Can a seed bank provide demographic and genetic rescue in a declining population of the endangered shrub <Emphasis Type="Italic">Acacia pinguifolia</Emphasis>?

Many threatened species suffer reduced genetic diversity as a result of small population size and isolation. However, species with a persistent seed bank may be buffered against genetic loss as seed banks are expected to accumulate the reproductive output of many seasons. For fire-dependent species in decline, prescribed ecological burning may be a means to stimulate germination and recover genetic diversity stored in the seed bank, providing a demographic and genetic rescue effect. Here we investigated the effectiveness of this strategy in a small, isolated and inbred population of the endangered shrub, Acacia pinguifolia. We surveyed genetic diversity and structure of remnant populations of A. pinguifolia and monitored regeneration before and after burning. Germination was stimulated by fire, but seedling numbers 18 months post-fire were low and barely above the number of adults killed by the fire. Genetic diversity was marginally higher in the post-fire seedling cohort than the pre-fire adults (H_E = 0.1 vs. 0.09, respectively). Outcrossing rates of open-pollinated seed from surrounding plants suggested moderately high levels of self-fertilisation (t _m  = 0.65) and analysis of fine-scale genetic structure implied pollen and seed dispersal over distances of several metres, suggesting that restricted gene flow and inbreeding may act to limit genetic diversity in the seed bank. We conclude that prescribed burning has not been immediately successful as a recovery strategy for this relictual population of A. pinguifolia, though future monitoring may detect additional recruits. Alternative conservation strategies, including performing inter-population crosses, may be required to restore genetic diversity and ameliorate extinction risks.     

Genetic comparisons between seed bank and <Emphasis Type="Italic">Stipa krylovii</Emphasis> plant populations

The soil seed bank represents the potential plant population since it is the source for population replacement. The genetic structure of a Stipa kryiovii (Roshev.) plant population and its soil seed bank was investigated in the Xilinguole Steppe of Inner Mongolia using random amplified polymorphic DNA (RAPD) analyses. The population was sampled at two sites that were in close proximity to each other (0.5 km apart). Thirty plants and 18 seed bank samples were taken from each site to determine the genetic diversity between sites and between sources (plant or seed). The material was analyzed using 13 primers to produce 92 loci. Eighty-six were multi-loci, of which 23 loci (26.74%) of allele frequencies showed significant differences (P ≤ 0.05). The genetic similarity between two seed bank sites was 0.9843 while the genetic similarity between two plant sites was 0.9619. Their similarities were all greater than that between the seed bank and plant populations. An analysis of their genetic structure showed that 87.86% of total variation was derived by two-loci. Genetic structures between plant and soil seed bank populations in S. krylovii were different due to the variance of mean gametic disequilibria and mean gene diversity. AMOVA results showed that the majority of variance (88.62%) occurred within sites, 12.75% was from between-groups. Further research is needed to investigate the selective function in maintaining the genetic diversity of Stipa krylovii plant populations.     

Seed bank influences on genetic diversity in the rare annual Clarkia springvillensis (Onagraceae)

The potential for seed banks to significantly affect the genetic structure of populations was recognized nearly two decades ago. However, there has been little empirical work that examines the problem. In this study, we explore the possibility that the seed bank of a rare annual, Clarkia springvillensis, could act as a buffer against the genetic consequences of small population size. We examined the adult and seed bank cohort in three natural populations. The seed bank was surveyed by collecting soil cores twice during the growing season: postgermination and post seed set. The genetic constitution of the adults and seed bank cohort was determined by examining eight polymorphic isozyme loci via starch gel electrophoresis. The total genetic diversity in the seed bank (Ht = 0.355) was significantly higher than in the adults (Ht = 0.260). Additionally, Fst estimates of genetic differentiation among populations showed significantly less differentiation among population seed banks (Fst = 0.008) than among adults (Fst = 0.045). These results are in agreement with the expectation that seed banks would act to maintain genetic diversity in populations as well as have the effect of slowing differentiation of populations.     

Can Soil Seed Banks Serve as Genetic Memory? A Study of Three Species with Contrasting Life History Strategies

We attempted to confirm that seed banks can be viewed as an important genetic reservoir by testing the hypothesis that standing (aboveground) plants represent a nonrandom sample of the seed bank. We sampled multilocus allozyme genotypes from three species with different life history strategies: Amaranthus retroflexus, Carduus acanthoides, Pastinaca sativa. In four populations of each species we analysed the extent to which allele and genotype frequencies vary in consecutive life history stages including the summer seed bank, which has been overlooked up to now. We compared the winter seed bank (i.e., seeds collected before the spring germination peak), seedlings, rosettes, the summer seed bank (i.e., seeds collected after the spring germination peak) and fruiting plants. We found that: (1) All three species partitioned most of their genetic diversity within life history stages and less among stages within populations and among populations. (2) All genetic diversity parameters, except for allele frequencies, were similar among all life history stages across all populations in different species. (3) There were differences in allele frequencies among life history stages at all localities in Amaranthus retroflexus and at three localities in both Carduus acanthoides and Pastinaca sativa. (4) Allele frequencies did not differ between the winter and summer seed bank in most Carduus acanthoides and Pastinaca sativa populations, but there was a marked difference in Amaranthus retroflexus. In conclusion, we have shown that the summer seed bank is not genetically depleted by spring germination and that a majority of genetic diversity remains in the soil through summer. We suggest that seed banks in the species investigated play an important role by maintaining genetic diversity sufficient for recovery rather than by accumulating new genetic diversity at each locality.     

No loss of genetic diversity in small and isolated populations of Medicago sativa subsp. falcata

Molecular allozyme markers of three polymorphic isozymes were used to estimate the genetic diversity among the seed progeny in fragmented Estonian populations of sickle medic Medicago sativa ssp. falcata L. depending on the population size and the isolation degree. Genetic diversity H_e was high in all populations, ranging between 0.795 and 0.893. No correlation between the genetic diversity measures and population size or isolation distance was found. Even the smallest population had equally high genetic diversity as about a hundred times larger population. Genetic differentiation of populations into two major groups was associated with the geographic position of populations, except one remote population. Elimination of seed progeny of reduced fitness by embryo abortion and continuous yearlong contribution of the highly heterozygous progeny through the soil seed bank are considered as important supplementary factors that have contributed to maintaining high levels of genetic diversity in populations of sickle medic in addition to its autotetraploid nature and perennial life form.     

A LIFE-HISTORY BASED STUDY OF POPULATION GENETIC STRUCTURE: SEED BANK TO ADULTS IN PLANTAGO LANCEOLATA

We explored the extent to which the soil seed bank differed genetically and spatially in comparison to two actively growing stages in a natural population of Plantago lanceolata. All seed-bank seeds, seedlings, and adults of P. lanceolata within eight subunits in a larger population were mapped, subjected to starch gel electrophoresis, and allozyme analysis in 1988. Gel electrophoresis was also used to estimate the mating system in two years, 1986 and 1988. The spatial distributions of seeds, seedlings, and adults were highly coincident. Allele frequencies of the dormant seeds differed significantly from those of the adults for four of the five polymorphic loci. In addition, a comparison of the genotype frequencies of the three life-history stages indicated that the seed bank had an excess of homozygotes. Homozygosity, relative to Hardy-Weinberg expectations, decreased during the life cycle (for seed bank, seedlings, and adults respectively: F_it = 0.19, 0.09, 0.01; F_is = 0.14, 0.04, -0.12). Spatial genetic differentiation increased sixfold during the life cycle: (for seed bank, seedling and adults: F_s1??? = 0.02, 0.05, 0.12). The apparent selfing rate was 0.01 in 1986 and 0.09 in 1988. These selfing rates are not large enough to account for the elevated homozygosity of the seed bank. Inbreeding depression, overdominance for fitness, and a “temporal Wahlund's effect” are discussed as possible mechanisms that could generate high homozygosity in the seed bank, relative to later life-history stages. In Plantago lanceolata, the influence of the mating system and the “genetic memory” of the seed bank are obscured by the time plants reach the reproductive stage.     

Can a seed bank maintain the genetic variation in the above ground plant population?

There are indications that a persistent seed bank can protect small and isolated plant populations from local extinction. Genetic mechanisms contributing to this phenomenon are the increase of local effective population size – and hence the decrease of genetic drift – through a reservoir of persistent seeds, and the accumulation of intergenerational genetic diversity in the seed bank. To find evidence for these mechanisms, we conducted two formal meta-analyses. First, we analyzed 42 published habitat fragmentation studies and investigated whether the degree of genetic differentiation between fragmented plant populations was mediated by seed longevity. Second, we reviewed 13 published studies reporting the genetic diversity of both the seed bank and the above ground plants, aiming at comparing genetic diversity contained in the seed bank with the above ground vegetation. We conclude that a persistent seed bank may indeed mitigate the consequences of habitat fragmentation and protect a species from genetic drift and population genetic differentiation. We found no evidence, however, of high levels of genetic diversity accumulating in the soil seed bank. If genetic differences are present between the standing crop and the seed bank, they are very likely the result of local selection acting either directly or indirectly as a filter on the alleles present in the seed bank. We finally suggest that 1) the role of the seed bank should not be neglected in habitat fragmentation studies and 2) it is not very fruitful to continue comparing seed bank genetic diversity with above ground plant genetic diversity, unless this is performed under different selection regimes.     

Comparison of genetic variation in populations of wild rice, Oryza rufipogon, plants and their soil seed banks

Wild rice, Oryza rufipogon, has endangered species conservation status and it is subject to in situ conservation in China. To understand the potential of the seed bank in species conservation and population restoration, this study compared the genetic diversity of O. rufipogon plants with that of its soil seed banks in two marshes. A total of 11 pairs of rice SSR primers were used and 9 were polymorphic. Allele frequencies of the seeds differed significantly from those of surface plants and varied between soil layers. Relatively more alleles and higher genetic diversity (H _e) were found in plant populations, relative to seed banks. The numbers of germinable seeds and the level of genetic variation in seed banks decreased with the increasing of soil depth, indicating a rapid seed loss. Genetic differentiation was detected between sites and between plant and seed populations, as well as among seeds of different soil strata. Rapid seed loss, partly dormancy loss, and nonrandom seed mortality are discussed as the possible contributors to the pattern of reduced genetic variation within seed banks, compared to plants. These could also be responsible for the considerable genetic differentiation between populations. The seed population held about 72% of the total genetic variation of O. rufipogon in each marsh, indicating the potential of seed banks for restoring population variabilities if the plant populations were lost.     

High genotypic diversity and strong spatial structure in populations of Trifolium alpestre with low seed production

Studies on clonal plants indicate that the proportion between clonal and sexual reproduction can be variable, depending on local habitat conditions and the biological characteristics of the species. In the present study, we assessed this question in Trifolium alpestre by assaying genetic diversity and spatial genotypic structure of natural populations with the use of allozyme markers. Populations revealed high genetic diversity as well as strong spatial structure of multilocus genotypes. The values of genetic diversity were moderately high. Spatially aggregated, identical genotypes spread up to 15 m along linear transects and across 4‐m² plots indicate extensive clonal propagation within populations. However, the existence of numerous unique and small‐sized clones reflects significant contribution from sexual reproduction. Spatially and temporarily stochastic soil disturbances have evidently opened new opportunities for the successful sexual recruitment from the permanent soil seed bank and thus counteracted losses of genetic and genotypic diversity. Seed production in all populations during the three study years was low, in average up to 1.5–2.4 seeds per shoot. The almost total lack of seed set for 57 bagged flower heads on genotypes grown in a common garden indicates that T. alpestre needs pollinators for seed production.     

The soil seed bank and understorey regeneration in Eucalyptus regnans forest,Victoria

Abstract The soil seed bank and its relation to the extant vegetation in a Eucalyptus regnans F. Muell. forest in the Central Highlands of Victoria were examined. The average seed density was 430 germinable seeds m^?2 to a depth of 2 cm. There was a polynomial regression relationship between the density and species richness of seeds in soil and forest age (0. 6–54 years). Species richness was not significantly different among soil depths (0- 2 , 2- 5 , 5–10 and 10–20 cm) in the forest stand of 54 years old. More seeds germinated from the 5–10 cm depth than from the other depths. Forbs accounted for 73% of the total germinable seeds and there was no germination of E. regnans. The number of species, particularly woody plant species, germinating from the soil seed bank were significantly lower than in the extant vegetation. However, almost all species present in the soil seed bank were present in the vegetation. The soil seed bank provides an important source for the rapid regeneration of understorey vegetation following clear-cutting and slash-burning in the E. regnans forest. The rapid understorey establishment may play an important role in protecting soil from erosion, in nutrient conservation, replacement and redistribution. The soil seed bank may also be a necessary source of maintaining genetic diversity in the forest over the long term.     

Seed bank composition and above-ground vegetation in response to grazing in sub-Mediterranean oak forests (NW Greece)

We investigate the persistent soil seed bank composition and its relation to the above-ground flora of grazed and non-grazed sub-Mediterranean deciduous oak forests of NW Greece. Twenty-eight taxa were recorded in the soil seed bank and 83 taxa (70 taxa in plots of seed bank sampling) in the above-ground vegetation. The dominant tree species and many woodland species found in the above-ground vegetation were absent from the soil seed bank. Similarity between the soil seed bank and the above-ground vegetation decreased with grazing, and grazing led to a decrease of species richness in above-ground vegetation and soil seed bank. Beta diversity of vegetation among grazed and among non-grazed plots did not differ, but was significantly higher between grazed and non-grazed areas. Beta diversity of the soil seed bank declined with grazing. When applying classification tree and logistic regression analyses, non-grazed forest sites are clearly differentiated by the presence of Phillyrea latifolia, Euphorbia amygdaloides and Brachypodium sylvaticum. PCA ordination of above-ground species composition reflected a gradient from sites grazed by ruminants to non-grazed sites, but no clear structure was detected in the seed bank.     

The production, storage and viability of seeds of Acacia karroo and A. nilotica in a grassy savanna in KwaZulu-Natal, South Africa

African Acacias are often major contributors to the progressive increase in the woody component of savannas, a phenomenon commonly referred to as bush encroachment. They produce large quantities of seed and may have large soil‐stored seed banks. In Hluhluwe–Umfolozi Park, the number of adult Acacia nilotica trees per hectare far exceed that of A. karroo adults. The relative dominance is reversed in the juvenile stage with A. karroo outnumbering A. nilotica threefold outside closed woodlands. Acacia karroo trees were smaller than A. nilotica trees on average, but produced more seeds for a given basal diameter size class. Acacia karroo showed less bruchid infestation than A. nilotica at all stages of pod development. Unlike A. nilotica, a proportion of A. karroo seeds was able to germinate after bruchid attack. We detected no difference between the two species in the soil‐stored seed bank or in the viability of seeds found in the seed bank.     

Historic DNA reveals genetic consequences of fragmentation in an endangered,endemic mustard

Understanding how anthropogenic disturbance affects genetic diversity is essential to appropriately incorporating genetic considerations into conservation plans. Unfortunately, we rarely have information about a population’s genetic diversity before it becomes imperiled. Here we reconstruct the historic range of the naturally rare annual mustard Streptanthus glandulosus subsp. niger (Sgn) and use herbarium specimens to quantify pre-disturbance genetic diversity. We compare this to the genetic diversity in the contemporary plant populations and to plants in the seed bank. We conclude that Sgn was recently a single, panmictic population composed of orders of magnitude more plants than exist today but experienced recent and abrupt declines following housing development. Today Sgn persists as two disjunct populations, the larger of which has retained historic levels of diversity although there is a downward trend in all measures. The smaller population has lost 21–28% of the diversity that was present only 50 years ago with an N_e?~?5–16. The contemporary populations have differentiated from each other due to drift. The seed bank contained no novel alleles and had high levels of homozygosity, indicating that it is incapable of providing genetic rescue. This novel combination of hDNA, the aboveground plant population and the seed bank can be used to design high impact conservation plans that appropriately incorporate genetic diversity for this and other imperiled species.

     

Soil seed bank contributes significantly to genetic variation of Hypericum sinaicum in a changing environment

The contribution of soil seed bank of a desert endemic plant species in maintaining genetic diversity has been addressed in this paper through investigating the differences in genetic diversity and structure (using AFLP markers) between plants grown from soil seed bank and standing crop plants within and among five populations of H. sinaicum growing at St. Katherine Protectorate, southern Sinai, Egypt. Standard genetic diversity measures showed that the molecular variation within and among populations was highly significantly different between standing crop and soil seed bank. While soil seed bank had lower genetic diversity than standing crop populations, pooling soil seed bank with standing crop samples resulted in higher diversity. The results revealed also that soil seed bank had lower differentiation (7 %) than among populations of the standing crop (18 %). Results of neighbor-joining, Bayesian clustering and principal coordinate analysis showed that soil seed banks had a separate gene pool different from standing crop. The study came to the conclusion that the genetic variation of the soil seed bank contributes significantly to the genetic variation of the species. This also stresses the importance of elucidating the genetic diversity and structure of the soil seed bank for any sound and long-term conservation efforts for desert species. These have been growing in small-size populations for a long time that any estimates gained only from aboveground sampling of populations may be ambiguous.     

Genetic variation in an ephemeral mudflat species: The role of the soil seed bank and dispersal in river and secondary anthropogenic habitats

Many ephemeral mudflat species, which rely on a soil seed bank to build up the next generation, are endangered in their natural habitat due to the widespread regulation of rivers. The aim of the present study was to elucidate the role of the soil seed bank and dispersal for the maintenance of genetic diversity in populations of near‐natural river habitats and anthropogenic habitats created by traditional fish farming practices using Cyperus fuscus as a model. Using microsatellite markers, we found no difference in genetic diversity levels between soil seed bank and above‐ground population and only moderate differentiation between the two fractions. One possible interpretation is the difference in short‐term selection during germination under specific conditions (glasshouse versus field) resulting in an ecological filtering of genotypes out of the reservoir in the soil. River populations harbored significantly more genetic diversity than populations from the anthropogenic pond types. We suggest that altered levels and patterns of dispersal together with stronger selection pressures and historical bottlenecks in anthropogenic habitats are responsible for the observed reduction in genetic diversity. Dispersal is also supposed to largely prohibit genetic structure across Europe, although there is a gradient in private allelic richness from southern Europe (high values) to northern, especially north‐western, Europe (low values), which probably relates to postglacial expansion out of southern and/or eastern refugia.     

The accumulation of genetic diversity within a canopy‐stored seed bank

Many plants regenerate after fire from a canopy‐stored seed bank, in which seed are housed in fire resistant confructescences (cones) that remain on maternal plants. This strategy would be favoured if plants accumulate a sufficiently large and genetically diverse seed bank during interfire intervals. We use a 16‐year demographic study and surveys of microsatellite variation to quantify and explain the rate of accumulation of genetic diversity within the canopy seed bank of the shrub Banksia spinulosa. Flowering and fruit set were highly variable. An initial sample in 1991 of 354 reproductively mature plants generated 426 cones over 16 years, of which only 55 cones from 40 maternal plants persisted until 2005. By genotyping seed from these 55 cones we demonstrated that genetic diversity accumulated rapidly within the seed bank. Resampling revealed that diversity was determined by the number, not the age, of cones. Cones were widely distributed among plants, outcrossing rates were high (mean t_m = 1.00 ± 0.04) and biparental inbreeding low. Adults displayed little evidence of isolation by distance and the genotypic diversity of seed cohorts was independent of the density of neighbouring potential sires. We therefore estimate that within at least 13 individual years the number of cones produced per year (14–63) would have contained 100% of the adult genetic diversity. We conclude that a highly outcrossed mating system and relatively widespread pollen dispersal ensure the rapid development of a genetically diverse and spatially and temporally homogeneous seed bank.     

Relationships between Population Size, Genetic Diversity and Fitness Components in the Rare Plant Dictamnus albus in Central Germany

An increasing number of studies support the hypothesis that smaller populations face a higher risk of extinction, and declining population sizes are therefore one of the focal points in plant conservation. In small populations, loss of genetic diversity is often related to reduced reproductive fitness. For the rare Dictamnus albus in Central Germany, an earlier study had already confirmed a significant correlation between population size and genetic diversity. In order to assess whether these variables correlate with fitness components, plant height; flower, fruit and seed production; and germination were studied in a total of 11 populations of different size. In the seven populations that were sampled over two consecutive years, differences among populations and among years were tested using a Two-Way ANOVA. Co-linearity among variables was assessed using principal component analysis (PCA), followed by calculating correlations between ordination axes and both population size and genetic diversity. Plant height and flower number were uncorrelated to the other variables and, together with germination, did not show any correlation to either population size or genetic diversity. However, both size and genetic diversity of populations correlated significantly with other PCA axes that reflected reproductive components such as fruit number, seed number, seed fruit ratio, and seed mass. Our results support the idea that reproduction is hampered in small populations and raise concerns over the loss of genetic diversity in D. albus.     

Restoration of genetic diversity from soil seed banks in a threatened aquatic plant, <Emphasis Type="Italic">Nymphoides peltata</Emphasis>

Populations of a threatened aquatic plant, Nymphoides peltata, have rapidly degenerated under the influence of recent artificial changes in Lake Kasumigaura of Japan. To estimate the potential of soil seed banks for genetic restoration of the species, we used 10 microsatellite markers to analyze the genetic variation in adults and in seedlings that emerged from soil seed banks. About 187 leaf samples from the cultured stocks that were collected in 17 adult subpopulations in 1995 and 2000 and from three subpopulations that were newly discovered in 2002 were analyzed. As a result, only 18 genets could be identified, suggesting that clonal diversity of the adult population had already become extremely low. Genetic tests were performed on 430 seedlings from seed banks at six locations of natural lakeshores and three of the restoration sites that were artificially constructed in an attempt to assign them to the remnant adult population; many of the seedlings showed genetic variation different from the adults. Furthermore, the seedlings preserved seven alleles that had been lost from remnant adults. However, they had lower average numbers of alleles and heterozygosity levels (NA = 1.5–3.1, H _E = 0.146–0.487) than the remnant adults (NA = 3.5, H _E = 0.539) and showed high inbreeding coefficients, suggesting that the seed banks were produced by inbreeding. Thus, although the seed banks had a certain potential to restore genetic diversity, the fitness reduction in seed banks caused by inbreeding could affect the success of restoration based on seed banks.     

Patterns of genetic diversity in the rare Erigeron lemmoni and comparison with its more widespread congener,Erigeron arisolius (Asteraceae)

Analysis of levels and patterns of genetic variation in a rare species is important for determining whether genetic factors associated with small population size, such as genetic drift or inbreeding, may be negatively affecting a species. In this study, we compared estimates of genetic diversity and patterns of population genetic structure in a rare cliff endemic, Erigeron lemmonii, to those of a widespread congener, E. arisolius. Our goals were to assess whether rarity and small population size have negatively affected levels of genetic diversity in E. lemmonii and to identify genetic threats that may limit the ability of E. lemmonii to persist. Levels of observed and expected heterozygosity and allelic richness in E. lemmonii were approximately 60 % of those found in E. arisolius. After correcting for null alleles, inbreeding coefficients in both species of Erigeron were very small, suggesting that both species are highly outcrossing and may demonstrate self-incompatibility. Patterns of genetic structure in both species revealed almost no population substructuring, indicating that widespread gene flow is occurring within each species. Because we found no evidence for inbreeding or a genetic bottleneck in E. lemmonii, it is likely that the species’ lower genetic diversity may be the result of genetic drift. Because E. lemmoni exists in a single population, no other populations exist to bolster population size or genetic diversity in the event of declines; thus, conservation efforts should focus on seed collection from as many individuals as possible to protect against possible future losses of genetic diversity. We also recommend continued monitoring of both population size and genetic diversity in E. lemmonii to ensure the species’ long-term persistence and viability.     

桂北喀斯特石漠化地区不同植物群落土壤种子库特征及其与土壤养分关系

土壤种子库作为地上植被遗传信息库，对植被自然演替更新以及生态修复建设具有重要作用。为探明桂北喀斯特石漠化地区植被自然恢复潜力和恢复策略，该文选取恭城瑶族自治县喀斯特石漠化地区3种典型植物群落为研究对象，分析不同群落的土壤种子库结构、多样性及其对土壤养分特征的响应，以期为该地区石漠化治理和植被恢复提供理论依据。结果表明：(1)共计监测到幼苗3 648株，隶属于33科51属55种，其中1年生和2年生草本幼苗共20种，多年生草本幼苗21种，藤本幼苗5种、灌木幼苗3种、乔木幼苗6种；不同植物群落土壤种子库平均密度为三华李经济林(22 493 grain·m^-2)>青冈次生林(1 033 grain·m^-2)>金竹灌丛(793 grain·m^-2)。(2)土壤种子库植物生活型方面，三华李经济林主要分布1年生恶性杂草，青冈次生林和金竹灌丛则以多年生草本为主，木本植物占比较少；不同植被类型中土壤种子库物种多样性和相似性总体较低，同时与地上群落物种组成的相似性也较低。(3)研究区域的土壤元素存在高氮低磷的现象，其中磷元素为金...