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Permanganate-oxidizable C (POXC) and mineralizable C (as determined by short-term aerobic incubation of rewetted soil) are measures of active organic matter that may provide early indication of soil C stabilization and mineralization processes. To date, the relationship between these two promising active organic matter tests has not been comprehensively evaluated, and little is known about their functional role in the soil ecosystem. Here, we examined the relationship between POXC and mineralizable C across a wide range of soil types, management histories, and geographic locations across the United states (13 studies, 76 total sites; n = 1071) and the ability of POXC and mineralizable C to predict crop yield and total aboveground biomass. Results from this comparative analysis showed that POXC and mineralizable C are related (r 2 = 0.15-0.80) but that the relationship was differentially influenced by management practices. Overall, POXC better reflected practices that promote organic matter accumulation or stabilization and therefore can be a useful indicator of long-term soil C sequestration. Conversely, mineralizable C better reflected practices that promote organic matter mineralization and therefore can be a useful indicator of short-term soil nutrient availability. Our results also show that both mineralizable C and POXC were better predictors of corn (Zea mays L.) grain yield, aboveground biomass, and tomato (solanum lycopersicum L.) fruit yield than other soil C fractions evaluated here. Thus, the integrated use of POXC and mineralizable C can provide a complementary framework to assess the relative dynamics of soil C stabilization and nutrient mineralization functions in agroecosystems. O f the three pools that constitute soil organic matter (SOM), the active or labile pool is comprised of rapidly cycling organic material that mostly turns over in a shorter time frame (days to a few years) relative to the intermediate (a few years to decades) and stable (decades to centuries) pools (Cambardella and Elliott, 1992;Gregorich et al., 1994;Parton et al., 1987;Wander, 2004 Core Ideas• POXC and mineralizable C were evaluated across diverse agroecosystems.• The two are related but differentially influenced by management practices.• POXC better reflected sOM stabilizing practices.• Mineralizable C reflected sOM mineralizing practices.• Both predicted agronomic performance better than other soil C fractions.

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Highlights d 347 site-years of yield data from 11 experiments show benefits of diversification d Rotation diversification increased maize yields under putative droughts d More diverse rotations also showed yield benefits across all growing conditions d Diverse rotations accelerated maize yield gains over time

Plant strategies to cope with future droughts may be enhanced by associations between roots and soil microorganisms, including arbuscular mycorrhizal (AM) fungi. But how AM fungi affect crop growth and yield, together with plant physiology and soil carbon (C) dynamics, under water stress in actual field conditions is not well understood. The well-characterized mycorrhizal tomato (Solanum lycopersicum L.) genotype 76R (referred to as MYC+) and the mutant nonmycorrhizal tomato genotype rmc were grown in an organic farm with a deficit irrigation regime and control regime that replaced evapotranspiration. AM increased marketable tomato yields by ~25% in both irrigation regimes but did not affect shoot biomass. In both irrigation regimes, MYC+ plants had higher plant nitrogen (N) and phosphorus (P) concentrations (e.g. 5 and 24% higher N and P concentrations in leaves at fruit set, respectively), 8% higher stomatal conductance (gs), 7% higher photosynthetic rates (Pn), and greater fruit set. Stem water potential and leaf relative water content were similar in both genotypes within each irrigation regime. Three-fold higher rates of root sap exudation in detopped MYC+ plants suggest greater capacity for water uptake through osmotic driven flow, especially in the deficit irrigation regime in which root sap exudation in rmc was nearly absent. Soil with MYC+ plants also had slightly higher soil extractable organic C and microbial biomass C at anthesis but no changes in soil CO2 emissions, although the latter were 23% lower under deficit irrigation. This study provides novel, field-based evidence for how indigenous AM fungi increase crop yield and crop water use efficiency during a season-long deficit irrigation and thus play an important role in coping with increasingly limited water availability in the future.

1. Reliance on ecosystem services instead of synthetic, non-renewable inputs is increasingly seen as key to achieving food security in an environmentally sustainable way. This process, known as ecological intensification, will depend in large part on enhancing below-ground biological interactions that facilitate resource use efficiency. Arbuscular mycorrhizas (AM), associations formed between the roots of most terrestrial plant species and a specialized group of soil fungi, provide valuable ecosystem services, but the full magnitude of these services may not be fully realized under conventional intensively managed annual agricultural systems. 2. Here, we use meta-analysis to assess how reducing soil disturbance and periods without roots in agricultural systems affect the formation of AM and the diversity and community composition of arbuscular mycorrhizal fungi (AMF). We compiled data from 54 field studies across five continents that measured effects of tillage and/or cover cropping on AMF colonization and/or communities and assessed effects of management and environmental factors on these responses. 3. Less intensive tillage and winter cover cropping similarly increased AMF colonization of summer annual cash crop roots by $ 30%. The key variables influencing the change in AMF colonization were the type of cover crop or the type of alternative tillage, suggesting that farmers can optimize combinations of tillage and cover crops that most enhance AM formation, particularly with no-till systems and legume cover crops. 4. Richness of AMF taxa increased by 11% in low-intensity vs. conventional tillage regimes. Several studies showed changes in diversity and community composition of AMF with cover cropping, but these responses were not consistent. 5. Synthesis and applications. This meta-analysis indicates that less intensive tillage and cover cropping are both viable strategies for enhancing root colonization from indigenous arbuscular mycorrhizal fungi (AMF) across a wide range of soil types and cash crop species, and possibly also shifting AMF community structure, which could in turn increase biologically based resource use in agricultural systems.

Flexible filamentous viruses make up a large fraction of the known plant viruses, but in comparison with those of other viruses, very little is known about their structures. We have used fiber diffraction, cryo-electron microscopy, and scanning transmission electron microscopy to determine the symmetry of a potyvirus, soybean mosaic virus; to confirm the symmetry of a potexvirus, potato virus X; and to determine the low-resolution structures of both viruses. We conclude that these viruses and, by implication, most or all flexible filamentous plant viruses share a common coat protein fold and helical symmetry, with slightly less than 9 subunits per helical turn.Flexible filamentous plant viruses include at least 19 recognized genera (22), almost all in three families of singlestranded, positive-sense RNA viruses, the Potyviridae, the Flexiviridae, and the Closteroviridae. Members of the family Potyviridae account for almost a third of the total known plant virus species (22) and are responsible for more than half the viral crop damage in the world (37), infecting most economically important crops (32). Members of the family Flexiviridae (2), and particularly of the large genus Potexvirus, are also of considerable significance to agriculture (42). Both families show great potential for biotechnological applications, including protein expression and vaccine production (12, 54). Despite their importance, however, little is known about the structures of any of the flexible filamentous plant viruses, in sharp contrast to the amount of data on the rigid tobamoviruses (48,63) or the icosahedral plant viruses (15); flexibility, instability, and in many cases low levels of expression have made these viruses particularly intractable to structural studies. Structural and evolutionary relationships among the flexible filamentous plant viruses have been suggested (18,47,56,60), but there is very little sequence homology between the coat proteins of viruses in the different families, and there has hitherto been no structural support for such relationships at the level of either viral symmetry or coat protein folding. Indeed, reports of viral symmetry until now appeared to contradict hypotheses of evolutionary relationships.Soybean mosaic virus (SMV) is a potyvirus, that is, a member of the genus Potyvirus, the largest genus in the family Potyviridae (3). SMV is a major pathogen of soybeans, transmitted efficiently through seed and by aphids in a nonpersistent manner; yield losses as high as 35% have been reported (30). Despite dramatic morphological differences, members of the family resemble the icosahedral plant comoviruses and animal picornaviruses in genomic organization and replication strategy (32). Early electron microscopic observations found the potyviruses to be about 7,500 Å long and 120 Å in diameter, with helical pitches of about 34 Å (44, 60). A fiber diffraction study (51) of the tritimovirus wheat streak mosaic virus (WSMV) suggested that WSMV has 6.9 subunits per turn of the viral helix, but there was consider...

The objectives of this study were to examine soil organic matter (SOM) functional group composition and its relationship to labile SOM fractions with diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). We analyzed soils from 13 organically managed tomato (Solanum lycopersicum) fields in northern California for labile organic C, N, and P fractions and by DRIFTS for bands representing organic functional groups, including aliphatic C‐H (2924, 2850, 1470, 1405, 1390 cm‐1), aromatic C=C (1650 cm‐1) and C‐H (920, 840 cm‐1), polysaccharide and phenol C‐O (1270, 1110, 1080 cm‐1), and amine and amide N‐H (3400, 1575 cm‐1). Significant differences in relative band intensities occurred among the 13 organic tomato fields, in particular a relative increase in absorbance of bands representing aliphatic C‐H positively associated with soil organic carbon (SOC), as well as permanganate‐oxidizable carbon (POXC), extractable organic carbon (EOC) and nitrogen (EON), and potentially mineralizable N (PMN). In comparison, organic P fractions like sodium bicarbonate extractable (NaHCO3–Po) and sodium hydroxide extractable organic P (NaOH‐Po) were poorly associated with SOC and functional groups represented by bands, including aliphatic C‐H. This could reflect limitations of DRIFTS, but is consistent with hypotheses of greater decoupling of C and P vs. C and N in soils. This study implicates relative differences in organic functional groups with differences in SOC and labile SOM fractions, and in agreement with previous studies, identifies absorbance of infrared bands representing aliphatic C‐H functional groups in these systems as a potential indicator of SOM transformations related to changes in its labile fractions.