密度对尖头叶藜生物量分配格局及异速生长的影响

植物器官指示植物不同的功能,而植物器官生物量分配比例的变化表征了植物对资源获取能力的调整。在植物生长发育过程中,植物各器官呈一种明显的异速生长规律。利用异速生长分析方法,通过模拟不同密度(16、44.4、100、400株/m~2)下尖头叶藜(Chenopodium acuminatum)的生长特性,研究密度对尖头叶藜器官生物量分配格局及异速生长的影响。结果表明,随密度增加,尖头叶藜地上和地下器官都存在不同程度的竞争:其中,根和主茎生物量分配增加,茎和地上生物量分配减少,而叶和繁殖生物量分配不随密度变化而变化。研究发现,尖头叶藜各器官间具有显著的异速生长关系:其中叶∶主茎、根∶地上部分、根∶茎、根∶主茎、繁殖器官∶地上部分及繁殖器官∶根生物量间的异速生长不随密度变化而变化,属于表观可塑性;而叶∶地上部分、叶∶根、叶∶茎、茎∶地上部分、主茎∶地上部分、繁殖器官∶茎、繁殖器官∶主茎生物量间具有极显著的异速生长关系,异速指数和个体大小显著受密度变化影响,属于真正可塑性,这表明密度能够影响尖头叶藜各器官的生长变化。尖头叶藜叶∶主茎、叶∶根及主茎∶地上部分生物量间的异速指数在D4-密度时与3/4差异不显著(P0.05),符合生态代谢理论,而在D1—D3密度时与3/4差异显著(P0.05),表明充分竞争的植株更符合代谢理论,而竞争不激烈的植株对资源的投入具有物种特异性。     

降雨格局变化对内蒙古典型草原优势种大针茅幼苗的影响

大针茅(Stipa grandis)是内蒙古草原的优势物种, 研究其幼苗在不同降雨格局下的响应特征, 可以为进一步研究降雨格局变化下内蒙古典型草原的响应特征提供科学依据。在中国科学院内蒙古草原生态系统定位研究站, 利用开顶式生长室进行控制试验模拟降雨格局变化, 研究了大针茅幼苗对总降雨量和降雨间隔时间变化的响应。结果表明: 1)总降雨量增加50%使大针茅幼苗生长季末的地上生物量平均增加23% (p < 0.05), 而降雨间隔时间由5天增长为15天使地上生物量平均增加48.8% (p < 0.001)。2)总降雨量对大针茅幼苗的地下生物量没有显著影响; 而在低降雨量条件下, 降雨间隔时间增长使地下生物量增加56.2% (p < 0.001), 在高降雨量条件下作用不显著。3)总降雨量和降雨间隔时间对根冠比的效应都依赖于对方水平的高低, 总降雨量增大只在较长降雨间隔条件下使根冠比发生改变(-28.4%, p < 0.05), 降雨间隔时间增长只在高降雨量条件下使根冠比发生改变(-28.8%, p < 0.05)。4)处理期间, 在处理时间分别为30天和45天时, 大针茅幼苗地上生物量、地下生物量和总生物量的差异都主要取决于总降雨量; 而在处理时间为75天时, 其差异则都主要取决于降雨间隔时间。该研究得到以下主要结论: 1)降雨间隔时间与总降雨量一样, 是影响大针茅幼苗生长的关键因素之一。2)总降雨量对大针茅幼苗生长的效应与降雨间隔时间的长短紧密相关。3)降雨格局对大针茅幼苗生长的影响机制随着幼苗的生长期不同而改变。     

降雨量变化对樟子松生理生态特性的影响

全球气候变化背景下大气环流及水文循环的改变,可导致区域降雨格局变化,作用于区域陆地生态系统物质循环与能量流动过程,从而影响植物群落对降水量变化的生理生态响应.以科尔沁沙地樟子松(Pinus sylvestris var.mongolica)人工林为对象,设置野外降雨变化实验样地(天然降雨(CK)、降雨量减少30％(-30％)、降雨量增加30％(+30％)3种处理)、选择2个不同的生长季降雨格局( DRY-236 mm、WET-357 mm),研究生长季樟子松针叶的光合速率、蒸腾速率、水分利用效率、叶绿素、脯氨酸、可溶性蛋白、丙二醛(MDA)、SOD活性以及生长变化,分析降雨变化对樟子松人工林的影响.结果表明,樟子松针叶光合、蒸腾速率和水分利用效率与降雨量呈正相关,降雨量变化对樟子松生理生态特征产生显著影响,其中生长季水分胁迫对樟子松生长的影响存在滞后效应,樟子松针叶N含量的变化可反映不同水分变化与土壤养分有效性共同作用模式.     

人工模拟降雨格局变化对红砂种子萌发的影响

气候变化改变降雨格局,会影响到种子出苗及幼苗生长,进而影响幼苗的更新动态。为探讨降雨格局变化对典型荒漠植物红砂种子萌发特性的影响,利用环境控制生长箱开展了降雨量和降雨间隔时间的双因素控制实验。结果表明:(1)总降雨量增加30%,红砂种子出苗率和发芽势分别平均提高45.69%、39.86%(P0.05),延长降雨间隔时间单次降雨量达到6mm其效果更明显,出苗率和发芽势达到最大值,分别为68.33%、63.33%,表明6mm降水量是促使红砂萌发的最小降雨阈量。(2)总降雨量增加30%显著提高了种子萌发指数和活力指数(P0.05),与自然总降雨量相比,分别平均提高57.67%、121%。总降雨量减少30%虽降低了萌发指数和活力指数,但与自然总降雨量相比差异不显著(P0.05)。(3)降雨量增加30%延长降雨间隔时间处理加快了红砂的萌发进程,缩短了种子的萌发持续时间,其萌发曲线较陡峭。降雨量减少30%对其种子萌发进程影响不大。该研究得到以下主要结论:1)红砂种子萌发主要受到降雨量的影响,但降雨量效应依赖降雨间隔时间,总降雨量一定降雨间隔延长所形成的单次降雨量增加均提高萌发率,增加了红砂繁殖成功率,对其幼苗更新起促进效应;2)在自然状态及降雨减少的情况下红砂种子具有推迟萌发的特性,使其幼苗在更适宜的环境条件下出现和生长的机会增多,从而提高植物对环境的长期适应性。     

降雨格局变化对红砂幼苗根系生长和生物量分配的影响

以自然生长的典型红砂(Reaumuria songarica(Pall.)Maxim.)群落中的幼苗为研究对象,以自然降雨为对照,设定降雨量减少30%(W~-)、不变(W)和增加30%(W~+)3个降雨量水平,2个降雨时间间隔即自然降雨时间(T)、延长降雨间隔时间至1.5倍(T~+)),研究降雨格局变化对红砂幼苗根系生长和生物量分配的影响。结果表明:(1)同一降雨量条件下,降雨间隔延长促进了红砂幼苗主根的伸长生长、增加了根表面积,增大了根冠比,有利于红砂幼苗根系生长。(2)降雨量较少的条件下(W~-、W),延长降雨间隔促使红砂幼苗地下、地上及总生物量累积;而降雨量较多(W~+)条件下,延长降雨间隔使各部分生物量有所降低,但差异不显著。(3)在自然降雨间隔条件下,降雨量的增加使红砂幼苗的总生物量和主根长呈增加的变化趋势,对其生长起到促进作用。研究认为,降雨格局的变化会明显影响自然生长的红砂群落中幼苗的生长和生物量分配。     

施氮量对不同藜麦品种幼苗生长的影响

通过盆栽试验,研究5个水平的施氮量(N₀,0 g·kg^-1;N₁,0.05 g·kg^-1;N₂,0.1 g·kg^-1;N₃,0.15 g·kg^-1;N₄,0.2 g·kg^-1)对8个不同藜麦品种幼苗生长的影响。结果表明: 1)不同施氮量处理下,藜麦品种GB22和OY的生物量最大,而品种B2的生物量最小。品种B2的花质量比最大,品种GB22的茎质量比最大,品种R1的根质量比最大,品种W23的叶质量比最大。2)施氮显著影响藜麦幼苗的生长。在较低施氮量(N₁、N₂)下,叶片最大净光合速率、植株生物量积累都比对照(N₀)明显增加;在较高施氮量(N₃、N₄)下,藜麦叶片光合速率出现降低趋势,生物量积累减少。品种和施氮量对植株生物量有显著的交互作用,表明不同藜麦品种对施氮量的响应不同。品种R1、MY11、GB22、OY的最佳施氮量为0.05 g·kg^-1,品种GB11、DB、B2的最佳施氮量为0.1 g·kg^-1,品种W23的最佳施氮量小于0.05 g·kg^-1。3)品种和施氮量之间的交互作用显著影响藜麦幼苗的生物量分配。在达到0.2 g·kg^-1施氮量前,随着施氮量增加,藜麦将更多的生物量分配到花和叶。4)不同品种和施氮量下,幼苗生物量与最大净光合速率、苗高、地径、比叶面积呈显著正相关。本研究可为不同藜麦品种的养分管理提供参考。     

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。     

高寒矮嵩草草甸群落植物多样性和初级生产力对模拟降水的响应

通过野外控制实验,研究了高寒矮嵩草草甸群落植物多样性、初级生产力对模拟降雨条件的响应.结果表明: 1 在植物生长期 6月 ,增加降雨20%、增加降雨40%,植物群落物种多样性指数 H 和均匀度指数 J 分别比对照提高了0.188和0.011、0.735和0.076,生长期 7月 增加降雨20%物种H和J提高了0.409和0.07; 2 禾草类:增加降雨20%处理的地上生物量与对照相比没有明显的显著性差异 P>0.05 ,增加降雨40%处理的地上生物量与对照相比差异显著 P<0.05 ,说明过多增加降雨会抑制禾草的生长发育.杂类草:减少降雨50%处理的地上生物量与对照相比差异显著 P<0.05 ,其地上生物量对减少降雨的反映比较敏感.莎草类:其地上生物量对增加和减少降雨都没有显著变化; 3 0～10cm和0～30cm土层地下生物量均在增加降雨20%时最高,地下生物量的总量也在增加降雨20%时最高; 4 矮嵩草草甸地下生物量与地上生物量、总生物量的比值接近于生长季末时最大,且在模拟增加降雨20%的水平时,7、8、9月份地下和地上生物量较其它处理组高.     

桢楠幼苗适应喀斯特岩溶裂隙生境及降雨时间格局变化的方式

喀斯特生态系统是全球陆地生态系统的重要组成部分，生态环境极为脆弱。由于碳酸盐岩长期强烈的化学溶蚀作用，其基本特征体现为地表土壤和地下岩溶裂隙及洞穴的二元结构。近年来，在全球气候变化下，我国西南地区降雨格局呈现降雨频次减少且单次降雨量增加的趋势。因此，岩溶裂隙和区域降雨时间格局改变将对喀斯特地区的植物生长产生重要影响。通过模拟不同岩溶裂隙生境(S₀:24 cm土壤；S_1/2:12 cm土壤层+12 cm裂隙层；S_3/4:6 cm土壤层+18 cm裂隙层)和不同降雨时间格局(I_2d:2 d降雨间隔；I_19d:19 d降雨间隔),探究二年生桢楠(Phoebe zhennan S. Lee)幼苗是否通过生物量分配及根系分布的调整来适应变化环境。结果显示：(1)短时间降雨格局下，相比全土生境，少量岩溶裂隙存在并不影响桢楠幼苗生物量的积累，然而随着岩溶裂隙层进一步增厚和降雨时间间隔延长，桢楠降低了总生物量，减少了茎且增大了根和叶的生物量分配。(2)桢楠幼苗的根系垂直分布随着深度增加而下降，...     

安塞人工沙棘林地上部生物量和净初级生产量

采用收获法测定安塞沙棘人工林不同林龄林分的地上部生物量,分析沙棘人工林发育过程中地上部生物量和净初级生产量的变化趋势,建立沙棘单株地上部各器官分量的回归模型.结果表明沙棘人工林4～5a即可郁闭,郁闭度为0.8～0.9.1～8龄内,地上部生物量随林龄增加而增加,8～11龄增加缓慢,11～13龄趋于稳定,13龄的沙棘人工林地上部生物量为1151g/m2,地上部生物量的器官分配为主茎410g/m2(占35.6%),枝478g/m2(占41.5%),叶215g/m2(占18.8%),果20g/m2(占0.02%),枯枝28g/m2(占0.02%).8龄沙棘人工林的净初级生产量为600g/(m2     

沙埋与水分对科尔沁沙地主要固沙植物出苗的影响

蒿属半灌木乌丹蒿(Artemisia wudanica)、白沙蒿(A. sphaerocephala)、差不嘎蒿(A. halodendron)是科尔沁沙地的主要固沙植物。其中乌丹蒿和差不嘎蒿是科尔沁沙地的本土植物,白沙蒿为来自于库布齐沙漠、毛乌素沙地的飞播植物。设置了 5个沙埋深度(0.5、1.0、1.5、2.0和3.0 cm)和 4个水分梯度(86、171、257和 342 mL,分别模拟每月25、50、75和100 mm的降雨量),以探讨3种植物幼苗出土对沙埋和水分的响应。结果表明,沙埋与水分均显著影响着3种蒿属植物的幼苗出土(P < 0.001)。3种植物最适沙埋深度在0.5-1.5 cm范围内,萌发出土时适宜水量要高于当地种子萌发期的平均降水量(50 mm/月)。两种固沙先锋植物乌丹蒿和白沙蒿的种子出苗率均显著高于差不嘎蒿,乌丹蒿较白沙蒿也明显为高,尤其在水分缺乏时,表现出两种先锋植物种子出苗对干旱有更好的适应性。协方差分析表明,乌丹蒿幼苗死亡率显著高于白沙蒿和差不嘎蒿(P < 0.05),在达到75 mm/月降水量时,3种植物的出苗较好,但不能满足乌丹蒿幼苗生长对水分的需求,而实际种子萌发期的降水量平均只有50 mm/月。因而降水的缺乏导致乌丹蒿种群更新出现问题,加之飞播植物的竞争,使得近几年科尔沁沙地较多乌丹蒿种群出现衰退。     

樟子松人工林原产地与不同自然降水梯度引种地土壤和植物叶片生态化学计量特征

降水格局是影响陆地生态系统结构和过程的重要环境要素,尤其对于干旱/半干旱地区,降水变化是植物生长驱动的关键生态因子。目前,针对降水变化对陆地生态系统C、N、P等元素生物地球化学循环过程影响开展了大量研究。然而,关于沙地樟子松重要引种地科尔沁沙地自然降水梯度下沙地樟子松人工林土壤、植物生态化学计量特征的研究未见报道。因此,本研究以樟子松原产地红花尔基和引种地科尔沁沙地自然降水梯度下4个典型沙地樟子松人工林为对象,研究樟子松引种地降水变化对土壤(0—10,10—20 cm和20—40 cm)和植物(1年和2年生叶)生态化学计量特征的影响。研究结果发现:(1)与红花尔基原产地樟子松人工林相比,科尔沁沙地引种的樟子松人工林土壤C、N、P元素含量显著降低;(2)科尔沁沙地自西向东,随降水量增加,沙地樟子松人工林土壤C、N、P含量以及C∶P和N∶P表现为逐渐增加趋势,而土壤C∶N呈减少趋势;(3)随着降水量增加,樟子松叶C含量呈下降趋势,叶N含量和N∶P比值呈增加趋势,植物叶P含量无一致性规律;(4)樟子松叶片P含量与土壤C、N、P含量呈极显著正相关关系,而叶片C和N含量与土壤C、N、P含量无显著相关性。研究表明,沙地樟子松引种地科尔沁沙地土壤C、N、P养分比较缺乏,且随着降水增加土壤N养分限制降低,而土壤P养分限制增加。本研究从生态化学计量特征角度,为今后开展科尔沁沙地不同降水梯度条件下引种樟子松人工林提供理论依据。     

Seedling bank dynamics of Fagus grandifolia var. mexicana before and after a mast year in a Mexican cloud forest

Abstract. Fagus grandifolia var. mexicana seedling dynamics were studied in a relict forest inside the crater of a volcano where it is the only canopy tree species. The objectives of the study were (1) to determine changes in seedling density before and after a mast year, as well as to monitor seedling recruitment, mortality and growth rate in relation to the micro‐environment, and (2) to discuss the impact of masting on seedling dynamics of the population. Before masting, seedling density was 8.8 seedlings m^–2, afterwards seedling density peaked at 51.5 seedlings m^–2, then decreased by 50% in 3 months and by 85% after 8 months, down to levels of before the mast year (9.9 seedlings m^–2) after 16 months. Seedlings in the forest floor before the mast‐seeding event showed a low relative growth rate – 0.14 mm mm^–1 mo^–1 against 1.27 mm mm^–1 mo^–1 for seedlings that emerged immediately after masting. Seed germination was high (83%) and rapid (L₅₀= 7 days) following masting. Seedling growth was positively correlated with soil water content but not with temperatures and relative humidity. Data suggested that seed production in mast years is important in maintaining the seedling bank, and thus the viability of relict Fagus populations.     

模拟氮沉降对克氏针茅草原土壤有机碳的短期影响

为更好地了解天然草地土壤有机碳对氮沉降增加的响应,2011年在内蒙古太仆寺旗的克氏针茅(Stipa krylovii)草原上开展了模拟氮沉降的控制实验,设置对照(CK)和5个模拟氮沉降(NO-3)处理,分别为2(N1)、5(N2)、10(N3)、25(N4)和50 g N m-2a-1(N5)。生长季末,采集每个样地中0—2 cm和2—10 cm深度土壤进行有机碳含量及组成的分析,并进行实验室矿化培养。结果表明,土壤颗粒态有机碳(POC)对氮添加响应敏感,N1和N2处理下的POC含量高于CK,N3、N4和N5处理则低于CK。5个模拟氮沉降处理下的矿质结合态有机碳(MOC)含量均高于对照,但差别不显著。不同氮沉降水平下0—2 cm土层的碳矿化潜势为N2N1N4N3CKN5,且N1,N2,N3和N4处理均显著高于CK和N5;2—10 cm土层的碳矿化潜势为N2N1N3CKN4N5,N1、N2和N3显著高于CK、N4及N5。不同施氮处理对群落净第一性生产力有明显影响,N5的净第一性生产力和地上生物量显著低于对照和其它施氮处理,N1的0—10 cm地下生物量显著高于对照和其它处理,N5的凋落物量显著高于对照。模拟氮沉降短期内对土壤总有机碳(SOC)含量无显著影响。     

Pasture seed dynamics in a dry monsoonal climate. I Germination and seedbed environment of Stylosanthes humilis and Digitaria ciliaris

Field germination behaviour and seedbed environment of the annual legume Townsville stylo (Stylosanthes humilis) and the vigorous annual grass weed (Digitaria ciliaris) were studied at Katherine, Northern Territory. Previous studies of the population dynamics of these pastures had indicated the importance of the germination-establishment phase in maintaining S. humilis as a pasture component. Analysis of seed samples at the time of sward establishment showed that near complete germination of viable seed (in the case of D. ciliaris) and of soft seed (in the case of S. humilis) occurred in the early storm period before the onset of the wet season. Swards of both species generally resulted from a single, major germination wave often after an isolated rainfall. The seedbed environment at the time of major germination waves was studied in detail for 2 years and environmental models were used with historical climate records to calculate probability distributions of temperature and moisture over 16 years. The main determinants of the seedbed environment were storms (most often occurring in the period from late afternoon to midnight) and high solar radiation levels (70% > 20 MJ m^-2 day^-1 in the days after rainfall. Surface soil generally dries to -1.5 MPa by noon. Minimum night surface temperatures showed little variation (～25°C) and were followed by high surface temperatures the following day (> 35°C). The use of a simple water balance model showed a high chance (80% of events) of the top 40 mm drying to – 1.5 MPa at the end of the second day following rainfall. Despite the low variation of annual rainfall at Katherine (cv of 20%) these self regenerating annual species have a high risk of seedling death. Germination and seedling establishment take place at a time of rapid fluctuations in surface moisture and seedbed temperature. The analysis of seedbed conditions indicated that intensive sampling of the seed population would be required in the early storm period to explain differential survival of the species and that laboratory work should concentrate on factors controlling speed of germination over short periods of available moisture (12–20 h).     

Soil seed densities and emergence patterns in pastures in the seasonally dry tropics of northeastern Australia

Germinable seed densities in the surface (0–10 cm) soil of pasture communities growing at Lansdown, near Townsville, were measured during the late dry season before the first germinating rain and again during the following wet season after germination but before the input of new seed. Seedlings emerging in the field were counted at approximately weekly intervals during this period to determine emergence patterns. Twelve communities were sampled in 1980–81 and six were re-sampled in 1981–82. During the late dry season germinable seed densities ranged from 5000 to 40 000 seeds m^-2. Seeds of the introduced legume, Stylosanthes hamata, were present in all pastures. There were many seeds of annual grasses (Digitaria ciliaris and Brachiaria miliiformis) and sedges (Cyperus and Fimbristylis spp.) but only few seeds of perennial grasses (both native and introduced). Soil seed densities were much lower during the wet season than during the preceding dry season, particularly for the grasses. Emergence commenced and approximately 70% of all seedlings emerged on the first major rainfall of the wet season. The subsequent emergence pattern varied between years. In 1980–81 there was a gradual and continuous increase in seedling numbers under the continuously moist conditions which prevailed. In 1981–82 further emergence occurred in discrete events related to rainfall and intervening dry periods. Maximum seedling densities exceeded 34 000 seedlings m^-2 including 29 000 grass seedlings (mainly annual species). The implications of these results for species survival and pasture composition are discussed.     

Changes in activities of antioxidant enzymes during <Emphasis Type="Italic">Chenopodium murale</Emphasis> seed germination

The activities and isoenzyme pattern of catalase (CAT), superoxide dismutase (SOD) and peroxidase (POD) have been studied during germination of Chenopodium murale seeds. CAT and SOD activities were similar in dry seeds and during first 2 d of imbibition. CAT activity increased during radicle protrusion and early seedling development. The maximum SOD activity was found at final stages of germination and early seedling development. POD activity was not detected until the 6^th day of germination, indicating POD involvement not until early seedling development. Gibberellic acid (GA₃, 160 μM) delayed and synchronized C. murale germination.     

Response of carbon and nitrogen content in plants and soils to vegetation cover change in alpine Kobresia meadow of the source region of Lantsang, Yellow and Yangtze Rivers

We conducted this study in lightly and severely degraded Kobresia pygmaea meadow in Gande County, Qinghai Province of China. The purpose of this research was to compare carbon and nitrogen concentrations, content and dynamics of aboveground tissue, belowground roots and soil (0-40 cm) between lightly and severely degraded Kobresia meadow. The results showed that C and N concentrations and C:N ratio of the aboveground tissue were significantly higher in lightly degraded grassland than in severely degraded grassland. In addition, total carbon and nitrogen concentrations of the aboveground tissue were ranked in order of forbs > grasses > sedges in the same grassland type. Total carbon and nitrogen concentrations of belowground roots were significantly higher in severely degraded grassland than in lightly degraded grassland. Total carbon and nitrogen concentrations were higher in the aboveground tissue than in the belowground roots. Total soil organic carbon concentration in severely degraded grassland was significantly lower than that in lightly degraded grassland, and decreased with depth. C and N content per unit area was ranked in order of 0-40 cm soil depth > belowground roots > aboveground issue in the same grassland type. The total carbon content per unit area of aboveground tissue, roots and 0-40 cm soil depth declined by 7.60% after degradation from lightly (14669.2 g m⁻²) to severely degraded grassland (13554.3 g m⁻²), i.e., 0-40 cm soil depth declined by 4.10%, belowground roots declined by 59.97% and aboveground tissue declined by 15.39%. The nitrogen content per unit area of aboveground tissue, roots and 0-40 cm soil depth increased after degradation by 12.76% from lightly (3352.7 g m⁻²) to severely degraded grassland (3780.6 g m⁻²), i.e., 0-40 cm soil depth increased by 13.07%, belowground roots declined by 55.09% and aboveground tissue declined by 16.00%. As a result of grassland degradation, the total carbon lost by 11149 kg hm⁻², and the total nitrogen increased by 4278 kg hm⁻².     

Conditions for seedling establishment and probable function of seed in the clonal sedge Carex rugulosa Kük. in riverside marshes

Carex rugulosa Kük. forms large meadows in moist zones along estuarine riversides. These meadows are usually maintained by rhizomatous ramet production (clonal growth), and the appearance of seedlings is uncommon. We studied the conditions required for seedling establishment. In areas in which clonal ramets were dense (906–1050/m²), and the relative light intensity at ground level was low (0.8–3.8%), seed germination was entirely suppressed. In contrast, many seedlings (288–513/m²) were observed in areas in which clonal ramets had been considerably reduced (13–269/m²) by continuous inundation in the previous year. In these areas, the relative light intensity had increased (20.5–79.3%). It was inferred that seeds resisted the prolonged inundation that killed the ramets, and that germination was induced under these open conditions. These results suggest that the main functions of sexual reproduction in C. rugulosa are recovery after severe damage to vegetation using seeds from the seed bank and the dispersal of seeds to areas without dense vegetation. Most seedlings died when the marshy meadow was temporarily inundated by heavy rain. However, transplanted seedlings survived better at artificially elevated sites that were not submerged. This shows that inundation during the seedling stage impedes seedling survival. Therefore, seeds can contribute to recovery after ramet decline or colonization to open area when (i) the rainfall is not heavy to cause seedling submergence or (ii) seeds are dispersed to higher area which is not inundated.     

不同放牧强度下短花针茅荒漠草原植被-土壤系统有机碳组分储量特征

草地生态系统作为陆地生态系统的重要组成部分,在全球碳循环中发挥着重要作用。以内蒙古短花针茅荒漠草原不同放牧强度样地为研究对象,通过分析地上植物、凋落物、根系、土壤中有机碳和土壤轻组有机碳,研究草原植被-土壤系统有机碳组分储量的变化特征,从碳储量角度为合理利用草原提供指导。研究结果表明:(1)不同放牧强度荒漠草原地上植物碳储量为11.98—44.51 g/m~2,凋落物碳储量10.43—36.12 g/m~2,根系(0—40cm)碳储量502.30—804.31 g/m~2,且对照区(CK)均显著高于中度放牧区(MG)、重度放牧区(HG);(2)0—40cm土壤碳储量为7817.43—9694.16 g/m~2,其中轻度放牧区(LG)碳储量为9694.16 g/m~2,显著高于CK、HG(P0.05);(3)植被—土壤系统的碳储量为8342.14—10494.80 g/m~2,LGMGCKHG,有机碳主要储存于土壤当中,占比约90.54%—93.71%,适度放牧利用有利于发挥草地生态系统的碳汇功能;(4)土壤轻组有机碳储量为484.20—654.62 g/m~2,LG储量最高,表明适度放牧有助于草原土壤营养物质的循环和积累。