大针茅和糙隐子草对养分资源的竞争策略Ⅰ.根和茎对施硫和其他养分的形态学反应

在德国植物营养和土壤科学研究所的温室中,用盆栽试验研究了3种不同的养分处理下(所有养分 硫肥、所有养分但无硫肥、空白对照(什么都不添加))大针茅(Stipa grandis L.)和糙隐子草(Cleistogenes squarrosa L.)对养分资源的竞争在形态学上的反应.竞争试验设计为替代序列设计,即每盆的植物密度为4株,大针茅的植株数从4→0,相反,糙隐子草的密度则从0→4.试验所用的土壤为内蒙古典型草原沙质栗钙土,2001年5月20日播种,待种籽发芽出苗后的第二天进行间苗.然后,每间隔10 d分别对两种草的叶层高度、叶片数、分孽数进行测定;并于试验的第80天,度量糙隐子草新近展开的顶部叶片的叶绿素含量,之后齐地面刈割地上部分测地上生物量,同时将试验盆浸泡在蒸馏水中,用60目的网筛轻轻冲洗根系,用滤纸吸干水分,称鲜重,以便测定根长、根半径和根表面积等;然后用无离子水冲洗根系,在65℃下烘48 h称重,过0.5mm筛粉碎装瓶备分析用.每个处理重复3次.结果表明,所有处理的大针茅和糙隐子草形态特征不存在竞争关系,即彼此比例的消长对对方无显著性的影响,且大针茅的根茎形态特征随两者比例的变化而变化不显著,在空白对照处理中糙隐子草也有类似的现象.然而,当供给养分时(无论是否同时添加硫肥),糙隐子草的比例大小显著影响其形态特征,即存在密度制约原理,且硫的供给与糙隐子草的比例间存在互作现象.养分添加显著增加了大针茅地上部分的生长利发育,但对根系的生长影响很小,且硫对其地上地下均无显著性的影响.而养分添加不仅增加了糙隐子草地上部分的生长发育,而且增加了根系的生长,硫的缺乏阻碍了糙隐子草地上地下的生长和发育.养分供给显著降低了糙隐子草的根茎比,但没有影响大针茅的根茎比.硫对糙隐子草根茎比的影响随糙隐子草比例的变化而变化,在其比例为100%和75%时,供硫显著降低了其根茎比.在所有养分处理中,25%比例的糙隐子草的根茎比显著小于100%比例的糙隐子草根茎比.供给其他养分而不供硫时,糙隐子草叶片的绿度显著淡于其它两种处理;且在养分供应(无论是否供硫)25%比例的糙隐子草叶片绿度显著深于100%比例的糙隐子草叶片绿度.该研究表明,大针茅与糙隐子草的形态之间似乎不存在竞争关系;由于所有处理大针茅种群生产力较低,其种间竞争很小,但糙隐子草种间竞争明显.养分的缺乏主要限制了大针茅地上部分的生长和发育,对地下部分影响较小,且对硫供给的状况反应不敏感.而养分供给对糙隐子草地上地下均有显著的影响,且硫的缺乏阻碍了糙隐子草的生长发育.土壤贫瘠时,由于糙隐子草种群生产力低,植物间竞争较小,相反,对养分资源的竞争加剧.对养分的竞争刺激了根系的生长,使更多的光合产物分配到根中.其他养分的供给,提高了糙隐子草的生产力,因而加剧了硫的缺乏,而在低养分状况下(不供给任何养分)则缓解了硫的缺乏症状.     

Spatial patterns of surface soil properties and vegetation in a Mediterranean semi-arid steppe

In arid and semi-arid areas with sparse vegetation cover, the spatial pattern of surface soil properties affects water and nutrient flows, and is a question of considerable interest for understanding degradation processes and establishing adequate management measures. In this study, we investigate the spatial distribution of vegetation and surface soil properties (biological crusts, physical crusts, mosses, rock fragments, earthworm casts, fine root accumulation and below-ground stones) in a semi-arid Stipa tenacissima L. steppe in SE Spain. We applied the combination of spatial analysis by distance indices (SADIE) and geostatistics to assess the spatial pattern of soil properties and vegetation, and correlation analyses to explore how these patterns were related. SADIE analysis detected significant clumped patterns in the spatial distribution of vegetation, mosses, fine root accumulation and below-ground stone content. Contoured SADIE index of clustering maps suggested the presence of patchiness in the distribution of earthworm casts, fine roots, below-ground stone content, mosses and biological crusts. Correlation analyses suggested that spatial pattern of some soil properties such as biological crusts, moss cover, surface rock fragments, physical crusts and fine roots were significantly related with above-ground plant distribution. We discuss the spatial arrangement of surface soil properties and suggest mechanistic explanations for the observed spatial patterns and relationships.     

西藏紫花针茅叶功能性状沿降水梯度的变化

植物叶功能性状与环境因子的关系是近10年来植物生态学的研究热点。该文以广泛分布于青藏高原干旱、半干旱草地的优势植物种紫花针茅(Stipa purpurea)为研究对象, 沿降水梯度(69-479 mm)系统测定了日土、改则、珠峰、当雄和纳木错5个调查地点紫花针茅比叶面积(SLA)、单位重量和单位面积叶氮含量(N_mass, N_area)、叶密度和厚度等叶功能性状以及土壤全氮含量等因子, 试图验证干旱胁迫地区同一物种内SLA-N_mass关系沿降水梯度的策略位移现象是否具有普遍性, 并对是否出现策略位移现象提出可能的解释。研究结果表明: 1) SLA和N_mass与生长季温度和降水以及土壤全氮含量均没有显著关系, SLA与N_mass的关系在干旱半干旱区(年降水/蒸发比< 0.11)与半湿润区(年降水/蒸发比> 0.11)之间并没有出现典型的位移现象; 2)叶密度是决定半湿润区SLA变化的主导因子, 而叶厚度则是干旱半干旱区SLA变化的控制因子, 两者与SLA均呈负相关, 随着温度增加或降水减少, 叶厚度增加而叶密度降低, 导致SLA随温度和降水变化不明显; 3)半湿润区的叶密度增加引起N_area增加, 而干旱半干旱区的叶厚度增加并没有造成N_area的显著变化, 导致N_area沿降水梯度没有显著变化; 4)紫花针茅地上生物量与N_area具有显著正相关关系, 表明N_area的增加有助于提高植被生产力。结果表明, 在干旱胁迫下, 植物通过增加叶厚度来维持不变的N_area可能有助于保持与较湿润地区相似的光合生产和水分利用效率。叶厚度和叶密度对比叶面积的相对影响在干旱半干旱区与半湿润区之间发生转变, 这为进一步检测高寒草地植被的水分限制阈值提供了新思路。     

西藏高原针茅草地土壤因子对丛枝菌根真菌物种多样性的影响

在对西藏高原北部针茅草地根围土壤中的丛枝菌根(AM)真菌种类分离鉴定基础上,研究了藏北针茅草地的土壤质地、pH、有机质和有效磷含量对AM真菌孢子密度、分离频度、相对多度、重要值、物种多样性指数和均匀度的影响.结果表明: 针茅草地根围土壤中共分离鉴定出AM真菌3属15种,其中,球囊霉属9种、无梗囊霉属6种、盾巨孢囊霉属1种.球囊霉属和无梗囊霉属为藏北针茅草地AM真菌的优势属;近明球囊霉和光壁无梗囊霉为藏北高寒草原针茅属植物根围AM真菌的优势种.不同质地土壤中AM真菌孢子密度、分离频度、相对多度和重要值均表现出球囊霉属＞无梗囊霉属＞盾巨孢囊霉属的趋势;土壤pH值对AM真菌种群组成无明显影响,球囊霉属和无梗囊霉属真菌分离频度、相对多度和重要值随土壤pH升高而增加,盾巨孢囊霉属则呈现相反趋势;不同土壤有机质含量范围内,AM真菌孢子密度等各项指标均呈球囊霉属＞无梗囊霉属＞盾巨孢囊霉属,而AM真菌属的分布没有明显规律;土壤有效磷含量对AM真菌种丰度和孢子密度影响较小.研究区域内AM真菌物种多样性指数和均匀度随着土壤有效磷含量升高而增加.     

Effects of biological soil crusts on a Mediterranean perennial grass (Stipa tenacissima L.)

In the last decades, there has been a growing interest on evaluating the effects of biological soil crusts (hereafter, biocrusts) on vascular plants. The purpose of this paper was to investigate the influence of biocrusts on Stipa tenacissima, key species in arid and semi-arid environments of the Mediterranean Basin. In fact, we explored the impact of biocrusts removal underneath S. tenacissima on soil chemical properties and leaf mineral uptake. Indeed, we studied the effect of mixed biocrusts on the seed germination of S. tenacissima under laboratory conditions. The research showed a greater availability of soil resources correlated with enhanced leaf nutrient levels of bioessential elements in the presence of intact biocrusts compared to fragmented biocrusts underneath S. tenacissima tussocks. We suggest that this is related to the loss of soil moisture as a result of biocrusts removal. In addition, we found that mixed biocrusts favored seed germination and viability of S. tenacissima. By improving soil chemical properties and leaf nutrient uptake, biocrusts can provide enhanced growth conditions for Stipa tenacissima. These findings with the positive effect on seed germination suggest that biocrusts can be used in the restoration of S. tenacissima.     

贝加尔针茅响应降水变化敏感指标及关键阈值

降水是影响中国北方草原群落结构和生产力的关键环境因子,弄清植物响应降水变化敏感指标,确定关键阈值,可为草原的科学管理与制定应对气候变化措施提供依据。以贝加尔针茅为材料,基于不同降水的模拟实验,采用正态总体统计容忍区间及容忍限的估算方法,对测定的叶面积、株高、叶绿素和叶N含量等14个植物生理生态指标响应降水变化的敏感性及其阈值进行了研究。结果表明,植株总叶面积、水势(或叶绿素含量)和地上生物量可分别从形态、生理和生物量积累三方面较好地指示贝加尔针茅对降水变化的敏感性,受到胁迫时的降水量(6、7和8月3个月份总降水量)阈值分别是283、276(276)mm和280 mm。研究结果可为客观辨识贝加尔针茅草原干旱的发生发展与监测预警提供参考。     

大针茅典型草原土壤CO2排放规律的研究

采用静态室/碱吸收法研究了内蒙古大针茅典型草原土壤呼吸的时空动态.大针茅群落地上部和地下部生物量的时空变异不同步,用地上部生物量不能很好地预测群落的根系量.群落土壤呼吸具有明显的时空动态,控制群落土壤呼吸空间变异与时间变异的因子是不同的.土壤呼吸的季节变化与地上部生物量及土壤水分状况关系密切.根据大针茅群落分别计算了大针茅群落1995、1997和1998年的年CO₂排放总量,分别为180、45.8和225gC·m^-2·a^-1,年际变异很大.过度放牧大大降低了群落的生物量,也降低了土壤CO₂排放量.讨论了建立以降水量为驱动因子的草地群落土壤呼吸动态模型的可能性.     

降水量季节分配对克氏针茅草原群落初级生产力的影响

本文根据克氏针茅草原群落初级生产力连续１４年的定位观察资料,分析了降水量及其季节分配对群落初级生产力力年度波动的影响,并应用积分回归模型,计算出１－８月各旬降水量对群落初级生产力的影响系数。结果表明：降水量的年度变化及其季节分配直接导致了克氏针茅草原群落初级生产力的年度波支１月上旬至４月上旬６旬至８月下旬的旬降水量对群落初级生产力均具有正效应。是植物对水分需求的两个关键时期。其中,１月上旬至４月上     

Seedling emergence and survival in contrasting soil microsites in Patagonian Monte shrubland

Abstract. The potential of two perennial species (Larrea divaricata and Stipa tenuis) to colonize different soil microsites was analyzed in the Patagonian Monte shrubland. We hypothesize that the short-lived grass S. tenuis is more able to colonize the soil of microsites beneath vegetation patches where N-fertility is higher than those in bare soil, while the long-lived shrub L. divaricata colonizes different soil microsites irrespective of their N fertility. A greenhouse experiment was carried out to evaluate the emergence and survival of both species in different soil microsites at different water, inorganic N and seed densities. In all cases soil microsites were seed limited since the addition of viable seeds increased seedling emergence. Both species showed, however, different abilities to emerge and survive in different soil microsites. Microsites of bare soil were more favourable for seedling emergence and survival of L. divaricata than those beneath vegetation patches, independent of their water status. This ability of L. divaricata can not be explained on the basis of increased water or N availability, but probably because of lower salt content of bare soil. The addition of inorganic N reduced the survival of L. divaricata in both microsites but increased individual plant performance. The emergence and survival of S. tenuis was not different in both types of soil microsites but the addition of inorganic N increased seedling emergence and plant biomass. According to these results, emergence and plant performance of S. tenuis may be promoted during humid years by increased concentration of inorganic N. Since N mineralization occurs at a higher rate in soil microsites beneath vegetation patches than in those of bare soil, higher plant performance and probably establishment of S. tenuis is to be expected. These results are consistent with an existing conceptual model of plant dynamics under various grazing intensities in the Patagonian Monte shrubland based on previous field observations.     

典型草原常见牧草春季萌动期可溶性糖及内源激素动态研究

在春季萌动期,分别对典型草原几种常见禾本科牧草老芒麦、披碱草、羊草、赖草和克氏针茅的幼芽和地下根系可溶性糖含量及内源激素动态变化规律进行研究.结果表明,高含量的GA和较低含量的ABA是根茎类禾草羊草和赖草春季萌动早的重要调控因子,而根系丰富的可溶性糖为根茎类禾草的萌动生长提供了物质基础;玉米素核苷动态变化趋势与根系可溶性糖含量动态相似,萌动初期呈下降趋势,4月底达到最低值,此后又逐渐上升;而内源激素IAA和GA的含量与牧草幼芽可溶性糖含量的变化趋势一致,均呈逐渐上升趋势;根茎类禾草羊草和赖草与须根系禾草老芒麦和披碱草之间幼芽的GA和ABA水平以及根系可溶性糖含量差异明显.