All rights reserved. No part of this periodical may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopying, recording, or any information storage and retrieval system, without permission in writing from the publisher. Permission for printing and for reprinting the material contained herein has been obtained by the publisher. Permanganate Oxidizable Carbon Refl ects a ProcessedSoil Fraction that is Sensitive to Management Soil Biology & Biochemistry P articulate organic C and MBC are important C fractions that refl ect key processes such as nutrient cycling and availability, soil aggregation, and soil C accrual (Wardle, 1992;Six et al., 1998;Wander, 2004). A large number of studies have shown that both POC and MBC are sensitive to changes in management such as reduced tillage, cover cropping and land use (Cambardella and Elliott, 1992;Wardle, 1992;Wander and Bidart, 2000;Grandy and Robertson, 2007). Th is sensitivity has led to wide adoption of these methods in soil science as indicators of change in the soil ecosystem (Wander, 2004;Gil-Sotres et al., 2005;Kaschuk et al., 2010).As informative as POC and MBC are, they are expensive soil measures for most applications outside of a research setting. Although adaptations have been made to streamline the extraction process of POC (Marriott and Wander, 2006a) and MBC (Fierer et al., 2003), these methods remain costly due to the required labor and combustion analyzer to quantify the total C in the extracted fraction. In addition to the cost, there is a large degree of variation on how researchers extract

Chlamydomonas reinhardtii is a unicellular eukaryotic alga possessing a single chloroplast that is widely used as a model system for the study of photosynthetic processes. This report analyzes the surprising structural and evolutionary features of the completely sequenced 203,395-bp plastid chromosome. The genome is divided by 21.2-kb inverted repeats into two single-copy regions of approximately 80 kb and contains only 99 genes, including a full complement of tRNAs and atypical genes encoding the RNA polymerase. A remarkable feature is that >20% of the genome is repetitive DNA: the majority of intergenic regions consist of numerous classes of short dispersed repeats (SDRs), which may have structural or evolutionary significance. Among other sequenced chlorophyte plastid genomes, only that of the green alga Chlorella vulgaris appears to share this feature. The program MultiPipMaker was used to compare the genic complement of Chlamydomonas with those of other chloroplast genomes and to scan the genomes for sequence similarities and repetitive DNAs. Among the results was evidence that the SDRs were not derived from extant coding sequences, although some SDRs may have arisen from other genomic fragments. Phylogenetic reconstruction of changes in plastid genome content revealed that an accelerated rate of gene loss also characterized the Chlamydomonas/Chlorella lineage, a phenomenon that might be independent of the proliferation of SDRs. Together, our results reveal a dynamic and unusual plastid genome whose existence in a model organism will allow its features to be tested functionally.

Organic producers in the mid-Atlantic region of the USA are interested in reducing tillage, labor and time requirements for grain production. Cover crop-based, organic rotational no-till grain production is one approach to accomplish these goals. This approach is becoming more viable with advancements in a system for planting crops into cover crop residue flattened by a roller–crimper. However, inability to consistently control weeds, particularly perennial weeds, is a major constraint. Cover crop biomass can be increased by manipulating seeding rate, timing of planting and fertility to achieve levels (>8000 kg ha−1) necessary for suppressing summer annual weeds. However, while cover crops are multi-functional tools, when enhancing performance for a given function there are trade-off with other functions. While cover crop management is required for optimal system performance, integration into a crop rotation becomes a critical challenge to the overall success of the production system. Further, high levels of cover crop biomass can constrain crop establishment by reducing optimal seed placement, creating suitable habitat for seed- and seedling-feeding herbivores, and impeding placement of supplemental fertilizers. Multi-institutional and -disciplinary teams have been working in the mid-Atlantic region to address system constraints and management trade-off challenges. Here, we report on past and current research on cover crop-based organic rotational no-till grain production conducted in the mid-Atlantic region.

Our objective is to provide an optimistic strategy for reversing soil degradation by increasing public and private research efforts to understand the role of soil biology, particularly microbiology, on the health of our world's soils. We begin by defining soil quality/soil health (which we consider to be interchangeable terms), characterizing healthy soil resources, and relating the significance of soil health to agroecosystems and their functions. We examine how soil biology influences soil health and how biological properties and processes contribute to sustainability of agriculture and ecosystem services. We continue by examining what can be done to manipulate soil biology to: (i) increase nutrient availability for production of high yielding, high quality crops; (ii) protect crops from pests, pathogens, weeds; and (iii) manage other factors limiting production, provision of ecosystem services, and resilience to stresses like droughts. Next we look to the future by asking what needs to be known about soil biology that is not currently recognized or fully understood and how these needs could be addressed using emerging research tools. We conclude, based on our perceptions of how new knowledge regarding soil biology will help make agriculture more sustainable and productive, by recommending research emphases that should receive first priority through enhanced public and private research in order to reverse the trajectory toward global soil degradation.