模拟增温对中亚热带杉木人工林土壤磷有效性的影响

气候变暖改变与土壤磷循环相关的生物地球化学过程,对陆地生态系统磷循环产生直接或间接影响。为研究亚热带地区杉木人工林土壤磷有效性对增温的响应,开展了模拟增温实验。实验设置对照组及增温组(5℃),经过1.5a的短期增温,对杉木人工林的土壤全磷、有机磷、微生物量磷、有效磷、酸性磷酸酶活性及相关土壤理化性质进行测定,结果表明:增温处理下,土壤酸性磷酸酶活性提高约1.5倍,土壤全磷、微生物量磷以及有机磷含量分别减少了6%、34%和12%,土壤有效磷含量增加25%。可见,短期增温通过提高土壤磷酸酶活性进而促进土壤有机磷矿化和降低土壤微生物固磷量,从而增加土壤磷有效性,但是增温导致潜在可利用的土壤微生物量磷大幅度的降低,将有可能加剧亚热带杉木人工林土壤磷限制。     

长白落叶松人工林心材变化规律

依据黑龙江省孟家岗林场49株人工落叶松1179个圆盘和轮盘数据,分析了心材半径的纵向变化规律.结果表明: 心材半径随树高增高而逐渐减小,与树干外形基本一致,其中去皮半径(XR)、胸径(DBH)及形成层年龄(CA)与心材半径之间关系较显著,利用逐步回归分析建立落叶松心材半径(HR)和面积(HA)模型:HR=b₁+b₂XR²+b₃CA+b₄XR, HA=b₁+b₂DBH·XR+b₃CA+b₄DBH·XR².应用AIC、BIC、对数似然值以及似然比检验等模型评价指标,对利用样地、样木效应拟合的心材半径和面积模型进行比较.当考虑样木效应拟合心材半径和面积模型时,将b₁、b₂、b₃作为混合参数得出的模型最好.混合模型的预测精度高于基本模型.在应用上,总体心材半径和面积可以通过混合模型来预测.采用Beta回归模型模拟了心材比例,模型中各参数均显著,决定系数较高,模型模拟效果较好.     

Analysis of household's energy consumption,forest degradation and plantation requirements in Eastern Tigray,Northern Ethiopia

This study examines the link between household's energy consumption, forest degradation and plantation requirements in Eastern Tigray. Data on household's fuelwood, cow‐dung, kerosene and electricity consumption in the study sites were collected from 557 urban and 114 rural households. Deforestation rate was estimated following FAO and Woody Biomass Inventory Strategy Planning Project (WBISPP's) conversion factors. The study showed that household's fuelwood consumption in urban areas (mean = 2.5 kg/day) was about 52% lower as compared to the rural villages (mean = 3.8 kg/day). The estimated area abandoned annually in the vicinity of urban areas as the result of urban fuelwood consumption varies from 217 ha around Maichew town to 12047 ha around Mekelle City. The estimated area abandoned in rural areas annually as the result of tree cutting for fuelwood also varies from 6.5 ha around Sinkata to 127 ha around Dergajen village. It is therefore recommended that an estimated annual tree plantation of area ranging from 286 ha around Maichew town to 21,684 ha around Mekelle city is required. Moreover, an estimated annual tree plantation of area ranging from 16 ha around Sinkata village to 229 ha around the Dergajen village is required taking the existing population into account.     

Effects of patch size and basal area on avian taxonomic and functional diversity in pine forests: Implication for the influence of habitat quality on the species–area relationship

Relationships between avian diversity and habitat area are assumed to be positive; however, often little attention has given to how these relationships can be influenced by the habitat structure or quality. In addition, other components of biodiversity, such as functional diversity, are often overlooked in assessing habitat patch value. In the Sandhills Ecoregion of Georgia, USA, we investigated the relationship between avian species richness and functional diversity, forest basal area, and patch size in pine forests using basal area as a surrogate for overstory structure which in turn impacts vegetation structure and determines habitat quality within a patch. We conducted bird surveys in planted mature pine stands, during breeding season of 2011. We used three classes of stand basal area (BA): OS, overstocked (BA ≥ 23 m²/ha); FS, fully/densely stocked (13.8 m²/ha ≤ BA < 23 m²/ha); and MS, moderately stocked (2.3 m²/ha ≤ BA < 13.8 m²/ha). MS patches showed more structural diversity due to higher herbaceous vegetation cover than other two pine stocking classes of patches. Total species richness and functional richness increased with the size of MS patches, whereas functional divergence decreased with the size of OS patches (p < 0.05). Functional richness tended to be lower than expected as the size of OS patches increased. Greater richness of pine–grassland species was also found at MS patches. Percent cover of MS patches within a landscape influenced positively the richness of pine–grassland species (p < 0.05). Our results suggest that (a) avian species–habitat area relationship can be affected by habitat quality (structural diversity) and varies depending on diversity indices considered, and (b) it is important to maintain moderate or low levels of pine basal area and to preserve large‐sized patches of the level of basal area to enhance both taxonomic and functional diversity in managed pine forests.     

Soil‐dwelling insect pests of tree crops in Sub‐Saharan Africa,problems and management strategies—A review

This review aims to draw the attention of researchers, ecologists and farmers to the threats of soil‐dwelling insect pests on important tree crops in sub‐Saharan Africa, with a special focus on termites. It synthesizes the information on the effects of various factors affecting soil pest occurrence and damage, suggesting that the resultant undesirable effects of soil pests in this region are largely as a result of indiscriminate tree cutting, slash‐and‐burn agriculture and indiscriminate use of pesticides. Major insect orders, their host ranges and the nature of damage on selected tree crops are described. This study further critiques existing soil pest management practices, showing that majority of soil pest management practices are ineffective. Thus, management strategies like “attract and kill” approach based on entomopathogenic fungi need to be studied, developed and emphasized for the management of soil insect pests in sub‐Saharan Africa. A conclusion section attempts to offer suggestions for ways in which future work on soil pests in sub‐Saharan Africa could proceed.     

The photosynthetic characteristics of differently shaped leaves in Populus euphratica Olivier

There is a distinct leaf shape polymorphism within a single plant of P. euphratica Olivier. The anatomical structure, carbon isotope discrimination (Δ¹³C), and stomatal and photosynthetic behaviour were investigated in broad-ovate (BOL) and lanceolate (LL) leaves, located at the top and bottom in crown, respectively, of a mature Euphrates poplar growing in its native habitat. Both types of leaves had a non-Kranz anatomy and low Δ¹³C values. However, Δ¹³C of a LL was in average 3.2‰ larger than that of a BOL. In comparison with the LL, the BOL had a smaller stomatal conductance, causing subsequent decreases in transpiration rate and ratio of CO₂ concentrations in intercellular spaces to air. Carbon assimilation rate and water use efficiency were higher in the BOLs than in the LLs. The BOL exhibited C₄-like enzymological features, the activity of glycollate oxidase, and the ratio of activities of ribulose-1,5-bisphosphate carboxylase (RuBPC) to phosphoenolpyruvate carboxylase (PEPC) was lower in BOL than in LL throughout the whole growing season. The lowered ratio of RuBPC/PEPC in BOL was mainly associated with a marked decline in the activity of RuBPC, and only a slight increase in the activity of PEPC. These differences might contribute to microclimate adaptation in both types of leaves. This revised version was published online in June 2006 with corrections to the Cover Date.     

The role of glycine in determining the rate of glutathione synthesis in poplar. Possible implications for glutathione production during stress

The terminal step of glutathione (GSH) synthesis is the condensation of γ-glutamyl-cysteine (γ-EC) with glycine. Relatively little information exists concerning the importance of photorespiratory glycine in determining the rate of conversion of γ-EC to GSH. Consequently, the effect of exogenous glycine and of illumination on foliar contents of γ-EC and GSH was studied in excised leaves and leaf discs from untransformed poplar ( Populus tremula × P. alba ) and poplar overexpressing γ-glutamylcysteine synthetase (γ-ECS; EC 6.3.2.2). Poplars strongly overexpressing γ-ECS (ggs28) had enhanced levels of γ-EC and GSH compared to untransformed poplars. The relationship between γ-EC and GSH contents in ggs28 was light dependent. In illuminated leaves, GSH contents were up to 50-fold higher than γ-EC. On darkening, γ-EC accumulated markedly and GSH declined, so that the GSH:γ-EC ratio was close to 1. These dark-induced changes were prevented by supplying glycine through the petiole or by incubation of leaf discs on glycine. Dark accumulation of γ-EC in leaf discs from untransformed poplar was also prevented by supplying glycine. Supplying cysteine in the dark to discs from untransformed poplar and ggs28 increased γ-EC levels markedly but GSH levels only slightly. Subsequent illumination caused γ-EC to decrease and GSH to increase. Supplying glycine in concert with cysteine had similar effects to illumination. The data suggest that photorespiratory glycine is essential for GSH synthesis, especially under stress conditions, where increased amounts of GSH are required.     

管理措施对人工林土壤质量的影响

可持续性生产力是人工林发展的一个关键问题。然而,人工林培育过程中常出现土壤质量退化和人工林生产力下降等问题。管理措施是人工林发展过程中土壤质量变化的一个重要因素,正确的管理措施能够维护和提高林地的土壤质量。管理措施主要包括整地、施肥、林地收获与凋落物管理和营造混交林等。不同的整地方式、整地强度、整地时间等能改变土壤物理、化学和生物学性状,进而对其土壤质量产生一定的影响;施肥措施能改善土壤质量、提高人工林生产力,而过量施肥能够导致林地养分的流失和地下水质的恶化;木材收获和林地凋落物焚烧导致人工林系统养分的大量流失,加强对人工林系统有机物质的保护有利于林地土壤质量的改善;营造混交林在一定程度上有利于土壤质量维护,由于物种间存在复杂的相互关系,其对混交树种、混交方式和立地条件的选择等管理措施均能影响土壤质量。最后,文章对今后人工林管理措施对土壤质量影响的重点研究方向作了展望。     

改变碳输入对亚热带人工林土壤微生物生物量和群落组成的影响

通过在亚热带杉木(Cunninghamia lanceolata)和米老排(Mytilaria laosensis)人工林中设置互换凋落物、去除凋落物、去除凋落物+去除根系和对照处理来分析改变地上、地下碳输入对人工林土壤微生物生物量和群落组成的影响。结果显示,改变地上、地下碳输入对土壤微生物生物量碳、氮的影响因树种而异。在米老排林中,土壤微生物生物量不受碳源的限制。而在杉木林中,加入米老排凋落物、去除凋落物和去除凋落物+去除根系3种处理中土壤微生物生物量碳、氮具有明显增加的趋势。磷脂脂肪酸分析结果显示,杉木林中,添加高质量的米老排凋落物后,革兰氏阳性细菌、阴性细菌、丛枝菌根真菌、放线菌和真菌群落生物量分别显著增加了24%、24%、53%、25%、28%,革兰氏阴性细菌和丛枝菌根真菌的相对丰度均有显著增加。与对照相比,杉木林中去除凋落物后革兰氏阳性细菌、阴性细菌、丛枝菌根真菌、放线菌和真菌群落生物量分别显著增加了22%、29%、44%、25%、52%,真菌与细菌比值显著增加了21%。但是,去除凋落物+去除根系处理对两个树种人工林土壤微生物群落组成均无显著影响。米老排和杉木林土壤微生物生物量碳、氮的季节变化格局不同,土壤养分有效性可能是驱动土壤微生物生物量季节变化的主要因子。未来研究需要关注凋落物和根系在不同树种人工林中对土壤微生物群落的相对贡献。