Forests Nutrients

Nitrogen cycle in trees

Leaf

Litter

Soil

Root

Stem

(Harada 1963 ;Tromp 1983; Millard, 1994; Aerts, 1996; Kolb and Evans, 2002;van Heerwaarden et al., 2003; Singh, 2014, 2015) )

Nitrogen resorption

Resorption mechanisms

• Many studies have dealt with the process of resorption

(Vergutz et al., 2012; Chavez-Vergara et al., 2015)

• The timing of resorption has not been looked in detail.

(Chapin and Kedrowski, 1983; Kobayashi and Tashiro, 2003)

• Protein hydrolysis (free amino acids) takes place during resorption.

(Vitousek et al., 1989; Killingbeck 2004; Mae 2004)

Focus

1. Determine the pattern of leaf N resorption in two tree species in humid mountainous areas of northeastern Japan.

2. Assess the difference in N demand between these two species.

Tree species used in this research

LarchLarix kaempferi

BeechFagus crenata

Deciduous

BroadleafConiferous

• Samples：

▶green leaf (GL)(Aug 2016)Beech, Larch → 6

▶pre- abscission (Pre-A) (Oct 2016)Beech, Larch → 6

▶post-abscission (Post-A)(Nov2016)Both species → 3

• Preparation

All samples were oven dried (70˚C)

Grinding of plant material

• Analysis

Nitrogen content (mg g-1)

Amino acid content (mg g-1)

• Statistical analysis

Tukey-Kramer method

Measurements and Analyses

Calculations

• Nitrogen resorption efficiency (NRE) (%) the percentage of N return from senescing leaves

(N content green leaf)－(N content post- abscission)/ (N content green leaf)×100

• Nitrogen resorption proficiency (NRP) (mg g-1)

the amount of N return from senescing leaves

(N content green leaf)－(N content post-abscission)

(Ozbucak et al., 2008)

19.8%

48.8%17.5%

33.4%

NRE NRP

Beech 68.7 14.8

Larch 50.9 8.6

Decrease of Leaf Nitrogen Content and NRE/NRP

Soil N content

0 5 10 15

0 - 5

5 - 15

15 - 30

0 - 5

5 - 15

15 - 30

N %

So

il d

ep

th (

cm

)

So

il d

ep

th (

cm

)

LarchForestBeech

Forest

N %

0

2

4

6

8

100

5

10

15

20

25

0

2

4

6

8

10

N c

on

ten

t (%

)

G.L. Pre-A Post-A

Seasonal movement of N

a

b b

a ab

a a

b

Leaf

Stem

Root

N c

on

ten

t (%

)

0

2

4

6

8

100

2

4

6

8

100

5

10

15

20

25

G.L. Pre-A Post-A

a ab

a

b b

aa

b

Beech Larch

Leaf N return

GL Pre- A Post- A

Each tree species return different amount of nitrogen

Hydrolysis and Amino acid content

• Proteins present in leaves

→Hydrolyzed during leaf

senescence (Ishida and Wada, 2008)

• Amino acids are derived from

hydrolysis (Ishida and Wada, 2008)

• In winter N is stored in stems and roots (decidious).

→Protein and amino acids(Tromp 1970, Chapin and Kedrowski, 1983)

Increase rate of each amino acid from GL to Pre-A

0 40 80 120 160

Ala

Arg

Asn

Asp

Glu

Gln

Gly

His

Ile

Leu

Lys

Met

Phe

Pro

Ser

Thr

Trp

Tyr

Val

Larch

0 40 80 120 160

Ala

Arg

Asn

Asp

Glu

Gln

Gly

His

Ile

Leu

Lys

Met

Phe

Pro

Ser

Thr

Trp

Tyr

Val

Beech

Asparagine

Glutamine

Conclusions

• Beech trees demand more N than larch trees do.

• There is more N resorption during the late autumn than

in early autumn.

• More proteins are probably absorbed at the beginning and

later more aminoacids are reabsorbed.

• Reabsorption is an important mechanism for N reuse in forests.