The Influence Mechanism Of Hommock Microtopography Pattern On Plant Litter Decomposition In Carex Peat Mire

Carex peat mire,widely spread in high latitude regions of northern hemisphere,plays an important role in maintaining global carbon balance and regulating climate.The plant litter decomposition is the key link of material cycling and energy flow in the peat mire ecosystem.Litter substrate quality and decomposition environment are the two important factors that affect the litter decomposition process.Tussock microtopography is a pervasive feature of Carex peat mire and the difference of microenvironment inside and outside tussocks created by Carex may lead to spatial heterogeneity in litter decomposition.A litter decomposition experiment through litterbag method was conducted to study the the litter decomposition process and influencing factors in a Carex schmidtii litter peat mire in Changbai Mountain,Northeast of China.The main conclusion as following:(1)In the reference site,there are 2.26 tussocks per m~2,the coverage of tussocks is 60%-80%.The litter dry weight inside tussocks(1.43±0.08)kg/m~2 was lower than that outside tussocks(1.13±0.04)kg/m~2.The root ratio of coarse/fine decreased from the center to edge of tussocks in the horizontal direction,and increased first and then decreased in the vertical direction.Litter decomposition rate was significantly affected by time in the field and decreased with the decomposition time.During the decomposition process,the litter leaf decomposition rate inside tussocks fluctuated little,while the litter decomposition rate outside tussocks fluctuated significantly;the litter leaf dry weight loss and decomposition rate inside tussocks was smaller than that outside tussocks.The microenvironment between tussocks promoted the litter decomposition rate.The litter decomposition rate of the coarse and fine root declined gradually.The litter decomposition rate of the coarse roots were higher than that of fine roots.The litter decomposition rate for coarse root and fine root was higher than that of litter leaf inside tussocks,indicating that different organs of the same species had different decomposition dynamics.(2)During litter decomposition,the C release rate was the fastest in the litter leaves outside tussocks and the slowest in the fine roots.At the end of the experiment,the C remaining mass of litter leaf outside tussocks and fine roots decreased to42.53%and 68.94%,respectively.The accumulation and release of N were related to the litter initial N content.In early decomposition stage,litter total N emergenced a great leaching release,and then the element migration basically follows:enrichment-release volatility cycle model.Litter total P in the first 3 months decomposition with a quite rapid releasing.The release of P was inversely proportional to the litter initial C/P.The mean C remaining mass inside tussocks(78.15±3.36%)was significantly higher than that outside tussocks(66.74±16.54%).The P release outside tussocks was higher than that inside tussocks.Those shown that environment between tussocks promoted the release of C and P.Correlation analysis demonstrated that,litter decomposition rate was significantly positively related with the litter initial P content,but negatively related with the litter initial cellulase content.The higher initial P concentration,the lower initial cellulase content made the litter with rapid decomposition rate.(3)The environmental factors had a significant effect on litter decomposition rate of Carex schmidtii.The soil temperature inside tussocks was 1.58°C-1.92°C higher than that outside tussocks.Correlation analysis demonstrated that the dry weight loss of litter was significantly positively related with the accumulated temperature.The water level inside tussocks are higher than that outside tussocks.The dry weight loss of litter was significantly negatively related with the water level inside tussocks,but are significantly positively related with the water level outside tussocks.It showed that the water regime outside tussocks promoted the decomposition of litter outside tussocks.(4)The litter dry weight loss in the large mesh litterbags were higher than those in the small mesh litterbags,so that soil fauna could promote the litter decomposition.But the difference in dry weight loss of litter in large and small mesh litterbags decreased with decomposition time,so that soil fauna had a significant effect on the litter decomposition at early stage.The decomposition contribution of soil microorganism to the litter leaf inside and outside tussocks,coarse and fine roots were significantly higher than that of soil fauna,so that soil microorganism were the major decomposers during the decomposition stage.Contribution of soil fauna and microorganism on litter decomposition outside tussocks were higher than that inside tussocks,so that the environment outside tussocks promoted the litter decomposition of soil fauna and microorganism.(5)The influencing the decomposition factors for different litters inside and outside tussocks had obvious heterogeneity.RDA analysis showed that(1)the litter quality was a key factor of litter leaf inside tussocks,(2)water regime outside tussocks,soil temperature and microorganisms affected the litter decomposition pattern in Carex peat mire,(3)the decomposition of coarse roots were more affected by initial P content and soil organisms,(4)the litter quality and soil organisms were key factors of fine roots decomposition.In conclusion,the decomposition of litter was mainly affected by the content of P,cellulose and lignin,microorganism and temperature and moisture under tussock microtography.The tussock microtopography is widely developed in peat mire.The decomposit-ion rate of litter is a key process related to the carbon accumulation and carbon emission in peat mire.This study are to(1)reveale the litter decomposition process and influencing factors,(2)deepen the process of material cycling and energy flow in the tussock microtopography peatland and providing scientific basis for the formation mechanism of tussock microtopography.