Effects of lumbricids and enchytraeids on nematodes in limed and unlimed coniferous mor humus

In a factorial laboratory experiment, specimens of Dendrobaena octaedra (Lumbricidae) and Cognettia sphagnetorum (Enchytraeidae) were added to microcosms with unlimed (pH 4.5) and limed (pH 5.5) coniferous mor humus containing bacteria, fungi, protozoans, and nematodes. Effects on the nematodes were assessed after an incubation period of 207 days at 15°C and a soil moisture content of 60% water-holding capacity. When D. octaedra was absent, nematodes were significantly more abundant in the limed humus than in the unlimed humus. The presence of D. octaedra markedly reduced the number of nematodes in the limed humus but not in the unlimed one, where D. octaedra lost weight and probably did not feed. Most nematodes (92–97%) were bacterial-feeders. The presence of D. octaedra did not decrease the number or biomass of bacteria, indicating that the reduction in nematode numbers was not the result of competition for bacteria between D. octaedra and the nematodes. The presence of C. sphagnetorum had no effect on the nematodes in either of the treatments. We suggest that the reason why D. octaedra, but not C. sphagnetorum, reduced nematode numbers is that the former was more likely to inadvertently ingest the nematodes because of its much greater size. The results provide a possible explanation for the observation that liming sometimes enhances nematode populations, when lumbricids do not respond to the treatment, and sometimes causes decreases, when lumbricids increase in number.     

Microbial biomass and activity in soil and litter underPinus sylvestris, Picea abies andBetula pendula at originally similar field afforestation sites

Microbial biomass C and N, and activities related to C and N cycles, were compared in needle and leaf litter, and in the uppermost 10 cm of soil under the litter layer in Scots pine (Pinus sylvestris L.), Norway spruce (Picea abies L.) and silver birch (Betula pendula L.) stands, planted on originally similar field afforestation sites 23–24 years ago. The ground vegetation was differentiated under different tree species, consisting of grasses and herbs under birch and pine, and mosses or no vegetation with a thick layer of needles under spruce. The C:N ratio of the soils was 13–21 and the soil pH_{CaCl 2} 3.8–5.2. Both showed little variation under different tree species. Microbial biomass C and N, C mineralization, net ammonification, reduction) did not differ significantly in soil under different tree species either. Birch leaf litter had a higher pH_{CaCl 2} (5.9) than spruce and pine needle litter (pH 5.0 and 4.8, respectively). The C:N ratio of spruce needles was 30, and was considerably higher in pine needles (69) and birch leaves (54). Birch leaves tended to have the highest microbial biomass C and C mineralization. Spruce needles appeared to have the highest microbial biomass N and net formation of mineral N, whereas formation of mineral N in pine needles and birch leaves was negligible. Microbial biomass C and N were of the same order of magnitude in the soil and litter samples but C mineralization was tenfold higher in the litter samples.     

Effect of earthworms on decomposition processes in raw humus forest soil: A microcosm study

Summary The earthworms Lumbricus rubellus (Hoffmeister) and Dendrobaena octaedra (Savigny) were studied in the laboratory to determine their effects on decomposition and nutrient cycling in coniferous forest soil. CO₂ evolution was monitored, and pH, PO ₄ ^3– –P, NH ₄ ⁺ –N, NO ₃ ^– –N, total N, and total C in the leaching waters were measured. After three destructive samplings, numbers of animals, mass loss, pH, and KCl-extractable nutrients were analysed.The earthworms clearly enhanced the mass loss of the substrate, especially that of litter. L. rubellus stimulated microbial respiration by 15–18%, whereas D. octaedra stimulated it only slightly. The worms significantly raised the pH of the leaching waters and the humus; L. rubellus raised the value by 0.2–0.6 pH units and D. octaedra by 0.1–0.4 units. Both worms increased N mineralization. Although the biomass of both worms decreased during the experiment, the N released from decomposing tissues did not explain the increase in N leached in the presence of earthworms. The worms influenced the level of PO ₄ ^3– –P only slightly.     

Growth of Lumbricus terrestris and Aporrectodea caliginosa in an acid forest soil, and their effects on enchytraeid populations and soil properties

A laboratory experiment was carried out to test the hypothesis that the earthworms Lumbricus terrestris and Aporrectodea caliginosa are able to maintain their populations and reproduce in the acid forest soil of a deciduous forest where no lumbricids were found in the field. The experiment was conducted in 45-l containers in which layers of mineral subsoil, humus and organic topsoil collected from the site were established. Both species survived and at least L. terrestris reproduced during the 60 weeks’ incubation. Burrows and middens of L. terrestris were recorded and quantities of litter were consumed. The presence of lumbricids increased the organic matter content of humus, reduced the acidity of the topsoil and humus layers, and suppressed the population of the enchytraeid Cognettia sphagnetorum. A dense population of Enchytraeus albidus was found in L. terrestris middens. It is concluded that edaphic factors do not explain the absence of earthworms, but isolation from cultural landscapes and lack of opportunity to colonize the site from the surroundings is the decisive factor.     

Influence of Cognettia sphagnetorum (Oligochaeta: Enchytraeidae) on nitrogen mineralization in homogenized mor humus

Summary The influence of the enchytraeid species Cognettia sphagnetorum on N mineralization in homogenized mor humus was examined in a laboratory study. The mor humus was incubated in containers (150 ml) for 8 months at various temperatures and with different moisture levels. Two series were used, one with C. sphagnetorum and one without. The presence of enchytraeids in the cultures increased the level of NH₄ ⁺ and NO₃ ^- by about 18% compared with the cultures without enchytraeids. Almost 40% of this difference was explained by the decomposition of dead enchytraeids. Temperature and soil moisture were the most important factors controlling the mineralization rate. The optimum moisture for N mineralization was between pF 1.6 and 1.1.Dedicated to the late Prof. Dr. W. Kühnelt     

氮添加对华北落叶松叶片化学计量与养分重吸收效率的影响

为了解华北落叶松林叶片化学计量特征和养分重吸收效率与N素供应的关系,以24年生华北落叶松人工林为研究对象,设置3个水平(0,8,15 g/(m~2·a))连续6年的野外氮添加控制试验,测定氮添加后华北落叶松成熟叶片、凋落叶片和林分土壤养分含量的变化。结果表明:成熟叶片C含量在年际间差异显著(P0.05),氮添加显著增加成熟叶2016—2018年的C、N含量,降低2018年的P含量,导致2018年N/P在轻度氮添加下比对照增加20.20%,重度氮添加下增加34.43%,2018年N/P在重度氮添加下出现峰值20.50,表明氮添加在一定程度上驱动该林分生长的P养分限制;凋落叶中的C、N、P含量及化学计量在年际间和氮添加处理下均呈显著差异(P0.05),氮添加显著增加凋落叶2016—2018年的C含量、C/P和N/P,显著降低2016—2018年的P含量;2016—2018年,轻度氮添加下NRE(氮重吸收效率)和NRE/PRE(氮重吸收效率/磷重吸收效率)显著降低,氮添加下PRE(磷重吸收效率)显著增加;相关分析表明,NRE与凋落叶N含量,PRE与凋落叶P含量呈显著负相关,相关系数分别为-0.860和-0.772;氮添加显著增加土壤有效氮的含量,降低土壤pH(除2016年)和速效磷含量。氮添加导致华北山地针叶林树木生长受不同程度的P养分限制,推测氮添加驱动的林分受P限制可能与该区土壤养分初始状况有关,为全球气候变化下森林的养分管理提供参考依据。     

Effects of endogeic earthworms on soil processes and plant growth in coniferous forest soil

Summary The effects of the endogeic earthworm, Aporrectodea caliginosa tuberculata (Eisen) on decomposition processes in moist coniferous forest soil were studied in the laboratory. The pH preference of this species and its effects on microbial activity, N and P mineralization, and the growth of birch seedlings were determined in separate pot experiments. Homogenized humus from a spruce stand was shown to be too acid for A. c. tuberculata. After liming, the earthworms thrived in the humus and their biomass increased (at pH above 4.8). In later experiments in which the humus was limed, the earthworms positively influenced the biological activity in humus and also increased the rate of N mineralization. A. c. tuberculata increased the growth of birch seedlings, with increases observed in stems, leaves, and roots. Neither NH ₄ ⁺ -N fertilizer nor mechanical mixing with artificial worms affected seedling growth. No plant-growth-affecting compounds (e.g., hormone-like compounds) due to the earthworms were present in the humus. The shoot: root ratio in the birch seedlings was not affected by either the earthworms or the fertilizer. The experiments revealed the impact of earthworm activity on soil processes and plant growth.     

Effects of mixing radiata pine needles and understory litters on decomposition and nutrients release

A microcosm experiment was conducted to understand the impacts of mixing radiata pine (Pinus radiata D. Don) needle litter and understory (gorse—Ulex europaeus L., broom—Cytisus scoparius L., bracken—Pteridium aquilinum L., and lotus—Lotus pedunculatus L.) litter materials on decomposition and nutrient release dynamics. Mixing of pine needle litter with understory litter material had significant impacts on both the rate of decomposition and nutrient release patterns of pine litter as well as that of the understory species. Incubation in microcosms over 10 months resulted in significantly lower mass loss of radiata pine needle litter mixed with broom and lotus litters (35.8±8.4 and 41.3±0.8%, respectively) than pure pine needle litter (63.5±2.3%). Mixing with pine needle litter significantly increased the mass loss of broom (53.1±6.1%) compared to that of pure broom (30.2±1.0%). Significant transfers of nutrients, especially of magnesium and potassium, were observed in litter mixture treatments. Concentration of K in litter materials was found to be the most limiting factor for the decomposing microorganisms in the present study. The findings of this study suggest that management of understory litter composition via weed control could be used to manipulate carbon turnover and nutrient release in the forest floor. Also, initial selection of understory species will be important and could be managed.     

The quantitative influence of enchytraeids (Oligochaeta) and microarthropods on decomposition of coniferous raw humus in microcosms

Material from the organic layer of a podsol soil in a spruce stand in southern Norway was incubated for 21/2 years at 15°C in microcosms with a volume of 0.1 dm³. The soil was sterilised and reinoculated with a mixed microflora before the incubation start, and given three different faunal communities: (1) A mixed assemblage of microarthropods plus the enchytraeid Cognettia sphagnetorum (“full fauna”, FF), (2) only C. sphagnetorum (“enchytraeids”, E), and (3) no animals added (“no fauna”, NF). The respiration rate was measured during the last 14 months of incubation, and was highest in FF throughout this period. When all respiration analyses were pooled, the value for FF was 33% higher than for NF and 25% higher than for E. The substrate dry mass loss, measured twice, was also highest in FF (17% higher in FF than in both the other treatments after 11/2 years of incubation, and 31% higher than in both the other treatments after 21/2 years). Both for respiration and for mass loss, the difference between FF and the other two treatments was statistically significant, while there was no apparent difference between the E and NF treatments. There was no sign of a general rise or fall in the respiration rate during the 14 months from the first to the last analysis. The ammonium (and total N) concentration in the soil water was higher in FF and E than in NF, whereas the nitrate concentration was lowest in FF and highest in E. The higher mineralisation activity in the FF treatment was probably caused by the higher diversity of mesofauna, and perhaps also by higher diversities of microflora and microfauna accidentally introduced together with the arthropods.     

不同密度樟子松固沙林土壤水分特征

[目的]探讨樟子松固沙林合理栽植密度,为进一步深入分析樟子松固沙林水量动态平衡、衰退原因及林分稳定性评价提供参考。[方法]以科尔沁沙地南缘3种密度(400,600和800株/hm2)的33a樟子松固沙林为研究对象,连续监测了生长季降雨、0—200cm土壤含水量、200cm以下渗漏量,分析了3种密度下土壤水分特征及差异。[结果](1)3种密度下土壤水分时空变化趋势基本一致,0—30cm为降雨影响剧烈层,60cm以下受40mm降雨影响,降雨结束后均表现蒸渗型水分消退特征,之后转换为蒸散型;(2)0—200cm土壤体积含水量大小为:400株/hm2600株/hm2800株/hm2,且差异显著(p0.05);(3)200cm以下均有水分渗漏,其中800株/hm2最低,为0.4mm。[结论]丰水年3种密度林分基本能够维持水量平衡,但正常降水或极端降水年份会增加土壤蓄存水消耗,可能出现水分亏缺或衰退现象。建议生产中樟子松固沙林适宜密度应控制在400株/hm2左右。     

Contribution of fine roots to ecosystem biomass and net primary production in black spruce, aspen, and jack pine forests in Saskatchewan

Fine root (<2 mm) processes contribute to and exhibit control over a large pool of labile carbon (C) in boreal forest ecosystems because of the high proportion of C allocated to fine root net primary production (NPP), and the rapid decomposition of fine roots relative to aboveground counterparts. The objective of this study was to determine the contribution of fine roots to ecosystem biomass and NPP in a mature black spruce (Picea mariana Mill.) (OBS), aspen (Populus tremuloides Michx.) (OA), and jack pine (Pinus banksiana Lamb.) (OJP) stand, and an 11-year-old harvested jack pine (HJP) stand in Saskatchewan. Estimates of fine root biomass and NPP were obtained from nine minirhizotron (MR) tubes at each of the four Boreal Ecosystem Research and Monitoring Sites (BERMS). Fine root data were collected once a month for May–September in 2003 and 2004. Additional C biomass and NPP data for various components of the forest stands were obtained from Gower et al. (1997) and Howard et al. (2004). Annual fine root biomass averaged 3.10 ± 0.89, 1.71 ± 0.49, 1.62 ± 0.32, and 2.96 ± 0.67 Mg C ha⁻¹ (means ± S.D.) at OBS, OA, OJP, and HJP, respectively, comprising between 1 and 6% of total stand biomass. Annual fine root NPP averaged 2.66 ± 0.97, 2.03 ± 0.43, 1.44 ± 0.43, and 2.16 ± 0.81 Mg C ha⁻¹ year⁻¹ (means ± S.D.) at OBS, OA, OJP, and HJP, respectively, constituting between 41 and 71% of total stand NPP. Results of this study indicate that fine roots produce a large amount of C in boreal forests. It is speculated that fine root NPP may control a large amount of labile C-cycling in boreal forests and that fine root responses to environmental and anthropogenic stress may be an early indicator of impaired ecosystem functioning.     

Tardigrade species composition in young soils and some aspects on life history of Macrobiotus richtersi J. Murray, 1911

In an afforested coal-mining site at Berzdorf, Germany, the soil tardigrade community was investigated. Tardigrade densities ranged from 300 to 33,600 individuals m⁻². Tardigrade distribution was very aggregated with standard deviations of up to 220% of mean densities. Fourteen species belonging to five eutardigrade genera were identified. Soils were dominated by the carnivorous tardigrade Macrobiotus richtersi that contributed 60% of overall densities. A comparison between nine soils of different forest ages (4–46 years) and tree species (poplar, alder, pine, mixed deciduous and mixed coniferous) showed no relationship of tardigrade species distribution and abundance to tree species, thickness of organic or litter layer, humus form, pH or soil moisture. Further, no correlation between nematode biomass and Macrobiotus richtersi abundances were detected. The age of afforested soils, however, affected tardigrade densities: younger soils (7–17 years) yielded higher tardigrade numbers compared to 46-year-old sites.Life history investigations on a strain of parthenogenetic Macrobiotus richtersi demonstrated a significant influence of temperature on egg development, survival rate, body growth and generation time. Hatching, first to fourth molts and maturing, on the other hand, were dependent upon body size alone. The simple, new culture method for carnivorous tardigrades described has successfully been utilized for parthenogenetic Macrobiotus richtersi for 6 years.     

Control of pitch pine seed germination and initial growth exerted by leaf litters and polyphenolic compounds

We investigated the influence of three concentrations of water extracts of three leaf litter species (pitch pine, huckleberry and white oak) and a mixture of all litters on the germination of pitch pine seeds and initial seedling growth in a microcosm experiment. All three plant species are important components of the pine barrens ecosystems in New Jersey, where it has been seen that pine seedling recruitment occurs only after stand replacing fire or in disturbed sites, where surface organic soil horizons and leaf litter have been removed. Leaf litter extracts did not influence seed germination, but significantly reduced seedling growth at high concentrations. There was little difference between the leaf litter species in growth suppression. As charcoal is a natural residue on the forest floor following fire, its influence on growth suppression was examined; it has been shown to immobilize polyphenols. Charcoal removed the inhibitory effect of leaf litter extracts and allowed the fertilizer effect of nutrients leached from the leaves to enhance seedling growth, particularly at the higher concentration of litter extract used. Responses to litter extracts were compared to four pure phenolic compounds, catchecol, p-coumaric acid, p-hydroxybenzoic acid and tannic acid. None of these compounds suppressed pine seedling growth, suggesting that these phenolics are not allelopathic to pine seedlings. The results are discussed in the context of fire as a driving factor in these oligotrophic and seasonally dry ecosystems and the interactions between nutrient supply and allelopathic chemistry of different leaf litters.     

冀西北山地华北落叶松和白桦林下枯落物水文特征

[目的]探讨冀西北山区不同人工林枯落物持水特性的差异,为该地区森林水文循环和森林开发管理提供基础依据。[方法]以冀西北张家口市崇礼山区的华北落叶松、白桦人工林为研究对象,在林下设置标准样地,测定枯落物层厚度和蓄积量,通过室内浸泡法测定持水特征。[结果]华北落叶松和白桦林下枯落物层厚度分别为4.2,3.4cm,枯落物蓄积量为10.90,4.92t/hm2;浸泡24h后华北落叶松枯落物(未分解层和半分解层)总持水量为4 228.5g/kg,白桦枯落物(未分解层和半分解层)总持水量为5 208.6g/kg,二者的有效拦蓄量分别为14.06,8.85t/hm2。在整个持水过程中,华北落叶松、白桦林下枯落物持水量、吸水速率与浸水时间的变化规律基本一致,均在前4h内持水作用较强,4~8h后逐渐变缓,10h后其持水量基本达到饱和;枯落物持水量与浸水时间存在对数曲线关系,而吸水速率与浸泡时间存在幂函数关系。[结论]森林枯落物层发挥水文功能由持水能力和蓄积量共同决定,在森林经营管理过程中应充分考虑包括树种组成和搭配、林分密度等因子的影响。     

Biomass and nutrient cycling in bamboo (Bambusa bambos) plantations of tropical areas

Biomass productivity and nutrient cycling in a Bambusa bambos plantation aged 4, 5, and 6 years were studied. The dry matter production of above-ground biomass increased progressively with age. Nutrient quantities in bamboo stands were in a range of 1–2 t ha^-1 for N and K, 0.5–1 t ha^-1 for Ca and Mg, and 0.1–0.2 t ha^-1 for P. Nutrient concentrations increased with the age of the plantation. About 10% year^-1 the nutrients present in the biomass of the bamboo stand are recycled to the soil by litter fall.     

Plant canopy effects on litter accumulation and soil microbial biomass in two temperate forests

The objective of this study was to determine whether differences in canopy structure and litter composition affect soil characteristics and microbial activity in oak versus mixed fir-beech stands. Mean litter biomass was greater in mixed fir-beech stands (51.9t ha⁻¹) compared to oak stands (15.7t ha⁻¹). Canopy leaf area was also significantly larger in mixed stands (1.96m² m⁻²) than in oak stands (1.73m² m⁻²). Soil organic carbon (C _org) and moisture were greater in mixed fir-beech stands, probably as a result of increased cover. Soil microbial biomass carbon (C _mic), nitrogen (N _mic), and total soil nitrogen (N _tot) increased slightly in the mixed stand, although this difference was not significant. Overall, mixed stands showed a higher mean C _org/N _tot ratio (22.73) compared to oak stands (16.39), indicating relatively low rate of carbon mineralization. In addition, the percentage of organic C present as C _mic in the surface soil decreased from 3.17% in the oak stand to 2.26% in the mixed stand, suggesting that fir-beech litter may be less suitable as a microbial substrate than oak litter.     

Seasonal distribution of Xenylla brevispina (Collembola) in the canopy and soil habitat of a Cryptomeria japonica plantation

We investigated the life cycle and habitat use of an arboreal collembolan species, Xenylla brevispina, in the canopy and soil of a conifer (Cryptomeria japonica D. Don) plantation. The adaptive significance of migration between arboreal and soil habitats in the maintenance of its population in relation to the vertical structure of the forest is discussed. We sampled dead branches with foliage in the canopy (canopy litter) and on the forest-floor (soil litter). X. brevispina had one generation a year throughout the 3 years of the study. The mean densities of X. brevispina were similar in the canopy litter (0.06 to 14.57 g⁻¹ dry weight) and the soil litter (0.44 to 18.99 g⁻¹ dry weight). Seasonal patterns of density and relative abundance indicate that individuals of X. brevispina in the canopy were closely associated with those in the soil. These results suggest that vertical migration between the canopy and the soil might be a strategy allowing X. brevispina to be a predominant collembolan species in this forest.     

Plant litter decomposition and microbial characteristics in volcanic soils (Mt Etna,Sicily) at different stages of development

Soils at different developmental stages were sampled from eight sites on the slopes of Mt Etna, Sicily (Italy) and characterized for total C, microbial biomass and microbial respiration. The values of these parameters were greatest for the most developed soils, but differences in recent management and site characteristics limited analysis of trends with soil development across the eight sites. The decomposition kinetics of both intact leaf litter and the water-insoluble fraction of leaf litter from three common species on Etna [Etnean broom (Genista aetnensis), European chestnut (Castanea sativa), and Corsican pine (Pinus nigra)] were determined in four of the soils (the two with the smallest and the two with the largest organic C contents) in a laboratory experiment over 168 days to test two hypotheses. First, that the readily mineralized fraction of added plant C is greater when the plant material decomposes in well-developed soils compared to less developed soils, and second, that the microbial communities in less developed soils are less efficient at mineralizing C from low quality plant residues. The first hypothesis held for Genista and Pinus litter, but not Castanea litter. The second hypothesis was supported for the Castanea and Pinus litter, but not for the Genista litter. Thus, the general applicability of the hypotheses was dependent on the precise source and characteristics of the litter.     

Microbial biomass and activity in soil and litter underPinus sylvestris, Picea abies andBetula pendula at originally similar field afforestation sites

Microbial biomass C and N, and activities related to C and N cycles, were compared in needle and leaf litter, and in the uppermost 10 cm of soil under the litter layer in Scots pine (Pinus sylvestris L.), Norway spruce (Picea abies L.) and silver birch (Betula pendula L.) stands, planted on originally similar field afforestation sites 23–24 years ago. The ground vegetation was differentiated under different tree species, consisting of grasses and herbs under birch and pine, and mosses or no vegetation with a thick layer of needles under spruce. The C:N ratio of the soils was 13–21 and the soil pH_{CaCl 2} 3.8–5.2. Both showed little variation under different tree species. Microbial biomass C and N, C mineralization, net ammonification, reduction) did not differ significantly in soil under different tree species either. Birch leaf litter had a higher pH_{CaCl 2} (5.9) than spruce and pine needle litter (pH 5.0 and 4.8, respectively). The C:N ratio of spruce needles was 30, and was considerably higher in pine needles (69) and birch leaves (54). Birch leaves tended to have the highest microbial biomass C and C mineralization. Spruce needles appeared to have the highest microbial biomass N and net formation of mineral N, whereas formation of mineral N in pine needles and birch leaves was negligible. Microbial biomass C and N were of the same order of magnitude in the soil and litter samples but C mineralization was tenfold higher in the litter samples.     

Effects of heavy metals on the litter consumption by the earthworm Lumbricus rubellus in field soils

Aim of this study was to determine effects of heavy metals on litter consumption by the earthworm Lumbricus rubellus in National Park the “Brabantsche Biesbosch”, the Netherlands. Adult L. rubellus were collected from 12 polluted and from one unpolluted field site. Earthworms collected at the unpolluted site were kept in their native soil and in soil from each of the 12 Biesbosch sites. Earthworms collected in the Biesbosch were kept in their native soils. Non-polluted poplar (Populus sp.) litter was offered as a food source and litter consumption and earthworm biomass were determined after 54 days. Cd, Cu and Zn concentrations were determined in soil, pore water and 0.01 M CaCl₂ extracts of the soil and in earthworms. In spite of low available metal concentrations in the polluted soils, Cd, Cu and Zn concentrations in L. rubellus were increased. The litter consumption rate per biomass was positively related to internal Cd and Zn concentrations of earthworms collected from the Biesbosch and kept in native soil. A possible explanation is an increased demand for energy, needed for the regulation and detoxification of heavy metals. Litter consumption per biomass of earthworms from the reference site and kept in the polluted Biesbosch soils, was not related to any of the determined soil characteristics and metal concentrations.