以山东省寿光市清水泊农场农田及7个不同复垦年限废弃盐田土壤为研究对象,采用空间代替时间序列方法对不同土层(0～20、20～40、40～60、60～80、80～100cm)土壤理化性状与微生物特性进行了研究.结果表明:(1)复垦后土壤含盐量降低,土壤有机质、全氮、速效磷及速效钾含量增加,各养分含量在复垦8a时达到最大值,基本达到农田水平;(2)土壤中细菌、放线菌数量随着复垦年限的增加呈先增加后下降的趋势,而真菌数量则持续上升;(3)复垦有利于土壤脲酶、碱性磷酸酶、蔗糖酶和过氧化氢酶的提高,复垦年限越长,酶活性提高越显著;(4)通过构建复垦质量变化预测定量模型,预测复垦土壤有机质、全氮、速效磷及速效钾含量达到对照农田水平分别需8.75、8.45、8.24、8.41a;(5)经主成分分析得出,影响复垦土壤质量演变的主要因子为蔗糖酶、过氧化氢酶、有机质和细菌.本文分析了废弃盐田复垦土壤各理化和微生物指标的变异特征及时空分布规律,可为科学指导黄河三角洲废弃盐田复垦区土壤综合治理和农业可持续发展提供理论依据.

The positive effects of humic acid (HA) in alleviating the toxicity of cadmium (Cd) were demonstrated in pot grown Hybrid Pennisetum. Twelve treatments consisting of six concentrations of Cd (0, 10, 20, 50, 70 and 100 mg kg−1) combined with two levels of HA (0 and 1.0 g L−1) were applied. Our results showed that although Cd toxicity significantly inhibited plant growth, decreased the dry weights of leaves, stems and roots and substantially increased the leaf malondialdehyde (MDA) and Cd concentrations in different plant tissues, Hybrid Pennisetum had a strong ability in the uptake and transfer of Cd and could be used for phytoremediation in Cd-contaminated soils. The chlorophyll content and photosynthetic capacity of the leaves also decreased under Cd stress. The foliar application of HA alleviated the symptoms of Cd toxicity by increasing the net photosynthetic rate (Pn) and the content of photosynthetic pigments, although HA did not significantly decrease the concentration of Cd in the leaf, stem and root tissues. Compared with the zero-HA treatment, 1.0 g L−1 HA increased the root, stem and leaf biomasses by approximately 2.7–99.4%, 3.9–11.2% and 18.2–87.1%, respectively. MDA had a significant negative relationship with Pn. The MDA content of the HA-treated Hybrid Pennisetum plants decreased by approximately 4.4–12.2% compared with that of the Cd-only plants, indicating the high Cd tolerance of Hybrid Pennisetum. It is concluded that foliar application of HA (1.0 g L−1) can alleviate Cd toxicity and increase Cd stress tolerance in Hybrid Pennisetum, thereby lowering the potential risk of soil Cd contamination.

Photosynthesis plays an essential role in plant growth and crop yield, and the mechanisms of the effects of cadmium (Cd) on photosynthetic performance require more attention. The acute toxicity of Cd in soil to the photosynthetic capacity of Hybrid Pennisetum was evaluated using gas exchange parameters, A/Ci curves, light response curves, and chlorophyll a fluorescence transients after exposure to elevated Cd concentrations (0, 10, 20, 50, 70, and 100 mg kg-1) for a 3-month period. The results indicated that leaf Cd concentration in Hybrid Pennisetum increased with the strength of soil Cd stress and ranged from 4.9 to 15.8 μg g-1 DW. The accumulation of leaf Cd severely restricted photosynthesis and its non-stomatal limitation in regulating the photosynthetic performance of Hybrid Pennisetum. The leaf chloroplasts at 10 and 20 mg kg-1 Cd concentrations showed no noticeable change, but the chlorophyll content significantly decreased by 9.0-20.4% at 50-100 mg kg-1 Cd concentrations. The Cd treatments also decreased plant ribulose-1,5-bisphosphate (RuBP) activity (Vcmax ) and regeneration capacity (Jmax ), triose phosphate utilization (TPU), light-saturated photosynthesis (Amax ), apparent quantum yield (AQY), light saturation point (LSP), and dark respiration (Rday ), but Cd treatment increased the light compensation point (LCP). The shape of chlorophyll a fluorescence transients in leaves was altered under different Cd treatments. The increased OJ phase and the decreased IP phase in fluorescence induction curves suggested that Cd toxicity inhibited both light use efficiency and photodamage avoidance ability. These results suggested that the decrease in photosynthesis through exposure to Cd may be a result of the decrease in leaf chlorophyll content, Rubisco activity, and RuBP regeneration, inhibition of triose phosphate utilization, reduction of the ability to use light and provide energy, and restrictions on electron transport in PSII.