高山森林林窗对凋落叶分解的影响

林窗对降水和光照等环境条件的再分配以及分解者群落的影响可能深刻作用于森林凋落物分解过程,但有关高山森林林窗大小对凋落物分解的影响尚无研究报道。采用凋落物分解袋法,研究了川西高山森林不同大小林窗对非生长季节和生长季节红桦(Betula albo-sinensis)和岷江冷杉(Abies faxoniana)凋落叶质量损失的影响。结果显示,经过1a的分解,不同生境下红桦和岷江冷杉凋落叶分别分解了27.25%—30.12%和27.04%—27.96%,其中非生长季节占53.83%—60.18%和50.23%—59.09%。林窗对红桦和岷江冷杉凋落叶质量损失的影响因物种不同而呈现季节差异。总体上,林窗加快了岷江冷杉凋落叶的分解而延缓了红桦凋落叶的分解。与郁闭林下相比,林窗显著增加了2种凋落叶非生长季节的质量损失速率,显著降低了生长季节2种凋落叶的质量损失速率;2种凋落叶质量损失速率在非生长季节随林窗面积增大而加快,在生长季节随林窗面积增大而减慢。林窗显著影响了初冻期、深冻期和融化期岷江冷杉凋落叶的质量损失率,但对红桦凋落叶质量损失率影响不显著。可见,高山森林凋落物分解过程受到林窗的显著影响,并且阔叶和针叶凋落叶在非生长季节和生长季节对林窗的响应具有明显差异。     

林窗对川西亚高山凋落叶总酚和缩合单宁损失动态的影响

总酚和缩合单宁作为重要组分参与并调控森林凋落物的分解过程,其可能受到林窗直接或间接的影响。该研究以川西亚高山6种常见植物(包括方枝柏(Juniperus saltuaria)、岷江冷杉(Abies fargesii var. faxoniana)、四川红杉(Larix mastersiana)、红桦(Betula albosinensis)、康定柳(Salix paraplesia)和高山杜鹃(Rhododendron lapponicum))凋落叶为研究对象,在林窗内外不同位置(林窗中心、林冠林窗、扩展林窗、郁闭林下)进行为期3年的原位分解实验,探究凋落叶总酚和缩合单宁在3年分解过程中冬季和生长季节的动态特征。研究发现凋落叶总酚和缩合单宁均在分解第一年具有较高的损失速率,分别为10.76和8.5mg·d–1;林窗对酚类物质降解的影响随分解进程逐渐减弱并具有明显的季节性差异;6种凋落叶总酚含量均在生长季降低较快,且初始缩合单宁含量较高的凋落叶在第一年冬季有较高的缩合单宁损失速率。研究表明森林林窗内的凋落叶在长期分解过程中,其酚类物质的降解受凋落叶质量和季节差异的影响更为显著。研究结果有...     

土壤动物对川西高山/亚高山森林凋落物分解的贡献

采用凋落物分解袋法,研究了土壤动物对川西高山/亚高山森林代表性植物康定柳、方枝柏、红桦和岷江冷杉凋落物在分解第一年(2011年11月-2012年10月)不同关键时期质量损失的贡献.结果表明: 在凋落物第一年的分解过程中, 不同物种凋落物的分解速率大小依次为康定柳＞红桦＞岷江冷杉＞方枝柏,且均为生长季节大于冻融季节.土壤动物对凋落物分解的贡献率(P_fau)为方枝柏(26.7%)＞岷江冷杉(18.8%)＞红桦(15.7%)＞康定柳(13.2%),其中康定柳和方枝柏的P_fau在生长季节大于冻融季节,而红桦和岷江冷杉的P_fau为冻融季节大于生长季节.冻融季节土壤动物的作用与凋落物初始C、P和N/P显著相关,而生长季节则与N、C/N、木质素、木质素/纤维素显著相关.     

亚高山森林林窗对凋落物分解过程中半纤维素动态的影响

亚高山森林林窗可能通过改变冬季雪被格局和生长季水热环境影响林窗内凋落物中半纤维素的分解动态, 但目前对此还缺乏研究。采用凋落物分解袋法, 以亚高山森林5种典型物种岷江冷杉(Abies faxoniana)、红桦(Betula albosinensis)、四川红杉(Larix mastersiana)、方枝柏(Sabina saltuaria)和高山杜鹃(Rhododendron lapponicum)凋落物为研究对象, 研究雪被形成期、雪被覆盖期、雪被融化期和生长季节从林窗中心、林冠林窗、扩展林窗到郁闭林下物种凋落物的半纤维素变化特征。经历一年分解后, 5种凋落物的半纤维素均呈现净累积现象。针、阔叶凋落物半纤维素分别在雪被覆盖期和融化期表现出相对较高的损失率。在雪被覆盖期和融化期, 凋落物半纤维素在林窗中心和林冠林窗具有相对较高的损失率; 而在生长季节, 林窗中心呈现相对较低的凋落物半纤维素累积率。统计分析结果表明凋落物分解过程中半纤维素损失率与环境因子和凋落物质量因子均显著相关。这些结果表明亚高山森林林窗对凋落物分解过程中半纤维素损失率具有显著影响, 分别促进了半纤维素在冬季的损失以及抑制了半纤维素在生长季节的累积, 意味着亚高山森林林窗的形成有利于凋落物半纤维素的降解。     

Effects of forest gap on hemicellulose dynamics during foliar litter decomposition in an subalpine forest

 亚高山森林林窗可能通过改变冬季雪被格局和生长季水热环境影响林窗内凋落物中半纤维素的分解动态, 但目前对此还缺乏研究。采用凋落物分解袋法, 以亚高山森林5种典型物种岷江冷杉(Abies faxoniana)、红桦(Betula albosinensis)、四川红杉(Larix mastersiana)、方枝柏(Sabina saltuaria)和高山杜鹃(Rhododendron lapponicum)凋落物为研究对象, 研究雪被形成期、雪被覆盖期、雪被融化期和生长季节从林窗中心、林冠林窗、扩展林窗到郁闭林下物种凋落物的半纤维素变化特征。经历一年分解后, 5种凋落物的半纤维素均呈现净累积现象。针、阔叶凋落物半纤维素分别在雪被覆盖期和融化期表现出相对较高的损失率。在雪被覆盖期和融化期, 凋落物半纤维素在林窗中心和林冠林窗具有相对较高的损失率; 而在生长季节, 林窗中心呈现相对较低的凋落物半纤维素累积率。统计分析结果表明凋落物分解过程中半纤维素损失率与环境因子和凋落物质量因子均显著相关。这些结果表明亚高山森林林窗对凋落物分解过程中半纤维素损失率具有显著影响, 分别促进了半纤维素在冬季的损失以及抑制了半纤维素在生长季节的累积, 意味着亚高山森林林窗的形成有利于凋落物半纤维素的降解。     

季节性雪被对高山森林凋落物分解的影响

季节性雪被可能对高山森林凋落物分解产生重要影响, 但一直没有深入的研究。该文采用凋落物分解袋法, 于2010-2012年雪被覆盖下几个关键时期(冻结初期、深冻期和融化期)以及生长季节, 研究了川西高山森林代表性树种岷江冷杉(Abies faxoniana)、红桦(Betula albosinensis)、四川红杉(Larix mastersiana)和方枝柏(Sabina saltuaria)凋落叶在不同厚度冬季雪被下的分解动态。经过两年的分解, 不同雪被覆盖下岷江冷杉凋落物分解率为33.98%-39.55%, 红桦为46.49%-48.22%, 四川红杉为42.30%-44.93%, 方枝柏为40.34%-43.84%。相对于无雪被覆盖环境, 厚型雪被覆盖均小幅提高了4种凋落物两年的失重率(1.57%-5.57%)。3个针叶树种(岷江冷杉、四川红杉和方枝柏) Olson凋落物分解系数k均以厚型雪被覆盖最大, 薄型雪被覆盖最小, 而阔叶树种红桦分解系数k则表现为无雪被>薄型雪被>较厚型雪被>厚型雪被>中型雪被。尽管在第二年生长季中雪被对红桦凋落物分解的促进作用不明显, 但雪被覆盖明显促进了两年各个关键时期岷江冷杉、四川红杉和方枝柏凋落物的分解。第一年雪被期凋落物分解对当年分解总量的贡献达42.5%-65.5%, 季节性雪被变化明显改变了凋落物冬季分解格局, 对深冻期凋落物分解过程影响尤为显著。综上所述, 当前气候变化情景下冬季雪被的减少可能减缓该区森林凋落物分解过程, 但相对于易分解的阔叶凋落物, 针叶凋落物的响应特征可能更为强烈。     

Loss of total phenols from leaf litter of two shrub species: dual responses to alpine forest gap disturbance during winter and the growing season

高山森林林窗能够通过调控水热动态进而控制林下生态系统过程。因此,本研究旨在通过两种典型灌木[华西箭竹(Fargeisia nitida (Mitford) Keng f.)和康定柳(Salix paraplesia Schneid.)]凋落叶分解,探索林窗干扰对分解过程中总酚释放的影响。我们在一个典型的岷江冷杉林(Abies faxoniana Rehd.)样地,通过设置不同林窗位置(林窗中心南侧、林窗中心北侧、林缘、扩展林缘和林下)进行了凋落物分解实验;并在两年的不同关键时期：雪被形成期、雪被覆盖期、雪被融化期、生长季节初期和生长季节后期,对两种灌木凋落叶分解袋进行采样,并测试其总酚释放率和微生物丰富度(真菌和细菌)。实验结束后,我们发现,雪被厚度、冻融循环以及真菌细菌比对凋落叶的总酚释放具有显著影响。在两年的雪被形成期、雪被覆盖期、雪被融化期和生长季节后期,真菌和细菌丰富度表现出从林窗中心到林下逐渐降低的趋势,而在两年的生长季节初期,其表现出从林窗中心到林下逐渐增加的趋势。而从不同林窗位置来比较,两种灌木凋落叶的总酚释放率仅在第一年各关键时期表现出同真菌细菌丰富度类似的规律。此外,在第一年的冬季,以及从整个第一年和整个两年分解时间段来看,林窗中心位置两种凋落叶的总酚释放率皆较其他林窗位置高。这些研究结果表明,高山森林林窗的形成能够促进凋落叶总酚的释放,尽管其释放对林窗干扰的响应在不同关键时间具有不同的表现。总之,在高寒生物区,林窗的更替消失以及在气候变化背景下冬季变暖导致的雪被覆盖厚度和持续时间的减少会降低凋落叶总酚的释放率。     

川西亚高山森林凋落物分解初期土壤动物对红桦凋落叶质量损失的贡献

2010年10月26日-2011年4月18日在川西亚高山地区季节性冻融期间,选择典型的红桦-岷江冷杉林,采用凋落物分解袋法调查了不同网孔(0.02、0.125、1和3 mm)凋落物分解袋内的凋落物质量损失,分析微型、中型和大型土壤动物对红桦凋落叶分解的贡献.结果表明:在季节性冻融期间,0.02、0.125、1和3 mm分解袋内的红桦凋落叶质量损失率分别为11.8％、13.2％、15.4％和19.5％,不同体径土壤动物对红桦凋落叶质量损失的贡献率为39.5％;不同孔径凋落物袋内土壤动物的类群和个体相对密度与凋落叶的质量损失率的变化趋势相对一致.在季节性冻融的初期、深冻期和融化期,不同土壤动物对红桦凋落叶质量损失的贡献率为大型土壤动物(22.7％)＞中型土壤动物(11.9％)＞微型土壤动物(7.9％).季节性冻融期间土壤动物活动是影响川西亚高山森林凋落物分解的重要因素之一.     

川西亚高山森林林窗对凋落枝早期分解的影响北大核心CSCD

林窗调控的土壤水热环境和分解者群落结构可能深刻影响凋落物分解过程,已有的研究结果具有不确定性。为了解高海拔森林林窗面积对凋落枝分解的影响,采用凋落物分解袋法,于2012–2016年冬季和生长季节,研究了川西亚高山森林255–290 m^2(FG1)、153–176 m^2(FG2)、38–46 m^2(FG3)3种面积林窗和林下对岷江冷杉(Abies faxoniana)凋落枝质量损失的影响。结果显示:林窗面积大小显著改变了林窗和林下的雪被厚度、温度和冻融循环频次;雪被厚度和温度以FG1林窗最高,林下最低;FG1、FG2、FG3林窗和林下枝条分解4年后的质量残留率分别为59.9%、59.5%、62.1%和55.3%,分解系数k值分别为0.127、0.131、0.120和0.135,95%分解时间分别为23.6、22.7、25.0和22.2 a;与林下相比,林窗显著增加了第一年和第二年生长季节的质量损失速率,降低了第一年和第四年冬季的枝条质量损失速率;林窗大小对质量损失速率的影响随分解时期变化差异明显,质量损失速率在第一年和第三年冬季随林窗面积增大而增大,在第三年生长季节随林窗面积增大而降低;枝条质量损失的比例在第一年最高,随林窗面积增加而增加,且冬季高于生长季节。综上所述,林窗环境变化深刻影响亚高山森林凋落枝分解,但这种影响随林窗面积和分解时间有所差异。     

高山森林三种细根分解初期微生物生物量动态

为了解川西高山森林凋落物分解过程的微生物生物量特征,采用凋落物分解袋法,测定了粗枝云杉(Picea asperata)、岷江冷杉(Abies faxoniana)和红桦(Betula albosinensi)细根分解几个关键时期微生物生物量碳(MBC)、氮(MBN)和磷(MBP)的动态特征。3个树种细根分解过程中的MBC均表现为在土壤深冻期下降至全年最低点后缓慢上升,至土壤融冻中期再次下降,到生长季节增长的趋势。然而,粗枝云杉与岷江冷杉细根分解过程中的MBC最大值出现在生长季节末期,红桦细根分解过程中的MBC最大值出现在土壤冻结初期。3个树种细根分解过程中的MBN表现出相似的动态规律:土壤深冻期急剧下降至全年最低,随后在冻融季节无显著变化,生长季节明显增加,到生长季节末期达到全年最大值。另外,粗枝云杉和岷江冷杉细根分解过程中MBP均随着分解的进行呈现增加趋势,而红桦细根分解过程中的MBP在土壤融冻末期出现最大值,在生长季节中期出现另一峰值,生长季节末期明显下降。这些结果表明冬季细根分解过程中仍存在一定的土壤微生物,但受到细根质量、温度及其驱动的环境因子的深刻影响。     

Lignin Degradation in Foliar Litter of Two Shrub Species from the Gap Center to the Closed Canopy in an Alpine Fir Forest

To understand the effects of forest gaps on lignin degradation during shrub foliar litter decomposition, a field litterbag experiment was conducted in an alpine fir (Abies faxoniana) forest of the eastern Tibet Plateau. Dwarf bamboo (Fargesia nitida) and willow (Salix paraplesia) foliar litterbags were placed on the forest floor from the gap center to the closed canopy. The litterbags were sampled during snow formation, snow coverage, snow melting and the growing season from October 2010 to October 2012. The lignin concentrations and loss in the litter were measured. Over 2 years, lignin loss was lower in the bamboo litter (34.64–43.89%) than in the willow litter (38.91–55.10%). In the bamboo litter, lignin loss mainly occurred during the first decomposition year, whereas it occurred during the second decomposition year in the willow litter. Both bamboo and willow litter lignin loss decreased from the gap center to the closed canopy during the first year and over the entire 2-year decomposition period. Compared with the closed canopy, the gap center showed higher lignin loss for both bamboo and willow litter during the two winters, but lower lignin loss during the early growing period. Additionally, the dynamics of microbial biomass carbon during litter decomposition followed the same trend as litter lignin loss during the two winters and growing period. These results indicated that alpine forest gaps had significant effects on shrub litter lignin loss and that reduced snow cover during winter warming would inhibit shrub lignin degradation in this alpine forest.     

冬季雪被对青藏高原东缘高海拔森林凋落叶P元素释放的影响

雪被是影响高海拔森林凋落物分解的重要生态因子,其是否影响到生长季节与非生长季节凋落物中的P元素释放,尚未量化。为了量化季节性雪被对高海拔森林凋落物分解过程中P元素释放的影响,于2010年10月至2012年10月间,在青藏高原东缘川西高海拔森林不同厚度冬季雪被斑块下,设置凋落物分解袋实验。检测该地区代表性树种岷江冷杉(Abies faxoniana)、红桦(Betula albo-sinensis)、四川红杉(Larix mastersiana)和方枝柏(Sabina saltuaria)凋落叶在雪被覆盖不同关键时期(雪被形成前期、完全覆盖期和消融期)以及生长季节的P元素动态。结果表明,凋落物质量与雪被厚度均显著影响了P元素的释放过程。雪被覆盖时期凋落物P元素释放率表现为有雪被覆盖大于无雪被覆盖,而生长季节中除岷江冷杉外的其他3种凋落物P元素释放率均为无雪被覆盖下最大。相对于无雪被覆盖斑块,冬季雪被的存在提供了保护绝缘层,促进凋落物P元素释放,提高了各物种冬季P元素释放贡献率。这些结果表明,全球变化情景下的雪被减少可能减缓高海拔森林凋落物P元素的释放过程,改变森林土壤P元素水平。所以在研究高寒、高海拔地区全球气候变化下生态系统功能的工作中,应注重雪被这一异质性环境因子对生态系统功能的影响。     

Contribution of Soil Fauna to Foliar Litter-Mass Loss in Winter in an Ecotone between Dry Valley and Montane Forest in the Upper Reaches of the Minjiang River

Litter decomposition during winter can provide essential nutrients for plant growth in the subsequent growing season, which plays important role in preventing the expansion of dry areas and maintaining the stability of ecotone ecosystems. However, limited information is currently available on the contributions of soil fauna to litter decomposition during winter in such ecosystems. Therefore, a field experiment that included litterbags with two different mesh sizes (0.04 mm and 3 mm) was conducted to investigate the contribution of soil fauna to the loss of foliar litter mass in winter from November 2013 to April 2014 along the upper reaches of the Minjiang River. Two litter types of the dominant species were selected in each ecosystem: cypress (Cupressus chengiana) and oak (Quercus baronii) in ecotone; cypress (Cupressus chengiana) and clovershrub (Campylotropis macrocarpa) in dry valley; and fir (Abies faxoniana) and birch (Betula albosinensis) in montane forest. Over one winter incubation, foliar litter lost 6.0%-16.1%, 11.4%-26.0%, and 6.4%-8.5% of initial mass in the ecotone, dry valley and montane forest, respectively. Soil fauna showed obvious contributions to the loss of foliar litter mass in all of the ecosystems. The highest contribution (48.5%-56.8%) was observed in the ecotone, and the lowest contribution (0.4%-25.8%) was observed in the montane forest. Compared with other winter periods, thawing period exhibited higher soil fauna contributions to litter mass loss in ecotone and dry valley, but both thawing period and freezing period displayed higher soil fauna contributions in montane forest. Statistical analysis demonstrated that the contribution of soil fauna was significantly correlated with temperature and soil moisture during the winter-long incubation. These results suggest that temperature might be the primary control factor in foliar litter decomposition, but more active soil fauna in the ecotone could contribute more in litter decomposition and its related ecological processes in this region.     

Forest Gaps Inhibit Foliar Litter Pb and Cd Release in Winter and Inhibit Pb and Cd Accumulation in Growing Season in an Alpine Forest

Aims

The release of heavy metals (such as Pb and Cd) from foliar litter play an important role in element cycling in alpine forest ecosystems. Although natural forest gaps could play important roles in the release of heavy metals from foliar litter by affecting the snow cover during the winter and solar irradiation during the growing season, few studies have examined these potential roles. The objectives of this study were to document changes in Pb and Cd dynamics during litter decomposition in the center of gaps and under closed canopies and to investigate the factors that controlled these changes during the winter and growing seasons.

Methods

Senesced foliar litter from six dominant species, including Kangding willow (Salix paraplesia), Masters larch (Larix mastersiana), Mingjiang fir (Abies faxoniana), Alpine azalea (Rhododendron lapponicum), Red birch (Betula albosinensis) and Mourning cypress (Sabina saltuaria), was placed in litterbags and incubated between the gap center and closed canopy conditions in an alpine forest in the eastern region of the Tibetan Plateau. The litterbags were sampled at the snow formation stage, snow coverage stage, snow melt stage and during the growing season. The Pb and Cd concentrations in the sampled foliar litter were determined by acid digestion (HNO₃/HClO₄).

Important findings

Over one year of decomposition, Pb accumulation and Cd release from the foliar litter occurred, regardless of the foliar litter species. However, Pb and Cd were both released from the foliar litter during the winter and accumulated during the growing season. Compared with the gap center and the canopy gap edge, the extended gap edge and the closed canopy showed higher Pb and Cd release rates in winter and higher Pb and Cd accumulation rates during the growing season, respectively. Statistical analyses indicate that the dynamics of Pb were significantly influenced by frequent freeze–thaw cycles in winter and appropriate hydrothermal conditions during the growing season, the dynamics of Cd were strongly influenced by species and the presence of a forest gap at different decomposition stages. These results show that forest gaps could inhibit Pb and Cd release from foliar litter in the alpine forest of western Sichuan. In addition, a decrease in the snow depth in the winter warming scenario would promote the release of Pb during foliar litter decomposition. There exist some difference that may be influenced by litter quality, microenvironment and microtopography during litter decomposition.     

季节性冻融期间亚高山森林凋落物的质量变化

凋落物质量是影响凋落物分解的重要生物因子,其在季节性冻融期间的变化可能对亚高山森林生态系统过程产生显著的影响。因此,采用凋落物分解袋法,研究了岷江冷杉(Abies faxoniana)和白桦(Betula platyphylla)凋落物质量在一个季节性冻融期间(2006年10月至2007年4月)的变化。季节性冻融期间,岷江冷杉和白桦凋落物的木质素(L)和纤维素的降解率为全年降解的70%-75%,岷江冷杉和白桦凋落物的C/N、L/N和纤维素/N均显著增加,而纤维素/P均有所降低。岷江冷杉凋落物的C/P和L/P有所增加,但白桦凋落物的C/P和L/P有所降低。可见,季节性冻融期间,亚高山森林凋落物的质量发生了较为显著的变化,其显著影响了亚高山凋落物分解过程。