**7. Conclusion**

190 International Perspectives on Global Environmental Change

NITNDL,*t* = [(0.0226 NE + 1.180) exp-0.27*t*] [(100 exp-0.27*t* – 120)/(-20)] 10 (13)

NITNDL,*t* = [(0. 0104 NE + 0.164) exp-0.03*t*] [(100 exp-0.03*t* – 110)/(-23)] 10 (14)

NITNDL,*t* = [(0. 0122 NE + 0.096) exp-0.02*t*] [(100 exp-0.02*t* – 105)/(-174)] 10 (15)

**6.4 Dynamics of dead plant tissues and excreta-derived nitrogen in colonized forest**  Using the empirical models in equations 7-9 and 13-15, long-term patterns of the remaining mass of dead plant tissues and in the N mass during decomposition were estimated for forest stands colonized by cormorants (Fig. 17). The models show the different roles of plant

At the time of litterfall (i.e., 0 year), needles, twigs, and CWD account for approx. 50%, 25%, and 25% of total litterfall, respectively (Fig. 17). However, needles almost disappear before 20 years of decomposition because the mass loss for them is much faster than that for twigs and CWD. After 20 years twigs and CWD constitute the dominant components of the detritus pool in the forest stand. Although not shown in Fig. 17, CWD becomes two times

0

0 10 20 30

**Nitrogen mass in remaining tissues**

CWD

Needles Twigs

Time (years)

50

100

kg/ha

Fig. 17. Estimated long-term changes in the remaining mass of dead plant tissues and the nitrogen mass in the remaining tissues during decomposition in forest stand colonized by cormorants at 200 nests/ha, the mean value at Isaki Peninsula in 2000 (Fujiwara, 2001). The models start with litterfall in a single year, and the figures show decomposition for 30

Needles account for 87% of N in dead plant tissues at the time of litterfall because the initial N contents are 3 and 15 times higher than in twigs and CWD, respectively (Fig. 17). During the first two years of decomposition, N mass in needles increased 1.8 times compared to that of the initial mass due to the net immobilization of excreta-derived N (Section 5.2). The N

150

tissues as components of the forest floor and reservoirs of excreta-derived N.

more important quantitatively than twigs at 60 years of decomposition.

0 10 20 30

CWD

**Remaining mass of dead plant tissues**

Time (years)

Needles:

Twigs:

CWD:

0

Needles

Twigs

2

4

6

t/ha

years.

8

10

The series of studies demonstrated that excess supply of excreta-derived N changed the community structure, nutrition, and substrate utilization of saprobic fungi, which by altering the decomposition processes led to carbon sequestration, accumulation of excretaderived N, and thus a slow turnover of carbon and N in forest soils affected by the cormorant (Fig. 18). Most of the previous studies examined the effects of excess supply of nutrients on fungal communities, microbial activities, decomposition processes, or soil carbon accumulation separately, and the interactions and possible causal relationships between these biological and ecosystem processes have rarely been explored. This case study of cormorant-derived excreta deposition in conifer plantations at Isaki Peninsula thus can provide useful implications for the understanding of biological mechanisms underlying the N-induced sequestration of soil carbon in forest ecosystems supplemented with excess nutrients.

The past century is the first time since the evolution of modern N cycle linked to microbial processes with robust natural feedbacks and controls that human activities may have produced the largest impact on global N cycle (Canfield et al., 2010). Disrupted N cycles due to excess supply of N of anthropogenic origin and the concomitant buildup of N and carbon sequestration in forest soils are one of major global issues because of its potential influence on the evolution of carbon dioxide and feedback to global warming (Nadelhoffer et al., 1999; de Vries et al., 2006). The present study highlights potential importance of fungi and their indispensable roles linking N deposition with carbon sequestration in soils. Future research directions include the dynamics of phosphorus (Conley et al., 2009), another major nutrient that is abundantly contained in excreta (Hobara et al., 2005), and which limits primary production more frequently than N and has different effects on soil processes and fungal activity.

Excess Supply of Nutrients, Fungal Community, and Plant Litter

*Sequestration*. Springer Verlag, Berlin

nitrogen cycle. *Science*, 330, 192-196

phosphorus. *Science*, 323, 1014-1015

*Change Biology*, 12, 1151-1173

*Biological Review*, 63, 433-462

*Advances in Ecological Research*, 15, 133-302

deposition*. Water, Air, and Soil Pollution*, 130, 679-684

66-71

Japanese)

English abstract)

*Ecology*, 57, 728-739

*Botany*, 66, 1539-1546

*Microbiology*, 9, 1306-1316

Decomposition: A Case Study of Avian-Derived Excreta Deposition in Conifer Plantations 193

Berg, B. (1986). Nutrient release from litter and humus in coniferous forest soils - a mini

Berg, B. (1988). Dynamics of nitrogen (15N) in decomposing Scots pine (*Pinus sylvestris*)

Berg, B.; Matzner, E. (1997). Effect of N deposition on decomposition of plant litter and soil

Berg, B.; McClaugherty, C. (2003). *Plant Litter, Decomposition, Humus Formation, Carbon* 

Blackwood, C.B.; Waldrop, M.P.; Zak, D.R.; Sinsabaugh, R.L. (2007). Molecular analysis of

Canfield, D.E.; Glazer, A.N.; Falkowski, P.G. (2010). The evolution and future of Earth's

Conley, D.J.; Paerl, H.W.; Howarth, R.W.; Boesch, D.F.; Seitzinger, S.P.; Havens, K.E.;

De Vries, W.; Reinds, G.J.; Gundersen, P.; Sterba, H. (2006). The impact of nitrogen

Fenn, P.; Choi, S.; Kirk, T.K. (1981). Ligninolytic activity of *Phanerochaete chrysosporium*:

Fog, K. (1988). The effect of added nitrogen on the rate of decomposition of organic matter.

Fujiwara, S. (2001). *Forest decline in cormorant colonies*. Master thesis, Kyoto University (in

Fujiwara, S.; Takayanagi, A. (2001). The influence of the common cormorant (*Phalacrocorax* 

Fukasawa, Y.; Osono, T.; Takeda, H. (2009). Effects of attack of saprobic fungi on twig litter decomposition by endophytic fungi. *Ecological Research*, 24, 1067-1073 Harmon, M.E.; Franklin, J.F.; Swanson, F.J.; Sollins, P.; Gregory, S.V.; Lattin, J.D.; Anderson,

Hassett, J.E.; Zak, D.R.; Blackwood, C.B.; Pregitzer, K.S. (2009). Are basidiomycete laccase

Hobara, S.; Osono, T.; Koba, K.; Tokuchi, N.; Fujiwara, S.; Kameda, K. (2001). Forest floor

needle litter. Long-term decomposition in a Scots pine forest. VI. *Canadian Journal of* 

fungal communities and laccase genes in decomposing litter reveals differences among forest types but no impact of nitrogen deposition. *Environmental* 

Lancelot, C.; Likens, G.E. (2009). Controlling eutrophication: nitrogen and

deposition on carbon sequestration in European forests and forest soils. *Global* 

physiology of suppression by NH4+ and L-glutamate. *Archives in Microbiology*, 130,

*carbo* Kuroda) on forest decline. *Applied Forest Science*, 10, 85-90 (in Japanese with

N.H.; Cline, S.P.; Aumen, N.G.; Sedell, J.R.; Lienkaemper, G.W.; Cromack, Jr., K.; Cummins, K.W. (1986). Ecology of coarse woody debris in temperate ecosystems.

gene abundance and composition related to reduced ligninolytic activity under elevated atmospheric NO3- deposition in a northern hardwood forest? *Microbial* 

quality and N transformations in a temperate forest, affected by avian-derived N

review. *Scandinavian Journal of Forest Research*, 1, 359-369

organic matter in forest systems. *Environmental Review*, 5, 1-25

Fig. 18. Schematic diagram showing the possible effects of excess supply of excreta-derived nitrogen on fungal community and activity and decomposition processes and its ecosystem consequences.
