Table 2. The contribution of nitrogenase activity, nitrogen fixation and carbon assimilation rates, the C₂H₄:N₂ ratio and the percentage of nitrogen fixation to the total PP^a and Pnew^b in the Porcelana hot spring.

Year	T (°C)	Hourly rates				Daily rates			Ratios		% Nitrogen fixation contribution to		Input of daily nitrogen fixation to microbial mat
		Nitrogenase activity (nmol cm−2 h−1)	Nitrogen fixation (nmol N cm−2 h−1)	Nitrogen fixationc (nmol N cm−2 h−1)	Carbon assimilation (nmol C cm−2 h−1)	Nitrogenase activity (nmol cm−2 per day)	Nitrogen fixation (nmol N  m−2 per day)	Carbon assimilation (nmol C cm−2 per day)	C2H4:N2	C:Nd	Total daily primary production PP (C)	Total new production Pnew (N)	g N m−2 per year
2009	46	50.0±7.0	ND*	ND*	ND*	600±84.1	ND*	ND*	ND*	ND*	ND*	ND*	ND*
2009	42	14.6±1.8	ND*	ND*	ND*	175±21.8	ND*	ND*	ND*	ND*	ND*	ND*	ND*
2009	40	11.3±3.1	ND*	ND*	ND*	136±36.6	ND*	ND*	ND*	ND*	ND*	ND*	ND*
2011	61	0.3±0.1	ND*	ND*	ND*	3.6±1.6	ND*	ND*	ND*	ND*	ND*	ND*	ND*
2011	57	0.5±0.3	ND*	ND*	ND*	6.1±3.0	ND*	ND*	ND*	ND*	ND*	ND*	ND*
2011	51	26.5±6.2	ND*	ND*	ND*	318±74.4	ND*	ND*	ND*	ND*	ND*	ND*	ND*
2012	52	16.5±2.7	2.6±0.3	1.4±0.1	53.0±4.1	198±32.4	31.4±3.24	636±49	6.3	18.7	92.2	99.1	1.6
2012	47	22.9±3.5	3.4±1.8	4.6±1.8	ND*	275±42.5	40.2±21.6	ND*	6.8	ND*	ND*	ND*	2.9
2013	66	0.2±0.01	ND*	ND*	ND*	2.8±0.1	ND*	ND*	ND*	ND*	ND*	ND*	ND*
2013	58	14.5±1.6	6.7±1.2	1.6±0.3	45.8±8.7	174±19.7	80.0±14.3	550±105	2.2	9.1	132	99.8	4.1
2013	48	32.4±3.6	7.8±0.6	6.3±1.8	ND*	388±42.9	94.1±6.9	ND*	4.1	ND*	ND*	ND*	4.8

Abbreviations: ND*, data not determined; Pnew, new nitrogen production; PP, primary production.

The values were calculated from those obtained during daytime (1200–1400 hours).

^aNmol C cm⁻² per day.

^bNmol N cm⁻² per day.

^cNitrogen fixation rates for 6 h in situ incubation.

^dC:N based on organic matter calculated by mass spectrometer instrument.