[Effects of nitrogen deposition on the concentration and spectral characteristics of dissolved organic matter in soil in Moso bamboo plantations.] / æ°®æ²‰é™å¯¹æ¯›ç«¹æž—åœŸå£¤å¯æº¶æ€§æœ‰æœºè´¨æ•°é‡ä¸Žå ‰è°±å­¦ç‰¹å¾çš„å½±å“.

The subtropical zone in China is one of the regions most affected by nitrogen deposition. Soil dissolved organic matter (DOM) is considered to be an important indicator of soil organic matter. Nitrogen deposition may alter the quality and quantity of soil DOM by changing soil microbial activity. In this study, we explored the effects of nitrogen addition on soil DOM content, its spectral characteristics and microbial extraceller enzyme activity in the Moso bamboo plantations by setting control (CT), low-nitrogen (LN), and high-nitrogen (HN) addition levels for three-year nitrogen addition. The results showed that there was no significant change in soil pH, dissolved organic carbon, dissolved organic nitrogen, and aroma index following nitrogen addition, while the humification index increased significantly, microbial enzyme activities increased first and then decreased with the increases of nitrogen addition. Fourier transform infrared spectroscopy results showed that soil DOM had similar absorption peaks in seven regions, and that the absorption peaks of 1000 to 1260 cm-1 were the strongest, indicating an enhanced amount of polysaccharides, alcohols, carboxyl acids, and esters after nitrogen addition. The results of three-dimensional fluorescence spectroscopy showed that soil DOM structure significantly changed following nitrogen addition, with a decrease in low-molecular substances such as protein-like substances and microbial metabolites and a significant increase in high-molecular substances such as humus-like substances. In general, nitrogen addition made soil nitrogen compatible with microbial requirements. Microorganisms decompose substances that were easily degraded in DOM. The structure of soil DOM was more complex after nitrogen addition. Therefore, short-term nitrogen deposition might be conducive to preserving soil fertility.

Effects of soil warming on soil microbial extracellular enzyme activities with different depths in a young Chinese fir (Cunninghamia lanceolata)plantation of subtropics.

Extracellular enzyme activitie (EEAs) are a sensitive indicator of microbial function and soil organic matter decomposition in response to climate warming. Up to now, most studies of climate warming and their effects on EEAs have been restricted on the relatively carbon rich topsoil (the upper 20 cm of the soil), whereas little is known about EEAs in subsoil (below 30 cm depth). This study focused on the responses of EEAs to soil warming in a subtropical forest at depths of 0-10 cm, 10-20 cm, 20-40 cm and 40-60 cm. The examined extracellular enzymes included ß-glucosidase (BG), cellobiohydrolase (CBH), phenoloxidase (PHO) and peroxidase (PEO), all being involved in the C-cycle. The results showed that, 1) warming significantly increased all EEAs (18%-69%) at the depth of 0-10 cm and 10-20 cm. Below the depth of 20 cm, warming did no affect or suppressed EEAs (13%-31%), except increasing PHO (10%) at 20-40 cm. 2) Results from the redundancy analysis showed that the EEAs were mainly driven by ammonium nitrogen (NH4+-N) and soil moisture (M) in organic carbon rich topsoil. Warming enhanced nutrient competition between soil microorganisms and plants. Thus, it increased EEAs to meet NH4+-N demands of microorganisms. In subsoil with relatively low substrate availability, the EEAs were dominated by dissolved organic matter and microbial biomass (MBC). Warming increased dissolved organic matter and thus provided more substrates for microorganisms, which relieved the dependence of microbes on EEAs. Consequently, warming diminished EEAs in subsoils. Our results suggested that EEAs at the four depths showed different responses to warming. In addition, environmental factors accounting for the variances in EEAs under soil warming condition were different at topsoil and subsoil. Paying more attention to microbes at different soil depths has important implications to precisely predict ecosystem C cycling in response to global warming.

[Effects of precipitation reduction on the composition and stability of soil organic matter in a young Cunninghamia lanceolata plantation.] / 减少降雨对杉木幼林土壤有机质组分及稳定性的影响.

It is hard to predict the response of soil organic matter (SOM) to global climate change due to its heterogenous chemical structure. With the development of molecular techniques to identify the structure, sources and stages of SOM degradation, long-standing questions regarding the composition and stability of SOM might be resolved. To investigate the effects of changes in precipitation patterns on the stability of SOM, we analyzed the specific compositions and extent of degradation of SOM using biomarkers, in a young Cunninghamia lanceolata plantation after reducing 50% of precipitation (P) for two years. The results showed that precipitation reduction (P-treatment) significantly reduced the levels of free lipids. Relative to control (CT), P-treatment decreased short-chain n-alkanoic acids (C16-18) and terpenoids and steroids by 62.8% and 19.1%, respectively. However, P-treatment did not significantly change the concentrations of other aliphatic compounds. Although there was no observable difference in the total lignin content between treatments, P-treatment significantly reduced the acid to aldehyde ratios for syringyl [(Ad/Al)s] and vanillyl [(Ad/Al)v]. Thus, the labile compositions of SOM were accelerated to decomposition under rainfall pattern change. Although the recalcitrant compositions (lignin) were relatively stable, their long-term stability should be further monitored.