Production And Nutrient Return In The Litterfall From Pinus Elliottii Plantation In Response To Nitrogen And Phosphorus Addition And Resin Tapping

Slash pine（Pinus elliottii）is one of the main afforestation tree species in the hilly areas of southern in China.As an excellent tree species for papermaking,timber and high-yield lipids,the efficient cultivation of slash pine plantation for timber and resin is of great significance to promote the sustainable development of forestry.Fertilization（addition of nitrogen and phosphorus）is the main measure for intensive management of plantations and improving soil nutrients in plantation,but excessive fertilization can also aggravate the nutrient enrichment of forest ecosystems.In this study,three ages of slash pine plantation（13a,24a,28a）in the northern margin of the subtropical region were taken as the research object which one year of nitrogen（N）and phosphorus（P）addition experiment.The addition experiment includes Low N(LN,50 kg N·hm^-2·a^-1),High N(HN,100 kg N·hm^-2·a^-1),High N and Low P(HN,100 kg N·hm^-2·a^-1+50 kg P·hm^-2·a^-1),High N and High P(HN,100 kg N·hm^-2·a^-1+100 kg P·hm^-2·a^-1)and Control（No N and P addition）.The study on the response of slash pine plantation for timber and resin on the northern margin of the subtropical region to the addition of nitrogen and phosphorus is from three aspects:litter production,nutrient content and nutrient return.The results are as follows.1.Litter and its components production.The litter production of slash pine plantation for tapping and no tapping different ages respectively are 13a(9.27 t·hm^-2·a^-1,5.94 t·hm^-2·a^-1),24a(9.33 t·hm^-2·a^-1,8.34 t·hm^-2·a^-1),28a(5.50 t·hm^-2·a^-1,5.77 t·hm^-2·a^-1).The main component of litter is leaf,accounting for85.09%～94.95%,and the overall appearance is leaf>twigs>detritus>reproductive organs.Resin tapping significantly increased the annual twigs litter and total litter production of the slash pine plantation of 13a.In the plantation for no tapping,the addition of nitrogen and phosphorus significantly increased the litter production of slash pine plantation of 13a（p<0.05）,and the performance was HN+LP>HN+HP>LN>HN>CK.There was no significant effect on the litter production of slash pine plantation of 24a and 28a（p>0.05）.In the plantation for tapping,The addition of nitrogen and phosphorus has no significant effect on the litter production of different forest ages（p>0.05）.2.Monthly dynamics of litterfall.The monthly dynamics of litterfall are unimodal pattern in different forest stands,and the highest peak occurs from October to November.The monthly dynamic patterns of each component of litterfall are different that leaf is unimodal pattern,twigs and debris is bimodal pattern and the flowers is mainly concentrated in April to May.The effects of nitrogen and phosphorus addition on litter production are mainly concentrated in the early growing season and dormant period of slash pine.3.Annual average nutrient content of litterfall.The nutrient content of litterfall is taken as an example of leaf litter.The annual average content of C,N,P,K,Ca,Mg in the leaf litter of slash pine of different forest age ranges from 497.02～500.83 g·kg^-1,5.90～8.54 g·kg^-1,0.13～0.21 g·kg^-1,1.25～1.47 g·kg^-1,8.62～12.75 g·kg^-1,1.12～1.29 g·kg^-1,respectively.The content of N and P in leaf litter increased with the increase of forest age,and the content of K decreased with the increase of forest age.Resin tapping significantly increased the N,P,K content of leaf litter in 13a slash pine.The P content in leaf litter of different plantation changed significantly under the treatment of nitrogen and phosphorus addition（p<0.05）,which showed that the addition of nitrogen has no significant effect on P content,and the co-addition of nitrogen and phosphorus significantly increased the P content in the leaf litter.The Ca content of leaf litter was significantly different under different treatments（p<0.05）,but there was no obvious change rule.4.Monthly dynamics of nutrient content.The monthly dynamics of C content in leaf litter showed a bimodal pattern,and the wet season was greater than that in the dry season.The monthly dynamics of P content in leaf litter showed a unimodal pattern,and it continued to increase during the growing season and reached its highest peak in May.The monthly dynamics of leaf litter N and K are bimodal pattern.The content of Ca and Mg in leaf litter had no obvious monthly dynamics.5.Nutrient stoichiometric ratio of leaf litter.The C/N,C/P and N/P of leaf litter of slash pine plantation of different ages all decreased with the increase of N and P content.The leaf litter N/P of 24a and 28a slash pine plantation was similar and much smaller than that of 13a slash pine.The C/N and C/P of leaf litter decreased with the increase of forest age.Resin tapping significantly reduced the stoichiometric ratio of leaf litter in the 13a forest.The addition of nitrogen and phosphorus changed the nutrient utilization efficiency of slash pine,which changed the stoichiometric ratio of leaf litter.6.Nutrient return of litterfall.The total nutrient return of litterfall from the different ages of slash pine plantation for tapping and no tapping respectively was 13a(3998.00 kg·hm^-2,2513.12 kg·hm^-2),24a(4074.97 kg·hm^-2,3440.94 kg·hm^-2),28a(2446.47 kg·hm^-2,2492.52 kg·hm^-2).The order of nutrient return amount is C>Ca>N>K>Mg>P.Resin tapping increased the nutrient return of13a and 24a slash pine plantation litterfall by 59.09%and 18.43%,respectively,and had no obvious effect on the nutrient return of 28a slash pine plantation litterfall.The addition of nitrogen and phosphorus increased the return amount of litterfall N and P,and the return amount of P increased more obviously.