【作者】 王江；

【导师】 余世孝；

【作者基本信息】 中山大学 ， 生态学， 2006， 博士

【摘要】 研究样地选择在广东省封开县黑石顶自然保护区附近,在黑石顶及周边地区进行植物种子收集。在采集82个植物种子的基础上建立了不同物种丰富度(1、2、4、6、8、10、15、20、25、30、35、40)的人工草地样地,在样地群落自然生长一年后,对样地同时进行干旱胁迫和正常对照处理。处理两个月和四个月后,对样地生物量和土壤氮等指标进行调查。并对生物多样性不同组成成分(物种丰富度、优势物种、功能群数量与组成)与生态系统功能(生物量、土壤氮和稳定性)之间的相互关系进行研究。在群落自然生长一年后,根据群落内物种生物量所占比例,将样地群落划分为七个优势物种类型(优势物种生物量所占比例均在60%以上,盖度在群落内均最大):刺蒴麻(Triumfetta bartramia)、肖梵天花(Urena lobata)、狗牙根(Cynodon dactylon)、黑莎草(Gahnia tristis)、藿香蓟(Ageratum houstonianum)、家艾(Artemisia argyi)和豚草(Ambrosia artemisiifolia),其余为均匀度较高没有优势物种的样地。并且,根据样地群落内主要33个物种(占样地群落地上初级生产力的95%以上)的生长型特征,将33个物种划分为三个功能群:一年生草本、多年生草本和灌木或半灌木。根据样地群落内不同功能群物种组合,将样地群落划分为七个功能群组成类型:一年生草本、多年生草本、灌木或半灌木、一年生草本+多年生草本、一年生草本+灌木或半灌木、多年生草本+灌木或半灌木和一年生草本+多年生草本+灌木或半灌木。(1)样地生物量研究表明,干旱胁迫条件下,具有不同优势物种样地的生物量之间存在显著差异。而且,不同优势物种样地的生物量在干旱胁迫下呈现明显不同的变化趋势。但是,具有不同物种丰富度样地的生物量之间不存在显著差异。这主要由于种间竞争导致优势物种生物量占样地生物量的比例较大,优势物种生物量特征以及干旱胁迫下生物量的变化对样地生物量有着重要的影响作用。研究同时发现,功能群组成对样地生物量同样存在明显的影响作用,随着干旱胁迫时间延长,影响作用在逐渐增强。三类功能群中,一年生草本功能群在干旱胁迫条件下对样地生物量有重要的影响作用。有一年生草本存在的样地,处理四个月时生物量变化率(干旱胁迫样地与正常对照样地相比生物量变化率)均高于两个月时的水平,其它功能群组成样地的生物量变化率均低于两个月时的水平。通径分析结果表明,干旱胁迫和正常对照条件下,优势物种和功能群组成对样地生物量有重要的影响作用,物种丰富度和功能群数量对样地生物量的影响作用较小。与正常对照相比,干旱胁迫条件下优势物种和功能群组成对样地生物量的影响作用明显改变。对功能群内主要物种生物量分析结果显示,同一功能群内物种作用存在明显差异,功能群内物种组成对功能群生物量产生明显的影响作用。然而,同一物种的生物量在不同功能群组成样地之间同样存在明显差异,竞争关系改变是影响物种生物量变化的一个重要因子。对土壤根生物量的研究表明,地下根生物量与地上生物量没有明显的相关性,样地根生物量的平均值随着物种丰富度增加而增加。(2)对土壤氮研究表明,干旱胁迫条件下,优势物种对土壤速效氮(硝态氮和铵态氮)的影响作用明显,而物种丰富度的影响作用较弱。研究同时发现,处理四个月时,干旱胁迫样地土壤速效氮的平均含量明显高于正常对照样地。而且,处理四个月时,干旱胁迫样地速效氮的平均含量显著高于处理两个月时的水平。这与干旱胁迫和正常对照样地之间土壤含水量存在显著差异有关。研究同时发现,干旱胁迫条件下,功能群组成对土壤速效氮(硝态氮和铵态氮)同样产生明显的影响作用。LSD检验结果显示,正常对照条件下,对不同功能群组成类型的样地进行配对比较,样地土壤速效氮含量均不存在显著差异。但是,干旱胁迫条件下,配对比较显示灌木或半灌木和多年生草本+灌木或半灌木组成样地与其它组成样地之间土壤速效氮含量存在显著差异。生物多样性对土壤全氮影响研究发现,物种丰富度对土壤全氮的影响作用明显,干旱胁迫条件下,不同物种丰富度样地土壤全氮之间存在显著差异。而优势物种和功能群组成对土壤全氮的影响作用相对较弱。与土壤速效氮相比,干旱胁迫条件下,土壤全氮含量相对比较稳定,受环境因素影响较小。(3)以生物量变化率绝对值(处理四个月时生物量与处理两个月时生物量相比)作为衡量群落、功能群和种群稳定性的指标,对稳定性进行研究。研究结果表明,干旱胁迫条件下,优势物种对样地群落稳定性的影响作用比较明显,而物种丰富度的影响作用较弱。这主要由于试验样地物种均匀度较低,多数样地生物量由一个或几个优势物种控制,优势物种对样地生物量变化存在重要的影响作用。研究同时发现,干旱胁迫条件下,功能群组成对样地群落稳定性的影响作用明显。干旱胁迫条件下,不同功能群组成样地,群落稳定性呈现明显不同的变化趋势。对不同组织水平稳定性研究发现,干旱胁迫条件下,群落、功能群到种群三个组织水平的生物量变化率依次升高,而稳定性依次降低。研究结果显示不同功能群和功能群内不同物种对干旱胁迫存在不同的响应机制,低组织水平组成成分对干旱胁迫不同的响应机制使得高组织水平具有更高的稳定性。(4)对29个常见物种竞争等级研究发现,以生物量百分率代表物种综合竞争等级,处理两个月和四个月时,干旱胁迫和正常对照样地内豚草Ambrosia artemisiifolia和黑莎草Gahnia tristis生物量百分率均最高,为竞争优势种。处理四个月时,干旱胁迫样地内有多数物种生物量百分率与两个月时相比发生明显变化,物种竞争等级发生改变。正常对照样地内,多数物种生物量百分率没有明显变化,竞争等级未发生改变。以消亡百分率代表物种存活特征竞争能力,干旱胁迫和正常对照样地内物种消亡百分率之间存在显著正相关,存活特征的竞争等级未发生明显的变化,说明干旱胁迫对物种存活特征的竞争等级的影响作用较弱。以物种生物量百分率增加值代表物种生长特征竞争能力,干旱胁迫和正常对照样地内物种生物量百分率增加值之间不存在显著相关性,生长特征竞争等级明显改变,说明干旱胁迫对物种生长特征的竞争等级有明显的影响作用。研究同时发现,干旱胁迫和正常对照条件下,不同物种丰富度样地内,豚草Ambrosia artemisiifolia和黑莎草Gahnia tristis的样地消亡百分率均最低,生物量增加百分率均最高,为竞争优势种。白背黄花稔Sida rhombifolia、含羞草决明Cassia mimosoides和小鱼仙草Mosla dianthera的样地消亡百分率均最高,生物量变化率均最低,为竞争劣势种。其他物种的样地消亡百分率和生物量增加百分率则明显不同,竞争等级变化非常明显。(5)对多样性作用机制研究表明,处理两个月时,干旱胁迫样地内对生物量影响作用微弱的“冗余”物种,处理四个月时,其影响作用有一定的增强。处理两个月时,正常对照样地内对生物量影响作用微弱的“冗余”物种,处理四个月时,其影响作用没有明显变化。研究同时发现,处理两个月时干旱胁迫样地内对生物量作用微弱的“冗余”物种,在处理四个月时所起作用明显不同。尤其,苍耳Xanthium sibiricum和青葙Celosia argentea在处理四个月时对样地群落生物量产生了重要的影响作用。因此,“冗余”只是一个相对的概念,功能相似的“冗余”物种在不同环境条件下作用可能会显著不同。研究同时发现干旱胁迫条件下,在14:00时一天中大气温度最高时段,物种丰富度越高的样地,其群落内相对湿度越高,温度越低。结果说明随着物种丰富度的增加,群落内的小气候环境越优越。而且,随着物种丰富度的增加,干旱胁迫样地内有更多物种的生物量变化率值高于正常对照样地,这些研究结果与胁迫环境下物种之间正相互作用机制有关。更多还原

【Abstract】 The experimental site is selected near the HeiShiDing Nature Reserve, Guangdong province, China. We collected the seed of 82 species in the HeiShiDing Nature Reserve and constructed artificial grassland plots with various species richness (1, 2, 4, 6, 8, 10, 15, 20, 25, 30, 35, 40). After one year, the drought and un-drought condition was exposed to plots. Some parameters, such as biomass and soil nitrogen, etc., were investigated in the plots after 2 months and 4 months of drought stress. The relationship between various components of biodiversity (species richness, dominant species, functional richness and functional composition) and ecosystem function (biomass, soil nitrogen and stability) was studied.Before the treatment of drought stress, most of communities can be classified into following seven types with biomass of dominant species which took account of 60% in the plots: Triumfetta bartramia, Urena lobata, Cynodon dactylon, Gahnia tristis, Ageratum houstonianum, A/rtemisia argyi and Ambrosia artemisiifolia. There was no dominant species in other communities. Totally, there are 33 common species distributed in these plots. They took account of 95% of the total biomass in the plots. These 33 species were classified into three functional groups with the traits of life form: annual herbage, perennial herbage and shrub-subshrub. According to the combination of species with different functional traits in the plots, we classified seven types of communities with various functional compositions: annual herbage, perennial herbage, shrub-subshrub, annual herbage + perennial herbage, annual herbage + shrub-subshrub, perennial herbage + shrub-subshrub, annual herbage + perennial herbage + shrub-subshrub.(1) Dominant species has more important effect on the biomass of plot than species richness. The change of species evenness is the main reason that dominant species has significant effect on biomass, while the competition interaction between species led the change of evenness. We also find that functional composition has significant effect on the biomass of plot, and with the continuance of drought stress the effect of functional composition was stronger. The species can be classified into three functional groups: annual herbage, perennial herbage and shrub-subshrub. Under drought stress, annual herbage is the key factor that influences the biomass change of plots with different functional composition. Path analysis showed that dominant species and functional composition had important direct-effect on the biomass of plots, but species richness and functional richness had little direct-effect. Besides, there was important indirect-effect between dominant species and functional composition, and they also had important indirect-effect on other components of biodiversity. These indirect-effects were influenced greatly by drought stress. The change of the biomass with those common species showed that various species had different roles in the same functional group. This means that the species composition of functional group has significant effect on the biomass of functional group. There was a significant difference between the plots with different functional composition for the biomass of a single species. The change of competition relationship between species is an important factor that influences species biomass.(2) Dominant species has more important effect on available nitrogen (nitrate nitrogen and ammonium nitrogen) than species richness under the stress of drought. The average concentration of available nitrogen in the plots with drought stress was significantly higher than that in the contrast plots after 4 months of drought stress. In the plots with the stress of drought, the average concentration of available nitrogen after 4 months of drought stress was significantly higher than that after 2 months of drought stress. Maybe it was related to the change of environmental factors caused by drought stress, such as soil temperature and moisture, etc.. Therefore, environmental factor is the key factor that influences soil available nitrogen. LSD analysis revealed that available nitrogen concentration between the plots with various functional composition appear no significant difference in the contrast plots. In the plots with the stress of drought, the available nitrogen concentration has significant difference. This may be the reason that under drought stress, different functional group species have different effect on microorganisms that control the mineralization of nitrogen. Our research also indicated that species richness had important effect on the soil total nitrogen either in drought or un-drought plots, but dominant species and functional composition has little effect. Contrast to soil available nitrogen, soil total nitrogen was not influenced by the environmental factors. Its concentration was relatively stable under drought stress.(3) Dominant species has significant effect on the stability of plots, while species richness has little effect. The reason is that the species evenness is low in experimental plots, and the biomass of most plots is determined by one or several dominant species. We also fund that functional composition had important effect on the stability of plots. Under drought stress, the stability of plots with various functional compositions has different trends of change. The stability also increases progressively along the hierarchy of organizational level, i.e., from species to the functional group, and then to community (plot). Variant components in the organizational level have different response mechanisms to the drought stress. (4) With the analysis of the competitive hierarchies in common 29 species, we fund that Ambrosia artemisiifolia and Gahnia tristis have the highest biomass percentage (biomass percentage is used to present the comprehensive competitive hierarchies) in drought and un-drought plots after 2 months and 4 months of drought stress. They are dominant species in competition. Contrast to un-drought plots, there were significant difference of the biomass percentage in drought plots between 2 months and 4 months of drought stress. This means that the competitive hierarchies of these species change greatly. Species mortality, which is used to present the competitive ability of species survival, was significantly positive correlated between un-drought plots and drought plots. This indicated that drought stress has no significant effect on the competitive hierarchies of species survival characteristic. The increscent of species biomass percentage, which is used to present the competitive ability of species growth, was not significantly correlated between un-drought plots and drought plots. This means that drought stress has significant effect on the competitive hierarchies of species growth characteristic. Either in the un-drought or drought plots with various gradients of species richness, both survival competition ability and growth competition ability of Sida rhombifolia, Mosla dianthera and Cassia mimosoides were the lowest. This indicated that they are competitive inferior species and their competitive hierarchies don’t change. In the un-drought and drought plots with various gradients of species richness, the survival competition ability of Ambrosia artemisiifolia and Gahnia tristis were the highest. Although the growth competition ability of Ambrosia artemisiifolia and Gahnia tristis changes, while their biomass percentage was still the highest. This means they are the competitive dominant species and their competitive hierarchies don’t change. However, in the un-drought and drought plots with various gradients of species richness, both survival competition ability and growth competition ability of the species that have moderate comprehensive competitive hierarchies changed greatly.(5) In the drought plots,“redundancy”species that has little effect on the biomass of plots after 2 months of drought stress has more or less effect on the biomass of plots after 4 months of drought stress. However, in the contrast plots, those“redundancy”species that had little effect on the biomass of plots after 2 months of drought stress, still no effect on the biomass after 4 months of drought stress. While in the plots with the stress of drought, we found that the species with little effect on the biomass of plots after 2 months of drought stress, had various effects after 4 months of drought stress. In particular, Xanthium sibiricum and Celosia argentea have great effect on the biomass of plots after 4 months of drought stress. Therefore,“redundancy”may be just a relative concept. The“redundancy”species which has similar function in a certain environment may be has significantly different function in a different environment.更多还原