Faster response to water level increase facilitatesSalix cavalerieisurvival in Lake Erhai

Abstract

The roles that adventitious roots play in flooding tolerance have been well-studied in willows, while which of the maximum height of adventitious roots and the abundance of adventitious roots in willows is more important for their flooding tolerance is not well known. In this study, we analyzed the effects of adventitious roots on the flooding tolerance of Salix cavaleriei by comparing the maximum height of adventitious roots and the abundance of adventitious roots in dead and live willows along a flooding gradient from 0 to 180 cm in Lake Erhai, China. The results showed that willow mortality increased drastically when the water depth suffered by willows exceeded 100 cm. Live willows developed more adventitious roots and produced them higher on the trees compared with dead willows, however, the pest infestation percentage of the dead willows was larger. Additionally, both the maximum height and the abundance of adventitious roots in live willows were significantly correlated with water depth, whereas in dead willows, these variables were not significantly correlated or only weakly correlated with water depth. The results indicate that producing adventitious roots higher on the trees may be more important than developing abundant adventitious roots lower on the trees when S. cavaleriei is subjected to high flooding levels. Our data highlight that a faster adventitious root response promotes this species' survival under flood stress, although pest infestation accounts for a small percentage of willow mortality. Accordingly, we should choose those willows that can develop more abundant adventitious roots and higher on the stems to plant in regions with abrupt water-level fluctuations.

Floating Mat Formation Makes Zizania latifolia More Competitive under the Conditions of Continuous Significant Water Level Rise

“…As far as plants are concerned, we believe that the uprooting or the floating mat formation of an emergent macrophyte is greatly influenced by the three factors (the plant root:shoot biomass ratio, the plant volume:mass ratio, and the angle between the plant and the horizontal plane) mentioned above, though other mechanisms may play important roles in these functions [23][24][25]. In our field survey, we found that the emergent community in Lake Erhai had changed from a Phragmites australis, Typha orientalis and Acorus calamus polydominant community to a Zizania latifolia monodominant community over the past decades during a long period of increasing water level, usually over 80 cm (and even 100 cm in some specific years) than before since 2003 by water level regulation, [20,26,27]. Furthermore, an increasing number of floating mats had formed and distributed throughout the lake's littoral zone (Figure 1).…”

“…In general, the formation of an emergent floating mat demands two habitat requirements: shelter from wind and wave action and stability of water level fluctuations [11]. The adaptations of macrophytes to deep water include increases in plant height, branch length, shoot internodes and shoot:root biomass ratio, and reductions in belowground biomass and branch number [2,6,7,19,20]. All these adaptations can be demonstrated by the root:shoot biomass ratio of a plant to some degree.…”