为探讨苔原植被对气候变暖的响应模式, 采用开顶箱增温法, 研究了3个生长季增温对长白山苔原3种代表植物——牛皮杜鹃(Rhododendron aureum)、笃斯越桔(Vaccinium uliginosum)和东亚仙女木(Dryas octopetala var. asiatica)的叶片及土壤碳(C)、氮(N)、磷(P)含量及其比值的影响。结果表明: 增温使土壤N和P的含量分别增加5.88%和4.83%, C含量降低13.19%; 增温和对照(不增温)条件下, 植物叶片的C、N、P含量及其比值在生长季有明显的变化。增温使笃斯越桔和东亚仙女木叶片的P含量分别增加10.34%和12.87%, 牛皮杜鹃则降低了16.26%, 增温并没有明显改变3种植物叶片的C、N含量, 但牛皮杜鹃和东亚仙女木叶片的C:N值在增温条件下呈现增加趋势。增温使土壤可利用的N、P含量增加。增温对3种植物的C:N值, 牛皮杜鹃、笃斯越桔的P含量, 以及东亚仙女木的C:P值都产生了显著的影响。结果表明增温增加了长白山苔原P元素对植物生长的限制, 且3种植物叶片的C、N、P化学计量学特性对增温的响应模式和尺度没有表现出一致性。
Aims Our objective was to investigate how warming affected C, N and P contents and C: N: P ratios in leaves of dominant tundra plants in Changbai Mountain. Methods Open-top chambers (OTCs) were used to raise the air and soil temperature in the Changbai Mountain tundra. Eight hexagon OTCs were established according to the standard of International Tundra Experiment (ITEX). The C, N and P contents and C:N:P ratios in soils and leaves of Dryas octopetala var. asiatica, Vaccinium uliginosum, Rhododendron aureum were measured during growing season (July to September). Important findings Warming increased the soil N and P contents by 5.88% and 4.83%, respectively, but reduced the C content by 13.19%. The contents of C, N and P in leaves showed significant variations for plants in both OTCs and control plots during growing season. The P content in V. uliginosum, R. aureum was increased by 10.34% and 12.87%, respectively, but decreased by 16.26% in D. octopetala var. asiatica, by warming. The C:N ratio in leaves of D. octopetala var. asiatica and R. aureum grown in OTCs showed an increasing trend. Warming resulted in increases in soil available N and P. The ratio of C:N in the three plants, the P content in R. aureum and V. uliginosum, and the ratio of C:P in D. octopetala var. asiatica were significantly affected by warming. The results indicate that warming would increase the P limitation to plant growth in this area. The pattern and magnitude of leaf stoichiometry of the three tundra plant species respond differently to warming in Changbai Mountain.
全 文 :植物生态学报 2014, 38 (9): 941–948 doi: 10.3724/SP.J.1258.2014.00088
Chinese Journal of Plant Ecology http://www.plant-ecology.com
——————————————————
收稿日期Received: 2014-02-24 接受日期Accepted: 2014-07-25
* 通讯作者Author for correspondence (E-mail: zhouyumei73@126.com)
增温对苔原土壤和典型植物叶片碳、氮、磷化学计
量学特征的影响
江肖洁1 胡艳玲2 韩建秋1 周玉梅1*
1上海应用技术学院生态技术与工程学院, 上海 201418; 2盘锦市环境保护局, 辽宁盘锦 124010
摘 要 为探讨苔原植被对气候变暖的响应模式, 采用开顶箱增温法, 研究了3个生长季增温对长白山苔原3种代表植物——
牛皮杜鹃(Rhododendron aureum)、笃斯越桔(Vaccinium uliginosum)和东亚仙女木(Dryas octopetala var. asiatica)的叶片及土壤
碳(C)、氮(N)、磷(P)含量及其比值的影响。结果表明: 增温使土壤N和P的含量分别增加5.88%和4.83%, C含量降低13.19%; 增
温和对照(不增温)条件下, 植物叶片的C、N、P含量及其比值在生长季有明显的变化。增温使笃斯越桔和东亚仙女木叶片的P
含量分别增加10.34%和12.87%, 牛皮杜鹃则降低了16.26%, 增温并没有明显改变3种植物叶片的C、N含量, 但牛皮杜鹃和东
亚仙女木叶片的C:N值在增温条件下呈现增加趋势。增温使土壤可利用的N、P含量增加。增温对3种植物的C:N值, 牛皮杜鹃、
笃斯越桔的P含量, 以及东亚仙女木的C:P值都产生了显著的影响。结果表明增温增加了长白山苔原P元素对植物生长的限制,
且3种植物叶片的C、N、P化学计量学特性对增温的响应模式和尺度没有表现出一致性。
关键词 碳, 氮, 磷, 苔原, 增温
Effects of warming on carbon, nitrogen and phosphorus stoichiometry in tundra soil and
leaves of typical plants
JIANG Xiao-Jie1, HU Yan-Ling2, HAN Jian-Qiu1, and ZHOU Yu-Mei1*
1Ecological Technique and Engineering College, Shanghai Institute of Technology, Shanghai, 201418, China; and 2Panjin Municipal Environmental Protection
Bureau, Panjin, Liaoning 124010, China
Abstract
Aims Our objective was to investigate how warming affected C, N and P contents and C: N: P ratios in leaves of
dominant tundra plants in Changbai Mountain.
Methods Open-top chambers (OTCs) were used to raise the air and soil temperature in the Changbai Mountain
tundra. Eight hexagon OTCs were established according to the standard of International Tundra Experiment
(ITEX). The C, N and P contents and C:N:P ratios in soils and leaves of Dryas octopetala var. asiatica, Vaccinium
uliginosum, Rhododendron aureum were measured during growing season (July to September).
Important findings Warming increased the soil N and P contents by 5.88% and 4.83%, respectively, but reduced
the C content by 13.19%. The contents of C, N and P in leaves showed significant variations for plants in both
OTCs and control plots during growing season. The P content in V. uliginosum, R. aureum was increased by
10.34% and 12.87%, respectively, but decreased by 16.26% in D. octopetala var. asiatica, by warming. The C:N
ratio in leaves of D. octopetala var. asiatica and R. aureum grown in OTCs showed an increasing trend. Warming
resulted in increases in soil available N and P. The ratio of C:N in the three plants, the P content in R. aureum and
V. uliginosum, and the ratio of C:P in D. octopetala var. asiatica were significantly affected by warming. The re-
sults indicate that warming would increase the P limitation to plant growth in this area. The pattern and magnitude
of leaf stoichiometry of the three tundra plant species respond differently to warming in Changbai Mountain.
Key words C, N, P, tundra, warming
温度是影响植物生长的关键因素, 温度升高能
改变植物的生理特性(蒋高明, 2005; Borjigidai et al.,
2009)。据联合国气候变化专门委员会(IPCC)(2013)
第五次气候变化评估报告, 2003–2013年大气平均温
942 植物生态学报 Chinese Journal of Plant Ecology 2014, 38 (9): 941–948
www.plant-ecology.com
度比1900–1950年上升了0.78 ℃, 全球变暖对冰冻
圈影响显著。高纬度高海拔地区生长的植物受到低
温(Bliss, 1962; Körner, 1999)和养分(Callaghan et al.,
1995; Klanderud & Totland, 2005)的共同限制, 土壤
温度升高能加快土壤微生物分解, 使土壤矿化增加,
进而改善土壤的养分状态(Nadelhoffer et al., 1991;
White et al., 1999), 促进植物生长。
氮(N)、磷(P)是限制植物生长的最主要的两种
元素(Reich & Oleksyn, 2004)。叶片的N、P含量在一
定程度上可表征高山苔原地区土壤N、P的供应状况
(He et al., 2008)。N:P值的大小常用作指示植物生长
受N、P中哪种元素限制, 当P素缺乏、N素含量较高
时, N:P比值相对较高; 反之, N素缺乏、P素较丰富
时 , N:P值就会降低 (Aerts & Chapin III, 1999;
Güsewell, 2004)。温度升高, 会改变叶片的N含量。
由于研究区域、增温方式、实验材料不同, 温度升
高对植物叶片总N含量的影响没有取得一致的结果,
有升高(Idso et al., 1987)、降低(Nybakken et al.,
2011) 或无明显变化(Chapin III et al., 1995)等情况。
Chapin III和Oechel (1983)发现, 生长在温度较低环
境的高山苔原植物叶片有较高的N、P含量; 而生长
在温度相对较高地区的植物生长更易受到P元素的
限制(Chadwick et al., 1999; Richardson et al., 2004)。
Kaarlejärvi等(2012)研究了增温对北欧林线交错带
笃斯越桔(Vaccinium uliginosum)叶片养分含量的影
响 , 发现增温使笃斯越桔叶片P含量降低 ; 但
Sardans等(2008)、Sardans和Peñuelas (2013)发现增温
使地中海灌木Erica multiflora叶P含量增加了42%。
Kudo等(1999)发现温度升高使叶片的碳(C)含量降
低, 这与Sardans等(2008)、Sardans和Peñuelas (2013)
对地中海Erica multiflora叶片C含量的研究结果一
致, 叶C含量降低可能是C从叶到根的再分配所致
(Arft et al., 1999)。C:N和C:P在一定程度上可反映单
位养分供应量所能达到的生产力, 因此植物的C、
N、P化学计量比值可以在一定程度上反映增温条件
下的养分状况及养分限制格局(He et al., 2008)。
北极及北方高纬度地区土壤拥有全球50%的有
机C储量, 以及大量目前无法被植物利用的有机N
(Nadelhoffer et al., 1991)。低温限制了土壤中微生物
的分解和有机质的矿化以及土壤中N的释放, 所以N
可能是苔原植被生长的限制因素, P可能是共同限制
因素(Hobbie & Chapin III, 1998)。温度升高可增加土
壤C、N的矿化(Rustad et al., 2001), 进而增加土壤可
利用N的含量(Chapin III et al., 1995), 将会对北方地
区植物的生长产生积极的影响(Keyser et al., 2000)。
苔原植被主要以多年生矮小灌木为主, 其生长
环境接近于植物的生理忍耐极限, 因此苔原植被对
温度变化极为敏感。本研究以长白山苔原代表植物
笃斯越桔、牛皮杜鹃(Rhododendron aureum)、东亚
仙女木(Dryas octopetala var. asiatica)为实验对象,
研究生长季增温是否会改变这3种植物叶片和土壤
C、N、P含量及其比值, 评价3种植物叶片C、N、P
含量对增温的响应是否一致。
1 材料和方法
1.1 研究地概况
试验地位于吉林省长白山国家自然保护区苔原
生态系统(127.67°–128.27° E, 41.58°–42.42° N, 海
拔2 028 m), 属于苔原-冰缘型气候, 常年低温, 年
平均气温–7.3 ℃, 冬季漫长, 寒冷而干燥, 夏季短
暂, 凉爽而潮湿, 全年多云雾(杨美华, 1981)。年降
水量1 400–1 800 mm, 降水量主要集中在6–9月, 积
雪时间达6个月以上。苔原植被主要为笃斯越桔、牛
皮杜娟、东亚仙女木、黑穗薹草(Carex atrata)、倒
根蓼(Polygonum ochotense)等, 其中笃斯越桔、牛皮
杜鹃和东亚仙女木为苔原生态系统优势物种, 其平
均覆盖度分别为29%、7%和56%。
1.2 实验设计
根据国际苔原计划 (International Tundra Ex-
periment, ITEX)标准, 2010年6月, 在长白山苔原带
建立 8个正六边形开顶箱 (OTC)被动增温系统
(Marion et al., 1997a, 1997b)。箱体高45 cm, 底边长
65 cm。开顶箱的增温原理是: 由于有机玻璃的阻挡,
箱内风速降低, 热量不易散失, 加之玻璃纤维可以
使红外线更好地穿过, 使箱内温度升高(Debevec &
MacLean, 1993)。开顶箱内外安装自动控制系统, 记
录光合有效辐射、空气和土壤温湿度(HOBO Data
Logger), 土壤传感器分别放置于地下5 cm和10 cm
处 , 同时在开顶箱附近设置同样面积的8块对照
(CK)样地。由于长白山苔原特殊的气候条件, 冬季
风大低温, 为避免箱体被积雪压垮或被强风吹散,
增温仅在生长季(6月初至9月末)进行。
1.3 样品采集
2013年7月6日、8月7日、9月2日, 在开顶箱和
江肖洁等: 增温对苔原土壤和典型植物叶片碳、氮、磷化学计量学特征的影响 943
doi: 10.3724/SP.J.1258.2014.00088
对照样地内分别取3种植物的叶片, 取回后立即于
100 ℃杀青, 并于60 ℃下烘干至恒重, 粉碎过筛,
备用。土壤样品仅在生长季末9月2日分别取开顶箱
和对照样地0–10 cm土层, 风干, 过筛待测。
1.4 研究方法
全N采用浓H2SO4-H2O2进行消煮, 靛酚蓝比色
法测定; P含量的测定用钼锑抗比色法; C含量的测
定采用重铬酸钾和硫酸(K2CrO7-H2SO4)氧化法(鲍
士旦, 2008)。
1.5 数据分析
利用SPSS 17.0软件, 采用三因素方差分析法分
析整个生长季不同处理(增温与对照)、不同时间(不
同月份) 以及不同物种间(笃斯越桔、牛皮杜娟、东
亚仙女木) C、N、P含量及其比值的差异; 采用单因
素方差分析法分析每个月开顶箱与对照间各指标的
差异。采用Origin 8.5软件进行作图。
2 结果和分析
2.1 开顶箱增温效应
2013年生长季, 开顶箱内平均空气温度比对照
样地增加1.41 ℃, 空气湿度增加1.19%, 地下5 cm
和10 cm土壤温度分别增加1.74 ℃和1.78 ℃ (表1)。
2.2 增温对土壤C、N、P含量的影响
增温明显改变了土壤C、N、P含量。与对照相
比 , 增温使土壤N和P含量分别增加了5.88%和
4.83%, 但使土壤C含量降低了13.19% (表2)。
2.3 增温对3种植物叶C、N、P含量及其比值的影响
增温明显改变了牛皮杜鹃和笃斯越桔叶片的P
含量以及C:N的比值, 同时对东亚仙女木的C:N和
C:P比值也产生了显著影响(表3)。增温使笃斯越桔
和东亚仙女木的P含量分别提高了10.34%和12.87%,
但牛皮杜鹃的P含量降低了16.26%, 增温对3种植物
的C、N含量没有产生显著影响。温度升高使牛皮杜
鹃和东亚仙女木的C:N比值分别增加了32.86%和
17.79%, 笃斯越桔降低了12.15%, 3种植物的N:P比
值在增温处理下没有表现出显著性差异 (p >
0.05)(表3)。
2.4 增温和对照条件下叶片C、N、P含量及其比值
的动态变化
叶片的C、N、P含量及其比值均呈现明显的月
份波动(表3)。7–9月, 增温与对照条件下3种植物叶
C含量变化范围分别为39.95%–44.01%和37.39%–
43.96%。8月份笃斯越桔C含量最高, 而东亚仙女木
叶C含量最低(图1)。3种植物叶N含量在7月份含量
最高, 而后呈降低趋势。对P含量来说, 牛皮杜鹃叶
片P含量随生长逐渐升高, 而笃斯越桔和宽叶仙女P
含量随生长先升高后降低。
增温与对照条件下3种植物叶片的C:N比值在8
月份最大, 9月降低, 但东亚仙女木叶片的C:N值9月
份略有增加。增温与对照条件下笃斯越桔和东亚仙
女木的C:P、N:P比值先降低后上升, 但牛皮杜鹃的
C:P、N:P比值在生长季一直呈下降趋势, 其C:P、
表1 生长季增温与对照条件下空气温度、空气相对湿度、地下5 cm和10 cm土壤温度
Table 1 Air temperature, air relative humidity, soil temperature at 5 cm and 10 cm depths in the open-top chambers and control
plots during growing season
开顶箱 Open-top chamber 对照样地 Control plot 差值 Difference
空气温度 Air temperature (°C) 24.13 22.72 +1.41
空气相对湿度 Air relative humidity (%) 86.56 85.37 +1.19
地下5 cm土壤温度 Soil temperature at 5 cm depth (°C) 22.66 20.92 +1.74
地下10 cm土壤温度 Soil temperature at 10 cm depth (°C) 21.74 19.96 +1.78
表2 增温与对照条件下土壤碳(C)、氮(N)、磷(P)含量(平均值±标准偏差)
Table 2 Contents of carbon (C), nitrogen (N) and phosphorus (P) of soil in open-top chambers and control plots (mean ± SD)
开顶箱 Open-top chamber 对照样地 Control plot
总碳含量 Total carbon content (%) 6.14 ± 3.12A 6.95 ± 2.07B
总氮含量 Total nitrogen content (%) 0.40 ± 0.09A 0.37 ± 0.03B
总磷含量 Total phosphorus content (%) 0.56 ± 0.11A 0.54 ± 0.03B
同行不同字母表示差异性显著(p < 0.05)。
Different letters in the same row indicate significant difference at the level of 0.05.
944 植物生态学报 Chinese Journal of Plant Ecology 2014, 38 (9): 941–948
www.plant-ecology.com
表3 双因素方差法分析增温、月份对牛皮杜鹃、笃斯越桔和东亚仙女木叶片碳(C)、氮(N)、磷(P)含量及其比值的影响
Table 3 Effects of warming and month on carbon (C), nitrogen (N) and phosphorus (P) contents and their ratios in leaves of Rho-
dodendron aureum, Vaccinium uliginosum and Dryas octopetala var. asiatica using two-way ANOVA
变异来源 Source of variation C N P C:N C:P N:P
牛皮杜鹃 Rhododendron aureum
增温 Warming (W) ns ns * * ns ns
月份 Month (M) ** ** ** ** ** **
增温×月份 W × M ns ns ** ns * *
笃斯越桔 Vaccinium uliginosum
增温 Warming (W) ns ns * * ns ns
月份 Month (M) ** ** ** ** ** **
增温×月份 W × M ns ns ** ns * *
东亚仙女木 Dryas octopetala var. asiatica
增温 Warming (W) ns ns ns * * ns
月份 Month (M) ** ** ** ** ** **
增温×月份 W × M ns ns ** ns * *
*, p < 0.05; **, p < 0.01; ns, p > 0.05.
图1 生长季增温与对照条件下牛皮杜鹃、笃斯越桔和东亚仙女木叶片碳(C)、氮(N)、磷(P)含量(平均值±标准偏差)。不同字
母表示每个月份不同处理间差异显著(p < 0.05)。
Fig. 1 Carbon (C), nitrogen (N) and phosphorus (P) contents in leaves of Vaccinium uliginosum, Rhododendron aureum, and Dryas
octopetala var. asiatica grown in open top chambers (OTC) and control plots during growing season (mean ± SD). Different letters
indicate significant difference between OTC and control in the same month at the level of 0.05.
江肖洁等: 增温对苔原土壤和典型植物叶片碳、氮、磷化学计量学特征的影响 945
doi: 10.3724/SP.J.1258.2014.00088
表4 生长季增温与对照条件下牛皮杜鹃、笃斯越桔和东亚仙女木叶片C:N、C:P、N:P比值(平均值±标准偏差)
Table 4 C:N, C:P, and N:P ratios in Vaccinium uliginosum, Rhododendron aureum, and Dryas octopetala var. asiatica grown in
open top chambers and control plots during growing season (mean ± SD)
C:N C:P N:P 月份
Month 开顶箱
Open-top chamber
对照样地
Control plot
开顶箱
Open-top chamber
对照样地
Control plot
开顶箱
Open-top chamber
对照样地
Control plot
7 20.02 ± 0.23A 9.11 ± 0.92B 513.78 ± 8.41A 346.75 ± 1.19B 27.57 ± 1.19A 38.45 ± 4.00B
8 32.16 ± 2.69A 27.73 ± 0.20B 326.42 ± 19.08A 281.95 ± 11.56B 11.14 ± 0.50A 10.54 ± 0.40B
牛皮杜鹃
Rhododendron
aureum
9 27.14 ± 0.17A 22.68 ± 0.91B 246.72 ± 1.32A 223.45 ± 0.14B 9.09 ± 0.03A 10.20 ± 0.19B
7 14.79 ± 0.72A 21.31 ± 0.30B 424.96 ± 17.46A 457.97 ± 11.19B 33.63 ± 1.43A 20.70 ± 0.07B
8 37.60 ± 0.81A 32.28 ± 0.13B 344.74 ± 7.67A 376.66 ± 1.67B 9.53 ± 0.49A 11.86 ± 0.16B
笃斯越桔
Vaccinium
Uliginosum
9 20.21 ± 1.19A 24.57 ± 0.08B 460.24 ± 18.50A 530.88 ± 41.74B 20.66 ± 1.66A 23.52 ± 0.60B
7 16.66 ± 0.10A 13.70 ± 0.10B 309.90 ± 4.85A 375.65 ± 0.68B 19.36 ± 1.15A 27.42 ± 0.05B
8 27.43 ± 0.38A 26.20 ± 0.32B 207.67 ± 3.59A 263.74 ± 3.10B 7.57 ± 0.14A 10.18 ± 0.05B
东亚仙女木
Dryas octopetala
var. asiatica
9 28.49 ± 1.02A 22.60 ± 0.60B 365.14 ± 0.03A 317.03 ± 11.65B 12.13 ± 0.24A 15.80 ± 0.86B
相邻两列同行不同字母表示差异显著(p < 0.05)。
Different letters in the same row of adjacent columns for a given variable indicate significant difference at the level of 0.05.
N:P值的变化范围分别是 207.67–513.78和 7.57–
38.45 (表4)。
2.5 增温对不同植物叶C、N、P含量及其比值的影响
增温明显改变了3种植物叶片的C:N值(表3),
整个生长季, 增温条件下的牛皮杜鹃、东亚仙女木
叶片的C:N值分别比对照高33.27%和16.13%, 而笃
斯越桔叶片的C:N值比对照低7.1% (表4)。增温明显
改变了牛皮杜鹃和笃斯越桔的P含量, 分别比对照
低15.83%和高12.21%。增温条件下, 东亚仙女木叶
片P含量的平均值最高, 分别比牛皮杜鹃和笃斯越
桔叶P含量高16.26%和34.02% (图1)。
增温处理下, 笃斯越桔的C:P和N:P值最大, 但
C:N值最小, 其C含量也最高, 比牛皮杜鹃和东亚仙
女木分别高6.49%和3.4%。对照条件下, 笃斯越桔的
P含量最低, C含量最高, 分别比牛皮杜鹃和东亚仙
女木高5.20%和7.52%。对照条件下, 笃斯越桔的
C:N和C:P值最高, 牛皮杜鹃的C:N和C:P值最低, 但
N:P值最高, 比笃斯越桔和东亚仙女木分别高5.56%
和10.28% (表4)。
3 讨论
本研究中增温使土壤总C含量降低。Xu和Wan
(2010)也发现增温使青藏高原土壤有机质含量下降
了12.7%, 可能增温促进了土壤微生物对有机质的
分解, 使得土壤C含量降低。但也有增温使土壤有机
质含量升高的研究结果, 如Carrillo等(2011)研究发
现, 一年增温(+1.5 °C)处理使土壤中易降解的有机
碳含量升高, 难降解的有机碳含量没有明显变化,
所以土壤C对增温的响应会随区域以及植被类型不
同而呈现不同响应。在苔原生态系统中, N是最常见
的限制元素, P可能是单一或共同限制因素(Hobbie
& Chapin III, 1998)。本研究中, 土壤N含量增加
5.88%, P含量增加8.11%, 增温促进了土壤N、P的矿
化, 使得可利用的N、P含量增加, N、P的增加将更
有利于植物的生长(Gordon et al., 2001; Welker et al.,
2005)。
Reich和Oleksyn (2004)在全球尺度上分析得出
温度升高会降低植物叶片的养分含量。本研究中,
增温使牛皮杜鹃叶片N和P含量分别降低了54.21%
和16.26%, 东亚仙女木的N含量降低19.97%, 而笃
斯越桔和东亚仙女木叶片的P含量分别升高了
10.34%和12.87% (图1)。Kaarlejärvi等(2012)发现增
温使北欧林线交错带笃斯越桔叶片N、P含量都降
低, 而Erica multiflora叶片P含量增加了42% (Sar-
dans et al., 2008; Sardans & Peñuelas, 2013)。不同植
物对增温响应的方向与尺度不同。与东亚仙女木和
笃斯越桔相比, 牛皮杜鹃对增温更加敏感。增温导
致土壤N、P含量增加, 但并未明显增加植物叶片的
N含量。可能是由于植物对土壤养分元素的吸收具
有一定的选择性, 但土壤养分元素的含量及其比值
必须要满足植物的生长所需, 也就是说, 土壤养分
元素含量可以在一定条件下处于过剩状态(Marion
et al., 1989)。但即使是同种植物在不同生长条件下
对增温也会存在不同响应, 不同植物生长在相同环
946 植物生态学报 Chinese Journal of Plant Ecology 2014, 38 (9): 941–948
www.plant-ecology.com
境条件下, 对增温的响应方式也会存在一定差异。
叶片养分含量的动态变化与植物生长状态是息
息相关的, 增温与对照条件下牛皮杜鹃、笃斯越桔
和东亚仙女木叶片的C、N、P及其比值在生长季呈
现明显的月份变化(表3), 且增温与对照条件下的变
化趋势相同。苔原生态系统生长季很短, 9月份植物
处于生长末期, 对多年生苔原矮小灌木来说, 落叶
前植物会最大限度地回收养分, 但牛皮杜鹃叶片的
P含量在9月份却呈上升趋势, 明显不同于笃斯越桔
和东亚仙女木, 说明牛皮杜鹃对P元素的回收可能
相对较低, 其生长受P元素限制也可能相对较小。
增温对3种植物叶片的C:N值以及东亚仙女木
的C:P值产生显著影响(表3)。C:N、C:P值大小表示
植物吸收单位养分元素含量所同化C的能力, 在一
定程度上可以反映植物体养分元素的利用率。增温
处理下, 3种植物的C:N平均值(表4)均高于全球水平
的22.5 (Elser et al., 2000), 说明增温使高山苔原地
区3种植物具有较高的养分利用率。在生长季不同时
期, 增温对3种植物叶的P含量以及C:P、N:P值的影
响不同(表3), 由于植物叶C含量较高, 变异较小,
因此P含量变化是影响C:P的主要因素, C:P值随P含
量的降低(升高)而升高(降低)。增温条件下, 牛皮杜
鹃的P含量呈降低趋势, C:P值在生长季内始终高于
对照组。C:P值增加会降低土壤微生物对凋落物的分
解速率, 进而减缓养分的周转时间, 导致植物生长
P限制的加剧(Hobbie, 1996; Welker et al., 2005)。
植物的最适生长要求一定的N:P比例(Dijkstra
et al., 2012), 且N:P值的大小在一定程度上可以指
示该地区的群落结构和功能(Güsewell, 2004), 同时
也可反映环境对植物生长的养分供应状况。当N:P >
16且P含量<0.1%时, 植物生长受P的限制; 当N:P <
14且N含量<2%时, 植物生长受N限制; 比值介于14
和16之间、P含量< 0.1%、N含量<2%时, 植物生长
受N、P的共同限制(Koerselman & Meuleman, 1996;
Drenovsky & Richards, 2004)。8月份, 3种植物的N:P
比小于或接近10, 且N含量<2%, 说明在苔原植物
旺盛生长时期, 植物消耗了大量N (孙书存和陈灵
芝, 2001; Freschet et al., 2010), 其C:N比值也呈现上
升趋势, 说明植物通过提高自身的养分利用率以减
缓N素的限制。本研究中, 增温条件下笃斯越桔在7
和9月份的P含量增加, 但其生长仍受到P素的限制
(N:P > 16, P含量<0.1%), 且C:N和C:P值呈现降低趋
势 , 这一变化趋势与Tessier和Raynal (2003)以及
Güsewell (2004)的研究结果相反, 他们的结果表明:
当植物叶中的N、P稀缺时, C:N和C:P值呈现上升趋
势。N、P含量的增加降低了植物对养分的利用率,
同时N增加的量大于P增加的量, 由于较高的N含量
对植物P的吸收起抑制作用(Sardans et al., 2004;
Harpole et al., 2011), 所以表现为P元素是限制
因素。
我们的研究结果是对长白山苔原生态系统进行
连续3个生长季增温而得出的, 全球变暖可能伴随
着夏季变暖和(或)冬季变暖, 甚至是温度的激烈波
动, 因此, 植物叶片养分对温度升高的响应模式和
尺度极其复杂, 而且短期响应可能不同于长期响应,
如我们的研究结果与Hansen等 (2006)和Walker等
(2006)的长期模拟增温实验有所不同。要深入准确
地揭示在未来气候变暖条件下苔原植被的响应模
式, 就必须建立长久的观测平台和开展全方位的
监测。
基金项目 国家自然科学基金(31170461)。
致谢 感谢中国科学院长白山森林生态系统国家野
外科学观测研究站王秀秀在野外实验工作中给予的
帮助。
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