降水量变化对藏北高寒草地养分限制的影响

生态系统净初级生产养分限制的模式是现代生态学关注的重要问题。养分的可利用性是草原生态系统生产力动态变化的关键决定因素, 但土壤养分可利用性与整个生态系统中养分限制之间的关系尚不清楚。该研究通过在藏北降水梯度上4种类型高寒草地(从东到西依次是高寒草甸、高寒草甸草原、高寒草原和高寒荒漠草原)设置氮磷养分添加试验, 系统研究氮磷养分添加对不同类型高寒草地的影响, 并探讨降水梯度上高寒草地的氮磷限制模式。结果表明: (1)氮磷添加对不同高寒草地的影响存在差异: 氮添加显著提高了高寒草甸和高寒草甸草原地上生产力, 而对高寒草原和高寒荒漠草原无影响; 单独磷添加对4种高寒草地均无显著影响, 而氮磷添加对4种高寒草地地上生产力均有促进作用。(2)通过计算氮磷共同限制指数发现: 随着降水量减少, 高寒草地氮限制指数从1.18逐渐降低到0.52-0.64, 养分限制模式从氮限制过渡到氮磷共同限制; 磷限制指数在高寒草甸草原和高寒草原为负值, 说明单独磷添加对高寒草甸的生产力有负向作用, 高寒草甸主要受氮限制; 高寒草甸草原介于氮限制与氮磷限制之间, 受到氮磷共同限制, 单独磷添加有负向作用; 高寒荒漠草原受到氮磷共同限制。研究表明, 高寒草地氮磷限制模式存在环境梯度上的递变规律, 随着降水量减少, 高寒草地养分限制模式从氮限制逐渐过渡到氮磷共同限制。由此推断, 未来气候变化条件下氮沉降增加对不同类型高寒草地的影响可能存在差异。同时, 利用养分添加恢复不同类型退化高寒草地时也应将氮磷限制模式的差异考虑进去。     

杉木采伐迹地营造阔叶树种对土壤微生物生态化学计量特征的影响

研究土壤微生物生物量及其生态化学计量特征对造林树种转换的响应,对深入了解森林生态系统土壤养分循环和有效性具有重要意义。本研究以1993年春在二代杉木采伐迹地上营造的26年生米老排和杉木人工林为对象,采用氯仿熏蒸法测定了0～40 cm土层土壤微生物生物量碳(MBC)、氮(MBN)、磷(MBP)的变化。结果表明: 与杉木人工林相比,米老排人工林0～10 cm土层MBC和0～20 cm土层MBN和MBP均显著提高, 0～20 cm土层MBC/MBP和10～20 cm土层MBN/MBP显著降低。两种人工林所有土层MBC/MBN均无差异。相关分析显示,土壤含水率、总有机碳、总氮、全磷、有效磷与MBC、MBN和MBP呈显著正相关,而与MBC/MBP和MBN/MBP呈显著负相关。逐步线性回归分析表明,MBN和MBP主要受土壤总氮和有效磷的影响,而MBC/MBP和MBN/MBP主要受有机碳和有效磷的驱动。研究表明,造林树种从杉木转换成米老排能够增加表层土壤微生物生物量,加速氮磷养分周转,增加土壤氮磷养分供应能力。米老排人工林土壤MBP的增加可能在一定程度上缓解了树木生长的磷限制。     

Different responses of biomass allocation and leaf traits of Dodonaea viscosa to concentrations of nitrogen and phosphorus

调整叶性状和生物量分配格局是植物适应环境变化的主要途径, 研究车桑子(Dodonaea viscosa)幼苗生物量分配与叶性状对氮磷浓度的响应对认识车桑子在氮磷浓度变化下的适应策略具有重要意义。该研究通过砂培法, 测定不同氮浓度(3、5、15、30 mmol·L^-1)与不同磷浓度(0.25、0.5、1、2 mmol·L^-1)下车桑子幼苗的生长、生物量分配、叶性状的响应特征及其相互关系。结果表明: 高浓度氮(30 mmol·L^-1)促进了车桑子幼苗生长、叶片氮含量和生物量积累, 其余氮添加条件(3、5、15 mmol·L^-1)下车桑子幼苗各性状无显著差异, 但相比高氮水平, 其生物量积累和叶片氮含量显著降低, 根冠比和氮利用效率显著增加。随着磷添加浓度的增加, 车桑子幼苗生物量显著增加, 低磷条件(0.25、0.5 mmol·L^-1)限制了车桑子幼苗生长和生物量积累, 其根冠比和磷利用效率均没有发生显著变化, 但比叶面积和叶/茎生物量比例显著增加, 叶干物质含量显著降低。氮处理下, 叶片氮含量与根冠比显著负相关; 磷处理下, 叶片氮含量与比叶面积显著正相关。同时, 氮处理下, 车桑子幼苗株高、基径、总生物量等生长性状均与根冠比显著负相关, 与叶片氮含量显著正相关, 表明根冠比和叶片氮含量的调整在车桑子适应氮限制中发挥重要作用; 而磷处理下, 株高、基径、总生物量与比叶面积显著负相关, 与叶干物质含量显著正相关, 表明叶片结构性状的调整在车桑子适应低磷环境中具有重要意义。该研究表明, 车桑子幼苗生物量分配和叶性状及性状间的权衡策略对氮、磷的响应具有明显差异性, 在今后的研究中, 应关注氮和磷对植物性状影响的差异性。     

车桑子幼苗生物量分配与叶性状对氮磷浓度的响应差异

调整叶性状和生物量分配格局是植物适应环境变化的主要途径, 研究车桑子(Dodonaea viscosa)幼苗生物量分配与叶性状对氮磷浓度的响应对认识车桑子在氮磷浓度变化下的适应策略具有重要意义。该研究通过砂培法, 测定不同氮浓度(3、5、15、30 mmol·L^-1)与不同磷浓度(0.25、0.5、1、2 mmol·L^-1)下车桑子幼苗的生长、生物量分配、叶性状的响应特征及其相互关系。结果表明: 高浓度氮(30 mmol·L^-1)促进了车桑子幼苗生长、叶片氮含量和生物量积累, 其余氮添加条件(3、5、15 mmol·L^-1)下车桑子幼苗各性状无显著差异, 但相比高氮水平, 其生物量积累和叶片氮含量显著降低, 根冠比和氮利用效率显著增加。随着磷添加浓度的增加, 车桑子幼苗生物量显著增加, 低磷条件(0.25、0.5 mmol·L^-1)限制了车桑子幼苗生长和生物量积累, 其根冠比和磷利用效率均没有发生显著变化, 但比叶面积和叶/茎生物量比例显著增加, 叶干物质含量显著降低。氮处理下, 叶片氮含量与根冠比显著负相关; 磷处理下, 叶片氮含量与比叶面积显著正相关。同时, 氮处理下, 车桑子幼苗株高、基径、总生物量等生长性状均与根冠比显著负相关, 与叶片氮含量显著正相关, 表明根冠比和叶片氮含量的调整在车桑子适应氮限制中发挥重要作用; 而磷处理下, 株高、基径、总生物量与比叶面积显著负相关, 与叶干物质含量显著正相关, 表明叶片结构性状的调整在车桑子适应低磷环境中具有重要意义。该研究表明, 车桑子幼苗生物量分配和叶性状及性状间的权衡策略对氮、磷的响应具有明显差异性, 在今后的研究中, 应关注氮和磷对植物性状影响的差异性。     

三江源地区高寒湿地土壤微生物生物量碳氮磷及其化学计量特征

微生物生物量及其化学计量特征是土壤养分循环的重要参数, 对预测气候变化和提高模型准确性及理解陆地生态系统养分循环都起到重要作用。为了明晰高寒生态系统土壤微生物生物量碳(MBC)、微生物生物量氮(MBN)、微生物生物量磷(MBP)浓度及其化学计量特征, 该研究通过在三江源区高寒湿地连续两年的野外调查和室内培养, 分析了50个样点的数据, 探究三江源高寒湿地MBC、MBN、MBP浓度及其化学计量特征, 明确了土壤理化特性和微生物群落特征对其影响。结果表明: (1)三江源高寒湿地MBC、MBN和MBP浓度分别为105.11、3.79和0.78 mmol·kg^-1, MBC:MBN、MBC:MBP、MBN:MBP和MBC:MBN:MBP分别为50.56、184.89、5.42和275:5:1。高寒湿地土壤的MBC浓度显著高于高寒草甸土壤, 而MBN和MBP浓度在高寒湿地和高寒草甸土壤之间没有显著差异; 高寒湿地土壤的MBC:MBN和MBC:MBP显著高于高寒草甸土壤, 而MBN:MBP在高寒湿地和高寒草甸土壤之间差异不显著。(2)土壤理化特性与MBC、MBN和MBP浓度具有显著相关性。土壤含水率与MBC:MBN和MBC:MBP存在显著负相关关系, 而土壤密度与MBC:MBN和MBC:MBP浓度存在显著正相关关系, 土壤全氮含量和MBC:MBP存在显著负相关关系, 而与MBC:MBN的相关关系不显著。土壤理化特性对MBN:MBP的影响不显著。(3)整体而言, 微生物群落结构与MBC、MBN和MBP浓度之间存在显著的相关性。微生物群落结构和MBC:MBN、MBC:MBP的关系是相似的, 总磷脂脂肪酸(PLFA)含量、革兰氏阳性菌、革兰氏阴性菌、细菌、放线菌、丛枝菌根真菌浓度和其他PLFA含量与MBC:MBN和MBC:MBP存在显著负相关关系, 而真菌:细菌与MBC:MBN和MBC:MBP之间存在显著正相关关系, 真菌浓度与MBC:MBN和MBC:MBP之间的相关关系不显著。除丛枝菌根真菌外, MBN:MBP与微生物群落结构均无显著相关关系。     

Plant biomass and nutrient levels of a tropical macrophyte (Cyperus papyrus L.) receiving domestic wastewater

The aboveground biomass and nutrient content ofCyperus papyrus were determined in a small tropical swamp receiving domestic wastewater. It was found that the biomass (4,955 g.m^–2 dry weight) was the highest ever reported for papyrus. The levels of both nitrogen and phosphorus in the plant organs were very high. The nitrogen concentrations of the various plant organs were 4.8% roots, 8.4% rhizomes, 4.5% scales, 4.8% culms, and 6.2% umbels on dry weight basis. As to phosphorus the concentrations were 0.09% roots, 0.11% rhizomes, 0.09% scales, 0.10% culms, and 0.13% umbels. The high biomass and nutrient contents of the plants may have been caused by the high nutrient levels in the surrounding water. Comparison of the nitrogen to phosphorus ratios in the plants to those in the surrounding water showed that the plants stored very high amounts of nitrogen.     

Micronutrient and phosphorus limitation of phytoplankton abundance in Gem Lake,Sierra Nevada,California

Nutrient addition experiments conducted during the ice-free seasons of 1983 and 1984 in Gem Lake, an alpine lake in the Sierra Nevada mountains of California, indicate that algal biomass is limited by phosphorus, in combination with iron or copper. Phosphorus additions were always required to stimulate growth, but did not do so when phosphorus was the only nutrient added. Simultaneous additions of phosphorus and iron resulted in increased levels of chlorophyll, particulate carbon, particulate nitrogen and particulate phosphorus. Simultaneous additions of phosphorus and copper resulted in increases in chlorophyll, particulate nitrogen and particulate phosphorus, not in particulate carbon. Neither iron nor copper by itself stimulated growth.Particulate N : P ratios from all seasons in Gem Lake suggest that simultaneous micronutrient and phosphorus limitation exists throughout the summer, when nutrient and biomass levels remain low; limitation by phosphorus alone may appear in the fall and spring, when biomass and major ion concentrations increase dramatically.     

鄱阳湖湿地两种优势植物叶片C、N、P动态特征

2011年2—6月在鄱阳湖南矶湿地国家级自然保护区逐月测定了灰化苔草(Carex cinerascens)、南荻(Triarrhena lutarioriparia)叶片C、N、P含量及其地上生物量,以阐明鄱阳湖湿地优势植物C、N、P含量及化学计量比动态特征与控制因子,探讨湿地养分利用与限制状况。结果表明：1）两种优势植物叶有机碳含量变化范围分别为365.3—386.6 mg/g和352.6—393.2 mg/g,平均值(?标准差)分别为(375.5?17.4) mg/g和(371.7?12.5) mg/g;叶N含量分别为6.96—17.59 mg/g和5.50—20.68 mg/g,平均值分别为(11.35?1.40) mg/g和(11.54?0.84) mg/g;叶P含量变化范围为0.65—2.14 mg/g和0.57—2.25 mg/g,平均含量为(1.56?0.69) mg/g和(1.55?0.68) mg/g。两种植物C:N、C:P、N:P平均值分别为37.65、413.60、9.62和41.05、410.29、9.57,C、N、P及其化学计量比种间差异不显著(P>0.05)。2）气温与地上生物量是N、P及其化学计量比季节变化的主要控制因子,气温和生物量对两种优势植物叶片氮、磷含量的影响要高于对叶有机碳含量的影响。3）植物C:N、C:P与地上生物量变化趋势基本一致,显示N、P养分利用效率随植物的快速生长而提高;根据两种优势植物及土壤N、P含量与化学计量比来判断,研究区植物更多地受氮限制。     

Species ecological strategy and soil phosphorus supply interactively affect plant biomass and phosphorus concentration

Excess soil phosphorus often constrains ecological restoration of degraded semi-natural grasslands in Western-Europe. Slow-growing species, often target of restoration (measures), are at a disadvantage because they are outcompeted by fast-growing species. Gaining insight into the responses of plant species and communities to soil phosphorus availability will help understanding restoration trajectories of grassland ecosystems. We set up two pot experiments using twenty grassland species with contrasting growth forms (i.e. grasses versus forbs) and nutrient use strategies (i.e. acquisitive versus conservative nutrient use). We quantified the nutrient use strategy of a species based on the stress-tolerance value of the CSR framework (StrateFy et al. 2017). We grew these species (1) as monocultures and (2) in mixtures along a soil phosphorus gradient and measured the aboveground biomass and plant phosphorus concentrations. Plant phosphorus concentration generally increased with soil phosphorus supply and biomass increased with soil phosphorus supply only in conservative communities. Forbs had higher plant phosphorus concentrations compared to grasses both in monocultures and mixtures. The species’ nutrient use strategy had contrasting effects on plant tissue phosphorus concentrations, depending on soil phosphorus supply (interaction effect) and vegetation biomass (dilution effect). Our findings contribute to the knowledge required for successful ecological restoration of species-rich grasslands. Our results suggest that under specific conditions (i.e. nitrogen limitation, no dispersal limitation, no light limitation), slow-growing species can survive and even thrive under excess soil phosphorus availability. In the field, competition by fast-growing species may be reduced by increased mowing or grazing management.     

Leaf C,N, and P concentrations and their stoichiometry in peatland plants of Da Hinggan Ling,China

叶片碳(C)、氮(N)、磷(P)含量及其化学计量特征为植物养分状况和元素限制性提供依据。为了解不同生活型植物叶片C、N、P化学计量特征的变化,该研究测定、分析了大兴安岭地区18个泥炭地常见的3种草本植物——白毛羊胡子草(Eriophorum vaginatum)、玉簪薹草(Carex globularis)、小叶章(Deyeuxia angustifolia), 5种落叶灌木——柴桦(Betula fruticosa)、越桔柳(Salix myrtilloides)、细叶沼柳(Salix rosmarinifolia)、笃斯越桔(Vaccinium uliginosum)、越桔(Vaccinium vitis-idaea)和3种常绿灌木——杜香(Ledum palustre)、地桂(Chamaedaphne calyculata)、头花杜鹃(Rhododendron capitatum)的叶片C、N、P含量。结果表明: (1)落叶和常绿灌木叶片C、N、P含量总体高于草本植物而C:N、C:P、N:P低于草本植物, 说明不同生活型植物具有不同的养分利用策略,灌木叶片C、N、P储存高于草本植物而N、P利用效率低于草本植物; (2)小叶章和头花杜鹃叶片N:P小于10, 同时其N含量小于全球植物叶片平均N含量, 相比其他植物来说更易受N限制; (3)采样地点解释了叶片C、N、P指标变异的12.8%-40.8%, 植物种类对叶片C、N、P指标变异的解释量占9.3%-25.5%; (4)草本植物C、N、P指标的地点间变异系数高于落叶和常绿灌木, 草本植物C、N、P指标对地点因素变化的响应较灌木敏感; (5)草本植物N含量种间变异系数高于落叶和常绿灌木, 落叶灌木P含量种间变异系数高于草本植物和常绿灌木, 草本植物和落叶灌木N、P吸收的种间生理分化较常绿灌木高。     

大兴安岭泥炭地植物叶片碳氮磷含量及其化学计量学特征

叶片碳(C)、氮(N)、磷(P)含量及其化学计量特征为植物养分状况和元素限制性提供依据。为了解不同生活型植物叶片C、N、P化学计量特征的变化,该研究测定、分析了大兴安岭地区18个泥炭地常见的3种草本植物——白毛羊胡子草(Eriophorum vaginatum)、玉簪薹草(Carex globularis)、小叶章(Deyeuxia angustifolia), 5种落叶灌木——柴桦(Betula fruticosa)、越桔柳(Salix myrtilloides)、细叶沼柳(Salix rosmarinifolia)、笃斯越桔(Vaccinium uliginosum)、越桔(Vaccinium vitis-idaea)和3种常绿灌木——杜香(Ledum palustre)、地桂(Chamaedaphne calyculata)、头花杜鹃(Rhododendron capitatum)的叶片C、N、P含量。结果表明: (1)落叶和常绿灌木叶片C、N、P含量总体高于草本植物而C:N、C:P、N:P低于草本植物, 说明不同生活型植物具有不同的养分利用策略,灌木叶片C、N、P储存高于草本植物而N、P利用效率低于草本植物; (2)小叶章和头花杜鹃叶片N:P小于10, 同时其N含量小于全球植物叶片平均N含量, 相比其他植物来说更易受N限制; (3)采样地点解释了叶片C、N、P指标变异的12.8%-40.8%, 植物种类对叶片C、N、P指标变异的解释量占9.3%-25.5%; (4)草本植物C、N、P指标的地点间变异系数高于落叶和常绿灌木, 草本植物C、N、P指标对地点因素变化的响应较灌木敏感; (5)草本植物N含量种间变异系数高于落叶和常绿灌木, 落叶灌木P含量种间变异系数高于草本植物和常绿灌木, 草本植物和落叶灌木N、P吸收的种间生理分化较常绿灌木高。     

翅荚木人工林不同径阶间细根主要功能性状与根际土壤养分的关系

细根能敏感地感知土壤环境变化,对植物生长发育具有重要影响.以6年生翅荚木人工林为对象,对其不同径阶的细根主要功能性状与根际土壤养分特征及两者间关系进行分析.结果表明:细根生物量、根长密度与根体积密度均随径阶增加而增加,比根长与比根面积则随径阶增加呈先升高再下降后升高的趋势,根组织密度则与径阶大小不相关.不同径阶翅荚木根际土壤的pH值及含水率、全碳、全磷、铵态氮、硝态氮和总有效氮含量均存在显著差异,大径阶林木的根际土壤全碳、全氮、硝态氮、总有效氮含量相对较高,小径阶林木的根际土壤含水率、土壤全磷、铵态氮含量相对较高.土壤全氮、全碳、硝态氮和总有效氮含量与林木细根的生物量、根长密度、根体积密度呈显著正相关;土壤全磷与林木细根的根组织密度呈显著正相关,与比根长、比根面积呈显著负相关;土壤含水率与林木细根的生物量和根体积密度均呈显著正相关;根际土壤pH和林木细根的比根长、比根面积呈显著正相关,与根组织密度则呈显著负相关.研究结果可为翅荚木优良种质资源选育提供科学依据.     

不同施肥条件下毛叶苕子的腐解及养分释放特征

利用田间埋袋法,研究不施肥、施氮肥、施石灰3种处理对豫南稻田毛叶苕子腐解及养分释放特征的影响.结果表明:不同施肥处理下毛叶苕子累积腐解率为65.3%~72.5%,腐解过程中呈现前11 d腐解较快、后期腐解缓慢并逐渐趋于平稳的趋势.不同处理养分释放率表现为钾>磷>碳>氮,试验结束时(翻压148 d),碳、氮、磷、钾的累积释放率分别为83.6%~84.6%、78.2%~81.2%、89.8%~91.4%、96.3%~97.0%.在整个腐解期内,毛叶苕子氮释放特征与腐解特征相似,与不施肥相比,施石灰促进毛叶苕子腐解及氮、磷、钾养分释放;施氮肥促进毛叶苕子磷释放,抑制钾释放;施石灰和氮肥对碳释放均无显著影响.施氮肥处理腐解0~11 d促进毛叶苕子腐解及氮释放,腐解11~148 d抑制毛叶苕子腐解及氮释放.采用一级动力学方程及对数函数方程拟合豫南稻区毛叶苕子腐解及碳、氮、磷、钾养分释放特征均达到显著水平,拟合方程的特征参数值与毛叶苕子腐解率及养分释放率呈显著相关.施用石灰促进毛叶苕子腐解及养分释放的效果优于施用氮肥;一级动力学方程及对数函数方程特征参数值可较好地描述毛叶苕子腐解及养分释放能力.     

人工湿地植物对观赏水中氮磷去除的贡献

研究了处理观赏用轻度富营养化水的人工湿地中植物的生长特性和氮磷去除作用。研究发现 ,所选用的 2 1种植物中 ,有17种植物在人工湿地中生长良好 ,稳定生长 10 5 d以后 ,其平均总生物量在 15 5～ 1317g/ m2之间 ,除了鸭跖草的地上地下生物量比 (A/ U)为 2 0 .5外 ,其余都在 1.18～ 4 .2 9之间。植株地上部 N和 P的浓度分别在 10 .99～ 34.74 mg/ g和 0 .5 9～ 3.81mg/ g之间 ;地下部 N和 P浓度分别在 6 .2 0～ 2 9.5 0 mg/ g及 0 .72～ 3.83mg/ g之间。大部分植物地上部 N和 P的浓度大于地下部 (p<0 .0 5 )。植物的 N、P积累量分别在 2 .10～ 2 4 .4 8g/ m2 和 0 .2 3～ 1.95 g/ m2 之间。在处理轻度富营养化水的人工湿地中 ,植物吸收对氮磷的去除起着主要作用——贡献率分别为 4 6 .8%和 5 1.0 %。植物的氮磷积累量与浓度及生物量之间均存在显著相关 ,所以可以直接以生物量为指标选择人工湿地植物。同时考虑净化和景观效果 ,可为处理城镇轻度富营养化水的人工湿地的植物选择提供参考     

Biomass and photosynthetic productivity of water hyacinth (Eichhornia crassipes) as affected by nutrient supply and mirid (Eccritotarus catarinensis) biocontrol

The biological control of water hyacinth is affected by water nitrogen and phosphorus content and this was investigated experimentally at five levels of nutrient supply by measuring plant photosynthetic and growth responses, and mirid reproduction and herbivory of nutrient treated plants. Low nitrogen (2–0.2 mg L⁻¹) and phosphorus (0.2–0.01 mg L⁻¹) supply decreased hyacinth photosynthesis, growth and biomass accumulation relative to plants supplied 200 mg L⁻¹ N and 20 mg L⁻¹ P. This effect depended more on nitrogen supply than phosphorus supply. Chlorophyll fluorescence showed that the photosynthetic light reactions of low nutrient plants were affected and leaves had decreased chlorophyll content, density of functional photosystems II and dissipated a greater proportion of absorbed energy as heat. Gas exchange parameters showed reduced carboxylation efficiency, rates of RuBP regeneration and light saturated photosynthetic rates, but not quantum yields. Effects on photosynthesis translated into lower plant dry biomass. Mirid herbivory exacerbated the effects of low nutrients noted for chlorophyll fluorescence, gas exchange parameters and biomass accumulation, however, these effects were not always significant and there was no obvious correlation between the level of nutrients supplied and the effect of mirid herbivory. Low nutrient supply did, however, affect mirid performance reducing the number of adult insects, nymphs and herbivory intensity suggesting that in the long-term mirid populations would be significantly affected by water nutrient status.     

Variation in nitrogen and phosphorus concentrations of wetland plants

The use of nutrient concentrations in plant biomass as easily measured indicators of nutrient availability and limitation has been the subject of a controversial debate. In particular, it has been questioned whether nutrient concentrations are mainly species' traits or mainly determined by nutrient availability, and whether plant species have similar or different relative nutrient requirements. This review examines how nitrogen and phosphorus concentration and the N:P ratio in wetland plants vary among species and sites, and how they are related to nutrient availability and limitation. We analyse data from field studies in European non-forested wetlands, from fertilisation experiments in these communities and from growth experiments with wetland plants. Overall, the P concentration was more variable than the N concentration, while variation in N:P ratios was intermediate. Field data showed that the N concentration varies more among species than among sites, whereas the N:P ratio varies more among sites than among species, and the P concentration varies similarly among both. Similar patterns of variation were found in fertilisation experiments and in growth experiments under controlled nutrient supply. Nutrient concentrations and N:P ratios in the vegetation were poorly correlated with various measures of nutrient availability in soil, but they clearly responded to fertilisation in the field and to nutrient supply in growth experiments. In these experiments, biomass N:P ratios ranged from 3 to 40 and primarily reflected the relative availabilities of N and P, although N:P ratios of plants grown at the same nutrient supply could vary three-fold among species. The effects of fertilisation with N or P on the biomass production of wetland vegetation were well related to the N:P ratios of the vegetation in unfertilised plots, but not to N or P concentrations, which supports the idea that N:P ratios, rather than N or P concentrations, indicate the type of nutrient limitation. However, other limiting or stressing factors may influence N:P ratios, and the responses of individual plant species to fertilisation cannot be predicted from their N:P ratios. Therefore, N:P ratios should only be used to assess which nutrient limits the biomass production at the vegetation level and only when factors other than N or P are unlikely to be limiting.     

Plant–herbivore interactions and ecological stoichiometry: when do herbivores determine plant nutrient limitation?

Recent studies on plant–herbivore indirect interactions via nutrient recycling have led to the hypothesis that herbivores with a low nitrogen: phosphorus ratio, feeding on plants with a higher nitrogen: phosphorus ratio, recycle relatively more nitrogen, driving plants into phosphorus limitation. We demonstrate in this paper that such a hypothesis is valid only under restricted conditions, i.e. the nitrogen: phosphorus ratio of inorganic nutrients supplied to the system must be neither too high nor too low compared with the nitrogen: phosphorus ratio of the whole plant + herbivore biomass. If plants have a greater affinity for phosphorus than for nitrogen, low herbivore nitrogen: phosphorus ratio can even promote nitrogen limitation. These results are qualitatively robust, whether grazing functions are donor-controlled or recipient-controlled. We present a graphical analysis of these conditions based on the Zero Net Growth Isocline method.     

入侵植物曼陀罗对本地植物功能性状和土壤碳、氮、磷化学计量特征的影响

为探讨不同入侵压力下入侵植物对本地植物功能性状土壤碳、氮、磷化学计量特征的影响,以入侵植物曼陀罗（Datura stramonium）及共存本地植物为研究对象,调查了无入侵区、轻度入侵区和重度入侵区（按入侵种盖度比例划分）的植物种类、株数、株高及本地植物群落的物种多样性,分析了各区入侵植物和本地植物叶片的比叶面积、碳含量、氮含量、碳氮比、叶片建成成本以及不同土层的碳、氮、磷化学计量特征。结果显示：随曼陀罗入侵压力的增加,本地植物种类及株数逐渐减少;曼陀罗株高和叶片氮含量在不同入侵压力下均显著高于本地植物,且随入侵压力的增加具有升高趋势;叶片碳氮比显著低于无入侵区本地植物;比叶面积、叶片碳含量和叶片建成成本等与入侵区本地植物相比不具有显著差异。随曼陀罗入侵压力的增加,土壤全氮含量、全碳含量、氮磷比与碳磷比显著增加,而全磷含量与碳氮比显著下降;土壤碳氮化学计量特征呈现出一定的表聚效应。这些研究结果表明,曼陀罗具有较高的资源捕获能力,并且改变了入侵地土壤特性,进而增强自身竞争能力以提高入侵力,这些可能是曼陀罗成功入侵的原因之一。     

Root architecture and hydraulic conductance in nutrient deprived Pistacia lentiscus L. seedlings

Plants respond to low nutrient availability by modifying root morphology and root system topology. Root responses to nitrogen (N) and phosphorus (P) limitation may affect plant capacity to withstand water stress. But studies on the effect of nutrient availability on plant ability to uptake and transport water are scarce. In this study, we assess the effect of nitrogen and phosphorus limitation on root morphology and root system topology in Pistacia lentiscus L seedlings, a common Mediterranean shrub, and relate these changes to hydraulic conductivity of the whole root system. Nitrogen and phosphorus deprivation had no effect on root biomass, but root systems were more branched in nutrient limited seedlings. Total root length was higher in seedlings subjected to phosphorus deprivation. Root hydraulic conductance decreased in nutrient-deprived seedlings, and was related to the number of root junctions but not to other architectural traits. Our study shows that changes in nutrient availability affect seedling water use by modifying root architecture. Changes in nutrient availability should be taken into account when evaluating seedling response to drought.     

水分和养分添加对羊草功能性状和地上生物量的影响

研究水分和养分添加对植物功能性状的影响, 对于揭示植物对环境变化的响应和适应规律至关重要。该文采用盆栽试验的方法, 进行不同水平水分处理(增水50%, 减水50%, 以498 mm降水量作为对照)和养分添加(无养分添加, 单施氮肥, 单施磷肥, 氮磷共施), 研究羊草(Leymus chinensis)的10种功能性状和地上生物量对水分和养分添加的响应。得出以下结论: (1)双因素方差分析结果表明, 水分主效应对羊草株高、分蘖数、茎生物量、叶生物量、叶面积、叶质量、净光合速率、蒸腾速率、水分利用效率存在显著影响; 养分主效应对羊草分蘖数、茎生物量、净光合速率、蒸腾速率、水分利用效率存在显著影响; 水分和养分的交互作用对羊草分蘖数、茎生物量、蒸腾速率、水分利用效率存在显著影响。(2)各功能性状对降水量的响应在不同养分添加水平是不同的, 分蘖数和叶面积在单施氮肥和氮磷共施条件下随降水量增加而增加, 而在无养分添加和单施磷肥条件下无显著变化; 茎生物量在无养分添加、单施氮肥和单施磷肥条件下随降水量增加而增加, 而在氮磷共施条件下无增加趋势; 比叶面积在单施氮肥条件下增水处理显著低于对照组, 而在其他养分添加条件下无明显变化。(3)短期氮磷处理显著影响羊草叶片光合生理性状, 而对叶形态性状影响不显著。(4)羊草地上生物量随降水量的增加呈现上升趋势, 并且在单施氮肥条件下, 增水处理使地上生物量达到最高, 为522.55 g·m ^-2。总之, 羊草的功能性状对降水量增加表现出明显的响应, 响应格局在不同养分条件下不同, 反映了其对水肥环境变化的适应。