[Soil enzyme stoichiometry revealed the changes of soil microbial carbon and phosphorus limitation along an elevational gradient in a Pinus taiwanensis forest of Wuyi Mountains, Southeast China]. / åœŸå£¤é ¶è®¡é‡æ­ç¤ºäº†æ­¦å¤·å±±é»„å±±æ¾æž—åœŸå£¤å¾®ç”Ÿç‰©æ²¿æµ·æ‹”æ¢¯åº¦çš„ç¢³ç£·é™åˆ¶å˜åŒ–.

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.

Enzyme stoichiometry evidence revealed that five years nitrogen addition exacerbated the carbon and phosphorus limitation of soil microorganisms in a Phyllostachys pubescens forest.

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.