稻田中藻类的生长状况及其对肥料氮的固持

为了确定藻类对稻田生态系统中氮素固持与迁移过程的影响程度,本研究采用田间小区和15N微区试验,在水稻生长的不同时期,观测了藻类在稻田中的生长状况,定量测定了藻类的生物量和氮素固持量.结果显示,稻田中的藻类具有明显的群落演替特征,水稻生育初期以球状藻为主,中后期则以丝状藻为主.藻类的生长可分为两个阶段,即生长期和衰亡期,其中,生长期从稻秧移栽初期至拔节期,衰亡期从拔节期至水稻收获.在衰亡期,藻类生物量随时间的变化符合生长曲线模式.藻类生物质干重在2007和2009年水稻生育期的变化范围分别为205～610 kg/hm2和12～353 kg/hm2,而藻类氮素固持量则分别为N 5.4～17.5 kg/hm2和N0.4～11.0 kg/hm2.15N微区试验结果显示,藻类对15N的固持量为N 0.3～6.0 kg/hm2,占氮素总固持量的54％～68％,平均为57％,表明藻类固持的氮素中大部分来源于当季施入的氮肥.

Proliferation of algae and effect of its on fertilizer-N immobilization in flooded paddy field

The objective of this study was to determine the extent of the impact of algae on N immobilization and transfer in the paddy field ecosystem. The algal proliferation was observed, and its biomass and N immobilization were quantitatively determined in the various stages of rice growth with plot and ¹⁵N micro plot experiments. Results indicated that the algae in paddy field had evident characteristics of community succession. Spherical algae dominated in the early stage of rice growth, and then filamentous algae were the main form in the mid later stage of rice growth. The algal proliferation could be divided into two phases: growth phase between rice seedling transplanting and shooting and decline phase between shooting and rice harvest, during the latter of which the variation in algal biomass fitted growth curve pattern. The dry weight of algal biomasses was within the range of 205-610 kg/ha and 12-353 kg/ha over the 2007 and 2009 rice seasons, respectively. N immobilizations by algae were between N 5.4 and 17.5 kg/ha and between N 0.4 and 11.0 kg/ha over two seasons, respectively. The results of ¹⁵N micro-plot experiment showed that ¹⁵N immobilization by algae ranged from N 0.3 to 6.0 kg/ha, accounting for 54%-68% of total N immobilizations with the average of 57%, which demonstrated that those were derived mostly from fertilizer N.