Enhanced nitrogen removal from rural domestic sewage via partial nitrification-anammox in integrated vertical subsurface flow constructed wetland.

This study aimed to improve the removal of nitrogen treating rural domestic sewage by developing a novel strategy for achieving partial nitrification-anammox (PNA) in an integrated vertical subsurface flow constructed wetland (VSFCW). The influent ammonia was oxidized to nitrite in the partial nitrification VSFCW (VSFCWPN), and 5 mg/L of hydroxylamine was added under the appropriate dissolved oxygen concentration level (1.2 ± 0.2 mg/L) to stabilize the average nitrite accumulation rate at 88.24% and maintain the effluent NO2--N/NH4+-N ratio at 1.26 ± 0.15. The effluent from VSFCWPN was introduced to the following chamber (VSFCWAN), where ammonia and nitrite were removed by the autotrophic anammox process. This implementation achieved high removal efficiencies for chemical oxygen demand, total nitrogen, and PO43--P, reaching 86.26%, 90.22%, and 78.94%, respectively, with influent concentrations of 120.75 mg/L, 60.02 mg/L, and 5.05 mg/L. Substrate samples were collected from 10 cm height (PN1, AN1) and 25 cm height (PN2, AN2). Microbial community analysis showed that Nitrosomonas dominated the community composition in VSFCWPN, with an increase from 1.61% in the inoculated sludgePN to 16.31% (PN1) and 12.09% (PN2). Meanwhile, Ca. Brocadia accounted for 44.81% (AN1) and 36.50% (AN2) in VSFCWAN. These results confirm the feasibility of the proposed strategy for establishing PNA and efficiently treating rural domestic sewage in an integrated VSFCW.

[Differences and mechanisms on water use of Pinus sylvestris var mongolica forests with different origins]. / 不同起源樟子松林水分利用的差异及机制.

Determining the differences of water use characteristics of a tree species with different origins (natural forests and introduced plantations) is significantly important for forest sustainable management. Pinus sylvestris var. mongolica is an important tree species of afforestation in the 'Three North' project in China. In this study, with Pinus sylvestris var. mongolica from two origins, we monitored the sap flow velocity of sapwood (Js) of trees by thermal dissipation sap flow probes, and analyzed the relationship between water transportation and the environmental factors during the growing season. The results showed that under the typical sunny day, daily sap flow velocity (Js-daily) of trees from plantations was significantly higher than that from natural forests. The mean value of Js-daily was 132.98 and 114.86 cm·d-1 for the two origins, respectively. Trees from plantations showed higher water transportation potential than natural forests. Vapor pressure deficit (VPD) mainly showed the driving effect on the water use process of trees from natural forests. In the plantations, there was an obvious threshold effect, and the inflection point of VPD was about 1.91 kPa, with the boundary function of Js-hour increased to the maximum of 17.88 cm·h-1. Atmospheric driven transpiration potential (Js-hour/VPD) of P. sylvestris var. mongolica trees with two origins decreased with the aggravation of soil drought, but sensitivity to drought was higher in the plantations than in the natural forests, suggesting the strong ability of Pinus sylvestris var. mongolica to regulate water use process.

Water Use by Chinese Pine Is Less Conservative but More Closely Regulated Than in Mongolian Scots Pine in a Plantation Forest, on Sandy Soil, in a Semi-Arid Climate.

The diversity of plant water use patterns among species and ecosystems is a matter of widespread debate. In this study, Chinese pine (Pinus tabuliformis, CP) and Mongolian Scots pine (Pinus sylvestris var. mongolica, MP), which is co-exist in the shelterbelt plantations in the Horqin Sandyland in northern China, were chosen for comparison of water use traits by monitoring xylem sap flow alongside recordings of the associated environmental factors over four growing seasons. Continuous sap flux density measurements were converted into crown projected area transpiration intensity (Tr) and canopy stomatal conductance (Gs). The results indicated that MP showed a higher canopy transpiration intensity than in CP, with Tr daily means (±standard deviation) of 0.84 ± 0.36 and 0.79 ± 0.43 mm⋅d-1, respectively (p = 0.07). However, the inter-annual variability of daily Tr in MP was not significant, varying only approximately a 1.1-fold (p = 0.29), while inter-annual variation was significant for CP, with 1.24-fold variation (p < 0.01). In particular, the daily mean Tr value for CP was approximately 1.7-times higher than that of MP under favorable soil moisture conditions, with values for relative extractable soil water within the 0-1.0 m soil layer (REW) being above 0.4. However, as the soil dried out, the value of Tr for CP decreased more sharply, falling to only approximately 0.5-times the value for MP when REW fell to < 0.2. The stronger sensitivity of Tr and/or Gs to REW, together with the more sensitive response of Gs to VPD in CP, confirms that CP exhibits less conservation of soil water utilization but features a stronger ability to regulate water use. Compared with MP, CP can better adapt to the dry conditions associated with climate change.

[Effect of soil moisture on water potential gradients in the soil-plant-atmosphere continuum (SPAC) of apple orchards in the Loess Plateau, Northwest China]. / 土壤水分对黄土区苹果园土壤-植物-大气连续体(SPAC)中水势梯度的影响.

The variations of water potential gradients through the soil-plant-atmosphere continuum (SPAC) are of great significance to reveal the responses of plant water use to environmental changes. We conducted a continuous experiment to monitor the potentials in the near-canopy atmosphere (Ψair), soil (Ψsoil) and plant xylems (Ψstem) during the growing season in an apple orchard located in the Loess Plateau. The results showed that the average Ψstem during the growing season ranged from -0.24 to -2.0 MPa, with a mean value of -0.57 MPa. The average water potential gradient in soil-plant-atmosphere system was 1:9.8:1155 (Ψsoil:Ψstem:Ψair). We found a significant positive linear correlation between the Ψstem:Ψsoil gradient and volumetric soil water content (VWC, %). The Ψstem was more strongly correlated with Ψsoil than Ψair. Moreover, the sensitivity of Ψstem to Ψsoil decreased when Ψsoil was lower than -0.08 MPa which corresponded to VWC=17%, 0.56 times of field capacity. This was reflected by the increased linearity between Ψair /Ψstem and Ψsoil as Ψsoil decreased. There was a threshold effect for the relationship between Ψair and Ψstem. That is, the Ψstem in a day increased with the increasing of Ψair before the latter reached -69 MPa, after which the Ψstem decreased. The decline of soil water content caused an obvious decrease in water potential gradient through the SPAC system, and the threshold effect existed when VWC was below 17%. The results provide a basis for understanding the mechanisms of plant water in response to soil and atmospheric drought.

[Radial variation and time lag of sap flow of Populus gansuensis in Minqin Oasis, Northwest].

Sap flow of tree trunk is very important to reflect the dynamics of physiological activities, as well as to estimate the water consumption of individual plant. In the present study, we used the thermal dissipation technique to monitor the sap flow velocity (J) at four depth loci (i. e. 2 cm, 3 cm, 5 cm, 8 cm) of three Populus gansuensis trees (30 year-old) in Minqin Oasis for two consecutive growing seasons. The results showed that there were significant differences among J values at four depth loci under tree trunk cambium. J value at the 3 cm depth locus (J3) of the tree trunk was the highest, and then in sequences, were 2 cm, 5 cm and 8 cm depth loci (J2, J5 and J8). J value (J3) on typical sunny days in June with the highest atmospheric potential evapotranspiration (ET0) was up to 28.53 g · cm(-2) · h(-1), which was 1.42, 2.74 and 4.4 times of J2, J5 and J8, respectively. In the process of diurnal variation of sap flow velocity, the peak value time of J at the four depth loci of the tree trunk was different, but the differences among them were within 20 min. Furthermore, the peak value time of sap flow velocity was very different to that of solar radiation (Rs) and air vapour pressure deficit (VPD). The time lag between J and Rs was from 55 to 88 min on typical sunny days during the main growing seasons (from June to August), and, positively related to the depth of the locus under tree trunk cambium, while the time lag between J and VPD reached 60-96 min, and was negatively related to the depth of the locus. The seasonal variation patterns of J were consistent with ET0. With the increase of tree physiological activities, there was a trend that the major water transportation layer extended to the interior sapwood. The most important meteorological factor was the solar radiation, which primarily drove sap flow at different depths of tree trunk. However, the secondary factor changed along with the depth, and VPD became increasingly important with increasing the depth.

[Drought resistibility of main tree species in water conservation forest of Qilian Moutains].

With P-V techniques, this paper determined and analyzed the water parameters of main tree species in the water conservation forest of Qilian Moutains. The results showed that the test water parameters varied with tree species, reflecting the complicacy of the drought-resistance mechanism of trees. Among 10 parameters, /phi pi100 - phi pi0/, RCV, ROWC0 epsilon(max) could reflect most information of drought resistibility. Based on their drought resistibility, the test tree species could be classified into 4 groups, i.e., high drought resistibility (Picea crassifolia and Rhododendron thymifolium ), sub-high drought resistibility (Sabina przeualwkii, Rhododendron anthopogonoides, Rhododendron capitaturn and Rhododendron przewalskii), low drought resistibility (Populus cathyana), and inferior drought resistibility (Poentilla fruticosa, Siraea salicifolia and Betula albosinensis). The relationships between predawn leaf water potential and soil water content could be well modeled by hyperbola function, power function or exponent function. Meanwhile, the test tree species could be also grouped as high potential delay dehydration species (Betula albosinensis and Rhododendron przeualskii), sub-high potential delay dehydration species (Picea crassifolia, Rhododendron thymifolium and Rhododendron capitatum), inferior potential tolerance species (Sabina przewalskii), and low potential tolerance species (Potentilla fruticosa, Spiraea salicifolia and Rhododendron anthopogonoides), based on their drought-resistance mechanism.

[Soil water characteristics in Picea crassifolia forestry lands in Qilian Mountains].

The study of soil water content and its main affecting factors in Picea crassifolia forestry lands in Qilian Mountains showed that the Picea crassifolia forestry lands were characterized by lower soil bulk weight and higher soil water infiltration rate, and the vertical distribution of soil water was apparently affected by precipitation. The soil bulk weight of shrub-Picea crassifolia forestry land, moss-Picea crassifolia forestry land and meadow land was 0.522, 0.641 and 0.874 g x cm(-3), initial water infiltration rate was 6.0, 21.0 and 2.5 mm x min(-1), and stable infiltration rate was 3.98, 11.2 and 0.5 mm x min(-1), respectively. The soil of moss-Picea crassifolia land in 100 cm depth could be partitioned into 4 layers, i.e., active layer (0 - 30 cm), regulation layer (30 - 60 cm), transmission layer (60 - 80 cm) and accumulation layer (below 80 cm), and the amount of stored water in each layer was 3.30, 3.17, 2.80 and 2.83 mm x cm(-1), respectively. The soil of shrub-Picea crassifolia land could be partitioned into 3 layers, i.e., stable layer (0 - 30 cm), active layer (30 - 60 cm) and transmission layer (below 60 cm), and the amount of stored water in each layer was 3.98, 3.65 and 3.48 mm x cm(-1), respectively. The seasonal variance of soil water content in Picea crassifolia forestry lands was strongly affected by precipitation. The water holding capacity of shrub-Picea crassifolia forestry land was higher and the water transmission capability was lower than that of Moss-Picea crassifolia forestry land.