Study On The Internal Cycle Of Leaf Nutrients In Natural Forest And Plantation Of Castanopsis Kawakamii

The research sites were located in Fujian Province,(Castanopsis kawakamii Natural Forest,NF)and(Castanopsis kawakamii Plantation,CK)and(Chinese fir(Cunninghamia lanceolata)plantation,CF)in Xinkou Forest Farm in Sanming City,and(Nanping Castanopsis kawakamii plantation,NCK)in the Xiqin Teaching Forest Farm in Nanping,Fujian were selected as researching object in this studyFollow randomized block design method,five 20 m × 20 m test plots were selected for each tree species.The determination of the seasonal dynamics of nutrient content in different leaf age stages(new leaves,mature leaves,and senescent leaves)of natural forest and plantation forests,calculation of nutrient reabsorption rates and their stoichiometric ratios,determination of soil physicochemical properties of soil layers(0～10 cm,10～20 cm,20～40 cm)in different tree species,The seasonal dynamics and re-absorption of nutrient contents in natural leaves and artificial forests of Castanopsis kawakamii were comparatively analyzed.The results of the study are as follows:(1)There were significant difference between the nutrient contents of new leaf,mature leaf and senescent leaf at different leaf ages of natural forest and plantation of Castanopsis kawakamii,and decrease with the increase of leaf age class,but the seasonal variation is not obvious among different tree species.Except for Ca,The nutrient elements in turn showed new leaf>mature leaf>senescent leaf.The contents of N and Ca were significantly different among Natural Forest and Plantation of Castanopsis Kawakamii(P<0.01),and the N and P contents of mature leaf were significantly different(P<0.01),senescent leaves consume a large numberof nutrients in the procession of transition,which will increase or decrease accordingly with the increase or decrease of the content of mature leaves.(2)The average rates of reabsorption of N,P,K,Ca and Mg in leaves of natural forest and plantation of Castanopsis kawakamii were 31.97%,40.20%,54.50%,-58.91%,and 25.88%,respectively.and followed the order of REK>REP>REN>REMg>RECa,K reabsorption rate may be related to its high liquidity,the reabsorption rate of Ca were negative transfer.The rate of reabsorption of large numbers of elements such as N and P did not show regularity with seasonal changes.The rate of N re-absorption of summer pine increased suddenly.It may be that rising temperatures and increasing precipitation require N elements to support physiological activities.The average reabsorption rates of Fe,Mn,Cu,Zn,and Na trace elements in the leaves were 21.68%,21.83%,41.88%,24.49%,and 24.42%,respectively and followed the order of RECu>REZn>RENa>REMn>REFe.The absorption efficiency of Cu is the highest among the trace elements,which is related to the rapid circulation and short cycle.Na is a beneficial "functional nutrient element".The reabsorption of trace elements is also an indispensable mechanism for plant growth.Together with a large number of elements,it regulates plant growth.(3)There were certain correlations between the nutrient contents of natural forestsof Castanopsis kawakamii and plantation forests.The relationship between the content of N and Mg,the content of Mn and Na reached an extremely significant level.There was a significant positive correlation between the content of P and Zn,the content of Ca and Na.and there was mutual promotion and synergy between a large number of elements and trace elements.There was a significant positive correlation between the content of Fe in mature leaves and Fe reabsorption rate among different tree species(P<0.01),and there was a significant negative correlation between the content of N、Ca and N、Ca reabsorption rate in aging leaves(P<0.01).There was a significant negative correlation between K content in senescence leaves and K reabsorption rate(P<0.05).(4)The interactions between nutrient content and reabsorption rate of leaf in different tree species and seasons indicate that:the contents of N,P,Ca,Mg,Fe,Mn,Zn,and Na were significantly different in different seasons(P<0.01).The contents of N,P,Ca,Mg,Fe,Mn,Cu,Zn,and Na in different tree species were significantly different(P<0.01),the interactions between different seasons and different tree species had extreme effects on the nutrient content of plants.Significantly affected(P<0.01).The re-absorption rates of N treatments in different seasons were significantly different(P<0.01),and the P re-absorption rates were significantly different(P<0.05).The N re-absorption rates of different tree species treatments were significantly different(P<0.01),and the K re-absorption rates were significantly different(P<0.05),The N,P reabsorption rates of the interactions between different seasons and different tree species were significantly different(P<0.01).(5)Significant seasonal changes in specific leaf area(SLA)of new leaves,mature leaves,and senescent leaves,which showed winter>autumn>summer>spring,and the average leaf area and SLA of new leaves were smaller than that of mature leaves and senescence leaves,and the sizes of different tree species were followed the order of NF>NCK>CK>CF,the natural forest SLA is larger than the artificial forest,the broad-leaved forest is larger than the coniferous forest,Castanopsis natural forest highest,the lowest fir,which indicated that the natural forest of Castnopsis kawakamii has a high nutrient retention rate,the Chinese fir has better conditions for poor site conditions Adaptability.The average water content of new,mature,and senescent leaves was 53.04%,45.42%,and 42.82%.The performance of new leaves>mature leaves>senescent leaves may be that the photosynthesis and metabolism activities of new leaves are stronger than those of senescent leaves.(6)Study on the number and seasonal dynamics of litterfall of natural forest and plantation in Castanopsis Kawakamii.The total amount of litters showed the order of NF>CK>NCK>CF.The litter between different tree species were dominated by litter and showed obvious seasonal dynamic changes,Following the order of spring>summer>winter>autumn season,The total amount of litter was high in spring and summer,but low in winter and autumn,and the seasonal variation curve was bimodal.(7)The N,P reabsorption rates of natural and artificial forests of Castanopsis kawakamii are significantly highly correlated with mature leaves and leaf litter C:N:P,but not significant correlation with soil.The higher ratios of C:N and C:P in leaves were the embodiment of high nutrient utilization of plants.The content of P in leaves showed the order of CF>NCK>CK>NF,and the utilization efficiency of P in the order of NF>CK>CF>NCK.There was a significant negative correlation between the content of P and use efficiency of P(P<0.01).The lower the nutrient content,the higher the use efficiency.(8)The reabsorption rate of N and P of plants was 26.13%～34.41%and 37.70%～418.89%respectively in this experimental.The average reabsorption rate of P was(40.02%),which was greater than that of N(31.97%).and mature leaf(N:P)was more than 16,meaning that the growth limiting factor of plants in this area was P element.