Decomposition of young water hyacinth leaves in lake water

Rates of weight loss and release of nutrients during different phases of decomposition in young water hyacinth leaves were determined under laboratory conditions. The leaves decomposed solely by physical leaching during the initial 4-day phase and later by microbial processes. The largest part of weight loss and nutrient release by physical leaching took place within the first 4 h of incubation and thereafter the decomposition rate declined. Microbial processes decayed leaves at a significantly higher rate than that by physical leaching. The overall decay rate constants were related inversely and the release of nutrients directly to the levels of leaf additions in the lake water. The dissolved inorganic and organic nutrients were released chiefly by abiotic processes during the initial as well as later phases of decay. The release was significantly higher during the initial phase in comparison with that during the later phase. Microbes utilized only a small amount of nutrients that were released during decomposition of water hyacinth leaves. The % release of various elements from the decaying leaves was in the order of K > P > C > Na > N.     

Foraging behavior as a determinant of asymmetric competitive interaction between two ant species in a tropical agroecosystem

This work is concerned with elucidating competitive interactions between two neotropical ants, Solenopsis geminata and Pheidole radoszkowskii, focusing on their foraging behavior. When released from competition from P. radoszkowskii, S. geminata increased its foraging activity. On the other hand, when released from competition from S. geminata, P. radoszkowskii did not respond, demonstrating asymmetric competition between the two species. Foraging experiments showed that P. radoszkowskii is more efficient at finding food resources, whereas S. geminata is better at defending the resources once they are encountered. These differences in foraging behavior appear to permit the coexistence of these two species. The practical implications of the results for the management of ant communities in tropical agroecosystems is discussed with respect to the potential use of ants as natural enemies.     

Decomposition and Mineralization of Organic Residues Predicted Using Near Infrared Spectroscopy

Characterization of decomposition characteristics is important for sound management of organic residues for both soils and livestock, but routine residue quality analysis is hindered by slow and costly laboratory methods. This study tested the accuracy and repeatability of near-infrared spectroscopy (NIR) for direct prediction of in vitro dry matter digestibility (IVDMD) and C and N mineralization for a diverse range of organic materials (mostly crop and tree residues) of varying quality (n = 32). The residue samples were aerobically incubated in a sandy soil and amounts of C and N mineralized determined after 28 days. IVDMD and quality attributes were determined using wet chemistry methods. Repeatability was higher with NIR than the original wet chemistry methods: on average NIR halved the measurement standard deviation. NIR predicted IVDMD and C and N mineralization more accurately than models based on wet chemical analysis of residue quality attributes: reduction in root mean square error of prediction with NIR, compared with using quality attributes, was IVDMD, 6%; C mineralization after 28 days, 8%; and N mineralization after 28 days, 8%. Cross-validated r ² values for measured wet chemistry vs. NIR-predicted values were: IVDMD, 0.88; C mineralization, 0.82; and N mineralization, 0.87. Direct prediction of decomposition and mineralization from NIR is faster, more accurate and more repeatable than prediction from residue quality attributes determined using wet chemistry. Further research should be directed towards establishment of diverse NIR calibration libraries under controlled conditions and direct calibration of soil quality, crop and livestock responses in the field to NIR characteristics of residues.     

Decomposition and nutrient release patterns of mistletoe litters in a semi‐arid savanna,southwest Zimbabwe

Nutrient loss from litter plays an essential role in carbon and nutrient cycling in nutrient‐constrained environments. However, the decomposition and nutrient dynamics of nutrient‐rich mistletoe litter remains unknown in semi‐arid savanna where productivity is nutrient limited. We studied the decomposition and nutrient dynamics (nitrogen: N, phosphorous; P, carbon: C) of litter of three mistletoe species, Erianthemum ngamicum, Plicosepalus kalachariensis, and Viscum verrucosum and N‐fixing Acacia karroo using the litter‐bag method in a semi‐arid savanna, southwest Zimbabwe. The temporal dynamics of the soil moisture content, microbial populations, and termite activity during decomposition were also assessed. Decay rates were slower for A. karroo litter (k = 0.63), but faster for the high quality mistletoe litters (mean k‐value = 0.79), which supports the premise that mistletoes can substantially influence nutrient availability to other plants. Nitrogen loss was between 1.3 and 3 times greater in E. ngamicum litter than in the other species. The litter of the mistletoes also lost C and P faster than A. karroo litter. However, soil moisture content and bacterial and fungal colony numbers changed in an opposite direction to changes in the decomposition rate. Additionally, there was little evidence of termite activity during the decay of all the species litters. This suggests that other factors such as photodegradation could be important in litter decomposition in semi‐arid savanna. In conclusion, the higher rate of decay and nutrient release of mistletoe than A. karroo litter indicate that mistletoes play an important role in carbon and nutrient fluxes in semi‐arid savanna.     

Decomposition and nutrient release in halophytes of a Mediterranean salt marsh

This study dealt with the decomposition and nutrient release from the halophytes Atriplex portulacoides, Arthrocnemum macrostachyum, Limoniastrum monopetalum, and Spartina densiflora, the dominant species in the Castro Marim salt marsh, Portugal. Environmental effects on decomposition were also assessed. The study was carried out for one year using the in situ litterbag technique. S. densiflora showed a lower decomposition rate (k = 0.003 day⁻¹) than the other study species (k = 0.005-0.009). Study species showed similar decomposition patterns, that is, the weight loss mostly occurred during the autumn-winter period (study beginning in November). This indicates that temperature in this period did not hamper the decomposition process. The decomposition rate was positively affected by the initial N concentration (r² = 0.87, P < 0.05) and negatively by the C:N ratio (r² = 0.86, P < 0.05) in decomposing materials. At the end of the study, S. densiflora and L. monopetalum, the species with lower initial N concentrations, retained much higher proportion of initial N (89-109%) than the others (5-14%). Also, S. densiflora with the lowest P concentration retained higher proportion of initial P (48%) than the others (5-20%). Release of K and Mg were also slower from S. densiflora and was associated with their initial low concentration in this species. The lowest Mn release was observed from A. macrostachyum and also in relation to the lowest initial concentration. Our study supports the hypothesis that decomposition patterns of marsh species are mostly associated with differences regarding their morphology and chemical composition. Given the higher resistance of S. densiflora to decomposition, its progressive spreading may result in accumulation of organic detritus overtime in invaded salt marshes.     

Influence of stand age on nutrient and energy release through decomposition in alder-cardamom agroforestry systems of the eastern Himalayas

The influence of stand age (5, 10, 15, 20, 30 and 40 years) on the decomposition of litter fractions, nutrient and energy release of mixtures of N₂-fixing alder (Alnus nepalensis) and non-N₂-fixing large cardamom (Amomum subulatum) systems was compared. Seasonal decomposition rates were distinct with the highest rate in the first 6 months followed by subsequent seasons. The decomposition rate was substantially high in younger stands (10- to 15-years) and declined in the older stands. Heat sink from the stand floor litter increased from 171 × 10⁶ kJ year⁻¹ in 5 years to 299 × 10⁶ kJ year⁻¹ at 15 years and then considerably decreased with advancing age. However, energy and nutrient releases were slow at a high initial lignin-to-initial N ratio and C-to-N ratio, and there was an inverse relationship between the k-value of ash-free-mass and N expressed as a function of the C-to-N ratio. Quantities of nutrient release and energy loss per unit area in 24 months of decomposition were highest in 15 years and subsequently they lowered with advancing age. Nutrient loss indicated approximately uniform absolute and relative rates. Absolute energy consistently decreased by 81–88% in 24 months. Ash-free mass of decomposing litter remaining at different retrieval dates was associated with a narrowing of the C-to-N ratio. The relative loss rate of ash-free mass, nutrients and energy content was strongly related to the C-to-N ratio, litter temperature and litter moisture. The influence of Alnus in the younger stands on nutrient and energy releases were rapid, indicating accelerated nutrient cycling and energy dynamics. The intensity of the processes was highly phenomenal and considerably high in younger stands up to 20 years. Thus, an appropriate management cycle of the Alnus-cardamom system for sustainability is 15–20 years.     

Growth and nutrient concentrations of alfalfa and common bean as influenced by soil acidity

Growth and nutrient utilization of alfalfa (Medicago sativa L. cv. Arc) and common bean (Phaseolus vulgaris L. cv. Carioca) were studied in an acid soil adjusted to eight levels of soil acidity by lime addition. Application of lime significantly (P<0.05) increased shoot and root growth for both species. However, common bean was far less sensitive to soil acidity than alfalfa. Maximum alfalfa growth was obtained at a soil pH of 5.8 and maximum bean growth was achieved at pH 5.0. Root and shoot growth of both legumes was positively correlated (P<0.01) with soil pH, exchangeable Ca and exchangeable Mg and negatively correlated (P<0.01) with soil exchangeable Al. Common bean had a lower internal P requirement for maximum growth and was more efficient than alfalfa in taking up Ca and Mg. These characteristics would contribute to the favorable growth of common bean in acid-infertile soils.     

Microclimatic changes and the indirect loss of ant diversity in a tropical agroecosystem

Recent changes in the coffee agroecosystem of Costa Rica were used to study the mechanism of biodiversity loss in transforming agroecosystems, focusing on the ground-foraging ant community. Coffee farms are being transformed from vegetationally diverse shaded agroforestry systems to unshaded coffee monocultures. We tested the hypothesis that the high-light environment and lack of leaf litter cover in the unshaded system are the determinants of the differences in ground-foraging ant diversity. Four treatments were established within the light gaps of a shaded plantation: shade, leaf litter, shade plus leaf litter, and a control (no shade or leaf litter added). Ants were sampled using tuna fish baits and light and temperature were measured. Shade and leaf litter had a significant effect on the ant fauna but probably for indirect reasons having to do with species interactions. In both shade treatments, Solenopsis geminata, the tropical fire ant, decreased significantly while the other species increased. The possibility that the physical factor changes the nature of competitive interactions between the most abundant species is discussed.     

Decomposition of emergent macrophytes in a Wisconsin marsh

Loss of both dry weight and nutrients during decomposition was measured using litter bags, both in a natural marsh and in controlled experiments. At 348 days dry weight remains of Typha latifolia, Sparganium eurycarpum, Scirpus fluviatilis shoot litter in the marsh were 47.5, 26.9, 51.4% respectively, and for the rootrhizome litter were 59.1, 42.1, 27.8% (Scirpus > Sparganium > Typha). Under controlled conditions both temperature and type of water produced significant effect on dry weight loss of Typha leaves. Sterilization and antibiotics effectively inhibited the growth and activities of decomposers. Initial weight, N, P, Ca, and Mg losses resulted chiefly from leaching. These elements accumulated in spring and summer; N exhibited the highest accumulation. In the laboratory, N accumulation occurred within 15 days, as a result of microorganisms inhabiting the litter. Increase in P, Ca, Mg in later stages of decomposition were attributed to microorganisms, epiphytes, and precipitation from solution. High C : N ratios and relatively low P, Ca, Mg in original standing crop may be the cause of low herbivore consumption, whereas the relative increases in N, P, Ca, Mg in decomposed litter provide a more nutrient-rich substrate for detritivores. Much of the nutrient uptake in the annual cycle is via microbial and detritivore growth rather than by macrophyte producers.     

Bioassays of nutrient limitation in a tropical rain forest soil

Summary Six speices of shrubs and one large herb with contrasting life history patterns were used as bioassays of nutrient availability in a Costa Rican lowland rain forest soil. Growth responses of the herb (Phytolacca rivinoides, Phytolaccaceae) confirmed soil measurements indicating high availability of N and potentially limiting levels of P, K, Mg and Ca. Growth responses of the shrub species (Miconia spp., Melastomataceae and Piper spp., Piperaceae) to a complete nutrient fertilizer were generally less than that of Phytolacca. Lack of a strong shrub response to +P fertilization is probably due to mycorrhizal associations and slower growth rates of woody species. In general, increased growth did not occur at the expense of phenolic production in the leaves. The results emphasize that assessment of specific nutrient limitations to plant growth vary depending on species selected for the bioassay, even among species from the same community.     

北方城市12种常见树木落花分解及其养分释放特征

城市绿化产生的树木落花量日益增加,由于落花富含养分,所以研究落花的分解及其养分释放特性,可以为落花作为施肥材料和制备生物质有机肥等农业再利用提供科学依据。以樱花(Cerasus sp.)、海棠(Malus spectabilis)、白玉兰(Magnolia denudata)、紫玉兰(Magnolia liliflora)、桃(Amygdalus persica)、红叶李(Prunus cerasiferaⅠ)、紫叶李(Prunus cerasiferaⅡ)、含笑(Michelia figo)、紫荆(Cercis chinensis)、杏梅(Prunus mume)、银杏(Ginkgo biloba)和栾树(Koelreuteria paniculate)等12种树木落花为研究对象,通过室内落花分解模拟试验,结果表明:(1)粗蛋白含量以桃花和白玉兰落花中较高(251.44—274.94 mg/g)(P<0.05),木质素含量以紫荆和银杏落花中较高(47.35—49.95μg/g)(P<0.5),N含量以桃花和白玉兰落花中较高(40.23—43.99 mg/g)(P<0.5),P含量以桃花和白玉兰落花中较高(1.37—1.58 mg/g)(P<0.5),K含量以红叶李、紫叶李和白玉兰落花中较高(4.53—4.72 mg/g)(P<0.5),Cu含量以白玉兰落花中较高(22.74μg/g),Zn含量以紫叶李落花中较高(249.06μg/g)(P<0.5),Fe含量以紫荆、樱花、紫叶李、杏梅、海棠和桃花中较高(85.81—118.34μg/g)(P<0.5),Mn含量以杏梅、樱花、桃花和海棠落花中较高(24.09—25.71μg/g)(P<0.5)。(2)12种落花中,除了银杏分解稍慢(周转期1.12 a)之外,其他落花分解均较快(周转期为1.00—1.05 a)。(3)落花养分释放速率较之分解速率表现为:N在樱花、海棠、紫玉兰、红叶李、含笑和紫荆落花中呈超速释出状态,而在其他落花中呈慢速释出状态,P在白玉兰、桃花、紫叶李、紫荆和银杏落花中呈超速释出状态,而在其他落花中呈慢速释出状态,K除了在紫荆落花中呈超速释出状态之外,在其他落花中均呈慢速释出状态。(4)相关性分析表明,落花中含有较高的粗蛋白、N、P和K含量可以加快落花分解,而落花中含有较高的木质素含量、木质素/N和N/P则导致落花分解速度减慢。研究结果将为落花的资源化利用奠定理论基础。     

Plant biomass and nutrient levels of a tropical macrophyte (Cyperus papyrus L.) receiving domestic wastewater

The aboveground biomass and nutrient content ofCyperus papyrus were determined in a small tropical swamp receiving domestic wastewater. It was found that the biomass (4,955 g.m^–2 dry weight) was the highest ever reported for papyrus. The levels of both nitrogen and phosphorus in the plant organs were very high. The nitrogen concentrations of the various plant organs were 4.8% roots, 8.4% rhizomes, 4.5% scales, 4.8% culms, and 6.2% umbels on dry weight basis. As to phosphorus the concentrations were 0.09% roots, 0.11% rhizomes, 0.09% scales, 0.10% culms, and 0.13% umbels. The high biomass and nutrient contents of the plants may have been caused by the high nutrient levels in the surrounding water. Comparison of the nitrogen to phosphorus ratios in the plants to those in the surrounding water showed that the plants stored very high amounts of nitrogen.     

氮负荷增强对闽江河口芦苇残体分解及其养分释放的影响

选择闽江河口鳝鱼滩西北部的纯芦苇湿地为研究对象,基于野外氮负荷增强分解试验,探讨了氮负荷增强对芦苇残体分解及其养分释放的影响。试验设置了4个氮负荷水平,即NL0（无氮负荷处理,0 g N m^-2 a^-1）、NL1（低氮负荷处理,12.5 g N m^-2 a^-1）、NL2（中氮负荷处理,25.0 g N m^-2 a^-1）和NL3（高氮负荷处理,75.0 g N m^-2 a^-1）。结果表明,不同氮负荷处理下残体的分解速率整体表现为NL2（0.00284 d^-1）>NL1（0.00263 d^-1）>NL0（0.00257 d^-1）>NL3（0.00250 d^-1）,低氮和中氮负荷总体促进了残体分解,而高氮负荷抑制了残体分解,原因主要与不同处理下残体分解过程中基质质量及pH的明显改变有关。不同氮负荷处理下,残体中的全碳（TC）含量在分解期间均呈不同波动变化特征;全氮（TN）和全磷（TP）含量均在分解初期（0-30 d）骤然降低,之后则呈不同波动变化,其中TN含量呈波动上升变化,而TP含量呈小幅波动变化。残留率是影响不同氮负荷处理下残体分解期间碳（C）、氮（N）和磷（P）净释放的共性因素,而氮负荷增强导致的残体基质质量（C/N、C/P、N/P）和主要环境因子（pH、电导率（EC））改变影响了其释放强度。研究发现,在氮负荷增强背景下残体养分的累积与释放发生了明显改变,闽江河口氮负荷水平的增加整体将抑制芦苇残体中C、N养分的释放,但其在分解中后期（90-240 d）可能对P养分释放具有较为明显的促进作用。     

亚热带红壤丘陵区四种人工林凋落物分解动态及养分释放

应用网袋分解法,连续2a对我国亚热带红壤丘陵区内有代表性的人工林类型马尾松（Pinus,massoniana）、湿地松（Pinus elliottii）、杉木（Cunninghamialanceolata）、木荷（Schimasuperba）＋马尾松（Pinus,massoniana）混交林的凋落物的分解速率,及其C、N元素释放动态进行了研究,凋落物样品分地上、地下两组处理方式。4种林分凋落物地上组的第1、2年分解速率（凋落物的年失重率）依次为马尾松林〉混交林〉湿地松林〉杉木林,马尾松林〉混交林〉杉木林〉湿地松林;地下组的第1、2年分解速率顺序分别为马尾松林〉混交林〉杉木林〉湿地松林,马尾松〉杉木林〉湿地松林〉混交林。各林分地上组凋落物分解速率明显快于地下部分,马尾松林凋落物的分解速率在不同时期均高于其它林分。4种林分凋落物的分解动态符合Olson指数衰减模型。根据拟合方程得出的凋落物分解95％时间为4～01a,介于暖温带常见树种凋落物95％被分解所需时间8～17a,地处南亚热带季风区的鼎湖山凋落物分解95％所需的时间2～8a。养分元素释放率的变化因不同林分和分解时期而异。C在各林分中始终表现为净释放,地上组凋落物的释放率大多数时间均高于地下组。N则于湿地松林、马尾松林和混交林中前期表现出富集现象,而后开始净释放,其中湿地松林凋落物的N富集现象最为显著,释放速率在两个试验年度均为各林分中最低,凋落物中初始的高C／N比是导致上述现象的原因。杉木林凋落物具有最低的初始C／N比,没有出现N富集现象,且在两个试验年度末期均维持了较高的N释放率.     

Soil water, nutrient availability and sapling survival under organic and polyethylene mulch in a seasonally dry tropical forest

We examine the effect of mulches on the soil volumetric water content (SVWC), pH, carbon (C), total and mineral (NH₄ and NO₃) nitrogen (N), total and bicarbonate phosphorus (P), and on the survival and relative growth rate of three species, Ipomea wolcottiana Rose, Lonchocarpus eriocarinalis Micheli and Caesalpinia eriostachys Benth, in a degraded seasonally dry tropical forest (SDTF) area. Our study year was unusually dry, with only half of the mean annual rainfall. Sixteen plots (5 × 6 m) for each of our four treatments, mulches with alfalfa (Medicago sativa L.) straw, forest litter (SDTF litter), polyethylene and bare soil (control), were used. In each plot, 20 tree saplings were planted of each species. The SVWC was higher in plots mulched with polyethylene than in bare soil plots. The soil pH did not change with mulching, and there were no differences between treatments in the concentrations of soil organic C, total N, NO₃ and total P. However, soil concentrations of NH₄ were highest in plots with alfalfa straw and of bicarbonate P in plots with polyethylene. Sapling survival was higher in polyethylene mulch plots than in other mulching treatments, in the order I.␣wolcottiana > C. eriostachys > L. eriocarinalis. Sapling survival under organic mulches, alfalfa straw and forest litter were similar, and lowest in bare soil. The relative growth rate followed the order L. eriocarinalis < C. eriostachys < I. wolcotiana, and the growth rate of all species was greatest under polyethylene mulch. We conclude that a combination of polyethylene mulch with species of high growth rate is best for restoring seasonally dry tropical areas.     

Biochemical and physiological properties of a protein inducing protoplast release during conjugation in theClosterium peracerosum-strigosum-littorale complex

When mating-type minus (mt⁻) and plus (mt⁺) cells of theClosterium peracerosum-strigosum-littorale complex were mixed together in a nitrogen-deficient mating medium, cells of both types released protoplasts, this release being the first step in the process of conjugation. Release of protoplasts by mt⁻ cells also proceeded without pairing in a medium in which mt⁻ and mt⁺ cells had previously been cultured together. A protein with the ability to induce the release of protoplasts was purified from this medium by sequential column-chromatographic steps, and named PR-IP (protoplast-release-inducing protein). The PR-IP had an apparent molecular mass (M_r) of 95000 on gel filtration and could be separated into several isoforms by anion-exchange chromatography. Each isoform consisted of two glycopolypeptides of M_rs 42000 and 19000, while the deglycosylated polypeptides had M_rs of 34000 and 18000, respectively. From an analysis of dose-response curves, the numbers of PR-IP molecules required for the release of a protoplast by a single cell was calculated as 1.5·10⁹ and the concentration required for 50% of the maximum response (ED₅₀) as 4.1·10⁻⁹M. We suggest that the PR-IP is a biologically active glycoprotein which induces the release of gametic protoplasts from mt⁻ cells of thisClosterium complex.     

Propagation of the tropical tree,Leucaena leucocephala K67, by in vitro bud culture

A tissue culture method is described for clonal multiplication of Leucaena leucocephala K67 using single lateral bud explants from 2–3 m tall greenhouse grown trees. N-6 benzyladenine (BA: 3.0 mg.1^-1) and napthaleneacetic acid (NAA: 0.05 mg.1^-1) in Murashige & Skoog's (MS) medium were found to be best suited for multiple shoot differentiation in 4–5 week old cultures. Analysis of variance of the main treatment effects of BA and NAA on shoot parameters showed that BA significantly (P=0.001) affected shoot development while NAA did not. A shoot multiplication rate of 22±3.63 shoots per bud explant was obtained in 150 days on 1/2 strength MS medium with 3.0 mg.1^-1 BA and 0.05 mg.1^-1 NAA. Shoots developed adventitious roots within 15 days in 1/2 strength MS medium containing indole-3-butyric acid (IBA: 3.0 mg.1^-1) and Kinetin (0.05 mg.1^-1). Eighty percent of the transplanted plantlets are being grown in greenhouse conditions.     

Decomposition of four macrophytes in wetland sediments: Organic matter and nutrient decay and associated benthic processes

Decomposition rates of Phragmites australis, Carex riparia, Nuphar luteum and Salvinia natans and benthic processes were measured from December 2003 to December 2004 in a shallow wetland (Paludi di Ostiglia, Northern Italy) by means of litter bags and intact cores incubations. Decay rate was highest for N. luteum (k = 0.0152 d⁻¹), intermediate for S. natans (k = 0.0041 d⁻¹) and similar for P. australis (k = 0.0027 d⁻¹) and C. riparia (k = 0.0028 d⁻¹).Benthic metabolism followed a seasonal pattern with summer peaks of O₂ demand and TCO₂, CH₄ and NH₄⁺ efflux whilst soluble reactive phosphorus (SRP) fluxes were negligible also under hypoxic conditions, indicating that P was mainly retained by sediment. The initial C:P ratio was similar in N. luteum and S. natans (170) and significantly lower than that of P. australis and C. riparia (360). During the detritus decay P was progressively lost by N. luteum and S. natans tissues, whereas, after an initial leaching, it was probably re-used during the microbial decomposition of the more refractory P. australis and C. riparia detritus. Nuphar luteum, P. australis and S. natans had comparable initial C:N mass ratio (15), significantly lower than that of C. riparia (26). The C:N ratio was rather constant for N. luteum (12.9 ± 1.5) and S. natans (14.6 ± 0.9), decreased slightly to below 20 for C. riparia and increased up to 30 for P. australis. Overall, differences among species were likely due to the recalcitrance of decomposing detritus, whilst process rates were controlled by limitation of microbial processes by nutrients and electron acceptor availability.     

马尾松人工林林窗大小对四种凋落叶质量损失和养分释放的影响

马尾松人工林乔木层植物凋落物的分解对林地养分平衡和系统物质循环具有重要意义,并可能受不同大小林窗下微环境差异的影响。采用凋落物袋分解法,以马尾松(Pinus massoniana)人工林人为砍伐形成的7个不同大小林窗(G1:100 m~2、G2:225 m~2、G3:400 m~2、C4:625 m~2、G5:900 m~2、G6:1225m~2、G7:1600 m~2)为研究对象,林下(G0)为对照,研究林窗大小对红椿(Toona ciliata)、桢楠(Phoebe zhennan)、香樟(Cinnamomum camphora)和马尾松4种乡土树种凋落叶质量损失及养分释放的影响。结果显示:1)林窗大小(G0-G7)显著影响林窗中心放置的红椿和桢楠凋落叶N和P释放率、香樟凋落叶失重率和N、P、K释放率以及马尾松凋落叶P和K释放率。相对于林下,中小型林窗(G1-G4)的凋落叶失重率和N、P释放率明显较大,而大型林窗(G6-G7)的凋落叶K释放率明显较大。2)林窗内放置位置显著影响红椿、桢楠和马尾松凋落叶的K释放率及香樟凋落叶的P释放率。红椿和桢楠的凋落叶K释放率从林窗中心到边缘显著减少,而马尾松凋落叶K释放率及香樟P释放率从林窗中心到边缘显著增加。3)4种凋落叶类型中红椿凋落叶分解最快,其分解50%和95%所需时间分别为5.29和23.14个月。上述结果表明,林窗大小和林窗内位置对凋落物质量损失及其养分释放具有显著影响,但影响大小及趋势随物种初始基质质量的差异具有明显变化,研究结果为亚热带低山丘陵区马尾松人工低效林的科学经营及管理提高了一定的科学依据。     

Soil nutrient status after bamboo flowering and death in a seasonal tropical forest in western Thailand

We have examined the surface (0–10 cm) soil characteristics of sites after bamboo (Cephalostachyum pergracile) mass flowering and death (DB sites) in comparison with sites with living bamboo (Bambusa tulda) (LB sites) in a seasonal tropical forest in Thailand. One year after bamboo flowering the DB sites were acidic with lower concentrations of exchangeable Ca and Mg and soil nitrogen than the LB sites. Therefore, although leaf and root litter of the dead bamboo was deposited in the DB sites after bamboo flowering, soil nutrient status decreased.