(J.P.H., M.J.B., S.T.M., R.S.)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 upregulated specifically by P starvation in an accessible tissue upstream of a marker gene such as ␤-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the expression of only four genes differed between shoots of P-starved and -replete plants 28 h after P was withdrawn.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.

No abstract

Stable-isotope DNA probing is a culture-independent technique that may provide a link between function and phylogeny of active microorganisms. The technique has been used in association with 13C substrates while here we evaluate feasibility and limitations of 15N-DNA stable-isotope probing (SIP) using labelled and unlabelled pure microbial cultures or soil extracts. Our results showed that (15)N-DNA probing is feasible for cultures as well as soil samples. Limitations of 15N-DNA-SIP are (a) the need for relatively large quantities of DNA to visualise bands (although molecular resolution is much higher) and (b) 15N-DNA enrichment needed to ideally be >50 at%; however, this requirement can be lowered to approx. 40 atom% 15N with pure cultures using a modified CsCl centrifugation method (140K g for 69 h). These advances in 15N-DNA-SIP methodology open new opportunities to trace active microbial populations utilising specific N substrates in situ.

This paper evaluates the existing policy frameworks for mitigation of diffuse water pollution from agriculture (DWPA) in England and China. With reference to a conceptual model of the process of policy transfer or international lesson drawing, and possible constraints to this, it assesses whether and how China can draw lessons to improve current policy from the supra-national and national provisions of the EU and a member state that by 2016 had comprehensively implemented EU agricultural and environmental policy. DWPA is first analysed as a public policy challenge to inform specification of a generic framework for its mitigation. The current policy frameworks for mitigation of DWPA in England and China are evaluated, and their potential for improvement is assessed. A number of barriers to lesson drawing for regulation, incentive payments schemes and advice provision are diagnosed. These barriers are potentially least in relation to advice provision and its use to promote voluntary action by farmers. Given its structure and capabilities the public agricultural extension system in China is also recognised as a key resource. A focus on three policy approaches to mitigate DWPA in China is recommended: i) targeted regulation to a 'reference level' of large intensive livestock, and ultimately other large commercial farms; ii) strategic use of incentive payment schemes to protect water resources from DWPA; and iii) reorientation of the ethos and modalities of operation of the extension system, informed by international lesson drawing, with the aim of rebalancing farm productivity and environmental protection.

An easy-to-use simulation model was developed with the aim of improving fertilizer practice when crop residues are incorporated instead of removed. It was tested against data from a well-monitored N fertilizer experiment in which three successive brassica crops were grown followed by barley. Experimental findings included: (a) that fertilizer-N greatly increased yield of 3 crops without increasing residual soil mineral-N at harvest unless supply exceeded crop demand; (b) that, by contrast, fertilizer-N increased both yield of and residual soil mineral-N left by the remaining crop throughout the range of applications; and (c) that at each harvest the apparent disappearance of fertilizer-N by immobilization and other processes was almost proportional to fertilizer-N. These phenomena were simulated by the model. Overall the model gave estimates of soil mineral-N, plant weight and O/ o N in the crop for each crop that were either in close agreement with or linearly related to the measured values. Deviations from this pattern are shown to result almost entirely from experimental error. In addition the model gave simulations of the time course of soil mineral-N and soil water that were in good agreement with measurement.Simulations with the model indicate that appreciable benefits from residue incorporation of crops will only be obtained when fertilizer-N is also applied, unless plant masses at harvest are small.