## 4 Discussion
### Effects of Root-Cutting Treatment on the Root Sprouting Ability  
The roots of plant species with sprout ability have adventitious and dormant buds/new shoots, which can be stimulated to regenerate into new sprouts by external disturbances (e.g., injuries and cutting, etc. ), and this phenomenon can be applied to promote plant sprout regeneration [29; 43]. Our study was also consistent with this phenomenon, i.e., the _A. elata_ plants without root cutting treatment did not produce root sprout. However, only the root sprout height and basal diameter of _A. elata_ in 2020 were affected by the interaction of root-cutting distance and root-cutting ratio. In the first growing season after root-cutting treatments (i.e., in 2018), our results showed that the number of root sprouts of small _A. elata_ plants reached the maximum at the root-cutting distance of 0.25 m, while the number of root sprouts of large _A. elata_ plants with 100% root-cutting ratio was significantly higher than those with other root-cutting ratios. Thus, the root sprouting ability of small _A. elata_ plants and large _A. elata_ plants were mainly affected by the root-cutting distance and root-cutting ratio, respectively. The plant root structure is closely related to the plant size [44] Thus, in this study, the root sprouting ability of _A. elata_ plants with different sizes showed different responses to root-cutting treatment. When cutting the roots of small _A. elata_, the root-cutting distance of 0.25 m could be the most conducive to the early formation of root sprouts. The root system can provide the initial carbon source for sprouts and play an important role in carbon balance and the allocation of sprouts [45]. Therefore, previous studies on sprout regeneration after disturbance indicated that the non-structural carbohydrates (NSCs) stored in root system can support the metabolism and growth of new sprouts to rapidly occupy the ecological niche [35], until the photosynthetic products can meet the carbon requirement of the sprouts. In this study, we found that, after three growing seasons (in November 2020), the root sprout height and basal diameter of small _A. elata_ reached the maximum at the root-cutting distance of 0.25 m with 100% root-cutting ratio. On the one hand, this may be because the roots which are closer to the plant stem with a larger diameter and dense distribution can provide sufficient carbon storage to support the growth of root sprouts before their photosynthates can meet the carbon requirement. On the other hand, previous studies have indicated that the degree of root disturbance and root-cutting diameter and location have a significant influence on the root sprouting ability of plants, but the effects vary between species [29; 43]. Our results concerning the best growth of small _A. elata_ may also relate to the residual root segment after cutting in the soil. As the root-cutting location was near the stem, the size of the residual root segment (i.e., length and diameter) in the soil was larger. The nutrients stored in the residual root segment were more abundant to support the early growth of root sprouts. Therefore, the optimum root-cutting method to promote the root sprout regeneration of the small plant was a 100% root-cutting ratio at a root-cutting distance of 0.25 m.  
Compared with the small _A. elata_ plants, the effect of root-cutting treatment on the root sprouting ability of large _A. elata_ plants was weakened. For large _A. elata_ plants, our results only showed the significant effect of root-cutting ratio on the number of root sprouts in the first growing season after root-cutting treatment, and the 100% root-cutting ratio was beneficial to the root sprouting ability of large _A. elata_ plants. However, the effect of root-cutting treatment vanished in the subsequent root sprout regeneration. Consequently, when cutting the roots of large _A. elata_ plants, only the optimum root-cutting ratio (100% root-cutting ratio) should be considered. These results supported our hypothesis (3).