桑树在模拟三峡库区消落带干旱条件下的生长状况及土壤氮磷元素的变化

Mulberry Growth and Variation of Soil Nitrogen and Phosphorus Content Under Artificial Drought Created to Simulate Hydro-fluctuation Belt of the Three Gorges Reservoir Area

在温室盆栽桑树并模拟三峡库区消落带出陆期(4～10月)的土壤干旱环境,设置常规水分条件(CK)、中度干旱胁迫(T1)和严重干旱胁迫(T2)3个土壤含水量梯度,调查与分析不同土壤水分条件下桑树的生长状况及土壤氮、磷含量的变化。随着土壤水分含量的减少,桑树生长被抑制程度增加,桑树的株高和地径均为CK>T1>T2,而比根面积为T2>T1>CK,差异显著(P<0.05)。受到中度干旱胁迫的桑树,其根冠比和根系活力均显著高于常规水分条件下生长的桑树,但受到严重干旱胁迫的桑树,其根冠比和根系活力显著低于常规水分条件下生长的桑树(P<0.05)。桑树生长7个月后,各处理组土壤的有机质、全氮和全磷含量均显著低于土壤初始含量(P<0.05),但各处理组之间的土壤全氮和全磷含量均无显著差异(P>0.05),各处理组的土壤铵态氮、硝态氮和有效磷的含量均为T2>T1>CK,并且与土壤初始含量相比显著下降(P<0.05),下降程度为CK>T1>T2。研究结果提示:三峡库区消落带的土壤干旱对桑树生长具有一定的影响,但适度的干旱有助于桑树根系向地下生长而增强对水分的吸收能力;不同水分条件下桑树的生长均对土壤中的氮、磷元素具有明显的吸收作用,因此可在一定程度上减少水体富营养化主导因子氮、磷释放进入水库。

To investigate and analyze mulberry growth and variation of soil nitrogen and phosphorus contents under dif-ferent water conditions, we grew potted mulberry in a greenhouse under three soil water treatments, namely normal irrigation （CK）, moderate drought stress （T1） and severe drought stress （T2）, which were designed to simulate the drought condition during land appearing peri- od （April to October） in hydro-fluctuation belt of the Three Gorges Reservoir Area. The results showed that, with soil moisture content decreased, the degree of inhi- bition on mulberry growth was increased. Mulberry plant height and base diameter was in the order of CK 〉T1 〉T2, while that of the specific root area was in the order of T2 〉 T1 〉CK, and the difference between different treatment groups were significant （P 〈0.05）. The root/shoot ratio and root vigor of mulberry trees in moderate drought stress group were both significantly higher than those in normal irrigation group, but the rooVshoot ratio and root vigor of mulberry trees in severe drought stress group were both significantly low- er than those in normal irrigation group （P 〈0.05）. After mulberry trees had been grown for seven months, the contents of organic matter, total nitrogen and total phosphorus of soil in each treatment group were all significantly lower than those of the initial contents in soil （ P 〈0.05）. However, there were no significant differences in the contents of total nitro- gen and total phosphorus of soil between each treatment group （P 〉0.05）. The contents of soil ammonium nitrogen, ni- trate nitrogen, and available phosphorus in each treatment group were in the order of T2 〉T1 〉CK, all of which were sig- nificantly lower than the initial contents in soil （P〈0.05） and the decreasing degree was in the order of CK 〉T1 〉T2. The results showed that soil drought in hydro-fluctuation belt of the Three Gorges Reservoir Area has a certain impact on the growth of mulberry trees, while moderate drought can promote the root system to grow downwards to improve the water absorption ability of root system. Under different soil water conditions, the growth of mulberry consumes remarka- ble quantity of nitrogen and phosphorus elements in the soil, which results in a reduced release of nitrogen and phos- phorous, the leading factors of water eutrophication, into water reservoirs.