中国四种森林类型主要优势植物的C:N:P化学计量学特征

为了评价不同森林类型的生态化学计量特征的差异, 以吉林长白山温带针阔混交林、广东鼎湖山亚热带常绿阔叶林、云南西双版纳热带季雨林和江西千烟洲亚热带人工针叶林为研究对象, 通过对2007年4月-2008年5月4种典型区域森林植物叶片和凋落物的碳(C)氮(N)磷(P)元素质量比与N、P再吸收率的分析, 探讨了4种森林类型N、P养分限制和N、P养分再吸收的内在联系。结果表明: 1)从森林类型上看, 温带针阔混交林叶片的C : N : P为321 : 13 : 1, 亚热带常绿阔叶林叶片的C : N : P为561 : 22 : 1, 热带季雨林叶片的C : N : P为442 : 19 : 1, 亚热带人工针叶林叶片的C : N : P为728 : 18 : 1; 凋落物的C : N : P也是亚热带人工林最高, 达1 950 : 27 : 1, 温带针阔混交林的最低, 为552 : 14 : 1, 热带季雨林的为723 : 24 : 1, 亚热带常绿阔叶林的为1 305 : 35 : 1, 不同森林类型凋落物的C : N : P的计量大小关系与叶片的结果一致; 2)从植物生活型上看, 常绿针叶林叶片的C : N均显著高于常绿阔叶林及落叶阔叶林; 叶片C : P与森林类型的关系并不十分密切; 常绿阔叶林叶片的N : P最高, 常绿针叶林次之, 落叶阔叶林最低; 3)植物叶片的N : P与月平均气温有显著的负相关关系, 但叶片的C : P基本不受月平均气温影响, 叶片的C、N、P计量比与降水的线性关系不显著; 4)高纬度地区的植物更易受N元素限制, 而低纬度地区植物更易受P元素的限制; 但受N或P限制的植物并不一定具有高的N或P再吸收率。研究结果表明, 不同类型森林的叶片与凋落物的化学计量特征具有一致性, 但是环境因子对不同类型植物化学计量比的影响并不相同。     

N limitation increases along a temperate forest succession: evidences from leaf stoichiometry and nutrient resorption

温带森林演替加剧了氮限制：来自叶片化学计量和养分重吸收的证据 森林生产力和碳汇功能在很大程度上取决于土壤氮和磷的有效性。然而,迄今为止,养分限制随森林演替的时间变化仍存在争议。叶片化学计量和养分重吸收是预测植物生长养分限制的重要指标。基于此,本研究测定了温带森林4个演替阶段所有木本植物叶片和凋落叶中氮和磷的含量,并分析了演替过程中非生物因子和生物因子如何影响叶片化学计量和养分重吸收。研究结果表明,在个体尺度上,叶片氮磷含量在演替末期显著增加,而叶片氮磷比无显著变化;氮的重吸收效率随演替显著增加,然而磷的重吸收效率先增加后减少;氮重吸收效率与磷重吸收效率的比值仅在演替末期显著增加。此外,植物氮素循环对土壤养分的响应比磷素循环更弱。在群落尺度上,叶片氮磷含量随森林演替呈现先降低后升高的趋势,主要受香农-维纳多样性指数和物种丰富度的影响;叶片氮磷比随演替而显著变化,主要由胸径的群落加权平均值决定;氮的重吸收效率增加,主要受物种丰富度和胸径的影响,而磷的重吸收效率相对稳定。因此,氮重吸收效率与磷重吸收效率的比值显著增加,表明随着温带森林演替,氮限制加剧。这些结果可能反映了较高生物多样性群落中物种间对有限资源的激烈竞争,强调了生物因子在驱动森林生态系统养分循环中的重要性,为中国温带和北方森林可持续经营的施肥管理提供了参考。     

A biome classification of China based on plant functional types and the BIOME3 model

A biome classification for China was established based on plant functional types (PFTs) using the BIOME3 model to include 16 biomes. In the eastern part of China, the PFTs of trees determine mostly the physiognomy of landscape. Biomes range from boreal deciduous coniferous forest/woodland, boreal mixed forest/woodland, temperate mixed forest, temperate broad-leaved deciduous forest, warm-temperate broad-leaved evergreen/mixed forest, warm-temperate/cool-temperate evergreen coniferous forest, xeric woodland/scrub, to tropical seasonal and rain forest, and tropical deciduous forest from north to south. In the northern and western part of China, grass is the dominant PFT. From northeast to west and southwest the biomes range from moist savannas, tall grassland, short grassland, dry savannas, arid shrubland/steppe, desert, to alpine tundra/ice/polar desert. Comparisons between the classification introduced here and the four classifications which were established over the past two decades, i.e. the vegetation classification, the vegetation division, the physical ecoregion, and the initial biome classification have showed that the different aims of biome classifications have resulted in different biome schemes each with its own unique characteristics and disadvantages for global change study. The new biome classification relies not only on climatic variables, but also on soil factor, vegetation functional variables, ecophysiological parameters and competition among the PFTs. It is a comprehensive classification that using multivariables better expresses the vegetation distribution and can be compared with world biome classifications. It can be easily used in the response study of Chinese biomes to global change, regionally and globally.     

Belowground carbon flux links biogeochemical cycles and resource‐use efficiency at the global scale

Nutrient limitation is pervasive in the terrestrial biosphere, although the relationship between global carbon (C) nitrogen (N) and phosphorus (P) cycles remains uncertain. Using meta‐analysis we show that gross primary production (GPP) partitioning belowground is inversely related to soil‐available N : P, increasing with latitude from tropical to boreal forests. N‐use efficiency is highest in boreal forests, and P‐use efficiency in tropical forests. High C partitioning belowground in boreal forests reflects a 13‐fold greater C cost of N acquisition compared to the tropics. By contrast, the C cost of P acquisition varies only 2‐fold among biomes. This analysis suggests a new hypothesis that the primary limitation on productivity in forested ecosystems transitions from belowground resources at high latitudes to aboveground resources at low latitudes as C‐intensive root‐ and mycorrhizal‐mediated nutrient capture is progressively replaced by rapidly cycling, enzyme‐derived nutrient fluxes when temperatures approach the thermal optimum for biogeochemical transformations.     

Global trends in senesced-leaf nitrogen and phosphorus

Aim Senesced‐leaf litter plays an important role in the functioning of terrestrial ecosystems. While green‐leaf nutrients have been reported to be affected by climatic factors at the global scale, the global patterns of senesced‐leaf nutrients are not well understood. Location Global. Methods Here, bringing together a global dataset of senesced‐leaf N and P spanning 1253 observations and 638 plant species at 365 sites and of associated mean climatic indices, we describe the world‐wide trends in senesced‐leaf N and P and their stoichiometric ratios. Results Concentration of senesced‐leaf N was highest in tropical forests, intermediate in boreal, temperate, and mediterranean forests and grasslands, and lowest in tundra, whereas P concentration was highest in grasslands, lowest in tropical forests and intermediate in other ecosystems. Tropical forests had the highest N : P and C : P ratios in senesced leaves. When all data were pooled, N concentration significantly increased, but senesced‐leaf P concentration decreased with increasing mean annual temperature (MAT) and mean annual precipitation (MAP). The N : P and C : P ratios also increased with MAT and MAP, but C : N ratios decreased. Plant functional type (PFT), i.e. life‐form (grass, herb, shrub or tree), phylogeny (angiosperm versus gymnosperm) and leaf habit (deciduous versus evergreen), affected senesced‐leaf N, P, N : P, C : N and C : P with a ranking of senesced‐leaf N from high to low: forbs ≈ shrubs ≈ trees > grasses, while the ranking of P was forbs ≈ shrubs ≈ trees < grasses. The climatic trends of senesced‐leaf N and P and their stoichiometric ratios were similar between PFTs. Main conclusions Globally, senesced‐leaf N and P concentrations differed among ecosystem types, from tropical forest to tundra. Differences were significantly related to global climate variables such as MAT and MAP and also related to plant functional types. These results at the global scale suggest that nutrient feedback to soil through leaf senescence depends on both the climatic conditions and the plant composition of an ecosystem.     

Latitudinal pattern of mountain vegetation zonation in southern and eastern Asia

A new scheme of altitudinal and latitudinal vegetation zonation is proposed for eastern Asia. The latitudinal patterns of mountain vegetation zonation show a clear boundary at ca. 20°–30° N. For the tropical mountains south of 20° N, the altitudinal series includes tropical lowland, tropical lower montane, and tropical upper montane zones. For the temperate mountains north of 30° N, the series includes temperate lowland, temperate lower montane, and temperate upper montane zones. The mountains located between 20° and 30° N show a transitional zonation pattern; the lower two zones are comparable to the lower two of the tropical zonation (tropical lowland and tropical lower montane), and the upper two zones are comparable to those of the temperate zonation (temperate lower montane and temperate upper montane). The tropical upper montane zone is not found north of 20°–30° N, while the tropical lower montane zone reaches down to sea level and constitutes the temperate lowland zone. Thus the zonation between 20° and 30° N includes tropical lowland, tropical lower montane/temperate lowland, temperate lower montane, and temperate upper montane zones. The latitudinal series of lowland rain forests follows the scheme of climatic division into tropical, subtropical/warm-temperate, cool-temperate and cold-temperate, with a shift of the respective life forms, evergreen, evergreen notophyllous, deciduous, and evergreen needle-leaved. The tropical lower montane forest can be correlated to the horizontal subtropical/ warm-temperate zone. The temperate altitudinal and latitudinal zonations above 30° N are correlated and show an inclined parallel pattern from high altitudes in the south to low altitudes down to sea level in the north.     

Nutrient Limitation on Ecosystem Productivity and Processes of Mature and Old-Growth Subtropical Forests in China

Nitrogen (N) is considered the dominant limiting nutrient in temperate regions, while phosphorus (P) limitation frequently occurs in tropical regions, but in subtropical regions nutrient limitation is poorly understood. In this study, we investigated N and P contents and N:P ratios of foliage, forest floors, fine roots and mineral soils, and their relationships with community biomass, litterfall C, N and P productions, forest floor turnover rate, and microbial processes in eight mature and old-growth subtropical forests (stand age >80 yr) at Dinghushan Biosphere Reserve, China. Average N:P ratios (mass based) in foliage, litter (L) layer and mixture of fermentation and humus (F/H) layer, and fine roots were 28.3, 42.3, 32.0 and 32.7, respectively. These values are higher than the critical N:P ratios for P limitation proposed (16–20 for foliage, ca. 25 for forest floors). The markedly high N:P ratios were mainly attributed to the high N concentrations of these plant materials. Community biomass, litterfall C, N and P productions, forest floor turnover rate and microbial properties were more strongly related to measures of P than N and frequently negatively related to the N:P ratios, suggesting a significant role of P availability in determining ecosystem production and productivity and nutrient cycling at all the study sites except for one prescribed disturbed site where N availability may also be important. We propose that N enrichment is probably a significant driver of the potential P limitation in the study area. Low P parent material may also contribute to the potential P limitation. In general, our results provided strong evidence supporting a significant role for P availability, rather than N availability, in determining ecosystem primary productivity and ecosystem processes in subtropical forests of China.     

Modelling the vegetation of China using the process-based equilibrium terrestrial biosphere model BIOME3

1 We model the potential vegetation and annual net primary production (NPP) of China on a 10′ grid under the present climate using the processed‐based equilibrium terrestrial biosphere model BIOME3. The simulated distribution of the vegetation was in general in good agreement with the potential natural vegetation based on a numerical comparison between the two maps using the ΔV statistic (ΔV = 0.23). Predicted and measured NPP were also similar, especially in terms of biome‐averages. 2 A coupled ocean–atmosphere general circulation model including sulphate aerosols was used to drive a double greenhouse gas scenario for 2070–2099. Simulated vegetation maps from two different CO₂ scenarios (340 and 500 p.p.m.v.) were compared to the baseline biome map using ΔV. Climate change alone produced a large reduction in desert, alpine tundra and ice/polar desert, and a general pole‐ward shift of the boreal, temperate deciduous, warm–temperate evergreen and tropical forest belts, a decline in boreal deciduous forest and the appearance of tropical deciduous forest. The inclusion of CO₂ physiological effects led to a marked decrease in moist savannas and desert, a general decrease for grasslands and steppe, and disappearance of xeric woodland/scrub. Temperate deciduous broadleaved forest, however, shifted north to occupy nearly half the area of previously temperate mixed forest. 3 The impact of climate change and increasing CO₂ is not only on biogeography, but also on potential NPP. The NPP values for most of the biomes in the scenarios with CO₂ set at 340 p.p.m.v. and 500 p.p.m.v. are greater than those under the current climate, except for the temperate deciduous forest, temperate evergreen broadleaved forest, tropical rain forest, tropical seasonal forest, and xeric woodland/scrub biomes. Total vegetation and total carbon is simulated to increase significantly in the future climate scenario, both with and without the CO₂ direct physiological effect. 4 Our results show that the global process‐based equilibrium terrestrial biosphere model BIOME3 can be used successfully at a regional scale.     

Stoichiometric patterns in foliar nutrient resorption across multiple scales

? Nutrient resorption is a fundamental process through which plants withdraw nutrients from leaves before abscission. Nutrient resorption patterns have the potential to reflect gradients in plant nutrient limitation and to affect a suite of terrestrial ecosystem functions. ? Here, we used a stoichiometric approach to assess patterns in foliar resorption at a variety of scales, specifically exploring how N?:?P resorption ratios relate to presumed variation in N and/or P limitation and possible relationships between N?:?P resorption ratios and soil nutrient availability. ? N?:?P resorption ratios varied significantly at the global scale, increasing with latitude and decreasing with mean annual temperature and precipitation. In general, tropical sites (absolute latitudes 相似文献   

Global pattern and controls of biological nitrogen fixation under nutrient enrichment: A meta‐analysis

Biological nitrogen (N) fixation (BNF), an important source of N in terrestrial ecosystems, plays a critical role in terrestrial nutrient cycling and net primary productivity. Currently, large uncertainty exists regarding how nutrient availability regulates terrestrial BNF and the drivers responsible for this process. We conducted a global meta‐analysis of terrestrial BNF in response to N, phosphorus (P), and micronutrient (Micro) addition across different biomes (i.e, tropical/subtropical forest, savanna, temperate forest, grassland, boreal forest, and tundra) and explored whether the BNF responses were affected by fertilization regimes (nutrient‐addition rates, duration, and total load) and environmental factors (mean annual temperature [MAT], mean annual precipitation [MAP], and N deposition). The results showed that N addition inhibited terrestrial BNF (by 19.0% (95% confidence interval [CI]: 17.7%?20.3%); hereafter), Micro addition stimulated terrestrial BNF (30.4% [25.7%?35.3%]), and P addition had an inconsistent effect on terrestrial BNF, i.e., inhibiting free‐living N fixation (7.5% [4.4%?10.6%]) and stimulating symbiotic N fixation (85.5% [25.8%?158.7%]). Furthermore, the response ratios (i.e., effect sizes) of BNF to nutrient addition were smaller in low‐latitude (<30°) biomes (8.5%?36.9%) than in mid‐/high‐latitude (≥30°) biomes (32.9%?61.3%), and the sensitivity (defined as the absolute value of response ratios) of BNF to nutrients in mid‐/high‐latitude biomes decreased with decreasing latitude (p ≤ 0.009; linear/logarithmic regression models). Fertilization regimes did not affect this phenomenon (p > 0.05), but environmental factors did affect it (p < 0.001) because MAT, MAP, and N deposition accounted for 5%?14%, 10%?32%, and 7%?18% of the variance in the BNF response ratios in cold (MAT < 15°C), low‐rainfall (MAP < 2,500 mm), and low‐N‐deposition (<7 kg ha^?1 year^?1) biomes, respectively. Overall, our meta‐analysis depicts a global pattern of nutrient impacts on terrestrial BNF and indicates that certain types of global change (i.e., warming, elevated precipitation and N deposition) may reduce the sensitivity of BNF in response to nutrient enrichment in mid‐/high‐latitude biomes.     

全球森林土壤微生物生物量碳氮磷化学计量的季节动态

土壤微生物生物量在森林生态系统中充当具有生物活性的养分积累和储存库。土壤微生物转化有机质为植物提供可利用养分, 与植物的相互作用维系着陆地生态系统的生态功能。同时, 土壤微生物也与植物争夺营养元素, 在季节交替过程和植物的生长周期中呈现出复杂的互利-竞争关系。综合全球数据对温带、亚热带和热带森林土壤微生物生物量碳(C)、氮(N)、磷(P)含量及其化学计量比值的季节动态进行分析, 发现温带和亚热带森林的土壤微生物生物量C、N、P含量均呈现夏季低、冬季高的格局。热带森林四季的土壤微生物生物量C、N、P含量都低于温带和亚热带森林, 且热带森林土壤微生物生物量C含量、N含量在秋季相对最低, 土壤微生物生物量P含量四季都相对恒定。温带森林的土壤微生物生物量C:N在春季显著高于其他两个森林类型; 热带森林的土壤微生物生物量C:N在秋季显著高于其他2个森林类型。温带森林土壤微生物生物量N:P和C:P在四季都保持相对恒定, 而热带森林土壤微生物生物量N:P和C:P在夏季高于其他3个季节。阔叶树的土壤微生物生物量C含量、N含量、N:P、C:P在四季都显著高于针叶树; 而针叶树的土壤微生物生物量P含量在四季都显著高于阔叶树。在春季和冬季时, 土壤微生物生物量C:N在阔叶树和针叶树之间都没有显著差异; 但是在夏季和秋季, 针叶树的土壤微生物生物量C:N显著高于阔叶树。对于土壤微生物生物量的变化来说, 森林类型是主要的显著影响因子, 季节不是显著影响因子, 暗示土壤微生物生物量的季节波动是随着植物其内在固有的周期变化而变化。植物和土壤微生物密切作用表现出来的对养分的不同步吸收是保留养分和维持生态功能的一种权衡机制。     

Maximum rooting depth of vegetation types at the global scale

The depth at which plants are able to grow roots has important implications for the whole ecosystem hydrological balance, as well as for carbon and nutrient cycling. Here we summarize what we know about the maximum rooting depth of species belonging to the major terrestrial biomes. We found 290 observations of maximum rooting depth in the literature which covered 253 woody and herbaceous species. Maximum rooting depth ranged from 0.3 m for some tundra species to 68 m for Boscia albitrunca in the central Kalahari; 194 species had roots at least 2 m deep, 50 species had roots at a depth of 5 m or more, and 22 species had roots as deep as 10 m or more. The average for the globe was 4.6±0.5 m. Maximum rooting depth by biome was 2.0±0.3 m for boreal forest. 2.1±0.2 m for cropland, 9.5±2.4 m for desert, 5.2±0.8 m for sclerophyllous shrubland and forest, 3.9±0.4 m for temperate coniferous forest, 2.9±0.2 m for temperate deciduous forest, 2.6±0.2 m for temperate grassland, 3.7±0.5 m for tropical deciduous forest, 7.3±2.8 m for tropical evergreen forest, 15.0±5.4 m for tropical grassland/savanna, and 0.5±0.1 m for tundra. Grouping all the species across biomes (except croplands) by three basic functional groups: trees, shrubs, and herbaceous plants, the maximum rooting depth was 7.0±1.2 m for trees, 5.1±0.8 m for shrubs, and 2.6±0.1 m for herbaceous plants. These data show that deep root habits are quite common in woody and herbaceous species across most of the terrestrial biomes, far deeper than the traditional view has held up to now. This finding has important implications for a better understanding of ecosystem function and its application in developing ecosystem models.     

氮、磷养分有效性对森林凋落物分解的影响研究进展

通过对相关研究文献的综述结果表明,氮(N)和磷(P)是构成蛋白质和遗传物质的两种重要组成元素,限制森林生产力和其他生态系统过程,对凋落物分解产生深刻影响。大量的凋落物分解试验发现在土壤N有效性较低的温带和北方森林,凋落物分解速率常与底物初始N浓度、木质素/N比等有很好的相关关系,也受外源N输入的影响;而在土壤高度风化的热带亚热带森林生态系统中,P可能是比N更为重要的分解限制因子。然而控制试验表明,N、P添加对凋落物分解速率的影响并不一致,既有促进效应也有抑制效应。为了深入揭示N、P养分有效性对凋落物分解的调控机制,"底物的C、N化学计量学"假说、"微生物的N开采"假说以及养分平衡的理论都常被用于解释凋落物分解速率的变化。由于微生物分解者具有较为稳定的C、N、P等养分需求比例,在不同的养分供应的周围环境中会体现出不同的活性,某种最缺乏的养分可能就是分解的最重要限制因子。未来的凋落物分解研究,应延长实验时间、加强室内和野外不同条件下的N、P等养分添加控制试验,探讨驱动分解进程的微生物群落结构和酶活性的变化。     

Organic matter inputs shift soil enzyme activity and allocation patterns in a wet tropical forest

Soil extracellular enzymes mediate organic matter turnover and nutrient cycling yet remain little studied in one of Earth’s most rapidly changing, productive biomes: tropical forests. Using a long-term leaf litter and throughfall manipulation, we explored relationships between organic matter (OM) inputs, soil chemical properties and enzyme activities in a lowland tropical forest. We assayed six hydrolytic soil enzymes responsible for liberating carbon (C), nitrogen (N) and phosphorus (P), calculated enzyme activities and ratios in control plots versus treatments, and related these to soil biogeochemical variables. While leaf litter addition and removal tended to increase and decrease enzyme activities per gram soil, respectively, shifts in enzyme allocation patterns implied changes in relative nutrient constraints with altered OM inputs. Enzyme activity ratios in control plots suggested strong belowground P constraints; this was exacerbated when litter inputs were curtailed. Conversely, with double litter inputs, increased enzymatic investment in N acquisition indicated elevated N demand. Across all treatments, total soil C correlated more strongly with enzyme activities than soluble C fluxes, and enzyme ratios were sensitive to resource stoichiometry (soil C:N) and N availability (net N mineralization). Despite high annual precipitation in this site (MAP ~5 m), soil moisture positively correlated with five of six enzymes. Our results suggest resource availability regulates tropical soil enzyme activities, soil moisture plays an additional role even in very wet forests, and relative investment in C, N and P degrading enzymes in tropical soils will often be distinct from higher latitude ecosystems yet is sensitive to OM inputs.     

Leaf litter carbon,nitrogen, and phosphorus stoichiometric patterns as related to climatic factors and leaf habits across Chinese broad-leaved tree species

Our understanding of how climate and leaf habit (evergreen vs. deciduous) drive leaf litter carbon (C), nitrogen (N), and phosphorus (P) stoichiometric patterns is largely limited but is particularly important for broad-leaved forests, since the forest is sensitive to climate change. Here, we investigated leaf litter C, N, and P stoichiometric ratios of broad-leaved tree species in relation to climate and leaf habit using previous publications and our additional samplings across China. We found that mean leaf litter C:N across Chinese broad-leaved tree species was within the range of the global flora, whereas C:P was lower and N:P higher. Evergreen species displayed higher leaf litter C:N, C:P, and N:P than their deciduous counterparts. Both leaf litter C:P and N:P for all species pooled were negatively correlated with latitude, driven by mean annual precipitation (MAP) and mean annual temperature, respectively, while leaf litter C:N displayed no clear latitudinal trend. The direction and magnitude of leaf litter C, N, and P stoichiometric ratios in response to climate diverged between leaf habits. For example, evergreen leaf litter C:N was negatively correlated with MAP, while deciduous counterparts did not respond significantly to MAP. We conclude that leaf litter C, N, and P stoichiometric ratios shifted along the climatic gradient, and the strength of such shifts differed between leaf habits. Therefore, leaf litter stoichiometric patterns across leaf habits suggest that any climate change-driven shift in species distribution may potentially alter the ecosystem’s nutrient cycling processes of evergreen- and deciduous-dominated broad-leaved forests differentially.     

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。     

Stoichiometric and nutrient resorption characteristics of dominant tree species in subtropical Chinese forests

This study investigated seasonal patterns in stoichiometric ratios, nutrient resorption characteristics, and nutrient use strategies of dominant tree species at three successional stages in subtropical China, which have not been fully understood. Fresh leaf and leaf litterfall samples were collected in growing and nongrowing seasons for determining the concentrations of carbon (C), nitrogen (N), and phosphorus (P). Then, stoichiometric ratios (i.e., C:N, C:P, N:P, and C:N:P) and resorption parameters were calculated. Our results found that there was no consistent variation in leaf C:N and C:P ratios among different species. However, leaf N:P ratios in late‐successional species became significantly higher, indicating that P limitation increases during successional development. Due to the P limitation in this study area, P resorption efficiency and proficiency were higher than corresponding N resorption parameters. Dominant tree species at early‐successional stage adopted “conservative consumption” nutrient use strategy, whereas the species at late‐successional stage inclined to adopt “resource spending” strategy.     

The effect of charcoal production on carbon cycling in African biomes

Using biomass for charcoal production in sub-Saharan Africa (SSA) may change carbon stock dynamics and lead to irreversible changes in the carbon balance, yet we have little understanding of whether these dynamics vary by biome in this region. Currently, charcoal production contributes up to 7% of yearly deforestation in tropical regions, with carbon emissions corresponding to 71.2 million tonnes of CO₂ and 1.3 million tonnes of CH₄. With a projected increased demand for charcoal in the coming decades, even low harvest rates may throw the carbon budget off-balance due to legacy effects. Here, we parameterized the dynamic global vegetation model LPJ-GUESS for six SSA biomes and examined the effect of charcoal production on net ecosystem exchange (NEE), carbon stock sizes and recovery time for tropical rain forest, montane forest, moist savanna, dry savanna, temperate grassland and semi-desert. Under historical charcoal regimes, tropical rain forests and montane forests transitioned from net carbon sinks to net sources, that is, mean cumulative NEE from −3.56 ± 2.59 kg C/m² to 2.46 ± 3.43 kg C/m² and −2.73 ± 2.80 kg C/m² to 1.87 ± 4.94 kg C/m² respectively. Varying charcoal production intensities resulted in tropical rain forests showing at least two times higher carbon losses than the other biomes. Biome recovery time varied by carbon stock, with tropical and montane forests taking about 10 times longer than the fast recovery observed for semi-desert and temperate grasslands. Our findings show that high biomass biomes are disproportionately affected by biomass harvesting for charcoal, and even low harvesting rates strongly affect vegetation and litter carbon and their contribution to the carbon budget. Therefore, the prolonged biome recoveries imply that current charcoal production practices in SSA are not sustainable, especially in tropical rain forests and montane forests, where we observe longer recovery for vegetation and litter carbon stocks.     

Mid-Holocene and glacial-maximum vegetation geography of the northern continents and Africa

BIOME 6000 is an international project to map vegetation globally at mid‐Holocene (6000 ¹⁴C yr bp ) and last glacial maximum (LGM, 18,000 ¹⁴C yr bp ), with a view to evaluating coupled climate‐biosphere model results. Primary palaeoecological data are assigned to biomes using an explicit algorithm based on plant functional types. This paper introduces the second Special Feature on BIOME 6000. Site‐based global biome maps are shown with data from North America, Eurasia (except South and Southeast Asia) and Africa at both time periods. A map based on surface samples shows the method’s skill in reconstructing present‐day biomes. Cold and dry conditions at LGM favoured extensive tundra and steppe. These biomes intergraded in northern Eurasia. Northern hemisphere forest biomes were displaced southward. Boreal evergreen forests (taiga) and temperate deciduous forests were fragmented, while European and East Asian steppes were greatly extended. Tropical moist forests (i.e. tropical rain forest and tropical seasonal forest) in Africa were reduced. In south‐western North America, desert and steppe were replaced by open conifer woodland, opposite to the general arid trend but consistent with modelled southward displacement of the jet stream. The Arctic forest limit was shifted slighly north at 6000 ¹⁴C yr bp in some sectors, but not in all. Northern temperate forest zones were generally shifted greater distances north. Warmer winters as well as summers in several regions are required to explain these shifts. Temperate deciduous forests in Europe were greatly extended, into the Mediterranean region as well as to the north. Steppe encroached on forest biomes in interior North America, but not in central Asia. Enhanced monsoons extended forest biomes in China inland and Sahelian vegetation into the Sahara while the African tropical rain forest was also reduced, consistent with a modelled northward shift of the ITCZ and a more seasonal climate in the equatorial zone. Palaeobiome maps show the outcome of separate, independent migrations of plant taxa in response to climate change. The average composition of biomes at LGM was often markedly different from today. Refugia for the temperate deciduous and tropical rain forest biomes may have existed offshore at LGM, but their characteristic taxa also persisted as components of other biomes. Examples include temperate deciduous trees that survived in cool mixed forest in eastern Europe, and tropical evergreen trees that survived in tropical seasonal forest in Africa. The sequence of biome shifts during a glacial‐interglacial cycle may help account for some disjunct distributions of plant taxa. For example, the now‐arid Saharan mountains may have linked Mediterranean and African tropical montane floras during enhanced monsoon regimes. Major changes in physical land‐surface conditions, shown by the palaeobiome data, have implications for the global climate. The data can be used directly to evaluate the output of coupled atmosphere‐biosphere models. The data could also be objectively generalized to yield realistic gridded land‐surface maps, for use in sensitivity experiments with atmospheric models. Recent analyses of vegetation‐climate feedbacks have focused on the hypothesized positive feedback effects of climate‐induced vegetation changes in the Sahara/Sahel region and the Arctic during the mid‐Holocene. However, a far wider spectrum of interactions potentially exists and could be investigated, using these data, both for 6000 ¹⁴C yr bp and for the LGM.     

Coloration and phenology manifest nutrient variability in senesced leaves of 46 temperate deciduous woody species

颜色和物候表明46种温带落叶木本植物衰老叶片的养分变异 不同共生植物的叶片养分含量差异显著,反映了不同的叶片养分利用策略。然而,衰老叶片养分的种间变异及其驱动因素尚不清楚。本研究旨在探讨衰老叶片养分的种间变异及其驱动因素。我们在中国东北的帽儿山森林生态系统研究站测定了46种共存温带落叶木本植物新鲜落叶的碳、氮、磷浓度。 采用随机森林模型量化10个生物因素(菌根类型、固氮类型、生长形态、耐阴性、叶片质地、变色程度、变色类型、叶片变色峰期、落叶峰期和落叶末期)的相对重要性。研究结果表明,落叶氮浓度种间变化为4倍,磷浓度变化达9倍。较高的氮和磷平均浓度(15.38和1.24 mg g⁻¹)表明该森林氮和磷限制较弱。功能群仅对特定养分及其比值有显著影响。磷浓度、氮磷比与外生菌根树种的落叶高峰日和落叶结束日呈负相关。颜色鲜艳的叶片(红色＞棕色＞黄色＞黄绿色＞绿色)倾向于比绿色叶片氮和磷浓度更低而碳氮比和碳磷比较高。随机森林模型表明,秋季叶变色和落叶物候贡献了80%的种间变异解释量。这些结果增加了我们对温带森林木本植物营养策略之衰老叶片养分变异性的理解。