Water use characteristics of different pioneer shrubs at different ages in western Chinese Loess Plateau: Evidence from δ2H offset correction

Caragana korshinskii Kom. and Tamarix ramosissima Ledeb. are pioneer shrubs for water and soil conservation, and for windbreak and sand fixation in arid and semi-arid areas. Understanding the water use characteristics of different pioneer shrubs at different ages is of great importance for their survival when extreme rainfall occurs. In recent years, the stable isotope tracing technique has been used in exploring the water use strategies of plants. However, the widespread δ²H offsets of stem water from its potential sources result in conflicting interpretations of water utilization of plants in arid and semi-arid areas. In this study, we used three sets of hydrogen and oxygen stable isotope data (δ²H and δ¹⁸O, corrected δ²H_{_c1} based on SW-excess and δ¹⁸O, and corrected δ²H_{_c2} based on -8.1‰ and δ¹⁸O) as inputs for the MixSIAR model to explore the water use characteristics of C. korshinskii and T. ramosissima at different ages and in response to rainfall. The results showed that δ²H_{_c1} and δ¹⁸O have the best performance, and the contribution rate of deep soil water was underestimated because of δ²H offset. During the dry periods, C. korshinskii and T. ramosissima at different ages both obtained mostly water from deeper soil layers. After rainfall, the proportions of surface (0-10 cm) and shallow (10-40 cm) soil water for C. korshinskii and T. ramosissima at different ages both increased. Nevertheless, there were different response mechanisms of these two plants for rainfall. In addition, C. korshinskii absorbed various potential water sources, while T. ramosissima only used deep water. These flexible water use characteristics of C. korshinskii and T. ramosissima might facilitate the coexistence of plants once extreme rainfall occurs. Thus, reasonable allocation of different plants may be a good vegetation restoration program in western Chinese Loess Plateau.     

Seasonal changes in the water-use strategies of three herbaceous species in a native desert steppe of Ningxia,China

Frequent periods of drought conditions are known to limit plant performance,primary production,and ecosystem stability in arid and semi-arid desert steppe environments.Plants often avoid competition by shifting their water use seasonally,which affects the water-use patterns of dominant species as well as the composition and structure of plant communities.However,the water-use strategies of dominant herbaceous species,which grow under natural field conditions in the desert steppe region of Ningxia Hui Autonomous Region,China,are poorly known.Here,we explored the possible sources of water uptake and water-use efficiency(WUE)of three dominant herbaceous plant species(Stipa breviflora,Agropyron mongolicum,and Glycyrrhiza uralensis)in a native desert steppe in the semi-arid area of Ningxia through an analysis of multiple parameters,including(1)the stable isotopic oxygen and hydrogen(δ18O andδ2H)compositions of precipitation,soil water,and stem water,(2)the carbon isotope(13C)composition of leaves,and(3)the soil water contents,based on field sampling across varying water conditions from June to September,2017.Frequent small precipitation events replenished shallow soil water,whereas large events only percolated down to the deep soil layers.Changes in soil water availability affected the water-use patterns of plants.Generally,during light precipitation periods,the deep root system of G.uralensis accessed deeper(>80 cm)soil water,whereas S.breviflora and A.mongolicum,which only have shallow roots,primarily absorbed water from the shallow and middle soil layers.As precipitation increased,all three plant species primarily obtained water from the shallow soil layers.Variation in soil water uptake between the dry and wet seasons enabled plants to make better use of existing satoil water.In addition,theδ13C values of G.uralensis and S.breviflora were higher than those of A.mongolicum.Theδ13C values of the three plant species were significantly negatively correlated with soil water content.Therefore,G.uralensis and S.breviflora maintained a higher WUE through their conservative and water-saving strategies across the entire growing season.In contrast,A.mongolicum,with a relatively low WUE in the wet season but a high WUE in the dry season,exhibited a more flexible water-use strategy.The different water-use strategies of these dominant plant species demonstrated the mechanisms by which plant communities can respond to drought.     

Biocrust-induced partitioning of soil water between grass and shrub in a desert steppe of Northwest China

Maintaining the stability of exotic sand-binding shrub has become a large challenge in arid and semi-arid grassland ecosystems in northern China. We investigated two kinds of shrublands with different BSCs (biological soil crusts) cover in desert steppe in Northwest China to characterize the water sources of shrub (Caragana intermedia Kuang et H. C. Fu) and grass (Artemisia scoparia Waldst. et Kit.) by stable ¹⁸O isotopic. Our results showed that both shrublands were subject to persistent soil water deficiency from 2012 to 2017, the minimum soil depth with CV (coefficient of variation) <15% and SWC (soil water content) <6% was 1.4 m in shrubland with open areas lacking obvious BSC cover, and 0.8 m in shrubland covered by mature BSCs. For C. intermedia, a considerable proportion of water sources pointed to the surface soil. Water from BSCs contributed to averages 22.9% and 17.6% of the total for C. intermedia and A. scoparia, respectively. C. intermedia might use more water from BSCs in rainy season than dry season, in contrast to A. scoparia. The relationship between shrub (or grass) and soil water by δ¹⁸O shown significant differences in months, which partly verified the potential trends and relations covered by the high variability of the water source at seasonal scale. More fine roots at 0-5 cm soil layer could be found in the surface soil layer covered by BSCs (8000 cm/m³) than without BSCs (3200 cm/m³), which ensured the possibility of using the surface soil water by C. intermedia. The result implies that even under serious soil water deficiency, C. intermedia can use the surface soil water, leading to the coexistence between C. intermedia and A. scoparia. Different with the result from BSCs in desert areas, the natural withdrawal of artificial C. intermedia from desert steppe will be a long-term process, and the highly competitive relationship between shrubs and grasses also determines that its habitat will be maintained in serious drought state for a long time.     

Water utilization of typical plant communities in desert steppe,China

Water is a limiting factor in the restoration and construction of desert steppe. Exploring plant water sources is necessary to understand soil-plant interactions and species coexistence; however, water sources of major plant communities within the desert steppe of Ningxia Hui Autonomous Region, China remain poorly understood. In this study, we analyzed the water uptake of plants in four typical communities: Agropyron mongolicum Keng.; Sophora alopecuroids Linn.; Stipa breviflora Griseb., and Achnatherum splendens (Trin.) Nevski communities. Stable isotopes δD and δ¹⁸O in the xylem of plant and soil water at different soil depths were analyzed. An IsoSource model was used to determine the soil depths from which plants obtained water. Results showed that A. mongolicum community obtained water predominantly from 0-20 and 40-80 cm depth, S. alopecuroids community from 0-20 cm depth, S. breviflora community from 0-40 cm depth, and A. splendens community from 0-20 and 80-140 cm depths. S. alopecuroides had a wider range of soil depths for water extraction, i.e., utilizing different water sources depending on habitat, and the plasticity of its water uptake pattern determined its role in different communities. Water source of plants relayed heavily on the distribution of their roots. Competition for soil water exists between different plant life forms in the sierozem habitat (A. mongolicum, S. alopecuroids, and S. breviflora communities), and in the sandy soil habitat (A. splendens community). The use of soil water by A. splendens community is more spatially differentiated, and shrubs and herbs can coexist stably. Under the pattern of extended drought period in the future, sierozem habitat may be more favorable for the formation of a dominant monoculture community type of perennial fibrous plants. In aeolian sandy soil habitat, A. splendens had a strong competitive advantage, and the growth of shallow-rooted plants was easily suppressed.     

Hierarchical responses of soil organic and inorganic carbon dynamics to soil acidification in a dryland agroecosystem,China

Soil acidification is a major global issue of sustainable development for ecosystems. The increasing soil acidity induced by excessive nitrogen(N) fertilization in farmlands has profoundly impacted the soil carbon dynamics. However, the way in which changes in soil p H regulating the soil carbon dynamics in a deep soil profile is still not well elucidated. In this study, through a 12-year field N fertilization experiment with three N fertilizer treatments(0, 120, and 240 kg N/(hm~2·a)) in a dryland agroecosystem of China, we explored the soil p H changes over a soil profile up to a depth of 200 cm and determined the responses of soil organic carbon(SOC) and soil inorganic carbon(SIC) to the changed soil p H. Using a generalized additive model, we identified the soil depth intervals with the most powerful statistical relationships between changes in soil p H and soil carbon dynamics. Hierarchical responses of SOC and SIC dynamics to soil acidification were found. The results indicate that the changes in soil p H explained the SOC dynamics well by using a non-linear relationship at the soil depth of 0–80 cm(P=0.006), whereas the changes in soil p H were significantly linearly correlated with SIC dynamics at the 100–180 cm soil depth(P=0.015). After a long-term N fertilization in the experimental field, the soil p H value decreased in all three N fertilizer treatments. Furthermore, the declines in soil p H in the deep soil layer(100–200 cm) were significantly greater(P=0.035) than those in the upper soil layer(0–80 cm). These results indicate that soil acidification in the upper soil layer can transfer excess protons to the deep soil layer, and subsequently, the structural heterogeneous responses of SOC and SIC to soil acidification were identified because of different buffer capacities for the SOC and SIC. To better estimate the effects of soil acidification on soil carbon dynamics, we suggest that future investigations for soil acidification should be extended to a deeper soil depth, e.g., 200 cm.     

三唑酮对木霉根际竞争定殖的影响

 在粘壤土中施用4~12μg/g土三唑酮能提高耐药木霉菌株在西瓜根尖4~1cm处根际土中的种群密度。4μg三唑酮处理的木霉根际竞争定殖指数、以及在4~8cm和10~14cm根段的根际木霉种群密度均高于不施药对照。土壤接种量为1×10³cfu/g土时木霉菌在西瓜根际增殖的比例较接种量为1×10⁶cfu/g土时大,2种接种量下三唑酮处理的根际木霉种群密度分别高于相应的不加药对照。在质地较好、C/N比值较高的粘壤土中木霉菌在西瓜根际的种群密度较砂壤土和粘土大,三唑酮对木霉在西瓜根际的增殖作用也较明显。     

2014年浑善达克沙地黄柳生长季水分来源同位素示踪研究

黄柳是我国内蒙古东部和辽宁西部沙丘上广泛分布的多年生灌木,是极佳的固沙树种.通过利用氢同位素示踪方法,测定了2014年浑善达克沙地黄柳生长季茎干水与潜在水源(降水、土壤水、地下水)氢同位素比率δD值,并利用多源线性混合模型IsoSource,计算了黄柳对各潜在水源的利用比例.结果表明:在5月黄柳80％以上利用120 ～ 160 cm土壤水和地下水;6月主要吸收0～40 cm土壤水;7月主要吸收120～160 cm土壤水;8月以地下水为主要水源,利用率为82％.这表明生长在不同季节的黄柳对于各潜在水源的利用有特定的适应结果,同时也说明荒漠灌木可以通过自身的调节朝着最优的方向发展,实现最大限度的水分利用.     

乌兰布和沙漠流动沙地土壤水分动态、土壤水势特征的研究

通过对乌兰布和沙漠流动沙地土壤水分动态的研究表明:沙土含水量的时空变化与降雨季节和降雨量有密切关系。100mm左右的降雨量对沙地和丘间地的影响深度主要在60cm左右,因此0-60cm土层为土壤水分受降雨影响的活跃层;通过对土壤含水量与土壤水势的关系研究表明:在相同土壤含水量下沙土水分对植物的有效性远大于粘土;通过降雨量对沙地贮水量影响的研究表明:只有38%左右的降雨量增加了土壤贮水量,其余62%被蒸散。     

Effect of pruning intensity on soil moisture and water use efficiency in jujube(Ziziphus jujube Mill.) plantations in the hilly Loess Plateau Region,China

Jujube(Ziziphus jujube Mill.) is a traditional economic forest crop and is widely cultivated in hilly areas of the Loess Plateau, China. However, soil desiccation was discovered in jujube plantations. Pruning is recognized as a water-saving method that can reduces soil water consumption. In this study, we monitored the jujube plots with control(CK), light(C_1), medium(C_2) and high(C_3) pruning intensities during the jujube growing period of 2012–2015 to explore the effect of pruning intensity on soil moisture and water use efficiency(WUE) of jujube plantations in the hilly Loess Plateau Region. The results showed that pruning is an effective method for soil water conservation in jujube plantations. Soil moisture increased with increasing pruning intensity during the jujube growing period of 2012–2015. C_1, C_2 and C_3 pruning intensities increased soil water storage by 6.1–18.3, 14.4–40.0 and 24.3–63.3 mm, respectively, compared to CK pruning intensity. Pruning promoted soil moisture infiltration to deeper soil layer. Soil moisture infiltrated to soil depths of 240, 280 and >300 cm under C_3 pruning intensity, 220, 260 and 260 cm under C_2 pruning intensity, 200, 240 and 220 cm under C_1 pruning intensity, and 180, 200 and 160 cm under CK pruning intensity in 2013, 2014 and 2015, respectively. Soil water deficit was alleviated by higher pruning intensity. In 2013–2015, soil water change was positive under C_2(6.4 mm) and C_3(26.8 mm) pruning intensities but negative under C_1(–20.5 mm) and CK(–40.6 mm) pruning intensities. Moreover, pruning significantly improved fresh fruit yield and WUE of jujube plants. Fresh fruit yields were highest under C_1 pruning intensity with the values of 6897.1–13,059.3 kg/hm2, which were 2758.4–4712.8, 385.7–1432.1 and 802.8–2331.5 kg/hm~2 higher than those under CK, C_2, and C_3 pruning intensities during the jujube growing period of 2012–2015, respectively. However, C_3 pruning intensity had the highest WUE values of 2.92–3.13 kg/m~3, which were 1.6–2.0, 1.1–1.2 and 1.0–1.1 times greater than those under CK, C_1 and C_2 pruning intensities, respectively. Therefore, C_3 pruning intensity is recommended to jujube plantations for its economic and ecological benefits. These results provide an alternative strategy to mitigate soil desiccation in jujube plantations in the hilly Loess Plateau Region, which is critical for sustainable cultivation of economic forest trees in this region.     

不同覆盖措施对塿土碳氮及水分的影响

通过田间试验,研究了陕西关中塿土区地膜覆盖和秸秆覆盖对表层土壤有机碳、全氮和微生物量碳氮,以及0~200 cm土壤剖面水分及硝态氮分布的影响。结果表明:与不覆盖(NM)相比,白色全膜覆盖(WF)、黑色全膜覆盖(BF)和秸秆覆盖(SM)的表层土壤有机碳分别降低了19.8%、26.3%和20.9%,土壤全氮也分别降低了4.8%、9.6%和10.6%。与NM相比,覆盖处理(WF、BF和SM)可以提高表层(0~20 cm)土壤硝态氮的含量,增加0~40 cm土层的硝态氮累积量(BF的差异不显著),降低40~120 cm土层的硝态氮累积量,但120~200 cm土层的硝态氮累积量差异不显著。SM和BF显著降低0~200 cm土层的硝态氮总累积量,而WF没有显著差异。与NM相比,地膜覆盖(WF和BF)和秸秆覆盖(SM)均可以提高表层0~40 cm土壤水分含量和储水量,但SM的效果低于地膜覆盖;WF可以降低深层土壤水分含量和储水量,而SM和BF与NM无显著差异。0~200 cm土层的总储水量,SM显著高于NM,而地膜覆盖则与NM无显著差异。各覆盖处理均显著降低了表层土壤微生物碳(MBC)和微生物氮(MBN)的含量,与NM相比,MBC分别降低了27.4%、55.4%和66.5%,MBN分别降低了4.6%、4.8%和6.8%。地膜覆盖(WF和BF)和秸秆覆盖(SM)均能够加速土壤有机碳的矿化分解,降低土壤微生物,减少土壤硝态氮的深层淋溶,其对塿土碳氮和水分的长期影响值得进一步研究关注。     

沙地樟子松人工林土壤氮矿化特征

土壤氮(N)的有效性是沙地林生态系统生产力和稳定性的关键限制因子。本研究以科尔沁沙地樟子松人工林为研究对象,分析测定了10~60 a林龄土壤NH₄⁺-N、NO₃^--N和矿质N含量、氨化速率、硝化速率和N矿化速率的变化规律。结果表明：樟子松人工林土壤NH₄⁺-N、NO₃^--N和矿质N含量,随着不同林龄在10~60 a内表现出增加的趋势,其中10~30 a增幅较小,40~60 a显著提高;随着土层深度增加而减小,主要集中在0~20 cm,呈现出表聚性。不同林龄樟子松人工林土壤氨化速率、硝化速率和矿化速率均随林龄增加而增加,随土层深度的增加而降低,其中0~40 cm土层明显大于40~100 cm。通过双因素方差分析,得出林龄与土层对各矿化指标影响显著。土壤矿化指标与人工林地上樟子松株高、胸径、冠幅以及土壤有机碳、全氮、碱解氮有显著的正相关关系。通过冗余分析(RDA)表明,影响不同林龄土壤矿化指标的主要环境因子为全氮、全磷、有机碳;影响不同土层土壤矿化指标的主要环境因子为全氮、碱解氮、有机碳。因此,樟子松人工林能够改善沙地土壤N的有效性,幼龄林和中龄林改善效果较小,近成熟林和成熟林改善效果明显;对表层土的改善效果优于深层土;土壤肥力是影响土壤矿化指标的主要环境因子。     

浑善达克沙地杨树水分利用特征

为探究浑善达克沙地杨树的水分利用特征。本文利用氢和氧同位素示踪技术,测定了降雨、土壤水与地下水的δ18O值,利用多元线性混合模型定量计算了杨树对不同土层土壤水分的利用比例。结果表明:①浑善达克沙地大气降雨方程线为:δDLWML=7.84δ^18OLWML+9.12,斜率比全国降雨方程偏小,体现了研究区降雨少,蒸发大的气候特征;②土壤含水量与地下水位埋深、降雨量、植物生长期的变化有着显著的相关关系。降雨量较大与地下水位埋深较浅的时期,土壤含水量明显增大,在植物生长前期和中期,土壤含水量明显较低;③杨树在雨季,利用了大量的浅层土壤水(0~40 cm),在较为干旱的旱季,利用了大量的深层土壤(160~200 cm)水与少量的地下水。     

Severe drought strongly reduces water use and its recovery ability of mature Mongolian Scots pine (Pinus sylvestris var. mongolica Litv.) in a semi-arid sandy environment of northern China

Trees growing in a semi-arid sandy environment are often exposed to drought conditions due to seasonal variations in precipitation, low soil water retention and deep groundwater level. However, adaptability and plasticity of individuals to the changing drought conditions greatly vary among tree species. In this study, we estimated water use (T_s) of Mongolian Scots pine (MSP; Pinus sylvestris var. mongolica Litv.) based on sap flux density measurements over four successive years (2013-2016) that exhibited significant fluctuations in precipitation in a semi-arid sandy environment of northern China. The results showed that fluctuations in daily T_s synchronously varied with dry-wet cycles of soil moisture over the study period. The daily ratio of water use to reference evapotranspiration (T_s/ET₀) on sunny days in each year showed a negative linear relationship with the severity of drought in the upper soil layer (0-1 m; P<0.01). The decrease in Ts induced by erratic drought during the growing season recovered due to precipitation. However, this recovery ability failed under prolonged and severe droughts. The T_s/ET₀ ratio significantly declined with the progressive reduction in the groundwater level (g_w) over the study period (P<0.01). We concluded that the upper soil layer contributed the most to the T_s of MSP during the growing season. The severity and duration of droughts in this layer greatly reduced T_s. Nevertheless, g_w determined whether the T_s could completely recover after the alleviation of long-term soil drought. These results provide practical information for optimizing MSP management to stop ongoing degradation in the semi-arid sandy environments.     

Seasonal patterns in water uptake for Medicago sativa grown along an elevation gradient with shallow groundwater table in Yanchi county of Ningxia,Northwest China

Lucerne(Medicago sativa L.) is a deep-rooted perennial leguminous forage with high evapo-transpiration rate exceeding the annual precipitation in semi-arid areas of Northwest China.Groundwater might be the potential water sources of lucerne in the area with shallow groundwater table.In this study,stable isotopic compositions of oxygen and hydrogen(δ18O and δD) of different water sources and xylem sap were analyzed to determine the seasonal(April,June,July and August) and topographic(three slope positions) variations in water sources for lucerne growing in Ningxia eastern semi-arid area adjacent to Mu Us Desert characterized by shallow groundwater table.Iso Source software was used to calculate the probable contribution of different water sources to the total plant water uptake.Stomatal conductance,stem water potential,carbon isotope discrimination(?~(13)C) of whole plant were also determined for evaluating the water status of lucerne growing at different slope positions.The results showed that soil water content increased as the elevation decreased.Oxygen compositions of soil water in the 0–40 cm profile fluctuated considerably.Soil water δ~(18)O values in deep profile(3.5 m) were similar to those in groundwater,implying the recharge of groundwater to this soil layer.Highest water utilization rate from deep soil profile(below 350 cm) was recorded for lucerne grown at the slope position 1(groundwater table depth of 3.5–3.9 m) in April,June and July.The lucernes at slope position 2(groundwater table depth of 5.8–6.4 m) and slope position 3(groundwater table depth 7.1–8.3 m) mostly used water from deep soil layers(below 350 cm) during dry period,and turned to use water from superficial soil layer in wet period.Higher yield,?~(13)C value of whole plant and stomatal conductance were observed for lucerne grown at the slope position 1 than those at other slope positions.These results indicated that groundwater is a significant water source for transpiration of lucerne grown in Ningxia semi-arid area with shallow groundwater table where lucerne grassland is suggested to be established so as to obtain better yield performance.     

Effects of mixed-based biochar on water infiltration and evaporation in aeolian sand soil

Aeolian sandy soil in mining areas exhibits intense evaporation and poor water retention capacity. This study was designed to find a suitable biochar application method to improve soil water infiltration and minimize soil water evaporation for aeolian sand soil. Using the indoor soil column method, we studied the effects of three application patterns (A (0-20 cm was a mixed sample of mixed-based biochar and soil), B (0-10 cm was a mixed sample of mixed-based biochar and soil and 10-20 cm was soil), and C (0-10 cm was soil and 10-20 cm was a mixed sample of mixed-based biochar and soil)), four application amounts (0% (control, CK), 1%, 2%, and 4% of mixed-based biochar in dry soil), and two particle sizes (0.05-0.25 mm (S1) and <0.05 mm (S2)) of mixed-based biochar on water infiltration and evaporation of aeolian sandy soil. We separately used five infiltration models (the Philip, Kostiakov, Horton, USDA-NRCS (United States Department of Agriculture-Natural Resources Conservation Service), and Kostiakov-Lewis models) to fit cumulative infiltration and time. Compared with CK, the application of mixed-based biochar significantly reduced cumulative soil water infiltration. Under application patterns A, B, and C, the higher the application amount and the finer the particle size were, the lower the migration speed of the wetting front. With the same application amount, cumulative soil water infiltration under application pattern A was the lowest. Taking infiltration for 10 min as an example, the reductions of cumulative soil water infiltration under the treatments of A2%_(S2), A4%_(S1), A4%_(S2), A1%_(S1), C2%_(S1), and B1%_(S1) were higher than 30%, which met the requirements of loess soil hydraulic parameters suitable for plant growth. The five infiltration models well fitted the effects of the treatments of application pattern C and S1 particle size (R²>0.980), but the R² values of the Horton model exceeded 0.990 for all treatments (except for the treatment B2%_(S2)). Compared with CK, all other treatments reduced cumulative soil water infiltration, except for B4%_(S2). With the same application amount, cumulative soil water evaporation difference between application patterns A and B was small. Treatments of application pattern C and S1 particle size caused a larger reduction in cumulative soil water evaporation. The reductions in cumulative soil water evaporation under the treatments of C4%_(S1), C4%_(S2), C2%_(S1), and C2%_(S2) were over 15.00%. Therefore, applying 2% of mixed-based biochar with S1 particle size to the underlying layer (10-20 cm) could improve soil water infiltration while minimizing soil water evaporation. Moreover, application pattern was the main factor affecting soil water infiltration and evaporation. Further, there were interactions among the three influencing factors in the infiltration process (application amount×particle size with the most important interaction), while there were no interactions among them in the evaporation process. The results of this study could contribute to the rational application of mixed-based biochar in aeolian sandy soil and the resource utilization of urban and agricultural wastes in mining areas.     

盐渍土的热力构型对水盐运移的影响研究

通过野外定位观测和室内分析,探讨了冻融季节苏打盐渍土的热力构型及对苏打盐渍土的水盐变化的影响。结果表明:土体热力梯度是水盐运移的诱导因素和驱动力。冬季松嫩平原西部土体热力构型为冷冻层-过渡层-暖土层;消融季节土体热力构型为暖土层-过渡层-冷冻层-过渡层-暖土层。受土体热力梯度和水势梯度驱动,潜水向冻结层积聚形成冻土。土壤类型不同,冻土的组成和性质存在显著差异。盐化草甸土和苏打草甸盐土成为水分迁移的汇集区,大量地下水汇集在盐化草甸土和盐土的冻层中,0-70 cm土层的含水率显著增加,最高含量达60%。苏打草甸盐土和白盖苏打碱土的冻层为盐分汇集区,苏打盐土和白盖苏打碱土0-70 cm土层土壤盐分增加明显,其中0-40 cm土层的盐分增量最显著。冻土层积聚大量盐分导致消融季节土壤的盐渍化程度不断加重。     

樟子松固沙林土壤理化特性对林分密度的响应

为了研究樟子松人工固沙林林分密度对土壤理化特性的影响,在章古台地区选取林分密度分别为625（P₁）、775（P₂）、1 025（P₃）、1 175（P₄）株·hm^-2和1 250（P₅）株·hm^-2的樟子松中龄林（林龄为23~27 a）为研究对象,对0~100 cm深度的樟子松林地土壤按0~10、10~20、20~40、40~60、60~80、80~100 cm进行分层,分析其理化特性。结果表明：0~10 cm土层全氮和20~40 cm土层土壤容重随密度增加呈上升趋势,P₅显著高于P₁（P < 0.05）;0~80 cm土层全钾和0~60 cm土层pH随密度增加先升高后降低,P₃最高,且P₃样地全钾在10~60 cm土层显著高于P₁（P < 0.05）;pH在0~40 cm土层显著高于其他样地（P < 0.05）;0~10 cm土层全磷随密度增加而减小,P₁显著高于P₃~P₅（P < 0.05）;P₄或P₅样地有效钾在0~40 cm土层显著高于P₁、P₂样地（P < 0.05）,在40~100 cm土层显著高于P₃样地（P < 0.05）;P₂~P₄样地的土壤孔隙度在40~100 cm土层低于P₁和P₅样地。综合考虑林分密度对樟子松中龄林土壤理化特性的影响,章古台地区樟子松林的合理林分密度为1 025~1 175株·hm^-2,可采取间伐等营林管理措施调节林分密度,确保樟子松固沙林生长具有良好的土壤条件。     

直插式根灌的土壤水分时空分布与节水效率

在塔里木河下游枣树生态经济林进行根灌试验,研究了直插式根灌条件下的土壤水分时空分布和节水效率。结果表明:(1)灌水过程中直插式根灌的土壤水分分布在0~100 cm土壤层,随灌溉时间增加,土壤含水量,0~20 cm土层呈波动变化,80~100 cm土层基本稳定,其余各土层呈S型增加;(2)不同时期1 m深土层平均土壤体积含水量最大值及达到最大值的时间,枣树生长初期为44.62%、7.5 h,花期为43.26%、12.5 h,幼果期为46.3%、15 h;(3)根灌过程中,各土层土壤含水量变异系数大小次序为80 cm20 cm40 cm60 cm100 cm;灌后土壤平均含水量,80、100 cm土层与其余各层之间差异显著,20、40、60 cm土层之间差异不显著,80 cm土层土壤含水量空间异质性最高;(4)三次试验后20 d内,0~100 cm土层的平均土壤体积含水量消退速率分别为0.21%·d~(-1)、0.19%·d~(-1)和0.17%·d~(-1),土壤体积含水量60 cm和100 cm土层消退速率稳定,40 cm土层呈先消退后增加的趋势,20 cm土层0~10 d迅速消退,80 cm土层11~20 d迅速消退;(5)直插式根灌的节水效率比地表滴灌高27.78%,水分利用效率分别比地表滴灌和漫灌高8.12%、52.46%。     

A drought resistance index to select drought resistant plant species based on leaf water potential measurements

The water deficit in arid and semi-arid regions is the primary limiting factor for the development of urban greenery and forestation. In addition, planting the species that consume low levels of water is useful in arid and semi-arid regions that have poor water management measures. Leaf water potential (Ψ) is a physiological parameter that can be used to identify drought resistance in various species. Indeed, Ψ is one of the most important properties of a plant that can be measured using a pressure chamber. Drought avoiding or drought resistant species have a lower Ψ than plants that use normal or high levels of water. To determine drought resistance of species that are suitable for afforestation in arid urban regions, we evaluated twenty woody species in the Isfahan City, central Iran. The experimental design was random split-split plots with five replications. The species were planted outdoor in plastic pots and then subjected to treatments that consisted of two soil types and five drip irrigation regimes. To evaluate the resistance of each species to drought, we used the Ψ and the number of survived plants to obtain the drought resistance index (DRI). Then, cluster analysis, dendrogram, and similarity index were used to group the species using DRI. Result indicates that the evaluated species were classified into five groups: (1) high water consuming species (DRI>-60 MPa); (2) above normal water consuming species (-60 MPa≥DRI>-90 MPa); (3) normal water consuming species (-90 MPa≥DRI>-120 MPa); (4) semi-drought resistant species (-120 MPa≥DRI>-150 MPa); and (5) drought resistant species (DRI≤-150 MPa). According to the DRI, Salix babylonica L., Populus alba L., and P. nigra L. are high water consuming species, Platanus orientalis L. and Albizia julibrissin Benth are normal water consuming species, and Quercus infectoria Oliv. and Olea europaea L. can be considered as drought resistant species.     

Spatio-temporal variations of soil water content and salinity around individual Tamarix ramosissima in a semi-arid saline region of the upper Yellow River,Northwest China

Ecological restoration by Tamarix plants on semi-arid saline lands affects the accumulation, distribution patterns and related mechanisms of soil water content and salinity. In this study, spatio-temporal variations of soil water content and salinity around natural individual Tamarix ramosissima Ledeb. were invetigated in a semi-arid saline region of the upper Yellow River, Northwest China. Specifically, soil water content, electrical conductivity(EC_e), sodium adsorption ratio(SAR_e), and salt ions(including Na~+, K~+, Ca~(2+), Mg~(2+) and SO_4~(2–)) were measured at different soil depths and at different distances from the trunk of T. ramosissima in May, July, and September 2016. The soil water content at the 20–80 cm depth was significantly lower in July and September than in May, indicating that T. ramosissima plants absorb a large amount of water through the roots during the growing period, leading to the decreasing of soil water content in the deep soil layer. At the 0–20 cm depth, there was a salt island effect around individual T. ramosissima, and the EC_e differed significantly inside and outside the canopy of T. ramosissima in May and July. Salt bioaccumulation and stemflow were two major contributing factors to this difference. The SAR_e at the 0–20 cm depth was significantly different inside and outside the canopy of T. ramosissima in the three sampling months. The values of SAR_e at the 60–80 cm depth in May and July were significantly higher than those at the 0–60 cm depth and higher than that at the corresponding depth in September. The distribution of Na~+ in the soil was similar to that of the SAR_e, while the concentrations of K~+, Ca~(2+), and Mg~(2+) showed significant differences among the sampling months and soil depths. Both season and soil depth had highly significant effects on soil water content, EC_e and SAR_e, whereas distance from the trunk of T. ramosissima only significantly affected EC_e. Based on these results, we recommend co-planting of shallow-rooted salt-tolerant species near the Tamarix plants and avoiding planting herbaceous plants inside the canopy of T. ramosissima for afforestation in this semi-arid saline region. The results of this study may provide a reference for appropriate restoration in the semi-arid saline regions of the upper Yellow River.