Compost application is viewed as an eco-friendly and sustainable method to improve agricultural soil fertility. However, composts vary in lability and recalcitrance, which drives energy supply for microbial biomass formation and microbial processes such as soil respiration, nitrogen mineralization, and enzyme production. To provide further insights into the issue, this study aimed to elucidate how microbial activities are affected by substrate quality, amendment volume, and frequency. We proposed three hypotheses: i) microbial biomass and microbial activities increase as soon as C substrate is amended compared to control soil; ii) microbe-mediated processes are affected by substrate lability as incubation progresses; iii) repeated amendment of smaller split C source sustains a more gradual increase of microbial activities as compared to a single input. To test these hypotheses, we incubated an agricultural soil at 25 °C, adding substrates of various assimilability (glucose, cellulose and lignin) once or in 2–3 split additions. Soil respiration was determined every 2–3 days throughout incubation, while microbial biomass (MBC, MBN), inorganic N (NO₃-N and NH₄-N) concentration, and potential enzyme activities were assayed at day 4, 32, 82, and 186 following substrate amendment. Regardless of C source amendments, soil respiration increased twofold in amended soils while microbial biomass C (MBC) was 1.5 times higher compared to control soil, indicating that microbial growth was C-limited in this agricultural soil. The association between high NO₃-N concentration and low microbial biomass at the end of the incubation, regardless of amended substrate, suggested increased microbial C turnover due to C exhaustion. The addition of cellulose mostly enhanced enzyme activities of β-1,4-glucosidase (BG), β-1,4-N-acetyl glucosaminidase (NAG) and tyrosine amino peptidase (TAP) while the additions of glucose and lignin either reduced or did not affect enzyme activities compared to control at respective measuring time. Based on the result, we supposed that the selective synthesis of different enzymes by microbial community was C-source lability dependent. In conclusion, substrate quality rather than substrate amendment volume and timing had greater impacts on soil microbial activities, and hence indirectly influenced soil fertility.

堆肥应用被视为提高农业土壤肥力的一种环保且可持续的方法。然而，堆肥的不稳定性和顽固性各不相同，这推动了微生物生物质形成和微生物过程（如土壤呼吸、氮矿化和酶生产）的能量供应。为了进一步深入了解这个问题，本研究旨在阐明微生物活动如何受底物质量、修正量和频率的影响。我们提出了三个假设：i) 与对照土壤相比，一旦 C 底物被修正，微生物生物量和微生物活动就会增加；ii) 随着培养的进行，微生物介导的过程会受到底物不稳定性的影响；iii) 与单一输入相比，较小的分裂 C 源的重复修正维持微生物活性的更逐渐增加。为了测试这些假设，我们在 25 °C 下培养了农业土壤，一次或分 2-3 次添加各种同化性底物（葡萄糖、纤维素和木质素）。在整个孵化过程中，每 2-3 天测定一次土壤呼吸，而微生物生物量（MBC、MBN）、无机氮（NO在底物修正后的第 4、32、82 和 186 天测定₃ -N 和 NH ₄ -N) 浓度和潜在的酶活性。无论碳源如何添加，改良土壤中的土壤呼吸增加了两倍，而微生物生物量碳 (MBC) 比对照土壤高 1.5 倍，表明微生物生长在这种农业土壤中受到碳限制。高NO ₃之间的关联-N 浓度和孵化结束时的低微生物生物量，无论底物如何，表明由于 C 耗竭导致微生物 C 周转增加。纤维素的添加主要增强了 β-1,4-葡萄糖苷酶 (BG)、β-1,4-N-乙酰氨基葡萄糖苷酶 (NAG) 和酪氨酸氨基肽酶 (TAP) 的酶活性，而葡萄糖和木质素的添加要么降低或与在各自测量时间的对照相比，不影响酶活性。基于该结果，我们假设微生物群落对不同酶的选择性合成具有碳源不稳定性依赖性。总之，基质质量​​而不是基质改良量和时间对土壤微生物活动的影响更大，因此间接影响了土壤肥力。