不同硼浓度对三种超富集植物吸收硼及重金属的影响

通过水培试验研究了0~15 mg·L-1的硼(B)对Zn/Cd超富集植物东南景天(Sedum alfredii)、Zn/Cd/Ni超富集植物遏蓝菜(Noccaea caerulescens)和Ni超富集植物庭荠属(Alyssum murale)在20 mg Zn·L-1及18 mg Ni·L-1胁迫下生长和吸收重金属的影响。试验结果显示:较低浓度的硼促进三种超富集植物的生长和重金属吸收,而高浓度的硼则表现出抑制作用;三种植物在硼处理浓度为10.0mg·L-1时都开始表现中毒的症状,三种植物地上部分的硼含量随硼处理浓度的增加而增大,S.alfredii叶部、N.caerulescens、A.murale地上部分的硼浓度范围分别为40.2~880、115~744、156~922 mg·kg-1干重;当硼处理的浓度为2.0、0.5 mg·L-1时,S.alfredii和N.caerulescens地上部分的重金属吸收达最大值,A.murale地上部Zn和Ni的含量则分别在硼处理浓度为2.0、5 mg·L-1时达到最大。     

不同氮水平对生姜产量和品质及氮素吸收的影响

采用田间试验研究不同基础肥力土壤、不同氮肥水平对生姜产量和品质及氮素吸收的影响。结果表明,氮肥对生姜根茎产量及品质有明显的影响,合理施氮能显著提高根茎产量,改善其营养及安全品质。两种不同基础肥力土壤下,生姜根茎产量均表现为随施氮量的加大先增加后降低,呈抛物线关系,所有处理中N450获得了最高根茎产量。品质分析结果显示,施用适量氮肥能明显提高生姜根茎蛋白质、维生素C、糖分和姜精油含量,有效控制硝酸盐及亚硝酸盐含量。其中,维生素C含量,基础肥力较高土壤以N225处理最高;肥力较低土壤N450处理达到高峰。粗蛋白含量,肥力较高土壤N225处理最高,N450最低;肥力较低土壤,随施氮量的增加,根茎粗蛋白含量相应提高,N600处理达最大值。糖分和姜精油含量,两种肥力土壤下分别是N600和N450处理最高。根茎硝酸盐和亚硝酸盐含量随施氮量的增加而升高,与氮肥用量呈极显著正相关。施用氮肥后生姜地上部茎、叶和地下根茎含氮量明显提高,氮素吸收量显著增多。     

超级早、晚稻的养分吸收和根系分布特性研究

为了阐明双季超级稻的高产机理和指导合理施肥,采用品种比较的方法,研究了超级早、晚稻品种的养分吸收和根系分布特性。结果表明,超级早、晚稻品种的养分吸收量平均分别为N 170.04、224.90 kg/hm2,P 21.97、39.88 kg/hm2,K 107.48、144.47 kg/hm2,均高于对照。生育中期（穗分化至抽穗）的养分吸收量与产量密切相关。生产100 kg稻谷所需要的养分较对照低10%左右。超级早、晚稻品种根系发达,根量较大。抽穗后15 d（早稻）或20 d（晚稻）的根量与产量密切相关,其中5—10 cm的根量与养分吸收总量密切相关。说明生育中期较多的养分吸收和发达的根系是超级早、晚稻高产的重要原因。     

温度、盐度和光照强度对鼠尾藻氮、磷吸收的影响

在实验室条件下,研究了不同的温度和盐度组合,温度和光照强度组合对鼠尾藻(Sargassum thunbergii)氮、磷吸收速率的影响.结果表明,上述3个环境因子对鼠尾藻氮、磷吸收速率均有显著影响.其中,温度和盐度对鼠尾藻氮、磷吸收速率有极显著影响(P<0.01),二者交互作用也极显著(P<0.01).在盐度20、温度25℃条件下和盐度30、温度30℃条件下,鼠尾藻对氮有较高吸收速率,分别为11.26μmol/[g(dw)·h]和11.01 μmol/[g(dw)·h];在盐度40、温度15～30℃范围内对磷的吸收速率较大,达到1.5μmol/[g(dw)·h]以上.温度和光照对鼠尾藻氮、磷吸收速率均有极显著影响(P<0.01),二者交互作用极显著(P<0.01).在温度15℃和光照强度140～180μE/(m2·s)以及温度20～25℃和光照强度60～100 μE/(m2·s)条件下,鼠尾藻对氮有较高吸收速率,均在9.60 μmol/[g(dw)·h]以上;在温度25℃和光照强度60μE(m2·s)条件下,鼠尾藻对磷的吸收速率达到最大,为1.30 μmol/[g(dw)·h].本研究结果表明,鼠尾藻总体上对水体中的氮、磷均具有较高的吸收速率,且能较好地同时吸收NH4+-N和NO3--N,显示了它对海水环境中营养盐具有较强的吸收能力.     

Effect of aluminum uptake on growth and enzyme activity in Pisum sativum var. ‘Alaska’ and ‘Little Marvel’

It is usually assumed that plant tissue responses to nutritional elements are due to specific genetic differences that may exist either between inbred or closely related species. Little Marvel (dwarf) and Alaska (normal) varieties of 14‐day old pea seedlings were treated with four different concentrations of Al‐containing nutrient solution (0.0mM, 0.2mM, 0.6mM and distilled H₂O), prior to being exposed for 14 days to either DARK, LIGHT, or UV. Selected tissues (root tip, main root, main stem and proximal stem) were bioassayed for peroxidase and polyphenol oxidase enzyme activities, fresh wt vs. dry wt, water uptake and stem growth. The present study suggests that Little Marvel and Alaska pea tissue responds to high toxicity levels of Al by demonstrating an enhancement of enzymic activity. Tissue weight, growth and water uptake also show differential tissue specificity in both Little Marvel and Alaska tissue, in terms of Al toxicity response, given a particular external exposure.     

Modeling the spatial structure of topical forests

The spatial structure of tropical forest stands under different management conditions was modeled as a series of different spatial point processes. Spatial patterns were first assessed by K-function analyses to help choose a point process appropriate for observed patterns. The homogenous Neyman–Scott process accurately described live tree distribution in clear cut areas, where tree patterns tended to be aggregated. Parameters were estimated by minimizing Diggle's modified least squares criterion, and goodness-of-fit was assessed by comparison to confidence envelopes constructed by Monte Carlo simulation. Parameter estimates can be interpreted to help understand the ecological processes influencing re-colonization of disturbed areas. The inhomogeneous Poisson process was investigated for simulating the spatial pattern of ingrowth trees in lower canopy strata. The intensity function of this process was inversely proportional to variables representing canopy density. As assessed by Monte Carlo generation of confidence envelopes, the inhomogeneous Poisson process successfully portrayed the influence of canopy structure on understory plant distribution in most stands. Tree mortality was modeled as a thinning process in which the probability of individual tree mortality was conditional on subject tree attributes and competitive environment. The thinning function took the form of a generalized linear model with a binomial error distribution and logit link function. In most stands, tree neighborhood variables were powerful predictors of mortality, but they were not important predictors in all plots. This suggests that the surrounding forest structure of a subject tree has considerable influence on its morality, but competition is not the sole cause of tree morality in tropical forests.     

Root exudation of diclofop-methyl and triasulfuron from foliar-treated durum wheat and ryegrass

In this study, we evaluated the release of diclofop-methyl and triasulfuron from the roots of foliar-treated ryegrass and wheat. The study with ¹⁴C-diclofop-methyl indicated a basipetal translocation of foliar-applied herbicide in wheat and ryegrass. No root exudation from ¹⁴C-diclofop-methyl-treated wheat plants was observed, while 20 days after treatment (DAT) 0.2–0.9% of radioactivity absorbed by ryegrass was found exuded in the growing medium. Root exudation was stimulated three to six times by the presence of untreated wheat or ryegrass sharing the growing medium with diclofop-methyl-treated ryegrass. No subsequent uptake of exuded radiolabel by untreated plants (ryegrass or wheat) in the same pot with ¹⁴C-diclofop-methyl-treated ryegrass was observed. The study with ¹⁴C-triasulfuron indicated a basipetal translocation of foliar-applied herbicide in wheat and ryegrass and also into the growing medium. By 20 DAT, 0.5–4.2% of radioactivity absorbed by wheat or ryegrass was found exuded in the growing medium. The presence of untreated plants (wheat or ryegrass) in the same pot as triasulfuron-treated ryegrass or wheat induced exudation seven to 32 times more. The study also revealed a subsequent uptake of exuded compounds by untreated wheat or ryegrass sharing the medium of ¹⁴C-triasulfuron-treated plants. This study has demonstrated for the first time that the root exudation of exogenous compounds can be related to plant arrangement in pots. The implication is that herbicide root exudation and transfer, a form of allelopathy, could be significant in the field. A precise estimation of environmental fate, unexpected ecological side effects and residual activity of herbicides may require quantification of such exudation.     

Patterns and drivers of seasonal water sources for artificial sand-fixing plants in the northeastern Mu Us sandy land, Northwest China

Understanding plant water-use patterns is important for improving water-use efficiency and for sustainable vegetation restoration in arid and semi-arid regions. However, seasonal variations in water sources and their control by different sand-fixing plants in water-limited desert ecosystems remain poorly understood. In this study, stable isotopic ratios of hydrogen (δ²H) and oxygen (δ¹⁸O) in precipitation, soil water, groundwater, and xylem water were determined to document seasonal changes in water uptake by three representative plant species (Pinus sylvestris var. mongolica Litv., Amygdalus pedunculata Pall., and Salix psammophila) in the northeastern Mu Us sandy land, Northwest China. Based on the depth distribution and temporal variation of measured gravimetric soil water content (SWC), the soil water profile of the three species stands was divided into active (0.01 g g^-1 < SWC < 0.08 g g^-1, 20% < coefficient of variation (CV) < 45%), stable (0.02 g g^-1 < SWC < 0.05 g g^-1, CV < 20%), and moist (0.08 g g^-1 < SWC < 0.20 g g^-1, CV > 45%) layers. Annually, P. sylvestris, A. pedunculata, and S. psammophila obtained most water from deep (59.2% ±9.7%, moist layer and groundwater), intermediate (57.4% ±9.8%, stable and moist layers), and shallow (54.4% ±10.5%, active and stable layers) sources, respectively. Seasonally, the three plant species absorbed more than 60% of their total water uptake from the moist layer and groundwater in the early (June) dry season; then, they switched to the active and stable layers in the rainy season (July–September) for water resources (50.1%–62.5%). In the late (October–November) dry season, P. sylvestris (54.5%–66.2%) and A. pedunculata (52.9%–63.6%) mainly used water from stable and moist layers, whereas S. psammophila (52.6%–70.7%) still extracted water predominantly from active and stable layers. Variations in the soil water profile induced by seasonal fluctuations in precipitation and groundwater levels and discrepancies in plant phenology, root distribution, and water demand are the main factors affecting the seasonal water-use patterns of artificial sand-fixing plants. Our study addresses the issue of plant water uptake with knowledge of proportional source-water use and reveals important implications for future vegetation restoration and water management in the Mu Us sandy land and similar desert regions around the world.     

Effect of levels and sources of nitrogen on concentration and uptake of nitrogen by a high yielding variety and a hybrid of rice

Field experiments were made on a sandy clay loam soil at the Indian Agricultural Research Institute, New Delhi to study the effect of levels and sources of nitrogen on concentration and uptake of nitrogen by a high yielding variety Pusa 834 and a hybrid PRH3 of rice. Nitrogen concentration in hybrid PRH 3 remained lower than in Pusa 834, but N uptake was significantly more in the hybrid PRH 3. Nitrogen fertilization increased N concentration as well as N uptake by rice. At 30 days after transplanting (DAT) N uptake was more in Pusa 834, but at 60 DAT and at harvest hybrid PRH 3 recorded significantly more N uptake than Pusa 834. Use of neem oil blended urea (PNGU) and neem coated urea (NCU) increased N concentration and uptake by rice in both Pusa 834 and hybrid PRH 3. Use of neem coated/blended urea is recommended for rice.     

两种模型分析方法下冬小麦根系吸水深度的对比研究

为了研究冬小麦根系吸水深度,应用塑料管土柱法在田间进行冬小麦种植试验,测定了冬小麦越冬期、拔节期、抽穗期、灌浆期和成熟期不同土层深度土壤水稳定同位素值,并应用耦合模型和IsoSource多元线性模型对比分析了水源贡献率。结果表明,冬小麦在越冬期、返青期主要利用0~20 cm土层的土壤水,拔节期主要吸水深度为0~40 cm;抽穗期,基于耦合模型的主要吸水深度为0~40 cm,基于IsoSource多元线性模型的为0~40 cm和80~180 cm;灌浆期,基于耦合模型和IsoSource多元线性模型的主要不同吸水深度为180~200 cm,且基于耦合模型的该层贡献率明显高于IsoSource多元线性模型;成熟期主要利用0~40 cm和80~100 cm土层的土壤水,基于2种模型的分析结果相同。应用耦合模型求解贡献率,当分组较多且组间水稳定同位素差异较小时,应结合其他方法来保证其准确性。