雪被斑块对川西亚高山森林6种凋落叶冬季腐殖化的影响

亚高山森林凋落叶腐殖化是联系植物与土壤碳库和养分库的重要通道, 在冬季可能受到雪被斑块的影响。该文采用凋落物网袋法, 于2012年11月-2013年4月研究了川西亚高山森林不同厚度雪被斑块(厚雪被、中雪被、薄雪被和无雪被)下优势树种岷江冷杉(Abies faxoniana)、方枝柏(Sabina saltuaria)、四川红杉(Larix mastersiana)、红桦(Betula albo-sinensis)、康定柳(Salix paraplesia)和高山杜鹃(Rhododendron lapponicum)凋落叶在不同雪被关键期(雪被形成期、雪被覆盖期和雪被融化期)的腐殖化特征。结果表明: 亚高山森林冬季不同厚度雪被斑块下6种凋落叶均保持一定程度的腐殖化, 其中红桦凋落叶腐殖化度最大, 达4.45%-5.67%; 岷江冷杉、高山杜鹃、康定柳、四川红杉和方枝柏凋落叶腐殖化度分别为1.91%-2.15%、1.14%-2.03%、1.06%-1.97%、0.01%-1.25%和0.39%-1.21%。凋落叶腐殖质在雪被形成期、融化期和整个冬季累积, 且累积量随雪被厚度减小而增加, 但在雪被覆盖期降解, 且降解量随雪被厚度减小而增大。相关分析结果表明, 亚高山森林凋落叶前期腐殖化主要受凋落叶质量影响, 且与氮和酸不溶性组分呈极显著正相关, 而与碳、磷、水溶性和有机溶性组分呈极显著负相关。表明冬季变暖情景下雪被厚度的减小可能促进亚高山森林凋落叶腐殖化, 但凋落叶腐殖化在不同雪被关键期受雪被斑块和凋落叶质量的调控。     

不同厚度雪被对高山森林6种凋落物分解过程中酸溶性和酸不溶性组分的影响

高山森林冬季不同厚度雪被格局可能通过影响凋落物的分解过程中酸溶性和酸不溶性组分特征,改变凋落物分解过程,但缺乏必要关注。采用凋落物分解袋法,研究了高山森林林窗中央至林下形成的天然雪被厚度梯度(厚型雪被、中型雪被、薄型雪被和无雪被)覆盖下,6种典型物种岷江冷杉(Abies faxoniana)、红桦(Betula albo-sinensis)、四川红杉(Larix mastersiana)、方枝柏(Sabina saltuaria)、康定柳(Salix paraplesia)和高山杜鹃(Rhododendron lapponicum)凋落物在不同关键时期(雪被形成期、雪被覆盖期和雪被融化期)的酸溶性组分和酸不溶性组分变化特征。经历一个冬季的分解后,6种凋落物酸溶性组分绝对含量呈降低趋势,除红桦外5种凋落物酸不溶性组分绝对含量呈增加趋势。不同厚度雪被显著影响雪被覆盖期和融化期凋落物酸不溶性和酸溶性组分绝对变化量;其中方枝柏、红桦和康定柳凋落物酸不溶性组分增加量在厚型雪被下显著高于其它雪被覆盖;而相对于阔叶凋落物酸溶性组分变化量在薄型雪被和无雪被梯度达到最大值,针叶凋落物酸溶性组分在厚型雪被下具有最大的变化量。一个冬季分解结束后,表征6种凋落物酸溶性和酸不溶性组分含量相对比例的LCI指数(Lignocellulose index)总体升高,雪被对LCI指数的影响主要表现在雪被覆盖期和融化期,且方枝柏、岷江冷杉和康定柳凋落物LCI在冬季分解后均在厚型雪被达到最高值。同时统计分析结果表明,物种极显著影响冬季不同阶段凋落物酸溶性和酸不溶性组分的变化。这些结果意味着气候变暖情景下,高山森林冬季雪被和冻融格局的改变将显著影响凋落物分解过程中酸溶性、酸不溶性组分以及LCI指数代表的抵抗性组分结构的变化,且影响趋势受到凋落物质量的调控。     

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。     

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。     

雪被覆盖对高山森林凋落物分解过程中水溶性和有机溶性组分含量的影响

季节性雪被可能通过冻结、淋溶以及冻融循环等对高山森林凋落物水溶性和有机溶性组分含量产生影响.本文采用凋落物分解袋法,以川西高山森林典型乔木（四川红杉、岷江冷杉、红桦、方枝柏）和灌木（高山杜鹃、康定柳）凋落物为研究对象,研究了雪被覆盖不同时期（雪被形成期、雪被覆盖期和雪被融化期）和雪被厚度（厚型雪被、中型雪被、薄型雪被和无雪被）下凋落物水溶性和有机溶性组分含量的动态变化特征.结果表明： 在一个冬季的分解过程中,6种凋落物水溶性组分含量在雪被形成期和融化期降低而雪被覆盖期增加,但除高山杜鹃凋落物有机溶性组分含量在雪被覆盖期增加外,其他5种凋落物有机溶性组分含量在整个冬季呈降低趋势.相对于凋落物有机溶性组分含量,不同厚度雪被斑块对凋落物水溶性组分含量变化的影响更大,且主要表现在雪被形成期和雪被覆盖期.相对于其他雪被斑块,薄型雪被斑块更加显著地促进了高山柳和高山杜鹃凋落物水溶性组分含量降低,但显著抑制了方枝柏凋落物水溶性组分含量降低,而其他凋落物水溶性组分含量变化在不同斑块间无显著差异.冬季高山森林雪被对凋落物水溶性和有机溶性组分含量的影响主要受控于凋落物质量.     

Effects of snow patch on the dynamics of potassium and sodium during litter decomposition in winter in a subalpine forest of western Sichuan

亚高山森林冬季不同厚度雪被斑块下显著的冻融格局差异可能对凋落物分解过程中钾(K)和钠(Na)的动态具有重要影响, 然而已有研究还不足以清晰地认识这一过程。以川西亚高山森林6种代表性树种凋落物为研究对象, 采用凋落物网袋法, 探讨冬季不同厚度雪被斑块下雪被形成期、覆盖期和融化期凋落物分解过程中K和Na元素释放或富集的特征。整个雪被覆盖时期, 6种凋落物分解过程中Na均表现为富集特征, 且以覆盖期最为明显; 而K表现为释放特征, 以雪被融化期释放率最大。相对于其他雪被斑块, 厚型和中型雪被斑块下凋落物K释放率相对较高; 除康定柳(Salix paraplesia)和高山杜鹃(Rhododendron lapponicum)外, 其他物种凋落物在厚型和中型雪被斑块下Na富集率较高。同时, 统计分析结果表明, 物种和雪被显著影响冬季不同关键时期凋落物K和Na元素动态。除红桦(Betula albosinensis)和方枝柏(Sabina saltuaria)凋落物外, 温度因子与凋落物K和Na动态变化呈显著正相关。这些结果表明气候变暖情景下冬季雪被覆盖的减小将抑制亚高山森林冬季凋落物分解过程中K和Na元素的释放, 但是释放程度受凋落物质量和雪被覆盖时期的显著影响。     

Short-term responses of winter soil respiration to snow removal in a Picea asperata forest of western Sichuan

Aims Seasonal snow cover is one of the most important factors that control winter soil respiration in the cold biomes. The warming-induced decreases in snowpack could affect winter soil respiration of subalpine forests. The aim of this study was to explore the effects of snow removal on winter soil respiration in a Picea asperata forest.Methods A snow removal experiment was conducted in a P. asperata forest stand in western Sichuan during the winter of 2015/2016. The snow removal treatment was implemented using wooden roof method. Soil temperatures, snow depth and soil respiration rate were simultaneously measured in plots of snow removal and controls during the experimental period.Important findings Compared to the control, snow removal increased the fluctuations of soil temperatures. The average daily temperature of the soil surface and that at 5 cm depth were 1.12 °C and 0.34 °C lower, respectively, and the numbers of freeze-thaw cycles of the soil surface and that at 5 cm depth were increased by 39 and 12, respectively, in plots of snow removal than in the controls. The average rate of winter soil respiration and CO₂ efflux were 0.52 μmol·m^-2·s^-1 and 88.44 g·m^-2, respectively. On average, snow removal reduced soil respiration rate by 21.02% and CO₂ efflux by 25.99%, respectively. More importantly, the snow effect mainly occurred in the early winter. The winter soil respiration rate had a significant exponential relationship with soil temperature. However, snow removal significantly reduced temperature sensitivity of the winter soil respiration. Our results suggest that seasonal snow reduction associated with climate change could inhibit winter soil respiration in the subalpine forests of western Sichuan, with significant implications for the carbon dynamics of the subalpine forests.     

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。     

雪被斑块对川西亚高山两个森林群落冬季土壤氮转化的影响

为了解气候变暖情景下雪况变化对高寒森林冬季土壤氮转化的影响,测定了川西亚高山冷杉(Abies faxoniana)+红桦(Betula albo-sinensis)混交林(MF)和冷杉次生林(SF)三类雪被斑块(浅雪被、中厚度雪被和厚雪被)内冬季土壤氮矿化特征。结果表明:经过一个冬季(2011-2012),两个森林群落土壤净氮氨化量都为负值,净氮硝化量都为正值,且净氮硝化量显著高于净氮氨化量;冬季土壤氮氨化、硝化、矿化和固持量都是中度雪被厚度最高,但各雪被斑块之间都未达到显著水平。各雪被斑块下,冷杉次生林土壤氮矿化参数都显著高于针阔混交林,但雪被斑块和林型交互作用对冬季土壤氮矿化无显著影响。这表明,该区冬季土壤氮矿化以硝化过程为主,硝化和氨化过程可能受不同微生物群落调控;短时期内,未来气候变化所导致的雪被减少对该区森林冬季土壤氮转化影响可能不明显。     

雪被斑块对川西亚高山森林凋落物冬季分解过程中钾和钠动态的影响

亚高山森林冬季不同厚度雪被斑块下显著的冻融格局差异可能对凋落物分解过程中钾(K)和钠(Na)的动态具有重要影响, 然而已有研究还不足以清晰地认识这一过程。以川西亚高山森林6种代表性树种凋落物为研究对象, 采用凋落物网袋法, 探讨冬季不同厚度雪被斑块下雪被形成期、覆盖期和融化期凋落物分解过程中K和Na元素释放或富集的特征。整个雪被覆盖时期, 6种凋落物分解过程中Na均表现为富集特征, 且以覆盖期最为明显; 而K表现为释放特征, 以雪被融化期释放率最大。相对于其他雪被斑块, 厚型和中型雪被斑块下凋落物K释放率相对较高; 除康定柳(Salix paraplesia)和高山杜鹃(Rhododendron lapponicum)外, 其他物种凋落物在厚型和中型雪被斑块下Na富集率较高。同时, 统计分析结果表明, 物种和雪被显著影响冬季不同关键时期凋落物K和Na元素动态。除红桦(Betula albosinensis)和方枝柏(Sabina saltuaria)凋落物外, 温度因子与凋落物K和Na动态变化呈显著正相关。这些结果表明气候变暖情景下冬季雪被覆盖的减小将抑制亚高山森林冬季凋落物分解过程中K和Na元素的释放, 但是释放程度受凋落物质量和雪被覆盖时期的显著影响。     

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.     

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.     

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。     

雪被斑块对川西高山森林凋落叶N和P释放的影响

采用凋落物网袋法,研究冬季不同关键时期雪被斑块对川西高山森林6种代表性树种凋落物分解过程中N和P释放的影响.结果表明: 整个雪被覆盖季节凋落物N表现为富集,P表现为释放,且雪被融化期P释放速率最大.厚型和中型雪被斑块下凋落物P释放速率大于薄型和无雪被斑块,而薄型和无雪被斑块下凋落物的N释放速率明显较高.6种凋落物N释放率和释放速率与日均温呈显著负相关;除岷江冷杉外,其他树种凋落物P释放率和释放速率与日均温表现为正相关.气候变暖情景下冬季雪被覆盖的减小将促进高山森林冬季凋落物分解过程中N释放,抑制P释放.     

Forest Gaps Alter the Total Phenol Dynamics in Decomposing Litter in an Alpine Fir Forest

The total phenol content in decomposing litter not only acts as a crucial litter quality indicator, but is also closely related to litter humification due to its tight absorption to clay particles. However, limited attention has been focused on the total phenol dynamics in foliar litter in relation to forest gaps. Here, the foliar litter of six representative tree species was incubated on the forest floor from the gap center to the closed canopy of an alpine Minjiang fir (Abies faxoniana) forest in the upper reaches of the Yangtze River and eastern Tibetan Plateau. The dynamics of total phenol concentration in the incubated litter was measured from November 2012 to October 2014. Over two-year incubation, 78.22% to 94.06% of total phenols were lost from the foliar litter, but 52.08% to 86.41% of this occurred in the first year. Forest gaps accelerated the loss of total phenols in the foliar litter in the winter, although they inhibited the loss of total phenols during the growing season in the first year. In comparison with the effects of forest gaps, the variations of litter quality among different species were much stronger on the dynamics of total phenols in the second year. Overall, the loss of total phenols in the foliar litter was slightly higher in both the canopy gap and the expanded gap than in the gap center and under the closed canopy. The results suggest that the predicted decline in snow cover resulting from winter warming or vanishing gaps caused by forest regeneration will retard the loss of total phenol content in the foliar litter of alpine forest ecosystems, especially in the first decomposition year.     

Spatial characteristics in decomposition rate of foliar litter and controlling factors in Chinese forest ecosystems

凋落物分解是森林生态系统碳循环的重要组成部分。建立中国森林凋落叶分解速率数据库, 分析凋落叶分解速率与其主要影响因素之间的关系, 对精确地预测中国森林生态系统碳收支具有重要意义。该研究通过收集已报道的中国森林凋落叶分解常数(k)及其相关变量, 分析探讨地理因素(纬度、经度和海拔)、气候因素(年平均气温和年降水量)、凋落叶质量(氮、磷、钾、木质素、木质素:氮和碳氮比)和叶特性(常绿与落叶、阔叶与针叶)对中国森林凋落叶分解速率的影响。结果表明, 在国家尺度上, k随年平均气温、年降水量、氮、磷和钾的增加而增加, 随纬度、经度、海拔、碳氮比、木质素和木质素:氮的增大而减小, 叶特性对k的影响不显著。气候与地理因素(年平均气温、年降水量和纬度)能解释k值变异的34.1%, 凋落叶质量(氮、钾、木质素和木质素:氮)能解释k值变异的21.7%, 它们能共同解释k值变异的74.4%。了解森林凋落叶分解速率在国家尺度上的格局和主控因素可为中国森林生态系统碳循环相关模型提供基础参数。     

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.     

亚高山森林林窗大小对凋落叶木质素降解的影响

木质素降解是认识高寒森林凋落物分解过程的关键环节,可能受到林窗大小及其在不同季节水热环境的影响。采用分解袋法,研究了川西亚高山森林不同面积大小林窗下红桦(Betula albo-sinensis)和岷江冷杉(Abies faxoniana)凋落叶在初冻期、深冻期、融化期、生长季节初期、生长季节中期和生长季节后期的木质素分解动态特征。研究结果表明,采样时间和林窗面积大小对两种凋落叶的木质素降解均有显著影响。经历1a分解,红桦凋落叶的木质素降解了21.53%—27.65%,而岷江冷杉凋落叶的木质素富集了7.95%—19.40%。较大林窗促进了冬季岷江冷杉凋落叶和生长季节红桦凋落叶木质素的降解,抑制了冬季红桦凋落叶木质素的降解;而生长季节岷江冷杉凋落叶木质素富集速率则为林下大林窗中林窗小林窗。逐步回归分析表明,凋落叶木质素的降解过程在冬季主要受到负积温和土壤冻融循环次数的影响(木质素结构的物理破碎),而在生长季节则主要受到平均温度和正积温的影响(木质素的生物降解)。可见,川西亚高山森林木质素降解受林窗格局变化的显著影响,且林窗大小对凋落叶木质素降解的影响与物种和分解时期有关。     

Effects of seasonal snow cover on decomposition and carbon,nitrogen and phosphorus release of Picea schrenkiana leaf litter in Mt. Tianshan,Northwest China

季节性雪被下显著的冻融格局差异可能对干旱区山地森林凋落叶分解过程产生重要影响, 但一直未见深入研究。2015年10月至2016年10月, 采用凋落物分解袋法, 研究了天山典型树种雪岭云杉(Picea schrenkiana)凋落叶在季节性雪被覆盖下的3个关键时期(冻融期、深冻期、融冻期)以及生长季(生长季早期和生长季末期)的分解动态和碳、氮、磷释放特征。结果表明: (1)经过一年的分解, 不同雪被厚度下雪岭云杉凋落叶分解率为24.6%-29.2%, 且存在显著性差异。分解系数k值厚雪被覆盖最大, 无雪被覆盖最小。(2)冬季雪被覆盖期雪岭云杉凋落叶分解对当年分解总量的贡献达46.0%- 48.5%, 其中对冻融期凋落叶分解影响较为明显。(3)随着凋落叶的分解, 雪岭云杉凋落叶氮含量总体呈增加趋势; 碳含量和碳氮比大致呈下降趋势, 在深冻期和生长季末期不同雪被处理下碳含量呈显著性差异; 而凋落叶磷含量呈不规则变化趋势, 且在冻融期和融冻期不同雪被厚度下呈显著性差异。(4)整个雪被覆盖季节凋落叶氮元素表现为富集, 碳和磷元素表现为释放; 其中, 在融冻期薄雪被和中雪被处理下碳元素富集率最大, 在冻融期薄雪被、中雪被和厚雪被处理下, 融冻期无雪被和厚雪被下以及生长季早期中雪被和厚雪被下氮元素富集率最大, 而雪被对凋落叶磷释放的影响不显著。     

Degree of Humification in Fresh Litter from a Subtropical Mixed Plantation Forest in Southwest China

The humification degree of fresh litter directly controls the accumulation of soil humus derived from plant litter, but very little information on this process is available. Planted forests are well known to restrict soil fertility, which is often indicated by the soil humus level. In this study, fresh litter was collected during different plant phenological stages during 2016 and 2017 in a mixed plantation in Southwest China. The values of hue coefficient ΔlogK (absorbance ratio of 400 nm and 600 nm on a logarithmic scale), optical density E4/E6 (absorbance ratio of 400 nm and 600 nm) and A600/C (absorbance at 600 mm per mg of carbon per ml of extraction) and the concentration of extractable humus carbon (HC) were determined in four litter components (foliar, twigs, reproductive organs and miscellaneous) of the dominant species (Pterocarya stenoptera, Quercus acutissima, Cunninghamia lanceolata and Toxicodendron vernicifluum). All of the litter components exhibited obvious humification characteristics, and showed the highest concentration of extractable HC during the leaf maturation period. The miscellaneous and foliar litters showed greater humification than the other litter types. The components of Pterocarya stenoptera litter exhibited greater degrees of humification than those of the other species, with lower ΔlogK and E4/E6 values and higher A600/C values. The litter from coniferous and evergreen species showed lower humification than that from broad-leaf and deciduous species regardless of the litter component examined. The present results provide new insights into the management of plantations and theoretical data to accurately improve the quality of plantations and maintain soil fertility under a global change.