The effect of hydrological regimes on the concentrations of nonstructural carbohydrates and organic acids in the roots of Salix matsudana in the Three Gorges Reservoir, China

Abstract

Hydrological fluctuations accelerate biodiversity loss and damage riparian ecosystems surrounding dams and reservoirs. Restoration of vegetation is urgently required in such highly impacted buffer zones. However, it is not known how the nonstructural carbohydrate (NSC) and organic acid concentrations of prominent woody plants such as Salix matsudana would alter under the hydrological regime described in the literature. The study aims to investigate the tap and lateral roots of S. matsudana in the Three Gorges Reservoir, as well as the NSC and organic acid metabolism of these roots. Three groups of two-year-old S. matsudana saplings were planted in this experiment: control (SS), moderate submergence (MS), and deep submergence (DS) at altitudes of 175 m, 170 m, and 165 m, respectively. The results indicated that hydrological regimes restrained the height of S. matsudana with less impact on diameter at P < 0.05 compared with SS but showed a 100 % survival rate throughout the experiment. Meanwhile, root starch concentrations of 108.46 ± 9.18 mg/g (mean ± standard error) were higher than those of soluble sugars (86.81 ± 12.98 mg/g) after hydrological stress. Moreover, the levels of soluble sugar, starch, and NSC in MS were higher than those of SS1 (1stphase of control). However, soluble sugar, starch, and NSC content in DS were lower than in SS2 (2ndphase of control), where lateral root starch and NSC content were more significant than those in the taproot. After 205 days of submersion (DS), oxalic acid, tartaric acid, and malic acid content were higher than after 135 days (MS). They followed the pattern of malic acid > tartaric acid > oxalic acid. The tartaric acid content of the lateral roots and the total roots was significantly higher in MS than in SS1. Conversely, the oxalic acid and malic acid levels in tap roots, lateral roots, and total roots were higher in DS than in SS2. There were strong Pearson's correlations between root starch and NSC with tartaric and malic acids; these correlations ranged from −0.898 < r < 0.981. These data indicate that S. matsudana can maintain certain levels of starch, malic acid, and tartaric acid to enable it to better adapt to its environment under in-situ flooding stress.