Influence Of Leaf Litter Input On Priming Effect Of Soil Organic Carbon Decomposition In China’s Forests

Soil priming effect refers to the change in soil organic carbon（SOC）decomposition caused by exogenous organic matter inputs,which could induce an increase of up to 4times in SOM decomposition rate and is a crucial process in driving soil carbon（C）dynamic.However,how leaf litter input,as one of the the most important exogenous organic matter input,influences priming effecs of SOC decomposition and their underlying mechanisms remains elusive,which largely limits our understanding of plant-soil feedbacks in terrestrial C cycle.In this study,stable ¹³C isotope technique was used to quantify the magnitude of priming effect on SOC decomposition rate induced by leaf litter input.Meanwhile,we examined how leaf economic spectrum（LES）,which was an important trade-off in resource acquisition and storage strategies in plants and represented by scores of axis 1 in principal component analysis,affected soil priming effect.In addition,we also elucidated microbial regulatory mechanisms of soil primig effects.Specifically,we collected leaf litter of dominant tree species to probe effects of LES on soil priming effect in Tiantong national forest ecosystem observation and research station,Zhejiang Province,China.We also used leaf litter of dominant tree species in seven forests sites to explore the determinants of priming intensity along temperature and precipitation gradient transects in China’s forests.Meanwhile,we selected leaf litter of six dominant species to examine impactsof species richness（1,2,4,6 species）,community-weighed mean（CWM）or functional diversity on soil priming effect.Our main findings are as follows:（1）By using stable ¹³C isotopic technique with leaf litter input of dominant tree species from subtropical forests,we explored effects of LES traits on soil priming effect induced by leaf litter input.Our results showed that soil priming effect induced by different leaf litter varied from-4.6%-+22.3%.Soil priming effect increased with LES change from conservative traits to acquisitive traits,and LES was the most important factor in regulating soil priming effect compared to single litter traits.Soil microbial biomass,the ratio of bacteria and fungal,and extracellular enzymatic activity increased with LES change from conservative traits to acquisitive traits.The structural equation model（SEM）analysis indicated that LES not only directly affected soil priming effect directly,but also indirectly influenced it by regulating microbial community structural and enzyme（R²=0.57,X²=13.92）.Theses finding shed light on the predomianant role of LES on SOC decomposition in subtropical forests,and provide new insights for incorporating LES into ecosystem models to predict terrestrial carbon dynamics in the future climate.（2）Using leaf litter of dominant tree species from seven forest sites across temperature and precipitation gradients,we examined spatial variation of soil priming effects.Our results showed that soil priming effect ranged from-10.4%to+52.9%for all seven sites.Soil priming effect increased with mean annual temperature（MAT）along a temperature transect but decreased with mean annual precipitation（MAP）along a precipitation transect.Similarly,we also found that LES was the most important factor in regulating priming effect induced by leaf litter along MAT and MAP transect by random forest approach.Specifically,total phospholipid fatty acids（total PLFAs）,the ratio of bacteria and fungal,the ratio of gram-negative and gram-positive bacteria（GN/GP）,and q CO₂ increased with LES from conservation traits to acquisitive traits along temperature and precipitation transects.Our results demonstrate the importance of LES in explaining spatial variation of soil priming effect induced by leaf litter over a broad geographic scale,which significantly advances our understanding of how litter inputs influence SOC decomposition at a regional scale.（3）Four levels of species richness（1,2,4,6 species）from six tree species was set to explore effects of leaf litter mixture inputs on soil priming effect.Our results showed soil priming effect（13.7±2.3%）induced by single species litter input were significantly lower than that in mixtures litter input（62.5±0.9%）.Meanwhile,we found that soil priming effect significantly increased with the functional diversity of specific leaf area（SLA）,lignin,and cellulose,lignin:N and multidimensional functional diversity.By variance partitioning approach,functional diversity contributed to 56.8%of variation of soil priming effect induced with leaf litter mixture,whereas CWM and microbes(i.e.,micaoribal biomass and community structure only explained 16.5%and 26.7%,respectively.These results indicated more important contributions of FDis than CWM in driving variability of soil priming effect.In summary,our results highlight the importance of LES in regulating soil priming effect at both a single site or the region scale,which decreased with LES change from acquisitive traits to conservative traits.Meanwhile,the magnitude of priming effect induced by leaf litter input of single species was significantly lower than that in leaf litter mixtures of multiple species.Functional diversity contributed to 56.8%of variation of soil priming effect,whereas CWM and microbes only explained 16.5%and26.7%,respectively.Our findings improve our understanding on the mechanisms of plant-soil feedbcks in forests,providing reliable parameters and a theoretical basis for the global models to accurately simulate terrestrial C cycling.