内蒙古半干旱草原土壤水分对降水格局变化的响应

在全球气候变化背景下, 未来我国北方半干旱地区的降水格局将呈现出季节与年际间降水波动增强和极端降水事件增加的趋势。水分是半干旱草原的主要限制因子, 降水格局变化导致的土壤水分状况的改变必然对生态系统的结构和功能产生显著的影响。该研究选取内蒙古多伦和锡林浩特两个典型半干旱草原群落, 通过分析2006-2013年的降水和多层次土壤(0-10 cm, 10 cm, 20 cm, 30 cm和50 cm)含水量连续观测数据, 研究降水格局变化对土壤水分状况及其垂直分布的影响, 特别是土壤水分对降水事件的脉冲响应过程。结果表明: 两个站点的土壤含水量均呈现显著的季节及年际间波动, 其中土壤表层 0-10 cm水分波动更剧烈。锡林浩特50 cm处土壤含水量波动较大, 主要由于春季融雪的影响。年际间多伦和锡林浩特生长季土壤表层0-10 cm土壤含水量与降水量存在显著的正相关关系, 下层(10-50 cm)土壤含水量与降水量相关性不显著。研究发现小至2 mm的降水事件就能够引起两个站点表层0-10 cm土壤含水量的升高, 即该地区有效降水为日降水量> 2 mm。表层0-10 cm土壤含水量对独立降水事件的脉冲响应可通过指数方程很好地拟合。降水事件的大小决定了降水后表层0-10 cm土壤含水量的最大增量和持续时间, 同时这个脉冲响应过程还受到降水前土壤含水量的影响, 但该过程中并未发现植被因子(叶面积指数)的显著影响。降水后水分下渗深度及该深度的土壤含水量增量主要由降水事件的大小主导, 同时受到降水前土壤含水量的影响。在多伦和锡林浩特, 平均每增加1 mm降水, 下渗深度分别增加1.06和0.79 cm。由此作者认为, 在内蒙古半干旱草原, 降水事件大小和降水前土壤干湿状况是影响土壤水分对降水响应的主要因素, 而植被因子的影响较小。     

Responses of soil respiration to simulated precipitation pulses in semiarid steppe under different grazing regimes

Aims Precipitation pulses and different land use practices (such as grazing) play important roles in regulating soil respiration and carbon balance of semiarid steppe ecosystems in Inner Mongolia. However, the interactive effects of grazing and rain event magnitude on soil respiration of steppe ecosystems are still unknown. We conducted a manipulative experiment with simulated precipitation pulses in Inner Mongolia steppe to study the possible responses of soil respiration to different precipitation pulse sizes and to examine how grazing may affect the responses of soil respiration to precipitation pulses.Methods Six water treatments with different precipitation pulse sizes (0, 5, 10, 25, 50 and 100 mm) were conducted in the ungrazed and grazed sites, respectively. Variation patterns of soil respiration of each treatment were determined continuously after the water addition treatments.Important findings Rapid and substantial increases in soil respiration occurred 1 day after the water treatments in both sites, and the magnitude and duration of the increase in soil respiration depended on pulse size. Significantly positive relationships between the soil respiration and soil moisture in both sites suggested that soil moisture was the most important factor responsible for soil respiration rate during rain pulse events. The ungrazed site maintained significantly higher soil moisture for a longer time, which was the reason that the soil respiration in the ungrazed site was maintained relatively higher rate and longer period than that in the grazed site after a rain event. The significant exponential relationship between soil temperature and soil respiration was found only in the plots with the high water addition treatments (50 and 100 mm). Lower capacity of soil water holding and lower temperature sensitivity of soil respiration in the grazed site indicated that degraded steppe due to grazing might release less CO₂ to the atmosphere through soil respiration under future precipitation and temperature scenarios.     

氮和水分添加对内蒙古荒漠草原放牧生态系统土壤呼吸的影响

土壤呼吸是生态系统碳循环的重要组成部分, 同时也是评价生态系统健康状况的重要指标, 对于评估退化草地恢复过程中生态系统功能具有重要意义。该研究在内蒙古四子王旗短花针茅(Stipa breviflora)荒漠草原长期放牧实验平台上进行, 该平台设置对照(CK)、轻度(LG)、中度(MG)和重度(HG) 4个放牧强度。通过在4个放牧处理区设置氮、水添加实验处理, 探讨不同放牧强度背景下, 氮、水补充对荒漠草原土壤呼吸过程的影响。结果表明: (1)历史放牧强度除2015年对土壤呼吸无显著影响, 2016和2017年都有显著影响, 放牧区3年平均土壤呼吸速率基本都高于对照区。此外, 氮和水分添加显著增加了MG区土壤呼吸速率, HG区氮、水同时添加对土壤呼吸速率有显著增加作用; (2)无论是历史放牧强度, 还是氮、水添加处理, 都没有改变荒漠草原生长季土壤呼吸速率的季节动态变化趋势, 土壤呼吸速率基本表现为单峰曲线模式, 峰值出现在水热同期的7月份; (3)不同年份生长季土壤呼吸速率对氮、水处理的响应并不相同, 氮添加至第3年产生显著影响。水分添加在平水年份(2015和2017年)对土壤呼吸产生显著影响, 但在丰水年份(2016年)无显著影响。氮、水共同添加分别在CK、LG和HG区3年平均土壤呼吸速率显著高于单独加水处理, 说明氮添加的有效性依赖于水分条件, 两者表现为协同作用; (4)不同处理下荒漠草原土壤呼吸的温度敏感性(Q₁₀)值介于1.13-2.41之间, 平均值为1.71。在无氮、水添加时, 放牧区的Q₁₀值都小于CK区, 总体表现为CK 大于 MG 大于 LG 大于 HG; 加水和氮水共同添加处理后, Q₁₀值都有明显增加, 其中NW处理下Q₁₀值都增加到2.0以上。上述结果说明在过去受不同放牧强度影响的荒漠草原在停止放牧后的恢复过程中, 土壤水分仍是影响土壤呼吸的主导环境因子, 外源氮添加只有在满足一定水分供给的基础上才起作用, 尤其是过去的重度放牧区土壤呼吸速率对氮、水补充的响应最为强烈。该研究结果可以为评估荒漠草原恢复过程中土壤呼吸速率受养分和水分影响提供基础资料和依据。     

Soil water use strategy of dominant species in typical natural and planted shrubs in loess hilly region

Aims Artemisia gmelinii is a dominant specie naturally established after abandonment of cultivated lands in the Loess Plateau, and Caragana korshinskii is one of the main planted shrub species to control soil erosion. Improved understanding of water use strategies of these two species is of great significance to evaluate the sustainable development of the Loess Plateau under the trend of climate warming and increasing drought events.
Methods Stable oxygen-18 isotope was used to determine seasonal variations in the water sources of native A. gmelinii communities established after abandonment of cultivated lands for 7 and 30 years and planted C. korshinskii after 30 years. The contributions of soil water from different depths to water uptake were estimated by the MixSIR Bayesian mixing model. The geometric mean regression method was used to fit the line of precipitation to get the local meteoric water line (LWML).
Important findings The stable hydrogen isotope rate (δD) and stable oxygen isotope rate (δ¹⁸O) of soil water and xylem water plotted to the right side of the LWML, indicating that the isotopic compositions of soil water were enriched due to evaporation. The native A. gmelinii communities established after abandonment of cultivated lands for 7 years and planted C. korshinskii after 30 years showed plasticity in switching water sources from different soil layers, extracting water from shallow soil (0-40 cm) when soil water was available, but deeper soil (40-80 cm) when shallow soil water was dry. In contrast, A. gmelinii growing in site after cultivation abandonment for 30 years mainly relied on water from the surface soil (0-10 cm) throughout the growing season. Our results suggest that the ability of A. gmelinii to compete for soil water reduces with aging of the community while the planted C. korshinskii will have competitive advantage under the condition of increasing frequency of drought events in the future.     

Dynamics of water usage in Haloxylon ammodendron in the southern edge of the Gurbantünggüt Desert

植物的水分来源是荒漠地区植物水分关系研究的重要方面, 有助于理解荒漠植物对干旱环境的适应。为了研究古尔班通古特沙漠主要建群种梭梭(Haloxylon ammodendron)生长季的水分利用动态, 以及其对发生在不同时期相似量级降水脉冲的响应, 利用稳定性同位素技术测量了梭梭小枝木质部水、降水、0-300 cm不同土层的土壤水和地下水的δ ¹⁸O值。水源依据深度划分为4个: 浅层土壤水(0-40 cm), 中层土壤水(40-100 cm), 深层土壤水(100-300 cm)和地下水。然后, 应用IsoSource模型计算了梭梭对潜在水源的利用比例。结果表明: 4月份, 梭梭主要利用浅层土壤水, 利用比例为62%-95%; 5-9月份梭梭主要利用地下水, 利用比例为68%-100%。梭梭对不同时期发生的两场相似量级的降水具有不同程度的响应。5月22日, 6.7 mm降水后第1天, 梭梭对土壤水的吸收达到最大值, 由降水前的9.8%增长为降水后的40.4%, 同时降低了对地下水的吸收, 由降水前的83%-98%下降为42%-81%。8月31日7 mm降水后, 梭梭对土壤水的吸收没有增加, 仍然保持对地下水的高比例利用, 达71%-98%。低的土壤含水量可能抑制了表层根系的活性, 导致梭梭对降水不敏感。由冬季融雪和春季降水补给的浅层土壤水和地下水是梭梭种群可利用的两个重要水源。梭梭的水分利用动态反映了其对干旱环境的适应。     

内蒙古西鄂尔多斯荒漠区降水入渗氘同位素特征

探讨我国干旱半干旱地区大气降水在土壤剖面中的时空分布特征将为西鄂尔多斯荒漠退化生态系统恢复和维持提供科学依据.本研究利用氘同位素技术研究了内蒙古西鄂尔多斯荒漠的大气降水、土壤水、地下水中的氘同位素值(δD),运用二元线性混合模型计算降水对各层土壤水的贡献率,并结合土壤含水量分析了不同降水条件下土壤剖面各层土壤水δD的时空分布特征.结果表明: 雨后9 d内,小雨(0～10 mm)影响0～10 cm土壤含水量和土壤水δD值,对表层土壤(0～10 cm)的贡献率在30.3%～87.9%;中雨(10～20 mm)影响0～40 cm土壤含水量和土壤水δD值,对0～40 cm土壤水的贡献率为28.2%～80.8%;大雨(20～30 mm)和特大暴雨(＞30 mm)影响0～100 cm土壤含水量和土壤水δD值.降水对100～150 cm深层土壤水δD值影响不显著.西鄂尔多斯荒漠土壤水δD介于大气降水δD与地下水δD之间,表明西鄂尔多斯荒漠土壤水主要来源于大气降水与地下水.在同一降水强度下,表层土壤水(0～10 cm)受降水的直接影响显著,随着土壤深度的增加,土壤水δD变化幅度降低,100～150 cm深层土壤水δD基本趋于稳定.降水强度越大,对土壤水δD影响的时间越长,影响的土壤深度也越深.     

Characteristics of normalized difference vegetation index of biological soil crust during the succession process of artificial sand-fixing vegetation in the Tengger Desert,Northern China

Aims Biological soil crust (hereafter crust) affects normalized difference vegetation index (NDVI) values in arid desert ecosystems. This study aimed to demonstrate the feasibility of combining crust NDVI values with meteorological data to distinguish the crust successional stage at the regional scale. Meanwhile, the characteristics of crust NDVI could provide the basis for the error analysis of NDVI-based surface ecological parameters estimation in desert ecosystems. We also suggested the optimum periods for crust observation based on the multi-temporal remote sensing images.Methods NDVI values of five types of dominant crusts, three typical sand-fixing shrubs and bare sand were collected by spectrometer in the field. Crusts and shrubs were randomly selected in revegetated areas established in 1956, 1964, and 1973 at Shapotou, which is on the southeastern edge of the Tengger Desert. We used the space-for-time method to study the characteristics of crust NDVI values and their responses to precipitation and temperature during the succession process of artificial sand-fixing vegetation. Additionally, we evaluated the contribution of crust NDVI values to the whole ecosystem NDVI values by comparing the NDVI values of crusts, shrubs and bare sand.Important findings 1) With succession process of the artificial sand-fixing vegetation, the crust NDVI values significantly increased. Among different crust types, we found the following order of NDVI values: Didymodon vinealis crust > Bryum argenteum crust > mixed crust > lichen crust > algae crust. 2) Crust NDVI values were significantly affected by precipitation, temperature and their interaction, and the influences showed significant seasonal differences. Furthermore, we found significantly linear correlations between crust NDVI value and precipitation, and between crust NDVI value and the shallow soil moisture content covered by crust. A significantly negative linear correlation between daily mean temperature and crust NDVI value, and a significantly exponential correlation between the surface temperature of crust and its NDVI value. With the succession process of artificial sand-fixing vegetation, the response of crust NDVI value to precipitation and temperature became more sensitive. In addition, the response of crust NDVI value to temperature was more sensitive in spring than in summer, while that to precipitation was less sensitive in spring than in summer. 3) Moss crust NDVI value was significantly higher than that of shrubs and bare sand after the rainfall event in spring, while shrubs NDVI value was significantly higher than that of crust after the rainfall event in summer. Considering the coverage weights of different ground features in sand-fixing areas, crust NDVI values contributed 90.01% and 82.53% in spring and summer, respectively, to the regional NDVI values, which were higher than those of shrubs (9.99% and 17.47% in spring and in summer, respectively). Additionally, with the succession process of artificial sand-fixing vegetation, crust NDVI values contributed more, while shrubs contributed less to regional NDVI values.     

Effects of precipitation intensity and temporal pattern on soil nitrogen mineralization in a typical steppe of Nei Mongol grassland

Aims Our objective is to: 1) explore the dynamics of soil nitrogen (N) mineralization in a grassland ecosystem in response to the changes in precipitation intensity and temporal distribution, and 2) identify the controlling factors.Methods The two study sites located in a typical steppe of the Nei Mongol grassland were fenced in 2013 and 1999, respectively. Our field experiment includes manipulations of three levels of precipitation intensity (increased 50%, decreased 50%, control) in three temporal patterns (increased or decreased precipitation for three years; increased or decreased precipitation for two years and no manipulation for one year; increased or decreased precipitation for one year and no manipulation for one year).Important findings 1) The soil net N mineralization and net nitrification rates decreased with changes in the temporal distributions of precipitation from one year to three years, with the maximum values of soil net N mineralization and nitrification rates observed in the treatments of increased or decreased precipitation for one year and no manipulation for one year (+PY1 or -PY1). This indicates that the high precipitation intensity and longer precipitation may have negative effects on soil net N mineralization and nitrification rates, while the moderate soilmoisture and temperature may stimulate soil mineralization. 2) The soil net N mineralization and nitrification rates, soil cumulative N mineralization, and nitrification in the fenced site in 1999 were higher than those in the site fenced in 2013, implying that a long-term enclosure may have promoted nutrient storage and soil quality restoration. 3) The long-term treatments of increased or decreased precipitation had significant effects on soil water content and temperature, whereas the short-term, discontinuous precipitation produced minor effects on soil moisture and temperature. Moreover, the controlling factors for soil N mineralization were different between the two fields. Soil moisture had a major effect on soil inorganic N content and net N mineralization rate in the site fenced in 2013, while soil temperature played a dominant role in the site fenced in 1999, with the net N mineralization rate depressed by higher soil moisture. Our findings suggest that the precipitation intensity and temporal distribution had important impacts on soil N mineralization in the Inner Mongolia grassland; these effects was site-dependent and particularly related to soil texture, community composition, and disturbance, and other factors.     

滇南喀斯特地区不同季节土壤和灌木叶片化学计量特征及对水分添加的响应

干旱是影响南方喀斯特地区植物生长的重要限制因子, 气候变化会影响该地区的降水量和分布格局。研究该地区土壤和植物化学计量特征及其水分响应格局, 具有重要意义。自2017年4月开始, 在云南建水喀斯特植物群落进行加水试验, 2018年4月(旱季)和8月(雨季)分别采集土壤和优势灌木鞍叶羊蹄甲(Bauhinia brachycarpa)和假虎刺(Carissa spinarum)叶片样品, 测定碳、氢、氮、磷、硫、钾、钙、镁、铝、钠、铁、锰、锌、铜14种元素含量。结果表明, 水分添加影响了表层土壤中碳、氮、钠的含量, 相比于旱季, 雨季土壤中钠和硫含量明显减少, 其余土壤元素在水分添加和季节变化下并未表现出明显差异。土壤水分含量的增加使得鞍叶羊蹄甲和假虎刺叶片中钾含量下降, 钙含量上升。在水分条件变化下, 两种植物叶元素含量的稳定性与植物中元素的含量有关, 含量越接近极大值(基本元素碳、氢、氮等)或极小值(微量元素铜、锌等)的元素其变异系数越小(越稳定), 两种植物中含量接近于1 mg·g^-1的元素磷、硫、镁的变异系数最高。在土壤水分条件变化下, 假虎刺中碳、氮、磷等大量元素含量的稳定性显著高于鞍叶羊蹄甲。降水变化和水分添加导致的土壤水分变化, 对滇南喀斯特地区土壤和植物中不同元素含量的影响不同, 这些结果将为该地区的土壤、植被修复和管理提供科学参考。     

Main factors driving changes in soil respiration under altering precipitation regimes and the controlling processes

Aims Our objective was to determine the effects of changes in global pattern of precipitation on soil respiration and the controlling factors. Methods Data were collected from literature on precipitation manipulation experiments globally and a meta-analysis was conducted to synthesize the responses of soil respiration to changes in precipitation regimes. Important findings We found that an increased precipitation stimulated soil respiration while a decreased precipitation suppressed it. When changes in rainfall were normalized to the average treatment level (41% of the current annual precipitation), the level of increases in soil respiration with increased precipitation (49%) were higher than that of decreases with decreased precipitation (21%), showing an asymmetric responses of soil respiration to increases and decreases in precipitation. Soil moisture occurred as the most predominant factor driving the changes in soil respiration under altered precipitation. Changes in soil moisture affected soil respiration directly and indiscreetly by changing aboveground/belowground net primary productivity and microbial biomass carbon, which collectively contributed 98% of variations in soil respiration. In addition, the responses of soil respiration to altered precipitation varied with background temperature and precipitation. The sensitivity of soil respiration increased with local mean annual temperature when precipitation was reduced, while remaining unchanged when precipitation was increased. Meanwhile, the sensitivity of soil respiration to either increases or decreases in precipitation decreased with increasing local mean annual precipitation. Under future altered precipitation regimes, the sensitivity of soil respiration to changes in precipitation is likely dependent of local environment conditions.     

Characteristics of soil water distribution and evaluation of recharge rate under different grazing history in the Xilin Gol Steppe

由人类活动所导致的锡林郭勒草原草场退化、土地沙化等问题日趋严重, 区域土壤水资源评价及其科学管理显得尤为重要。为确定锡林郭勒典型草原不同放牧条件对深层土壤剖面水分动态及降水入渗补给的影响, 选取1979年以来禁牧(UG79)、1999年以来禁牧(UG99)和持续放牧(CG) 3个小区6个土壤剖面, 基于不同深度土层的质量含水量、Cl ^-浓度等数据, 分析了放牧对深层土壤水分特征的影响, 且利用氯质量平衡法估算了降水入渗补给量。结果表明: 1)禁牧可以提高土壤含水量, 且禁牧时间越长, 效果越显著, 尤以表层最为明显。整个土壤剖面(0-5 m)土壤质量含水量的平均值表现为UG79 > UG99 > CG, 但各处理间差异不显著; 0-2 m UG79处理土壤剖面质量含水量分别比UG99和CG处理高26.6%和33.7%, 储水量分别高87.19 mm和82.52 mm, 且UG79处理与UG99、CG差异显著, 但UG99与CG之间差异不显著; 除局部地区受土壤颗粒组成影响含水量不同外, 各处理2-5 m土层含水量和储水量差异较小; 2)不同处理土壤含水量影响因素不同, 0-2 m土层含水量主要受地表植被状况和土壤性质的综合影响, 而2-5 m土层则主要受土壤颗粒组成的影响, 但随着禁牧年限的增加, 土壤有机质(SOM)含量对土壤水分的影响越来越大。UG79整个土壤剖面含水量与土壤颗粒含量和SOM含量呈极显著相关关系, UG99与CG处理0-2 m含水量与SOM含量呈极显著相关关系, 2-5 m土壤含水量与土壤颗粒含量呈极显著相关关系, 而与SOM含量相关性不显著; 3)氯质量平衡法估算得出年降水入渗补给率为UG79 > UG99 > CG, 35年和15年禁牧分别将降水入渗补给率提高了130.2%和44.5%; 考虑干沉降的不确定性, 研究区年降水入渗补给率为1.95-7.61 mm·a ^-1, 仅占年降水量的0.55%-2.13%。总之, 禁牧能够增加土壤含水量和储水量, 增加降水对土壤水分的补给, 但降水不是该区地下水的主要补给源。     

Water sources of Populus euphratica and Tamarix ramosissima in Ejina Delta,the lower reaches of the Heihe River,China

Aims We aim to evaluate the water sources of typical riparian arbor species (Populus euphratica) and shrub species (Tamarix ramosissima), and analyze the spatial and temporal dynamics of plant water source in Ejina Delta, the lower reaches of the Heihe River, China.Methods Eight sampling sites were selected in the riparian zones along the East River and West River in Ejina. The plant xylem water, soil moisture, rainwater, stream water and groundwater were taken and pretreated during the growing season in 2015-2016, and the stable oxygen isotope ratio (δ¹⁸O) for each water sample was measured. The δ¹⁸O of plant xylem water and soil moisture were compared to estimate the dominant depth of root water uptake, and the linear-mixed model called “IsoSource” were applied to determine plant water sources and quantify their proportions.Important findings This study indicated that the main recharge sources for P. euphratica and T. ramosissima were stream water and groundwater. The contributions of rain water to them was negligible due to the limited amount and the shallow infiltration depth of local rainfall. As affected by groundwater level fluctuation, soil physical properties, as well as lateral and vertical recharge of stream water on soil moisture, the dominant depth of root water uptake spatially varied. However, the relative contributions of stream water or groundwater to plant water sources did not change significantly across space. Populus euphratica used more stream water (68%), while T. ramosissima used more groundwater (65%). Plant water sources were sensitive to environmental flow controls. The contributions of stream water to the water sources of the two species went up to 84% and 48% for P. euphratica and T. ramosissima respectively during the discharge period, but dropped to 63% and 30% during the non-discharge period. On the other hand, the contributions of groundwater decreased to 16% and 52% during the discharge period, but increased to 37% and 70% during non-discharge period. It is noteworthy that the high similarity of δ¹⁸O between stream water and groundwater due to extensive water exchange in the riparian zone made increase the uncertain in quantifying plant water sources.     

Response of fine roots to precipitation change: A meta-analysis

细根对土壤水分含量变化十分敏感, 增加和减少降水直接影响土壤水分含量。为探索细根对降水变化的响应, 该文从48篇已发表的国内外研究论文中搜集到202组数据, 通过meta分析的方法揭示细根生物量、生产量、周转率、根长度密度、比根长及细根分解对增加和减少降水的一般响应规律, 用加权响应比评价降水对细根各指标的影响效应, 降水变化对细根分解的影响用土壤微生物生物量碳的响应比衡量。结果表明: 1)不同类型植物的细根对降水变化的响应程度不同, 灌木细根的响应强于乔木。2)细根各指标对降水变化的响应存在土层空间异质性, 并且降水变化量为50%时细根响应最显著。降水增加50%时, 显著增加20-40 cm土层的细根生物量和0-10 cm土层的细根比根长, 降水减少50%时, 显著减少20-40 cm土层的细根生产量和增加0-10 cm土层的细根根长度密度。3)降水变化实验持续时间的长短会影响细根的响应程度, 短期实验中细根通过形态适应对降水变化做出应对, 而长期实验中细根通过重新分配生物量对降水变化做出响应。4)增加降水促进了细根养分归还, 致使土壤微生物得到了充足的底物资源, 提高了自身活性, 使细根分解加快。     

Correlation between vein density and water use efficiency of Salix matsudana in Zhangye Wetland,China

Aims The correlation between vein density and water use efficiency (WUE) affects the balance between water supply and demand of plant leaves, which is significant for comprehending the ecological adaptation strategies of plants. The objective of this study was to study how Salix matsudana modulated vein density and WUE along a soil moisture gradient in Zhangye Wetland, China. Methods The study was conducted in floodplain wetland near Heihe River in Zhangye City, Gansu Province, China. Three sample plots, at a spatial interval of 70 m, were set up along a soil moisture gradient ordinally from the area near the water body to the wetland edge, plot I (69.23%), spot II (48.38%) and spot III (35.27%). Community traits were investigated by using diagonal method, and all individuals of S. matsudana were used for measurements of height and canopy. At each plot, 5 individuals of S. matsudana at 4 vertices and diagonal intersection were selected for measurements of vein density, WUE, net photosynthetic rate (P_n), transpiration rate (T_r), photosynthetically active radiation (PAR), saturated vapor pressure differences (VPD), specific leaf area, stomatal conductance (G_s) and intercellular CO₂ concentration (C_i). We used mathematical methods of correlation analysis and standardized major axis to investigate relationships between vein density and WUE. Important findings With decreasing soil moisture, the height, canopy, specific leaf area, G_s and C_i of S. matsudana decreased gradually, while the vein density, WUE, P_n, T_r, PAR and VPD increased gradually. The correlation between vein density and WUE was positive in all the three plots, but the relationship varied along the soil moisture plots gradient. There was a highly significant positive correlation (p < 0.01) between the vein density and WUE at plot I and III, whereas the correlation only reached a significant level (p < 0.05) at plot II; The correlation coefficient between vein density and WUE is significantly smaller than 1 at plot I (p < 0.05), while the correlation coefficient is significant greater than 1 at plot II and III (p < 0.05). We can conclude that varied relationships between vein density and WUE of S. matsudana along a soil moisture gradient could reflect plant acclimation.     

Plant species change and water budget in restored grasslands in Taibus Banner,Inner Mongolia,China

2008年和2009年(均为枯水年), 在半干旱区内蒙古太仆寺旗农田-草地生态系统国家野外站开展观测实验, 通过观测蒸散发(波文比系统)、土壤水分(烘干称重法)、降水量, 以及植被土壤特征调查, 基于水量平衡理论, 对比研究了3块天然草地、3块不同退耕时间草地共6个样地的水分收支, 旨在定量地评估退耕草地的水分收支, 为采取科学措施促进退耕草地尽快向天然草地过渡提供依据。结果表明: 1)随着退耕时间增加, 植被盖度逐渐增加, 但是群落中科、属、种的数量趋于减少, 且优势种从一年生的中旱生草本植物逐渐转变成多年生的旱生草本植物; 2)植被蒸腾是草原植被主要的耗水途径, 随着退耕时间增加, 退耕草地的蒸散发量呈增加趋势, 其最大值在4.5-5.8 mm·d^-1之间; 3)退耕草地土壤含水量平均值为0.09 m³·m^-3, 其水分剧烈变化主要发生在距地 表60 cm内, 且随退耕时间增加土壤含水量减少, 而天然草地土壤含水量平均值为0.06 m³·m^-3, 其水分剧烈变化发生在距地 表20 cm内; 4)随退耕时间增加, 退耕草地与天然草地的土壤水分与蒸散发在数值上差距逐渐缩小; 5)退耕草地水分收支基本平衡, 但在极枯年份(降水量174 mm)的生长季, 降水不能满足蒸散发需求, 呈现水分亏损。退耕草地逐步向天然草地过渡, 但是退耕草地的土壤水分在逐渐减少, 呈现“生境干旱化现象”。今后应加强对草地的封育与监测, 促进植物群落向水分利用效率更高、更适应半干旱环境的方向演替。     

Water-use process of two desert shrubs along a precipitation gradient in Horqin Sandy Land

Aims The determination of the source of plant water is an important research on the plant-water relationship in arid and semiarid regions and helps to understand the adaptation strategy of desert species to the dry environment. Plant water use pattern affects plant community composition and ecosystem water budget. This study aims to investigate the water use patterns of Caragana microphylla and Artemisia halodendron, two typical shrub species, under altered rainfall conditions in Horqin Sandy Land. Methods Water treatments include ambient rainfall (natural rainfall), 50% increase in rainfall (enhanced rainfall) and 50% decrease in rainfall (reduced rainfall) by artificially intercepting and redistributing natural rainfall. Stable hydrogen and oxygen isotope ratios (δD and δ¹⁸O) were measured for xylem water, rainfall, and soil water in different soil layers (0-120 cm depth). The possible ranges of potential water sources used by C. microphylla and A. halodendron were calculated using the IsoSource model. Important findings 1) Alteration of ambient rainfall mainly affected the soil water condition in the shallow soil (0-30 cm). Increase in rainfall significantly increased the above- and below-ground biomass, and δ¹⁸O values of soil water declined with soil depth. 2) Under the enhanced rainfall treatment, A. halodendron mainly used the soil water in the shallow soil (0-40 cm) and C. microphylla was able to extract water from multiple soil layers. Under the reduced rainfall treatment, both species increasingly relied on extracting water from deeper soil layers, 60-80 cm for A. halodendron and 60-120 cm for C. microphylla. 3) For the natural rainfall treatment, in the wet season, the upper soil water was recharged by rainfall, C. microphylla and A. halodendron extract the shallow soil water (0-60 cm). However, in the dry season, soil water content was dramatically reduced, and main water sources for C. microphylla shifted from topsoil to deeper soil, and A. halodendron can use multiple layers of soil water. In summary, A. halodendron is more capable of exploring deeper soil moisture under reduced rainfall in comparison with C. microphylla, and is likely to be more adaptive to this water-limiting desert environment.     

水分和养分添加对羊草功能性状和地上生物量的影响

研究水分和养分添加对植物功能性状的影响, 对于揭示植物对环境变化的响应和适应规律至关重要。该文采用盆栽试验的方法, 进行不同水平水分处理(增水50%, 减水50%, 以498 mm降水量作为对照)和养分添加(无养分添加, 单施氮肥, 单施磷肥, 氮磷共施), 研究羊草(Leymus chinensis)的10种功能性状和地上生物量对水分和养分添加的响应。得出以下结论: (1)双因素方差分析结果表明, 水分主效应对羊草株高、分蘖数、茎生物量、叶生物量、叶面积、叶质量、净光合速率、蒸腾速率、水分利用效率存在显著影响; 养分主效应对羊草分蘖数、茎生物量、净光合速率、蒸腾速率、水分利用效率存在显著影响; 水分和养分的交互作用对羊草分蘖数、茎生物量、蒸腾速率、水分利用效率存在显著影响。(2)各功能性状对降水量的响应在不同养分添加水平是不同的, 分蘖数和叶面积在单施氮肥和氮磷共施条件下随降水量增加而增加, 而在无养分添加和单施磷肥条件下无显著变化; 茎生物量在无养分添加、单施氮肥和单施磷肥条件下随降水量增加而增加, 而在氮磷共施条件下无增加趋势; 比叶面积在单施氮肥条件下增水处理显著低于对照组, 而在其他养分添加条件下无明显变化。(3)短期氮磷处理显著影响羊草叶片光合生理性状, 而对叶形态性状影响不显著。(4)羊草地上生物量随降水量的增加呈现上升趋势, 并且在单施氮肥条件下, 增水处理使地上生物量达到最高, 为522.55 g·m ^-2。总之, 羊草的功能性状对降水量增加表现出明显的响应, 响应格局在不同养分条件下不同, 反映了其对水肥环境变化的适应。     

Responses of soil respiration with biocrust cover to water and temperature in the southeastern edge of Tengger Desert,Northwest China

Aims Soil respiration of the lands covered by biocrusts is an important component in the carbon cycle of arid, semi-arid and dry-subhumid ecosystems (drylands hereafter), and one of the key processes in the carbon cycle of drylands. However, the responses of the rate of soil respiration with biocrusts to water and temperature are uncertain in the investigations of the effects of experimental warming and precipitation patterns on CO₂ fluxes in biocrust dominated ecosystems. The objectives of this study were to investigate the relationships of carbon release from the biocrust-soil systems with water and temperature in drylands. Methods Intact soil columns with two types of biocrusts, including moss and algae-lichen crusts, were collected in a natural vegetation area in the southeastern fringe of the Tengger Desert. Open top chambers were used to simulate climate warming, and the soil respiration rate was measured under warming and non-warming treatments using an automated soil respiration system (LI-8150). Important findings Over the whole observational period (from April 2016 to July 2016), soil respiration rates varied from -0.16 to 4.69 μmol·m^-2·s^-1 for the moss crust-covered soils and from -0.21 to 5.72 μmol·m^-2·s^-1 for the algae-lichen crust-covered soils, respectively, under different rainfall events (the precipitations between 0.3-30.0 mm). The mean soil respiration rate of the moss crust-covered soils is 1.09 μmol·m^-2·s^-1, which is higher than that of the algae-lichen crust-covered soils of 0.94 μmol·m^-2·s^-1. The soil respiration rate of the two types of biocrust-covered soils showed different dynamics and spatial heterogeneities with rainfall events, and were positively correlated with precipitation. The mean soil respiration rate of the biocrust-covered soils without warming was 1.24 μmol·m^-2·s^-1, significantly higher than that with warming treatments of 0.79 μmol·m^-2·s^-1 (p < 0.05). By increasing the evaporation of soil moisture, the simulated warming impeded soil respiration. In most cases, soil temperature and soil respiration rate displayed a similar single-peak curve during the diel cycle. Our results show an approximately two hours’ lag between soil temperature at 5 cm depth and the soil respiration rate of the biocrust-covered soils during the diel cycle.     

土石山区不同植物土壤水分利用方式对降雨的响应特征

植物的水分利用特征对浅层土石山区的植被恢复具有重要意义.本研究利用稳定同位素技术,通过采集降雨后丹江鹦鹉沟小流域侧柏和玉米的植物样及其植物根系周围的土壤样品,分析其氧稳定同位素特征,研究土石山区侧柏和玉米两种不同植物的土壤水分利用方式对降雨的响应特征.结果表明: 侧柏和玉米的土壤水分利用方式对降雨存在不同的响应特征.侧柏根系主要利用10～30 cm土层的土壤水分,而玉米主要利用0～20 cm土层的土壤水分.降雨量由29 mm减少至8 mm时,侧柏根系的主要吸水深度由20～30 cm减小到10～20 cm,玉米根系的主要吸水深度由10～20 cm转换为0～20 cm.降雨减少时,侧柏根系吸水的主要深度均由深层土壤向浅层土壤移动,而玉米的主要吸水深度由10～20 cm增加为0～20 cm.侧柏和玉米根系的土壤水分利用方式对降雨的响应特征较为明显.     

Effect of precipitation variability on net primary production and soil respiration in a Chihuahuan Desert grassland

Precipitation regimes are predicted to become more variable with more extreme rainfall events punctuated by longer intervening dry periods. Water‐limited ecosystems are likely to be highly responsive to altered precipitation regimes. The bucket model predicts that increased precipitation variability will reduce soil moisture stress and increase primary productivity and soil respiration in aridland ecosystems. To test this hypothesis, we experimentally altered the size and frequency of precipitation events during the summer monsoon (July through September) in 2007 and 2008 in a northern Chihuahuan Desert grassland in central New Mexico, USA. Treatments included (1) ambient rain, (2) ambient rain plus one 20 mm rain event each month, and (3) ambient rain plus four 5 mm rain events each month. Throughout two monsoon seasons, we measured soil temperature, soil moisture content (θ), soil respiration (R_s), along with leaf‐level photosynthesis (A_net), predawn leaf water potential (Ψ_pd), and seasonal aboveground net primary productivity (ANPP) of the dominant C₄ grass, Bouteloua eriopoda. Treatment plots receiving a single large rainfall event each month maintained significantly higher seasonal soil θ which corresponded with a significant increase in R_s and ANPP of B. eriopoda when compared with plots receiving multiple small events. Because the strength of these patterns differed between years, we propose a modification of the bucket model in which both the mean and variance of soil water change as a consequence of interannual variability from 1 year to the next. Our results demonstrate that aridland ecosystems are highly sensitive to increased precipitation variability, and that more extreme precipitation events will likely have a positive impact on some aridland ecosystem processes important for the carbon cycle.