川西亚高山森林凋落物去除对土壤腐殖质动态的影响

森林凋落物作为森林土壤腐殖质的主要来源, 在土壤腐殖质的形成中发挥着重要作用, 但不同森林类型凋落物因其含量、组成等的不同, 对土壤腐殖质的影响也不同。该研究以川西亚高山针叶林、阔叶林和针阔混交林3种不同森林类型为对象, 采用凋落物原位控制实验, 对比研究不同关键期凋落物去除对土壤可提取腐殖质、胡敏酸和富里酸含量及胡敏酸/富里酸、胡敏酸/可提取腐殖质的影响。主要结果: (1)土壤可提取腐殖质、胡敏酸和富里酸含量在不同森林类型中差异显著。土壤可提取腐殖质含量总体表现为针叶林>针阔混交林>阔叶林, 胡敏酸含量总体表现为针阔混交林>针叶林>阔叶林, 而富里酸含量则表现为针叶林>阔叶林>针阔混交林, 其中3种林型中土壤腐殖质的主要成分为富里酸, 总体均表现为富里酸型。不同采样时期也显著影响了土壤可提取腐殖质、胡敏酸和富里酸含量, 总体均表现为先升高后下降的趋势。除个别采样时期外, 凋落物去除总体降低了土壤可提取腐殖质、胡敏酸和富里酸的含量。(2)胡敏酸/富里酸和胡敏酸/可提取腐殖质的结果显示3种林型土壤总体腐殖化程度均较低, 整体表现为针阔混交林>阔叶林>针叶林, 凋落物去除在一定程度上有利于提高阔叶林与针阔混交林的腐殖质品质。(3)相关分析表明不同凋落物处理间土壤可提取腐殖质与土壤有机碳含量、全氮含量和土壤含水量呈显著正相关关系, 与温度呈显著负相关关系。综上所述, 短期的凋落物去除会降低土壤腐殖物质的含量, 但不同林型间由于凋落物类型差异会导致土壤腐殖质的不同变化, 说明土壤腐殖质的动态变化受凋落物类型以及环境因素的综合调控。因此, 关于凋落物变化对土壤腐殖质的影响还需进一步的长期研究。     

三种不同类型亚高山森林凋落物输入对土壤腐殖化的影响

森林凋落物既是土壤腐殖质的主要来源,也可以通过新鲜凋落物中易降解组分的输入激发土壤原有腐殖质的降解,导致其相互关系并不明确。以王朗国家级自然保护区内的典型亚高山针叶林、针阔混交林以及阔叶林为研究对象,开展土壤原位培养试验,设置允许凋落物正常输入和去除凋落物两种处理,分析2017年-2019年期间不同凋落物处理下森林土壤可提取腐殖物质的光密度特征,研究土壤腐殖化程度与凋落物的关系。结果表明,在2年的试验过程中,3种森林土壤的腐殖化程度整体表现为针叶林>混交林>阔叶林,均展现出在冬季降低,生长季增加的动态规律;凋落物对3个森林的土壤腐殖化程度均无显著影响,但凋落物输入明显改变了土壤腐殖化程度的季节性变化趋势,且在冬季的阔叶林和混交林中表现更为突出。冬季凋落物的输入使得阔叶林和混交林土壤的腐殖化程度明显降低,而生长季凋落物输入对3种森林土壤腐殖化程度无显著影响。这些结果表明气候变暖情景下冬季温度的上升可能导致土壤的腐殖化程度增加,但凋落物的存在可以减缓增加的趋势。这些结果对于具有明显季节性冻融且对气候变化敏感的亚高山森林土壤肥力管理及可持续经营具有一定的科学意义。     

冻融环境下凋落叶添加对亚高山森林土壤腐殖化程度的影响

亚高山森林凋落叶与土壤腐殖化的关系是了解森林土壤有机质动态过程的关键内容,且受到季节性冻融、凋落叶与土壤性质的综合作用,但缺乏深入认识。因此,在对亚高山凋落叶腐殖化认识的前期基础上,以川西亚高山典型的针叶林、针阔混交林以及阔叶林土壤为研究对象,采用控制冻融环境和凋落叶添加的方法,通过分析土壤可提取腐殖质的色调系数(Δlog K)、光密度值(E4/E6)以及A600/C值等光学指标,研究冻融循环与凋落叶添加对土壤腐殖化程度的影响。结果表明:冻融循环和凋落叶添加及其交互作用均明显影响土壤的腐殖化程度,但受到凋落叶类型和土壤类型的调控。在冻融循环初期,添加凋落叶能促进土壤的腐殖化进程,提高土壤的腐殖化程度;随着冻融循环次数的增加以及凋落叶的不断分解,阔叶凋落叶对土壤的腐殖化表现出促进作用,而针叶凋落叶则对土壤的腐殖化表现出抑制作用。此外,在冻融循环环境下,即使土壤的腐殖化程度增加,但腐殖质仍为相对年轻的Rp型,有利于提高土壤的肥力。这些结果表明,气候变化情景下高山森林地表冻融循环的改变将显著影响凋落叶与土壤腐殖质的密切关系,为进一步认识区域森林土壤有机质动态提供了一定的科学依据。     

模拟冻融环境下亚高山森林凋落物分解速率及有机碳动态

森林凋落物分解是森林生态系统物质循环的重要环节,季节性冻融交替是影响凋落物分解的重要环境因素之一,但不同林型的凋落物对冻融响应的差异性很少被量化。为了解冻融环境对森林凋落物分解进程的影响,以川西亚高山森林地区阔叶林、针叶林和针阔混交林3种典型林型的凋落物为实验材料,从凋落物基质质量、冻融环境等影响凋落分解的因素着手,采用模拟冻融循环过程（-5-5℃）,研究了冻融循环中3种林型凋落物分解速率和有机碳含量的动态变化。结果发现,3中典型林型凋落物经过不同冻融处理后,其质量损失、质量损失速率均存在显著差异（P<0.05）。混交林凋落物和针叶林凋落物的分解速率呈慢-快-慢的趋势,而阔叶林凋落物的分解速率逐渐减小。在冻融循环处理下,3种林型的凋落物碳绝对含量呈波动下降的趋势,说明微生物固定外源碳和凋落物释放碳间存在动态平衡。相同林型的凋落物在不同冻融处理下,有机碳释放有显著差异（P<0.05）。其中,冻融环境显著（P<0.05）促进了混交林凋落物和针叶林凋落物有机碳的释放,但是对阔叶林凋落物有机碳的释放没有起到促进作用。这表明全球气候变暖情景下,亚高山森林土壤冻融事件频发将加快凋落物的分解,但变化程度受到凋落物质量控制。     

冻融循环对川西亚高山森林土壤酶活性的影响

土壤酶活性的研究有助于认识植物-微生物-土壤有机质之间的相互关系,土壤酶的生产遵循"经济法则",冻融循环将会改变生产土壤酶的资源分配,最终影响土壤的有机质分解过程。亚高山森林土壤具有明显的季节性冻融循环,为深入研究亚高山森林冬季土壤生态过程,以川西亚高山针阔混交林、针叶林以及阔叶林土壤为研究对象,通过室内培养研究冻融循环对6种与碳(C)、氮(N)、磷(P)相关土壤酶活性的影响。结果表明,与N和P相关的土壤β-N-乙酰葡萄糖苷酶、磷酸酶活性受冻融循环影响显著,其中,β-N-乙酰葡萄糖苷酶活性在整个冻融处理过程中表现出先升高后降低并趋于平稳的趋势,磷酸酶活性在后期明显增加。与C相关的土壤纤维素酶、β-葡萄糖苷酶、过氧化物酶、多酚氧化酶在冻融循环过程中没有显著变化。林型对土壤酶活性产生了显著影响。其中,阔叶林的土壤纤维素酶活性显著低于针叶林;阔叶林的土壤过氧化物酶活性显著低于针阔混交林和针叶林;针叶林的土壤磷酸酶活性显著高于针阔混交林和阔叶林。冻融循环和林型的交互作用对土壤酶活性没有显著影响。结果表明,该地区土壤酶活性对冻融循环响应存在差异,气候变化引起的冻融循环将进一步影响川西亚高山森林土壤生态系统的有机质分解过程。     

川西亚高山两种树木不同径级根系腐殖化过程中胡敏酸和富里酸的累积特征

根系腐殖化过程中腐殖质的累积是土壤有机质形成和碳吸存的一个重要途径。该文采用凋落物袋法,研究了川西亚高山粗枝云杉(Picea asperata)和岷江冷杉(Abies faxoniana)两种优势林木3个径级根系(0–2、2–5和5–10 mm)在冬季和生长季胡敏酸和富里酸累积特征。结果表明:经过两年的腐殖化,粗枝云杉和岷江冷杉根系胡敏酸和富里酸含量受径级显著影响,并随径级增大而降低。不同径级间富里酸净累积量差异显著,而胡敏酸净累积量差异不显著;两个树种间胡敏酸和富里酸含量和净累积量差异不显著。胡敏酸在冬季降解而在生长季节累积,其中粗枝云杉0–2、2–5和5–10 mm根系净累积量分别为8.0、10.8和7.6 g·kg~(–1),岷江冷杉分别为15.2、8.0和7.8 g·kg~(–1)。富里酸总体表现为降解,其中粗枝云杉0–2、2–5和5–10 mm根系降解量为178.0、166.0和118.0 g·kg~(–1),岷江冷杉分别为170.0、160.0和128.0 g·kg~(–1)。根系径级对亚高山森林植物根系腐殖质累积有显著影响,而径级影响与分解时期有一定关联。     

改变凋落物输入对川西亚高山天然次生林土壤呼吸的影响

2019年5月-10月,采用LI-8100A土壤碳通量自动测量分析仪对川西米亚罗林区20世纪60年代采伐后经自然更新恢复形成的岷江冷杉（Abies faxoniana）次生针叶林（针叶林）、红桦（Betula albo-sinensis）+青榨槭（Acer davidii）+岷江冷杉次生针阔混交林（针阔混交林）和青榨槭+红桦+陕甘花楸（Sorbus koehneana Schneid）次生阔叶林（阔叶林）的土壤呼吸及土壤温湿度因子（对照、去除凋落物和加倍凋落物）进行观测。结果显示：去除和加倍凋落物对土壤温湿度的影响不显著,且3种林型之间的土壤呼吸速率差异不显著。与对照相比,去除凋落物使针叶林、针阔混交林、阔叶林的土壤呼吸速率分别降低了17.65%、21.01%和19.83%（P<0.05）;加倍凋落物则分别增加6.76%、7.28%、8.16%（P>0.05）。3种林分土壤呼吸速率均与土壤温度极显著指数相关,与土壤湿度不相关。对照Q₁₀值变幅为2.01-3.29,去除凋落物降低了3种林型的Q₁₀值;加倍凋落物分别提高了针叶林和降低了针阔混交林和阔叶林的Q₁₀值。土壤呼吸速率仅表现在天然次生林对照处理中受到土壤pH、有机质、可溶性有机氮和草本Pielou均匀度指数的显著影响。研究结果表明,天然次生阔叶林和针阔混交林凋落物对土壤呼吸的贡献及Q₁₀值高于天然次生针叶林,说明在未来CO₂浓度及温度升高背景下,地表凋落物增加并未引起天然次生林土壤呼吸速率成倍增加,更有利于该区域天然次生林尤其是针叶林的土壤碳吸存。     

张广才岭西坡不同起源林分土壤碳收支机制研究

对五常凤凰山林场皆伐迹地上45年生不同起源（人工更新、人天混更新、天然更新）形成的次生阔叶林、落叶松与阔叶树混交林和人工更新土壤碳输入和输出的季节动态进行研究,探讨不同起源对林分土壤碳收支的影响。结果表明：（1）不同起源土壤有机碳含量为针阔混交林显著高于落叶松纯林(P＜0.05),次生阔叶林居中,且与二者差异不显著（P＞0.05）;（2）不同起源林分叶凋落物总量表现出次生阔叶林＞针阔混交林＞落叶松纯林,且次生阔叶林显著高于落叶松纯林（P＜0.05）;（3）3种起源林分凋落物分解速率顺序为次生阔叶林>针阔混交林>落叶松纯林;（4）不同起源林分不同季节土壤呼吸速率均以次生阔叶林最高,落叶松人工林最低;（5）不同起源林分土壤微生物生物量碳（MBC）、土壤易氧化碳（ROC）6~10月平均值表现出针阔混交林>次生阔叶林>落叶松纯林,而土壤水溶性有机碳（WSOC）则为次生阔叶林>针阔混交林>落叶松纯林;（6）不同起源林分凋落物分解失重率与3种土壤活性碳的相关性均显著（P<0.05）,土壤呼吸速率与ROC和WSOC呈极显著负相关（P<0.01）。综合分析土壤碳收支过程表明,人天混更新更利于土壤碳的周转和贮存。     

不同类型城市森林对土壤肥力的影响

以东北林业大学城市林业示范研究基地中9种人工林(兴安落叶松林、樟子松林、黑皮油松林、黄波罗林、胡桃楸林、水曲柳林、白桦林、蒙古栎林、针阔混交林)及附近的农耕地和撂荒地土壤为研究对象,通过对林地土壤不同层次pH值、有机质及主要养分含量的测定分析,研究了不同林型对土壤肥力的影响.结果表明：阔叶林(除蒙古栎林)的土壤趋于中性,针阔混交林、兴安落叶松林、樟子松林和黑皮油松林的土壤呈微酸性,蒙古栎林的土壤呈酸性;随土壤深度增加,土壤有机质、水解氮、速效钾、有效磷、全氮、全磷含量均呈下降趋势.不同林地土壤同一层次化学指标整体差异显著(P＜0.05).土壤肥力优劣为：水曲柳林>黄波罗林>针阔混交林>胡桃楸林>白桦林>撂荒地>农耕地>樟子松林>兴安落叶松林>蒙古栎林>黑皮油松林,说明阔叶林(除蒙古栎林)和针阔混交林中的土壤肥力增加,而针叶林的土壤肥力趋于下降.     

长白山北坡自然保护区森林土壤微生物生态分布及其生化特性的研究

本文研究了长白山北坡自然保护区森林土壤微生物的生态分布和生化特性。土壤微生物的垂直分布与林型之间有着下列相关性:(1)阔叶林和针阔混交林下土壤中细菌的数量比针叶林下多;(2)不同土类中,放线菌的分布随海拔上升而减少;(3)亚高山针叶混交林下土壤中真菌数量很多。不同林型下土壤酶活性、内源呼吸、氧化代谢能力和土壤有机质中中性糖、氨基糖和糖醛酸的分布有很大差异,以阔叶林和针阔混交林下土壤中为最高,针叶林下土壤中为最低。针叶混交林下土壤中生化活性随阔叶树种增加而提高。不同海拔、不同植被和不同土类下,芽孢杆菌属、放线菌和真菌的生态分布及其种的组合不同。芽孢杆菌属的优势种和放线菌、真菌优势属的组成也不同。不同林型下优势种的组成与水热条件、植物残体的组成及土壤有机质的分解过程密切相关。     

冻融条件和土壤湿度对森林土壤渗漏液溶解性有机质含量与光谱结构特征的影响

土壤溶解性有机质(DOM)含量及其稳定性影响土壤碳氮循环关键过程,目前气候变化下森林土壤DOM含量及其光谱结构特征仍不明确.本研究利用长白山阔叶红松混交林和次生白桦林表层土壤进行室内冻融模拟试验,结合三维荧光光谱-平行因子分析方法,研究冻融强度和冻融循环次数及其交互作用对不同湿度温带森林土壤渗漏液DOM含量、组分和光谱结构特征的影响.结果表明: 森林土壤渗漏液DOM含量及其组分因林分类型、土壤湿度、冻融强度、冻融循环次数不同而存在差异.2种林分土壤渗漏液DOM含量均在中湿度下最低,并受高强度冻融影响显著,且随冻融循环次数增加呈现先增加后降低的趋势.可鉴别DOM的3个荧光组分:胡敏酸类DOM、富里酸类DOM和蛋白类DOM;阔叶红松混交林土壤渗漏液DOM组分以富里酸类物质为主,腐殖化程度较高;而次生白桦林土壤渗漏液DOM组分以胡敏酸类物质为主,3组分受冻融强度显著影响,稳定性较低.经冗余分析(RDA)发现,林分在很大程度上决定森林土壤DOM属性变化,次生白桦林土壤渗漏液DOM含量及其3组分荧光强度大于阔叶红松混交林;土壤湿度显著影响DOM芳香性,2种林分土壤渗漏液DOM芳香性均呈中湿度>高湿度>低湿度的趋势;随冻融强度增加,阔叶红松混交林土壤渗漏液DOM芳香性显著降低;多次冻融循环显著提高2种林分土壤渗漏液DOM腐殖化程度.因此,不同冻融作用下,低湿度温带森林土壤渗漏液DOM含量及其生物有效性呈现增加的趋势,尤其是次生白桦林土壤,可能会增加春季冻融期温带森林土壤溶解性有机质淋溶损失.这些结果可为深入研究野外冻融期温带森林土壤溶解性有机质周转机制提供参考.     

Contribution of bacterial cell nitrogen to soil humic fractions

Summary Living cells ofSerratia marcescens, uniformly labelled with¹⁵N, were added to samples of maple (Acer saccharum) and black spruce (Picea mariana) forest soils. After different periods of incubation from zero time to 100 days, the soils were subjected to alkali-acid and phenol extraction to provide humic acid, fulvic acid, humin and humoprotein fractions. Significant amounts of the cell nitrogen were recovered in the humic and fulvic acids immediately after addition. After incubation, less cell, nitrogen appeared in the humic acid and more in the fulvic acid. The amount of cell nitrogen recovered in the humin fraction increased with incubation. Roughly 5 to 10 per cent of the added cell nitrogen was found as amino acid nitrogen from humoprotein in a phenol extract of the humic acid. The data are consistent with the occurrence of co-precipitation of biologically labile biomass nitrogen compounds with humic polymers during the alkaline extraction procedure involved in the humic-fulvic fractionation.     

The influence of topography on the nature of humic substances in soil organic matter at a site in the Atlantic Coastal Plain of South Carolina

The effect of topography on the nature of humic substances, isolated as water soluble organic carbon (WSOC), fulvic acid (FA), and humic acid (HA) was evaluated by comparing relative proportion and chemical characteristics of these fractions in upland and bottomland Coastal Plain soils in South Carolina. The fractions were characterized by elemental analysis and¹³C cross-polarization magic angle spinning nuclear magnetic resonance (CPMAS NMR) spectroscopy. The majority of humic substances occur as humic acids, with bottomland soils having higher HA/FA ratios when compared to upland soils. We found no significant differences between upland and bottomland humic substances with respect to yields of WSOC and fulvic acids, and in the C and N content of humic and fulvic acids. Carbon-13 CPMAS NMR spectroscopy revealed that the WSOC and fulvic acid fractions were composed largely of O-alkyl-C structures with bottomland soils having higher amounts of these groups. Humic acid C distribution was similar between upland and bottomland soils and was largely composed of aromatic groups. Our results demonstrate that topography influences the formation of humic acid and the structural and chemical properties of the various humic fractions.requests for offprints     

Spatial pattern of soil nitrogen availability and its relationship to stand structure in a coniferous-broadleaved mixed forest with a dense dwarf bamboo understory in northern Japan

Natural disturbances create spatial patterns of the ecosystem processes and functions in natural forests. However, how dynamics and the spatial structure of forests relate to soil nitrogen dynamics is not well understood. We examined the spatial relationship between the distributions of canopy and understory species, and soil nitrogen dynamics in a natural coniferous-broadleaved mixed forest with a dense understory of Sasa dwarf bamboo in northern Japan. The O horizon was thick where coniferous litter predominated, and it was thin where broadleaved litter predominated. The soil water content was low in areas with a thick O horizon and a high abundance of coniferous trees. The soil nitrate content was low where the soil water content was low, and the soil nitrate content increased linearly with increasing net nitrification potential. These results suggest that the soil nitrate content under the coniferous canopy was lower because of the low nitrification potential of soil microbes in soils with low water contents. The soil nitrate content and nitrification potential were higher in the canopy gap than under the canopy. Our results suggest that forest structure, specifically the thickness of the forest floor, significantly affects the spatial pattern of the soil water content, thereby creating a spatial pattern of soil nitrogen availability at a relatively small scale with flat topography. The higher nitrification potential under the canopy gap could pose a long-term risk of nitrate leaching because of the suppression of the natural regeneration of canopy species by dense Sasa dwarf bamboo in this forest ecosystem.     

Accumulation of humic acid and fulvic acid during root humification of three diameters of two dominant subalpine trees in western Sichuan,China

Aims Plant roots store large amount of terrestrial carbon, but little is known about humus formation processes during the decomposing root litter. Compared with coarse roots, fine roots have greater nutrients, which may be favorable to humus formation. The objective of the study was to examine how root diameters affect their humus formation processes. Methods In this study, in order to examine the accumulation of humic acid and fulvic acid of three root diameter classes (0-2, 2-5 and 5-10 mm) of two subalpine tree species (Abies faxoniana and Picea asperata) on the eastern Qinghai-Xizang Plateau of China, a two-year field experiment was conducted using a litter-bag method. Air-dried roots of A. faxoniana and P. asperata were placed in litterbags and incubated at 10 cm of soil depth in October 11th, 2013. Duplicate litter bags were collected in May (late winter) and October (late in the growing season) of 2014 and 2015, respectively. Concentrations of humic acid and fulvic acid were measured, and net accumulations were calculated for different periods. Important findings The concentrations of humic acid and fulvic acid were significantly influenced by root diameter that humic acid and fulvic acid decreased with increase in root diameter. Root diameter had significant effects on the net accumulation of humic acid, but not for the accumulation of fulvic acid. However, there were no significant differences in both humic acid and fulvic acid between A. faxoniana and P. asperata roots. Regardless of tree species, humic acid degraded during the winter but accumulated during the growing season. After two years of decomposition, the net accumulations of humic acid in 0-2, 2-5 and 5-10 mm roots were 8.0, 10.8 and 7.6 g·kg^-1 for P. asperata and 15.2, 8.0 and 7.8 g·kg^-1 for A. faxoniana, respectively. Conversely, the degradation of fulvic acid in 0-2, 2-5 and 5-10 mm roots were 178.0, 166.0 and 118.0 g·kg^-1 for P. asperata and 170.0, 160.0 and 128.0 g·kg^-1 for A. faxoniana, respectively. Our results suggest that diameter-associated variations in substrate quality could be an important driver for root litter humification in this subalpine forest. Moreover, diameter effect is dependent on decomposition period in this specific area.     

贺兰山不同林分凋落物微生物群落特征与影响因素

贺兰山是我国重要生态屏障,贺兰山生态森林生态系统保护受到极大关注,森林凋落物及土壤微生物对全球气候变化研究具有重要意义。目前,贺兰山不同林分的凋落物分解过程中微生物群落结构特征差异、不同凋落物化学组成对微生物群落结构的影响尚不清楚。以贺兰山具有代表性的3种林分（油松林、青海云杉林以及油松-山杨混交林）凋落物为研究对象,开展凋落物化学组成、微生物群落组成及多样性特征研究,揭示不同林分凋落物的优势微生物群落特征和影响因子。结果表明,3种林分凋落物的细菌和真菌在多个多样性指数之间差异性均不显著,但是在多样性指数中真菌PD whole tree指数显著大于细菌,真菌Shannon指数与Ghao1指数却显著小于细菌。在门水平上不同林分凋落物的微生物优势菌类无显著差异,但在属水平上差异显著,而且细菌差异小于真菌,在各个分类水平上,凋落物细菌和真菌群落组成均表现为油松-山杨混交林＜青海云杉林＜青海云杉林,凋落物微生物多样性在青海云杉林中最为丰富。细菌不同节点间连接线负相关数量略大于正相关,真菌则相反。油松林凋落物与其它林分凋落物相比,微生物群落之间联系更加紧密。油松林凋落物OC含量最大、青海云杉林凋落物的TK含量最大、油松-山杨混交林的TN含量最大,且在3种林分中显著差异。相关性分析表明OC、TN、TP、TK是影响凋落物细菌和真菌群落组成及多样性的主要因素,冗余分析表明不同林分凋落物的微生物多样性指数受养分影响,凋落物OC、TN、TP、TK是影响微生物群落组成和多样性的重要因素,其中OC与微生物群落多样性相关性最显著,是影响凋落物细菌和真菌群落组成和多样性最主要的因子。     

不同树种混交林及其纯林对土壤理化性质影响的研究

对针阔混交林土壤理化性质的研究表明,针阔混交林比针叶树纯林对土壤的改良作用要好,它使土壤总孔隙度增加２—１９％,水分含量增加６—３１％,枯枝落叶年凋落量增加２—２００％;土壤养分含量全Ｎ、ＮＨ４－Ｎ、代换性Ｃａ、代换性Ｍｇ和腐殖质含量分别增加４５—７５％、３３—８２％、５５—８５％、４４—８４％和３７—４６％．     

Conversion of secondary broadleaved forest into Chinese fir plantation alters litter production and potential nutrient returns

Litter production, litter standing crop, and potential nutrient return via litterfall to soil were studied during a 4-year period (January 2004–December 2007) in a Chinese fir (Cunninghamia lanceolata (Lamb.) Hook) plantation and a secondary broadleaved forest in Hunan Province in subtropical China. Mean annual litterfall in the sampling sites varied from 358 g m⁻² in the pure plantation to 669 g m⁻² in the secondary broadleaved forest. Total litterfall followed a bimodal distribution pattern for both forests. Amount of litterfall was also related to the air temperature in both forests. During the period under this study, annual variation in the total litterfall in the pure plantation was significantly higher than that in the secondary broadleaved forest. Litterfall was markedly seasonal in the both forests. Leaf proportions of litterfall in the pure plantation and secondary broadleaved forest were 58.1 and 61.7%, respectively. Total potential nutrient returns to the soil through litterfall in the pure plantation were only 46.2% of those in the secondary broadleaved forest. Total litter standing crop was 913 and 807 g m⁻² in the pure plantation and secondary broadleaved forest, respectively. Our results confirm that conversion from a secondary broadleaved forest into a pure coniferous plantation changes the functioning of the litter system.