帽儿山地区不同土地利用方式下土壤-微生物-矿化碳氮化学计量特征

土地利用方式的变化导致土壤碳氮含量及其化学计量关系的变化,然而土壤微生物化学计量及其驱动的碳氮矿化过程如何响应这种变化仍不明确。以帽儿山地区天然落叶阔叶林、人工红松林、草地和农田4种不同土地利用类型为对象,测定其土壤有机碳(C_(soil))、全氮(N_(soil))、微生物生物量碳和氮(C_(mic)和N_(mic))、土壤碳和氮矿化速率(C_(min)和N_(min)),旨在比较不同土地利用方式对土壤、微生物碳氮化学计量特征及矿化速率的影响,探索土壤-微生物-矿化之间碳氮化学计量特征的相关性,揭示微生物对土壤碳氮化学计量变化的响应和调控机制。结果显示:C_(soil)、N_(soil)、C_(mic)、N_(mic)和C_(min)均呈现天然落叶阔叶林人工红松林草地农田,而天然落叶阔叶林和草地的N_(min)显著高于人工红松林和农田。土地利用方式显著影响土壤和微生物碳氮比(C∶N_(soil)和C∶N_(mic)),均呈现农田最高。不同土地利用方式的数据综合分析发现:碳氮矿化速率比与C∶N_(mic)呈负相关,而和微生物与土壤碳氮化学计量不平衡性(C∶N_(imb))显著正相关。单位微生物生物量的碳矿化速率(qCO_2)随着C∶N_(mic)的增加而降低,而单位微生物生物量的氮矿化速率(qAN)随着C∶N_(mic)的增加而增加。C∶N_(imb)与qCO_2正相关,与qAN负相关。以上结果表明,微生物会通过改变自身碳氮化学计量、调整碳氮之间相对矿化速率,以适应土地利用变化导致的土壤碳氮及其化学计量的变异性,以满足自身生长和代谢的碳氮需求平衡。

Soil-microbe-mineralization carbon and nitrogen stoichiometry under different land-uses in the Maoershan region

Different land-|uses lead to significant changes in soil carbon and nitrogen concentrations and their stoichiometry. However, how soil microbial stoichiometry and associated mineralization of soil carbon and nitrogen respond to such changes caused by land-uses is not conclusive. The present study investigated the soil organic carbon (C_soil), total nitrogen (N_soil), soil microbial biomass carbon and nitrogen (C_mic and N_mic), and carbon and nitrogen mineralization rates (C_min and N_min) of the topsoil (0-5 cm depth) under four land-uses (natural broad-leaved deciduous forest, Pinus koraiensis plantation, grassland, and cropland) in the Maoershan Forest Ecosystem Research Station, Northeast China (45°20''N, 127°30''E). Our objectives were to (1) examine the effects of land-uses on C_soil, N_soil, C_mic, N_mic, C_min, N_min, and their stoichiometric ratios; and (2) explore the carbon-nitrogen interactions among soil-microbe-mineralization in order to mechanistically understand microbial responses and adaptation to resource stoichiometry. The results showed that the contents of C_soil, N_soil, C_mic, N_mic, and C_min decreased in the following order:natural forest>plantation>grassland>cropland; whereas the natural forest and grassland had significantly higher N_min than the plantation and cropland. Land-uses significantly affected soil and microbial biomass carbon to nitrogen ratios (C:N_soil and C:N_mic). The cropland had the greatest C:N_soil and C:N_mic among the four land-|uses. The analysis of the pooled data across the four land-|uses showed that the ratio of carbon to nitrogen mineralization rates was correlated negatively with C:N_mic, but positively with the stoichiometric imbalance between microbes and their soil resources (i.e., C:N_soil divided by C:N_mic, C:N_imb). The carbon mineralization rate per unit microbial biomass carbon (qCO₂) decreased with increasing C:N_mic, whereas the nitrogen mineralization rate per unit microbial biomass nitrogen (qAN) increased with increasing C:N_mic. The C:N_imb was correlated positively with the qCO₂, but negatively with the qAN. Our study suggests that soil microbes may adapt to changes in soil stoichiometry induced by land-uses for the requirements of carbon and nitrogen for their growth and metabolism by adjusting their biomass stoichiometry and carbon to nitrogen mineralization rates.