The effects of natural and manipulated density regimes on Alliaria petiolata survival, growth and reproduction

Knowledge of the ecology of Alliaria petiolata, an alien invasive species in the USA, is essential to predict the efficacy of introduced biological control agents. Accordingly, we examined the growth and reproduction of second‐year A. petiolata rosettes under natural and manipulated density regimes. Plant survival was also studied under natural conditions. Similar survivorship patterns were observed for high‐ and low‐density populations, although survival in the low‐density populations was c. 10% higher. Under natural conditions, low‐density plants were larger and more fecund, on average, than high‐density plants; however, on a per‐area basis, high‐density populations were much more productive. When plant density was experimentally reduced, average seed production and plant size increased with thinning intensity, suggesting that thinning released plants from intra‐specific competition. Additionally, plants in thinned plots were able to recover from past competition and could approach production of the plants in un‐thinned lower density plots that had not experienced prior competition. However, seed production per unit area was lower in thinned versus un‐thinned plots of the same initial density. Results suggest herbivore‐induced plant mortality late in the life cycle, as might occur following the introduction of biological control agents, may reduce the contribution to the A. petiolata seedbank.     

金属腐蚀速度的计算机辅助测定(Ⅰ)数值实验研究

研究了在极化曲线测定的基础上，采用最优化方法测定腐蚀参数的方法，选用了３种非线性拟合的方法（高斯牛顿法、麦夸特法及离散型拉氏变换法），用能产生指定标准偏差的极化曲线模拟数值实验，对３种方法的实用性，从标准偏差、测量点的位置和数目、体系转移系数值等对方法的收敛性和计算结果的影响进行了考察．     

Simulation Study of the Impact of Permanent Groundcover on Soil and Water Changes in Jujube Orchards on Sloping Ground

Land degradation is recognized as a major environmental problem in rainfed fruit orchards on the Chinese Loess Plateau. Six treatments were used to investigate surface runoff and soil moisture by means of simulated rainfall experiments: (i) a control (clean cultivation) (CC); (ii) strip cock's foot (Dactylis glomerata L.) cover (SCF); (iii) strip crown vetch (Coronilla varia L.) cover (SCV); (iv) strip bird's foot trefoil (Lotus corniculatus L.) cover (SBF); (v) strip white clover (Trifolium repens L.) cover (SWC); and (vi) complete white clover cover (WCC). The time to runoff was significantly longer under WCC than under other treatments (p < 0·05). The total runoff volume and sediment yield were significantly greater under CC than under the vegetation cover treatments (p < 0·05). The mean infiltration rate under WCC and CC was the largest and lowest and differed significantly from that under other treatments (p < 0·05). The change of soil water storage was the largest under WCC and the least under CC. The soil moisture was significantly greater under SCF than under other treatments (p < 0·05). Treatment SCF seemed to be the best groundcover for rainfed sloping jujube orchards on the Chinese Loess Plateau. Copyright © 2014 John Wiley & Sons, Ltd.     

Selection for increased forage yield in alfalfa at different NaCl levels

Summary Alfalfa (Medicago sativa L.) forage yield may be reduced by moderate levels of salinity. Increasing forage yield in saline environments through plant breeding could partially ameliorate this problem. However, prior indirect selection either in cell culture, at germination, or during seedling growth has not resulted in agronomically relevant levels of salt tolerance. This study was conducted to determine whether mean forage yield of alfalfa grown in saline environments could be increased. To reduce the number of possible selection schemes, forage yield data for five harvests from Sonora and its parental cultivar African grown in a greenhouse and irrigated with 0, 30, 60, or 80 mM NaCl were used to simulate one cycle of selection at each NaCl environment. Greatest gains in forage yield were expected under non-saline conditions with decreased gains under saline conditions. Selection based on yield in regrowth harvests was also predicted to be more efficient than that based on seedling harvest. Experimental populations were developed from Sonora and African at each NaCl level using phenotypic selection for increased mean forage yield for harvests 3 to 5. After each of two cycles of selection, forage yield from selected, control (plants selected randomly under non-saline conditions), and parental populations was evaluated at 0, 30, 60, and 80 mM NaCl. Gains in forage yield were observed in African when the selection and evaluation environments were the same, but in Sonora this was observed only at 0 NaCl. Selection at 0 NaCl did not increase forage yield at 60 or 80 mM NaCl in either germplasm source. This suggests that selection for increased forage yield may be successful at low to moderate NaCl levels in germplasm with ample variation for yield when grown in saline environments, while selection for increased forage yield in non-saline conditions may be ineffective.     

Early Generation Selection for Grain Yield in Narrow-Leaf Lupin (Lupinus angustifolius L.)

Experiments were undertaken to identify an efficient method of selection for yield in early segregating generations of narrow-leaf lupin crosses. A first series of experiments involved simulation of F₂ populations with mixtures of ten cultivars and advanced breeding lines. The performance of genotypes in mixtures sown at different densities was compared with their monoculture [commercial density) yields m the same and the following year. These comparisons provided a basis for assessing the value of different planting designs and different selection criteria in early generation selection for yield. Correlated monoculture yield responses to simulated selection for single plant yield were similar for the honeycomb design and standard selection procedures at both low and commercial densities. These responses were much higher than that for grid selection in a low density population. Correlated monoculture yield responses to selection for other plant characters were substantial only for flowering time and number of pod bearing branches under certain conditions. These responses were greatest for selection in a low density mixture and in the year following selection. A procedure involving selection of the earliest flowering plants and selection within this group of plants with the highest number of pod bearing branches should be an effective approach to early generation yield selection in the narrow-leaf lupin.     

玉米茎秆汁液防治坡面土壤侵蚀的室内模拟试验

该文通过室内人工模拟降雨试验,研究了地表施加玉米茎秆汁液对降雨产流产沙强度的影响,旨在探索玉米茎秆汁液是否可以作为土壤改良剂来减少产流产沙强度。试验设计了2种玉米茎秆汁液的施加量(400和800 g)、4种施加浓度(10%、25%、50%和75%)和4种降雨强度(50、25、75、100 mm/h)。结果表明,各施加浓度和施加量的玉米茎秆汁液都能够减少降雨产流产沙强度,且相同条件下的产沙强度减小程度大于产流强度减小程度。当玉米茎秆汁液的施加量为400 g时,随着施加浓度从10%增加至25%、50%和75%,减流百分比分别为31.243%、31.685%、34.595%和39.475%,减沙百分比分别为23.167%、41.993%、37.918%和64.606%;当玉米茎秆汁液的施加量为800 g时,随着施加浓度从10%增加至25%、50%、75%,减流百分比分别为37.583%、56.433%、63.170%和76.360%,减沙百分比分别为48.214%、77.219%、88.572%和95.539%。当施加量和降雨强度相同时,产流产沙强度与施加浓度之间呈显著的指数函数递减关系,产沙强度随降雨强度的变化呈显著的幂函数递增关系。当施加量为400 g时,各施加浓度下的产流强度与降雨强度之间呈显著的线性函数递增关系,当施加量为800 g时,各施加浓度下的产流强度随降雨强度呈显著的指数函数递增关系。研究为水力侵蚀的防治提供了新思路,为水蚀荒漠化的防治提供了新方法。     

不同雨强条件下红壤坡地养分流失特征研究

采用人工模拟降雨装置 ,对红壤坡地养分流失特征进行了试验研究 ,结果表明 :在雨强较大情况下 ,土壤养分以泥沙形式随径流迁移 ;当雨强较小时 ,随径流迁移的可溶态养分流失量占流失泥沙养分量的比例较高 ,土壤养分流失氮、磷、钾分别达到 5 3.12 % ,2 3.1% ,2 1.5 % ;不同形态的养分在流失泥沙中均有养分富集现象 ,但富集率各不相同 ;土壤养分流失量与雨强及泥沙流失量呈正相关关系。     

模拟酸雨和酸雾对水稻生理和生长的影响

模拟酸雨和酸雾（ｐＨ２．０～５．６）的土培试验结果表明，低ｐＨ酸雨和酸雾处理对水稻产生明显伤害，水稻叶片出现坏死斑点，细胞膜透性增大，汁液ｐＨ值明显下降，叶绿素含量和光合速率明显降低，并随酸雨和酸雾的酸度增大、处理剂量增加而加重；叶片Ｎ，Ｐ和Ｋ养分被淋失，生长受抑制，产量明显下降。酸雨和酸雾处理诱导叶片过氧化物酶、过氧化氢酶和抗坏血酸氧化酶活性增高，但不同酶的活性峰值出现在不同的处理酸度梯度上。相同酸度下，对水稻生长的抑制作用以酸雾大于酸雨。     

模拟自然降雨条件下植物根系增强边坡土体抗剪强度特征

该研究以位于青藏高原东北部黄土区的西宁盆地作为试验区,采用柠条锦鸡儿(Caragana korshinskii Kom.)、霸王(Zygophyllum xanthoxylon(Bunge)Maxim.)、垂穗披碱草(Elymus nutans Griseb.)、细茎冰草(Agropyron trachycaulum(Linn.)Gaertn.)的单播种植,以及柠条锦鸡儿分别与细茎冰草、垂穗披碱草混播种植等2种方式,开展了原位模拟降雨试验并采用直接剪切试验,系统分析了模拟降雨试验前后试验区边坡表层以下3个不同位置处复合体抗剪强度大小及其随深度变化规律。结果表明:模拟降雨试验前,由柠条锦鸡儿与细茎冰草、垂穗披碱草混播的边坡a层(0~20 cm)根-土复合体黏聚力分别为19.5、18.9 k Pa,均较相同条件下单播边坡a层复合体黏聚力大;混播种植边坡各层根-土复合体黏聚力均较模拟降雨试验后裸坡a层土体黏聚力大,其中柠条锦鸡儿与细茎冰草混播边坡、垂穗披碱草混播边坡模拟降雨试验后,a层复合体黏聚力分别较裸坡a层黏聚力的增幅为30.65%~56.45%;柠条锦鸡儿、霸王、垂穗披碱草、细茎冰草单播边坡b层复合体黏聚力增幅为4.17%~38.89%;柠条锦鸡儿分别与细茎冰草、垂穗披碱草混播边坡b层黏聚力增幅为29.17%~34.72%;边坡c层土体黏聚力增幅相对不及a层、b层显著,反映了草本起到浅层加筋作用,灌木则起到深部锚固作用。