民勤荒漠绿洲过渡带退化人工梭梭林植被与土壤特性研究
Vegetation and Soil Characteristic of Artificial Haloxylon Ammodendron Forest with Different Degradation Grades in Minqin Oasis-desert Ecotone

荒漠绿洲过渡带植被的退化关系到绿洲边缘荒漠化的扩张和绿洲生态安全,是荒漠化防治中的重点关注对象。由于受气候变化和人类活动等因素的影响,民勤荒漠绿洲过渡带地下水位持续下降、土壤水分含量逐渐降低,起防风固沙作用的人工梭梭林出现不同程度的退化,已威胁到民勤绿洲的生存与发展。因此,本研究以民勤荒漠绿洲过渡带退化人工梭梭林为研究对象,在野外植被调查、土壤采集与化验的基础上,对梭梭群落进行退化程度的划分,探索不同退化程度的梭梭群落特征及其土壤特征,以及植被退化过程与土壤特征变化之间的关系,为荒漠区土壤质量监测评价、退化植被恢复以及荒漠生态系统可持续发展提供科学依据。研究结论如下:(1)随着人工梭梭林群落退化程度加重,梭梭枯枝率增大,新稍长变短,长势变差,重度退化阶段开始出现死株。梭梭的重要值在各退化程度中均远大于其他物种,随着退化程度的加重,沙拐枣的重要值无显著差异,梭梭、雾冰藜与黄花补血草的重要值总体上呈降低趋势,盐生草与沙蓬的重要值逐渐增加,沙蒿的重要值先增大后减小。(2)随着人工梭梭林群落退化程度加重,灌木层的α多样性指数无显著变化,草本层的物种数逐渐增加;草本层与整体的Simpson指数、Shannon-Wiener指数和Pielou指数总体为中度退化>轻度退化>重度退化>未退化。随着退化程度加重,人工梭梭林群落在相邻退化程度间的物种替代程度降低,群落相似性增强,且相似性表现为灌木层>整体>草本层。在人工梭梭林群落中,梭梭与黄花补血草、沙拐枣、沙蒿和猪毛菜存在一定程度的负相关,与雾冰藜、盐生草和沙蓬相关性很小。(3)各退化程度的土壤机械组成、含水率、全盐含量、容重、总孔隙度在各土层间均无显著差异,但含水率与全盐含量均随土层深度增加而减小;随着退化程度加重,土层间pH值的差异性由显著变为不显著。各土层的土壤机械组成、容重、总孔隙度与全盐含量随退化程度加重而无显著变化,但土壤机械组成在未退化阶段相对较细,中度退化相对较粗;土壤含水率与pH值在各退化程度间具有显著差异,含水率在重度退化最低,pH值在中度退化最低。(4)土壤速效N、速效P、全P和阳离子代换量在各土层间均无显著差异,全N与有机质在土层间的差异性随着退化程度的加重由显著变为不显著,养分含量总体上随土层深度增加而降低。随着退化程度的加重,土层速效N和全P含量无显著变化,但速效N含量在重度退化最低,0-5cm土层全P含量逐渐降低;速效P、有机质、全N和阳离子代换量具有显著变化,速效P和有机质含量逐渐降低,各土层全N含量总体在重度退化最低,未退化中10-20cm土层的阳离子代换量显著大于重度退化。(5)随着土层深度增加,土壤微生物总数与三大类微生物数量逐渐减小;细菌数量比例减小,放线菌数量比例增加。各土层中细菌数量总体最多,放线菌数量次之,真菌数量极少。随着退化程度加重,0-5cm土层与5-10cm土层的细菌数量、放线菌数量与微生物总数均显著减少,10-20cm土层无显著变化,各土层真菌数量无显著变化。中度退化的3个土层中细菌数量比例最大,放线菌数量比例最小。(6)4种酶的活性随土层加深而降低。随着退化程度加重,0-5cm土层酶活性逐渐降低,而5-10cm土层与10-20cm土层无显著变化;蛋白酶活性与脲酶活性在土层间的差异性由显著变为不显著,过氧化氢酶活性则相反,蔗糖酶活性无变化。人工梭梭林群落退化对土壤过氧化氢酶、脲酶与蛋白酶活性的影响大于对蔗糖酶活性的影响,过氧化氢酶、脲酶与蛋白酶的敏感性强于蔗糖酶。(7)人工梭梭林群落中物种α多样性指数间相关性较强,但其与土壤指标间的相关性极弱;除土壤机械组成间相关性较强外,其他理化指标间相关性总体上较弱;土壤生物学指标与粉粒、pH值、全盐含量、全N、速效P、有机质、阳离子代换量间相关性极强,土壤生物学指标与化学指标间的相关性总体上强于与物理指标间的相关性;除放线菌数量外,其他生物学指标间相关性极强。(8)人工梭梭林各退化群落与土层中土壤肥力大小为未退化0-5cm土层>未退化5-10cm土层>中度退化0-5cm土层>轻度退化0-5cm土层>未退化10-20cm土层>轻度退化5-10cm土层>中度退化5-10cm土层>重度退化0-5cm土层>中度退化10-20cm土层>轻度退化10-20cm土层>重度退化5-10cm土层>重度退化10-20cm土层,各土层中土壤肥力大小为未退化>轻度退化/中度退化>重度退化,各退化程度中土壤肥力大小为0-5cm土层>5-10cm土层>10-20cm土层。

Vegetation degradation of Oasis-desert Ecotone concerns the expansion of desertification in arid area and semi-arid area,therefore,it is extremely significant focus in the process of combating desertification.Haloxylon ammodendron was introduced to Minqin regions from Xinjiang province in the 1960 s,combined with local clay barrier and became the primary windbreak and sand-fixation mode.The total area of artificial H.ammodendron plantations in Minqin county is about 0.035 million hm2,occupies 51.5% of the total area of artificial forestry.Because of the impact of climatic change,human activities and other factors,the water table is falling and soil moisture content is gradually declining in Minqin Oasis-desert Ecotone,this have lead to degradation of artificial H.ammodendron community,and seriously threats to the survival and development of Minqin Oasis.In this dissertation,we focused on the research of the artificial H.ammodendron community and its soil in Minqin Oasis-desert Ecotone,based on the investigation of vegetation,collecting and testing of soil samples,firstly divided all communities into four degradation grades according to vegetation data,secondly explored vegetation and soil characteristic of communities with different degradation grades as well as the relation between vegetation degradation and change of soil characteristic,provided scientific basis for monitoring and evaluation of soil quality,restoration of degraded vegetation and sustainable construction of desert ecosystem in desert area.The results were as follows:(1)With the aggravation of degradation of artificial H.ammodendron community,rate of dead branch,shoot length,growth power and proportion of survival of H.ammodendron had significant differences,rate of dead branch increased,shoot length shortened,growth power got poor,and dead plants began to appear in SD.The importance value of H.ammodendron was considerably greater than that of other species in all degradation grades.With the aggravation of degradation,the importance value of Calligonum mongolicum had no significant differences,that of H.ammodendron,Bassia dasyphylla and Limonium aureum as a whole decreased,that of Halogeton glomeratus and Agriophyllum squarrosum gradually increased,that of Artemisia desertorum first increased and then decreased.(2)With the aggravation of degradation,species α diversity indexes of shrub layer had no obvious change,number of species of herb layer increased;the order of Simpson index,Shannon-Wiener index and Pielou index of herb layer and whole was MD>LD>SD>ND.Species replacement rate among communities of contiguous degradation grades decreased,similarity increased with the aggravation of degradation,and the order of similarity was shrub layer>whole>herb layer.H.ammodendron was negatively correlated to L.aureum,C.mongolicum,Artemisia desertorum and Salsola collina in artificial H.ammodendron community,and had little correlation with B.dasyphylla,H.glomeratus and A.squarrosum.(3)The differences of soil mechanical composition,moisture content,total salt content,bulk density and total porosity among three soil layers on the whole was not significant,but moisture content and total salt content decreased with the increase of soil depth;the difference of pH among soil layers altered from significant to non-significant with the aggravation of degradation.Soil mechanical composition,bulk density,total porosity and total salt content of all soil layers had no obvious change with the aggravation of degradation,but soil mechanical composition of ND was relatively fine,that of MD was relatively coarse;moisture content and pH among different degradation grades had significant differences,moisture content of SD and pH of MD were lowest.(4)Soil available N,available P,total P and cation exchange capacity had no significant differences among soil layers,the difference of total N and organic matter among soil layers changed from significant to non-significant with the aggravation of degradation,various nutrient content decreased with the increase of soil depth as a whole.With the aggravation of degradation,available N and total P had no obvious change in all soil layers,but available N of SD was lowest,total P of soil layer 0-5cm gradually decreased;available P,organic matter,total N and cation exchange capacity had significant differences,available P and organic matter gradually decreased,total N of all soil layers of SD on the whole was minimum,cation exchange capacity of soil layer 10-20 cm of ND was greater than that of SD.(5)With the increase of soil depth as a whole,the number of soil total microbes and three kinds of microbes was decreased,proportion of bacteria was decreased,proportion of actinomycetes was increased.Number of bacteria occupied first place,number of actinomycetes came second,number of fungi was few in all soil layers.With the aggravation of degradation,significant change of number of fungi was not observed;number of bacteria,actinomycetes and total microbes decreased in 0-5cm and 5-10 cm soil layer,but no obvious change in 10-20 cm soil layer.Proportion of bacteria was maximum in three soil layers of MD,but proportion of actinomycetes was minimum.(6)Overall,enzyme activities decreased with the increase of soil depth.Enzyme activities of 0-5cm soil layer decreased with the aggravation of degradation,but not had significant change in other soil layers.The difference of proteinase activity and urease activity among soil layers changed from significant to non-significant with the aggravation of degradation,catalase activity was the opposite,invertase activity remained unchanged.The impact of degradation of artificial H.ammodendron community on proteinase activity,catalase activity,urease activity was greater than invertase activity,and the former had higher sensitivity to the change of resource and environment.(7)There was strong correlation among species α diversity indexes of artificial H.ammodendron community,but correlation between them and soil indexes was extremely feeble.Correlation among other soil physicochemical indexes was feeble except soil mechanical composition.There was extremely strong correlation between soil biological indexes and silt,pH,total salt content,total N,available P,organic matter,cation exchange capacity;the correlation between soil biological indexes and chemical indexes was stronger than the correlation between soil biological indexes and physical indexes as a whole.Correlation among other soil biological indexes was extremely strong except number of actinomycete.(8)The order of soil fertility of different layers in artificial H.ammodendron community with different degradation grades was ND 0-5cm>ND 5-10cm>MD 0-5cm>LD 0-5cm>ND 10-20cm>LD 5-10cm>MD 5-10cm>SD 0-5cm>MD 10-20cm>LD 10-20cm>SD 5-10cm>SD 10-20 cm,the order of soil fertility of different degradation grades was ND>LD/MD>SD,the order of soil fertility of different layers was 0-5cm>5-10cm>10-20 cm.

民勤; 人工梭梭林; 退化; 植被特征; 土壤性质;

Minqin; artificial Haloxylon ammodendron forest; degradation; vegetation characteristic; soil property;

徐先英;

S718.5

174671474K