呼伦贝尔草地植物群落与土壤化学计量学特征沿经度梯度变化

植物化学计量学特征在大尺度上主要受纬度和经度两个因素影响。纬度梯度上温度因子变化对植物化学计量特征的影响已有大量研究,但是关于经度梯度上降雨因子变化对植物化学计量特征影响的研究却较少。选取呼伦贝尔草原,研究经度梯度上植物化学计量特征和土壤养分指标的变化规律,从经度梯度和养分供给两方面分析植物群落化学计量特征的变化规律,研究结果如下:1)植物群落叶片C含量变化范围为440.76—452.72 mg/g,N含量变化范围为17.79—30.88 mg/g,P含量变化范围为1.31—1.71 mg/g;群落叶片C含量、C/N随经度升高显著增加;群落叶片N含量随经度升高显著下降;植物群落P含量也呈下降趋势,但是关系不显著;植物群落C、N和P元素总量随着经度升高而显著增加。2)0—10 cm土壤全碳、全氮、全磷、有机碳受降雨量变化和植物群落元素总量影响,随着经度梯度升高而增加;但土壤铵态氮、硝态氮在经度梯度上没有表现出规律性的变化趋势。3)土壤全碳、有机碳、全氮、全磷和速效磷与植物群落叶片C、N和P含量没有显著相关关系,但与植物群落C、N和P元素总量呈显著正相关关系。该区土壤有效磷含量(8.13 mg/kg)高于全球平均值(7.65 mg/kg),但植物群落叶片磷含量平均值(1.5 mg/g)低于全球平均值(1.77 mg/g)。通过研究结果推测:植物通过对气候条件的长期适应,群落水平C、N和P含量沿经度梯度形成一定的分布格局;降雨量影响植物群落元素积累的总量,从而与土壤养分含量呈显著正相关关系;植物叶片P含量低的原因并非是由于土壤中磷的供给不足所致,而是植物对环境长期适应形成的策略。     

沙地植被碳氮磷化学计量特征与物种多样性的关系

植被化学计量特征表征植物营养限制.它是否会影响物种多样性需要进一步探究.本研究以宁夏哈巴湖国家级自然保护区沙地油蒿群落和沙柳群落为对象,计算了植被碳(C)、氮(N)、磷(P)含量,分析了植被C、N、P生态化学计量特征对沙地植物群落物种多样性的影响.结果表明: 在流动沙丘和半固定沙丘生境中的沙柳群落,物种多样性Simpson指数与植被C/N值存在显著的负相关关系,而与植被N/P值的相关性不显著;在半固定沙丘和固定沙丘生境中的油蒿群落,物种多样性Shannon指数与N/P值存在显著正相关关系,而与C/N值存在显著负相关关系.结合C、N、P生态化学计量特征与冗余分析可知,油蒿群落和沙柳群落的植被P含量对物种多样性的影响不同,导致两个群落的植被N/P值对物种多样性产生不同的影响.     

青藏高原筑路取土迹地恢复植物群落与土壤的碳氮磷化学计量特征

恢复筑路取土迹地植物群落是青藏高原退化高寒草地恢复的重要组分,而生态化学计量是揭示退化草地自然恢复过程中土壤和植物间养分互作的重要方法。通过调查青藏公路筑路取土迹地自然恢复群落和天然群落内植物和土壤C、N、P的含量及其比值,研究了恢复群落和天然群落的C、N、P生态化学计量特征。结果表明:经历18a自然恢复后,不同地点筑路取土迹地均已逐步实现植物群落的定居,但其恢复程度存在明显差异。恢复群落植物叶片N含量高于天然群落,导致其叶片C∶N较低,表明恢复群落植物的N利用效率较低,N含量较高的模式主要原因可能是豆科植物比例较高和土壤有效N的供应较充足所致。恢复样地在0—10 cm和10—20 cm的土层内的有机碳(SOC)都显著低于天然样地,恢复样地土壤全氮(STN)仍一定程度上低于天然样地但含量较接近,恢复样地在10—20 cm土层中土壤全磷(STP)含量较高,这说明恢复群落尽管在土壤恢复方面并未达到天然群落的水平,但已得到了明显改善,土壤肥力正发生着正向的演替。叶片N含量与土壤STN相关性不显著,叶片P含量与土壤STP含量显著地正相关,表明植物叶片P含量在一定程度上受到土壤环境中全磷的影响。综合N∶P判定阈值和叶片土壤养分相关分析结果表明研究地区草地植被主要受到P元素的限制,且工程迹地草地恢复群落比天然群落容易受到P元素的限制。     

云南杨梅碳、氮、磷化学计量特征

碳(C)、氮(N)、磷(P)在植物生长和各种生理调节机能中发挥着重要作用。为研究云南灌丛生态系统C、N、P含量之间的关系以及植物生物量、土壤C、N、P含量与植物C、N、P含量的相互影响,该研究采用样地调查的方法,在云南省云南杨梅(Myrica nana)灌丛主要分布区设立了29个样地,通过测量样地中云南杨梅灌丛C、N、P含量,系统分析了云南杨梅C、N、P的计量规律。结果显示:1)研究区域云南杨梅根、茎、叶的C、N、P含量的平均值分别是45.94%、0.54%、0.03%,46.32%、0.58%、0.03%和49.05%、1.70%、0.06%(干质量),其中叶的C、N、P含量均显著高于茎和根。在根中C:N:P为1 531:18:1,在茎中C:N:P为1 544:19:1,而在叶中C:N:P为818:10:1,反映了云南杨梅不同部位元素计量不同的分配关系;2)云南杨梅叶片中C含量和N:P值随生物量的增加而降低,但只有叶片C含量与生物量的相关关系极显著,而N:P值与生物量的相关关系不显著。叶片中N含量和P含量随生物量的增加而升高,其中P含量与生物量的相关关系显著,N含量与生物量的相关关系不显著。云南杨梅叶的N:P(34.2)明显大于8,说明P是云南杨梅生长的限制因素。3)根的C、N、P含量与土壤中的P含量都有显著的相关性,其中N、P为极显著正相关,C为显著负相关;茎的C含量与土壤的C、N、P含量都显著负相关,且N、P含量的相关性极显著,而茎的P含量与土壤中的P含量极显著正相关;叶的P含量与土壤的C、N、P含量都极显著正相关,叶的C含量则与土壤的P含量极显著负相关。该研究结果可为西南高原灌丛生态系统的研究提供数据支持。     

沙化草地土壤碳氮磷化学计量特征及其对植被生产力和多样性的影响

沙化草地土壤碳(C)、氮(N)、磷(P)化学计量特征及其对植被生产力与多样性的影响对于认识草地沙漠化过程中土壤与植被的互馈关系,以及沙漠化发展的生态学机理具有重要的意义。通过对科尔沁沙地75个沙化样地的野外调查,研究了科尔沁沙地不同程度沙化草地的表层土壤C、N、P化学计量特征及其与生产力和多样性的相关关系。结果表明:1)科尔沁沙地沙化草地表层土壤具有较低的有机C、全N、全P含量及C∶N、N∶P和C∶P,平均值分别为1.39 mg/g、0.117 mg/g、0.079 mg/g和7.50、2.22、16.91;草地沙漠化过程中,土壤有机C、全N、全P含量显著降低的同时,C∶N、N∶P和C∶P亦显著降低,表明土壤有机C、全N、全P在沙漠化过程中的损失是不同步的;2)科尔沁沙地沙化草地表层土壤有机C、全N、全P元素间均呈显著正相关,具有一定的耦合关系,且土壤有机C和全P间的耦合关系不随沙漠化的发展而发生改变;3)草地沙化过程中,土壤养分的损失限制着草地生产力,而土壤N∶P较全N、全P含量更能反映土壤养分对生产力的限制作用;4)沙化草地土壤全N含量与物种丰富度间具有显著正相关关系,而土壤全P含量与其无显著相关性;多样性指数与全N、全P含量间均具有显著正相关关系;相对于土壤全N、全P含量,N∶P能更好地反映养分平衡对物种多样性的影响作用。     

云南普洱季风常绿阔叶林152种木本植物叶片C、N、P化学计量特征

季风常绿阔叶林是亚热带地区结构最复杂、生产力最高、生物多样性最丰富的地带性植被类型之一,研究其化学计量学特征对于认识生态系统养分循环特征和限制状况以及系统稳定机制具有重要意义。本文基于云南普洱地区29块30 m×30 m的典型样地调查与取样,测定了152种木本植物叶片C、N、P含量,分析了其化学计量特征。结果表明,该区域季风常绿阔叶林叶片C、N、P含量算术平均值分别为458.17、20.88和1.42 mg·g-1,变异系数分别为7.12%、34.89%和51.81%;C/N、C/P及N/P算术平均值分别为24.96、394.74和16.50,变异系数分别为33.46%、38.79%和51.44%。相关分析表明,C含量和N含量呈极显著负相关(P=0.005),C含量和P含量负相关程度不明显(P=0.078),N含量和P含量呈极显著正相关(P0.001)。不同科植物叶片除C含量整体变异较小外,N、P及C/N、C/P、N/P变异较大。乔木与灌木,以及乔木与藤本之间,叶片除C含量的差异不显著外,N、P、C/N、C/P、N/P的差异均达显著水平(P0.05),其中乔木的N、P含量均显著低于灌木和藤本。152种木本植物叶片N/P算术平均值为16.50,说明普洱季风常绿阔叶林植物总体受P元素限制。     

黑河下游黑果枸杞叶片C、N、P特征及对土壤水盐的响应

研究植物叶片碳(C)、氮(N)、磷(P)计量特征及其与环境因子相关性将为揭示植物对营养元素需求和环境互馈能力提供理论基础。以内蒙古额济纳旗黑河下游距主河道由近及远选择的8个黑果枸杞(Lycium ruthenicum Murr.)优势种群落为研究对象,分析其在不同水分、盐分土壤层环境下叶片C、N、P含量及比值特征,探讨黑果枸杞群落分布的主要限制元素和土壤水盐对其化学计量的影响。研究结果显示:黑果枸杞群落C含量为(331.56±11.99) mg/g,N含量为(13.17±2.92) mg/g,P含量为(2.48±1.64) mg/g,元素C与N、N与P之间呈正相关关系,C与P呈负相关关系,N与C∶N、P与C∶P及N∶P之间呈极显著负相关关系(P0.01);浅层土壤(0—40 cm)水分与P含量呈极显著负相关(P0.01),与C∶P呈显著正相关(P0.05),深层土壤(40—80 cm)水分、盐分均与N含量呈显著负相关(P0.05),与C∶N呈极显著正相关(P0.01)。结果表明:黑果枸杞C∶N主要由N限制,C∶P、N∶P主要由P限制,N∶P小于限制性养分理论阈值14,指示其生长主要受到N限制;黑果枸杞叶片N含量及C∶N比值对深层土壤水分和盐分具有协同响应特征,反映了荒漠植物在干旱盐渍环境中的抗逆境策略。     

环青海湖地区天然草地和退耕恢复草地植物群落生物量对氮、磷添加的响应

植物群落生物量反映了植被的初级生产能力, 是陆地生态系统碳(C)输入的最主要来源, 往往受到自然界中氮(N)、磷(P)元素供应的限制。该试验以青藏高原环青海湖地区的高寒草原为研究对象, 探讨了天然草地和退耕恢复草地植被群落生物量对N (10 g·m^-2)、P (5 g·m^-2)养分添加的响应。N、P添加显著增加了天然草地禾草的生物量, 进而促使地上总生物量显著提高。退耕恢复草地禾草和杂类草的生物量对N添加均有一致的正响应, 从而促使地上总生物量显著增加174%, 群落地上和地下总生物量显著增加34%; 而P添加对恢复草地生物量各项参数均无显著影响。回归分析显示: 天然草地植物群落地上生物量随土壤中NO₃^--N含量的增加而增加(p < 0.05), 退耕恢复草地植被地上、地下和总生物量均与土壤NO₃^--N含量显著正相关(p < 0.01), 说明环湖地区高寒草原植物生长主要受N供应的限制, P的限制作用随土地利用方式的转变和群落演替阶段的不同而变化; 相比天然草地, 恢复草地在现阶段植被初级生产力受N的限制作用更强烈, 土壤中可利用N含量是限制其植被自然恢复和重建的关键因子。     

青藏高原东部窄叶鲜卑花碳、氮、磷化学计量特征

为了探究青藏高原东部窄叶鲜卑花(Sibiraea angustata)灌木不同器官碳(C)、氮(N)、磷(P)含量的分配格局及其生态化学计量特征,该文采用分层随机抽样方法布设样地,选择16个窄叶鲜卑花灌丛样地,分别采集窄叶鲜卑花灌木根、茎、叶、当年枝和果等植物器官样品,并分析样品C、N、P含量及其计量比。结果表明:C、N、P在不同器官中的含量分别表现为茎当年枝果根叶,叶果当年枝茎根,果叶当年枝根茎。窄叶鲜卑花各器官中C含量相对稳定,N、P含量变异系数较大,在根部的变异系数最大。在不同器官中N:P的范围为7.12–12.41,其值变化不大,N:P变异系数的最小值在当年枝中,说明N:P在当年枝中的内稳性较高。在该灌木植物体中C与N之间、C与P之间呈极显著的负相关关系,C对N、P具有稀释作用;N与P呈极显著正相关关系,N与P间具有较好的耦合协同性。分析发现:窄叶鲜卑花不同器官C、N、P化学计量特征在一定程度上符合内稳态理论和生长速率理论,其元素分配与器官所执行的功能密切相关;同时指出在物种水平上应当谨慎使用生态化学计量比来判断养分的限制情况。     

植物特性和环境因子对阔叶红松林暗多样性的影响

可能栖息在局域群落但在局部地区不存在的物种集合构成了暗多样性。为探究物种特性和环境因子对阔叶红松林内暗多样性的影响, 该研究利用比尔指数模型估计了黑龙江凉水国家级自然保护区的9 hm²阔叶红松(Pinus koraiensis)林动态监测样地内的主要组成物种的暗多样性概率。基于物种水平, 评估了耐阴性指数、重要值和暗多样性概率之间的相关性, 并分析了生活型和耐阴性对暗多样性概率的影响; 基于样方水平, 分析了群落完整性与环境因子、物种多样性的相关性。结果表明: (1)该样地物种的暗多样性概率平均值为77.79%, 对于乔木, 胡桃楸(Juglans mandshurica)的暗多样性概率最高, 为97.21%; 对于灌木, 暗多样性概率最高的是鸡树条(Viburnum opulus subsp. calvescens)和鼠李(Rhamnus davurica), 为98.01%。(2)暗多样性概率与重要值呈显著负相关关系, 耐阴性指数与重要值呈显著正相关关系。(3)乔木和灌木的暗多样性概率无显著差异, 喜光物种的暗多样性概率显著高于耐阴物种。(4)坡度和地面凹凸度均与群落完整性呈显著正相关关系; 土壤有机质含量、土壤速效钾(K)含量、土壤密度、土壤质量含水率、土壤pH、土壤有效氮(N)含量和土壤全N含量均与群落完整性无显著相关关系, 土壤体积含水率、土壤速效磷(P)含量、土壤全P含量均与群落完整性呈显著的负相关关系。物种多样性指数与群落完整性呈正相关关系。综上, 在阔叶红松林内喜光物种和稀有种的暗多样性概率较高, 坡度、地面凹凸度、土壤体积含水率、土壤速效P含量、土壤全P含量是导致群落完整性差异的主要环境因素; 群落完整性越高, 群落物种多样性越高。     

Seasonal dynamics of leaf C,N and P stoichiometry in plants of typical steppe in Nei Mongol,China

分析植物叶片(C)、氮(N)、磷(P)含量及其比值的季节动态, 不仅有助于认识植物生长发育和养分吸收利用等生理生态过程, 也有利于认识植物化学计量的动态平衡关系。该文选择内蒙古典型温带草原18种常见植物, 在生长季的6-9月, 每半月一次进行连续采样, 在此基础上分析了叶片C、N、P含量及其比值在生长季内的变化。主要结果: 1)植物叶片C、N、P含量及其比值的季节性变化在不同功能类群间不同步, 其中叶片N、P含量的季节变化体现了明显的稀释作用。2)叶片C、N、P含量及其比值在不同功能类群间差异显著, 单子叶、多年生禾草类的叶片N、P含量显著低于双子叶和多年生杂类草植物, 而其叶片C:N、C:P则高于双子叶和多年生杂类草植物。3)叶片N、P含量显著正相关, 叶片C:N和C:P分别与N和P含量显著负相关, 可能体现了植物体内营养元素间的内在耦合机制。4)叶片N含量与C:N, 叶片P含量与C:P以及叶片N含量与P含量均呈现等速生长关系, 且等速生长关系在生长季保持稳定。     

Carbon,nitrogen and phosphorus stoichiometry of Myrica nana in Yunnan,China

Aims Carbon (C), nitrogen (N) and phosphorus (P) play important roles in plant growth and physiological functions. We aimed at exploring the intrinsic relationships of C, N and P in Myrica nana—a common shrub in Yunnan Province—as well as their relationships with pant biomass and soil nutrients.
Methods We measured the concentration of C, N and P of M. nana from 29 sites for their magnitudes and correlations with soil nutrients.
Important findings 1) The arithmetic mean value of C, N and P concentration in the roots, stems and leaves of M. nana was 45.94%, 0.54%, 0.03%, and 46.32%, 0.58%, 0.03%, and 49.05%, 1.70%, 0.06%, respectively. C, N and P concentrations in the leaves were significantly higher than those in the roots and the stems. The C:N:P in roots, stems and leaves was 1531:18:1, 1544:19:1, and 818:10:1, respectively. 2) The C concentration and N:P in leaves of M. nana decreased with the increase of biomass of M. nana; the leaf C concentration was significantly correlated with biomass (p < 0.01), while the correlation between N:P and biomass was not significant (p > 0.05). The leaf N increased with the increase of plant biomass, the P was significantly correlated with biomass (p < 0.05), but the correlation between N concentration and biomass was not significant (p > 0.05). N:P in leaves was 34.2, suggesting that plant growth was limited by P. 3) C, N and P concentration in the roots were significantly correlated with soil P (p < 0.05), with N, P concentrations correlated with soil P positively (p < 0.01) and C negatively (p < 0.05). C concentration in the stems was significantly and negatively correlated with soil C, N, with significant correlation with C, N, and P concentration (p < 0.01). P concentration in the stems was significantly and positively correlated with soil P concentration (p < 0.01), while leaf P significantly and positively correlated with soil C, N and P (p < 0.01); leaf C concentration was significantly and negatively correlated with soil P (p < 0.01).     

Effects of desertification on the C:N:P stoichiometry of soil,microbes, and extracellular enzymes in a desert grassland

为探讨荒漠草地沙漠化对“土壤-微生物-胞外酶”系统生态化学计量的影响机理, 该研究采用空间序列代替时间演替的方法, 研究了宁夏盐池荒漠草地沙漠化过程中土壤、土壤微生物及土壤胞外酶碳(C)、氮(N)、磷(P)生态化学计量的变异特征。结果表明: (1)随着荒漠草地沙漠化的不断加剧, 土壤C、N、P含量和土壤C:P、N:P均呈降低趋势, 而土壤C:N逐渐增加。(2)荒漠草地沙漠化过程中, 土壤微生物生物量C (MBC):微生物生物量P (MBP)、微生物生物量N (MBN):MBP和土壤β-葡萄糖苷酶(BG):N-乙酰氨基葡萄糖苷酶(NAG)逐渐降低, 而土壤BG:磷酸酶(AP)和NAG:AP基本表现为增加趋势。(3)随着荒漠草地沙漠化程度的加剧, 土壤微生物C利用效率CUE_C:N和CUE_C:P与土壤微生物N利用效率NUE_N:C和土壤微生物P利用效率PUE_P:C的变化趋势相反。(4)荒漠草地土壤、土壤微生物生物量和土壤胞外酶C:N化学计量(C:N, MBC:MBN, BG:NAG)与土壤、土壤微生物生物量和土壤胞外酶N:P化学计量(N:P, MBN:MBP, NAG:AP)显著负相关, 而土壤和胞外酶C:N化学计量(C:N, BG:NAG)与土壤和胞外酶C:P化学计量(C:P, BG:AP)显著正相关。土壤N:P与土壤MBN:MBP显著正相关, 而与土壤NAG:AP显著负相关。分析表明, 荒漠草地沙漠化过程中土壤微生物生物量及胞外酶活性随着土壤养分的变化而发生变化; 微生物-胞外酶C:N:P生态化学计量与土壤养分存在协变关系, 为理解荒漠草地土壤-微生物系统C、N、P循环机制提供理论依据。     

Salt accumulation in vegetative organs and ecological stoichiometry characteristics in typical halophytes in Xinjiang,China

AimsStudying salt accumulation in vegetative organs and carbon (C), nitrogen (N), phosphorus (P) stoichiometry in halophytes contributes to understand the adaptive strategy to saline environment and the distribution mechanism of nutrients and salinity of the halophytes.MethodsFour typical dominant species, including three perennial shrubs (Halocnemum strobilaceum, Suaeda microphylla and Kalidium foliatum) and an annual herb (Salicornia europaea) were selected for analyzing the salt accumulation and C, N, P stoichiometry relationships.Important findings 1) The salt accumulation showed “salt island” effect at peak growing stage; Na⁺, Cl^- and electrical conductivity all showed significant positive trends, when salt ions were transported from the root to the shoot of 4 halophytes. 2) P was the limiting growth element of perennial shrubs, while both N and P were limiting factors for the annual herb. 3) Different organs, species and their interactions affected C, N, P stoichiometry and salt icons except Mg²⁺. 4) C was negatively correlated with N and P, but there was a significant positive correlation between N and P. 5) Electrical conductivity, Na⁺and K⁺ were positively correlated with N, N:P ratio, and negatively correlated with C, C:N and C:P ratios, and yet K⁺, CO₃^2- had significant positive correlation with P. These results implied that there were some kind of mutual promoting relationships between nutrients and salinity in halophytes in the saline environment, and fertilizing with N could promote sodium chloride desalination.     

Carbon,nitrogen and phosphorus stoichiometry in leaves and fine roots of dominant plants in Horqin Sandy Land

Aims The stoichiometric characteristics of carbon (C), nitrogen (N) and phosphorus (P) in plant organism is vital to understand plant adaptation to environment. In particular, the correlations of elemental stoichiometric characteristics between leaf and fine root could provide insights into the interaction and balance among the plant elements, nutrient use strategies and plant response to global change.Methods We measured C, N, P contents and C:N, C:P, N:P in leaves and fine roots of 60 dominant plants in Horqin sandy land. The 60 plant species were classified into five life forms and two categories such as perennial forb, annual forb, perennial grass, annual grass, shrub, legume, and non-legume. We statistically analyzed the differences and correlations of C, N and P stoichiometry either between fine root and leaf or among five life forms.Important findings The average C, N and P concentrations in leaves of 60 plant species in Horqin sandy land are 424.20 mg·g^-1, 25.60 mg·g^-1 and 2.10 mg·g^-1, respectively. In fine roots, the corresponding element concentrations are 434.03 mg·g^-1, 13.54 mg·g^-1, 1.13 mg·g^-1. N and P concentrations in leaf are approximately twice as high as averages in fine root. Furthermore, similar N:P between leaf and fine root indicates conservative characteristic of elemental stoichiometry in plant organism, suggesting that nutrients distribution is proportional between aboveground and underground of plants. There are significant difference of C, N, P, C:N, C:P and N:P in leaf and root among five life forms. N and P in forb and C:N and C:P in grass are averagely higher than those in other life forms. N:P in annual forb and grass, however, are lower than those in other life forms. C, N in legume are higher than those in non-legume, while C:N in legume is lower than in non-legume. These results imply that nutrient use strategies are significantly different among plant life forms. Correlations analysis showed that N and P in leaf or fine root positively correlated, but C and N, C and P in fine root negatively correlated, suggesting coupling relationship among C, N and P in leaf and fine root. Subsequently, we detected positively significant correlations in C, N, P and their ratios between leaf and fine root, suggesting proportional distribution of photosynthate and nutrient between aboveground and underground during plant growth. Generally, these results supplied fundamental data to understand mass turnover and nutrients cycling of leaves and roots in sand land.     

Characteristics of nitrogen and phosphorus stoichiometry across components of forest ecosystem in Shaanxi Province

Aims Nitrogen (N) and phosphorus (P) stoichiometry between vegetation, litter, and soil were important for understanding biogeochemical cycles in terrestrial ecosystems, but remain poorly understood. Here, our aims were to study characteristics of N and P stoichiometry for the plant, litter, and soil and the interactions between its components across forest ecosystems in Shaanxi Province.Methods A total of 121 sampling sites, covering the most main forest types in Shaanxi, were established across the whole province in 2012. And N and P concentration of vegetation (tree and understory), litter and soil layers were measured for each site.Important findings 1) There were significant differences in the N and P stoichiometry among the forest ecosystem components (p < 0.05). N and P contents were higher in understory and litter layer, and lower in tree and soil. Whereas the N:P was slightly different, highest in litter and lowest in the soil layer, with little differences among remaining components. The contents of N, P and N:P ranged from 0.72 to11.99 mg·g^-1, 0.47 to 1.07 mg·g^-1, and 1.86 to 14.84, respectively. Within top 1 m soil layer N content and N:P decreased with soil depth (p < 0.05), however the P content did not exhibit significant changes. 2) N and P contents, and N:P of each component were higher in broadleaf forest than in coniferous forest, although the difference is not significant. 3) N was positively correlated with P content except for soil and N:P was negatively correlated with P content, but positively correlated with N content within each component. In addition, there was a significant positive correlation for N and P stoichiometric characteristics between litter layer and tree, herb, soil layer. 4) Although spatial pattern of N and P contents, and N:P differed in relation to longitude, latitude, and elevation for forest ecosystem components, a stable distribution was exhibited in general.     

神农架常绿落叶阔叶混交林碳氮磷化学计量比

生态化学计量学是研究生态过程中化学元素平衡的科学, 碳(C)、氮(N)、磷(P)化学计量比是生态系统过程及其功能的重要特征。该研究测定了神农架常绿落叶阔叶混交林植物器官、凋落物及土壤的C、N、P含量, 利用生物量加权法计算其化学计量比, 并分析该生态系统不同组分间及不同器官间化学计量比的差异。研究结果发现: 在不同组分之间, C含量、C:N及C:P表现为植物>凋落物>土壤; N、P含量及N:P表现为凋落物>植物>土壤。在不同植物器官间, C含量的差异较小, 其变异系数相对N、P含量较低且保持稳定; N、P含量为叶片最高且变异系数最低; N:P为树皮最高, 而枝的变异系数最低。常绿与落叶树种的叶片N、P含量差异显著。与不同森林类型的化学计量比相比, 该常绿落叶阔叶混交林植物群落的C:P及N:P较低, 凋落物的C:P及N:P较高, 土壤的C、N、P化学计量比与亚热带常绿阔叶林基本一致, 生态系统的C:N相对较低。利用生物量加权法计算得到的该森林生态系统不同组分的C、N、P化学计量比的大小关系与前人利用枝叶取样算术平均的结果存在较大差异。C、N、P含量及其化学计量比在不同器官的分配及内稳性与器官的生理功能关系密切。     

Responses of plant community biomass to nitrogen and phosphorus additions in natural and restored grasslands around Qinghai Lake Basin

Aims Plant biomass reflects the primary productivity of community vegetation, and is the main resource of carbon input in the terrestrial ecosystem. It is usually limited by nitrogen (N) and phosphorus (P) availability in the soil. Alpine grassland around Qinghai Lake Basin has experienced extensive land-use changes due to the cultivation of native grassland and vegetation recovery on cropped land. In this experiment, two grassland types were chosen, natural alpine grassland (NG) and its adjacent restored grassland (RG), to determine the responses of plant community biomass to N and P additions with different land-use. Methods NH₄NO₃ and Ca(H₂PO₄)₂·H₂O were added in a completely randomized block design, with medium levels of 10 g N·m^-2 and 5 g P·m^-2. Soil NO₃^--N and available P contents, and the plant community biomass were measured in the two grasslands. Two-way ANOVA was used to determine the effects of nutrient additions on all measured indicators, and regression analysis was used to analyze the correlations between plant biomass and soil NO₃^--N and available P contents.Important findings Results showed: (1) N and P additions both increased grass biomass in the NG, and significantly elevated the total aboveground biomass, with the promoting effect of N addition higher than that of P addition; N addition significantly increased both grass and forb biomass in the RG, and markedly promoted the total aboveground biomass, while P addition had no effects on the functional groups and total aboveground biomass (p > 0.05). (2) N and P additions both had no effects on the belowground and total biomass in the NG, whereas N addition significantly increased the total biomass by 34% in the RG, which suggested that the effect of N limitation on the vegetation primary productivity was stronger in the RG at present stage. (3) The aboveground biomass in the NG increased with soil NO₃^--N content (p < 0.05), and the above- and below-ground as well as the total biomass were all positively correlated with soil NO₃^--N content in the RG (p < 0.01). These results indicated that the plant growth in alpine grassland around Qinghai Lake Basin was prone to N limitation, and the effect of P limitation changed with land-use. Soil available N might be the key limiting factor for vegetation restoration and reconstruction in the RG. The “Grain for Green” project (the land-use policy) and atmospheric N deposition are benefiting both plant growth and C accumulation in the alpine grassland ecosystem around Qinghai Lake Basin.     

中亚热带植被恢复阶段植物叶片、凋落物、土壤碳氮磷化学计量特征

为揭示植被恢复过程中生态系统的养分循环机制及植物的生存策略, 根据亚热带森林群落演替过程, 采用空间代替时间方法, 以湘中丘陵区地域相邻、环境条件基本一致的檵木(Loropetalum chinensis) +南烛(Vaccinium bracteatu) +杜鹃(Rhododendron mariesii)灌草丛(LVR)、檵木+杉木(Cunninghamia lanceolata) +白栎(Quercus fabri)灌木林(LCQ)、马尾松(Pinus massoniana) +柯(Lithocarpus glaber) +檵木针阔混交林(PLL)、柯+红淡比(Cleyera japonica) +青冈(Cyclobalanopsis Glauca)常绿阔叶林(LCC)作为一个恢复系列, 设置固定样地, 采集植物叶片、未分解层凋落物和0-30 cm土壤样品, 测定有机碳(C)、全氮(N)、全磷(P)含量及其化学计量比, 运用异速生长关系、养分利用效率和再吸收效率分析植物对环境变化的响应和养分利用策略。结果表明: (1)随着植被恢复, 叶片C:N、C:P、N:P显著下降, 而叶片C、N、P含量和土壤C、N含量、C:P、N:P显著增加, 其中LCC植物叶片C、N含量, 土壤C、N含量及其N:P, PLL植物叶片P含量, 土壤C:P显著高于其他3个恢复阶段, 各恢复阶段植物叶片N:P > 20, 植物生长受P限制; 凋落物C、N、P含量及其化学计量比波动较大。(2)凋落物与叶片、土壤的化学计量特征之间的相关关系较弱, 叶片与土壤的化学计量特征之间具有显著相关关系, 其中叶片C、N、P含量与土壤C、N含量、C:N (除叶片C、N含量外)、C:P、N:P呈显著正相关关系; 叶片C:N与土壤C、N含量、C:P、N:P, 叶片C:P与土壤C含量、C:N、C:P, 叶片N:P与土壤C:N呈显著负相关关系。(3)植被恢复过程中, 叶片N、P之间具有显著异速生长关系, 异速生长指数为1.45, 叶片N、P的利用效率下降, 对N、P的再吸收效率增加, LCC叶片N利用效率最低, PLL叶片P利用效率最低而N、P再吸收效率最高。(4)叶片N含量内稳态弱, 而P含量具有较高的内稳态, 在土壤低P限制下植物能保持P平衡。植被恢复显著影响叶片、凋落物、土壤C、N、P含量及其化学计量比, 叶片与土壤之间C、N、P含量及化学计量比呈显著相关关系, 植物通过降低养分利用效率和提高养分再吸收效率适应土壤养分的变化, 叶片-凋落物-土壤系统的N、P循环随着植被恢复逐渐达到“化学计量平衡”。     

Effects of N addition on ecological stoichiometric characteristics in six dominant plant species of alpine meadow on the Qinghai-Xizang Plateau,China

以青藏高原高寒草甸为研究对象, 通过人工氮肥添加试验, 研究6个群落优势种在不同施氮(N)水平下叶片碳(C)、N、磷(P)元素含量的变化以及生态化学计量学特征。结果表明: 自然条件下, 6个物种叶片N、P质量浓度存在显著的差异, 表现为: 黄花棘豆(Oxytropis ochrocephala)最高, 为24.5和2.51 g·kg^-1, 其叶片N含量低于而P含量高于我国其他草地的豆科植物; 其余5个物种叶片N、P质量浓度分别为11.5-18.1和1.49-1.72 g·kg^-1, 嵩草(Kobresia myosuroides)叶片N含量最低, 垂穗披碱草(Elymus nutans)叶片P含量最低, 与我国其他区域的研究结果相比, 其叶片N和P含量均低于我国其他草地非豆科植物。随氮素添加量的增大, 6种群落优势种叶片的C和P含量保持不变; 其他5种植物叶片N含量显著增加, 黄花棘豆叶片N含量保持不变。未添加氮肥时, 6种植物叶片N:P为7.3-11.2, 说明该区植物生长更多地受N限制。随N添加量的增加, 除黄花棘豆外, 其他5种植物叶片N:P大于16, 表现为植物生长受P限制。综合研究表明, 青藏草原高寒草甸植物叶片N含量较低, 植物受N影响显著, 但不同物种对N的添加反应不同, 豆科植物黄花棘豆叶片对N添加不敏感, 其他5个物种叶片全N含量随着N添加量的升高而增加, 该研究结果可为高寒草甸科学施肥提供理论依据。