Clive Rahn

Changes in Gene Expression in Arabidopsis Shoots during Phosphate Starvation and the Potential for Developing Smart Plants

Our aim was to generate and prove the concept of “smart” plants to monitor plant phosphorus (P) status in Arabidopsis. Smart plants can be genetically engineered by transformation with a construct containing the promoter of a gene up-regulated specifically by P starvation in an accessible tissue upstream of a marker gene such as β-glucuronidase (GUS). First, using microarrays, we identified genes whose expression changed more than 2.5-fold in shoots of plants growing hydroponically when P, but not N or K, was withheld from the nutrient solution. The transient changes in gene expression occurring immediately (4 h) after P withdrawal were highly variable, and many nonspecific, shock-induced genes were up-regulated during this period. However, two common putative cis-regulatory elements (a PHO-like element and a TATA box-like element) were present significantly more often in the promoters of genes whose expression increased 4 h after the withdrawal of P compared with their general occurrence in the promoters of all genes represented on the microarray. Surprisingly, the expression of only four genes differed between shoots of P-starved and -replete plants 28 h after P was withdrawn. This lull in differential gene expression preceded the differential expression of a new group of 61 genes 100 h after withdrawing P. A literature survey indicated that the expression of many of these “late” genes responded specifically to P starvation. Shoots had reduced P after 100 h, but growth was unaffected. The expression of SQD1, a gene involved in the synthesis of sulfolipids, responded specifically to P starvation and was increased 100 h after withdrawing P. Leaves of Arabidopsis bearing a SQD1::GUS construct showed increased GUS activity after P withdrawal, which was detectable before P starvation limited growth. Hence, smart plants can monitor plant P status. Transferring this technology to crops would allow precision management of P fertilization, thereby maintaining yields while reducing costs, conserving natural resources, and preventing pollution.

The Physical, Chemical and Microbial Characteristics of Biodegradable Municipal Waste Derived Composts

A comparative study of the physical, chemical and microbial properties of 12 composts sourced from United Kingdom commercial composting plants was carried out. The aim was to ascertain whether these composts could be used as growing media or for application to agricultural land. The composts were produced from either source segregated biodegradable municipal waste (BMW) or mixed municipal solid waste (MSW). Ten composts contained 100% source segregated BMW including green, fruit, vegetable, meat and kitchen waste, paper and cardboard. One compost was 72% mixed MSW plus 18% source segregated BMW, and one compost was 100% mixed MSW. Composts were analyzed for pH, electrical conductivity, carbohydrates, nutrients and contaminants. The composts sourced from mixed MSW contained higher levels of physical contaminants (glass, plastic and metal) than the source segregated BMW composts. Nitrogen concentrations (as % dry weight) were 1.7-2.2% where kitchen or meat waste was included and 1.0-1.6% otherwise. Phosphorus concentration ranged from 23 to 247 mg kg−1, and K from 1851 to 6615 mg kg−1. Total salts were higher in mixed waste composts (15-23 g kg−1), predominantly due to high concentrations of K, Ca, S and Na. Electrical conductivity varied from 670 μ cm−1 to 3320 μS cm−1. The levels of the heavy metals examined in the 10 source segregated BMW composts were much lower than the limits for composts in the United Kingdom (PAS 100). However, the 100% mixed MSW compost exceeded the PAS 100 levels in four of the seven heavy metals tested (Cu, Ni, Pb and Zn) which may have implications for repeated applications to agriculture. Salmonella was absent from all twelve composts, however, five composts contained levels of E. coli which exceeded the UK PAS 100 limits. Five composts produced from source segregated BMW could be applied to agricultural land, however, high levels of E. coli would exclude the other five. Moreover, high levels of heavy metals and physical contaminants would render the two mixed MSW composts unsuitable.

Chemical characterisation of vegetable and arable crop residue materials : a comparison of methods

Although it is widely recognised that chemical composition controls the patterns of decomposition and N mineralisation of crop residue materials, there has been little agreement as to the nature of the most important chemical fractions. We investigated whether this could be attributed to differences in methodologies employed for chemical characterisation of the lignin and cellulose fractions of plant materials. The cellulose and lignin contents of cauliflower, potato, red beet, Brussels sprouts and wheat crop residues were analysed by a number of contrasting methods. These were forage fibre and forest products analyses, which utilise KMnO4 and H2SO4 respectively to separate the two fractions, and a third method, which employs NaClO2. For all the materials, the forage fibre method gave substantially lower amounts of both lignin and cellulose than the other methods. There was correlation between lignin determined by the different methods. Low recovery of lignin by the forage fibre method was found to arise partly from incomplete delignification by KMnO4. The cellulose contents given by the different methods were highly correlated. However, it was apparent that the forage fibre method underestimated cellulose, since only alpha-cellulose was measured.

The performance of the EU-Rotate_N model in predicting the growth and nitrogen uptake of rotations of field vegetable crops in a Mediterranean environment.

The EU-Rotate_N model was developed as a tool to estimate the growth and nitrogen (N) uptake of vegetable crop rotations across a wide range of European climatic conditions and to assess the economic and environmental consequences of alternative management strategies. The model has been evaluated under field conditions in Germany and Norway and under greenhouse conditions in China. The present work evaluated the model using Italian data to evaluate its performance in a warm and dry environment. Data were collected from four 2-year field rotations, which included lettuce (Lactuca sativa L.), fennel (Foeniculum vulgare Mill.), spinach (Spinacia oleracea L.), broccoli (Brassica oleracea L. var. italica Plenck) and white cabbage (B. oleracea convar. capitata var. alba L.); each rotation used three different rates of N fertilizer (average recommended N1, assumed farmers practice N2=N1+0·3×N1 and a zero control N0). Although the model was not calibrated prior to running the simulations, results for above-ground dry matter biomass, crop residue biomass, crop N concentration and crop N uptake were promising. However, soil mineral N predictions to 0·6 m depth were poor. The main problem with the prediction of the test variables was the poor ability to capture N mineralization in some autumn periods and an inappropriate parameterization of fennel. In conclusion, the model performed well, giving results comparable with other bio-physical process simulation models, but for more complex crop rotations. The model has the potential for application in Mediterranean environments for field vegetable production.

Agricultural sustainable intensification improved nitrogen use efficiency and maintained high crop yield during 1980-2014 in Northern China

Global population increase will require rapid increase of food production from existing agricultural land by 2050, which will inevitably mean the increase of agricultural productivity. Due to agricultural sustainable intensification since the 1990s, crop production in Huantai County of northern China has risen to 15tha-1yr-1 for the annual wheat-maize rotation system. We examined the temporal dynamics of nitrogen (N) budget, N losses, and N use efficiency (NUE) during the 35years (1980-2014) in Huantai. The results revealed that atmospheric N deposition increased 220% while reactive N losses decreased by 21.5% from 1980s to 2010s. During 1980-2002, annual N partial factor productivity (PFPN), apparent NUE and N recovery efficiency (REN) increased from 20.3 to 40.7kggrainkg-1Nfert, from 36.5% to 71.0%, and from 32.4% to 57.7%, respectively; meanwhile, reactive N losses intensity, land use intensity and N use intensity decreased by 69.8%, 53.4%, 50.0%, respectively, but without further significant changes after 2002. Overall increases in NUE and decreases in N losses were largely due to the introduction of optimized fertilization practice, mechanization and increased incorporation of crop straw in Huantai. Straw incorporation was also significant in soil N stock accrual and fertility improvement. By 2030, northern China may reach the lowest end of PFPN values in developed countries (>45kggrainkg-1Nfert). These agricultural sustainable intensification practices will be critical in maintaining high grain yields and associated decreases in environmental pollution, although water use efficiency in the region still needs to be improved.

Effect of Five Municipal Waste Derived Composts on a Cereal Crop

Agricultural soils were amended with five mixed feedstock (four source segregated and one mechanical biological treatment) municipal waste derived composts to investigate the effect on a cereal crop over two years. Composts were applied at two rates to contain either 250 or 500 kg nitrogen ha−1 and compared to a control which received no fertilizer. In year one, three of the composts increased barley yield (by up to 21%), compared to the control (no compost and no fertilizer) and two reduced it (by up to 33%). Application of the municipal waste derived compost resulted in greater nitrogen concentration in the grain and 1000 grain weight but reduced nitrogen uptake and yield. Application of composts had no significant effect on levels of lead, nickel and cadmium in the barley grains. Levels of soil potentially toxic elements were not significantly increased by application of the composts. In year two, all composts gave comparable or greater wheat yields in comparison to the control.

Fertilization and Catch Crop Strategies for Improving Tomato Production in North China

Overuse of fertilizers and the resultant pollution and eutrophication of surface and groundwater is a growing issue in China. Consequently, improved management strategies are needed to optimize crop production with reduced nutrient inputs. Conventional fertilization (CF), reduced fertilization (RF), and reduced fertilization with maize (Zea mays L.) as a summer catch crop (RF+C) treatments were evaluated in 2008 and 2009 by quantifying tomato (Lycopersicon esculentum) fruit yield and soil nutrient balance in a greenhouse tomato double-cropping system. Fertilizer nitrogen (N) application was reduced by 37% in the RF and RF+C treatments compared to the CF treatment with no significant reduction in fruit yield. Mean soil mineral N (Nmin) content to a depth of 180 cm following tomato and maize harvest was lower in the RF and RF+C treatments than in the CF treatment. Residual soil Nmin content was reduced by 21% and 55% in the RF and RF+C treatments, respectively, compared to the CF treatment. Surplus phosphorus (P) and potassium (K) contents in the RF+C treatment were significantly lower than those in the RF treatment, mainly due to additional P and K uptake by the catch crop. We concluded that for intensive greenhouse production systems, the RF and RF+C treatments could maintain tomato fruit yield, reduce the potential for nitrate (NO−3-N) leaching, and with a catch crop, provide additional benefits through increased biomass production.

The stocks and flows of nitrogen, phosphorus and potassium across a 30-year time series for agriculture in Huantai county, China

In order to improve the efficiency of nutrient use whilst also meeting projected changes in the demand for food within China, new nutrient management frameworks comprised of policy, practice and the means of delivering change are required. These frameworks should be underpinned by systemic analyses of the stocks and flows of nutrients within agricultural production. In this paper, a 30-year time series of the stocks and flows of nitrogen (N), phosphorus (P) and potassium (K) are reported for Huantai county, an exemplar area of intensive agricultural production in the North China Plain. Substance flow analyses were constructed for the major crop systems in the county across the period 1983-2014. On average across all production systems between 2010 and 2014, total annual nutrient inputs to agricultural land in Huantai county remained high at 18.1kt N, 2.7kt P and 7.8kt K (696kg N ha-1; 104kgP ha-1; 300kgK ha-1). Whilst the application of inorganic fertiliser dominated these inputs, crop residues, atmospheric deposition and livestock manure represented significant, yet largely unrecognised, sources of nutrients, depending on the individual production system and the period of time. Whilst nutrient use efficiency (NUE) increased for N and P between 1983 and 2014, future improvements in NUE will require better alignment of nutrient inputs and crop demand. This is particularly true for high-value fruit and vegetable production, in which appropriate recognition of nutrient supply from sources such as manure and from soil reserves will be required to enhance NUE. Aligned with the structural organisation of the public agricultural extension service at county-scale in China, our analyses highlight key areas for the development of future agricultural policy and farm advice in order to rebalance the management of natural resources from a focus on production and growth towards the aims of efficiency and sustainability.