Spatial variability of NO and NO2 flux rates from soil of spruce and beech forest ecosystems

In order to evaluate differences in the magnitude of NO and NO₂ flux rates between soil areas in direct vicinity to tree stems and areas of increasing distance to tree stems, we followed in 1997 at the Höglwald Forest site with a fully automated measuring system a complete annual cycle of NO and NO₂ fluxes from soils of an untreated spruce stand, a limed spruce strand, and a beech stand using at each stand measuring chambers which were installed onto the soils in such a way that they formed a stem to stem gradient. Flux data obtained since the end of 1993 from measuring chambers placed at the interstem areas of the stands, which had been used for the calculation of the long year annual mean of NO and NO₂ flux rates from soils of the stands, are compared to both (a) those obtained from the interstem chambers in 1997 and (b) those from the stem to stem gradient chambers. Daily mean NO fluxes obtained in 1997 were in a range of 0.3 – 280.1 g NO-N m^–2 h^–1 at the untreated spruce stand, 0.5 – 273.2 g NO-N m^–2 h^–1 at the limed spruce stand and 0.5 - 368.8 g NO-N m^–2 h^–1 at the beech stand, respectively. Highest NO emission rates were observed during summer, lowest during winter. Daily mean NO₂ fluxes were in a range of –83.1 – 7.6 g NO₂-N m^–2 h^–1 at the untreated spruce stand, -85.1 – 2.1 g NO₂-N m^–2 h^–1 at the limed spruce stand and –77.9 to –2.0 g NO₂-N m^–2 h^–1 at the beech site, respectively. As had been observed for the years 1994–1996, also in 1997 NO emission rates were highest at the untreated spruce stand and lowest at the beech stand and liming of a spruce stand resulted in a significant decrease in NO emission rates. For NO₂ no marked differences in the magnitude of flux rates were found between the three different stands. Results obtained from the stem to stem gradient experiments revealed that at all stands studied NO emission rates were significantly higher (between 1.6- and 2.6-fold) from soil areas close to the tree stems and decreased – except at the beech stand - with increasing distance from the stems, while for NO₂ deposition no marked differences were found. Including the contribution of soil areas in direct vicinity to the beech stems in the estimation of the annual mean NO source strength revealed that the source strength has been underestimated by 40% in the past.     

Effect of tree distance on N2O and CH4-fluxes from soils in temperate forest ecosystems

Complete annual cycles of N₂O and CH₄ flux in forest soils at a beech and at a spruce site at the Höglwald Forest were followed in 1997 by use of fully automatic measuring systems. In order to test if on a microsite scale differences in the magnitude of trace gas exchange between e.g. areas in direct vicinity of stems and areas in the interstem region at both sites exist, tree chambers and gradient chambers were installed in addition to the already existing interstem chambers at our sites. N₂O fluxes were in a range of –4.6–473.3 g N₂O-N m^–2 h^–1 at the beech site and in a range of –3.7–167.2 g N₂O-N m^–2 h^–1 at the spruce site, respectively. Highest N₂O emissions were observed during and at the end of a prolonged frost period, thereby further supporting previous findings that frost periods are of crucial importance for controlling annual N₂O losses from temperate forests. Fluxes of CH₄ were in a range of +10.4––194.0 g CH₄ m^–2 h^–1 at the beech site and in a range of –4.4––83.5 g CH₄ m^–2 h^–1 at the spruce site. In general, both N₂O-fluxes as well as CH₄-fluxes were higher at the beech site. On a microsite scale, N₂O and CH₄ fluxes at the beech site were highest within the stem area (annual mean: 49.6±3.3 g N₂O-N m^–2 h^–1; –77.2±3.1 g CH₄ m^–2 h^–1), and significantly lower within interstem areas (18.5±1.4 g N₂O-N m^–2 h^–1; –60.2±1.8 g CH₄ m^–2 h^–1). Significantly higher values of total N, C and pH in the organic layer, as well as increased soil moisture, especially in spring, in the stem areas, are likely to contribute to the higher N₂O fluxes within the stem area of the beech. Also for the spruce site, such differences in trace gas fluxes could be demonstrated to exist (mean annual N₂O emission within (a) stem areas: 9.7±0.9 g N₂O-N m^–2 h^–1 and (b) interstem areas: 6.2±0.6 g N₂O-N m^–2 h^–1; mean annual CH₄ uptake within (a) stem areas: –26.1±0.6 g CH₄ m^–2 h^–1 and (b) interstem areas: –38.4±0.8 g CH₄ m^–2 h^–1), though they were not as pronounced as at the beech site.     

云冷杉林林隙内倒木腐烂等级及其形成的微立地类型对土壤理化性质的影响

为揭示倒木腐烂等级及其形成的微立地类型对土壤理化性质的影响,分析了小兴安岭凉水国家级自然保护区谷地云冷杉林由倒木形成的林隙内不同腐烂等级倒木形成的3种微立地(丘顶、坑底和倒木下)的土壤理化性质(容重、毛管孔隙度、总孔隙度、毛管持水量、饱和持水量、土壤有机碳、全氮、全磷、有效磷、速效钾和pH值)和化学计量特征(C/N、N/P和C/P)的差异.结果表明: 倒木腐烂等级对土壤物理性质的影响不显著,而倒木形成的微立地类型对其影响显著.除土壤饱和持水量外,倒木下的其他土壤物理性质均最好,坑底最差;随着倒木腐烂等级的上升,除有效磷外的其他土壤养分含量呈显著上升趋势;3种微立地中,坑底土壤养分含量最低,pH最高;随倒木腐烂等级的上升,3种微立地浅层土壤C/N、N/P和C/P下降,而丘顶和坑底深层土壤C/N上升,N/P和C/P下降,C/P的变化趋势与土壤有效磷的一致.综上,随倒木腐烂等级的提高,土壤养分含量显著增加,且不同类型微立地之间差异明显,其中坑底始终最低.     

云冷杉红松林掘根倒木及其微立地对凋落叶分解速率及养分释放的影响

采用凋落物分解袋埋藏法,将采集的红松（Pinus koraiensis）、紫椴（Tilia amurensis）和色木槭（Acer mono）凋落叶按自然比例混合装入袋中,于2019年7月将其埋入云冷杉红松林中不同腐烂等级（Ⅱ、Ⅲ、Ⅳ级）的掘根倒木（UT）及其形成的坑底（PB）与丘面（MF）以及对照（包括林隙（FG）和林分（IS））等11种微立地下。8-10月每月从每种微立地取回3袋,处理后测定凋落叶的质量、碳、氮、磷含量。采用相关分析和方差分析的统计分析方法,探究不同微立地下凋落叶的质量、分解速率与养分元素之间的相关性和差异显著性。结果表明：（1）微立地和分解时间对凋落叶质量具有极显著影响（P<0.01）。凋落叶分解90天后,各微立地的凋落叶质量残留率排列为：PB （85.64%） > MF （83.09%） > FG （81.33%） > IS （80.93%） > UT （80.27%）;（2）各微立地的凋落叶分解速率排列为：k_IS=k_UT>k_FG>k_MF>k_PB;Olson指数模型能够较好的模拟各微立地的凋落叶分解动态;年分解速率k为0.61-1.42,分解50%和95%所需时间分别为0.49-1.14 a和2.10-4.92 a。（3）各微立地的凋落叶C残留率总体呈下降趋势,表现为释放模式;UT和MF微立地的N、P残留率持续下降,表现为释放;PB微立地的N、P变化模式分别为释放-富集-释放、富集-释放模式,释放均大于富集,最终表现为释放模式。微立地对凋落叶P释放具有极显著影响（P<0.01）,对N释放具有显著影响（P<0.05）;微立地与掘根倒木腐烂等级的交互作用对C、N释放均具有极显著的影响（P<0.01）。（4）凋落叶质量残留率与P的残留率在所有微立地中均存在显著或极显著正相关关系,与N的残留率仅在Ⅱ级UT、PB微立地、Ⅲ级UT微立地、Ⅳ级UT、PB和MF微立地以及FG对照中呈显著或极显著的正相关关系,与C的残留率仅在Ⅱ级UT、PB微立地、Ⅳ级PB、MF微立地中存在极显著或显著正相关关系,与C/N在Ⅱ级UT微立地、Ⅲ级UT、MF微立地和FG对照中呈显著或极显著负相关关系。可见,与不同腐烂等级的掘根倒木相比,掘根倒木形成的微立地环境对凋落叶分解和养分释放的影响较大。     

Effect of shrubs and seasonal variability of rainfall on the establishment of Aspidosperma quebracho‐blanco in two edaphically contrasting environments

Abstract Three experiments were conducted to verify if an increase in environmental stress level would affect the interactions between two species of nurse shrubs and seedlings of Aspidosperma quebracho‐blanco. This is a mesic species with a generalist distribution over an extensive environments gradient. The relationship between Larrea divaricata and seedlings of A. quebracho‐blanco was studied in two contrasting soils, a silty loam soil with higher surface clay content and a sandy loam soil. The effect of seasonal variability of rainfall on the initial establishment of seedlings under the shade of L. divaricata was evaluated in three consecutive years. The effect of nurse plant shade was tested comparing two shrub species with different types of leaf life span (sclerophyllous‐evergreen and leguminous‐deciduous). The natural establishment of A. quebracho‐blanco depended on shaded microsites, but not on the type of shade provided by different nurse shrubs. Emergence and initial establishment depended on interactions of soil type and seasonal rainfall variation with nurse plants. The importance of facilitation increased with clay soil (CS). Sandy soil was ‘less humid’ than CS under shrub shade. However, establishment success depends on opportune even rainfall distribution in interaction with nurse plant presence.     

核桃园行内地面覆盖的土壤微域生态效应

为了探明核桃园行内地面覆盖的土壤微域生态环境效应、确立核桃园科学省力的土壤管理措施,以盛果期早实薄皮核桃‘绿岭’为试材,通过连续4 a的行内地面覆盖,研究了园地土壤的水分、通气、矿质营养及三大微生物区系等微域生态环境的状况,结果表明:通过连续四年覆盖,0—20 cm土层,覆盖牛粪、碎木屑、苜蓿处理及CK 2014年核桃生长期的土壤平均质量含水量的变异系数分别为9.27%、10.27%、12.15%和13.96%,最大变幅分别为1.86%、1.95%、2.17%和2.63%;20—40 cm土层,覆盖牛粪、碎木屑、苜蓿处理及CK的土壤平均质量含水量分别为13.23%、12.46%、11.77%和11.43%。覆盖牛粪、碎木屑、苜蓿及CK的0—60 cm土层的平均土壤容重为1.34、1.38、1.43 g/cm~3和1.48 g/cm~3,3类微生物总量分别为430.94×10~4、208.87×10~4、183.42×10~4个/g和160.46×10~4个/g。通过主成分分析对覆盖牛粪、碎木屑、苜蓿处理及CK的土壤肥力进行综合评价,得分分别为0.61、0.26、0.09和-0.96,各因子对土壤肥力水平的综合效应排序为:土壤有机质含量全氮含量全钾含量全磷含量土壤质量含水量孔隙度细菌数量真菌数量放线菌数量土壤容重。     

植物种群更新的补充限制

补充限制基于生态位理论, 从种子萌发、幼苗存活和生长、繁殖体扩散等生活史阶段的种群统计特征及环境因素(土壤水分、养分、凋落物等)着手, 探讨种群的更新问题。种源限制和微生境限制是补充限制理论研究的核心内容, 但是哪个更为重要并没有统一的结论。种源限制与种子生产、土壤种子库和地下芽库中的繁殖体数量不足有关。其中, 气候的年际波动、土壤种子库寿命和动物的捕食都会影响种子生产在种群更新中的作用; 土壤种子库常被视为种群更新的保险库, 与地上种子雨共同促进种群更新, 但是, 如果土壤里种子具有较高的死亡率和休眠率, 将会降低种子库的作用; 地下芽库及其产生的无性分株对于种群更新的意义更多地体现在干扰后种群更强的恢复能力上。扩散限制是种群更新中的普遍现象, 与种子产量、散布能力、传播媒介、幼苗密度等因素有关。微生境限制主要表现为水分、养分、凋落物等非生物因素以及竞争、捕食等生物因素对种子的活力、萌发性、幼苗的存活力、物质分配等过程的影响, 其重要性随着植物生活史阶段而发生变化。未来需要进行综合的、长期的实验, 并应着重加强种源限制及相关生态过程的进化与生态相结合的机理性研究, 从而更深刻地认识和理解种群更新问题, 建立更为综合、系统的种群更新理论体系。