Fiber length and fineness were used as the selection criteria in the development of four groups of lines from a composite‐cross of upland cotton ( Gossypium hirsutum L). These groups consisted of lines with long‐coarse, longfine, short‐coarse, and short‐fine fibers. These fiber groups were used to evaluate selection for fiber length and fineness on fiber strength and elongation, lint yield, earliness of crop maturity, stormproofness, lint percent, lint index, and seed index. All selections and evaluations were made in a semiarid environment without irrigation. Orthogonal comparisons, based on the fiber groups, were used to determine the response of these characters to selection for fiber length and fineness. Comparisons of linear regression coefficients from the parental and selected lines were used to estimate the changes in character relationships that occurred during selection. Significant residual variation for most characters, existed among the selected lines within each group. This residual variation suggested that selection had not eliminated all genetic variance. The orthogonal comparisons showed that fiber length was associated with fiber fineness and elongation, lint yield, stormproofness, lint percent, and seed index and that fiber fineness was associated with fiber strength and elongation, earliness of crop maturity, stormproofness, lint percent, lint index, and seed index. Correlation coefficients from the parental and the selected lines suggested that the relationships between fiber length and both lint yield and lint percent did not change during the selection process, but that the associations between fiber length and earliness of crop maturity, stormproofness, lint index, and seed index did change. The relationships between fiber fineness and both fiber strength and lint index were the same in both the parental and selected lines, whereas fiber elongation, earliness of crop maturity, stormproofness, and seed index did not show the same degree of relationship with fineness in the parental and selected lines.
Peatlands export significant amounts of dissolved organic carbon (DOC) to freshwaters, but the quantity of DOC reaching marine environments is typically le
Pocket planting reclamation techniques developed in the 1970s for revegetating blocky quarrying waste have met with very limited success, often because the low water-holding capacity of the waste and limited root development within a small volume of planting pocket material result in severe drought mortality. We tested pocket planting approaches for waste tip reclamation at Europe's largest slate quarry, and compared materials for enhancing the continuity of water- and nutrient-holding down into the interior of the waste tip. When small compost-filled pocket planting bags were placed above slate processing fines (SPF) or water absorbent cross-linked polyacrylamide gel ("hydrogel"), tree growth rates increased in comparison with pocket planting bags alone. The SPF significantly improved tree survival especially during severe drought, but survival was not enhanced by the use of hydrogel. The sorption characteristics of hydrogel indicated that its presence may help to reduce nutrient leaching, but that it may have a negative effect on nitrogen availability. A more likely explanation for the poor performance of pure hydrogel is that it did not maintain sufficient available water, because of discontinuities caused by shrinkage and movement of the hydrogel, and/or degradation of water-holding capacity with environmental exposure. However, the root growth observed in the hydrogel treatments suggests that this technique, if adapted to reduce the effects of hydrogel shrinkage by using finer-grade hydrogel, mixing it with other soil-forming material, and reducing its exposure to extremes of temperature or sunlight, might have the potential to improve the growth and survival of trees planted on sites where delivery of heavy materials such as SPF is impractical. Fine mineral processing waste is freely available at active quarries and should be seen as a key resource for reclamation schemes.
Soil samples from a historic copper mine tailing site at the Parys Mountain, North Wales (UK) were amended with green waste compost (GC), GC+30% sewage sludge (GCS), lime and diammonium phosphate (DAP), to determine the effect of amendments on DTPA- and Ca(NO3)2-extractable metals in the mine tailing and on the phytoavailability of heavy metals by a lettuce (Lactuca sativa L.). Both compost were added at the rate of 10% by weight, lime was added as calcium carbonate equivalent (pH = 7) and DAP at a 2 300 mg kg−1 soil level. The experiment was arranged in randomised complete design with three replicates in pots under control environment. Addition of lime resulted in the largest reduction in metal extractability with DTPA and Ca(NO3)2 and phytoavailability of Cu, Fe and Zn while DAP was effective in lowering Pb extractability and phytoavailability. With exception of Zn, all other metals extracted decreased with time after amendment applications. The distribution of heavy metals between and within the four procedures of potentially bioavailable sequential extraction (PBASE) varied significantly (P < 0.001). Stronger relationships were noted between the metals extracted with PBASE SE1 and Cu, Pb (P < 0.01) and Fe (P < 0.001) in the lettuce. These results indicate that addition of lime is sufficient to restore the vegetative cover to a high metal mine waste while DAP is good for stabilizing Pb, but its detrimental role on plant growth and the risk associated with presence of N in DAP (through N leaching) may restrict its chances for remediation of contaminated sites.
Aluminum inhibition of root growth is a major world agricultural problem where the cause of toxicity has been linked to changes in cellular calcium homeost
Rising atmospheric CO2 concentrations have highlighted the importance of being able to understand and predict C fluxes in plant-soil systems. We investigat
We review four hypotheses for the control of carbon acquisition by roots, and conclude that the functional equilibrium hypothesis can offer a good description of C acquisition by roots relative to shoots, but is deficient mechanistically. The hypothesis that import into roots is solely dependent on export from the shoot, itself determined by features of the shoot alone (the ‘push’ hypothesis), is supported by some but not all the evidence. Similarly, the idea that root demand, a function of the root alone, determines import into it (the ‘pull’ hypothesis), is consonant with some of the evidence. The fourth, general, hypothesis (the ‘shared control’ hypothesis) – that acquisition of C by roots is controlled by a range of variables distributed between root and shoot – accords with both experiment and theory. Top‐down metabolic control analysis quantifies the control of C flux attributable to root relative to source leaf. We demonstrate that two levels of mechanistic control, short‐term regulation of phloem transport and control of gene expression by compounds such as sugars, underlie distributed control. Implications for the impact of climate change variables are briefly discussed.
In this study, we first determined the low molecular weight dissolved organic carbon (LMW DOC) concentration-dependent kinetics of soil respiration in a temperate grassland soil sampled on successive occasions. We then used the established relationship to estimate in situ LMW DOC concentrations from basal respiration measurements. 14C-labelled glucose was used as a model substrate and was added to soil over a wide range of concentrations (0.05–4000 μg C g−1 DW soil; equivalent to ca. 2.5 μM–200 mM glucose-C). The time-dependent loss of 14C-glucose to 14CO2 was similar to previous assessments. The Michaelis–Menten parameter V ma x varied between 17 (September 2010) and 42 (October 2010) μg CO2–C g−1 h−1 (corresponding to 1.4–3.5 µmol CO2 g−1 h−1), while K m varied between 893 (September 2010) and 1990 (October 2010) μg glucose-C g−1 (41–92 mM glucose), thus within the span previously reported for soils, albeit in the higher end of the range. However, the estimates were 6 orders-of-magnitude greater than those found in previous studies in natural waters. A possible methodological reason for this difference was an induced multiphasic concentration dependence, biasing K m and V ma x with high concentrations of LMW DOC. By combining the established concentration dependences with measurements of basal respiration, we estimated in situ concentrations of LMW DOC of 131 (October 2010), 112 (January 2011) and 270 (September 2010) μg LMW DOC g−1, far exceeding the total DOC concentration in the soil (17–20 μg DOC g−1 soil), thus invalidating our approach. We propose a way forward, and suggest that although current estimates of LMW DOC cycling need revision, there is evidence for a rapidly cycling pool of LMW DOC, possibly turning over >30 times per day, that warrants further attention.
Proteases play a crucial role in the soil nitrogen (N) cycle by converting protein to oligopeptides and amino acids. They are often viewed as a bottleneck in terrestrial N cycling; therefore, it is vital that we have robust methods for evaluating protease activity in soil to understand global patterns of protease activity. In response to this, several laboratory-based protease methods have been developed and subsequently modified. However, the validity of these different approaches remains largely unknown. In addition, the lack of standardised protocols makes it difficult to compare protease activity across studies. In this systematic synthesis, we critically evaluate the most common colorimetric and fluorimetric methods used to measure soil protease activity involving 680 independent studies and 1,491 individual assays. To investigate the key regulators of soil protease activity, we collected associated metadata on environmental (mean annual temperature and soil pH) and methodological (assay temperature and pH) factors. Protease activity measured with colorimetric substrates were centred around ca. 1000 nmol product g−1 h−1, whilst rates measured with fluorimetric substrates were lower at ca. 100 nmol product g−1 h−1. Fluorimetric and colorimetric substrates target different proteases which are likely to have different abundances, kinetic parameters, catalytic mechanism or ecological function suggesting why colorimetric substrates have a higher protease activity. We found soil protease activity varied widely around these peaks, likely due to a wide range of environmental or methodological factors that may influence/bias the result. We present the following recommendations for measuring soil protease activity: 1) report assay conditions and soil characteristics, particularly pH and temperature, 2) conduct the assay at either field or optimised pH and temperature conditions, and, 3) check that measurements lie between 0 and 5000 nmol product g−1 h−1. This will help reduce the variation in soil protease activity measurements due to methodological bias and improve reporting of abiotic and biotic associated data. Altogether this will lead to a better understanding of the ecological drivers of protease activity and refine parameterisation of global biogeochemical models.
