| Litter is an important part of the forest ecosystem and plays a key role in maintaining ecosystem functions such as forest nutrient cycling and water balance.Chinese fir is an important fast-growing timber species in southern China,and its planting area and accumulation volume rank first in China's artificial forests.Therefore,it is of great significance to study the nutrient characteristics and ecological and hydrological functions of the litterfall of Chinese fir plantations in order to maintain and enhance the ecological functions such as soil fertility and soil and water conservation of Chinese fir plantations.In this study,8-11,16,21,25,29,and 32-year-old Chinese fir plantation forests were used as the research object to compare and analyze litter standing crop,litter biomass,composition characteristics,decomposition rate,turnover period,hydrological characteristics,nutrients of different forest age The content and stoichiometric characteristics clarify the effects of forest age on nutrient cycling,ecological hydrology,and other functional processes of Chinese fir plantations in Hunan Huitong.The results of the study can provide intellectual support for the improvement and maintenance of plantation productivity.The main findings of this study are as follows:(1)With the increase of forest age,the total amount of litter standing crop in Chinese fir plantation increased first and then decreased.The total amount of litter in the 8-11 year old Chinese fir plantation was the lowest,at 1.83 t·ha-1.When the forest was 25 years old,the current amount of litter standing crop reached the maximum,at 8.76 t·ha-1.Subsequently,the existing amount of litter standing crop of Chinese fir plantations gradually decreased.The litter stocks in different decomposition layers of Chinese fir plantations in different age series are different in different trends with age.With the increase of forest age,the standing crop of litter in the undecomposed layer showed an increasing trend and then stabilized.It reached the maximum value at the age of 29 years,which was 2.04 t·ha-1.With the growth of forest age,the standing crop of litter in the semi-decomposition layer first increased and then decreased,and reached the maximum value at 25 years,which was 3.90 t·ha-1.With the growth of forest age,the standing crop of litter in the fully decomposed layer increased first and then decreased,and reached the maximum value at the age of 25 years,which was 2.04 t·ha-1.The standing crop of litter in different decomposition layers appears as a semi-decomposition layer>undecomposed layer>completely decomposed layer.The existing amount of litter in the undecomposed layer accounts for 16-33%of the total standing crop litter,the standing crop of litter in the semi-decomposed layer accounts for 43-58%of litter standing crop,and the standing crop of litter in the fully decomposed layer accounts for the total surface litter 17-40%of the amount.(2)The annual litter biomass of Chinese fir plantations in different age series showed a trend of increasing first and then stabilizing with the increase of age.The litter biomass in 8-11 years was the lowest,and the largest in 21 years.The annual litter biomass of the 25-year-old Chinese fir plantation forest was only 3.46 t·ha-1,which was lower than the 4.97 t·ha-1,of 21 years old and 4.82 t·ha-1,of 29 years.Due to thinning of the stand for 25 years,the stand density is small,resulting in a small amount of annual litter biomass.With the age of the forest,the annual litter biomass of branch and leaf litter showed a significant upward trend and then stabilized.The annual litter biomass volume of fruit litter biomass increased significantly with increasing forest age.Among the litter biomass combinations in different forest age series,the amount of leaf litter>branch litter>fruit litter.The total litter,branch litter,leaf litter,and fruit litter fell in four seasons and increased with the age of the forest.The overall biomass showed a trend of spring>winter>summer>autumn.The decomposition rate of litter of Chinese fir in different forest ages was between 0.28 and 0.45,and the overall decomposition rate showed a trend of increasing with the increase of forest age.There was no obvious law among different forest ages during the turnover period,between 2.22-3.59 years.The mature Chinese fir forest has the characteristics of high decomposition rate and short turnover period,which can better return nutrients and maintain soil fertility.(3)Indoor soaking and natural air-drying methods were used to study the water-holding characteristics and water loss characteristics of Chinese fir plantations.The results showed that the water holding rate and water holding capacity of the surface branches and leaf litter of the Chinese fir plantation were generally near maturity forest>mature forest>middle and young forest age,consistent with the regularity of forest age on the surface litter of Chinese fir.The water-holding rate and water-holding capacity of Chinese fir in different forest ages all showed an increasing trend with increasing soaking time,which increased rapidly within 2.5 h before soaking,then flattened,and became saturated after 15 h.The water-holding rate,water-holding capacity and water infiltration time of Chinese fir litter are logarithmic relationships of R=a lnt+b and Q=a lnt+b,respectively.There is no obvious law between the ages of the forest,and the water absorption rate decreases with the increase of water absorption time.The water absorption effect of Chinese fir litter is mainly in the first two hours,especially in the first one hour,which is of great significance for intercepting Short-term Precipitation in the forest and slowing down the generation of surface runoff.Is of great significance.There is a power function of V=a tb between water absorption rate and water absorption time of Chinese fir litter.During the whole dehydration process,there was no obvious law among the ages of branches and litters.The overall water loss rate of leaf litter is as follows:near maturity forest>mature forest>middle forest age,young forest age,consistent with the law of water retention of Chinese fir litter.Water loss of Chinese fir litter tends to increase with time.The greater the water holding capacity of Chinese fir litter,the more water loss,and the order of maximum water loss is consistent with the maximum water holding capacity.The differences of water loss rate of branches and leaves litter are small,and there is no obvious law among the forest ages.The water loss rate,water loss rate and air-drying time of Chinese fir are power functions of S=a th and V=a th,and the logarithmic relationship between the water loss of Chinese fir litter and air-drying time is U=a lnt+b.Among the hydrological characteristics of Chinese fir litter,the effects of leaf litter on water retention and dehydration were significantly greater than those of branch litter,which dominated.(4)The content of total litter C in Chinese fir plantation tends to increase as the forest age increases.The total litter C content was the smallest at 8-11 years,and reached the maximum at 32 years.The total litter N content generally increased first,then decreased and then increased with the increase of forest age.It was the smallest at 8-11 years and reached the maximum at 21 years.On the whole,it increased first and then decreased with the increase of forest age.The content of total litter P was the smallest at 8-11 years and reached the maximum at 25 years.The total litter C:N showed no obvious regularity with the increase of forest age.It was the smallest at 21 years old and reached the maximum at 25 years old.The total litter N:P generally showed a downward trend with the increase of forest age.It was the smallest at 25 years old and reached the maximum at 8-11 years old.The total litter C:P generally decreased first and then increased with the increase of forest age.It was the smallest at 25 years and reached the maximum at 8-11 years.In the growth and development stages of Chinese fir plantation,the content of C-rich structural substances was relatively stable,and the contents of N-and P-rich functional substances and storage substances changed greatly.The main limiting element of litter decomposition in this study area is N.In the early stages of growth and development of Chinese fir,the litter decomposition is slower.As the stand matures,the litter in mature forest communities has a lower N:P value,and the decomposition rate is accelerated. |
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