| Litter decomposition,as the basic process of C and organic matter cycling in terrestrial ecosystems,is strongly controlled by various abiotic and biological factors.The redistribution of light,temperature,precipitation,humidity and other ecological environmental factors by altitude and canopy position may change the hydrothermal dynamics and biological activity related to litter decomposition,thus affecting litter decomposition.In the alpine mountain area,the redistribution of light,precipitation and other ecological environmental factors by altitude and canopy location will inevitably lead to differences in soil water and heat combination,and then affect microbial activity,which will lead to spatio-temporal differences in litter decomposition.However,up to now,there is no study report on the effects of altitude and canopy position on litter decomposition at different key periods.Therefore,in this study,the Qilian alpine mountain forest was taken as the study subject.The field in-situ decomposition method of litterbags was used to study the effects of the crown center(CC)and crown edge(CE)at 2850 m,2950 m,3050 m,3150 m,3250 m above sea level on the decomposition of leaf litter of Qinghai spruce(Picea crassifolia Kom.)forest.The main study results are as follows:(1)In terms of time,with extending of time,the cumulative dry weight loss rate of litter at all altitudes increases continuously,and litter decomposed ～ 2.7-fold faster in the growing season(warm)than in the non-growing season(cold).This seasonal effect was consistent at different altitudes.In space,with the decrease of altitude and the increase of temperature,the litter decomposition amount increased by ～ 17%-48%,which is controlled by temperature,but not linearly related to temperature.This temperature effect is more obvious in CE(adequate light and precipitation);The litter decomposition at CE was ～ 1.2 times higher than that at CC(insufficient light and precipitation),and the canopy position effect was observed in both growing and nongrowing seasons.Consequently,the annual growth season may assume most of the tasks of litter decomposition in that year.It can be inferred that climate warming may significantly accelerate the litter decomposition of CE.Our study has brought a new supplement to the C cycle of the forest ecosystem in the alpine region.(2)The results showed that according to the Olson index decay model of litter decomposition,the litter decomposition coefficient(k)at 3050 m above sea level was the largest(k = 0.361)and the minimum(k = 0.303)at 3250 m.At the same time,the litter decomposition was related to the initial Mn concentration,which means that lignin degradation has started at the initial stage of litter decomposition.Meanwhile,the decomposition of Qinghai spruce leaf litter was also related to the initial N,P,Ca concentrations and the ecological stoichiometric ratio C/N.Finally,we realized that at the initial stage of decomposition of Qinghai spruce leaf litter,there was not a common factor that determined the litter decomposition,but the result of the joint action of multiple factors in different order and intensity.The results will lay a foundation for understanding the process and mechanism of litter decomposition in alpine forest ecosystem.(3)The contents of MBC,MBN and MBP in leaf litter and soil of Qinghai spruce forests at different altitudes in Qilian Mountains showed significant spatial and temporal differences.On the time scale,MBC,MBN and MBP in CC and CE litter at different altitudes increased at the beginning of the growing season and decreased at the end of the growing season;However,MBC,MBN and MBP in the soil decreased at the beginning of the growing season and increased at the end of the growing season.However,the MBP content in the soil at 3050 m elevation CE and 3250 m elevation showed an inverted “N” pattern of “first decreased,then increased,and then decreased”.On the spatial scale,the contents of MBC and MBN in litter were higher than those in soil,but the opposite was true for MBP;The contents of MBC,MBN and MBP in CE were significantly higher than those in CC(P < 0.05);In general,the contents of MBC,MBN and MBP were significantly highest at middle altitude(P < 0.05),followed by low altitude,and significantly lowest at high altitude(P < 0.05).These results lay a foundation for a clear understanding of the process and mechanism of litter decomposition in alpine mountain forests,and for further understanding the structure and function of terrestrial ecosystems.In conclusion,the ecological environment characteristics of alpine forest at different altitudes and canopy positions are different,which has a significant effect on the mass degradation,chemical components and microbial biomass of litter. |
