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GEOGRAPHICAL RESEARCH >

2017 , Vol. 36 >Issue 11: 2239 - 2250

DOI: https://doi.org/10.11821/dlyj201711016

Articles

Investigating the relationship between photochemical reflectance index (PRI) and light-use efficiency (LUE) during different seasons in a subtropical needle-leaf and broadleaf mixed forest

  • LI Yanmu , 1, 2 ,
  • WANG Shaoqiang , 1, 2 ,
  • QIAN Zhaohui 1, 2 ,
  • CHEN Diecong 3 ,
  • ZHANG Leiming 1, 2 ,
  • ZHOU Guoyi 4 ,
  • YAN Junhua 4 ,
  • MENG Ze 4
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  • 1. Key Laboratory of Ecosystem Network Observation and Modeling, Institute of Geographic Sciences and Natural Resources Research, CAS, Beijing 100101, China
  • 2. College of Resources and Environment, University of Chinese Academy of Sciences, Beijing 100049, China
  • 3. Guangdong Ecological Meteorological Center, Guangzhou 510640, China
  • 4. South China Botanical Garden, CAS, Guangzhou 510650, China

Received date: 2017-05-04

  Request revised date: 2017-09-07

  Online published: 2017-11-20

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《地理研究》编辑部
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Abstract

：Light use efficiency (LUE) is a critical parameter for remote sensing estimation of ecosystem productivity. Therefore, accurate estimates of spatio-temporal variation of LUE is essentially required. Photochemical reflectance index (PRI) has been widely accepted to hold the potential to track the LUE variations. Here we combined spectral and eddy covariance observations in a subtropical mixed forest to investigate the ability of PRI to estimate LUE at a half-hourly time-scale in different seasons. The forest is located at Dinghu mountain forest ecological experiment station in Zhaoqing of Guangdong province and the observations ranged from April 2014 to March 2015. The results showed that: (1) LUE was significantly correlated with PRI but the correlation strength was different in different seasons; The correlation was the strongest in winter (R2=0.40, P<0.01) and the weakest in summer (R2=0.04, P<0.01). (2) The standardized PRI (∆PRI), which removes noises from canopy and soil background, did not well capture the dynamics of LUE. (3) Photosynthetic active radiation (PAR) had the largest influence on the relationship between LUE and PRI among various climatic variables. Our analysis featured the temporal limitation of PRI in estimating LUE in subtropical forests and similar efforts are needed to quantify PRI ability to estimate LUE in other ecosystem types.

Key words： theropencedrymion of the subtropic forest; photochemical reflectance index (PRI); light use efficiency (LUE); environment variables

Cite this article

LI Yanmu , WANG Shaoqiang , QIAN Zhaohui , CHEN Diecong , ZHANG Leiming , ZHOU Guoyi , YAN Junhua , MENG Ze . Investigating the relationship between photochemical reflectance index (PRI) and light-use efficiency (LUE) during different seasons in a subtropical needle-leaf and broadleaf mixed forest[J]. GEOGRAPHICAL RESEARCH, 2017 , 36(11) : 2239 -2250 . DOI: 10.11821/dlyj201711016

1 引言

植被光合作用的实时监测对于估算生态系统的初级生产力（gross primary productivity,GPP）和净初级生产力（net primary productivity,NPP）,以及认识气候变化对生态系统的影响具有重要的意义。利用卫星遥感数据和光能利用率模型能够实时大范围监测植被生产力的动态变化[1-3]。因此,获取不同生态系统光能利用效率的空间变异性是精确估算生态系统生产力的关键[4]。目前获取植被光能利用效率（light use efficiency,LUE）的方法主要是微气象[5,6]和卫星遥感方法。微气象（涡度相关方法）是当前测定大气—植被之间CO2和水热通量的标准方法,它基于站点尺度,对被测样地进行长期、连续的观测[7,8],获取精确的陆地生态系统的地—气交换数据[9],但涡度相关方法难以监测较大范围的生态系统碳水通量。而利用卫星遥感观测数据,可以获得区域尺度的光能利用效率空间特征。但该方法又存在时间分辨率较低、精度不高的缺点[10]。因此,利用地面光谱来衔接通量采样数据与卫星遥感数据,实现光能利用效率数据的尺度外推值得深入研究。
近年来,很多研究尝试利用多种植被指数对LUE进行估算和研究[11],其中归一化植被指数（Normalized Difference Vegetation Index,NDVI）和增强植被指数（Enhanced Vegetation Index,EVI）的应用非常广泛[12-15]。但是两者只能反映植被结构的变化特点[16],对于部分常绿植物,这两个指数难以准确反映植被生化组分的动态变化,与光合作用并无直接联系[17,18],难以从机理上解释光合作用的变化原因。光化学植被指数（Photochemical Reflectance Index,PRI）为531 nm和570 nm处反射率的植被指数[17],由Gamon等于1992年定义并被发现与LUE有密切的关系。当植物光合结构所接收的光能超过其所能利用的能量时,会产生光抑制,此时,植物通过叶黄素循环调整其内部能量的分配,耗散多余的能量对植物加以保护。叶黄素循环的生物化学过程是紫黄质（Violaxanthin,V）在脱环氧化作用下通过环氧玉米黄素（Antheraxanthin,A）转化为玉米黄素（Zeaxanthin,Z）[19],在较低光密度的情况下,会通过逆反应发生环氧化作用[19-24]。这种色素形态的变化将导致531 nm处反射率的显著变化,但对570 nm处的反射率几乎没有影响[25],因而PRI能够用来监测植被LUE的动态变化。
目前,对于PRI与LUE关系的研究主要集中在北半球温带北方针叶林,Hilker[26-29]等均发现PRI可以作为表征北方针叶林LUE的替代指标。Soudani等基于8年连续的地面观测结果,得出了对于落叶和常绿阔叶林,在较短的时间尺度内LUE和PRI具有显著的相关性,且两者的相关程度随着时间尺度的增大而减小的结论[30]。Nakaji等却发现在热带雨林地区,不同季节LUE-PRI的相关关系的显著程度区别较小[31]。因此,在研究LUE与PRI两者的相关关系时,要考虑不同季节和不同的生态系统的差异。另一方面,Liu[32,33]等通过引入特定时间的PRI值作为参考标准值（PRIRef）,利用∆PRI（∆PRI=PRI-PRIRef）建立与LUE间的统计模型,有效优化了冬小麦、玉米和赤杨等植物PRI表征LUE的效果。本文以中国科学院鼎湖山生态试验站亚热带针阔混交林为研究对象,对实测的植被冠层光谱和涡度通量观测数据（2014年4月-2015年3月）进行分析,探讨PRI和标准化后的∆PRI反演亚热带针阔混交林LUE动态变化的可靠性,分析环境要素对LUE-PRI相关性的影响。

2 研究方法与数据来源

2.1 研究区概况

中国科学院鼎湖山生态试验站位于广东省肇庆市鼎湖山国家自然保护区,地处北回归线附近,属于南亚热带季风湿润性气候。年平均气温为20.9 ℃,年平均降水量为1956 mm[34],主要降雨季节为4-9月,降雨量约占全年的80%,旱季为10月-次年3月。
鼎湖山通量观测塔（23°10′N、112°32′E,海拔240 m）设于鼎湖山自然保护区核心区的针阔混交林样地内,于2002年建立,是中国陆地生态系统通量观测研究网络（Chinaflux）站点之一,塔四周的森林植被类型为亚热带常绿针阔混交林以及地带性森林季风常绿阔叶林,冠层高度为17 m,主要树种有木荷（Schimasuperba）、锥栗（Castanopsjschinensis）和马尾松（Pinusmassoniana）,土壤为赤红壤和黄壤。
鼎湖山通量观测塔高38 m,共安装了两套开路涡度相关通量观测系统（Open Path Eddy Covariance,OPEC）,其中一套OPEC安装于1.5倍冠层高度的27 m处,对生态系统/大气界面的CO2和H2O通量进行观测,另外一套安装高度约为2 m,用于测量冠层下方/地表植被界面的通量。OPEC系统主要包括三维超声风温仪（CSAT3,Campbell Scientific Ltd.,USA）和快速响应红外CO2/H2O分析仪（Li-7500,Li-Cor Inc.,USA）,分别进行三维风速以及CO2/H2O浓度脉动的测量。CO2、H2O湍流通量数据采集器（CR10XTD、CR23XTD、CR5000）每秒采样10次,自动存储实时数据并在线计算半小时平均通量数据[35]。

2.2 PRI数据处理

光化学植被指数计算公式为：
PRI = R 531 - R 570 R 531 + R 570 （1）
式中：R531和R570分别表示植物叶片在531 nm和570 nm处的反射率,通常将531 nm波段称为测量波段,570 nm称为参考波段。
为了获取冠层植被的波段反射率,本文在鼎湖山通量观测塔的最高层（38 m）处安装了自动多角度光谱观测系统（Automated Multi-angular Spectro-radiometer,AMSPEC）。该系统由塔上的光谱分析系统（UniSpec-DC Spectral Analysis System）、上行光纤、下行光纤、自动倾斜旋转和数据传输系统（PTU-D46-17P70T）以及塔下的数据存储系统组成,其中上行光纤用于测定太阳下行辐射,下行光纤对植被冠层光谱反射率进行多角度自动观测。自动多角度光谱观测系统观测波段范围300~1100 nm,光谱分辨率为3.3 nm,每15 min存储一次数据。为配合LUE数据在相同时间尺度进行分析,选取2014年4月-2015年3月每天10:00-14:00期间每半小时的光谱数据为研究对象。通过Matlab软件首先读取波段白板校正参数和中心波长值进行质量控制,在处理完缺省数据后,提取531 nm和570 nm处的太阳辐射和植被冠层反射辐射,计算两波段处的反射率,通过式（1）计算得到植被冠层的初始PRI值。

2.3 ∆PRI数据处理

由于植被自身的色素含量以及观测区内部的冠层结构、土壤背景、观测和光照条件等方面存在差异,造成了LUE和PRI的相关关系在一定程度上被削弱。为了减小不同因素对LUE-PRI关系的影响,本文将正午时分所测的PRI最小值作为参照值（PRImin）,将实测的PRI值与其作差,从而将PRI在不同环境状态下的数值进行标准化处理[32]。∆PRI的计算公式为：
ΔPRI = PR I t - PR I min （2）
式中：PRIt表示一天内某时刻的PRI值;PRImin表示在正午时间段（10:00-14:00）内,PRI的最小值。将实测PRI进行标准化处理,可以有效降低各种干扰因素对LUE-PRI关系的影响,从而形成相关性更好的LUE-PRI统计模型。

2.4 LUE数据处理

首先,通过通量观测获得的CO2储存通量和湍流通量进行净生态系统CO2交换量（net ecosystem exchange,NEE）的计算,再将NEE拆分为生态系统总呼吸（ecosystem respiration, R e ）和总初级生产力[16],由此获得步长30 min的GPP：
GPP = NEP + R e （3）
式中：NEP为白天的净生态系统生产力（net ecosystem production,NEP=-NEE）; R e 为白天的生态系统呼吸,通过反推夜间NEE和5 cm处土壤温度之间指数关系获得。
本文采用NDVI来估算光合有效辐射吸收比率（fraction of absorbed photosynthetically active radiation,FPAR）和植物吸收的光合有效辐射（absorbed photosynthetic active Radiation,APAR）的数值。通过自动多角度光谱观测系统获取了植被在各个波段的植被反射率,本文采用式（4）获取NDVI：
NDVI = R 850 - R 680 R 850 + R 680 （4）
式中：R850和R680分别表示自动多角度光谱观测系统观测的植物叶片在850 nm和680 nm波段处的反射率。再通过式（5）和式（6）进行FPAR和APAR的计算[36]：
FPAR = ( NDVI - NDV I min ) ( FPA R max - FPA R min ) NDV I max - NDV I min + FPA R min （5）
APAR = FPAR × PAR （6）
式中：NDVImin和NDVImax分别是植被覆盖为5%和98%时的NDVI值,根据观测区植被冠层结构特点,取NDVImin=0.01,NDVImax=0.5[37]。FPARmin和FPARmax分别表示最小和最大的FPAR值,一般分别假定为0.001和0.95[38]。
光能利用效率被定义为总初级生产力与植被吸收的光合有效辐射的比值。在计算出GPP和APAR之后,即可通过式（7）计算LUE：
LUE = GPP / APAR （7）

3 结果分析

3.1 LUE-PRI关系的分析

遵循鼎湖山生态试验站冬夏季较长、春秋季较短的特殊气候特征,参考简茂球等在中国华南地区根据温度、降雨量及温度—降雨量矢量场所形成的划分方法,将季节划分如下[39]：4月为春季,5-9月为夏季,10月为秋季,11月-次年3月为冬季。本文以涡度相关通量观测获取的LUE数据和自动多角度光谱观测系统获取的PRI数据为基础,在经过LUE异常值去除、光谱反射率白板校正等数据质量控制之后,对LUE和PRI进行一元二次回归分析（图1）,结果表明：LUE-PRI在春、夏、秋、冬四个季节具有极显著的正相关关系（P<0.01）,其中冬季的相关性最好（R2=0.40,P<0.01）,秋季次之（R2=0.16,P<0.01）,但是在春季和夏季,两者的相关性较弱,R2值分别为0.09和0.04。同时,LUE在冬季较高,秋季较低,但各季节主要在0~4 gC/MJ范围内。同时,夏季和冬季植被的光化学植被指数的数值分布范围较广且较为一致,均集中于-0.06~0.02之间,春季的PRI值主要分布于±0.02区间内,秋季的PRI值主要分布于-0.04~0.00之间。
Fig. 1 Correlations between half-hourly LUE and PRI from April 2014 to March 2015.

图1 各季节半小时尺度LUE-PRI相关性

其次,对2014年4月-2015年3月间月尺度PRI对LUE的表征能力进行分析（图2）,发现PRI表征LUE的能力各月份差异较明显。其中,在11月和次年1月表征能力较强（分别为58%、53%）,在12月和次年2月次之（表征能力分别为44%和42%）,然而在其他月份,PRI对LUE的表征能力较弱（表征能力均在20%以下）。结合鼎湖山生态试验站的气候情况（表1）,4-9月为雨季,饱和水汽压差（VPD）的平均值在0.5左右,而在这期间的4-8月,LUE-PRI的相关关系较弱。尤其是在6-7月的梅雨季节,VPD均值约为0.62,同时LUE-PRI的相关性达到低谷,直至9月降雨逐渐减少,VPD值下降为0.36,两者的相关性情况才有所提高。而在降水相对较少,VPD均值在0.35左右的11月-次年1月,LUE与PRI的相关性显著增强,PRI可以表征44%~58%的LUE动态变化。过多的降水会导致光纤光谱仪的光谱观测结果发生重大误差,这可能是降水对LUE-PRI的相关性产生影响的重要原因。但是,在VPD相近的4月和2月,LUE-PRI的相关性却相差较大,R2值分别为0.09和0.42。从表1可以看出这两月的PAR值相差较小,但平均温度却相差7 ℃,这可能是导致两月LUE-PRI的相关性差异大的重要原因,也说明Ta是影响LUE-PRI之间相关性程度的要素之一。此外,在邻近的5月和6月,PRI对LUE的表征程度相差近20倍。从环境因子的变化来看,两月的Ta和VPD都比较相近,而PAR值相差了20 J,这说明PRI对LUE的表征程度对PAR的动态变化同样十分敏感。
Fig. 2 Correlations between half-hourly LUE and PRI in each month from April 2014 to March 2015

图2 半小时尺度LUE-PRI相关性

Tab.1 The mean of environmental factors from April 2014 to March 2015

表1 2014年4月-2015年3月各环境因子平均值

月份 PAR（J） Ta（℃） VPD
2014年4月 134 21.19 0.30
2014年5月 284 27.71 0.60
2014年6月 262 27.09 0.62
2014年7月 254 28.28 0.62
2014年8月 223 27.28 0.47
2014年9月 240 26.33 0.36
2014年10月 250 23.39 0.45
2014年11月 156 18.11 0.20
2014年12月 168 11.54 0.36
2015年1月 201 13.35 0.49
2015年2月 124 14.28 0.32
2015年3月 80 14.72 0.16

3.2 LUE-∆PRI关系的分析

Liu[31]在对冬小麦和玉米的实验观测中发现,通过标准化处理从而减小外界因素影响的∆PRI能够更好地表征LUE的变化规律。为了将LUE与PRI更加紧密的联系起来,提高PRI表征LUE的效果,本文对实测的PRI进行标准化,根据式（2）计算出∆PRI,探讨LUE-∆PRI的相关程度。统计结果表明,LUE-∆PRI具有显著正相关关系,但相关性较弱（R2<0.25,P<0.01）。图3将针阔混交林的LUE和∆PRI、PRI相关性进行比较,两种情况下R2的平均值分别用实线、虚线标出。结果发现,∆PRI与LUE的相关性在季节尺度上明显弱于LUE-PRI,没有形成较PRI表征LUE的优势,从均值来看,PRI表征LUE的能力是∆PRI的四倍左右。另一方面,LUE与∆PRI、PRI的相关性在不同月份有很大差异,尤其表现在冬季的11月、12月。此时LUE-PRI关系很强,LUE-∆PRI却呈现较弱的相关性,PRI表征LUE的能力约为∆PRI的十倍。10月较为特殊,∆PRI对LUE展现出较PRI更强的表征能力。将本文与实验条件下的冬小麦和玉米相比,亚热带针阔混交林具有更加复杂的冠层结构、土壤背景、观测和光照条件,可能是导致森林冠层∆PRI不能充分优化PRI与LUE关系的原因。
Fig. 3 Monthly comparison of correlation strength (R2) of LUE-PRI and LUE-∆PRI from April 2014 to March 2015

图3 不同月份LUE和∆PRI、PRI的相关性情况对比图

注：图中实线是LUE-∆PRI的R2平均值,虚线是LUE-PRI的R2平均值。

3.3 LUE、PRI与环境因素的关系

影响LUE和PRI关系的因素有很多,包括环境因素和非环境因素。本文基于光合有效辐射（PAR）、大气温度（Ta）和饱和水汽压差（VPD）三个环境要素,探讨三个环境要素对LUE-PRI相关性的影响情况,同时对比了各环境要素与PRI和LUE的相关性情况。结果如图4所示,不同环境变量对于LUE和PRI的影响差异较大,其中PAR对PRI和LUE的影响较为明显,并且在冬季1月份PRI-PAR的相关性达到峰值。而在温度较高、降水较多的夏季,LUE-PRI和LUE-PAR的相关性在6月份均出现最低值,PRI-PAR的相关性在7月也处于低谷,同期LUE-PRI、PRI-VPD、LUE-VPD、LUE-Ta相关性均较差。从各曲线的变化趋势来看,无论是季节尺度还是月尺度,PRI-PAR和LUE-PAR相关性大小的变化趋势与LUE-PRI的相关性大小变化趋势基本一致。结合鼎湖山生态试验站环境因素的观测情况,本文发现冬季的PAR值较低,植被对PAR的变化较敏感,叶黄素循环更易进行,导致PRI发生了变化,同时光能利用效率增强,LUE-PRI及其与环境变量的相关关系均较显著。
Fig. 4 Correlations between PRI/LUE and environmental variables (PAR, Ta and VPD) in each month (a and b) and each season (c and d)

图4 月尺度、季节尺度LUE-PRI及PRI、LUE与环境因子（PAR、Ta、VPD）的相关性

从季节角度来看,PRI-VPD、LUE-VPD的相关性变化趋势与PRI-LUE变化趋势也基本吻合,且两者的相关性大小数值十分接近,但从月尺度角度出发,两者的变化趋势和相关性大小差异较大。联系鼎湖山地区的气候情况,在4-9月为鼎湖山地区的雨季,雨量较充沛,雨季的LUE-PRI相关性与旱季相比较差,且PRI、LUE与各环境变量的R2值均处于较低水平。且夏季温度较高,光合作用有关酶的催化活性降低,持续的降雨造成VPD较大,导致大气湿度饱和,叶片表皮细胞吸水膨胀,挤压了保卫细胞,促使气孔关闭,从而限制了CO2的供应,使得光合作用能力下降[40],光能利用效率降低,导致LUE-Ta、LUE-VPD相关性较弱。而PRI-Ta和LUE-Ta相关性的变化趋势以及其R2值大小与LUE-PRI的情况均有较大差异。由此推断,温度对PRI表征LUE能力的影响小于前两者。
总体来看,PRI能够在一定程度上追踪LUE的动态变化,但是LUE-PRI相关性季节差异较大,在秋冬季节相关性较强,夏季较弱。LUE-PRI相关性的变化趋势与PRI-PAR和LUE-PAR的变化趋势基本一致,与PRI-VPD和LUE-VPD的变化趋势和R2值大小较吻合,与PRI-Ta和LUE-Ta的相关性情况存在较大差异。因此,LUE-PRI的相关性受PAR影响最大,VPD次之,Ta对其影响最小。

4 讨论

尽管本文认为亚热带针阔混交林的PRI难以更好地描绘LUE春季和夏季的变化趋势,但国际上Hilker等[26-28]对位于加拿大的罗奇波尔针叶林和山杨两树种进行了研究,发现对于四季物候分明的北方温带常绿针叶林,PRI可以作为LUE较好的替代指标。同时,叶面积指数LAI、冠层结构会对LUE-PRI相关性产生一定影响。有研究表明,随着季节的变化,温带常绿针叶林幼苗（扭叶松和北美黄松）PRI、电子传输速率、色素水平、LUE以及光合作用情况及其相互的联系紧密性有明显变化[24,29,41],在这种时间尺度下,影响PRI的最主要因素是类胡萝卜素库的变化,也可以认为是类胡萝卜素与叶绿素比率,其次是在骤冷情况下叶片反射率的变化,最后才是叶黄素循环[29,41,42]。另外,在温带落叶阔叶林和地中海气候常绿阔叶林的季节尺度研究中,植被吸收的光合有效辐射APAR被认为是影响PRI重要的因素[30]。本文中,与温带常绿针叶林相比,鼎湖山地区亚热带针阔混交林的LAI变化较小[43],物候变化不显著,亚热带针阔混交林叶片中色素含量变化较小,这些均可能是导致PRI表征LUE动态变化能力较弱的原因[44]。因此,利用PRI在季节尺度上的变化特征及多种环境因素对LUE-PRI的影响规律,提高PRI反演LUE的能力仍需进一步研究。对于日尺度,对温带落叶阔叶林和地中海气候常绿阔叶林的研究表明,PRI可以有效地反映叶黄素循环的变化情况,日尺度的LUE与PRI要优于季节尺度[43]。此外,通过每日的数据统计表明,晴天和阴天相关性会稍高,这可能与光谱仪光纤探头受天气影响较大有关,在多个研究均呈现出相似的结果。
国内,张乾等[3]在千烟洲生态试验站对中亚热带人工针叶林生长季期间（4-9月）的PRI-LUE相关关系进行了研究,结果表明在降水较多的5月,由于丰富的降水对于光谱观测产生一定影响,导致LUE与PAR、VPD、Ta的相关性较强,而PRI与环境变量的相关性极弱,最终LUE-PRI相关性极差;而在天气较为晴朗的7月,PRI、LUE与各环境因子的相关性均较强,因而LUE-PRI相关性最为显著。这些结果对本文进一步的研究有较强的参考价值。
本文采用的自动多角度光谱观测系统,虽经过多重数据处理与校正,但仍存在一些不确定因素。例如,① 获取植被冠层反射波谱的光纤探头虽装有15°视场角限制器（UNI688; PP Systems）,但由于客观条件的限制,在特定的观测角度仍会受到通量塔塔身部分的干扰;② 偶然的雷击致使自动多角度光谱观测系统无法正常工作,数据质量下降;③ 随着观测时间的推移,光纤探头污染导致观测系统误差。这些原因均会导致光谱观测数据出现异常,降低了特定时间PRI的准确性,在进一步的研究中应设法消除塔身所导致的误差。另外,鼎湖山站的植被主要为马尾松、木荷和锥栗等树种的针阔混交林,由于不同树种冠层结构差异性较大,植物叶片的叶绿素含量、光合作用能力也不相同,多角度光谱仪所测的冠层PRI对于LUE的指示精度还有待进一步探究。

5 结论

本文基于2014年4月-2015年3月连续一年对亚热带针阔混交林的自动多角度光谱观测系统观测以及涡度相关通量的测定,获得了冠层光化学植被指数（PRI）和光能利用效率（LUE）,结合环境变量Ta、VPD、PAR,探讨了PRI作为亚热带针阔混交林LUE替代指标的适用性,以及各环境变量对两者相关性的影响规律。结果表明：
（1）总体来看,LUE与PRI具有显著的相关关系（P<0.01）,但在不同的季节,PRI对LUE的表征能力差异较大。从季节尺度来看,PRI表征LUE能力最强的是冬季（40%）,最弱的是夏季（9%）。分月份来看,PRI对LUE表征程度在11月最高（58%）,而在处于梅雨季节阶段的6-7月,PRI表征LUE的程度最低。这是由于夏季鼎湖山生态试验站的降水较多、温度和PAR较高,光合作用有关酶的催化活性降低,且大气湿度饱和,促使气孔关闭,从而限制了CO2的供应,造成植被的光合作用能力下降,光能利用效率降低。
（2）削弱了各种环境干扰因素后得到的∆PRI,与LUE的相关性较弱,说明标准化后的∆PRI难以有效表征亚热带针阔混交林LUE的时间动态变化。
（3）在连续一整年的观测期内,PRI和LUE对各环境变量的敏感性各不相同。但从整体趋势来看,无论是季节尺度还是月尺度,PRI和LUE与PAR的相关性最强,VPD次之,而与Ta的相关关系较弱。
因此,对于亚热带常绿针阔混交林,PRI可以在一定程度上表征LUE的变化,但难以精确捕捉植被光合作用的季节变化趋势。雨季期间两者的相关性较差,PRI不能用于表征LUE的动态变化。同时,PAR是影响LUE-PRI关系的主要环境因素。

The authors have declared that no competing interests exist.

References

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[Chen Diecong, Wang Shaoqiang, Huang Kun, et al.An inversion of the efficiency of artificial coniferous forests in central Asia based on flux and spectral observations. Chinese Journal of Applied Ecology, 2015, 26(11): 3421-3432.]

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[18]
Penuelas J, Filella I, Gamon J A.Assessment of photosynthetic radiation-use efficiency with spectral reflectance. New Phytologist, 1995, 131(3): 291-296.Reflectance changes at 531 nm, associated with the zeaxanthin-antheraxanthin-violaxanthin interconversion and the related thylakoid energization, are widespread among plant species. We evaluated an index based on 531 nm reflectance ('PRI', Photochemical Reflectance Index calculated as (R 531 090808 R 570 )/(R 531 + R 570 )) as an indicator of efficiency of photosynthetic radiation use in seven species representing both C 3 and CAM photosynthetic pathways. Leaves exposed to a dark-lighted ark transition in a steady-state laboratory gas exchange system exhibited nearly parallel changes in PRI and PS II quantum yield (0200 F / F m '). Similar PRI and 0200 F / F m ' responses were seen in leaves exposed to diurnally changing sunlight levels outdoors. PRI was linearly related to 0200 F / F m ', and both 0200 F / F m ' and PRI were exponentially related to instantaneous efficiency of photosynthetic radiation-use in different species over a range of different field conditions. These results extend previous studies by indicating a functional relationship between PRI. 0200 F / F m ', and photosynthetic radiation-use efficiency. The narrow-band PRI index offers a simple, portable means of assessing PS II radiation-use efficiency, analogous to 0200 F / F m ', and with the potential for remote applications at scales larger than the leaf.

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[19]
Demmig-Adams B, Adams Iii W.Photoprotection and other responses of plants to high light stress. Annual Review of Plant Biology, 1992, 43(1): 599-626.

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[20]
Adams W W, Demmigadams B.Operation of the xanthophyll cycle in higher-plants in response to diurnal changes in incident sunlight. Planta, 1992, 186(3): 390-398.Changes in the carotenoid composition of leaves in response to diurnal changes in sunlight were determined in the crop species Helianthus annuus L. (sunflower), Cucurbita pepo L. (pumpkin), and Cucumis sativus L. (cucumber), in the diaheliotropic mesophyte Malva neglecta Wallr., and in the perennial shrub Euonymus kiautschovicus Loesner. Large daily changes were observed in the relative proportions of the components of the xanthophyll cycle, violaxanthin (V), antheraxanthin (A), and zeaxanthin (Z) in plants grown in full sunlight. In all leaves large amounts of Z were formed at peak irradiance, with the changes in Z content closely following changes in incident photon flux density (PFD) over the course of the day. All leaves also contained large total pools of the three xanthophyll-cycle components. However, the extent to which the V pool present at dawn became de-epoxidized during the day varied widely among leaves, from a 27% decrease in M. neglecta to a 90% decrease in E. kiautschovicus. The largest amounts of Z and the lowest amounts of V at peak irradiance (full sunlight) were observed in the species with the lower rates of photosynthesis (particularly in E. kiautschovicus and pumpkin), and smaller amounts of Z and a lesser decrease in V content were found at peak irradiance in those species with the higher rates of photosynthesis (particularly in M. neglecta and sunflower). In all species some Z was present in the leaves prior to sunrise. Furthermore, in individuals of sunflower, pumpkin, and cucumber grown at 85% of full sunlight and transferred to full sunlight, a further increase in the already large pool of the xanthophyll-cycle pigments occurred over the course of 1 d.

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[21]
Demmig B, Winter K, Kruger A, et al.Photoinhibition and zeaxanthin formation in intact leaves: A possible role of the xanthophyll cycle in the dissipation of excess light energy. Plant Physiology, 1987, 84(2): 218-224.Comparative studies of chlorophyll a fluorescence, measured with a pulse amplitude modulated fluorometer, and of the pigment composition of leaves, suggest a specific role of zeaxanthin, a carotenoid formed in the xanthophyll cycle, in protecting the photosynthetic apparatus against the adverse effects of excessive light. This conclusion is based on the following findings: (a) exposure of leaves of Populus balsamifera, Hedera helix, and Monstera deliciosa to excess excitation energy (high light, air; weak light, 2% O2, 0% CO2) led to massive formation of zeaxanthin and a decrease in violaxanthin. Over a wide range of conditions, there was a linear relationship between either variable,$F_{V}$, or maximum fluorescence,$F_{M}$, and the zeaxanthin content of leaves. (b) When exposed to photoinhibitory light levels in air, shade leaves of H. helix had a higher capacity for zeaxanthin formation, at the expense of -carotene, than shade leaves of M. deliciosa. Changes in fluorescence characteristics suggested that, in H. helix, the predominant response to high light was an increase in the rate of nonradiative energy dissipation, whereas, in M. deliciosa, photoinhibitory damage to photosystem II reaction centers was the prevailing effect. (c) Exposure of a sun leaf of P. balsamifera to increasing photon flux densities in 2% O2and 0% CO2resulted initially in increasing levels of zeaxanthin (matched by decreases in violaxanthin) and was accompanied by fluorescence changes indicative of increased nonradiative energy dissipation. Above the light level at which no further increase in zeaxanthin content was observed, fluorescence characteristics indicated photoinhibitory damage. (d) A linear relationship was obtained between the ratio of variable to maximum fluorescence,$F_{V}/F_{M}$, determined with the modulated fluorescence technique at room temperature, and the photon yield of O2evolution, similar to previous findings (O Bj rkman, B Demmig 1987 Planta 170: 489-504) on chlorophyll fluorescence characteristics at 77 K and the photon yield of photosynthesis.

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[22]
Gamon J A, Field C B, Bilger W, et al.Remote-sensing of the xanthophyll cycle and chlorophyll fluorescence in sunflower leaves and canopies. Oecologia, 1990, 85(1): 1-7.Sudden illumination of sunflower ( Helianthus annuus L. cv. CGL 208) leaves and canopies led to excess absorbed PFD and induced apparent reflectance changes in the green, red and near-infrared detectable with a remote spectroradiometer. The green shift, centered near 531 nm, was caused by reflectance changes associated with the de-epoxidation of violaxanthin to zeaxanthin via antheraxanthin and with the chloroplast thylakoid pH gradient. The red (685 nm) and near-infrared (738 nm) signals were due to quenching of chlorophyll fluorescence. Remote sensing of shifts in these spectral regions provides non-destructive information on in situ photosynthetic performance and could lead to improved techniques for remote sensing of canopy photosynthesis.

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[23]
Thayer S S, Bjorkman O.Leaf xanthophyll content and composition in sun and shade determined by hplc. Photosynthesis Research, 1990, 23(3): 331-343.

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[24]
Wong C Y S, Gamon J A. Three causes of variation in the photochemical reflectance index (PRI) in evergreen conifers. New Phytologist, 2015, 206(1): 187-195.Summary The photochemical reflectance index (PRI) reflects diurnal xanthophyll cycle activity and is also influenced by seasonally changing carotenoid02:02Chl pigment ratios. Both changing pigment pools and xanthophyll cycle activity contribute to photoprotection in evergreen conifers exposed to boreal winters, but they operate over different timescales, and their relative contribution to the PRI signal has often been unclear. To clarify these responses and their contribution to the PRI signal, leaf PRI, pigment composition, temperature and irradiance were monitored over 202yr for two evergreen conifers ( Pinus contorta and Pinus02ponderosa ) in a boreal climate. PRI was affected by three distinct processes operating over different timescales and exhibiting contrasting spectral responses. Over the 202yr study period, the greatest change in PRI resulted from seasonally changing carotenoid02:02Chl pigment ratios, followed by a previously unreported shifting leaf albedo during periods of deep cold. Remarkably, the smallest change was attributable to the xanthophyll cycle. To properly distinguish these three effects, interpretation of PRI must consider temporal context, physiological responses to evolving environmental conditions, and spectral response. Consideration of the separate mechanisms affecting PRI over different timescales could greatly improve efforts to monitor changing photosynthetic activity using optical remote sensing.

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[25]
陈晋, 唐艳鸿, 陈学泓, 等. 利用光化学反射植被指数估算光能利用率研究的进展. 遥感学报, 2008, 12(2): 331-337.植被光能利用率(LUE)是估计植被初级生产力(GPP)和净初级生产力(NPP)模型的一个重要输入,准确地估计LUE对于生态学研究有重要的意义.由于LUE随环境的变化关系十分复杂,现有的LUE估算模型过于粗糙简单,而通过遥感直接估计LUE将会更加可靠.研究表明,光化学反射植被指数(PRI)与LUE有很好的相关性,故PRI在利用遥感估计LUE方面具有极大的潜力.但是很多研究也发现了PRI-LUE的关系不够稳健,受许多因素的干扰,比如物种构成、冠层结构及大气等.因此,PRI的广泛应用还需要更多的研究.本文首先介绍了PRI的定义及PRI随LUE变化的生理机制,再综述了一些利用遥感手段建立PRI-LUE关系的例子,然后分析了影响PRI-LUE关系的各种干扰因素,最后对PRI研究取得的成果、存在的问题以及发展前景作了总结.

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[Chen Jin, Tang Yanhong, Chen Xuehong, et al.The progress of the study on the utilization of light energy by the photochemical reflection vegetation index. Journal of Remote Sensing, 2008, 12(2): 331-337.]

[26]
Hall F G, Hilker T, Coops N C.Data assimilation of photosynthetic light-use efficiency using multi-angular satellite data: I. Model formulation. Remote Sensing of Environment, 2012, 121: 301-308.78 A new data assimilation model for GPP is validated across forest ecosystems. 78 Multi-angular satellite observations are used to infer instantaneous ε. 78 Data is used determine a pixel specific εmaxvalue. 78 A spatially explicit and temporally variable εmaxdramatically enhances GPP.

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[27]
Hilker T, Hall F G, Tucker C J, et al.Data assimilation of photosynthetic light-use efficiency using multi-angular satellite data: Ii model implementation and validation. Remote Sensing of Environment, 2012, 121: 287-300.78 A new data assimilation model for GPP is validated across forest ecosystems. 78 Multi-angular satellite observations are used to infer instantaneous ε. 78 Data is used determine a pixel specific εmaxvalue. 78 A spatially explicit and temporally variable εmaxdramatically enhances GPP.

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[28]
Gamon J, Kovalchuck O, Wong C, et al.Monitoring seasonal and diurnal changes in photosynthetic pigments with automated pri and ndvi sensors. Biogeosciences, 2015, 12(13): 4149-4159.The vegetation indices normalized difference vegetation index (NDVI) and photochemical reflectance index (PRI) provide indicators of pigmentation and photosynthetic activity that can be used to model photosynthesis from remote sensing with the light-use-efficiency model. To help develop and validate this approach, reliable proximal NDVI and PRI sensors have been needed. We tested new NDVI and PRI sensors, ?spectral reflectance sensors (SRS CE1)? recently developed by Decagon Devices, during spring activation of photosynthetic activity in evergreen and deciduous stands. We also evaluated two methods of sensor cross-calibration ? one that considered sky conditions (cloud cover) at midday only, and another that also considered diurnal sun angle effects. Cross-calibration clearly affected sensor agreement with independent measurements, with the best method dependent upon the study aim and time frame (seasonal vs. diurnal). The seasonal patterns of NDVI and PRI differed for evergreen and deciduous species, demonstrating the complementary nature of these two indices. Over the spring season, PRI was most strongly influenced by changing chlorophyll : carotenoid pool sizes, while over the diurnal timescale, PRI was most affected by the xanthophyll cycle epoxidation state. This finding demonstrates that the SRS PRI sensors can resolve different processes affecting PRI over different timescales. The advent of small, inexpensive, automated PRI and NDVI sensors offers new ways to explore environmental and physiological constraints on photosynthesis, and may be particularly well suited for use at flux tower sites. Wider application of automated sensors could lead to improved integration of flux and remote sensing approaches for studying photosynthetic carbon uptake, and could help define the concept of contrasting vegetation optical types.

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[29]
Wong C, Gamon J A.The photochemical reflectance index provides an optical indicator of spring photosynthetic activation in evergreen conifers. New Phytologist, 2015, 206(1): 196-208.In evergreens, the seasonal down-regulation and reactivation of photosynthesis is largely invisible and difficult to assess with remote sensing. This invisible phenology may be changing as a result of climate change. To better understand the mechanism and timing of these hidden physiological transitions, we explored several assays and optical indicators of spring photosynthetic activation in conifers exposed to a boreal climate. The photochemical reflectance index (PRI), chlorophyll fluorescence, and leaf pigments for evergreen conifer seedlings were monitored over 1yr of a boreal climate with the addition of gas exchange during the spring. PRI, electron transport rate, pigment levels, light-use efficiency and photosynthesis all exhibited striking seasonal changes, with varying kinetics and strengths of correlation, which were used to evaluate the mechanisms and timing of spring activation. PRI and pigment pools were closely timed with photosynthetic reactivation measured by gas exchange. The PRI provided a clear optical indicator of spring photosynthetic activation that was detectable at leaf and stand scales in conifers. We propose that PRI might provide a useful metric of effective growing season length amenable to remote sensing and could improve remote-sensing-driven models of carbon uptake in evergreen ecosystems.

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[30]
Soudani K, Hmimina G, Dufrêne E, et al.Relationships between photochemical reflectance index and light-use efficiency in deciduous and evergreen broadleaf forests. Remote Sensing of Environment, 2014, 144(1): 73-84.In this study, we evaluate the relationships between the photochemical reflectance index (PRI) and light-use efficiency (LUE) based on eight years of continuous in situ measurements acquired on a half-hourly basis for PRI, NDVI (Normalized Difference Vegetation Index), the main micrometeorological variables and net CO 2 exchange data in two deciduous and evergreen mature forests. More specifically, the objectives of this study include investigating the daily, seasonal, and interannual variations of PRI and LUE; linking PRI variations to the main influencing meteorological and eco-physiological variables; and evaluating the performance of PRI as a remote-sensing proxy of LUE under different environmental conditions. The data analysis was performed at different time scales within the season using moving temporal windows and between years. On a seasonal scale, statistical analyses revealed positive relationships between PRI and absorbed photosynthetically active radiation (aPAR) and negative relationships between PRI and LUE. Over shorter periods of a few days, the signs of these relationships remained unchanged; however, their correlations were strongly improved. The highest correlations were most often observed over periods characterized by clear or slightly overcast skies. However, all the periods of clear skies did not involve improvements in the relations of PRI vs. aPAR or PRI vs. LUE. Temporal variations of the intercept (called PRI 0 in this study) of PRI vs. aPAR regressions suggest the presence of a temporal trend that may reflect seasonal changes of the biochemical characteristics of the canopy. Regardless of the cause of this trend, it is important to note that once PRI 0 was subtracted from the measured PRI, the correlations between the corrected PRI and LUE for each year were significantly improved, and a stable multi-year model was obtained. Nevertheless, further studies are required to explain the temporal changes of PRI 0 during the season and to develop a more accurate disentangling approach that would make PRI-based remote-sensing of ecosystem light-use efficiency less sensitive to confounding factors related to spatial and temporal changes in the structural and biochemical properties of the canopy.

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[31]
Nakaji T, Kosugi Y, Takanashi S, et al.Estimation of light-use efficiency through a combinational use of the photochemical reflectance index and vapor pressure deficit in an evergreen tropical rainforest at pasoh, peninsular malaysia. Remote Sensing of Environment, 2014, 150(7): 82-92.To improve the accuracy in estimating LUE, we examined the potential of combinational use of VIs and meteorological factors. Variable selection by stepwise multiple regression showed that the best variable combination for LUE estimation was the PRI and VPD ( R 02=020.612). The relative root mean square error ( r RMSE) in the simple regression models using PRI, VPD and PRI02×02VPD, and the multiple regression model using PRI and VPD, was 22.5%, 19.4%, 19.0% and 18.7%, respectively. Based on these results, we concluded that (1) the estimation method solely based on the PRI as in the case of other temperate deciduous forests is not suitable in the tropical evergreen rainforest, and (2) the combinational use of the PRI and VPD offers one of the better models for estimating LUE in tropical evergreen rainforests.

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[32]
Liu L, Zhang Y, Jiao Q, et al.Assessing photosynthetic light-use efficiency using a solar-induced chlorophyll fluorescence and photochemical reflectance index. International Journal of Remote Sensing, 2013, 34(12): 4264-4280.Photosynthetic light-use efficiency (LUE) is an important indicator of plant photosynthesis, but assessment by remote sensing needs to be further explored. In this study, two protective mechanisms for photosynthesis, chlorophyll fluorescence (ChlF) and heat dissipation in the deep oxidation state of the xanthophyll cycle, were explored to estimate photosynthetic LUE from canopy radiance spectra. Four independent experiments were carried out on summer maize (C4 plant) on 5 July 2008, and winter wheat (C3 plant) on 18 April 2008, 16 April 2010, and 13 May 2010, by synchronously measuring daily canopy radiance spectra and photosynthetic LUE. The competitive relationship between ChlF and photochemical yield made it possible to estimate photosynthetic LUE. LUE–ChlF models were developed for ChlF at 688 nm (R 202=020.72) and 760 nm (R 202=020.59) based on the experimental data from 13 May 2010 at the Guantao flux site. The LUE–ChlF models were validated by three independent experiments, and the results showed that the LUE–ChlF relationship was weakened, possibly by variation in species, canopy density, and environmental conditions. As an easy, rapid, non-intrusive method, a photochemical reflectance index (PRI) provides an instantaneous assessment of dynamic photosynthetic LUE. The significant negative relationship between non-photochemical quenching and PRI was confirmed. Although there was a significantly positive relationship between LUE and PRI in all four independent experiments, this was evidently weakened by the canopy and environmental conditions. Difference in PRI (ΔPRI) from the minimum reference PRI around noontime can largely eliminate interference factors. The LUE–ΔPRI model was developed based on experimental data from 13 May 2010 at the Guantao flux site (with an R 2 value of 0.85), and validated by the three other independent experiments. The validation result indicated that different species can markedly affect the precision of the PRI difference method.

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[33]
Weng J H, Chen Y N, Liao T S.Relationships between chlorophyll fluorescence parameters and photochemical reflectance index of tree species adapted to different temperature regimes. Functional Plant Biology, 2006, 33(3): 241-246.Chlorophyll fluorescence parameters and spectral reflectance at leaf level were measured at both predawn and noon, under different temperatures and natural light conditions from autumn to winter. Predawn F-v/F-m of both mango (Mangifera indica L.), a tropical fruit tree, and Podocarpus nagi Zoll. et Moritz., a subtropical conifer, decreased with decreasing temperature, with the former to a greater extent than the latter. Yet, predawn F-v/F-m of Taiwan alder (Alnus formosana Makino), a broadleaf tree widely distributed from the lowlands to 3000m above sea level in Taiwan, was less influenced by temperature. Nevertheless, taking all three species into consideration, predawn F-v/F-m showed a strong correlation with predawn photochemical reflectance index [(PRIp), PRI=(R-531-R-570)/(R-531+R-570), where R= reflectance]. For the data obtained at noon, Delta F/Fm' showed a significant but weak correlation with PRI (PRIn). However, stronger correlation between Delta F/Fm' and Delta PRI (PRIp-PRIn) was found. In addition, while a non-significant or weak correlation between non-photochemical quenching (NPQ) and PRIn was observed in species sensitive to low temperature, their NPQ was significantly correlated with Delta PRI. We conclude that PRIp can serve as an indicator of the seasonal variation of potential PSII efficiency; and Delta PRI reflects the actual photodissipation as well as actual PSII efficiency during illumination. For the three species in this study, the PRI provides a more consistent measure of the variation in predawn fluorescence values than for steady-state values measured under normal seasonally varying daylight illumination.

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[34]
李正泉. 中国通量观测网络(Chinaflux)能量平衡闭合状况的评价. 中国科学: 地球科学, 2004, 34(2): 46-56.

[Li Zhengquan.The evaluation of the energy balance of the China flux observation network (Chinaflux). Science China: Earth Sciences, 2004, 34(2): 46-56.]

[35]
王春林, 周国逸, 王旭, 等. 复杂地形条件下涡度相关法通量测定修正方法分析. 中国农业气象, 2007, 28(3): 233-240.复杂地形条件下涡度相关法通量观测修正方法以及夜间净生态系统CO2交换通量(NEE)质量评价方法,是世界范围内通量观测研究中的重大技术问题。本文以鼎湖山南亚热带针阔叶混交林生态系统涡度相关法碳通量观测数据,探讨典型订正方法对CO2通量估算的影响。主要结论有:1)基于流线坐标系统的二次坐标旋转(DR)、三次坐标旋转(TR)和平面拟合坐标旋转(PF),均使得CO2通量(Fc)绝对值趋于变小,变化幅度依次为:DR<PF<TR。坐标转换对Fc影响程度白天小于夜间,冬季小于夏季,冠层上方小于冠层下方。2)冠层下方和冠层上方CO2通量合适的u*订正阈值分别为0.05、0.2m s-1。3)对于涡度相关通量观测中普遍存在的夜间CO2涡度通量偏低问题,WPL订正没有帮助,坐标转换甚至起到反作用,冠层储存项订正在一定程度上减少夜间偏低程度,但效果不显著;u*订正可以明显减少夜间偏低幅度,但估算结果与箱式法相比依然偏低。夜间涡度通量观测数据最好能结合箱式法观测结果进行校正。

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[Wang Chunlin, Zhou Guoyi, Wangxu, et al. The method of the method of flux measurement in complicated terrain is analyzed. Chinese Journal of Agrometeorology, 2007, 28(3): 233-240.]

[36]
Liu L, Guan L, Liu X.Directly estimating diurnal changes in gpp for c3 and c4 crops using far-red sun-induced chlorophyll fluorescence. Agricultural and Forest Meteorology, 2017, 232: 1-9.Accurate estimation of gross primary production (GPP) is of great importance to global change research and also food and fuel security. Previous studies have demonstrated that values of sun-induced chlorophyll fluorescence (SIF) retrieved from hyperspectral data provide a direct measure of ecosystem GPP. However, global analysis of the relationship between satellite SIF and model-based GPP indicates that the relationship between the two parameters is highly dependent on the plant functional type (PFT). The overarching goal of this study is to examine the potential of far-red SIF retrieved at 76002nm (SIF 760 ) to track the diurnal variations in GPP for C3 and C4 crops, and to investigate whether the GPP–SIF relationship is dependent on the type of photosynthesis. GPP values are estimated from flux tower records and daily SIF 760 data are derived from ground-based spectral measurements. The results show that GPP and SIF 760 have similar diurnal patterns and are linearly correlated for C3 and C4 crops. However, the ratio of ε P 65 65 65 mathContainer Loading Mathjax to ε F mathContainer Loading Mathjax (the slope of the linear SIF-based GPP model, GPP02=02 ε P ε F × SIF mathContainer Loading Mathjax ) for C3 wheat is about 46% of that for C4 maize. The findings from the diurnal variation experiments imply that the ε F mathContainer Loading Mathjax is weakly sensitive to the photosynthetic pathway type (PsP type) and that the large difference in ε P mathContainer Loading Mathjax between C3 and C4 crops leads to the difference in the slopes. Our studies confirm the capability of the remotely sensed SIF signals to act as a direct proxy for GPP and suggest that the PsP type should be considered when trying to accurately quantify the ecosystem productivity using the straightforward empirical approach.

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[37]
江东, 王乃斌, 杨小唤, 等. 吸收光合有效辐射的时序变化特征及与作物产量的响应关系. 农业系统科学与综合研究, 2002, (1): 51-54.利用气象卫星资料,反演出大面积、从每日到每旬、每月不同时间分辩率的吸收光合有效辐射资料,在此基础上,以河南省高、中、低产县的冬小麦为例,深入探讨 了冬小麦各个生育期内APAR的波动规律,结果表明,APAR的时序变化与冬小麦生育节律有着很好的响应关系,并最终影响冬小麦产量的形成.图3,参 12.

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[Jiang Dong, Wang Naibin, Yang Xiaohuan, et al.The time sequence change characteristics of photosynthetic effective radiation and response relationship with crop yield were absorbed. System Sciemces and Comprehensive Studies in Agriculture, 2002, (1): 51-54.]

[38]
Sellers P J, Tucker C J, Collatz G J, et al.A global 1-degrees-by-1-degrees ndvi data set for climate studies .2. The generation of global fields of terrestrial biophysical parameters from the NDVI. International Journal of Remote Sensing, 1994, 15(17): 3519-3545.A satellite-based 100° by 100° normalized difference vegetation index (NDVI) data set has been processed to derive land surface parameters for general circulation models of the atmosphere (GCMs). Prior to calculation of the land surface parameters, corrections were applied to the source NDVI data set to account for (i) obvious anomalies in the data time-series, (ii) the effect of variations in solar zenith angle, (iii) data dropouts in cold regions where a temperature threshold procedure designed to screen for clouds also eliminates cold land surface points, and (iv) persistent cloud cover in the tropics. An outline of the procedures for calculating land surface parameters from the corrected NDVI data set is given, and a brief description is provided of source material that was used in addition to the NDVI data. The data sets summarized in this paper should represent improvements over prescriptions currently used in land surface parameterizations in that the spatial and temporal dynamics of key land surface parameters, in particular of those related to vegetation, are obtained from direct measurements rather than indirectly inferred from survey-based land cover classifications.

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[39]
简茂球. 华南地区气候季节的划分. 中山大学学报: 自然科学版, 1994, (2): 131-133.

[Jian Maoqiu.The division of climate season in south China. Acta Scientiarum Naturalium Universitatis Sunyatseni, 1994, (2): 131-133.]

[40]
王三根. 植物生理生化. 北京: 中国林业出版社, 2013.

[Wang Sangen.Plant Physiology and Biochemistry. Beijing: China Forestry Publishing House, 2013.]

[41]
Stylinski C D, Gamon J A, Oechel W C.Seasonal patterns of reflectance indices, carotenoid pigments and photosynthesis of evergreen chaparral species. Oecologia, 2002, 131(3): 366-374.This study examined the ability of the Photochemical Reflectance Index (PRI) to track seasonal variations in carotenoid pigments and photosynthetic activity of mature evergreen chaparral shrubs. Our results confirm that PRI scales with photosystem two (PSII) photochemical efficiency across species and seasons, as demonstrated by PRI's strong correlation with de-epoxidized (photoprotective) xanthophyll cycle pigment levels (normalized to chlorophyll) and with the chlorophyll fluorescence index, ΔF/Fm'. PRI and carotenoid pigment levels (de-epoxidized xanthophyll cycle pigments normalized to chlorophyll or total carotenoid pigments normalized to chlorophyll) were correlated with seasonal fluctuations in midday net CO60 uptake of top-canopy leaves. By contrast, chlorophyll levels (as measured by the Chlorophyll Index) were not as strongly linked to photosynthetic activity, particularly when all species were considered together. Likewise, the Normalized Difference Vegetation Index (NDVI, an index of canopy greenness) did not correlate with net CO60 uptake. Canopy NDVI also did not correlate with canopy PRI, demonstrating that these indices were largely independent over the temporal and spatial scales of this study. Together, these patterns provide evidence for coordinated regulation of carotenoid pigments, PSII electron transport, and carboxylation across seasons and indicate that physiological adjustments are more important than structural ones in modifying CO60- fixation capacity during periods of photosynthetic down-regulation for these evergreen species. The strong correlation between PRI of whole canopies and PRI of top-canopy leaves suggests that the canopy can be treated as a "big leaf" in terms of this reflectance index and that PRI can be used in "scalable" models. This along with the links between carotenoid pigments, PSII photochemical efficiency and carboxylation across species and seasons supports the use of optical assays of pigment levels and PSII activity in CO60 flux models to derive photosynthetic rates.

DOI PMID

[42]
Nakaji T, Oguma H, Fujinuma Y.Seasonal changes in the relationship between photochemical reflectance index and photosynthetic light use efficiency of japanese larch needles. International Journal of Remote Sensing, 2006, 27(3): 493-509.We investigated seasonal changes in the photochemical reflectance index (PRI) and its relation to the diurnal profile of photosynthetic light use efficiency (LUE) in mature Japanese larch (Larix kaempferi Sarg.) forest throughout the growing season from June to October 2003. The daily mean value of needle PRI showed seasonal variation, strongly correlated with the chlorophyll concentration and carotenoid/chlorophyll ratio of the needles. During the green period from early June to late September, the hourly values of both PRI and LUE showed significant midday depression, and were positively correlated. In late October, however, because the PRI of yellowing needles tended to increase slightly at midday in contrast to the LUE, this correlation became negative. Even before autumn senescence, the sensitivity of PRI to LUE changed with the season. Correlation analysis indicated that the slope and intercept of the regression line of the PRI UE relationship increased during summer, with peaks in July and August, respectively. The seasonal change in slope was strongly correlated with the foliar photosynthetic pigment concentration, nitrogen concentration, air temperature and the daily mean value of the normalized difference vegetation index (NDVI). The value of the intercept was positively correlated with the daily mean PRI. These results suggest that although diurnal change in LUE cannot be estimated quantitatively from PRI on its own throughout the growing season, the combined use of PRI and other variables such as foliar pigments or NDVI could improve the remote evaluation of seasonal changes in LUE of deciduous tree leaves.

DOI

[43]
任海, 彭少麟, 张祝平, 等. 鼎湖山季风常绿阔叶林林冠结构与冠层辐射研究. 生态学报, 1996, 16(2): 174-179.本文研究了鼎湖山自然保区的亚热带季风常绿阔叶林的林冠结构与冠层辐射，结果表明：１．该群落的叶面和指数为１７，叶面积指数在水平方向的分布是均一的，但在垂直方向上则是非均匀的，整个群落对光能的截获率力９６．３％，其中最上层乔木截获了总入射光强的７８．２８％，下野乔木及灌草层只截获１７．８３％，但冠层辐射仍遵循消光定律。２．群落的叶倾角影呐冠层辐射，该群落冠层上部的叶倾角在４５°－７０°处具有最大分布频率，而中下层则在５°－３５°有最大分布频率。高的叶面积指数与时的直立性相关。３．该群落上层乔木枝下高较高，且中上部枝条与树干夹角较小，枝的着叶数较多且枝的着叶长度较长；而下层乔木和灌木枝下高较低，大部分枝条与树干夹角较大，且叶多着生于枝端。这种冠层格局由冠层辐射引起。４．该群落植物叶和枝条的取向在各方向上机会均等。５．群落的叶片从上到下变大，这种格局对森林的能量分配和水分平衡有重要意义。６．该季风常绿阔叶林以林冠为活动面，林冠上层呈多孔体，中下层郁团，对太阳辐射有较强的吸收能力，因而反射率较低，年均仅３．１５％。７．植物个体结构与群体结构不同，当一个有良好结构的个体处于密度较大的群体中，将会因适应坏境而改变个体生产结构。

[Ren Hai, Peng Shaolin, Zhang Zhuping, et al.Study on canopy structure and canopy radiation of the evergreen broad-leaved forest of Dinghushan monsoons. Acta Ecologica Sinica, 1996, 16(2): 174-179.]

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