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We investigated how factors underlying local spatial variations controlled needle litter decomposition across a chronosequence of Chinese pine (Pinus tabuliformis Carr.) forests. Litterbag methods were used to measure changes in litter chemistry and the mass loss of leaf litter, as well as selective biotic and abiotic factors during the growing seasons (May-October) in 2013 and 2014 in a set of fully replicated P. tabuliformis Carr. secondary forest stands that differ in age in northern China. During the two growing seasons the path analysis identified the litter lignin/N ratio, soil microbial metabolic quotient (qCO2), soil diversity of fungal assemblages (SFD), and soil-water content (SWC) as dominant controlling factors in needle litter decomposition, collectively explaining 76.9% of the total variation in mass loss across the entire age sequence. Litter lignin/N and soil qCO2 had the greatest negative effects on the k value, followed by weaker positive effects of SFD and SWC. Our findings indicate that forest stand age has a great influence on needle litter decomposition by determining litter quality, with soil microbial activity and local environmental factors being secondary drivers in needle litter decomposition across a chronosequence of Chinese pine (Pinus tabuliformis Carr.) forests. [ABSTRACT FROM AUTHOR]

Litter quality is often considered the main driver of rates of decomposition. Litter decomposes faster in its home environment than in any other environment, which is called the home-field advantage (HFA). However, evidence for this phenomenon has not been universal. In addition, litter mixtures of different species can induce a non-additive effect (NAE) on decomposition processes. However, the direction and magnitude of NAE vary and underlying mechanisms remain unclear. The aim of our study was to assess the effect of litter quality on leaf-litter decomposition in the context of HFA and NAEs in temperate forests in China. Litterbags containing aspen (Populus davidiana), birch (Betula platyphylla), and oak (Quercus liaotungensis) litter were incubated in situ in pure aspen and broadleaved mixed forests in Chinese temperate forests for 360 days. The main results were: 1. Aspen litter with a low C/N ratio and high initial N concentration decomposed faster than birch litter, both of which decomposed faster than oak litter, which had the lowest quality. 2. The rate of decomposition of oak litter was significantly higher in the broadleaved mixed forest than in pure aspen stands; however, the rate of decomposition of birch litter was not significantly different from pure aspen stands and broadleaved mixed forest. 3. Contrary to what was predicted, the mixture of aspen and birch litter decomposed faster than expected. However, both the aspen/oak and birch/oak mixtures had a neutral mixing effect where the rates of decomposition were slightly faster than expected. 4. Controlling factors based on linear models show that the order of the relative importance of their effect on litter decomposition was as follows: litter quality, forest floor environment, and litter mixtures. This study indicates that: 1. The various litter species exhibited different litter-environment interactions, such as favoring or contradicting the HFA hypothesis. 2. Litter mixture treatments can induce different mixing effects. 3. Compared with environment and litter mixtures, litter quality is the dominant factor in controlling the rate of litter decomposition. [ABSTRACT FROM AUTHOR]

Knowledge about the impact of nitrogen (N) addition on soil respiration (Rs) is critical for understanding soil carbon (C) balance and its responses to climate change. We conducted a long-term field experiment to evaluate the response of Rs to N addition in a larch (Larix principis-rupprechtii) plantation during the growing season in northern China. We applied four N (in the form of NH4 NO3 ) levels, i.e., control (N0: 0 g N m-2 year-1 ), low-N (N1: 5 g N m-2 year-1 ), medium-N (N2: 10 g N m-2 year-1 ), and high-N (N3: 15 g N m-2 year-1 ) monthly starting in June 2015. The results showed that N addition – especially N2 and N3 levels – significantly stimulated Rs. N1 and N2 levels resulted in the increase of Rs in a short time, whereas the duration of N3 level can last across the whole month or at least 10 days. The results highlight the need for improving the Rs sampling interval after N addition to ensure more accurate evaluation of C emission. Soil temperature and soil moisture together explained more variations of Rs. N addition exhibited a slight increase in the sensitivity of Rs to temperature (Q10 ), but no significant differences were found for the Q10 among N levels [ABSTRACT FROM AUTHOR]