| Cunninghamia lanceolata is an important fast-growing timber tree in southern China.However,the blind pursuit of fast growth and high yield and expansion of the area of afforestation.There are serious phenomena such as pure forest,intensive forest,large area concentration and multiple generations of continuous planting,which results in a serious decline of soil fertility,which to a large extent poses a great threat to the sustainable development of plantation.However,under the condition that it is difficult to apply fertilizer to the forest land,the nutrient return of litter is of great significance to the growth of trees and the enhancement of self-sustaining land capacity.Therefore,it is particularly important to promote the decomposition of Chinese fir litter and accelerate its nutrient return and cycling.Some studies have shown that the quality and quantity can promote the decomposition process of litter to some extent by regulating the composition of litter.In view of this,the diversity of leaf litters was simulated by the diversity of tree specie in this study.From the perspective of leaf diversity,the experimental system for the decomposition of controlled artificial bowl was constructed by means of the technique of the experiment system of leaf litter and soil decomposition,which selectes four main local tree species-Chinesefir(PS),Michelia macclurei(PH),MangLietia Yuyuanensis(PR)and Phoeba bournei(PN)as the research objects.Based on the litter leaves of Chinese fir,a leaf diversity treatment(species richness ranging from 1 species to 4 species)was established with the litter leaves of different tree species.In addition,the leaf litter diversity treatments composed of Chinesefir andMichelia macclurei,Chinesefir and MangLietia Yuyuanensis with different ratios(3:1,1:3,1:1)were designed.On the basis of comparative study on the litter decomposition characteristics of Chinesefir,Michelia macclurei,MangLietia Yuyuanensis and Phoeba bournei single tree species,the research focuses on the study of litter decomposition rate,nutrient content and its release rules and the degradation characteristics of refractory organic compounds(lignin,cellulose)in litter diversity treatment and reveales the effects of litter diversity on the decomposition and mechanism of litter leaf of Chinese fir in order to select the best treatment of litter diversity,which can effectively promote the litter decomposition of Chinese fir.The main conclusions are as follows:(1)The mass loss rate of different leaf litter increased with the increase of decomposition time.In the whole process of decomposition,the mass loss rate of each leaf was significantly different.PR litter decomposition was the fastest,while PN litter decomposition was the slowest,PS and PH litter mass loss rates were close to each other.After decomposing for 1 year,the mass loss rate of four kinds of litter showed as follows:PR(57.73%)>PH(28.44%)>PS(22.20%)>PN(11.51%),basically consistent with the trend of decomposition rate.(2)For the leaf litter diversity treatments of Chinese fir and Michelia macclurei,the mass loss rate of SH3:1 was always lower than that of the other two treatments and PH litter,and the mass loss rate was lower in the first five stages of decomposition than that of PS.The mass loss rate at the end of the experiment was SH1:3>PH>SH1:1>SH3:1>PS.By comparing the measured values with the predicted values,it is found that the leaf litter of Chinese fir and Michelia macclureihave a certain degree of mutual promotion in the process of decomposition under SH1:3diversity treatment,mutual inhibition under SH3:1 diversity treatment and no obviousinteraction.in the treatment of SHl:1.At the same time,after one year of decomposition,only Chinese fir litter mass loss rate in SH1:3 treatment was slightly higher than mass loss rate of PS leaf litter.The decay rate of Chinese fir leaves in the leaf litter diversity treatments of Chinese firandMichelia macclureishowed as follows:PS>PSSH1:3>PSSH1:1>PSSH3:1,which indicated that the leaf litter diversity treatments of Chinese fir and Michelia macclurei was not conducive to promoting the decomposition of Chinese fir leaves.However,in the leaf litter diversity treatments of Chinese fir and Michelia macclurei,with the smaller the proportion of Chinese fir leaves,the larger the proportion of Michelia macclurei was,the faster the decomposition of Chinese fir leaves in the diversity of leaf litters would be.(3)For the leaf litter diversity treatments of Chinese fir and Manglietia yuyuanensis,mass loss rate of PS was always lower than that of the leaf litter diversity treatments of Chinese fir and Manglietia yuyuanensis.At the end of the experiment,the mass loss rate showed as follows:PR>SR1:3>SR1:1>SR3:1>PS.By comparing the measured and predicted values,it was found that with the increase of decomposition time,there was a certain mutual promotion between Chinese fir and Manglietia yuyuanensis litters,especially SRI:3 and SR3:1 treatments.The mass loss rate of Chinese fir in t the leaf litter diversity treatments of Chinese fir and Manglietia yuyuanensis was SR1:3>PS>SR3:1>SR1:1,consistent with the size of decomposition rates and the time required to decompose 50%and 95%.The results showed that decreasing the proportion of Chinese fir leaf littersor increasing the proportion of Manglietia yuyuanensis leaf litters could promote the decomposition of leaf litters of Chinese fir,the lack of one of which would inhibit the decomposition of Chinese fir leaf litters.(4)For the treatments of equal-proportion leaf litter diversity,at the end of the experiment,the mass loss rate showed as follows:SR1:1>SHR>SRN>SH1RN>SH1:1>SHN>PS>SN.By comparing the measured values with the predicted values,it was found that with the increase of decomposition time,there was interaction among the litter leaves in SN,SHN,SRN,SHRN four litter diversity treatments.At the same time,the mass loss rates of Chinese fir leaves in thetreatmentof leaf diversity showed as follows:SRN>SHRN>SHN>PS>SH1:1>SN>SHR>SR1:1,consistent with the size of its decomposition rates and the time required for its decomposition to complete 50%and 95%.The results showed that the three leaf litter diversity treatments of SRN,SHRN and SHN could significantly promote the decomposition of Chinese fir litterleaves.However,the litter leaves of Chinese fir in the litter diversity treatments of SHRN were not the fastest decomposed,which indicated that the more kinds of litters were not the best choice to promote the litter decomposition of Chinese fir.(5)The treatment of leaf litter diversity was beneficial to the decomposition of three broad-leaved species in different degrees.However,SHRN litter diversity treatment had a slight inhibition effect on litter decomposition of Manglietia yuyuanensis.And the promotion of SHRN litter diversity treatment onMichelia macclurei and Phoeba bournei was not as good as that of the diversity treatment of three or two litter combinations.Meanwhile,mass loss rate of SHRN treatment was not the largest in all litter diversity treatments,showed that the rate of leaf decomposition was not necessarily proportional to the species diversity of tree species.(6)The leaf litter diversity treatments of Chinese fir and Michelia macclurei had different effects on the nutrient content and release rates of leaf litters of Chinese fir.The nutrient content of Chinese fir was the same as that of control PS.For the leaf litter diversity treatments of Chinese fir and Michelia macclurei,C content and C/N ratio decreased monotonously;N content of Chinese fir was opposite to that of C/N ratio;The content of P increased at the initial stage,then decreased continuously;Mg showed a small fluctuation state.According to the Olson index equation and decomposition parameters,it was found that the leaf litter diversity treatments of Chinese fir and Michelia macclurei can promote the release of P element in Chinese fir,and inhibit the release of Mg element to some extent.Both increasing the proportion of Chinese fir leaves and Michelia macclurei leaves,it was beneficial to promote the release of C element in Chinese fir.The SH1:1 treatment had a slight inhibition on the release of C element in Chinese fir.The SH1:3 treament can promote the release of N element in Chinese fir.(7)The leaf litter diversity treatments of Chinese fir and Manglietia yuyuanensis had different effects on the nutrient content and release rates of leaf litters of Chinese fir.And the nutrient content of Chinese fir in the leaf litter diversity treatments of Chinese fir and Manglietia yuyuanensishad similar variation tendency to that of the control.C content and C/N ratio of Chinese fir declined monotonously;N content during the decomposition showed a small upward trend;P,Mg has a downward trend in the small amplitude fluctuation.Based on the Olson index equation and decomposition parameters of nutrients,it was found that the leaf litter diversity treatments of Chinese fir and Manglietia yuyuanensis was helpful to promote the release of P element in Chinese fir,especially the SR3:1 treatment.Both the SR1:3 and SR3:1 patterns could promote the release of C,Mg in Chinese fir,while the SR1:1 treatment could inhibit the release of them.SR1:3 treatment could promote the release of N element in Chinese fir..(8)The nutrient content and release rates of Chinese fir leaves were affected by the treatment of equal-proportion leaf diversity.The nutrient content of Chinese fir in the treatment of equal-proportion leaf diversity was the same as that of the control.C,C/N ratios,P and Mg showed a downward trend,while N content increased.According to the Olson exponent equation and its decomposition parameters of Chinese fir nutrient in the treatments of equal-proportion leaf litter diversity,it was found that the treatments of equal-proportion leaf litter diversity had different effects on the release of P,Mg,C,N four elements in Chinese fir,among which the SRN treatment was beneficial to promote the release of P,Mg and C three elements.The treatments of equal-proportion leaf litter diversity could promote the release of P element in Chinese fir to some extent,especially the SRN,SHN,SN treatment.At the same time,with the decomposition time,the more diversity of leaf litters may have some inhibition effect on the release of P element in Chinese fir.With the exception of SRN,the other equal-proportion leaf litter diversity treatments could inhibit the release of Mg elements in Chinese fir to some extent.The three diversity treatments of SHN,SHRN,SHR were beneficial to promote the release of N in Chinese fir.(9)By comparing the measured and predicted values of nutrient residue rate in diversity treatment,it was found that SH3:1 treatment promoted the release of P element in the early stage and inhibited it in the later stage.And it did not play a significant role in the early stage of N element but a certain inhibition in the later stage.And the effect of SH3:1 treatment on Mg was opposite with that of N.SH1:1 could promote the release of N,P elements.The threeleaf litter diversity treatments of Chinese fir and Michelia macclureihad no obvious effect on the release of C element.The three leaf litter diversity treatments of Chinese fir and Manglietia yuyuanensis had a certain influence on the release of P elements during the early stage of decomposition,but the later function was not obvious.For the release of C,N,it showed that the decrease of the proportion of leaf litters of Chinese fir or the increase of the proportion of leaf litters of Manglietia yuyuanensis could obviously promote;otherwise,it could be inhibited.SR1:1 treatment obviously promoted the release of Mg in the later stage.The SHR treatment significantly promoted the release of P,Mg,C,Nfour elements.In addition,SHRN,SRN and SRN could promote the release of Mg,C,N.SN and SHN could promote the release of C,N to a certain extent.The SRI:1 treatment could promote the release of Mg,N to a certain extent.SN also promotes Mg element.(10)The content of lignin and cellulose of Chinese fir decreased significantly at the beginning of decomposition,then fluctuated,but the change of lignin was larger than that of cellulose.Expect SH1:1 had no obvious effect on the cellulose content in Chinese fir,all the diversity in all diversity treatments could promote the decrease of lignin and cellulose content in Chinese fir.By comparing the lignin and cellulose content in Chinese fir among different proportion leaf litter diversitytreatments,it was found that with the decrease of the proportion of Chinese fir,the faster the degradation of ligninin Chinese fir was,and the lower the content of lignin in Chinese fir was.In addition,the increase of the proportion of leaf litters of Chinese fir or Manglietia yuyuanensis will be more conducive to promote the significant reduction of lignin in Chinese fir.The cellulose content in Chinese fir of the leaf litter diversity treatments of Chinese fir and Manglietia yuyuanensis showed the same rule as that of its lignin,but the leaf litter diversity treatments of Chinese fir and Michelia macclurei did not show obvious impact on the cellulose in Chinese fir.SN also inhibited the decrease of cellulose content in Chinese fir in the early stage and promoted it to some extent in the later stage.(11)The degradation rate of Chinese fir lignin and cellulose was basically consistent with the variation trend of its content in the diversity treatment of leaf litters.The effects of litter diversity on lignin and cellulose in Chinese fir were different.All leaf diversity treatments promoted the degradation of lignin in Chinese fir.In different proportion diversity treatments,reducing the proportion of Chinese fir litter leaves was helpful to promote the degradation of lignin more effectively.And as the decomposition continues,the increase of the proportion of broadleaved species litter leaves will more effectively promote the degradation of Chinese fir lignin.With the increase of decomposition time,Chinese fir and broad-leaved species showed a promoting effect on cellulose degradation in Chinese fir under the diversity treatment of 1:3 combination,while the effect onwhich was not obvious under the treatment of 1:1.There was a certain inhibition on the degradation of cellulose in Chinese fir under the treatment of 3:1.All equal-proportion leaf diversity treatments promoted the degradation of cellulose in Chinese fir.The degradation rate of cellulose was basically consistent with the mass loss rate of Chinese fir in the treatment of equal-proportion diversity,among which SHN,SHRN,SRN was the best choies in promoting the decomposition of cellulose and its leaf litter in Chinese fir. |
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