To date, little attention has been paid to the effects of leaf source reduction on photosynthetic matter production, root function and post-silking N uptake characteristics at different planting densities. In a 2-year field experiment, Xianyu 335, a widely released hybrid in China, was planted at 60 000 plants ha^–1 (conventional planting density, CD) and 90 000 plants ha^–1 (high planting density, HD), respectively. Until all the filaments protruded from the ear, at which point the plants were subjected to the removal of 1/2 (T1), 1/3 (T2) and 1/4 (T3) each leaf length per plant, no leaf removal served as the control (CK). We evaluated the leaf source reduction on canopy photosynthetic matter production and N accumulation of different planting densities. Under CD, decreasing leaf source markedly decreased photosynthetic rate (P_n), effective quantum yield of photosystem II (ΦPSII) and the maximal efficiency of photosystem II photochemistry (F_v/F_m) at grain filling stage, reduced post-silking dry matter accumulation, harvest index (HI), and the yield. Compared with the CK, the 2-year average yields of T1, T2 and T3 treatments decreased by 35.4, 23.8 and 8.3%, respectively. Meanwhile, decreasing leaf source reduced the root bleeding sap intensity, the content of soluble sugar in the bleeding sap, post-silking N uptake, and N accumulation in grain. The grain N accumulation in T1, T2 and T3 decreased by 26.7, 16.5 and 12.8% compared with CK, respectively. Under HD, compared to other treatments, excising T3 markedly improved the leaf P_n, ΦPSII and F_v/F_m at late-grain filling stage, increased the post-silking dry matter accumulation, HI and the grain yield. The yield of T3 was 9.2, 35.7 and 20.1% higher than that of CK, T1 and T2 on average, respectively. The T3 treatment also increased the root bleeding sap intensity, the content of soluble sugar in the bleeding sap and post-silking N uptake and N accumulation in grain. Compared with CK, T1 and T2 treatments, the grain N accumulation in T3 increased by 13.1, 40.9 and 25.2% on average, respectively. In addition, under the same source reduction treatment, the maize yield of HD was significantly higher than that of CD. Therefore, planting density should be increased in maize production for higher grain yield. Under HD, moderate decreasing leaf source improved photosynthetic performance and increased the post-silking dry matter accumulation and HI, and thus the grain yield. In addition, the improvement of photosynthetic performance improved the root function and promoted post-silking N uptake, which led to the increase of N accumulation in grain.

东北平原是中国最大的玉米产区。近年来滴灌技术开始在该区推广应用，以解决玉米生产中干旱频发和水分利用效率(WUE)低下的问题。为确定高效和环境友好的灌溉措施，2016-2018年针对滴灌结合不同农田保水措施进行了大田试验研究，处理如下：(1)塑料薄膜覆盖+滴灌(PI)，(2)生物降解膜覆盖+滴灌(BI)，(3)秸秆深翻还田+滴灌(SI)，(4)浅埋滴灌(OI)，以传统沟灌(FI)为对照。PI和BI处理根长密度(RLD)和营养生长期间土温较高，其产量、WUE和氮素利用效率(NUE)最高。与BI相比，PI处理在20-60 cm和60-100 cm土层中消耗了更多的土壤水分，且0-20 cm土壤上层根系较大，生殖生长期间土温较高，根系和叶片衰老进程加快。SI处理能有效提高土壤水分和硝态氮含量，促进深层RLD增加，从而维持了花后较高的生理活性。FI处理与滴灌相比，60-100 cm土壤深层硝态氮含量较高，增加了氮素淋溶损失的风险。0-20 cm土层中，RLD与产量、WUE和NUE极显著正相关(P<0.001)，与根系氮利用效率(NRE)显著负相关(P<0.05)，这一相关性随土层加深而减弱。在干旱条件下，降解膜覆盖与滴灌耦合有利于玉米稳产和提高土壤水氮利用效率，是一项东北区玉米可持续生产与环境友好的推荐技术。

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.