Mycorrhizas (fungal roots) play vital roles in plant nutrient acquisition, performance and productivity in terrestrial ecosystems. Arbuscular mycorrhizas (AM) and ectomycorrhizas (EM) are mostly important since soil nutrients, including NH
The heavier stable isotope 15N is discriminated against 14N during biochemical, biogeochemical and physiological processes, due to a greater atomic mass. In general, non-N2-fixing plants had greater 15N values than N2-fixing (~0) ones. Foliar 15N often varied by 5 to 10 in the order: non-mycorrhizas/AMs > EMs ≥ ericoid mycorrhizas. Differences in 15N () or 15N (atom%) values could thus provide N transfer information between plants. A range of between 0 to 80% of one-way N transfer had been observed from N2-fixing mycorrhizal to non-N2-fixing mycorrhizal plants, but generally less than or around 10% in the reverse direction. Plant-to-plant N transfer may provide practical implications for plant performance in N-limited habitats. Considering that N translocation or cycling is crucial, and the potential benefits of N transfer are great in both agricultural and natural ecosystems, more research is warranted on either one-way or two-way N transfers mediated by CMNs with different species and under field conditions.
According to conventional theory, larger plant species are likely to inflict more intense competition on other (smaller) species. We tested a deducible prediction from this: that a larger species should generally be expected to impose greater limits on the number of species that can coexist with it.
Species richness was sampled under plant canopies for a selection of woody species (‘host’ species) that display a wide range of adult sizes (from small shrubs to large trees), growing within natural vegetation of the Interior Douglas-fir zone of southern British Columbia, Canada. These data were compared with species richness levels sampled within randomly placed plots within the host species habitat.
A prominent host species size effect on species richness was detected but only narrowly at the small end of the species size range. Across most (90%) of the increasing size range of host species, the number of species residing under the host canopy showed no significant decrease relative to the number expected by random assembly, based on species richness within randomly defined equivalent areas within the habitat of the host species. This apparent ‘null effect’, we suggest, is explained not because these larger species have no effect on community assembly. We postulate that larger species are indeed likely to be more effective in causing competitive exclusion of some smaller species (as expected from conventional theory), but that any potential limitation effect of this on resident species richness is offset for two reasons: (i) larger species also generate niche spaces that they cannot exploit under their own canopies and so have minimal impact (as competitors) on smaller species that can occupy these niches and (ii) certain other small species—despite small size—have effective competitive abilities under the severe competition that occurs within host neighbourhoods of larger species. These and other recent studies call for re-evaluation of traditional views on the role of plant size in affecting competitive ability and community assembly.
In perennial species, the allocation of resources to reproduction results in a reduction of allocation to vegetative growth and, therefore, impacts future reproductive success. As a consequence, variation in this trade-off is among the most important driving forces in the life-history evolution of perennial plants and can lead to locally adapted genotypes. In addition to genetic variation, phenotypic plasticity might also contribute to local adaptation of plants to local conditions by mediating changes in reproductive allocation. Knowledge on the importance of genetic and environmental effects on the trade-off between reproduction and vegetative growth is therefore essential to understand how plants may respond to environmental changes.
We conducted a transplant experiment along an altitudinal gradient from 425 to 1 921 m in the front range of the Western Alps of Switzerland to assess the influence of both altitudinal origin of populations and altitude of growing site on growth, reproductive investment and local adaptation in Poa alpina.
In our study, the investment in reproduction increased with plant size. Plant growth and the relative importance of reproductive investment decreased in populations originating from higher altitudes compared to populations originating from lower altitudes. The changes in reproductive investment were mainly explained by differences in plant size. In contrast to genetic effects, phenotypic plasticity of all traits measured was low and not related to altitude. As a result, the population from the lowest altitude of origin performed best at all sites. Our results indicate that in P. alpina genetic differences in growth and reproductive investment are related to local conditions affecting growth, i.e. interspecific competition and soil moisture content.
The prediction that facilitation is the dominant interaction in physically stressful conditions has been supported by many but not all field studies. In the present paper, we tested the effects of the identity of species, the local environmental conditions and the currencies of performance measurement on such variation.
Using contrasting two plots, six species, and up to five multiple traits, we comprehensively explored the effects of the above factors on the assessment of plant interactions in an alpine meadow of the Qing-Hai Tibetan Plateau. Additionally, we attempted to figure out the possible mechanisms underlying the responses observed. The data were analysed by both standard ANOVAs and multivariate statistics.
Our results demonstrated that the response to the removal of neighbours was both species and trait specific, and the effect of the local environmental conditions was dependent on the species involved. The contrast between plots had crucial influence on the net interactions of Kobresia macrantha, but little effect on Elymus nutans. Regarding the abiotic conditions, neighbours had significant impact on soil temperature, moist and solar radiation. The results contribute to advance our knowledge on the potential underlying factors influencing the assessment of facilitation.
Many pine populations in Canada have fragmented distributions resulting from the effects of glaciations, overharvesting and white pine blister rust infections. Forest fragmentation can modify gene flow and reduce genetic diversity. Selective logging can reduce the density of trees, thereby altering mating patterns and increasing inbreeding. The hypothesis of the present study is that forest fragmentation will not increase inbreeding and will have no effect on genetic diversity parameters in the Canadian Pinus moniticola and P. strobus populations targeted because of (i) the long life span of the pine species, (ii) outbreeding and self-incompatibility of P. monticola and P. strobus and (iii) wind pollination resulting in high gene flow among populations. We studied the genetic diversity of P. strobus across its range in Canada, and we completed a detailed analysis of the genetic structure of P. monticola populations from western Canada using microsatellites genetic markers.
Seed samples from 10 P. monticola populations and 10 P. strobus populations were collected from western and eastern Canada, respectively. The mother trees included in seed lots were representative of each stand. Genomic DNA extracted from each sample was amplified with microsatellite primers. The intra- and interpopulation genetic diversity parameters were assessed using Popgene and Genepop softwares and the genetic distances among populations within each species using the PowerMarker software.
Pinus monticola and P. strobus exhibited moderate to high genetic diversity. Also, both species showed low levels of inbreeding despite the geographic isolation and small stand size. Gene flow estimates were high and population differentiation values were relatively low for these fragmented forest sites.
In recent years, there has been an increasing interest in the impact of invasive alien plant species on the soil seed bank. Soil seed banks play an important role in determining the composition and dynamics of the vegetation through time. Therefore, an ability to form a persistent seed bank and/or a capacity to alter the structure of the seed bank of invaded communities could be important factors in determining the success of many alien plant species. In this study, we report on a detailed assessment of the characteristics of the seed bank community associated with the herbaceous plant invader, Gunnera tinctoria, a newly emerging and potentially globally significant invasive plant species. This species, native to South America, is invasive in a range of wet habitats in Europe, Australasia and the USA.
A comprehensive assessment of the seed bank of invaded and comparable uninvaded areas was made at two points in time (May and October), at three sites in western Ireland. The seedling emergence approach was used to assess the structure (diversity, dominance and abundance) of the soil seed bank. Differences between invaded and uninvaded seed bank communities were investigated at the spatial scales of site, plot and depth.
Gunnera tinctoria formed a large persistent seed bank at the study sites. Approximately 30 000 seedlings per square metre emerged from soils collected from invaded areas, of which 30% were found in deep soil layers. Seedlings of this invader represented 53–86% of the total number of seedlings associated with invaded areas. Both the transient and the more persistent component of the seed bank of invaded communities were significantly less diverse and abundant than those of uninvaded areas, and were characterized by higher dominance, even when seedlings of the invader were not included in the analysis. The seed bank of invaded areas was largely composed of seeds of agricultural weeds in addition to those of the invader. These results suggest that G. tinctoria has the capacity to profoundly alter the seed bank of invaded communities. These results have direct relevance for the development of control and management strategies, for this and other comparable invasive species, which should account for both quantitative and qualitative alterations in the seed bank community. Our study also suggests that control measures that result in disturbance of areas colonized by G. tinctoria could promote the germination of undesirable weeds.
In this paper, we highlighted some key progresses in mangrove conservation, restoration and research in China during last two decades.
Based on intensive literature review, we compared the distribution and areas of existing mangroves among selected provinces of China, discussed the issues associated with mangrove conservation and restoration and highlighted major progresses on mangrove research conducted by key institutions or universities in mainland China, Hong Kong, Taiwan and Macao.
The population boom and rapid economic developments have greatly reduced mangrove areas in China since 1980s, leaving only 22 700 ha mangroves in mainland China in 2001. Chinese government has launched a series of programs to protect mangroves since 1980s and has established mangrove ecosystems as high-priority areas for improving environmental and living resource management. During last three decades, a total of 34 natural mangrove conservation areas have been established, which accounts for 80% of the total existing mangroves areas in China. Mangrove restoration areas in Mainland China accounted for <7% of the total mangroves areas in 2002. A great deal of research papers on Chinese mangroves has been published in international journals. However, more systematic protection strategies and active restoration measurements are still urgently needed in order to preserve these valuable resources in China.
Data assimilation is a useful tool to extract information from large datasets of the net ecosystem exchange (NEE) of CO2 obtained by eddy-flux measurements. However, the number of parameters in ecosystem models that can be constrained by eddy-flux data is limited by conventional inverse analysis that estimates parameter values based on one-time inversion. This study aimed to improve data assimilation to increase the number of constrained parameters.
In this study, we developed conditional Bayesian inversion to maximize the number of parameters to be constrained by NEE data in several steps. In each step, we conducted a Bayesian inversion to constrain parameters. The maximum likelihood estimates of the constrained parameters were then used as prior to fix parameter values in the next step of inversion. The conditional inversion was repeated until there were no more parameters that could be further constrained. We applied the conditional inversion to hourly NEE data from Harvard Forest with a physiologically based ecosystem model.
Results showed that the conventional inversion method constrained 6 of 16 parameters in the model while the conditional inversion method constrained 13 parameters after six steps. The cost function that indicates mismatch between the modeled and observed data decreased with each step of conditional Bayesian inversion. The Bayesian information criterion also decreased, suggesting reduced information loss with each step of conditional Bayesian inversion. A wavelet analysis reflected that model performance under conditional Bayesian inversion was better than that under conventional inversion at multiple time scales, except for seasonal and half-yearly scales. In addition, our analysis also demonstrated that parameter convergence in a subsequent step of the conditional inversion depended on correlations with the parameters constrained in a previous step. Overall, the conditional Bayesian inversion substantially increased the number of parameters to be constrained by NEE data and can be a powerful tool to be used in data assimilation in ecology.
Global climate change and ongoing plant invasion are the two prominent ecological issues threatening biodiversity world wide. Among invasive species, Lantana camara and Hyptis suaveolens are the two most important invaders in the dry deciduous forest in India. We monitored the growth of these two invasive species and seedlings of four native dry deciduous species (Acacia catechu, Bauhinia variegata, Dalbergia latifolia and Tectona grandis) under ambient (375–395 µ mol mol–1) and elevated CO2 (700–750 µ mol mol–1) to study the differential growth response of invasive and native seedlings.
Seedlings of all the species were exposed to ambient and elevated CO2. After 60 days of exposure, seedlings were harvested and all the growth-related parameters like plant height; biomass of root, stem and leaves; total seedling biomass; R/S ratio; allocation parameters; net assimilation rate (NAR) and relative growth rate (RGR) were determined.
Biomass, RGR and NAR of all the species increased under elevated CO2 but the increase was higher in invasive species and they formed larger seedlings than natives. Therefore under the CO2-enriched future atmosphere, competitive hierarchies could change and may interfere with the species composition of the invaded area.
The superior performance of many non-indigenous species in a new range can be attributed to different factors such as pre-adaptation to environmental conditions in new areas or to factors inherent to displacement mechanisms such as loss of co-evolved pathogens and herbivores that increase the speed of evolutionary change towards a shift in allocation from defence to growth and reproduction. To assess the importance of the different mechanisms governing the success of Conyza canadensis, a globally successful invader, we simultaneously tested several recent hypotheses potentially explaining the factors leading to biological invasion.
We tested (i) whether plants from the non-native range showed a higher fitness than plants from the native North American range, (ii) whether they differed in resistance against an invasive generalist herbivore, the slug Arion lusitanicus and against a recently established specialist aphid herbivore, Uroleucon erigeronense and (iii) experimentally assessed whether C. canadensis releases allelopathic chemicals that have harmful effects on competing species in the non-native range. We compared populations along a similar latitudinal gradient both in the native North American and invasive European range and analysed patterns of adaptive clinal variation in biomass production.
The invasion success of C. canadensis in Europe cannot be attributed to a single trait, but to a combination of factors. Invasive plants benefited from increased growth and above all, increased reproduction (a key trait in an annual plant) and were less attacked by a co-migrated specialist enemy. The observed loss of defence against generalist slugs did not translate into a decreased fitness as invasive C. canadensis plants showed a high re-growth potential. In contrast to earlier in vitro studies, we detected no allelopathic effects on the competing flora in the non-native range. The latitudinal cline in vegetative biomass production in the non-native range observed in our common garden study indicates a high adaptive potential. However, only further genetic studies will provide conclusive evidence whether the differentiation in the non-native range is caused by pre-adaptation and sorting-out processes of putatively repeatedly introduced populations of this composite, long-distance disperser with highly volatile seeds or evolved de novo as a rapid response to new selection pressures in the non-native range.
Although the niche concept is of prime importance in ecology, the quantification of plant species' niches remains difficult. Here we propose that plant functional traits, as determinants of species performance, may be useful tools for quantifying species niche parameters over environmental gradients.
Under this framework, the mean trait values of a species determine its niche position along gradients, and intraspecific trait variability determines its niche breadth. This trait-based approach can provide an operational assessment of niche for a potentially large number of species, making it possible to understand and predict species niche shifts under environmental changes. We further advocate a promising method that recently appeared in the literature, which partitions trait diversity into among- and within-community components as a way to quantify the species niche in units of traits instead of environmental parameters. This approach allows the switch of the focus from ecological niches to trait niches, facilitating the examination of species coexistence along undefined environmental gradients. Altogether, the trait-based approach provides a promising toolkit for quantifying the species ecological niche and for understanding the evolution of species niche and traits.
Aboveground biomass production commonly increases with species richness in plant biodiversity experiments. Little is known about the direct mechanisms that cause this result. We tested if by occupying different heights and depths above and below ground, and by optimizing the vertical distribution of leaf nitrogen, species in mixtures can contribute to increased resource uptake and, thus, increased productivity of the community in comparison with monocultures.
We grew 24 grassland plant species, grouped into four nonoverlapping species pools, in monoculture and 3- and 6-species mixture in spatially heterogeneous and uniform soil nutrient conditions. Layered harvests of above- and belowground biomass, as well as leaf nitrogen and light measurements, were taken to assess vertical canopy and root space structure.
The distribution of leaf mass was shifted toward greater heights and light absorption was correspondingly enhanced in mixtures. However, only some mixtures had leaf nitrogen concentration profiles predicted to optimize whole-community carbon gain, whereas in other mixtures species seemed to behave more ‘selfish’. Nevertheless, even in these communities, biomass production increased with species richness. The distribution of root biomass below ground did not change from monocultures to three- and six-species mixtures and there was also no indication that mixtures were better than monocultures at extracting heterogeneously as compared to homogeneously distributed soil resources. We conclude that positive biodiversity effect on aboveground biomass production cannot easily be explained by a single or few common mechanisms of differential space use. Rather, it seems that mechanisms vary with the particular set of species combined in a community.
The direct effects of atmospheric and climatic change factors—atmospheric [CO2], air temperature and changes in precipitation—can shape plant community composition and alter ecosystem function. It is essential to understand how these factors interact to make better predictions about how ecosystems may respond to change. We investigated the direct and interactive effects of [CO2], warming and altered soil moisture in open-top chambers (OTCs) enclosing a constructed old-field community to test how these factors shape plant communities.
The experimental facility in Oak Ridge, TN, USA, made use of 4-m diameter OTCs and rain shelters to manipulate [CO2] (ambient, ambient + 300 ppm), air temperature (ambient, ambient + 3.5°C) and soil moisture (wet, dry). The plant communities within the chambers comprised seven common old-field species, including grasses, forbs and legumes. We tracked foliar cover for each species and calculated community richness, evenness and diversity from 2003 to 2005.
This work resulted in three main findings: (1) warming had species-specific effects on foliar cover that varied through time and were altered by soil moisture treatments; (2) [CO2] had little effect on individual species or the community; (3) diversity, evenness and richness were influenced most by soil moisture, primarily reflecting the response of one dominant species. We conclude that individualistic species responses to atmospheric and climatic change can alter community composition and that plant populations and communities should be considered as part of analyses of terrestrial ecosystem response to climate change. However, prediction of plant community responses may be difficult given interactions between factors and changes in response through time.
We aimed to find out how a geophyte, Merendera montana, occupies a wide ecological, elevational and climatic range. This occurrence in that environmental array is outstanding not only among geophytes but also in the whole flora of the Iberian Peninsula, where only a very few plants show such an apparent success. Specifically, we compared morphological and reproductive traits, and frequency of different types of reproduction in disturbed and undisturbed grasslands. Furthermore, we have analyzed the phenology of this plant by trying to understand how it manages to spread in an exceptional elevational gradient of 2000 m, with contrasting climatic regimes between the mediterranean and the alpine regions.
We measured the plant density of M.montana populations in different types of Pyrenean grasslands either with or without small-scale disturbances at seven sites from the basal to the alpine belt (400–2300 m a.s.l.). In each one of these populations, 100 individuals—1200 in total—were uprooted to measure their morphological features as well as type and occurrence of reproduction. Phenology (flowering and fruiting dates and leaf lifespan) was estimated using 5 years of records in the studied areas and >200 herbarium sheets from the whole altitudinal rank and collected in the last 30 years. Differences in plant densities were analyzed with non-parametric Mann–Whitney U-test; differences in morphological traits, fruit and seed production associated with disturbance, with one-way analysis of covariance test (general linear model). Finally, linear regression analyses were used to determine the relationships between clonal reproduction and elevation and those between flowering, fruiting and senescence and date and elevation.
In all cases, plant density in disturbed grasslands was significantly higher than in undisturbed grasslands. Plant height and weight, bulb depth, leaf width and bulb and root weight were higher in disturbed plots. Disturbed and undisturbed plots were similar in most aspects of sexual reproduction, including fruiting percentage and seed production, but average seed weight was higher in the disturbed plots. Clonal reproduction and the synchrony of both types of reproduction were significantly higher in disturbed plots. Flowering and leaf emergence dates were not affected by disturbance but at the lowest elevations, they happened at least 2 months later than at the highest elevations. Summarizing, clonal reproduction, advantage in seedling establishment and an unusual but favorable phenology are the main factors in explaining the success of this geophyte colonizing disturbed soils that, in consequence, allow M.montana to settle in a wide range of climatic and ecological conditions.
We aim to examine the canopy gap characteristics and evaluate their influence on regeneration, dominance and the early growth of woody species in seasonally dry Shorea robusta forests (Sal forests).
Sixty canopy gaps were surveyed in six randomly located transects belts in seasonally dry subtropical Sal forests of central Nepal. Each transect belt was followed until 10 gap sites were encountered. The equation for the area of an ellipse was used to calculate the size of canopy gap, measuring the longest axis and its perpendicular shorter axis. Number, sizes, ages and causes of tree falls creating canopy gaps along with number and sizes of border trees were identified and recorded. Detailed gap inventories were carried out using square 25-m2 quadrats placed in the middle of each gap. All individuals >2 m in height within the quadrat were identified at the species level and their diameter at breast height was measured. We assigned a nested 4-m2 quadrat to the corner of each 25-m2 quadrat, within which all woody individuals >10 cm tall were identified at the species level, and counted them and their regeneration mechanisms were identified. The height and collar diameter of the tallest individuals were measured. Descriptive statistics was calculated for the variables of interests and Pearson correlation, linear regression, independent-sample t-test and chi-square test were used to relate them and to test for their associations.
The study found mean gap size of 283 m2 and ~50% gaps of 10–15 years old. Gaps created by natural single-tree falls were significantly more numerous, and their mean size was significantly smaller than those resulting from artificial causes or multiple-tree falls. Gap size correlated with the basal area of felled trees, but it did not correlate with the number of tree falls. While tree fall basal area was significantly positively correlated to the seed-originated seedling to resprout ratio, it was negatively correlated, along with gap area and the basal size of retained trees, to seedling growth. The relative seedling density of Terminalia alata increased with increases in gap areas, while that of S.robusta decreased with increases in tree fall basal area, thereby lowering the plot-level dominance. However, the relative seedling densities of Eugenia operculata and Syzigium cumini were negatively and positively correlated, respectively, with tree fall basal area.
Inferring environmental conditions from characteristic patterns of plant co-occurrences can be crucial for the development of conservation strategies concerning secondary neotropical forests. However, no methodological agreement has been achieved so far regarding the identification and classification of characteristic groups of vascular plant species in the tropics. This study examines botanical and, in particular, statistical aspects to be considered in such analyses. Based on these, we propose a novel data-driven approach for the identification of characteristic plant co-occurrences in neotropical secondary mountain forests.
Floristic inventory data were gathered in secondary tropical mountain forests in Ecuador. Vegetation classification was performed by coupling locally adaptive isometric feature mapping, a non-linear ordination method and fuzzy-c-means clustering. This approach was designed for dealing with underlying non-linearities and uncertainties in the inventory data.
The results indicate that the applied non-linear mapping in combination with fuzzy classification of species occurrence allows an effective identification of characteristic groups of co-occurring species as fuzzy-defined clusters. The selected species indicated groups representing characteristic life-form distributions, as they correspond to various stages of forest regeneration. Combining the identified ‘characteristic species groups’ with meta-information derived from accompanying studies indicated that the clusters can also be related to habitat conditions.
In conclusion, we identified species groups either characteristic of different stages of forest succession after clear-cutting or of impact by fire or a landslide. We expect that the proposed data-mining method will be useful for vegetation classification where no a priori knowledge is available.