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921.
不同供氮水平下水曲柳(Fraxinus mandushurica Rupr.)幼苗根系呼吸季节动态 总被引:2,自引:1,他引:1
根呼吸是林木根系获得吸收养分和水分所需能量的重要生理活动.为了探讨林木根系呼吸速率的季节变化及其影响因素,采用离体根系法(Li-6400-06叶室连接到Li-6400便携式CO2/H2O分析系统)研究了水曲柳(Fraxinus mandushurica Rupr.)苗木各径级根呼吸速率在不同供氮水平下季节变化规律.结果表明:水曲柳苗木根呼吸速率表现出明显的季节动态,且与气温的季节变化规律相同,其中比根呼吸速率在0.5732 μmolCO2 · g-1 · s-1(直径≤2 mm,10月份)~7.1861 μmolCO2 · g-1 · s-1(直径≤2 mm,7月份)之间变化,表面积呼吸速率也是7月份最高,达到0.6848 μmolCO2 · cm-2 · s-1(直径>5 mm),10月份最低,仅为0.0132 μmolCO2 · cm-2 · s-1(直径≤2 mm);比根呼吸速率随根直径变大而降低,表面积呼吸速率变化规律则完全相反.供氮水平对水曲柳苗木根呼吸速率的影响随气温升高明显增强,其在6~8月份各径级根系中均达到显著水平(0.00072mm)Q10值范围为2.07~2.96,Q10值随根系径级增大而降低的现象表明水曲柳苗木细根对温度变化反应更为敏感;细根Q10值在供氮水平间差异显著(P=0.0392<0.05),粗根则不明显,表明土壤供氮水平主要影响细根的Q10值变化. 相似文献
922.
肥披碱草叶片光合特性研究 总被引:4,自引:1,他引:3
以大田生长的肥披碱草为试验材料,利用Li-6400型光合作用测定系统监测其叶片光合生理生态特性及其环境因子日变化,并利用相关分析和逐步回归分析法探讨了净光合速率和蒸腾速率与生理生态因子间的关系.结果表明:(1)肥披碱草叶片的净光合速率(Pn)、蒸腾速率(Tr)和气孔导度(Gs)的日变化均呈双峰曲线,具有明显的光合"午休"现象;叶片水气压亏缺(VPD)和Tr及Gs的峰值出现时间不同步,胞间CO2浓度(Ci)不随气孔的降低而减小,抑制其光合速率的因子为非气孔限制;水分利用率(WUE)的变化呈单峰型,并且其上午WUE明显高于下午.(2)自然条件下,影响肥披碱草叶片Pn的主要因子是Tr和Ca(大气CO2浓度),影响Tr的主要因子是Gs和Ta(气温).(3)在干旱与半干旱自然条件下,肥披碱草的光补偿点(12.45 μmol·m-2·s-1)、光饱和点(1 750 μmol·m-2·s-1)、最大净光合速率(65.125 μmol·m-2·s-1)、表观光量子效率(0.128 9 μmol·mol-1)都较高,表现出较强的光环境的适应性和光能利用能力,是典型的阳性植物. 相似文献
923.
根据中国科学院长白山森林生态系统定位站1982—2001年太阳辐射和云的观测资料对散射辐射及散射比进行了分析,探讨了散射辐射及散射比的日、季节、年际变化特征以及云量、云状、太阳高度角与散射辐射及散射比的关系。结果表明:1)散射辐射日变化特点是,中午最大,早晚较小;季节变化特点是,7月最大,年初和年末较小;年际变化特点是从1982—2001年呈减少趋势;散射比1 d中中午最小,7月达到最大值,年际变化为0.38~0.55;2)散射辐射及散射比均随高云量或低云量增加而呈增加趋势;散射辐射日平均量及散射比与总云量和低云量的日平均值均呈线性正相关关系,且与总云量的关系比与低云量的关系更密切;3)不同云相比较,散射辐射和散射比最大的是高积云(Ac),卷云(Ci)次之,较小为对流性积云(积雨云Cb、积云Cu),碧空时散射辐射及散射比最小;4)散射辐射随太阳高度角增加而增大,呈二次函数关系;散射比随太阳高度角增加而减小且呈二次函数关系。 相似文献
924.
华南地区八种人工林的土壤物理性质 总被引:12,自引:0,他引:12
研究了华南地区8种林地的土壤物理性质,根据其土壤特点分为4类。第1类为马占相思林地、黎蒴-加勒比松林地、火力楠-木荷林地、木荷林地和湿地松林地,特点是上层的土壤容重小于中层和下层,毛管孔隙度中等或较小,非毛管孔隙度中等或较大,非毛管孔隙度和总孔隙度为上层大于中层和下层,自然含水量中等或较大,随着土壤深度的增加而下降或稳定。除了马占相思林地上层外,毛管持水量为中等或较小;第2类为柚木林地,土壤容重较大,且3层土壤的容重相近,毛管孔隙度和毛管持水量较大,非毛管空隙度和自然含水量较小;第3类为落羽杉林地,各层土壤的自然含水量远远大于其他林地。上层和中层的土壤容重、毛管孔隙度和非毛管空隙度中等,毛管持水量大。下层的土壤容重和非毛管空隙度大、毛管空隙度和毛管持水量小。第4类为尾叶桉林地,上层的土壤容重大于中层和下层,毛管孔隙度和毛管持水量较大,非毛管空隙度和自然含水量较小。 相似文献
925.
Edoardo Daly Sari Palmroth Paul Stoy Mario Siqueira A. Christopher Oishi Jehn-Yih Juang Ram Oren Amilcare Porporato Gabriel G. Katul 《Biogeochemistry》2009,94(3):271-287
Profiles of subsurface soil CO2 concentration, soil temperature, and soil moisture, and throughfall were measured continuously during the years 2005 and
2006 in 16 locations at the free air CO2 enrichment facility situated within a temperate loblolly pine (Pinus taeda L.) stand. Sampling at these locations followed a 4 by 4 replicated experimental design comprised of two atmospheric CO2 concentration levels (ambient [CO2]a, ambient + 200 ppmv, [CO2]e) and two soil nitrogen (N) deposition levels (ambient, ambient + fertilization at 11.2 gN m−2 year−1). The combination of these measurements permitted indirect estimation of belowground CO2 production and flux profiles in the mineral soil. Adjacent to the soil CO2 profiles, direct (chamber-based) measurements of CO2 fluxes from the soil–litter complex were simultaneously conducted using the automated carbon efflux system. Based on the
measured soil CO2 profiles, neither [CO2]e nor N fertilization had a statistically significant effect on seasonal soil CO2, CO2 production, and effluxes from the mineral soil over the study period. Soil moisture and temperature had different effects
on CO2 concentration depending on the depth. Variations in CO2 were mostly explained by soil temperature at deeper soil layers, while water content was an important driver at the surface
(within the first 10 cm), where CO2 pulses were induced by rainfall events. The soil effluxes were equal to the CO2 production for most of the time, suggesting that the site reached near steady-state conditions. The fluxes estimated from
the CO2 profiles were highly correlated to the direct measurements when the soil was neither very dry nor very wet. This suggests
that a better parameterization of the soil CO2 diffusivity is required for these soil moisture extremes. 相似文献
926.
Adrien C. Finzi 《Biogeochemistry》2009,92(3):217-229
It is commonly assumed that nitrogen (N) is the primary mineral resource limiting the productivity of temperate forests. Sustained
inputs of N via atmospheric deposition are altering the N status of temperate forests raising the possibility that nutrients
such as phosphorus (P) are increasingly limiting productivity. The objective of this study was to determine whether P availability
limits tree growth alone or in combination with N. This study was conducted in two forest types common throughout the New
England landscape of the northeastern United States; in sugar maple and white ash dominated stands growing on base rich parent
material characterized by rapid rates of N cycling and high N availability, and in red oak–beech–hemlock dominated stands
growing on base-poor parent material characterized by slow rates of N cycling and low N availability. Starting in 2004, N
and P were added to replicate plots in each forest type in factorial combination at a rate of 150 and 50 kg ha−1 year−1, respectively. Diameter growth rates of all trees >10 cm DBH were measured in 2005 and 2006 using dendrometer bands and converted
into units of basal area increment (BAI) and wood production. Following 2 years of fertilization, basal area increment in
the sugar maple–white ash forests remained strongly N limited. Fertilization with P did not significantly increase BAI alone,
although both N and P fertilization tended (P < 0.10) to increase diameter growth in white ash. Wood production in the N-fertilized plots increased by 100 g C m−2 year−1, roughly doubling production in the non-fertilized plots. In the red oak–beech–hemlock stands, there was no overall effect
of N or P fertilization on BAI or wood production because BAI in some species was stimulated by fertilization with N alone
(e.g., black cherry, red oak), while in other species BAI was unaffected (e.g., red maple, beech) or negatively affected by
fertilization with N or P (e.g., eastern hemlock). Given that BAI in several tree species responded to fertilization with
N alone and that only one species responded to P fertilization once N was added, this study suggests that decades of atmospheric
N deposition have not (yet) resulted in widespread P limitation or saturation of tree demand for N. 相似文献
927.
David E. Rothstein 《Biogeochemistry》2009,92(3):201-215
Despite increasing recognition that free amino acids can be an important source of N for plant uptake, we have a poor understanding
of environmental variation in the availability of amino-acid N in soils outside of arctic, alpine and boreal regions. I investigated
patterns of amino-acid availability along a temperate forest fertility gradient ranging from low mineral N availability, oak-dominated
forests to high mineral N availability, maple-basswood forests (5 sites). I measured standing pools of free amino acids, soluble
peptides, ammonium and nitrate, rates of amino acid production (native proteolysis activity) and rates of consumption of a
15N-labeled leucine tracer. Standing pools of amino acid N decreased consistently along the fertility gradient from the low
fertility black oak/white oak system to the high fertility sugar maple/basswood system, with a 25-fold difference in pool
sizes between the poorest and richest sites. Standing pools of soluble peptides varied little among sites, instead, the relationship
between free amino acids and peptides changed markedly across the gradient. At low fertility sites free amino acids were positively
correlated with soluble peptides, whereas free amino acid pools were universally low at high fertility sites, regardless of
peptide pools. Assays for native proteolysis activity indicated that amino acid production did not vary significantly among
sites. Recovery of leucine tracer in inorganic (NH4
+ and NO3
−) pools and in residual soil organic matter both increased with increasing soil fertility; however, total consumption of the
added amino-acid tracer did not vary among sites. Results from this study demonstrate that free amino acids can make an important
contribution to potentially plant-available N pools in temperate forest soils, particularly at low fertility sites. 相似文献
928.
Esther Imperlini Carmelina Bianco Enza Lonardo Serena Camerini Michele Cermola Giancarlo Moschetti Roberto Defez 《Applied microbiology and biotechnology》2009,83(4):727-738
We evaluated the effects of the main auxin phytohormone, indole-3-acetic acid (IAA), on the central metabolism of Sinorhizobium meliloti 1021. We either treated S. meliloti 1021 wild-type cells with 0.5 mM IAA, 1021+, or use a derivative, RD64, of the same strain harboring an additional pathway
for IAA biosynthesis (converting tryptophan into IAA via indoleacetamide). We assayed the activity of tricarboxylic acid cycle
(TCA) key enzymes and found that activity of citrate synthase and α-ketoglutarate dehydrogenase were increased in both 1021+
and RD64 as compared to the wild-type strain. We also showed that the intracellular acetyl-CoA content was enhanced in both
RD64 and 1021+ strains when compared to the control strain. The activity of key enzymes, utilizing acetyl-CoA for poly-β-hydroxybutyrate
(PHB) biosynthesis, was also induced. The PHB level measured in these cells were significantly higher than that found in control
cells. Moreover, 4-week-long survival experiments showed that 80% of 1021 cells died, whereas 50% of RD64 cells were viable.
Medicago truncatula plants nodulated by RD64 (Mt-RD64) showed an induction of both acetylene reduction activity and stem dry weight production. 相似文献
929.
930.
Ecosystem thresholds with hypoxia 总被引:2,自引:1,他引:1
Daniel J. Conley Jacob Carstensen Raquel Vaquer-Sunyer Carlos M. Duarte 《Hydrobiologia》2009,629(1):21-29
Hypoxia is one of the common effects of eutrophication in coastal marine ecosystems and is becoming an increasingly prevalent
problem worldwide. The causes of hypoxia are associated with excess nutrient inputs from both point and non-point sources,
although the response of coastal marine ecosystems is strongly modulated by physical processes such as stratification and
mixing. Changes in climate, particularly temperature, may also affect the susceptibility of coastal marine ecosystems to hypoxia.
Hypoxia is a particularly severe disturbance because it causes death of biota and catastrophic changes in the ecosystem. Bottom
water oxygen deficiency not only influences the habitat of living resources but also the biogeochemical processes that control
nutrient concentrations in the water column. Increased phosphorus fluxes from sediments into overlying waters occur with hypoxia.
In addition, reductions in the ability of ecosystems to remove nitrogen through denitrification and anaerobic ammonium oxidation
may be related to hypoxia and could lead to acceleration in the rate of eutrophication. Three large coastal marine ecosystems
(Chesapeake Bay, Northern Gulf of Mexico, and Danish Straits) all demonstrate thresholds whereby repeated hypoxic events have
led to an increase in susceptibility of further hypoxia and accelerated eutrophication. Once hypoxia occurs, reoccurrence
is likely and may be difficult to reverse. Therefore, elucidating ecosystem thresholds of hypoxia and linking them to nutrient
inputs are necessary for the management of coastal marine ecosystems. Finally, projected increases in warming show an increase
in the susceptibility of coastal marine ecosystems to hypoxia such that hypoxia will expand.
Guest editors: J. H. Andersen & D. J. Conley
Eutrophication in Coastal Ecosystems: Selected papers from the Second International Symposium on Research and Management of
Eutrophication in Coastal Ecosystems, 20–23 June 2006, Nyborg, Denmark 相似文献