【作者】 刘东；

【导师】 方升佐；

【作者基本信息】 南京林业大学 ， 森林培育， 2013， 博士

【摘要】 本文以杨树不同无性系[（1）南林895杨：I-69杨(Populus deltoides Bartr. cv.“Lux”）×I-45杨（P. euramericana (Dode) Guinier cv.‘I-45/51’)杂交组合F1（2）南林80351杨：I-69×I-63(P. deltoides Bartr. cv.“Harvard”)杂交组合F1（3）75杨：I-72(P×euramericana(Dode) Guinier cv.“San Matino” ex I-72/58)×I-63杂交组合F1纯林]及杨树（南林895杨）与江南桤木（Alnus trabeculosa）和苏柳799（Salix×jiangsuenis cv.J799）六种不同混交模式（杨树×柳树×桤木、杨树×柳树、杨树×桤木、杨树、柳树、桤木）作为研究对象，采用田间原位根箱试验与室内盆栽根箱试验相结合的方法，研究不同无性系及不同混栽模式下根际土壤养分和微生物群体特征及其季节动态变化，主要研究结果如下：（1）室内模拟盆栽试验条件下，不同混交模式根际土壤的矿化速率及无机态氮的含量显著高于非根际土壤，而在不同混交模式之间，杨树桤木混交模式根际土壤氮的矿化最为迅速，其根际无机态氮的含量也最高，随着根际土壤N净矿化速率的增大，铵态氮和硝态氮的含量均显著增加。（2）杨树与不同树种混栽根际土壤微生物生物量碳和生物量氮均显著高于杨树纯林。不同组成模式根际土的碳氮比值存在显著差异，其中杨树～桤木混交模式最高，其次为杨树～桤木～柳树混交模式、杨树纯林模式、柳树纯林模式、杨树～柳树混交模式，桤木纯林模式最低。杨树～柳树～桤木混交、杨树～柳树混交和杨树～桤木混交模式根际土壤天冬酰胺酶、尿酶活性显著高于杨树纯林，而蛋白酶活性不同混交模式差异不显著。相关性分析表明，根际土壤酶活性与土壤微生物量之间呈显著正相关或负相关。（3）杨树桤木混栽模式根际土壤细菌、真菌群落丰富度和多样性指数显著高于杨树纯林土壤。杨树～柳树、杨树～柳树桤木混栽模式根际土壤细菌、真菌群落丰富度和多样性指数显著低于杨树纯林土壤。不同混栽模式根际土壤细菌、真菌群落丰富度和多样性指数均显著高于非根际土壤。相关分析表明，土壤细菌和真菌群落多样性与土壤养分和微生物生物量间有很好的相关。土壤细菌和真菌群落多样性指数与土壤蛋白酶以及天冬酰胺酶活性均呈显著或极显著相关。（4）田间试验下，除2011年7月份根际与非根际土壤硝态氮含量无显著差异外，三种杨树不同无性系根际及非根际土壤铵态氮含量、无机态氮含量和pH值在相同采样时间下均存在显著差异，其中根际土壤pH值均显著低于非根际土壤，而铵态氮、硝态氮和无机态氮含量均显著高于非根际土壤。在同一采样时间下，杨树不同无性系根际土壤间铵态氮、硝态氮、无机态氮含量和pH值差异均不明显。从季节动态变化上来看，三种杨树不同无性系根际土壤硝态氮含量的季节动态变化存在显著差异。南林895杨根际土壤氮净矿化速率在夏季显著高于春季和冬季。75杨季节差异不显著。南林80351杨净矿化速率最高值出现在冬季。三种杨树无性系根际土壤硝化率趋于稳定，在不同采样时间下均无显著差异。同一采样时间下，三种杨树无性系根际土壤氮净矿化速率在3个不同采样季节都显著高于非根际土壤，而硝化率均显著低于非根际土壤。南林80351杨根际土壤氮净矿化速率在三个不同采样时间均显著高于75杨和南林80351杨。（5）三种杨树无性系在三个不同采样季节微生物生物量总的变化规律一致，均表现为南林895杨>75杨>南林80351杨，根际土>非根际土。从季节动态变化来看，南林895杨、75杨和南林80351杨根际土壤微生物生物量碳、氮冬季较高，而春夏季节较低。三个杨树无性系根际土壤MBC/MBN比值受季节影响差异显著，最高值均出现在2010年11月，最低值均出现在2011年7月，各无性系根际土壤MBC/MBN比值均在5.0以下。同一采样时间下，三种杨树无性系根际土壤尿酶、蛋白酶、天冬酰胺酶活性均存在显著差异。从季节动态变化来看，各种酶活性均在2011年7月份最高。相关分析表明，氮硝化速率与pH之间呈极显著正相关，与尿酶、蛋白酶、天冬酰胺酶活性和微生物碳含量呈极显著负相关；pH值与尿酶、天冬酰胺酶活性和微生物碳含量呈显著负相关，与蛋白酶活性呈极显著负相关；硝态氮含量与微生物碳氮均呈极显著正相关；铵态氮含量与尿酶活性呈显著相关，蛋白酶活性与天冬酰胺酶呈极显著正相关，与微生物量碳呈显著正相关，天冬酰胺酶活性与微生物量碳呈显著正相关。（6）通过对细菌16S rRNADGGE图谱分析发现，同一采样时间三种杨树无性系根际土壤之间条带数不同，说明各无性系的根际土壤细菌群落结构存在着多样性。各无性系之间均存在相同的条带，说明各无性系根际土壤细菌之间存在着相同的类群；并且各条带的亮度也不相同，说明相同细菌种类的数量也存在着差异。与细菌16S rRNADGGE图谱相比，每个土壤样品扩增产物真菌图谱条带数量明显少于细菌图谱，条带少而疏，说明根际土壤真菌类群数低于细菌。不同杨树无性系有许多共同条带，也有一些特殊条带。和细菌的DGGE图谱相比，各样品的泳道带型变异较小，优势条带明显。从季节动态变化上来看，三种杨树不同无性系均表现为11月份细菌、真菌条带数高于7月份和3月份。所以从整体看，冬季（11月份）土壤细菌、真菌多样性组成较春季（3月份）和夏季（7月份）有所提高。相同采样时间下，各无性系土壤细菌、真菌群落相似性系数不大。说明不同无性系在根际土壤微生物群落结构组成方面存在较明显的差异。（7）在长江滩地立地条件下，根际土壤微生物活性在0～2mm和2～4mm处，无显著差异，但与4～10mm处差异显著。因此，选择0～4mm处作为根际土壤采集，是比较正确可靠的根际土壤采集距离。土壤pH值、微生物生物量碳含量、微生物呼吸商、微生物量氮占总氮含量的比例、微生物生物量碳氮比可以作为评价土壤质量的重要参数。本研究中5种不同树种或无性系的根际土壤微生物系数在0.27～0.65之间，划分为4个等级。根据不同树种及不同无性系根际土壤的生物学特性和年平均树高、胸径生长量的研究调查，作者认为本试验中根际土壤微生物系数大于0.5的树种（南林895杨、苏柳799）适合在我国东南部地区季节性淹水滩地或人为干扰比较严重的土壤条件下栽植。更多还原

【Abstract】 This study was conducted with the primary aim of revealing characteristics of soil microbialproperties and nutrient conditions in the rhizosphere of different poplar genetypes and treespecies compositions. The pH values, available N, microbial biomass, enzyme activities,microbial diversities as well as net N mineralization and nitrification rates were investigated inrhizosphere and bulk soils of three poplar clones and six treatments of tree compositions. Threepoplar clones including Nanlin895(a hybrid of I-69(Populus deltoides Bartr. cv.‘Lux’)×I-45(P.euramericana (Dode) Guinier cv.‘I-45/51’),75(a hybrid of I-72(P×euramericana (Dode)Guinier cv.‘San Matino’ ex I-72/58)×I-63(P. deltoides Bartr. cv.‘Harvard’)) and NL80351(ahybrid of I-69×I-63), were selected to be used in this study. These poplars grew in eastern lowerreaches of the Yangtze River where near Ma-an-shan City, Anhui Province, in southeast China.At the same time, laboratory stimulus experiments also carried out of six tree speciescompositions including PAW（poplar×alder×willow）, PA (poplar×alder), PW (poplar×willow), P(poplar), A (alder) and W (willow). For the field study, three different sampling times (earlierNovember2010, later March2011and middle July2011) were selected to explore seasonalvariation of soil microbial properties and nutrient availability in rhizosphere soils of differentpoplar clones. The key findings are as follows:（1）Net N mineralization rate and inorganic N concentration in the rhizosphere soils weresignificantly higher than bulk soil among all six different tree coexistence treatments, whileamong different trees coexistence treatments, the highest N mineralization rate and inorganic Nconcentration were observed in treatment PA which significantly higher than other treatments.Among all six treatments, with the increasing of N mineralization rate in rhizosphere soil,concentration of ammonium nitrogen (NH4+-N) and nitrate nitrogen (NO3--N) were alsoproportionally increased.（2）Soil microbial biomass C (MBC) and microbial biomass N (MBN) varied significantlyin the rhizosphere soils among different tree species compositions. The content MBC and MBNin rhizosphere of PAW, PA, and PW were significantly higher than P. Significant difference ofmicrobial C/N ratios was observed in rhizosphere soils of treatments tested. The highest wasobserved in PA, followed by PAW, P, W and PW, with the lowest observed in A. Soil urease andL-asparaginase activities in the rhizosphere of PAW, PA, and PW were significantly higher than P.Significantly positive or negative correlation between tested enzyme activity and microbialbiomass were observed in soils evaluated.（3）Soil microbial bacterial and fungal diversity varied significantly in the rhizosphere soilsamong different tree species compositions. In PA microbial diversity was significantly higherthan in P, in the contrest in PAW and PW. Microbial diversity in rhizosphere soil wassignificantly higher than bulk soils in tree species compostions tested. There were significant positive correlations between L-asparaginase, protease enzyme activities, and soil microbialbiomass in the rhizosphere soils.（4）For the same sampling time, a significant difference in all measured chemicalproperties between rhizosphere and bulk soils of all three poplar colones were observed, exceptfor soils sampled in the middle of July2011. Generally, the pH value in the rhizosphere soils aresignificantly lower than in the bulk soils, on the anther hand the concentrations of NO3-N,NH4+-N and inorganic N were significantly higher in the rhizosphere than in bulk soils.Concentrations of NO3-N and NH4+-N in the rhizosphere showed significant variations amongdifferent sampling times, but clonal variation in these concentrations was not significant amongthe rhizosphere soils of the three tested poplar clones. There were significant differences inpotential net nitrogen mineralization and nitrification rate between the rhizosphere soils and bulksoils tested. The potential net nitrogen mineralization rate in NL80351was more than150%greater than the values of clones75, Nanlin-895and bulk soil at three sampling times. However,nitrogen nitrification rate was warkedly lower in the rhizosphere soils compared to bulk soils. Nosignificant seasonal variations in nitrogen nitrification rate was founded for each poplar clones aswell as for bulk soil, whereas a significant difference in net nitrogen mineralization rate amongthe three different sampling times for clones Nanlin-895and NL80351were observed.（5）The trends of microbial biomass among three poplar clones at all sampling times weresimilar, which was Nanlin-895>75> NL80351and rhizosphere soil> bulk soil. MBN and MBCof all three poplar clones were significantly higher in winter than summer or spring. Seasonalvariation had extremely significant influence on microbial biomass and soil enzyme activities ofall poplar rhizosphere soil. There was a significant difference in microbial C/N ratio in bothrhizosphere and bulk soils for all three poplar clones among different sampling times. Thehighest C/N ratio appeared in later October2010, while the lowest was observed in middle July2011, where the C/N ratios for three poplar clones were below5.0. Significant variations in thecontents of MBC and MBN as well as the C/N ratio were observed between rhizosphere and bulksoil for all tested poplar clones. In the rhizosphere soil, significant differences in tested enzymes(means of three poplar clones) were observed among three sampling times, and the greatestenzyme activities always appeared in the middle July2011. However, seasonal dynamics of theenzyme activities varied among the poplar clones.（6）Soil microbial bacteria and fungi diversities varied significantly in the rhizosphere soilsamong different three poplar clones in the same sampling time. In the early November of2010,Nanlin-895was observed significantly higher than in75and NL80351. In the later march of2011, Soil microbial bacteria and fungi diversities in the rhizosphere of Nanlin-895and NL80351were significantly higher than in75clones. Significant difference in microbial diversity was notobserved between Nanlin-895and NL80351. For the seasonal aspects, rhizosphere soil microbialdiversity of all three poplar clones was significantly higher in winter than in summer or spring.(7)RSMIs were estimated from various sampling positions of rhizosphere soils. The RSMIvalue varied from0.23to0.66for the rhizosphere soil sampled within0-2mm to the root mats,0.27-0.65within the0-4mm, and0.39-0.59within the0-10mm, respectively. However, a significant difference in RSMI was observed among the five tree species for all samplingpositions of rhizosphere soils. All the highest RSMI occurred in Nanlin-895, while the lowestwas found in alder. A significant difference in microbial biomass and enzymatic activities wasobserved among the three sampling positions. However little difference in microbial biomass andtested enzymes was detected between the0-2mm and2-4mm distances to the root mats. Resultsfrom this study suggest that defining the soil at0-4mm distance from the root mats asrhizosphere soil should be more reliable for this in situ rhizobox design and experiment.Microbial properties of rhizosphere soil are significantly affected by trees species. MBC, pH,MBN/TN, MBC/MBN and MBC/SOC could be important properties for appraising rhizospheresoil quality of seasonal flooded lands. The RSMI calculated by integrating microbial propertiessuggested that two poplar clones (Nanlin-895and75) and a willow clone (Salix×jiangsuensiscv. J799) could be used for afforestation at seasonal flooded lands of Yangtse River.更多还原