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1.
1
The stoichiometry of resources is increasingly acknowledged as a major control of consumer activity and abundance. Chemical properties of litter, the main source of food for decomposers, are likely to be important drivers of decomposer activity.
2
Theory predicts a high control of resource stoichiometry on the abundance of consumer organisms that maintain strict homeostasis, due to costs associated with the regulation of nutrient balance in their body tissue. Decomposer efforts in nutrient acquisition should be related to imbalances in resource stoichiometry.
3
A 21 year old experimental plantation of monospecific plots of trees with leaves of contrasting chemistry was used to test four hypotheses: (i) soil and litter nutrient stoichiometry (C, N, P) are linked; (ii); soil enzyme activity ratios and stoichiometry are linked; (iii) earthworms’ tissue stoichiometry does not depend on soil and litter stoichiometry (homeostasis); (iv) earthworm density is dependent upon phosphorus availability, the most limiting nutrient in soils at this site, and, to a lesser extent, to nitrogen availability.
4
We found (i) no relationship between litter and soil stoichiometry, (ii) microbial activity was linked to soil stoichiometry, (iii) earthworms showed strict homeostasis in their tissue and (iv) earthworm abundance increased with P availability.
5
We discuss the mechanisms that might lead to these patterns.
  相似文献   

2.
Silicon (Si) is widely distributed in nature and can promote plant growth under various biotic and abiotic stresses. Drought stress seriously affects plant growth and the concentration and ecological stoichiometry of nutrients. Integrated nutrient management effectively protects plants from stresses. However, the role of water and Si availability on element concentrations and stoichiometry in plantain (Plantago lanceolata L.) are unclear. Accordingly, this study observed changes in the concentration and stoichiometry of macro- and micro-elements in plantain leaves supplied with various levels of Si under variable water availabilities through a greenhouse experiment. Supplemental Si increased Si concentration of leaves under both well-watered and drought conditions. Without supplemental Si, drought conditions decreased concentrations of carbon (C), C: nitrogen (N), C: phosphorus (P), silicon (Si):N, Si:P and increased concentrations of N, P, N:P, Si:C, calcium (Ca2+), magnesium (Mg2+), iron (Fe), manganese (Mn), zinc (Zn), and copper (Cu). Increased Si under water stress increased concentrations of C, C:N, C:P, Si:C, Si:N, and Si:P, and decreased concentrations of Ca2+, sodium (Na+), and Mg2+. These results suggested that exogenous Si changed the concentrations and ecological stoichiometry of macro- and micro-elements.  相似文献   

3.
Two methods of N transfer between plants—by litter decomposition and root-to-root exchange—were examined in mixed plantations of N-fixing and non-fixing trees. Nitrogen transfers from decaying litters were measured by placing 15N-labelled litters from four actinorhizal tree species around shoots of containerized Prunus avium. Nitrogen transfers by root-to-root exchanges were measured after foliar NO3-15N fertilization of Alnus subcordata and Elaeagnus angustifolia growing in containers in association with P. avium. During the first 2 years of litter decomposition, from 5–20% of the N, depending on the litter identity, was released and taken up by P. avium. N availability in the different litters was strongly correlated with the amount of water-soluble N, which was highest in leaves of E. angustifolia. In the association between fixing and non-fixing plants, 7.5% of the A. subcordata N and 25% of E. angustifolia N was transferred to P. avium by root exchange. These results showed that the magnitude of N transfers by root exchange depended on the associated N2-fixing species. Among the species investigated, E. angustifolia displayed the highest capacity for exudating N from roots as well as for releasing N from litters. These qualities make this tree a promising species for enhancing wood yields in mixed stands.  相似文献   

4.
“稻鸭共生”养分归还特征及水稻植株对氮、磷的吸收   总被引：3，自引：0，他引：3  
"稻鸭共生"是对我国传统农业稻田养鸭的继承与发展。在长江流域双季稻主产区湖南布置了稻田养鸭田间试验,以常规稻作为对照,研究早、晚稻两季"稻鸭共生"养分归还特征及对水稻植株氮、磷吸收的影响。结果表明:两季"稻鸭共生"后,稻田可增加鸭粪碳229.87 kg.hm 2、鸭粪氮18.22 kg.hm 2、鸭粪磷17.75 kg.hm 2。"稻鸭共生"归还稻田土壤的碳、氮、磷量分别为1 491.21 kg.hm 2、66.02 kg.hm 2、25.14 kg.hm 2,比常规稻作分别提高20.43%(P>0.05)、55.81%(P<0.05)、379.00%(P<0.05)。"稻鸭共生"归还稻田土壤的碳、氮、磷量表现为碳>氮>磷,归还的碳、氮量以水稻根碳、氮占明显优势,归还的磷量以鸭粪磷占明显优势。与常规稻作相比,土壤全氮含量提高5.73%,全磷含量显著提高6.25%;"稻鸭共生"提高了早、晚稻根和秸秆的全氮、全磷含量及早、晚稻籽粒的全磷含量,增加了早、晚稻秸秆的氮、磷吸收量和早、晚稻根的磷吸收量,降低了双季稻产量及籽粒的氮、磷积累量。"稻鸭共生"对水稻植株磷的影响效果好于氮。  相似文献   

5.
黄河三角洲自然保护区植被与土壤C、N、P化学计量特征   总被引：2，自引：1，他引：1  
为阐明黄河三角洲自然保护区生态系统的元素含量水平和化学计量特征并判断该区域植被生长的限制因子,选择保护区5种典型植物群落翅碱蓬、碱蓬、芦苇、柽柳和白茅为研究对象,测定植物不同器官和土壤剖面中有机碳、全氮、全磷含量,分析保护区植物群落与土壤的C、N、P化学计量特征。结果显示:5种群落中典型植物各器官C和P含量规律大体一致,除白茅和柽柳外,均表现为叶根茎,白茅茎的C和P含量高于根。不同植物器官N含量则表现出一致的变化规律,均为叶茎根。各植被类型叶片N∶P值均小于12,且与根系的N∶P值接近。土壤C、N含量的平均值分别为4.78 g?kg~(-1)、0.32 g?kg~(-1),均低于全国水平。P含量的平均值为0.53 g?kg~(-1),略低于全国水平。不同土层之间土壤元素含量差异不显著。不同群落土壤C∶N∶P值不同,同一群落不同土层的土壤C∶N∶P值变异性较小。植物叶片C、N、P含量以及C∶N、C∶P与0~10 cm、10~20 cm、20~40 cm土层土壤C、N含量之间均存在显著的相关关系(P0.05)。以上结果表明,黄河三角洲自然保护区不同土层土壤C、N、P含量相对稳定,总体低于全国水平,土壤N的匮乏引起了C∶N和C∶P值的变化。植物叶片和根系的C∶P值接近,说明生态系统元素循环相对稳定,同时叶片N∶P值小于12,进一步说明土壤中N的匮乏使其成为植物生长的限制因子。  相似文献   

6.
Chronic N deposition to forests may induce N saturation and stand decline, leading to reduced ecosystem N retention capacity, triggered by a shift from N limitation of trees to limitation by another nutrient. We conducted a 15N soil labelling experiment in non-fertilized and P-fertilized plots at two elevations in an N-saturated Mediterranean-fir (Abies pinsapo) forest in southern Spain which shows P limitation symptoms. Root-exclusion was applied to identify the relative contributions of roots (plus mycorrhizal fungi) uptake, and heterotrophic immobilization by free-living microbes, to N retention. Overall 15N recovery from the litter, 0–15-cm soil and root-uptake components was c.a. 35% higher in P-fertilized than in non-fertilized plots at both elevations. In non-fertilized plots, soil was the biggest sink for added 15N. Phosphorus fertilization increased the competitive ability of tree roots for soil N resulting in equal importance of the autotrophic (roots plus associated mycorhizal fungi) and heterotrophic (free-living microbes) components with respect to total 15N recovery in P-fertilized plots. Phosphorus addition increased litter and soil N immobilization only if roots had been excluded. By combining in situ fertilization, root-exclusion and isotope labelling we have demonstrated that reduced N retention capacity and dominance of soil microbial over plant immobilization in a N-saturated forest results from a shift from N to P limitation of trees, while alleviation of P limitation makes tree roots and associated mycorrhizal fungi competitive for N against free soil microorganisms.  相似文献   

7.
Some herbaceous plant species have been shown to dynamically alter the hydraulic properties of their roots in response to sudden changes in the concentrations of mobile nutrients. These hydraulic adaptations effectively allow plants to ‘chase' mobile nutrients across the rhizosphere. Trees, on the other hand, could mitigate effects of heterogeneous, dynamic soil environments with extensive root systems as such systems would effectively equalize nutrient availability. In addition, large dendritic root systems would reduce the effectiveness of rapid, localized, physiological hydraulic changes as these local changes might cancel each other at lower‐order root junctions. Thus, the aim of this study was to determine if trees (Eucalyptus grandis) employ short‐term (minutes to hours), physiological hydraulic changes or rely on long‐term (days), growth‐based hydraulic acclimations to enhance mobile nutrient uptake. We used two nutrients, nitrogen (N) and phosphorus (P), that are characterized by contrasting soil mobility: N being mobile and P immobile. Transpiration, whole‐plant hydraulic resistance (liquid phase), and the hydraulic resistance of single roots of E. grandis plants grown in high and low N combined with high and low P availability were measured. In general, plants grown with high N availability had lower whole‐plant hydraulic resistance than plants grown with low N availability. When N or P were in short supply, a sudden addition of N or P did not change either single‐root or whole‐plant hydraulic resistance at a given leaf water potential. However, addition of N reduced the transpiration rate, thus, enhancing plant water status, suggesting that E. grandis behavior prioritizes water conservation over N uptake in short‐term. Prolonged exposure to low nutrient availability resulted in high overall hydraulic resistance further suggesting prioritization of water conservation over N gain.  相似文献   

8.
This study examines the potential, magnitude, and causes of enhanced biological N2 fixation (BNF) by common beans (Phaseolus vulgaris L.) through bio-char additions (charcoal, biomass-derived black carbon). Bio-char was added at 0, 30, 60, and 90 g kg−1 soil, and BNF was determined using the isotope dilution method after adding 15N-enriched ammonium sulfate to a Typic Haplustox cropped to a potentially nodulating bean variety (CIAT BAT 477) in comparison to its non-nodulating isoline (BAT 477NN), both inoculated with effective Rhizobium strains. The proportion of fixed N increased from 50% without bio-char additions to 72% with 90 g kg−1 bio-char added. While total N derived from the atmosphere (NdfA) significantly increased by 49 and 78% with 30 and 60 g kg−1 bio-char added to soil, respectively, NdfA decreased to 30% above the control with 90 g kg−1 due to low total biomass production and N uptake. The primary reason for the higher BNF with bio-char additions was the greater B and Mo availability, whereas greater K, Ca, and P availability, as well as higher pH and lower N availability and Al saturation, may have contributed to a lesser extent. Enhanced mycorrhizal infections of roots were not found to contribute to better nutrient uptake and BNF. Bean yield increased by 46% and biomass production by 39% over the control at 90 and 60 g kg−1 bio-char, respectively. However, biomass production and total N uptake decreased when bio-char applications were increased to 90 g kg−1. Soil N uptake by N-fixing beans decreased by 14, 17, and 50% when 30, 60, and 90 g kg−1 bio-char were added to soil, whereas the C/N ratios increased from 16 to 23.7, 28, and 35, respectively. Results demonstrate the potential of bio-char applications to improve N input into agroecosystems while pointing out the needs for long-term field studies to better understand the effects of bio-char on BNF.  相似文献   

9.
The objectives of this study were to evaluate the contribution of arbuscular mycorrhizal (AM) fungal hyphae to 15N uptake from vineyard cover crop litter (Medicago polymorpha), and to examine the soil microbial community under the influence of mycorrhizal roots and extraradical hyphae. Mycorrhizal grapevines (Vitis vinifera) were grown in specially designed containers, within which a polyvinyl chloride (PVC) mesh core was inserted. Different sizes of mesh allowed mycorrhizal roots (mycorrhizosphere treatment) or extraradical hyphae (hyphosphere treatment) to access dual labeled 15N and 13C cover crop litter that was placed inside the cores after 4 months of grapevine growth. Mesh cores in the bulk soil treatment, which served as a negative control, had the same mesh size as the hyphosphere treatment, but frequent rotation prevented extraradical hyphae from accessing the litter. Grapevines and soils were harvested 0, 7, 14, and 28 days after addition of the cover crop litter and examined for the presence of 15N. Soil microbial biomass and the soil microbial community inside the mesh cores were examined using phospholipid fatty acid analysis. 15N concentrations in grapevines in the hyphosphere treatment were twice that of grapevines in the bulk soil treatment, suggesting that extraradical hyphae extending from mycorrhizal grapevine roots may have a role in nutrient utilization from decomposing vineyard cover crops in the field. Nonetheless, grapevines in the mycorrhizosphere treatment had the highest 15N concentrations, thus highlighting the importance of a healthy grapevine root system in nutrient uptake. We detected similar peaks in soil microbial biomass in the mycorrhizosphere and hyphosphere treatments after addition of the litter, despite significantly lower microbial biomass in the hyphosphere treatment initially. Our results suggest that although grapevine roots play a dominant role in the uptake of nutrients from a decomposing cover crop, AM hyphae may have a more important role in maintaining soil microbial communities associated with nutrient cycling.  相似文献   

10.
Plants and microbes have limited stoichiometric flexibility to take up and store nitrogen (N) and phosphorus (P). Variation in the relative availability of N and P to plants and microbes may therefore affect how strongly N and P are held in terrestrial ecosystems with important implications for net primary productivity and carbon sequestration. We hypothesized that an increase in P availability in a P-poor soil would increase N uptake by plants and microbes thereby reducing N loss. We grew mixtures of the C3 grass Phalaris aquatica L. and the legume Medicago sativa L. in mesocosms with soils low in P availability and then used a novel technique by adding a 15N tracer with and without 1 g P m−2 to soil with different moisture and available N conditions, and measured the 15N recovery after 48 h in microbes, plants and soil. In contrast to our hypothesis, we found that P addition reduced 15N in microbes without water stress by 80% and also reduced total15N recovery, particularly without water stress. Water stress in combination with N addition further showed low total 15N recovery, possibly because of reduced plant uptake thereby leaving more 15N in the soil available for nitrification and denitrification. Our results suggest that P addition can result in large gaseous N loss in P-poor soils, most likely by directly stimulating nitrification and denitrification.  相似文献   

11.
Nonnodulated soybean plants (Glycine max. [L.] Merr. ‘Lee') were supplied with nutrient solutions containing growth limiting concentrations of N or P to examine effects on N‐ and P‐uptake efficiencies (mg nutrient accumulated/gdw root) and utilization efficiencies in dry matter production (gdw2/mg nutrient). Nutritional treatments were imposed in aerial environments containing either 350 or 700 μL/L atmospheric CO2 to determine whether the nutrient interactions were modified when growth rates were altered.

Nutrient‐stress treatments decreased growth and N‐ and P‐uptake and utilization efficiencies at 27 days after transplanting (DAT) and seed yield at maturity (98 DAT). Atmospheric CO2 enrichment increased growth and N‐ and P‐utilization efficiencies at 27 DAT and seed yield in all nutritional treatments and did not affect N‐ and P‐uptake efficiencies at 27 DAT. Parameter responses to nutrient stress at 27 DAT were not altered by atmospheric CO2 enrichment and vice versa. Nutrient‐stress treatments lowered the relative seed yield response to atmospheric CO2 enrichment.

Decreased total‐N uptake by P‐stressed plants was associated with both decreased root growth and N‐uptake efficiency of the roots. Nitrogen‐utilization efficiency was also decreased by P‐stress. This response was associated with decreased plant growth as total‐N uptake and plant growth were decreased to the same extent by P stress resulting in unaltered tissue N concentrations. In contrast, decreased total P‐uptake by N‐stressed plants was associated with a restriction in root growth as P‐uptake efficiency of the roots was unaltered. This response was coupled with an increased root‐to‐shoot dry weight ratio; thus shoot and whole‐plant growth were decreased to a much greater extent than total‐P uptake which resulted in elevated P concentrations in the tissue. Therefore, P‐utilization efficiency was markedly reduced by N stress.  相似文献   

12.
The availability of nitrogen (N) contained in crop residues for a following crop may vary with cultivar, depending on root traits and the interaction between roots and soil. We used a pot experiment to investigate the effects of six spring wheat (Triticum aestivum L.) cultivars (three old varieties introduced before mid last century and three modern varieties) and N fertilization on the ability of wheat to acquire N from maize (Zea mays L.) straw added to soil. Wheat was grown in a soil where 15N‐labeled maize straw had been incorporated with or without N fertilization. Higher grain yield in three modern and one old cultivar was ascribed to preferred allocation of photosynthate to aboveground plant parts and from vegetative organs to grains. Root biomass, root length density and root surface area were all smaller in modern than in old cultivars at both anthesis and maturity. Root mean diameter was generally similar between modern and old cultivars at anthesis but was greater in modern than in old cultivars at maturity. There were cultivar differences in N uptake from incorporated maize straw and the other N sources (soil and fertilizer). However, these differences were not related to variation in the measured root parameters among the six cultivars. At anthesis, total N uptake efficiencies by roots (total N uptake per root weight or root length) were greater in modern than in old cultivars within each fertilization level. At maturity, averaged over fertilization levels, the total N uptake efficiencies by roots were 292?336 mg N g?1 roots or 3.2?4.0 mg N m?1 roots for three modern cultivars, in contrast to 132?213 mg N g?1 roots or 0.93?1.6 mg N m?1 roots for three old cultivars. Fertilization enhanced the utilization of N from maize straw by all cultivars, but root N uptake efficiencies were less affected. We concluded that modern spring wheat cultivars had higher root N uptake efficiency than old cultivars.  相似文献   

13.
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   

14.
Competition for nutrients between plants and microbes is an important determinant for plant growth, biodiversity and carbon cycling. Perturbations such as drought affect the availability of nitrogen (N) and phosphorus (P), and may cause shifts in uptake of N and P between plants and microbes. Competitiveness for these nutrients may depend on how flexible plants and microbes are in taking up N and P. We used a novel dual isotope labelling technique (15N and 32P) to assess short-term uptake of N and P by plants and microbes affected by drought in two different plant–soil systems. Mesocosms were extracted from two grassland sites differing in soil nutrient availability and plant species. Half of the mesocosms were subjected to drought one week prior to injection of 15N (as KNO3) and 32P (as H3PO4) tracers. Uptake rates of NO3− and P in plants and microbes were estimated based on average source pool enrichment during the labelling period and on plant and microbial recovery of 15N and 32P measured after 4 days of labelling. Overall competition for N and P was reduced with drought as less NO3− and P was taken up in plants and microbes. However, plant uptake of NO3− was more sensitive to drought than microbial NO3− uptake, while microbial P uptake was more sensitive than plant P uptake. These different sensitivities to drought by plants and microbes may decouple the N and P cycle with increased drought conditions.  相似文献   

15.
Optimizing root phosphorus (P) acquisition to reduce intensive fertilizer use is a crucial pathway for sustainable agriculture, particularly as P is an important plant macronutrient, often limiting in a majority of soils worldwide. Although many studies have assessed plant growth and P acquisition, few studies have investigated the interactive effects of nitrogen (N)‐induced root modification on soil P processes or the understudied effects of soil calcium (Ca) dynamics on soil P bioavailability. In this study, we investigate soil P and Ca response in the rhizosphere of durum wheat (Triticum turgidum L. spp. durum). Wheat grown under controlled conditions preloaded for 20 d with two N treatments [preloaded low N (1 mmol KNO3 plant?1) and preloaded high N (2 mmol KNO3 plant?1)] were transferred to rhizoboxes for 12 d [days after transfer (DAT)]. Shoot and root biomass, P and Ca concentration, and plant‐available P and extractable Ca were determined every three days (0, 3, 6, 9, 12 DAT). Significantly higher root mass (P = 0.7%), root length (P = 1.8%) and total biomass (P = 2.2%) were found at the end of the experiment but exclusively for high N preloaded wheat. This greater root biomass was associated with lower root P concentration, suggesting a dilution response, while little difference was observed in shoot P concentration over the 12 d. However, Ca accumulated in both roots and shoots under both preloading N levels. Concurrently, soil‐extractable Ca declined, and plant‐available P increased (r = –0.62; P = 0.03%), presumably due to a promoting effect of Ca uptake on soil P availability; lower soil Ca in turn increased the repulsive forces between P ions and the negatively charged soil surface, resulting in an increased P availability in the soil solution. This study contributes to the understanding of the complex interplay between multi‐nutrient dynamics within the rhizosphere.  相似文献   

16.
Eutrofication is a threat against nutrient-poor habitats as increased amounts of nutrients in ecosystems may cause changes in the vegetation. Nitrogen (N) deposition leads to conversion of Calluna heathlands into graminoid dominated heath, but low availability of P may hinder or slow down this process.In this study the soil properties under two dominant heathland plants, the dwarf shrub Calluna vulgaris and the grass Deschampsia flexuosa, were investigated, with focus on nutrient content in the organic top soil and soil microbes during the main growing season and effects of nutrient amendments. The concentration of inorganic and dissolved organic N was significantly higher under D. flexuosa than C. vulgaris all though there were the same amounts of total N in the soil below the two species. N and P amendment enhanced available N and P in the soil, but added nutrients had little direct effects on microbes. The microbial biomass on the other hand was positively related to soil water content in fertilized plots indicating that this was due to an indirect effect of enhanced nutrient availability. Microbial N and P pools were respectively 1000 and 100 times higher than the pool of inorganic N and P, and microbes therefore may play an important role in regulating plant nutrient supply. Judged from responses of inorganic and microbial N and P concentrations to added N and P, N seemed to limit C. vulgaris and soil microbes below while P seemed to limit D. flexuosa and soil microbes below this species. There were lower rates of net nitrification, net ammonification and DOC and DON production rates during winter in the soil under C. vulgaris than below D. flexuosa, although all these rates were equal under the two species on an annual basis. This indicates that these microbial processes were taking place during winter but were affected by exudates from C. vulgaris.  相似文献   

17.
In this paper we try to interpret results from different investigations where an ecosystem with Norway spruce was manipulated with increased N and S deposition via the soil system. The site, in Skogaby in Southwest Sweden, had 1989–93 an annual deposition of 9 kg NH4-N; 7 kg NO3-N and 20 kg SO4-S ha–1. The stand was treated during 6 years with 100 kg N and 114 kg S ha– y–1 in the form of ammonium sulphate (NS treatment). The stand reacted with increased above ground production of 31% after 3 years of treatment. The uptake above ground of N was 155 kg ha–1 higher than in the control. Those trends were even stronger after 6 years of treatment. There were no decreases in the uptake of P, K, Ca or Mg (but for B) after 3 or 6 years of NS-treatment. Needle macro nutrient concentrations in relation to N decreased for several nutrients due to dilution effects. As result of the NS treatment pH increased markedly in the litter layer, and less, but significantly, in the humus layer. A decrease in pH value by about 0.3 units was found in the rest of the soil profile down to 50 cm. Dry mass of needle litter fall and litter layer both increased as a result of 6 years of NS-treatment. After three years of treatment 77–80% of all living fine roots in both control and NS treatment were found in the humus layer and the upper 10 cm of the mineral soil. The amount of living fine roots in the humus layer of NS-treated trees decreased to about one third of the control, and the amount of dead fine roots increased by 150% compared with untreated trees after 6 years of treatment. It is argued that the decreased amount of living and increased amount of dead fine roots not necessarily are indications of decreased root vitality. It can also be explained by increased root turnover rate and decreased decomposition rates of N rich new and old fine root litter. No inorganic N was leached from the control plots whereas the NS treated plots started to leach NO3 the second year of treatment. During 1989–1993 a total of 44 kg NO3-N and 30 kg NH4-N per ha was lost from the system which means that 88% of the N supplied was retained by the ecosystem. At first SO4 was adsorbed in the soil, but after five years of treatment the output was almost equal to the input.  相似文献   

18.
In experimental grasslands, a positive relationship between biomass production and plant diversity has often been found. Here, we compared a moderately species‐rich old sward with its grass‐dominated counterpart (12 vs. 8 species per 2.5 m2, or 8.3 vs. 0.7% yield proportion of dicots at the start of the experiment) established by herbicide application. We hypothesized an increased N, P and K uptake in the diverse sward related to a higher colonization rate with arbuscular mycorrhizal fungi (AMF), the presence of legumes, and complementary nutrient use of plant species. Phosphorus or N fertilizer application (according to contributions of AMF or legumes) were expected to balance the assumed smaller biomass production of the grass compared to the diverse sward. In two experimental years, N, P and K uptake, biomass production, N2 fixation, and intra‐ and extraradical AMF colonization were investigated in an untreated control and plots that were fertilized with P and N in a low (P1: 20 kg P ha?1; N1: 50 kg N ha?1) or a high dose (P2: 100 kg P ha?1; N2: 500 kg N ha?1) in both swards. Biomass production was larger in the grass compared to the diverse sward. The N, P and K uptake, accumulated over three harvests (or 1.5 years), was also larger in the grass sward. The biomass production ranged from 5.3 to 10.0 t ha?1 and accumulated nutrient uptake from 82 to191 kg N ha?1, 19 to 31 kg P ha?1 and 112 to 221 kg K ha?1. Small legume proportions resulted in an accumulated N2 fixation between 0 and 3 kg ha?1. In the second year, the root length colonized with AMF structures was larger in the diverse compared to the grass sward, and the root length colonized with arbuscules and coils was larger in the N2 treatment compared to the control in the diverse sward. There were hints to higher AMF abundance under conditions of limited P availability (low soil P content, high N:P ratio in plant biomass). We conclude that in semi‐natural grassland of moderate species richness several factors may affect the relationship between plant diversity and productivity, i.e., management, plant species identity, and the number of the plant species of the low‐diversity level.  相似文献   

19.
The introduction of N2‐fixing tree species in fast growing tree plantations is a sustainable management option aiming to reduce the risk of nitrogen (N) deficiency due to a large and frequent exportation of nutrients at harvest. Differences in soil mineral N preferences between Eucalyptus urophylla × grandis and Acacia mangium may, in addition to facilitation related to atmospheric N2 fixation, contribute to the success of mixed‐species plantations of the two species on nutrient‐poor soils of the coastal Congolese plains. We tested whether these two species differ in their preference for nitrate or ammonium by supplying either ammonium or nitrate enriched in 15N to six‐month‐old potted trees growing in an open‐air nursery. Although the uptake of nitrate tended to be higher than that of ammonium by both species, the difference was not significant and there was no significant difference between the species regarding their preferred form of soil mineral N. Despite much lower N contents in foliage, stems, and roots of eucalypt compared to acacia, the specific rates of N uptake were up to three times higher for eucalypt than acacia, which suggests that atmospheric N2 was the major source of N in the six‐month‐old acacias. We conclude that N2 fixation rather than complementarity for soil mineral nitrogen alleviates the competition between species in successful mixed eucalypt and acacia plantations.  相似文献   

20.
Mineral nutrient uptake can be enhanced in plants inoculated with vesicular‐arbuscular mycorrhizal fungi (VAMF). The effects of the VAMF Glomus fasciculatum on uptake of P and other mineral nutrients in sorghum [Sorghum bicolor (L.) Moench] were determined in greenhouse experiments for plants grown on a low P (3.6 mg kg‐1) soil (Typic Argiudolls) with P added at 0, 12.5, 25.0, and 37.5 mg kg‐1 soil. Enhancements of growth and mineral nutrient uptake because of the VAMF association decreased as soil applications of P increased above 12.5 nig kg‐1 soil. Root colonization with VAMF without added soil P resulted in increased dry matter yield equivalent to 12.5 mg P kg‐1 soil (25 kg P ha‐1). Total root length colonized with VAMF decreased as soil P level increased. Regardless of P added to the soil, mycorrhizal plants had higher leaf P concentrations and contents than did nonmycorrhizal plants. Enhanced contents, but not necessarily concentrations, of the other mineral nutrients were noted in shoots of mycorrhizal compared to nonmycorrhizal plants. Mycorrhizal plants had enhanced shoot contents of P, K, Zn, and Cu which could not be accounted for by increased growth. The VAMF associations with sorghum roots enhanced mineral nutrient uptake when P was sufficiently low in the soil.  相似文献   

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