【作者】 吴勇；

【导师】 李贤伟；

【作者基本信息】 四川农业大学 ， 森林培育， 2011， 博士

【摘要】 人工林配置优质牧草是退耕还林工程中广泛采用、同时兼顾生态效益和经济效益的一种生态恢复模式。在8年生台湾桤木人工林中,采用扇形挖掘法取样,对台湾桤木+扁穗牛鞭草(A+H)、台湾桤木+多花黑麦草(A+L)两种人工林草复合模式和台湾桤木+自然草(A+N)模式进行了对比研究,分析了林木细根在不同模式下的分枝特性、垂直分布、养分内循环、细根现存量、生产量和周转以及土壤有机碳的含量和分布,并对比了施肥后两种人工草模式(A+H+F, A+L+F)细根特性和土壤有机碳的变化。研究结果表明：1.未施肥地细根分枝能力顺序依次为A+N>A+H>A+L。施肥后,两种人工草模式1级细根分枝能力差异均达到显著(P<0.05), A+L与A+H、A+L+F林地2级细根分枝能力差异显著(P<0.05)而3级细根均不显著(P>0.05),。各模式台湾桤木细根生物量、根长密度和根表面积均随土壤深度增加而迅速减少,但根长密度和根表面积在0～20cm土层所占比例高于细根生物量,细根特征值与土层深度的相关性用y=ae-bx指数曲线方程拟合效果最好。2.5种模式细根月均现存量顺序依次为：A+N>A+H>A+L+F>A+L>A+H+F, la时间中,细根现存量均成明显的双峰型变化,活细根分别在6月和9月出现峰值,7～8月为一个相对低谷区,全年最低值出现在12月或者1月；细根年生产量顺序依次为：A+L+F>A+H>A+H+F>A+N>A+L,年周转率则依次是：A+H (1.384次.a-1)>A+L+F (1.369次.a-1)>A+H+F (1.341次.a-1)>A+N (1.068次.a-1)>A+L (1.038次.a-1)。3.台湾桤木根叶分解速度并不一致。从干物质的残留率来看,60d之前细根的损失率高于凋落叶,之后细根的损失率明显低于凋落叶。分解1a后凋落叶残留率低于细根,细根在不同分解环境中分解速率出现差异,分解常数k从大到小依次为凋落叶(1.7547a-1)>A+L林地细根(1.039a-1)>A+H林地细根(0.9332a-1)>A+N林地细根(0.9178 a-1)。凋落叶和细根分解过程中干物质和各元素的残留率可以用y=eax指数方程很好地拟合。N,P,K,Ca等养分元素的年归还量依次是：A+L+F (13.797 kg.hm-2) >A+H+F (10.063 kg.hm-2)>A+H (9.250 kg.hm-2)>A+L (7.863 kg.hm-2)>A+N (3.632 kg.hm-2),人工林草模式的自肥能力强于自然草模式,施肥后其自肥能力进一步增强。4.台湾桤木细根衰老过程中N和K出现明显迁移,Ca和P迁移不明显,Ca在细根衰老期间含量较为稳定,可以作为衡量其他元素变化的参照基准。各根序养分元素出现迁移的时间不同,低级根序先迁移,高级根序后迁移,说明细根的衰老顺序与生长顺序相反。台湾桤木细根和凋落叶在衰老死亡前都存在部分养分元素迁移,且随着土壤养分有效性提高,养分迁移率降低,证实了养分内循环是对贫瘠立地的一种适应。施肥后,细根养分迁移的响应比凋落叶更迅速。5. 5种模式细根中养分元素平均含量Ca>N>K>P, N素夏季含量较高,秋冬季节较低,K的含量则是夏季含量较低而冬春季节含量较高,P的含量夏季高,冬春较低,出现较为明显的单峰型变化规律,Ca的含量在5种模式细根中并无明显规律。5种模式细根中C/N从大到小依次为A+N>A+L+F>A+L>A+H>A+H+F; 0-20cm土层速效N含量与A+L+F模式细根中N含量极显著负相关(P<0.01),速效K的含量与A+H模式细根中K含量也极显著负相关(P<0.01),但土壤和细根中P和Ca的含量相关性并不显著(P>0.05)。6.林草复合模式土壤有机碳含量高于自然草模式。各模式中土壤有机碳的垂直均随着土层深度增加,有机碳含量减少,但减少幅度略有差异；土壤有机碳出现明显的季节变化规律：从冬季开始,土壤有机碳处于积累过程,直至次年夏季达到峰值,而后逐渐减少,到秋季达到最低值。施肥增加了植物生物量和凋落物量,从而增加了土壤有机碳的含量。更多还原

【Abstract】 Qualified pasture distribution dominated by plantation is a widely-used model in converting cultivated land into forests with the simultaneous combination of ecological and economic benefits. The paper makes a comparative reseach of Hemarthria compressa (L.F.)R.Br., Lolium multiflorum Lam. and natural grass marked "A+H", "A+L" and "A+N",by taking a sample with fan-shaped digging method in 8-year-old Alnus formosana artificial forests under different grass layers, carries an analysis of distribution characters in different models, vertical distribution, nutrients internal cycling, biomass, production and turnover rate of fine roots and the storage and distribution of soil organic carbon, and finally has a contrast of the fine roots characters of the two Alnus formosana artificial forests after being fertilized and changes of the soil organic carbon.Then we have come to the conclusions:1. The tillering ability of fine roots in unfertilized forest is A+N>A+H>A+L. There is a significant difference of tillering ability in the first order fine roots between fertilized and unfertilized forests, not significant difference in the third order of fine roots and significant difference in A+L and A+L+F, A+H forest only in the second order fine roots. The rules of fine roots eigenvalue dynamics are similar:the value decreased with soil deepening, the percentages of root length and area are more than biomass in the top soil layer. The relation-ship between fine root eigenvalue and soil depth can fit very well by y=ae-b2. The mean monthly biomass order of fine roots is:A+N> A+H> A+L+F> A+L> A+H+F, the live fine roots have two peak value in July and September during a year, the lowest value appears in December or next January; the order of fine roots annual production is:A+L+F> A+H> A+H+F> A+N> A+L, annual turnover rate is:A+H(1.384)> A+L+F(1.369)> A+H+F(1.341)> A+N(1.068)> A+L(1.038 times.a-1).3. The biomass retention rate of leaves is quicker than fine roots in the first 60 days, and then the rate is contrary because lignins of fine roots are more than leaves and biochemical process is dominant after 60 days. The retention rate of leaves is lower than fine roots after 1 year. Fine root have different release speeds in different inviroment, the order of decoposition constant K is:leaves(1.7547a-1)> fine root in A+L forest(1.039a-1)>fine root in A+H forest (0.9332a-1)>ine root in A+N forest (0.9178 a-1) The biomass and elements retention rate of fine roots and leaves biomass can fit very well by y=ae*bx. The nutrient return order is: A+L+F(13.797)>A+H+F(10.063)>A+H (9.250)>A+L(7.863)>A+N(3.632 kg.hm-2), it demonstrates that tree+pasture models can improve soil conditions.4. The N and K of Alnus formosana fine roots transport obviously in the course of senescence while not obvious about Ca and P. Ca can be looked on as a standard to evaluate other elements because it is steady in the course of senescence. The orders of nutrient transportation are not similar, the first is the 1st fine root, then 2nd fine root......it implies that the senescence orders are contrary to the growth order. The transport ratio decreases with the increase of soil nutrient; it proves that nutrient internal cycling is a strategy for plants to adapt to oligotrophic conditions. The nutrient transport response of fine roots is more obvious than leaves after fertilization.5. The mean nutrient content of fine roots is Ca>N>K>P, the peak value of N appears in Summer and the lowest value appeas in Autumn and Winter, while the peak of K appears in Winter and Spring, the content of P is contrary to K. Ca’s content of fine roots in five models has no obvious rules.The order of C/N is A+N>A+L+F>A+L>A+H>A+H+F; There is a strong correlation between soil available N, K and the N, K of fine roots. There is a significant correlation between 0-20cm soil available N content and N of A+L+F fine roots. There is a strong correlation between soil available K and K of A+H fine roots, while it is not correlation of P and Ca between soil and fine roots.6. The soil organic carbon of tree+pasture model is more than natural grass model.The rules of organic carbon distribution are similar: it decreases with soil depth increasing; The dynamics of soil organic carbon is:it accumulates from Winter and the peak value appears in Summer, then it decreases and the lowest value appears in Autumn. It increases biomass, litter and soil organic carbon reserves after fertilized.更多还原