叶片净光合速率(Pn)是研究光合作用机理的基本尺度; 而群落净光合速率(Pc)是研究群落光合能力及其与外部环境因子间关系的更好尺度, 特别是区域乃至全球尺度碳循环的研究, 需要将叶片尺度的生理生态模型扩展到冠层尺度。理论上, 群落内所有叶片的累积Pn与实测群落净气体交换速率(NCE)是相等的, 但在野外实际观测中, 两者之间的相互关系目前尚未见报道。该文选取敖汉苜蓿(Medicago sativa ‘Aohan’)人工草地, 采用美国LI-COR公司生产的便携式光合测定系统LI-6400测定Pn, 结合叶面积指数等参数推算Pc, 利用LI-8100连接同化箱测定生态系统净气体交换速率(NEE), 加上土壤呼吸速率, 得到NCE。结果表明: Pc为3.52 μmol CO2·m-2·s-1, 与实测NCE (3.56 μmol CO2·m-2·s-1)基本相等。这表明: 可利用Pn, 结合叶面积指数、群落叶片数目、健康叶片比例和群落可接收有效光照的平均比例等4个关键参数, 准确地换算Pc。然而, 利用同化箱式法测定群落呼吸速率时, 不可避免地会包含土壤呼吸, 所以在观测NCE时, 需要同时测定土壤呼吸。此外, 在冠层模型中, 群落垂直结构和光量子的非线性响应不可忽视。
Leaf net photosynthesis is crucial for detecting the mechanism of photosynthesis, whereas community net photosynthesis is useful for understanding the photosynthetic capacity of communities and its relationship with environmental factors. In particular, we need to scale up eco-physiological models from leaf scale to canopy level to study carbon cycling at regional or global scale. We hypothesized that accumulated leaf net photosynthetic rate (Pc) at community scale, i.e., calculated based on leaf net photosynthetic rate (Pn) and leaf area index (LAI), equals to measured net community CO2 exchange (NCE). The purpose of this study is to verify this hypothesis. Our field study was carried out in Duolun, Nei Mongol, China, where we constructed single-species communities by sowing Medicago sativa ‘Aohan’ seeds in three plots (3 m × 5 m) on May 30, 2012. On August 16, 2014, Pn of five healthy leaves of M. sativa ‘Aohan’ in each plot were measured with a LI-6400 portable photosynthesis system at 10:00, and net ecosystem CO2 exchange (NEE) in each plot was measured simultaneously with a LI-8100 system connected with a assimilation chamber (0.5 m × 0.5 m × 0.5 m). Pc was calculated based on Pn, number of leaves (n), LAI percentage of healthy leaves (r) and percentage of received effective light by leaves (m). NCE was derived from NEE and ecosystem respiration rate (Reco). Pc was 3.52 μmol CO2·m-2·s-1, and very close to NCE (3.56 μmol CO2·m-2·s-1), suggesting that leaf-scale photosynthesis may accurately predict community-scale photosynthesis. However, our method could not separate community respiration from soil respiration, and future studies, should be designed to counteract this effect. Scaling up from leaf photosynthesis to community photosynthesis should also consider vertical structure of communities and nonlinear responses of leaf photosynthesis to changes in light quantum.
全 文 :植物生态学报 2015, 39 (9): 924–931 doi: 10.17521/cjpe.2015.0089
Chinese Journal of Plant Ecology http://www.plant-ecology.com
——————————————————
收稿日期Received: 2015-03-24 接受日期Accepted: 2015-08-13
* 通讯作者Author for correspondence (E-mail: tanghp@bnu.edu.cn)
叶片和群落尺度净光合速率关系的探讨
唐海萍* 薛海丽 房 飞
北京师范大学地表过程与资源生态国家重点实验室, 北京师范大学资源学院, 北京 100875
摘 要 叶片净光合速率(Pn)是研究光合作用机理的基本尺度; 而群落净光合速率(Pc)是研究群落光合能力及其与外部环境
因子间关系的更好尺度, 特别是区域乃至全球尺度碳循环的研究, 需要将叶片尺度的生理生态模型扩展到冠层尺度。理论上,
群落内所有叶片的累积Pn与实测群落净气体交换速率(NCE)是相等的, 但在野外实际观测中, 两者之间的相互关系目前尚未
见报道。该文选取敖汉苜蓿(Medicago sativa ‘Aohan’)人工草地, 采用美国LI-COR公司生产的便携式光合测定系统LI-6400测
定Pn, 结合叶面积指数等参数推算Pc, 利用LI-8100连接同化箱测定生态系统净气体交换速率(NEE), 加上土壤呼吸速率, 得
到NCE。结果表明: Pc为3.52 μmol CO2·m–2·s–1, 与实测NCE (3.56 μmol CO2·m–2·s–1)基本相等。这表明: 可利用Pn, 结合叶面积
指数、群落叶片数目、健康叶片比例和群落可接收有效光照的平均比例等4个关键参数, 准确地换算Pc。然而, 利用同化箱式
法测定群落呼吸速率时, 不可避免地会包含土壤呼吸, 所以在观测NCE时, 需要同时测定土壤呼吸。此外, 在冠层模型中, 群
落垂直结构和光量子的非线性响应不可忽视。
关键词 净光合速率, 冠层模型, 尺度上推, 敖汉苜蓿
引用格式: 唐海萍, 薛海丽, 房飞 (2015). 叶片和群落尺度净光合速率关系的探讨. 植物生态学报, 39, 924–931. doi: 10.17521/cjpe.2015.0089
A comparison of measured and calculated net community CO2 exchange: Scaling from leaves
to communities
TANG Hai-Ping*, XUE Hai-Li, and FANG Fei
State Key Laboratory of Earth Surface Processes & Resource Ecology, Beijing Normal University, College of Resources Science & Technology, Beijing Nor-
mal University, Beijing 100875, China
Abstract
Leaf net photosynthesis is crucial for detecting the mechanism of photosynthesis, whereas community net photo-
synthesis is useful for understanding the photosynthetic capacity of communities and its relationship with envi-
ronmental factors. In particular, we need to scale up eco-physiological models from leaf scale to canopy level to
study carbon cycling at regional or global scale. We hypothesized that accumulated leaf net photosynthetic rate
(Pc) at community scale, i.e., calculated based on leaf net photosynthetic rate (Pn) and leaf area index (LAI),
equals to measured net community CO2 exchange (NCE). The purpose of this study is to verify this hypothesis.
Our field study was carried out in Duolun, Nei Mongol, China, where we constructed single-species communities
by sowing Medicago sativa ‘Aohan’ seeds in three plots (3 m × 5 m) on May 30, 2012. On August 16, 2014, Pn of
five healthy leaves of M. sativa ‘Aohan’ in each plot were measured with a LI-6400 portable photosynthesis sys-
tem at 10:00, and net ecosystem CO2 exchange (NEE) in each plot was measured simultaneously with a LI-8100
system connected with a assimilation chamber (0.5 m × 0.5 m × 0.5 m). Pc was calculated based on Pn, number of
leaves (n), LAI percentage of healthy leaves (r) and percentage of received effective light by leaves (m). NCE was
derived from NEE and ecosystem respiration rate (Reco). Pc was 3.52 μmol CO2·m–2·s–1, and very close to NCE
(3.56 μmol CO2·m–2·s–1), suggesting that leaf-scale photosynthesis may accurately predict community-scale pho-
tosynthesis. However, our method could not separate community respiration from soil respiration, and future
studies, should be designed to counteract this effect. Scaling up from leaf photosynthesis to community photosyn-
thesis should also consider vertical structure of communities and nonlinear responses of leaf photosynthesis to
changes in light quantum.
Key words net photosynthetic rate, canopy model, scaling up, Medicago sativa ‘Aohan’
唐海萍等: 叶片和群落尺度净光合速率关系的探讨 925
doi: 10.17521/cjpe.2015.0089
Citation: Tang HP, Xue HL, Fang F (2015). A comparison of measured and calculated net community CO2 exchange: Scaling from
leaves to communities. Chinese Journal of Plant Ecology, 39, 924–931. doi: 10.17521/cjpe. 2015.0089
植物的光合作用是地球上生物生长和繁衍的
基础, 是地球生命系统的能量来源。当前进行的光
合作用研究, 领域日益宽广, 层次愈加深入, 技术
越来越先进(程建和沈允钢, 2011)。世界各国大量的
研究工作集中在植物光合作用的机理反应(Yu et al.,
2002; Wang et al., 2007; 杨娟等, 2008; 孙东宝和王
庆锁, 2014), 深入探讨内部因子和外部环境因子对
光合作用的影响。群落尺度主要开展碳通量及其与
环境之间相互关系研究(Baldocchi, 2003; Xu et al.,
2005; 王海波等, 2014)。群落光合作用对环境因子
的响应不如个体水平上明显(平晓燕等, 2010), 需通
过尺度上推, 将叶片尺度的生理生态模型扩展到冠
层尺度上, 大体分为大叶模型、多层模型和二叶模
型。Farquhar等(1980)提出了叶片光合作用的生化模
型, 为较大尺度光合模型的建立奠定了基础。随后,
Sellers等(1992)和Amthor (1994)提出假设: 单叶尺
度上的模型可以直接应用到冠层水平, 并据此建立
了大叶模型, 随后又发展出多层模型(Leuning et al.,
1995)和双叶模型(Wang & Leuning, 1998), 并得到
了广泛的应用(Rinaldi, 2004; 张弥等, 2006; He et al.,
2013)。冠层尺度的模型模拟可以为区域乃至全球尺
度碳循环的研究提供基础 , 如: SiB (simple bio-
sphere model)(Sellers et al., 1992), GLO-PEM (Prince
& Goward, 1995)、Cfix (Veroustraete et al., 2002)、
E-VPM (vegetation photosynthesis model) (Xiao et al.,
2004)、CFlux (Turner et al., 2006; King et al., 2011)、
CLUE (eddy covariance-light use efficiency)(Yuan et
al., 2007)、VPRM (vegetation production and respi-
ration mode) (Mahadevan et al., 2008)等。
目前常用的群落尺度气体交换的观测方法为
箱式法; 另外, 可以通过上述冠层尺度模型来推算
群落净光合速率(Pc)。但是这些模型中采用的参数
多为生理生化指标(如韧皮部运移物质速率、羧化作
用速率和传输导度等), 参数多且观测比较复杂(张
弥等, 2006)。那么, 如何能够利用叶片尺度净光合
速率以及其他易观测的参数将其换算到群落尺度,
以及换算过程中应该考虑哪些因素?这是本文探讨
的核心问题。为了避免群落多样性增加研究的复杂
性, 本研究选取单一的敖汉苜蓿(Medicago sativa
‘Aohan’)人工草地群落为研究对象, 通过叶片和群
落两个尺度净光合速率的测定, 比较冠层模型自下
而上的假设基础及其推算方法是否合理, 试图找出
二者之间的定量关系, 并确定从叶片尺度上推到群
落以及生态系统尺度过程中的关键参数。
1 材料和方法
1.1 研究区概况
本研究在内蒙古多伦县贮草站试验小区
(42.76° N, 117.21° E)进行, 该地区海拔高度为1 368
m, 属于中温带半干旱向半湿润过渡的大陆性气
候。根据1954–2009年多伦县气象数据统计得到年降
水量为382 mm, 年蒸发量为1 748 mm, 其中6–8月
降水量占全年的70%; 年平均气温为2.3 , ℃ 最高气
温出现在7月, 7月平均气温为19.0 , ℃ 最低气温出
现在1月, 1月平均气温为–17.5 , ℃ 无霜期100天左
右, ≥10 ℃积温为1 917.9 , ℃ 全年以西北风为主,
年平均风速3.6 m·s–1, 年大风日数为67.3天(马骏,
2011)。
研究样地为人工敖汉苜蓿群落, 于2012年5月
30日播种, 小区内共播种3个亚小区, 每个亚小区面
积为15 m2 (3 m × 5 m), 播种方式为条播, 行距为
18.5 cm, 播种深度为2–3 cm, 播种密度为2.25 g·m–2,
群落中光分布比较均匀。试验小区在播种前浇水,
其后无灌溉, 播种前每hm2施用复合肥(NH4)3PO4)
80 kg, 播种后于6月10日、6月30日、7月15日、8月
13日拔除杂草, 在每个亚小区内选择5枚叶片进行
叶片净光合速率(Pn)测定。
1.2 植物群落尺度净光合速率测定
在每个亚小区选择0.5 m × 0.5 m的样方(面积为
0.25 m2), 在降雨过后放入同化箱基座(0.5 m × 0.5
m), 待稳定后开始测定。采用LI-8100 (LI-COR,
Lincoln, USA)连接开路式同化箱对生态系统净气体
交换速率(NEE, μmol CO2·m–2·s–1)进行测定, 透明同
化箱大小为0.5 m × 0.5 m × 0.5 m, 通过同化箱内的
气扇使得气室内气体均匀, 同化箱盖上双层不透光
布罩(外层为白色里层为黑色)测定生态系统呼吸速
率(Reco, μmol CO2·m–2·s–1), 测定时间为2014年8月
16日10:00, 每个亚小区中观测3个重复。在测定NEE
926 植物生态学报 Chinese Journal of Plant Ecology 2015, 39 (9): 924–931
www.plant-ecology.com
的同时, 记录每个重复测定群落内的叶片数目(n),
并估算健康叶片(假设绿色部分叶面积约占60%以
上为健康叶片)占所有叶片的比例(k)。
我们在同一区域的研究结果表明, 土壤呼吸占
生态系统呼吸的61.8%, 故群落净气体交换速率
(NCE)为:
NCE = NEE + 0.618 × Reco
1.3 植物叶片尺度净光合速率测定
叶片与群落尺度净光合速率同时进行测定, 采
用便携式光合测定系统(LI-6400, LI-COR, Lincoln,
USA), 利用开路法测定植株完全展开叶片的净光
合速率(Pn, μmol CO2·m–2·s–1), 每个亚小区选取群落
中健康、长势一致、无病斑、照光均一(保证光合活
性高)的5片叶子进行重复观测, 测定时间为2014年
8月16日10:00。每次测定时, 由系统自动记录相关
参数的值, 求其平均值作为该时刻的净光合速率值,
测 定 光 合 速 率 时 光 合 有 效 辐 射 为 1 721.09
μmol·m–2·s–1, 空气温度为26.24 ℃、大气相对湿度为
33.40%、叶周围CO2浓度为383.94 mol·L–1。
1.4 叶面积测定
采用方格法, 每个亚小区选择大、中、小15片
有效叶片, 将叶片的轮廓描在标准计算纸(最小方
格的规格为1 mm × 1 mm)上, 统计每片叶轮廓占的
小方格数(达到或超过半格的算1格, 不足半格的舍
去), 得到每片叶片的叶面积, 将所有叶片叶面积平
均即得到该亚小区的叶片平均叶面积指数(LAI)。
1.5 数据换算
测定的Pn, 通过以下换算公式得到Pc:
Pc = (Pn× LAI × n × k × m) / (10000 × 0.25) (1)
其中, n为每个样地内叶片总数; k为健康叶片占所有
叶片的比例; m为群落中所有叶片可接收有效光照
的平均比例(因为测定所选叶片为活性最高的叶片,
考虑到植株间的遮阴程度以及叶片角度, 群落光合
能力估算中引入该修正参数), m取值为0.7, 群落面
积为0.25 m2。
理论上, 群落光合速率主要包括植物叶片光合
速率和茎秆光合速率, 其相互关系如下:
NEE = P – Reco (2)
P = Pl + Pt (3)
Pl = (Pn × LAI × n × k × r) / (10000 × 0.25) + Rl
(4)
Pt = Pt′ + Rt (5)
其中NEE为生态系统净气体交换速率, Reco为生态系
统呼吸速率, P为群落内植物总光合速率, Pl为叶片
总光合速率, Pt为植物茎秆总光合速率, Rl为群落内
叶片总呼吸速率, Pt′为植物茎秆净光合速率, Rt为植
物茎秆总呼吸速率。
实际观测中, 呼吸速率为生态系统的总呼吸速
率, 主要包括自养呼吸和异养呼吸两部分, 其相互
关系如下:
Reco= Rl + Rs + Rt (6)
假设植物茎秆光合和呼吸两部分可以相互抵消,
根据以上的换算可以得出群落内植物叶片和茎秆总
呼吸速率,即群落呼吸速率(Rc):
Rc = Rl + Rt = Reco – (Pc – NEE) (7)
2 研究结果
2.1 叶片和群落尺度光合能力比较
根据表1, 亚小区1和亚小区3的Pn无显著差异,
但由于叶片数分别为650和740, 以及不同比例的健
康叶片数, 导致两个亚小区Pc差异显著, 相差2.16
μmol CO2·m–2·s–1。亚小区2叶片数为580, 其Pn显著
低于其他两个亚小区(p < 0.05), Pc也小于其他两个
亚小区。
三个亚小区Pc远低于Pn, 只占到Pn的20.1%–
表1 敖汉苜蓿叶片净光合速率(Pn)和群落净光合速率(Pc)比较
Table 1 The comparison of leaf net photosynthetic rate (Pn) and accumulated leaf net photosynthetic rate (Pc) of Medicago sativa ‘Aohan’
亚小区
Sub plot
Pn (μmol
CO2·m–2·s–1)
叶片数
No. of leaves
平均叶面积
Average leaf area
(cm2)
健康叶片比例
Percentage of
healthy leaves
叶片接受有效光照比例
Percentage of received
effective light by leaf
Pc (μmol
CO2·m–2·s–1)
Pc / Pn
(%)
亚小区1 Sub plot 1 15.025b 650 3.113 0.4 0.7 3.41b 22.7
亚小区2 Sub plot 2 7.854a 580 2.477 0.5 0.7 1.58a 20.1
亚小区3 Sub plot 3 14.536b 740 3.081 0.6 0.7 5.57c 38.3
平均 Average 12.472 656 2.890 0.5 0.7 3.52 27.0
不同小写字母表明差异显著(p < 0.05)。
Different lowercase letters indicate significant differences (p < 0.05).
唐海萍等: 叶片和群落尺度净光合速率关系的探讨 927
doi: 10.17521/cjpe.2015.0089
表2 敖汉苜蓿实测群落净气体交换速率(NCE)与群落净光合速率(Pc)比较
Table 2 The comparison of measured net community CO2 exchange (NCE) and accumulated leaf net photosynthetic rate (Pc) of Medicago sativa ‘Aohan’
亚小区
Sub plot
Pc (μmol
CO2·m–2·s–1)
NCE (μmol
CO2·m–2·s–1)
生态系统净气体交换速率
Net ecosystem CO2 ex-
change (NEE, μmol
CO2·m–2·s–1)
生态系统呼吸速率
Ecosystem respiration
rate (Reco, μmol
CO2·m–2·s–1)
群落呼吸速率
Community respiration
rate (Rc, μmol
CO2·m–2·s–1)
NEE/Pn
(%)
Pc/NEE
亚小区1 Sub plot 1 3.41 3.38 1.07 3.74 1.40 7.1 3.2
亚小区2 Sub plot 2 1.58 1.48 0.98 0.81 0.21 12.5 1.6
亚小区3 Sub plot 3 5.57 5.82 2.38 5.56 2.37 16.4 2.3
平均 Average 3.52 3.56 1.48 3.37 1.33 12.0 2.4
38.3%, 平均占到Pn的27.0%, 即群落尺度净光合速
率较叶片尺度净光合速率下降了73% (表1)。
2.2 换算的Pc的验证
根据表2, 敖汉苜蓿叶片尺度测定的Pn和换算
的Pc都大于NEE (1.48 μmol CO2·m–2·s–1), 其中Pc约
为NEE的1.6–3.2倍, 为Pn的7.1%–16.4%; 推算得到
的敖汉苜蓿Pc与测定的NCE基本相等; 3个亚小区平
均生态系统呼吸速率为3.37 μmol CO2·m–2·s–1, 群落
呼吸速率为1.33 μmol CO2·m–2·s–1。
3 讨论
3.1 Pn与Pc的关系
本研究结果表明, 敖汉苜蓿群落净光合速率为
3.52 μmol CO2·m–2·s–1, 为Pn (12.472 μmol CO2·m–2·s–1)
的27.0%, 低于其他学者在内蒙古地区对敖汉苜蓿
Pn的研究结果(王建丽等, 2006; 张丽妍等, 2008)。
除了由于苜蓿品种不同外, 本研究取样的人工草地
刚建植2年, 植物生长还未达到光合和呼吸作用的
旺盛期。在用箱式法测定群落净气体交换速率时,
测定的群落呼吸实际上是植物自养呼吸和异养呼吸
速率的总和, 所以在得出NCE时, 要把土壤呼吸消
耗部分加入。本研究结果表明, 土壤呼吸约占生态
系统呼吸速率的60.6%; 另外, 有研究显示在内蒙
古羊草生态系统中土壤呼吸占生态系统呼吸的59.4%
(耿元波和罗光强, 2010), 可见该部分不容忽视。
虽然亚小区2的Pn显著性低于其他亚小区, 但
验证结果表明3个亚小区叶片尺度净光合速率推算
得到的群落尺度净光合速率与实际观测到的群落净
气体交换速率均基本相等, 表明即使不同水平的叶
片净光合速率, 通过本文提出的推算方法均可准确
得到群落尺度净光合速率。叶面积指数在尺度转换
过程中为重要参数; 有研究表明叶面积指数对草地
NEE的解释份额达到86% (张文丽等, 2008)。此外,
叶片的叶位、叶龄, 以及同一叶片的不同部位的光
合速率都明显不同(Zhang et al., 2005), 而且不同叶
片取向或着生角度(平展和直立)也对叶片的光合速
率有影响(陈悦等, 2002)。因此, 除了叶面积参数和
叶片数目n, 同时引入了健康叶片占所有叶片的比
例k和群落可接收有效光照的平均比例m, 可通过这
些参数, 将叶片尺度净光合速率准确推算到群落尺
度, 与冠层模型相比, 参数更加简化和容易获得。
另外, 本研究中没有考虑敖汉苜蓿茎秆的光合
呼吸过程, 但有研究表明在农作物和林木中茎秆等
非叶器官光合作用在作物生产中同样存在很重要的
作用, 甚至在叶衰退的时候, 茎秆等非叶器官仍然
可以保持较高的光合能力(Wang et al., 2001; 李朝
霞等, 2004; 王文杰等, 2007), 在草地群落中, 该部
分在叶片与群落尺度净光合速率转换过程中的作用
如何, 需开展更加细致的观测和研究才能确定。
3.2 对冠层模型研究的启示
本研究在一定程度上揭示了冠层模型中存在的
问题, 比如大叶模型的应用中, 以下原因会导致模
拟结果偏高: (1)大叶模型是将冠层看作叶片的拓展,
并且没有对冠层进行受光照叶片和被遮阴叶片的区
分, 而已有的研究表明, 冠层不同高度上的微环境
存在差别, 由此会造成模拟结果的偏差(于强等,
1999; 王靖等, 2008), 且大叶模型的计算结果比双
叶模型高出13% (陶寅, 2007); 多叶模型和二叶模
型是在大叶模型的基础上发展而来的, 多叶模型提
出了冠层的垂直结构, 而二叶模型在多叶模型的基
础上将冠层分为受光照的叶片与被遮阴的叶片两大
部分, 避免了以上问题。本文中引入了参数m, 即考
虑对冠层进行受光照叶片和被遮阴叶片的区分 ,
若不引入该参数, 估算结果将增加42.8%, 可见在
具体从叶片尺度上推到群落尺度的模型中应考虑群
落的垂直结构。(2)需考虑叶片对光量子的非线性响
应。在实际测定叶片净光合的过程中, 往往选取刚
刚完全展开的光合活性最高的叶片为样品叶(许大
928 植物生态学报 Chinese Journal of Plant Ecology 2015, 39 (9): 924–931
www.plant-ecology.com
全, 2006), 但是实际上群落中每个叶片的光合活性
是不同的, 大叶模型中对该因子的忽视会造成光合
速率估算的整体高估, 若将本研究中健康叶片所占
比例增加10%, Pc将增加20%, 也证实了大叶模型中
忽视光量子非线性反应的不合理。在今后模型中应
该根据观测植物的群落类型以及叶片着生位置、倾
角、生长状况等引入适当的修正参数。
另外, 不同尺度光合作用对环境因子的响应方
式是不同的。叶片尺度上, 生物因子如遗传特性、
生长阶段和叶片氮含量等(Elberse et al., 2003; Lit-
ton et al., 2007; Feng et al., 2007; 张绪成等, 2010)以
及环境条件(如光照、温度、水分和CO2浓度等)
(Pearson & Dawson, 2003; Llorens et al., 2004; 赵平
等, 2005; 赵晓松等, 2006; Niu et al., 2008)极易影响
叶片光合作用; 同时, 群落尺度上碳通量也受到生
物因子(生物量、生物多样性等)(Davidson et al.,
2006; 马文红等, 2008)和环境因子(温度、水分等)
(Zha et al., 2004; Xu & Baldocchi, 2004; Fu et al.,
2006; 马月存等, 2007; Bellarby et al., 2013)的影响。
在今后的研究中需加强不同尺度光合作用与环境因
子之间的响应方式和差异的研究, 在冠层模型中考
虑这些因素。
本研究启示我们: (1)在草原生态系统研究中,
相比参数比较复杂的冠层模型, 可利用叶片尺度净
光合速率, 结合叶面积指数、群落叶片数目、健康
叶片比例和群落中所有叶片可接收有效光照的平均
比例等4个关键参数, 准确地推算出群落尺度净光
合速率; (2)采用同化箱式法测定群落呼吸速率时,
不可避免地会包含土壤呼吸, 所以我们观测群落净
气体交换速率时, 需要同时测定土壤呼吸。生态系
统净气体交换速率加上土壤呼吸速率才是同化箱式
法测定最终得出的群落净气体交换速率。(3)冠层模
型中, 群落垂直结构和光量子的非线性响应不可忽
视。
基金项目 国家重点基础研究发展计划(973计划)
项目(2014CB138803)和国家自然科学基金重点项
目(41030535)。
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