Effects of grazing intensity and grazing exclusion on litter decomposition in the temperate steppe of Nei Mongol,China

Aims Grazing intensity and grazing exclusion affect ecosystem carbon cycling by changing the plant community and soil micro-environment in grassland ecosystems. The aims of this study were: 1) to determine the effects of grazing intensity and grazing exclusion on litter decomposition in the temperate grasslands of Nei Mongol; 2) to compare the difference between above-ground and below-ground litter decomposition; 3) to identify the effects of precipitation on litter production and decomposition. Methods We measured litter production, quality, decomposition rates and soil nutrient contents during the growing season in 2011 and 2012 in four plots, i.e. light grazing, heavy grazing, light grazing exclusion and heavy grazing exclusion. Quadrate surveys and litter bags were used to measure litter production and decomposition rates. All data were analyzed with ANOVA and Pearson’s correlation procedures in SPSS. Important findings Litter production and decomposition rates differed greatly among four plots. During the two years of our study, above-ground litter production and decomposition in heavy-grazing plots were faster than those in light-grazing plots. In the dry year, below-ground litter production and decomposition in light-grazing plots were faster than those in heavy-grazing plots, which is opposite to the findings in the wet year. Short-term grazing exclusion could promote litter production, and the exclusion of light-grazing could increase litter decomposition and nutrient cycling. In contrast, heavy-grazing exclusion decreased litter decomposition. Thus, grazing exclusion is beneficial to the restoration of the light-grazing grasslands, and more human management measures are needed during the restoration of heavy-grazing grasslands. Precipitation increased litter production and decomposition, and below-ground litter was more vulnerable to the inter-annual change of precipitation than above-ground litter. Compared to the light-grazing grasslands, heavy-grazing grasslands had higher sensitivity to precipitation. The above-ground litter decomposition was strongly positively correlated with the litter N content (R² = 0.489, p < 0.01) and strongly negatively correlated with the soil total N content (R² = 0.450, p < 0.01), but it was not significantly correlated with C:N and lignin:N. Below-ground litter decomposition was negatively correlated with the litter C (R² = 0.263, p < 0.01), C:N (R² = 0.349, p < 0.01) and cellulose content (R² = 0.460, p < 0.01). Our results will provide a theoretical basis for ecosystem restoration and the research of carbon cycling.     

Effects of streams on lignin degradation during foliar litter decomposition in an alpine forest

AimsStreams are widely distributed in alpine forests, and litter decomposition in which is an important component of material cycling across the forest landscape. The leaching and fragmenting effects as well as the unique environmental factors in streams may have significant impacts on lignin degradation during litter decomposition, but studies on this are lacking.
Methods Using litterbag methods, we investigated the dynamics of lignin mass remaining and concentration (percent litter mass, %) during the decomposition of four foliar litters, which varied significantly in the initial litter chemical traits, from the dominant species of Salix paraplesia, Rhododendron lapponicum, Sabina saltuaria, and Larix mastersiana under different habitats (forest floor, stream, and riparian zone) in the upper reaches of the Minjiang River.
Important findings After two year’s incubation, litter lignin mass remaining for a specific litter species varied significantly (p < 0.05) among habitats, with an order of stream < riparian zone < forest floor. Lignin was degraded substantially in the early stage of litter decomposition process, and the lignin concentration first decreased and then increased with the proceeding of litter decomposition, but varied significantly (p < 0.05) among different litter species. Lignin mass showed a general trend of decrease across the 2-year decomposition course. In addition, habitat type, decomposition period and microenvironmental factors (e.g., temperature, pH value and nutrient availability) showed substantial influences on lignin degradation rate. These results suggest that the traditional view that lignin was relatively recalcitrant with an increase of concentration in the early stage of litter decomposition is challenged, but the loss of lignin in the early phrase is in line with recent findings about the fate of lignin during litter decomposition. Moreover, the significant differences of lignin degradation rates among different decomposition period and habitat types indicated that local-scale environmental factors can play a significant role in litter decomposition and lignin degradation processes.     

细根对竹林-阔叶林界面两侧土壤养分异质性形成的贡献

土壤养分异质性是竹林-阔叶林界面(bamboo and broad-leaved forest interface, 以下简称竹阔界面)的重要特征, 细根生长、周转和分解影响土壤养分供应能力, 但其在竹阔界面养分异质性形成中的贡献尚不清楚。该文选取竹阔界面两侧的毛竹(Phyllostachys pubescens)林和常绿阔叶林为研究对象, 开展土壤养分(C、N、P)含量、细根生物量及周转、细根分解及养分回归等指标的对比研究。结果表明: (1)竹阔界面两侧毛竹林和常绿阔叶林土壤养分差异明显, 毛竹林0-60 cm土壤有机碳(SOC)和土壤总氮(STN)含量分别为20.51和0.53 g·kg^-1, 常绿阔叶林0-60 cm土壤有机碳(SOC)和土壤总氮(STN)含量分别为13.42和0.26 g·kg^-1, 前者比后者分别高出34.53%和50.35%, 但毛竹林土壤全磷(STP)含量低于常绿阔叶林25.54%; (2)竹阔界面两侧细根生物量、养分密度及养分回归量差异明显, 毛竹林细根生物量高达1201.60 g·m^-2, 是常绿阔叶林的5.86倍; 养分密度分别为591.42 g C·m^-2、5.44 g N·m^-2、0.25 g P·m^-2, 分别是常绿阔叶林的6.12倍、3.77倍和3.11倍; 年均养分回归量分别为278.54 g C·m^-2·a^-1、2.36 g N·m^-2·a^-1、0.11 g P·m^-2·a^-1, 是常绿阔叶林的6.93倍、4.29倍和3.67倍; (3)细根对界面两侧土壤SOC、STN异质性形成的年均潜在贡献分别为76.79%和28.33%, 但对STP异质性形成起减缓作用, 贡献率为6.17%。这些结果说明毛竹扩张可以改变常绿阔叶林土壤的养分状况, 且细根对不同养分的异质性形成贡献不一致, 是土壤SOC、STN异质性形成的重要原因。     

Response of fine roots to precipitation change: A meta-analysis

细根对土壤水分含量变化十分敏感, 增加和减少降水直接影响土壤水分含量。为探索细根对降水变化的响应, 该文从48篇已发表的国内外研究论文中搜集到202组数据, 通过meta分析的方法揭示细根生物量、生产量、周转率、根长度密度、比根长及细根分解对增加和减少降水的一般响应规律, 用加权响应比评价降水对细根各指标的影响效应, 降水变化对细根分解的影响用土壤微生物生物量碳的响应比衡量。结果表明: 1)不同类型植物的细根对降水变化的响应程度不同, 灌木细根的响应强于乔木。2)细根各指标对降水变化的响应存在土层空间异质性, 并且降水变化量为50%时细根响应最显著。降水增加50%时, 显著增加20-40 cm土层的细根生物量和0-10 cm土层的细根比根长, 降水减少50%时, 显著减少20-40 cm土层的细根生产量和增加0-10 cm土层的细根根长度密度。3)降水变化实验持续时间的长短会影响细根的响应程度, 短期实验中细根通过形态适应对降水变化做出应对, 而长期实验中细根通过重新分配生物量对降水变化做出响应。4)增加降水促进了细根养分归还, 致使土壤微生物得到了充足的底物资源, 提高了自身活性, 使细根分解加快。     

Dynamics in foliar litter decomposition for Pinus koraiensis and Quercus mongolica in a snow-depth manipulation experiment

气候变化导致的冬季雪被格局变化将改变地表水热环境及分解者活性, 从而显著影响高寒地区森林凋落物分解过程。2014-2016年采用凋落物分解袋法, 研究了帽儿山森林生态站人工林控雪模拟试验下红松(Pinus koraiensis)和蒙古栎(Quercus mongolica)的凋落叶于雪被期和无雪期不同阶段的分解动态。控雪试验包括增雪、除雪和对照3个处理。结果发现: 树种、控雪处理、分解阶段以及环境因子(凋落物层平均温度、冻融循环次数、有机层全氮、全磷含量等)均影响着凋落叶分解率。分解试验的两年内, 不同控雪处理下红松凋落叶的分解率为52.1%-54.5%, 蒙古栎为53.9%-59.1%。两种凋落叶的分解系数均以增雪处理最大, 除雪处理最小。此外, 控雪处理改变了两种凋落叶雪被期或无雪期对分解总量的贡献率。与对照相比, 增雪处理使红松和蒙古栎凋落叶雪被期的分解贡献率分别提高9.1%和10.4%; 而除雪处理使两种凋落叶无雪期的分解贡献率分别提高10.4%和12.7%。因此, 由气候变化带来的冬季雪被改变不但会显著影响温带森林凋落叶的分解过程, 而且会改变雪被期和无雪期的分解量对年分解总量的贡献率。     

Interactive effects of soil warming and nitrogen addition on fine root production of Chinese fir seedlings

Aims There have been a large number of studies on the independent separate responses of fine roots to warming and nitrogen deposition, but with contradictory reporting. Fine root production plays a critical role in ecosystem carbon, nutrient and water cycling, yet how it responds to the interactive warming and nitrogen addition is not well understood. In the present study, we aimed to examine the interactive effects of soil warming and nitrogen addition on fine root growth of 1-year-old Chinese fir (Cunninghamia lanceolata) seedlings in subtropical China.
Methods A mesocosm experiment, with a factorial design of soil warming (ambient, +5 °C) and nitrogen addition (ambient, ambient + 40 kg·hm^-2·a^-1, ambient + 80 kg·hm^-2·a^-1), was carried out in the Chenda State-owned Forest Farm in Sanming City, Fujian Province, China. Fine root production (indexed by the number of fine roots emerged per tube of one year) was measured biweekly using minirhizotrons from March of 2014 to February of 2015.
Important findings (1) The two-way ANOVA showed that soil warming had a significant effect on fine root production, while nitrogen addition and soil warming × nitrogen addition had no effect. (2) The three-way ANOVA (soil warming, nitrogen addition and diameter class) showed that soil warming, diameter class and soil warming × diameter class had significant effects on fine root production, especially for the number of fine roots in 0-1 mm diameter class that had been significantly increased by soil warming. Compared with the 1-2 mm roots, the 0-1 mm roots seemed more flexible. (3) Repeated measures of ANOVA (soil warming, nitrogen addition and season) showed that soil warming, season, soil warming × season, and soil warming × nitrogen addition × season had significant effects on fine root production. In spring, the number of fine roots was significantly increased both by soil warming and soil warming × season, while soil warming, nitrogen addition, soil warming × nitrogen addition significantly decreased fine root production in the summer. (4) Soil warming, soil layer, soil warming × soil layer had significant effects on fine root production. The number of in-growth fine roots was significantly increased by soil warming at the 20-30 cm depth only. It seemed that warming forced fine roots to grow deeper in the soil. In conclusion, soil warming significantly increased fine root production, but they had different responses and were dependent of different diameter classes, seasons and soil layers. Nitrogen addition had no effect on fine root production. Only in spring and summer, soil warming and nitrogen addition had significant interactive effects.     

Effects of short-term nitrogen addition on fine root biomass,lifespan and morphology of Castanopsis platyacantha in a subtropical secondary evergreen broad-leaved forest

Aims Fine roots are the principal parts for plant nutrients acquisition and play an important role in the underground ecosystem. Increased nitrogen (N) deposition has changed the soil environment and thus has a potential influence on fine roots. The purpose of this study is to reveal the effect of N deposition on biomass, lifespan and morphology of fine root.Methods A field N addition experiment was conducted in a secondary broad-leaved forest in subtropical China from May 2013 to September 2015. Three levels of N treatments: CK (no N added), LN (5 g·m^-2·a^-1), and HN (15 g·m^-2·a^-1) were applied monthly. Responses of fine root biomass, lifespan, and morphology of Castanopsis platyacantha to N addition were analyzed by using a minirhizotron image system from April 2014 to September 2015. Surface soil sample (0-10 cm) was collected in November 2014 and soil pH value, and concentrations of NH₄⁺-N and NO₃^--N were measured.Important findings The biomass and average lifespan of the fine roots of C. platyacantha were 128.30 g·m^-3 and 113-186 days, respectively, in 0-45 cm soil layer. Nitrogen addition had no significant effect on either fine root biomass or lifespan in 0-45 cm soil layer. However, LN treatment significantly decreased C. platyacantha root superficial area in 0-15 cm soil layer. HN treatment significantly decreased soil pH value. Our study indicated that short-term N addition influences soil inorganic N concentration and thus decreased pH value in surface soil, and thereafter affect fine root morphology. Short-term N addition, however, did not affect the fine root biomass, lifespan and morphology in subsoil.     

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。     

亚热带不同树种凋落叶分解对氮添加的响应

为探究不同质量凋落物对氮(N)沉降的响应, 该研究采用尼龙网袋分解法, 在亚热带福建三明格氏栲(Castanopsis kawakamii)自然保护区的米槠(Castanopsis carlesii)天然林, 选取4种本区常见的具有不同初始化学性质的树种凋落叶进行模拟N沉降(N添加)分解实验(施N水平为对照0和50 kg·hm ^-2·a ^-1)。研究结果表明: 在2年的分解期内, 对照处理的各树种凋落叶的分解速率依次为观光木(Michelia odora, 0.557 a ^-1)、米槠(0.440 a ^-1)、台湾相思(Acacia confusa, 0.357 a ^-1)、杉木(Cunninghamia lanceolata, 0.354 a ^-1); N添加处理凋落叶分解速率依次为观光木(0.447 a ^-1)、米槠(0.354 a ^-1)、杉木(0.291 a ^-1)、台湾相思(0.230 a ^-1), 除杉木凋落叶外, N添加显著降低了其他3种凋落叶分解速率。N添加不仅使4种树木凋落叶分解过程中的N释放减慢, 同时还抑制凋落叶化学组成中木质素和纤维素的降解; N添加在凋落叶分解过程中总体上提高β-葡萄糖苷酶(βG)和酸性磷酸酶活性, 对纤维素水解酶的活性影响不一致, 而降低β-N-乙酰氨基葡萄糖苷酶活性和酚氧化酶活性。凋落叶分解速率与凋落叶中的碳获取酶(βG)活性以及其化学组分中的可萃取物含量极显著正相关, 与初始碳浓度、纤维素和木质素含量极显著负相关, 与初始N含量没有显著相关性。凋落物类型和N添加的交互作用虽未影响干质量损失速率, 但对木质素和纤维素的降解具有显著效应。综上所述, 化学组分比初始N含量能更好地预测凋落叶分解速率, 而N添加主要通过抑制分解木质素的氧化酶(如PHO)来降低凋落叶分解速率。     

地表臭氧浓度升高与干旱交互作用对杨树非结构性碳水化合物积累和叶根分配的短期影响

人类活动加剧和全球变化导致植物在生长季同时受到高浓度地表臭氧(O₃)和干旱的双重胁迫。为了探究两者对植物非结构性碳水化合物(TNC)积累和分配的影响, 该实验采用开顶式气室研究了2种O₃浓度(CF, 过滤空气; NF40, NF (未过滤空气) + 40 nmol·mol ^-1 O₃)和2个水分处理(对照, 充分灌溉; 干旱, 非充分灌溉)及其交互作用对杨树基因型‘546’ (Populus deltoides cv. ‘55/56’ × P. deltoides cv. ‘Imperial’)叶片和细根中TNC及其组分(葡萄糖、果糖、蔗糖、多糖、总可溶性糖和淀粉)含量的影响。结果表明: O₃浓度升高显著降低杨树叶片中淀粉和TNC的含量, 增加葡萄糖、果糖和总可溶性糖含量, 但对细根中淀粉和总可溶性糖含量的影响不显著。干旱胁迫显著增加细根中果糖和多糖含量, 降低蔗糖含量, 但对叶片中淀粉和总可溶性糖含量的影响不显著。充分灌溉下O₃浓度升高显著增加了杨树叶片多糖和总可溶性糖含量, 而干旱下O₃浓度升高显著增加了TNC含量的根叶比。该研究结果发现O₃主要影响叶片中TNC及各组分的含量, 而干旱主要影响细根中TNC及各组分的含量。从杨树叶片TNC的响应来看, 适度的水分限制有助于减缓O₃的负面伤害。     

Effect of geographical sources and biochemical traits on plant litter decomposition in a peatland

不同地理来源的泥炭地植物残体在同一环境中的分解速率一直缺乏比较研究。该研究沿纬度梯度, 选择大九湖、哈泥和满归3处泥炭地, 以三地的10种植物为分解材料, 使用分解袋包装, 埋藏于长白山哈泥泥炭地, 开展为期1年的分解实验, 研究地理来源及生物化学属性对泥炭地植物残体分解的影响。结果表明, 如不考虑物种差异, 从总体上看, 随着纬度增加, 3处泥炭地植物残体的初始氮(N)含量下降, 初始木质素含量、碳氮比(C/N)和木质素/N上升。经一年分解后残体分解速率因植物类群不同而不同, 桦木属(Betula)和薹草属(Carex)植物残体的干质量损失率均接近50%, 远大于泥炭藓属(Sphagnum)植物(约为10%)。3处来源地植物残体干质量损失率总体上无差异, 但比较同种植物残体发现, 来自中纬度泥炭地哈泥的中位泥炭藓(S. magellanicum)的干质量损失率(19%)远高于来自高纬度泥炭地满归的(9%)。制约残体分解的因素因植物类群不同而不同, 残体初始总酚/N是决定属间残体干质量损失率差异的重要指标。薹草属植物初始N含量和C/N与残体分解速率、泥炭藓属植物初始Klason木质素含量和总酚/N与残体分解速率均呈正相关关系。该研究一定程度上表明, 若以纬度降低指代气候变暖, 当前持续的气候变暖可能通过改变高纬度泥炭地的植物组成和植物的生物化学属性, 来改变植物残体分解速率, 进而影响泥炭地的碳汇功能。     

鄂西南亚高山湿地泥炭藓的生长与分解

泥炭藓(Sphagnum)是湿地土壤碳的重要来源, 在土壤碳累积过程中发挥着关键作用, 但有关亚热带湿地泥炭藓生长与分解的研究鲜有报道。该研究选择鄂西南亚高山泥炭藓湿地为研究区域, 原位开展不同微生境泥炭藓的生长及其凋落物的分解实验, 室内测试凋落物的化学成分, 探讨亚热带亚高山湿地泥炭藓的生长与分解规律。结果表明: 泥炭藓在自然状态生长12个月后, 丘上和丘间两种微生境下泥炭藓的平均高度增长量分别为2.9和2.7 cm, 对应的净生产量分别为270.94和370.88 g·m ^-2, 生长时间与微生境对泥炭藓的高度增长量及净生产量均有显著影响, 且两者之间存在交互作用, 但是两种微生境下泥炭藓的生长变化过程不同; 两种微生境下泥炭藓的平均生长速率(2017年7-10月)为0.33 mm·d ^-1, 其生长速率高于寒温带地区。另外, 分解时间对泥炭藓的分解量有显著影响, 其残留率随时间增加表现为先减少后增加的趋势。12个月后, 丘间、丘上和水坑3种微生境下最终残留率分别为100.67%、90.54%和85.63%。凋落物中碳含量、碳氮比和多酚含量相比初始值均有所下降, 氮含量则为增加。同时, 微生境对凋落物分解的影响取决于分解时间。分解3个月时, 微生境之间凋落物的分解量差异显著, 其他时间段差异不明显。     

Interactive effects of phenolic acid and nitrogen on morphological traits of poplar (Populus × euramericana ‘Neva’) fine roots

Aims The relationship between rhizosphere process and fine root growth is very close but still obscure. In poplar plantation, phenolic acid rhizodeposition and soil nutrient availability were considered as two dominant factors of forest productivity decline. It is very hard to separate them in the field and they might show an interactive effect on fine root growth. The objective of this study is to examine the influence of phenolic acids and nitrogen on branch orders of poplar fine roots and to give a deeper insight into how the ecological process on root-soil interface affected fine root growth as well as plantation productivity. Methods The cuttings of health annual poplar seedlings (I-107, Populus × euramericana ‘Neva’) serve as experiment materials, and were cultivated under nine conditions, including three concentration of phenolic acids at 0X, 0.5X, 1.0X (here, X represented the contents of phenolic acids in the soil of poplar plantation) and three concentration of nitrogen at 0 mmol·L^-1, 10 mmol·L^-1, 20 mmol·L^-1, based on Hoagland solution. The roots were all separated from poplar seedlings after 35 days, and 30 percent of total fine roots of every treatment were taken as fine root samples. These fine roots were grouped according to 1 to 5 branch orders, and then the morphological traits of each group of fine roots were scanned via root analyzer system (WinRHIZO, Regent Instruments Company, Quebec, Canada) including total length, surface area, volume and average diameter. Meanwhile, the dry mass of fine root samples of every order was measured to calculate specific root length (SRL), root tissue density (RTD). All data were analyzed via SPSS 17.0 software, and interactive effect of phenolic acids and nitrogen on roots was analyzed through univariate process module. Principal component analysis (PCA) and redundancy analysis (RDA) were conducted via Canoco 4.5 software. Important findings Under the conditions without phenolic acids application, the fine roots growth was significantly inhibited in deficiency and higher nitrogen treatments, especially for 1-3 order roots. Only specific root length appeared decreased with nitrogen level, and other traits of fine roots did not demonstrate linear relationship with nitrogen concentrations. Compared to 0.5X phenolic acids treatment, 1.0X phenolic acids significantly promoted the diameter and volume of 1-2 order roots (p < 0.05). Both phenolic acids and nitrogen demonstrated influence on poplar fine root traits. However, the diameter and volume of 1-2 order roots were significantly affected by phenolic acids, while the total length and surface area of 4-5 order roots was affected by nitrogen. Two way ANOVA showed that phenolic acids and nitrogen made a synergistic or antagonistic effect on morphological building of fine roots. Furthermore, PCA and RDA indicated that the interactive effects of phenolic acids and nitrogen led to significant differences among 1-3 order, 4th order and 5th order of poplar fine roots. The PC1 explained about 60.9 percent of root morphological variance, which was related to foraging traits of roots. The PC2 explained 25.3 percent of variance, which was related to root building properties. The response of poplar roots to phenolic acids and nitrogen was closely related to root order, and nitrogen played more influence on poplar roots than phenolic acids. Thus, phenolic acids and nitrogen level would affect many properties of root morphology and foraging in rhizosphere soil of poplar plantation. But nitrogen availability would serve as a dominant factor influencing root growth, and soil nutrient management should be critical to productivity maintenance of poplar plantation.     

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.     

Effects of leachate from understory medicinal plants on litter decomposition and soil enzyme activities of Betula albo-sinensis and Eucommia ulmoides

Aims Forest litter decomposition is an important factor affecting nutrient cycling and ecosystem stability. In a complex system with forest and understory medicinal plants, leachate from the medicinal plants enriched in plant secondary metabolites (PSM) may inhibit litter decomposition and soil enzyme activity of forest trees. Thus, inspection on whether or not this phenomenon exits is one important basis for selecting understory medicinal plants.Methods In this paper, typical forest species Betula albo-sinensis and Eucommia ulmoides and six species of common medicinal plants (Corydalis bungeana, Mentha haplocalyx, Houttuynia cordata, Nepeta cataria, Gynostemma pentaphyllum and Prunella vulgaris) in Qinling Mountains area were taken as objects, and the litter decomposition experiment was carried out. The leachate (water-extraction solution) from the stems and leaves of the medicinal materials were sprayed onto the litter in order to study the effects of leachate from understory plants on forests litter decomposition, nutrient release (carbon, nitrogen and phosphorus) and soil enzyme activity.Important findings For litter of B. albo-sinensis, the decomposition half-life and the turnover period were extended by 76% and 4.3 times, respectively, under H. cordata leachate treatment and the inhibitory effects on the release of carbon and nitrogen were also significant. While under G. pentaphyllum leachate treatment, the half-life of litter decomposition and turnover period were extended by 35% and 2.7 times, respectively, and the inhibitory effects on the release of carbon, nitrogen and phosphorus were all significant. The leachate from these two species of medicinal plants displayed significant inhibitory effects on seven kinds of soil enzymes (invertase, carboxymethyl cellulase, β-glucosidase, dehydrogenase, polyphenol oxidase, protease and phosphatase) activity. For litter of E. ulmoides, the decomposition half-life and the turnover period were extended by 1.7 times and 4.2 times respectively, under H. cordata leachate treatment; while they were extended by 1 times and 9 times respectively, under G. pentaphyllum leachate treatment. The leachate from these two species of medicinal plants displayed significant inhibitory effects on the release of carbon, nitrogen and phosphorus from litter decomposition and the activities of all seven kinds of soil enzymes. Therefore, results suggested that H. cordata and G. pentaphyllum should not be planted under B. albo-sinensis and E. ulmoides forests, or the interplanting density must be low to reduce the inhibitory effects of litter decomposition.     

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。     

Carbon,nitrogen and phosphorus stoichiometry in leaves and fine roots of dominant plants in Horqin Sandy Land

Aims The stoichiometric characteristics of carbon (C), nitrogen (N) and phosphorus (P) in plant organism is vital to understand plant adaptation to environment. In particular, the correlations of elemental stoichiometric characteristics between leaf and fine root could provide insights into the interaction and balance among the plant elements, nutrient use strategies and plant response to global change.Methods We measured C, N, P contents and C:N, C:P, N:P in leaves and fine roots of 60 dominant plants in Horqin sandy land. The 60 plant species were classified into five life forms and two categories such as perennial forb, annual forb, perennial grass, annual grass, shrub, legume, and non-legume. We statistically analyzed the differences and correlations of C, N and P stoichiometry either between fine root and leaf or among five life forms.Important findings The average C, N and P concentrations in leaves of 60 plant species in Horqin sandy land are 424.20 mg·g^-1, 25.60 mg·g^-1 and 2.10 mg·g^-1, respectively. In fine roots, the corresponding element concentrations are 434.03 mg·g^-1, 13.54 mg·g^-1, 1.13 mg·g^-1. N and P concentrations in leaf are approximately twice as high as averages in fine root. Furthermore, similar N:P between leaf and fine root indicates conservative characteristic of elemental stoichiometry in plant organism, suggesting that nutrients distribution is proportional between aboveground and underground of plants. There are significant difference of C, N, P, C:N, C:P and N:P in leaf and root among five life forms. N and P in forb and C:N and C:P in grass are averagely higher than those in other life forms. N:P in annual forb and grass, however, are lower than those in other life forms. C, N in legume are higher than those in non-legume, while C:N in legume is lower than in non-legume. These results imply that nutrient use strategies are significantly different among plant life forms. Correlations analysis showed that N and P in leaf or fine root positively correlated, but C and N, C and P in fine root negatively correlated, suggesting coupling relationship among C, N and P in leaf and fine root. Subsequently, we detected positively significant correlations in C, N, P and their ratios between leaf and fine root, suggesting proportional distribution of photosynthate and nutrient between aboveground and underground during plant growth. Generally, these results supplied fundamental data to understand mass turnover and nutrients cycling of leaves and roots in sand land.     

Leaf decomposition and nutrient release of dominant species in the forest and lake in the Jiuzhaigou National Nature Reserve,China

AimsLitter decomposition is an important ecological process in nutrient cycling and productivity of ecosystems. Our objective is to quantify the differences of litter decomposition and nutrient release (N and P) under the forest and in an alpine lake among the dominant tree species in the Jiuzhaigou National Nature Reserve.
Methods Fresh leaf litters of Abies ernestii, Pinus tabulaeformis, Betula albo-sinensis, and Salix cupularis were collected and placed in bags under the forest and in an alpine lake for a year.
Important findings The mass remaining ratio (MR) of the leaf litters was well predicted with Olson’s decay model (r > 0.93, p < 0.01). The time for 99% decomposition was the shortest for S. cupularis (6.80 a), followed by B. albo-sinensis (10.34 a), A. ernestii (18.88 a), and P. tabulaeformis (27.21 a). These values were 1.48-, 1.55-, 1.80-, and 1.65-folds of the corresponding values in the lake, respectively. Both MR and nitrogen remaining ratio (NR) had significantly negative correlations with the leaf initial N concentration, but significantly positive correlations with the initial C:N. The nutrient release was significantly different among the four species and between the two sites (i.e., forest and alpine lake). The N release of S. cupularis was consistent between forest and the lake (i.e. directly released in the beginning of decomposition), while other species had an obvious N enrichment process before it released. The release of P among was similar among the four species and between the two sites, with a release—enrichment—release pattern. Overall, the leaf litter decomposition appeared as an intricate process that was affected by the litter chemistry and and the environment. The fast litter decomposition in the lake may have a profound influence on the water quanlity in the Jiuzhaigou National Nature Reserve.     

极端干旱区沙土掩埋对凋落物分解速率及盐分含量动态的影响

极端干旱区由于降水稀少, 植被盖度低, 太阳辐射强烈, 以及土壤稳定性差, 导致其凋落物周转不同于非干旱区。为探究极端干旱区凋落物分解规律, 该研究利用凋落物分解袋法, 以塔克拉玛干沙漠南缘沙漠-绿洲过渡带优势物种花花柴(Karelinia caspia)、骆驼刺(Alhagi sparsifolia)和胡杨(Populus euphratica)凋落叶为研究对象, 设置不同的沙土掩埋处理: 地表、2 cm和15 cm埋深, 以模拟自然条件下凋落物分解环境, 测定分解过程中凋落物质量和水溶性盐的变化特征。结果表明: 极端干旱区凋落物分解速率与凋落物初始碳(C)含量、氮(N)含量、C:N和木质素含量的关系与非干旱区存在较大差异, 在地表处理下, 木质素含量越高, 质量损失越快。不同分解环境下凋落物质量和水溶性盐损失具有显著差异, 与15 cm埋深相比, 地表和2 cm埋深处理显著增加了凋落物的质量损失和水溶性盐总量损失。地表处理增加了凋落物分解前期的水溶性盐溶解量。该研究表明, 极端干旱区凋落物分解的驱动机制具有独特性, 由于降水稀少, 土壤微生物的活性较低, 掩埋深度不是驱动凋落物分解的主要因素, 极端干旱区凋落物的分解主要受其他非生物过程如太阳光辐射的影响。     

Decomposition of different root branch orders and its dominant controlling factors in four temperate tree species

细根分解是森林生态系统土壤碳和养分的主要输入途径, 但目前人们对于影响细根分解的主要因素和细根分解模式的了解仍然很少。该研究采用根序划分等级方法, 将红松(Pinus koraiensis)、落叶松(Larix gmelinii)、水曲柳(Fraxinus mandschurica)和白桦(Betula platyphylla)细根组分前四级根划分为两个等级: 一级和二级根混合为低级根, 三级和四级根混合为高级根。利用埋袋法对东北地区4个树种不同根序细根进行连续4年的分解实验, 并对其分解速率以及影响因素进行研究。结果显示, 红松低级根和高级根分解系数分别为0.342和0.461, 落叶松依次分别为0.304和0.436, 水曲柳分别为0.450和0.555, 白桦为0.441和0.579。4个树种均显示低级根分解速率较慢, 而高级根分解速率较快。实验表明, 根系分解系数与酸不溶性物质(AUF)和非结构性碳水化合物(TNC)均具有显著相关性。出现上述结果的主要原因是低级根含有较多的AUF, 很难被分解, 以及含有较少的TNC, 为分解者提供能量较少。