Leaf Litter Decomposition And N, P Dynamics Of Several Urban Trees In Different Environments

Litter decomposition and related nutrient release are fundamental process of nutrient cycling in terrestrial ecosystems.This process is strongly influenced by the property of litter and environment conditions.In comparison with the natural ecosystems,the urban green-land ecosystem has its specific characteristics.This may determine the specificity of litter decomposition and the soil and litter respiration during the decomposition processes in urban environment.In order to determine the major controls on decomposition process, and to reveal the relationships between decomposition rate and the soil and litter respiration,litter decomposition experiment was conducted using the litter-bag method at urban(Campus of Anhui Agricultural University)and suburban(Shushan Forest Park)area in Hefei.In this study,four types of foliar litter from three tree species,Biscofia polycarpa, Liquidambar formosana,Pinus massoniana and L.formosala-P,massoniana mixture were used.The results are as follows.1.Decomposition rateResults from the study revealed that there existed the significant differences in decomposition rates amongst species and between sites as well.After one year decomposition,the rates of the initial weight loss for the four leaf litter decomposed in Shushan Park showed a decreasing order as:P.massoniana(86.3%)＞L.formosana-P. massoniana(65.7%)＞B.polycarpa(52.4%)＞L.formosana(48.9%).However,in Anhui Agricultural University Campus,the order was:B.polycarpa(73.7%)＞L.formosana-P. massoniana(63.6%)＞L.formosana(41.6%)＞P.massoniana(40.0%).In Shushan Park,the decomposition coefficients of the four litter types were P. massoniana,0.2288;L.formosana-P.massoniana,0.0994;B.polycarpa,0.0656;L. formosana,0.0629.However,in the Anhui Agricultural University Campus,the order of decomposition coefficients of the four litter types were:B.polycarpa 0.1208＞L. formosana-P.massoniana,0.0958＞L.formosana,0.0502＞P.massoniana,0.0425.The times for 95%decomposition for the litter types were,respectively,L.formosana,3.97 a in the park and 4.98 a in the campus;B.polycarpa 3.81 a and 2.07 a;L.formosana-P. massoniana,2.51 a and 2.61 a;and P.massoniana,1.09 a and 5.88 a.2.Nutrient dynamicsDuring the decomposition processes,notable differences in nutrient concentrations were observed amongst the four litter types.In general,N contents of the four litters had an increasing trend at both sites(Park and Campus)during the decomposition,whilst P contents fluctuated with an increasing trend at the initial phase and then decreased at the late phase.However,Ca contents showed evidently different patterns during the decomposition at the two sites.In Shushan Park,Ca contents of all litter types decreased from the initial phase.In the campus,Ca contents of four litter types increased constantly during decomposition.After one year decomposition,the Ca contents increased nearly 1.5 times for the four litters compared with the initial Ca contents.The possible reason for the enrichment of Ca at campus site was due to the high Ca concentration in the soil.3.Soil and litter respirationThe soil and litter respirations at two sites were measured during the decomposition. Soil respiration,soil water content(0-10 cm)and soil temperature(0-5 cm)at both sites were analyzed by multi-factor and interaction regression.The results showed that soil respiration rate in Shushan Park was positively correlated with soil temperature r=0.984, (p＜0.0001),while was not correlated with soil water content and their interaction(p＞0.05).-However,soil respiration rate in the Campus was positively correlated with soil temperature r=0.985,(p＜0.0001)and interaction between soil temperature and soil water content r=0.961,(p＜0.001),while was not correlated with soil water content(p＞0.05).Although the rates of respiration changed evidently with litter types at two sites,a similar pattern was observed for all litter types,with a greater respiration rate in May and June and a lower rate in April and October.The average respiration rates of both litters and soils were greater in Shushan Park than in the Campus.This could be one of the important cause contributing the rapid decomposition in Shushan Park.4.Relationship between decomposition rate and soil and litter respirationBoth soil and liter respirations were determined by microbial amount,species and physiological activities.Environmental conditions can also affect the soil and litter respirations.The results from the study showed that the seasonal course of both soil and litter respiration synchronized with that of the litter weight loss at the initial phase during decomposition.To a certain extent,the litter weight loss was not correlated with its respiration rate R~2 = 0.392(p=0.26).