Soil Seed Bank Characteristics of the Mbe and Nguela Shrub Savannas, and Implications for the Reforestation, Republic of Congo

The soil seed bank is an important source of restoration and resilience of disturbed ecosystems. This study evaluates the regeneration potential through the soil seed bank of the shrub savannas of Nguela and Mbe in order to predict the eventual dynamics. Three plots of 0.25 ha subdivided into four sub-plots of 0.015 ha have been installed in each savannah. In total, 48 samples of each savannah, i.e. 96 samples of both savannas, have been taken from the soil layers, 0 - 5 cm, 5 - 10 cm, 10 - 15 cm and 15 - 20 cm. Species diversity and abundance of the soil seed bank have been assessed after germination. The results reveal 167 seedlings belonging to 23 species in the Mbe savannah and 144 seedlings belonging to 14 species in the Nguela savannah. The total densities of the germinated seeds were respectively 463.63 seeds/m2 and 400 seeds/m2. Nevertheless, the 20 cm deep layers have illustrated themselves compared to the superficial layers with densities of 16.29 seeds/m2 and 21.66 seeds/m2, respectively, in the savannas of Mbe and Nguela. Herbaceous species largely dominated, with percentages of 91% and 100%, respectively, in the savannas of Mbe and Nguela. Alone, the Trema orientalis (L.) Blume species has been identified as woody species in the Mbe savannah. The greatest specific richness has been obtained in the first five centimeters of soil, with 21.73% and 28.57% of exclusive species, respectively, in the savannas of Mbe and Nguela. The results reveal that restoration through the soil seed bank would be limited to a single woody species found (T. orientalis). Consequently, the study suggests silvicultural interventions based on planting or enrichment techniques for sustainably managed savannas exposed to anthropogenic disturbances.

Effects of Shrub on Runoff and Soil Loss at Loess Slopes Under Simulated Rainfall

Improved understanding of the effect of shrub cover on soil erosion process will provide valuable information for soil and water conservation programs.Laboratory rainfall simulations were conducted to determine the effects of shrubs on runoff and soil erosion and to ascertain the relationship between the rate of soil loss and the runoff hydrodynamic characteristics.In these simulations a 20° slope was subjected to rainfall intensities of 45,87,and 127 mm/h.The average runoff rates ranged from 0.51 to 1.26 mm/min for bare soil plots and 0.15 to 0.96 mm/min for shrub plots.Average soil loss rates varied from 44.19 to 114.61 g/(min·m^2) for bare soil plots and from 5.61 to 84.58 g/(min·m^2) for shrub plots.There was a positive correlation between runoff and soil loss for the bare soil plots,and soil loss increased with increased runoff for shrub plots only when rainfall intensity is 127 mm/h.Runoff and soil erosion processes were strongly influenced by soil surface conditions because of the formation of erosion pits and rills.The unit stream power was the optimal hydrodynamic parameter to characterize the soil erosion mechanisms.The soil loss rate increased linearly with the unit stream power on both shrub and bare soil plots.Critical unit stream power values were 0.004 m/s for bare soil plots and 0.017 m/s for shrub plots.

Shrubs proliferated within a six-year exclosure in a temperate grassland—Spatiotemporal relationships between vegetation and soil variables

Overgrazing has been considered one of the maj or causes that trigger shrub encroachment of grassland. Proliferation of shrubs in grassland is recognized as an important indicator of grassland degradation and desertification. In China, various conservation measures, including enclosures to reduce livestock grazing, have been taken to reverse the trend of grassland desertification, yet shrubs have been reported to increase in the grasslands over the past decades. In late 2007, we set up a 400-m-by-50-m exclosure in a long-term overgrazed temperate grassland in Inner Mongolia, with the ob- jective to quantify the spatiotemporal relationship between vegetation dynamics, soil variables, and grazing exclusion. Soil moisture was continuously monitored within the exclosure, and cover and aboveground biomass of the shrubs were measured inside the exclosure in 2007, 2009, 2010, 2012, and 2013, and outside the exclosure in 2012 and 2013. We found the average shrub cover and biomass significantly increased in the six years by 103 % and 120%, respectively. The result supported the hypothesis that releasing grazing pressure following long-term overgrazing tends to trigger shrub invasion into grassland. Our results, limited to a single gradient, suggest that any conservation measures with quick release of overgrazing pressure by enclosure or other similar means might do just the opposite to accelerate shrub en- croachment in grassland. The changes in vegetation cover and biomass were regressed on the temporal average of the soil moisture content by means of the generalized least square technique to quantify the effect of the spatial autocor- relation. The result indicates that the grass cover and biomass significantly increased with the top, but decreased with the bottom layer soil moisture. The shrub cover and biomass, on the other hand, decreased with the top, but increased with bottom soil moisture, although the regression coefficients for the shrubs were not statistically significant. Hence this study supports the two-layered soil model which assumes grasses and shrubs use belowground resources in dif- ferent depths.

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.

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.

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。

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。

祁连山东缘高寒草甸灌丛化对植被群落与土壤理化特性的影响

为明晰祁连山东缘高寒草甸灌丛化对其植被群落与土壤理化特性的影响,选取甘肃省天祝藏族自治县高寒草甸灌丛化区域,调查其植被,采集土壤测定理化性质,分析植被与土壤的互馈关系。结果表明:高寒草甸植被的均匀度指数、高度、盖度、地上生物量、土壤含水率随灌丛化过程增加(P<0.05),而多样性指数和容重均降低;全磷含量在各土层以灌丛区最高,但C∶P和N∶P以草甸区最高;土壤N∶P<14表明土壤养分主要受限于氮;土壤脲酶和过氧化氢酶活性在草甸区各土层显著高于灌丛区(P<0.05);冗余分析显示前两个排序轴的累计解释量为54.88%,土壤过氧化氢酶与植被特征拟合的结果最好(Pr=0.010),表明高寒草甸灌丛化过程中土壤过氧化氢酶受植被特征的制约最大。可见,高寒草甸灌丛化显著影响了植被群落结构与土壤理化特性,在祁连山生态保护和管理中应该予以重视。

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。

猫儿山三种森林类型林下植物叶片与土壤化学计量特征

为探究猫儿山不同森林类型林下植物叶片与土壤化学计量特征,揭示其林下植物适应策略。该文对猫儿山针阔混交林(ZK)、常绿阔叶次生林(CLC)和常绿阔叶林(CL)林下草本层和灌木层主要植物叶片与土壤的化学元素含量进行测定,分析其化学计量特征及其相互之间的内在联系。结果表明:(1)从总体上看,草本层和灌木层植物叶片的C、N含量差异不显著,草本层植物叶片P、K含量极显著高于灌木层,N∶P显著低于灌木层;草本层植物更易受N限制,灌木层植物更易受P限制且其N和P利用效率更高;不同森林类型之间的灌木层植物叶片化学计量差异不显著,草本层植物叶片N含量、C∶N和C∶P差异显著,针阔混交林草本层植物的养分利用效率较高。(2)3种森林类型的土壤C、N含量显示,CL>CLC>ZK且彼此之间差异极显著,针阔混交林土壤的P含量最高而C∶P、N∶P最低。(3)针阔混交林的土壤显著影响林下植物部分叶片化学计量,另外2种森林类型的土壤影响不显著。综上认为,猫儿山不同森林类型的土壤化学计量存在显著或极显著差异,林下不同层次的植物对营养元素的需求以及环境适应策略不同;针阔混交林土壤对林下植物叶片化学计量影响较强,由于有机质分解效率较低导致土壤受N限制,因此应加强针阔混交林的N素管理。该研究结果为森林管理提供了数据支持。

灌木根系形态对土体强度影响的大型直剪试验研究

根系形态显著影响根土复合体强度,然而现有研究局限于草本根系根土复合体和室内常规直剪试验。为探究多年生灌木根系形态及空间分布对固土效果的影响,采用大型直剪试验装置(直径400 mm),对原状根土复合体进行了剪切试验。试验中测量了根系形态参数(根面积比RAR、根长密度、根体积密度和根表面积密度)、根土复合体抗剪强度和剪胀特性,探讨了根系沿深度的分布特征、根土复合体剪胀性以及根系形态参数与根土复合体抗剪强度的相关关系。结果表明,根系加剧了根土复合体的剪胀;在4个根系形态参数中,剪切带上的RAR和根表面积密度与根系对剪切强度的贡献之间相关性较好;Wu模型能反映根系固土的本质,却存在强度被高估或低估的问题。研究成果有助于推动植物根系在固土领域的应用。

川西锦鸡儿灌木扩张对高寒草地土壤有机碳矿化的影响

以川西锦鸡儿(Caragana erinacea)灌丛草地为研究对象,分析川西锦鸡儿灌木不同扩张程度下(原生草地、中度灌木扩张和重度灌木扩张)0—10 cm、10—20 cm和20—40 cm土壤理化性质及土壤有机碳(SOC)矿化的变化特征,探究灌木扩张对高寒草地SOC矿化的影响机制。结果表明:(1)灌木扩张对土壤全氮(TN)含量无显著影响,显著增加各土层SOC含量,显著增加10—20 cm土壤矿物矿质结合态有机碳(MAOC)含量及其占SOC比例,显著减小0—20 cm土壤含水量(SWC)。重度灌木扩张显著增加10—40 cm土壤微生物生物量碳(MBC)含量,显著减小0—10 cm土层MBC/SOC和MAOC/SOC。(2)不同土壤深度对SOC矿化激发效应存在差异,灌木扩张显著降低0—10 cm土壤有机碳潜在矿化碳库(C_(0)),重度灌木扩张显著增加10—40 cm土层C_(0)。(3)相关性分析表明,SOC矿化过程与SWC、SOC、TN、MBC和MAOC显著正相关,与MAOC/SOC显著负相关。逐步回归分析表明,SOC矿化与MBC和SWC相关性最强,可以有效解释C_(0)变化的91.1%。由此推断,川西锦鸡儿灌木扩张后该区域SOC矿化的变化,主要是由于灌木扩张影响MBC和SWC所致,土壤浅表水分减少影响微生物活动使得SOC矿化减弱,灌木根系发育土层微生物量增多使得SOC矿化增强。

锦鸡儿属灌木阻止干旱草地沙漠化生态过程

纵观全球沙漠化的研究进展,从宏观上研究沙漠化现状和后果的报道较多,对沙漠化内在过程的综合研究较少,灌木在阻止干旱区草原沙漠化中的生态作用缺乏研究。研究假设:在干旱地区,灌木的存在提高土壤营养水平,提升土壤保水能力,促进林下植物和土壤生物群落,进而减轻风蚀和固结土壤,这些相互联系的生态过程共同阻止了草原沙漠化。为了验证上述假设,我们以内蒙古阿拉善地区的荒漠化草原为样地,研究锦鸡儿属灌木的固土能力、提高土壤保水能力、改善土壤营养能力和促进生物群落能力,从生物、土壤、水分和沙物质运动等多过程来探讨锦鸡儿属灌木在阻止草原沙漠化中的作用。目的是弄清灌木阻止干旱草地沙漠化的生态过程。在阿拉善荒漠化草原区,锦鸡儿属灌木盖度大约为12.40%。在100 m^(2)的土地上现有灌木固土2.01 m^(3),固土效率为167 cm^(3)/g鲜重,每年灌木生长可以增加固土能力0.264 m^(3)/100 m^(2)土地。锦鸡儿属灌木提高了土壤湿度(灌丛效应SE=0.120)和土壤对雨水的保持能力(SE 0.155),改善了土壤营养(有机质SE 0.234、有效氮SE 0.338、有效磷SE 0.256和有效钾SE 0.089),增加了植物群落的物种丰度、多度、植株高度和生物量(SE 0.298)以及土壤生物(微生物和线虫)群落的物种丰度和多度(SE 0.302),提高了土壤酶活性(碱性磷酸酶、蔗糖酶、脲酶和过氧化氢酶,SE 0.191-0.365)。综合分析表明锦鸡儿属灌木通过保水(路径系数PC=0.43)、增肥(PC 0.39)、促进植物(PC 0.34)和土壤微生物群落(PC 0.20),以及它们共同导致的固土效应等多个相互联系的生态过程阻止干旱草原转变为沙漠。在防止沙漠化的不同过程中,5个锦鸡儿属灌木种各有优劣,这可能是这些种共存于荒漠区的原因之一。灌木作为极端干旱荒漠区的主要植被,在阻止干旱地区草地沙漠化中发挥着重要作用。

宁夏荒漠草原典型灌丛根际土壤酶活性及微生物代谢多样性

开展荒漠灌丛根际土壤酶活性和微生物代谢多样性研究,对于荒漠土壤的生态修复具有重要意义。运用可见分光光度法和Biolog微平板法,对宁夏白芨滩荒漠草原内柠条、沙冬青、毛刺和猫头刺4种典型的豆科灌丛不同发育期根际土壤酶活性及微生物代谢功能多样性进行了研究。结果表明:不同灌丛各发育期根际土壤的酶活性存在显著差异。从灌丛种类来看,沙冬青根际土壤脲酶活性均显著高于其他3种灌丛,毛刺根际土壤碱性磷酸酶活性均显著低于其他灌丛。从发育期来看,营养期沙冬青根际土壤脲酶和碱性磷酸酶活性显著高于其他时期,柠条根际土壤脲酶和蔗糖酶活性显著低于其他时期;盛花期柠条根际土壤脲酶和碱性磷酸酶活性、沙冬青根际土壤蔗糖酶活性、猫头刺根际土壤脲酶和脱氢酶活性显著高于其他时期;果实期沙冬青根际土壤脲酶和碱性磷酸酶活性最高,柠条根际土壤蔗糖酶和脱氢酶活性最高;毛刺的盛花期和果实期根际土壤中酶活性普遍较低。不同灌丛各发育期根际土壤微生物群落代谢多样性大多存在显著差异。4种灌丛根际土壤平均颜色变化率(average well color development,AWCD)均随培养时间的延长而逐渐增加,碳源利用类型主要为碳水化合物、氨基酸和羧酸。柠条营养期根际土壤中微生物分布较均匀,代谢活性强,生长旺盛。主成分分析(principal component analysis,PCA)显示,营养期沙冬青、毛刺和猫头刺根际土壤微生物的碳源利用模式相似;盛花期柠条、沙冬青和猫头刺根际土壤微生物的碳源利用模式相似;果实期柠条和沙冬青、毛刺和猫头刺根际土壤微生物的碳源利用模式相似。随着发育期的变化,土壤微生物碳源利用模式发生不同程度的变化。冗余分析(redundancy analysis,RDA)显示,酶活性和微生物代谢功能与土壤理化性质关系密切。脲酶与铵态氮(NH_(4)^(+)-N)正相关;碱性磷酸酶与土壤含水量(SWC)显著正相关;蔗糖酶与全氮(TN)、铵态氮(NH_(4)^(+)-N)、土壤有机质(SOM)和全磷(TP)正相关,且与TN显著正相关;TN、有效磷(AP)、TP、速效钾(AK)和亚硝态氮(NO_(2)^(-)-N )显著影响脱氢酶活性。NH_(4)^(+)-N、NO_(2)^(-)-N 、TP、AP和NO_(3)^(-)-N是影响微生物代谢多样性的主要理化因子。该研究结果对于了解宁夏荒漠根际土壤微环境以及微生物群落对环境响应特征具有积极意义。

高寒草甸土壤有机碳活性组分对灌丛化的响应

[目的]草地灌丛化过程的植被群落演替会影响土壤有机碳库,而土壤有机碳(SOC)活性组分能够敏捷反映土壤有机碳库变化。分析灌丛化对高寒草甸SOC活性组分的影响,为全球气候变化背景下青藏高原草地土壤有机碳库变化和固碳研究提供数据支撑。[方法]以青藏高原川西锦鸡儿(Caragana erinacea)灌丛草甸为研究对象,分析不同灌丛化阶段(未灌丛化、中度灌丛化和重度灌丛化草甸)0—10,10—20,20—40 cm土壤理化性质、碳转化酶活性和SOC活性组分特征。[结果](1)灌丛化使得0—20 cm土壤含水量(SWC)显著减小,各土层SOC含量均在重度灌丛化草甸最大,中度灌丛化草甸土壤pH值显著增大。(2)中度灌丛化草甸土壤淀粉酶活性(SAA)显著低于未灌丛化草甸,10—40 cm土壤蔗糖酶活性(SSA)也显著较低,SSA在重度灌丛化阶段显著强于未灌丛化草甸。(3)与未灌丛化草甸相比,中度灌丛化草甸0—10,10—20,20—40 cm易氧化有机碳(ROOC)含量分别显著减少16.79%,21.73%和31.11%,0—10 cm土壤可溶性有机碳(DOC)和微生物生物量碳(MBC)含量也显著减少;重度灌丛化草甸0—10 cm土壤颗粒态有机碳(POC)和ROOC含量分别增大24.37%和29.54%,10—20 cm土壤MBC和DOC分别增大12.96%和10.38%,20—40 cm土壤MBC和DOC分别增大57.62%和22.10%。(4)土壤有机碳活性组分均与TN,SWC,SOC以及碳转化酶活性显著正相关,ROOC与pH值显著负相关。[结论]研究区域川西锦鸡儿灌丛化初期土壤有机碳活性组分含量降低,而灌丛化后期土壤有机碳及其各活性组分均得到积累,可能对该区域土壤有机碳积累和土壤质量提升产生积极效应。

雄黄桂林下栽植不同灌木对林分因子和土壤理化性质的影响

为给雄黄桂(Osmanthus fragrangs'Xionghuanggui')林下栽植适宜灌木和改善种植环境提供科学依据,以雄黄桂+红花檵木(Loropetalum chinense var.rubrum)(Ⅰ)、雄黄桂+山茶(Camellia japonica)(Ⅱ)、雄黄桂+红枫(Acer palmatum'Atropurpureum')(Ⅲ)和雄黄桂+金边黄杨(Euonymus japonicus'Aurea-marginatus')(Ⅳ)为研究对象,分析雄黄桂林下栽植不同灌木对雄黄桂林分因子和土壤理化性质的影响。结果表明,林分Ⅲ的雄黄桂平均胸径、平均树高、平均枝下高、平均冠幅、平均郁闭度和平均林分密度均最大。林分Ⅲ的土壤有机质、全钾、速效钾、全磷和全氮含量及含水率和pH值均最高,土壤容重最小。雄黄桂林下栽植红枫对土壤理化性质影响最大,更有利于雄黄桂生长。栽培后,应注意氮、磷和钾肥的施用,添加有机质,促进雄黄桂林健康生长。

基于文献计量学分析的草地植被灌丛化研究现状

灌丛化会改变草本植物的分布格局,影响生态系统结构和功能。为了解“灌丛化”相关领域的发展现状、研究热点及前沿趋势,理清该领域研究的知识结构。本研究依托中国知网数据库(CNKI)及Web of Science(WOS)核心合集数据库,以1982~2023年“灌丛化”相关领域已发表的4114篇文献为数据源,利用VOSviewer和CiteSpace可视化软件对“灌丛化”相关研究领域发文情况(数量、趋势、被引频次)、合作关系(团队、机构、国家)和关键词等进行可视化分析。结果显示:(1)国内国际相关研究总体呈稳步增长趋势,外文研究的热度大于中文研究,且高被引论文均发表在国内外影响力较高的期刊上,表明“灌丛化”相关研究成果在该领域认可度较高,具有较高学术价值;(2)“灌丛化”相关研究国际合作关系(团队、机构、国家)较国内更为密切,且美国、中国、南非、澳大利亚及德国是“灌丛化”相关领域研究的中坚力量。(3)目前“灌丛化”相关领域的研究内容主要包括灌丛化形成机制及生物多样性对灌丛化的响应,草、灌木之间的竞争关系和土壤性质对灌丛化的响应等。研究指出:我国“灌丛化”相关研究尚处于起步阶段,且前人对灌丛化的研究多针对具体研究区域,相对分散,且合作较少;同时在全球尺度上的研究及大数据整合分析相对较少,仍需进一步研究。随着“灌丛化”研究的深入发展,灌丛化对微生物群落组成的影响、灌丛化对干旱胁迫等环境因子的响应及控制灌丛化有效措施等相关研究将在未来一段时间持续热门。

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。

黄土高原水蚀风蚀交错区生物结皮对灌草生态系统水分耗散的影响

[目的]为研究生物结皮对灌草生态系统水分耗散的影响。[方法]采用原状土柱试验,以裸土为对照,设置灌草(单株灌木-20%盖度草本)、灌草-30%生物结皮和灌草-50%生物结皮3个处理,研究生物结皮对灌草生态系统水分耗散的影响。[结果]模拟30 mm降水12 h后,灌草-生物结皮处理0-20 cm土层水分含量较裸土处理平均提高15.4%,较灌草处理平均提高12.8%。与裸土相比,灌草及灌草与2个盖度生物结皮处理显著增加土壤水分耗散,其中灌草处理较裸土增加120.3%,灌草-生物结皮较裸土平均增加116.5%。生物结皮降低灌草生态系统的水分耗散。与灌草处理相比,灌草-生物结皮水分耗散平均降低1.7%,降低程度与生物结皮盖度、时段及土层深度有关。其中,灌草-50%生物结皮的水分耗散量较灌草-30%生物结皮处理降低13.4%。生物结皮对灌草生态系统水分耗散的降低作用在雨后1~4天表现明显。生物结皮对灌草生态系统水分耗散的降低主要取决于20-45 cm土层耗散的降低。与灌草处理相比,灌草-生物结皮的0-20 cm土层水分蒸散损耗平均提高14.4%,而20 cm以下土层水分耗散平均降低15.5%。[结论]30 mm降雨量条件下生物结皮降低灌草生态系统的水分耗散,有利于缓解风蚀水蚀交错区灌草植被的水分亏缺。研究结果揭示生物结皮对灌草生态系统水分耗散影响,可为旱区生态恢复提供理论依据。