| Nowadays, Acid rain and greenhouse effect are facing two serious environmental problems to humanity, they react upon each other, the global warming may reduce or damage the capacity of the soil carbon sink. Acid rain affected severely on vegetation and soil, it may increase or retard this phenomenon. Soil respiration is a complex biological and non-biological process, it is also one of the plant-soil system indicator to response to environmental stress, the change of soil respiration rate and direction of change will response the plant-soil system on the stress sensitivity and response mode. Evergreen broad-leaved forest is the climax community of subtropical forest ecosystem, it is a zonal vegetation in subtropics. The object of this thesis was to master and understand the response of soil respiration of plant-soil system to acid precipitation and to local climate change. This thesis researched the effect of acid rain on composite plant-soil system by the method of spraying simulated acid rain of different pH 2.5,4.0 and 5.6 on the three plant seedling-soil system units, including Schima superb, Cyclobalanopsis glauca and Castanopsis eyrei in Zhejiang Province, where the forest ecological system has bear environmental pressure of severe acid rain in long term. The study revealed the relationships between soil respiration and atmospheric and soil water and heat conditions under acid rain sress. Meanwhile the soil was sampled and the soil chemical properties and soil enzyme activities, including soil urease, sucrase and cellulase, were analyzed. On the base of the analysis, this research discussed that the pattern of soil respiration of seedling-soils treated with acid rain of different pH, the response of soil respiration to acid rain, and the internal mechanism in the response of soil respiration to simulated acid rain. This thesis aimed to enrich and accumulate the research on carbon cycle and provided the scientific basis and reference not only for ecological planning but also for nursery selection and breeding in forestation. Results were displayed as follows:1) Analysis of the soil chemical properties in three kinds of seedlings showed that decreased soil pH gradually with increased acidity, compared with CK(pH 5.6), the change of soil pH under moderate acid rain (pH 4.0) was not obvious, but soil pH decreased significantly under severe acid rain (pH 2.5), about 3.5. The order of soil organic carbon of Cyclobalanopsis glauca was severe acid rain> CK> moderate acid rain, but Schima superb and Castanopsis eyrei of soil organic carbon showed severe acid rain> moderate acid rain> CK. The order of mean soil total nitrogen was CK> severe acid rain> moderate acid rain in Cyclobalanopsis glauca, Schima superb was severe acid rain> moderate acid rain> CK, Castanopsis eyrei was moderate acid rain> severe acid rain> CK. The order of soil C/N was severe acid rain> moderate acid rain> CK in three kinds of species. Soil available P and K content showed mainly be inhibited by acid rain in Cyclobalanopsis glauca and Schima superb. The content alkali-hydrolyzable nitrogen was not sensitive to acid rain stress.2) Analysis of the change of soil activities in three kinds of seedings under acid rain stress. The results revealed that soil urease activity showed a different degree of inhibition under acid rain stress, soil urease activity showed a different degree of inhibition. Sucrase activity mainly was activated by acid rain, but sucrase activity of Cyclobalanopsis glauca and Schima superb was not obvious from April to June, before July have a significant role in promoting. Soil sucrase activity of Castanopsis eyrei has a significant role in promoting. Acid rain effect on soil cellulase enzyme activity mainly showed the inhibition, soil cellulase enzyme activity of Castanopsis eyrei showed activation under moderate acid rain treatment, but revealed inhibition under severe acid rain treatment.3) The change of soil respiration of three kinds of seedings under acid rain stress. The results showed that soil respiration of three seedings emerged typical diumal and seasonal dynamic patterns. The diurnal variation showed a single peak dynamic change, the maximum appeared at 12:00 or 14:00. The mean soil respiration showed significant difference among months (P< 0.05); the minimum appeared in April, the maximum appeared in June or July. Contribution of root respiration to soil respiration in three seedings; the range of contribution was from 45% to 85% under CK treatment (pH 5.6), the range of contribution was from 36% to 79% under moderate acid rain treatment (pH 4.0), the range of contribution was from 22% to 76% under severe acid rain treatment(pH 2.5).4) The relationships between soil respiration of three seedings and environment factors were analyzed under acid rain stress, they could be used exponential or linear regression. Results showed that the atmospheric environmental factors, only between the air temperature and soil respiration showed significant exponential correlation, the relationship between other atmospheric factors and soil respiration was not significant. The relationship between soil respiration and soil temperature of 5 cm could be described as an exponential equation, and it was very significant (P< 0.001). Under CK treatment, soil temperature could explain seasonal variation in soil respiration of 66.58 %,83.60%,57.09% in Cyclobalanopsis glauca, Schima superb and Castanopsis eyrei, respectively; Under moderate acid rain treatment, soil temperature could explain seasonal variation in soil respiration of 51.17%,62.59%,37.24%, respectively; Under severe acid rain treatment, the soil temperature could explain seasonal variation in soil respiration of 52.78%,55.89%,49.47%, respectively. The relationship between soil respiration and soil moisture showed a negative linear, but compared with soil temperature, it was not a main foctor to the seasonal variation of soil respiration.5) Under acid rain stress, the correlation between soil respiration and soil enzyme activity, soil pH, soil organic carbon and soil nutrients showed that the relationship between soil respiration and root respiration and cellulase were highly significant or significant correlation in Cyclobalanopsis glauca. The relationship between soil respiration and root respiration, cellulase activity, available P were highly significant or significant correlation, but soil organic carbon showed significantly negative correlation in Schima superb. The relationship between soil respiration and root respiration, cellulase activity, soil pH were highly significant or significant correlation, but soil organic carbon showed significantly negative correlation.In conclusion, acid rain effect on soil respiration through a multi-factor interaction to achieve the result, but soil temperature is a dominant factor to impact soil respiration, the difference of soil respiration increased with the increase of soil temperature among different acid rain treatments. Moreover, near-surface atmospheric conditions and soil enzyme activity and soil chemical properties could not be ignored. |
PDF Full Text Request