Litter Decomposition Characteristics Of Ancient And Evolved Tree Species And Their Response Of To Nitrogen Deposition

Litter decomposition is an important link in carbon turnover and mineral nutrient cycling in forest ecosystems.Under the background of atmospheric nitrogen deposition,soil nutrients and litter nutrient contents increased and then affect the forest carbon turnover and soil carbon sink function,which directly or indirectly affect the litter decomposition process.Due to the differences in the morphological anatomy and nutrient content of the leaf and roots of ancient and evolutionary tree species,which means that the ecological functions of the two tree species and their responses to global climate change are different,but no relevant research data support this speculation at present.Therefore,studying the response of litter decomposition of ancient and evolutionary tree species to nitrogen deposition is important for understanding the ecological status of the two tree species in carbon turnover and predicting the functional response of the two tree species in the context of global change.For these purposes,3 ancient tree species and 3 evolutionary tree species were chosen for the research objects.Simulated nitrogen deposition by applying nitrogen fertilizer to study the differences of the decomposition rate and nutrient loss rate of fine roots and leaves between different types of tree species and their responses to nitrogen deposition.The results are as follows:(1)The rate of leaf litter and root decomposition of ancient tree species was higher than that of evolutionary tree species.Nitrogen application tends to promotes debris decomposition of evolution and ancient tree species(P<0.05).The decomposition rates of litter and fine roots were well fitted by Olson negative exponential decay model,and the R~2of litter and fine roots were 0.805-0.917 and 0.880-0.986.The leaf litter turnover period of evolutionary tree species and ancient tree species is 4.092a and 2.291a,the fine root turnover period of evolutionary tree species and ancient tree species is 3.994a and3.161a;Under nitrogen application treatmen,the leaf litter turnover period of evolutionary tree species and ancient tree species was 4.432a and 2.540a,the fine root turnover period of evolutionary tree species and ancient tree species was 3.291a and 2.475a.These results suggest that roots and leaves of ancient tree species decomposed faster than that of evolutionary tree species.(2)During the whole decomposition process,there was no significant difference in the C content of the leaf litter of the evolutionary tree species and the ancient tree species,the P and N contents of the leaf litter of the ancient tree species were significantly higher than those of the evolutionary tree species(P<0.05).The C content in the fine roots of the evolutionary tree species was significantly higher than that of the ancient tree species(P<0.05);the N content in the fine root of the evolutionary tree species was significantly lower than that of the ancient tree species(P<0.05);There was not obvious dissimilarity in fine root p content between evolutionary tree species and ancient tree species.Nitrogen treatment promoted the enrichment of N and P and the release of C in the leaf litter of evolved and ancient tree species,it promoted the release of C and N enrichment in fine roots of evolved and ancient tree species,and inhibited the release of P from fine roots.(3)The C/N、C/P and N/P of leaf litter of evolutionary tree species were higher than the ancient tree species,N/P did not reach a significant difference between the two types of litter.The fine root C/N、C/P and N/P of evolutionary tree species were significantly higher than those of ancient tree species(P<0.05).Nitrogen treatment decreased the C/N and C/P of leaf litter and fine roots of evolutionary tree species and ancient tree species,and nitrogen treatment made fine root C/N reach a significant difference(P<0.05);Nitrogen application increased the N/P of leaf litter and fine roots of evolutionary tree species and ancient tree species,and nitrogen application made a significant difference in the N/P of ancient fine roots(P<0.05).(4)Nitrogen application significantly decreased soil pH(P<0.05),increased soil N content(P<0.05)and significantly inhibited the increase of soil P content.Through the correlation analysis,The C contents of litter and fine roots were significantly negatively correlated with soil organic carbon content,the N contents of litter and fine roots were significantly positively correlated with soil total nitrogen content,and the P content of litter leaves and soil total phosphorus content were significantly negatively correlated(P<0.05),there was a very significant positive correlation between P content in fine roots and soil total phosphorus content(P<0.01).Nitrogen treatment changed the correlation between soil pH and litter C and P,changed the correlation between soil P and litter C and N,changed the correlation between soil pH and fine root C,changed soil C and fine root correlation of P.(5)The decomposition rate of leaf litter was significantly negatively correlated with initial C、C/N、C/P、lignin、cellulose、lignin/N,and significantly positively correlated with initial N、P、leaf thickness、leaf area;the decomposition rate of fine roots showed a very significant positive correlation with N(P<0.01),and a significant negative correlation with the initial C、C/N、lignin and lignin/N;Nitrogen treatment changed the correlation between the decomposition rate of litter and the initial P.Nitrogen treatment changed the correlation between the decomposition rate of fine roots and the initial lignin,cellulose and N/P of fine roots.(6)The decomposition rates of leaf litter and fine roots were significantly positively correlated with soil pH and soil total nitrogen(P<0.01)the decomposition rate of leaf litter and the bacterial flora diversity index(Shannon index)showed a significant positive correlation(P<0.05).The leaf decomposition rate and the fungal flora richness index(Chaol index and ACE index)showed a very significant negative correlation(P<0.05).P<0.01).The decomposition rate of fine roots was significantly negatively correlated with the fungal flora richness index(Chaol index and ACE index)(P<0.01).The above results show that:The decomposition period of ancient tree species is faster than that of evolutionary tree species regardless of root or leaf litter,the decomposition period of ancient tree species is shorter than that of evolutionary tree species,and the decomposition period of leaves of two species is shorter than that of fine root.The decomposition process of the two tree species responded differently to nitrogen application.The overall performance is that fertilization improved and then reduces the decomposition rate of leaf litter and increases the turnover period,however,N application accelerated the decomposition rate of fine roots and reduced the turnover period.The litter decomposition of two tree species is related to its N,C,lignin,cellulose content,etc.And is affected by soil microorganisms,soil nitrogen,soil pH and other environmental factors.This study revealed differences in above-ground and underground litter decomposition processes,responses to nitrogen deposition and its influencing factors between ancient tree species and evolutionary tree species.The results provided an important theoretical basis for predicting the functions of the two species in the global carbon and nitrogen cycle and their responses to nitrogen deposition.