ABSTRACT
As an important parameter regulating soil carbon mineralization, microbial carbon use efficiency (CUE) is essential for the understanding of carbon (C) cycle in terrestrial ecosystems. Three nitrogen supplemental levels, including control (0 kg N·hm-2·a-1), low nitrogen (40 kg N·hm-2·a-1), and high nitrogen (80 kg N·hm-2·a-1), were set up in a Castanopsis fabri forest in the Daiyun Mountain. The basic physical and chemical properties, organic carbon fractions, microbial biomass, and enzyme activities of the soil surface layer (0-10 cm) were measured. To examine the effects of increasing N deposition on microbial CUE and its influencing factors, soil microbial CUE was measured by the 18O-labelled-water approach. The results showed that short-term N addition significantly reduced microbial respiration rate and the activities of C and N acquisition enzymes, but significantly increased soil microbial CUE. ß-N-acetyl amino acid glucosidase (NAG)/microbial biomass carbon (MBC), microbial respiration rate, ß-glucosidase (BG)/MBC, cellulose hydrolase (CBH)/MBC, and soil organic carbon content were the main factors affecting CUE. Moreover, CUE significantly and negatively correlated with NAG/MBC, microbial respiration rate, BG/MBC, and CBH/MBC, but significantly and positively correlated with soil organic carbon. In summary, short-term N addition reduced the cost of soil microbial acquisition of C and N and microbial respiration, and thus increased soil microbial CUE, which would increase soil carbon sequestration potential of the C. fabri forest.
Subject(s)
Carbon , Soil , Soil/chemistry , Nitrogen/analysis , Soil Microbiology , Ecosystem , ForestsABSTRACT
The differences of artificial measures, such as logging residue management, between assisted natural regeneration and afforestation may change the content and structure of soil dissolved organic carbon (DOC) and affect forest carbon cycle. In this study, we investigated the effects of managements on the content and spectral characteristics of DOC in a subtropical forest, which contained the forest of assisted natural regeneration (â ¡), and the plantation (â ¢), both were converted from mature secondary forests (â ). Results showed that DOC content in the 0-10 cm soil layer was significantly decreased by 21% and 50% in â ¡ and â ¢, respectively, compared with that in â . The DOC/SOC (soil organic carbon) ratios of 0-10 cm and 10-20 cm soil layers were significantly decreased by 27% and 43% after the conversion, respectively. In the 0-10 cm soil layer, the aromatic index and humification index of DOC in â ¡ were significantly higher than that in â ¢. The infrared absorption ratio of soil DOC in the range of 3700-3000 cm-1, 1650-1620 cm-1, 1160-1000 cm-1, and 690-530 cm-1 in â ¡ was higher than that in â ¢, indicating that the DOC in â ¡ had higher carboxylic acids and aromatic substances than â ¢. The fluorescence index of DOC in â ¡ and â ¢ ranged from 1.4 to 1.9, and the biological index of â ¡ was significantly higher than that of â ¢, indicating that â ¢ had higher protein components in DOC and being more bioavailable. Thus, the differences of the content and structure of DOC between â ¡ and â ¢ might cause higher soil carbon pool of â ¡ than that of â ¢.
Subject(s)
Carbon , Soil , Carbon/analysis , China , Dissolved Organic Matter , Forests , Soil/chemistry , Soil MicrobiologyABSTRACT
Soil phosphatases are important in the mineralization of organophosphates and in the phosphorus (P) cycle. The kinetic mechanisms of phosphatases in response to nitrogen (N) deposition remain unclear. We carried out a field experiment with four different concentrations of N: 0 g N·hm-2·a-1(control), 20 g N·hm-2·a-1(low N), 40 g N·hm-2·a-1(medium N), and 80 g N·hm-2·a-1(high N) in a subtropical Moso bamboo forest. Soil samples were then collected from 0 to 15 cm depth, after 3, 5 and 7 years of N addition. We analyzed soil chemical properties and microbial biomass. Acid phosphatase (ACP) was investigated on the basis of maximum reaction velocity (Vm), Michaelis constant (Km), and catalytic efficiency (Ka). Results showed that N addition significantly decreased soil dissolved organic carbon (DOC), available phosphorus, and organophosphate content, but significantly increased soil ammonium, nitrate-N content, and Vm. There was a significant relationship between Vm and the concentrations of available phosphorus, organophosphate, and soil DOC. In general, N addition substantially increased Ka, but did not affect Km. The Km value in the high N treatment group was higher than that in the control group after five years of N addition. Km was significantly negatively associated with both available phosphorus and organophosphate. Medium and high N treatments had stronger effects on the kinetic parameters of ACP than low N treatment. Results of variation partition analysis showed that changes in soil chemical properties, rather than microbial biomass, dominated changes in Vm(47%) and Km(33%). In summary, N addition significantly affected substrate availability in Moso bamboo forest soil and modulated soil P cycle by regulating ACP kinetic parameters (especially Vm). The study would improve the understanding of the mechanisms underlying soil microorganisms-regulated soil P cycle under N enrichment. These mechanisms would identify the important parameters for improving soil P cycling models under global change scenarios.
Subject(s)
Nitrogen , Soil , Acid Phosphatase , Carbon/analysis , China , Forests , Nitrogen/analysis , Organophosphates , Phosphoric Monoester Hydrolases , Phosphorus/analysis , Poaceae , Soil/chemistry , Soil MicrobiologyABSTRACT
Understanding changes in soil enzyme activities and ecoenzymatic stoichiometry is important for assessing soil nutrient availability and microbial nutrient limitation in mountain ecosystems. However, the variations of soil microbial nutrient limitation across elevational gradients and its driving factors in subtropical mountain forests are still unclear. In this study, we measured soil properties, microbial biomass, and enzyme activities related to carbon (C), nitrogen (N), and phosphorus (P) cycling in Pinus taiwanensis forests at different altitudes of Wuyi Mountains. By analyzing the enzyme stoichiometric ratio, vector length (VL), and vector angle (VA), the relative energy and nutrient limitation of soil microorganisms and its key regulatory factors were explored. The results showed that ß-glucosaminidase (BG) activities increased along the elevational gradient, while the activities of ß-N-acetyl glucosaminidase (NAG), leucine aminopeptidase (LAP), acid phosphatase (AcP) and (NAG+LAP)/microbial biomass carbon (MBC) and AcP/MBC showed the opposite trend. Enzyme C/N, enzyme C/P, enzyme N/P, and VL were enhanced with increasing elevation, while VA decreased, indicating a higher degree of microbial P limitation at low elevation and higher C limitation at high elevation. In addition, our results suggested that dissolved organic carbon and microbial biomass phosphorus are critical factors affecting the relative energy and nutrient limitation of soil microorganisms at different elevations. The results would provide a theoretical basis for the responses of soil carbon, nitrogen, and phosphorus availability as well as the relative limitation of microbial energy and nutrition to elevational gradients, and improve our understanding of soil biogeochemical cycle process in subtropical montane forest ecosystems.
Subject(s)
Pinus , Soil , Carbon/analysis , China , Ecosystem , Forests , Nitrogen/analysis , Phosphorus/analysis , Soil MicrobiologyABSTRACT
The activity and stoichiometry of soil extracellular enzyme can provide a good indication for changes in soil nutrient availability and microbial demands for nutrients. However, it remains unclear how would nitrogen (N) deposition affect nutrient limitation of microbes in subtropical forest soils. We conducted a 5 years N addition experiment in a subtropical Phyllostachys pubescens forest. The soil nutrients and enzyme activities associated with carbon (C), N, and phosphorus (P) cycles were measured. We also examined the nutrient distribution of microorganisms using enzyme stoichiometry and vector analysis. The results showed that N addition significantly decreased the contents of soil soluble organic C and available P and increased that of available N. Furthermore, N addition significantly decreased ß-N-acetyl-glucosaminidase (NAG) activity and NAG/ microbial biomass carbon (MBC), and increased acid phosphatase (ACP) and ACP/MBC. The low and moderate N addition levels significantly increased enzyme C/P, vector length, and vector angle, but significantly decreased enzyme N/P. Results of redundancy analysis showed that the change in soil enzyme activity and enzymatic stoichiometry were mainly driven by soil available P content under N addition. In summary, N addition altered the microbial nutrient acquisition strategy, which increased nutrient allocation to P-acquiring enzyme production but reduced that to N-acquiring enzyme production. Moreover, N addition exacerbated the C and P limitation of soil microorganisms. Appropriate amount of P fertilizer could be applied to improve soil fertility of subtropical P. pubescens forest in the future.
Subject(s)
Nitrogen , Phosphorus , Carbon/analysis , China , Forests , Nitrogen/analysis , Phosphorus/analysis , Soil , Soil MicrobiologyABSTRACT
Phosphorus (P) is an important nutrient for plant and microbial growth. Soil P availabi-lity is poor in subtropical areas. Long-term heavy nitrogen (N) deposition might further reduce P availability. The experiment was performed in a Phyllostachys pubescens forest in Daiyun Mountain. The effects of N application on soil basic physical and chemical properties, soil P fractions, microbial biomass, and acid phosphomonoesterase activity were analyzed after three years of N application. The results showed that N application significantly increased NO3--N content and thus soil N availability, while it significantly reduced the percentage of decomposable organic P to total P, with the ratio of carbon (C) to organic P being over 200. The soil microbial biomass C, microbial biomass P, acid phosphomonoesterase, and the ratio of microbial biomass N to microbial biomass P and microbial biomass C to microbial biomass P were increased as the N application rate increased. There was a significant negative correlation between the percentage of decomposable organic P to total P and microbial biomass P. Consequently, N application enhanced soil P limitation and increased microbial P demand.
Subject(s)
Nitrogen , Phosphorus , Biomass , Carbon , China , Forests , Soil , Soil MicrobiologyABSTRACT
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.
Subject(s)
Nitrogen/analysis , Poaceae , Soil/chemistry , Carbon , China , Humic Substances/analysisABSTRACT
We examined the effects of warming (+5 â) and reduced natural precipitation (-50%) on nutrient status and physiological indices of Cunninghamia lanceolata seedlings during winter and summer in subtropical China. The results showed that seasonal changes in temperature and precipitation caused the seasonal differences in plant nutrient contents and metabolites levels. Contents of carbon, nitrogen, phosphorus, and potassium in leaves in winter were significantly higher than those in summer. In summer, reduced precipitation and warming had no significant effects on antioxidant enzyme activities in C. lanceolata leaves. In winter, superoxide dismutase and peroxidase activities in the leaves significantly decreased with reduced precipitation by 20.7% and 17.8%. Additionally, in winter, warming treatment significantly increased non-enzymatic ascorbic acid content by 132.5%. Carbon content decreased, whereas proline accumulation and nitrogen content increased under stress induced by combined warming and reduced precipitation in winter. However, carbon content increased by 3.3% under the treatment of simultaneous warming and reduced precipitation in summer. In addition, combined warming and reduced precipitation had no significant effects on the antioxidant system irrespective of the season. In conclusion, the adaptation mechanism of C. lanceolata to warming in summer might be different from that in winter. The changes in nutrient contents in C. lanceolata leaves were more sensitive to stress induced by combined warming and reduced precipitation. Nutrient demand and supply and seasonal changes in plant responses under climate change scenarios should be considered for better managing forest plantations and improving plant productivity.
Subject(s)
Cunninghamia , China , Nutrients , Seasons , SeedlingsABSTRACT
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.
Subject(s)
Cunninghamia , Soil Microbiology , Carbon , Nitrogen , SoilABSTRACT
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.
