It is well known that the growth of wetland plants is often limited by multiple stresses (e.g. inundation and sedimentation) in wetland ecosystems. Therefore, wetland plants have evolved various acclimations in plant morphology to adapt to these stresses. When different environmental stressors occur simultaneously, plant morphology is likely to adjust to the primary limiting factor if limited energy resources prevent adaptation to multiple stressors. This implies that environmental stressors would affect plant morphological plasticity in a hierarchical manner (i.e. play different roles). However, direct experimental evidence for this hypothesis is lacking.

Inundation and sedimentation are recurring events in wetlands; these processes often occur simultaneously, and can have a profound influence on plant growth. Most studies have investigated the individual effects of sedimentation or inundation on the performance of wetland plants, but few have examined the combined influence of these processes. Therefore, it is surprisingly unclear whether these two stresses have equally important roles on plant morphology. Inundation generally is more inhibiting to wetland plant growth than sedimentation due to more easily reduced oxygen availability in the root zones, suggesting that morphological adjustments to anaerobiosis might be more pronounced under inundated conditions, especially when inundation and sedimentation operate simultaneously.

Using laboratory microcosm, a team of researchers led by XIE Yonghong from China Agricultural University, the Institute of Subtropical Agriculture, Chinese Academy of Sciences (ISA), spent 3 months to test the hypothesis of hierarchical adjustment of plant morphology under inundation and sedimentation.

The researches found that P. hydropiper exhibited morphological adaptations to both deep burial and high water level, including adjustments in root morphology and biomass allocation. Therefore, it is not surprising that shallow burial lone stimulated the growth of P. hydropiper since sediment deposition would reduce the range of daily temperature fluctuation and can provide an additional source of nutrients for plant growth.

The researchers also found that high water level impeded plasticity in biomass allocation to adapt to sedimentation, which led to a further decrease in biomass, suggesting that inundation plays a more important role than sedimentation in determining plant morphology. These results provide direct evidence support for the hypothesis of hierarchical effects of environmental stressors on plant morphology.

This research was supported by National Key Technology Research and Development Program of China (2014BAC09B03), National Basic Research Program of China (2012CB417000) and the National Natural Science Foundation of China (30770362; 31300361).

The study entitled “High water level impedes the adaptation of Polygonum hydropiper to deep burial: Responses of biomass allocation and root morphology” has been published in Volume 4, July 2014 of Scientific report (IF 5.078), details could be found at http://www.nature.com/srep/2014/140708/srep05612/full/srep05612.html