Is nutrient availability related to plant nutrient use in humid tropical forests?

Data on soil nutrient availability for humid tropical forests are often reported, but are rarely integrated in an ecologically meaningful way with other measures of nutrient cycling. In this paper, estimates of soil nutrient availability and the inverse of litterfall nutrient concentrations (as an index of plant nutrient use) were compared, using data from 36 sites throughout the humid tropics, to determine if relationships exist between commonly used indices of nutrient cycling for plants and soils. Measures of both extractable and total soil P were significantly and positively correlated with the ratio of litterfall mass/P, particularly for montane tropical forests. Extractable soil P was also significantly correlated with litterfall mass for lowland humid tropical forests, explaining 58% of the variability in litterfall mass. A weak, albeit significant correlation was found between exchangeable soil Ca and litterfall mass/Ca, even though soil extraction techniques vary greatly. No significant relationship was found for total soil N, the most commonly measured soil N pool, and the inverse of litterfall N concentrations. The results suggest that our indices of soil P are related to litterfall processes, but that other measures, particularly total soil N, may not be as relevant to nutrient cycling by the vegetation.     

What is a plant nutrient? Changing definitions to advance science and innovation in plant nutrition

Plant and Soil - Current definitions of essential or beneficial elements for plant growth rely on narrowly defined criteria that do not fully represent a new vision for plant nutrition and...     

What controls variation in carbon use efficiency among Amazonian tropical forests?

Why do some forests produce biomass more efficiently than others? Variations in Carbon Use Efficiency (CUE: total Net Primary Production (NPP)/ Gross Primary Production (GPP)) may be due to changes in wood residence time (Biomass/NPP_wood), temperature, or soil nutrient status. We tested these hypotheses in 14, one ha plots across Amazonian and Andean forests where we measured most key components of net primary production (NPP: wood, fine roots, and leaves) and autotrophic respiration (R_a; wood, rhizosphere, and leaf respiration). We found that lower fertility sites were less efficient at producing biomass and had higher rhizosphere respiration, indicating increased carbon allocation to belowground components. We then compared wood respiration to wood growth and rhizosphere respiration to fine root growth and found that forests with residence times <40 yrs had significantly lower maintenance respiration for both wood and fine roots than forests with residence times >40 yrs. A comparison of rhizosphere respiration to fine root growth showed that rhizosphere growth respiration was significantly greater at low fertility sites. Overall, we found that Amazonian forests produce biomass less efficiently in stands with residence times >40 yrs and in stands with lower fertility, but changes to long‐term mean annual temperatures do not impact CUE.     

What controls TOR?

The target of rapamycin (TOR) is a protein kinase with numerous functions in cell growth control. Some of these functions can be potently inhibited by rapamycin, an immunosuppressive and potential anticancer drug. TOR exists as part of two functionally distinct protein complexes. The functions of TOR complex 1 (TORC1) are effectively inhibited by rapamycin, but the mechanism for this inhibition remains elusive. The identification of TORC2 and recent reports that rapamycin can inhibit TORC2 functions, in some cases, challenge current models of TOR regulation. This review discusses the latest findings in yeast and mammals on the possible mechanisms that control TOR activity leading to its many cellular functions     

What controls liana success in Neotropical forests?

Aim   We seek to determine the factors which control the success of lianas across macroecological gradients. Lianas have a strong impact on the growth, mortality and biomass of tropical trees, and are reported to be increasing in dominance, so understanding their behaviour is important from the perspectives of both ecological and global change.
Location   Lowland and montane Neotropical forests.
Methods   Using 65 standardized samples of lianas (≥ 2.5 cm diameter) from across the Neotropics, we attempted to account for characteristics of both the environment and the forest in explaining macroecological variation in liana success in Neotropical forests, using regression analyses and structural equation modelling.
Results   We found that both liana density and basal area were unrelated to mean annual precipitation, dry season length or soil variables, except for a weak effect of mean annual precipitation on liana basal area. Structural characteristics of the forest explained more of the variation in liana density and basal area than the physical environment. More disturbed forests generally tended to have a higher liana density. Liana basal area, however, was highest in undisturbed forests.
Main conclusions   The availability of host trees and their characteristics may be more important than the direct effects of the physical environment in controlling the success of lianas in Neotropical forests. Changes to the tropical climate in the coming century may not strongly affect lianas directly, but could have very substantial indirect effects via changes in tree community structure and dynamics.     

What controls glycolysis in bloodstream form Trypanosoma brucei?

On the basis of the experimentally determined kinetic properties of the trypanosomal enzymes, the question is addressed of which step limits the glycolytic flux in bloodstream form Trypanosoma brucei. There appeared to be no single answer; in the physiological range, control shifted between the glucose transporter on the one hand and aldolase (ALD), glyceraldehyde-3-phosphate dehydrogenase (GAPDH), phosphoglycerate kinase (PGK), and glycerol-3-phosphate dehydrogenase (GDH) on the other hand. The other kinases, which are often thought to control glycolysis, exerted little control; so did the utilization of ATP. We identified potential targets for anti-trypanosomal drugs by calculating which steps need the least inhibition to achieve a certain inhibition of the glycolytic flux in these parasites. The glucose transporter appeared to be the most promising target, followed by ALD, GDH, GAPDH, and PGK. By contrast, in erythrocytes more than 95% deficiencies of PGK, GAPDH, or ALD did not cause any clinical symptoms (Schuster, R. and Holzhütter, H.-G. (1995) Eur. J. Biochem. 229, 403-418). Therefore, the selectivity of drugs inhibiting these enzymes may be much higher than expected from their molecular effects alone. Quite unexpectedly, trypanosomes seem to possess a substantial overcapacity of hexokinase, phosphofructokinase, and pyruvate kinase, making these "irreversible" enzymes mediocre drug targets.     

Got silicon? The non-essential beneficial plant nutrient

Research on a possible nutritional role for the element silicon has been hampered by the diverse beneficial effects that it has on monocots and dicots, and the subsequent difficulties in focusing studies on a single genetic model system. Although deemed a non-essential nutrient for the majority of plants, the benefits of silicon include increasing pest and pathogen resistance, drought and heavy metal tolerance, and the quality and yield of agricultural crops. Although the pathways and molecular mechanisms by which silicon is absorbed and deposited in plants are still unclear, recent progress has been achieved through the use of rice mutants that are deficient in silicon uptake. Additionally, the application of electron-energy-loss spectroscopy (EELS) allows one to determine the composition of silica deposits conclusively. Thereby shedding light upon the role of silicon in heavy metal tolerance. With the complete sequence of the genomes for a dicot (Arabidopsis) and a monocot (rice) available for large-scale genetic analysis, the future bodes well for a more complete understanding of the biological role of silicon and its mode of transport into and through plants.     

Is Calluna vulgaris a suitable bio-monitor of management-mediated nutrient pools in heathland ecosystems?

In the face of ongoing atmospheric nutrient loads the employment of management measures to remove nutrients from heathland ecosystems has increased in importance. The present study is the first to analyse whether Calluna vulgaris is a suitable bio-monitor of management-mediated nutrient pools in heathland ecosystems. If Calluna vulgaris proves to be an appropriate indicator, its bio-indicative usage may prove to be a helpful tool for an assessment of management success in heathland ecosystems. In the Lüneburger Heide nature reserve (NW Germany) we analysed the impacts of grazing, mowing, prescribed burning, choppering and sod-cutting on the nutritional status of Calluna vulgaris by measuring nutrient contents (N, P, Ca, Mg, K) of current year's shoots 1 and 5 years after application of management measures. Results were related to management-induced nutrient flows and nutrient pools at the focal heath sites. Our results indicate that the less the physical environment of a heath site was affected by management measures the better the nutrient contents of current year's shoots of Calluna vulgaris mirrored changes in nutrient pools. For low-intensity measures (i.e. grazing, mowing, prescribed burning), shoot nutrient contents were a suitable indicator for changes in nutrient pools, particularly for nutrients with conservative cycles such as P. At grazed and mown sites high output rates of P caused by these measures were well reflected by decreased shoot P content. At burned sites, Calluna vulgaris proved to be a good indicator of changes in nutrient pools of the organic layer, mainly attributable to the deposition of nutrients with ash. In contrast, at sites subjected to high-intensity measures, shoot nutrient contents did not reflect management-mediated shifts in nutrient pools, despite the high nutrient losses caused by choppering and sod-cutting. At these sites, shoot nutrient contents mirrored only the effects of altered mineralisation rates attributable to changes in the physical environment following high-intensity measures. As plant growth and competition in heathlands is considered to be controlled by N or P, shoot N:P ratios are recommended as a tool to indicate whether plant growth tends to be limited by N, by P or by N and P. This, in turn, allows for an assessment of long-term effects of both atmospheric nutrient loads and management-mediated shifts in N and P pools at a focal heath site.     

What happened to plant caspases?

The extent of conservation in the programmed cell death pathways that are activated in species belonging to different kingdoms is not clear. Caspases are key components of animal apoptosis; caspase activities are detected in both animal and plant cells. Yet, while animals have caspase genes, plants do not have orthologous sequences in their genomes. It is 10 years since the first caspase activity was reported in plants, and there are now at least eight caspase activities that have been measured in plant extracts using caspase substrates. Various caspase inhibitors can block many forms of plant programmed cell death, suggesting that caspase-like activities are required for completion of the process. Since plant metacaspases do not have caspase activities, a major challenge is to identify the plant proteases that are responsible for the caspase-like activities and to understand how they relate, if at all, to animal caspases. The protease vacuolar processing enzyme, a legumain, is responsible for the cleavage of caspase-1 synthetic substrate in plant extracts. Saspase, a serine protease, cleaves caspase-8 and some caspase-6 synthetic substrates. Possible scenarios that could explain why plants have caspase activities without caspases are discussed.     

What drives plant stress genes?

Currently, there is a lot of interest in the plant stress response. Using large-scale genomics approaches, more and more genes are being identified that are involved in or even regulate this complex process. The recent boost in expression profile analyses for several plant stress responses has enabled the identification of new promoter elements as important factors in establishing the expression regulatory network controlling plant stress response.     

What controls polyspermy in mammals,the oviduct or the oocyte?

A block to polyspermy is required for successful fertilisation and embryo survival in mammals. A higher incidence of polyspermy is observed during in vitro fertilisation (IVF) compared with the in vivo situation in several species. Two groups of mechanisms have traditionally been proposed as contributing to the block to polyspermy in mammals: oviduct‐based mechanisms, avoiding a massive arrival of spermatozoa in the proximity of the oocyte, and egg‐based mechanisms, including changes in the membrane and zona pellucida (ZP) in reaction to the fertilising sperm. Additionally, a mechanism has been described recently which involves modifications of the ZP in the oviduct before the oocyte interacts with spermatozoa, termed “pre‐fertilisation zona pellucida hardening”. This mechanism is mediated by the oviductal‐specific glycoprotein (OVGP1) secreted by the oviductal epithelial cells around the time of ovulation, and is reinforced by heparin‐like glycosaminoglycans (S‐GAGs) present in oviductal fluid. Identification of the molecules contributing to the ZP modifications in the oviduct will improve our knowledge of the mechanisms of sperm‐egg interaction and could help to increase the success of IVF systems in domestic animals and humans.     

The native–invasive balance: implications for nutrient cycling in ecosystems

We conducted single- and mixed-litter experiments in a hardwood forest in Long Island, New York, using leaf litter from phylogenetically paired native and invasive species. We selected long-established, abundant invasive species with wide-ranging distributions in the eastern United States that likely make substantial contributions to the litter pool of invaded areas. Overall, leaf litter from invasive species differed from native litter, though differences varied by phylogenetic grouping. Invasive litter had lower carbon:nitrogen ratios (30.9 ± 1.96 SE vs. 32.8 ± 1.36, P = 0.034) and invasive species lost 0.03 ± 0.007 g of nitrogen and had 23.4 ± 4.9 % of their starting mass remaining at the end of 1 year compared with a loss of 0.02 ± 0.003 g nitrogen and 31.1 ± 2.6 % mass remaining for native species. Mixing litter from two species did not alter decomposition rates when native species were mixed with other native species, or when invasive species were mixed with other invasive species. However, mixing litter of native and invasive species resulted in significantly less mass and nitrogen loss than was seen in unmixed invasive litter. Mixtures of native and invasive litter lost all but 47 ± 2.2 % of initial mass, compared to 37 ± 5.8 % for invasive litter and 50 ± 5.1 % for native litter. This non-additive effect of mixing native and invasive litter suggests that an additive model of metabolic characteristics may not suffice for predicting invasion impacts in a community context, particularly as invasion proceeds over time. Because the more rapid decomposition of invasive litter tends to slow to rates typical of native species when native and invasive litters are mixed together, there may be little impact of invasive species on nutrient cycling early in an invasion, when native leaf litter is abundant (providing litter deposition is the dominant control on nutrient cycling).     

What controls the length of noncoding DNA?

Several recent studies of genome evolution indicate that the rate of DNA loss exceeds that of DNA gain, leading to an underlying mutational pressure towards collapsing the length of noncoding DNA. That such a collapse is not observed suggests opposing mechanisms favoring longer noncoding regions. The presence of transposable elements alone also does not explain observed features of noncoding DNA. At present, a multidisciplinary approach--using population genetics techniques, large-scale genomic analyses, and in silico evolution--is beginning to provide new and valuable insights into the forces that shape the length of noncoding DNA and, ultimately, genome size. Recombination, in a broad sense, might be the missing key parameter for understanding the observed variation in length of noncoding DNA in eukaryotes.     

What makes a plant species specialist in mixed broad-leaved deciduous forests?

Knowledge about relationships between specialization degree of species, i.e. the width of their realized niche and functional traits, may have important implications for the assessment of future population developments under environmental change. In this study, we used a recently introduced method to calculate ecological niche widths of plant species in mixed broad-leaved deciduous forests and to investigate the dependence between niche widths of plants and their functional traits and Ellenberg indicator values. The research is based on a dataset of 4556 phytosociological relevés of mixed broad-leaved deciduous forests in Slovenia. We calculated theta indices for 326 species, which ranks them along a continuous gradient of habitat specialization. For 272 species, we compiled 26 functional traits and Ellenberg indicator values. We found some significant correlations between theta indices of species and their functional traits and Ellenberg indicator values; habitat specialists thrive primarily on the highest altitudes, on colder, dry sites and achieve the age of first flowering later than generalists. They also have smaller seed diameter, lower leaf dry matter content, lower mean canopy height and bigger specific leaf area than generalists. Two species groups, chamaephytes and spring green species, are particularly characterized as specialist species. The added value of our work is in complementing the knowledge about the niche differentiating along different environmental gradients and species coexistence in mixed broad-leaved deciduous forests.