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光合作用是自然界最为重要的原初生物化学反应之一,光能向生物能的转化是生命存在的基础。林木的光合作用主要通过冠层进行,而冠层环境的异质性会引起叶片光合响应特征的差异[1-3]。叶片的光合响应特征可通过光合响应曲线来反映,获得的光合响应参数有助于判定叶片光合机构的运转状况,也能反映叶片利用光、CO2等资源的能力。
目前,应用在植物光响应曲线方面的模型主要有直角双曲线、非直角双曲线和修正模型,应用在植物CO2响应曲线方面的模型主要有直角双曲线、直角修正、Michaelis-Menten模型,这些模型各有优缺点:非直角和直角双曲线模型在测算光抑制型树种时最大净光合速率(Pnmax)常大于观测值[4],而光饱和点(LSP)、CO2饱和点(CiSP)常低于观测值[5-6];修正模型在光饱和点的拟合上存在不足[7];非直角双曲线模型更适合未饱和型和弱光环境型数据,直角修正模型更适于拟合光抑制型和光饱和型数据且表现出良好的稳定性[8]。不同的植物,其适宜的光合响应模型不一,不同模型对同一植株光合响应的拟合也存在差异,这些差异究竟在多大程度上影响着叶片光合响应参数的准确性?模型间的差异更大还是部位间的差异更大?适宜的光合响应模型是否对测算的所有光合响应参数均具有最优的结果?这些问题值得关注,因为光合响应参数值的合理性会影响我们对植株光合生理过程的判断。
近年来,植物光合的研究已进入到冠层水平,在用材林和经济林方面[3,8-9]均开展了相关研究,但南方重要的山区农业经济树种无患子(Sapindus mukorossi)冠层不同部位叶片光合生理的研究却鲜有报道,作为喜光树种,无患子自然分层现象较为明显,在冠层尺度上探讨叶片的光合生理更有意义,能更好地揭示生理生化过程和资源利用效率。赵娜等[10]、赖金莉等[11]和刁松锋等[12]分别采用二次曲线模型、直角修正模型和非直角双曲线模型对无患子盆栽苗、2年生幼苗和8年生无患子叶片的光响应曲线进行了拟合,所获得的生理参数差异明显,这些研究虽有助于了解无患子的生理生态习性,但都没有对模型的合理性进行分析,也缺乏冠层尺度上的研究,而且对经济林而言,进入稳定结实期的树体,其在生长旺盛期的生理状况更值得关注。鉴于此,本研究以进入稳定结实期的无患子为研究对象,采用不同的光合响应模型拟合各层级和各方向上叶片的Pn-PAR和Pn-Ci响应曲线获得相应的响应参数,旨在探究不同模型对冠层各部位叶片光合响应参数计算结果的影响,以期得到适合无患子的光合响应模型和合理的光合响应参数,并为在其他植物中开展光合响应模型的研究提供一定的依据。
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研究地位于福建省三明市建宁县,处于福建省的西北内陆山区,属中亚热带海洋季风性气候。该地区热量充沛,无霜期长,降雨多集中在春夏季,年均降水量达1 950 mm,年均气温为17.0 ℃。试验于2017年在建宁县经开区绿化带(116°51′47″E、26°51′56″N)内进行,绿化带内土壤为砂壤土,土壤肥力中等偏上,有机质含量为22.3 g/kg,土壤全氮含量为1.22 g/kg,速效磷为28.24 mg/kg,速效钾为106.8 mg/kg,pH为5.21。无患子的种源地为浙江天台,2年生实生苗,于2009年栽植。
首先对绿化带内46株无患子树进行普查,平均树高为(5.184 ± 0.473)m、平均胸径为(13.283 ± 1.369)cm、东西冠幅均值为(5.202 ± 0.743)m、南北冠幅均值为(4.915 ± 0.738)m。选取3株能代表绿化带内无患子平均生长状况的树作为研究对象,树形结构和树势基本一致,连年坐果较好,近3年的年产量稳定在20 kg/株,试验树的树体特征如表1所示。
表 1 试验树的树体特征
Table 1. Features of the test trees
试验树编号
No. of test trees树高
Tree height/m东西冠幅
Crown width of
east and west/m南北冠幅
Crown width of
north and south/m胸径
DBH/cm枝下高
Under branch height/m上层厚度
Thickness of
upper layer/m中层厚度
Thickness of
middle layer/m下层厚度
Thickness of
lower layer/m1号 No.1 5.132 5.113 4.952 13.1 1.401 1.676 1.215 1.132 2号 No.2 5.158 5.217 4.913 13.4 1.362 1.723 1.264 1.068 3号 No.3 5.251 5.320 5.186 12.8 1.312 1.757 1.311 1.253 -
试验于2017年7—8月晴朗天气下进行,根据树冠较为明显的自然分层现象分为上、中、下3层,试验树冠层厚度如表1所示,每层按不同方位选取叶片,叶片选自枝条中部复叶上健康的功能叶,共计12片叶/株,3棵树作为重复,最后将测定的各层级、各方位叶片的光合响应参数做均值化处理获得各层级、各方位叶片的光合响应特征,具体测点位置如图1所示。
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使用Li-6400光合仪(LI-COR,USA)对叶片进行Pn-PAR和Pn-Ci响应的测定。测定时间为上午08:30—11:00,使用CO2注入系统将CO2浓度设为400 μmol/mol,流速设为500 μmol/s,温度设为环境温度(33 ± 1)℃,相对湿度约为60%。测量Pn-PAR响应时,光合有效辐射(PAR)依次设为1 800、1 500、1 200、1 000、800、500、300、100、80、50、30、10、0 μmo/(m2·s);测量Pn-Ci响应时,将PAR设为1 200 μmol/(m2·s),CO2浓度设为2 000、1 800、1 500、1 200、1 000、800、600、400、300、200、150、100、50 μmol/mol,自动测量后可获得光合响应参数仪器测定值Pnmax(I)、LSP、Rd和Pnmax(C)。
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Pn-PAR响应曲线分别采用直角双曲线模型[13](rectangular hyperbolic model,RHM)、非直角双曲线模型[14](non-rectangular hyperbolic model,NRHM)、直角修正模型[15](modified rectangular hyperbolic model,MRHM)和指数修正模型[16](modified exponential model,MEM)进行拟合,各模型及参数依次表达如下:
$${P_{{\rm{n}}\left( I \right)}} = \frac{{{\alpha _{\left( I \right)}}I{P_{{\rm{nmax}}\left( I \right)}}}}{{{\alpha _{\left( I \right)}}I + {P_{{\rm{nmax}}\left( I \right)}}}} - {R_{\rm{d}}}$$ (1) $$\begin{aligned} {P_{{\rm{n}}\left( I \right)}} = & \Big\{ {{\alpha _{\left( I \right)}}I + {P_{{\rm{nmax}}\left( I \right)}} - \left[ {{{\left( {{\alpha _{\left( I \right)}}I + {P_{{\rm{nmax}}\left( I \right)}}} \right)}^2} - } \right.} \Big.\\ & \left. {{{\Big. {4\theta {\alpha _{\left( I \right)}}I{P_{{\rm{nmax}}\left( I \right)}}} \Big]}^{\frac{1}{2}}}} \right\}/2\theta - {R_{\rm{d}}} \end{aligned}$$ (2) $${P_{{\rm{n}}\left( I \right)}} = \frac{{{\alpha _{\left( I \right)}}I\left( {1 - \beta I} \right)}}{{\left( {1 + \gamma I} \right)}} - {R_{\rm{d}}}$$ (3) $${P_{{\rm{n}}\left( I \right)}} = \alpha {{\rm{e}}^{ - \beta I}} - \gamma {{\rm{e}}^{ - \xi I}}$$ (4) 式中:Pn(I)为光响应净光合速率;I为光合有效辐射(PAR);α(I)为初始量子效率;Pnmax(I)为光响应最大净光合速率;Rd为暗呼吸速率;θ为曲线的凸度;α、β、γ、ζ均为系数。
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Pn-Ci响应曲线分别采用直角双曲线模型[17]、直角修正模型[18]和Michaelis-Menten模型[19](Michaelis-Menten model,MMM),各模型及参数意义依次如下:
$${P_{{\rm{n}}\left( C \right)}} = \frac{{{\alpha _{\left( C \right)}}{C_{\rm{i}}}{P_{{\rm{nmax}}\left( C \right)}}}}{{{\alpha _{\left( C \right)}}{C_{\rm{i}}} + {P_{{\rm{nmax}}\left( C \right)}}}} - {R_{\rm{p}}}$$ (5) $${P_{{\rm{n}}\left( C \right)}} = \frac{{{\alpha _{\left( C \right)}}{C_{\rm{i}}}\left( {1 - \beta {C_{\rm{i}}}} \right)}}{{\left( {1 + \gamma {C_{\rm{i}}}} \right)}} - {R_{\rm{p}}}$$ (6) $${P_{{\rm{n}}\left( C \right)}} = \frac{{{C_{\rm{i}}}{P_{{\rm{nmax}}\left( C \right)}}}}{{{C_{\rm{i}}} + {{K}}}} - {R_{\rm{p}}}$$ (7) 式中:Pn(C)为CO2响应净光合速率;Ci为胞间CO2浓度;α(C)为初始羧化效率;Pnmax(C)为CO2响应最大净光合速率;Rp为光呼吸速率;β、γ为系数;K为Michaelis-Menten参数。
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数据处理由Excel 2007完成,运用SPSS 18.0软件的非线性回归功能模块完成光合模型的构建,先基于生物学意义对各模型参数的取值进行限制,如各模型的参数均大于0[6];基于C3途径每同化1分子CO2理论上量子效率不超过0.125,将α(I)设为小于0.125;NRHM曲线凸度θ应在0 ~ 1之间。通过RHM和NRHM的构建可直接获得α(I)、α(C)、Pnmax(I)、Pnmax(C)、Rd和Rp,但无法通过Pnmax(I)和Pnmax(C)计算得到LSP和CiSP,学者们[20-21]提出利用弱光(≤ 200 μmol/(m2·s))和低Ci(≤ 200 μmol/mol)下Pn-PAR和Pn-Ci的线性关系,代入Pnmax(I)和Pnmax(C)值来获取LSP和CiSP;通过MRHM的构建可直接获得α(I)、α(C)、Rd和Rp,根据公式
${\rm{LSP}}\left( {{{\rm{C}}_{\rm{i}}}{\rm{SP}}} \right) = \left( {\sqrt {\left( {\beta + \gamma } \right)/\beta } - 1} \right)/\gamma $ ,将获得的LSP(CiSP)代入模型中得到Pnmax(I)和Pnmax(C);通过构建MEM可直接得到模型参数α、β、γ和ζ,根据公式${R_{\rm{d}}} = \alpha - \gamma $ ,$\alpha = \gamma \xi - \alpha \beta $ ,${\rm{LCP}} = \left( {{\rm{In}}\alpha - {\rm{In}}\gamma } \right)/\left( {\beta - \xi } \right)$ ,$ {\rm{LSP}} = $ $\left( {{\rm{In}}\alpha \beta - {\rm{In}}\gamma \xi } \right)/\left( {\beta - \xi } \right)$ 计算获得各参数,将获得的LSP代入模型中得到Pnmax(I);通过MMM的构建可直接获得K、Pnmax(C)和Rp,MMM与RHM在本质上一致[20]。通过均方误差(MSE)和决定系数(R2)检验各模型的拟合精度;采用SPSS软件的一般线性模型模块进行多因素方差分析并通过Duncan多重比较法检验模型和层级间叶片光合响应特征的差异。MSE和R2的计算如下:
$${\rm{MSE}} = \frac{1}{{{n}}}\mathop \sum \nolimits_{i = 1}^n {\left( {{y_i} - {\hat y_{{i}}}} \right)^2}$$ (8) $${{{R}}^2} = 1 - \frac{{\displaystyle \mathop \sum \nolimits_{i = 1}^n {{\left( {{y_i} - {\hat y_{{i}}}} \right)}^2}}}{{\displaystyle \mathop \sum \nolimits_{i = 1}^n {{\left( {{y_i} - \overline {{y_i}} } \right)}^2}}}$$ (9) 式中:yi、
${\hat y_{{i}}}$ 和$\overline {{y_i}} $ 分别代表实测值、模型拟合值和实测平均值。各模型拟合结果较好,各个模型可以解释超过90%的光合速率变化(表2)。
表 2 不同Pn-PAR和Pn-Ci模型的拟合精度
Table 2. Fitting accuracy of different Pn-PAR and Pn-Ci models
位置 Position 拟合精度
Fitting accuracy光响应模型 Pn-PAR model CO2响应模型 CO2 response model RHM NRHM MRHM MEM RHM MRHM MMM 上层 Upper layer MSE 0.823 0.536 0.127 0.161 0.581 0.470 0.581 R2 0.977 0.985 0.997 0.996 0.993 0.995 0.993 中层 Middle layer MSE 0.724 0.489 0.148 0.180 0.438 0.338 0.438 R2 0.982 0.988 0.995 0.994 0.994 0.995 0.994 下层 Lower layer MSE 0.741 0.532 0.236 0.277 0.466 0.223 0.466 R2 0.975 0.982 0.992 0.990 0.994 0.997 0.994 东 East MSE 0.661 0.437 0.150 0.169 0.358 0.255 0.358 R2 0.979 0.986 0.996 0.995 0.995 0.997 0.995 西 West MSE 0.633 0.411 0.144 0.181 0.538 0.505 0.538 R2 0.980 0.987 0.996 0.994 0.993 0.995 0.993 南 South MSE 0.755 0.497 0.195 0.226 0.469 0.295 0.469 R2 0.977 0.985 0.994 0.993 0.994 0.996 0.994 北 North MSE 0.711 0.539 0.213 0.240 0.463 0.309 0.463 R2 0.977 0.982 0.994 0.992 0.994 0.996 0.994 注:RHM. 直角双曲线模型;NRHM. 非直角双曲线模型;MRHM. 直角修正模型;MEM. 指数修正模型。下同。Notes: RHM, rectangular hyperbolic model; NRHM, non-rectangular hyperbolic model; MRHM, modified rectangular hyperbolic model; MEM, modified exponential model. The same below. -
叶片光合响应参数在东、西、南、北4个方向间均没有显著差异,所有参数在不同模型间和不同树冠层次间均有极显著差异;各参数均受到模型和层级的显著影响,层级对LCP、α(C)、CiCP和Rp的影响大于模型的影响;CiSP还受到模型 × 层级和模型 × 层级 × 方向交互作用的显著影响,LSP受到模型 × 层级交互作用的显著影响,α(C)和CiCP均受到层级 × 方向交互作用的显著影响(表3)。各光合参数在模型间、树冠层级间、方向间的F值显示模型和层级是影响参数的主要因素,故本文重点讨论叶片光合作用参数在模型和层级间的差异。
表 3 不同模型及无患子冠层不同部位叶片光合响应参数的方差分析
Table 3. Variance analysis of photosynthetic response parameters of different models in different parts of S. mukorossi canopy
指标
Index变异来源
Source of variation光合响应参数 Photosynthetic response parameter α(I) Pnmax(I) LSP LCP Rd α(C) Pnmax(C) CiSP CiCP Rp F值
F value模型
Model1 281.861 452.813 8 279.844 18.759 77.626 228.505 710.224 2 239.936 82.198 89.757 层级
Layer21.404 110.418 27.748 39.821 56.245 451.515 38.443 5.841 115.697 117.487 方向
Direction2.374 2.275 2.453 3.726 2.220 1.370 0.315 0.927 2.296 2.898 模型 × 层级
Model × layer2.136 1.220 7.200 0.285 0.433 2.172 0.939 20.255 1.138 0.118 模型 × 方向
Model × direction0.934 0.169 0.808 0.320 0.164 0.416 0.227 0.520 0.535 0.180 层级 × 方向
Layer × direction0.760 1.581 1.104 1.855 1.420 10.120 1.043 1.759 6.385 1.729 模型 × 层级 × 方向
Model × layer × direction0.514 0.217 0.583 0.194 0.046 0.303 0.043 2.218 0.147 0.135 P值
P value模型
Model< 0.01 < 0.01 < 0.01 < 0.01 < 0.01 < 0.01 < 0.01 < 0.01 < 0.01 < 0.01 层级
Layer< 0.01 < 0.01 < 0.01 < 0.01 < 0.01 < 0.01 < 0.01 0.004 < 0.01 < 0.01 方向
Direction0.056 0.106 0.068 0.055 0.358 0.156 0.714 0.432 0.122 0.105 模型 × 层级
Model × layer0.061 0.303 < 0.01 0.943 0.855 0.067 0.447 < 0.01 0.370 0.976 模型 × 方向
Model × direction0.500 1.000 0.610 0.967 0.997 0.866 0.967 0.791 0.780 0.981 层级 × 方向
Layer × direction0.703 0.161 0.366 0.131 0.248 < 0.01 0.405 0.076 < 0.01 0.257 模型 × 层级 × 方向
Model × layer × direction0.946 1.000 0.904 1.000 1.000 0.987 1.000 0.019 1.000 1.000 注:α(I). 初始量子效率;Pnmax(I). 光响应最大净光合速率;LSP. 光饱和点;LCP. 光补偿点;Rd. 暗呼吸速率;α(C). 初始羧化效率;Pnmax(C). CO2响应最大净光合速率;CiSP. CO2饱和点;CiCP. CO2补偿点;Rp. 光呼吸速率。下同。Notes: α(I), initial carboxylation efficiency; Pnmax(I), maximum photosynthesis rate of response for light; LSP, light saturation point; LCP, light compensation point; Rd, dark-respiration rate; α(C), initial carboxylation efficiency; Pnmax(C), maximum photosynthesis rate of response for CO2; CiSP, CO2 saturation point; CiCP, CO2 compensation point; Rp, photo-respiration rate. The same below. -
不同模型计算的光响应参数值与仪器测定值在树冠不同层级间均有差异(表4)。RHM和NRHM计算的各层级叶片Pnmax(I)值分别比仪器测定值高28.950% ~ 30.104%和7.675% ~ 12.158%,MRHM和MEM计算的各层级叶片Pnmax(I)值分别比仪器测定值低6.368% ~ 9.281%和6.003% ~ 9.530%,修正模型计算值与仪器测定值在树冠各层级的差异均不显著,MRHM计算的下层叶片Pnmax(I)值最接近仪器测定值,MEM得到的上、中层叶片Pnmax(I)值最接近仪器测定值;RHM和NRHM计算的各层级叶片LSP值均远低于仪器测定值,不符合叶片实际生理状况,MRHM和MEM计算的各层级叶片LSP值分别比仪器测定值低7.392% ~ 9.401%和10.019% ~ 14.114%,MRHM计算值最接近仪器测定值;4种模型计算的树冠各层级叶片LCP值均在仪器测定值范围内;RHM计算的各层级叶片Rd值比仪器测定值高10.793% ~ 17.421%,NRHM、MRHM和MEM计算的各层级叶片Rd值比仪器测定值分别低9.438% ~ 18.610%、8.216% ~ 13.763%和14.138% ~ 19.021%,MRHM计算的Rd值与仪器测定值在树冠各层级的差异均不显著且两者较为接近,MRHM的计算更合理。
表 4 无患子树冠各层级叶片不同Pn-PAR模型拟合的光响应参数值
Table 4. Pn-PAR response parameters of leaves in different layers of S. mukorossi canopy
位置
Position模型
Model光合响应参数 Photosynthetic response parameter α(I) Pnmax(I)/
(μmol·m− 2·s− 1)LSP/
(μmol·m− 2·s− 1)LCP/
(μmol·m− 2·s− 1)Rd/
(μmol·m− 2·s− 1)上层
Upper layerRHM 0.075 ± 0.002aA 18.044 ± 0.469aA 391.458 ± 5.125aA 40.009 ± 3.446aA 2.568 ± 0.124aA NRHM 0.038 ± 0.002bA 15.067 ± 0.377bA 468.455 ± 15.438bA 47.812 ± 5.546aA 1.780 ± 0.136bA MRHM 0.044 ± 0.002cA 13.102 ± 0.544cA 1 110.128 ± 28.085cA 45.820 ± 4.986aA 1.886 ± 0.113bcA MEM 0.040 ± 0.002bA 13.153 ± 0.504cA 1 079.776 ± 12.353cA 46.608 ± 5.263aA 1.771 ± 0.111bA 仪器测定
Measured by instrument13.993 ± 0.393cA 1 200dA 40 ~ 60 2.187 ± 0.191cA 中层
Middle layerRHM 0.076 ± 0.001aAB 16.276 ± 0.797aB 373.078 ± 11.500aB 43.640 ± 4.275aAB 2.751 ± 0.232aAB NRHM 0.043 ± 0.003bB 14.031 ± 0.896bAB 382.385 ± 24.289aB 52.099 ± 7.272aA 2.142 ± 0.234bB MRHM 0.049 ± 0.004cA 11.349 ± 0.972cB 1 111.302 ± 22.801bA 50.241 ± 5.389aA 2.219 ± 0.335bAB MEM 0.043 ± 0.003bA 11.437 ± 0.921cB 1 063.319 ± 29.289bAB 51.312 ± 5.608aAB 2.076 ± 0.348bA 仪器测定
Measured by instrument12.510 ± 1.122bcB 1 200cA 40 ~ 60 2.483 ± 0.221abAB 下层
Lower layerRHM 0.077 ± 0.002aB 15.940 ± 0.230aB 376.081 ± 3.619aB 48.014 ± 3.801aB 2.988 ± 0.204aB NRHM 0.043 ± 0.002bB 13.726 ± 0.305bB 412.835 ± 6.835aB 58.259 ± 5.786bA 2.370 ± 0.157bcB MRHM 0.047 ± 0.002cA 11.253 ± 0.473cB 1 087.184 ± 40.961bA 56.661 ± 5.973abA 2.402 ± 0.166bcB MEM 0.041 ± 0.001bA 11.107 ± 0.466cB 1 030.631 ± 24.385cB 58.513 ± 6.141bB 2.247 ± 0.169bA 仪器测定
Measured by instrument12.277 ± 0.756cB 1 200dA 40 ~ 60 2.617 ± 0.200cB 注:同列数据后不同小写字母表示模型间差异显著,同列数据后不同大写字母表示层级间差异显著。下同。Notes: different lowercase letters behind the same column represent significant difference among different models; different capital letters behind the same column represent significant difference among different canopy layers. The same below. -
不同模型计算的CO2响应参数值与仪器测定值在各层级间的差异见表5。RHM/MMM计算的各层级叶片Pnmax(C)值比仪器测定值高57.717% ~ 62.405%,而MRHM计算的各层级叶片Pnmax(C)值略低于仪器测定值,MRHM对Pnmax(C)的计算更准确;RHM/MMM计算的各层级叶片CiSP值均远低于仪器测定值,不符合叶片实际生理状况,MRHM计算的各层级叶片CiSP值与仪器测定值也存在较大的偏差;MRHM计算的各层级叶片CiCP值均偏低,RHM/MMM对CiCP值的计算更接近仪器测定值。
表 5 无患子树冠各层级叶片不同Pn-Ci模型拟合的CO2响应参数值
Table 5. CO2 response parameters of leaves in different parts of S. mukorossi canopy by varied Pn-Ci fitting models
位置
Position模型
Model光合响应参数 Photosynthetic response parameter α(C) Pnmax(C)/
(μmol·m− 2·s− 1)CiSP/
(μmol·m− 2·s− 1)CiCP/
(μmol·m− 2·s− 1)RP/
(μmol·m− 2·s− 1)上层
Upper layerRHM 0.157 ± 0.017aA 41.143 ± 1.600aA 532.685 ± 3.228aA 72.363 ± 2.706aA 8.983 ± 1.092aA MRHM 0.111 ± 0.013bA 25.695 ± 0.727bA 1687.327 ± 69.859bA 67.928 ± 3.153aAB 6.687 ± 1.087bA MMM 0.157 ± 0.017aA 41.143 ± 1.600aA 532.685 ± 3.228aA 72.363 ± 2.706aA 8.983 ± 1.092aA 仪器测定
Measured by instrument25.595 ± 0.737bA 1 372.517 ± 148.994cAB 67.685 ~ 90.082 中层
Middle layerRHM 0.143 ± 0.011aA 36.972 ± 0.987aB 524.590 ± 6.366aA 71.313 ± 1.560aA 8.078 ± 0.570aAB MRHM 0.096 ± 0.011bA 23.355 ± 0.629bB 1 686.436 ± 126.385bA 65.764 ± 1.082bA 5.591 ± 0.575bAB MMM 0.143 ± 0.011aA 36.972 ± 0.987aB 524.590 ± 6.366aA 71.313 ± 1.560aA 8.078 ± 0.570aAB 仪器测定
Measured by instrument23.442 ± 0.419bB 1 251.471 ± 21.290cA 73.015 ~ 82.999 下层
Lower layerRHM 0.088 ± 0.009aB 37.678 ± 0.614aB 682.982 ± 27.242aB 80.555 ± 1.698aB 5.939 ± 0.455aB MRHM 0.056 ± 0.002bB 23.095 ± 0.450bB 1 539.553 ± 108.241bA 71.589 ± 3.047bB 3.738 ± 0.091bB MMM 0.088 ± 0.009aB 37.678 ± 0.614aB 682.982 ± 27.242aB 80.555 ± 1.698aB 5.939 ± 0.455aB 仪器测定
Measured by instrument23.200 ± 0.324bB 1 420.349 ± 32.852bB 71.451 ~ 91.422 -
RHM和NRHM作为常用的光响应模型被广泛应用于植物的光合响应研究中。RHM通过较高的初始斜率来保证对实测点的准确拟合,但由于未考虑曲线的凸度,得到的Pnmax(I)和LSP值均不准确;NRHM考虑了曲线的凸度,曲线的拐点比RHM更明显,饱和光下的Pn-PAR曲线更为平缓,但依然不能从根本上解决RHM面临的两个问题:(1)无法准确拟合光抑制条件下的光响应数据。(2)光合参数测算值和仪器测定值差异较大[6]。针对以上两种模型拟合存在的缺陷,学者们[15-16]相继提出了MRHM和MEM,有效弥补了前两种模型的不足且拟合精度更高,对Pn-PAR曲线的拟合效果更好,但模型拟合精度高仅能反映模型拟合值更接近实测值,并不能说明模型测算得到的光合响应参数就越符合植物实际的生理状况[7,22-23]。本文采用4种光响应模型对无患子叶片Pn-PAR曲线的拟合结果显示:MRHM的拟合精度最高,计算得到的光合响应参数也较准确,但其对无患子叶片LSP值的计算仍显著低于仪器的测定,且其对特定部位叶片和特定光合参数的测算结果也未必最优。由于模型会出现拟合精度高但光合响应参数测算结果不理想的“过拟合”现象[6,16],不同模型对同一植株的光合响应参数测算结果也存在差异[24-26],而目前有关植物光合响应特征的研究又常常忽视模型的筛选,因此为了更准确地描述植物叶片光合响应特征,加强光合模型的研究是有必要的。叶片光响应参数的合理性和模型、叶片的选取密切相关,而叶片选取涉及到的叶片性状和生理功能差异与冠层部位的环境异质性有关也已被诸多研究[27-28]所证实,模型和冠层部位对光响应参数均有影响,对α(I)、Pnmax(I)、LSP和Rd而言,模型的影响要大于层级的影响,模型与层级的交互作用对LSP也具有显著影响,模型的选取很重要;对LCP值而言,层级的影响要大于模型的影响,其可通过拟合低光强下Pn-PAR的线性方程得到,各模型对低光强下Pn的拟合精度均较高且差异较小,LCP值模型间的差异也较小,而LCP值层级间的差异显著可能是由于环境异质性加大所形成的叶片性状差异所造成的。模型虽然对光响应参数的影响均极显著,但对LSP的影响最大,其次分别为:α(I)、Pnmax(I)、Rd和LCP。
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国内对Pn-Ci曲线的研究相对较少,本文采用3种CO2响应模型(RHM、MMM和MRHM)对Pn-Ci曲线进行拟合。3种CO2响应模型拟合的R2和MSE均显示MRHM的整体拟合精度更高,其获得的Pnmax(C)值更准确性;RHM/MMM对低Ci范围的Pn-Ci拟合效果较好,对CiCP值的测算更准确。叶片Pnmax(C)和CiSP值在模型间的差异均最大,反映了模型的影响是主要的,CiSP还受到模型 × 层级和模型 × 层级 × 方向交互作用的显著影响;叶片α(C)、CiCP和Rp值层级间的差异均大于模型间的差异,体现了环境异质性的影响。碳同化过程中多种光合酶的活性受光调控[29],光照对Rubisco活化酶具有促进作用[30],增强Rubisco羧化活性[31],而低光强能诱导气孔关闭,气孔开度的降低将直接影响叶片的羧化效率CE,可见,层级对α(C)值的影响更大。CiCP值可通过拟合低Ci下Pn-Ci的线性关系来测算,即CiCP = Rp/CE[17],Rp被定义为Ci = 0时的Pn,由于各模型对低Ci下Pn-Ci线性拟合的R2均在0.99以上,模型引起的CiCP和Rp差异均较小,而CE受层级的影响更大,层级对CiCP和Rp值影响也大于模型的影响,方差分析显示α(c)和CiCP还受到层级 × 方向交互作用的显著影响。模型对CiSP和Pnmax(C)的影响最大,其次为:α(C)、Rp和CiCP。
综上,在本研究中,光合模型对无患子叶片光合响应参数的影响是极显著的,模型的筛选非常重要。从整体的拟合效果来看,MRHM能较好地拟合无患子叶片光合响应曲线,得到的光合响应参数也较为准确。
Effects of photosynthetic models on the calculation results of photosynthetic response parameters in Sapindus mukorossi leaves
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摘要:
目的旨在探究光合模型对无患子冠层不同部位叶片光合响应参数计算结果的影响,并得到合适的光合响应应用模型和合理的光合响应参数。 方法本研究以福建建宁地区进入稳定结实期的无患子为研究对象,采用直角双曲线模型、非直角双曲线模型、直角修正模型和指数修正模型来拟合无患子冠层不同部位叶片的光响应曲线,采用直角修正模型、直角双曲线模型和Michaelis-Menten模型来拟合CO2响应曲线,通过均方误差和决定系数来检验光合响应模型的拟合精度,采用Duncan多重比较法检验不同模型和不同部位叶片光合响应参数的差异并进行方差分析。 结果(1)4种模型对光响应曲线拟合结果的优劣为:直角修正模型 > 指数修正模型 > 非直角双曲线模型 > 直角双曲线模型,3种模型对CO2响应曲线拟合优劣的结果类似:直角修正模型 > 直角双曲线模型/Michaelis-Menten模型。(2)层级间叶片光合响应参数的差异显著性因模型而有别,各模型得到的方向间叶片光合响应参数值的差异均不显著。(3)模型对初始量子效率、光响应最大净光合速率、光饱和点、暗呼吸速率、CO2响应最大净光合速率和CO2饱和点的影响更大,层级对光补偿点、初始羧化效率、CO2补偿点和光呼吸速率的影响更大,方向对光合响应参数无显著影响,光饱和点、CO2饱和点、初始羧化效率和CO2补偿点还受到交互作用的显著影响。 结论相对于其他模型,直角修正模型能更好地拟合无患子光合响应曲线,得到的光合响应参数也较准确;模型对所有光合响应参数的影响是极显著的,模型的筛选很重要。 Abstract:ObjectiveThe aim of this study was to explore the effects of photosynthetic models on the results of photosynthetic response parameters ’ values of leaves in different parts of Sapindus mukorossi canopy, and to obtain appropriate application model and reasonable values. MethodIn this study, S. mukorossi trees with stable fruiting stage were selected as the test trees in Jianning County of Fujian Province, southern China for determining photosynthetic response parameters of leaves in different parts of canopy. The rectangular hyperbolic model (RHM), non-rectangular hyperbolic model (NRHM), modified rectangular hyperbolic model (MRHM), and modified exponential model (MEM) were used for fitting the Pn-PAR response curves. The rectangular hyperbolic model (RHM), Michaelis-Menten model (MMM), and modified rectangular hyperbolic model (MRHM) were used for fitting the Pn-Ci response curves. The fitting accuracy of the models was tested by comparing mean square errors and determinant coefficients. The differences of photosynthetic response parameters ’ values among different models and different parts of canopy were examined by Duncan multiple comparison method and the data were also analyzed with ANOVA. Result(1) The fitting accuracy of the 4 models for Pn-PAR response curve was as follows: MRHM > MEM > NRHM > RHM. The 3 models for Pn-Ci response curve produced the similar results: MRHM > RHM/MMM. (2) The significant difference of photosynthetic response parameters’ values among different layers varied by different models and the difference of these values among different directions was not significant. (3) The influence of different models on α(I), Pnmax(I), LSP, Rd, Pnmax(C) and CiSP was greater, the influence of different layers on LCP, α(C), CiCP and Rp was greater, while the influence of different directions on these all response parameters was little. The values of LSP, CiSP, α(C) and CiCP were also significantly influenced by interaction. ConclusionCompared with other models, MRHM could be better for fitting the photosynthetic response curve and obtaining more accurate values. The influence of models on the values of all photosynthetic response parameters was very significant, so the screening of models was important. -
表 1 试验树的树体特征
Table 1. Features of the test trees
试验树编号
No. of test trees树高
Tree height/m东西冠幅
Crown width of
east and west/m南北冠幅
Crown width of
north and south/m胸径
DBH/cm枝下高
Under branch height/m上层厚度
Thickness of
upper layer/m中层厚度
Thickness of
middle layer/m下层厚度
Thickness of
lower layer/m1号 No.1 5.132 5.113 4.952 13.1 1.401 1.676 1.215 1.132 2号 No.2 5.158 5.217 4.913 13.4 1.362 1.723 1.264 1.068 3号 No.3 5.251 5.320 5.186 12.8 1.312 1.757 1.311 1.253 表 2 不同Pn-PAR和Pn-Ci模型的拟合精度
Table 2. Fitting accuracy of different Pn-PAR and Pn-Ci models
位置 Position 拟合精度
Fitting accuracy光响应模型 Pn-PAR model CO2响应模型 CO2 response model RHM NRHM MRHM MEM RHM MRHM MMM 上层 Upper layer MSE 0.823 0.536 0.127 0.161 0.581 0.470 0.581 R2 0.977 0.985 0.997 0.996 0.993 0.995 0.993 中层 Middle layer MSE 0.724 0.489 0.148 0.180 0.438 0.338 0.438 R2 0.982 0.988 0.995 0.994 0.994 0.995 0.994 下层 Lower layer MSE 0.741 0.532 0.236 0.277 0.466 0.223 0.466 R2 0.975 0.982 0.992 0.990 0.994 0.997 0.994 东 East MSE 0.661 0.437 0.150 0.169 0.358 0.255 0.358 R2 0.979 0.986 0.996 0.995 0.995 0.997 0.995 西 West MSE 0.633 0.411 0.144 0.181 0.538 0.505 0.538 R2 0.980 0.987 0.996 0.994 0.993 0.995 0.993 南 South MSE 0.755 0.497 0.195 0.226 0.469 0.295 0.469 R2 0.977 0.985 0.994 0.993 0.994 0.996 0.994 北 North MSE 0.711 0.539 0.213 0.240 0.463 0.309 0.463 R2 0.977 0.982 0.994 0.992 0.994 0.996 0.994 注:RHM. 直角双曲线模型;NRHM. 非直角双曲线模型;MRHM. 直角修正模型;MEM. 指数修正模型。下同。Notes: RHM, rectangular hyperbolic model; NRHM, non-rectangular hyperbolic model; MRHM, modified rectangular hyperbolic model; MEM, modified exponential model. The same below. 表 3 不同模型及无患子冠层不同部位叶片光合响应参数的方差分析
Table 3. Variance analysis of photosynthetic response parameters of different models in different parts of S. mukorossi canopy
指标
Index变异来源
Source of variation光合响应参数 Photosynthetic response parameter α(I) Pnmax(I) LSP LCP Rd α(C) Pnmax(C) CiSP CiCP Rp F值
F value模型
Model1 281.861 452.813 8 279.844 18.759 77.626 228.505 710.224 2 239.936 82.198 89.757 层级
Layer21.404 110.418 27.748 39.821 56.245 451.515 38.443 5.841 115.697 117.487 方向
Direction2.374 2.275 2.453 3.726 2.220 1.370 0.315 0.927 2.296 2.898 模型 × 层级
Model × layer2.136 1.220 7.200 0.285 0.433 2.172 0.939 20.255 1.138 0.118 模型 × 方向
Model × direction0.934 0.169 0.808 0.320 0.164 0.416 0.227 0.520 0.535 0.180 层级 × 方向
Layer × direction0.760 1.581 1.104 1.855 1.420 10.120 1.043 1.759 6.385 1.729 模型 × 层级 × 方向
Model × layer × direction0.514 0.217 0.583 0.194 0.046 0.303 0.043 2.218 0.147 0.135 P值
P value模型
Model< 0.01 < 0.01 < 0.01 < 0.01 < 0.01 < 0.01 < 0.01 < 0.01 < 0.01 < 0.01 层级
Layer< 0.01 < 0.01 < 0.01 < 0.01 < 0.01 < 0.01 < 0.01 0.004 < 0.01 < 0.01 方向
Direction0.056 0.106 0.068 0.055 0.358 0.156 0.714 0.432 0.122 0.105 模型 × 层级
Model × layer0.061 0.303 < 0.01 0.943 0.855 0.067 0.447 < 0.01 0.370 0.976 模型 × 方向
Model × direction0.500 1.000 0.610 0.967 0.997 0.866 0.967 0.791 0.780 0.981 层级 × 方向
Layer × direction0.703 0.161 0.366 0.131 0.248 < 0.01 0.405 0.076 < 0.01 0.257 模型 × 层级 × 方向
Model × layer × direction0.946 1.000 0.904 1.000 1.000 0.987 1.000 0.019 1.000 1.000 注:α(I). 初始量子效率;Pnmax(I). 光响应最大净光合速率;LSP. 光饱和点;LCP. 光补偿点;Rd. 暗呼吸速率;α(C). 初始羧化效率;Pnmax(C). CO2响应最大净光合速率;CiSP. CO2饱和点;CiCP. CO2补偿点;Rp. 光呼吸速率。下同。Notes: α(I), initial carboxylation efficiency; Pnmax(I), maximum photosynthesis rate of response for light; LSP, light saturation point; LCP, light compensation point; Rd, dark-respiration rate; α(C), initial carboxylation efficiency; Pnmax(C), maximum photosynthesis rate of response for CO2; CiSP, CO2 saturation point; CiCP, CO2 compensation point; Rp, photo-respiration rate. The same below. 表 4 无患子树冠各层级叶片不同Pn-PAR模型拟合的光响应参数值
Table 4. Pn-PAR response parameters of leaves in different layers of S. mukorossi canopy
位置
Position模型
Model光合响应参数 Photosynthetic response parameter α(I) Pnmax(I)/
(μmol·m− 2·s− 1)LSP/
(μmol·m− 2·s− 1)LCP/
(μmol·m− 2·s− 1)Rd/
(μmol·m− 2·s− 1)上层
Upper layerRHM 0.075 ± 0.002aA 18.044 ± 0.469aA 391.458 ± 5.125aA 40.009 ± 3.446aA 2.568 ± 0.124aA NRHM 0.038 ± 0.002bA 15.067 ± 0.377bA 468.455 ± 15.438bA 47.812 ± 5.546aA 1.780 ± 0.136bA MRHM 0.044 ± 0.002cA 13.102 ± 0.544cA 1 110.128 ± 28.085cA 45.820 ± 4.986aA 1.886 ± 0.113bcA MEM 0.040 ± 0.002bA 13.153 ± 0.504cA 1 079.776 ± 12.353cA 46.608 ± 5.263aA 1.771 ± 0.111bA 仪器测定
Measured by instrument13.993 ± 0.393cA 1 200dA 40 ~ 60 2.187 ± 0.191cA 中层
Middle layerRHM 0.076 ± 0.001aAB 16.276 ± 0.797aB 373.078 ± 11.500aB 43.640 ± 4.275aAB 2.751 ± 0.232aAB NRHM 0.043 ± 0.003bB 14.031 ± 0.896bAB 382.385 ± 24.289aB 52.099 ± 7.272aA 2.142 ± 0.234bB MRHM 0.049 ± 0.004cA 11.349 ± 0.972cB 1 111.302 ± 22.801bA 50.241 ± 5.389aA 2.219 ± 0.335bAB MEM 0.043 ± 0.003bA 11.437 ± 0.921cB 1 063.319 ± 29.289bAB 51.312 ± 5.608aAB 2.076 ± 0.348bA 仪器测定
Measured by instrument12.510 ± 1.122bcB 1 200cA 40 ~ 60 2.483 ± 0.221abAB 下层
Lower layerRHM 0.077 ± 0.002aB 15.940 ± 0.230aB 376.081 ± 3.619aB 48.014 ± 3.801aB 2.988 ± 0.204aB NRHM 0.043 ± 0.002bB 13.726 ± 0.305bB 412.835 ± 6.835aB 58.259 ± 5.786bA 2.370 ± 0.157bcB MRHM 0.047 ± 0.002cA 11.253 ± 0.473cB 1 087.184 ± 40.961bA 56.661 ± 5.973abA 2.402 ± 0.166bcB MEM 0.041 ± 0.001bA 11.107 ± 0.466cB 1 030.631 ± 24.385cB 58.513 ± 6.141bB 2.247 ± 0.169bA 仪器测定
Measured by instrument12.277 ± 0.756cB 1 200dA 40 ~ 60 2.617 ± 0.200cB 注:同列数据后不同小写字母表示模型间差异显著,同列数据后不同大写字母表示层级间差异显著。下同。Notes: different lowercase letters behind the same column represent significant difference among different models; different capital letters behind the same column represent significant difference among different canopy layers. The same below. 表 5 无患子树冠各层级叶片不同Pn-Ci模型拟合的CO2响应参数值
Table 5. CO2 response parameters of leaves in different parts of S. mukorossi canopy by varied Pn-Ci fitting models
位置
Position模型
Model光合响应参数 Photosynthetic response parameter α(C) Pnmax(C)/
(μmol·m− 2·s− 1)CiSP/
(μmol·m− 2·s− 1)CiCP/
(μmol·m− 2·s− 1)RP/
(μmol·m− 2·s− 1)上层
Upper layerRHM 0.157 ± 0.017aA 41.143 ± 1.600aA 532.685 ± 3.228aA 72.363 ± 2.706aA 8.983 ± 1.092aA MRHM 0.111 ± 0.013bA 25.695 ± 0.727bA 1687.327 ± 69.859bA 67.928 ± 3.153aAB 6.687 ± 1.087bA MMM 0.157 ± 0.017aA 41.143 ± 1.600aA 532.685 ± 3.228aA 72.363 ± 2.706aA 8.983 ± 1.092aA 仪器测定
Measured by instrument25.595 ± 0.737bA 1 372.517 ± 148.994cAB 67.685 ~ 90.082 中层
Middle layerRHM 0.143 ± 0.011aA 36.972 ± 0.987aB 524.590 ± 6.366aA 71.313 ± 1.560aA 8.078 ± 0.570aAB MRHM 0.096 ± 0.011bA 23.355 ± 0.629bB 1 686.436 ± 126.385bA 65.764 ± 1.082bA 5.591 ± 0.575bAB MMM 0.143 ± 0.011aA 36.972 ± 0.987aB 524.590 ± 6.366aA 71.313 ± 1.560aA 8.078 ± 0.570aAB 仪器测定
Measured by instrument23.442 ± 0.419bB 1 251.471 ± 21.290cA 73.015 ~ 82.999 下层
Lower layerRHM 0.088 ± 0.009aB 37.678 ± 0.614aB 682.982 ± 27.242aB 80.555 ± 1.698aB 5.939 ± 0.455aB MRHM 0.056 ± 0.002bB 23.095 ± 0.450bB 1 539.553 ± 108.241bA 71.589 ± 3.047bB 3.738 ± 0.091bB MMM 0.088 ± 0.009aB 37.678 ± 0.614aB 682.982 ± 27.242aB 80.555 ± 1.698aB 5.939 ± 0.455aB 仪器测定
Measured by instrument23.200 ± 0.324bB 1 420.349 ± 32.852bB 71.451 ~ 91.422 -
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