The impact of soil carbon management on soil macropore structure: a comparison of two apple orchard systems in New Zealand

We analysed the long‐term effect of the addition of organic carbon (C) on the macropore structure of topsoils. For this purpose we compared the top 50 mm in the tree rows of an organic apple orchard with those in an adjacent conventional orchard with the same soil type, texture and previous land‐use history in New Zealand. After 12 years the topsoils of the organic orchard had 32% more soil organic carbon (SOC) sequestered than those of the conventional, integrated orchard because of regular compost applications and grass coverage. We quantified the macropore structure (macropores = pores > 0.3 mm) of nine undisturbed soil columns (43 mm long, 20 × 17 mm in the plane) within each orchard using 3D X‐ray computed tomography. The macroporosity (7.5 ± 2.1%) of the organic orchard soil was significantly greater than that of the integrated orchard (2.4 ± 0.5%). The mean macropore radius was similar in the organic and integrated systems, with 0.41 ± 0.02 mm and 0.39 ± 0.01 mm, respectively. The connectivity of macropores tended to be greater in the organic than in the integrated system, but this was not statistically significant. The pronounced soil C management in the organic orchard increased both the formation of macropores by roots and a larger fresh weight of anecic earthworms, and the stabilization of the macropore structure was increased by a larger aggregate stability and microbial biomass compared with those of the integrated orchard. We simulated the diffusion through the measured pore structures of segments of the soil columns. The segments had the length of the mean aggregate size of the soils. The relative diffusion coefficients at this aggregate scale were significantly greater in the organic (0.024 ± 0.0009) than in the integrated (0.0056 ± 0.008) orchard. In a regression analysis with both the porosity and connectivity of macropores as significant variables, 76% of the variability of the relative diffusion coefficients was explained in the integrated, and, with the porosity as the only significant factor, 71% of the variability in the organic orchard. We hypothesize that a greater relative diffusion coefficient at the aggregate scale would reduce nitrous oxide (N₂O) production and emission in a wet soil and suggest that soil C management combats climate change directly by sequestering C and indirectly in the form of a reduction of N₂O emissions, by creating more macropores.     

Characteristics of phosphorus accumulation in soils under organic and conventional farming in plastic film houses in Korea

Organic farming (OF) is a fast growing alternative for sustainable agriculture in Korea. However, information on the effects of OF on the soil properties and environmental conservation is limited. In order to determine the effects of OF on the soil properties, 31 fields under OF (hereafter referred to as "OF fields") and 61 fields under conventional farming (CF) (hereafter referred to as "CF fields") in plastic film houses were selected throughout Korea and the soil chemical properties were investigated, including the P distribution characteristics. Average organic matter (OM) content was significantly higher (44 g kg^-1) in the OF fields then in the CF fields (24 g kg^-1). Bray-2 P values were 986 and 935 mg kg^-1 in the OF and CF soils, respectively, markedly exceeding the optimum range. Average total P (T-P) values were 2,973 mg kg^-1 in the OF fields and 1,830 mg kg^-1 in the CF fields. The high T-P values were due to repeated application of manure compost with a low N/P ratio. Inorganic P was the dominant fraction with 62–65% of T-P. The amounts of residual and organic P were significantly lower. The level of OF organic P was significantly higher (453 mg kg^-1) compared to the 106 mg kg^-1 value for the CF fields. Fractionation of soil inorganic P showed that Ca-P predominated with 1,332 mg kg^-1 in the OF fields, which was associated with soil pH values over 6.0. The main inorganic P fraction in the CF soils whose pH values were generally less than 6.0 consisted of Al-/Fe-P. The levels of water-soluble P was significantly higher (65 mg kg^-1) in the OF fields than in the CF fields (24 mg kg^-1). These results indicated that the OF system may lead to a serious degradation of the soil environment due to the accumulation of phosphorus and may be an important source of water pollution compared to the CF systems in Korea.     

Microsatellite-based analysis of genetic diversity in 91 commercial Brassica oleracea L. cultivars belonging to six varietal groups

Brassica oleracea L. includes various types of important vegetables that show extremely diverse phenotypes. To elucidate the genetic diversity and relationships among commercial cultivars derived by different companies throughout the world, we characterized the diversity and genetic structure of 91 commercial B. oleracea cultivars belonging to six varietal groups, including cabbage, broccoli, cauliflower, kohlrabi, kale and kai-lan. We used 69 polymorphic microsatellite markers showing a total of 359 alleles with an average number of 5.20 alleles per locus. Polymorphism information content (PIC) values ranged from 0.06 to 0.73, with an average of 0.40. Among the six varietal groups, kohlrabi cultivars exhibited the highest heterozygosity level, whereas kale cultivars showed the lowest. Based on genetic similarity values, an UPGMA clustering dendrogram and a two-dimensional scale diagram (PCoA) were generated to analyze genetic diversity. The cultivars were clearly separated into six different clusters with a tendency to cluster into varietal groups. Model-based structure analysis revealed six genetic groups, in which cabbage cultivars were divided into two subgroups that were differentiated by their head shape, whereas cauliflower and kai-lan cultivars clustered together into a single group. Furthermore, we identified 18 SSR markers showing 27 unique alleles specific to only one cultivar that can be used to discriminate 22 cultivars from the others. Our phylogenetic and population structure analysis presents new insights into the genetic structure and relationships among 91 B. oleracea cultivars and provides valuable information for breeding of B. oleracea species. In addition, we demonstrate the utility of SSR markers as a powerful tool for discriminating between the cultivars. The SSR markers described herein will also be helpful for Distinctness, Uniformity and Stability (DUS) test of new cultivars.     

Spray-drying of the microalga Dunaliella salina: effects on beta-carotene content and isomer composition.

The effects of spray-drying of the unicellular microalga Dunaliella salina on its beta-carotene content and geometric isomer composition have been studied. The efficacy of a range of synthetic and natural antioxidants in preventing degradation of beta-carotene has been determined. Losses of beta-carotene and isomerization were minimal during processing for both the control (no exogenous antioxidants) and the samples containing butylated hydroxytoluene (BHT) and tert-butylhydroquinone (TBHQ). However, the use of tocopherol-based antioxidants resulted in degradation of 52-72% of beta-carotene during the drying process. All dried powders of Dunaliella proved to be unstable during storage in the presence of light and air, with beta-carotene degraded according to a first-order kinetic model. Of the antioxidants studied, only TBHQ was successful in significantly minimizing degradation (degradation constants of 0.03 and 0.04 days(-)(1), compared to 0.53 days(-)(1) for the respective control). For control powders and those with BHT added to the feed, the degradation constants were reduced to values between 0.27 and 0.37 days(-)(1) by restricting light and flushing with nitrogen; however, storage in the dark alone had no effect. For more slowly degrading powders having TBHQ added to the feed, it was clear that degradation of beta-carotene was influenced by both light and oxygen. During storage the 9-cis isomer of beta-carotene was significantly more unstable than the all-trans form. TBHQ was, however, successful in reducing relative losses of this isomer for samples stored in the dark. The results suggest a dominant photodegradative mechanism for the loss of the 9-cis isomer of beta-carotene.     

Antioxidative, antimutagenic, and anticarcinogenic activities of rice bran extracts in chemical and cell assays

Ethanol-water (70:30 v/v) extracts from rice brans removed from seeds of two blackish-purple pigmented (Sanhaehyanghyulla and Suwon 415) and one nonpigmented (Chuchung) brown rice cultivars were evaluated for antioxidative, anti-tumor-promoting, and anticarcinogenic activities in chemical assays and in mammalian cells (human leukemia HL-60, marmoset B lymphoblastoid B95-8, and Chinese hamster V79 lung cells) by the following tests: inhibition of xanthine oxidase activity; chelation of ferrous ions; reduction of potassium ferricyanide; scavenging of superoxide anions, hydroxyl radicals, and intracellular peroxides; inhibition of 4-nitroquinoline N-oxide-induced mutagenesis; and inhibition of phorbol ester-induced tumor promotion. The extracts from the pigmented rice seeds had generally higher activities in all tests than did the extract from the nonpigmented variety. The results suggest that brans from pigmented rice varieties may provide a source of new natural antioxidants and anticarcinogens and that such rice cultivars with high antioxidative potential also provide a genetic resource for the development of new, improved rice cultivars that may make it possible to enhance both the nutritional and medical value of rice-based diets.     

Root Plasticity Not Evident in N-Enriched Soil Volumes for Wheat (Triticum aestivum L.) and Barley (Hordeum vulgare L.) Varieties

Root plasticity is a unique characteristic of root systems that may enhance the nutrient foraging capacity of plants. Here we investigated the effect of localized high nitrogen (N) concentration on plasticity of wheat and barley roots in soil. We conducted a series of experiments to maintain localized high concentration of N in soil and to evaluate any root morphological variation in the enriched N zone. Wheat and barley seedlings were grown in N responsive Red Ferrosol with an enriched subsurface N band for 12 days. Wheat and barley roots did not proliferate in N-enriched soil volumes. Rather, higher root length density (~1.6 times) was observed in low N surface soil. Shoot dry matter and shoot N uptake of banded N treatment was statistically similar between uniform and low N treatments. Results indicated the absence of plastic root response of the wheat and barley seedlings in subsurface N band.     

Alpine flora may depend on declining frugivorous parrot for seed dispersal

Globally, bird numbers are declining, with potentially serious flow-on effects on ecosystem processes, such as seed dispersal mutualisms. However, management to maintain seed dispersal may be inappropriate if unexpected animals are the most important dispersers. Numbers of the world’s only alpine parrot, the New Zealand kea (Nestor notabilis), have declined drastically over the last 120 years after an intense period of official persecution. Today <5000 kea remain in the wild. Previously it has been assumed that like other parrots, kea would destroy most of the seeds they eat, thereby contributing little to seed dispersal. The New Zealand alpine flora is rich in fleshy-fruited species yet has a limited disperser fauna. Consequently, we investigated the relevance of kea as a seed disperser in New Zealand’s alpine ecosystems. Field-based foraging observations coupled with faecal analyses showed kea were by far the most important extant alpine avian frugivore. Kea selected more fruiting species (21 vs. 17 species), consumed more fruit, and dispersed more seeds (8137 vs. 795) than all other birds combined. Rates of seed predation by kea were extremely low, and evident in only 25% of species eaten. Kea are the only species that make frequent long-distance flights within and between mountain ranges. Hence, much of the effective long-distance dispersal of the alpine flora may be currently performed by kea. Conservation of kea is therefore important both for ensuring the survival of the species and for their role in seed-dispersal mutualisms for which there are few extant substitutes.     

Tillage, habitat space and function of soil microbes

This review examines the effect of tillage on microbial habitat space, and the roles of microbes in influencing N-transformation processes within a heterogeneous soil environment. Literature relating tillage to microbial processes is assessed critically focusing on (a) degrees of physical disruption and N-processes, (b) interactions between organisms and the soil pore network, and (c) the role of soil structure in mediating oxygen movement to sites of microbial activity in soil. Spatial heterogeneity is shown to be a key characteristic of soil structure and N-transformation processes, impacting on predator:prey relations, microbial habitable pore space, and the modelling of the soil system with respect to denitrification. The latter area is discussed with respect to the notion of how a functional appraisal of soil structure may be approached theoretically, at the aggregate and soil profile scale.     

Justification of unilateral hysterectomy-ovariectomy as a model to evaluate uterine capacity in swine

Experimental objectives were to measure the effect of ovulation rate on litter size at 86 d of gestation and at farrowing in 110 unilaterally hysterectomized-ovariectomized (UHO) gilts and in 142 intact, control gilts and to evaluate postnatal survival and development of progeny. Surgery (UHO) was performed on gilts 8 to 12 d following first estrus. Control and UHO gilts were mated and then randomly assigned to be slaughtered at d 86 of gestation or allowed to farrow. Gilts scheduled to farrow were observed by laparoscopy on d 40 of gestation to count corpora lutea (CL). Ovulation rate (number of CL) was similar for control (12.1 CL) and UHO (11.9 CL) gilts, thus indicating that compensatory ovarian hypertrophy had occurred in UHO gilts and resulted in a near doubling of ova per uterine horn relative to control gilts. Average litter size at 86 d of gestation and farrowing was greater (P less than .01) for control than UHO gilts. At farrowing, litter size for control and UHO gilts was 9.0 +/- .3 and 5.7 +/- .3 pigs, respectively. Fetal losses were greater and pig weights at birth were less in litters by UHO gilts. Postnatal pig survival, growth rate to 14 d of age and 14-d individual pig weight did not differ for progeny of control and UHO gilts, and performance of UHO pogeny did not appear to compromise the usefulness of this animal model. Regression of litter size on ovulation rate was .41 +/- .15 pigs/CL for UHO and .60 +/- .12 pigs/CL for control gilts at d 86 of gestation. Regression was .07 +/- .17 pigs/CL for UHO and .42 +/- .14 pigs/CL for control gilts at farrowing.(ABSTRACT TRUNCATED AT 250 WORDS)