Response Of Litter Production And Soil Respiration Of Phyllostachys Pubescens Forest To Simulated Nitrogen Deposition

The Phyllostachys pubescens forest is an important forest resource in southern China,which has strong carbon sequestration capacity.The P.pubescens forest can releases a large amount of CO2 to the atmosphere through litter decomposition and soil respiration each year.In recent years,the atmospheric nitrogen deposition becamean increasing trend.Therefore,study on the responseof forest litter production and soil respiration to nitrogen deposition has a very important significance.This study was conducted at Caicun,Jingxian County where is one of the main area of P.pubescens production in Anhui Province.In order to reveal the response of litter production,soil nutrient dynamics,soil respiration and understory plant diversity to nitrogen deposition,a field simulation experiment was conducted in a P.pubescens forest for two year.The experiment designed two treatments,i.e.high N(HN,100 kg N·hm^-2·a^-1)and low N(LN,50 kg N·hm^-2·a^-1)additions with one control?CK,no N addition?.The litterfall was collected monthly and soil respiration,soil temperature and soil relative humidity was measured bimonthly by EGM-4 CO2 Analyzer.The main results obtained in this study are as follows.The mean annual litterfall mass of the P.pubescens stands was 5.36 t·hm^-2·a^-1 for non-cutting and HN?NC+HN?,5.40 t·hm^-2·a^-1 for non-cutting and LN?NC+LN?,4.08 t·hm^-2·a^-1 for CK?non-harvesting?,3.49 t·hm^-2·a^-1 for cutting and HN?C+HN?,3.18 t·hm^-2·a^-1 for cutting and LN?C+LN?,2.44 t·hm^-2·a^-1 for CK?cutting?.The patterns of monthly litterfall for the different treatment were unimodal type curve.Litterfall peaked in April(NC+HN 1.43 t·hm^-2,NC+LN 1.61 t·hm^-2,CK 1.17 t·hm^-2,C+HN 1.35 t·hm^-2,C+LN 0.88 t·hm^-2,CK 0.82 t·hm^-2)while the least in January 2014(NC+HN 0.03 t·hm^-2,NC+LN 0.03 t·hm^-2,CK 0.02 t·hm^-2)and in February 2015(C+HN 0.04 t·hm^-2,C+LN 0.04 t·hm^-2,CK 0.02 t·hm^-2).The amount of litter throughout the year focused on the March to July.The monthly litterfall was significantly higher in April than in other months?p<0.05?.Our results demonstrate that the annual litter production of P.pubescens forest was enhanced by both high and low nitrogen additions.The nutrient concentration of litterfall for different treatments was ranked as N>Ca>K>Mg>P.The nutrient concentrations of sheath for HN were in order of K>N>Mg>Ca>P,The nutrient concentrations of sheath for LN were in order of N>K>Mg>Ca>P,The nutrient concentrations of sheath for CK?cutting?were in order of N>K>Mg>Ca>P,and for CK?non-cutting?were N>K>Ca>Mg>P.The difference of nutrient concentrations in litterfall component for different treatments was not significant?p>0.05?,while was significant for sheath?p<0.05?.In comparison with the concentrations in the two components stand for different treatments,litterfall had higher nutrient concentrations than sheaths did except for total K.Our results demonstrate that the nutrient concentrations of P.pubescens forest was enhanced by both high and low nitrogen additions except for total Ca.The annual total nutrient input from litterfall to the forest floor was 121.10 kg·hm^-2·a^-1 for NC+HN,123.24 kg·hm^-2·a^-1 for NC+LN,94.27 kg·hm^-2·a^-1 for CK?non-cutting?,77.58 kg·hm^-2·a^-1 for C+HN,68.92 kg·hm^-2·a^-1 for C+LN,49.59 kg·hm^-2·a^-1for C+CK.Our results demonstrate that annual total nutrient input from litterfall of P.pubescens forest was enhanced by both high and low nitrogen additions.There was no significant difference between the amount of litter nutrient return each processing P.pubescens?p>0.05?.The dynamics of litterfall nutrient input from litterfall was the same as the litterfall biomass with a single-peak.The annual total carbon input from litterfall to the forest floor was 2.28 t·hm^-2 for NC+HN,2.34 t·hm^-2 for NC+LN,1.77 t·hm^-2 for CK?non-cutting?,1.50 t·hm^-2 for C+HN,1.39 t·hm^-2 for C+LN,1.04 t·hm^-2 for CK?cutting?.The dynamics of annual carbon input from litterfall was the same as the litterfall biomass with a single-peak.Our results demonstrate that the annual carbon input of P.pubescens stand was enhanced by both high and low nitrogen additions.The diurnal change of soil respiration in P.pubescens stands showed a single-peak appeared at 8:00 in non-cutting stands but single-peak appeared from 12: 00 to 16:00 in cutting stand,HN>CK>LN in non-cutting stand,LN>CK>HN in cutting stand.Compared to the two-year soil respiration dynamic changes daily,the soil respiration rate in non-cutting stands was significantly higher than in cutting stands.The monthly change of soil respiration in P.pubescens stands showed a single-peak appeared July in non-cutting stands and CK?cutting?,but appeared May in C+HN and LN stands.The results from the regression analysis indicated that soil respiration was significantly correlated with soil temperature both non-cutting and cutting stands?p<0.01?.In addition,soil respiration was significantly correlated with soil relative humidity both NC+HN and LN stands?p<0.05?,and was significantly correlated with soil relative humidity in cutting stands?p<0.01?.The Q10 values of the soil respiration was 2.98 for C+HN,2.21 for NC+LN,2.53 for CK?non-cutting?,2.03 for C+HN,2.68 for C+LN,2.52 for CK?cutting?.Among all the sampling stands,the concentrations of soil organic carbon?SOC?,total nitrogen?TN?,ammonium?NH4+-N?,nitrate?NO3--N?,dissolved organic carbon?DOC?and total Kdecreased with increasing depth of soil.Our results demonstrate that the SOC,TN,NH4+-N,NO3--N,DOC and Mg were enhanced by both high and low nitrogen additions,the total Ca and total P were reduced by both high and low nitrogen additions.The monthly change of SOC and NH4+-N in P.pubescens stands showed a single-peak,the soil NO3--N showed bimodal curve.All the diversity index of understory shrub and the Margalef index of understory herbaceous were reduced by both high and low nitrogen additions.The Simpson index and Pielou index of understory herbaceous were reduced by high nitrogen additions.The Simpson index and Pielou index of understory herbaceous were enhanced by low nitrogen additions.The Shannon-Wiener index of understory herbaceous was reduced by both high and low nitrogen additions.The Species richness index,Margalef index,Simpson index and Pielou index of understory shrub were higher than those of understory herbs.