Precipitation Pulses and Soil CO_2 Emission in Desert Shrubland of Artemisia ordosica on the Ordos Plateau of Inner Mongolia,China

Precipitation is the major driver of ecosystem functions and processes in semiarid and arid regions. In such waterlimited ecosystems, pulsed water inputs directly control the belowground processes through a series of soil drying and rewetting cycles. To investigate the effects of sporadic addition of water on soil CO2 effux, an artificial precipitation event （3 mm） was applied to a desert shrub ecosystem in the Mu Us Sand Land of the Ordos Plateau in China. Soil respiration rate increased 2.8 4.1 times immediately after adding water in the field, and then it returned to background level within 48 h. During the experiment, soil CO2 production was between 2 047.0 and 7 383.0 mg m^-2. In the shrubland, soil respiration responses showed spatial variations, having stronger pulse effects beneath the shrubs than in the interplant spaces. The spatial variation of the soil respiration responses was closely related with the heterogeneity of soil substrate availability. Apart from precipitation, soil organic carbon and total nitrogen pool were also identified as determinants of soil CO2 loss in desert ecosystems.

Seasonal Patterns of Soil Respiration in Three Types of Communities along Grass-Desert Shrub Transition in Inner Mongolia, China

The seasonal dynamics of soil respiration in steppe （S. bungeana）, desert shrub （A. ordosica）, and shrubperennial （A. ordosica ＋C. komarovii） communities were investigated during the growth season （May to October） in 2006; their environmental driving factors were also analyzed. In the three communities, soil respiration showed similar characteristics in their growth seasons, with peak respiration values in July and August owing to suitable temperature and soil moisture conditions during this period. Meanwhile, changes in soil respiration were greatly influenced by temperatures and surface soil moistures. Soil water content at a depth of 0 to 10 cm was identified as the key environmental factor affecting the variation in soil respiration in the steppe. In contrast, in desert shrub and shrub-perennial communities, the dynamics of soil respiration was significantly influenced by air temperature. Similarly, the various responses of soil respiration to environmental factors may be attributed to the different soil textures and distribution patterns of plant roots. In desert ecosystems, precipitation results in soil respiration pulses. Soil carbon dioxide （CO2） effluxes greatly increased after rainfall rewetting in all of the ecosystems under study. However, the precipitation pulse effect differed across the ecosystem. We propose that this may be a result of a reverse effect from the soil texture.

Drought Resistance of Twelve Desert Shrubs at Seedling Stage of Ulan Buh Desert Ecosystem

[Objective] To establish drought resistance evaluation index system of desert shrubs,and provide scientific support for selecting quality tree species.[Method] Taking 2-year-old seedlings of 12 desert shrubs in Ulan Buh Desert ecosystem as the test materials,7 water physiological indexes were tested,principal component analysis and cluster analysis were applied to explore drought resistance of the shrubs.[Results](a) Water potential of Ephedra distachya Linn.,Nitraia tangutorum Bobr.,Caragana korshinski Kom.was lower than that of the other 9 species;bound water content(V_a) and bound water/free water ratio(V_a/V_s) of Zygophyl um xanthoxylon Maxim.was 64.20% and 3.3,higher than the others';transpiration rate of Atraphaxis bracteata A.Los.,Nitraia tangutorum Bobr.and Tamarix elongata Ldb.was significantly lower than the others';constant weight time of Haloxylon ammodendron(C.A.Mey.) Bunge and Ephedra distachya Linn.was the longest(144 h);residual moisture content of Ammopiptanthus mongolicus Maxim.was the highest(44.80%).(b) Water potential,bound water/free water(V_a/V_s),residual moisture content,bound water,constant weight time,and transpiration rate had great impact on drought resistance of plant,and the accumulative variance contribution rate achieved 87.59%.[Conclusion] According to the drought resistance,the 12 species were classified into 3 categories,namely shrubs with strong drought resistance(Ephedra distachya Linn.),shrubs with moderate drought resistance(Haloxylon ammodendron(C.A.Mey.) Bunge,Nitraia tangutorum Bobr.,and Zygophyllum xanthoxylon Maxim.);shrubs with poor drought resistance(Hedysarunn scoparium Fisch,Hedysarum mongolicum Turcz.,Tamarix elongata Ldb.,Caragana korshinskii Kom.,Ammopiptanthus mongolicus Maxim.,Atraphaxis bracteata A.Los.,Cal igonum mongolicum Mattei.,and Caragana microphylla Lam.).

Liquefaction and FTIR analysis of two desert shrubs Salix psammophila and Caragana intermedia

In order to extend the investigation of the characteristics of desert shrub liquefaction and the structure of liquefied desert shrubs, we studied the liquefaction of Salixpsammophila and Caragana intermedia in the presence of phenol and used FTIR analysis on unliquefied and liquefied S. psammophila and C. intermedia. The results showed that the liquefaction effects are enhanced with an increase in temperature, catalyst content and liquid ratio. FTIR analysis proved that more active functional groups appeared after S. psammophila and C. intermedia were liquefied in the presence of phenol. These results can provide a theoretical basis for the further utilization of liquefied S. psammophila and C. intermedia and the development of desert shrubs in a new utilization field.

Rainfall partitioning by desert shrubs in arid regions

We measured the rainfall partitioning among throughfall, stemflow, and interception by desert shrubs in an arid region of China, and analyzed the influence of rainfall and canopy characteristics on this partitioning and its ecohydrological effects. The percent-ages of total rainfall accounted for by throughfall, stemflow, and interception ranged from 78.85±2.78 percent to 86.29±5.07 per-cent, from 5.50±3.73 percent to 8.47±4.19 percent, and from 7.54±2.36 percent to 15.95±4.70 percent, respectively, for the four shrubs in our study (Haloxylon ammodendron, Elaeagnus angustifolia, Tamarix ramosissima, and Nitraria sphaerocarpa). Rain-fall was significantly linearly correlated with throughfall, stemflow, and interception (P < 0.0001). The throughfall, stemflow, and interception percentages were logarithmically related to total rainfall (P < 0.01), but were quadratically related to the maximum 1-hour rainfall intensity (P < 0.01). The throughfall and stemflow percentages increased significantly with increasing values of the rainfall characteristics, whereas the interception percentage generally decreased (except for average wind speed, air temperature, and canopy evaporation). Regression analysis suggested that the stemflow percentage increased significantly with increasing crown length, number of branches, and branch angle (R2 = 0.92, P < 0.001). The interception percentage increased significantly with increasing LAI (leaf area index) and crown length, but decreased with increasing branch angle (R2 = 0.96, P < 0.001). The mean funnelling percentages for the four shrubs ranged from 30.27±4.86 percent to 164.37±6.41 percent of the bulk precipitation. Much of the precipitation was funnelled toward the basal area of the stem, confirming that shrub stemflow conserved in deep soil layers may be an available moisture source to support plant survival and growth under arid conditions.

Effects of shrubs and precipitation on spatial-temporal variability of soil temperature in microhabitats induced by desert shrubs

Soil temperatures at 0, 5, 10 and 20 cm depths were monitored cominuously at different microhabitats （beneath shrub canopy （BSC）; bare intershrub spaces （BIS）） induced by xerophytic shrub （Caragana korshinskii Kom.） canopy, respectively. We mainly aimed to assess the effects of shrub canopy and precipitation on the spatial-temporal variability of soil temperature. Results indi- cate that both precipitation and vegetation canopy significantly affect soil temperature. In clear days, soil temperatures within the BSC area were significantly lower than in the BIS at the same soil depth due to shading effects of shrub canopy. Diurnal variations of soil temperature show a unimoclal sinusoidal curve. The amplitude of soil temperature tended to decrease and a hysteresis of di- urnal maximum soil temperature existed at deeper soil layers. Vertical fluctuations of soil temperature displayed four typical curves. In the nighttime （approximately from sunset to sunrise）, surface temperature within the BSC area was higher than in the BIS. In rainy days, however, soil temperatures were affected mainly by precipitation and the shrub canopy had a negligible effect on soil temperature, and little difference in soil temperature at the same soil depth was found between the BSC area and in the BIS. Diurnal variations in soil temperature decreased exclusively as rainfall continued and the vertical fluctuations of soil tempera~＇e show an increased tendency with increasing soil depth.

Advanced studies on adaptation of desert shrubs to environmental stress

The combined stress of drought, high temperature and excessive light characterizes the desert area. In order to survive the desert habitat, desert shrubs have evolved a number of special eco-physiological mechanisms to resist environmental stress during long-term evolution. In this paper, adaptation mechanisms of desert shrubs to environmental stress are reviewed in terms of morphological structure, water potential, photosynthesis and water use efficiency, transpiration and stomatal conductance, osmotic adjustment and anti-oxidation protection. In addition, some suggestions for future research are proposed.

Root distribution of three dominant desert shrubs and their water uptake dynamics

Aims Root architecture is a crucial determinant in the water use of desert shrubs.However,lack of integrated research on the root functional type and water uptake dynamic hinders our current understanding of the water-use strategies of desert species.Methods A field experiment was conducted to investigate the root functional type of three dominant desert species,Haloxylon ammodendron,Nitraria tangutorum and Calligonum mongolicum,and the dynam-ics of their root water uptake.the stem sap flow and microclimate were monitored,and the intact root systems of these shrubs were excavated in their native habitats on the oasis-desert ecotone of northwestern china during the summer of 2014.Important Findings Based on root functional type,H.ammodendron is phreatophytic,while N.tangutorum and C.mongolicum are non-phreatophytic species,which means H.ammodendron can utilize multiple potential water sources,N.tangutorum and C.mongolicum mainly utilize shallow and middle soil water.the average root water uptake rates(RWU)of H.ammodendron,N.tangutorum and C.mongolicum were 0.56(±0.12),1.18(±0.19)and 1.31(±0.30)kg m^(−2)h^(−1),respectively,during the experimental period;the contributions of night-time RWU to total water uptake amount for the corresponding species were 12.7,2.9 and 10.6%,respec-tively.the diurnal and seasonal dynamics of RWU in the three species were significantly different(P<0.05),and closely related to environmental variables,especially to photosynthetically active radiation and vapor pressure deficit.Our results suggested that the three species have distinct water-use patterns in combination with the patterns of root distribution,which may alleviate water competition during long-term water shortages.H.ammodendron appears to be more drought tolerant than the other species due to its use of multiple water sources and stable water uptake rates during growing season.

Resorptions of 10 mineral elements in leaves of desert shrubs and their contrasting responses to aridity

Aims We aim to investigate variations in the resorption efficiencies of 10 mineral nutrients[i.e.nitrogen(N),phosphorus(P),potassium(K),magnesium(Mg),calcium(Ca),manganese(Mn),zinc(Zn),alu-minum(Al),iron(Fe)and copper(Cu)]in leaves of desert shrubs and to explore effects of aridity on resorption efficiency of these nutrients.Methods Plant samples were collected from 10 sites in northern Xinjiang Uygur Autonomous Region of China.Samples of green and senesced leaves were analysed to determine concentrations of N,P,K,Mg,Ca,Mn,Zn,Al,Fe and Cu and thus the nutrient resorption efficiency.Important Findings The mean nutrient concentrations in the desert shrubs varied,with the stoichiometric ratio Ca:N(19.3 mg g−1):K(10.5 mg g−1):Mg:P(1.01 mg g−1):Al:Fe:Mn:Zn:Cu(4.78 mg kg−1)=4038:2950:2199:1816:211:37:32:11:2:1 in green leaves;and Ca:N(12.6 mg g−1):Mg:K(7.6 mg g−1):P(0.56 mg g−1):Fe:Al:Mn:Zn:Cu(2.85 mg kg−1)=5583:3710:2943:2523:178:133:119:19:3.7:1 in senesced leaves.Resorption generally occurred for six elements(N,P,K,Cu,Mg and Mn,with average resorption efficiency 47.8%,52.0%,38.6%,41.0%,12.7%and 7.89%,respectively)during leaf senescence,while the other four nutrients tended to accumulate in senesced leaves,showing averagely negative resorption efficiencies[Ca(-3.87%),Al(−57.1%),Zn(−62.6%),Fe(−89.6%)].Aridity showed strikingly different effects on the resorption process of the 10 nutri-ents.Of the four elements with totally(N/P/K)or mostly(Cu)posi-tive observations of resorption efficiency,their resorption generally decreased with aridity,suggesting that drought stress had negative effects on the resorption efficiencies of these elements.In contrast,with at least one-third observations of resorption efficiency being negative,the other elements(Mg/Mn/Ca/Zn/Al/Fe)showed gener-ally increasing resorptive tendency with aridity,except for Zn.This research provided a systematic analysis on the large variation and contrasting responses of the resorption of multi-elements to aridity in typical desert shrubs.Our findings foster the understanding of nutrient resorption patterns of desert plants and enable us to better predict the contrastive effects of drought stress on the cycling of diverse nutrients and the consequent stoichiometric decoupling in plants of desert ecosystems.

The effects of the identity of shrub species on the distribution and diversity of ground arthropods in a sandy desert ecosystem of northwestern China

Shrub is an important factor on structuring ground arthropod communities in desert ecosystems. In this study, in order to determine how shrubs and their species influence ground arthropod distribution patterns in a sandy desert scrubland dominated by two different shrub species, Calligonum mongolicum and Nitraria sphaerocarpa, the ground arthropods were sampled with pitfall traps during spring, summer and autumn. At the community level, total arthropod abundance was shown to be significantly higher under shrubs than in intershrub bare areas in spring; similar patterns occurred in terms of the richness of arthropod groups in the spring and over three seasons, suggesting season-specific shrub presence effects on arthropod activity. In addition, more arthropods were found under N. sphaerocarpa shrubs than under C. rnongolicum shrubs in autumn, suggesting season-specific effects of shrub species of arthropod activity, whereas more arthropods taxa were captured under C. mongoIicum than N. sphaerocarpa. At the trophic group level, the abundances of predator and herbivore arthropods were significantly greater under shrubs than in intershrub bare habitats, whereas herbivore arthropods were more abundant under N. sphaerocarpa than C. rnongolicum, and an opposite rule was detected for predator arthropods At the family level, the mean abundances of Carabidae, Curculionidae, Gnaphosidae and Lycosidae were significantly higher in the shrub microhabitats than in the intershrub bare habitat, there was no significant difference between habitats on the mean abundances of Formicidae and Tenebrionidae. The study results suggested that shrub presence and shrub species variation are important determinants of ground arthropod assemblages in this desert ecosystem, but the responses of ar- thropods differed among trophic and taxonomic groups.

荒漠草原灌丛转变过程土壤水分亏缺空间特征及影响因素

草地灌丛化对生态系统结构、功能与服务产生重要影响,目前已经认识到其对土壤水分的负面影响,但还缺乏其在区域尺度的定量评价及其驱动机制研究。在宁夏荒漠草原选取43块成对样地(即荒漠草地和灌丛地),引入样地土壤水分相对亏缺指数(PCSWDI)评价荒漠草原向灌丛转变后土壤水分亏缺空间格局现状及其驱动因子。结果表明:荒漠草原转变为灌丛后0~100 cm和100~200 cm土壤含水量分别显著下降了27.80%和57.92%,0~100 cm灌丛地的PCSWDI显著低于荒漠草地,表明0~100 cm灌丛地目前不存在土壤水分亏缺现象。地统计学分析表明,荒漠草地和灌丛地的0~100 cm土壤水分相对亏缺指数的结构方差比分别为94.73%和95.29%,均属于强空间自相关,主要受结构性因子控制。此外,地理探测器的因子探测发现0~100 cm土壤储水量、坡向和田间持水量是影响灌丛地土壤水分相对亏缺指数的主导因子;交互探测表明,灌丛地0~100 cm土壤水分相对亏缺指数空间分异是多因子共同作用的结果。尽管分析得到0~100 cm灌丛地不存在土壤水分亏缺,但100~200 cm土壤含水量显著下降已经预示了深层土壤水分的消耗。因此,干旱半干旱地区的植被恢复必须考虑其植被承载力和水分阈值,基于自然的解决方案可能是未来植被恢复的主流思路。

昆仑山北坡两种优势荒漠灌木的生物量预测模型

构建数学模型是估算灌木生物量的重要方法之一。本研究以中昆仑山北坡山前荒漠带常见的两种荒漠灌木红砂(Reaumuria soongarica)和合头草(Sympegma regelii)为研究对象。采用全株收获法采集植株,分别以株高(H)、冠幅面积(S)、植株体积(V)为自变量,植株地上生物量(W_(1))、地下生物量(W_(2))、全株生物量(W_(3))为因变量,建立函数模型,选取决定系数(R^(2))、估计标准差(SEE)、回归检验显著水平(P值)为评价指标,以P<0.001为前提,选取R^(2)尽量大、SEE尽量小的模型为红砂和合头草生物量最优预测模型。结果显示:红砂和合头草的生物量最优预测模型均为二次函数模型,合头草全株最优预测模型为一次函数模型除外。红砂植株体积(V)与生物量的相关性最高,生物量最优预测模型R^(2)为0.820~0.920。合头草冠幅面积(S)与生物量相关性最高,生物量最优预测模型R^(2)为0.935~0.973。红砂和合头草生物量最优预测模型均通过(P<0.001)显著性检验,拟合率在84.1%~95.6%之间,可用于生物量估算,本研究为预测荒漠生态系统碳储量和评价碳汇潜力提供科学依据。

温带荒漠灌丛和藓类结皮对土壤养分的贡献

灌丛与生物土壤结皮镶嵌分布是温带荒漠常见的地表景观之一,二者的发育均显著影响了地表土壤养分的空间分布特征及循环过程。然而,灌丛和生物土壤结皮对荒漠土壤表层养分的影响存在怎样的差异,二者对养分变化的贡献度如何尚不清楚。因此,选择中国北方典型温带荒漠古尔班通古特沙漠为研究区,以荒漠中的优势灌丛膜果麻黄(Ephedra przewalskii)灌丛和生物土壤结皮发育高级阶段的藓类结皮的结皮层及结皮下层土壤为研究对象,采集不同微生境(裸露地、灌丛下)的裸沙与藓类结皮的土壤样品。为探究不同微生境下不同土层碳、氮、磷和钾养分变化特征,测定了不同土层土壤有机碳(SOC)、全氮(TN)、全磷(TP)、全钾(TK)、速效氮(AN)、速效磷(AP)和速效钾(AK)含量。结果表明:(1)相较于裸露地,灌丛显著提高了藓类结皮不同土层有机碳、全氮和全钾的含量和裸沙全磷的含量,降低了灌丛下藓类结皮土壤全磷的含量。(2)对于速效养分而言,与裸沙相比,裸露地藓类结皮覆盖降低了土壤速效氮含量,增加了速效磷和速效钾含量;而灌丛下藓类结皮覆盖提高了土壤速效氮和速效钾的含量,但降低了速效磷的含量。(3)相关性分析显示,在0—2 cm土壤中速效磷与速效氮呈现显著负相关,而在2—6 cm速效磷与速效氮呈现显著正相关(P<0.01)。(4)贡献度分析表明,土壤中灌丛效应对养分的贡献(42.54%)要远大于藓类结皮的贡献(2.43%),但二者交互作用却降低了除速效氮以外的其他土壤养分含量。综上,灌丛、藓类结皮覆盖和土层深度变化对土壤碳、氮、磷和钾养分均具有显著影响(P<0.05),但三者间的交互效应对养分的影响不显著(P>0.05)。相对于裸露地,灌丛与藓类结皮的覆盖均对表层土壤碳、氮、磷和钾养分具有促进作用,且随着土层深度的下降,土壤养分含量呈现显著的下降趋势(P<0.05)。因此,在荒漠生态系统中耐旱灌丛与生物土壤结皮这两个最重要的斑块单元联合调控了微尺度土壤养分的空间异质性变化。

荒漠草原灌丛转变土壤有机碳矿化及其对降水梯度的响应

为探究灌丛引入对荒漠草原土壤有机碳稳定性的影响,选取近40年的典型草原-灌丛镶嵌体(荒漠草地,草地边缘,灌丛边缘、灌丛地)为研究对象,开展荒漠草原向灌丛人为转变过程野外原位观测结合室内培养的土壤有机碳矿化及其对降水变化(+40%、+20%、CK、-20%、-40%)的响应特征研究,主要结果如下:荒漠草原人为灌丛转变的过程中土壤有机碳、全氮和全磷含量显著降低;土壤有机碳累积矿化量、碳矿化速率、碳矿化及微生物代谢熵均随着转变过程呈上升趋势,且灌丛地较荒漠草地分别增加了26.6%、27%、25.8%和26.8%;土壤潜在可矿化有机碳量随转变波动上升,灌丛地显著高出荒漠草地31.55%;转变样地在不同降水梯度下土壤有机碳矿化速率呈下降趋势,但灌丛地、灌丛边缘土壤有机碳矿化始终高于荒漠草地和草地边缘地,其中灌丛地与灌丛边缘有机碳矿化对降水降低响应更加敏感和积极,结果表明荒漠草原向灌丛转变过程增强了土壤有机碳微生物矿化的同时,还提高了其应对干旱的能力,这种能力或许是以更高的微生物代谢熵和二氧化碳通量为代价。

载畜率对短花针茅荒漠草原灌木及其邻近土壤养分含量的影响

草地灌丛化现象在草地生态系统上广泛发生。放牧是人类利用草原的重要方式,通过分析不同载畜率下荒漠草原灌木种群及其邻近土壤养分含量的变化,可研究放牧干扰下不同灌木种群的耐牧特性,对深入了解荒漠草原植物群落演替机制具有重要意义。以荒漠草原灌木小叶锦鸡儿(Caragana microphylla)、半灌木驼绒藜(Ceratoides latens)及小半灌木冷蒿(Artemisia frigida)和木地肤(Kochia prostrata)(下称为“灌木”)为研究对象,探究不同载畜率下各个灌木种群的密度、高度、盖度及地上生物量(下称为“数量特征值”)及其邻近土壤养分含量。结果表明:冷蒿的数量特征值均随着载畜率的增加而降低,其他植物种群的数量特征值均在CK或LG区出现最大值,且不同灌木邻近土壤养分含量随着土壤深度的增加而下降(P<0.05)。不同灌木邻近土壤全氮含量随着载畜率增加而下降;冷蒿邻近有机碳含量在CK区最高,小叶锦鸡儿邻近速效磷含量在HG区最高,其余灌木邻近有机碳、速效磷含量在LG区最高。灌木种群数量特征与土壤养分的关系为:土壤有机碳与冷蒿和驼绒藜的高度、盖度、地上生物量呈正相关,土壤速效磷与木地肤高度、地上生物量呈显著负相关。因此,载畜率均会对灌木植物种群的数量特征值及其邻近土壤养分含量产生影响。

阴山北麓4种豆科荒漠灌木地上生物量及其环境解释

以阴山北麓柠条锦鸡儿(Caragana korshinskii)、垫状锦鸡儿(Caragana tibetica)、狭叶锦鸡儿(Caragana stenophylla)和刺叶柄棘豆(Oxytropis aciphylla)4种豆科荒漠植被群系及其环境因子为研究对象,采用样方调查法,揭示不同荒漠灌丛生物量变化规律及其与群落特征及土壤因子之间关系。结果表明:不同灌木群系中,建群种地上生物量受群落内植物种种间竞争以及土壤钙积层和湿土层厚度的影响,主要表现为伴生种长势越好,建群种生物量越低,并且随着湿土层厚度的增加,钙积层厚度的减少,建群种地上生物量增加。同时利用拟合函数求得柠条锦鸡儿和刺叶柄棘豆群系建群种地上生物量最佳预测模型为幂函数模型,垫状锦鸡儿、狭叶锦鸡儿群系建群种地上生物量最佳预测模型为多项式函数模型。

准噶尔荒漠两种灌木冠下土壤无机氮含量变化特征

土壤无机氮作为植物可直接吸收和利用的氮源,其含量变化反映了土壤供氮能力。大量研究表明荒漠生态系统中土壤无机氮含量受到灌木种类和空间位置的影响。然而,有关采样方向对土壤无机氮含量的影响,目前仍所知甚少。基于此,本研究以准噶尔荒漠西北缘两种广泛分布的优势灌木为对象-梭梭和里海盐爪爪,通过测定和计算两物种个体大小(大、中、小和较小个体)在4个空间位置(主根周围、冠幅中央、冠幅边缘和株间空地)和4个采样方向(东、南、西和北)上0~10 cm和10~20 cm土层中土壤铵态氮、硝态氮含量和铵硝比,分析了灌木个体大小、空间位置和采样方向主效应及其交互效应对各土层无机氮含量的影响。研究结果发现:1)梭梭和里海盐爪爪冠下土壤无机氮含量均受到个体大小主效应的影响。两物种大个体冠下硝态氮含量均显著高于较小个体,梭梭大个体冠下铵态氮含量和铵硝比最低,而里海盐爪爪大个体冠下则拥有最高的铵态氮含量和铵硝比,表明土壤无机氮含量变化存在灌木个体大小依赖性。2)两物种冠下0~10 cm土层中硝态氮和铵态氮含量都显著高于10~20 cm,意味着灌木对表层土壤无机氮的影响幅度更大。3)梭梭冠下土壤无机氮含量还受到个体大小与采样方向交互作用的影响,且在冠幅东侧和南侧存在无机氮富集特征。4)空间位置和采样方向对里海盐爪爪冠下土壤无机氮存在显著交互作用,在里海盐爪爪冠下东侧和南侧,主根周围无机氮含量普遍高于其他3个空间位置。这些结果表明荒漠生态系统中土壤无机氮的变化特征因物种而异,同时受到个体大小、空间位置和采样方向等多种因素的影响。

海东市荒漠草原柠条灌丛堆不同生长期土壤养分状况分析

为了解荒漠草原柠条灌丛堆不同生长期土壤养分状况,以海东市荒漠草原地区柠条灌丛为研究对象,在发育期、成熟期和衰退期3种不同时期下分别选择15个长势均匀、外形差异较小,但大小有区别的柠条灌丛堆,并分别测定柠条灌丛堆0~20 cm、>20~40 cm、>40~60 cm土层土壤养分及其真菌丰富度和多样性。结果表明:发育期、成熟期和衰退期柠条灌丛堆不同土层土壤pH和总磷比较无差异(P>0.05);不同生长期柠条灌丛堆不同土层土壤有机碳、总氮、速效磷和电导率存在显著差异(P<0.05);不同生长期柠条灌丛堆不同土层土壤真菌多样性比较无明显差异(P>0.05),真菌丰富度中Sobs和Chao1两项指标比较无差异(P>0.05),但成熟期柠条灌丛堆不同土层Ace均高于发育期和衰退期,发育期其次,衰退期最低(P<0.05)。不同生长期柠条灌丛土壤养分状况存在显著差异,可根据柠条灌丛堆不同生长时期土壤养分状况进行土壤结构优化,从而促进柠条生长与发育。

围栏封育对荒漠草原灌丛草地土壤优先流的影响研究

为探究围封对灌丛草地土壤优先流的影响,以宁夏吴忠市盐池县典型荒漠草原区为研究区,通过野外入渗染色试验、图像处理分析等方法,对围封荒漠草原灌丛草地土壤优先流的影响进行评价。结果表明:(1)围栏封育与放牧管理样地土壤水分入渗特征存在差异,在围栏封育样地,草地、天然柠条林地、人工柠条林地的入渗染色图像分别在0—125,0—115,0—105 cm呈现均匀分布,而在125—240,115—150,105—140 cm呈现染色分支,在放牧管理样地,草地、天然柠条林地、人工柠条林地入渗染色图像分别在0—80,0—70,0—80 cm呈现均匀分布,围栏封育导致土壤优先流发生深度更大;(2)土壤剖面染色面积比表现为围栏封育草地>围栏封育天然柠条林地>围栏封育人工柠条林地>放牧管理人工柠条林地>放牧管理天然柠条林地>放牧管理草地,土壤染色深度表现为围栏封育草地>围栏封育天然柠条林地>放牧管理草地>放牧管理天然柠条林地>围栏封育人工柠条林地>放牧管理人工柠条林地,围栏封育管理会导致土壤剖面染色面积比及染色深度增大;(3)土壤优先流变异系数表现为放牧管理天然柠条林地>放牧管理人工柠条林地>围栏封育天然柠条林地>放牧管理草地>围栏封育人工柠条林地>围栏封育草地,放牧管理导致土壤优先流程度增加,而围栏封育降低灌木林地及草地的优先流程度。因此,在荒漠草原等干旱半干旱地区,围栏封育可作为提升土壤水分均匀入渗深度、降低优先流发生程度、提高土壤水分利用效率的重要管理方式。

基于参数优化的人工灌丛生态系统碳水通量模拟

荒漠草原是陆地生态系统中最为脆弱且受人类干扰较为严重的生态类型之一,精准模拟其碳水通量及对人为干扰的响应,不仅能够揭示其复杂的生态学过程,而且还可为人为生态修复和保护提供决策依据。生态模型能够有效地模拟陆地生态系统的碳水循环过程,但模型众多的参数及其取值的合理性限制了其普遍应用,故探索参数优化是提升生态模型应用的有效途径。利用PEST参数优化方法和涡度相关观测数据对Biome-BGC模型的生理生态参数进行优化,在评估参数优化效果的基础上模拟了1986—2018年宁夏盐池荒漠草原区人工灌丛生态系统的总初级生产力(Gross primary productivity,GPP)和蒸散(Evapotranspiration,ET)。结果表明:(1)参数优化可以改善Biome-BGC模型对荒漠草原区人工灌丛生态系统GPP和ET的模拟效果,参数优化后模拟的GPP和ET均更接近于观测值,其中月尺度的模拟效果更佳;(2)基于PEST的Biome-BGC模型参数优化方法具有较强的普适性,优化后的参数可推广应用于荒漠草原区人工灌丛生态系统长时间序列的GPP和ET模拟;(3)宁夏盐池荒漠草原区人工灌丛生态系统的GPP在1986—2018年呈缓慢上升趋势,增幅为1.47 g C m^(-2)a^(-1),但ET的年际变化率较大,且无显著变化趋势。