模拟水淹-干旱胁迫对水杉幼树实生土壤营养元素含量的影响

模拟三峡库区消落带水位变化情况,对2年生水杉幼树实生土壤p H值和主要营养元素含量进行研究。试验共设置3个处理阶段,阶段1为淹水处理阶段,包括常规供水组(C),半淹组(H)和全淹组(F);阶段2为干旱处理阶段,包括常规供水(C),半淹(H),全淹(F),常规供水-轻度干旱(CD),半淹-轻度干旱(HD)和全淹-轻度干旱(FD)6种不同水分处理组;阶段3时将所有处理组恢复到正常供水处理,每种水分处理均设置水杉幼树实生土壤与无植物空白对照土壤。测试的指标包括p H值,有机质(OM)、碱解氮(AN)、有效磷(AP)、速效钾(AK)、全氮(TN)、全磷(TP)和全钾(TK)含量。研究结果表明,阶段1结束时,C组和H组水杉幼树盆栽土壤的氮素及TP含量较无植物组显著下降,H组的AP含量及F组的氮素和TP含量显著升高;与正常供水组(C组)相比,淹水处理增高了水杉幼树盆栽土壤的p H值和OM含量,降低了其AP含量,而F组水杉土壤的TN、TP和AN含量分别较C组显著升高17.1%,16.9%和34.2%。阶段2结束时,前期水淹增加了水杉幼树实生土壤p H值、OM、AN和AP含量后期对干旱的敏感性;与无植物组相比,水杉幼树的栽植增加了除C组外的其他水分处理组土壤的OM含量;在水杉盆栽土壤中,与C组相比,H和F组的p H值分别升高2.6%和3.8%,OM含量却未出现显著差异。经过21 d的正常供水处理,H、HD组水杉土壤的p H值较无植物组土壤显著下降,所有水淹组土壤的OM含量则显著升高,与此同时,C组、CD组的TN和CD组的TP含量显著升高;各淹水处理组的水杉土壤在恢复生长后,其p H值及多项营养元素含量均已恢复至C组水平,HD和FD组水杉土壤的所有化学性质亦恢复至CD组水平。在对水杉幼树盆栽土壤化学性质的相关分析中发现,OM、TN、TP和AN含量两两之间存在极显著的正相关,p H值与OM、TN、TP、TN含量呈极显著负相关关系。研究证实,在三峡库区消落带适度营造水杉对于恢复库区植被、改良土壤肥力状况具有积极作用,但是在水库退水期时应及时浇水灌溉,避免将其置于干旱环境当中。

Effects of simulated submergence and drought on the nutrient content of soils planted with Dawn Redwood (Metasequoia glyptostroboides) saplings

This study investigated the effect of how water availability influences the pH and nutrient content of soils planted with two-year-old Dawn Redwood (Metasequoia glyptostroboides) saplings, by applying different water treatments to simulate the water-level-fluctuation zone of the Three Gorges Reservoir in this study. The treatments involved 3 phases. In the first phase, the treatments were presented with a conventional water supply (C), half flooding (H), and full flooding (F). Light drought was introduced in the second phase, and included six: conventional water supply (C), half flooding (H), full flooding (F), conventional water supply followed by light drought (CD), half flooding followed by light drought (HD), and full flooding followed by light drought (FD). In the third phase, all treatments were returned to the conventional water supply. Each treatment group lasted 166 days in total, and contained soil samples planted with two-year-old M. glyptostroboides saplings and soils without vegetation. The pH value, organic matter (OM), total nitrogen (TN), total phosphorus (TP), total potassium (TK), alkali hydrolysable nitrogen (AN), available phosphorus (AP), and available potassium (AK) content in soils containing M. glyptostroboides soils and non-vegetated soils were measured after each 166-day treatment. After phase I, compared to non-vegetated soils (control), M. glyptostroboides soil in groups C and H had highly significant lower nitrogen and TP content and the H treatment had lower AP content, while the F treatment had higher nitrogen and TP content. Compared with the control (group C), flooding treatment increased the pH value and content of OM, whereas AP content decreased. Compared to the control, the TN, TP, and AN content in group H of M. glyptostroboides soils increased by 17.1%, 16.9%, and 34.2%, respectively. After the drought treatment of phase II, flooding had a significant effect on the subsequent sensitivity of pH value, as well as OM, AN, and AP content in M. glyptostroboides soils. Compared to the control, the OM content in the soils of all the water treatment groups (excluding group C) increased significantly in the soils planted with M. glyptostroboides. Concurrently, compared with group C, the pH value increased by 2.6% and 3.8% in group H and F, respectively;however, the OM content was not significantly different in M. glyptostroboides soils. After the water supply was resumed to the level of the control for all treatments, compared to the control, the pH value of M. glyptostroboides soils in group H and HD decreased. In contrast, the OM content in the soils of all the flooding treatment groups and the TN content in soils of group C and CD content increased significantly. In addition, compared to the control, the OM content significantly increased in all the previous flooding treatment groups. The pH value and a number of nutrient contents under the flooding treatments recovered to the level of the control group after recovery growth treatment. All of the chemical properties of the HD and FD groups in M. glyptostroboides soils also recovered to the level of the CD group. The correlation analysis of soil chemical properties in M. glyptostroboides saplings soils showed that a very significant, positive correlation was present among OM, TP, TN, and AN content. However, the pH value exhibited a highly negative relationship with OM, TN, TP, and TN content. The results showed that M. glyptostroboides is viable for revegetating the water-level-fluctuation zone of the Three Gorges Reservoir, but that timely irrigation during the drawdown time period is necessary.