Abstract
To understand the relative importance of plant community composition and plant-induced soil properties on N transformations, the soil N mineralization, ammonification and nitrification characteristics of natural secondary forests (Quercus mongolica-Juglans mandshurica forest: QJF, and Quercus mongolica-Populus davidiana forest: QPF) and the adjacent larch plantations (Larix kaempferi forest: LF1 and LF2) were studied during the growing season. All of the forest types showed seasonal dynamics of N mineralization rates. The total cumulative N mineralization was significantly higher in QPF (73.51 kg hm−2) than in LF1 (65.64 kg hm−2) and LF2 (67.51 kg hm−2) (p < 0.05). The total cumulative nitrification from May to November was significantly higher in QJF (65.16 kg hm−2) and QPF (64.87 kg hm−2) than in LF1 (52.62 kg hm−2) and FL2 (54.17 kg hm−2) (p < 0.05). Based on the variation partitioning, independent soil properties were the primary determinants of the N transformations (13.5%). Independent climate conditions explained 5.6% of the variations, while plant variations explained 3.2% of the variations in N transformations. We concluded that different forest types with various plant community compositions have different influences on the litterfall quantity and quality and the nutrient availability, and these differences interact with seasonal climate conditions that in turn drive the differences in N mineralization.
Highlights
Nitrogen (N) is an essential element for the growth of organisms and the productivity of forest ecosystems [1]
This study aimed to (1) investigate and compare seasonal N mineralization rates under field conditions in natural secondary forests and the adjacent larch plantations; and (2) assess the extent to which N mineralization rates could be explained by the plant-soil properties that are associated with plant community compositions and seasonal climate conditions in temperature and precipitation
We suggest that shifts in plant species composition and resulting plant diversity, forest biomass and soil properties are the most probable explanations for the soil N mineralization patterns of natural secondary forest converted into larch plantations
Summary
Nitrogen (N) is an essential element for the growth of organisms and the productivity of forest ecosystems [1]. Soil N mineralization of organic matter plays an important role in determining soil N availability, primary productivity and N losses from soil to stream, contributing to ground water contamination and the pollution of the water environment [1,2,3,4]. Numerous previous studies and practices have shown that seasonal changes in N mineralization result in patterns with the highest mineralization rates in the summer and the lowest rates in the winter, which appears to follow seasonal patterns of temperature and precipitation [8,9,10,11]. Moisture, and precipitation patterns are important drivers of soil N transformations, and each of these seasonal climate conditions may have different impacts on various forest types [12]. Forest types with varying plant communities may have different influences on the N cycle due to differences in Forests 2018, 9, 386; doi:10.3390/f9070386 www.mdpi.com/journal/forests
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