Allelopathic potential of watermelon tissues and root exudates

Allelopathic potential of watermelon in hydroponic culture was investigated using the continuous root exudates trapping system (CRETS). Laboratory bioassays and high-performance liquid chromatography (HPLC) were used for quantification of phytotoxins in different plant tissues and root exudates collected using XAD-4 resin. Seedling growth of both watermelon and lettuce was significantly inhibited by watermelon root exudates and the degree of inhibition increased with increasing concentration of exudates. Root exudates had inhibitory effects throughout the experiment and these were most pronounced during the period 41–50 days after transplanting. Inhibitory effects of various plant tissues were demonstrated using the bioassay tests. Frulic acid was the dominant component found using HPLC and the amounts of allelochemicals found in the plant extracts were correlated with the bioassay results using the Petri dish test. The results indicate that the allelopathic potential of watermelon may play an important role in the phenomenon referred to as ‘soil sickness’.     

The Effect of Levothyroxine Treatment on Resting Energy Expenditure of Hypothyroid Dogs

Thirty adult, client-owned dogs were diagnosed with hypothyroidism based on history, physical examination findings, hematologic and biochemical abnormalities, thyrotropin (TSH) response testing, endogenous canine thyrotropin (cTSH) concentration, or both, and total serum thryoxine concentration. All dogs received levothyroxine (L-thyroxine) at an initial dose of 22 μg/kg PO sid in either a tablet (13 dogs) or chewable form (17 dogs). Energy expenditure of each dog during apparent rest was estimated with an open-flow indirect calorimetry system by determining the rates of carbon dioxide production and oxygen consumption. Energy expenditure of apparent rest (EE) was lower in untreated hypothyroid dogs compared with reference values for EE. After treatment with L-thyroxine, EE of the hypothyroid dogs was significantly ( P < .05) higher than pretreatment values.     

丝茅入侵对高羊茅根系及土壤性状的影响

针对南方地区丝茅(Imperata koenigii (Retz.) P. Beauv.)入侵对冷季型草坪造成严重危害的实践生产问题,通过模拟高羊茅(Festuca arundiacea L.)草坪建植时丝茅入侵形成的混生群落,连续测定群落中根长密度、根干重密度和根体积密度等根系性状指标,土壤容重、土壤含水量及pH等土壤性状指标,分析丝茅入侵对高羊茅草坪根系及土壤性状影响的动态变化。结果表明:丝茅入侵对高羊茅草坪根长密度、根干重密度和根体积密度均有极显著影响(P<0.01);丝茅入侵60 d起影响根长密度,90 d起影响根干重密度,150 d起影响根体积密度;侵入持续时间对高羊茅根系指标影响排序为根体积密度>根干重密度>根长密度;丝茅对草坪分层土壤的含水量、容重和pH均有极显著影响(P<0.01);入侵60 d起首先影响高羊茅根系主要分布的10~20 cm层的土壤性状,影响逐渐向上、向下扩展;持续时间对土壤性状的影响排序为土壤含水量>容重>pH;丝茅入侵使高羊茅根系分生和更新能力下降,使其根系分布土壤层的含水量降低、透气性变差、酸度增高,从而降低高羊茅根系活性与吸收能力,使其竞争力降低而逐渐退化。本试验结果将为草坪中丝茅的防治提供基础数据。     

西藏自治区森林枯落物碳储量估算

利用典型样地采样,建立了枯落物碳密度与厚度关系方程,并结合森林资源连续清查的样地坡度与枯落物厚度因子,估算出西藏自治区森林枯落物碳储量.结果表明,西藏自治区丰富的森林植被生产了巨大的枯落物层碳库,有机碳分解和碳库消耗缓慢.研究该部分碳库状况,为估算和评价陆地生态系统碳储量并据此制定相应的对策提供了基础数据.     

CO2浓度升高与增施钾肥对土壤化学性质的影响

采用土培和开顶箱法,研究了大气CO_2浓度升高与增施K肥共同作用对土壤化学性质的影响.结果表明,土壤中N、P的含量在高CO_2浓度和高K肥水平下下降,K的含量随K肥用量增加而增加.高K(200、300 mg/kg)处理和高浓度CO_2下温室次生盐渍化土壤中的NO_3~(-)、PO_4~(3-)、Ca~(2+)、Mg~(2+) 含量也显著降低.因此,在未来CO_2浓度升高的环境中,更多的K肥供应能促进作物对此生盐渍化土壤中养分的吸收,降低此生盐渍化土壤中盐分的积累.     

便携式X射线荧光光谱仪实验室异位检测法的实用性研究

采用分步取样法验证便携式X射线荧光光谱仪的实验室异位检测法的实用性,以ICP-AES法为基准,对土壤重金属Cr、Cu、As、Pb的含量进行测定,试验中选用70%土壤样品建立一元线性校准模型,30%土壤样品进行校准模型的验证。结果表明,便携式X射线荧光光谱仪实验室异位检测法的检出限分别为Cr 17.7 mg/kg,Cu 10.4 mg/kg,As 5.4 mg/kg,Pb 6.2 mg/kg,均低于国家土壤环境质量一级标准。对国内外标准物质进行多次重复测定,RPD在–8.9%~7.9%,说明仪器在异位测定重金属含量时具有较好的精密度与准确度。分析PXRF法与传统方法测定建立的拟合方程,其决定系数分别为0.817 3、0.787 0、0.673 3和0.722 1,表明PXRF室内异位法可用于土壤重金属Cr、Cu、As、Pb的快速测定;二次采样建立的验证模型R2分别为0.912 4、0.897 9、0.772 3、0.872 9,逐渐靠近理想模型,充分验证PXRF异位法的实用性和校准曲线的准确性,可适用于农田土壤Cr、Cu、As、Pb的快速测定、污染筛查,为土壤重金属速效测定提供有力依据;但仪器在异位测定As元素时准确性降低,建议异位测定时需进行数据校准。     

土壤供氮能力测试方法与指标

研究了土壤供氮能力的主要测试方法和指标,包括培养矿化法、化学提取法、起始矿质氮指标和电超滤法测定指标等。对各种方法和指标的发展应用作了叙述,并对有关方法和指标的效果进行了比较。     

森林生态系统土壤碳库对氮沉降的响应研究进展

大气氮沉降的不断加剧,改变了土壤理化性质,直接影响植物的生长与发育,间接影响了陆地生态系统碳库,进而可能改变全球气候变化进程。森林是陆地生态系统的主体,因此,弄清氮沉降如何影响森林生态系统碳库,对预测全球气候变化具有重要意义。笔者旨在详细分析氮沉降对森林生态系统土壤碳库输入和输出的影响,阐述氮沉降对森林生态系统凋落物分解、细根周转和土壤呼吸的影响研究进展和作用机制。截至目前,关于氮沉降对于陆地生态系统的影响研究报道较多,且国内外诸多学者也在森林生态系统土壤碳库对氮沉降的响应领域开展了较多试验研究,但多集中于碳输入和输出的总量分析,而对输入和输出各个组分的研究相对较少。笔者综述了国内外有关森林生态系统碳库输入和输出各组分对氮沉降响应的相关研究,为进一步揭示其响应机制和途径提供参考依据。     

The effect of lupins as compared with peas and oats on the yield of the subsequent winter barley crop

New high yielding early maturing cultivars of lupins have been introduced in north-west Europe as grain protein crops in crop rotations. This paper reports on a comparative study of lupins with peas and oats, and of their effect on yield of subsequent winter barley crops. These crops were given five levels of N under irrigated and non-irrigated conditions on sand and loam. Under rain fed conditions the grain yield of pea, oat and lupin varied between 24–36, 34–53 and 18–37 hkg DM ha⁻¹, respectively. Supplemental irrigation raised grain yield of oat to 50–60 hkg DM ha⁻¹, while grain yield in pea was not affected and grain yield in lupin in most cases decreased due to gray mould attack and excessive vegetative growth in the indeterminate lupin variety. Under rain fed conditions, the grain nitrogen content of pea, oat and lupin varied between 137–172, 61–80 and 189–226 kg N ha⁻¹, respectively, and was significantly higher in lupin as compared with pea. On sandy soil, similar low-root densities were found for pea, oat and lupin below 30 cm depth. On sand, at final harvest the residual soil-N of lupin and pea, as measured in a subsequent winter barley crop not supplied with N fertilizer, was 15 and 8–10 kg N ha⁻¹ higher than in winter barley following oat, respectively. The nature of the probably more N-root residues of lupin is discussed. On loam, the residual N of lupin and pea was similar, 18–27 kg N ha⁻¹. On sand, under rain fed conditions preceding lupin and pea as compared with oat, increased the barley grain yield at zero N-application 77 and 49%, respectively; the effect of lupin was significantly higher than that of pea until the highest N-level 120 kg N-application ha⁻¹. On loam under rain fed conditions preceding lupin and pea increased the barley grain yield at zero N-application by 36 and 62%, respectively, as compared with oat; at N-application>60 kg N ha⁻¹ the grain yield was similar after all three crops. For both soil types the same level of effect was found under irrigated conditions. Conclusions: Supplemental irrigation might result in lower grain yield in lupin due to gray mould attack and excessive growth if indeterminate lupin varieties are used. Grain nitrogen yield of lupin is significantly higher than that of pea. On sand, the effect of lupin on the subsequent winter barley grain yield is significantly higher than that of pea, probably due to greater N-root nitrogen residues. On loam, lupin and pea have similar effects on the subsequent winter barley crop.     

不同施肥处理对保护地土壤非交换性钾释放能力的影响

以沈阳农业大学蔬菜保护地长期定位试验为基础,系统研究了长期定位条件下,不同施肥处理对蔬菜保护地土壤非交换性钾释放能力的影响。结果表明,不同施肥处理土壤非交换性钾的释放量和释放速率不同,有机肥和无机肥配施的土壤的释放量和释放速率大于单施化肥的各个处理;其中氮、钾肥配施处理的释放量和释放速率最高,而氮、磷肥配施处理最低。