Decomposition of Cynodon dactylon (L.) Pers. in the seasonally flooded areas of the Pongolo river floodplain: pattern and significance of dry matter and nutrient loss

Cynodon dactylon meadows occupying seasonally inundated areas of the Pongolo river floodplain, South Africa, decompose during periods of submergence. The loss of dry matter and nutrients from both fresh and dried material enclosed in litter bags was studied. The pattern of loss of dry matter was diphasic. Loss was more rapid from dried than from fresh material, half the mass being lost in 18 and 28 days respectively. Nutrient loss followed an exponential pattern. Nitrogen, phosphorus and magnesium were lost more rapidly from dried than from fresh material whilst rates of loss of sodium, potassium and calcium were similar. The significance of Cynodon decomposition in the functioning of the floodplain is assessed from estimates of the above- and below-ground standing crop around one small lake before and after submergence. It is concluded that decomposition of plants growing in seasonally inundated areas of the floodplain may contribute significantly to the productivity of the system, but that the extent of the contribution can be greatly influenced by the flooding regime. The completion of the Pongolapoort dam upstream of the floodplain will alter the natural flooding pattern, effecting a reduction in floodplain productivity, unless a programme for flood release can be initiated.     

三峡消落带不同坡度狗牙根及实生土壤生态化学计量特征

三峡库区消落带反季节水位波动驱使下植物的养分适应策略和内稳态特征研究对消落带植被恢复及生态功能调控有重要意义。然而,三峡消落带范围广、地形复杂,不同生境下植物适应特征仍存在不确定性。本研究以三峡消落带广泛分布的优势植物狗牙根为研究对象,选取28个地形差异较大的样地进行采样分析,重点探讨不同坡度（0-5°、5-10°、10-15°、15-20°、>20°）狗牙根及其实生土壤生态化学计量特征的变异关系,揭示坡度对狗牙根养分适应及内稳态的影响机制。结果表明：（1）坡度对狗牙根实生土壤的养分及化学计量特征具有显著影响,土壤有机碳（SOC）、全氮（STN）、速效氮（SAN）、全磷（STP）、速效磷（SAP）含量均随坡度增加而降低,<10°的缓坡消落带土壤养分显著高于10°以上的样地;土壤碳氮比（C ∶ N）、碳磷比（C ∶ P）均随坡度增加而降低,而氮磷比（N ∶ P）比相对稳定,表明坡度增大,土壤营养物的流失具有同步性,且流失速度较有机碳慢;（2）随坡度增加,狗牙根各营养器官C含量呈增加趋势,而氮（N）、磷（P）则呈降低趋势,且坡度变化改变了狗牙根各营养器官间的养分分配;植物根、茎C ∶ N、C ∶ P随坡度增加而增加,N ∶ P随坡度增加而降低,而叶片均没有明显变化,表明在坡度改变了土壤养分供应水平的情况下,狗牙根优先稳定其叶片化学计量比以提高适应能力;（3）坡度与土壤中SOC、STN、SAN含量呈现显著负相关,而土壤STN与狗牙根植物养分及化学计量特征均有显著相关关系,由此可见,坡度变化导致土壤氮素流失增加是影响狗牙根生态化学计量特征分异的主要机制;（4）狗牙根与实生土壤的碳氮磷元素内稳性整体表现为C>P>N,化学计量比内稳性表现为C ∶ P>C ∶ N>N ∶ P,随着坡度增加,狗牙根N、P的内稳性呈增强趋势,而C ∶ N、N ∶ P呈显著降低,表明坡度变化导致狗牙根形成了不同的适生策略。研究表明,在三峡库区复杂的地形条件下,狗牙根能有效维持体内化学计量平衡以响应不同的坡度条件,并且内稳性较好,是三峡库区消落带植被恢复与保护的优势植物物种。     

Nitrate and ammonium accumulation in bermudagrass in relation to nitrogen fertilization and season

Seasonal changes in nitrate and ammonium concentrations were studied inCynodon dactylon (L.) Pers. plants grown for one year in the field in a Mediterranean area. Plants cultivated in a sandy loam soil were fertilized with nitrate-N or ammonium-N at two application rates (250 and 1000 kg N ha⁻¹ year⁻¹) and compared to controls with no added N. Plots were harvested every three weeks from May to November. Shoots were separated into leaves and stems and analyses carried out in both fractions. Nitrogen applications generally led to elevated nitrate concentrations both in leaves and stems at all sampling dates but had little influence on the ammonium concentrations of the tissues. Higher nitrate and ammonium concentrations were found in stems than in leaves, although no levels higher than 0.22% NO ₃ ⁻ −N and 0.10% NH ₄ ⁺ −N were detected in either fraction. Nitrate tended to accumulate mostly in autumn and spring whereas low accumulations were found in summer. Ammonium showed both in leaves and stems a progressive but limited accumulation throughout the period with a peak in October, followed by a strong decrease in November.     

上海地区新入侵草坪害虫早熟禾拟茎草螟的鉴定及危害

在上海发现一种取食观赏草坪矮生百慕大Cynodon dactylon的草螟科新害虫。为了明确这一新害虫的分类地位、 寄主及危害状况, 本研究在形态鉴定的基础上, 结合线粒体细胞色素氧化酶亚基Ⅰ （COI/cox1）的测序和比对方法, 对其分类地位进行了核实; 并调查了其在上海地区草坪草上的发生及危害现状。形态鉴定结果表明, 这一新害虫为原产于北美的早熟禾拟茎草螟Parapediasia teterrella, 是中国新记录属种。序列比对显示, 目标样本656 bp的cox1序列与NCBI中已提交的P. teterrellus的4个COI条形码序列覆盖率为100%, 同源性达100%, 表明分子遗传数据支持形态鉴定结果。调查发现, 早熟禾拟茎草螟寄主主要为矮生百慕大, 已在上海多个区县形成危害, 局部地区危害严重, 种群密度最高的区域达740头/m²。早熟禾拟茎草螟是中国新发现的入侵害虫, 已明确其在上海地区能定殖、 扩散, 并形成经济危害, 其入侵将威胁我国草坪产业和园林绿化的健康发展, 需引起足够重视。     

Sulfate Ion Effect on Stability and Regulatory Properties of PEP Carboxylase from the C4Plant Cynodon dactylon

When Tris–SO₄was used as an extraction buffer for phosphoenolpyruvate carboxylase (PEPC) from leaves of the C₄plant Cynodon dactylon(L.) Pers., a higher extractable activity was obtained as compared to Tris–HCl, especially at low phosphoenolpyruvate concentrations and an assay pH of 7.2. The Tris–SO₄-extracted PEPC activity was stable under dilution and remained unchanged for at least 24 h at 22°C. This enzyme was less sensitive to both activation by glucose-6-phosphate and inhibition by L-malate. The effects of Tris–SO₄could be attributed to its preferential exclusion from the enzymic protein domain and, therefore, to a shifting of this oligomeric enzyme to a more aggregable form that is more stable and active.     

Anti-<Emphasis Type="Italic">Helicobacter pylori</Emphasis> substances from endophytic fungal cultures

The human pathogenic bacterium Helicobacter pylori has been ascertained to be an aetiological agent for chronic active gastritis and a significant determinant in peptic and duodenal ulcer diseases. Endophytic metabolites are being recognized as a versatile arsenal of antimicrobial agents, since some endophytes have been shown to possess superior biosynthetic capabilities owing to their presumable gene recombination with the host, while residing and reproducing inside the healthy plant tissues. A total of 32 endophytic fungi isolated from the medicinal herb Cynodon dactylon(Poaceae) were grown in in vitroculture, and the ethyl acetate extracts of the cultures were examined in vitro for the anti-H. pylori activity. As a result, a total of 16 endophyte culture extracts were identified as having potent anti-H. pyloriactivities. Subsequently, a detailed bioassay-guided fractionation of the extract of the most active endophyte (strain number: CY725) identified as Aspergillussp., was performed to afford eventually four anti-H. pylori secondary metabolites. The four isolated compounds were identified through a combination of spectral and chemical methods (IR, MS, ¹H- and ¹³C-NMR) to be helvolic acid, monomethylsulochrin, ergosterol and 3β-hydroxy-5α,8α-epidioxy- ergosta-6,22-diene with corresponding MICs of 8.0, 10.0, 20.0 and 30.0 μg/ml, respectively. The MIC of ampicillin co-assayed as a reference drug against H. pylori was 2.0 μg/ml. Furthermore, preliminary examination of the antimicrobial spectrum of helvolic acid, the most active anti-H. pylori metabolite characterized from the endophyte culture, showed that it was inhibitory to the growth of Sarcina lutea, Staphylococcus aureusand Candida albicans with MICs of 15.0, 20.0 and 30.0 μg/ml, respectively.     

狗牙根、白三叶草对淡剑纹灰翅夜蛾生长发育和繁殖的影响

利用室内饲喂法,以高羊茅分别为对照,研究狗牙根(Cynodon dacyton)、白三叶草(Trifolium repens)对淡剑纹灰翅夜蛾Spodoptera depravata(Butler)存活、生长发育及繁殖的影响。结果表明,用狗牙根、白三叶草饲喂淡剑纹灰翅夜蛾的化蛹率、幼虫成蛾率均显著低于对照组。幼虫历期显著长于对照组。用狗牙根、白三叶草饲喂幼虫时,淡剑纹灰翅夜蛾的蛹期、产卵前期、产卵期、产卵量、♀成虫寿命与对照组均无显著差异,但幼虫龄期明显增加。狗牙根、白三叶草饲喂的淡剑纹灰翅夜蛾种群增长参数与对照组相比存在明显差异:(1)世代净生殖率(R0);(2)内禀增长率(rm);(3)周限增长率(λ);(4)种群数量趋势指数(I)明显降低;世代平均周期(T)和种群加倍时间(DT)明显延长。由此可见,狗牙根和白三叶草并不是淡剑纹灰翅夜蛾喜好的寄主植物。     

Seed dispersal in the dung of large herbivores: implications for restoration of Renosterveld shrubland old fields

Species-rich, winter-rainfall, microphyllous Renosterveld vegetation in the Western Cape Province of South Africa has largely been transformed for production of wheat and wine. Remaining fragments thus have high conservation value. Abandoned old fields adjacent to natural vegetation fragments could potentially be restored as corridors and habitat for indigenous flora and fauna. We hypothesised that indigenous antelope maintained in a matrix of natural vegetation and abandoned field could play a role in restoration of Renoserveld via seed dispersal.We collected dung of indigenous ungulates in an abandoned field at various distances from natural Renosterveld vegetation, in order to assess the potential of large herbivores to contribute to restoration of plant diversity through seed dispersal. Emerged seedlings from the collected dung represented 29 forb, 13 grass, four sedge, four geophyte and one shrub species. The most abundant emerging seedlings were lawn grass Cynodon dactylon (38%), alien pasture grasses (31%) and indigenous geophyte Romulea rosea (12%). Whereas seeds of annual forbs and grasses were dispersed, only one shrub species was dispersed at very low density. We concluded that large herbivores could retard the rate of recovery of Renosterveld vegetation because viable seeds of herbaceous plants, particularly alien annual grasses and lawn-grasses were more abundant in the dung than the shrub, geophyte or perennial tussock grass species that characterise this vegetation type.     

水淹对狗牙根营养繁殖植株的生理生态学效应

通过控制实验,测定了经过水淹处理的狗牙根营养繁殖体在恢复阶段的光合作用及其相关的生理生化指标的变化。结果显示,水淹时间对恢复阶段营养繁殖体的蒸腾作用和叶片温度的影响达到显著水平,水淹深度对该时期营养繁殖体的光合作用、气孔导度、胞间二氧化碳浓度和叶片温度有显著影响。水淹还导致了恢复期间植株叶片光合色素含量的显著变化。经过水淹的植株的各类光合色素含量以及色素总含量都显著高于对照植株,其中全淹处理的植株显著高于半淹处理的植株,叶绿素a与叶绿素b的比例也是全淹处理的植株显著高于半淹处理的植株。结果表明狗牙根营养繁殖体具有较强的恢复生长和生理活动的能力,是一种适宜于水电工程库区消落带生态恢复的物种。