Carbon sequestration and soil restoration potential of grazing lands under exclosure management in a semi‐arid environment of northern Ethiopia

Exclosures are used to regenerate native vegetation as a way to reduce soil erosion, increase rain water infiltration and provide fodder and woody biomass in degraded grazing lands. Therefore, this study assessed the impact of grazing exclosure on carbon sequestration and soil nutrients under 5 and 10 years of grazing exclosures and freely grazed areas in Tigray, northern Ethiopia. Carbon stocks and soil nutrients increased with increasing grazing exclusion. However, open grazing lands and 5 years of grazing exclosure did not differ in above‐ and belowground carbon stocks. Moreover, 10 years of grazing exclosure had a higher (p < 0.01) grass, herb and litter carbon stocks compared to 5 years exclosure and open grazing lands. The total carbon stock was higher for 10 years exclosure (75.65 t C ha^‐1) than the 5 years exclosure (55.06 t C ha^‐1) and in open grazing areas (51.98 t C ha^‐1). Grazing lands closed for 10 years had a higher SOC, organic matter, total N, available P, and exchangeable K + and Na + compared to 5 year's exclosure and open grazing lands. Therefore, establishment of grazing exclosures had a positive effect in restoring degraded grazing lands, thus improving carbon sequestration potentials and soil nutrients.     

华北退化荒地建植豆类和禾本植物人工草地对土壤真菌群落结构和功能的影响

阐明植被恢复过程中土壤真菌群落的变化及其生态功能,对于制定科学有效的退化生态系统管理措施有重要参考价值。利用扩增子高通量测序技术和生物信息学分析解析了华北退化荒地自然恢复（对照组,CK）和建植豆科植物和禾本植物人工草地（分别为LG和GG处理）过程中土壤真菌群落结构和功能群特征差异。结果表明：（1）退化荒地土壤表层样品中共获取6315个真菌OTU,隶属于17门60纲145目347科896属,优势菌门为Ascomycetes、Mortierellomycota和Basidiomycetes,LG处理相较于CK的Basidiomycetes相对丰度明显升高,GG处理相较于CK的Mortierellomycota相对丰度明显提高。（2）土壤真菌功能群类型以腐生真菌为主,共生真菌次之,病原真菌占比最少。建植人工草地对腐生真菌和共生真菌相较于病原真菌的功能群组成影响更明显,并导致腐生真菌相对丰度升高,共生真菌相对丰度降低。（3）土壤真菌群落结构受植物物种丰富度、根系生物量等植被参数变化的显著（P<0.05）影响,且与土壤有机碳、总氮、速效氮、总磷等土壤养分水平显著（P<0.05）相关。本研究的结果有助于深入理解建植人工草地对土壤真菌群落结构和功能的影响,并为华北退化荒地植被恢复策略提供理论依据。     

荒漠草原区弃耕地植被演替过程中植物群落生物量及土壤养分变化

采用空间变化代替时间变化的方法,以荒漠草原区不同年限(1、4、9、12和20年)弃耕地为对象,研究弃耕演替过程中植物群落生物量与土壤养分的变化特征.结果表明： 随弃耕年限的增加,弃耕地植物群落地上生物量呈先减少后增加的趋势,0～60 cm土层的土壤全氮、全磷和有机碳含量及碳密度均呈先增大后减小再增大的趋势,4年和20年弃耕地的土壤全氮、全磷含量达到峰值.弃耕演替过程中土壤全氮和有机碳含量对植物群落生物量的影响大于土壤容重和土壤全磷.     

Growth of Jatropha curcas on heavy metal contaminated soil amended with industrial wastes and Azotobacter. A greenhouse study

The aims of the study were to evaluate the effect of organic wastes (biosludge and dairy sludge) and biofertilizer (Azotobacter chroococcum) on the planting conditions of Jatropha curcas in metal contaminated soils. Results showed that the plants survival rate in heavy metal contaminated soil increased with addition of amendments. Treatment T6 (heavy metal contaminated soils+dairy sludge+biofertilizer) observed to be the best treatment for growth (height and biomass) as compared with the treatment T5 (heavy metal contaminated soils+biosludge+biofertilizer). In addition, organic amendments provided nutrients such as carbon, N, P and K to support plant growth and reduced the metal toxicity to plant. The present study showed that metal contaminated lands/soils could be suitably remediated by adapting appropriate measures.     

Site preparation impacts on soil biotic and abiotic properties,weed control,and native grass establishment

In severely degraded systems active restoration is required to overcome legacies of past land use and to create conditions that promote the establishment of target plant communities. While our understanding of the importance of soil microbial communities in ecological restoration is growing, few studies have looked at the impacts different site preparation techniques have on these communities. We trialed four methods of site preparation: fire, top‐soil removal (TSR; removal of top 50 mm of soil), slashing (vegetation cut to 30 mm, biomass removed), and carbon (C; as sugar and saw‐dust) addition, and quantified resulting soil bacterial communities using DNA metabarcoding. We compared the effectiveness of these techniques to reduce weed biomass, improve native grass establishment, and induce changes in soil nutrient availability. TSR was the most effective technique, leading to a reduction in both available nutrients and competition from weeds. In comparison, the remaining methods had little or no effect on weed biomass, native grass establishment, or soil nutrient availability. Both TSR and C addition resulted in changes in the soil bacterial community. These changes have the potential to alter plant community assembly in many ways, such as via nutrient acquisition, pathogenic effects, nutrient cycling, and decomposition. We recommend TSR for ecological restoration of old‐fields and suggest it is a much more effective technique than burning, slashing, or C addition. Restoration practitioners should consider how their management techniques may influence the soil biota and, in turn, affect restoration outcomes.     

Composted soil conditioner and mulch promote native plant establishment from seed in a constructed seasonal wetland complex

Three thicknesses of composted soil conditioner, and one combined with mulch, surface‐applied and then incorporated into the sandy topsoil, were tested against controls for promotion of native plant establishment by direct seeding in construction of a seasonal wetland complex. Located 50 km south of Perth, Western Australia in a Mediterranean climate, the site typically dries out in summer. In wetter seasons ponds intercept contaminants in freeway runoff and act as a buffer for peak flows. The 20 mm thickness of soil conditioner was the most effective. The 40 mm thick 40:60 blend of soil conditioner and mulch was also effective – the mulch can help reduce soil erosion. Composted soil conditioner, typically produced by recycling accumulated municipal waste, counteracts soil organic matter and nutrient depletion.     

Switchgrass Biofuel Production on Reclaimed Surface Mines: I. Soil Quality and Dry Matter Yield

Growing food crops for biofuel on productive agricultural lands may become less viable as requirements to feed a growing human population increase. This has increased interest in growing cellulosic biofuel feedstocks on marginal lands. Switchgrass (Panicum virgatum L.), a warm-season perennial, is a viable bioenergy crop candidate because it produces high yields on marginal lands under low fertility conditions. In other studies, switchgrass dry matter (DM) yields on marginal croplands varied from 5.0 to 10.0 Mg ha^?1 annually. West Virginia contains immense areas of reclaimed surface mined lands that could support a switchgrass-based biofuel industry, but yield data on these lands are lacking. Field experiments were established in 2008 to determine yields of three switchgrass cultivars on two West Virginia mine sites. One site reclaimed with topsoil and municipal sludge produced biomass yields of 19.0 Mg DM ha^?1 for Cave-in-Rock switchgrass after the sixth year, almost double the varieties Shawnee and Carthage, at 10.0 and 5.7 Mg ha^?1, respectively. Switchgrass yields on another site with no topsoil were 1.0 Mg ha^?1 after the sixth year, with little variation among cultivars. A second experiment was conducted at two other mine sites with a layer of topsoil over gray overburden. Cave-in-Rock was seeded with fertilizer applications of 0, 34, and 68 kg N-P₂O₅-K₂O ha^?1. After the third year, the no fertilizer treatment averaged biomass yields of 0.3 Mg ha^?1, while responses to the other two rates averaged 1.1 and 2.0 Mg ha^?1, respectively. Fertilization significantly increased yields on reclaimed mine soils. Where mine soil fertility was good, yields were similar to those reported on agricultural soils in the Northeastern USA.     

Organic and inorganic fertilizer effects on a degraded Patagonian rangeland

The forest-steppe ecotone in NW Patagonia is a semiarid ecosystem affected by natural and anthropogenic fires, and overgrazing by sheep. Following a wild fire in the driest portion of this ecotone, a 3-year study was conducted to assess the impacts of a single application of inorganic and organic fertilizers on soil and vegetation recovery. Organic fertilizers were composts derived from biosolids and municipal solid wastes. Six treatments were evaluated: screened and unscreened biosolids compost and municipal solid wastes compost (40 Mg ha^?1), inorganic fertilizer (100 kg N and 35 kg P ha^?1), and no application. Soils were chemically characterized, and soil microbial activity was assessed as potential respiration and N-mineralization. Vegetation responses included plant cover, composition, phytomass, and N resorption prior to abscission, and leaf litter quality of the dominant species. Organic fertilizers increased soil organic matter, nutrients and microbial activity. Plant cover and aboveground phytomass, dominated by the native perennial tussock grass Poa ligularis, showed a higher increase with inorganic than with organic fertilization. While vegetation responded more to inorganic fertilizer, due to its higher initial pulse of available N, organic fertilizers had a positive impact on soil chemical and biological properties.     

东祁连山高寒草甸不同退化阶段植被/土壤磷素特征及其与生物量的关系

磷素是高寒草地生态系统的重要支持元素,高寒草甸退化导致较为严重的生态和生产问题,同时也引起了生态系统物质循环的变化。为揭示高寒草甸退化中土壤磷素特征及其对植被特征的效应,以东祁连山轻度(LD)、中度(MD)、重度退化(SD)高寒草甸退化阶段为研究对象,以多年围封高寒草甸(FG)为对照,在春季和夏季分别对不同高寒草甸阶段样地不同土层深度土壤全磷、有效磷、微生物量磷含量及碱性磷酸酶活性等磷素特征进行了研究,并对夏季植被地上生物量和磷素含量等植被特征进行了调查。结果表明：东祁连山高寒草甸退化导致植被地上生物量和磷含量急剧下降,重度退化高寒草甸地上生物量干重仅是围封草地的35.93%,退化高寒草甸地上部磷含量仅为围封草地的60%,且不同退化阶段地上部磷含量没有明显差异。退化导致高寒草甸表层土壤的全磷、有效磷含量升高,相比FG,土壤有效磷含量春季LD、MD和SD分别升高了16.67%、36.67%和3.33%,夏季分别升高了4.35%、26.09%和4.35%,且有效磷含量具有夏季低于春季的季节差异性。退化导致土壤微生物量磷含量明显降低,而对碱性磷酸酶活性影响没有明显的规律性,但围封草地夏季碱性...     

云南南涧干热退化山地人工植被恢复初期生物量及土壤环境动态

 研究了云南南涧干热河谷退化山地人工恢复植被初期阶段(3～5年)主要植物群落的地上生物量和恢复植被后土壤水分及养分的相关动态。结果表明,几种外来植物的适应性强,早期生长迅速并能很快郁闭。人工群落生物量都高于当地次生的坡柳灌草丛。引进种的地上生物量和总平均生长量分别是坡柳的3～16倍和5～20倍,其生长速度也高于乡土树种云南松。雨季人工植被下土壤含水量比光坡地增加约100％,表土层则增加2倍以上。但在旱季,林地土壤含水量与光坡地相近甚至低于光坡地。植被的恢复使土壤养分朝着良性循环转变。土壤有机质、速效钾含量提高,全氮含量稍有降低但不明显,速效磷含量降低,pH值有所下降。这些变化主要发生在土壤表层,人工植被及其土壤生态系统的恢复仍处于不稳定状态。     

温带草原退化对土壤剖面微生物学特征的影响

【目的】草地退化已成为我国草原当前面临的最主要问题。土壤微生物量和土壤酶活性是反映土壤养分和土壤环境质量的重要指标。揭示退化程度对温带草原土壤剖面微生物学特征的影响规律。【方法】以内蒙古温带草原为研究对象,选取成熟自然草地以及中、重度退化草地和极度退化草地4种典型不同退化程度的草地,按不同土壤深度分层采样并进行土壤微生物量和土壤微生物酶活性的测定。【结果】表层土壤微生物生物量及其酶活性在不同退化样地中呈现出一致的趋势:成熟自然样地中度退化样地重度退化样地极度退化样地;10-20 cm土层土壤微生物学特征与表层的差异随着退化程度的加深逐渐减少,甚至在极度退化样地中10-20 cm层土壤微生物指标高于表层。【结论】表层土壤微生物生物量及其酶活性随着退化程度的加深而减少。同时,退化程度越严重,表层与10–20 cm土层之间土壤微生物学特征的差异越小。这一结果为评价草地退化程度提供了新思路,为温带草原的恢复和重建提供了重要的理论依据。     

陕西渭北柿子园种植白三叶草对土壤养分和生物学性质的影响

种植豆科绿肥可以有效增加氮肥来源,提高水土保持能力,改善生态环境与土壤质量,是促进农业生产可持续发展的重要措施之一.本试验研究了柿子园种植白三叶草对土壤养分和生物学性质的影响,以探明果园种植豆科绿肥在土壤肥力改良与经济效益提升方面的潜力.设柿子园清耕、种植白三叶草2个处理,于2017年9月14日分别采集0～10、10～20、20～30和30～40 cm土层样品,以分析两个处理对土壤有机质、速效氮、微生物生物量碳、氮和酶活性的影响.结果表明: 与清耕相比,生草后的整个被测土层的有机质、速效氮、微生物生物量碳、氮及脲酶、蔗糖酶、过氧化氢酶、碱性磷酸酶活性均增加,其中,0～10 cm土层生草处理的有机质、微生物生物量碳增加效果显著,10～20 cm土层速效氮含量增加效果显著,0～20 cm土层中脲酶活性显著增加,而过氧化氢酶活性、蔗糖酶及土壤酶活性的几何平均值(GME)则在整个被测土层都显著增加.表明果园生草能改善土壤肥力状况,在一定程度上可减少化肥氮投入量,提高果园经济效益,是一种优良的果园栽培模式.     

Soil Seed Bank as an Input of Seed Source in Revegetation of Lead / Zinc Mine Tailings

The goal of the present study was to assess a soil seed bank as an input seed source for revegetating lead/zinc (Pb/Zn) mine tailings. The seed bank source was abandoned farmland, whose top 10‐cm layer of topsoil contained 6,850 ± 377 seeds/m² from 41 species. The seeds in the soil were principally distributed in the upper 0–2 cm, which held 75.8% of total seeds and 92.7% of species composition. The top 2‐cm layer of topsoil may be sufficient to serve the purpose of providing a seed source for revegetation on derelict lands, including mined lands. Four different thicknesses of topsoil (1, 2, 4, and 8 cm, redistributed from the total 0–10‐cm layer from the farmland) were field‐tested on the Pb/Zn mine tailings. There was no significant difference in seedling density among the 4 thickness treatments. Many seeds in the treatments with more than 1‐cm of topsoil were unable to emerge from the deeper layer. Seedlings in plots with topsoil of 1‐, 2‐ and 4‐cm failed to establish within 1 year due to the extremely high acidity (pH 2.39 to 2.76). A shallow layer of topsoil cannot neutralize the sulfuric acid generated from oxidation of pyrites in the tailings. For establishment of seedlings on metalliferous lands, an insulating layer such as subsoil, building rubble, or domestic refuse is necessary before covering with valuable topsoil. The woody legume Leucaena leucocephala grown on the tailings with a topsoil cover of 8‐cm was the most dominant species. Lead was accumulated in root, branch, stem bark, and xylem, which accounted for more than 80% of the total metal concentration in the plant. This portion of Pb will reside in the plant for a long period, while the smaller portion of Pb in the leaf (about 15%) could be returned to the environment as litter during growth. Woody plants may have an advantage in metal‐phyto‐remediation over herbaceous plants.     

Restoration of native vegetation following exclosure establishment on communal grazing lands in Tigray,Ethiopia

Questions: Is plant species richness, diversity and above‐ground standing biomass enhanced after establishing exclosures on communal grazing lands? What factors influence the effectiveness of exclosures to restore degraded native vegetation in Tigray, Ethiopia? Location: Northern Ethiopia. Methods: We used a space‐for‐time substitution approach to detect changes in plant species richness, diversity and above‐ground standing biomass after conversion of communal grazing lands to exclosures. We selected replicated (n=3) 5‐, 10‐, 15‐ and 20‐year‐old exclosures and paired each exclosure with an adjacent communal grazing land to ensure that soil and terrain conditions were as similar as possible among each pair. Results: All exclosures displayed higher plant species richness, diversity and biomass than the communal grazing lands. Differences in plant species richness and biomass between an exclosure age and adjacent communal grazing land were higher in oldest than in youngest exclosures. In exclosures, much of the variability in plant species composition and biomass was explained by a combination of edaphic (total nitrogen, phosphorus, texture and soil pH) and site (precipitation and altitude) variables (R²=0.72–0.82). Edaphic and site variables also explained much of the variability in plant species composition in communal grazing lands (R²=0.76–0.82). Our study shows that all exclosures are at an early stage of succession. The increase in economically important indigenous shrub and tree species with exclosure age suggests that, with time, a valuable afromontane forest may develop. Conclusions: Establishment of exclosures on communal grazing lands is a viable option to restore degraded native vegetation. However, before expanding exclosures, the ecological consequences of additional exclosures should be investigated as further expansion of exclosures could increase grazing pressure on remaining grazing areas. Furthermore, consideration of edaphic and site variables will help optimize selection of areas for establishment of exclosures and enhance natural regeneration in exclosures in the future.     

辽西北沙地苹果-大豆间作对土壤养分和微生物量分布的影响

为了解辽西北沙地果农间作系统中土壤养分及微生物量分布特征,选取研究区具有代表性的苹果(Malus pumila)-大豆(Glycine max)间作系统为研究对象,对间作系统0～60 cm 土层、0～300 cm水平距离范围内的土壤养分和微生物量进行了测定,并与大豆单作、苹果单作进行对比.结果表明:辽西北沙地苹果与大豆...     

Degraded soil increases the performance of a dominant grass, <Emphasis Type="Italic">Andropogon gerardii</Emphasis> (Big bluestem)

Dominant grasses can suppress subordinate species in grassland restorations. Examining factors that influence performance of a dominant grass when interacting with subordinate forbs may provide insights for maintaining plant community diversity. The objective of our study was to determine how soils of different restoration ages and functionally different forbs influence the performance (using biomass and tillering rate as proxies) of a dominant grass: Andropogon gerardii. Sites included a cultivated field and two restored prairies (4 or 16 years after restoration) at Konza Prairie (NE Kansas). We hypothesized A. gerardii performance would be greater in more degraded soils and when interacting with legumes. Soil structure, nutrient status, and microbial biomass were measured in soil that was used to conduct the plant interaction study. Andropogon gerardii performance was measured during an 18-week greenhouse experiment using the relative yield index calculated from net absolute tillering rate and final biomass measurements in three soil restoration age treatments combined with four interacting forb treatments. Restoration improved soil structure, reduced plant-available nutrients, and increased microbial biomass. Relative yield index values of A. gerardii were greater with non-legumes than legumes. Andropogon gerardii performed best in degraded soils, which may explain the difficulty in restoring tallgrass prairie diversity in long-term cultivated soil. Results from this study suggest practices that promote soil aggregation and fungal biomass, coupled with including a high abundance of legumes in seed mixes could reduce dominance of A. gerardii and likely increase plant diversity in tallgrass prairie restorations.     

Effect of topsoil storage on microbial activity,primary production and decomposition potential

Summary The effects of disturbing (cultivating) and stockpiling prairie grassland topsoil on microbial activity, microbial biomass C, plant production and decomposition potentials were studied by measuring CO₂ efflux from unamended and glucose amended soil in the laboratory and by conducting a pot and litter bag study in the greenhouse. Stockpiling appeared to have very little effect on soil respiratory activity, but did reduce the microbial biomass C levels. Throughout the 3 year study the microbial biomass C in the surface soil of the stockpile was less than that in the undisturbed soil, while the biomass C in soil at the bottom of the stockpile was at no time significantly different from that in the undisturbed soil. The reduction in microbial biomass C in the surface soil immediately after stockpiling was attributed to a decrease in the soil organic C levels caused by a slight dilution of the topsoil with subsurface mineral soil, and the exposure of the stockpile surface to extreme environmental conditions. Soils from all depths of the stockpile responded more slowly to the addition of glucose than soil from the undisturbed and cultivated treatments even when no differences in biomass were detected between the undisturbed and stockpiled soils. It is postulated that the rapidity with which the soil microbial biomass responds to glucose additions may be a sensitive indicator of stress on the soil biological components. The reduction in biomass after storage for 1 year had no adverse effects on the decomposition or primary production potential of the stored soil. Rather, shoot production by fall rye was stimulated in the stored topsoil, presumably a result of better N nutrition.     

生活污水慢渗生态处理对土壤及杨树生长的影响

为了观测生活污水杨树林地处理对土壤和林木生长的影响,2008—2009年在郑州市龙湖镇,采用不同水力负荷(0、3、6、9、12、15cm/周),进行了污水慢渗生态处理试验。测定了污水处理期间杨树地上部分生长量,对表层(0—40cm)和下层(40—100cm)土壤理化性质进行了分析。选用土壤容重、有机质、全氮、全磷、全钾、速效氮、速效磷、速效钾作为土壤质量因子,运用土壤质量综合指标评价不同处理表层土壤质量,对下层土壤的理化性状的变化进行了研究。结果表明:在3—9cm/周水力负荷时,表层土壤质量综合指标值(QI值)和杨树地上部分生长量均随着水力负荷的增加而增加,在9cm/周水力负荷时达到最大;水力负荷大于9cm/周,QI值和杨树地上部分生长量随着水力负荷增加而降低。在水力负荷较低时,污水处理对下层土壤性状影响较小,水力负荷大于9cm/周,污水处理对下层土壤性状产生了不良影响。生活污水杨树林地处理比较适宜的水力负荷是6—9cm/周。     

Small vegetation gaps increase reseeded yellow-flowered alfalfa performance and production in native grasslands

Reseeding yellow-flowered alfalfa (YFA) in degraded grasslands may require a vegetation-free microsite for germination and subsequent establishment. This study aimed to examine the role of microclimates of different-sized vegetation gaps on seedling performance and adult plant production of YFA. Field microsites were established in the meadow steppe of Hulunber, Inner Mongolia, China. Seedling performance, plant production, the microclimate within vegetation gaps, and soil nutrients (plant-available N, P, and K, total N concentration) were assessed at the end of each growing season from 2013 to 2015. Our results indicate light availability, and topsoil temperature of each gap were significantly increased as gap size increased, while topsoil moisture and air relative moisture were decreased in larger gaps. Small gaps (diameter ≤10 cm) improved seedling emergence, survival, biomass, and root nodulation, as compared with seedling performance associated with the larger gaps, presumably in response to increased shade and moisture. Additionally, large gaps (>20 or >40 cm) were characterized by significantly lower plant-available P, total N concentrations, plant-available K, and soil pH. However, root exclusion treatments did not improve overall seedling performance, plant production, or soil properties, as compared to corresponding microsites with root presence, regardless of gap size. Our results suggest that reseeding YFA into grasslands where disturbance, such as light grazing, has resulted in small gaps will be more effective than in highly degraded grasslands.     

科尔沁沙地封育恢复过程中植物群落特征变化及影响因素

封育是退化沙地植被恢复与生态重建的重要措施, 理解长期处于封育状态下不同类型沙地植物群落特征变化及其影响因素有利于沙地植被恢复和生态重建。该文基于对科尔沁沙地长期封育的流动沙丘(2005年封育)、固定沙丘(1985年封育)和沙质草地(1997年封育)连续多年(2005-2017年)的植物群落调查, 结合土壤种子库、土壤养分以及气象数据, 分析了植物群落特征变化及其对环境变化的响应。研究结果表明流动沙丘植被盖度显著增加, 群落生物量和物种多样性年际间波动变化, 但无明显趋势; 固定沙丘植物群落存在逆行演替趋势, 具体表现为群落生物量、灌木和半灌木以及豆科优势度显著下降, 而一年生和多年生杂类草优势度显著增加; 沙质草地群落物种丰富度和多年生禾草优势度存在降低趋势, 并且一年生杂类草优势度明显高于其他功能群, 群落存在退化现象。3类沙地土壤种子密度变化不显著, 而种子丰富度在流动沙丘显著增加, 在固定沙丘和沙质草地有下降趋势, 土壤养分仅有有效氮和有效磷含量增加。回归分析结果表明气温和降水是影响年内生物量积累的主要因素, 但对年际间群落生物量和物种丰富度变化影响不大。除趋势对应分析结果显示土壤种子库与植物群落之间存在很高的相似性, 典型相关分析结果表明沙质草地植物群落与土壤养分紧密相关, 而固定沙丘群落主要与土壤水分紧密相关。综合以上结果可知, 封育33年的固定沙丘群落和封育21年的沙质草地群落都存在退化现象, 而封育11年的流动沙丘群落正在缓慢恢复, 因此封育年限的设定对退化沙地植被恢复至关重要, 封育时间过长不仅不利于植物群落恢复, 反而会使群落发生逆行演替, 建议封育年限的设定应综合考虑植被退化程度、土壤养分状况、土壤种子库基础以及气候条件等因素的影响。