Appendix S1. A brief description of the model of solar radiation transmission through the canopy.
Solar radiation (S
0
) was separated into diffuse (S d0
) and direct beam components (S b0
) as described in
Leuning et al. (1995) [31]:
S d 0
 f d

S
0
(1)
S b 0
  f d
)

S
0
(2) where f d
is the fraction of diffuse radiation. S
0
was observed, and f d
was estimated using a segmented function of atmospheric transmissivity (τ a
) [57]: f d



1 2
 
1 a
0.2

0.3
 for for for
0.3
 a

0.3
  a

0.7
 a

0.7
(3) where τ a
was estimated using;
 a

S
0

S c
 sin
 
S c



  t d
 


(4)
(5) where t d
is Julian day; S c
is solar radiation; β is solar altitude (°) and sinβ can be calculated as: sin
 a b
  t h

12) / 24
 where t h
is solar time, and the a and b parameters can be calculated using functions 7 to 11: a
 sin
 l
 sin
 s b
 cos
 l
 cos
 s
(6)
(7)
(8)

sin
 s
      t d

10) / 365

(9) where λ l
is latitude and δ s
is solar declination.
The Q varied with canopy location; therefore, the Q of each canopy layer was calculated separately.
Q d 0
 f d

Q
0
Q b 0

1 f d
 
Q
0
(10)
(11) where Q d0
and Q b0
represent the diffusion and direct radiation components of the observed Q
0
, respectively, and 1 W∙m -2 (S
0
) =2 μmol∙m -2 s -1 (Q
0
) [31]. Shaded leaves receive diffuse radiation only, and sunlit leaves receive diffuse and direct beam radiation. The Q absorbed by shaded (Q sh
) and sunlit leaves
(Q sl
) was calculated as:
Q sh

Q ld

Q lbs
(12)
Q sl

Q lb

Q sh
(13)
In equation (12), ξ is cumulative leaf area index from the top canopy; Q ld
′ and Q lbs
represent the incident diffuse and scattered beam radiation, respectively, which are related to the extinction coefficient for radiation and the leaf area index (LAI) [58-59]. In equation (13), Q lb
represents absorbed beam radiation
[31]. Q ld
′ and Q lbs
were calculated as:
Q ld

Q d 0
 k d
' (1
 cd
 k d

(14)
Q lbs

Q b 0
 k b
' (1
 cb
) exp( k b
 k b
(1
 l
) exp( k b

)

(15) where ρ cb
is the canopy reflection coefficient for direct radiation, which can be calculated with the canopy reflection coefficient for horizontal leaves (ρ h
) using equation (16) [58]. ρ cd
is the canopy

reflection coefficient for diffusion radiation, with values of 0.057 and 0.389 for visible and near-infrared light, respectively, when diffusion radiation is uniformly distributed in a canopy with spherical leaf angle distribution [31, 59]. k d
′ and k b
′ represent the canopy extinction coefficient of diffusion and direct beam radiation, respectively, calculated using k b
and k d
in equations (17)-(18):
 cb
1 exp
 
2
 h
 k b
 
1
 k b
 
(16) k d
'
 k d

1
 l

1/ 2 k b
'
 k b

1
 l

1/ 2
(17)
(18)
In equation (16), ρ h
can be calculated as:
 h

1

1
 l

1/ 2
1

1
 l

1/ 2
(19)
In equations (17)-(18), k b
and k d
represent the extinction coefficients of direct beam and diffusion radiation, respectively, in an ideal canopy where a leaf is viewed as a “black body”. σ l
is the scattering coefficient (σ l
= 0.2 for visible light; σ l
= 0.8 for near-infrared radiation). Goudriaan and Van Laar (1994) reported that k d
is approximately 0.8 for spherical leaf angle distributions [59]. k b
is a function of β as follows: k b

0.5 sin

(20)