Understanding how nitrogen（N） availability interacts with soil acidity and phosphorus（P） availability to affect soil-atmosphere exchanges in CO_2, CH_4 and N_2O in forest ecosystems is important for understanding ...Understanding how nitrogen（N） availability interacts with soil acidity and phosphorus（P） availability to affect soil-atmosphere exchanges in CO_2, CH_4 and N_2O in forest ecosystems is important for understanding the mechanisms driving ecosystem responses to enhanced N deposition. Here, we conducted an experiment with N, P and acid（H） addition in a mixed forest in subtropical China to investigate how acid and P addition affects CO_2, CH_4 and N_2O exchange under N addition. Our results showed that soil NH4^＋-N and NO3^--N increased after N addition, but CO_2 emissions in N addition plots remained unaffected. CH_4 uptake in N–, P–, NP–, NH– and NPH–addition plots were reduced by 21.1%, 15.7%, 39.1%, 26.6%, and 28.4%, respectively. CH_4 uptake in NP–addition plots were lower compared to N–addition and P–addition plots, indicating that N and P addition had an additive effect on inhibiting CH_4 uptake. N_2O emission in N–, NP–, NH– and NPH–addition plots increased by 158.6%, 176.0%, 117.2%, and 91.8%, respectively. N_2O emissions in NPH–addition plots were lower compared to NP–addition plots while showed no difference between N–addition and NH–addition plots. This suggests that only under P rich conditions, acid addition would greatly mitigate N_2O emissions under N addition. Our results demonstrate that for N and P co-limited forest ecosystems with acidic soils, low P availability constrains the inhibition of soil CH_4 uptake by N deposition. When P availability is low, a weak soil acidation induced by N deposition may have less influence on the stimulation of N_2O emissions by N deposition.展开更多
The boiling behavior of the liquid nitrogen (LN2) under the transient high heat flux urgently needs to be researched systematically. In this paper, the high power short pulse duration laser was used to heat the satura...The boiling behavior of the liquid nitrogen (LN2) under the transient high heat flux urgently needs to be researched systematically. In this paper, the high power short pulse duration laser was used to heat the saturated LN2 rapidly, and the high-speed photography aided by the spark light system was employed to take series of photos which displayed the process of LN2's boiling behavior under such conditions. Also, a special temperature measuring system was applied to record the temperature variation of the heating surface. The experiments indicated that an explosive boiling happened within LN2 by the laser heating, and a conventional boiling followed up after the newly-defined changeover time. By analyzing the temperature variation of the heating surface, it is found that the latent heat released by the crack of the bubbles in the bubble cluster induced by the explosive boiling is an important factor that greatly influences the boiling heat transfer mechanism.展开更多
基金Natural Sciences Foundation of China(No.31290221)
文摘Understanding how nitrogen（N） availability interacts with soil acidity and phosphorus（P） availability to affect soil-atmosphere exchanges in CO_2, CH_4 and N_2O in forest ecosystems is important for understanding the mechanisms driving ecosystem responses to enhanced N deposition. Here, we conducted an experiment with N, P and acid（H） addition in a mixed forest in subtropical China to investigate how acid and P addition affects CO_2, CH_4 and N_2O exchange under N addition. Our results showed that soil NH4^＋-N and NO3^--N increased after N addition, but CO_2 emissions in N addition plots remained unaffected. CH_4 uptake in N–, P–, NP–, NH– and NPH–addition plots were reduced by 21.1%, 15.7%, 39.1%, 26.6%, and 28.4%, respectively. CH_4 uptake in NP–addition plots were lower compared to N–addition and P–addition plots, indicating that N and P addition had an additive effect on inhibiting CH_4 uptake. N_2O emission in N–, NP–, NH– and NPH–addition plots increased by 158.6%, 176.0%, 117.2%, and 91.8%, respectively. N_2O emissions in NPH–addition plots were lower compared to NP–addition plots while showed no difference between N–addition and NH–addition plots. This suggests that only under P rich conditions, acid addition would greatly mitigate N_2O emissions under N addition. Our results demonstrate that for N and P co-limited forest ecosystems with acidic soils, low P availability constrains the inhibition of soil CH_4 uptake by N deposition. When P availability is low, a weak soil acidation induced by N deposition may have less influence on the stimulation of N_2O emissions by N deposition.
文摘The boiling behavior of the liquid nitrogen (LN2) under the transient high heat flux urgently needs to be researched systematically. In this paper, the high power short pulse duration laser was used to heat the saturated LN2 rapidly, and the high-speed photography aided by the spark light system was employed to take series of photos which displayed the process of LN2's boiling behavior under such conditions. Also, a special temperature measuring system was applied to record the temperature variation of the heating surface. The experiments indicated that an explosive boiling happened within LN2 by the laser heating, and a conventional boiling followed up after the newly-defined changeover time. By analyzing the temperature variation of the heating surface, it is found that the latent heat released by the crack of the bubbles in the bubble cluster induced by the explosive boiling is an important factor that greatly influences the boiling heat transfer mechanism.
