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1.
Comparisons were made of three different 15N-feeding techniques, leaf, petiole and stem feeding, to identify the most efficient technique for labelling above-and below-ground plant biomass under controlled environment conditions. 15N-urea (0.5%, 10 atom % excess 15N) was applied to chickpea (Cicer aritenium var. ICCV 5003) plants twice during early growth. Leaf feeding was found to be the most efficient in terms of 15N-solution uptake (5.9 ml 48 h−1) and 15N-enrichment at harvest, with 0.95, 0.41, 0.79, 0.67 and 0.22 atom % excess 15N in the leaves, stems, grain, grain straw and clean root fractions, respectively. Solution uptake was low in the second stem feeding event due to blockage of the drilled hole, resulting in low 15N-enrichment of leaves (0.29 atom % excess 15N). Although petiole feeding resulted in more even relative enrichments among plant parts our results highlight the usefulness of leaf 15N-feeding to estimate below-ground plant N and to trace the long-term fate of plant-derived N within the soil.  相似文献   

2.
This study aimed to determine the effects of delayed harvest, irrigation and nitrogen fertilization on yield and fuel quality of the Jerusalem artichoke (JA) (Helianthus tuberosus L.). The biomass, calorific value, ash content and total calories per hectare of the Jerusalem artichoke were assessed in Inner Mongolia, China, at various harvest times, after irrigation and nitrogen application. The results showed that fresh and dry weights of tubers and underground biomass were higher when harvested after freezing; the dry yields of leaves and stems decreased with harvest time. In addition, irrigation significantly enhanced the yields of underground biomass, aboveground biomass and tubers, compared with non-irrigation conditions (p < 0.05). Interestingly, the highest yield was obtained with irrigation and treatment with nitrogenous fertilizers (20 to 50 kg ha?1). The calorific values of tubers and roots were significantly higher for samples harvested after freezing (p < 0.05); the calorific values of leaves and stems significantly decreased with harvest time and without irrigation (p < 0.05). The calorific values of stems and leaves were higher than those of tubers and roots, when JA was harvested before freezing, and the opposite trend was obtained for harvest done after freezing. The highest calories per hectare was obtained in WN2 (585247.42 MJ ha?1) on 30 September 2010 harvest. No correlation was found between the effects of water or nitrogenous fertilizers and ash content. However, the ash contents of stems, leafs, tubers and roots were significantly decreased (p < 0.05) with harvest time. Finally, in all treatment conditions, leaves produced the highest ash amounts among all plant parts, including stems, tubers, leaves and roots.  相似文献   

3.
Vegetation structure parameters are key elements in the study of ecosystem functioning and global scale ecosystemic interactions. The detailed retrieval of many of these parameters by direct measurements is impractical due to the quantity of plant material in trees. Terrestrial LiDAR Scanners (TLSs) have been shown to hold great potential as an indirect means of estimating plant structure parameters with a high level of detail, while some studies identified a number of challenges inherent to this approach. In this study we investigate the use of a voxel-based approach to retrieve leaf area distribution of individual trees. The approach is based on the contact frequency method applied to co-registered TLS returns from two or more scanning positions. The contact frequency was computed for voxels being 10, 30, and 50 cm in size and subsequently corrected for the influence of occlusion effects, leaf inclination, the presence of non-photosynthetic material, and the laser beam size. The leaf area of voxels for which occlusion effects were too pronounced was estimated using modeled values based on the availability of light. We compared the TLS derived leaf area estimates against direct measurements, obtained by the harvesting of leaves, in a broad-leaved savanna of central Mali. The measured leaf area values of the sampled trees ranged from 30 to 530 m2, and crown LAI values between 0.8 and 7.2. The leaf area estimates lay on average 14% from the reference measurements (general bias). Our method provides vertical as well as radial distributions of leaf area in individual trees, and lends itself to the estimation of savanna vegetation structural parameters with a high level of detail.  相似文献   

4.
增铵对小白菜生长和叶绿素含量的影响   总被引：11，自引：1，他引：11       下载免费PDF全文
在营养液中添加一定量的铵态氮能提高作物生物量和叶绿素含量。为研究增铵对植物生长及叶绿素含量的影响机理,采用了6个NO3-∶NH4 浓度比为5·0∶0·0、5·0∶2·5、5·0∶5·0、5·0∶7·5、5·0∶10·0和0·0∶5·0的处理对小白菜进行培养试验。结果表明,在5mmolL-1硝态氮存在时,适当添加一定量的铵态氮(2·5mmolL-1)小白菜生物量和叶面积分别增加39·6%和16·3%,叶面积与生物量显著相关(r=0·941,p<0·01)。营养液中铵态氮浓度与叶片SPAD值、活性铁及叶绿体蛋白质含量均显著相关,相关系数r分别为0·914、0·954和0·964。适当提高铵态氮浓度增加小白菜产量的机制在于其促进了叶片扩展,提高了总光合面积,其原因可能是适当提高铵态氮浓度促进了叶片细胞分裂。进一步研究表明,提高铵态氮浓度提高叶绿素含量的原因,可能在于其促进了小白菜体内全铁的再利用,从而提高了叶片活性铁含量和叶绿体蛋白质含量。  相似文献   

5.
ABSTRACT

Mao bamboo (Phyllostachys pubescens) with a high production and wide utilization has been planted in large scale in southern China, but little information about bamboo nutrition is available. The objective of this study was to reveal the dynamics of nutrition with growing time and the distribution of nutrition in different organs. It was found that the nutrition concentration of the whole plant generally declined with time during the period of 1–6 weeks owing to a dilution effect with the result of quickly increasing the biomass. The leaf concentration of nitrogen (N), phosphorus (P), and potassium (K) changed regularly with high concentrations observed at age 1, 2, 4, and 6, and lower at age 3 and 5. While the concentration of N, P, and K in the branch and stem generally declined with the weeks, a rapid decrease occurred from weeks 1 to 2. The concentrations of calcium (Ca) and magnesium (Mg) in bamboo leaf, branch, and stem appeared to be opposite to those of N, P, and K in corresponding plant parts. The elemental concentrations were greater (P < 0.05) in the leaves than in the branches and stems, while the storage of nutrition was greater (P < 0.05) in stem than in leaves and branch. A relative large total storage of nutrition, except P and Mg, were found in bamboo under an intensive management (IM) stand than those under extensive management (EM) stand. The total storage of different nutritions in the above-ground parts was in the order: K (243.0–285.6 kg ha?1) > N (154.5–207.8 kg ha?1) > P (10.4–12.2 kg ha?1). The nutrition stored in the bamboo plant would be removed away from the soil in every other year by the means of harvest of the bamboo trunk which is the largest nutrition pool of the bamboo plant. Therefore, supplementary nutrients, especially N and K, are strongly recommended in order to keep the productivity of bamboo.  相似文献   

6.
Two species of sunflower, i.e., Tithonia diversifolia and Helianthus annuus, were investigated for their potential to remove heavy metals from contaminated soils. Dried and mature T. diversifolia (Mexican flower) seeds were collected along roadsides, while H. annuus (sunflower) seeds were sourced from the Department of PBST, University of Agriculture Abeokuta, Nigeria. The contaminants were added as lead nitrate (Pb (NO3)2) and zinc nitrate (Zn (NO3)2) at 400 mg/kg which represents upper critical soil concentration for both Pb and Zn. The results indicated that T. diversifolia mopped up substantial concentrations of Pb in the above-ground biomass compared to concentrations in the roots. The concentrations in the leaf compartment were 87.3, 71.3, and 71.5 mg/kg at 4, 6, and 8 weeks after planting (AP), respectively. In roots, it was 99.4 mg/kg, 97.4 mg/g, and 77.7 mg/kg while 79.3, 77.8, and 60.7 mg/kg were observed in the stems at 4, 6, and 8 weeks AP, respectively. Observations with H. annuus followed the pattern found with T. diversifolia, showing significant (p?<?0.05) accumulation of Pb in the above-ground biomass. Results obtained from Zn contaminated soils showed significant (p?<?0.05) accumulation in the above-ground compartments of T. diversifolia and H. annuus compared with root. However, the highest accumulation of Zn was observed in the leaf. The translocation factor and enrichment coefficient of Pb and Zn with these plant species are greater than 1, indicating that these metals moved more easily in these plants. However, this result also showed that the translocation of Zn from root to the shoot of the two plants was higher than Pb. In conclusion, this experiment showed that these plants accumulated substantial Pb and Zn in their shoots (leaf and stem) at 4 weeks AP which diminished with time. This implies that the efficiency of these plants in cleaning the contaminated soils was at the early stage of their growth.  相似文献   

7.
The agar-film method was used to assess fungal biomass and standing crop in several analogous decomposition stages of two leaf species (the fast decomposing Michelia nilagirica and the slow decomposing Semecarpus coriaceae), both from an upper montane rainforest in Sri Lanka. At all decomposition stages the fungal biomass on Michelia litter was significantly higher (P<0.001) than for Semecarpus and had developed much more rapidly (17.04 mg g−1 at the first decomposition stage compared with 4.39 mg g−1 for Semecarpus). These figures are considerably higher than those for a cool temperate deciduous forest, but when the data are given as fungal biomass per area the reverse is true. Data are given on the contribution of different hyphal types showing a trend for change (hyaline to dark hyphae) during the course of decomposition. The mass of dead hyphae is considerably lower than data from temperate forests. Data on immobilization of C and of plant nutrients (N, P, K, Ca, Mg and Na) are provided plus hyphal nutrient contents expressed as % of total contents in the leaf litter. These data are comparable to those from temperate forests.  相似文献   

8.
Phosphorus(P) is a major limiting factor for plant productivity in many ecosystems and agriculture. The projected increase in atmospheric CO_2 is likely to result in changes in plant mineral consumption and growth. We studied P depletion by common bean(Phaseolus vulgaris) cultured hydroponically under ambient(377 ± 77 μmol mol~(-1)) or elevated(650 ± 32 μmol mol~(-1)) CO_2 in media of low or high P. Under elevated CO_2 compared to ambient CO_2, the maximum P depletion rate increased by 98% at low P and250% at high P, and P was depleted about 2–5 weeks sooner; leaf acid phosphatase(APase) activity and chlorophyll content both increased significantly; root-to-shoot ratio increased significantly at high P, although it was unaffected at low P; lateral root respiration rate showed no change, suggesting that CO_2 did not affect P depletion via metabolic changes to the roots; the total biomass at final harvest was significantly higher at both low and high P. Our data showed that the increased rate and amount of P depletion during plant growth under elevated CO_2 occurred in association with alterations in leaf biochemical properties, i.e., enhanced activities of leaf APase and increased leaf chlorophyll content.  相似文献   

9.
Interrelationships between ontogeny, allometric mass, and carbon (C): nitrogen (N): phosphorus (P) ratios were quantified in Cuphea, a semi-domesticated indeterminate and phenotypically plastic potential oilseed crop. Relative growth rate and net assimilation rate were estimated as functions of growth stages, phenotypic traits and C:N:P ratios. Ontogenically, N:P ratios in reproductive and metabolic tissues were least variable and were mainly affected by allometric leaf mass and relative growth rate. Reproductive mass is best predicted by allometric stem mass and C:N ratio in structural and metabolic tissues; whereas, net assimilation rate is best predicted by allometric total branch length and relative growth rate. The conservative N:P ratios found in reproductive and metabolic tissues are important in determining reproductive allocation in Cuphea. Large antagonistic effects of C:N on N:P ratios found in different plant tissues suggest that maximum reproductive allocation can be attained by manipulating N:P ratio during ontogeny. A greater investment of resources in reproduction may be possible for this semi-domesticated crop if nutrient and mass allocation to supporting stems and roots can be altered for the benefit of reproductive biomass.  相似文献   

10.
ABSTRACT

Nutrient requirements of the saskatoon (Amelanchier alnifolia: Rosaceae), a relatively new horticultural crop on the Canadian prairies, are unknown. In this study, two-year old saskatoon plants of the cultivar ‘Smoky’ were grown in a greenhouse in pots under four different soil nitrogen (N) regimes (20, 40, 60, and 80 mg N L?1). Half the plants were harvested after one growing season. After a five-month period of dormancy, the remaining plants were grown for a second growing season under the same soil N regimes. At harvest, plant growth, dry weight biomass, and leaf N concentration were measured, and soil N uptake was calculated. In both years, leaf N concentration and plant N uptake were strongly positively correlated (first year r = 0.93; second year r = 0.95) and increased linearly with an increase in soil N. Stem diameter and new shoot growth increased in both years of the study in response to additional N. The soil N treatments had no significant effect on plant biomass during the first growing season. In the second year, stem, root, total shoot and total plant biomass increased with increasing soil N.  相似文献   

11.
不同品种油菜生长后期体内氮素转运及再分配差异研究   总被引：1，自引：0，他引：1  
为探明影响油菜生长后期氮素再分配的生理因素及其与氮素利用效率的关系,本文在严格控制氮素供应水平的砂培条件下,采用15N示踪技术研究了不同氮素水平下2个油菜品种吸收氮素后在体内的分配、转运及损失情况。结果表明,供试2个油菜品种的生物产量、籽粒产量、籽粒含氮量、植株全氮、籽粒全氮、收获指数和氮收获指数均存在较大差异,且以上差异因氮素水平不同而有所不同。常氮处理下,品种"742"的生物产量、籽粒产量、籽粒全氮、收获指数和氮素收获指数均高于品种"814";低氮处理下,品种"742"的植株含氮量、籽粒含氮量、收获指数和氮素收获指数高于品种"814",而生物产量、籽粒产量、植株全氮和籽粒全氮低于品种"814"。采用15N示踪方法测定油菜生长后期氮素再分配的结果表明,供试油菜品种生长后期营养器官氮素减少量及其比例、转向生殖器官的氮素再分配量存在明显差异。不同氮素水平下,品种"742"大多数营养器官的氮素减少量均高于品种"814",而且茎的减少量差异最为明显。常氮水平下,品种"742"根、叶中氮素减少比例均少于品种"814",而茎中氮素减少量远远大于品种"814";低氮水平下,品种"742"根、茎、叶中氮素减少比例均大于品种"814"。在常氮和低氮处理下转向生殖器官的氮素再分配量均表现为,品种"742"向角果皮再分配的氮素低于品种"814",向籽粒再分配的氮素则高于"814"。T检验结果表明,2个品种除常氮条件下向角果皮再分配的氮素之外,其他再分配氮素的差异都达到显著水平,说明油菜生长后期由营养器官向生殖器官的氮素再分配有助于提高氮素利用效率。油菜生长后期氮素损失量表现为,品种"742"在常氮处理下的氮素损失量及其比例小于品种"814",低氮处理时反之。  相似文献   

12.
Substrate quality and decomposition (measured as CO2 release in laboratory microcosms) of fresh leaf litter and fine roots of Cupressus lusitanica, Pinus patula, Eucalyptus grandis and native forest trees were studied. Changes in litter chemistry in each forest stand were analysed by comparing fresh leaf litter (collected from trees) and decomposed litter from the forest floor. Elemental concentrations, proximate fractions including monomeric sugars, and cross polarisation magic-angle spinning (CPMAS) 13C NMR spectra were analysed in leaf litters, decomposed litter and fine roots. Leaf litters and fine roots varied in their initial substrate chemistry with Ca concentration in leaf litters being higher than that in fine roots. In each stand, fine roots had a higher acid unhydrolysable residue (AUR) (except for the Pinus stand), higher holocellulose concentration and lower concentration of water-soluble extractives (WSE) and dichloromethane extractives (NPE) than fresh leaf litter. Likewise, 13C NMR spectra of fine roots showed lower alkyl and carboxyl C, and higher phenolic (except P. patula), aromatic and O-alkyl C proportions than leaf litters. Compared with fresh leaf litter, decomposed litter had lower concentrations of potassium, holocellulose, WSE, NPE, arabinose and galactose, similar or higher concentrations of Mg, Ca, S and P, and higher concentrations of N and AUR. CPMAS 13C NMR spectra of decomposed litter showed a higher relative increase in signal intensity due to methoxyl C, aromatic C, phenolic C and carboxylic C compared with alkyl C. In a microcosm decomposition study, the proportion of initial C remaining in leaf litter and fine roots significantly fitted an exponential regression model. The decomposition constants (k) ranged between 0.0013 and 0.0030 d−1 for leaf litters and 0.0010-0.0017 d−1 for fine roots. In leaf litters there was a positive correlation between the k value and the initial Ca concentration, and in fine roots there was an analogous positive correlation with initial WSE. Leaf litters decomposed in the order Cupressus>native forest>Eucalyptus∼Pinus, and fine roots in the order Pinus>native forest>Cupressus∼Eucalyptus. In each stand the fine root decomposition was significantly lower than the leaf litter decomposition, except for the P. patula stand where the order was reversed.  相似文献   

13.
This study investigated management strategies to increase deep root growth and crop nitrogen (N) uptake by rocket grown as baby leaf in coarse sandy soil. Stage I (sowing to first harvest) measured the effects of two sowing densities and two N fertilizer rates on root growth and total N uptake. In Stage II (first to second harvest), effects of leaf harvesting and late season N fertilizer application on root growth, total N uptake and deep 15N uptake were measured. At the end of Stage I, root depth was 0.68–0.90 m, and the large fertilizer application increased N uptake. Plant density increased root depth, N uptake and nitrogen use efficiency (NUE) early in this stage and biomass production at harvest. Leaf harvesting in Stage II affected root density but not root depth that reached 1.4 m. The ability for N uptake was greater from 0.6 m due to more roots and larger N inflow than from 1.1 m depth. Late season fertilizer increased N concentration and uptake but did not affect NUE and deep N uptake. During the growing season, 330–349 kg Ninorg/ha was lost from 0 to 1.0 m depth most likely by leaching. Management practices that increased root growth and N uptake were found to increase NUE in rocket production early in the season. The production system used N inefficiently and smaller applications, plant density, leaf harvesting and other changes of management are required to reduce leaching.  相似文献   

14.
Herbivores can indirectly affect ecosystem productivity by modifying feedbacks that occur between dominant plants and below-ground properties, especially through altering nutrient availability in soil. The aim of this study was to examine, under controlled conditions, the effect of simulated browsing by large herbivores on the growth characteristics of downy birch (Betula pubescens), a dominant tree species of native regenerating forests in northern Britain, and to determine how effects of browsing on tree growth cascaded through to soil microbial communities, thereby affecting nutrient availability in soil. Downy birch seedlings were grown in mesocosms for 2 years and subjected to simulated browsing in the form of defoliation and clipping treatments. Upon destructive harvest, a number of measures of both tree growth characteristics and soil biological and nutrient properties were made. Clipping of birch trees significantly reduced total root biomass (27%), fine root biomass (29%), coarse root biomass (27%) and above-ground biomass (18%), whereas defoliated trees were significantly shorter than non-defoliated trees. Despite these significant and negative effects of browsing on tree growth, soil biological properties remained largely unaffected, other than rates of N mineralisation, which were greater under defoliated trees. We conclude that other factors, such as herbivore effects on litter quantity and quality which feedback to soil biological properties in the longer-term are more important in determining ecosystem responses to browsing.  相似文献   

15.
This research was designed to study the effects of drought on pigeon pea [Cajanus cajan (L.) Millsp.] morphology, biomass, and vessel diameter. Cultivated seeds of pigeon pea (cv. Georgia-II) were germinated, maintained in an environmental chamber, and arranged as a split-plot design with four replications; harvest was the main effect and watering regimens were tested against residual error. Plants were watered every 2, 4, 8, 16, or 32 days. Number of stems and leaves, as well as total plant height, were measured weekly. Dry weight (DW) of roots, stems, and leaves were recorded at each harvest, and root cross sections were viewed to determine vessel diameter. Results indicated that plant morphology, biomass, and vessel diameter were significantly affected by harvest and watering regimen. Plants watered more frequently had more stems and leaves, grew taller, accumulated greater DW, and had larger diameter vessels within root tissue.  相似文献   

16.
We present novel length to ash-free dry mass and preclitellar diameter to ash-free dry mass allometric equations for seven earthworm species from the families Megascolecidae and Lumbricidae, all of which are exotic and most of which are of ecological concern in North America: Eisenia hortensis, Eisenia fetida, Dendrodrilus rubidus, Lumbricus rubellus, Octolasion sp., Amynthas hilgendorfi, and Perionyx excavatus. We also present a length-biomass allometric equation for one enchytraeid, Mesenchytraeus sp. All relationships between length and biomass, and diameter and biomass were statistically significant at the species and family level (P<0.001). The predictive powers of these allometric regressions (as coefficients of determination, r2) were species-specific, and ranged widely from 0.27 to 0.93. Length-biomass regressions provided more predictive power and precision overall than preclitellar diameter-biomass calculations at both the species and the family levels. An ANCOVA followed by orthogonal contrasts determined that, while the slopes of these regressions did not differ significantly between the two earthworm families, significant differences in slopes of length-biomass regressions existed among species within families, indicating the utility of having species-level equations for accurate biomass predictions. With these allometric relationships, we aim to improve the estimation of earthworm biomass in order to facilitate investigations of how exotic-invasive earthworm species impact soil ecosystems.  相似文献   

17.
The role of tree leaf mulch and nitrogen fertilizer on turfgrass soil quality   总被引：11，自引：0，他引：11  
 The influence of tree leaf amendment and N fertilization on soil quality in turfgrass environments was evaluated. Our objective was to assess changes in soil quality after additions of leaf materials and N fertilization by monitoring soil chemical and physical parameters, microbial biomass and soil enzymes. Established perennial ryegrass (Lolium perenne) plots were amended annually with maple (Acer spp.) leaves at three different rates (0, 2240, and 4480 kg ha–1 year–1) and treated with three nitrogen rates (0, 63, and 126 kg N ha–1 year–1). Tree leaf mulching did not significantly affect water infiltration or bulk density. However, trends in the data suggest increased infiltration with increasing leaf application rate. Tree leaf mulching increased total soil C and N at 0–1.3 cm depth but not at 1.3–9.0 cm. Extracted microbial phospholipid, an indicator of microbial biomass size, ranged from 28 to 68 nmol phospholipid g–1 soil at the 1.3–9.0 cm depth. The activity of β-glucosidase estimated on samples from 0–1.3 cm and 1.3–9.0 cm depths, and dehydrogenase activity estimated on samples from 1.3–9.0 cm were significantly increased by leaf mulching and N fertilizer application. Changes in microbial community composition, as indicated by phospholipid fatty acid methyl ester analysis, appear to be due to seasonal variations and did not reflect changes due to N or leaf amendment treatments. There were no negative effects of tree leaf mulching into turfgrass and early data suggest this practice will improve soil chemical, physical, and biological structure. Received: 10 December 1997  相似文献   

18.
紫茎泽兰叶片凋落物对入侵地4 种草本植物的化感作用   总被引：5，自引：2，他引：3  
为了明确紫茎泽兰叶片凋落物对入侵地草本植物的化感作用, 研究了不同浓度紫茎泽兰叶片凋落物水提液对入侵地草本植物多年生黑麦草、白三叶、辣子草和紫花苜蓿种子萌发和幼苗生长的影响, 同时结合土培试验研究了叶片凋落物在入侵地土壤中的化感作用。结果表明, 除多年生黑麦草外, 水提液对其他3 种草本植物种子萌发均产生了显著的化感抑制作用, 且水提液的浓度越高抑制效果越强; 低浓度水提液对紫花苜蓿和辣子草的幼苗生长存在显著化感促进作用, 高浓度的水提液对除多年生黑麦草外的其他3 种植物幼苗的生长存在显著化感抑制作用, 水提液对多年生黑麦草幼苗生长的影响不显著; 土壤中按照50 g·kg-1的比例添加叶片凋落物后, 显著抑制了白三叶的生长, 而添加活性炭后, 白三叶的单株生物量相对于未添加活性炭的处理增加71.25%, 进一步证实叶片凋落物在土壤中的化感抑制作用。这说明外来入侵植物紫茎泽兰可能通过其叶片凋落物在入侵地土壤中降解, 释放化感物质, 抑制伴生植物的种子萌发和幼苗生长, 为自身创造有利的生长环境, 实现其成功入侵和扩张。  相似文献   

19.
Partitioning of the quantities of C lost by leaf litter through decomposition into (i) CO2 efflux to the atmosphere and (ii) C input to soil organic matter (SOM) is essential in order to develop a deeper understanding of the litter-soil biogeochemical continuum. However, this is a challenging task due to the occurrence of many different processes contributing to litter biomass loss. With the aim of quantifying different fluxes of C lost by leaf litter decomposition, a field experiment was performed at a short rotation coppice poplar plantation in central Italy. Populus nigra leaf litter, enriched in 13C (δ13C ∼ +160‰) was placed within collars to decompose in direct contact with the soil (δ13C ∼ −26‰) for 11 months. CO2 efflux from within the collars and its isotopic composition were determined at monthly intervals. After 11 months, remaining litter and soil profiles (0-20 cm) were sampled and analysed for their total C and 13C content. Gas chromatography (GC), GC-mass spectrometry (MS) and GC-combustion-isotope ratio (GC/C/IRMS) were used to analyse phospholipid fatty acids (PLFA) extracted from soil samples to identify the groups of soil micro-organisms that had incorporated litter-derived C and to determine the quantity of C incorporated by the soil microbial biomass (SMB). By the end of the experiment, the litter had lost about 80% of its original weight. The fraction of litter C lost as an input into the soil (67 ± 12% of the total C loss) was found to be twice as much as the fraction released as CO2 to the atmosphere (30 ± 3%), thus demonstrating the importance of quantifying litter-derived C input to soils, in litter decomposition studies. The mean δ13C values of PLFAs in soil (δ13C = −12.5‰) showed sustained incorporation of litter-derived C after one year (7.8 ± 1.6% of total PLFA-C). Thus, through the application of stable 13C isotope analyses, we have quantified two major C fluxes contributing to litter decomposition, at macroscopic and microscopic levels.  相似文献   

20.
套作大豆形态、光合特征对玉米荫蔽及光照恢复的响应   总被引：6，自引：3，他引：3  
为探寻大豆在荫蔽胁迫及光照恢复后的形态建成和光合生理的响应策略,选用‘简阳九月黄’、‘江浦黑豆’和‘永胜黑豆’3个大豆材料,以单作和玉米?大豆带状套作种植模式为研究对象,分析套作荫蔽及光照恢复后大豆形态特征、光合速率、叶片解剖结构、光合色素含量等参数的响应特征。结果表明:套作种植下,大豆在第5片复叶展开(V5)期明显受玉米荫蔽胁迫,与单作大豆相比,株高显著增加,茎粗和地上部分生物量显著降低;其茎、叶和柄生物量分别是地上部生物量的58%、37%和6%,而单作下分别为36%、50%和14%,套作荫蔽下大豆的地上部分生物量分配中心由叶片改变为茎秆。同时,叶片厚度、栅栏组织厚度、海绵组织厚度、叶绿素a含量、叶绿素a/b及净光合速率下降,但叶绿素b含量和栅栏组织厚度/海绵组织厚度比值增加。玉米收获解除荫蔽胁迫后,在大豆鼓粒期(R6),株高、茎粗、叶面积和地上部分生物量积累与单作的差异缩小,茎、叶和柄生物量为地上部生物量的41%、49%和10%;叶片、栅栏组织和海绵组织厚度比V5期(玉豆共生期)分别增加117%、99%和81%;光合色素与单作相比差异不显著,但净光合速率显著低于单作。玉米?大豆带状套作下的3个大豆材料的单株产量差异较大,‘简阳九月黄’、‘江浦黑豆’和‘永胜黑豆’的单株产量分别较单作下降33%、64%和40%。因此,大豆能够通过形态、光合生理特征的可塑性来适应光环境,但品种间存在差异。  相似文献   

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