stoichiometriccharacteristicsofvegetationsuccessionalstages...

49卷南方农业学报·440·

Recieved date：2017-05-15Foundation item：National Natural Science Foundation of China（31460135）；Science and Technology Development Fund Project

of Guangxi Academy of Agricultural Sciences（2017JM08，2015JZ17）；Guangxi Eighteenth Batch of“Ten HundredThousand Talent Project”Special Funds（2017）

Biography：* for corresponding authors，HE Tie-guang（1976-），researcher，interested in agricultural environment and ecology，E-mail：tghe118@163. com. YU Yue-feng（1988-），interested in agricultural environment and ecology，E-mail：[email protected]

Stoichiometric characteristics of vegetation successional stagesin karst area of northwest Guangxi

YU Yue-feng1，HE Tie-guang1*，SONG Tong-qing2，3，DU Hu2，3，SU Tian-ming1，WEI Cai-hui1，TANG Hong-qin1

（1Agricultural Resources and Environment Research Institute，Guangxi Academy of Agricultural Sciences，Nanning

530007，China；2Institute of Subtropical Agriculture/Key Laboratory of Agro-ecological Processes in Subtropical Region，

Chinese Academy of Sciences，Changsha 410125，China；3Huanjiang Observation and Research Station of Karst

Ecosystem，Chinese Academy of Sciences，Huanjiang，Guangxi 547100，China）

Abstract：【Objective】Ecological stoichiometry of karst communities at different vegetation successional stages innorth west Guangxi were explored to provide references for further understanding nutrient change regulation and nutrientlimitation during vegetation succession and system stability of karst ecosystems in the vegetation succession process.【Method】Through establishing plots，sampling and laboratory analysis，the carbon（C），nitrogen（N）and phospuros（P）contents and stoichiometric ratio in plant，litter and soil of four successional stages（grass，shrub，secondary forest andprimary forest）were analyzed. Variance analysis and correlation analysis were used to analyze their differences and corre-lations.【Result】Along the succession series，the contents of C，N and P in plant showed upward trend. C，N and P con-tents of litter were lower than those in plants. The performance of plant N and P reabsorption rate was as follows: primaryforest>shrub>secondary forest>grass. The highest C and N contcent at 0-10 cm soil layer appeared in secondary forest.The highest P concent lied in shurb. C∶N，C∶P and N∶P ratios showed the rule of litter>plant>soil. Grass displayed thehighest plant C∶N，plant C∶P and litter C∶N，and the lowest plant N：P and litter N∶P. Primary forest showed the highestlitter C∶P and litter N∶P. The highest plant N∶P ratio appeared in the secondary forest. C∶P and N∶P ratios in soil rosealong the successional stage. There were significant correlations between C，N and P and their ratios in plants，litter andsoil（P<0.05）.【Conclusion】Soil nutrients have no direct impact on plant nutrients，but play an important role in plantgrowth. However，plant leaf N∶P ratios are mainly influenced by soil N and P. Plant growth is vulnerable to nutrient limi-tation in the early vegetation successional stages.

Key words：karst；stoichiometry；vegetation successional stages；plant–litter–soil；C∶N∶P

CLC number：S718.5 Document code：A Article：2095-1191（2018）03-0440-08

桂西北喀斯特地区植被不同演替阶段生态化学计量特征

俞月凤1，何铁光1*，宋同清2，3，杜虎2，3，苏天明1，韦彩会1，唐红琴1

（1 广西农业科学院农业资源与环境研究所, 南宁 530007；2 中国科学院亚热带农业生态研究所/亚热带农业生态过程

重点实验室，长沙 410125；3 中国科学院环江喀斯特生态系统观测研究站，广西环江 547100）

摘要：【目的】探讨桂西北喀斯特地区植被不同演替阶段生态化学计量特征，为进一步了解植被演替过程中的养

分循环和喀斯特生态系统的稳定性提供参考。【方法】通过野外样地设置、取样及室内试验，采用方差分析和相关性分

析等经典统计方法对桂西北喀斯特地区四个演替阶段（草丛、灌丛、次生林和原生林）植物、凋落物和土壤的碳（C）、

氮（N）和磷（P）含量、化学计量比及其相关性进行分析。【结果】植物C、N和P含量随植被正向演替呈增长趋势，凋落物

的养分含量均低于植物。植物N和P再吸收率表现为原生林>灌丛>次生林>草丛。次生林中0~10 cm土壤以C和N含

量最高，但灌丛以P含量最高。养分化学计量比C∶N、C∶P和N∶P在各层次中表现出一定的规律：凋落物>植被>土壤。

南方农业学报 Journal of Southern Agriculture 2018，49（3）：440-447ISSN 2095-1191；CODEN NNXAABhttp://www.nfnyxb.comDOI：10.3969/j.issn.2095-1191.2018.03.05

3期 ·441·

0 Introduction【Research significance】The biological world is

made up of elements；therefore，stoichiometric regu-larity exists in ecological systems（Zeng and Chen，2005）. Ecological stoichiometry，which approachesecological questions by asking how the balance of themultiple elements required by organisms affects pro-cesses and interactions，provides new perspectives forstudying ecosystem processes at different levels，fromleaf physiology to ecosystem productivity（Sterner andElser，2002；Dodds et al.，2004；Hessen et al.，2004）. Carbon（C），nitrogen（N）and phosphorus（P）are the three main elements that exist in relatively sta-ble ratios in living organisms，and the key characteris-tics of organisms and ecosystems are determined bythe dynamics of element ratios（Michaels，2003）. Inecosystems，the cycling of C，N and P is betweenplants，litter and soil. As a study on biological systemenergy and the balance of various elements，ecologi-cal stoichiometry provides an effective means forstudying C，N，P and other elements in plant-litter-soil processes（Agren and Bosatta，1998；Elser et al.，2000，Elser et al.，2007）. Southwestern China is oneof the largest karst regions in the world and is consi-dered fragile because of its special geological back-ground and small environmental carrying and anti-in-terference capacities（Yuan，2003）. Over the past se-veral decades，vegetation degradation rates in this re-gion have accelerated due to resource overexploita-tion，including intensive mining，deforestation，over-grazing and overcultivation，as a result of increasedpopulation pressure（Wang et al.，2004；Du et al.，2011）. This has changed the dominant vegetationtypes across most of the karst region from primary fo-rest to grasses，shrub and secondary forest. There areplant communities in different successional stages.It is of significance to explore C，N and P ecologicalstoichiometry in plant -litter-soil of vegetation succes-sional stages in the karst area，which is helpful for fur-ther understanding the nutrient change regulation andnutrient limitation during vegetation succession andsystem stability of karst ecosystems in vegetation suc-cession process.【Research progresses】C∶N∶P stoichio-metry studies have reached deep into all levels ofecology（cell，individual，kinds of group，communi-

ty，ecosystem）and regions. There were many studiesin the relationship between N and P stoichiometry andproductivity in plants，which mainly focused on large-scale biomes（Reieh et al.，1999；Wright et al.，2004）.In China，studies in ecological stoichiometry havemainly concentrated on the regional and ecosystemscales. For example，Han et al.（2005）studied the leafN and P stoichiometry across 753 terrestrial plant spe-cies over 127 research sites in China. Ren et al.（2007）studied the characteristics of N and P stoichiometry of654 plants over 168 research sites in eastern Chinaand found that vegetation growth in China was morelikely to be restricted by P compared with the globalscale. He et al.（2008）reported patterns of leaf P andN∶P ratios，and analyzed the relative contribution ofclimatic variables and phylogeny in structuring pat-terns of leaf N∶P stoichiometry using a systematiccensus of 213 species over 199 research sites in thegrassland biomes of China. Gao et al.（2007）and Yanet al.（2008） studied leaf N and P stoichiometry ofcommon species in successional stages of evergreenbroad-leaved forest in Tiantong National Forest Park，Zhejiang Province，China. Cui et al.（2015）studiedcharacteristics of N and P stoichiometry for plant，litter, and soil and the interactions between its compo-nents across forest ecosystems in Shaanxi Province.Bi et al.（2017）explored the ecological stoichiometryof different forest types in mountainous region ofeastern Liaoning Province.【Research break throughpiont】The C，N and P stoichiometry at different suc-cessional stages can reflect the main limiting elementsand be used as an indicator of N and P in the ecosys-tem. However，most studies have focused on the Nand P stoichiometry of different ecosystems and thereare few reports on the C，N and P stoichiometry ofplants，litter and soil in karst plant communities atdifferent successional stages.【Solving problems】Aninvestigation of typical plant communities at fourdifferent vegetation successional stages（grass，shrub，secondary fo-rest and primary forest）was conductedin a depression between karst hills in Huanjiang Countyof northwes-tern Guangxi，southwest China. Based onthis，C，N，P contents，ecological stoichiometry，andtheir correlation were analyzed in plants，litters andsoils，as well as nutrient（N，P）resorption efficiencyin successional stages.

在草丛中，植物C∶N、C∶P和凋落物C∶N最高，植物和凋落物的N∶P最低；凋落物C∶P、N∶P和植物N∶P分别出现在原生

林和次生林；土壤C∶P、N∶P沿植被正向演替而增加。植物、凋落物和土壤中C、N和P含量及其化学计量比间存在显

著相关（P<0.05）。【结论】土壤养分对植物养分含量影响不明显，但在植物生长过程中发挥重要作用；植物叶片N∶P

受土壤N和P含量的影响；植物生长在演替阶段早期易受土壤养分限制。

关键词：喀斯特；化学计量；植物演替阶段；植物—凋落物—土壤；C∶N∶P

YU et al.：Stoichiometric characteristics of vegetation successional stages in karst area of northwest Guangxi


1 Materials and methods1. 1 Study area

This study was conducted at the Huanjiang Ob-servation and Research Station for Karst Ecosystem ofChinese Academy of Sciences（108° 18 ′ 56.9″ E-108°19 ′ 58.4″ E，24° 43 ′ 58.9″N-24° 44 ′ 48.8″N）and theMulun National Natural Reserve（107°54 ′ 01″E-108°05 ′ 51″ E，25° 07 ′ 01″N-25° 12 ′ 22″N）in HuanjiangCounty，Guangxi，southwestern China. A subtropicalmonsoon climate dominates the area，with an averageannual precipitation of 1389.1 mm，average annualsunshine time of 1451 h and average annual tempera-ture of 15.7 ℃ . The wet season usually lasts fromApril to September，with about 70% of the total annualpreci-pitation falling in these months. The coldestmonth is January，with an average daily temperatureof 10.1 ℃ and the hottest month is July with an aver-age daily temperature of 28.0 ℃ . The mean annualfrost-free period lasts 290 d. The average annual evap-

oration is 1571.1 mm and the average humidity is70%.

Huanjiang Observation and Research Station forKarst Ecosystem of Chinese Academy of Sciences is atypical karst peak cluster depression landscape. Befor1984，felling，reclamation，grazing，fires and otherlarge area destruction have stricken this region. Butsince then the region were protected and have naturallydeveloped grasses，shrubs，and secondary forest com-munity. In the site，six plots of grassland，six plots ofshrubland，and six plots of secondary forest were es-tablished in September 2010. Mulun National NaturalReserve was established in 1991 to protect a remnantof undisturbed mixed evergreen and deciduous broad-leaved forest in the karst region. The primary forest atthis site has not been disturbed for more than 200years. So the six plots of primary forest were estab-lished here at the same time and all plots were 20 m×20 m. General plot information was presented in Ta-ble 1.

SuccessionalstageGrassShrubSecondary forestPrimary forest

Dominantspecies

Ischaemum indicum，Imperata cylindricaVitex negundo，Rhus chinensis

Alangium chinense，Itoa orientalisRadermachera sinica，Platycladus orientalis

Slope angle（°）

8.33±4.086.50±1.01

17.50±4.1825.00±3.16

Slopeposition

DownhillDownhill

UphillUphill

Elevation（m）

301-307382-393303-355420-609

Vegetation coveragerate（%）

62.50±2.8994.17±2.0497.50±3.5495.50±2.81

Soiltype

Brown limestone soilBrown limestone soilBrown limestone soilBrown limestone soil

Table 1 Characteristics of the eight vegetation communities

1. 2 Sampling methodEach plot was further divided into 16 subplots

（5 m×5 m）. In each subplots，all trees with diameterat breast height（DBH）≥1 cm were tagged，identi-fied，measured and georeferenced following the stan-dard formulated by Center for Tropical Forest Sci-ence. Plant community structural indexes were deter-mined，which included density，crown width，cover-age，DBH and height. In each plot，15-20 completemature leaves of branches in four directions and theupper，middle and lower parts of the canopy were col-lected from three to five individuals of each dominantspecies and mixed as the sample for each species.Three subplots（1 m×1 m）were established randomlyin the grass plots. All herbs above the ground and litterwere collected from each subplot. After collection，the plant samples were immediately placed in polyethy-lene bags and shipped to the laboratory，then ovendried at 70.0 ℃ for at least 48 h to constant weight.Finally，the samples were ground to pass through a0.154 mm-mesh sieve for elemental analysis.

In each plot，five soil cores were taken fromeach of five soil layers：0-10，10-20，20-30，30-50，and 50-100 cm. The five cores per layer were mixedto form a composite sample. The mixed samples were

then placed in polyethylene bags and carried to thelaboratory，where they were air dried，ground to passthrough a 2.000 mm-mesh sieve and mixed for soilphysicochemical analysis.1. 3 Chemical analysis

Plant C and soil organic carbon（SOC）concentra-tions were measured using wet oxidation by KCr2O7 +H2SO4 and titration with FeSO4，while leaf N and Pwere digested in a mixed acid solution of H2SO4+H2O2

（Zheng and Shangguan，2007）. Plant N concentrationswere then determined using a flow injection analyzer（FIAstar 5000 Analyzer，FOSS，Denmark），and plantP concentrations were colorimetrically analyzed withblue phosphor-molybdate（Du et al.，2011）. Total soilN was measured using the Kjeldahl method，and totalsoil P was digested in a solution of H2SO4+HClO4 andanalyzed as plant P.1. 4 Statistical analysis

Data treatment and calculations were performedusing Excel 2010 and IBM SPSS Statistics 19.0 soft-ware packages. Single factor variance（least significantdifference）analysis was used to determine the effectsof different vegetation successional stages on C，Nand P contents and stoichiometric ratios of plants，li-tter and soil. The correlation analysis method was

Journal of Southern Agriculture

3期 ·443·

used to determine the relationship between C，N andP contents in plants，litter and soil. The nutrient（N，P）resorption efficiency was the percentage differencebetween plant and litter nutrient content and plant nu-trient content.

2 Results and analysis2. 1 Plant and litter C，N and P contents

There were large differences in C，N and P con-tents of plants and litter of the communities in the foursuccessional stages（Table 2）. Grass had much lowerleaf C，N and P contents than the other three succes-

sional stages. Leaf C content was the highest in shrub，followed by primary forest and secondary forest.Leaf N did not significantly（P<0.05，the same below）differ among shrub，secondary forest and primary fo-rest. Primary forests had the highest leaf P and therewas no difference with shrub. There were no differen-ces in litter C between the communities in the foursuccessional stages. Secondary forest had the highestlitter N and P. Litter P was the lowest in primary fo-rest. Litter N followed the order：secondary forest>pri-mary forest>shrub>grass.

Table 2 C，N and P contents in plants and litter at different successional stages

Different lowercase letters in the same column represented significant difference among the different successional stages（P<0.05）

2. 2 N and P resorption efficiency of plantsAlong the successional stages，N and P resorp-

tion efficiency of plants showed a similar pattern（Fig.1）. Both N and P resorption efficiency of plantswere the lowest in grass，increased in the shrub stage，then decreased in secondary forest，and finally in-creased and tended to be stable in primary forest stage.P resorption efficiency of plants was the highest in pri-mary forest，which was in late successional stage. TheN resorption efficiency of plants was the highest inshrub，which was in the middle stage of vegetationsuccession. In addition，P resorption efficiency ofplants in all vegetation succession stages was higherthan N resorption efficiency.

2. 3 Soil C，N and P contentsC and N contents decreased significantly and

exponentially with soil depth（Fig.2-Fig.4）. P contentshowed irregular variations with soil depth，which in

secondary forest and primary forest increased at firstand then decreased，while it decreased first and thenincreased in grass and shrub（Fig.2 and Fig.3）. Alongthe successional stages，soil C and N contents at 0-10 cmincreased up to secondary forest，but decreased fromsecondary forest to primary forest. However，P con-tent increased from grass to shrub then decreased afterthat.

2. 4 C，N and P stoichiometryThe stoichiometric characteristics of plant，litter

and soil were different in each community（Fig.5）. Inthe four vegetation successional stages，C∶N，C∶Pand N∶P ratios in different community layers fol-lowed the order：litter>plant>soil. Plant C∶N and lit-ter C∶N ratios were the greatest in grass，and not sig-nificantly different among shrub， secondary forestand primary forest. Different vegetation successional

Fig.1 N and P resorption efficiency of plants in differentsuccessional stages

Fig.2 Changes in soil C content with depth for differentsuccessional stages

Nut

riti

onre

sorp

tion

effi

cier

cy（

%）

0

1020

3040

5060

70

Grass Shrub Secondaryforest

Primaryforest

N

P

C content（g/kg）

Dep

th（cm

）

0-10

10-20

20-30

30-50

50-100

0 10 20 30 40 50 60

GrassShrubSecondary forestPrimary forest

Successionalstage


Plant leafC（g/kg）

453.55±10.87c507.65±11.26a473.94±14.34b484.24±7.03b

N（g/kg）9.11±0.00b18.32±2.01a19.81±1.50a18.88±7.38a

P（g/kg）1.13±0.29b1.84±0.37a1.41±0.00b1.97±0.21a

LitterC（g/kg）

435.41±13.72440.47±25.71466.68±4.13458.33±45.84

N（g/kg）8.76±1.32b

11.88±2.47ab15.08±3.67a13.41±4.48a

P（g/kg）0.76±0.22a0.85±0.07a0.89±0.28a0.59±0.10b


Primaryforest



c ba

bC BC

B

A

b ba a

0.00

10.00

20.00

30.00

40.00


Primaryforest

Plant Litter Soil

abc b c

B B B

A

b b a a

0.00

400.00

800.00

1200.00 Plant Litter Soil

a

b cb

AB

CB

0.00

20.00

40.00

60.00

Plant Litter Soil

stages did not cause significant differences in the soilC∶N ratio. Plant C∶P ratio followed the order：grass >secondary forest>shrub>primary forest. Primary foresthad the highest litter C∶P and litter N∶P ratios，and nosignificant difference in litter C∶P ratio was foundamong grass，shrub and secondary forest. Grass hadthe lowest litter N：P ratio，which in shrub and secon-dary forest was intermediate. Soil C∶P and soil N∶Pratios varied in the same order，increasing along thesuccessional stages：primary forest>secondary forest>shrub>grass. Plant N∶P ratio was the highest in se-condary forest and the lowest in grass.2. 5 Relationships among C，N and P contentsand stoichiometry in plants，soil and litter

The correlations among C，N and P contents andstoichiometry in plants，litter and soil among all theplots（Table 3-Table 5） were analyzed. The resultsshowed that plant C content was significantly positive-ly correlated with soil N and P contents，while it wasnegatively correlated with the soil C∶P and N∶P ratios.Negative correlations were found between plant C∶Nand soil C∶N ratios，between plant N∶P ratio and soilC，and between P content and soil N∶P ratio. In addi-

tion，a positive correlation was found between plantN∶P and soil N∶P ratios. Extremely significant posi-tive correlations were observed between litter N andplant N（P<0.01，the same below） and between litterC∶N and plant C∶N；significant positive correlationswere found between litter N∶P ratio and plant P.

The litter N content had negative correlationswith plant C∶N and C∶P ratios. Also，there were ne-gative correlations between litter C∶N ratios and plantN and N∶P ratio，as well as between litter N∶P andplant C∶P. There were also notable relationships amongC，N and P contents and between litter stoichiometryand soil stoichiometry. Litter N was extremely signifi-cantly positively correlated with soil C and N，andthere was significant positive correlation between lit-ter N and C∶P ratio，and between litter N and N∶Pratio. Significant negative correlations were foundbetween litter C∶N ratio and soil C，between litter C∶Nratio and soil N content，between the litter N∶P ratioand soil P，and extremely significant negative correla-tion was detected between litter N∶P and soil C∶N ratio.

Fig.3 Changes in soil N content with depth for differentsuccessional stages

Fig.4 Changes in soil P content with depth for differentsuccessional stages

Fig.5 C∶N，C∶P and N∶P ratios in plant，litter and soilfor different successional stages

Different lowercase letters representd significant difference betweendifferent successional stages（P<0.05）

C∶N

C∶P

N∶P


Primaryforest

N content（g/kg）

Dep

th（cm

）

0-10

10-20

20-30

30-50

50-100


0.0 1.5 3.0 4.5 5.0

P content（g/kg）

Dep

th（cm

）

0-10

10-20

20-30

30-50

50-100


0.0 0.5 1.0 1.5


Primaryforest


Primaryforest


bb b

a

bc

b

cbc

b

a

a

3期 ·445·

3 Discussion3. 1 C，N and P contents and nutrient resorptionefficiency

The content of nutrient elements in plant leaveswas influenced by structural characteristics and thegrowth rhythm of plants，which varied greatly be-tween the different growth stages（Baldwin et al.，2006）. Along the succession series，the C，N and Pcontents in plants showed an increasing trend. Grasshad the lowest C，N and P contents. As quantitativeindicators to measure the degree of soil fertility，soilnutrient content had an important ecological functionin soil，and it was also the basis of plant growth anddevelopment. Ecological processes such as photosyn-thesis and mineral metabolism were closely related tothe supply of soil nutrients. In this study，C，N and Pcontents of litter in the four vegetation successionalstages were lower than those in plants. Compared withnon-karst region，litter C，N and P contents in karstvegetation communities showed low C content and

high N content pattern. The temperature and humidityconditions in karst region were conducive to biologi-cal reproduction and growth，and biological growthwas strong. However，these conditions also accelerat-ed rock dissolution，weathering，and soil formationand development processes. Plant nutrient resorptionefficiency could reflect the ability of nutrient conser-vation，nutrient use efficiency and adaptation to nutri-entpoor habitat（Aerts，1996）. P resorption efficiencywas significantly higher than N resorption efficiency，which was consistent with a previous study on domi-nant tree species of the four forest types in China（Wang et al.，2011）. It could be seen that，in Karstarea，the proportion of N element returned to soil bylitter was higher than that in P，and the possibility ofsoil P deficiency was higher than N. The study pointedto nutrient transfer as the inherent characteristic of spe-cies，and the genetic diversity of plants might be amajor factor affecting leaf senescence after nutrienttransfer（Oleksyn et al.，2003；Luyssaert et al.，2005）.3. 2 Stoichiometric characteristics in plant，soiland litter

As important physiological indexes，C∶N andC∶P ratios of plants could reflect plant growth rateand nutrient use efficiency in plants（Agren，2004）. Inthis study，the plant C∶N and C∶P ratios in grasswere 49.79 and 420.16， which were the highestamong the four vegetation successional stages. This in-dicated that grass had a faster growth rate than the oth-er successional stages. Plant growth was expected tobe limited by N and P availability in most terrestrialecosystems. Plant leaf N∶P values could reflect thelimiting element affecting ecosystem productivity，which changed with the external environment. In ter-restrial plant organs，a relatively constant N∶P was animportant adaptive mechanism of plants to survive onearth. Studies on wetland plants showed that an N：Pratio<14.00 indicated N limitation，N∶P ratio>16.00indicated P limitation，and N∶P ratios between thesevalues indicated either N and P colimitation or no limi-ting element（Tessier and Raynal，2003）. A study onN∶P ratios in terrestrial plants found that biomass pro-duction was most likely to be enhanced by N fertiliza-tion in vegetation with N∶P ratios<10.00 and by P ferti-lization in vegetation with N∶P ratios>20.00，whereaswithin this range，the effects of fertilization were notunequivocally related to N∶P ratios（Güsewell，2004）.In this study，the plant N∶P ratios in the four vegeta-tion successional stages were between 8.07 and 14.08，less than the national average（14.40）based on the da-ta of 753 species in China（Han et al.，2005）. Only theN∶P ratio in secondary forest was slightly higher thanthe global average（13.80）（Reich and Oleksyn，2004）.A previous study of N∶P ratios in terrestrial plants

Soil

CNPC∶NC∶PN∶P

PlantC

0.360.53*

0.63**-0.35-0.54*

-0.74**

N-0.12-0.17-0.100.24-0.300.11

P0.330.31-0.380.02-0.42-0.15

C∶N0.190.280.004

-0.61**-0.050.07

C∶P-0.22-0.200.36-0.08-0.34

-0.62**

N∶P-0.56*0.58**-0.66**-0.21-0.40

-0.65**

Plant

CNPC∶NC∶PN∶P

LitterC

0.08-0.05-0.11-0.080.010.12

N0.02

0.66**-0.12

-0.66**-0.52*0.49

P-0.060.08-0.12-0.07-0.010.18

C∶N-0.11

-0.67**-0.50

0.64**0.55*-0.46*

C∶P0.05-0.030.18-0.03-0.07-0.12

N∶P0.050.410.52*-0.42-0.45*0.15

Table 5 Spearson’s correlation among C，N and P con⁃tents and stoichiometry in soil and litter

Soil

CNPC∶NC∶PN∶P

LitterC

0.440.37-0.20-0.040.420.33

N0.82**0.74**-0.310.010.55*0.52*

P0.240.010.280.340.02-0.12

C∶N-0.62*-0.60*0.100.08-0.05-0.35

C∶P-0.100.11-0.47-0.410.230.33

N∶P-0.080.20

-0.54*-0.58**

0.240.40

Table 3 Spearson’s correlation among C，N and P con⁃tents and stoichiometry in soil and plants

Table 4 Spearson’s correlation among C，N and P con⁃tents and stoichiometry in plants and litter

* represented significant differece（P<0.05），and ** represented extre-mely significant difference（P<0.01）. The same was applied in Table 4and Table 5



found that plant N∶P ratios in grass，shrub and prima-ry forest were<10.00，indicating N limitation，whilethat in secondary forest was within the range of 10.00-20.00（Güsewell，2004）. This result suggested that ab-sorption and utilization of N and P were relatively sta-ble in secondary forest in the karst region. However，using N∶P ratios of plants as indicators of N or P limi-tation，various studies have suggested that shifts inlimitation led to changes in plant traits，vegetationcomposition and species diversity（Koerselman andMeuleman，1996；Roem and Berendse，2000）. Soil C∶N∶P ratio was the ratio of the total mass of organicmatter（or carbon in other components）to N and P，and was an important indicator of soil organic mattercomposition and quality. In general，the soil organicmatter C∶N ratio was inversely proportional to its de-composition rate. There were no significant differenc-es in the soil C∶N ratio across the four successionalstages（9.79-11.76），but they were below those foundin red-yellow soil of tropical and subtropical regions（Huang，2000）. Soil C∶P and N∶P ratios in seconda-ry forest and primary forest were higher than those ingrass and shrub. This showed that nutrient-use pat-terns changed in the late successional stages. McGrod-dy et al.（2004）found that the average litter C∶N andC∶P ratios in all biomes were higher than those in thecorresponding leaves. In this study，the litter C∶N，C∶Pand N∶P ratios were higher than those of leaves inkarst region. Plants absorbed N and P from soil，andthen reabsorbed N and P through the process of nu-trient reabsorption before leaf litter fell. Therefore，lit-ter C∶N，C∶P and N∶P were higher than those ofplants，and litter C∶N，C∶P and N∶P of plants werelarger than those of soil.3. 3 Relationships among stoichiometric charac⁃teristics in plant，soil and litter

Plants fix carbon through photosynthesis andtransfer carbon and nutrients to the soil through litterdecomposition. There are mutual connections amongsoil nutrient supply，plant nutrient demand and self-regulation，and the return of nutrients in the processof litter decomposition，they also change and influ-ence each other. Ecological stoichiometry provides aneffective mean to determine the stoichiometry of C，Nand P and other elements in plant–litter–soil ecologi-cal processes. However，this study showed no correla-tion between N and P contents in plants and those insoil，and plant C content was significantly positivelycorrelated with soil N and P contents. This indicatedthat soil nutrients had no direct impact on plant nu-trients，but played an important role in plant growth.One possible explanation for this result was that withshallow soil，plant roots in rock cracks were forced to

absorb some of the excess elements in weatheredrock，so the correlation between soil and vegetationwas not significant. There were significant correla-tions between plant N∶P ratio and soil C，N and P con-tents and N∶P ratio. It has been proposed that leaf N∶Pratios were mainly impacted by soil N and P. There-fore，the results of this study were in accordance withthe theory of ecological stoichiometry（Elser et al.，1996），which stated that soil N and P were the mainfactors shaping leaf N∶P stoichiometry across all func-tional groups. Plant nutrients were transferred or re-sorbed in the process of leaf fading. The difference be-tween the C∶N∶P ratios of litter and leaf reflected thenutrient resorption efficiency. Therefore，significantcorrelations were observed between N and C∶N ratioof plants and litter in karst region. This was probablydue to the low N resorption efficiency of plants. Accu-mulation of soil organic matter and nutrients from va-rious forms of litter returned C，N and P to the soil.There were some relationships between the nutrientcontents of litter and soil. Litter N and C∶N ratio weresignificantly correlated with soil C and N，respective-ly. In addition，litter N and the N∶P ratio affected soilC∶P ratio，and N∶P ratio and P content affected C∶Nratio. This illustrated that the decomposition rate of li-tter C，as an important component of soil organic mat-ter，was affected by N content and C∶N ratio，andplayed an important role in nutrient content of soil andstoichiometric ratio.

4 ConclusionAlong the succession series，the content of C，N

and P in plants showed upward trend. Grass had thelowest content of C，N and P. Compared with non-karst area，litter C，N and P contents in karst vegeta-tion communities showed that the low C content andhigh N content pattern was consistent with the law ofplants. In four vegetation succession stages of karstarea，N resorption efficiency of plant was lower thanP resorption efficiency. The possibility of P deficiencyin karst was more than that of N deficiency. Grass hadhigher plant C∶N and C∶P and lower plant N∶P ratiosthan shrub and forests. It was showed that plantgrowth was vulnerable to nutrient limitation in earliervegetation succession. In karst area，soil nutrients hadno direct impact on plant nutrients，but played an im-portant role in plant growth. However，plant leaf N∶Pratios were mainly impacted by soil N and P. Litter Nand C∶N were significantly correlated with soil C andN respectively. As an important component of soil or-ganic matter，litter C，N content and C∶N ratio couldaffect its decomposition rate，which played an impor-tant role on nutrient content of the soil and stoichio-metric ratio.


3期 ·447·

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