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1.
Human management practices and large detritivores such as earthworms incorporate plant litter into the soil, thereby forming a heterogeneous soil environment from which plant roots extract nutrients. In a greenhouse experiment we investigated effects of earthworms and spatial distribution of 15N-labelled grass litter on plants of different functional groups [Lolium perenne (grass), Plantago lanceolata (forb), Trifolium repens (legume)]. Earthworms enhanced shoot and root growth in L. perenne and P. lanceolata and N uptake from organic litter and soil in all plant species. Litter concentrated in a patch (compared with litter mixed homogeneously into the soil) increased shoot biomass and 15N uptake from the litter in L. perenne and enhanced root proliferation in P. lanceolata when earthworms were present. Growth of clover (T. repens) was rather independent of the presence of earthworms and organic litter distribution: nevertheless, clover took up more nitrogen in the presence of earthworms and exploited more 15N from the added litter than the other plant species. The magnitude of the effects of earthworms and organic litter distribution differed between the plant species, indicating different responses of plants with contrasting root morphology. Aphid (Myzus persicae) reproduction was reduced on P. lanceolata in the presence of earthworms. We suggest that earthworm activity may indirectly alter plant chemistry and hence defence mechanisms against herbivores.  相似文献   

2.
Leys, used for grazing or production of forage to be conserved as silage or hay, are very important crops in northern areas. In order to measure the N2 fixation in leys of varying ages and during different parts of the season, detailed measurements were taken of yield, N2 fixation and the amounts of N remaining in the field after harvesting red clover (Trifolium pratense L.)-grass leys at a site in northern Sweden, where they are generally harvested twice per growing season. Entire plants, including stubble and roots, were sampled at the time of first and second harvest and, in addition, at the end of the growing season in three neighbouring fields, carrying a first, a second and a third year ley, respectively. N2 fixation was measured by both 15N isotope dilution (ID) and 15N natural abundance (NA) methods. The proportion of clover dry matter (DM) in the stands increased from the first to the second harvest, but the grasses dominated throughout the entire season, especially below ground. The N concentrations, in both herbage and whole plants, were about twice as high in the clover as in the grasses. Seasonal variations in N concentrations were minor, and total N contents followed the same trends as DM. The clover acquired nearly all of its N from N2 fixation: the proportion of N in clover herbage derived from N2 fixation was often >0.8 throughout the season. The variations in the amounts of N2 fixed during the course of the season corresponded well to the seasonal changes in clover biomass. Amounts of fixed N2 allocated to clover herbage during the whole season were in the range 4 to 6 g N m−2 in this unusually rainy year. Calculations of daily N allocation rates to herbage showed that N uptake rates were similar, and high, in grasses during May–June and July–August, while N2 fixation rates in clover were about 10-fold as high in July–August as in May–June, reflecting the need for N in clover growth. The proportion of N remaining in clover stubble and roots after the first and second harvests was about 60 and 25%, respectively, while about 60% of the N in grasses remained in stubble and roots after both harvests. The considerable amounts of biomass and N that were left in field after harvesting red clover-grass leys are important for re-growth of the plants and provide substantial N fertilization for the next crop in the crop rotation.  相似文献   

3.
The apparent transfer of N from clover to associated grass was evaluated over a four year period both on the basis of harvested herbage and by taking account of changes in N in stubble and root (to 10 cm depth) in swards with perennial ryegrass and three different white clover cultivars differing in leaf size. The large leaved Aran transferred 15% of its nitrogen while Huia transferred 24% and the small leaved Kent Wild White transferred 34%. When changes in stubble and root N were taken into account the percentage of N transferred was calculated to be 5% less than in harvested herbage only, as the small leaved types had proportionately more N in the roots and stolons, but the large leaved type was probably more competitive towards the grass.Loss of N from clover roots from July to October was compared to that from grass roots in a grass/white clover sward continuously stocked with steers using a method which incorporated tissue turnover and 15N dilution techniques. Less than 1 mg N m-2 d-1 was lost from the grass roots. In contrast 8 mg m-2 d-1 were estimated to be lost from clover roots while 12 mg N m-2 d-1 were assimilated.It is concluded that clover cultivar and competitive ability on grass have to be taken into account together with the relationship between N turnover in roots and N available for grass growth when modelling N transfer in grass/clover associations.  相似文献   

4.

Background and aims

Intercropping of legumes and cereals appears as an alternative agricultural practice to decrease the use of chemical fertilizers while maintaining high yields. A better understanding of the biotic and abiotic factors determining interactions between plants in such associations is required. Our study aimed to analyse the effect of earthworms on the legume–cereal interactions with a focus on the modifications induced by earthworms on the forms of soil phosphorus (P).

Methods

In a glasshouse experiment we investigated the effect of an endogeic earthworm (Allolobophora chlorotica) on the plant biomass and on N and P acquisition by durum wheat (Triticum turgidum durum L.) and chickpea (Cicer arietinum L.) either grown alone or intercropped. The modifications of the different organic and inorganic P forms in the bulk soil were measured.

Results

There was no overyielding of the intercrop in the absence of earthworms. Earthworms had a strong influence on biomass and resource allocation between roots and shoots whereas no modification was observed in terms of total biomass production and P acquisition. Earthworms changed the interaction between the intercropped species mainly by reducing the competition for nutrients. Facilitation (positive plant–plant interactions) was only observed for the root biomass and P acquisition in the presence of earthworms. Earthworms decreased the amount of organic P extracted with NaOH (Po NaOH), while they increased the water soluble inorganic P (Pi H2O) content.

Conclusions

In this experiment, earthworms could be seen as “troubleshooter” in plant–plant interaction as they reduced the competition between the intercropped species. Our study brings new insights into how earthworms affect plant growth and the P cycle.  相似文献   

5.
An experiment is described in which the magnitude of N transferred from damaged white clover roots to perennial ryegrass was determined, using 15N labelling of the grass plant. There was no effect on the growth and N-fixation of the clover plants after removing part of the root system. The 15N data suggested that N had been acquired by all grass plants, even in plants grown alone with no further N supplied after labelling. However, after quantifying the mobile and stored N pools of the grass plants it was evident that significant transfer of N from clover to grass only took place from damaged clover roots. Dilution of the atom% 15N in the roots of the grass plants grown alone, and in association with undamaged clover roots, was explained by remobilisation of N within the plant.  相似文献   

6.
Ke X  Scheu S 《Oecologia》2008,157(4):603-617
Management practices of arable systems determine the distribution of soil organic matter thereby changing decomposer animal activity and their impact on nutrient mineralization, plant growth and plant-herbivore interactions. Decomposer-mediated changes in plant growth and insect pest performance were investigated in wheat-aphid model systems in the greenhouse. Three types of litter distribution were established: litter patch at the soil surface (simulating mulching), litter patch deeper in soil (simulating ploughing) and litter homogeneously mixed into soil (simulating disk cultivation). The litter was labelled with (15)N to follow the mineralization and uptake of nutrients by the plants. Earthworms (Aporrectodea caliginosa) and Collembola (Protaphorura armata) were included as representatives of major functional groups of decomposers. Wheat (Triticum aestivum) was planted and aphids (Rhophalosiphum padi) were introduced to leaves as one of the most important pests. Earthworms, Collembola and litter distribution affected plant growth, N acquisition and aphid development in an interactive way. Earthworms and Collembola increased biomass of seeds, shoots and roots of wheat. Increased plant growth by earthworms and Collembola was mainly due to increased transfer of N from soil (rather than litter) into plants. Despite increasing plant growth, earthworms reduced aphid reproduction. Aphid reproduction was not correlated closely with plant N concentrations, but rather with the concentration of litter N in wheat. Unexpectedly, both Collembola and earthworms predominantly affected the mobilization of N from soil organic matter, and by altering the distribution of litter earthworms reduced infestation of crops by aphids via reducing plant capture of litter N, in particular if the litter was concentrated deeper in soil. The results suggest that management practices stimulating a continuous moderate increase in nutrient mobilization from soil organic matter rather than nutrient flushes from decomposing fresh organic matter result in maximum plant growth with minimum plant pest infestation.  相似文献   

7.
A pot experiment was conducted in a 14C-labelled atmosphere to study the influence of living plants on organic-N mineralization. The soil organic matter had been labelled, by means of a 200-days incubation, with 15N. The influence of the carbon input from the roots on the formation of microbial biomass was evaluated by using two different light intensities (I). Mineralization of 15N-labelled soil N was examined by following its fate in both the soil biomass and the plants. Less dry matter accumulated in shoots and roots at the lower light intensity. Furthermore, in all the plant-soil compartments examined, with the exception of rhizosphere respiration, the proportion of net assimilated 14C was lower in the low-I treatment than in the high-I treatment. The lower rates of 14C and 15N incorporation into the soil biomass were associated with less root-derived 14C. During the chamber period (14CO2-atmosphere), mineralized amounts of 15N (measured as plant uptake of 15N) were small and represented about 6.8 to 7.8% of the initial amount of organic 15N in the soil. Amounts of unlabelled N found in the plants, as a percentage of total soil N, were 2.5 to 3.3%. The low availability of labelled N to microorganisms was the result of its stabilization during the 210 days of soil incubation. Differences in carbon supply resulted in different rates of N mineralization which is consistent with the hypothesis that roots induce N mineralization. N mineralization was higher in the high-I treatment. On the other hand, the rate of mineralization of unlabelled stable soil N was lower than labelled soil 15N which was stabilized. The amounts of 15N mineralized in planted soil during the chamber period (43 days) which were comparable with those mineralized in unplanted soil incubated for 210 days, also suggested that living plants increased the turnover rate of soil organic matter.  相似文献   

8.
A previously undocumented association between earthworms and red wood ants (Formicaaquilonia Yarr.) was found during an investigation of the influence of wood ants on the distribution and abundance of soil animals in boreal forest soil. Ant nest mounds and the surrounding soil of the ant territories were sampled. The ant nest mound surface (the uppermost 5-cm layer) harboured a much more abundant earthworm community than the surrounding soil; the biomass of the earthworms was about 7 times higher in the nests than in the soil. Dendrodrilusrubidus dominated the earthworm community in the nests, while in soils Dendrobaenaoctaedra was more abundant. Favorable temperature, moisture and pH (Ca content), together with abundant food supply (microbes and decomposing litter) are likely to make a nest mound a preferred habitat for earthworms, provided that they are not preyed upon by the ants. We also conducted laboratory experiments to study antipredation mechanisms of earthworms against ants. The experiments showed that earthworms do not escape predation by avoiding contact with ants in their nests. The earthworm mucus repelled the ants, suggesting a chemical defence against predation. Earthworms probably prevent the nest mounds from becoming overgrown by moulds and fungi, indicating possible mutualistic relationships between the earthworms and the ants. Received: 21 November 1996 / Accepted: 3 April 1997  相似文献   

9.
Dominant tree species influence community and ecosystem components through the quantity and quality of their litter. Effects of litter may be modified by activity of ecosystem engineers such as earthworms. We examined the interacting effects of forest litter type and earthworm presence on invasibility of plants into forest floor environments using a greenhouse mesocosm experiment. We crossed five litter treatments mimicking historic and predicted changes in dominant tree composition with a treatment of either the absence or presence of nonnative earthworms. We measured mass loss of each litter type and growth of a model nonnative plant species (Festuca arundinacea, fescue) sown into each mesocosm. Mass loss was greater for litter of tree species characterized by lower C:N ratios. Earthworms enhanced litter mass loss, but only for species with lower C:N, leading to a significant litter × earthworm interaction. Fescue biomass was significantly greater in treatments with litter of low C:N and greater mass loss, suggesting that rapid decomposition of forest litter may be more favorable to understory plant invasions. Earthworms were expected to enhance invasion by increasing mass loss and removing the physical barrier of litter. However, earthworms typically reduced invasion success but not under invasive tree litter where the presence of earthworms facilitated invasion success compared to other litter treatments where earthworms were present. We conclude that past and predicted future shifts in dominant tree species may influence forest understory invasibility. The presence of nonnative earthworms may either suppress of facilitate invasibility depending on the species of dominant overstory tree species and the litter layers they produce.  相似文献   

10.
Earthworms and plants greatly affect belowground properties; however, their combined effects are more attractive based on the ecosystem scale in the field condition. To address this point, we manipulated earthworms (exotic endogeic species Pontoscolex corethrurus) and plants (living plants [native tree species Evodia lepta] and artificial plants) to investigate their combined effects on soil microorganisms, soil nutrients, and soil respiration in a subtropical forest. The manipulation of artificial plants aimed to simulate the physical effects of plants (e.g., shading and interception of water) such that the biological effects of plants could be evaluated separately. We found that relative to the controls, living plants but not artificial plants significantly increased the ratio of fungal to bacterial phospholipid fatty acids (PLFAs) and fungal PLFAs. Furthermore, earthworms plus living plants significantly increased the soil respiration and decreased the soil NH4+‐N, which indicates that the earthworm effects on the associated carbon, and nitrogen processes were greatly affected by living plants. The permutational multivariate analysis of variance results also indicated that living plants but not earthworms or artificial plants significantly changed the soil microbial community. Our results suggest that the effects of plants on soil microbes and associated soil properties in this study were largely explained by their biological rather than their physical effects.  相似文献   

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