Comparative effects of humic acid biostimulation on soil properties, growth, and fragrance of Rosa rugosa
Yong Xu, Meng Li, Haiquan Ding, Yuanxiao Ma, Yang Yang, Liguo Feng
Abstract
The excessive use of chemical fertilizers has raised significant environmental concerns, driving interest in plant biostimulants such as humic acid (HA) as sustainable alternatives in agriculture. This study investigated the effects of varying HA ratios—15 % (HA1), 30 % (HA2), and 45 % (HA3)—on the growth of Rosa rugosa , using field soil as the control (CK). HA application significantly ( P < 0.05) increased soil total nitrogen (TN), available potassium (AK), organic matter (OM), and iron (Fe). Soil pH shifted from alkaline to neutral with HA application. Furthermore, leaf nitrogen (N) and phosphorus (P) contents exhibited a bell-shaped response, peaking in HA2. Although excessive HA application (HA3) enhanced root absorption of some micronutrients, it had lower leaf accumulation. HA significantly influenced rhizosphere microbial communities, with bacterial operational taxonomic units and α-diversity index peaking in HA2, whereas fungal diversity exhibited an opposite trend. The changes of microbial community abundances were correlated with soil pH, OM, TN, AK, and Fe. Moreover, HA application influenced plant agronomic indexes, with HA2 achieving the highest values, including a significant increase in root dry weight, rose yield and flower fragrance compounds. Transcriptomic analysis revealed that HA application stimulated differentially expressed genes (DEGs) across 27 biological processes and 37 metabolic pathways in roots, with HA2 exhibiting the highest enrichment. Notably, DEGs related to monoterpene synthesis identified in rose flowers were also most prevalent in HA2. This study demonstrated that HA served as a dose-dependent plant biostimulant, with moderate application (HA2) significantly improving rhizosphere microbial communities, plant growth, and fragrance through itself and improvements in soil nutrition. The effects were decreased with less HA application (HA1), while excessive application (HA3) even inhibited these benefits. These findings provide both practical evidence and theoretical insights for optimizing the use of HA in the cultivation of R. rugosa and other crops. • The effects of varying humic acid (HA) ratios on the growth of R. rugosa in the field were investigated. • 30 % HA increased the abundance of four main bacteria phyla and decreased the abundance of four dominant fungal phyla. • 30 % HA exhibited the highest number of up-regulated differentially expressed genes in GO and KEGG enriched pathways. • 30 % HA maximized benefits not only in soil health, plant growth, yield but also in rose fragrance.