土壤微生物生物量氮（MBN）在土壤中包含了最大比例的生物活性氮（N），是土壤氮循环的重要参与者。农业活动（例如作物轮作和单作）极大地影响了农业生态系统中的MBN。但是，目前农业生态系统中作物轮作和单作对MBN影响的研究极其缺乏。因此，本文基于203个已发表的文献进行整合分析（Meta 分析），以量化在合成氮肥施用下轮作和单作系统对MBN的影响。本研究发现，作物轮作显著提高了MBN的响应比（RR），并在旱地轮作条件下达到最高水平。然而，旱地作物单作并没有改变MBN的响应比，但是，水稻单作中MBN的响应比有所增加。作物轮作和单作系统之间的差异可能是由于不同的种植管理方式、氮素添加的方式、添加量和施肥年限所致。与作物单作系统相比，作物轮作对土壤总氮（TN）的增加幅度更大，对土壤pH的降低幅度较小。MBN的RR与矿质N的RR仅在作物轮作系统中正相关，MBN的RR与土壤pH的RR仅在单作系统中正相关。随机森林和结构方程模型的结果表明，MBN变化的主要驱动因素在作物轮作系统中是土壤矿质N和TN，在单作系统中是土壤pH。总之，本研究表明，轮作由于改善了土壤氮源，可以作为提高MBN的有效途径，从而提高MBN对由于大量施用化学氮肥导致的低pH的抵抗力。

Polyimide (PI) is a type of important membrane material. A soluble polymer was synthesized from 4,4´-(hexafluoroisopropylidene) diphthalic anhydride (6FDA) and 2,2-bis[4-(4-aminophenoxy) phenyl] hexafluoropropane (BDAF) by the two-step polymerization method. The polymer was proved to be polyimide 6FDA-BDAF by the Fourier transform infrared (FT-IR), the 1H-NMR and 19F-NMR spectra. An asymmetric membrane was prepared with the synthesized polyimide 6FDA-BDAF, it was porous in the 50 μm height bulk and dense in a 3–5 μm height surface. The membrane was used to separate n-heptane/ thiophene mixtures by pervaporation with sulfur (S) contents from 50 to 900 μg g–1. The total flux was enlarged from 7.96 to 37.61 kg m–2 h–1 with temperature increasing from 50 to 90°C. The membrane’s enrichments factor for thiophene were about 3.13 and dependent on the experimental conditions. The experimental results demonstrated that polyimide 6FDA-BDAF would be a potential membrane material for desulfurization and controlled release of the S-containing fertilizer.