Land-use history has a stronger impact on soil microbial community composition than aboveground vegetation and soil properties

The response of soil microbial communities following changes in land-use is governed by multiple factors. The objectives of this study were to investigate (i) whether soil microbial communities track the changes in aboveground vegetation during succession; and (ii) whether microbial communities return to their native state over time. Two successional gradients with different vegetation were studied at the W. K. Kellogg Biological Station, Michigan. The first gradient comprised a conventionally tilled cropland (CT), mid-succession forest (SF) abandoned from cultivation prior to 1951, and native deciduous forest (DF). The second gradient comprised the CT cropland, early-succession grassland (ES) restored in 1989, and long-term mowed grassland (MG). With succession, the total microbial PLFAs and soil microbial biomass C consistently increased in both gradients. While bacterial rRNA gene diversity remained unchanged, the abundance and composition of many bacterial phyla changed significantly. Moreover, microbial communities in the relatively pristine DF and MG soils were very similar despite major differences in soil properties and vegetation. After >50 years of succession, and despite different vegetation, microbial communities in SF were more similar to those in mature DF than in CT. In contrast, even after 17 years of succession, microbial communities in ES were more similar to CT than endpoint MG despite very different vegetation between CT and ES. This result suggested a lasting impact of cultivation history on the soil microbial community. With conversion of deciduous to conifer forest (CF), there was a significant change in multiple soil properties that correlated with changes in microbial biomass, rRNA gene diversity and community composition. In conclusion, history of land-use was a stronger determinant of the composition of microbial communities than vegetation and soil properties. Further, microbial communities in disturbed soils apparently return to their native state with time.     

Random amplified polymorphic DNA (RAPDs) markers for genetic analysis in micropropagated plants of Robinia pseudoacacia L.

Four years' old micropropagated plants regenerated by enhanced axillary branching from shoot buds of a single genotype of Robinia pseudoacacia were characterized by RAPDs. Random amplified polymorphic DNA analysis was carried outusing 19 random 10-mer DNA primers and 286 RAPD bands were examined which showed 30% polymorphism. Similarity indices ranged from 0.86 to 0.96 among different plants based on RAPD data. The UPGMA dendrogram was constructed based on similarity indices which showed clustering of different plants into subgroups based on similarity values. Our results suggest that somaclonal DNA sequence variations are present even when organized cultures such as shoot buds were used as explant for micro-propagation. This revised version was published online in August 2006 with corrections to the Cover Date.     

N-Source Effects on Temporal Distribution of NO3-N Leaching Losses to Subsurface Drainage Water

Understanding the temporal distribution of NO₃-N leaching losses from subsurface drained ‘tile’ fields as a function of climate and management practices can help develop strategies for its mitigation. A field study was conducted from 1999 through 2003 to investigate effects of the most vulnerable application of pig manure (fall application and chisel plow), safe application of pig manure (spring application and no-tillage) and common application of artificial nitrogen (UAN spring application and chisel plow) on NO₃-N leaching losses to subsurface drainage water beneath corn (Zea mays L.)–soybean (Glycine max L.) rotation systems as a randomized complete block design. The N application rates averaged over five years ranged from 166 kg-N ha^?1 for spring applied manure to 170 kg-N ha^?1 for UAN and 172 kg-N ha^?1 for fall applied manure. Tillage and nitrogen source effects on tile flow and NO₃-N leaching losses were not significant (P?<?0.05). Fall applied manure with CP resulted in significantly greater corn grain yield (10.8 vs 10.4 Mg ha^?1) compared with the spring manure-NT system. Corn plots with the spring applied manure-NT system gave relatively lower flow weighted NO₃-N concentration of 13.2 mg l^?1 in comparison to corn plots with fall manure-CP (21.6 mg l^?1) and UAN-CP systems (15.9 mg l^?1). Averaged across five years, about 60% of tile flow and NO₃-N leaching losses exited the fields during March through May. Growing season precipitation and cycles of wet and dry years primarily controlled NO₃-N leaching losses from tile drained fields. These results suggest that spring applied manure has potential to reduce NO₃-N concentrations in subsurface drainage water and also strategies need to be developed to reduce early spring NO₃-N leaching losses.     

Agrobacterium-mediated Cry1A(b) gene transfer in Punica granatum L. cv. Kandhari Kabuli using different In Vitro regeneration pathways

Three different regeneration systems, viz. regeneration through callus cultures using embryonic explant, direct regeneration using shoot bud/nodal segments as explant and regeneration through cell suspension culture using cotyledonary explant (for the induction of transgenic callus for suspension culture) were evaluated to see their effect on transfer of Cry1A(b) gene to Punica granatum L. cv. Kandhari Kabuli through Agrobacterium mediated transformation. Pre-conditioning and co-cultivation durations had a marked effect on transformation frequency of different explants. Out of different explants used (embryo, shoot bud, and cotyledon) for different regeneration systems cotyledonary explant showed highest putative transformation frequency (13.54%) inducing callus on selective medium for carrying out cell suspension culture to regenerate transgenic shoots. Despite of the highest transformation frequency obtained from the cotyledon explant, the plating efficiency of the transgenic cells generated through the transgenic callus (callus formed from the cotyledonary explant) during cell suspension culture was found to be very low (0.7%). Thus the plating efficiency has also played worth mentioning role in the regeneration of transformants following cell suspension culture. Among the three regeneration systems, regeneration through callus cultures using embryonic explant was found to be best for regeneration of transformants. The highest per cent regeneration of 23.33 was obtained from the putative transgenic embrogenic calli. Successful genetic transformation in the transformed plantlets was confirmed by PCR analysis. The transformation system thus developed is valuable and may be used to produce insect resistant trees.     

Tissue culture micropropagation of Douglas-fir

A procedure was developed for plantlet production from embryos of Douglas-fir [Pseudotsuga menziesii (Mirb.) Franco]. The Medium for Conifer Morphogenesis, used at full strength, and supplemented with 10 M benzyladenine for 17 days produced an average of 6.8 shoots on more than 90% of the embryos. The percentage of shoot-forming embryos as well as the average number of shoots per embryo varied significantly among eight seedlots. For secondary multiplication, 89% of the adventitious shoots produced axillary buds on MCM with 5 M benzyladenine. However, 0.5 M BA was more suitable for the elongation of axillaries. Rooting ranged from 0–87% depending upon the treatment. The highest percentage was obtained with a 7-week incubation in peat:perlite containing 1/5-strength medium, 1% sucrose and 2.7 M naphthaleneacetic acid, followed by 5 weeks on peat:perlite with 1/5-strength major and minor salts, full iron and organics, 1% sucrose and 0.1% charcoal.     

Rejuvenation influences indirect organogenesis from leaf explants of Pomegranate (Punica granatum L.) ‘Kandhari Kabuli’

Sequential subculturing leads to a gradual physiological change in cells that may be termed ‘rejuvenation’. The effect of repetitive subculturing on callus induction and shoot regeneration from leaf explants of Punica granatum L. ‘Kandhari Kabuli’ were investigated. Surface-sterilised leaves were cultured on 1.0× Murashige and Skoog (MS) medium supplemented with 4.0 mg l^–1 α-naphthaleneacetic acid (NAA) and 2.0 mg l^–1 6-benzyladenine (BA) for callus induction. Shoots were regenerated from callus on 1.0× MS medium supplemented with 1.5 mg l^–1 BA, 0.5 mg l^–1 kinetin, and 0.25 mg l^–1 NAA. Subculturing of callus onto fresh medium maintained the rate of shoot formation and substantially increased the production of shoot buds up to the second subculture. Following further subculture passages, a lower shoot regeneration potential from callus was observed. A maximum shoot bud induction from callus of 63.9% was observed at the second subculture passage. The rate of multiplication of in vitro shoots increased until the fourth subculture, then became constant. Similarly, in vitro rooting of micro-shoots increased up to the third subculture, followed by a decline during further subculturing.     

Rock phosphate-P enhances biomass and nitrogen accumulation by legumes in upland crop production systems in humid West Africa

Experiments were conducted during 1996–1998 in screen house and in the field in the humid forest zone of Côte d’Ivoire, to evaluate the effects of phosphorus (P) from phosphate rock (PR) on the performance of the root nodulating legume Crotalaria micans grown for 8 weeks. The experimental soils were acid Ultisols with <4 mg/kg extractable Bray-1 P. Tilemsi PR from Mali and triple superphosphate (TSP) were applied at 60 kg P ha^?1 (screen house) and 90 kg P ha^?1 (field) to the legume. Legume N-fixed (BNF) was estimated by the ¹⁵N-isotope dilution and δ ¹⁵N natural abundance methods, using Cassia obtusifolia L. as a non-fixing legume reference plant. Without P supply, and under the field conditions, C. micans produced less than 1 tonne of biomass and accumulated 29 kg N/ha. The application of PR-P enhanced legume N by about fourfold over the unfertilised control. There was no significant difference between the effects of TSP and PR. Phosphorus application mainly affected the total amount of N accumulated rather than the percentage derived from the atmosphere (%N dfa) per se. Furthermore, the cumulative effects of PR-P on the performance of C. micans greatly improved with time in the screen house. This study confirms that Tilemsi PR is an agronomically effective source of P for short-duration legume green manure (GM) even in the first year of its application to acid P-deficient soils in the West African humid zone.     

Evaluating and predicting agricultural management effects under tile drainage using modified APSIM

An accurate and management sensitive simulation model for tile-drained Midwestern soils is needed to optimize the use of agricultural management practices (e.g., winter cover crops) to reduce nitrate leaching without adversely affecting corn yield. Our objectives were to enhance the Agricultural Production Systems Simulator (APSIM) for tile drainage, test the modified model for several management scenarios, and then predict nitrate leaching with and without winter wheat cover crop. Twelve years of data (1990-2001) from northeast Iowa were used for model testing. Management scenarios included continuous corn and corn-soybean rotations with single or split N applications. For 38 of 44 observations, yearly drain flow was simulated within 50 mm of observed for low drainage (< 100 mm) or within 30% of observed for high drain flow. Corn yield was simulated within 1500 kg/ha for 12 of 24 observations. For 30 of 45 observations yearly nitrate-N loss in tile drains was simulated within 10 kg N/ha for low nitrate-N loss (< 20 kg N/ha) or within 30% of observed for high nitrate-N loss. Several of the poor yield and nitrate-N loss predictions appear related to poor N-uptake simulations. The model accurately predicted greater corn yield under split application (140-190 kg N/ha) compared to single 110 kg N/ha application and higher drainage and nitrate-N loss under continuous corn compared to corn/soybean rotations. A winter wheat cover crop was predicted to reduce nitrate-N loss 38% (341 vs. 537 kg N/ha with and without cover) under 41-years of corn-soybean rotations and 150 kg N/ha applied to corn. These results suggest that the modified APSIM model is a promising tool to help estimate the relative effect of alternative management practices under fluctuating high water tables.