This review provides an assessment of sediment trap accuracy issues by gathering data to address trap hydrodynamics, the problem of zooplankton "swimmers," and the solubilization of material after collection. For each topic, the problem is identified, its magnitude and causes reviewed using selected examples, and an update on methods to correct for the potential bias or minimize the problem using new technologies is presented. To minimize hydrodynamic biases due to flow over the trap mouth, the use of neutrally buoyant sediment traps is encouraged. The influence of swimmers is best minimized using traps that limit zooplankton access to the sample collection chamber. New data on the impact of different swimmer removal protocols at the US time-series sites HOT and BATS are compared and shown to be important. Recent data on solubilization are compiled and assessed suggesting selective losses from sinking particles to the trap supernatant after collection, which may alter both fluxes and ratios of elements in long term and typically deeper trap deployments. Different methods are needed to assess shallow and short-term trap solubilization effects, but thus far new incubation experiments suggest these impacts to be small for most elements. A discussion of trap calibration methods reviews independent assessments of flux, including elemental budgets, particle abundance and flux modeling, and emphasizes the utility of U-Th radionuclide calibration methods.

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Detecting QTLs (quantitative trait loci) that enhance cotton yield and fiber quality traits and accelerate breeding has been the focus of many cotton breeders. In the present study, 359 SSR (simple sequence repeat) markers were used for the association mapping of 241 Upland cotton collections. A total of 333 markers, representing 733 polymorphic loci, were detected. The average linkage disequilibrium (LD) decay distances were 8.58 cM (r2 > 0.1) and 5.76 cM (r2 > 0.2). 241 collections were arranged into two subgroups using STRUCTURE software. Mixed linear modeling (MLM) methods (with population structure (Q) and relative kinship matrix (K)) were applied to analyze four phenotypic datasets obtained from four environments (two different locations and two years). Forty-six markers associated with the number of bolls per plant (NB), boll weight (BW), lint percentage (LP), fiber length (FL), fiber strength (FS) and fiber micornaire value (FM) were repeatedly detected in at least two environments. Of 46 associated markers, 32 were identified as new association markers, and 14 had been previously reported in the literature. Nine association markers were near QTLs (at a distance of less than 1–2 LD decay on the reference map) that had been previously described. These results provide new useful markers for marker-assisted selection in breeding programs and new insights for understanding the genetic basis of Upland cotton yields and fiber quality traits at the whole-genome level.

Global soil salinization is increasingly a serious threat to agriculture worldwide. Therefore, it is imperative to improve crop salt tolerance as a means of adaptation to saline habitats. Some halophytes and most monocotyledonous crops are salt-excluders. Understanding the regulatory mechanisms of salt exclusion at the molecular level in salt-exclusion plants is critical for improving the salt tolerance of monocotyledonous crops such as maize, wheat, rice, and sorghum. In this review, we summarize recent research into salt-exclusion mechanisms and the genes that underlie them. Findings related to salt exclusion may accelerate the process of breeding tolerant cultivars by using genomic and molecular tools.

Iron (Fe) is mostly complexed with the organic ligands or colloids that are very abundant in natural seawater. In this study, natural colloids were isolated by ultrafiltration and radiolabeled with 59 Fe. The biological uptake of radiolabeled colloid-bound Fe of different sizes (1-10 kDa and 10 kDa-0.2 m) and ages (1 and 15 d) by diatoms (Thalassiosira pseudonana) and copepods (Acartia spinicauda) was then determined. The uptake of radiolabeled colloid-bound Fe was compared with the uptake of low molecular weight (LMW) complexed Fe (Ͻ1 kDa) or that of EDTA-Fe (at a ratio of 1 : 2 for Fe : EDTA). Our study demonstrates that the colloid-bound Fe of different sizes and ages was bioavailable to the diatoms. The uptake of colloidal bound Fe was, however, 6-31 times lower than the uptake of LMW Fe, suggesting that colloidal binding reduced Fe bioavailability to diatoms. Fe bound with small colloids (1-10 kDa) was taken up at a higher rate than Fe bound with large colloids (10 kDa-0.2 m) at typical colloidal organic carbon concentrations. The uptake of colloid-bound Fe was also much higher when the Fe had been bound with the colloids for 1 d rather than for 15 d. Differences in the colloidal organic carbon concentration did not appreciably affect the uptake of colloid-bound Fe by the diatoms. Similarly, copepods accumulated colloid-bound Fe at a much higher rate when the Fe was associated with small colloids rather than with large colloids. Direct ingestion of colloidal particles by the copepods appeared to be negligible. In both diatoms and copepods, Fe uptake may involve its dissociation from the colloids before being accumulated by the organisms. The study therefore demonstrates that colloid-bound Fe is less available for marine phytoplankton and that colloidal size and thus the colloidal speciation may be critical in controlling colloid-bound Fe uptake by aquatic organisms.