Mechanism and deterioration pattern of sandstone surrounding rock voiding at bottom of heavy-haul railway tunnel.

This study combines laboratory experiments and discrete element simulation methods to analyze the mechanism and deterioration patterns of sandstone surrounding rock voiding the bottom of a heavy-haul railway tunnel. It is based on previously acquired measurement data from optical fiber grating sensors installed in the Taihangshan Mountain Tunnel of the Wari Railway. By incorporating rock particle wastage rate results, a method for calculating the peak strength and elastic modulus attenuation of surrounding rock is proposed. Research indicates that the operation of heavy-haul trains leads to an instantaneous increase in the dynamic water pressure on the bottom rock ranging 144.4-390.0%, resulting in high-speed water flow eroding the rock. After 1-2 years of operation, the bottom water and soil pressures increase by 526.5% and 390.0%, respectively. Focusing on sandstone surrounding rock with high observability, laboratory experiments were conducted to monitor the degradation stages of infiltration, particle loss, and voiding of rock under the action of dynamic water flow. The impact of water flow on the "cone-shaped" bottom rock deformation was also clarified. The extent of rock deterioration and voiding was determined using miniature water and soil pressure sensors in conjunction with discrete element numerical simulations. The measured rock particle loss was used as a criterion. Finally, a fitting approach is derived to calculate the peak strength and elastic modulus attenuation of surrounding rock, gaining insight into and providing a reference for the maintenance and disposal measures for the bottom operation of heavy-haul railway tunnels.

Leaf gas exchange and water relations of the woody desiccation-tolerant Paraboea rufescens during dehydration and rehydration.

Desiccation-tolerant (DT) plants can withstand dehydration to less than 0.1 g H2O g-1 dry weight. The mechanism for whole-plant recovery from severe dehydration is still not clear, especially for woody DT plants. In the present study, we evaluated the desiccation tolerance and mechanism of recovery for a potentially new woody resurrection plant Paraboea rufescens (Gesneriaceae). We monitored the leaf water status, leaf gas exchange, chlorophyll fluorescence and root pressure of potted P. rufescens during dehydration and rehydration, and we investigated the water content and chlorophyll fluorescence of P. rufescens leaves in the field during the dry season. After re-watering from a severely dehydrated state, leaf maximum quantum yield of photosystem II of P. rufescens quickly recovered to well-watered levels. Leaf water status and leaf hydraulic conductance quickly recovered to well-watered levels after re-watering, while leaf gas exchange traits also trended to recovery, but at a slower rate. The maximum root pressure in rehydrated P. rufescens was more than twice in well-watered plants. Our study identified P. rufescens as a new DT woody plant. The whole-plant recovery of P. rufescens from extreme dehydration is potentially associated with an increase of root pressure after rehydration. These findings provide insights into the mechanisms of recovery of DT plants from dehydration.

[Potential suitable area and niche shift of different ploidy kiwifruit]. / 不同倍性猕猴桃的适生区预测及生态位分化.

Niche shift between polyploid and diploid plants is an important requirement for the success of polyploid. Diploid, tetraploid, and hexaploid of kiwifruit distribute in different areas. Whether there is obvious niche differentiation and the major environmental factors which could influence the ecological niche of different ploidy kiwifruits are still unknown. Based on the natural distribution information collected from literature and by field works, the maximum entropy model (MaxEnt) was used to predict the potentially suitable ranges and the major climatic factors affecting distribution of different ploidy kiwifruits. Niche divergence between different ploidy kiwifruits was quantified by niche identity test. The results showed that there were obvious differences in the potential suitable areas of different ploidy kiwifruits. Diploid occurred in lower altitude Hunan foothills. Tetraploid nearly overlapped with diploid but tended to northern Guizhou and eastern Chongqing. Hexaploid were centered in Guizhou Plateau, northwestern Hunan, southwestern Hubei and southern Shanxi. Hexaploid kiwifruits preferred higher altitudes and latitudes. In addition, the hexaploid had wider highly suitable areas. Results of niche identity test showed overlapped niches between diploid and tetraploid, and different niches between diploid/tetraploid and hexaploid kiwifruits. Minimum temperature of the coldest month (Bio6) and precipitation of the driest month (Bio14) were key environmental factors driving the niche shift of ploidy kiwifruits. Polyploid kiwifruits could maintain a higher probability of existence under lower Bio6 and Bio14, which indicated more extreme niche in cold and arid mountains for polyploids.

[Research progress on the methods for measuring xylem embolism vulnerability]. / æ¤ç‰©æœ¨è´¨éƒ¨æ “å¡žæµ‹å®šæŠ€æœ¯çš„ç ”ç©¶è¿›å±•.

Changes in the frequency and severity of drought events associated with climate change could affect plant growth, development, and adaptability. Hydraulic failure caused by xylem embo-lism is the main physiological consequences of drought stress. How to accurately quantify xylem embolism is particularly important for understanding plant responses to drought stress. The vulnerability of xylem to embolism is usually evaluated by constructing vulnerability curves (VCs). Several methods have been developed to construct VCs, but be inconsistent in their results. A deep understanding of the design principles of xylem embolism measurement methods and comparison of the similarities and differences of various methods in actual research are particularly important for the rational interpretation of literature results, and properly using VCs in models for predicting plant responses to water deficits. Here, we compared seven methods for constructing xylem vulnerability curves to embolism: bench dehydration, centrifugation, air injection, acoustic measurements, synchrotron and X-ray microtomography (Micro-CT), optical visualization method, and pneumatron method. We summarized current achievements and controversial viewpoints of the application of these methods in specific research. Finally, we provided prospects for measuring the vulnerability of xylem embolism and the selection of relevant methods for practical application in future studies.

Two strategies by epiphytic orchids for maintaining water balance: thick cuticles in leaves and water storage in pseudobulbs.

Epiphytes are an important component of tropical and subtropical flora, and serve vital ecological functions in forest hydrology and nutrient fluxes. However, they often encounter water deficits because there is no direct contact between their roots and the soil. The strategies employed by epiphytes for maintaining water balance in relatively water-limited habitats are not completely understood. In the present study, we investigated the anatomical traits, water loss rates, and physiology of leaves and pseudobulbs of four Dendrobium species with different pseudobulb morphologies to understand the roles of leaf and pseudobulb in maintaining water balance of epiphytic orchids. Our results showed that two species (D. chrysotoxum and D. officinale), with lower rates of water loss, have thicker leaves and upper cuticles, but lower epidermal thickness and leaf dry mass per area. In contrast, the other two species (D. chrysanthum and D. crystallinum) with thinner cuticles and higher rates of water loss, have less tissue density and greater saturated water contents in their pseudobulbs. Therefore, our results indicate that these latter two species may resist drought by storing water in the pseudobulbs to compensate for their thin cuticles and rapid water loss through the leaves. Under the same laboratory conditions, excised pseudobulbs with attached leaves had lower rates of water loss when compared with samples comprising only excised leaves. This implies that epiphytic orchids utilize two different strategies for sustaining water balance: thick cuticles to conserve water in leaves and water storage in pseudobulbs. Our results also show that Dendrobium species with thin cuticles tend to have pseudobulbs with high water storage capacity that compensates for their faster rates of water loss. These outcomes contribute to our understanding of the adaptive water-use strategies in Dendrobium species, which is beneficial for the conservation and cultivation of epiphytic orchids.

Determinants of water circulation in a woody bamboo species: afternoon use and night-time recharge of culm water storage.

To understand water-use strategies of woody bamboo species, sap flux density (Fd) in the culms of a woody bamboo (Bambusa vulgaris Schrader ex Wendland) was monitored using the thermal dissipation method. The daytime and night-time Fd were analyzed in the dry and rainy seasons. Additionally, diurnal changes in root pressure, culm circumference, and stomatal conductance (gs) were investigated to characterize the mechanisms used to maintain diurnal water balance of woody bamboos. Both in the dry and rainy seasons, daytime Fd responded to vapor pressure deficit (VPD) in an exponential fashion, with a fast initial increase in Fd when VPD increased from 0 to 1 kPa. The Fd and gs started to increase very fast as light intensity and VPD increased in the morning, but they decreased sharply once the maximum value was achieved. The Fd response of this woody bamboo to VPD was much faster than that of representative trees and palms growing in the same study site, suggesting its fast sap flow and stomatal responses to changes in ambient environmental factors. The Fd in the lower and higher culm positions started to increase at the same time in the morning, but the Fd in the higher culm position was higher than that of the lower culm in the afternoon. Consistently, distinct decreases in its culm circumference in the afternoon were detected. Therefore, unlike trees, water storage of bamboo culms was not used for its transpiration in the morning but in the afternoon. Nocturnal sap flow of this woody bamboo was also detected and related to root pressure. We conclude that this bamboo has fast sap flow/stomatal responses to irradiance and evaporative demands, and it uses substantial water storage for transpiration in the afternoon, while root pressure appears to be a mechanism resulting in culm water storage recharge during the night.

The maximum height of grasses is determined by roots.

Grasses such as bamboos can produce upright stems more than 30 m tall, yet the processes that constrain plant height in this important group have never been investigated. Air embolisms form commonly in the water transport system of grasses and we hypothesised that root pressure-dependent refilling these embolisms should limit the maximum height of grass species to the magnitude of their root pressure. Confirming this hypothesis, we show that in 59 species of bamboo grown in two common gardens, the maximum heights of culms of 67 clones are closely predicted by the maximum measured root pressure overnight. Furthermore, we demonstrate that water transport in these bamboo species is dependent on root pressure to repair hydraulic dysfunction sustained during normal diurnal gas exchange. Our results established the critical importance of root pressure in the tallest grass species and provide a new basis for understanding the limits for plant growth.

Recovery of diurnal depression of leaf hydraulic conductance in a subtropical woody bamboo species: embolism refilling by nocturnal root pressure.

Despite considerable investigations of diurnal water use characteristics in different plant functional groups, the research on daily water use strategies of woody bamboo grasses remains lacking. We studied the daily water use and gas exchange of Sinarundinaria nitida (Mitford) Nakai, an abundant subtropical bamboo species in Southwest China. We found that the stem relative water content (RWC) and stem hydraulic conductivity (K(s)) of this bamboo species did not decrease significantly during the day, whereas the leaf RWC and leaf hydraulic conductance (K(leaf)) showed a distinct decrease at midday, compared with the predawn values. Diurnal loss of K(leaf) was coupled with a midday decline in stomatal conductance (g(s)) and CO(2) assimilation. The positive root pressures in the different habitats were of sufficient magnitude to refill the embolisms in leaves. We concluded that (i) the studied bamboo species does not use stem water storage for daily transpiration; (ii) diurnal down-regulation in K(leaf) and gs has the function to slow down potential water loss in stems and protect the stem hydraulic pathway from cavitation; (iii) since K(leaf) did not recover during late afternoon, refilling of embolism in bamboo leaves probably fully depends on nocturnal root pressure. The embolism refilling mechanism by root pressure could be helpful for the growth and persistence of this woody monocot species.

Cyclic electron flow plays an important role in photoprotection for the resurrection plant Paraboea rufescens under drought stress.

Resurrection plants could survive severe drought stress, but the underlying mechanism for protecting their photosynthetic apparatus against drought stress is unclear. Cyclic electron flow (CEF) has been documented as a crucial mechanism for photoprotection in Arabidopsis and tobacco. We hypothesized that CEF plays an important role in protecting photosystem I (PSI) and photosystem II (PSII) against drought stress for resurrection plants. To address this hypothesis, the effects of mild drought stress on light energy distribution in PSII and P700 redox state were examined in a resurrection plant Paraboea rufescens. Cyclic electron flow was not activated below the photosynthetic photon flux density (PPFD) of 400 µmol m⁻² s⁻¹ in leaves without drought stress. However, CEF was activated under low light in leaves with mild drought stress, and the effective quantum yield of PSII significantly decreased. Meanwhile, non-photochemical quenching (NPQ) was significantly stimulated not only under high light but also under low light. Compared with the control, the fraction of overall P700 that cannot be oxidized in a given state (PSI acceptor side limitation) under high light was maintained at low level of 0.1 in leaves with water deficit, indicating that the over-reduction of the PSI acceptor side was prevented by the significant stimulation of CEF. Furthermore, methyl viologen could significantly increase the PSII photo-inhibition induced by high light compared with chloramphenicol. These results suggested that CEF is an important mechanism for protecting PSI and PSII from drought stress in resurrection plants.

Food habits of Rhinopithecus bieti as assessed by fecal analysis at Mt. Longma, Southwest China.

The food habits of Rhinopithecus bieti were studied at Mt. Longma in Tianchi Nature Reserve, Yunnan Province, China using microhistological analysis of feces and phytochemical component analysis of food items, from January 2007 to March 2008. This region is the southernmost location of R. bieti with the most complex and varied vegetation types. R. bieti fed on 83 plant species of 26 families, at least 3 species of lichens and bamboos, respectively. The number of food items exploited varied markedly among seasons, with dietary diversity being greatest in summer and autumn. Young leaves of broadleaf plant, monocotyledonous plant leaves (bamboos), and 3 species of lichens in the genera Bryoria (Bryoria confuse) and Usnea (Unsea longissima and Unsea florida) were frequently eaten. Bamboos (Poaceae) and lichens formed a stable dietary constituent throughout the year, contributing about 24 and 13%, respectively, of the total feeding records. There was seasonal variation in the proportion of each food type in the diet of the R. bieti. Results of the phytochemistry analysis showed that food selectivity of R. bieti was positively correlated with the ratio of crude protein to neutral detergent fibre (CP/NDF) and negatively correlated with condensed tannins (CT). Results from the study also showed that the primary food items eaten by R. bieti in summer had higher CP and lower CT than in winter.

Investigation of basic properties of fly ash from urban waste incinerators in China.

Basic properties of fly ash samples from different urban waste combustion facilities in China were analyzed using as X-ray fluorescence (XRF), scanning electron microscopy (SEM), X-ray diffraction (XRD). The leaching toxicity procedure and some factors influencing heavy metals distribution in fly ash were further investigated. Experimental results indicate that the fly ash structures are complex and its properties are variable. The results of XRF and SEM revealed that the major elements (>10000 mg/kg, listed in decreasing order of abundance) in fly ash are O, Ca, Cl, Si, S, K, Na, Al, Fe and Zn. These elements account for 93% to 97%, and the content of Cl ranges from 6.93% to 29.18 %, while that of SiO2 does from 4.48% to 24.84%. The minor elements (1000 to 10000 mg/kg) include Cr, Cu and Pb. Primary heavy metals in fly ash include Zn, Pb, Cr, Cu etc. According to standard leaching test, heavy metal leaching levels vary from 0 to 163.10 mg/L (Pb) and from 0.049 to 164.90 mg/L (Zn), mostly exceeding the Chinese Identification Standard for hazardous wastes. Morphology of fly ash is irregular, with both amorphous structures and polycrystalline aggregates. Further research showed that heavy metals were volatilized at a high furnace temperature, condensed when cooling down during the post-furnace system and captured at air pollution control systems. Generally, heavy metals are mainly present in the forms of aerosol particulates or tiny particulates enriched on surfaces of fly ash particles. The properties of fly ash are greatly influenced by the treatment capacities of incinerators or the variation of waste retention time in chamber. Fly ash from combustors of larger capacities generally has higher contents of volatile component and higher leaching toxicity, while those of smaller capacities often produce fly ash containing higher levels of nonvolatile components and has lower toxicity. The content of heavy metals and leaching toxicity maybe have no convincing correlation, and high alkali content of CaO greatly contribute to leaching toxicity of heavy metal and acid neutralization capacity against acid rain.

[Immobilization technology and mechanism of fly ash using H3PO4].

Chemical composition and toxicity leaching characteristics of fly ash was analyzed. The experiment results show that many heavy metals were contained; leaching concentration of Pb is 67.03 mg/L, which exceeds the limit of identification standard for hazardous wastes. Effect of input mass of H3PO4 on immobilization of heavy metals and its long-term environmental stability was studied. The results show that when input 8% - 14% (H3PO4 mass/ fly ash mass) of H3PO4 sound immobilization effect can be achieved; 8% and 12% of H3PO4 will bring a satisfactory environmental stability of heavy metals, while more H3PO4 led to less buffer capacity to acid conditions. In fly ash treated by 12% H3PO4, a small quantity of crystal Cr2P2O7, ZnP2, Pb3P4O13, Pb3P2O7, NaZnPO4, NaPbP3O9, Ca2ZnSi2O7 can be detected by XRD; many independent fly ash particles and bar-shaped Pb5 (PO4)3Cl with a diameter of 0.3 - 0.5 microm were observed by SEM; concentrated heavy metal materials were not obtained by CHBr3 floatation. Conclusions can be drawn that, through neutralization reaction of H3PO4 with strongly alkaline fly ash, stabilization reaction conditions were improved, entrapped heavy metals were chemically activated and PO4(3-) needed in stabilization was produced. Activated heavy metals combined with PO4(3-) on surface of fly ash,generated phosphates existing as forms of solid solution in SiO2, CaCO3, CaSO4, KCl, NaCl.

[Fundamental properties of fly ash from municipal solid waste incineration].

Fundamental properties and the factors that influence the distribution of heavy metals of several fly ashes are analyzed. Experiments indicate that the structures are complex and the properties are changeable. The study results show that the chemical composition is Cl, Ca, K, Na, Si, Al, O, etc, and heavy metals are Zn, Pb, Cr, Cu etc. The main structures of fly ash are irregularly amorphous forms and polycrystalline aggregates. Generally, the ieaching toxicity exceeds the identification standard for hazardous wastes. Heavy metals are chiefly in the forms of tiny aerosol particles and aggregates on the surface of fly ash. The properties of fly ash are greatly influenced by the change of incinerators or the variation of incinerating time. The content of Cl ranges from 6.93% to 29.18%, while that of SiO2 does from 4.48% to 24.84%. The leaching toxicity varies between 0 and 163.10 mg x L(-1) (Pb) and between 0.049 and 164.90 mg x L(-1) (Zn).

Isolation and characterization of mesophilic cellulose-degrading bacteria from flower stalks-vegetable waste co-composting system.

Fifteen mesophilic bacteria with high C(x) cellulase activities were isolated and purified from a mixed-culture enriched from a flower stalks-vegetable waste co-composting system. A CMCase test showed that the enzyme activity of these isolates ranged from 7.9 to 28.0 U ml(-1). Although filter paper degrading capability was low in single culture, significant synergetic cellulose degradation were detected in four groups of mixed cultures, their degradation rates were 23.5%, 26.3%, 19.4% and 24.5%, respectively. Study of morphological and physiological characters of five predominant isolates which possess high CMCase and had positive effect on synergetic cellulose degradation in mixed culture system showed that two of them were closely related to Bacillus pasteurii and Bacillus cereus, whereas the rest belong to the genus Halobacillus, Aeromicrobium and Brevibacterium, respectively.