Immediate and legacy effects of snow exclusion on soil fungal diversity and community composition

Background:Soil fungi play crucial roles in ecosystem functions.However,how snow cover change associated with winter warming affects soil fungal communities remains unclear in the Tibetan forest.Methods:We conducted a snow manipulation experiment to explore immediate and legacy effects of snow exclusion on soil fungal community diversity and composition in a spruce forest on the eastern Tibetan Plateau.Soil fungal communities were performed by the high throughput sequencing of gene-fragments.Results:Ascomycota and Basidiomycota were the two dominant fungal phyla and Archaeorhizomyces,Aspergillus and Amanita were the three most common genera across seasons and snow manipulations.Snow exclusion did not affect the diversity and structure of soil fungal community in both snow-covered and snow-free seasons.However,the relative abundance of some fungal communities was different among seasons.Soil fungal groups were correlated with environmental factors(i.e.,temperature and moisture)and soil biochemical variables(i.e.,ammonium and enzyme).Conclusions:These results suggest that the season-driven variations had stronger impacts on soil fungal community than short-term snow cover change.Such findings may have important implications for soil microbial processes in Tibetan forests experiencing significant decreases in snowfall.

Naphthalene exerts non-target effects on the abundance of active fungi by stimulating basidiomycete abundance

As an arthropod biocide,naphthalene has been used in studies of the ecological functions of soil fauna for decades.However,its potential non-target effects on soil microorganisms may affect soil mineralization and litter decomposition processes.Therefore,we conducted an experiment with naphthalene adding to soil surface at a rate of 100 g·m-2 per month to examine the potential non-target effects of this treatment on soil fungal phospholipid fatty acids(PLFAs),18 S rDNA gene copy numbers and community diversity in a subalpine forest of western Sichuan,China.The results showed that naphthalene addition significantly increased fungal PLFAs but did not significantly alter fungal gene copy numbers.A total of 16 phyla,62 genera and 147 Operational taxonomic units(OTUs)were identified through Illumina Mi Seq sequencing analysis.Basidiomycota and Ascomycota were the most abundant phyla in both the control and naphthalene addition plots.Naphthalene addition did not affect the diversity or structure of the soil fungal community,but the increase in some genera of Basidiomycota might contribute to the increase in fungal PLFAs in the naphthalene addition plots.These results suggest that naphthalene exerts non-target effects on the active fungal abundance by stimulating the abundance of specific taxa in subalpine forest soils.The non-target effects of naphthalene on the fungal community should be taken into consideration when it is used to exclude soil fauna.

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 coefficientΔlogK(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 lowerΔlogK 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.

Do root modules still exist after they die?

Background:The terminal branch orders of plant root systems are increasingly known as an ephemeral module.This concept is crucial to recognize belowground processes.However,it is unknown if root modules still exist after they die?Methods:The decomposition patterns of the first five root orders were observed for 3 years using a branch-order classification,a litter-bag method and sequential sampling in a common subalpine tree species(Picea asperata)of southwestern China.Results:Two root modules were observed during the 3-year incubation.Among the first five branch orders,the first three order roots exhibited temporal patterns of mass loss,nutrients and stoichiometry distinct from their woody mother roots throughout the experimental period.This study,for the first time,reported the decomposition pattern of each individual root order and found a similar decomposition dynamic among ephemeral root branches in a forest tree species.Conclusions:Results from this study suggest that root modules may also exist after death,while more data are needed for confirmation.The findings may further advance our understanding of architecture-associated functional heterogeneity in the fine-root system and also improve our ability to predict belowground processes.

Characteristics of fungal community structure during the decomposition of mixed foliage litter from Pinus massoniana and broadleaved tree species in southwestern China

针叶树凋落物相当顽强且养分含量低,而阔叶凋落物通过增加可降解养分和促进微生物代谢来促进针叶凋落物的分解。马尾松(Pinus massoniana)凋落物和三个阔叶凋落物混合可能会增加真菌分解者的多样性和丰富性,并且会随着阔叶树种的数量和比例而有所差异。我们使用高通量测序技术分析了西南地区马尾松与香椿(Toona sinensis),香樟(Cinnamomum camphora)和檫木(Sassafras tzumu)凋落叶混合分解过程中的真菌群落组成和多样性,共设置35种实验处理。研究结果表明,与单一凋落叶相比,除马尾松+香椿,马尾松+檫木+香椿和马尾松+檫木+香樟组合中马尾松凋落叶占70%-80%以及马尾松+檫木+香樟+香椿组合中香椿凋落叶所占比例较小外,其余混合凋落叶均增加了真菌的多样性和丰富性。其中马尾松+香樟+香椿组合中的7:1:2的真菌多样性和丰富性显著高于其他处理。子囊菌门和担子菌门是最主要的优势门,曲霉属是最丰富的真菌群落属。一针一阔(6:4)和一针两阔(阔叶凋落叶占30%-40%)组合的凋落叶在整个分解过程中均表现出较强的协同作用,并且增加了可分解较难分解物质真菌菌群的相对丰度。可见马尾松+香樟+香椿组合中阔叶凋落物占30%-40%比例时增加了真菌的多样性,促进了针叶凋落物中难分解物质的分解。因此,香椿和香樟可能是构建马尾松混交林潜在的候选阔叶伴生树种。

Cumulative cellulolytic enzyme activities and initial litter quality in prediction of cellulose degradation in an alpine meadow of the eastern Tibetan Plateau

植物凋落物分解是决定陆地生态系统碳和养分循环的关键生态系统过程。作为凋落物的主要组成部分,纤维素是与凋落物分解相关的微生物的重要能量来源。纤维素酶在凋落物纤维素降解过程中的重要作用已为人们所熟知,然而纤维素降解的季节模式、累积酶活性和凋落物质量是否能预测高寒草甸的纤维素降解仍是一个未解之谜,这限制了我们对草本植物凋落物纤维素降解的认识。为了探究纤维素降解的季节性模式以及累积纤维素分解酶活性和凋落叶初始质量对纤维素降解的影响,我们在青藏高原东部的高山草甸选取了三种优势种[圆叶筋骨草(Ajuga ovalifolia)、藏羊茅(Festuca wallichanica)和草甸马先蒿(Pedicularis roylei)],进行了为期两年的凋落物网袋分解实验。我们的研究发现,纤维素在第一年中迅速降解且降解率超过50%,而且主要发生在第一个生长季(31.9%-43.3%)在两年的分解过程中,纤维素降解由累积内切葡聚糖酶(R^(2)=0.70),累积纤维二糖水解酶(R^(2)=0.59)和累积1,4-β-葡糖苷酶(R^(2)=0.57)共同驱动。此外,在这两年的分解过程中,纤维素、可溶性有机碳、总酚、木质素的浓度和木质素/N可以解释纤维素降解变异的(52%-78%)。用初始纤维素浓度模型预测纤维素降解效果最佳(R^(2)=0.78)。在凋落物的分解过程中,酶效率和微生物对纤维素分解酶的分配因物种而异。藏羊茅凋落物中纤维素酶效率较高,但质量相对较低。与草甸马先蒿相比,完全降解圆叶筋骨草和藏羊茅的纤维素需要4倍和6.7倍的内切葡聚糖酶、3倍和4.5倍的纤维二糖水解酶、1.2倍和1.4倍的1,4-β-葡糖苷酶。我们的研究结果表明,虽然微生物酶活性和凋落物初始质量都对高山草甸纤维素降解有显著影响,但使用纤维素浓度来预测纤维素降解是简化凋落物分解过程中纤维素降解和C循环模型的好方法。

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。

3个小型高原湖泊水陆交错带中植物叶片pH值变异及其潜在影响因素

陆生植物叶片pH值是与植物生理功能和养分利用状况息息相关的重要植物属性,并随植物功能型和环境的变化而变化。然而,水生植物叶片pH值的变异特征及其与陆生植物间的差异性仍不清楚。在3个自然形成的小型高原湖泊的湖滨植物群落中,我们采集植物、土壤和湖水样品,检测了植物叶片pH值与碳、氮含量以及环境条件(水或土壤pH值、土壤水位状况)。从植物功能型和群落两个水平分析了湖滨植物叶pH值沿水分梯度的变化及其潜在影响因素。研究结果表明,不同类型的水生植物,以及水生、沼生和陆生环境中生长的植物的叶pH存在较大差异;浮叶植物叶片pH值(4.21±0.05)显著低于挺水植物(5.71±0.07)和沉水植物(5.82±0.06);水生草本植物叶片pH值(5.43±0.10)显著低于沼生草本植物(6.12±0.07)和陆生草本植物(5.74±0.05);陆生草本植物叶片pH值显著高于木本植物。植物功能群间叶片pH值的变异可能与叶片的结构、光利用特性和养分特性有关。群落水平的结果与植物功能型水平相一致:水生群落叶片pH值显著低于陆生群落。群落水平叶片pH值可能主要受物种组成、水分条件和环境pH值的影响。本研究首次探索了水生植物的pH值,并且在景观尺度上对比了不同功能型植物的叶片pH值,为深入探索植物pH值变异机制以及其在水生和湿地生态系统中的生态意义提供参考。

植物叶片pH值的测定及样品预处理和保存方法的比较研究

植物叶片pH值是叶片能量运转、新陈代谢、养分平衡等生理活动的重要调节因素。但目前尚缺乏一套合适的植物叶片样品的保存和测试方法,能同时满足叶片样品的长期保存和接近鲜叶片pH值测定的要求。本文通过探索植物叶样品的预处理和保存方式以及叶:水混合比例对叶片pH测定值的影响,提出一种能够长期保存植物叶片,同时对叶片pH值影响较小的测定方法,并且建立不同处理方法间的转换关系。本研究采集多种植物的叶片样品,并分别进行短期冷藏、冷冻和烘干处理保存,以刚采摘的新鲜绿色叶片作为对照,研究叶片样品不同保存方式对其pH值的影响。对烘干绿色叶片按叶片和水1:8的体积比和1:10的质量比分别进行pH值测定,对冷冻叶片:水按质量比为1:10和1:15的比例分别进行测定,分析不同加水比例对所测叶片样品pH值的影响。结果表明,短期冷藏和冷冻处理对植物叶片pH值的测量结果没有显著影响,但是烘干处理一般会使测定值偏高。因此,在长时间的野外采样工作中,通过便携式冷藏箱对植物样品进行冷冻保存,是保持叶片样品pH值稳定、即更接近新鲜叶pH测量值的较好的样品保存方式。对于长时间野外采样,冷冻预处理是植物叶样品保存的最佳选择;而冷藏预处理是短时间保存的最佳选择。不同的叶片:水比例对pH测量值存在显著影响:样品稀释比例越高,氢离子浓度越低,测量到的叶片pH值越大。因此,为了建立现有不同植物叶pH值测量方法之间的联系,本文为叶片样品的不同前处理和测量方式提供了转换关系。本研究结果将有助于植物叶片pH值的研究,从而提高对这一功能性状的认识。

Physiological and biomass partitioning shifts to water stress under distinct soil types in Populus deltoides saplings

土壤类型是影响植物分布和生产力的重要环境因素,但有关土壤环境异质性对植物抗逆性效应的研究非常缺乏。本研究以美洲黑杨(Populus deltoids)为对象,以3种典型土壤类型(红壤、黄壤和黄棕壤)为栽培基质,在控制实验条件下,经过三个月的干旱胁迫(25%田间持水量)处理,测定了不同处理条件下美洲黑杨的气体交换速率、抗氧化能力、氮代谢特征、生物量积累与分配特征。研究结果表明,在红壤和黄壤条件下,与对照(75%田间持水量)相比,干旱胁迫显著降低了美洲黑杨各器官的生物量、光合速率、叶片氮同化酶的活性,显著增加了叶片中过氧化氢、丙二醛和无机氮的含量。在黄棕壤条件下,干旱对美洲黑杨总生物量、光合速率、氮同化酶以及质膜完整性的负面影响较小,这与其维持较高的超氧化物歧化酶,过氧化物酶和过氧化氢酶的活性相关,也与其生物量分配模式(如提高根冠比)密切相关。由此可见,生长在黄棕壤条件下的美洲黑杨表现出较强的抗旱能力,这可能与其土壤母质中较高的土壤养分和良好的通气状况相关。因此,就土壤类型而言,与红壤和黄壤相比,黄棕壤提供的土壤环境条件有利于美洲黑杨的抗逆表现和栽培利用。