放牧对全球草地生态系统碳氮磷化学计量特征影响的Meta分析

为明确全球尺度下放牧管理措施对草地生态系统碳(C)、氮(N)、磷(P)化学计量特征的影响,提高草地生态系统管理水平,本研究选取国内外83篇中英文文献进行Meta分析,并通过亚组分析探讨了放牧家畜组合(羊单牧、牛单牧和牛羊混牧)和放牧强度(轻度、中度、重度)对草地生态系统叶片、凋落物、根系,以及土壤C、N、P化学计量特征的影响。结果表明: 放牧会显著降低叶片和凋落物C含量、C/N、C/P,增加N、P含量及N/P;显著降低根系和土壤C、N含量,C/P和N/P,增加P含量和C/N。叶片、凋落物化学计量特征变化对牛、羊单独放牧响应更为明显,而根系、土壤化学计量特征变化则对混牧响应更为明显,重度放牧会对草地生态系统化学计量特征产生更大的影响。放牧会降低土壤N含量,增加P含量,表明放牧对草地N、P含量的影响路径不同。进一步研究N、P含量变化对放牧活动不平衡响应机制,将放牧方式、强度的影响纳入草地生态系统预测、管理模型,能够有效提高草地生态系统管理水平。     

不同林龄杉木人工林植物-凋落叶-土壤C、N、P化学计量特征及互作关系

以贵州8年、16年、28年生杉木人工林为研究对象,分析植物-凋落叶-土壤的C、N、P化学计量特征及其内在联系,探讨林龄对杉木人工林生态化学计量的影响,为杉木人工林可持续经营提供参考。结果表明:(1)杉木人工林植物-凋落叶-土壤均呈高C低N、P元素格局,两两组分间差异显著(P0.05);成熟叶C/N(38.58)、C/P(376.67)偏低,其养分利用效率较低;与成熟叶相比,凋落叶N、P偏低,C/N、C/P偏高;土壤C/P、N/P偏低,C/N较高,说明土壤P素分解较快而N保存较好,反映了凋落叶分解不利。(2)成熟叶C、P以及根、凋落叶、土壤的C、N、P、C/N、C/P、N/P均受林龄的显著影响;从8年到28年,C、N、P含量在植物体呈先增后减趋势,而在土壤中相反,呈先减后增趋势,但在凋落物中C、P显著减小,且C/P,N/P显著增加,反映杉木林早期对养分需求旺盛,随年龄增大需求减小,凋落物分解受制于P素,加剧中幼期杉木生态系统养分供需矛盾。(3)成熟叶与凋落叶N、C/N、N/P之间显著正相关,凋落叶养分源自成熟叶;成熟叶重吸收率P(0.518—0.645)N(0.292—0.488),即对P的利用效率高于N。凋落叶与土壤C、C/N之间显著负相关,表明土壤C、N来源于凋落叶分解,但凋落叶分解缓慢,导致大量元素滞留于凋落叶,土壤损耗元素得不到补给,两者间养分循环缓慢。土壤与根C、P、C/N、C/P、N/P之间均显著正相关,土壤与成熟叶的C、N、P均不相关,表明土壤养分是杉木生长养分的主要来源,但土壤C、N、P含量对成熟叶C、N、P含量影响不大。     

喀斯特区不同退化程度植被群落植物-凋落物-土壤-微生物生态化学计量特征

为摸清喀斯特植被退化对群落各组分C、N、P生态化学计量特征及内稳态特征的影响,为喀斯特退化生态系统植被恢复与重建提供科学依据,以桂西北喀斯特地区5种退化程度植被群落为研究对象,测定了不同退化程度植被群落植物叶片、凋落物、土壤和微生物生物量的C、N、P含量,分析其化学计量比特征、相互关系及植物内稳性特征。结果表明：(1)随着退化程度加剧,叶片C、N、P含量、N∶P和凋落物N∶P、微生物量C显著下降,而叶片C∶N、C∶P则显著增加,且植物叶片N∶P<14;随退化程度加剧,凋落物N、P含量、土壤C、N、P含量、微生物量N、P呈先略有增后显著降低的趋势,且不同退化程度群落土壤N∶P和微生物量C∶N无显著差异。(2)叶片N、P含量与土壤N、P含量,叶片C∶P与土壤C∶N、C∶P、N∶P,叶片N∶P与凋落物N、N∶P,叶片C、N、P含量与微生物量C呈显著或极显著正相关关系;叶片C∶N与土壤C、N,叶片C∶P与土壤N、P,叶片N∶P与土壤P呈显著或极显著负相关关系。(3)喀斯特地区植物叶片N、P元素的内稳性指数(H)平均值分别为2.74和2.31,属于弱稳态型,叶片N∶P的H值为5.14,为稳...     

不同林龄油松(Pinus tabulaeformis)人工林植物、凋落物与土壤C、N、P化学计量特征

在陕西省北部延安市境内子午岭林区,采用时空互代的方法选取9、23、33、47年生油松(Pinus tabuliformis)人工林为研究对象,比较油松不同器官(叶、枝、干、根)、凋落物及土壤C、N、P含量及其比值的差异,探讨它们随林龄的变化及其相互间的关系,以期为油松人工林的生产、改善和林木生长环境的调节提供参考。结果表明:除根中C含量在林龄间差异不显著外,其它器官C、N、P含量及其比值在林龄间均差异显著且随林龄增加变化趋势不尽相同。9、23、33、47年生油松林C、N、P含量及N∶P比值均在叶中最高;C∶N比值均在干中最高,根中次之;C∶P比值均在干中最高,其它器官大小次序不一。除33年生油松林叶中N∶P比值大于14外,其它各器官各林龄N∶P比值均小于14,且N∶P比值随林龄先增加后减少,故可判断油松在该区域受N限制较为严重,且随林龄的增加受N限制的情况有所缓解。不同林龄土壤和凋落物C、N、P含量及其比值差异显著,且后者均大于前者。土壤与凋落物C、P含量及C∶N、C∶P、N∶P比值随林龄增加变化趋势完全一致,表明土壤与凋落物之间有着密切的关系。叶片与凋落物N、P含量及C∶N、C∶P、N∶P比值之间显著相关,表明凋落物的养分承自植物叶片,二者之间关系紧密;植物和土壤的C、N、P含量之间均不存在显著相关性,说明土壤C、N、P供应量对乔木叶片C、N、P含量影响不大。     

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”。     

High‐frequency fire alters C : N : P stoichiometry in forest litter

Fire is a major driver of ecosystem change and can disproportionately affect the cycling of different nutrients. Thus, a stoichiometric approach to investigate the relationships between nutrient availability and microbial resource use during decomposition is likely to provide insight into the effects of fire on ecosystem functioning. We conducted a field litter bag experiment to investigate the long‐term impact of repeated fire on the stoichiometry of leaf litter C, N and P pools, and nutrient‐acquiring enzyme activities during decomposition in a wet sclerophyll eucalypt forest in Queensland, Australia. Fire frequency treatments have been maintained since 1972, including burning every 2 years (2yrB), burning every 4 years (4yrB) and no burning (NB). C : N ratios in freshly fallen litter were 29–42% higher and C : P ratios were 6–25% lower for 2yrB than NB during decomposition, with correspondingly lower 2yrB N : P ratios (27–32) than for NB (34–49). Trends in litter soluble and microbial N : P ratios were similar to the overall litter N : P ratios across fire treatments. Consistent with these, the ratio of activities for N‐acquiring to P‐acquiring enzymes in litter was higher for 2yrB than NB, whereas 4yrB was generally intermediate between 2yrB and NB. Decomposition rates of freshly fallen litter were significantly lower for 2yrB (72 ± 2% mass remaining at the end of experiment) than for 4yrB (59 ± 3%) and NB (62 ± 3%), a difference that may be related to effects of N limitation, lower moisture content, and/or litter C quality. Results for older mixed‐age litter were similar to those for freshly fallen litter although treatment differences were less pronounced. Overall, these findings show that frequent fire (2yrB) decoupled N and P cycling, as manifested in litter C : N : P stoichiometry and in microbial biomass N : P ratio and enzymatic activities. Furthermore, these data indicate that fire induced a transient shift to N‐limited ecosystem conditions during the postfire recovery phase.     

C : N : P stoichiometry of dominant riparian trees and arthropods along the Middle Rio Grande

1. We examined the role of flooding on the leaf nutrient content of riparian trees by comparing the carbon : nitrogen : phosphorus (C : N : P) ratio of leaves and litter of Rio Grande cottonwood (Populus deltoides ssp. wislizenii) in flood and non‐flood sites along the Middle Rio Grande, NM, U.S.A. The leaf C : N : P ratio was also examined for two non‐native trees, saltcedar (Tamarix chinensis) and Russian olive (Elaeagnus angustifolia), and six species of dominant riparian arthropods. 2. Living leaves and leaf litter of cottonwoods at flood sites had a significantly lower leaf N : P ratio and higher %P compared with leaves and litter at non‐flood sites. A non‐flood site downstream from wastewater effluent had a significantly lower litter C : N ratio than all other sites, suggesting N fertilisation through ground water. The non‐native trees, saltcedar and Russian olive, had higher mean leaf N content, N : P ratio, and lower C : N ratio compared with cottonwoods across study sites. 3. Riparian arthropods ranged from 5.2 to 7.1 for C : N ratio, 56–216 for C : P ratio, and 8.9–34 for N : P ratio. C content ranged from 25 to 52% of dry mass, N content from 4.7 to 10.8%, and P content from 0.59 to 1.2%. Differences in stoichiometry between high C : nutrient leaf litter and low C : nutrient invertebrates suggests possible food‐quality constraints for detritivores. 4. These results suggest that spatial and temporal variation in the C : N : P ratio of cottonwood leaves and leaf litter is influenced by surface and subsurface hydrologic connection within the floodplain. Reach‐scale variation in the elemental composition of riparian organic matter inputs may have important implications for decomposition, nutrient cycling, and food webs in river floodplain systems.     

Combined effects of nitrogen addition and litter manipulation on nutrient resorption of Leymus chinensis in a semi‐arid grassland of northern China

Plant growth in semi‐arid ecosystems is usually severely limited by soil nutrient availability. Alleviation of these resource stresses by fertiliser application and aboveground litter input may affect plant internal nutrient cycling in such regions. We conducted a 4‐year field experiment to investigate the effects of nitrogen (N) addition (10 g N·m^?2·year^?1) and plant litter manipulation on nutrient resorption of Leymus chinensis, the dominant native grass in a semi‐arid grassland in northern China. Although N addition had no clear effects on N and phosphorus (P) resorption efficiencies in leaves and culms, N fertilisation generally decreased leaf N resorption proficiency by 54%, culm N resorption proficiency by 65%. Moreover, N fertilisation increased leaf P resorption proficiency by 13%, culm P resorption proficiency by 20%. Under ambient or enriched N conditions, litter addition reduced N and P resorption proficiencies in both leaves and culms. The response of P resorption proficiency to litter manipulation was more sensitive than N resorption proficiency: P resorption proficiency in leaves and culms decreased strongly with increasing litter amount under both ambient and enriched N conditions. In contrast, N resorption proficiency was not significantly affected by litter addition, except for leaf N resorption proficiency under ambient N conditions. Furthermore, although litter addition caused a general decrease of leaf and culm nutrient resorption efficiencies under both ambient and enriched N conditions, litter addition effects on nutrient resorption efficiency were much weaker than the effects of litter addition on nutrient resorption proficiency. Taken together, our results show that leaf and non‐leaf organs of L. chinensis respond consistently to altered soil N availability. Our study confirms the strong effects of N addition on plant nutrient resorption processes and the potential role of aboveground litter, the most important natural fertiliser in terrestrial ecosystems, in influencing plant internal nutrient cycling.     

陕西黄土高原刺槐枯落叶生态化学计量学特征

生态系统元素平衡是当前全球变化生态学和生物地球化学循环研究的焦点和热点,生态化学计量学结合了生物学、物理学和化学等基本原理,是研究生物系统能量平衡与多重化学元素平衡的科学,为研究元素在生物地球化学循环与生态过程中的规律及其之间的计量关系提供了一种综合的方法。以陕西黄土高原人工刺槐林为研究对象,结合纬度和坡向两个因素,分析了三原、淳化、耀州区、宜君、黄陵、洛川、富县、甘泉、宝塔区、安塞、米脂、神木12个县区的刺槐枯落叶生态化学计量学特征。结果发现,阳坡刺槐枯落叶C、N、P含量的变化范围分别为318.34—428.01 g/kg、13.27—24.07 g/kg、1.66—2.57 g/kg;阴坡刺槐枯落叶C、N、P含量的变化范围分别为306.70—433.68 g/kg、12.55—24.39 g/kg、1.62—2.99 g/kg。阳坡刺槐枯落叶C∶N、C∶P、N∶P的变化范围分别为14.23—24.61、148.67—215.92、7.37—14.47;阴坡刺槐枯落叶C∶N、C∶P、N∶P的变化范围分别为16.87—26.54、130.06—234.41、7.05—13.22。随着纬度的升高,刺槐枯落叶C、N显著下降,刺槐枯落叶P、C∶N、C∶P、N∶P无明显差异。刺槐枯落叶C、N、P之间呈显著正相关。刺槐枯落叶C、N、P、C∶N、C∶P、N∶P在阴坡和阳坡之间无明显差异。研究区,阴坡和阳坡的刺槐枯落叶N∶P均较低,刺槐林土壤的全氮平均含量也低于全国平均水平,推测陕西黄土高原刺槐林的生长可能主要受到氮素的限制。     

氮磷添加对荒漠草原植物群落多样性和土壤C:N:P生态化学计量特征的影响

为了深入了解P添加是否有助于缓解N沉降增加引起的植物群落多样性降低等问题,以宁夏盐池县长期围封的荒漠草原为研究对象,探讨了连续两年(2015—2016年) 5 g/m~2/a的N水平下,P添加对植物生物量、群落多样性和土壤C∶N∶P生态化学计量特征的影响,分析了植物群落多样性与土壤C∶N∶P比及其他关键因子的关系。结果表明:少量N添加下,增施P肥促进了植物生物量积累,但中高量P添加抑制了多数植物生长,使牛枝子(Lespedeza potaninii)、草木樨状黄芪(Astragalus melilotoides)和苦豆子(Sophora alopecuroides)等物种重要值降低;随着P添加量增加,Shannon-Wiener多样性指数和Patrick丰富度指数先增加后降低,Simpson优势度指数逐渐增加,Pielou均匀度指数变化幅度较小;随着P添加量增加,土壤C∶P和N∶P比逐渐降低;土壤N∶P比、C∶P比、全P含量、速效P浓度以及微生物量C∶P比与植物群落多样性关系密切,意味着N沉降增加下趋于解耦的土壤元素平衡关系可能会影响到植物群落组成。综合以上结果,适量P添加可以通过提高土壤P有效性、增加凋落物归还量和刺激微生物P释放等途径,调节土壤P供给和植物P需求间的压力,从而缓解N添加引起的植物群落多样性降低。     

Miscanthus × giganteus leaf senescence,decomposition and C and N inputs to soil

Energy crops are currently promoted as potential sources of alternative energy that can help mitigate the climate change caused by greenhouse gases (GHGs). The perennial crop Miscanthus × giganteus is considered promising due to its high potential for biomass production under conditions of low input. However, to assess its potential for GHG mitigation, a better quantification of the crop's contribution to soil organic matter recycling under various management systems is needed. The aim of this work was to study the effect of abscised leaves on carbon (C) and nitrogen (N) recycling in a Miscanthus plantation. The dynamics of senescent leaf fall, the rate of leaf decomposition (using a litter bag approach) and the leaf accumulation at the soil surface were tracked over two 1‐year periods under field conditions in Northern France. The fallen leaves represented an average yearly input of 1.40 Mg C ha^?1 and 16 kg N ha^?1. The abscised leaves lost approximately 54% of their initial mass in 1 year due to decomposition; the remaining mass, accumulated as a mulch layer at the soil surface, was equivalent to 7 Mg dry matter (DM) ha^?1 5 years after planting. Based on the estimated annual leaf‐C recycling rate and a stabilization rate of 35% of the added C, the annual contribution of the senescent leaves to the soil C was estimated to be approximately 0.50 Mg C ha^?1yr^?1 or 10 Mg C ha^?1 total over the 20‐year lifespan of a Miscanthus crop. This finding suggested that for Miscanthus, the abscised leaves contribute more to the soil C accumulation than do the rhizomes or roots. In contrast, the recycling of the leaf N to the soil was less than for the other N fluxes, particularly for those involving the transfer of N from the tops of the plant to the rhizome.     

C,N and P fertilization in an Amazonian rainforest supports stoichiometric dissimilarity as a driver of litter diversity effects on decomposition

Plant leaf litter generally decomposes faster as a group of different species than when individual species decompose alone, but underlying mechanisms of these diversity effects remain poorly understood. Because resource C : N : P stoichiometry (i.e. the ratios of these key elements) exhibits strong control on consumers, we supposed that stoichiometric dissimilarity of litter mixtures (i.e. the divergence in C : N : P ratios among species) improves resource complementarity to decomposers leading to faster mixture decomposition. We tested this hypothesis with: (i) a wide range of leaf litter mixtures of neotropical tree species varying in C : N : P dissimilarity, and (ii) a nutrient addition experiment (C, N and P) to create stoichiometric similarity. Litter mixtures decomposed in the field using two different types of litterbags allowing or preventing access to soil fauna. Litter mixture mass loss was higher than expected from species decomposing singly, especially in presence of soil fauna. With fauna, synergistic litter mixture effects increased with increasing stoichiometric dissimilarity of litter mixtures and this positive relationship disappeared with fertilizer addition. Our results indicate that litter stoichiometric dissimilarity drives mixture effects via the nutritional requirements of soil fauna. Incorporating ecological stoichiometry in biodiversity research allows refinement of the underlying mechanisms of how changing biodiversity affects ecosystem functioning.     

Experimental litterfall manipulation drives large and rapid changes in soil carbon cycling in a wet tropical forest

Global changes such as variations in plant net primary production are likely to drive shifts in leaf litterfall inputs to forest soils, but the effects of such changes on soil carbon (C) cycling and storage remain largely unknown, especially in C‐rich tropical forest ecosystems. We initiated a leaf litterfall manipulation experiment in a tropical rain forest in Costa Rica to test the sensitivity of surface soil C pools and fluxes to different litter inputs. After only 2 years of treatment, doubling litterfall inputs increased surface soil C concentrations by 31%, removing litter from the forest floor drove a 26% reduction over the same time period, and these changes in soil C concentrations were associated with variations in dissolved organic matter fluxes, fine root biomass, microbial biomass, soil moisture, and nutrient fluxes. However, the litter manipulations had only small effects on soil organic C (SOC) chemistry, suggesting that changes in C cycling, nutrient cycling, and microbial processes in response to litter manipulation reflect shifts in the quantity rather than quality of SOC. The manipulation also affected soil CO ₂ fluxes; the relative decline in CO ₂ production was greater in the litter removal plots (?22%) than the increase in the litter addition plots (+15%). Our analysis showed that variations in CO ₂ fluxes were strongly correlated with microbial biomass pools, soil C and nitrogen (N) pools, soil inorganic P fluxes, dissolved organic C fluxes, and fine root biomass. Together, our data suggest that shifts in leaf litter inputs in response to localized human disturbances and global environmental change could have rapid and important consequences for belowground C storage and fluxes in tropical rain forests, and highlight differences between tropical and temperate ecosystems, where belowground C cycling responses to changes in litterfall are generally slower and more subtle.     

Litter fingerprint on microbial biomass,activity, and community structure in the underlying soil

Aims

Little is known about how plant leaf litter decomposing on the soil surface is affecting microbial communities in the underlying soil. Here we examined the effects of decomposing leaf litter of different initial chemistry on biomass, stoichiometry, community structure and activity of microorganisms in the soil underneath the decaying litter layer.

Methods

Leaf litter from six different neotropical tree species with contrasted quality decomposed on top of a common tropical soil in a laboratory microcosm experiment over 98 days. At the end of the experiment we determined microbial biomass C, N, and P, microbial community structure (PLFA), and community level physiological profiles (CLPP) from the top soil.

Results

Despite growing in a common soil substrate, soil microorganisms were strongly affected by litter species, especially by the soluble litter fraction. While litters with low soluble C content did not affect the soil microbial community, litters with high soluble C content led to an increase of microbial biomass and to a structural shift to relatively more Gram-negative bacteria. Changing community structure resulted in changes of catabolic capacity of microorganisms to metabolize a range of different C substrates. The large differences in leachate N and P among litter species, in contrast, had no effect on soil microbial parameters.

Conclusions

Our data suggest that plant litter decomposing on the soil surface exhibit a strong and predictable leachate C-control over microbial community biomass, structure and function in the underlying soil.

     

鄱阳湖湿地优势植物叶片-凋落物-土壤碳氮磷化学计量特征

2013年11月初在鄱阳湖南矶湿地国家级自然保护区,采集芦苇(Phragmites australis)、南荻(Triarrhena lutarioriparia)、菰(Zizania latifolia(Griseb.))、灰化苔草(Carex cinerascens)、红穗苔草(Carex argyi)和水蓼(Polygonum hydropiper)等6种优势植物新鲜叶片、凋落物及表层0—15cm土壤样品测定了碳(C)、氮(N)、磷(P)含量,以阐明不同物种、不同生活型间C、N、P化学计量差异,探讨化学计量垂直分异。结果表明:1)C、N、P含量变化范围分别为:叶片380.6—432.2 mg/g,15.3—32.6 mg/g和1.3—2.0 mg/g;凋落物345.4—416.1 mg/g,10.8—20.8 mg/g和1.1—1.7 mg/g;土壤15.0—38.1 mg/g,1.2—3.1 mg/g和0.7—1.1mg/g,不同物种间叶片、凋落物及土壤C、N、P含量差异显著,且叶片C、N、P含量显著高于凋落物与土壤。2)土壤C∶N、C∶P及N∶P值显著低于叶片与凋落物,且土壤C、N、P化学计量关系与凋落物更为密切,凋落物的C∶N、N∶P分别能解释土壤C∶N、N∶P变异的35%、18%。3)挺水植物与湿生植物之间叶片C∶N、N∶P值差异显著,C∶P则差异不显著,凋落物C∶N、C∶P与N∶P均未达到显著性差异。     

Carbon : nitrogen stoichiometry in forest ecosystems during stand development

Aim Carbon (C) and nitrogen (N) stoichiometry is a critical indicator of biogeochemical coupling in terrestrial ecosystems. However, our current understanding of C : N stoichiometry is mainly derived from observations across space, and little is known about its dynamics through time. Location Global secondary forests. Methods We examined temporal variations in C : N ratios and scaling relationships between N and C for various ecosystem components (i.e. plant tissue, litter, forest floor and mineral soil) using data extracted from 39 chronosequences in forest ecosystems around the world. Results The C : N ratio in plant tissue, litter, forest floor and mineral soil exhibited large variation across various sequences, with an average of 145.8 ± 9.4 (mean ± SE), 49.9 ± 3.0, 38.2 ± 3.1 and 18.5 ± 0.9, respectively. In most sequences, the plant tissue C : N ratio increased significantly with stand age, while the C : N ratio in litter, forest floor and mineral soil remained relatively constant over the age sequence. N and C scaled isometrically (i.e. the slope of the relationship between log‐transformed N and C is not significantly different from 1.0) in litter, forest floor and mineral soil both within and across sequences, but not in plant tissue either within or across sequences. The C : N ratio was larger in coniferous forests than in broadleaf forests and in temperate forests than in tropical forests. In contrast, the N–C scaling slope did not reveal significant differences either between coniferous and broadleaf forests or between temperate and tropical forests. Main conclusions These results suggest that C and N become decoupled in plants but remain coupled in other ecosystem components during stand development.     

云南药山自然保护区黄背栎林和巧家五针松林生态化学计量特征

以云南药山自然保护区黄背栎林和巧家五针松林的4块样地为研究对象,旨在揭示这2种森林生态系统营养元素含量状况和土壤养分的供给能力。通过分析4块样地"叶片-凋落物-土壤"C、N、P含量、生态化学计量特征及其相关性,结果表明:(1)不同样地同一组分的C、N含量差异显著,P含量差异不显著,同一样地各组分间C、N含量差异显著,均为叶片凋落物土壤,P含量则为叶片土壤凋落物;(2)不同样地叶片C∶P、N∶P比值和凋落物与土壤C∶N比值差异不显著,其余指标差异均显著。同一样地叶片、凋落物、土壤的C∶N、C∶P、N∶P比值差异显著,均为凋落物叶片土壤;(3)黄背栎林叶片-土壤C含量、C∶P比值和凋落物-叶片N∶P比值呈极显著或显著相关,巧家五针松林凋落物-叶片C、N含量和叶片-土壤P含量、C∶N、N∶P比值呈极显著或显著相关;(4)土壤N元素缺乏是限制植物生长的主要因素,P元素主要源于土壤矿物风化释放,而非生物小循环。     

氮沉降和经营强度对毛竹林凋落叶生态化学计量特征的影响

为探讨氮沉降和经营强度对毛竹凋落叶化学计量特征的影响,研究了不同强度模拟氮沉降(低氮: 30 kg N·hm^-2·a^-1;中氮: 60 kg N·hm^-2·a^-1;高氮: 90 kg N·hm^-2·a^-1)对两种经营强度(粗放经营和集约经营)毛竹林凋落叶生态化学计量特征的影响.结果表明: 相比于粗放经营,集约经营使毛竹凋落叶C、N、P含量分别显著提高9.3%、32.4%和22.7%, 而C∶N、C∶P和N∶P分别显著降低17.4%、54.3%和44.6%.粗放经营条件下,低、中氮沉降显著提高了毛竹凋落叶C、N、P含量,但显著降低了C∶N、C∶P和N∶P;高氮沉降显著提高了C、N含量及C∶P、N∶P,但显著降低了P含量.集约经营条件下,低氮沉降显著提高了毛竹凋落叶P含量,降低了C含量及C∶P、N∶P;中氮沉降显著提高了N、P含量,降低了C含量及C∶N、C∶P和N∶P;高氮沉降显著提高了C∶N、C∶P和N∶P,降低了P含量.经营方式和氮沉降的交互作用显著影响了凋落叶除C∶N以外的生态化学计量特征.毛竹凋落叶P与土壤P含量呈显著相关.     

三峡库区森林凋落叶化学计量学性状变化及与分解速率的关系

凋落物分解是森林生态系统生物元素循环和能量流动的重要环节,其过程是植物与土壤获得养分的主要途径。为了量化凋落叶化学计量学性状变化过程对分解的影响及对凋落物-土壤生物化学连续体的深层理解,用凋落物分解袋法研究了不同林型各自凋落叶化学计量学性状变化及与分解速率关系,结果表明:林下各自凋落叶分解速率是马尾松林栓皮栎林马尾松-栓皮栎混交林,马尾松林、栓皮栎林、马尾松-栓皮栎混交林凋落叶分解50%和95%的时间分别是2.11 a和9.15 a,1.93 a和8.45 a,1.76 a和7.77 a;凋落叶分解过程中,化学计量学性状变化明显,分解450 d后马尾松-栓皮栎混交林碳释放最快,栓皮栎林最慢;3种凋落叶起始N含量是栓皮栎林最高,马尾松林最低,分解450 d后马尾松林、栓皮栎林和马尾松-栓皮栎混交林N含量分别增加了66.67%、44.91%和44.52%,而P含量分别释放了30.80%、38.89%和42.29%。凋落物不同化学计量学性状与分解速率关系不同,3种林型凋落叶分解速率均与N含量呈正相关(P0.01),与C含量(P0.01)、C/N比(P0.01)呈负相关,与N/P比呈负二次函数关系(P0.01),而P含量与3种林型关系不同,与栓皮栎林(P0.01)和马尾松林(P0.05)呈负线性关系,与马尾松-栓皮栎混交林呈负二次函数关系(P0.05)。研究表明,不同林型凋落叶分解中的养分动态趋向利于分解变化,N、P养分动态是生态系统碳平衡和凋落物分解速率的主要因素,混交林中混合凋落物的养分迁移是分解相对较快的原因。     

The Altitudinal Patterns of Leaf C∶N∶P Stoichiometry Are Regulated by Plant Growth Form,Climate and Soil on Changbai Mountain,China

Understanding the geographic patterns and potential drivers of leaf stoichiometry is critical for modelling the nutrient fluxes of ecosystems and to predict the responses of ecosystems to global changes. This study aimed to explore the altitudinal patterns and potential drivers of leaf C∶N∶P stoichiometry. We measured the concentrations of leaf C, N and P in 175 plant species as well as soil nutrient concentrations along an altitudinal transect (500–2300 m) on the northern slope of Changbai Mountain, China to explore the response of leaf C∶N∶P stoichiometry to plant growth form (PGF), climate and soil. Leaf C, N, P and C∶N∶P ratios showed significant altitudinal trends. In general, leaf C and C∶N∶P ratios increased while leaf N and P decreased with elevation. Woody and herbaceous species showed different responses to altitudinal gradients. Trees had the largest variation in leaf C, C∶N and C∶P ratios, while herbs showed the largest variation in leaf N, P and N∶P ratio. PGF, climate and soil jointly regulated leaf stoichiometry, explaining 17.6% to 52.1% of the variation in the six leaf stoichiometric traits. PGF was more important in explaining leaf stoichiometry variation than soil and climate. Our findings will help to elucidate the altitudinal patterns of leaf stoichiometry and to model ecosystem nutrient cycling.