Reframing Citrus Iron Deficiency Chlorosis as a Whole-Tree Iron Homeostasis Disorder

Abstract Iron deficiency chlorosis is a recurrent nutritional disorder that limits citrus growth, productivity and fruit quality, especially in calcareous, saline-alkaline and bicarbonate-rich orchards. Although it is often attributed to poor iron bioavailability in the rhizosphere, its persistence and recurrence cannot be explained by soil chemistry or root uptake alone. Citrus trees are perennial evergreen fruit crops with concurrent sinks, including roots, mature leaves, young flushes, flowers and developing fruits; therefore, iron nutrition depends on rootstock genotype, vascular transport, phloem remobilization, leaf-level iron bioavailability and seasonal source-sink allocation. Here, we reframe citrus iron deficiency chlorosis as a systemic disorder of whole-tree iron homeostasis. We synthesize citrus-specific evidence and broader plant iron-homeostasis concepts to connect rhizosphere iron mobilization, Strategy I root responses, rootstock-mediated acquisition, long-distance transport, the leaf iron paradox, reproductive sink allocation, management strategies and emerging multi-omics approaches. We emphasize that total iron concentration alone is insufficient for diagnosis because iron may be spatially misallocated, chemically immobilized or physiologically unavailable even when bulk levels appear adequate. We further propose a bottleneck-oriented diagnostic workflow linking symptom timing, soil and irrigation constraints, active iron status, root acquisition capacity, vascular transport, spatial localization and confounding stresses to targeted management. This framework provides a crop-specific roadmap for identifying dominant homeostasis bottlenecks, improving iron-efficient rootstock selection and designing precision strategies for recurrent citrus chlorosis.