四川盆地亚热带常绿阔叶林不同物候期凋落物分解与土壤动物群落结构的关系

为了解植物生长不同物候时期凋落物分解过程中土壤动物群落结构动态及其与凋落物分解的关系,以四川盆地亚热带常绿阔叶林典型人工林树种马尾松和柳杉,次生林树种香樟和麻栎凋落物为研究对象,采用凋落物分解袋试验研究,凋落物分解过程中土壤动物的群落特征。4种凋落物分解袋共获得土壤动物8047只,其中,柳杉(2341只)>香樟(2105只)>马尾松(2046只)>麻栎(1555只)。其中,秋末落叶期、萌动期和展叶期,马尾松凋落物袋中主要以捕食性土壤动物为优势类群,而后以菌食性土壤动物为主;香樟凋落物袋中除秋末落叶期和叶衰期以菌食性土壤动物为主要优势类群外,其他各时期均以捕食性土壤动物为主要优势类群;柳杉凋落物分解各时期均以菌食性土壤动物为主要优势类群;麻栎凋落物分解在前3个时期以菌食性为主,而后以植食性土壤动物为主要优势类群。相关分析表明,在秋末落叶期和萌动期土壤动物的个体密度主要和氮、磷含量及其格局密切相关,叶衰期主要和难分解组分木质素显著相关。除在秋末落叶期土壤动物对凋落物分解的贡献率与土壤动物的个体密度显著相关外,其余主要物候关键时期均与土壤动物的类群密度及其食性显著相关。     

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.     

长白山北坡主要森林群落凋落物现存量月动态

以长白山北坡4种主要森林群落类型为研究对象,于2006年群落生长季节(5-10月)每月初采用直接收获法对森林凋落物现存量进行连续定位调查研究。结果表明:各群落内凋落物现存量大小依次为阔叶红松林(6.43 t/hm²)>白桦林(6.02 t/hm²)>云冷杉林(5.51 t/hm²)>山杨林(5.50 t/hm²);凋落叶和枝现存量占现存凋落物总量的比例最大,达50%以上,其次为半分解物(>35%),花果皮等所占比例较少,各占总量的10%和5%以下。凋落物现存量月动态阔叶红松林、白桦林和山杨林呈双峰型变化,峰值出现在5月和7月;云冷杉林则呈单峰型变化,峰值仅出现在7月。位于相近海拔高度的阔叶红松林、白桦林和山杨林,凋落物各组分现存量月动态变化趋势相似,其中白桦林和山杨林变化趋势基本相同,凋落枝、皮及半分解物现存量5月和7月较高,凋落叶则呈现下降趋势,而阔叶红松林凋落叶和枝现存量5月和7月较高,而位于较高海拔的云冷杉林,则与前者呈现不同变化趋势,8月前波动较大,从5月开始明显上升,7月达到峰值,8月后曲线渐趋平缓或略有下降。进一步对阔叶红松林和云冷杉林内凋落叶现存量月动态进行比较得出,阔叶红松林7月份凋落叶现存量高不完全取决于红松叶现存量,主要由色木槭、紫椴和水曲柳等阔叶树种叶凋落物现存量变化决定,而云冷杉林则取决于红松和云冷落叶的凋落物的量。     

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.     

Potential impacts of climate warming on active soil organic carbon contents along natural altitudinal forest transect of Changbai Mountain

Understanding soil carbon fractions and their responses to the global warming is important for improving soil carbon management of natural altitudinal forest ecosystem. In this study, the contents of soil total organic carbon (SOC), soil labile organic carbon (LOC), and microbial biomass carbon (MBC) in soil upper layers (0–20 cm) were measured along a natural altitudinal transect in the north slope of Changbai Mountain. The results showed that under natural conditions the contents of SOC and LOC were largest in Betula ermanii forest (altitude 1996 m), moderate in spruce-fir forest (altitude 1350 m), and smallest in Korean pine mixed broad-leaf tree forest (altitude 740 m). MBC contents in different forest ecosystems decreased in the order of Betula ermanii forest, Korean pine mixed broad-leaf tree forest, and dark coniferous forest. In addition, the responses of SOC, LOC, and MBC to soil warming were conducted by relocating intact soil cores from high- to low-elevation forests for one year. As expected, the soil core relocation caused significant increase in soil temperature but made no significant effect on soil moisture. After one year incubation, soil relocation significantly decreased SOC contents, whereas the contents of LOC, MBC, and the ratios of LOC to SOC and MBC to SOC increased.     

Distribution characteristics and factors influencing the ecosystem in western Hubei

Western Hubei is the most concentrated area of forest resources in Hubei Province, and the knowledge of the distribution characteristics of ecosystem carbon density is important to understand the regional characteristics of carbon density and its mechanism of formation. Carbon density and factors influencing different layers in the ecosystem were studied by using field data. The average carbon density of ecosystems in western Hubei was 159.05 t/hm²; the carbon density of different forest types in descending order was Abies fargesii forests (362.25 t/hm²), mixed broadleaf-conifer forests (154.13 t/hm²), broad-leaved forests (146.09 t/hm²), and coniferous forests (135.76 t/hm²), and ecosystem carbon density increased with increasing age. The carbon density of the arborous layer, shrub layer, and soil layer of A. fargesii forests was significant higher than that of the other forests (P < 0.05), indicating the carbon storage per unit area of A. fargesii forests, which grow at higher elevations, was the greatest. The carbon density in arborous layers of broad-leaved forests, mixed broadleaf-conifer forests, and coniferous forests was 39.29 t/hm², 48.99 t/hm², and 48.39 t/hm², respectively. Those of the soil layer were 102.96 t/hm², 100.97 t/hm², and 82.37 t/hm², respectively, and there were no significant differences among them. Among the three forest types, carbon density in the litter layer was greater than that of the shrub layer, which indicated the litter layer plays an important role in carbon storage. The carbon density of mixed broadleaf-conifer forests was greatest, excluding A. fargesii forests, in medium (58.71 t/hm²) and mature forests (79.66 t/hm²). Thus, the carbon sink of mixed broadleaf-conifer forests had more potential than the others at the medium and mature forest stage. The soil layer carbon density in different forests constituted 60.67—70.48% of the entire ecosystem, and was 1.70—2.62 times greater than that of the arborous layer. There are many factors influencing ecosystem carbon density, which result from the interaction of environmental and topographical factors. The main explanatory variables of carbon density of the region were altitude, precipitation, and canopy density. The vegetation and soil layer carbon density increased as altitude increased, and the rate of change for every vertical 100 m was 1.3 t/hm² and 1.9 t/hm², respectively (P < 0.05). Although the annual average precipitation only affected the carbon density of the vegetation, it increased to 4 t/hm² (P < 0.01) when average precipitation was >100 mm.     

云南省三种典型气候带凋落物层弹尾类多样性分布格局

弹尾类是土壤动物中常见的优势类群,其作为土壤微食物网的重要组成部分,参与凋落物分解、土壤团聚体形成等重要生态过程。以往对弹尾类分布格局的研究通常关注其在不同海拔梯度或者不同生境类型下的分布情况,但在不同气候带下弹尾类多样性沿纬度分布格局仍不清楚。为讨论不同气候带下弹尾类沿纬度的分布格局及其潜在的环境影响机制,于2017年10月(雨季末期)在云南省同一经度(E 101°)分布的三种典型气候带设置海拔梯度样带:热带雨林(西双版纳,800 m、1000 m、1200 m、1400 m)、亚热带常绿阔叶林(哀牢山,2000 m、2200 m、2400 m、2600 m)、亚高山针叶林(丽江玉龙雪山,3200 m、3400 m、3600 m、3800 m),采集凋落物层弹尾类并调查分析土壤温度、土壤含水量、凋落物厚度、土壤pH、土壤容重及土壤孔隙度等环境因子。利用Berlese-Tullgren法收集土壤动物,共获得弹尾类19150只,隶属于10科29属,其中符■属(39.9%,等节■科)数量最多,其余优势属为棘■属(21.7%,棘■科)和球角■属(10.1%,球角■科),这3个属合计占总体的71.7%。凋落物层弹尾类的密度在亚高山针叶林明显高于热带雨林和亚热带常绿阔叶林,弹尾类的属数排序由多到少依次为热带雨林、亚高山针叶林、亚热带常绿阔叶林。通过最小二乘回归法对弹尾类多样性的海拔格局进行回归分析,得出弹尾类的丰富度指数(Margalef′s指数、Menhinick′s指数)、多样性指数(Shannon-Wiener多样性指数、Simpson多样性指数)和均匀度指数(Pielou均匀度指数)沿热带雨林、亚热带常绿阔叶林、亚高山针叶林呈单调递减格局。通过全模型子集回归筛选最佳环境模型表明,温度是影响弹尾类多样性沿不同气候带分布格局的主要环境因子。本研究为预测不同气候带下弹尾类多样性如何响应环境变化提供参考。     

长白山苔原带土壤动物群落结构及多样性

长白山苔原生态系统对环境变化非常敏感,一旦破坏很难恢复。土壤动物是陆地生态系统的重要组成部分,联系着地上和地下生态系统。为探讨长白山苔原带土壤动物群落的组成、结构和多样性特征,于2009年5月、7月和9月对上部和下部苔原带土壤动物进行了研究。研究表明:长白山整个苔原带土壤动物优势类群为甲螨亚目、节跳虫科和球角跳虫科。下部苔原亚带土壤动物个体数和类群数多,群落结构较为复杂。土壤动物的个体数随生境和时间变化有很大波动,类群数变化则较小。在7月份个体数最少,而类群数随着时间的变化有减少的趋势。土壤动物的垂直分布随时间和生境的不同而异。上部苔原亚带9月的甲螨亚目(P﹤0.01)、革螨亚目(P﹤0.05)及下部苔原亚带5月的甲螨亚目、革螨亚目、辐螨亚目(P=0.03,P=0.011,P=0.027)0—5 cm土层显著高于凋落物层;下部苔原亚带5月的球角跳虫科(P=0.001)及各月的节跳虫科和山跳虫科在各层之间存在显著差异(P=0.001,P=0.036,P=0.005,P=0.001,P=0.04,P=0.009)。两个亚带土壤动物多样性随时间的变化都有递减的趋势。土壤动物的多样性指数、丰富度指数和均匀度指数均是下部苔原亚带高于上部苔原亚带,而优势度指数则相反。相似性指数表明两个亚带土壤动物群落组成上存在一定的差异,各类群的相对数量差异在9月最大。下部苔原亚带的生境条件较适宜土壤动物生存,生物多样性较高。     

季节性冻融期间土壤动物对高山草甸两种凋落叶失重的贡献

季节性冻融期间高山草甸凋落叶的分解可为生长季节植物生长提供必要的养分,对于维持生态系统物质循环和养分平衡具有重要作用。然而,土壤动物对凋落叶分解是否具有明显的贡献仍然缺乏一致认识。因此,以高山草甸代表性植物黄花亚菊(Ajania nubigena)和黑褐苔草(Carex atrofusca)凋落叶为研究对象,采用不同孔径凋落叶袋排除土壤动物的方法,研究冬季不同冻融时期(冻结前期、冻结期和融化期)土壤动物对凋落叶失重的贡献。整个季节性冻融期间土壤动物对黄花亚菊和黑褐苔草两种凋落叶失重率的作用分别为12.07%和4.03%,总贡献率分别为46.39%和24.14%。土壤动物对两种凋落叶失重率的作用均在融化期最大,而土壤动物对黄花亚菊凋落叶失重率的作用在冻结初期最小,土壤动物对黑褐苔草凋落叶失重率的作用在冻结期最小。整个季节性冻融期,土壤动物对凋落叶失重率的作用和贡献率与正积温和凋落叶初始C、N浓度和C/N比均呈显著的正相关关系。因此,季节性冻融期间土壤动物对高山草甸凋落叶分解具有明显的贡献,但这些过程受冻融格局和凋落叶初始质量的调控。     

Seasonal dynamics of soil fauna in the subalpine and alpine forests of west Sichuan at different altitudes

The climate (especially temperature) often plays an important role in the structure, function as well as composition of soil organisms in different latitudes and altitudes. As one of the essential components of soil ecosystem, soil faunal community not only lays their roles as soil engineer in material cycling and energy flow, but also acts as the sensitive bio-indicator to environmental change. However, little information has been available on the responses of soil faunal community to the changed environment at different altitudes and seasons. In order to understand the seasonal dynamics of soil faunal diversity under different forests with varying altitudes, three fir (Abies faxoniana) forests were selected covering a 600 m vertical transition zone. The primary fir forest at 3600 m (A1) of altitude, mixed fir and birch forest at 3300 m (A2) of altitude, and secondary fir forest at 3000 m (A3) of altitude are representative forests in the subalpine and alpine region of west Sichuan. A 2 years study was conducted in the three subalpine and alpine forests from May in 2009 until October in 2010. Soil samples were collected in both the soil organic layer and mineral soil layer. Soil macro-fauna were picked up by hand in the fields. Meso/micro-fauna and damp living fauna were separated and collected from the soil samples by Baermann and Tullgren methods in laboratory, respectively. A total of 74,827 individuals were collected in the 2 years, belonging to seven phyla, 16 classes, 31 orders and 125 families by preliminary identification. Similar dominant groups were detected in different forests at different altitudes, consisting of Spirostreptida, Formicidae, Staphylinidae, Hesperinidae, Onychiuridae, Isotomidae, Oribatuloidae, Alicoragiidae, Secernentea, and Adenophorea. In contrast, the ordinary species of macro-fauna and the ratios of Acarina to Collembolan were obviously different. For instance, the ordinary species were dominated by Cydmaenidae and Mycetophilidae at the A1, Scaphidiidae and Helicinidae at the A2, and Lumbricida and Agelenidae at the A3, respectively. Both the individual density and the number of soil faunal groups were significantly higher in soil organic layer than those in mineral soil layer. The density and group of macro-, meso- and micro-fauna in different forests showed the order as A2 > A1 > A3, but the density of damp living fauna showed the order as A1 > A2 > A3. The functional groups of macro-fauna were mainly dominated by saprozoic. The highest density and group of macro-fauna was observed in August, while the highest value of meso/micro-fauna was detected in October. In addition, the Jacard similarity indices showed that the composition and structure of soil fauna were similar in the different forests varied with altitudes, but the Shannon–Wiener indices were significantly different. The highest values of Shannon–Wiener indices were observed in October at both the A1 and A3, and in August at the A2. The results suggested that soil faunal community kept a high diversity in the subalpine and alpine forests of west Sichuan, and their structures were significantly affected by the variation of altitudes, which provided important scientific evidences for understanding the ecological processes in the subalpine and alpine coniferous forests.     

红松阔叶混交林凋落叶、土壤动物、土壤的微量元素含量

对小兴安岭凉水国家自然保护区红松阔叶混交林的凋落叶、土壤动物、土壤中微量元素含量进行了分析.结果表明, 3种微量元素在凋落叶、土壤动物和土壤中含量排序均为Mn＞Zn＞Cu.不同环境组分中的微量元素含量不同.其中,Mn的含量为土壤＞凋落叶＞土壤动物;Zn的含量为土壤动物＞凋落叶、土壤;Cu的含量为土壤动物＞土壤＞凋落叶.阔叶凋落叶中微量元素变化幅度大于针叶凋落叶.不同土壤动物对不同元素的富集能力不同,蚯蚓体内Mn含量最高,蜈蚣体内Zn含量最高,而马陆体内Cu含量最高.土壤动物体内微量元素的含量均与环境本底值、凋落物分解速度、土壤动物食性以及对微量元素的选择性吸收和富集作用等有关.3种微量元素在土壤中的含量均是土壤层(5～20 cm)大于腐殖质层(0～5 cm),不同土层中微量元素的动态变化不同.     

Leaf Litter Decomposition and Monodominance in the Peltogyne Forest of Marací Island, Brazil1

The forest type dominated by Peltogyne gracilipes (Caesalpiniaceae) on the riverine Marací Island is the least speciesrich of any recorded for Brazilian Amazonia. Because the forest has high soil and foliar Mg concentrations, and Mg is known to be toxic to plant growth at high concentrations, this study tested the hypothesis that dominance by Peltogyne is related to Mg leaf litter amounts and decomposition. We predicted that decomposition of Peltogyne leaves would differ from that of other species, and that their decomposition would result in a pulse of Mg release. Three plots (50 × 50 m) were established in each of three forest types: Peltogyne‐rich forest (PRF; dominated by P. gracilipes),Peltogyne‐poor forest (PPF), and forest without Peltogyne (FWP). Three leaf litter decomposition experiments tested if decomposition of mixed leaf litter in coarse‐ mesh (CM) litterbags differed among forests (experiment 1); whether or not decomposition and nutrient release of Ecclinusa guianensis, Lueheopsis duckeana, and Peltogyne in CM litterbags differed among forests and species (experiment 2); and using fine‐mesh (FM) litterbags, investigated the differences in the influence of fauna! activity on Ecclinusa and Peltogyne decomposition (experiment 3). Decomposition was independent of the presence and dominance of Peltogyne, since decomposition rates in both PRF and FWP were in general lower than in PPF. These differences appeared to be related to fauna] activity. The decomposition of Peltogyne leaves was lower than that of the other species tested and was more affected by microbial and physical action. It is possible that the monodominance of Peltogyne is related to its deciduousness and faster decomposition in the dry season, which coincides with a large leaf fall. Magnesium was lost quickly from the Peltogyne leaves and the resultant pulses of Mg into the soil during the heavy rains at the beginning of the wet season may be deleterious for other species that are not adapted to high solution Mg concentrations. Results obtained were consistent with the hypothesis that Peltogyne dominance is related to the pattern of its leaf decomposition and the seasonal pulses of toxic Mg.     

Phragmites australis and silica cycling in tidal wetlands

Tidal marshes have recently been shown to be important biogenic Si recycling surfaces at the land–sea interface. The role of vegetation in this recycling process has not yet been quantified. In situ and ex situ decomposition experiments were conducted with Phragmites australis stems. In a freshwater tidal marsh, litterbags were incubated at different elevations and during both winter and summer. Biogenic Si (BSi) dissolution followed a double exponential decay model in the litterbags (from ca. 60 to 15 mg g⁻¹ after 133 days), irrespective of season. Si was removed much faster from the incubated plant material compared to N and C, resulting in steadily decreasing Si/N and Si/C ratios. Ex situ, decomposition experiments were conducted in estuarine water, treated with a broad-spectrum antibiotic, and compared to results from untreated incubations. The bacterial influence on the dissolution of dissolved Si (DSi) from P. australis stems was negligible. Although the rate constant for dissolved Si dissolution decreased from 0.004 to 0.003 h⁻¹, the eventual amount of BSi dissolved and saturation concentration in the incubation environment were similar in both treatments. P. australis contributes to and enhances dissolved Si recycling capacity of tidal marshes: in a reed-dominated small freshwater tidal marsh, more than 40% of DSi export was attributable to reed decomposition. As the relation between tidal marsh surface and secondary production in estuaries has been linked to marsh Si cycling capacity, this provides new insight in the ecological value of the common reed.     

Soil bacterial community structure and physicochemical properties in mitigation wetlands created in the Piedmont region of Virginia (USA)

Wetland creation is a common practice for compensatory mitigation in the United States. Vegetation attributes have been used as a quick measure of mitigation success in most post-creation monitoring, while little attention has been paid to soils that provide the substrate for flora and fauna to establish and develop. Created wetland soils are often found not indicative of ‘hydric soil’ with a lack of development of physicochemical properties (i.e., bulk density, moisture content, and carbon and nitrogen contents) comparable to those in natural wetlands. Moreover, soil bacterial communities are rarely examined though they are integrally involved in biogeochemical functions that are critical for ecosystem development in created wetlands. We analyzed soil physicochemistry and profiled soil bacterial community structure using amplicon length heterogeneity polymerase chain reaction (LH-PCR) of 16S ribosomal DNA in three relatively young wetlands (<10 years old) created in the Piedmont region of Virginia. We examined the data by site and by specific conditions of each site (i.e., induced microtopography and hydrologic regime). Multidimensional scaling (MDS) and analysis of similarity (ANOSIM) showed clear clustering and significant differences both in soil physicochemistry (Global R = 0.70, p = 0.001) and in soil bacterial community profiles (Global R = 0. 77, p = 0.001) between sites. Soil physicochemistry (Global R = 1, p = 0.005) and bacterial community structure (Global R = 0.79, p = 0.005) of soils significantly differed by hydrologic regime within a wetland, but not by microtopography treatment. A significant association was found between physicochemistry and bacterial community structure in wetland soils, revealing a close link between two attributes (ρ = 0.39, p = 0.002). C/N (carbon to nitrogen) ratio was the best predictor of soil bacterial community patterns (ρ = 0.56, p = 0.001). The diversity of soil bacterial community (Shannon's H′) differed between sites with a slightly higher diversity observed in a relatively older created wetland, and seemed also fairly determined by hydrologic regime of a site, with a relatively dry site being more diverse.     

Stayin' alive: survival of mycorrhizal fungal propagules from 6-yr-old forest soil

Spores and sclerotia are the main propagules that allow fungi to persist through unfavorable conditions and disperse into new environments. Despite their importance, very little is known about their longevity and dormancy, especially in ectomycorrhizal fungi. To assess the viability of ectomycorrhizal fungal spores in forest soil, we collected and buried non-sterile forest soil, in pots, in the field distant from an inoculum source. After 6 yr, a subset of this soil was assayed for viable spores by baiting the fungi with Bishop pine (Pinus muricata) seedlings. Our results show that the three most frequent colonizers in year 1 continued to colonize significant percentages of seedlings in year 6: Wilcoxina mikolae (77 %), Rhizopogon vulgaris (13 %) and Suillus brevipes (9 %). While three species that colonized low percentages of seedlings in year 1, Suillus pungens (1 %), Rhizopogon salebrosus (2 %), and Thelephora terrestris (5 %) were not recovered in year 6. Laccaria proxima, a species not seen in year 1, was recovered on a single seedling in year 6. This is the first report of long-term survival of S. brevipes and W. mikolae. Our results reveal a more complete picture of ectomycorrhizal fungal spore longevity in soil spore banks.     

Chara hispida beds as a sink of nitrogen: Evidence from growth,nitrogen uptake and decomposition

Chara hispida forms dense beds (0.78–0.95 kg DW m⁻²) in Colgada Lake. The ability of Chara meadows to act as a nitrogen source or sink was evaluated by the following methods: (1) investigating Chara growth, (2) nitrogen incorporation and decomposition laboratory experiments and (3) relating experimental results to field conditions. Sediment oospores were germinated in large aquaria and observed growth rates were 0.001 m day⁻¹ (shoot length) and 0.0002 g day⁻¹ (dry weight). Nitrogen uptake rates were determined by addition of K¹⁵NO₃ during two different periods of Chara growth and the rates were 1.21 and 3.86 μM g DW⁻¹ h⁻¹ when charophytes were 166 days old (not sexually mature) and 323 days old (sexually mature), respectively. After the uptake experiments, the same charophytes were allowed to decompose within two types of litter bags (3 mm-pore litter bags and entire, non-porous plastic litter bags). Decomposition rates of Ch. hispida were 0.016 and 0.009 day⁻¹ in perforated and non-perforated bags, respectively, and fit a negative exponential model. The nitrogen release rate, calculated as the disappearance of N content from Chara tissues, was 0.012 day⁻¹ and there were no statistically significant differences between the values from the two different bag types. The dissolved organic nitrogen concentrations in aquarium and non-perforated litter bags waters increased linearly with time due to the leaching of soluble compounds from Chara. The rate of N loss from Chara tissues, total nitrogen and dissolved organic nitrogen release rates and the decrease in initial dry weight rate were all lower than the daily rate of Chara N uptake. By extrapolating laboratory data to field situations, we determined that approximately 38% of the N taken up by charophytes in Colgada Lake during the growth period is retained. Given the high charophyte biomass in the lake, its ability to incorporate nitrogen, its low decomposition rate and its ability to over-winter, we conclude that Chara beds could be acting as nitrogen sinks in this ecosystem.     

Soil nitrate accumulation explains the nonlinear responses of soil CO2 and CH4 fluxes to nitrogen addition in a temperate needle-broadleaved mixed forest

The responses of soil-atmosphere carbon (C) exchange fluxes to growing atmospheric nitrogen (N) deposition are controversial, leading to large uncertainty in the estimated C sink of global forest ecosystems experiencing substantial N inputs. However, it is challenging to quantify critical load of N input for the alteration of the soil C fluxes, and what factors controlled the changes in soil CO₂ and CH₄ fluxes under N enrichment. Nine levels of urea addition experiment (0, 10, 20, 40, 60, 80, 100, 120, 140 kg N ha⁻¹ yr⁻¹) were conducted in the needle-broadleaved mixed forest in Changbai Mountain, Northeast China. Soil CO₂ and CH₄ fluxes were monitored weekly using the static chamber and gas chromatograph technique. Environmental variables (soil temperature and moisture in the 0–10 cm depth) and dissolved N (NH₄⁺-N, NO₃⁻-N, total dissolved N (TDN), and dissolved organic N (DON)) in the organic layer and the 0–10 cm mineral soil layer were simultaneously measured. High rates of N addition (≥60 kg N ha⁻¹ yr⁻¹) significantly increased soil NO₃⁻-N contents in the organic layer and the mineral layer by 120%-180% and 56.4%-84.6%, respectively. However, N application did not lead to a significant accumulation of soil NH₄⁺-N contents in the two soil layers except for a few treatments. N addition at a low rate of 10 kg N ha⁻¹ yr⁻¹ significantly stimulated, whereas high rate of N addition (140 kg N ha⁻¹ yr⁻¹) significantly inhibited soil CO₂ emission and CH₄ uptake. Significant negative relationships were observed between changes in soil CO₂ emission and CH₄ uptake and changes in soil NO₃⁻-N and moisture contents under N enrichment. These results suggest that soil nitrification and NO₃⁻-N accumulation could be important regulators of soil CO₂ emission and CH₄ uptake in the temperate needle-broadleaved mixed forest. The nonlinear responses to exogenous N inputs and the critical level of N in terms of soil C fluxes should be considered in the ecological process models and ecosystem management.     

长白山原始林红松径向生长及林分碳汇潜力

长白山地处温带针阔混交林的中心地带,其植物生长对气候变化反映较为敏感。运用树木年代学的基本原理与方法,以该区保存完好的地带性顶级群落阔叶红松林为研究对象,探讨了红松(Pinus koraiensis)径向生长对气候变化的响应,以期揭示全球气候变化对阔叶红松林及红松树木生长的影响。以长白山自然保护区北坡为研究地点,建立红松树轮年表,计算年均生物量生长量,与逐月各气候因子进行相关和响应函数分析,以期揭示红松径向生长与气候变化的关系。同时利用多元逐步回归分析方法分别建立了红松树轮指数、年均生物量生长量与主要气候因子的模拟回归方程。主要结论如下:(1)长白山红松年表特征分析表明其生长对气候变化敏感,适用于进行树轮气候学分析;(2)红松径向生长受当年生长季前期温度影响较大;(3)温度是限制红松径向生长的主要因子,气候变暖将促进红松的径向生长;(4)目前林分单位面积地上生物量为310.88t/hm~2,单位面积林分生物量生长量约为5.077t hm~(-2)a~(-1),即每公顷每年固碳约2.539t,表明该地区老龄阔叶红松林仍具有较强的固碳能力。     

Intraspecific functional trait variability across different spatial scales: a case study of two dominant trees in Korean pine broadleaved forest

Intraspecific functional trait variability plays an important role in the response of plants to environmental changes. However, it is still unclear how the variability differs across three nested spatial scales (individual, plot, and site) and which determinants (climatic, soil, and ontogenetic variables) shape the trait variability. Along a latitudinal gradient in Korean pine broadleaved forest of northeast China, we quantified the extent of intraspecific variability of four functional traits in two dominant trees Pinus koraiensis and Fraxinus mandshurica at eight sites, including specific leaf area, leaf dry matter content (morphological traits) and leaf nitrogen content, leaf phosphorus content (physiological traits). Results showed a large trait variation within and between species (coefficient variation: 6.07–23.3%). The leaf physiological traits of F. mandshurica and morphological traits of P. koraiensis were more responsive at site scale, while the morphological traits of F. mandshurica and physiological traits of P. koraiensis were more responsive at individual scale. In addition, abiotic and biotic factors explaining functional trait variation differ markedly between the two tree species, with physiological trait of F. mandshurica being more associated with climate and soil, while traits variability in P. koraiensis was not affected by climate, soil, and ontogeny, except for leaf phosphorus content. Overall, we can predict that the physiological traits of broadleaved species tend to be more sensitive to environmental changes, while pines are more sensitive to competition. It is critical to determine which spatial scale and trait type should be taken into account in predictive models of vegetation dynamics.     

Towards the application of soil organic matter as an indicator of forest ecosystem productivity: Deriving thresholds,developing monitoring systems,and evaluating practices

Soil organic matter (SOM), typically measured as soil organic carbon (SOC), has been widely recognized as a critical linkage between forest management and long-term site productivity. However, its use as an indicator of sustainable forest management practices has been limited both by difficulties in detecting changes in soil carbon due to inherent high variability and by challenges associated with determining appropriate thresholds for loss. In this study we evaluate a methodology for using field measures of total SOC (forest floor to 60 cm depth in mineral soil) in conjunction with a mechanistic forest growth model to derive threshold values for total SOC with respect to the maintenance of ecosystem productivity for a lodgepole pine (Pinus contorta) forest in the central interior region of British Columbia. We also examine the practicality of implementing a sustainable forest management (SFM) monitoring program around this measure and the potential long-term impact of alternative management scenarios on the indicator.Total SOC contents for the different site types sampled in the Quesnel region ranged from 35 to 57 t ha^?1. Long-term simulations of biomass extraction over several rotations showed a near 1:1 ratio in the relative decline of ecosystem productivity associated with relative declines in total SOC. A power analysis revealed that a mean sampling intensity of n = 12–25 and n = 8–17 would be required to detect 20% and 30% losses of total SOC, respectively, depending on the level of statistical power desired. The sampling intensity required for an effective monitoring program was significantly reduced by summing SOC for all soil layers to limit sampling error related to determination of layer boundaries. A modelling analysis of the effect of rotation length on SOC for the Quesnel forest types, suggests that rotation lengths shorter than 75 years should be avoided to prevent declines in ecosystem productivity. Our results confirm that the combination of modelling and statistical techniques can be successfully used to develop cost-efficient monitoring plans of sustainability of forest management, with SOC as a valid indicator of ecosystem productivity.