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71.
Carbon assimilation and allocation were studied in a tundra ecosystem in northern Scandinavia. Seasonal variation in the below-ground carbon allocation to dissolved organic carbon (DOC), coarse-, fine-, and hair roots was investigated using in situ 14C pulse-labelling, adding 2-3 MBq 14CO2 dm−2 to the above-ground vegetation. Combining the allocation data with regression models of the seasonal carbon flux made it possible to estimate a temporally explicit ecosystem carbon allocation budget.The ecosystem was a net source of CO2, losing on average 0.97 g C m−2 d−1 to the atmosphere, with little variation through the season. There was, however, significant temporal variation in partitioning of recently assimilated carbon. Allocation to below-ground compartments over 32 days following labelling increased from 18% in June to 55% in September. Above-ground allocation showed the opposite trend. Hair roots and DOC were strong sinks in the autumn. Transport of newly assimilated carbon occurred rapidly throughout the season, 14C appearing in all sampled pools within 4 h of labelling.The seasonal variation in carbon partitioning observed in this study has implications for the residence time of assimilated carbon in the ecosystem. A relatively greater allocation to rapidly decomposing pools, such as hair roots and DOC, would tend to reduce incorporation into woody tissue, increasing the overall rate of carbon cycling and decreasing ecosystem storage. The results of this study will be of value for building and validating mechanistic models of ecosystem carbon flow in tundra and subarctic ecosystems. 相似文献
72.
Total lipid extracts from an acid andic soil profile located on Madeira Island (Portugal) were analysed using gas chromatography (GC) and GC-mass spectrometry (GC/MS). The profile was covered mainly by grass. Bulk soil characteristics determined included soil pH (H2O) ranging from 4.5 to 4.0 and TOC, ranging from 84 to 30 g kg−1. A decrease of the contribution of lipids per TOC with depth was observed. The absence of typical bacterial markers might be an indication for reduced bacterial activity, most likely related to the low soil pH and the presence of Al and Fe (oxides). The distribution observed in the top layer with a dominant C26n-alkanol, steroids and triterpenoids, reflected mainly an input by grass leaves. A strong decrease in both relative and absolute concentration of these leaf-derived compounds was observed when comparing the litter layer with the mineral soil. The presence of C22-C32n-alkanoic acids, C22-C26 ω-hydroxy acids, C31n-alkane and C22-C32n-alkanols observed in the sub-soil is indicative of an important contribution by (grass) roots. In summer, a signal most likely reflecting the leaching of microbially derived products from the litter and/or aerial vegetation at the surface was observed. 相似文献
73.
Matti J. Salmela Stephen Cavers Joan E. Cottrell 《Forest Ecology and Management》2011,262(6):1020-1029
Environment-driven genetic differentiation among populations is a common feature among forest trees, and an understanding of how populations have adapted to their home site conditions is essential for management and conservation practices. In Scotland, 84 native Scots pine (Pinus sylvestris L.) woodlands are recognised by the Forestry Commission and they occupy highly diverse environments from the maritime west coast to continental sites in eastern Scotland. However, it is not known whether adaptations to local environments along sharp temperature and rainfall gradients have occurred in different populations and as a result, the seed transfer guidelines of the species are based only on data from isozymes and monoterpenes. In this study of an outdoor common-garden trial, we used chlorophyll fluorescence to examine whether seedlings from 32 open-pollinated families and eight populations from sites experiencing contrasting annual temperature regimes differed in their response to variation in natural outdoor temperatures between September 2009 and May 2010. In addition, growth initiation in spring was recorded. Photochemical capacity at photosystem II Fv/Fm showed a distinct seasonal trend and remained at relatively high levels (∼0.7) until November. Following a period of over 2 weeks with temperatures below or close to 0 °C, Fv/Fm started decreasing towards its minimum values recorded in early March when population means varied between 0.35 and 0.45. By early May and along with rising temperatures, photochemical capacity had recovered to the same level as observed in early November. Populations were found to respond differently to the cold period starting in December. The largest drop in photochemical capacity was observed in seedlings from a low-altitude population located in the maritime western Scotland, while in seedlings from higher-altitude locations in the cooler eastern Scotland, the response was smaller. In March, the recovery of photochemical capacity was slowest in seedlings from the mildest and coolest sites. Evidence of adaptive genetic differentiation was also found in spring phenology. Initiation of shoot elongation and needle flush were earlier in families from higher altitudes (cooler areas), but population differences were not significant at the α = 0.05 level. These results suggest that adaptation to the spatially heterogeneous environment in Scotland has taken place in Scots pine and that in order to minimise the risk of planting maladapted seed stock, the patterns of environmental and adaptive genetic variation should be taken into account in the management of genetic resources in this species. 相似文献
74.
江西省降水集中期及其期间降水量的变化特征及趋势分析 总被引:2,自引:0,他引:2
根据江西省地方标准中有关降水集中期的定义,统计1971~2008年4~9月的降水集中期,并用季节性Kendall检验方法做趋势分析。结果表明,1971~2008年4~9月期间,6~8月是降水集中期及其期间雨量较多的月份,4、5、9月是降水集中期及其期间雨量较少的月份。随时间变化,全省6~8月降水集中期及其雨量呈可能增多趋势,4、5、9月呈可能下降趋势。 相似文献
75.
季节性淹水对长江滩地69杨木材材性及其变异的影响 总被引:4,自引:0,他引:4
刘盛全 《安徽农业大学学报》1999,26(1):9-15
以安微新洲滩地上生长的69杨为材料,研究季节性淹水对69杨木材材性及其变异的影响。结果表明,与未淹水相比,长江滩地季节性淹水对69杨纤维形态特征影响不大,0.05水平下方差分析检验不显著;对木材微纤丝角,木材密度,木材干缩率和力学性质影响较大,0.05水平下方差分析检验显著,其中,微纤丝角,基本密度,抗弯弹性模量,抗 度和气干体积缩率分别增加了15.6%,5.9%,15.75,17.2%和28.5 相似文献
76.
云南松蠹害林分动态变化研究 总被引:1,自引:0,他引:1
1996~2000年对滇中地区路南长湖及宜良小白龙两个云南松蠹害林区的各847株样树进行了跟踪调查.调查初期两样地在树木长势和蠹害程度上存在明显差异,长湖样地树木长势逊于小白龙,蠹害程度轻于小白龙.4年来两样地的蠹害发展极不一致.长湖样地云南松健康木比例下降12.6%;云南松受纵坑切梢小蠹蛀害致死466株,死亡率55.0%,蠹害未得到控制.小白龙样地云南松健康木比例增加29.7%;云南松受纵坑切梢小蠹蛀害致死219株,死亡率25.9%,蠹害有所控制.研究结果表明树木长势与蠹害发生及其程度直接相关,树木长势影响蠹害的发展过程,蠹害的发展制约树木长势的增强、 相似文献
77.
应用6个微卫星分子标记位点评价了扎龙自然保护区包括野生、散养和笼养丹顶鹤3个小群体的遗传变异水平,以及野生与散养小群体间的基因流水平。结果表明,3个丹顶鹤小群体均表现出较高且相近的遗传变异水平,杂合度期望值(HE)为野生0.83300,散养0.80000,圈养0.81000,F-Statistics结果有97.5%以上的遗传多样性存在于群体内。同时还应用两种计算方法计算了野生与散养丹顶鹤小群体间基因流水平:应用稀有等位基因法计算两个小群体间的基因流值为每代1.9个个体;应用FST指数计算方法,并根据基因流值计算公式得出基因流值Nm为1个个体。这个基因流水平和机制能够维持扎龙自然保护区野生与散养丹顶鹤小群体间相近且较高的遗传变异水平。 相似文献
78.
79.
1993年5~11月份、1999年4~10月份和2006年的5~11月份,在地处晋西南的隰县阳头升乡竹干村和后堰村,以铗捕率或笼捕率的变化作为衡量种群数量的标准,开展了对社鼠(Rattus confucianus sacer)种群数量季节消长的研究。结果表明,社鼠种群数量存在着明显的季节变化,主要是繁殖和死亡两大因素相互作用的结果。种群每年在9月份出现一次数量高峰,由5、6、7、8月份的繁殖行为形成。10月份以后,由于气候和食物等条件恶化,致使部分鼠体死亡,特别是上一年越冬鼠的大量死亡,使社鼠种群数量随之下降。 相似文献
80.
以南阳牛、南阳牛、中国西门塔尔牛为试验动物,利用PCR-SSCP和PCR-RFLP技术研究了GHR基因上第8外显子、第9外显子、5’端、第3外显子的遗传变异。结果表明在GHR基因第8外显子、5’端既没发现PCR-SSCP多态,又没发现HaeⅢ、HindⅢ、PstⅠ、SpeⅠ、MspⅠ、RsaI酶切多态;在GHR基因第9外显子、第3外显子也没检测到PCR-SSCP多态。 相似文献