Bamboo Plantations for Phytoremediation of Pig Slurry: Plant Response and Nutrient Uptake.

On Réunion Island, a French overseas territory located in the western Indian Ocean, increasing pig livestock farming is generating large quantities of slurry. Most of it is spread on a little agricultural land due to the insular context. Considering the limitation of the quantities that can be spread on agricultural areas (European "Nitrate Directive" 91/676/EEC), the use of wastewater treatment systems using phytoremediation principles is an attractive option for the pig slurry treatment. A wastewater treatment system using bamboo groves was assessed for the pig slurry treatment. Three field plots were designed on an agricultural area and planted with 40 bamboo clumps on each plot. A total of 67 m3 of pig slurry was spread on two plots in two forms: raw slurry and centrifuged slurry. The latter plot was watered with tap water. The total amount of nitrogen, phosphorus and potassium was 5.3, 1.4 and 5.5 t·ha-1, respectively, for the raw slurry treatment and 4.2, 0.4 and 5.1 t·ha-1, respectively, for the centrifuged slurry treatment. The response of bamboo species to pig slurry application was determined using morphologic parameters, Chlorophyll a fluorescence measurements and biomass yield. Compared to the control, the biomass increased by 1.8 to 6 times, depending on the species and the form of slurry. Depending on the species, the average biomass ranged from 52 to 135 t.DM.ha-1 in two years of experiment.

Ectomycorrhizal fungi affect the physiological responses of Picea glauca and Pinus banksiana seedlings exposed to an NaCl gradient.

We tested the effects of ectomycorrhizal (ECM) inoculation on greenhouse-grown white spruce (Picea glauca (Moench) Voss) and jack pine (Pinus banksiana L.) seedlings to be used for revegetation of salt-affected tailing sands resulting from the exploitation of oil sand in northeastern Alberta, Canada. White spruce and jack pine seedlings were inoculated with three ECM fungi selected for their in vitro tolerance to excess Na+ and Cl-: Hebeloma crustuliniforme (Bull) Quel. UAMH 5247, Laccaria bicolor Maire (Orton) UAMH 8232 and a Suillus tomentosus (Kauff.) Sing., Snell and Dick isolate from a salt-affected site. The physiological responses of the seedlings to a gradient of NaCl concentration (0, 50, 100 and 200 mM) were assessed over four weeks by: (1) Na+ accumulation and allocation; (2) chlorophyll a fluorescence; (3) growth, (4) water content; and (5) organic osmolyte accumulation. Jack pine seedlings were more sensitive than white spruce seedlings to increasing Na+ and Cl- concentrations. Both species showed decreasing biomass accumulation, and increasing concentrations of organic osmotica and Na with increasing NaCl concentration. White spruce seedlings inoculated with the S. tomentosus isolate had the best growth response at all NaCl concentrations tested. Although jack pine seedlings inoculated with the L. bicolor or S. tomentosus isolate exhibited the highest growth in the 50 and 100 mM NaCl treatments, both fungi increased the photochemical stress and dehydration of their hosts in the 200 mM NaCl treatment. At the latter concentration, jack pine seedlings inoculated with H. crustuliniforme showed the greatest tolerance to salt stress. Although the different fungi altered the physiological response of the host in different ways, inoculation with salt-stress-tolerant ECM fungi increased growth and reduced the negative effects of excess NaCl. Use of controlled mycorrhization may increase survival of coniferous seedlings used for revegetation of salt-affected sites.

Effects of high nutrient supply on the growth of seven bamboo species.

Over the last decade, bamboo has emerged as an interesting plant for the treatment of various polluted waters using plant-based wastewater treatment systems. In these systems, nitrogen and phosphorous concentrations in wastewater can exceed plant requirements and potentially limit plant growth. The effects of two nutrient rates on the growth of seven bamboo species were assessed in a one-year experiment: Dendrocalamus strictus, Thyrsostachys siamensis, Bambusa tuldoides, Gigantochloa wrayi, Bambusa oldhamii, Bambusa multiplex and Bambusa vulgaris. Nutrient rates were applied with a 20:20:20 NPK fertilizer as 2.6 and 13.2 t.ha.yr(-1) NPK to three-year-old bamboo planted in 70 L containers. Morphological characters, photosynthetic responses, and NPK content in bamboo tissues were investigated. Under high-nutrient supply rate, the main trend observed was an increase of culm production but the culms' diameters were reduced. For the seven species, the above ground biomass yield tended to increase with high-nutrient rate. Increasing in nutrient rates also improved the photosynthetic activity which is consistent with the increase of nitrogen and phosphorus contents measured in plant tissues. All the bamboo species tested appears suitable for wastewater treatment purposes, but the species Bambusa oldhamii and Gigantochloa wrayi showed the higher biomass yield and nutrient removaL

Novel insight into vascular, stress, and auxin-dependent and -independent gene expression programs in strawberry, a non-climacteric fruit.

Using cDNA microarrays, a comprehensive investigation of gene expression was carried out in strawberry (Fragaria x ananassa) fruit to understand the flow of events associated with its maturation and non-climacteric ripening. We detected key processes and novel genes not previously associated with fruit development and ripening, related to vascular development, oxidative stress, and auxin response. Microarray analysis during fruit development and in receptacle and seed (achene) tissues established an interesting parallelism in gene expression between the transdifferentiation of tracheary elements in Zinnia elegans and strawberry. One of the genes, CAD, common to both systems and encoding the lignin-related protein cinnamyl alcohol dehydrogenase, was immunolocalized to immature xylem cells of the vascular bundles in the strawberry receptacle. To examine the importance of oxidative stress in ripening, gene expression was compared between fruit treated on-vine with a free radical generator and non-treated fruit. Of 46 genes induced, 20 were also ripening regulated. This might suggest that active gene expression is induced to cope with oxidative stress conditions during ripening or that the strawberry ripening transcriptional program is an oxidative stress-induced process. To gain insight into the hormonal control of non-climacteric fruit ripening, an additional microarray experiment was conducted comparing gene expression in fruit treated exogenously with auxin and control fruit. Novel auxin-dependent genes and processes were identified in addition to transcriptional programs acting independent of auxin mainly related to cell wall metabolism and stress response.