Modeling effects of changes in diffuse radiation on light use efficiency in forest ecosystem. Wei Nan

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1 Modeling effects of changes in diffuse radiation on light use efficiency in forest ecosystem Wei Nan

2 Outline 1. Background 2. Material and methods 3. Results & Discussion 4. Conclusion 2

3 1 Background 3

4 Background Diffuse radiation Light use efficiency (LUE) (Gu et al., 2002; Law et al., 2002). Quantitative analysis of the effect of diffuse radiation on LUE needs to be further studied (He et al., 2011). Soil-Plant-Atmosphere Continuum (SPAC) multiple layers, separated into sunlit and shaded components (Williams et al., 1996). 4

5 Objectives Applying the modified light response model, we analyze the initial quantum efficiency and the capacity of a canopy to resist photosynthetic saturation at high levels of photosynthetically active radiation (PAR) under direct PAR and diffuse PAR in order to clarify the effects of diffuse PAR on photosynthetic characteristics of vegetation. Furthermore, we used Soil-Plant-Atmosphere Continuum (SPAC) model to simulate LUE in different layers of canopy and analyze the impacts of changes in diffuse radiation on LUE. 5

6 2 Material and methods 6

Experimental Sites Sites Landscape Latitude and Longitude Altitude

Korean pine forest of Changbai Mountain (CBS) 42 24 N, 128 6 E 784

7 Experimental Sites Sites Landscape Latitude and Longitude Altitude (m) Annual mean temperature ( ) Annual rainfall mm) Broad leaved Korean pine forest of Changbai Mountain (CBS) N, E Subtropical plantation coniferous forest at Qianyanzhou (QYZ) N, E Coniferous and subtropical broad-leaved mixed forest in Dinghushan (DHS) N, E

8 Material min CO 2 flux data Routine meteorological data (S 0, PAR, T a, T s, VPD, Wspd, PAR, Rain et al.) 站点地形通量观测高度 (m) 辐射观测高度 ( 两层 ) (m) 降水观测高度 (m) 温度和相对湿度观测高度 (m) 土壤温度测定深度 ( 五层 ) (m) 土壤水分测定深度 ( 三层 ) (m) CBS 平坦 40 32, , 8.0, 22.0, 26.0, 32.0, 50.0, , 0.10, 0.20, 0.50, , 0.2, 0.5 QYZ 丘陵 39 42, , 7.6, 11.6, 15.6, 23.5, 31.6, , 0.05, 0.20, 050, , 0.2, 0.5 DHS 山地 27 36, , 9.0, 15.0, 21.0, 27.0, 31.0, , 0.10, 0.20, 0.50, , 0.2, 0.4 8

APAR represents the total amount of photosynthetic effective radiation absorbed by the

9 Light use efficiency (LUE): (1) (2) where GPP is ecosystem gross primary productivity, mg CO 2 m -2 s -1 ; PAR is photosynthetic active radiation, μmol m -2 s -1. APAR represents the total amount of photosynthetic effective radiation absorbed by the ecosystem leaves (μmol m - 2 s - 1 ). (3) R e =R ref e E 0 (1/ (T ref T 0 ) 1/ (T s T 0 )) (4) 9

10 Clearness index, k t : k t = S 0 S e S e =S sc [ cos 2 (360t d /365)]sinh (5) (6) Diffuse radiation: 0 k S k t 0.3; Sf / S f / Se = kt ( kt sinh) 0.3< kt < 0.78; 0.1k t Sf / Se 0.97k t S S = k ( k 0.177sin h) f / e t t + kt Sf / Se 0.1 Sf / Se = kt (0.486k t 0.78; k e t t 0.182sin h) (7) (8) (9) (10) (11) (12) 10

11 Light Responsive Curve Models NEE= αparβ αpar R e (13) NEE= (α f I f+α r I r ) (β f I f +β r I r ) (β f I f +β r I r )+ (α f I f +α r I r )I t R e (14) where α f (mgco 2 μmol -1 photon) and α r are the initial canopy quantum yield for diffuse (I f ) and direct (I r ) PAR, respectively, and β f (mgco 2 m 2 s 1 ) and β r are the capacity of a canopy to resist photosynthetic saturation at high levels of PAR for diffuse and direct PAR, respectively. (Gu et al., 2002) 11

12 SPAC model 12

13 Input parameters Table2-1 Layers of canopy in SPAC Canopy layers site la_frac CBS/QYZ nit_frac CBS/QYZ CBS ht(m) QYZ Table2-2 Layers of soil in SPAC in CBS Soil layers core Layer_thickness(m) Organic_fraction Mineral_fraction Initial_water_fraction Initial_soil_temp (K) rootfrac

14 Soil layers core Layer_thickness(m) Organic_fraction Mineral_fraction Initial_water_fraction Initial_soil_temp (K) rootfrac Parameters Input values CBS QYZ Source totla (m 2 m -2 ) observed value totn (gn m -2 ) observed value gplant (mol m -1 s -1 MPa -1 ) Default value minlwp(mpa) Optimal value iota(n/a) Optimal value capac(mol m -2 MPa -1 ) Optimal value rootresist(mpa s g mol -1 (biomass based)) Table2-3 Layers of soil in SPAC in QYZ Table2-4 Parameters of vegetation in SPAC Optimal value kappac(mol g -1 s -1 ) literature(zhang,2006) kappaj(mmol g -1 s -1 ) literature(zhang,2006) 14

15 3 Results & Discussion 15

16 光能利用率 (gco 2 mol -1 photon) 气温 ( ) 饱和水气压差 (kpa) Environmental factors : CBS QYZ DHS 月份 CBS QYZ DHS 月份 CBS QYZ DHS CBS 趋势线 R 2 =-0.1 P=0.5 QYZ 趋势线 R 2 =0.3 P=0.2 DHS 趋势线 R 2 =0.2 P= 年份 16

17 光能利用率 (gco 2 mol -1 ) 光能利用率 (gco 2 mol -1 ) 光能利用率 (gco 2 mol -1 ) The variation of LUE in forest ecosystem with the ratio of diffuse radiation to global solar radiation: 4 3 R 2 =0.61 P< 年 CBS 4 3 R 2 =0.60 P< 年 QYZ 4 3 R 2 =0.50 P< 年 DHS 散射辐射占总辐射的比例散射辐射占总辐射的比例散射辐射占总辐射的比例 The increase of LUE in the ratio of diffuse radiation to global solar radiation (S f / S 0 ) range of 70% to 85% than that in the S f / S 0 range of 55% to 70%: CBS 19.7% 3.9% 6.6% 21.9% 16.5% 15.6% QYZ 6.3% 12.8% 13.2% -0.7% 29.3% -0.5% DHS 13.0% 23.1% -3.6% 11.7% 32.2% 19.7% 17

18 初始量子效率 (gco 2 mol -1 ) 光饱和时最大潜在光合速率 (mgco 2 m -2 s -1 ) 净生态系统生产力 NEE(mg CO 2 m -2 s -1 ) Photosynthetic efficiency of three typical forest ecosystems under cloudy and clear sky conditions and direct and diffuse radiation conditions: CBS 2 多云条件晴空条件多云条件下的拟合曲线 R 1 2 =0.62 P<0.05 晴空条件下的拟合曲线 R 2 =0.49 P< r f CBS 2006 年光合有效辐射 PAR( mol m -2 s -1 ) r f CBS 2006 年 0 6/5 6/25 7/15 8/4 8/24 日期 0 6/5 6/25 7/15 8/4 8/24 日期 18

19 初始量子效率 (gco 2 mol -1 ) 光饱和时最大潜在光合速率 (mgco 2 m -2 s -1 ) 初始量子效率 (gco 2 mol -1 ) 净生态系统生产力 NEE(mg CO 2 m -2 s -1 ) RESEARCH RESULTS 2 多云条件晴空条件多云条件下的拟合曲线 1 R 2 =0.56 P<0.05 晴空条件下的拟合曲线 R 2 =0.42 P< QYZ r f QYZ 2006 年 -16 r 5 f QYZ 2003 年光合有效辐射 PAR( mol m -2 s -1 ) /5 6/25 7/15 4 8/4 8/24 日期 r f QYZ 2006 年 0 6/5 6/25 7/15 8/4 8/24 日期 0 6/5 6/25 7/15 8/4 8/24 日期 19

20 初始量子效率 (gco 2 mol -1 ) 光饱和时最大潜在光合速率 (mgco 2 m -2 s -1 ) 净生态系统生产力 NEE(mg CO 2 m -2 s -1 ) DHS r f 多云条件晴空条件多云条件下的拟合曲线 R 2 =0.53 P<0.05 晴空条件下的拟合曲线 R 2 =0.62 P<0.05 The initial -1 quantum efficiency under diffuse PAR condition (α f ) is higher than that (α r ) under direct PAR condition by averaged g CO mol -1 photon, 0.26gCO mol -1 photon and 0.31gCO 2 mol光合有效辐射 -1 photon in PAR( mol m CBS, QYZ -2 and s -1 ) DHS respectively without drought stress from June to August from 2003 to Compared with diffuse PAR condition, 5 the capacity of canopy to r resist photosynthetic saturation at high levels of PAR (β f ) is DHS 2006 more DHS 2006 年年 than that (β r ) under direct PAR condition in CBS, QYZ, and DHS by averaged about 0.4 mg 3 CO 2 m -2 s -1 approximately during study period f 0 6/5 6/25 7/15 8/4 8/24 日期 0 6/5 6/25 7/15 8/4 8/24 日期 20

21 生态系统总初级生产力 GPP(mgCO 2 m -2 s -1 ) GPP 模拟值 (mgco 2 m -2 s -1 ) 生态系统总初级生产力 GPP(mgCO 2 m -2 s -1 ) GPP 模拟值 (mgco 2 m -2 s -1 ) The comparison between the simulated and measured GPP: CBS GPP 观测值 GPP 模拟值 CBS 2006 年 y=1.02x R 2 =0.86 P<0.05 CBS 2006 年日序 QYZ GPP 模拟值 GPP 观测值 QYZ 2006 年日序 GPP 观测值 (mgco 2 m -2 s -1 ) 2.0 y=1.2x R 2 =0.68 P< QYZ 2006 年 GPP 观测值 (mgco 2 m -2 s -1 ) 21

22 RESEARCH RESULTS Assessment index between simulated and observed values for GPP Year r R 2 RMSE (mgco 2 m -2 s -1 ) MBE (mgco 2 m -2 s -1 ) CBS QYZ CBS QYZ CBS QYZ CBS QYZ CBS QYZ NS

23 Sensitivity of SPAC model parameters parameters effect on GPP when ±10% bias is applied (CBS) effect on GPP when ±10% bias is applied (QYZ) parameters effect on GPP when ±10% bias is applied (CBS) effect on GPP when ±10% bias is applied (QYZ) iota(n/a) 43.60% 19.40% VPD(kpa) 2.80% 3.40% CO 2 (ppm) 12.80% 12.80% capac(mol m-2 MPa-1) 1.80% 0.50% minlwp(mpa) 6.50% 3.10% Dimen(m) 0.80% 0.20% fdiff (μmol m-2 s-1) 5.00% 4.40% WSPD(m/s) 0.40% 0.10% PAR(μmol m-2 s-1) 4.20% 5.30% kappac(mol g-1 s-1) 0.30% 1.70% T( ) 3.80% 11.70% lai(m m-2) 2.50% 4.40% rootresist(mpa s g mol-1 (biomass based)) kappaj(mmol g-1 s-1) 3.00% 2.90% gplant(mol m-1 s-1 MPa-1) 3.70% 2.20% N 8.20% 4.90% 0.10% 2.90% Initial_water_fracti on 0.80% 3.80%

24 Uncertainty analysis and relative error contribution of parameters of SPAC model parameters parameters effect on GPP by situ uncertainty (CBS) Relative error contribution (CBS) effect on GPP by situ uncertainty (QYZ) Relative error contribution (QYZ) PAR(μmol m -2 s -1 ) 39.8% 39.2% 34.3% 39.9% fdiff (%) 31.6% 39.5% 27.1% 4.0% CO 2 (ppm) 17.4% 0.1% 7.2% 3.3% VPD(kpa) 9.9% 68.4% 3.4% 40.8% minlwp(mpa) 6.5% 5.8% 3.1% 0.1% iota(n/a) 3.9% 37.4% 1.7% 68.2% T( ) 3.9% 0.5% 11.2% 3.6% rootresist(mpa s g mol % 2.0% 2.2% 0.5% (biomass based)) kappaj(mmol g -1 s -1 ) 3.0% 2.4% 2.9% 4.7% capac(mol m -2 MPa -1 ) 1.8% 0.4% 0.5% 0.03% WSPD(m/s) 1.7% 5.6% 0.3% 8.7% lai 17.7% 38.6% 1.1% 102.9% N 22.9% 6.2% 34.9% 23.7% Initial_water_fraction 6.3% 24.1% 10.0% 87.4% Dimen (m) 0.8% 0.06% 0.2% 2.7% kappac(mol g -1 s -1 ) 0.3% 4.0% 1.7% 0.3% gplant(mol m -1 s -1 MPa -1 ) 0.1% 0.2% 0.1% 0.05% 24

25 The results of the ten layers LUE (gco 2 mol -1 photon)in CBS Layers June July August June July August June July August Entire canopy

26 The results of the ten layers LUE (gco 2 mol -1 photon)in QYZ Layers June July August June July August June July August Entire canopy

27 Increasing proportion of the ten layers LUE when the diffuse radiation increased by 10% in CBS Layers June July August June July August June July August % 10.3% 15.5% 6.5% 14.1% 17.0% 4.0% 11.2% 13.0% % 10.3% 15.7% 6.6% 14.3% 17.1% 4.2% 11.5% 13.1% % 10.4% 15.9% 6.8% 14.4% 17.3% 4.4% 11.6% 13.2% % 11.1% 16.2% 7.5% 14.7% 17.6% 4.9% 12.0% 13.5% % 12.1% 16.7% 8.8% 15.8% 17.9% 6.3% 13.0% 14.0% % 13.2% 17.3% 10.4% 16.9% 18.3% 8.0% 14.2% 14.5% % 14.7% 18.0% 12.1% 18.2% 18.8% 10.1% 15.5% 15.4% % 16.3% 18.9% 13.7% 19.3% 19.8% 12.0% 16.6% 16.2% % 17.9% 19.4% 15.2% 20.3% 20.4% 13.8% 17.9% 17.0% % 19.0% 20.2% 16.8% 21.4% 21.2% 15.4% 18.9% 17.6% Entire canopy 17.4% 25.3% 16.2% 11.2% 22.1% 17.1% 8.7% 16.2% 13.5% 27

28 Increasing proportion of the ten layers LUE when the diffuse radiation increased by 10% in QYZ Layers June July August June July August June July August % 2.9% 10.1% 11.8% -1.0% 10.2% 21.3% 5.3% 10.5% % 3.0% 10.2% 11.8% -0.2% 10.3% 21.3% 5.4% 10.6% % 3.2% 10.2% 12.2% 0.0% 10.4% 21.3% 5.5% 10.6% % 3.9% 10.5% 13.3% 0.0% 10.6% 21.4% 5.9% 10.8% % 6.2% 10.9% 14.7% 3.1% 11.0% 21.4% 7.0% 11.1% % 7.8% 11.1% 16.6% 4.5% 11.3% 21.5% 8.7% 11.3% % 9.4% 11.3% 18.0% 6.6% 11.5% 21.3% 9.7% 11.4% % 10.4% 11.5% 19.4% 7.7% 11.9% 21.2% 10.8% 11.5% % 11.3% 11.7% 20.4% 8.7% 12.4% 21.2% 11.2% 11.8% % 12.2% 11.9% 23.5% 9.6% 12.9% 20.9% 11.7% 11.8% Entire canopy 14.6% 6.5% 11.1% 14.7% 3.6% 11.3% 21.6% 7.9% 11.3% 28

4 % from June to August from 2006 to 2008 in QYZ.

29 The change of the LUE for entire canopy when the diffuse radiation increased by 10% For the entire canopy, the gross primary productivity (GPP) and LUE increase respectively by average of 2.8 % and 11.4 % from June to August from 2006 to 2008 in QYZ. For the entire canopy, the gross primary productivity (GPP) and LUE increase respectively by average of 3.4 % and 16.4 % from June to August from 2006 to 2008 in CBS. 29

30 4 Conclusion 30

31 Conclusion (1)The increase of diffuse radiation fraction in global solar radiaton can enhance light use efficiency (LUE) in CBS, QYZ and DHS. (2)The diffused PAR can enhance LUE than the direct PAR under weak light conditions without air temperature and water stress. The diffuse PAR was more benefit to improve the photosynthetic capacity of forest ecosystem compared to direct radiation. (3)When the other environmental factors kept normal daily variation and the diffuse radiation in global solar radiation increased by 10 %, for the entire canopy, the gross primary productivity (GPP) and LUE increase by average of 3.4 % and 16.4 % in CBS, and GPP and LUE increase by average of 2.8 % and 11.4 % in QYZ, respectively. 31

32 Thank you for your attention! 32

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