根表面养分吸收通量和根围溶质浓度的近似解析解

该文用Nye-Tinker-Barber模型来研究植物根系表面的养分吸收通量和根围溶质浓度的近似解析解。将根围区域分为远场区域和近场区域, 在远场用相似变量, 在近场用尺度变换, 将远场解在根表面展开并与近场解进行待定函数的匹配, 从而获得对流扩散方程根表面通量和浓度的一阶近似解析解, 该解能够简化到扩散方程的解的形式。对氮、钾、硫、磷、镁、钙的养分吸收通量和氮、钾的浓度分别进行数值模拟, 比较模型的数值解、Roose的近似解析解和该文的近似解析解。结果表明: 在扩散方程中, 6种元素通量的解析解与Roose解析解相近, 但均高于数值解, 钾和磷的通量在短时间内迅速衰减; 钾和氮浓度的全局近似解析解与Roose解析解接近, 并与数值解的变化趋势一致。在对流扩散方程中, 除氮外的5种元素通量的近似解较Roose的解析解更接近于数值解, 且没有奇性。     

滇南喀斯特地区不同季节土壤和灌木叶片化学计量特征及对水分添加的响应

干旱是影响南方喀斯特地区植物生长的重要限制因子, 气候变化会影响该地区的降水量和分布格局。研究该地区土壤和植物化学计量特征及其水分响应格局, 具有重要意义。自2017年4月开始, 在云南建水喀斯特植物群落进行加水试验, 2018年4月(旱季)和8月(雨季)分别采集土壤和优势灌木鞍叶羊蹄甲(Bauhinia brachycarpa)和假虎刺(Carissa spinarum)叶片样品, 测定碳、氢、氮、磷、硫、钾、钙、镁、铝、钠、铁、锰、锌、铜14种元素含量。结果表明, 水分添加影响了表层土壤中碳、氮、钠的含量, 相比于旱季, 雨季土壤中钠和硫含量明显减少, 其余土壤元素在水分添加和季节变化下并未表现出明显差异。土壤水分含量的增加使得鞍叶羊蹄甲和假虎刺叶片中钾含量下降, 钙含量上升。在水分条件变化下, 两种植物叶元素含量的稳定性与植物中元素的含量有关, 含量越接近极大值(基本元素碳、氢、氮等)或极小值(微量元素铜、锌等)的元素其变异系数越小(越稳定), 两种植物中含量接近于1 mg·g^-1的元素磷、硫、镁的变异系数最高。在土壤水分条件变化下, 假虎刺中碳、氮、磷等大量元素含量的稳定性显著高于鞍叶羊蹄甲。降水变化和水分添加导致的土壤水分变化, 对滇南喀斯特地区土壤和植物中不同元素含量的影响不同, 这些结果将为该地区的土壤、植被修复和管理提供科学参考。     

Effects of simulated nitrogen deposition on fine root morphology,nitrogen and phosphorus efficiency of Pinus massoniana clone under phosphorus deficiency

Aims In forest ecosystems with phosphorus (P) deficiency, the impact of atmospheric nitrogen (N) deposition on nutritional traits related to N and P uptake potentially affect plant growth and vegetation productivity. The objective of this study was to explore the effects of simulated N deposition on fine root morphological characteristics and effiency of N and P absorption in Pinus massoniana under under low P stress.
Methods Two clones of P. massoniana seedling with different P efficiency (high P efficiency 19-5 vs. low P efficiency 21-3) were used. A two-year pot experiment was applyed with treatments of two P conditions, (i.e. homogeneous low P availability vs. heterogeneous low P availability) and three N deposition levels (0, 30 and 120 kg N·hm^-2·a^-1; i.e., N0, N30, or N120, respectively) .
Important findings 1) The growth of P. massoniana seedling was interactively affected the three factors: simulated N deposition, P condition and genotypes. Simulated N deposition increased the seedling height and dry mass under heterogeneous P deficiency, but did not significantly affect those traits under homogeneous P deficiency. Under heterogeneous P deficiency and N120 treatment, the seedling height and dry mass of clone 19-5 were 1.1 times and 1.6 times higher than that of clone 21-3, respectively. 2) Fine root length and surface area decreased as root diameter increased. N deposition significantly stimulated proliferation of fine root with diameter ≤1.5 mm, while roots with diameters ranged from 1.5 to 2.0 mm and over 2.0 mm were not influenced. The length of fine root ≤1.5 mm in diameter accounted for 90.4%-92.8% of the total root length and was not affected by N deposition. 3) Under the heterogeneous low P condition, clone 19-5 was found to respond to the simulated N deposition with increased root length and surface area in fine-root diameter class of ≤1.5 mm. Additionally, in compared with control, its N and P absorption efficiency were significantly enhanced 93.3% and 148.4%, respectively under N120 treatment. However, the N and P absorption efficiency of clone 21-3 was less affected by the simulated N deposition. The N and P use efficiency had no notable variation. Finally, we found that the proliferation of fine-root ≤1.5 mm in diameter and high N (P) absorption efficiency maybe the adaptive mechanisms of P. massoniana responding to atmospheric N deposition under P deficiency.     

Effects of enhanced UV-B radiation and nitrogen deposition on the growth of invasive plant Triadica sebifera

Aims Exotic plant invasions are important components of global change, threatening both the stability and function of invaded ecosystems. Shifts in competitive ability of invasive plants versus their native congeners have been documented. Enhanced UV-B radiation and nitrogen (N) deposition might interact with soil biota communities impacting the invasion process of exotic plant species. To understand the potential effects by UV-B and N with soil biota on plant growth would enhance our understanding of the mechanisms in plant invasions in the context of global change.
Methods We conducted a full-factorial pot experiment in the native range (China) of Triadica sebifera invading US to investigate how UV-B radiation, N and soil biota together determined their seedling growth.
Important findings The results showed that UV-B radiation, N and soil sterilization together impacted the growth of T. sebifera seedlings. UV-B radiation induced changes in biomass allocation with larger leaf biomass observed in response to UV-B radiation. In addition, N increased aboveground biomass and decreased root biomass simultaneously. Soil biota imposed positive effects on growth of T. sebifera, and the addition of N amplified these positive effects. The negative effects by UV-B radiation on growth of T. sebifera showed no response to N addition. Plant height, leaf biomass and total biomass of the invasive T. sebifera populations out- performed those of the native ones. In addition, invasive T. sebifera populations weakened the dependence of root/shoot ratio and root biomass on local soil microorganisms than native populations, but enhanced that of leaf area ratio.     

摩西斗管囊霉改善连作花生根际土壤的微环境

花生(Arachis hypogaea)长期连作导致土壤环境恶化, 严重影响产量和品质。丛枝菌根真菌(AMF)作为有益真菌能够与80%的陆生植物根系形成共生关系, 这种共生体能够改善植物根系微环境, 提高植物对营养物质的吸收和对逆境胁迫的抗性。为了探究AMF对花生连作土壤微环境的影响, 该研究通过对花生连作土壤接种和未接种摩西斗管囊霉(Funneliformis mosseae)试验, 在花生不同生长期检测根际土壤的酶活性、土壤矿物质含量、土壤微生物群落结构和多度的变化情况, 以及对连作花生产量和品质的影响。研究结果表明: 1)摩西斗管囊霉能够显著提高花生根际土壤蔗糖酶、脲酶、碱性磷酸酶和硝酸还原酶的活性; 2)摩西斗管囊霉显著增加花生连作土壤中全氮、全磷、全钾、速效磷和速效钾的含量; 3)摩西斗管囊霉显著降低土壤中有害真菌曲霉菌属(Aspergillus)的多度, 减少镰刀菌属(Fusarium)和赤霉菌属(Gibberella)的多度, 但是没有达到显著水平, 显著增加有益细菌放线菌Gaiella属的多度; 4)摩西斗管囊霉显著提高连作花生的产量, 增加籽仁中蛋白质、油酸和亚油酸的含量。因此, 摩西斗管囊霉能够改善连作花生根际土壤微生态环境, 增强连作土壤对致病菌的抵抗能力, 从而缓解连作障碍对花生根系的危害。     

Impacts of nitrogen addition on foliar nitrogen and phosphorus stoichiometry in a subtropical evergreen broad-leaved forest in Mount Wuyi

Aims Our purpose was to explore the effects of nitrogen addition on foliar nitrogen (N), phosphorus (P) and N:P stoichiometry and to assess their differences among different species and functional groups.
Methods N addition experiment has been conducted in a subtropical evergreen broad-leaved forest in Mount Wuyi, Fujian Province since 2011. Foliar concentrations of nitrogen and phosphorus were measured and foliar stoichiometry was estimated in tree, shrub, herb, fern and moss species following the N addition treatments from 2013 to 2015.
Important findings Generally, foliar N increased for almost all species and herbaceous plants are much more sensitive than trees and shrubs under N addition. Foliar N of Castanopsis carlesii, Amomum villosum, Woodwardia japonica increased significantly under N addition. Foliar P for most species was sensitive to the N addition. Foliar P of herbaceous plants increased significantly but foliar P of Leucobryum chlorophyllosum decreased significantly. The results showed the subtropical evergreen forest in Mount Wuyi was mainly limited by P and mean foliar N:P ratios enhanced from 18.67 to 19.72 under N addition, indicating that the strength of P limitation was enhanced by N addition. N:P ratios of the dominant arboreal species in the communities tended to be stable, while N:P ratios of herbaceous plants and shrubs increased. The changes in N:P ratios were mainly determined by P dynamics instead of N dynamics under N addition, and our results confirmed that increasing N availability can affect P cycling.     

Foliar nitrogen and phosphorus stoichiometry of alien invasive plants and co-occurring natives in Xishuangbanna

Aims How alien invasive plants and co-occurring native plants utilize nutrients is one of major issues in invasion ecology. Foliar nitrogen (N) and phosphorus (P) contents and stoichiometry can elucidate the uptake ability and limitation status of nutrients in plants, which provides basic knowledge for understanding the invading ability and co-occurrence or disappearance of plants.
Methods Based on typical alien invasive plants (Chromolaena odorata, Ageratina adenophora) and native plants in southwestern China, this study focused on strategies of N and P utilization among invasive plants and native plants under different invasion conditions. The species compositions, aboveground biomass, leaf N and P contents and leaf N:P were investigated for plants in plots with no invasion and with different invasion extents (estimated by the plot-based percentage of invaders’ biomass in total community) at Mt. Kongming in Xishuangbanna region, Yunnan Province, China.
Important findings The species number decreased significantly with the invasion extent of both C. odorata and A. adenophora, although the aboveground biomass was greatly enhanced. Leaf N and P contents did not differ between the two studied invaders, but they showed significantly higher N and P levels than both co-occurring and only native species (p < 0.05). Besides, leaf N and P contents of invaders increased with the invasion extent, and leaf N of native plants also showed an increasing trend with the invasion extent. When the influence of invasion was checked for the same species, leaf P contents decreased, whereas leaf N and N:P increased for most native plants under invasion. Based on the absolute foliar N and P contents, N:P values, we inferred that native plants were still limited by N, although N availability might be enhanced by invasion. Both invasive plants had leaf N:P values lower than 10, suggesting a higher P uptake relative to N uptake. All above results highlighted a higher N and P uptake of typical alien invasive plants in southwestern China.     

多花木蓝根截面微观结构对其抗拉特性的影响

根截面微观结构由连通的骨架和相互贯通或封闭的孔洞构成, 其与根系抗拉力学特性有密切的联系。该文通过单根拉拔测试根系力学特性并采用扫描电镜获取根截面微观特征, 探讨根截面微观结构特征与根抗拉力学特性的关系。主要结果显示: 1)根系截面单位面积承受拉力和拉伸应变的能力均随根直径的增大而降低。2)根系抗拉强度和韧性随平均孔径的增加而降低, 其次孔径的均匀性对二者也存在一定的影响。3)导管排列方式随根直径的增加, 呈现单管孔→复管孔→管孔链→管孔团的排列方式, 导管排列方式和分布均匀性对根抗拉力学特性都有影响, 其中排列方式较分布均匀性的影响大。4)根截面管孔面积比对根抗拉特性的影响还受木质部和根皮及导管特征的影响。该研究从根系微观结构的角度揭示了根直径的增大影响截面微观结构进而影响根系的抗拉力学特性, 为进一步解析灌木根系固土力学机制提供了一定的理论基础。     

Effects of short-term nitrogen addition on fine root biomass,lifespan and morphology of Castanopsis platyacantha in a subtropical secondary evergreen broad-leaved forest

Aims Fine roots are the principal parts for plant nutrients acquisition and play an important role in the underground ecosystem. Increased nitrogen (N) deposition has changed the soil environment and thus has a potential influence on fine roots. The purpose of this study is to reveal the effect of N deposition on biomass, lifespan and morphology of fine root.Methods A field N addition experiment was conducted in a secondary broad-leaved forest in subtropical China from May 2013 to September 2015. Three levels of N treatments: CK (no N added), LN (5 g·m^-2·a^-1), and HN (15 g·m^-2·a^-1) were applied monthly. Responses of fine root biomass, lifespan, and morphology of Castanopsis platyacantha to N addition were analyzed by using a minirhizotron image system from April 2014 to September 2015. Surface soil sample (0-10 cm) was collected in November 2014 and soil pH value, and concentrations of NH₄⁺-N and NO₃^--N were measured.Important findings The biomass and average lifespan of the fine roots of C. platyacantha were 128.30 g·m^-3 and 113-186 days, respectively, in 0-45 cm soil layer. Nitrogen addition had no significant effect on either fine root biomass or lifespan in 0-45 cm soil layer. However, LN treatment significantly decreased C. platyacantha root superficial area in 0-15 cm soil layer. HN treatment significantly decreased soil pH value. Our study indicated that short-term N addition influences soil inorganic N concentration and thus decreased pH value in surface soil, and thereafter affect fine root morphology. Short-term N addition, however, did not affect the fine root biomass, lifespan and morphology in subsoil.     

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.     

Biomass estimation models and allocation patterns of 14 shrub species in Mountain Luya,Shanxi, China

Aims Shrub species have evolved specific strategies to regulate biomass allocation among various organs or between above- and belowground biomass and shrub biomass model is an important approach to estimate biomass allocation among different shrub species. This study was designed to establish the optimal estimation models for each organ (leaf, stem, and root), aboveground and total biomass of 14 common shrub species in Mountain Luya, Shanxi Province, China. Furthermore, we explored biomass allocation characteristics of these shrub species by using the index of leaf biomass fraction (leaf to total biomass), stem biomass fraction (stem to total biomass), root biomass fraction (root to total biomass), and root to shoot mass ratio (R/S) (belowground to aboveground biomass).
Methods We used plant height, basal diameter, canopy diameter and their combination as variables to establish the optimal biomass estimation models for each shrub species. In addition, we used the ratios of leaf, stem, root to total biomass, and belowground to aboveground biomass to explore the difference of biomass allocation patterns of 14 shrub species.
Important findings Most of biomass estimation models could be well expressed by the exponential and linear functions. Biomass for shorter shrub species with more stems could be better estimated by canopy area; biomass for taller shrub species with less stems could be better estimated by the sum of the square of total base diameter multiply stem height; and biomass for the rest shrub species could be better estimated by canopy volume. The averaged value for these shrub species was 0.61, 0.17, 0.48, and 0.35 for R/S, leaf biomass fraction, stem biomass fraction, and root biomass fraction, respectively. Except for leaf biomass fraction, R/S, stem biomass fraction, and root biomass fraction for shrubs with thorn was significantly greater than that for shrubs without thorn.     

北方农牧交错带温性盐碱化草地土壤呼吸对不同形态氮添加和刈割的响应

农牧交错带草地生态系统兼受农业和牧业的影响, 属于脆弱生态系统, 尤其是养分贫瘠的盐碱化草地, 其生态系统结构和功能对外界干扰的响应更加强烈。位于晋西北地区的农牧交错带盐碱化草地, 地理位置独特, 区别于天然牧区草地生态系统。由于毗邻农田, 农业氮肥的过量使用促进了活性氮气体排放, 同时使得农牧交错带草地土壤碳氮循环发生改变。刈割是北方农牧交错草地生态系统的主要管理方式, 为了深入探究氮添加和刈割管理方式对农牧交错带草地碳循环的影响, 进一步厘清该区域草地生态系统的碳动态问题, 该研究设置了一个不同形态氮添加和刈割的裂区实验, 测定土壤呼吸对不同形态氮肥添加和刈割的响应, 为进一步科学管理该区域草地提供可靠的依据。实验样地位于山西省右玉县境内的“山西农业大学农牧交错带草地生态系统野外观测研究站”, 于2017年设置不同形态氮添加和刈割处理, 实验处理包括对照(不刈割和刈割)、尿素添加、缓释尿素添加、刈割+尿素添加、刈割+缓释尿素添加, 每种处理6个重复, 共36个小区。在不同处理条件下测定土壤呼吸速率、土壤温度、土壤水分、土壤微生物生物量、土壤无机氮含量、植物地上和地下生物量, 并计算土壤累积碳排放量及CO₂通量。研究结果表明: (1)短期(2017-2018年)尿素和缓释尿素的添加显著提高了该地区土壤呼吸速率和土壤累积碳排放量。与添加缓释尿素相比, 添加尿素处理下的土壤呼吸速率和累积碳排放量更高; (2)刈割显著降低土壤呼吸速率和累积碳排放量; (3)短期氮添加和刈割的交互作用对土壤呼吸速率没有显著影响。因此, 短期氮添加促进了北方农牧交错带盐碱化草地土壤碳释放, 刈割抑制土壤呼吸, 降低了累积碳排放量, 这可能是由于刈割移除地上植物, 减少了凋落物的输入, 底物减少导致土壤微生物活性降低。但是随着处理时间的延长, 氮添加和刈割对该农牧交错带盐碱化草地土壤碳动态的影响还有待进一步探究和发现。     

入侵植物加拿大一枝黄花根际解钾菌多样性及解钾活性

入侵植物加拿大一枝黄花(Solidago canadensis)具有较强的钾(K)富集能力, 这可能和其对土壤微生物群落的改变有关。根际解钾菌能够将植物难以利用的矿物态钾转化为植物可以利用的可溶性钾, 而加拿大一枝黄花如何影响根际解钾菌多样性和解钾活性尚未明了。该研究以浙江省杭州湾湿地围垦区内自然生长的加拿大一枝黄花和其伴生本地植物白茅(Imperata cylindrica)为研究对象, 比较了加拿大一枝黄花和白茅体内及土壤中的钾含量水平, 钾供给水平对生物量积累的影响, 以及根际解钾菌的数量、多样性和解钾活性的差异。结果表明, 加拿大一枝黄花茎、叶中的钾含量均显著高于白茅, 分别是白茅的1.59和7.33倍; 加拿大一枝黄花和白茅的土壤全钾含量差异不显著, 速效钾含量在0-10 cm土层中差异显著、在10-20 cm土层中差异不显著。随着钾供应水平提高, 加拿大一枝黄花和白茅的生物量均显著增加。利用解钾培养基计数培养后发现, 加拿大一枝黄花根际解钾菌的数量是白茅的3.51倍。分离培养后将出现解钾圈的菌株进行鉴定, 利用解钾液体培养实验测定其解钾量, 发现从加拿大一枝黄花根际土中分离得到的15个解钾菌株中, 有9个具有高效解钾能力, 其处理液中K ⁺含量较空白对照高出85.11%-192.54%, 其中菌株H2-20解钾能力最强, 解钾量为10.657 mg·L ^-1。加拿大一枝黄花根际解钾菌解钾作用显著高于白茅。经16S rDNA鉴定发现, 加拿大一枝黄花15个根际解钾菌株分属11个属, 其中有6个属已经被报道证实具有明显解钾能力。这些结果表明加拿大一枝黄花根际解钾菌数量较为丰富, 且大多具有较高解钾活性, 可能对其钾富集具有重要贡献。     

Effects of fine root decomposition on bacterial community structure of four dominated tree species in Mount Taishan,China

为了理解细菌群落结构和多样性对森林生态系统细根凋落物分解的影响, 该研究以泰山4种主要优势造林树种刺槐(Robinia pseudoacacia)、麻栎(Quercus acutissima)、油松(Pinus tabulaeformis)和赤松(Pinus densiflora)为研究对象, 采用凋落物分解袋法及Illumina Miseq测序平台对细菌16S rDNA V4-V5区扩增产物进行双端测序, 分析了4种树种细根分解对细菌群落结构及多样性的影响。结果表明: (1) 4种植物细根分解速率差异显著, 阔叶树种分解速率显著高于针叶树种, 表现为刺槐>麻栎>油松>赤松。(2) 4个树种细菌序列操作分类单元(OTU)、观测到的物种数、Ace指数和系统发育多样性之间差异显著, 且阔叶树种刺槐和麻栎显著低于针叶树种赤松和油松。4种细根分解的细菌群落结构存在极显著差异。细根初始碳(C)含量、木质素:氮(N)和C:N对细菌群落结构的影响较大。(3)细菌群落相对丰度在5%以上的优势类群是变形菌门、放线菌门、拟杆菌门、酸杆菌门, 且变形菌门、酸杆菌门在4个树种之间差异显著, 特别是阔叶树种变形菌门显著高于针叶树种。在纲水平上, α-变形菌纲、β-变形菌纲、γ-变形菌纲、不明放线菌纲、鞘脂杆菌纲为主要的优势纲, 其中α-变形菌纲、不明放线菌纲在4个树种之间差异显著。(4) Pearson相关性分析表明, 细菌优势门和纲相对丰度受到凋落物初始化学性质的影响, 特别是变形菌门和α-变形菌纲; 变形菌门和α-变形菌纲相对丰度与细根分解速率显著正相关。冗余分析结果也显示, 细根初始N、磷(P)含量和木质素含量对细菌群落结构的影响较大。研究结果有助于理解细菌群落结构和多样性对森林生态系统细根凋落物分解的影响。     

Effects of transportation direction of photosynthate on soil microbial processes in the rhizosphere of Phyllostachys bissetii

分株间光合产物的整合作用对克隆植物适应生存环境具有重要作用, 但有关光合产物传输方向对克隆植物根际土壤微生物过程的影响尚不清楚。该研究以根状茎克隆植物蓉城竹(Phyllostachys bissetii)为研究对象, 通过剪除分株地上部分控制光合产物传输方向(顶向传输和基向传输), 研究光合产物传输方向对蓉城竹分株根际土壤微生物过程的影响, 其中顶向传输组是将远端分株地上部分剪除(保留地面以上20 cm), 近端分株自然生长; 基向传输组则是将近端分株地上部分剪除(保留地面以上20 cm), 远端分株自然生长。两组实验中保持根状茎连接或切断处理。测定了地上部分被剪除分株根际土壤中碳和氮有效性、微生物生物量参数以及氮转化相关土壤胞外酶活性等指标。结果表明: 光合产物顶向传输中, 根状茎保持连接的远端分株根际土壤总有机碳(TOC)、溶解性有机碳(DOC)、溶解性有机氮(DON)、铵态氮(NH₄ ⁺-N)、硝态氮(NO₃ ^--N)含量显著高于切断的远端分株, N-乙酰基-β-D-氨基葡萄糖苷酶(NAGase)、多酚氧化酶(POXase)和脲酶(Urease)活性显著升高, 光合产物的顶向传输对远端分株根际碳、氮有效性和根际微生物过程产生了显著性影响; 光合产物的基向传输中, 根状茎保持连接的近端分株根际与切断分株相比具有更高的微生物生物量氮(MBN)含量、Urease、POXase活性, 较低的NAGase活性和NH₄ ⁺-N、NO₃ ^--N含量, 但碳的有效性无显著性差异。蓉城竹分株间光合产物的非对称性传输对根际微生物过程的影响可能是对动物取食或人为砍伐等干扰的有益权衡, 这有助于理解克隆植物对生存环境的种群适应机制。     

C,N and P stoichiometry in different organs of Vitex rotundifolia in a Poyang Lake desertification hill

Aims The objectives were to clarify the responses of C, N and P stoichiometry of Vitex rotundifolia to desertification, and determine the C, N and P stoichiometric relationships among the organs.
Methods In this study, different organs (e.g. flowers, leaves, twigs, creeping stems, fine roots) of V. rotundifolia were sampled along a desertification gradient in a typical Poyang Lak sandy hill. Subsequently, C, N and P contents of various organs were measured.
Important findings The results showed nutrient contents in different organs ranged from 386.28 to 449.47 mg·g^-1 for carbon, 11.40 to 25.37 mg·g^-1 for nitrogen and 0.89 to 1.54 mg·g^-1 for phosphorus, respectively. C, N and P contents differed significantly among the five organs. The maximum N and P content were found in flowers, whereas the minimums were observed in twigs and creping stems. Moreover, desertification intensity only significantly affected C, N and C:P. C:N and N:P ratios maintained relatively stable. Except N:P, the other nutrient elements and associated stoichiometry significantly differed among the organs. Hence, organs, rather than desertification intensity mainly controlled the C, N and P content and their stoichiometry variability. Although there was a positive correlation between mass-based N content (N_mass) and P content (P_mass) across the three desertification zones, the N_mass-P_mass relationship in V. rotundifolia did not shift. Irrespective desertification intensity and organs, N:P stoichiometry of V. rotundifolia was well constrained. In addition, significant correlations of C, N and P contents among organs were mainly found in the above-ground parts, especially between twigs and creeping stems.     

Plant nutrient dynamics and stoichiometric homeostasis of invasive species Spartina alterniflora and native Cyperus malaccensis var. brevifolius in the Minjiang River estuarine wetlands

Aims Stoichiometric homeostasis is an important mechanism in maintaining ecosystem structure, function, and stability. The invasion of exotic species, Spartina alterniflora, has largely threatened the structure and function of native ecosystems in the Minjiang River estuarine wetland. However, how S. alterniflora invasion affect plant stoichiometric homeostasis is largely unknown. This could enhance our understanding on wetland ecosystem stability and expand the applications of ecological stoichiometry theory.
Methods Nitrogen (N) and phosphorus (P) contents of plant organs and soils in the S. alterniflora, Cyperus malaccensis var. brevifolius, and S. alterniflora-C. malaccensis var. brevifolius mixture were measured, and the homeostatic index (H) was calculated according to the stoichiometric homeostasis theory.
Important findings Our results showed that the invasion of S. alterniflora significantly increased soil N:P ratio (p < 0.05), but did not affect soil N or P contents. The N and P contents of leaf and stem were the highest for S. alterniflora, and those of the stem were the highest for C. malaccensis var. brevifolius. At the ecosystem level, the average of homeostatic index (H) of N (H_N, 25.31) was larger than those of P (H_P, 10.33) and N:P (H_N:P, 2.50). At the organ level, root H_N was significantly larger than stem H_N (p < 0.05) and sheath H_N:P was greater than root H_N:P (p < 0.05), while there was no significant difference for H_P among root, stem, leaf, and sheath (p > 0.05). As for species, root H_N of S. alterniflora was significantly larger than that of C. malaccensis var. brevifolius in the mixture community (p < 0.05). In the monoculture, stem H_N:P of S. alterniflora was significantly higher than that of C. malaccensis var. brevifolius (p < 0.05). Furthermore, root H_N, leaf H_N and sheath H_N of S. alterniflora in the mixed community was significantly larger than that of S. alterniflora in the monoculture (p < 0.05), suggesting that S. alterniflora invasions increased their stoichiometric homeostasis. Meanwhile, the stoichiometric homeostasis of invasive and native plants were influenced by multiple factors, such as nutrients, organs, vegetation, and invasion. However, larger homeostasis was found in S. alterniflora than in C. malaccensis var. brevifolius in some particular organs either in mixture or monoculture communities. Therefore, the successful invasion of S. alterniflora may result from higher homeostatic index than the native species, C. malaccensis var. brevifolius.     

Storage of carbon,nitrogen and phosphorus in temperate shrubland ecosystems across Northern China

Aims Studying storage of carbon (C), nitrogen (N) and phosphorus (P) in ecosystems is of significance in understanding carbon and nutrient cycling. Previous researches in ecosystem C, N and P storage have biased towards forests and grasslands. Shrubland ecosystems encompass a wide gradient in precipitation and soil conditions, providing a unique opportunity to explore the patterns of ecosystem C, N and P storage in relation to climate and soil properties.
Methods We estimated densities and storage of organic C, N and P of shrubland ecosystems in Northern China based on data from 433 shrubland sites.
Important findings The main results are summarized as follows: the average organic C, N and P densities in temperate shrubland ecosystems across Northern China were 69.8 Mg·hm^-2, 7.3 Mg·hm^-2 and 4.2 Mg·hm^-2, respectively. The average plant C, N and P densities were 5.1 Mg·hm^-2, 11.5 × 10^-2 Mg·hm^-2 and 8.6 × 10^-3 Mg·hm^-2, respectively, and were significantly correlated with precipitation and soil nutrient concentrations. The average litter C, N and P densities were 1.4 Mg·hm^-2, 3.8 ×10^-2 Mg·hm^-2, 2.5 ×10^-3 Mg·hm^-2 and were significantly correlated with temperature and precipitation. The average soil organic C, N and P densities in the top 1 m were 64.0 Mg·hm^-2, 7.1 Mg·hm^-2 and 4.2 Mg·hm^-2, respectively and the former two were significantly correlated with temperature and precipitation. The total organic C, N and P storage of shrublands in Northern China were 1.7 Pg, 164.9 Tg and 124.8 Tg, respectively. The plant C, N and P storage were 128.4 Tg, 3.1 Tg and 0.2 Tg, respectively. The litter C, N and P storage were 8.4 Tg, 0.45 Tg, 0.027 Tg, respectively. Soil is the largest C, N and P pool in the studied area. The soil organic C, N and P storage in the top 1 meter were 1.6 Pg, 161.3 Tg and 124.6 Tg, respectively.     

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。