Photosynthetic and bacterial production rates of 20 study ponds

Table 2. 
Photosynthetic and bacterial production rates of 20 study ponds. Mean values (n = 4) with SD in brackets.

Abstract
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 (r2 = 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] > 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 (r2 = 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 >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.

表2. 20个研究池塘的光合与细菌生产力速率。平均值（样本量n=4），标准差（SD）标注于括号内。

摘要
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初级生产与浮游次级生产的对比研究，其中部分池塘存在由永久分层作用（meromictic stratification）形成的基底卤水。表层水体的初级生产力范围为1.07~65.72 mgC·m⁻³·h⁻¹。在分层池塘中，基底卤水的初级生产力始终较对应的混合层（mixolimnion）高出10倍以上。回归树分析（regression tree analysis，决定系数r²=0.80）确定无机氮（以铵根离子NH₄⁺计）为限制浮游初级生产的核心限制因子。不过，部分寡营养（oligotrophic）水体中也存在无机碳共同限制光合作用的证据。当[NH₄–N]＞50 mg·m⁻³时，碳与氮均不会限制固碳过程，此时光抑制（photoinhibition）最有可能成为限制光合作用的主导因素。初级生产力是唯一与细菌生产力显著相关的变量，二者的非线性相关关系决定系数r²=0.56。尽管所有池塘均拥有高储量的溶解有机碳库（1.2~260 g·m⁻³）与有机氮库（浓度均＞130 mg·m⁻³），但这些池塘中存在氮限制以及浮游初级生产与细菌生产紧密耦合的现象，这一结果颇具反常识性。溶解有机碳与有机氮库似乎为难降解（recalcitrant）性物质，细菌生产力受限于浮游植物释放的活性有机物（labile organics）不足。