Abstract
Myricaria laxiflora (Tamaricaceae) is an endangered plant that is narrowly distributed in the riparian zone of the Three Gorges, along the Yangtze River, China. Using bright-field and epifluorescence microscopy, we investigated the anatomical and histochemical features that allow this species to tolerate both submerged and terrestrial environments. The adventitious roots of Myr. laxiflora had an endodermis with Casparian bands and suberin lamellae; the cortex and hypodermal walls had lignified thickenings in the primary structure. In the mature roots, the secondary structure had cork. The apoplastic barriers in stems consisted of a lignified fiber ring and a cuticle at the young stage and cork at the mature stage. The leaves had two layers of palisade tissue, a hyaline epidermis, sunken stomata, and a thick, papillose cuticle. Aerenchyma presented in the roots and shoots. Several Myr. laxiflora structures, including aerenchyma, apoplastic barriers in the roots and shoots, were adapted to riparian habitats. In addition, shoots had typical xerophyte features, including small leaves, bilayer palisade tissues, sunken stomata, a thick, papillose cuticle, and a hyaline epidermis. Thus, our study identified several anatomical features that may permit Myr. laxiflora to thrive in the riparian zone of the Three Gorges, China.
Highlights
Myricaria laxiflora (Tamaricaceae) is an endangered species that prior to the construction of the Three Gorges Dam (TGD) was narrowly distributed in the riparian zone along the Yangtze River, China, from Banan County, Chongqing Province, to Zhijiang County, Hubei Province [1,2,3,4,5]
In the amphibious species Cynodon dactylon, Artemisia lavandulaefolia, and Alternanthera philoxeroides, which we have studied from the Jianghan Plain down to the Three Gorges, air spaces included aerenchyma and pith cavities in roots and shoots, and barriers included the endodermis, exodermis, and suberized peripheral ring [22,23,24,25]
Palisade tissue was observed below and above the adaxial and abaxial epidermis, respectively; scant spongy mesophyll tissue was observed between the layers of palisade tissue (Figure 4c–e)
Summary
Myricaria laxiflora (Tamaricaceae) is an endangered species that prior to the construction of the Three Gorges Dam (TGD) was narrowly distributed in the riparian zone along the Yangtze River, China, from Banan County, Chongqing Province, to Zhijiang County, Hubei Province [1,2,3,4,5]. After TGD construction was completed in 2009, only a few natural populations of Myr. laxiflora remained, all downstream of Yidu and Zhijiang counties; as Myr. laxiflora habitats upstream of the TGD were lost, some of the plants from the upstream localities have been preserved ex situ [4,6,7,8,9]. In its native environment along the Yangtze River, Myr. laxiflora remains dormant while completely submerged during summer flood pulses and sprouts in the autumn and winter after the floods recede [1,2,3,4,5]. Like many other wetland plants, Myr. laxiflora is typically subjected to anoxic submersion during summer flooding [2,3,15,16,17]. Aquatic and amphibious plants have aerenchyma and tight barriers to store and retain oxygen
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