Soil texture is well known to directly affect bioavailability of organic matter to heterotrophs, but it also steers their activity by moderating soil moisture fluctuation. Disentangling these direct and indirect textural controls is, however, not trivial and attempts to do so are very scarce. Most attention has just gone to the stimulation of soil carbon (C) mineralization by soil moisture fluctuation per se. To quantify the indirect moisture-mediation control of soil texture on C mineralization, we monitored maize straw degradation in various soil texture/moisture regime combinations. Moisture levels were firstly kept fixed at 32% WFPS (experiment Fixed₃₂) in a sand, sandy loam and silt loam soil or allowed to fluctuate between 20% and 50% water-filled pore space (WFPS, Dry-wet_20-50). Total maize-C (C_maize) mineralized was highly similar between these three textures and thus the direct textural control was minor. On the contrary with the fluctuating moisture level, around threefold more added C_maize was mineralized (P < 0.01) in the sand (86%) than in the silt loam (25%) soil. We owe this boost in C_maize mineralization to the rewetting of larger pores in the sandy soil which should contain most of the ground maize residue. This determining control of texture on distribution of moisture as well as the maize substrate clearly exceeded the direct impact of texture on organic matter stability. In a third and fourth experiment, timing and dose to remoisten a silt loam soil back to 50% (experiment Equal_20-50) or 35% WFPS (experiment Equal_20-35) when dried out to 20% WFPS were additionally mimicked in the sand and sandy loam soils. These scenarios correspond more closely to a field situation in which nearby differently textured soils all receive the same precipitation input. After several rewetting cycles, the silt loam soil eventually had a 13.9% higher WFPS than the sandy soils. By then moisture stress clearly limited C_maize mineralization in the sandy soil (0.13 (Equal_20-50) and 0.05 (Equal_20-35) mg kg⁻¹ h⁻¹) as it proceeded at only half of the rate as in the silt loam soil (0.21 (Equal_20-50) and 0.12 (Equal_20-35) mg kg⁻¹ h⁻¹). The amount of C_maize mineralized after 120 days in the silt loam soil was simulated to surpass that in the sandy soil. We conclude that the effect of soil texture on decomposition of a fresh substrate is largely indirect, i.e. through mediation of soil water content and its distribution in the soil matrix. Moreover, our data suggests that in the event of prolonged drought C_maize mineralization will be less limited in finer textured soil, contradicting the widespread idea that organic matter would degrade more rapidly in coarser textured soils.

众所周知，土壤质地会直接影响有机物对异养生物的生物利用度，但它也会通过缓和土壤水分波动来控制其活动。然而，解开这些直接和间接的纹理控制并不是微不足道的，而且这样做的尝试非常少。最为关注的只是土壤湿度波动本身对土壤碳（C）矿化的刺激作用。为了量化土壤水分对碳矿化作用的间接水分调节控制，我们监测了玉米秸秆在各种土壤质地/水分制度组合中的降解。首先在沙子，沙质壤土和粉质壤土中保持水分含量固定为32％WFPS（实验固定为₃₂），或者让其在20％至50％的充满水的孔隙空间（WFPS，干湿）之间波动_20-50）。这三种质地之间矿化的总玉米-C（C_玉米）高度相似，因此直接的质地控制很小。在具有波动水分水平相反，周围三倍多C添加_玉米被矿化（P 在砂（86％）<0.01）比在粉砂壤土（25％）的土壤。我们欠_玉米的这种提振矿化到沙质土壤中较大孔隙的重新润湿，其中应包含大部分地面玉米残留物。对水分和玉米底物分布的质地的确定控制明显超出了质地对有机物稳定性的直接影响。在第三个和第四个实验中，将粉质壤土恢复湿润至50％（试验等于_20-50）或35％WFPS（试验等于_20-35）的时间和剂量）当干燥至20％时，在沙子和沙壤土中模拟WFPS。这些场景与现场情况更为接近，在现场情况下，附近质地不同的土壤都接收相同的降水输入。经过数次再湿润循环后，粉壤土最终的WFPS比沙质土壤高13.9％。到那时，水分胁迫明显限制了沙质土壤中_玉米的矿化作用（0.13（等于_20-50）和0.05（等于_20-35）mg kg ^-1 h ^-1），因为它的速度仅为淤泥的一半壤土（0.21（等于_20-50）和0.12（等于_20-35）mg kg ^-1 h ^-1）。模拟了粉壤土中120天后矿化的C_玉米的数量超过了沙质土壤中的C。我们得出结论，土壤质地对新鲜基质分解的影响在很大程度上是间接的，即通过土壤水含量的介导及其在土壤基质中的分布。此外，我们的数据表明，如果长期干旱，C_玉米的矿化作用将在较细的带纹理的土壤中受到限制，这与有机物在较粗的带纹理的土壤中降解更快的普遍观点相矛盾。