Physicochemical variables of all ponds studied, and of the monimolimnion brines of the three meromictically stratified ponds

<b>Table 1.</b> Physicochemical variables of all ponds studied, and of the monimolimnion brines of the three meromictically stratified ponds. <strong>Abstract</strong> We compared planktonic primary and secondary production across twenty meltwater ponds on the surface of the McMurdo Ice Shelf in January 2007, including some ponds with basal brines created by meromictic stratification. Primary production ranged from 1.07 to 65.72 mgC m⁻³ h⁻¹ in surface waters. In stratified ponds primary production was always more than ten times higher in basal brines than in the corresponding mixolimnion. Regression tree analysis (<em>r</em>² = 0.80) identified inorganic nitrogen (as {\mathrm{NH}}_{4}^{+}) as the main factor limiting planktonic primary production. However, there was also evidence of inorganic carbon co-limitation of photosynthesis in some of the more oligotrophic waters. Neither C nor N limited carbon fixation at [NH₄–N] &gt; 50 mg m⁻³, with photoinhibition the factor most likely limiting photosynthesis under such conditions. Primary production was the only factor significantly correlated to bacterial production and the relationship (<em>r</em>² = 0.56) was non-linear. Nitrogen limitation and tight coupling of planktonic primary and bacterial production is surprising in these ponds, as all have large pools of dissolved organic carbon (1.2–260 g m⁻³) and organic nitrogen (all &gt;130 mg m⁻³). The dissolved pools of organic carbon and nitrogen appear to be recalcitrant and bacterial production to be constrained by limited release of labile organics from phytoplankton.

<b>表1.</b> 所有研究池塘以及3个永久分层（meromictically stratified）池塘的下层滞水带（monimolimnion）卤水的理化变量。
<strong>摘要</strong> 本研究于2007年1月对麦克默多冰架（McMurdo Ice Shelf）表面的20个融水池塘开展浮游生物初级与次级生产力的对比分析，其中部分池塘因永久分层（meromictic stratification）作用形成了底部卤水层。表层水体的初级生产力介于1.07至65.72 mgC·m⁻³·h⁻¹之间。在分层池塘中，底部卤水层的初级生产力始终比对应上层混合带（mixolimnion）高出10倍以上。回归树分析（regression tree analysis，<em>r</em>² = 0.80）表明，无机氮（以NH₄⁺计）是限制浮游生物初级生产力的核心因子。但在部分贫营养（oligotrophic）水体中，也存在无机碳与氮共同限制光合作用的证据。当[NH₄–N] > 50 mg·m⁻³时，碳与氮均不会限制碳固定，此时光抑制（photoinhibition）最可能成为该条件下光合作用的限制因子。初级生产力是唯一与细菌生产力显著相关的因子，二者的非线性关系决定系数<em>r</em>² = 0.56。尽管所有池塘均含有大量溶解有机碳（浓度范围1.2~260 g·m⁻³）与有机氮（浓度均高于130 mg·m⁻³），但这些池塘中存在氮限制以及浮游生物初级生产力与细菌生产力紧密耦合的现象，这一点颇为出人意料。溶解态有机碳与氮库似乎难降解（recalcitrant），细菌生产力的限制因素为浮游植物（phytoplankton）释放的易降解有机物含量不足。