Key message

Plant biostimulants did not improve citrus health and productivity in an HLB-endemic environment after two years, but fulvic acids increased concentrations of some nutrients and influenced the rhizosphere microbial community.

Abstract

Fibrous root loss is one of the main factors associated with citrus tree decline due to Huanglongbing (HLB) disease in Florida, and there is increased interest to use soil amendments such as plant biostimulants to improve root health and crop production. The effect of individual and combined applications of seaweed extracts, humic substances, and microbial inoculants on root and tree health, tree nutritional status, and productivity was investigated in an HLB-endemic environment. Experiments were conducted in two differently managed commercial citrus orchards. The effect of the treatments on the composition and structure of the citrus rhizosphere bacterial and fungal community was examined and linked to variations in root macro- and micronutrient concentrations. Overall, treatments had no effect on disease index ratings, total and specific root lengths, root physiological responses, and fruit quality and yield after two years of application. Only the individual applications of fulvic acids resulted in statistically significant increases in root and leaf macro- and micronutrient concentrations compared to the control treatment, an effect that differed between trials. These increases in root macro- and micronutrient concentrations were linked to variations in the relative abundance of specific bacterial and fungal taxa in the citrus rhizosphere. Our results suggest that longer-term and higher application rates of fulvic acids may be necessary to translate rhizosphere effects into measurable effects on tree health and productivity in HLB-endemic conditions. We show that factors such as different management practices and soil and environmental conditions may determine efficacy of biostimulants on root and tree health.

中文翻译：

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黄龙病流行条件下植物生物兴奋剂对柑桔根和植物健康及根际微生物组的影响

关键信息

两年后，植物生物刺激剂并未在HLB流行环境中改善柑橘的健康和生产力，但黄腐酸增加了某些养分的浓度并影响了根际微生物群落。

抽象的

纤维根系丧失是佛罗里达州因黄龙病（HLB）病而导致柑橘树衰落的主要因素之一，人们越来越关注使用土壤改良剂（例如植物生物刺激剂）来改善根系健康和作物生产。在HLB流行环境中，研究了海藻提取物，腐殖质和微生物接种剂单独和组合施用对根和树健康，树营养状况和生产力的影响。在两个不同管理的商业柑桔园中进行了实验。检查了处理对柑橘根际细菌和真菌群落组成和结构的影响，并将其与根部宏观和微量营养素浓度的变化联系起来。总体而言，治疗对疾病指数评分没有影响，施用两年后，总根和特定根的长度，根的生理反应以及果实的质量和产量。与对照处理相比，仅单独施用黄腐酸会导致根部和叶片中的宏观和微量营养素浓度在统计学上显着增加，各试验之间的效果有所不同。根部大量营养素和微量营养素浓度的增加与柑橘根际中特定细菌和真菌类群的相对丰度变化有关。我们的结果表明，在HLB流行条件下，长期和较高的黄腐酸施用量可能需要将根际效应转化为对树木健康和生产力的可衡量影响。