南亚热带10种造林树种的水力结构和水力安全

南亚热带地区人工纯林面积大, 但是结构简单, 对气候变化响应敏感。在区域气候干旱化的背景下, 造林树种的生理生态策略及其对季节性干旱的响应亟待研究。该研究选择南亚热带地区10种造林树种(包括6种乡土种和4种外来种), 测定这些树种的平均生长速率、水力学性状以及经济学性状, 分析性状与生长速率之间的相关关系, 并比较水力安全边际和气孔安全边际的种间差异。结果发现: (1)造林树种的生长速率与木质部导水率显著正相关, 但与木材密度、比叶面积以及水力安全性指标无显著相关性。(2)造林树种的水分传导效率性和安全性之间没有权衡关系, 外来树种Acacia crassicarpa和Eucalyptus grandis × urophylla同时具有较高的木质部导水率和较强的抗栓塞能力。(3)造林树种的水力安全边际和气孔安全边际的种间差异显著, 大叶相思(Acacia auriculiformis)、红锥(Castanopsis hystrix)、壳菜果(Mytilaria laosensis)和阴香(Cinnamomum burmannii)在干季发生水力失败的风险较高。建议南亚热带人工林的生态监测指标体系中应包括树木水力学性状, 进而为人工林的可持续经营管理提供重要参考。     

樟子松固沙林林水关系研究进展及对营林实践的指导

中国有着世界上最大面积的人工林, 如何维持人工林的可持续性已成为气候变化背景下需要面对的重大挑战。樟子松(Pinus sylvestris var. mongolica)以其抗旱、抗寒、耐贫瘠等优良特性成为中国北方生态治理中最主要的常绿针叶树种之一, 近70年来发挥了巨大的防风固沙与生态固碳功能。然而, 随着林分的生长与气候变化, 樟子松人工固沙林正经历着越来越严峻的环境胁迫, 部分地区出现了林分“早衰”或死亡的现象, 引起了人们对樟子松固沙林适应与应对气候变化能力的担忧。该文在回溯樟子松基本生物学特征与引种推广历史, 系统总结近年来樟子松林林水关系研究新成果的基础上, 全面分析了樟子松固沙林林水关系存在的主要矛盾, 并提出了基于林水关系相协调的林分经营措施的调整: 由倡导防护功能为主的单一目标向包含林分稳定性、生态固碳功能、可持续发展等多目标平衡方向调整; 由以沙地森林景观培育为主向以良好土壤生境培育为主的方向调整; 由倡导天然更新为主向以人工造林与天然更新相结合的世代更新方向调整。在立足于北方沙地脆弱生境与气候变化客观现实的基础背景下, 应坚持樟子松在固沙林生态系统演化过程中的先锋种与建群种地位, 基于“以水定绿”原则, 采取“隔行带伐+再造林”等方式开展林分密度动态调控, 促进林分向异龄林结构演化, 促进樟子松固沙林生态服务的优质化和生态固碳功能的最大化。     

广州闽楠-樟人工混交林物种组成与多样性研究

为了解人工混交林群落结构特征和物种多样性关系,对广州龙眼洞林场内闽楠(Phoebebournei)-樟(Cinnamomum camphora)人工混交林进行群落结构分析。结果表明, 0.37 hm2样地内共有128种植物9 563株,隶属于57科99属;其中乔木35种,灌木61种,草本98种。在乔木层中,重要值排名前5的植物分别是山乌桕(Triadica cochinchinensis)(33.86%)、闽楠(17.24%)、樟(12.96%)、三桠苦(Melicopepteleifolia)(7.92%)和山苍子(Litseapungens)(3.70%);灌木层以茜草科(Rubiaceae)植物为主;草本层以禾本科(Poaceae)植物为主。乔木层、灌木层和草本层的Shannon-Wiener指数分别为1.230、1.708和1.754,Simpson指数分别为0.635、0.680和0.707,表明该人工混交林下草本物种丰富。非度量多维尺度分析(NMDS)表明,不同样方的物种组成相似性并不一致,部分样方含有偶见种。群落的径级结构呈倒“J”型,其中11.64%为幼苗,苗木占比6....     

Phylogenetic analyses of symbiotic genes and characterization of functional traits of Mesorhizobium spp. strains associated with the promiscuous species Acacia seyal Del.

Aims: To assess the phenotypic, symbiotic and genotypic diversity scope of Mesorhizobium spp. strains associated with Acacia seyal (Del.) isolated from different agro‐ecological zones in Senegal, and uses of susceptible microbial inoculum in a reafforestation process. Methods and Results: A polyphasic approach including phenotypic and genotypic techniques was used to study the diversity and their relationships with other biovars and species of rhizobia. The geographical origins of the strains have limited effect on their phylogenetic and phenotypic classification. Nodulation tests indicated promiscuity of the strains studied, because they were capable of nodulating six woody legume species (Acacia auriculiformis, Acacia senegal, A. seyal, Acacia tortilis ssp. raddiana, Leucaena leucocephala and Prosopis juliflora). Sequencing and phylogenetic analyses of nodA, nodC and nifH genes pointed out that in contrast to nodA gene, the phylogenies of nodC and nifH genes were not consistent with that of 16S rRNA, indicating that these genes of the A. seyal‐nodulating rhizobia might have different origins. Microbial inoculation on nonsterile soil had significant effect on the nodules number and the growth of the seedlings, indicating that these strains of rhizobia might be used as inoculum. Conclusions: The results indicated that A. seyal is a nonselective host that can establish effective symbiosis with Mesorhizobium spp. strains from diverse genomic backgrounds and that the selected A. seyal‐nodulating rhizobia could enhance plant growth. Significance and Impact of the Study: These results showed the important role that A. seyal could play in the improvement of reafforestation process as a promiscuous host, which can establish effective symbiosis with rhizobia from diverse genomic backgrounds.     

Seedling responses of three Australian tree species to toxic concentrations of zinc in solution culture

A frequently desired outcome when rehabilitating Zn toxic sites in Australia is to establish a self-sustaining native ecosystem. Hence, it is important to understand the tolerance of Australian native plants to high concentrations of Zn. Very little is known about the responses of Australian native plants, and trees in particular, to toxic concentrations of Zn. Acacia holosericea, Eucalyptus camaldulensis and Melaleuca leucadendra plants were grown in dilute solution culture for 10 weeks. The seedlings (42 days old) were exposed to six Zn treatments viz., 0.5, 5, 10, 25, 50 and 100 M. The order of tolerance to toxic concentrations of Zn was E. camaldulensis> A. holosericea> M. leucadendra, the critical external concentrations being approximately 20, 12 and 1.5 M, respectively. Tissue Zn concentrations increased as solution Zn increased for all species. Root tissue concentrations were higher than shoot tissue concentrations at all solution Zn concentrations. The critical tissue Zn concentrations were approximately 85 and 110 g g^–1 DM for M. leucadendra, 115 and 155 g g^–1 DM for A. holosericea and 415 and 370 g g^–1 DM for E. camaldulensis for the youngest fully expanded leaf and total shoots, respectively. The results from this paper provide the first comprehensive combination of growth responses, critical external concentrations, critical tissue concentrations and plant toxicity symptoms for three important Australian genera, viz., Eucalyptus, Acacia and Melaleuca, for use in the rehabilitation of potentially Zn toxic sites.     

Soil Organic Carbon and Water Retention after Conversion of Grasslands to Pine Plantations in the Ecuadorian Andes

Tree plantations in the high elevations of the tropics constitute a growing land use, but their effect on ecosystem processes and services is not well known. We examined changes in soil organic carbon (C) and water retention in a chronosequence of Pinus radiata stands planted in páramo grasslands in Cotopaxi province, Ecuador. Water retention at 10, 33, and 1,500 kPa declined with stand age, with soils in the oldest pine stands retaining 39%, 55%, and 63% less water than grassland soils at the three pressures tested. Soil organic C in the 0–10-cm depth also declined with stand age, from 5.0 kg m^–2 in grasslands to 3.5 kg m^–2 in 20–25-year-old pine stands (P < 0.001); at greater depth in the A horizon, C contents decreased from 2.8 to 1.2 kg m^–2 (P = 0.047). There were no significant differences among age classes in the AC and C horizons (P = 0.15 and P = 0.34, respectively), where little or no weathering of the primary material has occurred. Inputs of C may be affected by the significantly higher carbon–nitrogen (C:N) ratio of the litter under older pine stands (P = 0.005), whereas outputs are influenced by substrate quality as well as soil environmental factors. Soil ratios at the 0–10 cm depth were significantly higher in grasslands and young pine stands (P < 0.001), whereas carbon–phosphorous (C:P) ratios at 0–10-cm depth followed a similar but not significant trend. However, there was no significant difference in short-term decomposition rates (P = 0.60) when the soils were incubated under uniform temperature and moisture conditions. In páramo ecosystems, where high soil moisture plays an important role in retarding decomposition and driving high C storage, the loss of water retention after afforestation may be the dominant factor in C loss. These results suggest that soil C buildup and water retention respond rapidly to changes in biota and need to be assessed with regard to implications for C sequestration and watershed management.     

Transient expression of reporter genes introduced in tissues of two <Emphasis Type="Italic">Acacia</Emphasis> species using a biolistic method

Summary The biolistic method was used to introduced DNA into cotyledons of Acacia mangium and A. mearnsii. The β-glucuronidase gene (gus) and the green fluorescent protein gene (gfp) were tested as reporter genes to study the effects of acceleration pressure and pre- and post-bombardment osmotic treatments. These consisted of incubating the explants in the presence of sucrose, mannitol, and sorbitol for several hours before or after bombardment with microprojectiles. High acceleration pressure slightly enhanced gus expression in both species tissues. Osmotic treatments significantly improved expression of both reporter genes introduced into A. mearnsii cotyledons. The best transient expression was observed in these tissues when they were treated with mannitol and sorbitol (0.3 or 0.4M each) for 3–4h before the bombardment and 3h afterwards. However, the same treatments did not affect the expression of the gus gene introduced in A. mangium explants.     

Purification of anthocyanins from species of Banksia and Acacia using high-voltage paper electrophoresis

A new method has been developed for the isolation and rapid identification of anthocyanins from two floricultural crops based on the use of high-voltage paper electrophoresis with bisulphite buffer. Using this method, anthocyanin pigments were successfully purified as their negatively charged bisulphite-addition compounds from crude extracts of plant tissue. In conjunction with liquid chromatography-electrospray mass spectrometry, the method enabled the anthocyanins from the flowers of two Banksia species and the leaves of two Acacia species to be identified. The Banksia flowers contained both cyanidin and peonidin-based pigments, while the Acacia leaves contained cyanidin and delphinidin derivatives.     

Clonal propagation of Acacia catechu Willd. by shoot tip culture

A method is described for in vitromicropropagation through shoot apices of Acaciacatechu Willd., a semi-arid tree valued for Katha (atanin-like substance obtained from red heart wood of10–20 year old trees) and timber. Explants wereexcised from 15-days-old in vitro grownseedlings raised from superior seed stocks. Shoot budinduction from shoot apex explants was observed onMurashige and Skoog's (MS) [12] medium containingvarious growth regulators. A maximum of 12 shoots wasobtained on MS medium supplemented with 1.5 mg/l 6-benzylaminopurine (BAP) and 1.5 mg/l kinetin.Well-developed shoots (3–4 cm long) were rooted on strength MS medium with 3.0 mg/l indole-3-acetic acid (IAA) and sucrose 1.5%. In vitro regenerated plantlets of A. catechu were transferred to field conditions.