Soil attributes and microclimate are important drivers of initial deadwood decay in sub-alpine Norway spruce forests

Deadwood is known to significantly contribute to global terrestrial carbon stocks and carbon cycling, but itsdecay dynamics are still not thoroughly understood. Although the chemistry of deadwood has been studied asa function of decay stage in temperate to subalpine environments, it has generally not been related to time.We therefore studied the decay (mass of deadwood, cellulose and lignin) of equal-sized blocks of Picea abieswood in soil-mesocosms over two years in the Italian Alps. The 8 sites selected were along an altitudinal sequence,reflecting different climate zones. In addition, the effect of exposure (north- and south-facing slopes)was taken into account. The decay dynamics of the mass of deadwood, cellulose and lignin were related to soilparameters (pH, soil texture, moisture, temperature) and climatic data. The decay rate constants of Picea abiesdeadwood were low (on average between 0.039 and 0.040 y−1) and of lignin close to zero (or not detectable), while cellulose reacted much faster with average decay rate constants between 0.110 and 0.117 y−1. Our fieldexperiments showed that local scale factors, such as soil parameters and topographic properties, influencedthe decay process: higher soil moisture and clay content along with a lower pH seemed to accelerate wooddecay. Interestingly, air temperature negatively correlated with decay rates or positively with the amount ofwood components on south-facing sites. It exerted its influence rather on moisture availability, i.e. the lowerthe temperature the higher the moisture availability. Topographic features were also relevant with generallyslower decay processes on south-facing sites than on north-facing sites owing to the drier conditions, the higherpH and the lowerweathering state of the soils (less clayminerals). This study highlights the importance of a multifactorialconsideration of edaphic parameters to unravel the complex dynamics of initial wood decay.