浅埋对三倍体毛白杨落叶分解的影响

凋落物分解在森林生态系统养分循环及能量流动中具有十分重要的作用,为实现三倍体毛白杨纸浆林养分的科学管理,加快落叶分解,采用网袋法研究了2、4、6年生3个不同年龄的林分落叶在浅埋条件下的分解情况.结果表明:与在地表分解相比,浅埋显著促进了三倍体毛白杨落叶的分解,1年的分解率显著提高,分别为落叶在地表年分解率的130％、194％和186％;浅埋落叶分解50％所需天数分别只有地表的58％、39％和38％,而分解95％所需的天数分别只有地表的60％、38％和36％;浅埋对不同年龄林分落叶的促进程度不同.     

The geographic selection mosaic for squirrels, crossbills and Aleppo pine

The interactions between many species are structured in a geographic mosaic of populations among which selection is divergent. Here we tested the hypothesis that such a geographic selection mosaic arises for common crossbills (Loxia curvirostra) feeding on seeds in the cones of Aleppo pine (Pinus halepensis) because of geographic variation in the occurrence of European red squirrels (Sciurus vulgaris). On the Iberian Peninsula, Sciurus exerted directional selection favouring larger cones with larger scales, which has caused cones there to be larger than in the Balearic Islands where Sciurus are absent. Moreover, cones on the Iberian Peninsula are so large that they are apparently little used by the relatively small-billed crossbills on the Peninsula; selection by Sciurus seems to have made the cones so difficult to feed on that crossbills rely mostly on the seeds of other conifers. Where crossbills are present but Sciurus are absent (Mallorca Island), cones were smaller as a result of relaxation of selection by Sciurus. However, cones on Mallorca had proportionally thicker scales in comparison to where both Sciurus and crossbills are absent (Ibiza Island), presumably as an adaptation against crossbill predation. Here crossbills specialize on Aleppo pine, have relatively large bills and have apparently coevolved in an arms race with Aleppo pine. These results suggest that Sciurus has influenced both the geographic selection mosaics for crossbills and conifers and the adaptive radiation of crossbills in Eurasia much like Tamiasciurus has done in the North America.     

Effects of forest plantations on the genetic composition of conspecific native Aleppo pine populations

Afforestation is a common and widespread management practice throughout the world, yet its implications for the genetic diversity of native populations are still poorly understood. We examined the effect of Aleppo pine (Pinus halepensis) plantations on the genetic composition of nearby conspecific native populations. We focused on two native populations in Israel with different levels of isolation from the surrounding plantations and compared the genetic diversity of naturally established young trees within the native populations with that of local native adults, using nine nuclear microsatellite markers. We found that the genetic composition of the recruits was significantly different from that of local adults in both populations, with allelic frequency changes between generations that could not be ascribed to random drift, but rather to substantial gene flow from the surrounding planted Aleppo pine populations. The more isolated population experienced a lower gene-flow level (22%) than the less isolated population (49%). The genetic divergence between native populations at the adult-tree stage (F(st) = 0.32) was more than twice as high as that of the young trees naturally established around native adults (F(st) = 0.15). Our findings provide evidence for a rapid genetic homogenization process of native populations following the massive planting efforts in the last decades. These findings have important implications for forest management and nature conservation and constitute a warning sign for the risk of translocation of biota for local biodiversity.     

Red oak litter promotes a microarthropod functional group that accelerates its decomposition

The contribution of microarthropod activity to litter decomposition varies widely but can be substantial. Oribatid mites are the most diverse and abundant of the microarthropod groups in forest litter. This experiment was designed to examine the effect of litter type and complexity on the diversity and species composition of oribatid mites, and to test whether alterations in species composition due to litter type affected litter decomposition. In an array of plots on a mixed-hardwood site in the mountains of North Carolina, I exposed microarthropod assemblages to a range of litter types: yellow birch, sugar maple, red oak and two mixed litters. Over several years, the litter types selected oribatid mite assemblages of different species composition. By comparing the decomposition of consecutive cohorts of litter, it was possible to detect differences in decomposition accompanying the shifts in the assemblage. A comparison of the mass loss rates between the two litter cohorts over eighteen months reveals similar trajectories for four litter types. In the oak litter, however, the second cohort disappeared significantly faster than the first. In both years, the litters came from the same trees and were nearly identical in initial carbon and nitrogen contents. Since the response was specific to oak litter, it is unlikely that differences in environmental factors are responsible for the faster mass loss of oak. A significant increase of endophagous oribatid mites, those that burrow into plant material, in the second cohort of oak may account for its accelerated decomposition. The woody petioles and thick leaf-planes of oak leaves provide microhabitats for burrowing mites. Endophage activity can accelerate the litter decomposition both through direct comminution of leaf material and by facilitating microbial growth. Because of their low population growth rates, oribatid populations that are reduced by disturbance are slow to recover and by disrupting these non-resilient populations, disturbance may have long-term repercussions for decomposition. This revised version was published online in June 2006 with corrections to the Cover Date.     

土壤线虫群落对森林凋落物分解主场效应的作用

以大连西郊国家森林公园作为样地,以黑松和辽东栎两种叶凋落物作为分解基质,采用两种不同网孔的凋落物袋法,从土壤线虫群落组成、凋落物分解速率、凋落物养分释放、土壤线虫群落多样性及其与凋落物理化指标的相关性等几个方面来探究森林凋落物分解的主场效应及土壤线虫群落的作用。结果表明:研究期间共鉴定出4570条土壤线虫,隶属于35个属。0.1mm网袋中共鉴定4407条线虫,远高于0.02mm网袋的163条;而0.02mm网袋控制了土壤线虫参与凋落物分解,可视为仅由微生物参与分解过程。凋落物在主场与客场分解损失率差值(Ph-Pa、Qh-Qa)、元素残留率差值(Pa-Ph、Qa-Qh)总体呈增加趋势,说明土壤线虫对主场凋落物分解作用明显。凋落物质量损失和C、N释放量表现为0.1mm网袋0.02mm网袋,主场客场,主场与客场存在一定差异,表明土壤线虫促进了凋落物分解,且对主场凋落物分解贡献较大。主场线虫数量和种类较多,调控着微生物的群落结构及活动,进而加速了凋落物分解和养分释放,同时主场效应又决定着凋落物的分解速率和养分释放。研究结果可为今后森林凋落物分解的相关研究中主场效应、客场效应以及土壤生物驱动效应研究提供参考。     

Leaf and root litter decomposition is discontinued at high altitude tropical montane rainforests contributing to carbon sequestration

We investigated how altitude affects the decomposition of leaf and root litter in the Andean tropical montane rainforest of southern Ecuador, that is, through changes in the litter quality between altitudes or other site‐specific differences in microenvironmental conditions. Leaf litter from three abundant tree species and roots of different diameter from sites at 1,000, 2,000, and 3,000 m were placed in litterbags and incubated for 6, 12, 24, 36, and 48 months. Environmental conditions at the three altitudes and the sampling time were the main factors driving litter decomposition, while origin, and therefore quality of the litter, was of minor importance. At 2,000 and 3,000 m decomposition of litter declined for 12 months reaching a limit value of ~50% of initial and not decomposing further for about 24 months. After 36 months, decomposition commenced at low rates resulting in an average of 37.9% and 44.4% of initial remaining after 48 months. In contrast, at 1,000 m decomposition continued for 48 months until only 10.9% of the initial litter mass remained. Changes in decomposition rates were paralleled by changes in microorganisms with microbial biomass decreasing after 24 months at 2,000 and 3,000 m, while varying little at 1,000 m. The results show that, irrespective of litter origin (1,000, 2,000, 3,000 m) and type (leaves, roots), unfavorable microenvironmental conditions at high altitudes inhibit decomposition processes resulting in the sequestration of carbon in thick organic layers.     

Effects of CO2 and N fertilization on decomposition and N immobilization in ponderosa pine litter

Naturally senesced needles from ponderosa pine (Pinus ponderosa Dougl.), grown from seed in open-top chambers under three levels of CO₂ (350, 525 and 700 μl l^-1) and three levels of N fertilization (0, 10 and 20 g N m^-2 yr^-1), were used in a field litterbag decomposition study and in a laboratory study on potential microbial and nonmicrobial N immobilization. The litterbag studies revealed no statistically significant effects of either CO₂ or N treatment on mass loss, N concentration, or N content over a 26-month period. The laboratory study of potential ¹⁵N immobilization revealed no statistically significant effects of CO₂ or N treatment on either total or microbial immobilization. Elevated (CO₂) did have a significant negative effect on nonmicrobial immobilization, however. Natural abundance of ¹⁵N was significantly greater with elevated (CO₂) in both live and naturally senesced needles under all N treatments. This pattern combined with ¹⁵N natural abundance in soils suggests that saplings grown under elevated (CO₂) were either taking up more N from surface horizons or from a more recalcitrant soil N pool in either horizon. This revised version was published online in June 2006 with corrections to the Cover Date.     

Shifts in plant functional community composition under hydrological stress strongly decelerate litter decomposition

Litter decomposition is a key process of nutrient and carbon cycling in terrestrial ecosystems. The decomposition process will likely be altered under ongoing climate change, both through direct effects on decomposer activity and through indirect effects caused by changes in litter quality. We studied how hydrological change indirectly affects decomposition via plant functional community restructuring caused by changes in plant species’ relative abundances (community‐weighted mean (CWM) traits and functional diversity). We further assessed how those indirect litter quality effects compare to direct effects. We set up a mesocosm experiment, in which sown grassland communities and natural turf pieces were subjected to different hydrological conditions (dryness and waterlogging) for two growing seasons. Species‐level mean traits were obtained from trait databases and combined with species’ relative abundances to assess functional community restructuring. We studied decomposition of mixed litter from these communities in a common “litterbed.” These indirect effects were compared to effects of different hydrological conditions on soil respiration and on decomposition of standard litter (direct effects). Dryness reduced biomass production in sown communities and natural turf pieces, while waterlogging only reduced biomass in sown communities. Hydrological stress caused profound shifts in species’ abundances and consequently in plant functional community composition. Hydrologically stressed communities had higher CMW leaf dry matter content, lower CMW leaf nitrogen content, and lower functional diversity. Lower CWM leaf N content and functional diversity were strongly related to slower decomposition. These indirect effects paralleled direct effects, but were larger and longer‐lasting. Species mean traits from trait databases had therefore considerable predictive power for decomposition. Our results show that stressful soil moisture conditions, that are likely to occur more frequently in the future, quickly shift species’ abundances. The resulting functional community restructuring will decelerate decomposition under hydrological stress.     

Pine volatiles mediate host selection for oviposition by Thaumetopoea pityocampa (Lep., Notodontidae)

The oviposition behaviour and host selection by females of the pine processionary moth, Thaumetopoea pityocampa, was studied under two conditions: in a field insectary and in a pine stand. An oviposition choice test was conducted in an insectary cage, using artificial Christmas trees (ACTs) baited with extracts from four pine species: Pinus pinea, Pinus pinaster, Pinus halepensis and Pinus brutia, plus a control. Females oviposited significantly more egg batches on the ACT baited with a P. brutia extract, while no oviposition occurred on the control ACT. In a large P. pinea stand, two groups of randomly selected trees were marked and baited respectively with an extract of P. brutia, which was the preferred species under insectary conditions and with a solvent, to act as control. Results showed that oviposition in the field followed an aggregated pattern, fitting a negative binomial distribution and that trees baited with P. brutia extracts, received a significantly larger number of egg‐batches than control trees. In parallel, the volatiles emitted by all pine extracts tested where analysed by gas chromatography and mass spectrometry (GC‐MS), coupled to a time‐of‐flight (TOF) mass analyser after solid phase microextraction (SPME), resulting in the identification of 26 compounds. Comparative chromatograms showed qualitative differences among the pine species used, some compounds being present in one of them only. Findings demonstrate for the first time that: (i) T. pityocampa females discriminate among bouquets extracted from different host pine species and exhibit oviposition preferences; and (ii) olfactory cues play an important role in mediating the selection process.     

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。     

Detection of haplotypic variation and natural hybridization in halepensis-complex pine species using chloroplast simple sequence repeat (SSR) markers

In this investigation, nine chloroplast, paternally inherited simple-sequence repeat (cpSSR) markers were used to describe genetic variation of three closely related species belonging to the halepensis complex ( Pinus halepensis Ait., P. brutia Mill. and P. eldarica Medwed.). Both the infinite allele model (IAM) and stepwise-mutation model (SMM) have been applied to the analysis of the genetic structure of natural populations and the geographical distribution of haplotypic variation. SMM-based estimators performed better than IAM-based estimators for large values of within-population diversity and divergence between population pairs. Overall, large haplotypic variation and high genetic divergence were detected for both P. halepensis and P. brutia . The genetic structures of the three species are discussed with consideration to the evolutionary and ecological characteristics of these species. Three highly informative markers showing size variants distinguishing P. halepensis from the other two species were used to provide more information on the occurrence of natural hybridization in a Turkish sympatric population of P. halepensis and P. brutia . Strong evidence of introgression of ' halepensis ' chloroplast haplotypes into P. brutia seeds (but not vice versa) was detected. According to previous evidence from controlled crossings, matings between the above species seem to be successful only when P. halepensis is the pollen donor and P. brutia is the female parent (but not reciprocally). The existence of unidirectional gene flow in sympatric populations confirms previous evidence about partial reproductive barriers between P. halepensis and P. brutia . Implications of the above evidence for the evolutionary history of these species are discussed.     

滇中亚高山人工林凋落物分解对模拟氮沉降的响应

2018年2月至2019年1月,利用尼龙网袋法对滇中亚高山华山松和云南松两种人工林开展模拟氮(N)沉降下凋落叶和凋落枝原位分解试验,N沉降水平分别为对照(CK, 0 g N·m^-2·a^-1)、低N(LN, 5 g N·m^-2·a^-1)、中N(MN, 15 g N·m^-2·a^-1)和高N(HN, 30 g N·m^-2·a^-1)。结果表明: 华山松凋落叶和凋落枝年分解率分别为34.8%和18.0%,分别高于云南松凋落叶的32.2%和凋落枝的16.1%。模拟N沉降下,LN处理使华山松凋落叶、枝分解95%所需时间较对照分别减少0.202和1.624年,MN处理分别减少0.045和1.437年,HN处理则分别增加0.840和2.112年;LN处理使云南松凋落叶、枝分解95%所需时间较对照分别减少0.766和4.053年,MN处理分别增加0.366和0.455年,HN处理分别增加0.826和0.906年。经过1年的分解,低N处理促进了华山松和云南松凋落物(叶、枝)的分解,而高N处理表现为抑制作用;N沉降对两种林型凋落物分解的影响与凋落物中纤维素和木质素含量密切相关。可见,凋落物基质质量在一定程度上决定了凋落物分解对N沉降的响应情况,尤其是纤维素和木质素含量。     

Analysis of spatial genetic structure in an expanding Pinus halepensis population reveals development of fine-scale genetic clustering over time

We analysed the change of spatial genetic structure (SGS) of reproductive individuals over time in an expanding Pinus halepensis population. To our knowledge, this is the first empirical study to analyse the temporal component of SGS by following the dynamics of successive cohorts of the same population over time, rather than analysing different age cohorts at a single time. SGS is influenced by various factors including restricted gene dispersal, microenvironmental selection, mating patterns and the spatial pattern of reproductive individuals. Several factors that affect SGS are expected to vary over time and as adult density increases. Using air photo analysis, tree-ring dating and molecular marker analysis we reconstructed the spread of reproductive individuals over 30 years beginning from five initial individuals. In the early stages, genotypes were distributed randomly in space. Over time and with increasing density, fine-scale (< 20 m) SGS developed and the magnitude of genetic clustering increased. The SGS was strongly affected by the initial spatial distribution and genetic variation of the founding individuals. The development of SGS may be explained by fine-scale environmental heterogeneity and possibly microenvironmental selection. Inbreeding and variation in reproductive success may have enhanced SGS magnitude over time.     

Morphological and Chemical Differentiation between Tunisian Populations of Pinus halepensis,Pinus brutia,and Pinus pinaster

The lipid fraction of seeds from different pine species and populations was studied regarding total lipid content, fatty acid profile and vitamin E composition. The investigated seeds contained a high percentage of lipid (13.6 to 31.5 %). Lipid fractions were found to be rich in vitamin E, which varied significantly among species and populations. P. halepensis (Ph−Hn) showed the highest content of vitamin E (256.3 mg/kg of seeds) and the uppermost content of α-tocopherol (44 mg/kg). However, P. halepensis (Ph−Kas) was the richest in γ-tocopherol (204.9 mg/kg). Lipid fractions had a low content of δ-tocopherol (1.2 to 3.6 mg/kg. The highest content of γ-tocotrienol (∼18 %) was determined for P. halepensis (Ph−Dc and Ph−Hn). Thirteen fatty acids were identified by GC-FID with significant variation between the investigated species. The linoleic acid was the major fatty acid followed by oleic acid and palmitic acid. The chemical differentiation among species for the composition of fatty acids and vitamin E was confirmed by PCA. Significant correlations were observed between the content of vitamin E and fatty acids and ecological parameters of P. halepensis populations.     

UV-B辐射对马尾松凋落叶分解和养分释放的影响

由大气臭氧层减薄导致的UV-B辐射变化将直接影响到凋落物的分解。目前,有关UV-B辐射影响木本植物凋落物分解的研究还很少,在国内还没有开展。采用分解袋法开展了马尾松凋落叶在自然环境和UV-B辐射滤减两种辐射环境下的分解试验。结果表明：在UV-B辐射滤减环境下的马尾松凋落叶年分解速率比对照环境减慢了47.74%。UV-B辐射极显著(p<0.01)地加快了马尾松凋落叶的分解速率,促进了凋落叶中碳、磷、钾的释放和木质素的降解,对氮的释放无明显影响。研究结果意味着UV-B辐射将加快马尾松林的营养循环速度,降低马尾松林凋落物层的碳储量。     

The value of leaf cuticle characteristics in the identification and classification of Iberian Mediterranean members of the genus Pinus

This study reports the value of leaf cuticle characteristics in the identification and classification of Iberian Mediterranean species of the genus Pinus (P. nigra subsp. salzmannii, P. pinaster, P. pinea and P. halepensis), with the aim of using these characters to identify isolated cuticles and stomata in palynology slides. Preparations were made of the cuticles of pine needles belonging to one natural Iberian population of each of the above species. A number of epidermal morphological characteristics were then recorded with the aim of distinguishing these species from one another. The structure of the stomatal complex (the shape and arrangement of the subsidiary cells) was different in each species. The aperture of the epistomatal chamber was significantly smaller in P. pinea than in the other species examined, and the variables recorded for the thickening of the guard cells provided relationships that clearly distinguished all four taxa. The width and length of the stomata and the upper woody lamellae, the central distance between the external limits of the medial lamellae borders and the length of the stem were the most useful variables in this respect. The present results contribute to the ongoing discussion regarding the taxonomic classification of the members of Pinus, and provide valuable clues for the identification of Iberian Mediterranean pine species from small pine needle fragments or isolated stomata. After validation of the present results for multiple populations, these results could also be used to help identify fossil leaf macroremains and the scattered/isolated stomata commonly observed in palaeopalynological samples. © 2009 The Linnean Society of London, Botanical Journal of the Linnean Society, 2009, 161 , 436–448.