Abstract
Taxodium ascendens is a typical tree species with high flood tolerance, and it can generate knee roots in the wetlands. This study investigated the number and size of knee roots and the soil flooding conditions. Furthermore, we also measured physiology, biochemical responses, and the anatomical structure of knee roots and underground roots at different developmental stages. This study aimed to understand the adaptation mechanism of T. ascendens to flooding stress and the formation mechanism of the knee roots. The results showed that the formation of knee roots was significantly affected by the soil water table (P < 0.05). The middle water table was more conducive to the formation of knee roots. In the middle water table, the 1-aminocyclopropane-1-carboxylic acid (ACC) content and ACC synthase activity were significantly lower in the knee roots than in the underground roots. The knee roots at the young-aged stage showed the highest ACC oxidase activity among the development stages of the knee roots. The ethylene release rate was significantly higher in the knee roots than in the underground roots (P < 0.05). Indole-3-acetic acid (IAA) content first increased, then decreased with knee root development. The periderm cells at the apex of the knee roots were dead and had many intercellular spaces, which was beneficial for the growth of T. ascendens. In conclusion, the middle water table induced the ethylene and IAA production, which promoted the formation of knee roots, which improved roots ventilation and flooding tolerance of T. ascendens. The results obtained can provide information about mechanisms of knee roots formation and provide scientific evidence for the afforestation and management under wetland conditions.
Highlights
Nowadays, flood damage is receiving a lot of attention, as flooding phenomena tend to be closely associated with global climate changes (Hirabayashi et al, 2013; Zhou et al, 2020)
Our results showed that the diameter at breast height and tree height of T. ascendens were positively and significantly correlated with the number and size of knee roots (Table 2)
Our results indicate that the middle water table is more suitable for the formation and development of knee roots, which is similar to the study of Tang et al (2008), who reported that T. ascendens formed adventitious roots in the high water table and knee roots in the middle water table
Summary
Flood damage is receiving a lot of attention, as flooding phenomena tend to be closely associated with global climate changes (Hirabayashi et al, 2013; Zhou et al, 2020). Flooding is a major abiotic stress that determines species distribution, growth, and yield (Herzog et al, 2016). In China, about 6.6 × 105 km land is waterlogged, accounting for 6.6% of the total land area; in 2020, 16 provinces and 30.20 million people were adversely affected by floods. Uneven precipitation and poor drainage result in frequent waterlogging, seriously constrain crop growth and productivity (Kuai et al, 2015; Xiong et al, 2019). Flooding Affecting Knee Roots Formation shelter forest is essential. Flooding stress can impede the gas exchange between soil and atmosphere, restricting oxygen diffusion in plant tissues. Since oxygen is critical for mitochondrial respiration, this process cannot be maintained under flood conditions, which seriously constrains plant growth (Voesenek and Baileyserres, 2013)
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