Above- and belowground carbon inputs affect seasonal variations of soil microbial biomass in a subtropical monsoon forest of southwest China

Soil microbial activity drives carbon and nutrient cycling in terrestrial ecosystems. Soil microbial biomass is commonly limited by environmental factors and soil carbon availability. We employed plant litter removal, root trenching and stem-girdling treatments to examine the effects of environmental factors, above- and belowground carbon inputs on soil microbial C in a subtropical monsoon forest in southwest China. During the experimental period from July 2006 through April 2007, 2 years after initiation of the treatments, microbial biomass C in the humus layer did not vary with seasonal changes in soil temperature or water content. Mineral soil microbial C decreased throughout the experimental period and varied with soil temperature and water content. Litter removal reduced mineral soil microbial C by 19.0% in the ungirdled plots, but only 4.0% in girdled plots. Root trenching, stem girdling and their interactions influenced microbial C in humus layer. Neither root trenching nor girdling significantly influenced mineral soil microbial C. Mineral soil microbial C correlated with following-month plant litterfall in control plots, but these correlations were not observed in root-trenching plots or girdling plots. Our results suggest that belowground carbon retranslocated from shoots and present in soil organic matter, rather than aboveground fresh plant litter inputs, determines seasonal fluctuation of mineral soil microbial biomass.     

Root development of Thuja plicata in peat-substitute rooting media

In this study we investigated the potential usefulness of different substrates produced from gorse (Ulex europaeus L.) for propagating cuttings of Thuja plicata ‘Atrovirens’. The gorse was composted by different methods, to produce four types of compost. These composts were then used as such (100% compost) or in mixes with coarse sand and pine bark compost (25% compost, 25% coarse sand and 50% pine bark compost, v/v/v) to prepare eight different substrates. The substrates were compared in cutting propagation trials carried out in a greenhouse, with a standard rooting medium consisting of 25% Sphagnum peat moss, 25% coarse sand and 50% pine bark compost (v/v/v). Cuttings were taken from a garden hedge in March 2003, and comprised shoots of the previous year's growth. The bases of the cuttings were treated with a 0.4% solution of IBA rooting hormone, then inserted into cells filled with the corresponding substrate and placed on a propagation bench. Rooting percentage and visual rooting score were determined in July. The quality of roots was evaluated, as total root length and number of root tips, in July, September and November 2003, by use of a Delta-T Scan system. The rooting success of the cuttings ranged from 75% to 90%, except when the substrate comprised the pure composted gorse, obtained after the shorter period in an enclosed composting system with addition of fertilizer and reuse of leachates. Most of the cuttings in this substrate died and only 4% of the cuttings rooted successfully. Physicochemical characteristics of this rooting medium included very high electrical conductivity, low C/N ratio and high water retention. Addition of coarse sand and pine bark compost to the composted gorse significantly increased the rooting success. The root quality variables differed depending on the substrate considered and date of harvest. The results showed that substrates made from gorse compost are of potential use as a peat substitute for propagating cuttings of T. plicata ‘Atrovirens’. The physicochemical properties of the composted gorse should be determined before its use to establish whether it can be used pure as a substrate for rooting or whether it should be mixed with other substances.     

Effect of arbuscular mycorrhizal fungal inoculation on root system architecture of trifoliate orange (Poncirus trifoliata L. Raf.) seedlings

Plant root system architecture is essential characteristics in relation to nutrient acquisition by root system from soil volume. Many environmental factors can affect the establishment of root system architecture, e.g. arbuscular mycorrhizal (AM) fungi. We inoculated the trifoliate orange (Poncirus trifoliata L. Raf.) seedlings with four AM fungal species in rhizoboxes, with non-inoculated seedlings as control. Using the WinRHIZO^® image analysis system, the root system architecture of seedlings was characterized. Results indicated that AM colonization did not affect the tap root length, the average root diameter, the basal root growth angle in spite that four AM fungal species exerted differential influence on the plant growth. Contrastingly, AM colonization significantly reduced the total root length, the root volume, the root surface area, but promoted the formation of lateral roots of high order. In addition, AM colonization induced more fine roots and less coarse roots. To our knowledge, it is the first report on the influence of AM fungi on the distribution of root diameter size classes. The mechanisms and implication of AM fungi on root system architecture is discussed.     

伐根适宜高度的研究

分析了伐根过低给森林采运作业带来的不利影响。阐述了伐根高度与根部形状的关系。为了研究伐木作业时伐根的适宜高度，引进了根形系数，并根据数数理统计的原理，计算出白桦，红松，白杨，云杉和榆树５种树种的根形系数。由此得出结论，不同树种的根形系数不同；可根据具体树种的根形系数确定其伐根的适宜高度。     

马铃薯茎尖培养脱毒率的影响因素试验

试验结果表明:茎尖表面消毒用5%次氯酸钠比0.1%二氯化汞效果好。茎尖取材的来源对茎尖培养过程中的成活率和脱毒率没有影响。切取的茎尖越小,脱毒率越高,成活率越低。高温预处理对提高茎尖脱毒率效果明显。合适的激素配方可以促进茎尖的分化。     

长尾滑刃线虫对四川苏铁的专一寄生性研究

在根腐的四川苏铁球茎组织及根围土壤中检测出长尾滑刃线虫,在未根腐的该品种球茎组织中未检测到长尾滑刃线虫。在未根腐的该品种苏铁根周围土壤中检测出长尾滑刃线虫时,苏铁以后大多发生根腐。在其他多种根腐的苏铁品种中未检测到该线虫;在根腐的多个品种苏铁中都分离出镰刀菌。研究结果表明,长尾滑刃线虫对川铁可能存在专一寄生性;镰刀菌与长尾滑刃线虫可能共同危害四川苏铁。     

乔砧苹果断根对根系及新梢的促控研究

通过早春断根后连续3年的观察，较完整地记载了苹果断根根系的再生状况及对新梢生长的影响。调查表明，盛果期乔砧苹果在发芽前断根，当年的抑梢效果不明显，第2年表现出显著的控长效果；距主干80cm左右断根后，根系再生复原期至少需2年以上，恢复期内对果实产量及品质无不良影响。     

宿根花卉在城市园林绿化中的应用

本文在分析宿根花卉在城市绿化中现实意义的基础上,对宿根花卉在城市绿化中的应用原则进行论述,对宿根花卉在城市绿化中的具体应用进行阐述,为宿根花卉的开发利用提供指导。     

氮对低镉处理下东南景天根系形态及镉积累的影响

通过水培试验,本文研究了施氮肥(尿素)对低镉处理下两种生态型东南景天根系形态及镉积累的影响。结果表明,在一定范围内供氮(4.0￣16.0mmol/L)能明显促进东南景天的根系生长,各项根系形态指标,如根系长度、根系表面积、根系直径、根体积和侧根均有升高,在16.0mmol/L达到最大值。但是,随着供氮(32.0￣64.0mmol/L)增加,表现出一定的负效应:东南景天的各项根系形态指标明显受到抑制,与对照相比差异达显著或者极显著水平。氮素对东南景天的镉积累有一定的促进作用,随着氮素用量的增加,体内镉积累逐渐升高,与根系形态不同的是,镉含量在氮水平32.0mmol/L条件下达到最大。研究结果表明适当提高营养液氮素水平有利于提高东南景天的各项根系形态指标以及对镉的吸收积累。