. Microbial community analysis revealed that continuous planting led to a significant decrease in the abundance of Nitrobacter, a key endophytic bacterium in the root system, which may weaken the nitrogen metabolism functions mediated by nitrate reduction, nitrogen respiration, and nitrate respiration, and to some extent undermine the nitrogen conversion efficiency of the root system. At the same time, continuous planting promoted the enrichment of pathogenic endophytic fungi (Phomopsis, Pseudocercospora and Diaporthe) in the root system, which may be accompanied by enhanced plant pathogen functions, and this may be associated with a reduction in the antioxidant and nutrient uptake capacities of the C. equisetifolia root system. It was shown that continuous planting inhibited C. equisetifolia growth through a dual microbial mechanism: on the one hand, it reduced functional flora, which may in turn weaken nitrogen metabolism and stress tolerance; on the other hand, it increased pathogenic fungi, which may intensify disease impact. This study offers a new perspective on the microecological mechanism of continuous planting disorder and a theoretical basis for its mitigation via root microbiome regulation. SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1007/s12088-026-01561-9.