[Effect of litterfall input on soil respiration and its temperature sensitivity in moso bamboo forest under simulated drought.] / æ¨¡æ‹Ÿå¹²æ—±ä¸‹å‡‹è½ç‰©è¾“å ¥å¯¹æ¯›ç«¹æž—åœŸå£¤å‘¼å¸åŠæ¸©åº¦æ•æ„Ÿæ€§çš„å½±å“.

Increases in drought frequency and intensity under climate change will have great impacts on the carbon cycle of forest ecosystems. Understanding the responses of soil respiration and its temperature sensitivity to drought is necessary, when we assess whether soil is a carbon sink or source. The effects of litterfall input on soil respiration, temperature sensitivity and its lagging effect were studied in moso bamboo forests under simulated drought by ceiling method in the field with three litterfall treatments, i.e., ambient litterfall (unchanged, LU), litter addition (LA) and litter removal (LR). The results showed that LU decreased annual soil respiration rate in drought treatment (2.34 Μmol·m-2·s-1), compared with that in the control (3.15 Μmol·m-2·s-1) with ambient natural rainfall. LR showed stronger effect on soil respiration than LA. Compared with LU, LR decreased soil respiration rate by 21.0% in ambient condition and by 20.9% in drought treatment, while LA led to 5.3% increase only in drought treatment. Such a result indicated that the effects of LA and LR on soil respiration rate were stronger than LU in the drought condition. Drought decreased the temperature sensitivity of soil respiration by 8.4%, while LA and LR reduced that by 15.4% and 7.6%, respectively. The cumulative CO2 emissions during the whole 18 months were 7.35 and 5.40 kg CO2·m-2 in the control and drought treatment. Compared with LU, LA increased the cumulative CO2 emissions by 1.8% and 10.7%, and LR decreased that by 19.9% and 18.0% in the control and drought treatments. Our results indicated that the relationship between the litterfall amount (addition or removal) and soil respiration rate was nonlinear. The significant lagging effect may be caused by the decrease in root growth and microbial activity due to decreased soil water availability in drought treatment. Litterfall played a more important role in soil CO2 emission under drought, and thus litterfall was a crucial factor in soil carbon emission in the context of climate change.

[Photo-physiological and photo-biochemical characteristics of several herbaceous and woody species based on FvCB model]. / 基于FvCBæ¨¡åž‹çš„å‡ ç§è‰æœ¬å’Œæœ¨æœ¬æ¤ç‰©å ‰åˆç”Ÿç†ç”ŸåŒ–ç‰¹æ€§.

To explore the photosynthetic capacity and the leaf photosynthetic apparatus for plants with different life forms, CO2 response curves of 7 woody species and 4 herbaceous species were fitted by the modified rectangular hyperbolic model and the FvCB model, and the photosynthetic parameters, including maximum net photosynthetic rate (Pn max), maximal Rubisco carboxylation rate (Vc max), maximal electron transport rate (Jmax), day respiration (Rd), and mesophyll resistance to CO2 transport (rm), were compared among different woody species, among different herbaceous species, and between woody and herbaceous life-forms, respectively. The results showed Pn max of seven woody species descended in the order of Sapium sebiferum and Boehmeria nivea ＞ Machilus pingii and Pittosporum tobira ＞ Cyclobalanopsis glauca, Castanopsis sclerophylla, and Quercus nuttallii. Vc max of S. sebiferum, B. nivea, M. pingii, and P. tobira was significantly higher than that of C. glauca and C. sclerophylla. Jmax of woody species was in descending order as S. sebiferum ＞ B. nivea and P. tobira ＞ Q. nuttallii, C. sclerophylla, and C. glauca. rm of M. pingii and C. sclerophylla was higher than that of S. sebiferum, P. tobira and B. nivea. Pn max of Phytolacca acinosa was significantly higher than that of Ageratum conyzoides and Achyranthes aspera. There was no significant difference in Vc max among 4 herbaceous species. Jmax of P. acinosa was higher than that of A. conyzoides. rm of S. nigrum and A. aspera was higher than that of A. conyzoides. Rd of P. acinosa was higher than that of A. conyzoides and A. aspera. The photosynthetic parameters (Pn max, Vc max, Jmax and rm) of woody species were significantly higher than those of herbaceous species, but no significant difference was found in Rd between woody and herbaceous species. In conclusion, the difference in photosynthetic capacity among different species and between the two plant life-forms resulted from the difference in Rubisco carboxylation capacity, electron transport capacity, and mesophyll resistance among these species.

[Effects of flash scheme on maximum chlorophyll fluorescence under illumination and its derived parameters]. / ä¸åŒå ‰è„‰å†²æ–¹æ¡ˆå¯¹å ‰ä¸‹æœ€å¤§è§å ‰å‚æ•°åŠå ¶è®¡ç®—å‚æ•°çš„å½±å“.

The maximum chlorophyll fluorescence yield under illumination (Fm') is one of the most important parameters in plant eco-physiological research, and usually was estimated with rectangular flush scheme (RF). However, the estimation accuracy of RF for Fm' was affected by the rapid turnover of photosystem 2 (PS2). In order to eliminate the effect of the rapid turnover of photosystem 2 (PS2), the multiphase flush scheme (MPF) based on the linear relationship between the flush (Q') and chlorophyll fluorescence (F') is proposed to estimate Fm' at infinite irradiance. Leaf gas exchange and chlorophyll fluorescence of three woody species (Castanopsis sclerophylla, Cyclobalanopsis glauca, and Sapium sebiferum) were respectively measured with RF and MPF, Fm' and the derived parameters [the quantum efficiency of PS2 (ΦPSII), the electron flux through PS2 (J), the maximum electron transfer rate (Jmax), mesophyll conductance (gm) and chloroplast CO2 concentration (Cc)] were compared between the two different schemes, and the effects of RF and MPF on these parameters were analyzed. The results showed that no significant difference was found in the parameters for the three species between RF and MPF at the light intensity lower than 200 µmol·m-2·s-1. Fm' estimated with MPF for the three species were 3.5%-5.2%, 11.7%-18.0%, and 3.2%-7.1% higher than those with RF, respectively, at the light intensity higher than 200 µmol·m-2·s-1. The derived parameters (ΦPSII, J and Jmax) estimated with MPF for the three species were higher than those with RF, while the derived parameters(gm and Cc) estimated with MPF were lower at the light intensity higher than 200 µmol·m-2·s-1. In conclusion, estimates of parameters (Fm', ΦPSII, and J) were not significantly affected by the two different schemes at the light intensity lower than 200 µmol·m-2·s-1. The estimates of parameters (Fm', ΦPSII, J, Jmax, gm, and Cc) were significantly affected by the two different schemes at the light intensity higher than 200 µmol·m-2·s-1. Compared with MPF, parameters of Fm', ΦPSII, J and Jmax estimated with RF were underestimated, while parameters of gm and Cc were overestimated.