Nutrient Dynamics Assessment Of Coarse Wood Debris And Its Effect On Soil Properties Subjected To Successional Decay Levels Of Three Forests Types In Northeast,China

Coarse wood debris（CWD）is an important functional and structural component of forested ecosystems and plays a critical role in forest productivity,nutrient cycling,decomposition,biological diversity and carbon（C）sequestration,and shapes the carbon pool in the forest ecosystem.During the past decades,numerous studies have attempted to relate CWD characteristics with forest succession,community composition,nutrient cycling and forest management.However,less attention has been paid to the stoichemistry of CWD and the elemental composition of CWD.CWD is considered to differ in basic underlying mechanisms of their soil,and therefore,the responses of soils in different forest types or species varied greatly.Therefore,the explicit mechanism of these soils is still not fully understood.In order to assess the effects of CWD on soil chemical properties like nitrogen（N）and C concentration,exchangeable cations,soil nutrient concentration and enzymatic activity in three different forest types.Therefore,a factorial experiment was laid out at the Liangshui National Nature Reserve（47°10′50″N,128°53′20″E）,in Heilongjiang,northeast China in three different forests types,Picea koraiensis-Abies nephrolepis-Pinus koraiensis forest（PAPF）,Betula costata-Pinus koraiensis forest（BPF）and Tilia amurensis-Pinus koraiensis forest（TPF）,respectively.The following results were revealed from the statistical analyses of the collected data.（1）Results showed that N,phosphorus（P）,magnesium（Mg）,manganese（Mn）,sodium（Na）,zinc（Zn）,sulfur（S）,aluminum（Al）,and iron（Fe）concentrations almost totally increased with decay level for all three forest types,except for K in all three forest types and B in PAPF.Similarly,maximum concentrations of N,P,boron（B）,Mg,potassium（K）,C,Zn,and Mn of CWD were observed in BPF forest under varying decay classes,but their maximum concentrations of Fe and S were found in PAPF forest and TPF forest,respectively.（2）The results showed that the decay class IV,soil organic C,N,p H,nutrients and enzymatic activity were significantly influenced by forest types,decay class and distance from the decaying logs of PAPF,BPF and TPF forest types.At a distance of50 cm,the effect of decaying logs was either negligible or not evident.The highest p H was observed in the BPF forest.Similarly,the maximum concentration of N,C,NH₄⁺,P,K⁺,Mg²⁺and Ca²⁺were observed for the PAPF forest followed by the BPF forest.（3）There was a reliable correlation between overall CWD and soil nutrient concentrations among three forest types（PAPF,BPF,and TPF）.Yet,the arrangement of correlation differed among PAPF,BPF,and TPF forests.This should be a note of attention about the simplification of attribute interrelation,which wants to be reconnoitered across conflicting ecological gradients.We observed that overall CWD P and C were positively correlated with soil p H,while Al was negatively correlated.CWD N was positively correlated with urease enzyme,in contrast,CWD C and N were negatively correlated with invertase and dehydrogenase enzymes respectively.（4）The results from this experiment revealed that the decay rates were significantly related to N concentration and C:N ratio in decay classes across all forest types.The concentration of K decreased with increasing decaying class in all the three forest types.The variation in nutrient concentrations observed here underscores the complexity of nutrients stored in wood debris in forested ecosystems.In this study,we observed that CWD can sequester C and contribute to functional diversity in the flora of the different forests.（5）The study also suggests that CWD plays a key role in decaying logs in forest ecosystems to enhance C and nutrient budget with the improved enzymatic activity of the soil.The study also points out that the CWD plays a key role in the nutrient cycling process under the decaying logs of forest ecosystems.（6）CWD S was positively correlated with soil S,while CWD C with soil C,CWD K with soil K and CWD Mg with soil Mg were found negatively correlated.This study indicated that the variation in soil nutrient concentrations and enzymatic activity were equally affected by decomposition levels.From the above results,we concluded that CWD play a vital role in the northern ecosystem in different biogeochemical progressions.Logs of PAPF,BPF and TPF forests in northern ecosystems accumulate a significant amount of nutrients during decomposition and create comparatively nutrient-rich microsites in northern ecosystems.The study also indicated that the CWD occurrence and perseverance have an ecological importance in forest ecosystems that should be engaged in contemplation for managing pronouncements concerning C sequestration and functional diversity in different forest ecosystems.