不同物候时期华西雨屏区四个树种新鲜凋落物可提取腐殖质碳动态

凋落物的可提取腐殖质碳可随着植物生长节律及物候时期的变化而变化,并进而影响物质循环的过程,为深入了解以凋落物为载体的生态系统物质循环特征,该研究以华西雨屏区麻栎(Quercus acutissima)、楠木(Phoebe zhennan)、柳杉(Cryptomeria fortune)和喜树(Camptotheca acuminate)为对象,通过定点动态收集萌芽期、展叶期、盛叶期和落叶期的不同类型凋落物,分析其可提取腐殖质碳(extractable humus carbon,HC)、胡敏酸碳(humic acid carbon,HAC)、富里酸碳(fulvic acid carbon,FAC)以及胡敏酸碳/富里酸碳(humic acid carbon/fulvic acid carbon,HAC/FAC)的差异。结果表明:相对于其他凋落器官,在同一物候时期凋落叶中的HC和HAC含量都最高,大致都表现为凋落叶>凋落枝>凋落果,且在落叶树种中更为显著;相对于其他时期,展叶期四个树种凋落叶均表现出较高的FAC含量,但不同物候期凋落枝和凋落果的HAC含量以及FAC含量受物种的影响较大。尽管HAC/FAC在各器官间差异并不显著,但落叶树种相同器官的HAC/FAC低于常绿树种,表明落叶树种凋落物富里酸相对含量较高,形成速度相对较快,难降解程度也相对较大。统计分析表明关键时期、物种类型、器官类型及其相互作用对凋落物中HC、HAC、FAC含量和HAC/FAC均具有不同程度的影响,这为进一步深入认识区域生态系统以凋落物为载体的物质循环过程提供了理论依据及新的思路。     

Decomposition and macroinvertebrate colonization of aquatic and terrestrial leaf material in alkaline and acid still water

• 1 Decomposition of the leaves of Nymphaea alba L. and Betula pubescens Ehrh. was studied in two ponds of contrasting pH, buffering capacity and trophic level. Rates of carbon loss, concentrations of nitrogen, protein and phenolics and colonization of the leaf material by macroinvertebrates were studied.
• 2 Decomposition of B. pubescens leaves was slower than that of N. alba in both ponds. Protein and phenolic concentrations were higher in the decomposing N. alba material, whereas no significant difference was found for nitrogen concentrations.
• 3 Decomposition of both species was slower in the acid water. The effect of acid water on decomposition rate was similar for both species. Both nitrogen and protein concentrations of N. alba remained higher under acid conditions, whereas no effect of study site was observed on the protein and nitrogen concentrations in B. pubescens litter. The concentration of phenolic compounds was higher in N. alba litter from the acid pond; no such difference was observed for B. pubescens litter. The high concentrations of phenolic compounds in N. alba litter from the acid pond probably induced chemical immobilization (tanning reaction), yielding high concentrations of nitrogen and protein in the litter.
• 4 Diversity of the detritivorous macroinvertebrate fauna on the litter of both species was extremely low in the acid pond, while a relatively high diversity occurred in the alkaline water. Exclusion of large macrofauna inhibited decomposition in the alkaline water, while there was no comparable influence in the acid water.
• 5 The effects of low pH on the decomposition of both terrestrial and aquatic macrophyte litter appeared to be caused by interactive effects of low pH on the microbial decomposition, on the detritivorous macroinvertebrates and, in the case of N. alba, on the resource quality of the detritus.

     

模拟N沉降下不同林龄马尾松林凋落叶分解-土壤C、N化学计量特征

模拟N沉降对森林生态系统的影响是当今全球变化生态学研究的一个热点问题,土壤碳库对N沉降比较敏感,N沉降增加了凋落叶分解过程中外源N含量,间接影响凋落叶分解的化学过程并改变凋落叶分解速率,因此,研究模拟N沉降下凋落叶分解-土壤C-N关系对预测森林C吸存有重要意义。利用原位分解袋法研究了模拟N沉降下三峡库区不同林龄马尾松林(Pinus massoniana)凋落叶分解过程中凋落叶-土壤C、N化学计量响应及其关系;N沉降水平分对照(CK,0 g m~(-2)a~(-1))、低氮(LN,5 g m~(-2)a~(-1))、中氮(MN,10 g m~(-2)a~(-1))和高氮(HN,15 g m~(-2)a~(-1))。结果表明:分解540 d后,N沉降促进20年生和30年生马尾松林凋落叶分解,46年生马尾松林中仅低氮处理促进凋落叶分解,4种处理均是30年生分解最快,说明同一树种起始N含量低的凋落叶对N沉降呈正响应,N沉降处理促进起始N含量低的凋落叶分解,起始N含量高的凋落叶分解过程中易达到"N饱和"。N沉降抑制20年生和46年生凋落叶C释放(低于对照0.62%—6.69%),促进30年生C释放(高于对照0.28%—5.55%);30年生和46年生林分N固持量均高于对照(高于对照0.15%—21.34%),20年生则低于对照(5.70%—13.87%),说明模拟N沉降处理促进起始C含量低的凋落叶C释放和起始N含量低的凋落叶N固持。N沉降处理下仅30年生马尾松林土壤有机碳较对照增加,且土壤有机质与凋落叶C、N和分解速率呈正相关,与凋落叶C/N比呈显著负相关;土壤总氮与凋落叶分解速率、凋落叶N含量呈正相关,土壤有机碳/总氮比与凋落叶C、N含量呈正相关;对照处理中凋落叶分解指标对土壤养分影响顺序是分解速率凋落物C含量凋落物C/N比凋落物N含量,低、中、高氮处理中则是凋落物C含量分解速率凋落物N含量凋落物C/N比。研究表明低土壤养分含量马尾松林对N沉降呈正响应,N沉降促进低土壤养分马尾松林凋落叶分解并提高土壤肥力;凋落叶质量和土壤养分含量低的生态系统土壤C对N沉降响应更显著。     

Phosphorus dynamics during decomposition of mangrove (Rhizophora apiculata) leaves in sediments

Rhizophora apiculata leaf litter decomposition and the influence of this process on phosphorus (P) dynamics were studied in mangrove and sand flat sediments at the Bangrong mangrove forest, Phuket, Thailand. The remaining P in the mangrove leaf litter increased with time of decomposition to 174% and 220% of the initial amount in the litter in sand flat and mangrove sediment, respectively, although about 50% of the dry weight had been lost. The incorporation of P into the litter was probably associated with humic acids and metal bridging, especially caused by iron (Fe), which also accumulated in considerable amounts in the litter (5-10 times initial concentration). The addition of leaves to the sediment caused increased concentrations of dissolved reactive phosphate (DRP) in the porewater, especially in sand flat sediment. The DRP probably originated from Fe-bound P in the sediment, because decomposition of buried leaf litter caused increased respiration and reduced the redox potential (E_h) in the sediments. Binding of P to refractory organic material and oxidized Fe at the sediment-water interface explains the low release of DRP from the sediment. This mechanism also explains the generally low DRP concentration in the mangrove porewater, the low nutrient content of the R. apiculata leaves, but also the higher total sediment P concentration of the mangrove sediment as compared to sediments outside the mangrove. Both the low release rates for DRP from the sediment and the accumulation of P associated with leaf litter decomposition tend to preserve P in the sediments.     

Higher temperature reduces the effects of litter quality on decomposition by aquatic fungi

1. We investigated the effects of riparian plant diversity (species number and identity) and temperature on microbially mediated leaf decomposition by assessing fungal biodiversity, fungal reproduction and leaf mass loss. 2. Leaves of five riparian plant species were first immersed in a stream to allow microbial colonisation and were then exposed, alone or in all possible combinations, at 16 or 24 °C in laboratory microcosms. 3. Fungal biodiversity was reduced by temperature but was not affected by litter diversity. Temperature altered fungal community composition with species of warmer climate, such as Lunulospora curvula, becoming dominant. 4. Fungal reproduction was affected by litter diversity, but not by temperature. Fungal reproduction in leaf mixtures did not differ or was lower than that expected from the weighted sum of fungal sporulation on individual leaf species. At the higher temperature, the negative effect of litter diversity on fungal reproduction decreased with the number of leaf species. 5. Leaf mass loss was affected by the identity of leaf mixtures (i.e. litter quality), but not by leaf species number. This was mainly explained by the negative correlation between leaf decomposition and initial lignin concentration of leaves. 6. At 24 °C, the negative effects of lignin on microbially mediated leaf decomposition diminished, suggesting that higher temperatures may weaken the effects of litter quality on plant litter decomposition in streams. 7. The reduction in the negative effects of lignin at the higher temperature resulted in an increased microbially mediated litter decomposition, which may favour invertebrate‐mediated litter decomposition leading to a depletion of litter stocks in streams.     

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.     

冻融环境下亚高山森林凋落叶添加对土壤腐殖质动态的影响

亚高山森林土壤形成过程中,胡敏酸、富里酸等腐殖物质的累积是维持土壤肥力及物质循环的重要途径,它受到土壤基质质量、凋落叶和环境因素的调控.本研究以川西亚高山典型的针叶林、针阔混交林和阔叶林土壤为对象,采用室内培养控制冻融环境和凋落叶添加的方法,研究冻融环境下凋落叶添加对土壤腐殖物质累积的影响.结果表明:冻融循环环境下针叶林土壤腐殖质含量升高,而针阔混交林和阔叶林土壤腐殖质含量降低,且凋落叶对土壤腐殖质含量无显著影响.培养前期冻融环境下3种林型土壤胡敏酸净累积,净累积量大小为针阔混交林>针叶林>阔叶林,富里酸含量下降,下降程度为阔叶林>针阔混交林>针叶林,且凋落叶对土壤胡敏酸和富里酸含量无显著影响.随培养时间的延长,3种林型土壤胡敏酸及富里酸含量均下降.这表明,凋落叶对土壤腐殖质含量的影响与土壤基质质量存在密切关系,且受到冬季土壤冻融时间长短的影响.     

The effects of low pH and palliative liming on beech litter decomposition in acid-sensitive streams

The decomposition of allochthonous leaf litter is retarded by stream acidification, but few studies have evaluated whether this effect can be offset by liming – the palliative addition of calcium carbonate either to streams or their catchments. We assessed the response of litter decomposition to pH and experimental liming in Welsh upland streams. Small-mesh (<335 μm) litter-bags containing common beech (Fagus sylvatica L.) were submerged in main river sites along the River Wye, and in replicate acid, circumneutral and experimentally limed tributaries (all n = 3) for 20 days. Beech decomposition was inhibited in acid tributaries and main river sites compared to circumneutral tributaries. Despite having only moderately increased pH relative to acid streams, limed sites had increased decomposition rates that were indistinguishable from naturally circumneutral streams. Decomposition rates increased highly significantly with pH across all 12 sites studied, and values were near identical to those in more prolonged experiments elsewhere. There were no significant variations in shredder numbers with decomposition rate, and no evidence that sites with faster decomposition had smaller shredder proportions. Although based on short-term observations and leaves from just one tree species, these results are consistent with the well-known retardation at low pH of some aspect microbial decomposition (e.g. by hyphomycete fungi). They are among the first to suggest that stream liming to combat acidification might reverse such impacts of low pH. Further data are required on the microbiological causes and ecological consequences of altered detrital processing in acid-sensitive and limed streams.     

Leaf litter decomposition as a bioassessment tool of acidification effects in streams: Evidence from a field study and meta-analysis

Atmospheric acid deposition affects many streams worldwide, leading to decreases in pH and in base cations concentrations and increases in aluminum (Al) concentration. These changes in water chemistry induce profound changes in the diversity, structure and activity of biological communities and in ecosystem processes. However, monitoring programs rely only on chemical and structural indicators to assess stream integrity. Nevertheless, the ability of ecosystems to provide services rely on their functional integrity and thus ecosystem processes should be considered in monitoring programs. We assessed the potential for leaf litter decomposition, a fundamental ecosystem process in forest streams, to be used as a bioassessment tool of acidification effects on stream ecosystem functioning. In a field study in the Vosges Mountains (North-eastern France), using three leaf litter species (Alnus glutinosa, Acer pesudoplatanus and Fagus sylvatica) enclosed in fine and coarse mesh bags and incubated in streams flowing over granite or sandstone bedrock along an acidification gradient, we assessed if the response of litter decomposition to acidification depended on litter species, mesh size, parent lithology and acidification level. In a meta-analysis of 17 primary studies on the effect of acidification on leaf litter decomposition, reporting 67 acidified – reference stream comparisons, we assessed the consistency in the response of litter decomposition to acidification cross studies and the robustness of litter decomposition to be used as a bioassessment tool. Both the field study and meta-analysis revealed an overall strong inhibition (>60%) of leaf litter decomposition in acidified streams likely resulting from previously well described altered decomposer community structure and activity. No effect of leaf species was found in the field study, while in the meta-analysis inhibition of leaf litter decomposition in acidified streams was stronger for Fagus than for Acer, Quercus and Liriodendron. However, differences among leaf species in the meta-analysis might have been confounded by other differences among studies. The response of leaf litter decomposition to acidification was stronger in coarse than in fine mesh bags, indicating strong impairment of detritivore community structure and activity. The magnitude of inhibition also depended on parent lithology, but this is likely related to differences in the degree of acidification. Indeed, the magnitude of the inhibition of leaf litter decomposition increases with increases in H⁺ in Al concentration. Litter decomposition has the potential to be used as a bioassessment tool of acidification effects in streams since it shows consistent response to acidification across regions and is robust to experimental choices.     

沈阳城市和城郊油松凋落叶的分解动态

为了检测分解地点和凋落物类型对分解的影响,采用交互分解实验分析了油松凋落叶在城市林分和城郊林分中分解时不同立地条件(城市和城郊)以及不同油松凋落叶类型(城市油松凋落物和城郊油松凋落物)对凋落物的分解速率以及N、P残留率的相对作用。结果表明:不同的立地条件对油松凋落叶分解速率有显著影响(P<0.05):城郊林分中的油松凋落叶比城市林分中分解快,说明外在环境条件对分解的影响显著;在同一林分里,凋落物类型对凋落叶分解速率也有显著影响(P<0.05):城市凋落物分解快于城郊凋落物,说明凋落物内在特性对分解的影响显著。分解地点对于N、P残留率没有显著的影响,然而凋落物类型对N、P残留率有显著影响:城郊凋落物由于具有较高的C/N以及C/P初始值,比城市凋落物更容易富集N、P。     

氮添加对中亚热带杜鹃灌丛凋落物生产和叶分解的影响

凋落物的生产和分解是生态系统养分循环的重要过程,受到大气氮沉降的深刻影响。但目前相关研究主要集中于森林和草地生态系统,氮沉降对灌丛生态系统凋落物养分归还的影响规律尚不清楚。因此选择亚热带分布广泛的杜鹃灌丛为研究对象,进行了为期两年的模拟氮沉降试验。试验设置4个处理:对照(CK, 0 g m-2 a-1)、低氮(LN, 2 g m-2 a-1)、中氮(MN, 5 g m-2 a-1)和高氮(HN, 10 g m-2 a-1)。结果显示:CK、LN、MN和HN 4种处理下,群落年平均凋落物量分别为(1936.54±358.9)、(2541.89±112.5)、(2342.97±519.8)、(2087.22±391.8) kg/hm²,LN、MN和HN处理样地的凋落量分别比对照样地高出32.68%、21.16%和7.93%;凋落叶、花果、凋落枝和其他组分占总凋落量的比例分别为75.75%、15.09%、7.70%和1.45%,不同浓度氮处理下各组分的凋落量均高于对照样地;凋落物组分表现出明显的季节动态:凋落叶在10—11月份达到峰值,凋落枝在10月份达到峰值,花果凋落物则在5月份凋落量最高,不同氮处理下凋落物的季节动态基本一致;白檀凋落叶分解速率显著高于杜鹃,二者分解95%所需时间分别为5.08—11.11 a和7.69—17.65 a,施氮使白檀凋落叶分解周期比对照样地缩短18.18%—54.28%;凋落叶分解过程中,N元素表现为富集-释放模式,P元素表现为富集模式。研究表明,氮添加能够促进群落中白檀凋落叶分解及N、P元素的释放,说明施氮可以调节凋落叶养分释放模式,对灌丛生态系统的养分循环具有调控作用。     

Foliage litter turnover and earthworm populations in three beech forests of contrasting soil and vegetation types

Summary Leaf litter decomposition, levels of accumulated litter as well as the abundance and biomass of earthworms were measured in three mature beech forests in southern Sweden: one mor site, one poor mull site, and one rich mull site. The disappearance rate of beech litter, measured with litter bags, increased with increasing soil fertility. On the rich mull site, the disappearance rate was much higher than in the two other forests, due to the combined effects of higher earthworm activity, more favouable soil moisture conditions, and higher litter quality. Incubating the litter in finely meshed bags (1-mm mesh) to exclude macrofauna had a great effect on litter mass loss in the rich mull site, but it had only a minor effect in the other sites. Simultaneous incubations of local and transplanted leaf litter on the three study sites showed that the substrate quality of the litter increased in the order: mor site — poor mull site — rich mull site. Lignin, N, and P concentrations of the leaf litter failed to explain the observed differences in decomposition rates, and acid/base properties are suggested to be more important. Earthworm numbers per m² were 2.5 (1 species) in the mor, 40 (6 species) in the poor mull and 220 (9 species) in the rich mull forest. Soil chemical conditions, notably pH, were suggested as the main factors determining the inter-site differences in abundance and species composition of earthworms. The role of litter decomposition and earthworm activity in the accumulation of organic matter in the forest floor in different types of beech woodlands are discussed.     

亚热带3种树种凋落叶厚度对其分解速率及酶活性的影响

对中国亚热带树种杉木(Cunninghamia lanceolata)、香樟(Cinnamomum camphora)、银杏(Ginkgo biloba)3个树种在不同凋落物厚度下凋落物分解速率和分解酶活性进行了探究.利用分解网袋法,根据浙江省的平均酸雨水平,在酸雨(pH4.0)条件下设置了凋落物40g、凋落物20g、凋落物10g 3个梯度.结果表明:凋落物分解速率随厚度的增加呈加快的趋势,杉木凋落物10、20、40g的年分解系数K分别为0.24、0.27、0.34,香樟凋落物10、20、40g的年分解系数K分别为0.25、0.3、0.32,银杏凋落物10、20、40g的年分解系数K分别为0.42、0.5、0.58;脲酶活性表现为:凋落叶40g＞凋落叶20g＞凋落叶10g,纤维素酶活性表现为:凋落叶40g、凋落叶20g＞凋落叶10g,蔗糖酶活性表现为:后期凋落叶40g＞凋落叶20g＞凋落叶10g,凋落物分解过程是多种酶共同作用的结果.     

天童国家森林公园常见植物凋落叶分解的研究

 选择天童地区常绿阔叶林及其退化群落常见植物种为对象,着重探讨分解速率和基质营养含量以及比表面积(Specific Leaf Area, SLA)的关系,并试图通过单独分解试验和混合分解试验的比较,从物种、功能群角度探讨凋落叶多样性和分解这一生态系统过程的关系,为深入研究常绿阔叶林常见植物种的营养策略、群落养分循环等奠定基础,也为植被恢复、森林生态系统管理提供理论依据。结果表明：所有凋落叶随时间进程失重率增大,但失重率并不与时间呈线性相关;凋落叶分解后N、P均发生了变化,大多数凋落叶在分解初期N、P均发生了积累,营养元素的释放和富集与凋落叶初始营养状况无明显的相关性。凋落叶的年分解系数与凋落叶中的初始N含量有较高的相关性,而与初始P含量则无显著的相关性;凋落叶的分解速率与成熟叶的面积无相关性,而与其SLA有很强的相关性。通过模型分析,天童地区大多数常见树种凋落叶分解95%需1～4年,平均是2.54年;分解率最高的物种为山鸡椒(Litsea cubeba),其值为6.280,最低的为黄丹木姜子(Litsea elongata),其值为0.558。凋落物混合对分解有很大的影响,虽在初期对分解有阻碍作用,但长期是促进的。若不考虑功能群差异,则可得出多样性的增加有利于分解的结论。功能群数目的增加在凋落物分解前期对分解起促进作用,但这种作用随分解的进展逐渐减小。混合物种的特性往往是决定分解过程的最重要的因素。     

南亚热带两种优势树种叶凋落物分解对模拟酸雨的响应

通过对模拟酸雨处理下鼎湖山季风常绿阔叶林优势树种锥栗(Castanopsis chinensis)和木荷(Schima superba)叶凋落物分解的研究,试图探讨南亚热带区域日益严重的酸雨对森林凋落物分解的影响规律以及可能的机制。试验应用分解袋法进行,并设计4个模拟酸雨强度处理:CK(p H值4.5左右的天然湖水)、T1(p H值4.0)、T2(p H值3.5)和T3(p H值3.0)。21个月的分解结果表明,模拟酸雨抑制了两种优势树种叶凋落物的分解。CK、T1、T2和T3 4个处理下的分解速率常数k值分别为:锥栗(1.18、0.93、0.94和0.86)和木荷(1.10、0.97、0.88和0.94),与CK相比,k值在T1、T2和T3均有下降的趋势。同时,模拟酸雨下两种优势树种叶凋落物的质量残留率均为:T3T2T1CK。酸雨对凋落物分解的抑制作用可能与酸雨胁迫下土壤酸化从而导致土壤微生物活性下降有关。     

模拟氮沉降对华西雨屏区慈竹林凋落物分解的影响

试验设对照(CK,0 kg·hm^-2·a^-1)、低氮(LN,50 kg·hm^-2·a^-1)、中氮(MN,150 kg·hm^-2·a^-1)和高氮(HN,300 kg·hm^-2·a^-1)4个施氮水平,通过原位试验,研究了模拟N沉降对华西雨屏区慈竹(Neosinocalamus affinis)林凋落物分解的影响.结果表明：不同组分凋落物分解过程中,慈竹叶片分解速率最快,其次是箨,枝最慢,分解15个月时,叶片、箨、枝的质量残留率分别为26.38%、46.18%和54.54%,三者差异极显著(P<0.01);叶片在凋落后第1～2月和7～10月分解较快,而箨和枝则在第5～8月分解较快;凋落叶片分解95%需要的时间(2.573年)分别比箨和枝短1.686年和3.319年.凋落叶分解15个月时,各N沉降处理间分解率差异不显著;凋落箨分解95%需要2.679～4.259年,其中MN分解率最高,CK最低;凋落枝经过15个月的分解,各处理分解率大小顺序为MN>HN>LN>CK,MN与LN处理间差异达显著水平(P<0.05).说明N沉降对3种凋落物分解均有明显的促进作用,且对凋落箨促进作用最强;但随着N沉降浓度的增加和时间的延长,其促进作用减缓.     

Effect of legume understorey on decomposition and nutrient content of eucalypt forest litter

Summary In Jarrah (Eucalyptus marginata Donn ex Sm.) forest of south-western Australia dense germination and regeneration of the native legumeAcacia Pulchella R. Br. can occur following moderate to high intensity fire. The effect of this legume understorey on rate of decomposition and change in nutrient content ofE. marginata litter was investigated using the mesh bag techniques and by examining four components of forest floor litter representing increasing stages of decomposition. E. marginata leaf litter confined in mesh bags lost 37% of its initial dry weight in the first 8 months on the forest floor and 44% of its initial dry weight after 20 months. During this period weight loss was similar for leaf litter located in forest without legume understorey and for leaf litter placed under dense stands ofA. pulchella. MixingA. pulchella litter withE. marginata litter had no significant effect on rate ofE. marginata litter breakdown. The presence of understorey vegetation had a marked effect on chemical composition of decomposingE. marginata leaves. After 8 and 20 months exposure on the forest floor, leaf litter in mesh bags placed underA. pulchella understorey had significantly (P<0.001) higher concentration and contained significantly (P<0.001) greater amounts of N, P, K, S, Ca and Mg than leaf litter placed in areas without legume understorey. This effect was particularly marked for N and P. In forest without legume understorey the amounts of these two nutrients inE. marginata leaf litter changed little during the first 20 months of decomposition, but forE. marginata leaf litter in mesh bags underA. pulchella there were absolute gains of up to 68% in the amount of N and 109% in the amount of P during this period. This represents accumulation of N and P from sources outside the litter bags. The concentration of N, P, S, Ca and Mg were higher at each of the four stages of decomposition in eucalypt leaf litter collected from the forest floor beneathA. pulchella compared to eucalypt leaf litter collected in forest without understorey. Concentrations of N, P and S increased with stage of decomposition. Levels of these three nutrients in eucalypt litter from under the legume were 1.5 to 2.9 fold higher than in the same component of litter from forest without understorey. The effect of legume understorey on nutrient concentrations in the forest floor and on Cielement ratios in decomposing litter is discussed in relation to long term rates of litter breakdown and net mineralisation of litter nutrients.     

中国温带和亚热带8个树种叶和吸收根协同分解

叶和细根(2mm)是森林生态系统的分解主体,二者是否协同分解,将极大影响所属植物在生态系统碳(C)循环中的物种效应。已有研究显示,叶和细根的分解关系具有极大的不确定性,认为很大程度上归因于细根内部具有高度的异质性,导致叶和细根在功能上不相似。为此,使用末梢1级根和细根根枝作为研究对象,它们在功能上同叶类似,称为吸收根。通过分解包法,分别在黑龙江帽儿山和广东鹤山,研究了2个阔叶树种和2个针叶树种(共8个树种)的叶和吸收根持续2a多的分解。结果发现,分解速率k(a~(-1),负指数模型)在8个树种整体分析时具有正相关关系(P0.05),在相同气候带或植物生活型水平上是否相关,受叶的分解环境及吸收根类型的影响;N剩余量整体上并不相关,亚热带树种的叶和细根根枝的N剩余量在分解1a后高度显著正相关,温带树种的叶和1级根的N剩余量在分解2a后显著高度正相关。本研究中,根-叶分解过程是否受控于相同或相关的凋落物性质是决定根-叶分解是否相关的重要原因,其中分解速率与酸溶组分正相关、与酸不溶组分负相关。比较已有研究,总结发现,根-叶分解关系受物种影响较大,暗示气候变化导致物种组成的改变将极大影响地上-地下关系,也因此影响生态系统C循环。     

不同水分条件下杨树-玉米复合系统凋落物分解特性

为探讨水分变化对农林复合生态系统凋落物分解特性的影响,以河西走廊杨树（Populus）-玉米（Zea mays）凋落物为研究对象,设置正常水分（9200 m³/hm²,对照）,轻度干旱胁迫（减少15%,7800 m³/hm²）,中度干旱胁迫（减少30%,6400 m³/hm²）3种不同水分处理条件,采用分解袋法研究了不同水分条件下杨树叶和玉米秸秆的质量残留率、分解速率和养分含量变化特征。结果表明：（1）随着干旱胁迫的加剧,两种凋落物的质量残留率均增加,而分解速率降低。经过164 d的分解后,杨树叶和玉米秸秆的质量残留率分别为70.43%-77.49%、63.55%-68.29%。分析表明：水分和时间对各类型凋落物的质量残留率均有极显著的影响（P<0.001）,但二者的交互作用不显著（P>0.05）;干旱胁迫显著降低了玉米秸秆的分解速率,但杨树叶的分解速率却只是在中度干旱胁迫下显著降低（P<0.05）。对于不同类型凋落物而言,分解速率表现为玉米秸秆>杨树叶。（2）两种类型凋落物的氮（N）残留率在分解过程中表现为降低的趋势,但随着干旱程度的加大,N的残留率增加,表明水分抑制了N的释放过程。分解164d后,同一类型凋落物不同水分条件下的N残留率均存在显著差异。对于同一水分条件下不同凋落物而言,玉米秸秆的N残留率最低,而杨树叶最高。总的来说,水分降低对干旱区农林复合系统内凋落物的分解和氮元素含量具有显著的抑制作用。     

Enhanced ozone exposure of European beech (Fagus sylvatica) stimulates nitrogen mobilization from leaf litter and nitrogen accumulation in the soil

Abstract

In a lysimeter study with young beech trees, the effects of elevated ozone concentration on the decomposition and fate of nitrogen in ¹⁵N‐labeled leaf litter were analyzed after one growing season. Nitrogen in the litter was dominated by a relatively inert, residual fraction, but easily decomposable nitrogen was present in substantial amounts. Nitrogen loss was significantly higher at twice‐ambient ozone which was largely attributed to an enhanced mobilization of residual nitrogen. Enhanced mobilization of nitrogen from litter at twice‐ambient ozone exposure resulted in additional ¹⁵N incorporation into the soil down to 30 cm depth. Only 0.41–0.62% of the nitrogen in the litter was incorporated into plant material at both ozone concentrations. Twice‐ambient ozone exposure changed the distribution of the nitrogen taken up from litter inside the beech trees in favor of the shoot, where it may have been used in biosynthetic processes required for defense reactions.