茂兰喀斯特原生林不同坡向及分解层的凋落物现存量和养分特征

以茂兰喀斯特原生林3种坡向林下凋落物为研究对象,通过野外调研采样和室内分析测试相结合的方法,探讨了不同喀斯特原生林生态系统下坡向和分解层的凋落物现存量、主要营养元素含量、储量及元素释放率的分布特征。结果表明:1)阴坡凋落物现存总量((0.568±0.024)kg·m~(-2))高于阳坡((0.504±0.03)kg·m~(-2))和半阴坡((0.295±0.02)kg·m~(-2)),不同坡向林下凋落物现存量在各分解层均表现为:未分解层(L层)半分解层(F层)全分解层(Y层);2)不同坡向林下凋落物各营养元素平均含量表现为:C((388.7±11.2)g·kg-1)N((24.90±3.49)g·kg-1)K((9.78±1.82)g·kg-1)P((1.53±0.32)g·kg-1),在各分解层的含量表现不同,碳含量和钾含量:LFY,氮含量和磷含量:YFL;3)3种坡向林下凋落物的碳、氮、钾元素总储量表现为:阴坡阳坡半阴坡,磷元素总储量表现为:阳坡阴坡半阴坡;4)凋落物营养元素储量在L层占总储量的37.1%~64.2%,并随分解加剧而减少;L层和F层的元素释放率均表现为:阴坡半阴坡阳坡,且碳、钾元素释放率高于氮、磷元素。在喀斯特原生林凋落物分解的养分释放过程中,坡向对林下凋落物的理化性质及分解速率有较大影响,且阴坡林下凋落物分解较快、营养元素内部循环周期较短。     

中亚热带四种森林凋落物及碳氮贮量比较

在湖南省长沙县大山冲省级森林公园内,选择立地条件基本一致的4种森林类型为研究对象,于2011年12月(凋落物高峰期)对森林凋落物现存量及其碳、氮贮量进行调查.结果表明:4种森林凋落物现存量大小依次为青冈-石栎林(12.04±3.60)t·hm-2＞马尾松-石栎林(11.65±2.15) t·hm-2＞南酸枣林(9.12±2.30)t·hm-2＞杉木林(8.92±1.80)t·hm-2;凋落叶在凋落物未分解层中所占比例最高,凋落果在4种林分中比例最小(＜5％),凋落物各分解亚层现存量规律性不明显;4种森林凋落物C含量的变化范围为177.90 ～ 581.34 g·kg-1,N含量的变化范围为5.18～15.48 g· kg-1,C含量变化随凋落物分解程度的加深而下降,且变化极显著( P＜0.0001);凋落物半分解层和已分解层现存量在总凋落物现存量中所占比例与C/N呈负相关;4种森林凋落物C贮量为3.37 ～ 5.69t·hm-2,N贮量为81.52 ～152.18 kg·hm-2;马尾松-石栎针阔叶混交林由于凋落物分解较慢,凋落物现存量较大,林下凋落物层C、N贮量最高.     

亚热带不同植被恢复阶段林地凋落物层现存量和养分特征

为揭示亚热带森林植被自然恢复过程中,凋落物层现存量及其养分元素储存能力的演变,采用空间代替时间的方法,在位于亚热带丘陵区的长沙县选取地域相邻、生境条件基本一致的檵木+南烛+杜鹃灌草丛（Loropetalum chinense+Vaccinium bracteatum +Rhododendron simsii scrub-grass-land,LVR）、檵木+杉木+白栎灌木林（L.chinense+Cunninghamia lanceolata+Quercus fabri shrubbery,LCQ）、马尾松+柯+檵木针阔混交林（Pinus massoniana +Lithocarpus glaber +L.chinense coniferous-broad leaved mixed forest,PLL）、柯+红淡比+青冈常绿阔叶林（L.glaber+Cleyera japonica+Cyclobalanopsis glauca evergreen broad-leaved forest,LAG）作为一个恢复序列,设置固定样地,采集未分解层（U层）、半分解层（S层）、已分解层（D层）凋落物样品,测定凋落物层现存量和主要养分元素含量、储量及其释放率,分析植物多样性指数与凋落物层现存量、养分元素含量的相关性。结果表明：1）凋落物层及各分解层凋落物现存量随着植被恢复而增加;同一恢复阶段D层凋落物现存量最高,占凋落物层现存量的41.59%-51.02%,不同分解层凋落物现存量的差异随着植被恢复而增大;各恢复阶段凋落物分解率为0.44-0.61,周转期为1.65-2.28 a。2）凋落物层及各分解层凋落物主要养分元素含量均表现为：N > Ca > Mg > K > P,随着植被恢复呈现出不同的变化特征,其中N、P含量总体上呈增加趋势,K含量LAG（除U层外）最高,PLL最低,Ca含量LCQ最高,PLL最低,Mg含量LAG（除U层外）最高,LVR最低;同一恢复阶段N、P（除PLL、LAG外）、K、Ca、Mg含量随着凋落物的分解而下降。3）不同恢复阶段凋落物层主要养分元素的储量依次为：N > Ca > Mg > K > P;凋落物层及各分解层凋落物主要养分元素总储量及各种养分元素的储量总体上随着植被恢复而增加;同一恢复阶段随着凋落物的分解,N、P储量增加,而K、Ca、Mg储量变化不大;随着植被恢复,凋落物层养分元素储存能力和转化归还能力提高,特别是N,养分元素总释放率下降,有利于养分的固持。4）乔木层、灌木层、草本层的植物多样性指数对凋落物层现存量和主要养分元素含量的影响不同,其中乔木层的影响最明显。     

杉木、火力楠纯林及其混交林生态系统C、N贮量

研究比较第2代连载杉木纯林、杉木与火力楠混交林以及火力楠纯林3种人工林生态系统的C、N贮量。结果表明,杉木与火力楠混交林生态系统C贮量要高于杉木纯林和火力楠纯林,而生态系统N贮量是火力楠纯林和杉木与火力楠混交林高于杉木纯林;生态系统C和N贮量的空间分布基本一致,土壤层占主要部分,其次为乔木层,再次是根系,林下植被层和凋落层所占比例最小;相关分析表明,土壤C、N贮量分别和林下植被生物量以及与森林凋落物现存量之间都具有良好的线性关系,说明林下植被和森林凋落物对土壤C、N贮量有着深刻的影响。     

红松混交林凋落物氮储量及分解释放对土壤氮的影响

2012年5—10月,采用直接收获法,研究了小兴安岭地区云冷杉红松混交林和枫桦红松混交林两种林型凋落物的未分解层(L层)、半分解层(F层)和腐殖质层(H层)以及土壤表层(S层)氮储量及凋落物分解释放对土壤氮影响。结果表明:研究期间两种林型凋落物现存量变化范围分别为19.43~27.25和21.25~24.28 t·hm-2,氮储量变化范围分别为287.21~418.22和274.81~351.21 kg·hm-2,各层氮含量大小次序均为LFHS;云冷杉红松混交林各层凋落物现存量及其氮储存量5月和9月达到峰值,每月氮储量从L~H层均增加,凋落物分解释放氮在F和H层易富集,输入到土壤中较少;枫桦红松混交林各层凋落物现存量及其氮储量5月和10月达到峰值,每月氮储量从L~H层均减少,氮在凋落物各层中均易迁移,输入到土壤中的氮比云冷杉红松混交林多;两种林型L、F、H层凋落物现存量以及H层氮含量与S层氮含量之间,L和F层凋落物现存量与H层氮含量之间均呈显著正相关。     

内蒙古东部天然白桦林的凋落物性质和储量及其随温度和降水梯度的变化格局

作为碳素和养分循环的重要组分, 地表凋落物如何响应全球气候变化日益受到重视。中国北方半干旱地区森林草原过渡带斑块状分布的森林对气候变化引起的水热变化的响应较为敏感, 但是对这些森林地表处于不同分解阶段的凋落物的化学性质和储量的格局及其如何响应温度、降水变化的报道较少。该研究分析了内蒙古东部地区处于年平均气温和年降水量梯度上的12个天然白桦(Betula platyphylla)林不同凋落物层次(最上层的初步分解层L1, 中间的半分解层L2, 最下层的腐殖质层L3)的化学性质及现存量后发现: 1)随着分解的进行(即从L1到L3层), 氮、磷浓度显著增加, 可提取物浓度基本不变, 酸溶性组分(acid soluble fraction, AS)浓度下降, 酸不溶性组分(acid insoluble fraction, AIF)浓度增加。2)各元素现存量均在L3层最高, 表明凋落物分解缓慢, 养分积累。3)年平均气温和年降水量对凋落物有机组分(AS组分和AIF组分)的性质无显著影响, 但L3层元素储量随年平均气温升高而增加, 可能由于年平均气温较高的地点森林生产力更高, 从而导致叶凋落物量增加, 但由于受水分限制(尤其是在夏天), 这些地点的凋落物分解速率不变或更低, 使凋落物积累更为明显。上述结果表明: 腐殖质层是这些白桦林的一个重要的碳及养分库, 未来在降水没有明显变化的情况下, 这一区域的升温可能会增加白桦林地表凋落物储量。     

秦岭西部山地针叶林凋落物层的化学性质

凋落物作为土壤和植物的结合点在森林生态系统的养分和能量循环方面起着重要作用。凋落物的产量及其元素浓度制约着林下凋落物层和矿质土壤的养分归还。本研究利用野外实地观测和室内分析相结合的方法对秦岭西部山地不同针叶林凋落物层分解过程的特性（如凋落物储量、分解速率、周转时间和养分元素贮量及回归量）进行了研究,结果表明：1）林下凋落物现存量（8.46～29.81 t·hm^-2）远大于年凋落物量（2.96～4.23 t·hm^-2·a^-1）,凋落物分解速率相对较低、积累很强,系统养分循环参数小;2）营养元素在凋落物层中含量的分布格局因树种不同而不同,但不同树种凋落物层营养元素（N、P、K、Ca、Mg、Fe）的储量均为：未分解层（U层）<半分解层（S层）<分解层（D层）;3）不同树种林下凋落物层平均营养元素的储量为：Ca：357.71 kg·hm^-2>N：175.72 kg·hm^-2 >Fe：102.50 kg·hm^-2>Mg：54.21 kg·hm^-2>K：31.96 kg·hm^-2>P：16.78 kg·hm^-2;4）林下凋落物的分解过程是一个养分积累的过程,营养元素最终普遍在分解层（D层）中富集;5）树种和人为经营情况对森林凋落物层的性质和分解状况有较大影响,林下凋落物分解速率表现为：云杉林< 松林< 落叶松林。     

不同氮素添加频率模拟氮沉降对桤木人工林生态系统碳储量的影响

为探究不同频率氮素添加模拟大气氮沉降对桤木人工林生态系统碳储量的影响,采用野外固定样地观测的方法,研究1年12次氮素添加(高频率)和1年2次氮素添加(低频率),对桤木人工林生态系统乔木层、林下植被层、凋落物层、土壤层生物量及碳储量的影响。经过3年不同氮沉降模拟实验,结果表明:(1)高频与低频施氮均能增加桤木叶、枝、皮、根、总生物量及碳储量,其中高频施氮显著增加根生物量及碳储量,较对照增加了22.98%、24.05%;而低频施氮显著增加叶、干生物量及枝、叶碳储量。(2)低频与高频施氮均显著降低了桤木林下植被生物量及碳储量,较对照分别降低67.95%、83.97%和79.73%、70.27%,对碳含量影响不显著。(3)高频与低频施氮均显著增加L层(0—20 cm)凋落物生物量及L层和F层(20—40cm)凋落物碳储量,且高频施氮>低频施氮;低频施氮显著降低20—40cm土壤碳储量,较对照降低20.83%,高频施氮则对土壤碳含量和土壤碳储量无显著影响。高频施氮显著增加桤木林人工生态系统中凋落物层碳储量,显著降低林下植被层碳储量,生态系统总碳储量增加;低频施氮显著降低乔木层、林下植被层和...     

三种阔叶林凋落物对下层土壤养分的影响

对天津八仙山国家级自然保护区3种典型阔叶林,即栓皮栎(Quercus variabilis)林、核桃楸(Juglans mandshurica)林、槲栎(Quercus aliena)林凋落物的未分解层、半分解层及下层土壤的养分进行分析,结果表明:(1)在凋落物的未分解层,C含量槲栎林最高为486.1 g·kg-1,栓皮栎林最低为447.5 g·kg-1。N、P含量核桃楸林均最高,分别为17.9和1.2 g·kg-1,槲栎林最低为13.2和0.8 g·kg-1;半分解层,C、P含量三者差异不显著,N含量以槲栎林最高为17.1 g·kg-1,栓皮栎林最低为10.5 g·kg-1。土壤C、N、P含量差异显著(P0.05),均表现出槲栎林最高,栓皮栎林最低。表明槲栎林自肥能力较强,土壤养分状况良好。(2)C/N、C/P值,在凋落物未分解层中,核桃楸林均小于栓皮栎林和槲栎林,而在半分解层中,3种林分无明显差异;从未分解层到半分解层,栓皮栎林的C/N、C/P值分别下降了17%和11%,槲栎林分别下降了19%和35%,而核桃楸林无明显变化。(3)矿质营养元素含量在凋落物未分解层中按照核桃楸林、栓皮栎林、槲栎林的顺序递减,矿质营养元素含量越大其pH值越接近中性;各林分凋落物矿质营养元素积累总量顺序为:栓皮栎林槲栎林核桃楸林。     

鼎湖山秀风常绿阔叶林凋落物层化学性质的研究

研究鼎湖山自然保护区内秀风常绿阔叶林林下凋涂物层现存量及其化学性质,研究结果表明：１）林下凋落物现存量与年凋落物总量相当,分别为８．７４和．８４（７￣１１）ｔ·ｈｍ＾－２,系统养分循环速率参数为０．９９,循环费品率强烈,说明枯枝落叶分解快,养分周转快;２）营养元素在凋落物层中的含量分布格局为：Ｎ、Ｃａ、Ｍｇ、Ｍｎ元素未分解层（Ｌ层）〉半分解层（Ｆ层）〉已分解层（Ｙ层）,Ｐ、Ｋ、Ｆｅ则是Ｙ层〉Ｆ层〉     

Effects of understory removal, N fertilization, and litter layer removal on soil N cycling in a 13-year-old white spruce plantation infested with Canada bluejoint grass

Canada bluejoint grass [Calamagrostis canadensis (Michx.) Beauv., referred to as bluejoint below] is a competitive understory species widely distributed in the boreal region in North America and builds up a thick litter layer that alters the soil surface microclimate in heavily infested sites. This study examined the effects of understory removal, N fertilization, and litter layer removal on litter decomposition, soil microbial biomass N (MBN), and net N mineralization and nitrification rates in LFH (the sum of organic horizons of litter, partially decomposed litter and humus on the soil surface) and mineral soil (0–10 cm) in a 13-year-old white spruce [Picea glauca (Moench.) Voss] plantation infested with bluejoint in Alberta, Canada. Removal of the understory vegetation and the litter layer together significantly increased soil temperature at 10 cm below the mineral soil surface by 1.7 and 1.3°C in summer 2003 and 2004, respectively, resulting in increased net N mineralization (by 1.09 and 0.14 mg N kg⁻¹ day⁻¹ in LFH and mineral soil, respectively, in 2004) and net nitrification rates (by 0.10 and 0.20 mg N kg⁻¹ day⁻¹ in LFH and mineral soil, respectively, in 2004). When the understory vegetation was intact, nitrification might have been limited by NH₄ ⁺ availability due to competition for N from bluejoint and other understory species. Litter layer removal increased litter decomposition rate (percentage mass loss per month) from 2.6 to 3.0% after 15 months of incubation. Nitrogen fertilization did not show consistent effects on soil MBN, but increased net N mineralization and nitrification rates as well as available N concentrations in the soil. Clearly, understory removal combined with N fertilization was most effective in increasing rates of litter decomposition, net N mineralization and nitrification, and soil N availability. The management of understory vegetation dominated by bluejoint in the boreal region should consider the strong effects of understory competition and the accumulated litter layer on soil N cycling and the implications for forest management.     

Impacts of litter and understory removal on soil properties in a subtropical Acacia mangium plantation in China

In forest ecosystems, the effects of litter or understory on soil properties are far from being fully understood. We conducted a study in a pure Acacia mangium Willd. plantation in southern China, by removing litter or understory or both components and then comparing these treatments with a control (undisturbed), to evaluate their respective effects on soil physical, chemical and biological properties. In addition, a litter decomposition experiment was conducted to understand the effects of understory on litter decomposition. Our data showed that the presence of understory favored litter decomposition to a large extent. In 1 year, 75.2 and 37.2% of litter were decomposed in the control and understory removal treatment (UR), respectively. Litter had a profound significance in retaining soil water and contributing to soil fertility, including organic matter (OM), available phosphorus (P) and alkali-hydrolyzable nitrogen (N), but understory exerted less influence than litter on soil physical and chemical properties. Both litter and understory played an important role in soil biological activity as indicated by microbial biomass carbon (MBC), while there were no significant impacts on soil exchangeable potassium (K) after either or both were removed. Contrary to our hypothesis, the effects of understory or litter removal were not always negative. A significant soil pH increase with litter removal was a positive factor for acid soil in the studied site. Except for soil moisture, significant effects, caused by removal of litter or/and understory, on measured soil chemical characteristics were only observed in the top 10 cm soil layer, but not in the 10–20 cm layer. Soil available P and exchangeable K contents were significantly higher in the rainy season than in the dry season, however, for the other soil properties, not substantially affected by season.     

亚热带不同植被恢复阶段生态系统N、P储量的垂直分配格局

氮(N)、磷(P)是影响生态系统生产力的主要养分因子,为科学评估植被恢复对生态系统N、P积累、分配及其耦合关系的影响,采用时空互代法,以湘中丘陵区地域相邻、环境条件基本一致,且处于不同恢复阶段的4个植物群落(4—5年灌草丛、10—12年灌木林、45—46年马尾松针阔混交林和>90年常绿阔叶林)作为一个恢复序列,设置固定样地,采用收获法和建立主要树种各器官生物量相对生长方程估算群落生物量,采集植被层(叶、枝、干、根)、凋落物层(未分解层、半分解层、已分解层)、土壤层(0—10、10—20、20—30、30—40 cm)样品,测定全N、全P含量,估算生态系统各组分(植被层、凋落物层、土壤层)全N、全P储量。结果表明：植被层全N、全P储量均随植被恢复增加,全N储量增长速率呈先慢后快的特征,而全P储量则呈慢—快—慢增长,地上(叶、枝、干)、地下(根)部分表现为异速增长;随植被恢复,凋落物层全N、全P储量先增加后下降,增长速率为先快后慢,4—5年灌草丛全N、全P储量最低;土壤层全N、全P储量随植被恢复显著增加(P<0.05),全N储量增长速率呈快-慢-快特征,而全P储量呈先慢后快特征...     

鼎湖山马尾松、荷木混交林生态系统碳素积累和分配特征

选取鼎湖山保护区3个马尾松9Pinus massoniana),荷木（Schima superba)针阔混交林样地,研究其生态系统的碳素积累和分配特征。结果表明,鼎湖山马尾松,荷木混交林乔木尾生物量（thm^-2)为：174.41-270.11。平均227.36,且均以马尾松的生物量居多（占54.9%-84.4%)。林下层植物生物量和地表现存凋落物量（thm^-2)分别为7.41-28.28和7.06-11.56。平均14.41和9.03。三个混交林生态系统总碳贮量（thm^-2)分别为146.35,215.30和205.79。平均为189.15,其中植被层碳贮量贡献率最大,依次占62.9%,61.9%和69.9%。平均65.0%;土壤层贡献率次之,依次占34.3%,35.5%和28.5%。平均32.8%;而地表现存凋落物层的贡献最小,仅占2.8%,2.6%和1.6%。平均为2.3%。此外,本文还对该生态系统植被碳吸存潜力进行了讨论。     

Effects of litter removal and mowing on germination and establishment of two fen-grassland species along a productivity gradient

To study the factors that limit the occurrence of species in fen grasslands, the effects of mowing and litter removal on germination, growth and establishment of two common species (Silene flos-cuculi andLotus pedunculatus) were analyzed along a productivity gradient at seven sites in Northern Germany. The sites differed in nutrient availability, vegetation composition and standing crop. In autumn 2002 a field experiment was set up at each site, including factorial combinations of two treatments (litter removal, mowing). Seeds and juvenile individuals of both species were transferred within the treatment combinations. The number of germinated and transplanted individuals was recorded during the 2003 and 2004 seasons and biomass of survived plants weighed in late summer 2004. Mowing and litter removal had positive effects on the number of germinated seeds of both species. The effect of litter removal was mostly significant at sites with a comparatively low nutrient availability and standing crop (350 g/m²), while the effect of mowing was more important at the site with the highest standing crop (1000 g/m²). In some cases the presence of litter had a positive effect on the survival of individuals, which may be caused by extremely dry weather conditions in 2003. The experiment showed that plant species reaction on mowing and litter removal differed both according to their life stage and the site conditions. These differences could be interpreted in context with Shifting Limitation Hypothesis because the abolition of seed limitation by sowing and creation of additional gaps for germination was most efficient at low productive sites, while the high standing crop reduced first of all the establishment probability, which could be increased by mowing.     

喀斯特峰丛洼地不同类型森林养分循环特征

以中国西南喀斯特峰丛洼地为研究区域用标准木法和收获法对人工林、次生林、原生林3个不同类型森林的6个代表性群落的生物量、营养元素生物循环量及循环特征进行了研究。结果表明:(1)不同类型森林群落乔木各器官的养分含量大小顺序为:叶枝根干,林下植被层和凋落物层的养分含量比较高,其含量普遍高于乔木层各组分,仅次于乔木叶片;各组分中营养元素以K、Ca最高,P、Mg最低;(2)3种类型森林间乔木层的养分积累量总规律表现为原生林(4540.30 kg/hm~2)次生林(2107.09 kg/hm~2)人工林(719.51 kg/hm~2),分别占林分养分积累量的88.30%、79.57%和62.60%;(3)3种类型森林生态系统养分总贮量相差不大,均主要集中在土壤层在各层分配格局有所差异;营养元素的年吸收量和年归还量均为次生林原生林人工林,年吸收量分别为:418.80、271.17和148.79 kg hm~(-2)a~(-1);年归还量分别为:182.98、111.43和43.37 kg hm_(-2)a~(-1);(4)不同类型森林养分利用系数总规律为人工林(0.35)次生林(0.20)原生林(0.10);循环系数则相反,为原生林(0.48)次生林(0.46)人工林(0.30);而周转时间为原生林(37.32)人工林(18.63)次生林(13.93)。喀斯特峰丛洼地土层薄,养分贮存能力差,森林养分循环能力相对较弱,沿着强、中、弱干扰递减梯度,3种类型森林养分利用效率和循环能力呈增长趋势。     

Asymbiotic Nitrogen Fixation and Litter Decomposition on a Long Soil-Age Gradient in Hawaiian Montane Rain Forest1

We determined rates of decomposition and asymbiotic nitrogen fixation in the leaf litter of Cheirodendron spp. on the Hawaiian Islands. Leaf litter was collected from four sites on a long soil-age gradient (300 yr to 4.1 M yr) and decomposed at two sites that differed widely in substrate age and nutrient availability. Rates of decomposition were higher in litter decomposed at the older site, where nutrient availability was greater. A substantial amount of nitrogen and phosphorus immobilization occurred in litter decomposed at the older site, with more immobilization occurring in litter with lower initial nitrogen and phosphorus concentrations, suggesting both supply and demand controls on nutrient immobilization. Potential rates of nitrogen fixation were very low in the first 25 d (0–5 nmol acetylene/gdw/h), rose to much higher rates by 70 d (20–45 nmol), and then declined by 140 d. We found no significant difference in rates of potential nitrogen fixation between sites of decomposition, but there was a strong substrate effect, with higher rates in litter with low lignin, low nitrogen, and high phosphorus. Where significant immobilization of nitrogen occurred for decomposing Cheirodendron, nitrogen fixation could have comprised no more than 10 percent of immobilized nitrogen. Overall, rates of nitrogen fixation were dependent on the source of the decomposing substrate but not on the site of decomposition, while short-term decomposition and nutrient immobilization were strongly dependent on the site of decomposition but not as much on the source of the decomposing substrate.     

Mixing Effects of Understory Plant Litter on Decomposition and Nutrient Release of Tree Litter in Two Plantations in Northeast China

Understory vegetation plays a crucial role in carbon and nutrient cycling in forest ecosystems; however, it is not clear how understory species affect tree litter decomposition and nutrient dynamics. In this study, we examined the impacts of understory litter on the decomposition and nutrient release of tree litter both in a pine (Pinus sylvestris var. mongolica) and a poplar (Populus × xiaozhuanica) plantation in Northeast China. Leaf litter of tree species, and senesced aboveground materials from two dominant understory species, Artemisia scoparia and Setaria viridis in the pine stand and Elymus villifer and A. sieversiana in the poplar stand, were collected. Mass loss and N and P fluxes of single-species litter and three-species mixtures in each of the two forests were quantified. Data from single-species litterbags were used to generate predicted mass loss and N and P fluxes for the mixed-species litterbags. In the mixture from the pine stand, the observed mass loss and N release did not differ from the predicted value, whereas the observed P release was greater than the predicted value. However, the presence of understory litter decelerated the mass loss and did not affect N and P releases from the pine litter. In the poplar stand, litter mixture presented a positive non-additive effect on litter mass loss and P release, but an addition effect on N release. The presence of understory species accelerated only N release of poplar litter. Moreover, the responses of mass loss and N and P releases of understory litter in the mixtures varied with species in both pine and poplar plantations. Our results suggest that the effects of understory species on tree litter decomposition vary with tree species, and also highlight the importance of understory species in litter decomposition and nutrient cycles in forest ecosystems.     

林下植被抚育对樟人工林生态系统碳储量的影响

以亚热带东部地区48年生樟(Cinnamomum camphora)人工林为研究对象, 探讨不同林下植被处理方式对植被和土壤碳储量的影响。研究结果表明: 1)林下植被抚育增加了植被的碳储量, 增幅为48.87%, 平均每年比未抚育林分增加了0.62 t·hm^-2; 2)林下植被抚育降低了土壤有机碳含量, 降低幅度介于4.79%-34.13%之间, 其中0-10 cm、10-20 cm土层比未抚育林分分别降低了10.16 g·kg^-1和8.58 g·kg^-1, 差异达到显著水平(p < 0.05); 3)林下植被抚育降低了森林土壤碳储量, 降低幅度介于1.98%-43.45%之间, 其中0-10 cm和10-20 cm土层分别降低了15.39 t·hm^-2和11.58 t·hm^-2, 差异达到极显著水平(p < 0.01)和显著水平(p < 0.05); 4)林下植被抚育降低了森林生态系统总碳储量, 降低幅度为4.27%, 但差异不显著。因此, 林下植被抚育虽有利于植被碳储量的积累, 但降低了土壤有机碳含量和储量。