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PubMed2005

Short-term invasibility patterns in burnt and unburnt experimental Mediterranean grassland communities of varying diversities.

This paper reports the findings of a short-term natural invasibility field study in constructed Mediterranean herbaceous communities of varying diversities, under a fire treatment. Three components of invasibility, i.e. species richness, density and biomass of invaders, have been monitored in burnt and unburnt experimental plots with resident diversity ranging from monocultures to 18-species mixtures. In general, species richness, density and biomass of invaders decreased significantly with the increase of resident species richness. Furthermore, the density and biomass of invading species were significantly influenced by the species composition of resident communities. Although aboveground biomass, leaf area index, canopy height and percent bare ground of the resident communities explained a significant part of the variation in the success of invading species, these covariates did not fully explain the effects of resident species richness. Fire mainly influenced invasibility via soil nutrient levels. The effect of fire on observed invasibility patterns seems to be less important than the effects of resident species richness. Our results demonstrate the importance of species richness and composition in controlling the initial stages of plant invasions in Mediterranean grasslands but that there was a lack of interaction with the effects of fire disturbance.

Analysis of Variance↗

PubMed2005

Induced resistance in the indeterminate growth of aspen (Populus tremuloides).

Studies of induction in trees have examined rapid induced resistance (RIR) or delayed induced resistance (DIR), but have not examined induction that occurs in leaves produced by indeterminately growing trees subsequent to, but in the same season as, damage. We refer to induction that occurs during this time period as intermediate-delayed induced resistance (IDIR). We assessed the influences of genetic and environmental factors, and their interactions, on temporal and spatial variation in induction and on tradeoffs between induced and constitutive levels of resistance in indeterminately growing saplings of aspen (Populus tremuloides). We utilized a common garden of 12 aspen genotypes experiencing two levels of defoliation and two levels of soil nutrients. We assessed concentrations of phenolic glycosides and condensed tannins in damaged leaf remnants collected 1 week after defoliation to examine rapid and local induction, and in undamaged leaves produced 8 weeks after defoliation to assess intermediate-delayed and systemic induction. In general, tannins showed RIR, while phenolic glycosides expressed IDIR. For both classes of allelochemicals, we found high estimates of broad-sense heritability and genetic variation in both induced and constitutive levels. Genetic variation may be maintained by both direct costs of allelochemicals and by costs of inducibility (phenotypic plasticity). Such costs may drive the tradeoff exhibited between induced and constitutive levels of phenolic glycosides. IDIR may be important in reducing total-season tissue loss by providing augmented resistance against late summer herbivores in trees that have experienced damage earlier in the season. Herbivore-resistant compensatory growth is especially beneficial to young trees growing in competitive environments.

Animals↗

PubMed2006

Genotype and environment determine allocation to and costs of resistance in quaking aspen.

Although genetic variability and resource availability both influence plant chemical composition, little is known about how these factors interact to modulate costs of resistance, expressed as negative correlations between growth and defense. We evaluated genotype x environment effects on foliar chemistry and growth of quaking aspen (Populus tremuloides) by growing multiple aspen genotypes under variable conditions of light and soil nutrient availability in a common garden. Foliage was analyzed for levels of nitrogen, phenolic glycosides and condensed tannins. Bioassays of leaf quality were conducted with fourth-stadium gypsy moth (Lymantria dispar) larvae. Results revealed strong effects of plant genotype, light availability and nutrient availability; the importance of each factor depended upon compound type. For example, tannin concentrations differed little among genotypes and across nutrient regimes under low light conditions, but markedly so under high light conditions. Phenolic glycoside concentrations, in contrast, were largely determined by genotype. Variation in phenolic glycoside concentrations among genotypes was the most important factor affecting gypsy moth performance. Gypsy moth biomass and development time were negatively and positively correlated, respectively, with phenolic glycoside levels. Allocation to phenolic glycosides appeared to be costly in terms of growth, but only under resource-limiting conditions. Context-dependent trade-offs help to explain why costs of allocation to resistance are often difficult to demonstrate.

Animals↗

PubMed2002

Arbuscular mycorrhizas in cycads of southern India.

Root and soil samples of three potted or ground-grown cycads ( Cycas circinalis, C. revoluta, Zamiasp.) were collected between November 1999 and June 2000 and surveyed for arbuscular mycorrhizal (AM) colonization and spore populations. AM fungi were associated with all root systems and rhizosphere samples examined. Root colonization was of a typical Arum type and AM colonization levels differed significantly between species and between potted and ground-grown cycads. Mycorrhizal colonization levels were inversely related to root hair number and length. Spores of nine morphotypes belonging to three genera ( Acaulospora, Glomus, Scutellospora) were extracted from soil. The percentage root length colonized by AM fungi was not related to soil factors, but total AM fungal spore numbers in the rhizosphere soil were inversely related to soil nitrogen and phosphorus levels. AM fungal spore numbers in the soil were linearly related to root length colonized. The co-occurrence of septate non-mycorrhizal fungi was recorded for the first time in cycads. These observations and the relationship between plant mycorrhizal status and soil nutrients are discussed.

Cycas↗

PubMed1990

Use of selected autochthonous soil bacteria to enhanced degradation of hydrocarbons in soil.

A mixed population of soil hydrocarbon degrading bacteria was used to accelerate the biodegradation of a petrochemical waste. An aromatic hydrocarbon storage tank bottom was mixed with soil (10% w/w). After a month 43% of the hydrocarbons were degraded in uninoculated and in fertilized soil, while 65% were degraded in inoculated soil. Nutrient supplemented vermiculite seems to be a good possibility to produce effective hydrocarbon degrading inoculants.

Journal Article↗

PubMed1999

Improving nutrient capture from soil by the genetic manipulation of crop plants

Modern agricultural practices require the massive application of fertilizer to soils worldwide. In the USA alone, millions of tons of fertilizer are applied to agricultural soils each year. The adverse environmental impact and high cost of fertilizer use underscore the importance of improving the capability of plants to capture nutrients from soil. Therefore, engineering plants with improved micronutrient uptake may help in creating sustainable agriculture in the next century.

Journal Article↗

PubMed2006

Characterization of a carbohydrate transporter from symbiotic glomeromycotan fungi.

The symbiotic relationships between mycorrhizal fungi and plants have an enormous impact on terrestrial ecosystems. Most common are the arbuscular mycorrhizas, formed by fungi belonging to the phylum Glomeromycota. Arbuscular mycorrhizal fungi facilitate the uptake of soil nutrients by plants and in exchange obtain carbohydrates, thus representing a large sink for atmospheric plant-fixed CO(2). However, how carbohydrates are transported through the symbiotic interface is still unknown. Here we report the characterization of the first known glomeromycotan monosaccharide transporter, GpMST1, by exploiting the unique symbiosis of a glomeromycotan fungus (Geosiphon pyriformis) with cyanobacteria. The GpMST1 gene has a very low GC content and contains six introns with unusual boundaries. GpMST1 possesses twelve predicted transmembrane domains and functions as a proton co-transporter with highest affinity for glucose, then mannose, galactose and fructose. It belongs to an as yet uncharacterized phylogenetic monosaccharide transporter clade. This initial characterization of a new transporter family involved in fungal symbiosis will lead to a better understanding of carbon flows in terrestrial environments.

Biological Transport↗

PubMed1998

Biodiversity and ecosystem functioning: a mechanistic model.

Recent experiments have provided some evidence that loss of biodiversity may impair the functioning and sustainability of ecosystems. However, we still lack adequate theories and models to provide robust generalizations, predictions, and interpretations for such results. Here I present a mechanistic model of a spatially structured ecosystem in which plants compete for a limiting soil nutrient. This model shows that plant species richness does not necessarily enhance ecosystem processes, but it identifies two types of factors that could generate such an effect: (i) complementarity among species in the space they occupy below ground and (ii) positive correlation between mean resource-use intensity and diversity. In both cases, the model predicts that plant biomass, primary productivity, and nutrient retention all increase with diversity, similar to results reported in recent field experiments. These two factors, however, have different implications for the understanding of the relationship between biodiversity and ecosystem functioning. The model also shows that the effect of species richness on productivity or other ecosystem processes is masked by the effects of physical environmental parameters on these processes. Therefore, comparisons among sites cannot reveal it, unless abiotic conditions are very tightly controlled. Identifying and separating out the mechanisms behind ecosystem responses to biodiversity should become the focus of future experiments.

Ecosystem↗

PubMed2003

A globally consistent richness-climate relationship for angiosperms.

Species richness, the simplest index of biodiversity, varies greatly over broad spatial scales. Richness-climate relationships often account for >80% of the spatial variance in richness. However, it has been suggested that richness-climate relationships differ significantly among geographic regions and that there is no globally consistent relationship. This study investigated the global patterns of species and family richness of angiosperms in relation to climate. We found that models relating angiosperm richness to mean annual temperature, annual water deficit, and their interaction or models relating richness to annual potential evapotranspiration and water deficit are both globally consistent and very strong and are independent of the diverse evolutionary histories and functional assemblages of plants in different parts of the world. Thus, effects of other factors such as evolutionary history, postglacial dispersal, soil nutrients, topography, or other climatic variables either must be quite minor over broad scales (because there is little residual variation left to explain) or they must be strongly collinear with global patterns of climate. The correlations shown here must be predicted by any successful hypothesis of mechanisms controlling richness patterns.

Adaptation, Physiological↗

PubMed1999

Dynamics of the forest communities at Pasoh and Barro Colorado: comparing two 50-ha plots.

Dynamics of the Pasoh forest in Peninsular Malaysia were assessed by drawing a comparison with a forest in Panama, Central America, whose dynamics have been thoroughly described. Census plots of 50 ha were established at both sites using standard methods. Tree mortality at Pasoh over an eight-year interval was 1.46% yr(-1) for all stems > or = 10 mm diameter at breast height (dbh), and 1.48% yr(-1) for stems > or = 100 mm dbh. Comparable figures at the Barro Colorado Island site in Panama (BCI) were 2.55% and 2.03%. Growth and recruitment rates were likewise considerably higher at BCI than at Pasoh. For example, in all trees 500-700 mm in dbh, mean BCI growth over the period 1985-1995 was 6 mm yr(-1), whereas mean Pasoh growth was about 3.5 mm yr(-1). Examining growth and mortality rates for individual species showed that the difference between the forests can be attributed to a few light-demanding pioneer species at BCI, which have very high growth and mortality; Pasoh is essentially lacking this guild. The bulk of the species in the two forests are shade-tolerant and have very similar mortality, growth and recruitment. The Pasoh forest is more stable than BCI's in another way as well: few of its tree populations changed much over the eight-year census interval. In contrast, at BCI, over 10% of the species had populations increasing or decreasing at a rate of >0.05 yr(-1) compared to just 2% of the species at Pasoh). The faster species turnover at BCI can probably be attributed to severe droughts that have plagued the forest periodically over the past 30 years; Pasoh has not suffered such extreme events recently. The dearth of pioneer species at Pasoh is associated with low-nutrient soil and slow litter breakdown, but the exact mechanisms behind this association remain poorly understood.

Ecosystem↗

PubMed2004

Origins of the southeastern Australian vegetation.

Australia is an ancient continent with an interesting geological history that includes a recent major shift in its position, both globally and compared with neighbouring land masses. This has led to a great deal of confusion over many years about the origins of the Australian biomes. The plant fossil record is now clarifying this, and it is clear that the ancient Gondwanan rainforests that covered Australia while it was still part of that supercontinent contained many of the elements of the modern vegetation. However, major climatic sifting, along with responses to other factors, including soil nutrient levels, disturbance regimes, atmospheric CO2 levels, fire frequency and intensity, glaciations and the arrival of humans, have had profound impacts on the Australian vegetation, which today reflects the sum of all these factors and more. The origins of Australian vegetation and its present-day management cannot be properly understood without an appreciation of this vast history, and the fossil record has a vital role to play in maintaining the health of this continent's vegetation into the future.

Biological Evolution↗

PubMed1967

Auxin-gibberellin interaction in apical dominance.

Indoleacetic acid and gibberellic acid were added to decapitated light-grown ;Alaska' pea seedlings as substitutes for the intact apex in the control of apical dominance. Of various concentrations and combinations tried, a combination of 1% indoleacetic acid + 1% gibberellic acid was the most inhibiting to side bud growth. The greatest degree of hormonally induced side bud inhibition was achieved when seedlings were deprived of soil nutrients.

Journal Article↗

PubMed2002

Novel plant-microbe rhizosphere interaction involving Streptomyces lydicus WYEC108 and the pea plant (Pisum sativum).

A previously undescribed plant-microbe interaction between a root-colonizing Streptomyces species, S. lydicus WYEC108, and the legume Pisum sativum is described. The interaction is potentially of great importance to the health and growth in nature of this nodulating legume. The root-colonizing soil actinomycete S. lydicus WYEC108 influences pea root nodulation by increasing root nodulation frequency, possibly at the level of infection by Rhizobium spp. S. lydicus also colonizes and then sporulates within the surface cell layers of the nodules. Colonization leads to an increase in the average size of the nodules that form and improves the vigor of bacteroids within the nodules by enhancing nodular assimilation of iron and possibly other soil nutrients. Bacteroid accumulation of the carbon storage polymer, poly-beta-hydroxybutyrate, is reduced in colonized nodules. Root nodules of peas taken from agricultural fields in the Palouse hills of northern Idaho were also found to be colonized by actinomycete hyphae. We hypothesize that root and nodule colonization is one of several mechanisms by which Streptomyces acts as a naturally occurring plant growth-promoting bacterium in pea and possibly other leguminous plants.

Pisum sativum↗

PubMed2003

Physical separation of straw stem components to reduce silica.

In this paper, we describe ongoing efforts to solve challenges to using straw for bioenergy and bioproducts. Among these, silica in straw forms a low-melting eutectic with potassium, causing slag deposits, and chlorides cause corrosion beneath the deposits. Straw consists principally of stems, leaves, sheaths, nodes, awns, and chaff. Leaves and sheaths are higher in silica, while chaff, leaves, and nodes are the primary sources of fines. Our approach to reducing silica is to selectively harvest the straw stems using an in-field physical separation, leaving the remaining components in the field to build soil organic matter and contribute soil nutrients.

Agriculture↗

PubMed2000

[Numerical simulation on maize growth in a regular windbreak system in Huanghuaihai Plain].

The modified production ecological model SUCROS was used to simulate the growth process of summer corn with the protection of windbreaks in Huanghuaihai Plain, and the simulated result was compared with the field monitoring data. The effects of various physiological and ecological factors that affect the growth of the summer corn were analyzed. The modified SUCROS could simulate the growth process successfully. The leaf area index and organ biomass simulated by the model could be fairly consistent with the monitoring data when the effects of insect and disease pests and weeds were considered simultaneously. As compared with the simulated data in the monoculture field, the corn yield in the windbreak system was about 6.8% higher due to the improved microclimate. Based on the simulation of the relationships between sowing density, sowing date and seed production, the density standard for high yield in the region was 6.75-7.50 plants.m-2, even high as 9.00 plants.m-2 in the fields with sufficient soil nutrients and water supply. It is suggested that the optimal sowing period is from May 21 to June 5. Through simulating the influence of "cool summer" on the growth of summer corn in southern Huanghuaihai Plain, it was found that the growth period of corn would extend 3 to 4 days if the average air temperature during the growing period lowered by one degree. The "less radiation" and correspondent "lower temperature" were the direct reasons of yield reduction in "cool summer".

Biomass↗

PubMed2003

Effects of litter removal on plant species diversity: a case study in tropical Eucalyptus forest ecosystems in South China.

The removal of litterfall in the Eucalyptus plantations in South China affected the plant biodiversity in these ecosystems was found based on the field observation and lab analysis. The protection times of species diversity of three Eucalyptus communities were different (Community I with no protection, Community II with 7-year-protection, Community III with 35-year-protection). The total numbers of species in these communities (from Community I to II to III) are 1, 6, and 17 respectively. The results showed that the protection of litterfall from being taken out of the ecosystem is important and can increase plant species diversity. This study combined biomass data, the chemical and physical properties of the soil, and the diversity of microbes in the communities. It is concluded that the mechanism of the effects of litter removal on biodiversity includes three factors: removing the suitable habitat of microbe and animal, decreasing the soil nutrient, and changing the special habitat for the germination and growth of invading plants. These results should have important implications for managing these Eucalyptus forest ecosystems in South China.

Biomass↗

PubMed2003

[Effect of plastic film mulching on soil microbial biomass in spring wheat field in semi-arid loess area].

This paper studied the effect of different periods of plastic film mulching (M0-no mulching, M30-mulching for 30 days, M60-mulching for 60 days, and M-mulching for whole growth period) on soil microbial biomass carbon (SMBC) of spring wheat field in semi-arid loess plateau. The mean SMBC in 1999 and 2000 was 335.3 and 259.3 mg.kg-1 dry soil, respectively. It was 29.3% higher in 1999 than in 2000. The highest SMBC was recorded at the harvest stage in M treatment for the two years. In 1999, a wet year with more rainfall, the SMBC of M60 and M treatments was significantly higher than those of M0 and M30 in the mid-period of growth, reached its top at the end of the growth period. The highest grain yield was also achieved in M60. It was a dry year in 2000, but rainfall was rich in the latter growth period of spring wheat. SMBC increased at the beginning period of growth, and did not increase during the mid-growth period. It increased again during the latter period of growth, and showed a significant difference among the treatments. At the harvest stage of 2000, SMBC in M0 was the highest among all the treatments. It was similar between M and M60, and lower than that of M30. In the two years, the ratio of C/N ranged between 7.732-9.042, being lower than the threshold of 11.3, and the ratio of C/P was 300.8-719.6, being higher than the threshold of 300. The two parameters showed that the increase of SMBC was inhibited because of the competition of soil available nutrients between soil microbes and crops. These indicated that soil organic matter content was so shortage that it became the key factor to restrict crop productivity. Under this condition, increasing crop productivity through the input of chemical fertilizers would conceal the problem of soil degradation, and result in a further decrease of soil quality. A long term plastic film mulching would make the problem more serious.

Biomass↗

PubMed2004

[A review on disturbance ecology of forest].

More than 80% of terrestrial ecosystems have been influenced by natural disasters, human activities and the combination of both natural and human disturbances. Forest ecosystem, as one of the most important terrestrial ecosystems, has also been disturbed without exception. Under the disturbance from natural disasters and human activities, particularly from the unreasonable activities of human beings, forest decline or forest degradation has become more and more severe. For this reason, sustaining or recovering forest service functions is one of the current purposes for managing forest ecosystems. In recent decades, the studies on disturbed ecosystems have been carried out frequently, especially on their ecological processes and their responses to the disturbances. These studies play a very important role in the projects of natural forest conservation and the construction of ecological environment in China. Based on a wide range of literatures collection on forest disturbance research, this paper discussed the fundamental concepts of disturbance ecology, the relationships between forest management and disturbance, and the study contents of forest disturbance ecology. The major research topics of forest disturbance ecology may include: 1) the basic characteristics of disturbed forests; 2) the processes of natural and human disturbances; 3) the responses of forests ecosystem to the disturbances; 4) the main ecological processes or the consequential results of disturbed forests, including the change of biodiversity, soil nutrient and water cycle, eco-physiology and carbon cycle, regeneration mechanism of disturbed forests and so on; 5) the relationships between disturbances and forest management; and 6) the principles and techniques for the management of disturbed forests. This review may be helpful to the management of disturbed forest ecosystem, and to the projects of natural forest conservation in China.

Disasters↗