遮阴对米槠和杉木原位排放甲烷的影响

Effects of shadowing on methane Emissions from Castanopsis carlesii and Cunninghamia lanceolata

尽管植物在有氧环境是否有氧排放甲烷(CH4)一直存在很大的争议,但越来越多的研究证实植物自身可以排放CH4,而光照是影响植物排放CH4的重要因素。利用13C同位素标记技术结合盆栽实验,探讨了米槠和杉木叶片原位排放CH4的来源及其对太阳光照和遮阴处理的响应。结果表明,标记米槠和杉木叶片的碳稳定同位素13C值分别比未标记的高128.9和71.1倍;密封标记米槠和杉木叶片2h后的δ13CH4值分别比0h时高21.1倍和28.2倍,而未标记米槠和杉木在密封0h与2h时的δ13CH4值之间均没有显著差异,这证实了米槠和杉木排放的CH4主要源于他们自身。自然光照下,杉木的平均CH4排放速率比米槠的平均CH4排放速率高29%。自然光照下的米槠和杉木的CH4排放速率具有相同的波动规律;遮阴对米槠和杉木的CH4排放的影响不同,遮阴处理米槠的CH4排放速率显著低于自然光照处理,平均低23%;遮阴处理杉木的平均CH4排放速率与自然光照处理的没有显著差异,但在遮阴处理5d之后,其CH4排放速率比自然光照下的高71%,之后其CH4排放速率急剧下降,且明显低于自然光照下的CH4排放速率。以上结果表明,太阳光照促进了植物排放CH4的速率。

Although there were controversies on whether terrestrial plants emit methane （CH_4 ） under aerobic conditions, more and more researches confirmed that plants themselves did emit CH_4., and sunlight was one of the important factors which effected the CH_4 emissions from plants. In this study, we used stable carbon isotope-labelling technique combining with potted experiments to discussed the source of methane emitted in situ from Castanopsis carlesii and Cunninghamia lanceolata and their responses to sunlight and shadowing. The results showed that there were significant differences in the stable carbon isotopic value of labeled and unlabeled leaves between Castanopsis carlesii and Cunninghamia lanceolata, the stable carbon isotopic value （δ-13C）of the labeled Castanopsis carlesii and Cunninghamia lanceolata leaves was 128.9.and 71.1 times higher than that of the unlabeled ones. Similarly, there were significant differences in the stable carbon isotopic value of methane from the labeled branch leaves of Castanopsis carlesii and Cunninghamia lanceolata and that from the unlabeled ones. Been sealed 2 hours, the stable carbon isotopic value of methane （δ-13CH_4） isotopic signatures of methane, which emitted from Castanopsis carlesii and Cunninghamia lanceolata were 21.1 and 28.2 times higher than that of the unlabeled ones. These results indicated that the most detected CH_4 emission during our experiments were from plants themselves. Shadowing and natural lighting experiments showed that the CH_4 emission rate of Cunninghamia lanceolata was 29% higher than Castanopsis carlesii under sunlight, the mean CH_4 emission rates of them were 6.3 and 4.88 ng CH4· g-1 DW · h-1, respectively. The fluctuation rule of CH_4 emission rates are similar between the two species under sunlight, both of them were reduced at first, and then increased, finally, they were reduced again. However, the rule was different under shadowing, the mean CH_4 emission rate of Cunninghamia lanceolata was 23% lower than under sunlight, especially after 15 days, the CH_4 emission rate reduced significantly, until June 30-th, it was only 15.1% of that detected under sunlight. The mean CH_4 emission rate of Castanopsis carlesii were not significantly different under sunlight and shadowing, they were 6.3 and 5.67ng CH·g-1DW·h-1, respectively; but after 5 days, the CH_4 emission rate was 71% higher than under sunlight, it reached up to 10.45 ng CH_4· g-1DW· h-1 , then it dropped sharply, and obviously lower than under sunlight, until June 30-th, it was only 43.1% of that detected under sunlight. These results suggested that sunlight promoted methane emission rate from plants.