Study On Leaf And Fine Root Stoichiometry Characteristic In The Burned Areas Of Larix Gmelinii Forests In Great Xing’an Mountains

Wildfire is the universal disturbance factor of the ecosystem and one of the most important driving factors during boreal forest succession.The forest ecosystem structure in Great Xing ’an mountain was frequently destroyed by wildfire,which also changed the nutrient utilization strategies and vegetation restoration processes of plants in this area.The researches on the boreal forest ecosystem recovery process disturbed by wildfire were mainly learned from the quantitative ecology,but there were still many deficiencies in the study of plant nutrient utilization in burned area.Thus,to fully reveal the synergistic changes of aboveground and belowground plants stoichiometry and the restoration process of plant nutrients homeostasis will be of great ecological significance for further study of forest nutrient cycling and guidance of community recovery after wildfire disturbance.Our study selected the burned area of Larix gmelinii forests in Great Xing ’an Mountains as the research matrials,and established three fire severities(low severity,moderate severity and heavy severity)and five different recovery stages(2years after burn,10 years after burn,20 years after burn,30 years after burn,>80 years after burn(unburned))as research sample,using the theory of ecological stoichiometry to reveal the changes of leaves and fine root C,N,and P stoichiometry characteristics in species level and community level,the nutrients homeostasis,and the allocation strategies between leaves-fine roots stoichiometry after wildfire.The main results obtained include:(1)Soil bulk density,soil moisture concentration,and soil p H changed significantly in the early stage of recovery after 2 years recovery.The soil total N concentration after low,moderate and heavy fire severity was significantly increased after 10,2 and 20 years of recovery,respectively.The changes of N and P concentrations in litters also showed a relatively significant increase after 20 years recovery.(2)At the species level,the concentrations of plant C and N after low and moderate fire severity significantly decreased after 2 years recovery.With the increase of recovery period,the concentrations of C and N in leaves and fine roots after low and moderate fire severity returned to unburned level after30 years of recovery.The total P concentration in plant leaves decreased firstly and then increased with the increase of post-fire recovery time,and reached the lowest after 10 years recovery.At the community level,due to the increase of regeneration species,the total N concentration in leaves reached the maximum after 2 years of recovery,while the total N concentration in fine roots reached the minimum after 20 years of recovery.Wildfire significantly reduced the total P concentration in fine roots at community level.The mean values of leaf N:P ratio at the species and community levels showed that plant growth was restricted by P after 10 years’ recovery at moderate fire severity.The stoichiometric characteristics of plant leaves and fine roots were significantly or extremely significantly positive correlated with the changes of soil and litter nutrient,which reflected the plant stoichiometry was directly affected by the changes of soil and litter nutrient.(3)Stoichiometric homeostasis reflects the ability of plants to maintain their nutrient stability in the response to environmental changes.According to the analysis of stoichiometric homeostasis coefficient results,compared with unburned,wildfire reduced the homeostasis of plant nutrient,and the homeostasis gradually increased with the increase of recovery periods.The average homeostasis value of fine roots to nutrient changes was less than that of leaves.The homeostasis of leaf P increased significantly with the increase of recovery time.Compared with moderate severity,P homeostasis of fine roots recovered more quickly with time after heavy severity.(4)The allocation coefficient obtained from the allometric equation showed that,at species level,allocation scaling exponent of plant C,N,and P between fine roots(y)and leaves(x)showed significant differences with recovery after the burn under the different fire severity.Especially,the allocation of C,N,and P in fine roots changed greatly in the later stage of fire restoration(30 years after burn).The C,N,and P allocations between leaves and fine roots will be translated at certain periods.At the community level,the allocation of total C changed more in fine roots after 2 years recovery and more in leaves after 30 years recvoery.The C(y)-N(x),C(y)-P(x)and N(y)-P(x)allocation in leaves and fine roots showed significantly different under different fire severities at different recovery periods.For example,at low and heavy severity,the allocation of N in leaves changed greatly after 2 years recvoery.Therefore,plants actively regulated stoichiometric concentrations due to the changes of nutrient supply,and these changes further affected the redistribution of aboveground and belowground nutrients.This study provided a new sight of plant nutrient adaptation research after wildfire,and also showed important conclusions for the study of the elements cycle and the recovery in disturbed ecosystem.The results concluded that plants could adjust their stoichiometric characteristics during the recovery process after wildfire.At the same time,the vegetation restoration in the burned area mainly depended on the high homeostasis plants,and in the short term,the regeneration of the low homeostasis plants promoted the rapid recovery of the community.In addition,the differences in the utilization strategies of above-belowground elements in the restoration process should also be fully considered when learning the material cycle of forest vegetation in burned areas.The above results provided theoretical basis for revealing the material cycle process of the ecosystem in the burned area and protecting the post-fire ecosystem.