Differential Growth Responses of Alternanthera philoxeroides as Affected by Submergence Depths

Effects of Complete Submergence on Growth, Survival and Recovery Growth of Alisma orientale (Samuel.) Juz

Intense precipitations caused by global climate change will result in the occurrence of greater frequencies and longer durations of flooding, influencing the survival and yields of wetland plants. Alisma orientale (Samuel.) Juz., an important traditional medicine with edible scape and inflorescence, naturally grows in wetlands and artificially cultivates in paddy fields prone to flood in China. However, we lack understanding of the effect of complete submergence on A. orientale. Here, experiments with four durations of complete submergence including 5 days (ds), 10 ds, 15 ds and 20 ds followed by 20 ds recovery were performed. In the submergence experiments, the number of, length of and biomass of surviving leaves and the total biomass and new blade biomass were measured; in recovery experiments, number and length of surviving leaves were measured. A. orientale grew out longer new leaves during complete submergence, with a dramatic decline in the biomass of both the leaves and tubers as well as the total biomass at the ends of the submergence experiments. The A. orientale plants had a high survival rate after submergence. The duration of submergence did not influence the time for A. orientale needed to start regrowing. At the end of recovery period, the submerged A. orientale plants generated more leaves, had more surviving leaves, had shorter new leaves and a shorter total length of surviving leaves than the control plants. This study highlights that A. orientale plants can resist at least 20 ds of complete submergence caused by flooding and regrow rapidly after submergence and improves our understanding of the flooding tolerance mechanisms of A. orientale plants.

Stem elongation and gibberellin response to submergence depth in clonal plant Alternanthera philoxeroides

Clonal plants are widely distributed in the riparian zone and play a very important role in the maintenance of wetland ecosystem function. Flooding is an environmental stress for plants in the riparian zone, and the response of plants varies according to the depth and duration of flooding. However, there is a lack of research on the growth response of clonal plants during flooding, and the endogenous hormone response mechanism of clonal plants is still unclear. In the present study, Alternanthera philoxeroides, a clonal plant in the riparian zone, was used to investigate the time-dependent stem elongation, the elongation of different part of the immature internodes, and the relationship between growth elongation and the phytohormone gibberellin (GA) under a series of submergence depths (0 m, 2 m, 5 m, and 9 m). The results showed that stem elongation occurred under all treatments, however, compared to 0 m (control), plants grew more under 2 m and 5 m submergence depth, while grew less under 9 m water depth. Additionally, basal part elongation of the immature internode was the predominant factor contributing to the stem growth of A. philoxeroides under different submergence depths. The phytohormone contents in basal part of the mature and immature internodes showed that GA induced the differential elongation of internode. Plant submerged at depth of 2 m had the highest GA accumulation, but plant submerged at depth of 9 m had the lowest GA concentration. These data suggested that GA biosynthesis are essential for stem elongation in A. philoxeroides, and the basal part of the immature internode was the main position of the GA biosynthesis. This study provided new information about the rapid growth and invasion of the clonal plant A. philoxeroides around the world, further clarified the effects of submergence depth and duration on the elongation of the stem, and deepened our understanding of the growth response of terrestrial plants in deeply flooded environments.

Water depth-dependent stem elongation of completely submerged Alternanthera philoxeroides is mediated by intra-internodal growth variations

Complete submergence, especially deep submergence, poses a serious threat to the growth and survival of plants. One study previously showed that Alternanthera philoxeroides (a herbaceous perennial plant) submerged at depth of 2 m presented fast stem elongation and reduced stem elongation as water depth increased. In the present study, we aimed to figure out from the morphological and anatomical perspective how the differential growth response of the plant to water depth was achieved. We investigated the elongation of different stem parts and the relationship of stem elongation to cell size and number in A. philoxeroides by conducting experiments using a series of submergence depths (0 m, 2 m, 5 m, and 9 m). The results showed that, in comparison with unsubmerged plants, completely submerged plants exhibited enhanced elongation at depths of 2 m and 5 m but suppressed elongation at depth of 9 m in immature stem internodes, and displayed very little elongation in mature stem internodes at any depths. The stem growth of A. philoxeroides at any submergence depth was chiefly caused by the elongation of the basal parts of immature internodes. The elongation of the basal parts of immature internodes was highly correlated to both cell proliferation and cell enlargement, but the elongation of the middle and upper parts of immature internodes correlated nearly only with cell enlargement. This study provided new information on the growth responses of A. philoxeroides to heterogeneous submergence environments and deepened our understanding of the growth performance of terrestrial plants in habitats prone to deep floods.