Can differences in 15N natural abundance be used to quantify the transfer of nitrogen from legumes to neighbouring non-legume plant species?

Natural variations in the stable isotope ¹⁵N are often exploited in studies of N cycling in ecosystems. Lower ¹⁵N natural abundance in non-legume plants growing in association with legumes, compared with the non-legume grown alone in pure stands have been observed in cropping, forage, and agroforestry systems. Such observations have frequently been attributed to the transfer of biologically-fixed nitrogen (N) from the legume to the companion non-legume, and various methodologies have been employed to calculate the extent of the N transfer. While some of these ¹⁵N natural abundance-based estimates of N transfer were within the range previously reported using equivalent ¹⁵N-enriched techniques (<20% of non-legume plant N and <10 kg N ha⁻¹ derived from fixed N contributed by neighbouring legumes), many of the values obtained using natural abundance were much higher (30%–83% of the non-legume N derived from fixed N representing up to 30–40 kg N ha⁻¹) than generally measured by ¹⁵N-enriched methods; with even greater estimates being determined where data were available to allow N transfer to be re-calculated on the basis of total legume N rather than fixed N (42% to >100%, and up to 110 kg N ha⁻¹ per year). This review raises concerns about the assumptions behind the natural abundance approach, and provides some alternative interpretations for the observed differences in natural ¹⁵N abundance between plants grown in the presence and absence of legumes. It was concluded that simple comparative measures of non-legume δ¹⁵N alone cannot provide a quantitative estimate of N transfer between plant species if the dominant source and the isotopic identity of the transferred N cannot be validated, and if the extent of any isotopic fractionation associated with relevant N transformations occurring during transfer cannot be defined. To date this information is not forthcoming. There is a need to greatly improve our understanding of the transfer processes before the real value of the δ¹⁵N technology can be realized. In the first instance this will primarily be achieved by carefully executed experiments under controlled conditions, and in the field, employing both ¹⁵N natural abundance and enrichment approaches so estimates of transfer can be compared, and the data interrogated using modelling approaches to explore isotopic fractionation.     

Cross‐linked polyacrylates in post‐mining substrates: persistence and effects on plant growth

Application of hydrophilic polymers composed of cross‐linked polyacrylate can improve soil water‐holding capacity and accelerate the restoration of post‐mining substrates. In this work, we studied the persistence of a polyacrylate polymer incorporated into a soil and its impact on plant nutrients at a reclamation site of former lignite mining in Lusatia (Germany). In contrast to autumn application, the incorporation of the polymer enhanced the sequestration of plant‐derived carbon in the soil, which was reflected by a significant increase in the concentration of a lignin marker. Attenuated total reflexion–Fourier transform infrared spectra (ATR‐FTIR) and total elemental contents in the applied polymer suggested an intensive cation exchange between the polymer framework and the soil‐forming substrate. In addition, there was an enrichment of carbonaceous material, which seems to reduce the swelling and thus the water‐holding capacity of the cross‐linked polyacrylate. Conversely, this process protected the polymer structure from rapid decomposition.     

不同发育阶段日本落叶松人工林枯落物层微生物群落特征

为探寻日本落叶松人工林在中龄林或近熟林阶段地力衰退的机制，以分子生物学实验手段与常规实验分析方法结合，分别对不同发育阶段林分枯落物未分解层、半分解层以及全分解层微生物的数量、群落结构以及理化性质进行分析，并采用冗余分析法探索枯落物层微生物群落结构与理化性质的相关性。结果表明：枯落物储量及养分储量随林分发育呈倒“V”字型变化趋势，在近熟林阶段最大，微生物数量、均匀度指数在中龄林或近熟林最低。不同发育阶段林分优势细菌种类基本相同，但相对含量不同；优势真菌的种类明显不同，尤其是在近熟林半分解层。中龄林与近熟林未、半分解层受环境因素影响较大，主要受pH、有效磷、碱解氮、速效钾、全钾、C/N以及林下植被生物量影响。因此，日本落叶松纯林在中龄林与近熟林阶段需强化植被管理，适时开展修枝间伐等经营措施，促进林下植被发育、改善枯落物性质，加速养分循环，缓解地力衰退。     

局地尺度高寒草原土壤真菌多样性对地上植物多样性与生产力关系的调控作用

为研究局地尺度高寒草原土壤真菌多样性对地上植物多样性与生产力关系的调控作用，本研究以青海省湟源县局地尺度高寒草原为研究对象，对不同植物多样性梯度的地上生产力、土壤理化性状和土壤真菌多样性等指标进行调查、采样和分析。通过偏回归分析（partial least squares regression，PLSR）、方差分解分析（variance partitioning analysis，VPA）、构建结构方程模型（structural equation model，SEM）等分析手段，分析了土壤真菌多样性对地上植物多样性与生产力关系的调控作用。结果表明，高寒草原植物多样性与地上生产力存在显著线性正相关关系；土壤真菌多样性分别与植物多样性和地上生产力呈显著正相关关系；通过PLSR，VPA，SEM等方法控制土壤非生物因子效应后，真菌多样性与二者的显著正相关关系仍存在。综上所述，局地尺度下青海省湟源县高寒草原土壤真菌多样性是调控地上植物多样性与生产力正向关系的关键生物因子。     

二氧化硅改性处理桉树生材的材性分析

采用溶胶-凝胶法,对含水率142％～146％的速生桉树生材进行改性处理,采用电镜SEM、X-射线能谱仪DAX及红外光谱FTIR分析,观察木材微观结构和SiQ分布状态,并检测理化性能.结果表明:浸渍时间不同,改性材中的SiO2含量和分布不同;改性材的增重率最大达45％,气干密度可提高至0.6 g/cm3左右,抗弯强度、硬度及耐光老化性能等均相应提高.     

Thermal and rheological properties of brown flour from Indica rice

The thermal, paste and rheological properties of brown flours from four Indica rice subspecies with different amylose content were examined using Differential scanning calorimetry (DSC), Brabender Viscometer and rheometer. Peak, final and setback viscosities (p < 0.05) increased with increasing amylose content from Brabender micro Visco-Amylo-Graph (MVA), but the phase transition temperatures of brown rice flour from DSC (p < 0.05) decreased with increasing amylose content. Rheological properties were determined by steady shear, small amplitude oscillatory shear (SAOS) and thixotropic experiments. SAOS results showed a gel-like viscoelastic behavior with G′ higher than G″. Steady-shear results showed that the brown rice flour exhibited a non-Newtonian shear-thinning behavior and the flow curves can be well described by the Herschel-Bulkley model. The upward-downward rheograms showed that brown rice flour gel, except IR-1, had a hysteresis loop, indicating a strong thixotropic behavior.     

青土湖水面形成区土壤颗粒组成与化学特性变化

青土湖输水作为石羊河流域治理的一项关键措施,对保护湖区水资源和生态环境具有重要意义。在距青土湖水面边缘东南方向0-450 m的10个样点中分3层取0-60 cm土样,测定土壤粒径的质量百分比与全氮、全磷、全钾和电导率,分析青土湖水面形成后土壤颗粒组成与化学特性变化。结果表明,随着离水面边缘距离的增加,土壤颗粒与化学特性呈有规律的增减变化,土壤粘粉粒组成与其全磷、全钾之间存在正线性相关。青土湖水面形成加剧了距水面边缘0-150 m处的土壤理化性质变化;土壤细粒及养分出现富集,分别在距水面边缘100-150 m和300 m处达到最大值。因此,土壤养分与土壤细物质的良好相关性表明,土壤粘粉粒变化可作为反映该区域土壤性状变化和评价衡量水面形成后土壤恢复程度的定量指标之一。     

花椰菜主要性状遗传规律以及性状相关性分析

总结了花椰菜的单球质量、成熟期、株高株展、花球品质等主要性状的遗传规律以及性状之间的相关性,并得出结论:花椰菜主要性状遗传规律以及性状相关性研究对育种研究具有重要指导意义,但必须注重与田间调查相结合,只有将遗传规律与田间调查有机结合才能提高育种效率,提高育种水平。     

花后不同强度遮光对糯小麦和非糯小麦淀粉组分和理化特性的影响

花后弱光影响小麦淀粉分子积累和结构形成,进而使面粉的加工品质和食用品质变劣。本研究以非糯小麦轮选987和糯小麦农大糯50206为材料,设置3个花后遮光处理(不遮光、遮光30%和遮光60%),研究了花后不同强度遮光对小麦籽粒中淀粉组分及其理化特性的影响。结果表明,花后弱光胁迫使小麦籽粒中总淀粉含量减少,A-型淀粉粒比例增加,淀粉相对结晶度增大。花后光照强度降低,轮选987淀粉的峰值黏度、谷值黏度、最终黏度、稀澥值和反弹值增大,而农大糯50206淀粉的上述参数则呈减小趋势。轮选987淀粉的起始温度、峰值温度和终止温度随弱光胁迫的增强而降低,而糊化焓呈增加趋势;相反,农大糯50206淀粉的上述热力学特征参数呈降低趋势。相关性分析表明,直链淀粉含量、直/支比、A-型淀粉粒体积比例与相对结晶度、峰值黏度、谷值黏度、稀澥值、糊化时间和糊化焓呈显著负相关,与最终黏度和反弹值存在极显著正相关。可见,小麦花后光照强度降低影响籽粒淀粉组分和粒度分布,从而改变了淀粉的晶体、糊化和热力学特性。     

滴灌条件下秸秆覆盖和土壤含水量对冬小麦灌浆特性的影响

为阐明滴灌条件下秸秆覆盖和土壤含水量以及两因素交互作用对冬小麦籽粒灌浆、产量形成的影响,以冬小麦矮抗58为试验材料,设计了秸秆处理(覆盖T、不覆盖T0)与土壤相对含水量(40%(W1)、50%(W2)、60%(W3)、70%(W4)4个水平)两因素裂区试验。结果表明:Richards方程拟合秸秆覆盖和水分调控下冬小麦籽粒灌浆过程的决定系数在0.977 5~0.999 6,达到极显著水平。秸秆覆盖和水分调控间的交互作用对除最大灌浆速率和平均灌浆速率(V)外其他冬小麦籽粒灌浆特征参数的影响达到显著或极显著水平。其中,秸秆覆盖下土壤相对含水量60%(TW3)处理组合具有最长的灌浆持续期T(51.91 d),最长的灌浆中期持续期T_2(15.230 d)和灌浆后期持续期T_3(26.556 d),最大的灌浆中期灌浆速率R_2(0.897 mg/d)和灌浆后期灌浆速率R_3(1.365 mg/d)。产量、水分利用效率和耗水量的二次曲线关系表明,在耗水量240~270 mm可达到产量与水分利用效率双高的效果。本试验中以秸秆覆盖与土壤相对含水量60%(TW3)处理组合水分利用效率最高(29.02 kg/(mm·hm~2)),较秸秆覆盖下土壤相对含水量的70%(TW4)提高了5.30%;产量为7 097.7 kg/hm~2,与TW4处理组合差异不显著。