Dissolved and water-extractable organic matter in soils: a review on the influence of land use and management practices

Despite that dissolved organic matter (DOM) and water-extractable organic matter (WEOM) represent only a small part of soil organic matter, they appear to be involved in many soil processes. This review intends to compile the current information on the influence of land use and management practices on soil DOM and WEOM, and to identify the gaps in our knowledge that sometimes preclude from drawing general conclusions. The literature on DOM and WEOM dynamics in different ecosystems is derived mainly from studies on temperate forest soils. Although less abundant, literature on temperate grassland and arable soils is also available, whereas very few studies have been published on tropical ecosystems. Similarly, studies on DOM and WEOM have focused mainly on the carbon fraction, whereas nitrogen and phosphorus have received much less attention. On the short term, temporal and spatial variations in DOM and WEOM are complex and influenced by environmental conditions. Laboratory studies have shown that management practices, such as liming and N fertilization, can induce marked fluctuations in DOM and WEOM. Under field conditions, however, the net effect of management practices often remains unclear because many soil properties, which can interact and counterbalance, are influenced at the same time. Changes in DOM and WEOM upon management practices are generally of short duration, whereas long-term effects are more related to vegetation type and to the amount of plant litter returned to the soil. So far, research on soil DOM and WEOM as influenced by land use and management practices has offered fragmented and sometimes contradictory information. It is concluded that the standardization of collection and extraction methods for DOM and WEOM measurements is crucial to reduce the uncertainty when comparing results from different studies. More research would also be required (i) under field conditions and especially in tropical ecosystems, (ii) to determine the biological significance of measured fluctuations in DOM and WEOM concentration and composition, and (iii) to elucidate the mechanisms determining DOM/WEOM dynamics following changes in land use and management practices.