Litter Characteristics And Pine Needle Decomposition Process And The Impact Of Control Measures On Its Decomposition Under The Pinus Massoniana Forests

Pinus massoniana is the most important timber species in southern China.Litter decomposition products are the main part of the mineral resources of the forest,and are very important to the soil fertility.The inherent characteristics of pine needles restrict the activity of microorganisms,and they are not conducive to the mechanical destruction of precipitation and soil animal.The pine needles are decomposed slowly.Therefore,to keep sustainable management of P.massoniana plantation,the key measures are to promote the decomposition of P.massoniana litter,and to improve the rate of nutrient return and maintain the stability of soil.The characteristics of litter,the pine needle decomposition process and the response of soil to litter decomposition were studied under the P.massoniana forests,which are helpful to understand the nutrient cycling law of P.massoniana ecosystem and the maintenance mechanism and ecological process of forest productivity.It is important to explore the effect of various regulatory factors on decomposition of pine needles that can provide scientific basis for improving decomposition rate by artificial means and sustainable utilization of P.massoniana forest resources.The litter was collected with tailor-made net each month for a total of one year.The characteristics of litter in different density P.massoniana plantation were studied.The decomposition process of pine needles in different community types was continuously observed for 24 months through litter bag technique.In the case of litter layer removed,the decomposition process of pine needles was studied for 26 months in different density stands.In addition,based on L9(34)orthogonal design,the pine needles decomposition experiments were carried out to study the effects of different control measures by field litter bag technique.The results show:1.The difference of five kinds of litterfall was significant(P<0.05),pine needles are the mainstay of the canopy litter of P.massoniana.The proportion of reproductive organs occupying the total amount of litter can not be ignored in spring and summer.The stand density effects on the litterfall(P<0.05).The quantities of different kinds of litter varied with seasons.This is determined by the bionomics of P.massoniana and the climatic factors(temperature,precipitation and wind velocity).Nutrient returns of different organs were discrepant(P<0.05).The sequence of N,P,K returned is needle>reproductive organs or debris>twig or bark.The litter nutrient return also showed a certain seasonal variation.The seasonal variation of the major nutrient elements return was consistent with the seasonal variation of litter quantity.There were significant differences in the chemical quality of the different litters.The debris are relatively lower,which is beneficial to the release of nutrients;the bark was the highest,which meant that it was the most difficult to decompose;reproductive organs,pine needles and twigs was higher than the nutrient release threshold,which was not conducive to nutrient release.The chemical quality of pine needles,twigs and bark showed a certain seasonal variation.The change of chemical quality of litter was closely related with the growth rhythm of P.massoniana,and it was also affected by climatic conditions(temperature and precipitation).The chemical quality of the pine needle closely related with the quantity of litter,which meant that more litterfall would be accompanied by lower Chemical quality,and a slower decomposition rate.2.In the three coenotypes of P.massoniana forest,the cumulative mass loss rate of pine needles in the first year was approximately 50%,and about 70% in the second year.There was no significant difference in the decompostion rate of pine needles among forest types.The temporal mode of the decomposition was obvious,which can be divided into two stages: rapid decomposition period(0~60 days)and slow decomposition period.In the process of pine needles decomposition,the migration of N,P and P was enriched firstly and then released.The migration of K,Ca and Mn was the net release model.The lignin concentration increased firstly and then decreased,lignin was degraded and the lignin peroxidase and manganese catalase could act as the enzyme that represented the degradation rate of lignin from P.massoniana.With the decomposition of pine needles,the chemical quality of pine needles was improved.The dynamic change of chemical quality closely related to the rate of decomposition.The mass loss rate was positively correlated with the concentration of N,P and negatively correlated with C/N,C/P,L/N,L/P ratio.The critical value of C/N ratio was 38 or 39,and the L/N ratio was between 27 and 34 when N release of pine needle kept a stable release rate in three different community types.The C/P ratio may be between 850 and 1000,and the L/P ratio may be between 700 and 900 when P release of pine needle kept a stable release rate.3.In the three densities of the pure P.massoniana forest with litter layer removed,the cumulative mass loss rates of pine needles were not more than 50% under the decomposition of 26 months.The decay rates of pine needles between density stands have no significant difference.The process of Pine needle decomposition could be divided into three stages: slow early decomposition stage(0~120/180d),rapid middle decomposition period(120/180~480/540d)and slow late decomposition period(480/540~780 d).During the decomposition process of pine needles,the transfer model of N was firstly enriched and then released.The release rate of P was significantly different among forest stands.On the?site,it was enrichment-release-enrichment model.On the?and ? stands,it was released firstly,then enriched;The mode of K was net release;Lignin was firstly cumulated,and then degraded.The change rule of the chemical quality and the relationship between the chemical quality and the decomposition rate in the experiment was same with that in the three coenotypes of P.massoniana.In addition,the mass loss rate of pine needle had a significant negative correlation with the concentration of lignin in the?site and ? site.The critical value of C/N ratio was between 43 and 49,and the L/N ratio was between 32 and 47 when N release of pine needle kept a stable release rate in the three densities of the pure P.massoniana forest with litter layer removed.Enrichment or release of P didn't relate to C/P or L/P.The relative concentration of P shown decrease induced by high C/P,L/P ratio,whereas increase with lower C/P,L/P ratio.4.In the response of pine needle decomposition experiment,the removal of litter from the forest is not conducive to the initial decomposition of pine needles,which will cause the rapid decomposition of soil organic matter,nitrogen loss and cation exchange capacity(CEC)reduction.The content of alkali-hydrolyzable nitrogen in soil was positively correlated with the accumulated mass loss of pine needles;the content of available phosphorus in soil was positively correlated with the monthly mass loss of pine needle.And the pine needle decomposition could increase soil organic matter content and the capacity of soil nutrient preserving.There was significant correlation between urease and soil available N,available potassium,and between acid phosphatase and soil organic matter,CEC,alkali-hydrolyzable nitrogen.5.The mass loss rate decreased gradually with the decomposition time.The cumulative mass loss rate of group 7 was 52.8%;it was 19.86% higher than that of CK after 6 months of the decomposition.'Organic fertilizer' and 'fungicide' significantly affected the decomposition rate of pine needles.The combined effect of decomposer 2 and chicken manure was more conducive to the decomposition.Compared with the natural decomposition of pine needles,the control measure promoted the change of chemical quality parameters which was conducive to the decomposition,N,P were mainly accumulated,and C/N,C/P,L/N and L/P were decreased.The effects of the different additives varied considerably.After the addition of organic fertilizer,the concentrations of nitrogen and phosphorous were raised,and the ratios of C/N,C/P,L/N and L/P were reduced.The addition of microbial inoculants resulted in lower C/P and L/P ratios;surface-active agents could help lower the L/N ratio of debris.The litter decomposition rate in all control treatments positively correlated with N concentration and negatively with the C/N ratio,and the leaf litter decomposition rate was not obviously related to its P content,L/N ratio,C/P ratio,and L/P ratio.Under artificial control,the decomposition rate can be affected by changing the litter chemical quality;the N content and C/N ratio were the main factors involved in regulating litter decomposition.The effect of control measures could adjust the mode of N and P release and help the accumulation of N and P.The addition of exogenous substances only could slow down the release of K,but it is difficult to change the migration mode of its net release.The control measures were followed by the inhibition of lignin degradation.The measures of pretreating pine by OP-10 needles and adding chicken manure/oil cake could reduce the pine needle lignin concentration.The cellulose would be degraded prior to lignin,the mode of cellulose and lignin decomposition was that one rose while another fell.The control measures could promote cellulose degradation,but the impacts of different control measures on the cellulose degradation were not obvious.