Marine microbes use extracellular phosphatases to hydrolyze phosphate from organic matter. Dissolved organic phosphorus (DOP) is typically present in higher concentrations than phosphate in oceanic surface waters. Yet, the fate and role of different DOP components, such as phosphomonoester and phosphodiester, are poorly understood. Most of the investigations on extracellular enzymatic hydrolysis of marine DOP have focused on phosphomonoesterase (MEA) activity (i.e., alkaline phosphatase), whereas phosphodiesterase (DEA) measurements are scarce. This limits our understanding of the ecological and biogeochemical role of DOP sources other than P-monoesters in the sea. We determined extracellular MEA and DEA activities including their cell-free fractions on a bimonthly basis over 14 months in surface and mesopelagic subantarctic waters, thus covering a wide range of phosphate availability levels (from <0.5 to 2.3 µM). We found that DEA and MEA exhibit similar hydrolysis rates in surface as well as in mesopelagic waters. The MEA:DEA ratio varied between 0.38 and 5.42 during the study period, indicating potential differences in function and/or expression among the two enzyme groups, potentially reflecting differences in the availability and/or utilization of P-monoester and P-diester pools. Interestingly, the MEA:DEA was negatively correlated to phosphate (r = −0.82, p = 0.02, R²=0.67) and positively with the inorganic N:P ratio (r = 0.84, p = 0.02, R² = 0.67), suggesting that the relative importance of DEA vs. MEA is linked to inorganic P availability and the N:P ratio. DEA was also related to the N:P ratio, both at the surface and at depth, suggesting DEA alone is sensitive to changes in the N:P ratio. The majority (>70%) of extracellular MEA and DEA was found in the cell-free fraction, increasing with depth for MEA. Our results indicated that DOP hydrolysis mediated by DEA in the surface as well as in dark ocean is as important as the frequently measured MEA.

海洋微生物利用细胞外磷酸酶将有机物中的磷酸盐水解。在海洋地表水中，溶解性有机磷（DOP）的浓度通常高于磷酸盐。但是，人们对不同的DOP成分（例如磷酸单酯和磷酸二酯）的命运和作用知之甚少。关于海洋DOP的细胞外酶水解的大多数研究都集中在磷酸单酯酶（MEA）活性（即碱性磷酸酶）上，而磷酸二酯酶（DEA）的测量却很少。这限制了我们对海洋中P-单酯以外DOP来源的生态和生物地球化学作用的了解。我们在14个月的两个月内，在地表水和中弹性南极水域中，每两个月确定了细胞外MEA和DEA活性，包括它们的无细胞组分，因此涵盖了广泛的磷酸盐可用性水平（<0.5至2.3 µM）。我们发现，DEA和MEA在地表水和中弹性水域中均显示出相似的水解速率。在研究期间，MEA：DEA比率在0.38和5.42之间变化，表明两个酶基团在功能和/或表达上可能存在差异，这可能反映了P-单酯和P-二酯池的可用性和/或利用率的差异。有趣的是，MEA：DEA与磷酸盐呈负相关（表示两个酶组在功能和/或表达上可能存在差异，可能反映了P-单酯和P-二酯库的可用性和/或利用率上的差异。有趣的是，MEA：DEA与磷酸盐呈负相关（表示两个酶组在功能和/或表达上可能存在差异，可能反映了P-单酯和P-二酯库的可用性和/或利用率上的差异。有趣的是，MEA：DEA与磷酸盐呈负相关（[R = −0.82， p = 0.02， [R² = 0.67），并且与无机N：P比正相关（[R = 0.84， p = 0.02， [R² = 0.67），表明DEA的相对重要性与MEA与无机磷的有效性和氮磷比有关。在表面和深度上，DEA均与N：P比率有关，这表明仅DEA对N：P比率的变化敏感。在无细胞级分中发现了大多数（> 70％）的细胞外MEA和DEA，随着MEA深度的增加而增加。我们的结果表明，DEA介导的DOP水解在海面和暗海中与经常测量的MEA一样重要。