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Stomatal regulation in field-grown Douglas-fir
G.J. Heij and J.W. Erisman (Editors). Acid Rain Research: Do we have enough answers ? 9 1995 Elsevier Science BV. All rights reserved.
STOMATAL
W.W.P.
REGULATION
Jans
and E.G.
IN F I E L D - G R O W N
473
DOUGLAS-FIR.
SteingrSver
IBN-DLO, I n s t i t u t e for F o r e s t r y P . O . B o x 23, 6700 A A W a g e n i n g e n ,
and N a t u r e R e s e a r c h The N e t h e r l a n d s .
1 9INTRODUCTION
S t o m a t a l a p e r t u r e is i m p o r t a n t in r e g u l a t i n g CO 2 and H20 exchange between leaf and e n v i r o n m e n t . Knowledge of s t o m a t a l regulation under various ambient conditions is i m p o r t a n t for m o d e l s in w h i c h u p t a k e of g a s e o u s air p o l l u t a n t s is e s t i m a t e d . N e e d l e s h i g h and low in the t r e e c r o w n are s u b j e c t to d i f f e r e n t a m b i e n t c o n d i t i o n s and m a y a l s o d i f f e r in s t o m a t a l r e g u l a t i o n (i). T h e r e f o r e , s t o m a t a l b e h a v i o u r was s t u d i e d on c u r r e n t - y e a r and o n e - y e a r - o l d needles high (sun adapted) and low (shade adapted) in the t r e e crown. B e t w e e n M a y and S e p t e m b e r in 1992 and 1993 2 t r e e s w e r e c l i m b e d e v e r y 2 w e e k s to m e a s u r e gas exchange with a portable gas exchange unit (ADC, LCA-2). T r a n s p i r a t i o n r a t e (E), s t o m a t a l c o n d u c t a n c e (gs) and m e t e o r o l o g i c a l d a t a w e r e m e a s u r e d . A f t e r w a r d the s h o o t w a s cut and the shoot w a t e r p o t e n t i a l (P) was m e a s u r e d d i r e c t l y at the f o r e s t floor, u s i n g a p r e s s u r e bomb.
2 .RESULTS
In g e n e r a l the gs and E of n e e d l e s h i g h in the c r o w n w a s h i g h e r c o m p a r e d w i t h n e e d l e s low in the crown. No d i f f e r e n c e was f o u n d in gs and E b e t w e e n c u r r e n t - y e a r and o n e - y e a r old needles. H i g h in the c r o w n s t o m a t a l closure was only found u n d e r low l i g h t c o n d i t i o n s . No r e l a t i o n was e v i d e n t b e t w e e n gs and PAR. A clear relation was found between E and gs: E increased with increasing gs, but the slope was highly d e p e n d e n t on V P D (fig i). At h i g h VPD, t r a n s p i r a t i o n was m o r e s e n s i t i v e to c h a n g e s in gs. T h i s was a l s o f o u n d for o n e - y e a r old n e e d l e s and n e e d l e s low in the crown. E was also more s e n s i t i v e to c h a n g e s in gs at low P v a l u e s (more n e g a t i v e ) (fig 2). P decreased (became more negative) with increasing t r a n s p i r a t i o n to r e a c h a m i n i m u m at ca -17 Bar,
474 w h i l e E still increased (fig 3). E v i d e n t l y low P v a l u e s did not induce stomatal closure, as s o m e t i m e s r e p o r t e d in l i t e r a t u r e (2) N e e d l e s low in the c r o w n showed m u c h the same r e l a t i o n b e t w e e n E and P, a l t h o u g h E did not e x c e e d i000 ~Mol H20/m2.s.
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Gs (mm/a)
Gs ( m m l s ) 9
9
9
4
+
II
o
-15 - 0
Figure
9
2
<-1S
E (IJMol H , O I m ' . a )
Figure
3
F i g u r e 1: The r e l a t i o n b e t w e e n gs and E u n d e r d i f f e r e n t VPDr a n g e s of c u r r e n t - y e a r n e e d l e s high in the tree crown. (VPD (Pa): 1<500; 2=500-1000; 3 = 1 0 0 0 - 2 0 0 0 ; 4 = 2 0 0 0 - 3 0 0 0 ; 5>3000). F i g u r e 2: The r e l a t i o n b e t w e e n gs and E u n d e r d i f f e r e n t P ranges of c u r r e n t - y e a r needles high in the tree crown. (P (Bar): >-15 and <-15). F i g u r e 3: The r e l a t i o n b e t w e e n E and P of c u r r e n t - y e a r n e e d l e s h i g h in the tree crown.
3 9C O N C L U S I O N S
1 T r a n s p i r a t i o n rates w e r e m o r e s e n s i t i v e to gs at h i g h VPD ranges, and low shoot w a t e r potentials. 2 U n d e r these conditions, shoot w a t e r p o t e n t i a l s did not induce stomatal closure, high or low in the crown. 3 No d i f f e r e n c e s were found in stomatal regulation between n e e d l e s high and low in the crown and b e t w e e n c u r r e n t - y e a r and o n e - y e a r - o l d needles.
4. R E F E R E N C E S
1 W. Jans and E. Steingr~ver. IBN, Wageningen, The N e t h e r l a n d s , D o r s c h k a m p R e p o r t 695, 1992. 2 C. Tan and T. Black. B o u n d a r y - L a y e r M e t e o r o l o g y i0 (1976).
STOMATAL
W.W.P.
REGULATION
Jans
and E.G.
IN F I E L D - G R O W N
473
DOUGLAS-FIR.
SteingrSver
IBN-DLO, I n s t i t u t e for F o r e s t r y P . O . B o x 23, 6700 A A W a g e n i n g e n ,
and N a t u r e R e s e a r c h The N e t h e r l a n d s .
1 9INTRODUCTION
S t o m a t a l a p e r t u r e is i m p o r t a n t in r e g u l a t i n g CO 2 and H20 exchange between leaf and e n v i r o n m e n t . Knowledge of s t o m a t a l regulation under various ambient conditions is i m p o r t a n t for m o d e l s in w h i c h u p t a k e of g a s e o u s air p o l l u t a n t s is e s t i m a t e d . N e e d l e s h i g h and low in the t r e e c r o w n are s u b j e c t to d i f f e r e n t a m b i e n t c o n d i t i o n s and m a y a l s o d i f f e r in s t o m a t a l r e g u l a t i o n (i). T h e r e f o r e , s t o m a t a l b e h a v i o u r was s t u d i e d on c u r r e n t - y e a r and o n e - y e a r - o l d needles high (sun adapted) and low (shade adapted) in the t r e e crown. B e t w e e n M a y and S e p t e m b e r in 1992 and 1993 2 t r e e s w e r e c l i m b e d e v e r y 2 w e e k s to m e a s u r e gas exchange with a portable gas exchange unit (ADC, LCA-2). T r a n s p i r a t i o n r a t e (E), s t o m a t a l c o n d u c t a n c e (gs) and m e t e o r o l o g i c a l d a t a w e r e m e a s u r e d . A f t e r w a r d the s h o o t w a s cut and the shoot w a t e r p o t e n t i a l (P) was m e a s u r e d d i r e c t l y at the f o r e s t floor, u s i n g a p r e s s u r e bomb.
2 .RESULTS
In g e n e r a l the gs and E of n e e d l e s h i g h in the c r o w n w a s h i g h e r c o m p a r e d w i t h n e e d l e s low in the crown. No d i f f e r e n c e was f o u n d in gs and E b e t w e e n c u r r e n t - y e a r and o n e - y e a r old needles. H i g h in the c r o w n s t o m a t a l closure was only found u n d e r low l i g h t c o n d i t i o n s . No r e l a t i o n was e v i d e n t b e t w e e n gs and PAR. A clear relation was found between E and gs: E increased with increasing gs, but the slope was highly d e p e n d e n t on V P D (fig i). At h i g h VPD, t r a n s p i r a t i o n was m o r e s e n s i t i v e to c h a n g e s in gs. T h i s was a l s o f o u n d for o n e - y e a r old n e e d l e s and n e e d l e s low in the crown. E was also more s e n s i t i v e to c h a n g e s in gs at low P v a l u e s (more n e g a t i v e ) (fig 2). P decreased (became more negative) with increasing t r a n s p i r a t i o n to r e a c h a m i n i m u m at ca -17 Bar,
474 w h i l e E still increased (fig 3). E v i d e n t l y low P v a l u e s did not induce stomatal closure, as s o m e t i m e s r e p o r t e d in l i t e r a t u r e (2) N e e d l e s low in the c r o w n showed m u c h the same r e l a t i o n b e t w e e n E and P, a l t h o u g h E did not e x c e e d i000 ~Mol H20/m2.s.
m
8000
9
V"
,
IIF
e I
m
"
ye I
9
o
Z
"4
~, 9
o
w
o
9
0o
~~ m
+o o
9
o
O0
-II
O~
~ ~
~ ~
o
,
0~000
oo o o
0
-
O
1
l
,
,
I
I
4
$
0
1
1
0
4)
Figure
,,,
i
$
1
4
o
|
Gs (mm/a)
Gs ( m m l s ) 9
9
9
4
+
II
o
-15 - 0
Figure
9
2
<-1S
E (IJMol H , O I m ' . a )
Figure
3
F i g u r e 1: The r e l a t i o n b e t w e e n gs and E u n d e r d i f f e r e n t VPDr a n g e s of c u r r e n t - y e a r n e e d l e s high in the tree crown. (VPD (Pa): 1<500; 2=500-1000; 3 = 1 0 0 0 - 2 0 0 0 ; 4 = 2 0 0 0 - 3 0 0 0 ; 5>3000). F i g u r e 2: The r e l a t i o n b e t w e e n gs and E u n d e r d i f f e r e n t P ranges of c u r r e n t - y e a r needles high in the tree crown. (P (Bar): >-15 and <-15). F i g u r e 3: The r e l a t i o n b e t w e e n E and P of c u r r e n t - y e a r n e e d l e s h i g h in the tree crown.
3 9C O N C L U S I O N S
1 T r a n s p i r a t i o n rates w e r e m o r e s e n s i t i v e to gs at h i g h VPD ranges, and low shoot w a t e r potentials. 2 U n d e r these conditions, shoot w a t e r p o t e n t i a l s did not induce stomatal closure, high or low in the crown. 3 No d i f f e r e n c e s were found in stomatal regulation between n e e d l e s high and low in the crown and b e t w e e n c u r r e n t - y e a r and o n e - y e a r - o l d needles.
4. R E F E R E N C E S
1 W. Jans and E. Steingr~ver. IBN, Wageningen, The N e t h e r l a n d s , D o r s c h k a m p R e p o r t 695, 1992. 2 C. Tan and T. Black. B o u n d a r y - L a y e r M e t e o r o l o g y i0 (1976).