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Responses Of Litterfall Production And Nutrient To Simulated Nitrogen Deposition In Subtropical Evergreen Broad-leaved Forest Across An Age Sequence

Posted on:2019-12-18Degree:MasterType:Thesis
Country:ChinaCandidate:Z F WangFull Text:PDF
GTID:2370330551459635Subject:Garden Plants and Ornamental Horticulture
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Since the industrial revolution,the emissions of NH3 and NOx have increased significantly with the continuous development of industry and agriculture.After Europe and North America,China has become the third largest nitrogen deposition area in the world.Atmospheric nitrogen deposition can cause a series of ecological environmental problems,resulting in changes of soil property,reduction of biodiversity and eutrophication of aquatic ecosystem.Therefore,atmospheric nitrogen deposition has been attracted great attention worldwide.As the linkage of nutrient cycling and energy flow from plant to soil,litterfall plays an important role in maintenance of water balance,community structure and soil fertility in forest ecosystems.In this study,an experiment of N addition was conducted in subtropical evergreen broad-leaved forest in Southern Anhui Province,including an old-growth stand?ca 200a?in Dashan village of Shitai County,a mature stand?ca 80a?on Zhawan Natural Reserve in Qimen County and a mid-aged stand?ca 50a?in Jitan village of Shitai County.The experiment began in 2011,and a randomized complete block design was used.Three treatments were performed:Control?CK,without N and P addition?,N(100 kg N·hm-2·a-1),and N+P(100 kg N·hm-2·a-1+50 kg P·hm-2·a-1),with three replicate plots for each treatment.During the three-year experiment,litterfall production and related nutrients return across an age sequence to simulated nitrogen deposition were analysed.The main results are as follows.1.Litterfall production and dynamic patternsNutrient addition increased the annual litterfall production in old-growth stand,with the trend of N+P(8.19 t·hm-2·a-1)>N(7.57 t·hm-2·a-1)>CK(7.05 t·hm-2·a-1).The annual litterfall pattern showed somewhat fluctuation with the trend of going down first and up afterward.However,the overall pattern was in decline.The nutritional organs in litterfall accounted for 63%-92%of the total,and the reproductive organs for 8%-37%.The monthly dynamic pattern of litterfall was bimodal,with the peak value mainly in Spring?April and May?and Autumn?November?.The nutrient addition increased the peak to a certain extent.The monthly litterfall was the lowest was in January and February.In the mature stand,nutrient addition resulted in increase of litter production,with the trend of N+P(9.46 t·hm-2·a-1)>N(8.82 t·hm-2·a-1)>CK(7.56 t·hm-2·a-1).The annual pattern was an increasing trend.The nutritional organs accounted for 73%-84%of litterfall and 16%-27%from the reproductive organs.Compared with the CK,the annual litterfall production decreased in N addition,while increased in N+P addition.The result indicates that the continuous high N deposition may result in P limitation in mature stand.In the mid-aged stand,nutrient addition also resulted in increase of litter production,with the mean annual litterfall of N+P(8.11 t·hm-2·a-1)>N(7.49 t·hm-2·a-1)?CK(7.42t·hm-2·a-1).The effect of nutrient addition on litterfall production was not significant compared to old-growth and mature stands.The nutritional organs in litterfall accounted for 76%-86%of the total and 14%-24%from reproductive organs.The annual dynamic model appeared a unimodal pattern,with one of the most obvious peak in December,as well as another peak in April and May.The lowest values mainly appeared in January and February.Overall,N and P additions had a positive effect on litterfall production.In general,litterfall production was higher in mature stand than in the old-growth stand and mid-aged stand.The effects of nutrient addition on annual litterfall was much greater in mature stand,the stand litterfall production was higher than in both old-growth and mid-aged stands.The results of variance analysis indicated that both nutrient addition and forest age had no significant effect on litter production.However,a significant correlation?p<0.001?was observed between year and litterfall production in this subtropical evergreen broad-leaved forest.2.Nutrient content of litterfallThe nutrient contents of litterfall for the three different aged stands showed the similar pattern as C>N>Ca>K>Mg>P.Compared with CK,nutrient addition increased the contents of N,C and P,while decreased contents of Ca and K,Mg in the old-growth stand.In mature stand,nutrient additions made an increase of N content,while a decrease of Ca and Mg contents in litterfall.The P and K contents decreased in N addition and increased in N+P addition.In mid-aged stand,The N addition caused decrease of contents of N,P,Ca and Mg,and increase in N+P addition.Moreover,nutrient additions resulted in decrease of C content.In general,compared with CK,the nutrient content in litterfall appeared the trend of old-growth stand>mid-aged stand>mature stand.The results from variance analysis showed that N,P,Ca and Mg contents had significant correlations with treatment,year and forest age.The K content was not correlated to treatment,while significantly correlated to year and forest age.The C content was relatively stable without significant correlation to treatment,year and forest age.3.Nutrient return by litterfallThe nutrient return by litterfall for the three stands showed the similar trend as C>N>Ca>K>Mg>P.In old-growth stand,K return was shown N>N+P>CK,and N+P>N>CK for the other elements.The total amount of nutrient return was consistent as N+P(4090.80 kg·hm-2·a-1)>N(3813.02 kg·hm-2·a-1)>CK(3483.50kg·hm-2·a-1).In mature stand,the Mg return was decreased in nutrient additions.The returns of N,C,P,Ca and K showed a consistent pattern as N+P(4720.25 kg·hm-2·a-1)>N(4449.38 kg·hm-2·a-1)>CK(3858.24 kg·hm-2·a-1).In mid-aged stand,the K return increased and the returns of other elements decreased in N addition.However,the nutrient returns were increased in N+P additions.The total amount of nutrient return was ranked by N+P(4039.77 kg·hm-2·a-1)>CK(3751.36 kg·hm-2·a-1)>N(3678.30kg·hm-2·a-1).
Keywords/Search Tags:Nitrogen deposition, Subtropical evergreen broad-leaved forest, Forest age, Litterfall production, Nutrient return
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