施肥对毛竹种群不同年龄分株间胸径大小关系的影响

克隆植物不同年龄分株间可以通过生理整合作用相互传递资源, 实现资源共享。施肥可以改变林地资源状况, 进而可能影响分株间的整合作用及不同年龄分株间的生长关系。该文采用标准主轴(SMA)估计法和多元回归分析, 对不同施肥管理下大型克隆植物毛竹(Phyllostachys edulis)种群不同年龄分株(1年生分株、3年生分株和5年生分株)间的胸径(DBH)关系进行了研究, 探讨毛竹不同年龄分株DBH大小关系对施肥的响应。结果表明: 连续5年施肥有效地增加了毛竹1年生分株的DBH, 而施肥1年处理下, 1年生分株DBH与3年生分株和5年生分株平均DBH差异不显著(p > 0.05)。1年生分株与3年生分株和5年生分株DBH之间的SMA斜率为0.88-1.10, 均与1.00不存在显著差异(p > 0.05), 表现为等速生长关系。施肥1年和连续施肥5年没有改变不同年龄分株DBH之间的SMA斜率, 但连续5年施肥导致SMA的y轴截距显著增大(p < 0.001), 即在3年生分株和5年生分株DBH相同的情况下, 连续5年施肥使1年生分株具有更大的DBH增长量。采用多元线性逐步回归分析发现, 毛竹1年生分株的DBH大小在很大程度上受3年生分株DBH大小的影响, 而连续5年施肥可增强5年生分株对1年生分株DBH大小的影响。     

模拟氮沉降对北京东灵山辽东栎林树木生长的影响

传统的元素限制模型认为氮是温带森林生长的限制元素, 不过该结论更多是从地上生物量以及群落水平进行阐述, 忽视了不同物种以及不同径级树木对外源氮的响应差异。辽东栎(Quercus wutaishanica)林是华北地区常见的森林类型, 该研究以北京东灵山辽东栎林为研究对象, 通过设置3个氮添加水平的实验, 即对照CK (0 kg·hm ^-2·a ^-1), N50 (50 kg·hm ^-2·a ^-1)和N100 (100 kg·hm ^-2·a ^-1), 模拟氮沉降对群落和物种水平以及不同径级树木生长的影响。经过7年氮添加, 实验结果显示: 物种水平上, 氮添加明显促进了优势树种辽东栎的生长; 群落水平上, 树木生长随氮浓度增加有不断上升趋势, 但统计学差异不显著; 氮添加显著抑制了辽东栎以及群落内小径级(3-10 cm)树木生长, 中(10-20 cm)、大径级(>20 cm)树木生长随氮沉降水平增加呈上升趋势, 但统计学差异不显著。表明氮是辽东栎以及温带森林树木生长的限制元素; 不同径级的辽东栎和群落内其他植物对氮添加响应不一致, 氮添加抑制了小径级树木生长, 中、大径级树木生长对氮添加响应不明显。     

华北地区落叶松林的分布、群落结构和物种多样性

华北落叶松(Larix principis-rupprechtii)林、日本落叶松(L. kaempferi)林及太白红杉(L. chinensis)林是华北地区常见的3种落叶松林类型, 其中日本落叶松林为人工林, 华北落叶松林既有天然分布又有人工种植, 太白红杉林则主要是天然林。该研究基于野外调查数据, 对这3种落叶松林的分布、物种组成、群落结构、物种多样性及其与环境间的关系进行了分析。研究发现, 3种落叶松林的分布受年平均气温的影响较大, 随着年平均气温的增加, 落叶松林的天然分布减少而人工种植的分布增加。3种森林中落叶松的林分径级及树高均为右偏分布, 说明3种落叶松林均处于相对稳定的演替阶段。3种落叶松林均拥有较高的物种丰富度且差异显著, 其中太白红杉林的物种丰富度最大(39.3 ± 17.9), 而华北落叶松林的物种丰富度最小(人工林27.2 ± 17.7, 天然林27.5 ± 13.8)。除最大树高与经度的关系不显著以外, 落叶松林的最大胸径和最大树高及物种丰富度均随经纬度的增加而显著降低, 随着年降水量的增加而显著增加。此外, 年平均气温对落叶松林的总物种丰富度影响不大, 但是对其群落结构影响显著。随着年平均气温的升高, 落叶松林的最大胸径显著降低而最大树高却显著增加。落叶松天然林和落叶松人工林物种多样性的地理分布格局及与气候因子间的关系与落叶松林总体的基本一致, 但群落结构的格局不尽相同: 随着经纬度的增加, 落叶松人工林的最大树高增加而天然林的最大树高减小; 落叶松天然林的最大胸径和最大树高分别随年平均气温的升高和年降水量的增加而减小, 而落叶松人工林的最大胸径和最大树高分别随年平均气温的升高和年降水量的增加而增大。     

华北地区胡桃楸林分布规律及群落构建机制分析

探究植物分布规律和群落构建机制是揭示植物群落空间分布、群落物种多样性的形成、发展及其影响因素的重要途径。该文以华北地区胡桃楸(Juglans mandshurica)林为研究对象, 基于野外84个样方的调查数据, 通过径级分析、典范对应分析等方法研究了胡桃楸林的空间分布规律, 并通过亲缘关系指数计算、植物功能性状等方法研究了胡桃楸林的物种共存机制。结果表明, 华北地区胡桃楸的胸径相对较小(平均5.36 cm), 种群年龄较低; 海拔、坡度、坡位和人为干扰程度是影响华北地区胡桃楸分布的主要因子。研究区域内的胡桃楸大部分生长于山体中下部海拔较低的缓坡, 且人为干扰相对较少的区域, 各分布区域中胡桃楸林的分布规律各异。胡桃楸林物种的构建由生态位机制主导, 其中河北、陕西、天津的胡桃楸林物种共存过程主要受负密度制约的影响, 北京、山西的胡桃楸林的物种共存过程主要受环境选择驱动。     

模拟采食干扰下克隆整合对两种箭竹分株种群更新的影响

动物对植物的采食会刺激植物进行补偿性更新生长, 克隆整合效应能够通过分株之间的物质传输增强克隆植物的这种补偿生长。现今对克隆整合效应在箭竹(Fargesia)补偿更新中的作用仍未得到全面认识。2011年10月到2012年11月, 设立了糙花箭竹(Fargesia scabrida)和缺苞箭竹(F. denudata)各40个样方, 分别进行不剪除样方内分株和剪除样方内分株数量的25%、50%、75%四种模拟采食干扰处理, 并将样方四周的根状茎切断或保持连接。从2012年6月起观测并统计了箭竹分株种群的累积出笋率、总出笋率、补充率, 以及新生分株的株高、基径和单株生物量。结果表明: (1)在不剪除分株的样方, 切断根状茎连接显著增加了糙花箭竹的出笋率和补充率, 但降低了新生分株的株高和单株生物量, 也显著降低了缺苞箭竹的出笋率和补充率; (2)保持根状茎连接时, 25%的剪除强度仅仅降低了糙花箭竹新生分株的单株生物量; 同样在保持根状茎连接的条件下, 25%、50%的剪除强度使缺苞箭竹种群的补充率有所降低, 而切断根状茎后缺苞箭竹在25%的剪除强度下的分株补充率反而升高; (3) 75%的剪除强度并未影响两种箭竹新生分株数量更新, 但造成新生分株质量显著下降; 切断根状茎连接显著降低了糙花箭竹的新生分株的株高和基径, 对缺苞箭竹影响不显著。实验证明克隆整合影响了两种箭竹新生分株的萌发、存活和生长, 但不是两种箭竹进行补偿更新的主要机制, 仅在糙花箭竹分株种群受到重度采食干扰后的更新中才起到明显的促进作用; 两种箭竹均能在50%的剪除强度下通过补偿生长恢复种群的稳定, 75%的剪除强度则会造成箭竹新生分株质量的下降。     

Age of arboreous Tamarix austromongolica and its growth response to environment in Tongde County of Qinghai,China

Aims The objectives were to identify the age of the arboreous Tamarix austromongolica in the flood plain area of the Qinghai Plateau and clarify the response patterns of T. austromongolica’s growth to the environmental factors. We focused on social issues about whether the T. austromongolica should be protected and how to protect in the reservoir area of a hydropower station. Methods In this study, arboreous T. austromongolica in both reservoir submerged and non-submerged areas were sampled and measured based on the dendrochronology method. The ages were estimated based on the geometrical characteristics of the pith and the identified age of the inner ring. The correlation and response analysis showed the relationship between T. austromongolica’s growth and environmental factors. Important findings We accurately determined the age and historical growth dynamics of the T. austromongolica with large diameter at breast height (DBH). The results showed a special accretion phenomenon in arboreous T. austromongolica, which accelerated the DBH increasing, i.e. no direct relationship existed between the plants’ DBH and ages of the individuals. Radial growth of T. austromongolica, increased rapidly in the 1970s and 1980s and began to stabilize in the late 1980s, and mainly responded to the runoff in July and August of the Yellow River. Increasing runoff would promote the radial growth of T. austromongolica. The growth of the immaturate plant showed significant negative correlation with the wind speed in the growing season. The results will be of theoretical significance to the formation of the special morphology of the T. austromongolica, and will provide scientific practical guidance in designing the protection schemes.     

Effects of plant interspecific interaction and warming on soil microbial community in root zone soil of two dominant tree species in the subalpine coniferous forest in southwestern China

温度与植物种类是生态系统土壤微生物群落组成与结构的重要影响因子。气候变暖背景下, 不同树种及树种互作对土壤微生物群落产生的影响仍不清楚。该文以西南亚高山针叶林主要建群种粗枝云杉(Picea asperata)和岷江冷杉(Abies faxoniana)为研究对象, 采用红外加热器模拟增温, 通过不同种植方式(云杉、冷杉单种和二者混种, 以及裸地对照), 研究不同物种及增温对土壤微生物磷脂脂肪酸(PLFAs)含量与群落结构的影响。结果表明: (1)无论增温与否, 与裸地相比, 云杉与冷杉单种均显著增加了土壤微生物群落主要类群及总PLFAs含量, 而混种仅在非增温条件下增加了微生物群落PLFAs含量; 另一方面, 增温显著促进了裸地真菌(F)和云杉根区革兰氏阴性菌(GN)的生长, 但对冷杉与冷杉-云杉混种小区微生物群落具有显著的抑制作用。(2)主成分分析(PCA)表明, 非增温条件下, 植物种植对土壤微生物群落组成的影响更为明显。非增温情况下云杉、冷杉单种和混种均对微生物群落结构有显著影响, 显著降低了土壤革兰氏阳性菌/阴性菌(GP/GN), 增加了土壤真菌细菌比(F/B)(64.29%-35.71%), 而增温时, 仅冷杉单种对GP/GN和F/B有显著影响。(3) PLFAs含量与土壤碳含量显著正相关, 微生物群落结构(F/B)则与土壤pH及无机氮含量有显著相关关系。以上结果说明, 在非增温情况下, 无论单种还是混种均有利于土壤微生物生长, 但在增温情况下混种对微生物群落PLFAs含量无显著影响, 两个物种对微生物群落结构的影响在增温条件下也有减弱的趋势。     

Change of growth characters and carbon stocks in plantations of Pinus sylvestris var. mongolica in Saihanba,Hebei, China

Aims Pinus sylvestris var. mongolica is one of the main afforestation tree species in North China. It is important to study the characters of growth and carbon (C) sequestration, which can provide scientific basis for the sustainable management. Therefore, our study aims at quantifying the growth characters and C sequestration in these middle-aged plantations, and to investigate the effect of diameter at breast height (DBH) on those dynamics. Methods We selected a middle-aged P. sylvestris var. mongolica plantation as our permanent experimental plot, which is located in Saihanba, Hebei Province, China. DBH and height of all stands in this plot were measured in 2006 and 2016. Based on the anatomical trees and allometric equation, we calculated C density and sequestration from 2006 to 2016. We also analyzed C sequestration in different DBH groups in the study area. Important findings Our results showed that the carbon sink of those middle-age (age between 28 and 38 years old) plantation would be enhanced in future, and there were differences in characters of growth and C sequestration among DBH groups. The decadal increment rate of DBH and height were 4.19% and 1.97%, and the increment rate was the lowest in the 0-10 cm DBH class. The mortality rate of the plantation was 8.39%, with 7.82% mortality occurred in 0-10 cm tree size class. The forest stands biomass carbon stocks in 2006 and 2016 were 59.04 and 109.64 t?hm^-2, respectively, and almost 87.1% of the carbon stocks were in the middle DBH-class, even though the number of trees only accounted for nearly 59.2%. The small class’s number of trees accounted for 39.1%, while the carbon stocks accounted for 8.3%. Our results also demonstrate that forests in Saihanba would continue to act as a carbon sink in the coming years. The variations among DBH groups highlights that the diameter class should be taken into consideration while assess the ecological efficiency and carbon sequestration capacity in a certain area.     

高寒草地狼毒枝-叶性状的坡度差异性

枝条与叶片的生长关系是植物形成不同冠层结构充分利用空间资源的一种策略, 有利于植株通过构型调整增强自身的光合效率和竞争力, 以适应不同的生境条件。在石羊河上游高寒退化草地, 利用ArcGIS建立研究区域的数字高程模型(DEM), 并提取样地坡度数据, 采用标准化主轴估计(SMA)方法, 研究了不同坡度狼毒(Stellera chamaejasme)种群枝与叶的生长。结果表明: 随着坡度增大, 狼毒叶大小、枝长度和分枝数均呈逐渐减小趋势; 狼毒分枝数与枝长度、叶片数与枝长度均呈异速生长关系, 枝长度增加的速度大于叶片数增加的速度, 分枝数增加的速度大于枝长度增加的速度; 不同坡度间的比较显示, 较大坡度上狼毒分枝数与枝长度、叶片数与枝长度的异速斜率均较大, 在枝长度一定的条件下, 较大坡度的狼毒具有更大的叶片数与枝长度的比值和分枝数与枝长度的比值。坡度差异造成环境因子和植被群落环境的变化, 进而影响狼毒的资源利用策略, 表现为枝条与叶片构型以及二者之间关系的变化, 反映了毒杂草较强表型可塑性的适应机制。     

Duration of mulching caused variable pools of labile organic carbon in a Phyllostachys edulis plantation

Aims Soil total organic carbon and labile organic carbon are important indicators in evaluating soil quality. Mulching is widely applied to promote the emergence of bamboo shoot in winter time through stand management. Yet the consequences of mulching on soil quality in Phyllostachys edulis have not been well studied. We aim at the quantitative effect of mulching duration on soil quality in P. edulis stands.
Methods Several P. edulis stands located in Huangyan District of Taizhou, Zhejiang Province of China, had been applied with mulching for 1-2 years and were used in this study to assess the mulching effects. We also selected stands without mulching treatment as the reference sites (or control, CK) for comparisons.||||Important findings Total soil organic carbon (TOC), light fraction organic matter (LFOM), and easily-oxidized carbon (EOC) contents at stands with 1-year and 2-year mulching treatments were significantly increased compared with those at the CK sites. The 1-year mulching increased TOC, LFOM and EOC by 11.2%-74.2%, 31.7%-196.9% and 5.0%-79.6%, respectively, than those of CK sites, while by 22.2%-90.8%, 36.7%-238.5%, and 21.9%-97.5% with 2-year treatment. However, the contents of water-soluble organic carbon (WSOC) changed insignificantly. Among the indicators, we found that WSOC:TOC in CK was higher than that with the mulching treatments, while EOC:TOC with 1-year treatment was higher than that with 2-year treatment, and EOC:TOC with 2-year treatment was higher than that of CK. Additionally, WSOC, EOC, and LFOM at all three treatments showed high correlations with TOC, with a higher correlation coefficient of WSOC with TOC of 0- 30 cm soil layers in CK than those with mulching treatments. The correlation coefficient of EOC and LFOM with TOC was the highest at the 2-year mulching sites. More importantly, TOC, WSOC, EOC, and LFOM were significantly (p < 0.05), or extremely significantly (p < 0.01), correlated with soil nutrient content, including total N, hydrolysis N, available P, available K, exchangeable Ca, and exchangeable Mg in all treatments. In sum, it appeared that mulching in short term can increase the contents of TOC, soil labile organic carbons and soil nutrients in bamboo soils, yielding an improved soil quality and thus can be promoted as a plausible practice for the sustainable management of P. edulis stands.     

Short-term nitrogen fertilization decreased root and microbial respiration in a young Cunninghamia lanceolata plantation

Aims As the primary pathway for CO₂ emission from terrestrial ecosystems to the atmosphere, soil respiration is estimated to be 80 Pg C·a^-1 to 100 Pg C·a^-1, equivalent to 10 fold of fossil fuel emissions. As an important management practice in plantation forests, fertilization does not only increase primary production but also affects soil respiration. To investigate how nitrogen (N) fertilization affects total soil, root and microbial respiration, a N fertilization experiment was conducted in a five-year-old Cunninghamia lanceolata plantation in Huitong, Hunan Province, located in the subtropical region. MethodsOne year after fertilization, soil respiration was monitored monthly by LI-8100 from July 2013 to June 2014. Soil temperature and water content (0-5 cm soil depth) were also measured simultaneously. Available soil nutrients, fine root biomass and microbial communities were analyzed in June 2013. Important findings Total soil, root and microbial respiration rates were 22.7%, 19.6%, and 23.5% lower in the fertilized plots than in the unfertilized plots, respectively. The temperature sensitivity (Q₁₀) of soil respiration ranged from 1.81 to 2.04, and the Q₁₀ value of microbial respiration decreased from 2.04 in the unfertilized plots to 1.84 in the fertilized plots. However, neither the Q₁₀ value nor the patterns of total soil respiration were affected by N fertilization. In the two-factor model, soil temperature and moisture accounted for 69.9%-79.7% of the seasonal variations in soil respiration. These results suggest that N fertilization reduces the response of soil organic carbon decomposition to temperature change and may contribute to the increase of soil carbon storage under global warming in subtropical plantations.     

山东省滨海湿地柽柳种群的空间分布格局及其关联性

柽柳(Tamarix chinensis)是暖温带滨海盐碱湿地的先锋灌木物种, 在滨海湿地植物群落演替和防止沿海地区海水入侵中发挥着重要的作用。研究柽柳种群的空间分布格局和不同径级柽柳个体之间的空间关联性, 揭示种群发展规律, 可以为盐碱地柽柳种群的保护提供指导, 并为滨海湿地生态系统的演替和生态管理提供依据。该研究在昌邑国家海洋生态特别保护区核心区内沿平行海岸线方向设置两条间隔800 m左右的样带, 每条样带上设置3个50 m × 50 m的样地, 共设置6块样地进行每木调查, 绘制柽柳种群空间位置分布图, 并将调查的柽柳按照其基径大小分为≤4 cm、4-8 cm、>8 cm 3个不同径级。利用Programita软件对柽柳种群的分布格局以及不同径级间的空间关联性进行分析。结果显示: (1) 6块样地共调查柽柳个体374株; (2)不同样地间柽柳植株密度差别较大, 说明柽柳在区域尺度上的分布并不均匀; (3)柽柳种群在小尺度(小于5 m)上表现为聚集分布, 在大尺度(大于15 m)上表现为随机分布, 总体表现为随空间尺度的增大柽柳种群呈现由聚集分布过渡到随机分布的趋势; (4) 3个径级两两之间在小尺度上表现为正关联, 在大尺度上表现为无关联, 但在15 m尺度上径级II与径级III因为竞争而呈空间负相关关系。     

Correlation analysis between vein density and stomatal traits of Robinia pseudoacacia in different aspects of Beishan Mountain in Lanzhou

AimsThe relationship between leaf venation and stomatal traits reflects leaf water potential of plants, and is fundamental to probe the relationship between physiological functions and water use. Our objective was to study the changes in the relationship between venation density and stomatal traits (stomatal density and stomatal length) in Robinia pseudoacacia with the changes in slope aspects.MethodsIn Beishan Mountain of Lanzhou in Gansu Province, China, 20 transects were laid out horizontally along the contour at intervals of 50 m from an elevation of 1550-1750 m in four different slope aspects, and 12 plots were set up along each transect at intervals of 5 m. A handed GPS (global positioning system) was used to measure latitude, longitude and altitude at each plot. Community characteristics, including crown density, tree height and soil moisture, were investigated. Robinia pseudoacacia within all plots were sampled and used for measurements of individual leaf area, venation density, stomatal density and stomatal length in laboratory in each plot. The 240 plots were categorized into groups of southern, eastern, western and northern aspects, and the standardized major axis (SMA) estimation method was then used to examine the relationship between the stomatal density, stomatal length and vein density.Important findings The results showed that with a change of the aspect from south to east, west, and north, the crown density, average tree height and soil moisture of the plant community increased, while leaf net photosynthetic rate (P_n), transpiration rate (T_r), photosynthetically active radiation (PAR), vein density and stomatal density decreased. In addition, stomatal length and individual leaf area increased. Venation density of each aspect of R. pseudoacacia was positively correlated with stomatal density (p < 0.05) and negatively with stomatal length (p < 0.05). These correlations were strongest in south slope (p < 0.01).     

Trade-off between height and branch numbers in Stellera chamaejasme on slopes of different aspects in a degraded alpine grassland

权衡关系是生活史对策理论的基础, 株高和枝条数的权衡关系对理解植物在不同生境下的表型可塑性有重要意义。该研究选择祁连山北坡高寒退化草地, 利用ArcGIS建立研究区域的数字高程模型(DEM), 并提取样地坡向数据, 采用广义相加模型(GAM)与偏相关分析相结合的方法, 分析了不同坡向影响下狼毒(Stellera chamaejasme)种群株高和枝条数的关系。结果表明: 随着坡向由北坡转向东坡、南坡、西坡, 草地群落地上生物量和盖度呈“减小—增大—减小”的变化趋势, 群落高度则先增大后减小; 坡向是影响狼毒株高和枝条数空间分异的主要地形因子; 随着坡向由北、东转向西、南, 狼毒种群株高呈下降趋势, 而枝条数呈上升趋势, 二者表现出此消彼长的权衡关系, 狼毒植株比叶面积先增大后减小。不同坡向狼毒株高和枝条数的权衡关系, 反映了异质生境中资源多重竞争下狼毒生物量分配机制和提高种群适应性的种群更新策略。     

Season dynamics of carbon use efficiency and its influencing factors in the old-growth Abies fabri forest in Gongga Mountain,western Sichuan,China

碳利用效率(CUE)是植被生态系统的一个重要功能参数, 反映了植被生态系统的固碳能力, 适用于分析不同时间段内器官、个体和群落等不同层次的碳收支趋势, 因而有助于对陆地生态系统碳功能的确定与预测, 引起了广泛关注。该研究采用生物计量法, 测定和计算了川西贡嘎山东坡峨眉冷杉(Abies fabri)成熟林树木不同器官的呼吸与净生产力动态, 分析了乔木层及其各器官CUE动态及主要影响因子, 并估算了乔木层不同径级树木CUE。主要结果: (1)乔木层各器官月呼吸速率与温度呈正相关关系, 以细根月呼吸速率为最大; 不同径级树木年呼吸量无显著差异, 以小径级树木树干的年呼吸量为最小。(2)乔木层细根和树干月净初级生产力(NPP)均随温度增加而增加, 以细根月NPP为最大。小径级树木年NPP最大, 其针叶年NPP也显著高于中径级和大径级树木。(3)林分乔木层及其各器官CUE大多集中在0.30-0.60之间, 其中细根、树干CUE具有相似的月变化动态, 均随温度的升高而上升。不同径级树木CUE及树干和针叶CUE均随树木个体的增大而明显下降。(4)气温和土壤温度与乔木层树干和细根CUE呈正相关关系, 而降水量与针叶CUE呈负相关关系。细根CUE与树干CUE呈正相关关系,与针叶CUE呈负相关关系。峨眉冷杉成熟林乔木层CUE主要取决于树干和细根CUE。该研究证实了川西亚高山暗针叶成熟林仍具有较强的碳汇功能, 在区域碳储存和森林生态系统碳循环中发挥着极其重要的作用。     

宁夏六盘山3种针叶林降水利用效率的年际变化及其对气象因子的响应

为揭示我国西北山地温带针叶林降水利用效率(RUE)的年际变化及其对气象因子响应的差异性, 在宁夏六盘山研究了华山松(Pinus armandii)天然林、华北落叶松(Larix principis-rupprechtii)和油松(Pinus tabulaeformis)人工林的RUE及其与气象因子间的关系。结果表明: 3种针叶林RUE及其年际变化存在种间差异。生产力高的林分(两种人工林)具有更高的RUE, 华北落叶松林年平均生产力和RUE分别为6.72 t·hm ^-2·a ^-1和1.12 g·m ^-2·mm ^-1, 是华山松林的2.53倍和2.49倍; 油松林分别为5.76 t·hm ^-2·a ^-1和0.97 g·m ^-2·mm ^-1, 也远高于华山松林。在林龄小于32年时, 3种林分RUE总体表现出随林龄而增加的趋势, 但存在着种间差异, 其中两种人工林增速更快; 华山松林在林龄为32-45年时, RUE呈波动变化, 之后呈下降趋势。RUE的年际变化趋势与林分生产力相似, 即在生产力较高的年份RUE也较高。气象因子对RUE的影响有明显的“滞后效应”和种间差异。RUE受年降水量及其年内分配格局的影响。随年降水量增加, 华山松林RUE逐渐减小, 而华北落叶松和油松林RUE均先升高后降低; 在干旱年份3种针叶林RUE趋向于相近的值(不一定是最大值), 而在湿润年份趋向于相同的最小值; 除受当年春季(4月)或秋季(9-11月)的降水量影响外, 3种针叶林的RUE还受上一年夏秋(8-9月)的降水量影响。3种针叶林的RUE都极显著地受到上年6月、当年3与6月气温的影响; 此外, 华山松林RUE与当年2月气温负相关, 两人工林均受到当年4、5月气温的显著促进作用。     

Plastic responses of stem and leaf functional traits in Leymus chinensis to long-term grazing in a meadow steppe

植物对不同功能性状进行权衡, 通过表型可塑性达到对异质生境的适应是植物的一种生态对策。羊草(Leymus chinensis)是欧亚温带草原东缘的主要优势植物, 研究其对放牧的表型反应对揭示草原生态系统的放牧响应机制具有代表意义。该文以内蒙古呼伦贝尔草甸草原为例, 通过设置不同放牧压力与围封的长期试验, 研究了羊草茎叶功能性状对放牧的可塑性响应模式。结果表明: 1)与长期围封相比, 长期放牧导致羊草茎叶性状显著小型化, 其中, 株高和个体地上生物量分别降低76.82%和89.88%, 但3年短期围封对茎性状影响不显著, 说明羊草表型矮小化现象具有一定的保守性; 2)通过排序构建羊草性状可塑性变化谱, 发现茎质量、总质量、茎高、株高、叶面积等为对放牧响应的敏感性状, 而叶片数、茎粗、叶宽等较为稳定, 为惰性性状; 3)放牧干扰下, 羊草性状可塑性程度与其变异性之间符合y = y₀ + ae^bx拟合关系, 随着植物性状的响应强度增大, 其变异性增强; 4)偏最小二乘法分析发现茎长、株高、叶面积、叶长等性状的投影重要性指标大于1, 对地上生物量变化的解释率为68.6%, 是导致长期放牧下羊草个体生物量降低的主要因子。研究认为, 矮化型变是羊草的避牧适应对策, 在亚稳态下, 通过不同性状的权衡, 充分利用环境资源完成其生活史。     

Relationships between leaf thickness and vein traits of Achnatherum splendens under different soil moisture conditions in a flood plain wetland,Heihe River,China

Aims The correlations between leaf thickness and vein traits influenced the leaf hydraulic dynamic balance, and there were important meanings to reveal ecophysiological mechanisms of plant leaves water transport and growth rate. Our objective was to study the changes in the relationship between leaf thickness and vein traits (vein diameter, vein density) of Achnatherum splendenspopulations by using standardized major axis estimation (SMA) method under different soil moisture conditions located in flood plain wetland of Zhangye.Methods The study site was located at flood plains wetland of Zhangye, Gansu Province, China. Selecting a starting point along the vertical direction of the river, in turn, along the soil moisture gradient, four plots were set up at intervals of 40 m, plot I (50.07%), plot II (38.77%), plot III (31.5%) and plot IV (20.4%). From each of the four sample plots, seven samples were collected, resulting in (5 m × 5 m) a total of 28 samples. Community traits (height, density) and soil physical and chemical properties were investigated. Six individual samplings of A. splendens from each plot were used to measure the leaf thickness, vein density and vein diameter in laboratory. In addition, the photosynthetically active radiation (PAR), leaf net photosynthetic rate (P_n) and transpiration rate (T_r) of A. splendens were measured in natural environment. The 28 plots were categorized into groups I, II, III and IV, and SMA estimation method was then used to examine the allometric relationship among leaf thickness, vein density and vein diameter. Important findings With a decreased soil moisture, the plant density and height displayed a pattern of steadily declining, while the soil electrical conductivity increased, In addition, the vein density, leaf thickness, water use efficiency (WUE), PAR and twig number of A. splendens displayed a pattern of initial decrease, whereas the vein diameter and T_r increase gradually, P_n and plant high displayed changing trends of increasing-decreasing. The leaf thickness was negatively associated with the vein density, vein diameter, and the relationship varied with the soil moisture conditions (p< 0.05). There was a significant positive relationship (p < 0.05) between the leaf thickness and vein density. The SMA slope of the regression equation gradually decreased and was significantly different from 1.0 (p < 0.05) on plot I and IV. In addition, along decreased soil moisture, the standardized major axis slope of regression equation in the scaling relationships between the leaf thickness and vein diameter gradually increased and was significantly different from -1.0 (p < 0.05) on plot I and IV.     

Responses of soil heterotrophic respiration to changes in soil temperature and moisture in a Stipa krylovii grassland in Nei Mongol

土壤异养呼吸在野外自然条件下除受温湿度影响外, 还受其他多种因子的综合影响, 很难利用野外观测数据确定土壤异养呼吸对温湿度变化的响应方程形式, 以及温湿度间是否存在交互作用。该研究在严格控制温湿度的条件下对内蒙古克氏针茅(Stipa krylovii)(西北针茅(Stipa sareptana var. krylovii))草原土样进行室内培养实验, 旨在解决上述问题。该研究的正交实验包括5个温度梯度(9、14、22、30、40 ℃)和5个湿度梯度(土壤持水力(water holding capacity, WHC)分别为20%、40%、60%、80%、100%)。室内培养实验持续71天, 土壤异养呼吸速率测定为2天(后期为1周)一次, 土壤可溶性有机碳和微生物生物量碳含量测定约为18天一次。研究结果显示: 土壤异养呼吸与温度呈显著正相关(p < 0.001)且温度间差异显著(p = 0.001), 呼吸温度敏感性(Q₁₀)与土壤水分含量呈正相关(p < 0.001); 呼吸与土壤水分二项式拟合效果较好, 在80% WHC时呼吸速率最大, 且最适湿度随温度上升而增加。土壤温度和水分的交互作用显著(p < 0.05), 土壤异养呼吸最适响应方程为lnRh = 0.914 + 0.098T + 0.046M + 0.001TM - 0.002T² - 0.001M² (Rh为异养呼吸, T为温度, M为湿度), 这说明加和形式的温湿度响应模型可能优于乘积形式。微生物生物量碳与土壤异养呼吸的相关性随培养时间发生变化, 土壤可溶性有机碳与土壤异养呼吸无显著相关(培养第20天除外), 原因可能是培养期间微生物死亡或群落结构改变导致微生物总体代谢活性的变化。     

Dominant species and ecosystem gas exchange in temperate grassland under different land use patterns

在内蒙古温带草原围封、放牧和割草3种处理下的样地内, 对生态系统尺度和大针茅(Stipa grandis)、冷蒿(Artemisia frigida)、羊草(Leymus chinensis) 3种优势种植物叶片尺度上的气体交换和水分关系进行了测定, 对比研究了植物碳水对环境的响应。结果表明, 在优势种单株尺度和生态系统尺度上, 大气-植被CO₂交换因草地利用方式的不同而具有不同的表现。在生态系统层面, 放牧样地的群落净CO₂气体交换量和总初级生产力都与围封样地和割草样地有差异, 群落总初级生产力受生态系统呼吸的影响。在放牧处理下, 群落净CO₂气体交换量日变化表现为生态系统对碳的吸收, 而围封和割草则以碳释放为主。单叶光合速率出现负值并随时间推移而恢复的现象, 应是植物对干旱高温、高光照的特殊反应。生态系统水分利用效率没有明显不同, 但各样地的蒸散能力有趋势上的变化; 对于同种植物, 放牧样地植物单叶水分利用效率的日变化波动幅度最大, 围封样地最小。