Early Snowmelt Enhances the Carbon Sequestration of Hummock-Forming Sphagnum Mosses on Boreal Wetlands

Sphagnum mosses are globally important owing to their considerable peat-forming ability and their potential impact on global climatic cycles acting as a long-term net carbon sink. However, changes in climatic conditions due to global warming may affect the relations between Sphagnum mosses and vascular plants but also the competition among Sphagnum, and thus alter the accumulation of carbon on boreal wetlands. Sphagnum mosses are a plant genus with a favorable ability to grow in low solar irradiance and temperature conditions compared to vascular plants. This may be increasingly beneficial in increased wintertime temperatures and predated snowmelt conditions. To understand particularly the importance of early spring photosynthetic activity and thus the role of the length of growing season on carbon balance, we analyzed the CO2 exchange of Sphagnum mosses with closed chamber technique in two categories of microtopographical habitats, hummocks and lawns, during four seasons 2010-2013 on a raised bog in Central Finland. During CO2 exchange measurements, instantaneous net ecosystem exchange (NEE) and ecosystem respiration (RE) were measured. Our results show that the mean measured seasonal NEE, i.e. the instantaneous net carbon sequestration, of hummocks was generally only slightly higher than the NEE of lawns, but the mean measured seasonal RE of hummocks was clearly and significantly higher than the RE of lawns in every study year. A reason for the observed still higher seasonal carbon sequestration of hummocks than that of lawns besides the slightly higher rate of carbon accumulation was the longer duration of physiologically active growing season. Therefore, hummock-forming Sphagnum mosses exposed firstly from snow cover showed to get the extra time for photosynthesis and thus extra benefit compared to other mire plants. This may be further enhanced by the expansion of hummock-forming Sphagnum moss dominated raised bogs towards northern aapa-mire region due to the global warming.

利用藓袋法监测广州市大气重金属沉降研究

工业生产和交通排放的增加导致了城市大气重金属污染,并威胁城市居民的健康。苔藓是常用的大气重金属污染指示植物之一,具有分布广、成本低、效果直观等优点。该研究利用藓袋法(泥炭藓)监测广州市大气重金属Cd、Cr、Cu、Pb、Zn的污染水平并评价其污染风险。结果表明:与暴露前泥炭藓的重金属含量相比,暴露后的Cd、Cu、Pb、Zn的几何平均值分别是其暴露前的1.2、2.3、1.4和2.3倍,而Cr元素在暴露期间稍微下降(0.9倍)。工业区的泥炭藓中Cd、Cu、Pb、Zn几何平均含量普遍较高;与风景区和居民区相比,商业区的Cu、Pb、Zn含量较高。聚类分析和主成分分析结果显示,工业活动和交通污染源是广州大气重金属污染的主要来源。利用污染因子法对4个功能区的泥炭藓样品的重金属污染情况进行评估,其中重金属污染程度为极高和高的监测点主要受工业生产及其重金属废弃物排放的影响(Cu、Pb、Zn);中度污染的监测点主要受到交通污染源影响(Cu、Zn);低污染的监测点都是远离工业排放源和交通源。该研究结果证明藓袋法(泥炭藓)在城市大气重金属污染监测中具有较高的适用性。

不同外源钙物质对蝴蝶兰栽培基质水苔EC值和pH值的影响

以蝴蝶兰品种"大辣椒"为试材,研究了不同外源钙物质对蝴蝶兰栽培基质水苔EC、p H值的影响。结果表明:浇灌清水的情况下EC值随着时间的延长逐渐降低,由0.92 m S/cm下降至0.56 m S/cm。正常肥水管理条件下的EC值逐渐上升,由0.94 m S/cm上升至1.30 m S/cm。而添加Ca O能加剧基质EC值的提升,并随着处理次数的增加,EC值持续增高,第4次处理后测定数值达到1.35~1.38 m S/cm并趋于稳定。与正常肥水管理相比,添加Ca CO3对基质的EC值基本没有影响。随着处理时间的延长,对照组水苔的p H值逐渐降低,浇灌清水的基质p H值由处理前的4.76降至4.57,正常肥水管理的p H值下降趋势更为明显,由开始的4.81下降至最终的4.46。但添加外源钙物质能明显改变水苔p H值。其中,200~600倍Ca O对水苔p H值的改善效果较为明显且效果较为接近,可使基质p H值由4.74~4.77提高至4.88~4.91;添加Ca CO3后,水苔的p H值与对照相比均有提高,但随时间延长呈降低趋势。

Rooting Response of Air-Layered Shea (<i>Vitellaria paradoxa</i>) Trees to Media and Hormonal Application under Two Different Climatic Conditions

Shea tree (Vitellaria paradoxa Gaertn. Family;Sapotaceae) indigenous to the Sudano-sahelian zone of Africa has great economic and ecological potential and attributes. Commercial cultivation of the tree is however, hampered by the poor rooting success of its planting material with adverse consequences on field establishment and total fruit yield. A 3 × 2 factorial experiment arranged in a randomized complete block design was carried out in 2012 at Bole in the Interior Savanna agro-ecological zone. The objective was to assess the rooting success of Shea shoots by the air-layering technique using two media types (palm fibre and Sphagnum moss) and three IBA hormone concentrations (0, 5000 and 10,000 ppm) under contrasting climatic (wet and dry) conditions. Layered shoots which were sprayed with 10,000 ppm IBA and wrapped with Sphagnum moss gave significantly (P < 0.05) higher rooting success in terms of more roots per cutting (73.3%) and longer roots per cutting (9.0 cm) than palm fibre at both 5000 ppm (30.0%;3.7 cm) and 10,000 ppm (46.7%;7.9 cm) concentrations. Higher rooting success was significantly achieved in the wet season than in the dry season. Sphagnum moss treated with 10,000 ppm IBA facilitated the translocation of higher levels of sugar and total free phenol (TFP) to the base of the layered shoots which resulted in significantly (P < 0.05) higher number of roots and better roots protection from fungal infection than the other treatments. Rooting of layered shoots was affected to a greater extent by low temperatures (Rooting = 836 – 34.2 Temp (low);R2 = 82%, p < 0.001) than by high temperatures (Rooting = 5250 – 175.0 Temp (high);R2 = 64.5%, p < 0.009). Rooting of layered shoots was also significantly and negatively affected by the spread of the canopy of the selected tree such that closed canopy trees resulted in higher and better rooting that open canopy trees (Rooting = 113.87-23.697(Canopy spread);R2 = 89%, p = 0.002;n = 9). Furthermore, significant and positive correlations were found between IBA concentration level and simple sugars (r = 0.99;P < 0.0001;n = 9) and also between IBA concentration level and total free phenols (r = 0.98;P < 0.0002;n = 9). The study concluded that to achieve high rooting success in the propagation of Shea nut tree by the air-layering technique, a combination of Sphagnum moss treated with 10,000 ppm of IBA hormone should be used and the whole set up carried out in the wet season.

Response of C and N cycles to N fertilization in Sphagnum and Molinia-dominated peat mesocosms

Plant communities play an important role in the C-sink function of peatlands. However,global change and local perturbations are expected to modify peatland plant communities,leading to a shift from Sphagnum mosses to vascular plants. Most studies have focused on the direct effects of modification in plant communities or of global change(such as climate warming, N fertilization) in peatlands without considering interactions between these disturbances that may alter peatlands' C function. We set up a mesocosm experiment to investigate how Greenhouse Gas(CO_2, CH_4, N_2O) fluxes, and dissolved organic carbon(DOC)and total dissolved N(TN) contents are affected by a shift from Sphagnum mosses to Molinia caerulea dominated peatlands combined with N fertilization. Increasing N deposition did not alter the C fluxes(CO_2 exchanges, CH_4 emissions) or DOC content. The lack of N effect on the C cycle seems due to the capacity of Sphagnum to efficiently immobilize N. Nevertheless, N supply increased the N_2O emissions, which were also controlled by the plant communities with the presence of Molinia caerulea reducing N_2O emissions in the Sphagnum mesocosms. Our study highlights the role of the vegetation composition on the C and N fluxes in peatlands and their responses to the N deposition. Future research should now consider the climate change in interaction to plants community modifications due to their controls of peatland sensitivity to environmental conditions.

模拟氮沉降对鄂西南贫营养泥炭地两种藓类植物生长与分解的影响

以泥炭藓属(Sphagnum)植物为优势种的贫营养泥炭地是陆地生态系统重要的碳汇,其优势植物的生长与分解动态关系着贫营养泥炭地碳汇潜力,但有关氮沉降对贫营养泥炭地优势藓类植物生长与分解的影响还存在很大争议,并且氮沉降对亚热带贫营养泥炭地优势藓类植物生长与分解的研究鲜有报道。该研究以鄂西南贫营养泥炭地为研究对象,通过原位喷洒不同浓度的NH_(4)Cl溶液,采用生物量收割法和分解袋法,探讨模拟氮沉降对泥炭藓(S.palustre)与金发藓(Polytrichumcommune)生长及分解的影响。研究结果表明:(1)氮沉降对两种藓类植物生长高度与生物量均有明显的影响,且两种藓类植物生长存在一定的氮沉降阈值,约为3g·m^(-2)·a^(-1);(2)氮沉降对两种藓类植物生长影响程度不同,金发藓对氮沉降的响应灵敏度要大于泥炭藓;(3)高浓度氮沉降(6和12g·m^(-2)·a^(-1))抑制了泥炭藓分解,低浓度氮沉降(3g·m^(-2)·a^(-1))对泥炭藓分解的影响取决于分解时间,而所有浓度氮沉降均抑制了金发藓凋落物的分解;(4)分解1年以后,泥炭藓的最终质量残留率平均值为105.99%,金发藓的最终质量残留率平均值为70.79%,金发藓的分解速率远大于泥炭藓;(5)氮沉降对两种藓类凋落物化学元素含量与化学计量比有显著影响,且与分解时间密切相关。