Manganese losses induced by severe soil acidification in the extensive Lei bamboo (Phyllostachys violascens) plantation stands in Eastern China.

Manganese (Mn) is a critical element in soils, essential to plant growth. Long-term and intensively managed Lei bamboo (Phyllostachys violascens) stands are usually subjected to severe soil acidification and Mn activation. However, Mn migration from topsoil to deep soil induced by severe soil acidification was poorly recognized and studied. The distribution and changes of the total and the operationally defined Mn forms in soil profiles and its potential stress and environmental effect were investigated in a chronosequence of Lei bamboo stands (0, 2, 6, 11, and 16 years of stand age). The results showed that the Mn amount was significantly decreased in topsoil and accumulated in subsoil with the long-term and intensive fertilizer application. Soil exchangeable Mn and superphosphate extractable Mn demonstrated large different variation to total Mn, whereas their sum was largely higher than and highly correlated with 8-hydroxyquinoline (HQN) extractable Mn. Soil organic carbon, pH value, exchangeable bases, and soil redox simultaneously controlled soil Mn depletion. In conclusion, long-term and intensive fertilizer application leads to soil acidification and accelerated soil Mn depletion in bamboo stand soil, promoting Mn accumulation in bamboo shoots.

Effects of aeration treatments on root and rhizome growth parameters of Phyllostachys violascens (Lei bamboo) under intensive cultivation: A field study.

Aeration through underground tunneling in mulched Phyllostachys violascens (Lei bamboo) forests can improve soil quality. Nevertheless, the effect of soil ventilation on the growth of bamboo roots and rhizomes at different distances, directions and depths of the forest are still unclear. In a field experiment, four treatments including organic mulching without aeration (MNA), organic mulching with aeration (MA), non-mulched with aeration (NMA), and non-mulched and non-aeration treatment (control) were set up to investigate the effects of soil aeration treatment on bamboo root and rhizome growth at different depths and radii distances from the bamboo trunk in both perpendicular (PD) and horizontal (HD) aeration directions. The results show that root and rhizome quantity and quality decreased vertically and linearly in the soil layers and this trend was more significant in the PD direction and near the trunk. MA treatment induced the most significant effects on the determined root and rhizome growth parameters. At 10 cm depth, the number of rhizomes in CK was 70.8 %, 77.1 %, and 18.8 % higher than that in MA, NMA, and MNA plots, respectively. However, fewer rhizomes appeared in CK and MNA plots at 20 and 30 cm depths relative to 10 cm while the number was increased by 149 % in MA and 151 % NMA plots at 20 cm. This suggest that in CK and MNA plots, soil hypoxia and soil acidification were prevalent which inhibited rhizome growth by inducing rhizome up-floating and preventing root elongation, respectively. Also, the root morphological parameters including lengths, surface areas, and volumetric areas were significantly increased in MA and MNA treatments compared to the control and NMA. For example, root length, surface area, and volumetric area in MA were increased by 56 %, 44.9 %, and 28.3 % while that in MNA increased by 40 %, 55.8 %, and 81.0 % compared with roots from the control plot. This study provides both a theoretical and practical guide for improving soil quality and bamboo growth under intensive management using aeration treatment.

Strigolactone Mediates Moso Bamboo Root Response to Phosphate Stress.

Both phosphate (Pi) deficiency and high Pi significantly affect moso bamboo growth and degrade bamboo forests. A novel plant hormone, strigolactone (SL), plays a crucial role in root growth under low Pi, but the SL regulatory mechanism has not been systematically reported in moso bamboo. In our study, we investigated the SL-mediated root growth mechanism in response to Pi stress in moso bamboo. With the decrease of the Pi level, 5-deoxystrigol and strigol significantly increased in the root exudates. Transcriptome sequencing of the primary root tip and lateral root primordium zone (LRP) under low, sufficient, and high Pi indicated that SL-biosynthesis and -signaling changes are part of the early root responses. The effects of the SL analogue (rac-GR24) and SL inhibitor (TIS108) on the root architecture under low and high Pi revealed that SL mediates bamboo root responses by regulating its biosynthesis and signal transduction and influencing other hormone pathways.

Subsurface aeration mitigates organic material mulching-induced anaerobic stress via regulating hormone signaling in Phyllostachys praecox roots.

Organic material mulching has been used extensively to allow Phyllostachys praecox to promote growth and development of shoots. However, the bamboo forest always showed a significant degradation, probably due to anaerobic damage caused by the mulching after several years. Therefore, we have innovatively proposed an improvement measure to aerate the underground pipes for the first time. We investigated the role of subsurface pipe aeration in regulating root hypoxia to reduce the stress and to identify the degradation mechanism. Results showed that aeration increased oxygen concentration, shoot yield and root growth compared with mulching, and the aeration enhanced the concentration of indole-3-acetic acid (IAA) and the expression of Aux/IAAs (Aux1, Aux2, Aux3, and Aux4). Aeration reduced gibberellin (GA), ethylene (ETH), and abscisic acid (ABA) contents as well as anaerobic enzyme activities (alanine transaminase, AlaAT; alcohol dehydrogenase, ADH; pyruvate decarboxylase, PDC; and lactate dehydrogenase, LDH), which alleviated root damage in anoxic conditions. Furthermore, correlation showed that the activities of ADH, LDH, PDC, and AlaAT showed significant linear correlations with soil oxygen levels. RDA analyses showed that ABA, IAA, and ETH were found as the key driving hormones of Aux/IAAs in the root of the forest mulched with organic material. Here we show that subsurface aeration increases soil oxygen concentration, shoot yield, root growth and regulates phytohormone concentrations and Aux/IAAs expression, which reduces anaerobic enzyme activities. Consequently, subsurface pipe aeration is an effective measure to mitigate the degradation of bamboo forests caused by soil hypoxia that results from organic material mulching.

The acid invertase gene family is involved in internode elongation in Phyllostachys heterocycla cv. pubescens.

Acid invertases (INVs) play a pivotal role in both vegetative and reproductive growth of plants. However, their possible functions in fast-growing plants such as bamboo are largely unknown. Here, we report the molecular characterization of acid INVs in Phyllostachys heterocycla cv. pubescens, a fast-growing bamboo species commercially grown worldwide. Nine acid INVs (PhINVs), including seven cell wall INVs (PhCWINV1, PhCWINV2, PhCWINV3, PhCWINV4, PhCWINV5, PhCWINV6 and PhCWINV7) and two vacuolar INVs (PhVINV11 and PhVINV12) were isolated. Bioinformatic analyses demonstrated that they all share high amino acid identity with other INVs from different plant species and contain the motifs typically conserved in acid INV. Enzyme activity assays revealed a significantly higher INV activity in the fast-growing tissues, such as the elongating internodes of stems. Detailed quantitative reverse-transcription PCR analyses showed various expression patterns of PhINVs at different developmental stages of the elongating stems. With the exception of PhCWINV6, all PhINVs were ubiquitously expressed in a developmental-specific manner. Further studies in Arabidopsis exhibited that constitutive expression of PhCWINV1, PhCWINV4 or PhCWINV7 increased the biomass production of transgenic plants, as indicated by augmented plant heights and shoot dry weights than the wild-type plants. All these results suggest that acid INVs play a crucial role in the internode elongation of P. heterocycla cv. pubescens and would provide valuable information for the dissection of their exact biological functions in the fast growth of bamboo.

Overexpression of PvCO1, a bamboo CONSTANS-LIKE gene, delays flowering by reducing expression of the FT gene in transgenic Arabidopsis.

BACKGROUND: In Arabidopsis, a long day flowering plant, CONSTANS (CO) acts as a transcriptional activator of flowering under long day (LD) condition. In rice, a short day flowering plant, Hd1, the ortholog of CO, plays dual functions in respond to day-length, activates flowering in short days and represses flowering in long days. In addition, alleles of Hd1 account for ~ 44% of the variation in flowering time observed in cultivated rice and sorghum. How does it work in bamboo? The function of CO in bamboo is similar to that in Arabidopsis? RESULTS: Two CO homologous genes, PvCO1 and PvCO2, in Phyllostachys violascens were identified. Alignment analysis showed that the two PvCOLs had the highest sequence similarity to rice Hd1. Both PvCO1 and PvCO2 expressed in specific tissues, mainly in leaf. The PvCO1 gene had low expression before flowering, high expression during the flowering stage, and then declined to low expression again after flowering. In contrast, expression of PvCO2 was low during the flowering stage, but rapidly increased to a high level after flowering. The mRNA levels of both PvCOs exhibited a diurnal rhythm. Both PvCO1 and PvCO2 proteins were localized in nucleus of cells. PvCO1 could interact with PvGF14c protein which belonged to 14-3-3 gene family through B-box domain. Overexpression of PvCO1 in Arabidopsis significantly caused late flowering by reducing the expression of AtFT, whereas, transgenic plants overexpressing PvCO2 showed a similar flowering time with WT under LD conditions. Taken together, these results suggested that PvCO1 was involved in the flowering regulation, and PvCO2 may either not have a role in regulating flowering or act redundantly with other flowering regulators in Arabidopsis. Our data also indicated regulatory divergence between PvCOLs in Ph. violascens and CO in Arabidopsis as well as Hd1 in Oryza sativa. Our results will provide useful information for elucidating the regulatory mechanism of COLs involved in the flowering. CONCLUSIONS: Unlike to the CO gene in Arabidopsis, PvCO1 was a negative regulator of flowering in transgenic Arabidopsis under LD condition. It was likely that long period of vegetative growth of this bamboo species was related with the regulation of PvCO1.

Soil hypoxia induced by an organic-material mulching technique stimulates the bamboo rhizome up-floating of Phyllostachys praecox.

Phyllostachys praecox bamboo stands significantly recede after 3 or 4 years using an organic-material mulching technique consecutively. We hypothesized that the bamboo recession is caused by the up-floating of underground rhizome stimulated by soil hypoxia through the mulching technique. This study aimed to validate this hypothesis by field investigation. Bamboo underground rhizome distribution in the soil profile of P. praecox subjected to various mulching times was investigated. Results showed that bamboo rhizome weights and lengths increased with increased mulching time. However, after 4 years of mulching, the number of fresh rhizomes decreased significantly, and more than 50% of rhizomes floated upward to the shallow soil layer (0-10 cm). Moreover, the 0-10 cm soil layer suffered severe acidification that severely impeded bamboo-rhizome growth. The soil hypoxia induced by the mulching technique must be responsible for the bamboo rhizome up-floating. We confirmed that bamboo rhizome up-floating was the critical factor that caused the bamboo growth to recede under the mulching technique. Therefore, managing this bamboo rhizome up-floating is the key to sustainable bamboo production. The effect of soil hypoxia in the absence of flooding or waterlogging on plant root growth also warrants further and extensive study.

Identification of genes involved in color variation of bamboo culms by suppression subtractive hybridization.

Phyllostachys vivax cv. aureocaulis is a widely planted ornamental bamboo with evergreen leaves. This plant's culm exhibits a golden-yellow background color marked randomly with narrow and broad green stripes but is occasionally light green with yellow stripes. In this study, we attempt to identify the molecular mechanism underlying the color variation in striped culms. We found that neither stroma nor grana lamellas were observed in plastids in yellow tissue cells, while complete chloroplasts were observed in green tissue. In addition, chlorophyll a and b were mainly distributed in ground tissue under the epiderm and in the cells surrounding the bundle sheath in the green portion of internodes. The amount of chlorophyll contained in cross-sections of the green portion of culms is significantly higher than in the yellow portion. However, carotenoid was nearly undetectable in both samples. In addition, we found that the expression levels of 7 ESTs, including PvESTs-F641 (JZ893845), PvESTs-F681 (JZ893885) and PvESTs-F798 (JZ894002), were significantly higher in green samples than that in yellow samples, while PvESTs-R200 (JZ894906), PvESTs-R541 (JZ895247), PvESTs-R333 (JZ895039) and PvESTs-R266 (JZ894972) were found at a higher level in yellow samples. These ESTs are thought to play a role in this color variation in plants. Our current results indicate that insufficient photosynthetic membrane proteins and lipids in yellow tissue could lead to chloroplast dysfunction and could result in the yellow appearance on certain P. vivax cv. aureocaulis culms.

Strigolactone Inhibition of Branching Independent of Polar Auxin Transport.

The outgrowth of axillary buds into branches is regulated systemically via plant hormones and the demand of growing shoot tips for sugars. The plant hormone auxin is thought to act via two mechanisms. One mechanism involves auxin regulation of systemic signals, cytokinins and strigolactones, which can move into axillary buds. The other involves suppression of auxin transport/canalization from axillary buds into the main stem and is enhanced by a low sink for auxin in the stem. In this theory, the relative ability of the buds and stem to transport auxin controls bud outgrowth. Here, we evaluate whether auxin transport is required or regulated during bud outgrowth in pea (Pisum sativum). The profound, systemic, and long-term effects of the auxin transport inhibitor N-1-naphthylphthalamic acid had very little inhibitory effect on bud outgrowth in strigolactone-deficient mutants. Strigolactones can also inhibit bud outgrowth in N-1-naphthylphthalamic acid-treated shoots that have greatly diminished auxin transport. Moreover, strigolactones can inhibit bud outgrowth despite a much diminished auxin supply in in vitro or decapitated plants. These findings demonstrate that auxin sink strength in the stem is not important for bud outgrowth in pea. Consistent with alternative mechanisms of auxin regulation of systemic signals, enhanced auxin biosynthesis in Arabidopsis (Arabidopsis thaliana) can suppress branching in yucca1D plants compared with wild-type plants, but has no effect on bud outgrowth in a strigolactone-deficient mutant background.

Phylogenetic variation of phytolith carbon sequestration in bamboos.

Phytoliths, the amorphous silica deposited in plant tissues, can occlude organic carbon (phytolith-occluded carbon, PhytOC) during their formation and play a significant role in the global carbon balance. This study explored phylogenetic variation of phytolith carbon sequestration in bamboos. The phytolith content in bamboo varied substantially from 4.28% to 16.42%, with the highest content in Sasa and the lowest in Chimonobambusa, Indocalamus and Acidosasa. The mean PhytOC production flux and rate in China's bamboo forests were 62.83 kg CO2 ha(-1) y(-1) and 4.5 × 10(8)kg CO2 y(-1), respectively. This implies that 1.4 × 10(9) kg CO2 would be sequestered in world's bamboo phytoliths because the global bamboo distribution area is about three to four times higher than China's bamboo. Therefore, both increasing the bamboo area and selecting high phytolith-content bamboo species would increase the sequestration of atmospheric CO2 within bamboo phytoliths.

[Determination of trace elements in Lophatherum gracile brongn from different habitat by microwave digestion-atomic absorption spectroscopy].

A method of microwave digestion technique was proposed to determine the content of Zn, Fe, Cu, Mn, K, Ca, Mg, Ni, Cd, Pb, Cr, Co, Al, Se and As in Lophatherum gracile brongn of different habitat by atomic absorption spectroscopy. The RSD of the method was between 1.23% and 3.32%, and the recovery rates obtained by standard addition method were between 95.8% and 104.20%. The results of the study indicate that the proposed method has the advantages of simplicity, speediness and sensitivity. It is suitable for the determination of the contents of metal elements in Lophatherum gracile brongn. The experimental results also indicated that different areas' Lophantherum gracile brongn had different trace elements content. The content of trace elements K, Mg, Ca, Fe and Mn beneficial to the human body was rich. The content of the heavy metal trace element Pb in Lophantherum gracile brongn of Hunan province was slightly high. The content of the heavy metal trace element Cu in Lophantherum gracile brongn of Guangdong province and Anhui province is also slightly higher. Beside, the contents of harmful trace heavy metal elements Cd, Cu, Cr, Pb and As in Lophatherum gracile brongn of different habitat are all lower than the limits of Chinese Pharmacopoeia and Green Trade Standard for Importing and Exporting Medicinal Plant and Preparation and National Food Sanitation Standard. These determination results provided the scientific data for further discussing the relationship between the content of trace elements in Lophantherum gracile brongn and the medicine efficacy.