Studies On The Leaching Characteristics Of Leaf Litter In Primary Pinus Koraiensis Forest And Secondary Broad-leaved Forest

In this study,the primary Pinus koraiensis forest and the secondary broad-leaved forest after clear cutting and restoration succession were taken as the objects.The dissolution characteristics of nutrient elements and dissolved organic matter of litter,the pH value of canopy and litter leaching solution,the dissolution amount and spectral characteristics of litter dissolved organic matter at different decomposition degrees were studied by in-situ and indoor leaching methods respectively.This study explored the reasons for the differences,and analyzed the relationship between the nutrient release characteristics of leaf litter and the initial leaf characters of two dominant tree species.The main conclusions are as follows:(1)In the field in-situ leaching experiment,the initial chemical components of leaf litter in the two forest types were significantly different(p<0.05).The total carbon,lignin,cellulose,C/N and lignin/N of leaf litter in the primary Pinus koraiensis forest were significantly higher than those in the secondary broad-leaved forest(p<0.05),while the total nitrogen,total phosphorus,total potassium and total magnesium were on the contrary(p<0.05).After one year of field leaching treatment,compared with the secondary broad-leaved forest,the total amount of nutrient elements dissolved in leaf litter in the primary Pinus koraiensis forest was significantly higher(p<0.05).Although the dissolution rules of different elements were not consistent,the release peak of nutrients from litter was mostly concentrated in June and July.The change rules of nutrient elements in the two forest types were consistent with the leaching solution.Compared with the secondary broad-leaved forests,the total dissolved organic matter(DOM),soluble organic carbon(DOC)and soluble organic phosphorus(DOP)in the litter of the primary Pinus koraiensis forest were significantly higher,while the dissolved organic nitrogen(DON)was significantly lower(p<0.01).The change rule of DOM in the two forest types was basically consistent with that of the leaching solution.During the whole experiment period,the pH variation range of the two forest types throughfall was 5.34to7.21,while the pH variation range of litter leaching solution was 6.37to7.65.The litter layer could effectively adjust the pH of throughfall.Compared with the two forest types,the litter layer of the primary Pinus koraiensis forest has a larger adjustment range to throughfall in the forest.(2)After 24 hours indoor simulation leaching,the total dissolution amount of DOC and DOP of litter in the two forest types and the total dissolution amount of litter DON in the primary Pinus koraiensis forest in the undecomposed layer(U layer)were significantly higher than the semi-decomposed layer(S layer)(p<0.05).The total dissolution amount of litter DOC in S layer of primary Pinus koraiensis forest was significantly higher than that of secondary broad-leaved forest(p<0.01),but the total dissolution amount of litter DOC in U layer was significantly lower than that in secondary broad-leaved forest(p<0.01).The total dissolution amount of litter DON and DOP in the U and S layers of primary Pinus koraiensis forest was significantly higher than that in the secondary broad-leaved forest(p<0.01).During the leaching period of 6-24hours,in general,the DOM dissolution amounts of different samples increased at first and then decreased with the increase of the leaching time.And DOM presented the characteristics of release and anti-adsorption at the same time.(3)In the indoor simulation leaching experiment,the SUVA values of DOM of the two forest types litter were significantly higher in the S layer than in the U layer(p<0.05).HIX values of DOM of the two forest types litter were significantly higher in the S layer than in the U layer(p<0.05).After 24 hours leaching,the maximum fluorescence intensity of the two forest types litter DOM gradually increased from the U layer to the S layer,and the corresponding wavelength moved from short wave to long wave.This is a reflection of the increasing degree of humus and increasing of the electron conjugated system.The infrared spectra of all samples showed four similar absorption bands,but the relative proportions of each absorption band were different for different samples.The increase of the infrared absorption ratio of litter DOM from U layer to S layer in the same forest layer indicated that the conjugated system became larger with the increase of aromatics,alkoxy substances or carboxylic acids..The SUVA value and HIX value of the litter DOM in S layer in primary Pinus koraiensis forest were significantly higher than that in the secondary broad-leaved forest(p<0.05).The infrared absorption ratio of the litter DOM in primary Pinus koraiensis forest in 1680-1560cm-1 was greater than that in the secondary broad-leaved forest,which showed that the litter DOM in primary Pinus koraiensis forest had more unsaturated bonds and aromatic compounds,It is beneficial to the maintenance of soil fertility and the formation of carbon sink.(4)After 24 hours indoor simulation leaching,there were significant differences in the dissolved amount of various nutrient elements such as C,N,P,K,Ca and Mg from leaf litter of the six dominant tree species(p<0.05).The species with the highest dissolving capacity of nutrient element was Fraxinus mandschurica,and the smallest species was Pinus koraiensis.The weight loss rate of leaf litter also showed the same rule.Compared with broadleaf tree species,the leaching ability of nutrient elements of leaf litter in Pinus koraiensis leaves was poor.The solubility of K,Ca,Mg and P was significantly higher than that of C and N(P<0.01).After leaching,there was no significant change in the C:N value of leaf litter of six species(paired t-test,p=0.08),and both C:P and N:P value increased significantly(paired t-test,p<0.001).The initial leaf characters of six tree species were significantly different(p<0.01).There was a significant correlation between the initial characters of leaves and the dissolution amount of nutrient elements in litter.Standard water retention was the most important factor affecting C,P,K and Mg dissolution,specific leaf area was the most important factor affecting N dissolution,leaf toughness was the most important factor affecting Ca dissolution,and cellulose content was also the main factor affecting C dissolution.