豆科植物的氮固定及其向禾本科植物的氮转移被认为是禾本科/豆科间作系统增产和氮素高效利用的一种重要途径。然而间作作物的根系形态变化对氮固定和氮转移的贡献尚不清楚，本研究通过连续两年的双因素（两个氮水平，三种根系分隔方式）温室实验，运用15N同位素标记技术测定了玉米/紫花苜蓿间作系统的氮素固定，氮素转移以及根系形态特征变化。研究结果表明，施氮显著抑制了玉米/紫花苜蓿的氮素固定和转移。不考虑施氮水平，与塑料膜分隔相比，尼龙网分隔和不分隔处理使总生物量和总吸氮量分别提高了36%和28%，同时使氮素固定率显著升高了75-134%；不分隔处理的间作系统氮素转移量是尼龙网分隔处理的1.24-1.42倍。冗余度分析(RDA) 表明玉米冠根干重和苜蓿侧根数量与间作氮素固定和转移的相关性最强。我们的研究强调了根系接触和根系形态变化对增强玉米/紫花苜蓿间作系统的氮素固定与转移的重要性，这种间作系统产量的增加是通过较大的促进玉米生长，同时以降低一小部分苜蓿的生长为代价来实现的。

The adsorption of Cu(II) from aqueous solution onto humic acid (HA) which was isolated from cattle manure (CHA), peat (PHA), and leaf litter (LHA) as a function of contact time, pH, ion strength, and initial concentration was studied using the batch method. X-ray absorption spectroscopy (XAS) was used to examine the coordination environment of the Cu(II) adsorbed by HA at a molecular level. Moreover, the chemical compositions of the isolated HA were characterized by elemental analysis and solid-state 13C nuclear magnetic resonance spectroscopy (NMR). The kinetic data showed that the adsorption equilibrium can be achieved within 8 h. The adsorption kinetics followed the pseudo-second-order equation. The adsorption isotherms could be well fitted by the Langmuir model, and the maximum adsorption capacities of Cu(II) on CHA, PHA, and LHA were 229.4, 210.4, and 197.7 mg g–1, respectively. The adsorption of Cu(II) on HA increased with the increase in pH from 2 to 7, and maintained a high level at pH>7. The adsorption of Cu(II) was also strongly influenced by the low ionic strength of 0.01 to 0.2 mol L–1 NaNO3, but was weakly influenced by high ionic strength of 0.4 to 1 mol L–1 NaNO3. The Cu(II) adsorption on HA may be mainly attributed to ion exchange and surface complexation. XAS results revealed that the binding site and oxidation state of Cu adsorbed on HA surface did not change at the initial Cu(II) concentrations of 15 to 40 mg L–1. For all the Cu(II) adsorption samples, each Cu atom was surrounded by 4 O/N atoms at a bond distance of 1.95 Å in the first coordination shell. The presence of the higher Cu coordination shells proved that Cu(II) was adsorbed via an inner-sphere covalent bond onto the HA surface. Among the three HA samples, the adsorption capacity and affinity of CHA for Cu(II) was the greatest, followed by that of PHA and LHA. All the three HA samples exhibited similar types of elemental and functional groups, but different contents of elemental and functional groups. CHA contained larger proportions of methoxyl C, phenolic C and carbonyl C, and smaller proportions of alkyl C and carbohydrate C than PHA and LHA. The structural differences of the three HA samples are responsible for their distinct adsorption capacity and affinity toward Cu(II). These results are important to achieve better understanding of the behavior of Cu(II) in soil and water bodies in the presence of organic materials.