Studying the anatomy and apoplastic barrier features of Triarrhena lutarioriparia var. humilior adapted to Jianghan floodplain environments

The anatomical structures and apoplastic barriers of Triarrhena lutarioriparia var. humilior are still unknown although this species has adapted to the Yangtze River Basin riparian zone. The vegetative organs of T. lutarioriparia var. humilior distributed in the Jianghan Floodplain along the Yangtze River were used as experimental materials. We employed manual sectioning under a stereoscopic microscope, and histochemical, bright-field microscope, and fluorescence microscope methods to observe and record the results; we investigated the anatomical structures and apoplastic barriers of the adventitious roots, stems, and leaves of T. lutarioriparia var. humilior. The results showed that: 1) the air spaces and apoplastic barriers of T. lutarioriparia var. humilior had adapted to the Jianghan Floodplain; the air spaces included lysigenous aerenchyma in the adventitious roots, stems and leaves; and the apoplastic barriers included suberinized and lignified endodermis, exodermis, stele, sclerenchyma tissues, and a vascular system in the vegetative organs. 2) The adventitious roots, stems, and leaves of T. lutarioriparia var. humilior had a suberinized stele and vascular system, which are associated with material transport, and the leaves had a typical C₄ plant-Kranz anatomy, which comprised bundle sheath cells and parenchymatous sheaths. 3) The apoplastic barriers coupled the conducting and mechanical tissues, which surrounded the air spaces to transport air and material under submerged environments, to effectively ensure the aerobic respiration and structural integrity of the plants for survival. The anatomical and barrier structure characteristics of T. lutarioriparia var. humilior facilitated its adaptation to the seasonal flood environments of the Jianghan Floodplain, while also providing important plant resources and a theoretical basis for the ecological restoration of the Yangtze River Basin.