The CESA gene superfamily of Arabidopsis and other seed plants comprises the CESA family, which encodes the catalytic subunits of cellulose synthase, and eight families of CESA-like (CSL) genes whose functions are largely unknown. The CSL genes have been proposed to encode processive beta-glycosyl transferases that synthesize noncellulosic cell wall polysaccharides. BLAST searches of EST and shotgun genomic sequences from the moss Physcomitrella patens (Hedw.) B.S.G. were used to identify genes with high similarity to vascular plant CESAs, CSLAs, CSLCs, and CSLDs. However, searches using Arabidopsis CSLBs, CSLEs, and CSLGs or rice CSLFs or CSLHs as queries identified no additional CESA superfamily members in P. patens, indicating that this moss lacks representatives of these families. Intron insertion sites are highly conserved between Arabidopsis and P. patens in all four shared gene families. However, phylogenetic analysis strongly supports independent diversification of the shared families in mosses and vascular plants. The lack of orthologs of vascular plant CESAs in the P. patens genome indicates that the divergence of mosses and vascular plants predated divergence and specialization of CESAs for primary and secondary cell wall syntheses and for distinct roles within the rosette terminal complexes. In contrast to Arabidopsis, the CSLD family is highly represented among P. patens ESTs. This is consistent with the proposed function of CSLDs in tip growth and the central role of tip growth in the development of the moss protonema.
In seed plants, different groups of orthologous genes encode the CELLULOSE SYNTHASE (CESA) proteins that are responsible for cellulose biosynthesis in primary and secondary cell walls. The seven CESA sequences of the moss Physcomitrella patens (Hedw.) B. S. G. form a monophyletic sister group to seed plant CESAs, consistent with independent CESA diversification and specialization in moss and seed plant lines. The role of PpCESA5 in the development of P. patens was investigated by targeted mutagenesis. The cesa5 knockout lines were tested for cellulose deficiency using carbohydrate-binding module affinity cytochemistry and the morphology of the leafy gametophores was analyzed by 3D reconstruction of confocal images. No defects were identified in the development of the filamentous protonema or in production of bud initials that normally give rise to the leafy gametophores. However, the gametophore buds were cellulose deficient and defects in subsequent cell expansion, cytokinesis, and leaf initiation resulted in the formation of irregular cell clumps instead of leafy shoots. Analysis of the cesa5 knockout phenotype indicates that a biophysical model of organogenesis can be extended to the moss gametophore shoot apical meristem.
Studies on N losses from ornamental plantings -other than turf -are scant despite the ubiquity of these landscaping elements. We compared pore water NO 3 and extractable soil NO 3 and NH 4 in areas with turf, areas with seven different types of ornamental landscape plantings, and a native woodland. Turf areas received annual N inputs of~48 kg ha −1 and annual flowers received~24 kg N ha −1 at the time of planting. None of the other areas were fertilized during the course of the study. Data were collected on 23 occasions between June 2002 and November 2003. Pore water NO 3 concentrations at a 60-cm depthbased on pooled data -were highest (1.4 to 7.8 mg NO 3 -N l −1 ) under ground covers, unplanted-mulched areas, turf, deciduous trees, and evergreen trees, with no differences among these vegetation types. Lower values were observed under woodlands, annual and perennial flowers, and evergreen and deciduous shrubs. Pore water NO 3 concentrations exceeded the drinking water regulatory limit of 10 mg NO 3 -N l −1 under ground covers, turf and unplanted-mulched areas in 39, 20 and 10% of samples, respectively. Leaching losses of NO 3 -N over 18 months ranged from 0.17 kg N ha −1 in the woodlands to 34.97 kg N ha −1 under ground covers. Annual NO 3 losses under unplantedmulched areas and ground covers were approximately twice the average N input (10 kg N ha −1 year −1 ) from atmospheric deposition. Extractable NO 3 in woodland soils (0.5 μg NO 3 -N g −1 ) was lower than for all other vegetation types (3.1-7.8 μg NO 3 -N g −1 ). Extractable NH 4 levels were highest in woodlands, deciduous trees, and annual flowers (6.7-10.1 μg NH 4 -N g −1 ). Most vegetation types appear to act as net N sinks relative to atmospheric inputs, whereas unplantedmulched areas and areas planted with ground covers act as net sources of NO 3 to groundwater.
The stability of nitrogen within a turf‐soil ecosystem is important both for efficient turf management and preventing the contamination of ground water by nitrate. The objective of this study was to quantify responses of the microbial community and the mobility of soil nitrogen following the sudden death of established turf. Twelve‐year‐old turf plots comprising four cool‐season turfgrass species fertilized with five N sources were maintained on an Enfield silt loam (coarse‐silty over sandy or sandy‐skeletal, mixed, active, mesic Typic Dystrudept) at Kingston, RI. Half of the plots were killed with glyphosate in early September and any regrowth was removed mechanically. Measurements of soil physical, chemical, and microbiological properties and nitrate leaching in killed and healthy plots were compared for 12 mo. Turf death did not alter soil moisture, temperature, pH, or extractable ammonium. Nitrate levels were higher in both the root zone and at 60 cm following turf death and this difference persisted for the sampling year. Carbon mineralization and microbial biomass C were not different between soils from healthy and killed plots. Killed plots leached three times more nitrate than healthy plots but this amounted to less than 10% of total soil N present. Retention of nitrate in a turf‐soil system depends on absorption by living grass roots, although reasonable N stability is also provided by N cycling within the soil microbiota. Protecting ground water from nitrate contamination is optimized by maintaining a vigorous turfgrass cover.
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