沉水植物性状对不同氨氮脉冲的响应差异

全球气候变化背景下,未来降水强度和频率发生改变,极端降水事件可使水体中的氨氮含量在短时间内显著增加,对沉水植物的生长造成影响。然而,沉水植物对氨氮脉冲式变化(浓度与频率)的形态和生理响应机制仍不明确。选取两种常见的沉水植物苦草(Vallisneria natans)和黑藻(Hydrilla verticillata),设置不同底质(黏土和砂土)、不同氨氮脉冲模式(CK:对照组,即不加氨氮;P1:低浓度×高频率;P2:高浓度×低频率)和处理阶段(氨氮脉冲阶段和解除脉冲阶段),测定植株形态和生理性状,研究不同脉冲模式的影响差异和脉冲解除后的潜在影响。研究结果表明,(1)氨氮脉冲改变沉水植物的形态和生理性状,其中高浓度低频率氨氮脉冲对沉水植物的生长抑制作用最大。(2)氨氮脉冲解除一个月后,两种沉水植物的生物量较对照组无显著差异,而生理性状(如游离氨基酸和可溶性碳水化合物含量)较对照组差异较为明显,表明形态性状基本得到恢复,而氨氮脉冲对沉水植物生理性状的影响更为强烈而持久。(3)在解除脉冲阶段,苦草游离氨基酸含量仍显著高于对照组,而黑藻游离氨基酸含量较对照组差异较小,表明黑藻对氮的利用周转效率更高。(4)底质类型影响了苦草生理性状对氨氮脉冲的响应,即砂土中游离氨基酸和可溶性碳水化合物含量的变化幅度较黏土中更大。因此,氨氮脉冲效应与脉冲浓度和频率、底质类型、植物种类及其形态和生理性状密切相关。研究结果说明了沉水植物生理性状作为评估植物环境适应性的重要性,可为全球气候变化背景下湖泊生态系统沉水植被的管理提供科学参考。

Plant trait changes of submerged macrophytes in response to ammonium pulses

Under the background of global climate change, the intensity and frequency of precipitation will change in the future, and extreme precipitation events can significantly increase the ammonium content in water column in a short period of time, which will affect the growth of submerged macrophytes. However, the physiological and morphological response of submerged macrophytes to different ammonium pulse pattern (i.e., concentration and frequency) is still unclear. Two common submerged macrophytes (i.e., Vallisneria natans and Hydrilla verticillata) were selected, and different substrates (i.e., clay and sand), ammonium pulse patterns (i.e., CK: control, no ammonium addition; P1: low concentration×high frequency; P2: high concentration×low frequency) and experimental phases (ammonium pulse phase and release pulse phase) were set up to assess the effects of different pulse patterns on plant traits and potential effects after pulse release by measuring plant morphological and physiological traits. The results showed that: (1) Ammonium pulse changed the morphological and physiological traits of submerged macrophytes, with ammonium pulse pattern of high concentration and low frequency having the greatest inhibitory effect on plant growth compare to the pattern of low concentration and high frequency. (2) One month after the release of ammonium pulse, plant biomass of the two species had no difference compared to the control, while the physiological traits (e.g., free amino acid and soluble carbohydrate) showed significant differences compared with the control. These results indicated that the morphological traits were mostly recovered from ammonium pulse, while the effects on the physiological traits of the submerged macrophytes were still intense and time-lasting. (3) In the phase of releasing pulse, the free amino acid content of V. natans was still significantly higher than that of the control, while the free amino acid content of H. verticillata was less different from that of the control, indicating that the assimilation and turnover efficiency of ammonium was higher in H. verticillata than V. natans. (4) The substrate type affected the response of physiological traits to ammonium pulse, that is, the change of free amino acid and soluble carbohydrate contents in sand was larger than that in clay. Therefore, the ammonium pulse effects were closely related to the pulse concentration and frequency, substrate type, plant species and their morphological and physiological traits. Our findings highlight the importance of plant physiological traits in assessment of plant environmental adaptability, and provide scientific reference for the management of submerged macrophytes in lake ecosystems under global climate change.